CA2132525C - Methods for coating adhesive polymers - Google Patents

Abstract

A method of coating an adhesive polymer comprising hot-melt coating a composition of a hydrophobic adhesive polymer and a transient polar processing aid onto a substrate is provided. In addition, a method of coating a hydrophobic adhesive polymer when contacted with a transient polar processing aid, and a hot-melt coatable adhesive composition are also provided.
These methods provide clear, smooth, and foam-free coatings; that are also substantially free of high temperature, low temperature, and processing aid-induced coating defects.

Description

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Field of the Invention This invention relates to methods of hot-melt coating adhesive polymers, and in particular, pressure-sensitive adhesive polymers, using processing aids.
Ba~IC round of the Inv~ation The coating of adhesive polymers, including pressure-sensitive adhesives, such as rubber-based materials, onto suitable backings is well-known in the art.
Typically, these adhesive polymers are formed by solution or emulsion polymerization techniques.
Thereafter; the resultant adhesive polymers are coati either directly from their reaction medium, or subsequent to isolation and dissolution, onto a substrate. See e"~;,,, D. Sates, ~d., "~Iandboole of Pressure Sensitive Adhesive Technology," 'hen IeTostrand, PoTew ~t'ork, Chapter 13, pg. 298 ~198~).
beer the past several years, research has focuses upon the production of adhesive polymers through solvent-free polymerization techniques. For example, U.S. Patent rlos. 4,833,1?9, and 4,95~,65~0 disclose the production of acrylate-based pressure-sensitive adhesive copolymers in an aqueous medium via suspension polymerization techniques.
However, to date, these adhesives are isolated from the aqu~us medium, dissolved in an or~annic solvent, and c.~atec~ therefrom onto a suitable substrate, such as a tape backing material. Thus; while organic sblvents can be eliminatal as a reaction medium for the pol3rmaeriz~tion of many adhesive polymers; that' are still typically use to coat these adhesive materials.
A nuryber of problems arise from the use of organic solvents as a coating rhedia: Most useful organic solvents are flammable, and thus, can pose a safety hazard, both during and after coating: Also, the relatierely high post of organic solvents can substantially increase the (anal cost of the adhesive-coated product: Finally, the organic solvents must be removed from the ct~ated adhesive, typically by evaporative drying, after coating. This subsequent removal of organic solvents results in additional energy and equipment costs, and poses safety and environin~ntad disposal problems.
In an effort to overcome the problems associated with organic solvent-coated adhesives, hot-melt e~trusi~n coating of adhesive polymers has been employed.
In theory, hot-melt extrusion coating of a dry adhesive polymer from the melt state should provide 3S numero~is advantages, including elimination of unwanted organic solvents, and nearly an instantaneous 'blending mf the hot adhesive to a suitabte substrate. however, in practice, useful hot-melt coating can be difficult to achieve, particularly where odor-free adhesive coatings, such as in the medical field, are required. For example, many desirable adhesive ~~~ a~;,~~J
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polymers, such as acrylate-based pressure-sensitive adhesives, exhibit high viscosities, even at normally elevated temperatures. Accordingly, these adhesive polymers must be subjected to increased processing temperatures to lower their melt viscosity to a sufficient level that a smooth, clear, hot-melt coating can be obtaln~I. However, these higher processing temperatures also Dead to significant thermal degradation of the adhesive polymer. It is this thermal degradation that results in unwanted odors, off-color coatings, and potential reduction in adhesive and cohesive properties of the coated adhesive polymer.
Numerous pre-processing and post-processing chemical modifications of adhesive polymers have been proposed to help alleviate this thermal degradation problem.
For example, U.S. Patent No. 4,851,278 discloses thermally-reversible crosslinking, through the use.of metal ions, such as zinc, to lower the melt viscosity of acrylate-based adhesives at elevated temperatures. fee also, U.S. Patent Nos. 4,360,638 and 4,423,182.
Similarly, U.S. Patent No. 3,925;282 utilizes both tertiary-amine containing monomers and organometallic salts to lower melt viscosity of acrylate polymers at elevated temperatures.
Also, U:S: Patent Nos. 4;554;324; 4,SSI;388, and 3,558,?46 alD describe acrylate graft copolymers with favorable viscosity profiles.
Further; U.S. Patent I~o: 4,762,888 discloses certain specified miactures of acryDic copolymers that exhibit thermally-reversible hydrogen bonding. Also, the admixture of photocrosslinking agents to lower-molecular weight polymers, followed by radiation curing after coating, is described in U.S: Patent Nos. 4,052,527 and 4,234,662.
However, in all of these instances, special equipment, unusual and expensive moztomers, and/or additives which are undesirable in the final coated adhesive, product are re~uir~d to yield the disclosed results.
In another approach, various processing aids can be added to polymers to Limit their thermal degradation during general melt processing. For example, lubricating 2~ processitlg aids; such as fatty acids fatty alcohols; metallic soaps, waxes, and various inorganic materials, modify the melx flow behavior of polymers, and thereby, limit the degree of'thermal degradation. to the polymer during melt processing. g,g,,,, Radian Corporation, "Chemical Additives for the ~'lastics Industry: Properties, Applications, Toxicologies"> pp.
99-101; Noyes Data Corp., Park Ridge, New Jersey (1987); "Plastics Additives Handbook:
Stabilizers, Processing Aids, PlasticizeTS, Fillers, Reinforcements, Colorants for Thermoplastics", R. G~chter and H. MuDDer~ lds.> pp. 423-467; Hanser, New York (3rd.
~~~ l~). However, these processing aids are typicatDy non-volatile materials that remain as a compoaaent of the pvly~er after processing; and thereby, can adversely ~ffffect the polymers ultimate properties; such as transparency, toxicity, odor; ~trength>
and adhesive pr~perties. Furthermore; the processing aid may bleed tv the surface of the extruded ,, .' . 3 .v g r r s v T r ,5,~
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V w -'~ g3/2016S ~ ~ ~ ~ ~ ~ p~/~gg3/02437 polymer, and impart undesirable surface properties thereto. egg "Encyclopedia of Polymer Science and Engineering", H. Mark et al.. Eds., Index volume, pp. 307-324, John Wiley &
Sons, New York (1990).
Water is recognized as a processing aid in the melt extrusion of hydrophilic polymers. Specifically, the addition of water to hydrophilic polymers has been shown to lower their melt temperature and melt viscosity during general melt extrusion.
For example, U.S. Patent No. 3,941,865 discloses the addition of water to solid polyethylene oxide resin prior to extrusion, while U.S. Patent Nos. 4,761,453, 4,876,307, and 4,874,307 disclose injection molding or extrusion of golyketones subsequent to saturation with water. Similarly, ZO U.S. Patent No. 4;094,948, and B.G. Frushour, 4 Polymer Bulletin, 305-314 (1981); 7 ~,~~~rner Bul,~,,~in, 1-8 (1982); and .~.~, Pol3rmer Bulletin, 375-382 (1984), all show that the addition of water to acrylonitr~le copolymers reduces their melt temperature for extrusion purposes.
While water has been used as a processing aid for hydrophilic polymers, it is considered to be an incompatible and undesirable additive in the hot-melt extension coating of hydrophobic adhesive polymers. For example, it is known that injection of water into a molten hydrophobic polymer can cause the composition to bubble and foam. egg gigs, M.
Mack; "choosing an Extruder for Melt Devolatilization", Plastics Engineering, pg. 49 (July, 1986). Thds, it is a fast held belief by those skilled in the art that inclusion of all but the smallest quantity-of water in a hydrophobia adhesive polymer during hot-melt coating will lead to foaming of the polymer extrudate at the coatiyg die/substrate interface, and accordingly; to a defective, nonuseable adhesive coating with bubbles, coating gaps, and other coating irregulaslties.
Furthermore, the inclusion of water is considered so deleterious to obtaining an effective adhesive coating, that'those skilled in the art teach that optimum hot-melt coatings of hydrophobic adhesive polymers can only be obtained by coating as close as possible to a 100% solids, water-free; composition onto a suitable substrate. However, as noted above, this requires the use of costly curing equipment; exotic monomers, or additives with unwanted side-effects to avoid unwanted thermal degradation. Likewise, if the hydrophobic adhesive polymer is coated at~a lower melt temperature, the high melt viscosity of the polymer will lead to defects in the adhesive coating, including a whitish translucent coloration, visible melt-flow lines, an irregular "shark skin" surface, as well as other coating irregularities. ~'hus, present nnethods of hot-melt coating hydrophobic adhesive polymers necessitate unwanted eomprornises in coating qualaty an an effort to bot-anelt ex~usion coat these materials.
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dVLI 93/20165 ' PC1'/ US93102437 Surnmarx of the Invention Surprisingly, it has been discovered that a hydrophobic adhesive polymer can be hot-melt coated onto a suitable substrate using water, or other transient polar materials as processing aids. Unexpect~lly, no foaming of the adhesive eAtnadate is observed from the orifice of the coating die, or if foaming is observed, it is eliminated through the use of a contact coating die. Thus, a uniform, clear coating, that is free of foam-induced adhesive gaps, bubbles, or other coating defects, is obtained. Furthermore, inclusion of the transient polar processing aid can be used to significantly reduce the melt temperature and melt viscosity of the hydrophobic adhesive polymer relative to the same hydrophobic adhesive polymer lacking the processing aid. Thus, the resultant hydrophobic adhesive coating is substantially free from thermal degradation, as well as melt flow lines, translucent coloration, andlor a shark skin appearing surface. Furthermore, due to their fugitive nature, the transiernt polar processing aids do not significantly affect the ultimate properties of the final hydrophobic adhesive polymer coatings:
Specifically, the present invention provides a method of coating an adhesive polymer comprising hot-melt coating an adhesive composition of a hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a coating die onto a substrate, wherein the transient polar processing aid comprises at Least 0:5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions; and wherein the adhesive composition is hot-melt coated at a temperature below the boiling poizat of the transient polar processing aid at atmospheric pressure.
Also, the present invention can provide a method of coating an adhesive polymer comprising hot-melt coating an adhesive composition of a hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a contact coating die onto a substrate; wherein the transient polar processing aid comprises at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions9 and v~rherein the adhesive composition is hot-melt coated at a .
temperature at or above the boiling point of the processing aid at atmospheric pressure.
1fie present invention also can provide a method of coating an adhesive polymer comprising hot-melt coating a hydrophobic adhesive polymer and a transient polar processing ~d from an orifice of a ~~~g die onto a substrate, wherein the transient polar processing aid comprises at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer ealuilibrated at ambient conditions, and wherein the hy~.~phobic adhesive polymer and the transient polar processing aid are not substantially mixed prior to hot-melt coating of the hydrophobic adhesive polymer.

In addition, the present method can provide a method of coating an adhesive polymer comprising: (a) providing a hydrophobic adhesive polymer suitable for hot-melt coating; (b) adding a transient polar processing aid along with the hydrophobic adhesive polymer, wherein the transient polar processing aid comprises at least 0.5 percent by weight above the weight of .residual water present in the hydraphobic adhesive polymer onto a substrate utilizing control means for elimination of foaming of the hydrophobic adhesive e~trudate.
Further, the present invention can pravide a hot-melt coatable adhesive composition comprising a hydrophobic adhesive polymer in combination with a transient: polar processing aid, wherein the transient polar processing aid comprises at: least 0.5 percent by weight above the weight of residual water present. in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the adhesive composition is capable of being hot-melt coated onto a substrate to provide a. substantially foam-free adhesive coating.
According to one aspect of the present invention, there is provided a method of coating an adhesive polymer comprising hot-melt coating an adhesive composition of hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a coating die onto a substrate, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the composition is hat-melt coated at a temperature below the boiling point of the transient polar processing aid at atmospheric pressure.

According to another aspect of this method, the hydrophobic adhesive polymer can be pressure-sensitive and can be selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.
According to another aspect of the present invention there is provided a method of coating an adhesive polymer comprising hot-melt coating an adhesive composition of a hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a contact coating die onto a substrate, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the composition is hot-melt coated at a temperature at or above the boiling point of the processing aid at atmospheric pressure.
According to another aspect of this method, the hydrophobic adhesive polymer can be pressure-sensitive, can exhibit a glass transition temperature of 20°C or less and can be selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.
According to still another aspect of the present invention there is provided a method of coating an adhesive polymer comprising hot-melt coating a hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a coating die onto a substrate, wherein the transient 5a polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the hydrophobic adhesive polymer and the transient polar processing aid are not substantially mixed prior to hot-melt coating of the hydrophobic adhesive polymer.
According to another aspect of this method, the hydrophobic adhesive polymer can be pressure-sensitive and can be selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.
According to yet another aspect of the present invention, there is provided a method of coating an adhesive polymer comprising: (a) providing a hydrophobic adhesive polymer suitable for hot-melt coating; (b) adding a transient polar processing aid along with the hydrophobic adhesive polymer, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions; and (c) hot-melt coating the hydrophobic adhesive polymer onto a substrate utilizing control means for elimination of foaming of the hydrophobic adhesive extrudate.
According to another aspect of this method, the control means can include means for regulating the temperature of the hydrophobic adhesive polymer prior to the hot-melt coating.
5b According to another aspect of this invention, as an alternative, the control means can include means for limiting the mixing of the transient polar processing aid with the hydrophobic adhesive polymer prior to hot-melt coating of the hydrophobic adhesive polymer.
According to a further aspect of the present invention there is provided a hot-melt coatable adhesive composition comprising a hydrophobic adhesive polymer in combination with a transient polar processing aid, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the adhesive composition is capable of being hot-melt coated onto a substrate to provide a substantially foam-free adhesive coating.
According to another aspect of this method, the hydrophobic adhesive polymer can be pressure-sensitive and can be selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects obtained by its use, reference should be had to the accompanying descriptive matter, in which there is illustrated and described preferred embodiments of the invention.
5c Definitions For the purposes of this invention:
"Polymer" refers to a homopolymer, a copolymer, or an oligomer, as well as any mixtures or blends of one or more homopolymers, and/or one or more copolymers, and/or one or more oligomers.
"Copolymer" refers to a polymeric material produced by the polymerization of two or more dissimilar monomers, either with or without another functional group grafted thereto, as well as to a homopolymer with a functional group grafted thereto. Thus, the term "copolymer" includes, without limitation, random copolymers, block copolymers, sequential copolymers, and graft copolymers.
"Adhesive polymer" refers to a polymer that is inherently adhesive, or has been rendered adhesive by combining additives and/or modifiers with the polymer.
Examples of suitable additives and/or modifiers include, without limitation, tackifiers, plasticizers, stabilizers, pigments, antioxidants, cross-linking agents, and combinations thereof.
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WO 93120165 PC.'T/US93/02437 A "hydrophobic adhesive polymer" refers to an adhesive polymer that has a strong tendency to repel, and is essentially incapable of dissolving in, water.
An "equilibrated" hydrophobic adhesive polymer refers to a hydrophobic adhesive polymer in which the residual water content remains constant at ambient conditions, S as defined below. Thus, at equilibrium, the number of water molecules leaving the hydrophobic adhesive polymer is equal to the number of water molecules entering it.
"Ambient conditions" refers to the temperature and relative humidity conditions of a typical room in which a hydrophobic adhesive polymer is allowed to equilibrate prior to processing by the method of the present invention. In general, ambient conditions includes temperatures of from about 20°C to about 25°C, and relative humidifies of from about 409b t~ about 609b. For the purposes of determining the equilibrium residual water content of a hydrophobic adhesive polymer according to the present invention, ambient conditions are den to be about Z1°C and about 509'0 relative humidity.
"Transient polar processing aid" refers to a compound or composition with a dipole moment that is used to facilitate the hot-melt coating of a hydrophobic adhesive polymer, and that is only present for a short period of time after the hot-melt coating of the hydrophobic adhesive polymer: Thus, a tranSiem polar processing aid is a fugitive material that does not substantially affect the ultimate properties of the hot-melt coated hydrophobic adhesive polymer.
An "adhesive composition" refers fro a substantially uniformly dispersed heterogeneous mixture of at Ieast one hydrophobic adhesive polymer with at least oae transient polar processing aid: In general, the adhesive composition will appear as a creamy or butter-like composition when substantially uniformly mixed according to the method of the present iniventiozt.
As used herein, "coating die" refers to a mechanical device, typically connected to the output end of a heated single- or twin-screw extruder, in which a molten adhesive or adhesive composition as extruded from an orifice adjacent a suitable substrate, such that the ' substrate is hat-melt coated with the molten adhesive or adhesive composition.
In general, gating dies are used to apply an adhesive coating to a backing material during the preparation of tapes; dressings; envelopes, abrasive products, and the like.
Examples of typical coating dies; includes! without limitation, draw dies, wipe-film dies, slot-orif ce dies, .
drop-film dies; and roll waters.
"Contact coating die" refers to ~ coating die in which the orifice of the coating die and the substrate to be coated are, or nearly are; in intimate contact during the hot-melt coating process: Typically, the contact between the extruded molten adhesive or adhesive -ab-R , .. ... ,: ;,.', . . ,;. ..., ; . .." .: ,: . _ . _-, .. . ., .:.
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~''~ 93/20165 PCT/iJ~93/02437 composition and the substrate results in a uniform pressure across the coating die orifice that can be manipulated, along with the proximity of the orifice to the substrate surface, as well as the coating speed, to regulate the thickness and uniformity of the resultant adhesive coating. A wipe-film coating die comprises but one example of a preferred contact coating die according to the present invention.
As used herein, "atmospheric pressure" refers to the pressure exerted by the air at the location where a hydrophobic adhesive polymer is being hot-melt coated according to the present method, which will support a column of mercury 7f0 mm high. For example, at sea level, atmospheric pressure is taken to be about 0.01 MPa (14.696 psi).
Detailed Descriptign of Embodim~ of the Invention I'~'sinE Aids IS Any polar material; preferably a polar liquid, that is incompatible with the hydrophobic adhesive polymers used in the method of the present invention, and that rapidly dissipates after the hot-melt coating of he hydrophobic adhesive polymers, can serve as a transient polar processing ofd in the present method: Nonlimiting examples of suitable transient polar processing aids for use in the method of the present invention include, water, methanol; ethanol, isopropanol, and combinations thereof, with water being preferred.
Importantly,: utilization of transient polar liquids; such as water, ensures that the processing aid is a filgitive mateaal that does not remain along with, or as a component of, the hydrophobic adhesive polymer after hot-melt coating. Thus; the transient polar processing aid does not substantially affect ;the ultimate properties, including; without limitation, the clarity, smoothness, tack, or shear strength, of the hydrophobic adhesive coating.
~'he transient polar processing aid utilized in the method of the present invention should comprise at least 0.596 by weight shave the weight pf residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions. Preferably, the transient polar processing aid should comprise from about 0:5~ to about 10~ by weight, more preferably from about 196 to about 596 by weight above the weight of residual water present ~ ~e hydrophobic adhesive polymer equilibrated at ambient conditions. In this regard, the residual water present in the hydrophobic adhesive polymer fan derive from a member of s~urces. For example;' the residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions could come from excess water remaining after separation of the hydrophobic adhesive solids from the aqueous reactioh medium of a suspension or emulsion polymerize hydrophobic adhesi~re polymer.

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WO 931ZUi6~ ~ ~ ~ ~ ~ ~ , PCT/US93/02437 In any of the embodiments of the method of the present invention, the transient polar processing aid can occur in a liquid form, vapor form, or a combination thereof. For example, when the hydrophobic adhesive polymer is hot-melt coated at temperatures that exceed the boiling point of the transient polar processing aid at atmospheric pressure, the processing aid will typically vaporize immediately after coating to leave a smooth, clear adhesive coating that is substantially free of any residual transient polar processing aid. On the other hand, when the hydrophobic adhesive polymer is hot-melt coated at temperatures below the boiling point of the transient polar processing aid at atmospheric pressure, the processing aid will typically occur as a liquid, or a liquidlvapor combination. In this case, if a contact coating die is used, the pressures generated at the die orifice/substrate interface may be such that the transient polar processing aid flashes off almost immediately after the hot-melt coating of the hydrophobic adhesive polymer. Conversely, if a non-contact coating die, such as a draw die, is employed, the transient polar processing may occur in a substantially liquid form, that will evaporate or otherwise dissipate from the hydrophobic adhesive soon after hot-melt coating.
In this regard, the inherent incompatibility between the transient polar processing aid and the hydrophobic adhesive polymer will greatly enhance the tendency of the transient polar processing aid to dissipate from the resultant hydrophobic adhesive coating as rapidly as possible. In addition, the elevated coating temperatures preferably used according to the method of the present invention will further enhance the tendency of the transient polar processing aid to evaporate or otherwise dissipate from the resultant hot-melt adhesive coating. 'Ifius, whether the hydrophobic adhesive polymer is hot-melt coated at temperatures andlor pressures above or below the boiling paint of the transient polar processing aid external to the coating die, the transient polar processing aid will act as a fugitive processing aid that rapidly dissipates from the hot-melt coated adhesive coating, without substantially affecting the ultimate properties of the coating: Furthermore, whatever the farm of the transient polar processing aid; whether liquid, vapor, or a combination thereof, practice of the method of the present inv~htion provides smooth, clear hot-melt coatings of hydrophobic adhesive polymers, where such coatings were not previously possible.
H~f~rO~hoi~ie AdhP ive Polymers Any hydrophobic adhesive polymer, as defaned herein, can be processed according to the method of the present invention. For example, hydrophobic adhesive polymers displaying ~ T$ ~f greater than ZO°C, such as wax E't'A
(ethylene vinyl acetate) hydrophobic adhesive blends suitable for carton sealing, can be processed by the method of _g_ the present inveaotion. Preferably, however, the hyd:ophobic adbesive polymer comprises a hy~ p . ' 've adhesive polymer. Wore preferably, the hydrophobic pressure-sensitive adhesive polymer should exhibit a glass transition tempeiadrre (Tg) of 20°C .or less, and most preferably a Tg of 0°C or less. Examples of hydrophobic presune-sensitive adhesive polymars, aid then methods of prepua<i~, are died in U.S.
Patau No. 2,?48,192 (pheaolic arced robber based adhesives), U.S: Patent No. Re 24,906 (water-based and solvent-based adbeSives), and U.S. Parrot Nos. 4,833,179, and 4,952,650 .
. (swsp~ion~olyma~izod aaylate pressure-sensitive adbaive'copolymaa~
Specific ales of a i~ybropbobic preasnro-smsitive adhesive polymar for use in the mabod of the invesi<ion include, withart 1'mi>tavotr, an adhesive . .
copolymer of isooayl acxylate pOA) and mdhaaylic uid (MAA) in a 96:4wraght ratio, prepared as per acample No. 5 of U.S. Patent No. 4,952;650; KRATONTM~Sed rains of styreaeJbutadieaeJatyreae or ayreae!'sso~elayrene adhesive block oopolymaa (Shill .
Chemical Co., Hoaston, TX); a polyisobutyleae~ed sdtiesive~ prepped using VISTANEXTI!'1 resim (Eaton t7~earical Co., Houston, T7n, aocardiDg to the procedure deta0ed on page 291 of , rubber~ased adhesive resin No. 820-33&BE (F'mdley Adhesives, Inc., Wsoavvatoaa, li4n; .
GET.VATM 737 resin, an etbylhexyl saylatelvinyl a~teJdhyl aaylate. adhesive copolymer (Moa~anto Co., St. Louis, MO); DURO-TAKTM resin No. 34-42223, a ~bba-based adhesive resin (National Starch and (~niail Gorp., ~idg~rata, Nn; and No. 355 dimdhylpolys0o~ume medical adhesive (Dow Corning Cocp., lid, Mi).
Hydrophobic pressure-sensitive adhesive polymers can be selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.
In ~a preferred embodiment, the hydmpbob~ presSUrn-se~itive~sdbaive polymer comprises an aaylate pressure-sensitive adhesive polymer, more preferably. a water~ased acxylate pressure-sensitive adhesive polymer formed ~thmugh emulsion or anion , .
polymerization techniques. In a particularly preferred embodiment, the hydrophobic pressure-sensitive adhesive polymer comprises a suspension-polymerized.
acrylate pressure-seasitive adhesive copolymer having a Tg of 0'C or less, as desa~ed in F~m~ple No. S of U.S. Patent No. 4,952,650.

~.geaeral, these preferred anspeasion~olym~a~izod aciylate prtsmre~itive adhesive-copolynøers are produced by the following methodology. An~acrylfc acid ester of a non-tertiary alcohol, having frog 1 to 14 carbon atoms, a polar monomer ec~polymerizable with the acrylic acid ester, a chain transfer agent, a free-radial initiator, and a modifier moiety selected from 2=polystyryletbyl methacrylate macronwlecular monomers, reactive zinc salts, and hydrophobic s0icas is combined into a mono~r premix. This premix is they combined with a water phase containing a sufficient amount of a suspending agent, such as an anionic surfactant, to form a suspension. The suspension is then concurrently agitated and polymerized for about 2-16 hours, at a temperature of from about 40°C
to about 90°C, until polymer beads are formed. At this point, the polymer beads comprise about 409b ofthe suspension, and can thereafter be washed and separated as needed.
In the preferred suspension-polymerized acrylate pressure-sensitive adhesive copolymer, the acrylic acid ester of a non-tertiary alcohol should comprise at least about 80 parts by weight, based on a 100 parts total monomer content. Preferred acrylic acid ester monomers include, without limitation, isooctyl acrylate, isononyl acrylate, 2-ethylhexyl acrylate, and butyl acrylate, with isooctyl acrylate being particularly preferred. Also, preferred polar monomers include, without limitation, acrylic acid, methacrylic acid, N-vinyl pyrrolidone, vinyl acetate, acrylanudes, and substituted acrylamides, while preferred modifier moieties include, without limitation, reactive zinc salts, and macromers, such as 1-polystyrylethyl methacrylate. In the especially preferred suspension-polymerized acrylate pressure-sensitive adhesive copolymer described in Example No. 5 of U.S.
Patent No.
4,952,650, the acrylic acid ester monomers, polar monomers and modifier moieties comprise isooctyl acrylate, methacrylic acid, and ZnO, respectively.
The suspension polymerized acrylate pressure-sensitive adhesive polymer can comprise an acrylate pressure-sensitive adhesive copolymer of an acrylic acid ester monomer selected from the group consisting of isooctyl acrylate, isononyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, and combinations thereof, and at least one other monomer selected from the group consisting of acrylic acid, methacrylic acid, N-vinyl pyrrolidone, vinyl acetate, acrylamides, substituted acrylamides, and combinations thereof.

vVhile no direct correlation exists, the molecular weight of the hydrophobic ' adhesive polymers processed by the method of the present invention can influence the degree to which the present method enhances the coating characteristics of a given hydrophobic adhesive polymer. In general, higher molecular weight hydrophobic adhesive polymers of up to about one million, or higher, molecular weight will more greatly benefit when processed by the method of the present invention. 'Ibis is especially true with respect to the preferred suspension-polymerized acrylate pressure-sensitive adhesive copolymers processed by the method of the present invention. In particular, these materials exhibit molecular weights ranging from about 105 to about 10'6, and when hot-melt coated from the conventional dry state, undergo significant thermal degradation. However, when processed with the transient polar processing aids of the present invention, their melt temperatures and viscosities can be reduced to the point that virtually no thermal degradation occurs during the hot-melt coating process.
Whether polymerized in a solvent-based system or a water-based system, the majority, if not all, of the reaction medium in which the hydrophobic adhesive polymer is polymerized should be removed from the adhesive solids prior to processing by the method of the present invention. The particular separation method employed will depend upon whether the hydrophobic adhesive polymer is in a solution of an organic solvent, or in a two--l0a-p>mse water-based system, such as an camlsion or suspension polymerized hydrophobic adhesive polymer. In .either instance, the_~oe hod ~ployed. is not critical to the practice of the method of the present inv~ion. Thus, those skilled in the art will readily choose a ,given separation technique that best fits their specific needs, based at least in part on the characteristic of the chorea hydrophobic adhesive polymer, and the hot-melt coating techniques and equto be employod.
For example, solution polymerized adhesive polymers are typically recovered by evaporative techniqaes, such as the use of aged Zlwrfilm evapaabors. ,~ ~, .
"Ferry's Chemical Engineers' Handbook", R.H. Ferry et al. Eds., McGraw HOI, New York, NY (sixes ed., 1984). On the her hand, adhesive polymers prepued emulsion or suspension techniques as be removed by ehher evaporative techniques or physical soon methods, such as suing, filtration, centrifugatiwn, or expression.processes.
,~ ~,g"
"Ferry's Chemical Engnaeers' Handbook", ; 'Solid-Liquid Septuration", L.
Svarovsky, td., Buttaworths, London, England (197» "Handbook of Separatmn Tedmiques for Cheanical Engineers", McGraw Hill, New York, NY (2nd ai., 19$8). Furthermore, c~agalants and flocaulants may also be added to the hydropl~obic adhesive polymer emulsions or suspensions to agglomerate the solids, and thereby, improve the efficiency of the separation technique.
In a preferred aabodimeox, the preferred lion-polyme~ed acrylate pressure-sensitive adhesive copolymer is recovered from 'rts aqueous reaction m0dinm by mechanical separation m~hods. More poly, the excess water remaining after polymerization of tire adhesive copolymer is expressed from the adhesive solids component through the use of a mechanical prrss. ~ ~, "Ferry's Chemical F.ngineaa' Handbook", at (fir 19, pp. 103-107.
In a particularly preferred embodiment, a continuous-screw extrusion press is used to separate the aqueous reaction medium from the preferred suspension~olymerizod acryiate pressure-sensitive adhesive copolymer of the present invention. ~
ggt, ~. at 104-105. Low-temperature, mechanical expression of the reacxion medium from the adhesive solids avoids excessive adhesive thermal degradation problems typically associated with. other separation techniques, such as thermal evaporation of the excess reacxion modium.
Coati ~ ~
As previously noted, traditional hot-melt coating of hydrophobic adhesive polymers often results in a mm~ber of coating defects resulting from the conditions employed, ! ? s~~.; 7 ' J.. . , . ~.. J-1~:
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,...': . ~: y n.. , '..;,. . .'., .~ , ......,.. . ,..... _' . - ~...~. .
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!~V(7~ 93/20165 ' PC'I'/US93/02437 and/or the additives utilized. In particular, at Ieast three dififerent classes of coating defects can result from the traditional hot-melt coating of hydrophobic adhesive polymers.
As used herein, "high-temperature coating defects" refers to coating defects that result from the thermal degradation of a hydrophobic adhesive polymer when hot-melt coated at the traditional temperatures required to lower the melt viscosity of the polymer so that the molten polymer easily flows through the extruder and coating die orifice.
Typical high-temperature coating defects, include, without limitation, discoloration of the coated adhesive polymer, an objectionable burnt odor, and/or loss of adhesive properties. ~, g,,g,,, L.
Mascia, "The hole of Additives in Plastics," pg. 16, John Whey & Sons, New York, NY
(1974); "Additives for Plastics," R. Seymour, Ed., pg. 250, Academic Press, New York, NY
(1978).
"Low-temperature coating defects" refer to defects resulting from the hot-melt coating of hydrophobic adhesive polymers at emperatures where the molten polymer exhibits ~' higher melt viscosities, and thus, has a tendency to adhere, at least in part, to the metal surfaces of the extruder and coating dis during hot-melt Boating. Accordingly, while utilization of these coating temperatures may reduce the degree of thermal degradation of the hydrophobia adhesive polymer, low-temperature coating defects, including, without limitation, whitish or ~anslucent coloration, melt-flow lines, a "shark skin"
appearing surface, and other surface irregularities; typically result. ,~ g~, "Plastics Additives 2U Handbook", supra at pp. 43b-4~8.
As noted above; utilization of typical processing aids in the general melt extavsion of hydrophobic polymers can detrimentally affect the ultimate properties of those polymers; due to the tendency of these processing aids to remain as a component of the hydrophobia polymer after' extrusion: ;~ g~,, "Encyclopedia of Polymer Science and Engineering", supra, at pp. 307-324. As used herein, "processing aid-induced coating defects" refers to the extension of these problems to the hot-melt coating of hydrophobic ~~ive polymers with processing aids. In particular, these processing aid-induced coating defects can include; without limitation, loss of adhesive or cohesive properties, as well as undesirable discoloration, odor, and/or toxicity, being imparted to the resulting adhesive coating:
practice of the method of the present invention yields a smooth, clear, foam-free adhesive coating that is substantially free of all three classes of coating defects. Specifically, in a first embodiment: of the method of the present invention, an adhesive composition of a hydrophobia adhesive polymer ahd a transient polar processing aid are hot-melt Boated from 3S an orifice of a coating die onto a substrate. In this regard, the temperature of the transient polar processing a~ at exic pres~re is an i~or~ consideration in the type of coating die nsed-to hot-smelt coat-the sdlresive aomposltioa.
1n a fast aspax, the adhesive o~o~posifion is hot-melt coatod oooto the sure at a temperature below the booing point of the transient polar processing aid at atmospheric pressure. For e~mple, an adhesive composition of the preferred suspeasi~on-pdymnaized acrylate pressure-sensitive adhesive copolymer, with water as the tra~ieat polar processing aid, is hot~nelt coated at a temperature of less than 100°C axording to this aspect of the mdhod of the present invention. Even t6oagh the hydrophobic ~esive polymer and transient polar processing aid are well-3mixod into a substantially uniformly did adhesive composition, surprisingly, no of the adhesive composition is obsayed at the coating die orifice. Fmrthamore, whey the adhesive composition is hot-melt coated onto a su~tabie substrate, a smooth, clear, ~ and fbam-free ~d6esive coating, that is five:
from high_ temperature, low-tempersca~re, and proaasing aid-induced defects, is .
The ability to extzude a foam-free adhesive composition from the orifice of a i5 a~adng die allows virtually any type of ooatmg die to be asod wixh this aspect of the mdhod of the present invention. Thus, draw dies, wipe-film dies, slot-orifice dies, drop-film dies, roll, as well as other coatiavg dies readily known and used by those akdled in the art, are considered to be useable with this aspecx of the method of the preset invention. For a thorough review of hot-melt coating dies and as5ociatod c~aating equipment, reference can be had to die "Handbook of Pressure-Sensitive Adhesive Technology", , at (~pter 28, pp.
558 573 .
Furthermore, the ability to produce a foam-free ooaauog at temperatures below the boding point of the transient polar processing aid at at~heric pressure, virtually ensures that the resulting hydrophobic adhesive coating will be free of thermal degradation, and its resulting high~empe:ature taoating defects. Una~peaedly, however, the hot~aelt coating of the adhesive composition also results in an adhesive coating that is also substantially free of any low-temperabare coating defecxs. In comparison, the hot-melt cx~tiag of the hydrophobic adhesive polymer in the absence of the transient polar processing aid, at tempauarres below the boiling point of the transient polar processing aid at atmospheric pressure, would result in an adhesive coating with mimerous low-temperature coating defects, such as melt flow lines,~traaslucear ooioration, and a shark skin appearance, if in fact, the hydrophobic adhesive polymer could even be fed into the extruder and coated at these temperatures.
In a sxond aspect of the first embodimtat of the present invention, the adhesive composition is hot-melt coated onto the substrate at a temperawre at or above the boiling .;,..;, ..:.:' u' ..;~;.. ,, ~.~..::;,'.- '. ,:..: ,'.' . ...,,:.:.'. .-;
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Vd~ ~3/20165~ ~ ~ ~ ~ ~'' '~ ~ , , . . ' ~ PCT/US93/02437 point of floe transient polar processing aid at atmospheric pressure. For example, a temperature at or above 1~0°C is used to hot-melt coat the preferred adhesive composition of a suspension-polymeriz~i acrylate pressure-sensitive adhesive copolymer and water onto a substrate. However, when these temperature conditions are employed with the substantially S uniformly dispersed adhesive composition, at least some foaming of the adhesive composition at the coating die orifice will be observed. As used herein, "foaming" of the adhesive extrudate includes the occurrence of bubbles, such as moisture bubbles, or other observable discontinuities, within the adhesive extrudate, as well as the actual bubbling and/or frothing of the adhesive extrudate. Surprisingly, if a contact coating die is used, a smooth, clear, and foam-free adhesive coating is obtained, despite the tendency of the adhesive extrudate to foam from the die orifice. Thus, while those skilled in the art have to date viewed a foaming hydrophobic adhesive polymer extrudate as being non-coatable, this embodiment of the method of the present invention has shown otherwise.
Furthermore, utilization of a transient polar processing aid, such as water, can lower the coating temperature of the adhesive composition, relative to the hydrophobic adhesive polymer lacking the transient polar processing aid, so that virtually no thermal degradation; as indicated by high-temperature coating defects, of the resulting hydrophobic adhesive coating occurs: Likewise, the melt viscosity of the adhesive composition can be lowered such that the composition can be cleanly fed through the extruder, and thereafter, the contact coating die; without incurring low-temperature coating defects, such as melt-flow lines, taanslucent coloration, a shark skin surface, or the like. In addition, at the temperatures employed; the transient polar processing aid vaporizes upon exiting the coating die orifice: Thus, the resulting adhesive coating is smooth, clear, foam-free, and does not exhibit processing aid-induced coating defects resulting from excess processing aid remaining iai' the resultant hydrophobic adhesive coating.
Any contact coating die can be used with this aspect of the method of the present invention, as lone as there is intimate, or nearly antimate, contact between the orifice of the coating die and the surface of the substrate to be coated. In a preferred embodiment, the contact coating die comprises a wipe-film coating die, such as those available from Extrusion hie, Inc.; Chippewa Falls, VVi. I~owever, it should also be realized that in certain instances; a foamed adhesive coating may be desired. In this regard, a coating die other than a contact die, such as a drop-film die, could be used to grovide such a coating.
In a second embodiment of the method of the present invention, a hydrophobic adhesive polymer and a transient polar processing aid are contacted and hot-melt coated from an orifece of a coating die onto a substrate. In contrast to the casting of the substantially ~~~? ~2 ,VO 93/20165 PCT/US93102437 uniformly dispersed adhesive composition of the first embodiment of the present invention, the hydrophobic adhesive polymer and transient polar processing aid are not substantially mixed prior to hot-melt coating. In fact, it is desirable to utilize extruders, coating dies, and other equipment that impart little, or more preferably, essentially no mixing of the hydrophobic adhesive polymer and transient polar processing aid prior to hot-melt coating.
Unexpectedly, when the transient polar processing aid is not substantially mixed with the hydrophobic adhesive polymer; no foaming of the hydrophobic adhesive polymer is observed at the orifice of the coating die; even when the hydrophobic adhesive is hot-melt coated at a temperature above the boiling point of the transient polar processing aid at atmospheric pressure. Thus; in contrast to the first embodiment of the method of the present invention, the temperature of the transient polar processing aid at atmospheric pressure is not an ~~t ~~ideration in obtaining a foam: free extrudate, and accordingly, a foam-free hot-melt hydrophobic adhesive coating.
As with the first aspect of the first embodiment of the method of the present invention; the non-foaming nature of thie hydrophobic adhesive extrudate allows virtually any type of coating die to be used with this embodiment. Thus, draw dies, wipe-film dies, slat-orifice dies, drop-film dies, roll-coolers, as well as other coating dies readily Icaawn and used by those skilled in the art, can be used with this embodiment of the method of the present invention:
ZO As noted above; the degree of muting of the hydrophobic adhesive polymer and the- ransient polar processing aid can be controlled, at least in part, through the selection of appropriate hot-melt coating equipment; including extruders; coating dies, and associated equipment. In this regard, one way of limiting he mixing of the hydrophobic adhesive polymer and transient'polar gmcessing aid is to not'hring the two components into contact until immediately prior to hot-melt coating. For example, in a typical embodiment, die hydrophobic adhesive polymer is fed into a single- or twin-screw extruder connected to any appropriate coating die. In addition, an injection port, connected to a high:
pressure pump, is included in the extruder immediately prior to the coating die; and after any veal ports in the extruder barrel In practice, the r~lten hydrophobic adhesive polymer progresses down the heated extruder until it encounters the injection port, where a pre-determined quantity of the transient polar processing aid is injected into the extruder along with the molten adhesive polymer. Immediately thereafter; the hydmphobic adhesive polymer reaches the coating die, without undergoing any substantial mixing with the transient polar processing aid; and is hot-melt coated onto a suitable substrate.

WO 93/ZOI65 ~ ~ ~ ~ j ~ r~ 1'CT/US93/02437 ' Late addition of the transient polar processing aid ensures minimal, if any, mixing of the hydrophobic adhesive polymer and transient polar processing aid prior to hot-melt coating. In addition, by injecting the transient polar processing aid after any extruder vent ports, the hot-melt coating operator can be assured that essentially all of the processing aid will come in contact with the molten hydrophobic adhesive polymer prior to its hot-melt coating onto the substrate. Alternatively, the transient polar processing aid could be brought into contact with the hydrophobic adhesive polymer at an earlier point in the process, provided that no miring, or low mixing was maintained. For example, an extruder of relatively short length, with a smooth inner barrel surface, and lacking in any mixing pins or blades could be used to simply heat and convey the two components to the coating die. In either instance, the transient polar processing aid will flash-off, or otherwise dissipate from the resulting hot-melt adhesive coating, depending upon the coating temperature employed, to yield a clear, smooth; and foam-free hot-melt coating that is substantially free of any residual transient polar processing aid.
As with the previously described embodiment of the present invention, wherein a substantially uniformly dispersed adhesive composition is hot-melt coated, the addition of a ~~ieat polar processing aid provides a resultant hydrophobic adhesive coating that is substantially free of high-temperature; lowaemperature, and processing aid-induced coating defects. Thus; whether the transient polar processing aid is intimately combined with the hydrophobic adhesive polymer to yield a substantially uniformly dispersed adhesive composition, or is just contacted with the hydrophobic adhesive polymer with little or no mixing, the method of the present invention provides clear, smooth, and foam-free hydrophobic adhesive coatings where such coatings were previously thought to be unobtainable:
In any of the embodiments or aspects of the method of the present invention, the hydrophobic adhesive polymer and transient polar processing aid can be brought together in various points in the process. For example, is one typical methodology, the transient polar processing aid is added along with the hydrophobic adhesive polymer immediately prior to coating: Typically this addition is accomplished through the high pressure injection of the transient 'polar processing aid into a heath extruder near the attachment point for the coating die; and after any vent ports located in the extruder barrel. As previously noted, this late addition of the transient polar processing aid is esp~ially useful with the second embodiment of the present invention, wherein aninimal or no mixing of the transient polar processing aid and hydrophobic adhesive polymer is desired prior to hot-mail coating.
However, this late injection of the transient polar processing aid can also be utilized with the first embodiment -lb-"7 93120165 ~ ~ ~ ~ r~ ~ J ~ PCT/US93102437 of the present invention, as long as the hydrophobic adhesive polymer and transient polar processing aid are adequately mixed to form the substantially uniformly dispersed adhesive composition prior to hot-melt coating.
In a second typical methodology of the present invention, the transient polar processing aid is incorporated into, or is an existing component of, the hydrophobic adhesive polymer prior to feeding of the polymer into a non-vented extruder, and thereafter, to the coating die. For example, when the preferred suspension-polymerized acrylate pressure-sensitive adhesive copolymer used in the method of the present invention is polymerized, it forms adhesive beads in an aqueous medium. During the initial separation of the hydrophobic adhesive polymer from he reaction medium, a certain percentage of the aqueous reaction medium can be allowed to remain with the adhesive solids, This residual water can then serve as the transient polar processing aid of the method of the present invention, thereby obviating the need to inject a transient polar processing aid into the molten adhesive unmediately prior to hot-melt coating. Similarly, even when a previously dried, essentially 10096 solids, hydrophobic adhesive polymer is used, the transient polar processing aid can be added to the adhesive composition prior to its beiag fed into the non vented extruder, and thereafter; the coating die.
The early addition, or maintenance of, the transient polar processing aid with the hydr~phobic adhesive polymer is especially useful with the first embodiment of the ~20 . method of the present invention. For example, a substantially uniformly dispersed adhesive composition often directly results from the mechanical separation of the aqueous .reaction medium from the hydrophobic adhesive solids, such as through the use of the preferred continuous-screw extrusion press. Furthermore; by combining the transient polar processing aid and hydrophobic adhesive polymer prior ta; or immediately after, feeding of the materials into a non-vented extruder, a thorough' mixing of these components to form the adhesive composition can be accomplished prior tn' the hot-melt coating of the composition. In this regard, those skilled in the art will readily select appropriate equipment to facilitate the ~~g, or limit the mixing, of the transient polar processing aid and the hydrophobic ~esive polymeir as the particular' cireumstanee5 require.
For example, extruder screws with mixing pins or blades, as well as various ~Iters and gear pumps can be used to thoroughly naix the adhesive composftion inw a ubstantially un'sform dispersion. Conversely; these coanponents can be eliminated, and short, srmootb extruders can, be used to reduce or essentially eliminate the mixing of the hydrophobic adhesive polymer and transient polar processing aid pxior to hot melt coating.
Thus, it is within ~th~.scope of the present invention for the transient polar processing aid to .:,:;~ . ~ .: . :.::; : . ::: .; :,.. : : . . - , . ,:, . . .
a .. : . ,:. , :. ....::, .. ;. .. .. . ., .: .. ..-:;. . .:.... .. .. .",.a :...:. .
,: ::: ... .-.:.".. ,-:. ..:..: . : .:: ,. :....... , ,.... - .. : .. , ::- :
.-. ...,.:,.....
. . .., a . . ,~ . - , . , r W~ 93/20165 ~ ~ ~ ~ ~~3 ~ .~ PCT/US93/02437 be incorporated with the hydrophobic adhesive polymer at any stage of the process, including, during polymerization of the adhesive, prior to feeding of the adhesive into the non-vented extruder, and at any point within an extruder that is prior to the coating die and after any vent ports in the extruder barrel. .. , The ability to maintain a set quantity of the aqueous reaction medium in a suspension or emulsion polymerized hydrophobic pressure-sensitive adhesive, to serve as a transient polar processing aid, directly contradicts the standard teaching in the industry.
Traditional processing methodology dictates that an emulsion or suspension hydrophobic adhesive polymer be dried to remove essentially all of the water prior to hot-melt coating.
Failure to remove essentially all of the residual water would be expected to result in a non-coatable foaming extrudate. Further, even if one were to try and coat this foaming extrudate, it would be expected that undesirable adhesive coating with gaps, bubbles, and other irregularities would result. Surprisingly; the method of the present invention allows for the maintenance of a certain percentage of water along with the hydrophobic adhesive polymer, while still providing a hydrophobic adhesive, or an adhesive composition, that does not foam upon exiting the coating die; or should foaming occur, can be coated to provide a clear, smooth, and faatn-free adhesive coating through the use of a contact coating die.
The specific percentage of water, or other transient polar processing aid, that is allowed to remain with the hydrophobic adhesive polymer prior to extrusion and hot-melt 20' coating depends upon the particular adhesive being employal, and the coating characteristics desired to be obtained. For example, when coating the preferred suspension-polymerized acrylate pressure-sensitive adhesfve copolymer, once a preferred water content is determined, appropriate adjustments can be made iai the starting water content of the hydrophobic adhesive as seeded. If need be, the water-based adhesive can be subject~l to additional ZS drying or separation techniques to lower the water content to the desired hot-melt coating level. Likewise; vvater~ or other transient polar processing aids, can be added to the dried composition prior to extrusion and coating to arrive at the desired water content. In addition, these sane adjustments can be made with other hydrophobic adhesive polymers, and transient polar processing aids other than water 30 ' The specific hot-melt coating conditions to be employed with any given hydrophobic adhesive polymer can be readily determinai by those skilled in the art. For example, in one aspe<;t; optimum coating conditions cawbe established by coating the hydrophobic adhesive polymer in the absence of a transient polar processing aid, at a baseline temperature well below the thermal degradation point for that adhesive. At such a 35 temperature, the resulting hot-melt coating will likely show numerous low-temperature _18_ '' 'O 93/2U165 ~ ~ ~ ~ d ' PC1'/US93t02a37 coating irregularities; such as melt flow lines, shark skin, and a translucent coloration.
Thereafter, increasing amounts of a desired transient polar processing aid can be injected, or otherwise added, along with the molten adhesive polymer while observing the quality, as a reflection of the melt viscosity, of the resulting hot-melt coating. At a determinable point, the combination of the coating temperature and quantity of transient polar processing aid added will yield a high quality, hat-melt coating, that is foam-free and substantially free from low-temperature coating defects. Similarly, those skilled in the art will recognize that other optimum conditions can be readily determined by varying the temperature andlor pressure of the extruder and coating die at a pre-determined rate of addition of a transient polar processing aid according to the method of the present invention.
The hot-melt coating method of the present invention can be utilized to hot-melt coat a hydrophobic adhesive polymer onto virtually any substrate materiat.
Options in substrates to be utilized will be apparent, and readily selected, by those skilled in the art.
For example, when the method of the present invention is utilized to prepare tapes, including medical tapes, both woven! nonwoven, paper and plastic film backings, as well as combinations thereof; can be utilized:
The coating advantages obtained by the method of the present invention depend upon a number of factors, including the specific hydrophobic adhesive polymer, transient polar processing aid; and coating die employed, the quantity of processing aid used, the 2p degree of mixing of these components, and the coating temperatures and pressures employed.
Preferably; the transient polarprocessing aid is incorporated into the hydrophobic adhesive polymer at superatmospheric pressures. The specific pressure employed will depend upon the hydrophobic adhesive polymea~ employ, and the amount of processing aid to be added.
However; in general, it is preferable to maintain the extruder and coating die at pressures of from about Q.5 mega lPascals (MPa) to about 20 lVIFa, more preferably from about 1 MPa to about 10 MPa, and mast preferably from about 2 IVdPa to about 6 lVIPa.
Addition or injection of the transient polar processing aids at these pressures generally ensures that the transient polar processing aids remain in liquid form when combined, or brought in contact, with the hydrophobic adhesive polymer. This in turn provides a more exacting means of determining and regulating the quantity of the transient polar processing aid. added with the hydrophobic adhesive polymer to be hot-melt coated according to the present invention. In addition, it is also within the scope of the method of the present invention to add the transient polar processing aid at, or below, atmospheric pressures. gIowever, in such instances, the transient polar processing aid is often added in vapor form. Thus, the ability to exactly determine and WO 93120165 ~ ~ ~ ~ ~ ~ 'I PCT/US93/~2437 regulate the amount of transient polar processing aid combined or in contact with hydrophobic adhesive polymer is often lost.
As with the pressures employed, the specific temperatures used in the hot-melt coating method according to the piesent invention will depend on the embodiment or aspect of the present invention to be practiced, the chosen materials, the pressures employed, and the desired coating speed; among other factors. More importantly, inclusion of the transient polar processing aid can result in a significant reduction in the coating temperature of the hydrophobic adhesive polymer, or adhesive composition, below that observed when hot-melt coating the same hydrophobic adhesive polymer in the absence of a transient polar processing aid. For example, wben cauating the preferred suspension-polymerized acrylate pressure-sensitive adhesive copolymer with about 2.? 96 by weight of water as a transient polar processing aid, and at a pressure of from about 2 MPa to about 3 MPa, a coating temperature reduction of at least 40°~ (e.g. an about 2496 reduction from about 1?0°C to about 130°C) can be obtained. In general; utilization of the method of the present invention can be used to I5 reduce the coating temperature of hydrophobic adhesive polymers by up to fifty percent (5096), or more, relative to the temperatures required to hot-melt coat these same hydrophobic adhesive polymers in the absence of transient polar processing aids. This in turn can reduce; or completely eliminate, thermal degradation, and the resulting high-temperature coating defects; in the foal hydrophobic adhesive coating.
~Oe the addition of a ransient polar processing aid to a hydrophobic adhesive pt~lymer can be used to directly lower the hot-melt coating temperature.of that hydrophobic adhesive, or adhesive composition, it can atso be used to modify the coating characteristics of those materials at a pre-determined set temperature. For example, it may be desirable to maintain the extruder and coating die at a temperature well below the point where the 2~ hydrophobic adhesive polymer will undergo thermal degradation. However, as previously noted; these lower temperatures often lead to tow-temperature coating defects, such as melt flow lines, translucent coloration; a shark skin appearance, and other coating irregularities.
Addition of a transient polar processing aid according to the method of the present invention can lower the melt viscosity of the hydrophobic adhesive polymer, or adhesive composition, and thereby reduce or eliminate these coating defects.
Fox example, hot-melt coating of GELVATM ?37 resin, a hydrophobic pressure-sensitive adhesive copolymer of ethylhexyl acrylate/vinyl acetate/ethyl acrylate (Monsanto Ca., fit. Louis, M~), at a temperature of 1S0°C, and pressures between about 2.I
MPx to about 2.4 MPa, in the absence of a transient polar processing aid, results in an 3S adhesive coating with. a very irregular surface, and visible melt flow lines. Addition of ''O 93!20165 ~ ~. ~ ~ ~ ~ ~ pcrivs~3ioa4~~
increasing amounts of water as a transient polar processing aid reduces, and eventually eliminates, these coating defects, when 3.5~ by weight of water is injected along with the molten adhesive prior to hot-melt coating. Thus, the method of the present invention can be used to eliminate both high-temperature and low-temperature coating defects.
Virtually any type of extrusion equipment, including both twin- and single-screw extruders can be used to fe~1 and melt the hydrophobic adhesive polymers prior to coating by the method of the present invention. Preferably, the method of the present invention uses a single-screw extruder with an appropriate coating die attached thereto. In this regard, the selection of the particular. extruders and coating dies to be utilized to coat a IO hydrophobic adhesive polymer according to the method of the present invention will be readily apparent to, and subject to the specific needs of, those skilled in the art. ,~ ,~,,g,,, "handbook of Pressure-Sensitive Adhesive Technology", supra, at Chapter 28, pp. 558-573.
An important consideration in the practice of the method of the present invention is where the transient polar processing aid and the hydrophobic adhesive polymer I5 are brought together, relative to the location of vent ports located in the extruder barrel, if any. In particular, if a more exact determination and regulation of the quantity of transient polar processing aid added with the hydrophohic adhesive polymer is needed, the transient polar processing aid should be added at a paint in the extnader where essentially none of the aid will dissipate until after the hot-nnelt coating of the hydrophobic adhesive or adhesive 20 composition. Thus, the transient polar processing aid should preferably be added along with the hydrophobic adhesive polymer in a non vented extruder, or at a point in the extruder barrel after any vent ports, and before the coating die.
~ a preferred embodiment, the present method is utilized to coat substrates used in medical applications; such as tapes; dressings; surgical drapes and electrodes. When 25 coating hydrophobic adhesive polyrhers for m~dical applications, certain characteristics are required: Forexample' the adhesive coating should exhibit little, if any, odor. Problems with objectionable odor can result from an excess of residuat volatile components, such as un-reacted monomer; remaining in tire adhesive composition after polymerization, or due to thermal degradation of the adhesive during the hot-melt coating process. In addition, these 30 residnaH volatile components can' also present skin sensitivity issues with certain patients.
Practice of~ or enhancennents to, the method of the present invemion can be used to reduce these residual components, and thus, help to alleviate both these odor and sensitivity problems:
In the fist instance; residual volatile camponents, such as un reacted 35 W ononomers; can be removed by melt de<rolatiliaing (i.e. steam-strippiatg) the hydrophobic adhesive polymer prior to hot-~mdt gag. Spxific aumapies of anch melt ~izarion mixheds ~md,ap~m.din lrt. W, ''ng an E~v~da for Melt I?evolat0ization", pl,~,$~~~I~. pp. 47 51 (July 1986) .
In general, the process consists of repeated injection of ~m in'o the adhesive pdymer as it travels down the length of an e~atcnder. The injection of storm causal the tnoltea polymer to >wbble. At various jmt, a vacuum line, . m ~ p~ ~ ~e aatrnder, is used to dew-off residual volatr~ized mouomaa that are L'ba>red during the babbling of the molten polymer. ~ Melt devolad'liz~ion cm be inclndod along with the pta~icx of any of the embodim~ts ~ aspaxs of the me~Od of t~
pre~t Win. F~ Vie, when irot~ndt coating the preferred lion-pdymamed aaylaute pressure-sensitive sdhesive copolymer, the sdhesive copolymer cam be first melt devolat0izod to'remave rraidnal ~mreaotod moors. Tba~fter, a final inj~tion of water, or other bra~i~ polar processing aid, withoat v~tiag, cad vviih or with mixing of the pc~ssiag aid and hydrophobic adhesive polymer, can be added saoord~g oo t>u nu~d of the present invention. Than, a clear, :moth, and fwm~ree adhesive-coated pm~rct can be obramod, that is snallly free of unwsmted residaal movomer-odor.
1n the surd instance, the te~a~nre and/or melt viscosity lowing effect of the mdhod-of the present invention reduces, or essaa~ly eliminates, Mature ding defeas associated with the thermal degradaban of the hydrophobic adhesive polymer during hot-melt coating. For example, co~iag of the preferred sutp~sioa-polym~zod aayla~te arc-s~sitive sdhesive copolymer of the presaas imrartion wirbont a tnmsient polar processing aid typically results in highature ding defects, such as an objectionable "burnt" odor aadJor a bmwraiish discoloration of the adhesive e~udate.
However, whey this preferred adhesive is canted using water, or another transient polar processing aid, the melt temperature sad melt viscas'tty of the adhesive polymer an be lowered, each that virdially no objaxionsble burns odor or discoloration is obtained.
In a further enhancement to the mid of the presets invauion, sdditives, and in particular, thermallyaab0e additives, can be incorporated into the adhesive composition separately, or st the same time, as the transient polar processing aid. Ice pacti~lar, utilization of strategically placed injection port(s), connected to high-pcmue pumps, can be used to deliver these additives .into or sdjacant the hydr~hObic adhesive or adhesive composition, as detailed in S. Houl~an, "On Line Additive Injection in the Extrusion Process", ~i~ ~f ~~p 1988 ~13~m ~~9~~~~l~~pfetau<e pp. 9-11, Tappi press, Atlat~a, GA (1988) . By taking advantage of the lower coating temperatures produced by the method of the present ' 60557-4836 invention, hot-melt adhesive coatings can be produced which include thermally labile additives that previously could not be included therein due to their tendency to degrade at conventional hot-melt coating temperatures.
Virtually any additive that can be incorporated iruo a hydrophobic adhesive polymer utilizing standard solution-coating methods, can be incorporated therein according to the method of the present invention. Though not absolutely necessary, it is preferable that the chosen additive be soluble in, and not complex with, the transient polar processing aids) to be used for hot-melt coating of the bydrophobic adhesive polymer. The particular choice of additive to be used will be readily apparent to those skilled in the art, and can include, without limitation, stabilizers, colorants, biological actives, cross-linking agerna, and combinations thereof. Furthermore, examples of useful thermally-labile additive include, without limitation, medicaments, pharmaceuticals and antimicrobials, such as chlorohexidine and povidone/iodine, as well as perfumes, cross-linking agents and other temperature-sensitive reactants.
Advantages of the Invention To date, the hot-melt coating of hydrophobic adhesive polymers has been less than an ideal process. Typically, a balance has had to be struck between desired properties and undesired side effects resulting from the hot-melt coating process. Hot-melt coating of hydrophobic adbesive polymers at a sufl~cient temperature to lower their melt viscosity provided a generally smooth adhesive coating, but at the expense of thermal degradation, and its resultant high-temperature coating defects. Conversely, coating at a lower temperature eliminated some of the thermal degradation problems, but resulted in low temperature coating defects, such as melt flow lines, uanslucent coloration, and sharp skin surfaces, due to an inability to sufficiently lower the melt viscosity of the hydrophobic adhesive polymer.
Similarly, the use of conventional processing aids, and various post-processing treatments have proved less than ideal. Addition of conventional non-volatile processing aids can result in processing aid-induced coating defects. Also, use of water as processing aid for hot-melt coating of hydrophobic adhesive polymers has been strictly avoided due to assumed problems with foaming of the eatrudate. Further, as already noted, conventional additives, and post-processing ueatments are inconvenient, expensive, and impart often undesirable properties to the resulting adhesive-coated products.
The method of the present invention has alleviated, or completely eliminated, the trade-offs and other problems associated with hot-melt coating of hydrophobic adhesive polymers. Conuary to conventional teaching, the coating of a composition of a uansient VlrO 93/20165 ~ ~ ~ F'' '~ ~ v ' PCT/US93/0243?
polar processing aid and a hydrophobic adhesive polymer according to the method of the present invention yields a clear, smooth, and foam-free adhesive coating.
Also, the lower coating temperatures and/or melt viscosities are such that both high-temperature and low-temperature coating defects can be eliminated. Furthermore, due to their fugitive nature, the transient polar processing aids do not significantly affect the ultimate properties of the adhesive coating.
The specific advantages resulting from the method of the present invention are numerous. Lack of thermal degradation of the hydrophobic adhesive polymer helps to ensure that the final adhesive coating does not exhibit high-temperature coating defects, such as adhesive discoloration; an objectionable burnt odor, or a significant loss of adhesive or other properties. Also, enhanced melt viscosity profiles can be used to eliminate low-temperature coating defects, such as melt-flow lines, shark skin, and/or translucent coloration. Similarly, the fugitive nature of the transient polar processing aid also helps to ensure that processing aid-induced coating defects will not substantially affect the ultimate properties of the resultant adhesive coating: : Furthermore; expensive curing equipment, exotic monomers, and undesirable additives are not needed with the method of the present invention.
The ability ',of the transient polar processing aid to dmg the coating temperature of the adhesive composition; and/or to allow for the coating of the hydrophobic adhesive polymers at a pre-determined; lower coating temperature, means that hot-melt coating of the adhesive composition can be accomplished at lower temperatures, and faster line coating speeds, without a sacrifice in coating quality: This, in turn leads to inherent time efficiencies; as well as energy savings.
The use of water as a transient polar processing aid entails its own advantages above those seen for other transient polar processing aids. 'Specifically, water is a cheap, safe material that is biologically and environmentally friendly, bath to the coating-line operator, and to the ultimate consumer of the coati products. In fact, the advantages of water as a transient polar processing aid are especially important in the preparation of adhesive-coated medical tapes; 'dressings, and other similar materials, where lack of odor and mxieity are required.
' Furthermore, the method of the present invention is very versatile. In particular, a wide variety of coating conditions can be applied, all of which will arrive at a smooth, clear, foam free adhesive coating, that is also substantially free of high-temperature, low-temperature, and processing aid-induced coating defects. For example, the transient ~lar processing aid and hydrophobic adhesive polymer can be well mixed to form a substantially uniformly dispersed adhesive composition, not mixed at all, or mixed to any x s:;
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''O 93/20165 PC: T/US93/02437 degree in between, and still provide a foam-free hydrophobic adhesive extrudate capable of being coated from virtually any coating die, as long as the hydrophobic adhesive polymer is hot-melt coated at a temperature below the boiling point of the transient polar processing aid at atmospheric pressure. Even should any foaming of the adhesive extrudate occur, a smooth, clear and foam-free coating can still be obtained by use of a contact coating die, such as a wipe-fiilm die.
In addition, any of the embodiments or aspects of the method of the present invention can be combined with melt devolatilization of the hydrophobic adhesive polymer.
Use of melt devolatilization with the method of the present invention can substantially reduce 1~0 volatile companenta; such as residual monomers, and their attendant odor, from the hydrophobic adhesive poiymer prior to hot-melt coating:
A, further advantage of the method of the present invention is that thermally labile additives fan be added to the Hydrophobic adhesive polymer to be coated, without significant thermal breakdown of the material during hot-melt coating. Thus, thermally-labile additives that, to date, could not be incorporated into hot-melt coati hydrophobic adhesive polymers, can now be included therein.
~e ~vention will be fearther illustrated by reference to the following non-limiting Examples. All parts and percentages are expressed as parts by weight unless otherwise indicated:
F~CAMI'LE 1 An adhesive copolymer of isooctyl acrylate (IOA) and methacrylic acid (MAA) in a 96:4 weight ratio, and with an eQuiIibrium water content of about 0.2296 by weight at ambient conditions, was prepared accordiaig to the procedures disclosed in U.S. Patent No. 4,952,650, Example No. 5. After polynerization, the adhesive copolymer was spread on a silicone release liner aa~d allowed to dry under aanbient: conditions.
The dried adhesive copolymer ways removed from the release Iiner and rolled into a rope.
The adhesive copolymer rope wras fed into a Haake-Buchler RHEOCOIaDTM
System 40 extruder, equipped with a 190 mm diameter screw and a S.1 cm wipe-film die ~o extrusion coating Head (Haake-Buckler Instruments, Inc., Saddlebrook, NJ).
In addition, the extruder was modified to aeevmmodofs the precise injection of water, or other transient polar processing aids, adjacent the melted adhesive by connecting the output line from a Model 6000A liquid chromatography pump (VKaters Chromatography Division, Millipore Corp., Milford, ll~) to an injection port located on the. extruder barrel, near the end of the screw, 3S and just prior to the heck section of the extrusion coating die so that there was minimal, if -ZS-~1~!~~~:~
a'VO 93!20165 PC'1'f 0593/02437 any mixing of the adhesive copolymer and water. The injection port was designed so that there was no leakage of either the melted extrudate or pressurized water. Upon exiting the wipe-film coating die, the molten IOA:MAA adhesive was coated onto a polyethylene terephthalate (PET) backing material at a thickness of 0.1 mm, and a delivery rate of approximately 15 glmin. Thereafter, the coated IOA/1VIAA adhesive copolymer returned to its equilibrium water content of about 0.22 ~ by weight at ambient conditions.
The temperature of the inlet and feed sections, representing approximately the fu~st two-thirds of the extruder, were adjusted as need be to permit uniform feeding of the IOA:MAA adhesive copolymer into and through the extruder. The temperature of the later third of the extruder and the wipe-film coating die were maintained at three set temperatures of approximately 130°C, 150°C, or 170°C. A baseline value without water injection was established at each of these temperatures. Thereafter, increasing amounts of water were injected along with the melted adhesive by adjusting the flow rate on the chromatography pump. The effect of water injection on the appearance of the coated adhesive film was observed, with particular attention being paid to the presence or absence of melt-flow lines, the smoothness of the coated adhesive film, and the translucency or transparency of the adhesive coating. Table 1 illustrates coating temperatures, pressures, and the effect of water addition on the appearance of the hot-melt coated IOAIR~AAA adhesive copolymer of Example 1.
Examination of the data in Table 1 indicates that, absent the addition of water, higher extrusion temperatures are required to enhance the flow properties of the I9A:MAA
adhesive copolymer, and thereby reduce melt flow lines, and otherwise improve the appearance of the adhesive coating: In fact, without the addition of water, a temperature of greate><: then 170°C is needed to hot-melt coat the IOA:IIaIAA adhesive copolymer. However, even at a temperature of 170°~C, when no water is added, the It~AIIVdAA
adhesive copolymer is undergoing thermal degradation; as evidenced by a noticeable burnt odor emanating from the restalting adhesive coating, and a brownish discoloration of the extruded adhesive.
Furthermore; subjecting the adhesive copolymer to the higher temperatures required to obtain a smooth adhesive coating, would result in further significant thermal degradation of the adhesive copolymer, as evidenced by discoloration, a burnt odor, as well as probable loss of adhesive properties.
In contrast to these thermal degradation problems, the results of Table 1 show that the addition of water as a transient polar processing aid significantly reduces the temperature needal to obtairn a clear coating with the adhesive copolymer of Example 1. For 3~ example, the addition of 2.?9b by weight water, above the equilibrium water content of the w ~ c~ is :~ ~.r ''O 93120165 PCT/US93102437 IOA:MAA adhesive copolymer, yields a clear coating, essentially free of melt-flow lines or other coating irregularities at all of the coated temperatures. In addition, a coating temperature reduction of at least 40°C, from 170°C without water to 130°C with 2.796 by weight water, can be obtained and used to provide a smooth, clear, and foam-free adhesive coating that is essentially free of thermal degradation. Also, the addition of any level of water at 170°C virtually eliminated the burnt odor and brownish discoloration characteristic of the adhesive when coated without water. Quite unexpectedly, no foaming of the extruded adhesive was observed from the die orifice, at the coating die/backing interface, or in the coated adhesive product. However, when water addition was stopped, and the waterless melt extrusion esluilibrium allowed to reestablish, melt flow lines and other low-temperature coating defects reappeared in the coated adhesive film.
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'O 93/20165 PCTIU~93/02~t37 EXAlI~'LE Z
A pressure-sensitive adhesive composition, with an equilibrium water content of about 0.12 fo by weight at ambient conditions, and consisting of 50 parts by weight of KRATONTM 1107 resin (a styrene/isaprene/styrene block copolymer; Shell Chemical Co., Houston, TX), 50 parts by weight of WINGTACK PLUSTM (an aliphatic resin tackifier;
Goodyear Tire and Rubber Co., Chemical Division, Akron, OH), and 1.5 parts by weight of IRGANOXTM 1076 (an antioxidant, comprised of octyldecyl 3-(3,5-di-tart-butyl-4-hydroxyphenyl) propionate; Ciba Geigy Corp., Hawthorns, NY) was prepared by melt blending the components in the indicated weight ratios in a twin screw extruder maintained at 155°C, utilizing melt blending techniques as described in the "Encyclopedia of Polymer Science and Engineering", Vol 6, pp. 6I7-629, John Whey & Sons, New York, NY
(1990).
The adhesive extrudate was collected in a silicone lined box, and cut into strips to facilitate feeding into the extruder and coating die described in Example 1 above. Table 2 shows the _ coating conditions at 150°C; and their effect on the coating appearance at various percent additions of water for the pressure-sensitive adhesive of Example 2.
Table 2 Coating conditions at 150C, and their effect on the coating appearance at various percent additions of water for the pressure-sensitive adhesive of Example 2.

'Temp. Percent by Weight Water Addition ( C) 096 0.596 2.5 ~ 4 R6 150 Visible Melt Clear, SmoothClear, SmoothClear, ' Flow Lines Coating Coating Smooth Coating pressure 3.6 3.7 3.8 4.0 (MPa) Coating the KRAT~NTM-based pressure-sensitive adhesive onto a PET film at a thickness of approximately 0.12 mm' produced a clear film containing visible melt flow lines. Upon injection of water into the adhesive;
a clear adhesive film with no melt flow lines was produced.
Thereafter, the adhesive coating returned to its equilibrium water content of about 0.1296 by weight at ambient conditions.
No foaming was observed at the coating die/FET
film backing interface, or o~ the adhesive-coated film. However, when the adhesive extrudate was not coated;
but instead allowed to freely drop from the die, some water drops or b~abb~es were observed within the adhesive f~Hm, indicating that water was sa. " ~ ;: ..:;, .. . , ~ .... .. .;:. . . :, . .::> .,,. , ~; ~...: . . ._::;
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A polyisobutylene based pressure-sensitive adhesive composition, with an equilibrium water content of about 0.196 by weight at ambient conditions, was prepared according to the procedure disclosed on page 291 of The Handbook ~ Pressure-Sensitive Adhesive Technolo~v, D. Satas, ed., Yon Nostrand Reinhold Co., New York, NY, (1982).
In particular, the adhesive was prepared by adding 100 parts by weight of VISTANEXTM
' 10 MM L-110 (a polyisobutylene homopolymer; approximate molecular weight=I,I00,000;
Exxon Chemical Co., Houston, The and 75 parts by weight of iTISTANEXTM LM-MS
(a polyisobutylene hpmopolymer; approximate molecular weight=44,000; Exxon Chemical Co.) into toluene, to yield an about 2Q96 solids pressure-sensitive adhesive composition. This ~~iv~ composition was coated onto a silicone release liner, and dried in a circulating air 15 w oven at approximately IOO~C for about 12 minutes to produce the dried adhesive. The dried adhesive was removed from the release liner, rolled into a rope and fed into the extruder and coating die described in Eaaynple 1 above. Coating conditions at 150°C, and their effect on the coating appearance at various percent additions of water for the pressure-sensitive adhesive of Example 3 are shown below in Table 3.

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WO 93l2016S PCT/US93/02437 Extrusion of the polyisobutylene pressure-sensitive adhesive without water injectian at approximately 150pC produced a whitish, translucent coating, with visible melt-flow lines on the PET film backing. 1-Iowever, with injection of approximately 4~o water by weight essentially eliminated the melt-flow lines, and produced a transparent coating with no moisture bubbles. The extruded adhesive was then allowed to fall freely from wipe-film die lip during water injection as in Example 2. The resulting adhesive extrudate included randomly dispersed moisture drops and or bubbles within the extnrdate.

A rubber-based, precompounded adhesive resin (hlo. 820-338-BE ~Iot-Melt Adhesive; Findley Adhesives, Inc., Wauwatosa, Wn, with an equilibrium water content of about 0.z4~ by weight at ambient conditions; was cut into strips and fed into the extruder and coating die as described in Example 1 above. Coating conditions at 150°C, and their effect on the coating appearance at various percent additions of water for the adhesive resin of Example 4 are shown below in Table 4.

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dv~ s3izo~6s ~ ~ ~ ~ ~ ~ J ~ mcrivsg~ioza37 As with the previous Examples, hot-melt coating of the adhesive of Example 4 without water produced a adhesive coating with visible melt flow lines.
However, upon adding approximately 2.6R'o to about 49'° by weight of water as a transient polar processing aid, a smooth adhesive coating with no melt flow lines, foaming, or other coating irregularities, was produced.

GELVATM 737 resin, a pressure-sensitive adhesive copolymer of ethylhexyl acryIate/vinyl acetate/ethyl acrylate (available as a 3096 solids solution;
Monsanto Co., St.
Louis, MQ), with an equilibrium water content of about 0:1296 by weight at ambient conditions, was coated onto a release liner, and dried under ambient conditions. The dried adhesive was removed from the release liner; rolled into a rope, and fed into the extruder and wipe-filan coating die described in Example 1 above. Coating conditions at 150°C, and their effect on the coating appearance at various percent additions of water for the adhesive resin of Example 5 are shown b~Iow in Table 5.

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9~V~ 93/20165 PCT/tJS93lo2437 ' Hot-melt coating of the hydrophobic pressure-sensitive adhesive polymer of Example 5, without water as a transient polar processing aid, produced an adhesive coating with numerous coating defects. The addition of approximately 3.59'o water by weight significantly reduced these coating defects, and produced a uniform clear, and foam-free adhesive coating.

The IOA/MAA adhesive of Example 1 was extruded onto PET backings at a temperature of 1S0°C; and 1.8 MPs, and at varying percent by weight additions of water, according to the procedure of Example 1. To demonstrate that water, as a transient gotar processing aid, did not affect the ultimate properties of the resulting adhesive casting, each of ~~ Example coated backings was tested for shear strength on a stainless steel plate according to the procedures of ASTM D3654-88: Six samples of each coated backing were tested at each water addition level. The percent by weight of water added as a transient polar iS processing aid, and the average shear time in minutes for each of the Example coated backings are shown below in Table 6:
Table 6 Percent bar weight of Wrater added as a transient polar processing aid, and the average sheer time in-minutes for each of the coati backings of Ekample 6.

Percent by Weight Average Shear Time , 25 Water Addition (min) 1.3 15Z I

4>2' 1059 6.9 ' 1136 Analysis of:
the' data, illustrated in Table 6 showed no significant difference in shear strength between any of the Sample coated backings.
Thus, addition of water as a teansient goIar processing aid during hot-melt'coating according w the method of the present invention does not >iave a noticeable ai~ect on the ultimate adhesive properties of the resulting 35 adhesive coating.

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'O 93/20165 PCTlUS93/~2437 The IOA/MAA adhesive of Example 1 was extruded onto a PET backing at a temperature of 150°C, and 1.8 MPs, according to the procedure of Example 1, except that 0.'796 by weight of a 1:1 (volume:volume) solution of methanol and water, rather than solely water, was injected into the extruder along with the adhesive material prior to coating. As in Example 1, prior to injection of the processing aid, the coated film was translucent, and captained visible melt-flow lines, as well as other coating irregularities.
However, after injection of the processing aid, the extruded adhesive film was clear, smooth, and free from melt-flow lines or other irregularities. Further, although the extruder and die temperatures were above the boiling point bf both the water and methanol, no evidence of melt instability, such as foaming of the adhesive extrudate from the coating die oriftce, was observed.
. EXA14IPLE 8 I5 The IOA/ARAA adhesive of Example 1 was coated onto a PET backing at a temperature of 150°C, and 1.9 IVIPa, according to the procedure of Example 1, except that ~,0796 by weight of a 596 by weight solution of chlorohexidine acetate (a thermally labile antimicrobiat) in methanol was injected into the adhesive prior to coating.
After injection, the resulting adhesive-coated backing was smooth, etear, and free of coating defects. Solvent vapors were observed emanating from the extrudate, bui no formation of foam in the adhesive extrudate; or in the adhesive coating was observed. In addition, no discoloration, fuming; odor, ox other evidence of thermal degradation of the chlorohexidine acetate was observed: Furthermore, after cot~ling; the adhesive coated backing was analysed for the presence of p-chloroaniline, a toxic by-product resulting from the thermal decomposition of chlorahexidine acetate; utilizing gas chromatography. No evidence of this decomposition product was found in the hot-melt coated adhesive film at a sensitivity Level of I ppm.
Ex m l An approximately 4096 solids suspeasion of the IOA/14IAA adhesive copolymer of Example' 1 was pumped into an 8.9 cm diameter, I.5 m length, continuous-screw extrusion pass; compressed, and de-v~ratered to approximately 9596 solids. The de~-water adhesive ~pgly~er composition was piped into an 8.9 cm, I.S m length, single-screw extruder modified ~ ~~ serve as a- spelt devolatilizer. After being fed into the heated extruder, the IOAIMAA
adhesive c~polymer was melt devolatilized under a starve feed condition to remove unreacted _37_ err ~ ~,'.. A,~'.yr . 9 :.-~' :. ~. : ... ... ..
a..,.:.. ~ .,. ..,. ., .... , WO 93I20~6~ ~ , FJ f PCT/US93/02~137 residual monomers. Throughout the melt devolatilization (e.g. steam-stripping) process, the temperature of the devolatilizer ban'el was maintain~i between approximately 132°C to 143°C.
During melt devolatilization, approximately 5~ to 1096 by weight water was injected into the molten adhesive polymer through an injection port located approximately 30 cm downstream from the adhesive feed port on the barrel of the melt devolatilizer. The injected water was metered into the devolatilizer barrel using a precision calibrated pump. Thereafter, a vacuum of approximately 25 mm was applied at three vent ports, located at approximately 15 cm, 64 cm, and 106 cm downstream from the water injection port, to remove the volatilized residual unreacted monomers present in the molten hydrophobic adhesive composition.
At approximately l5 cm from the end of the devolatilizer barrel, a final injection of 2.590 by weight of water as a transient polar processing aid was made into the molten adhesive polymer without venting. Thereafter, the water and IOA/MAA adhesive copolymer were mixed into a substantially unif~rmly dispersed adhesive composition, through at least in . part; the action of mixing pins attached to the screw of the melt devolatilizer, and a screen filter located thereafter. A gear pump attached to the output end of the devolatilizer barrel by a heated pipe delivered the processing aid-containing adhesive composition to a wipe-film coating die, maintained at a temperature of 138°Cfor hot-melt coating of the adhesive composition onto a film backing (polyethylene/vinyl acetate copolymer film; I4TA4~b3-003, Quantum Chemical Co., Cincinnati; OIL; or ESCORENETM LD-312.09 backing, Exxon Chennical Co., Houston,1'3~
' at a rate of 18 kg/hourl2:5 cm die width. The resulting adhesive-coated film had an average thickness of approximately G~.OS mm.
Immediately after coating, the adhesive coating had a milky colored appearance, that rapidly became transparent. Vaporization of the water was apparent from the steam escaping from the orifice of the coating die. Upon roaling; a clear, smooth, foam-free adhesive coating, free from high-temperature; low-temperature, and prpcessing aid-induced coating defects, was obtained. However, when the film backing was removed from contact with the wipe-film coating die, some foaming of the adhesive extrudate was observ~i at the die oxi~ce.
~a ' The , hot-melt coating of the IOA/MAA adhesive copolymer of Example 1 was repeated utilizing the equipment and procedures of ExarFaple g; except that no water was added as a transient polar processing acid prior to the hot-welt coating of the molten adhesive. The molten adhesiee was coated onto the swine film backing material of Example ~, at a coating t,e~~a~.e of hut 138°C, at about 13.13 l4iPa, and a coating rate of approximately 0.225 ?,v '?VO 93/20155 PCf/U~'~3/~2437 kg/hour/2.5 cm die width. The resulting adhesive coating was of nonuniform width, and contained open gaps and visible melt-flow lines.
Exam~ele ll The hot-melt coating of the IOAIMAA adhesive copolymer of Example 1 was regeated utilizing the equipment and procedures of Example 9, including the final injection of 2.5 ~ by weight of water as a transient polar processing aid prior to the hot-melt coating of the molten adhesive. The molten adhesive was coated onto the same film backing material of Example 9, at a coating temperature of 138C, of about 4 MPs, and a coating rate of approximately ?.~ kglhour/2:5 cm die width. The resulting adhesive coating was smooth, clear, foam-free, and free of other casting defects.

F~$myle 12 The hot-melt coating of the IOA/MAA adhesive copolymer of Example 1 was repeated utilizing he equipment and procedures of Example 9, except that 596 by weight of water was injected as'a transient polar processing aid prior to the hot-melt coating of the molten adhesive. Thu molten adhesive was coated onto the same film backing material of Example 9, at a coating temperature of 138C, at about ~:8 MPs, and a coating rate of approximately 3.6 kg/hoaarl2.5 cm die width. Except'for the occurrence of free water under the lip of the wipe film die, the resulti~ag adhesive coating was essentially mooch, uniform, and free of foam and other coating defects: Furthermore, any. irregularities due to excess free water could be eliminated by a vacuum siphon maintained under the lip of the' wipe film die to siphon off excess free-water escaping from the wipe-f~lm coating die:

Fxamole 13 The hot-melt coating of the IOA/MAA adhesive copolymer of Example 1 was repeated utilizing the equipnnent and procedures of Example 9:
As in Example 9, the adhesive copolymer composition was fed into the melt devolatilizer from the continuous-screw extrusion press with 596 by weight of residual water from the polymerizatidn of the copolymer as a ' 30 transient polar processing aid. However, in this Example, the melt devolatilizer was only used as a riaechanisr~n to convey the adhesive and water conuposition tc~ a draw-film coating die. Thus, the melt devolatilizer was maintained at a temperature of 66C, and no residual monomers were removed. No foaming of the extruded adhesive composition was observe~sI
at the coating die orifice:

W~ 9312016 ~ ~ ~ ~ ~ ~ PCT/US93102437 The hydrophobic adhesive composition was hot-melt coated at a temperature of 66°C; a pressure of 8.5 MPa, a coating rate 17 kg/hr/2.5 cm die width, and a coating speed of 1.5 m/min, to yield an approximate 0.04 mm thick adhesive coating on the same film backing as that of Example 9. This adhesive coating was clear and free of any surface irregularities, including foam or bubbles. Further, due to the low hot-melt coating temperatures, no significant high-temperature coating defects were observed.
E.x~m~tle 14 The IOA/MAA adhesive copolymer of Example 1 was coated as described in Exa~pie 1, except that a coating temperature of 90°C was used, and the adhesive extrudate was coated from a draw Elm coating die onto the PET backing of Example 1. The orifice of the coating die was maintained approximately 4 cm from the PET backing tall, which was moving at a speed of approximately 10 m/min. The coating conditioms at 90°C, and their effect on the coating appearance at various percent additions of water for the pressure-sensitive adhesive of IS Exaanple 14 are shown in Table 7 below.
Table 7 C~ating conditions at 90C;
and eheir effect on the coating appearance at various percent additions of water for the pressure-sensitive adhesive of Example 14.

Temp. Fervent by Weight Water Addition ~pC~ ~g6 1.4~ 2.TE% 4.2%

g0 TFan~luc. Clearer Coating,Clearer, Clear, ~isfble Melt Some Melt Flow Smooth Smooth Flow Lines Lines Costing Coating py:~sure 3.6 3:7 3.8 4.0 ~pa>

In addition;
six samples of each of the coati backings o~ this Example were tested for comparative shear strength ~tili2ing ASTI~I
D3654-88, as provide in Example 6 herein.
The percent by weight of water added as a transient polar processing aid, and the average shear time in mninutes for each of the Example coated backings are shown below in Table 8.

5 POi'/US93/02437 Table ~
S Percent by weight of water added as a transient polar processing aid, and the average shear tame in minutes for each of the coated backings of Example 14.

Percent by l~Jeight Average Shear Time Water Addition (gin) 1.4 570 2.7 535 4.2 432 I

The results of Table 7 indicate that IOA/MAA adhesive copolymer of Example 1 can be hot-melt coated at a temperature below the bowling point of water external to the coating die; and still provide a foam-free eztrudate, and a clear; smooth, foam-free, and coating defect h.~ ~~ive coating through the addition of water along with the molten adhesive copolymer.
Furthernqore, the results of Table 8 show that there is no significant difference in shear strength betvNeen the sample coated backings, and thus; use of water as a transient polar processing aid did not substantially affect the ultimate properties of the resulting adhesive coatings.
EXAlVip'LE 1S
~ $Ppr~ximately 401o solids adhesive composition of IOA and MAA in a 96:4 weight ratio was grepared according to the procedures disclosed in U.S. Patent Ido. 4,~33,I79, Example No. 10, except that a nreixture of 372 g of IOA, 12 g of polystyryl methacrylate, 16 g ~,f ~A.A, and'2 g of ~nO was used as the monomer charge.
One portion of the adhesive copolymer eras dewatered to about ~ 96 by weight water 3p and hot-melt coated with a vmripe-~Im coating die at a temperature of SS°C onto a biaxial oriented Polypropylene ~80PP) backing at a 7 grain coating weight. Another portion of the adhesive copc~ly~er was dried at ambient conditions, dissolved in ethyl acetate, solution coated onto a EOPP backing at a ~ graiai' coating wvei~ht, and drib in an oven at 65°C for 3~ minutes.
Three samp3e~ each of both tl~e hot-melt coated and solution-coated EOPP
backings 3~' were tested for the shear strength of the adhesive coatings according to the procedures of Example 6. The average shear strength of the hot-melt coated adhesive coatings was 95 minutes, while the average shear strength of the solution-coated adhesive coatings was 83 minutes. Thus, WO 93/2~~ ~ ~ ~ ~ ;~ PC'I'/US93/02437 there was no significant difference in the shear strength of the IOA/IvIAA
adhesive copolymer hot-melt coated with water as a transient polar processing aid, and the same adhesive capolymer coated by conventional solution coating techniques.
ExamQIe 16 The KItATON~ 1107 resin adhesive copolymer of Example 2 was hot-melt coated using the equipment and procedures of Example 1, except that the injection port for the addition of water as a transient polar processing aid was moved to a point in the extruder barrel that was approximately half way between the extruder feed port and the entrance to the wipe film coating die.
This earlier injection of water allowed for more thorough mixing of the adhesive copolymer and water prior to the hot-melt coating of the adhesive composition.
In addition, the extruder barrel temperatures were set at 100C, I25C, and 150C, and the coating die was maintained at 150C, throughout the hot-melt coating process.

Prior to hs~t-melt gating, uniform mixing of the water and adhesive copolymer was IS checked by injecting 1.5~
by weight water into the extruder, and examining the adhesive ~xtrudate as it dropp~i frown the die orifice.
Moisture bubbles were visually apparent and uniformly disgez~sed throughout the adhesive extrudate, and steam was observed escaping from the die orifice.

The backup roll holding the PET
backing material was brought into pressure ~0 intact with the wipe-film die, and hot-melt coated wine the adhesive composition.
Table Shows the c~ating conditions at I50C;
and their effect on the coating appearance at various percent additions of water for the pressure-sensitive adhesive'of Example I6.

ZS Table 9 Coating conditions at 150C;
and their effect on the coating appearance at various percent additions of water for the pressure-sensitive adhesive of Example 16.

Temp. Percent by Weight llVaterAddition ~0 (C) Oy~ 1 ~ 296 3.59&

150 Visible llrleltClear; Sanoothdear, Smooth Clear, ~gow y~ines Coating Coating Smooth Coating pressure 3.9 4:5 4.7 4.6 ' (~~D

~% ~ ~ ~~ pi ~ .
~e i c,~ ro :~ ~ ~J
"VO 93!20165 PCTlUS93l02437 Coating the KRATONTM-based pressure-sensitive adhesive onto a PET film at produced a clear film containing visible melt flow lines. Upon injection of water into the adhesive to form an adhesive composition, a clear adhesive film with no melt flow lines was produced. No .foaming was observed at the coating die/PET film backing interface, or on the S adhesive-coated film. However, tiny moisture droplets were observed on the surface of the coated film, but no moisriare droplets were observed within the film. These moisture droplets completely evaporated by the time the coated PET backing was 50 cm from the coating die.
Thereafter, the water injection was discontinued. After approximately 15-20 minutes, the adhesive coating again displayed visible melt flow lines>
While in accordance with the patent statutes, description of the preferrexi weight fractions, and processing conditions have been provided, the scope of the invention is not to be limited thereto or thereby. Various modifications and alterations of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention.
1$ Consequently, far an understanding of the scope of the present invention, reference is made to the following claims.

Claims (56)

CLAIMS:

1. A method of coating an adhesive polymer comprising hot-melt coating an adhesive composition of a hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a coating die onto a substrate, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the composition is hot-melt coated at a temperature below the boiling point of the transient polar processing aid at atmospheric pressure.

2. A method of coating an adhesive polymer according to claim 1, wherein the transient polar processing aid is selected from the group consisting of water, methanol, ethanol, isopropanol, and combinations thereof.

3. A method of coating an adhesive polymer according to claim 1, wherein the transient polar processing aid is present in a concentration of from about 0.5 percent to about 10 percent by weight above the weight of residual water present in the hydrophobia adhesive polymer equilibrated at ambient conditions.

4. A method of coating an adhesive polymer according to claim 1, wherein the transient polar processing aid is present in a concentration of from about 1 percent to about percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions.

5. A method of coating an adhesive polymer according to claim 1, wherein the hydrophobic adhesive polymer comprises a hydrophobic pressure-sensitive adhesive polymer.

6. A method of coating an adhesive polymer according to claim 5, wherein the hydrophobic pressure-sensitive adhesive polymer exhibits a glass transition temperature of 20°C or less.

7. A method of coating an adhesive polymer according to claim 6, wherein the hydrophobic pressure-sensitive adhesive polymer exhibits a glass transition temperature of 0°C or less.

8. A method of coating an adhesive polymer according to claim 5, wherein the hydrophobic pressure sensitive adhesive polymer is selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, anal combinations thereof.

9. A method of coating an adhesive polymer according to claim 8, wherein the acrylate pressure-sensitive adhesive polymer is formed by suspension polymerization, emulsion polymerization, or solvent polymerization.

10. A method of coating an adhesive polymer according to claim 9, wherein the suspension polymerized acrylate pressure-sensitive adhesive polymer comprises an acrylate pressure-sensitive adhesive copolymer of an acrylic acid ester monomer selected from the group consisting of isooctyl acrylate, isononyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, and combinations thereof, and at least one other monomer selected from the group consisting of acrylic acid, methacrylic acid, N-vinyl pyrrolidone, vinyl acetate, acrylamides, substituted acrylamides, and combinations thereof.

11. A method of coating an adhesive polymer according to claim 10, wherein the transient polar processing aid comprises water, and the composition is hot-melt coated at a temperature of less than 100°C at atmospheric pressure.

12. A method of coating an adhesive polymer according to claim 1, wherein the coating die comprises a wipe-film coating die, a draw die, a drop-film die, a slot-orifice die, or a roll coater die.

13. A method of coating an adhesive polymer comprising hot-melt coating an adhesive composition of a hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a contact coating die onto a substrate, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the composition is hot-melt coated at a temperature at or above the boiling point of the processing aid at atmospheric pressure.

14. A method of coating an adhesive polymer according to claim 13, wherein the transient polar processing aid is selected from the group consisting of water, methanol, ethanol, isopropanol, and combinations thereof.

15. A method of coating an adhesive polymer according to claim 13, wherein the transient polar processing aid is present in a concentration of from about 0.5 percent to about 10 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions.

16. A method of coating an adhesive polymer according to claim 13, wherein the transient polar processing aid is present in a concentration of from about 1 percent to about percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions.

17. A method of coating an adhesive polymer according to claim 13, wherein the hydrophobic adhesive polymer comprises a hydrophobic pressure-sensitive adhesive polymer.

18. A method of coating an adhesive polymer according to claim 17, wherein the hydrophobic pressure-sensitive adhesive polymer exhibits a glass transition temperature of 20°C or less.

19. A method of coating an adhesive polymer according to claim 18, wherein the hydrophobic pressure-sensitive adhesive polymer exhibits a glass transition temperature of 0°C or less.

20. A method of coating an adhesive polymer according to claim 18, wherein the hydrophobic pressure sensitive adhesive polymer is selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.

21. A method of coating an adhesive polymer according to claim 20, wherein the acrylate pressure-sensitive adhesive polymer is formed by suspension polymerization, emulsion polymerization, or solvent polymerization.

22. A method of coating an adhesive polymer according to claim 21, wherein the suspension polymerized acrylate pressure-sensitive adhesive polymer comprises an acrylate pressure-sensitive adhesive copolymer of an acrylic acid ester monomer selected from the group consisting of isooctyl acrylate, isononyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, and combinations thereof, and at least one other monomer selected from the group consisting of acrylic acid, methacrylic acid, N-vinyl pyrrolidone, vinyl acetate, acrylamides, substituted acrylamides, and combinations thereof.

23. A method of coating an adhesive polymer according to claim 22, wherein the transient polar processing aid comprises water, and the composition is hot-melt coated at a temperature of at least 100°C at atmospheric pressure.

24. A method of coating an adhesive polymer according to claim 13, wherein the contact coating die comprises a wipe-film coating die.

25. A method of coating an adhesive polymer comprising hot-melt coating a hydrophobic adhesive polymer and a transient polar processing aid from an orifice of a coating die onto a substrate, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the hydrophobic adhesive polymer and the transient polar processing aid are not substantially mixed prior to hot-melt coating of the hydrophobic adhesive polymer.

26. A method of coating an adhesive polymer according to claim 25, wherein the transient polar processing aid is selected from the group consisting of water, methanol, ethanol, isopropanol, and combinations thereof.

27. A method of coating an adhesive polymer according to claim 25, wherein the transient polar processing aid is present in a concentration of from about 0.5 percent to about 10 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions.

28. A method of coating an adhesive polymer according to claim 25, wherein the transient polar processing aid is present in a concentration of from about 1 percent to about percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions.

29. A method of coating an adhesive polymer according to claim 25, wherein the hydrophobic adhesive polymer comprises a hydrophobic pressure-sensitive adhesive polymer.

30. A method of coating an adhesive polymer according to claim 29, wherein the hydrophobic pressure-sensitive adhesive polymer exhibits a glass transition temperature of 20°C or less.

31. A method of coating an adhesive polymer according to claim 30, wherein the hydrophobic pressure-sensitive adhesive polymer exhibits a glass transition temperature of 0°C or less.

32. A method of coating an adhesive polymer according to claim 29, wherein the hydrophobic pressure sensitive adhesive polymer is selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.

33. A method of coating an adhesive polymer according to claim 32, wherein the acrylate pressure-sensitive adhesive polymer is formed by suspension polymerization, emulsion polymerization, or solvent polymerization.

34. A method of coating an adhesive polymer according to claim 33, wherein the suspension polymerized acrylate pressure-sensitive adhesive polymer comprises an acrylate pressure-sensitive adhesive copolymer of an acrylic acid ester monomer selected from the group consisting of isooctyl acrylate, isononyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, and combinations thereof, and at least one other monomer selected from the group consisting of acrylic acid, methacrylic acid, N-vinyl pyrrolidone, vinyl acetate, acrylamides, substituted acrylamides, and combinations thereof.

35. A method of coating an adhesive polymer according to claim 25, wherein the coating die comprises a wipe-film coating die, a draw die, a drop-film die, a slot-orifice die, or a roll coater die.

36. A method of coating an adhesive polymer comprising:
(a) providing a hydrophobic adhesive polymer suitable for hot-melt coating;
(b) adding a transient polar processing aid along with the hydrophobic adhesive polymer, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic. adhesive polymer equilibrated at ambient conditions; and (c) hot-melt coating the hydrophobic adhesive polymer onto a substrate utilizing control means for elimination of foaming of the hydrophobic adhesive extrudate.

37. A method of coating an adhesive polymer according to claim 36, wherein the transient polar processing aid is selected from the group consisting of water, methanol, ethanol, isopropanol, and combinations thereof.

38. A method of coating an adhesive polymer according to claim 36, wherein the adding step comprises retaining a residual component of a reaction medium in which the hydrophobic adhesive polymer was polymerized to serve as the transient polar processing aid.

39. A method of coating an adhesive polymer according to claim 36, further comprising, prior to step (b), substantially removing residual volatile components from the hydrophobic adhesive polymer.

40. A method of coating an adhesive polymer according to claim 39, wherein the residual volatile components include unreacted monomers remaining from the polymerization of the hydrophobic adhesive polymer.

41. A method of coating an adhesive polymer according to claim 39, wherein the residual volatile components are removed by melt devolatilization of the hydrophobic adhesive polymer prior to hot-melt coating.

42. A method of coating an adhesive polymer according to claim 36, further comprising, prior to step (c), adding selected additives to the hydrophobic adhesive polymer and transient polar processing aid.

43. A method of coating an adhesive polymer according to claim 42, wherein the selected additives comprise thermally-labile additives.

44. A method of coating an adhesive polymer according to claim 43, wherein the thermally-labile additives are selected from the group consisting of medicaments, antimicrobials, pharmaceuticals, perfumes, cross-linking agents, and combinations thereof.

45. A method of coating an adhesive polymer according to claim 36, wherein control means includes means for regulating true temperature of the hydrophobic adhesive polymer prior to hot-melt coating.

46. A method of coating an adhesive polymer according to claim 45, wherein the transient polar processing aid and hydrophobic adhesive polymer comprise an adhesive composition that is hot-melt coated at a temperature below the boiling point of the transient polar processing aid at atmospheric pressure.

47. A method of coating an adhesive polymer according to claim 45, wherein the transient polar processing aid and hydrophobic adhesive polymer comprise an adhesive composition that is hot-melt coated using a contact coating die at a temperature above the boiling point of the transient polar processing aid at atmospheric pressure.

48. A method of coating an adhesive polymer according to claim 36, wherein control means include means for limiting the mixing of the transient polar processing aid with the hydrophobic adhesive polymer prior to hot-melt coating of the hydrophobic adhesive polymer.

49. A hot-melt coatable adhesive composition comprising a hydrophobic adhesive polymer in combination with a transient polar processing aid, wherein the transient polar processing aid is present in a concentration of at least 0.5 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions, and wherein the adhesive composition is capable of being hot-melt coated onto a substrate to provide a substantially foam-free adhesive coating.

50. A hot-melt coatable adhesive composition according to claim 49, wherein the transient polar processing aid is selected from the group consisting of water, methanol, ethanol, isopropanol, and combinations thereof.

51. A hot-melt coatable adhesive composition according to claim 49, wherein the transient polar processing aid is present in a concentration of from about 0.5 percent to about 10 percent by weight above the weight of residual water present in the hydrophobic adhesive polymer equilibrated at ambient conditions.

52. A hot-melt coatable adhesive composition according to claim 49, wherein the hydrophobic adhesive polymer comprises a hydrophobic pressure-sensitive adhesive polymer.

53. A hot-melt coatable adhesive composition according to claim 52, wherein the hydrophobic pressure-sensitive adhesive polymer exhibits a glass transition temperature of 20°C or less.

54. A hot-melt coatable adhesive composition according to claim 52, wherein the hydrophobic pressure sensitive adhesive polymer is selected from the group consisting of an acrylate pressure-sensitive adhesive polymer, a rubber-based pressure-sensitive adhesive polymer, an olefin pressure-sensitive adhesive polymer, a polysiloxane pressure-sensitive adhesive polymer, and combinations thereof.

55. A hot-melt coatable adhesive composition according to claim 54, wherein the acrylate pressure-sensitive adhesive polymer is formed by suspension polymerization, emulsion polymerization, or solvent polymerization.

56. A hot-melt coatable adhesive composition according to claim 55, wherein the suspension polymerized acrylate pressure-sensitive adhesive polymer comprises an acrylate pressure-sensitive adhesive copolymer of an acrylic acid ester monomer selected from the group consisting of isooctyl acryl.ate, isononyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, and combinations thereof, and at least one other monomer selected from the group consisting of acrylic acid, methacrylic acid, N-vinyl pyrrolidone, vinyl acetate, acrylamides, substituted acrylamides, and combinations thereof.