CA1210886A - Adhesive cyanoacrylate compositions with reduced adhesion to skin - Google Patents

Abstract

ABSTRACT
A cyanoacrylate-based adhesive composition com-prises 55-92% by weight of a 2-cyanoacrylic acid ester, preferably the ethyl ester, from 4-30% by weight of a vinyl chloride/vinyl acetate copolymer and not more than 25% by weight of a plasticizer (the plasticizer may be omitted entirely). The copolymer is preferably a vinyl chloride/
vinyl acetate/maleic acid terpolymer. The adhesive composi-tions have greatly reduced adhesion to skin, not forming strong skin bonds for at least 30 seconds, in contrast to conventional cyanoacrylate adhesive compositions which form, within in about one second bonds strong enough to tear skin.

Description

This invention relales Lo adhesive compositions with reduced adhesion to skin.
More par~icularly, it relates to adhesive compositions containing alkyl cyano-acrylates and having reduced adhesion to skin.
lt has been known îor many years that 2-cyano~crylic ccid esters make very 05 powerful adhesiYes. Such cyanoacrylate adhesive compositions have become widely used because they form very powerful bonds t,etween a wide variety of substrates; for example, cyanoacrylate adhesive compositions will rapidly form very strong bonds between glass, metals, plastics, wood, textiles and paper. A
general review of conventional 2-cyanoacrylic acid ester adhesives mav be i~ound in I.
10 Skeist (ed.), Handbook of Adhesives, 2nd Edn., Van Nostrand Reinhold Co. (1977), Chapter 34, pages 569-80. Unf ortuna~ely, such cyanoacrylate adhesive compositions suffer from the serious disadvantage that they also form very powerful bonds with human skin, and thus if the user of such an adhes;ve composition inadvertently gets even a very smaU amount of the adhesive composition on his 15 finger tips or other exposed areas of skin while he is using the composition, the adhesive composition will rapidly bond the skin with which it comes into contact to another portion of the user's skin, the substrate being glued or to any other article with which the adhesive-covered skin ~omes into contact. Such sccidental bondingof skin takes place very rapi~y (within a few seconds) and the bonds thus formed are 20 considerably stronger than human skin itself, so that if an attempt is made to tear the skin away from the object to which it has accidentally become adhered, serious damage to the skin and underlying tissue may result. Indeed, the bonds formed bycyanoacrylate with body tissues are so strong that such adhesive compositions have been recommended for medical ~nd surgical use as an alternative to con-25 ventional surgical sutures for closing incisions and wounds and for repairing breaksor ruptures in bone and other tissues. Moreover, if the cyanoacrylate adhesive composition is allowed ~o bond for more than a few minutes, it cures to such a degree that it is almost insoluble in all common solvents; thus by the time a person who has accidentally adhered his skin to itself or to some other material has had 30 time to reach a first aid station or hospital emergency room, the adhesive composition has cured to a point at which the bond cannot be broken quiekly or readily with any common solvents, and the breaking of such bonds is a complicated t~sk even for skilled medical personnel. Hospital emergency room personnel frequently come into contact with such problems caused by the use of cyanoacrylate 35 adhesive compositions. Methyl cyanoacrylic acid ester adhesive compositions ,h ~'.J.~

produce skin bonds which are almost lotally ir~oluble in all cornmon solvents and are extremely difficult to break; the dangers thus associated with methyl cyanoacrylate compositions appear to have been at least a substantial fac~or in the withdrawal of m~st9 if not all, methyl cyano~crylate compositions forrr erly sold for household use.
05 The possibility of accidental skin adhesions does reduce the use of cyanoa-crylate~, since people requiring adhesive compositions may prefer to use an adhesive composition which, although forming a less powerful bond than a cyano-acrylate c~mposition, does not calry the risk of accidental skin ~dhesions. In an industrial environment, the safety precautions necessary to prevent accidental 10 skin adhesions may slow up the work of applying cyano~crylate adhesive compositions to substrates, and thus reduce productiYity. In domestic use, not or~y does the possibility of accidental skin adhesions make the use of cyanoacrylate adhesive compositions awkward in many inst~nces, but it may reasonably be suppose~ that some domestic users will not buy such adhesive compositions at all, î5 prefering the use of less powerful, and possibly more expensive, adhesive comp~
sitions rather than risk accidental skin adhesions. The risk of such accident~l skin adhesions is exacerbated by the fact that mcst commerciall~aYailable cyan~
acrylate adhesive compositions are, in their uncured state as ~pplied to substrates9 relatively mobile liguids which-easily run from the substrate onto the 20 fingers of a person holding the substrate.
Vntil now, it has been believed that the possibili~y of accidental skin adhesions is an inevitable concomitant to the use of cy~noacrylate adhesive compo-sitions. It is believed that the curing of such compositions proceeds ~hrough ananionic mechan!sm, the composition being so easily polymerized that water alone is 25 a sufficiently active compound to initiate such anionic polymerization. Indeed, it is believed that in normal use the curing- of such compositions is initiated by atmospheric moisture and/or the minute ~mounts of water adsorbed onto most substrates. In view of the large proportion of water present in ~he human epidermis, it would appear inevitable that the polymerization of cyanoacrylate adhesive 30 compositions would be ~reatly accelerated by contact with the human epidermis, and thus that all cyanoacrylate adhesive compositions would suffer from problems of skin adhesion.
Thus, although the problems of accidental skin adhesion associated with the use of cyanoacrylate adhesive compositions are well known ancl serious, and 35 although these problems have reduced the desirability and volume of Isuch adhesive compositions sold, no prior art cyanoacryla~e adhesive composition is known ,, . ;

which significantly reduces such problems, and hereto there have been good grounds for supposing that it was not pos-sible to significantly reduce the skin adhesion of such compositions.
Surprisingly, we have now discovered that by addirlg colltrolled amountâ oi certain aynthetic resins to cyanoacrvlate adhesive compositions, the skin adhesion o~
such compositions is greatly red~lced, thus rendering acci-dental skin adhesions much less likely and markedly facil-itating the use of such adhesive compositions.
Accordingly, this invention provides an adhesive composition comprising from about 55 to about 92% by weight of a 2-cyanoacrylic acid ester; from about 4 to about 30% by weight of a vinyl chloride/vinyl acetate copolymer, thiâ
copolymer comprising a major proportion of vinyl chloride and a minor proportion, though not less than about 5% by weight, of vinyl acetate; and from about zero to not more than about 25% by weight of a plasticizer. The copolymer, which is dissolved in the cyanoacrylate, has a molecule weight of not less than about 8000.
This invention also provides a process for forming this adhesive composition, which comprises: forming a stabilized cyanoacrylate composition omprising a 2-cyano-acrylic acid ester and an anionic polymerization inhibitor;
and dissolving the vinyl chloride/vinyl acetate copolymer in pulverulent form in the cyanoacrylate composition at a temperature of about 70 to about 85C until the copolymer is completely dissolved in the cyanoacrylate composition, such that the adhesive composition formed comprises from about 55 to about 92% by weight of the cyanoacrylate and about 4 to about 30% by weight of the copolymer.
~ereinafter, all parts and proportions are by weight unless otherwise stated.
In the composition of the invention, the skin adhesion of a cyanoacrylate adhesive composition is reduced by adding to the composition a minor proportion of a vinyl chloride/vinyl acetate copolymer and, optionally, a plastic-izer in the amount of from about zero to not more than 25%

lcm/rlt -3-by weight. As shown in more detail by the examples below, although a typical prior art cyanoacrylate adhesive composi-tion forms a very strong skin bond (a bond which can damage skin if attemp~s are made to separate it) within about one second, preferred compositions of the invention can have ~their skin adhesion reduced ~o such an extent that only a relatively weak skin bond is formed after 60 seconds, such weak skin bonds being more easily broken by common solvents.
Any of the known cyanoacrylate adhesives may be used as the ester component of the composition of the in-vention. For example, methyl, ethyl, isopropyl and allyl 2-cyanoacrylates may be used. ~owever, we prefer to use ethyl lcm/~lt -3a-

2-cyanoacrylate since this compound shows the best storage stability. In the compositions of the invention, both methyl and isopropy~ 2-cyanoacrylates exhibit poor storage stability; the methyl ester tends to cause phase separation in the composition, leading to thickening a few hours ~fter rnixing, while a composition 05 containing the isopropyl ester gels overnight. In contrast~ the composi~ions of the invention containing ethyl 2-cyanoacrylate are normally stable for approximatelyone year when stored in containers under ambient condi~ions at (75~F (24C) and 50%
relative humidity). Preferably, the cyanoacrylate comprises from about 75 to about 85% by weight of the composition. We prefer to use an ethyl 2-cyanoacrylste lO preparation having a viscosity of from 5 to 50cPs. ~The viscosity of an ethyl 2-cyanoacrylate preparation may be increased by polymerizing a sma1l proportion ofthe ester, as described f~ example in British patent 1,1239360 or by adding to the monomeric ester a small proportion of a thickening agent such as polymethyl methacrylate, as described for example in U.S. patents 4,038,345 and 3,654,239.)Examples of suitable ethyl ~-cyanoacrylic acid ester preparations are those ~vailable commercially under the trade marks ACE EE, ACE E-50, CN-2 and CN-4 ~all produced by Alteco V.S.A., Inc., 23510 Telo Avenue, Uni~ 99 Torrance, California 905039 United States of America), PT~-E3 and PTR E-40 (both produced by Pacer Technolo~y ~ Resources, 1550 Dell Avenue, Suite K, Campbell, California 95008 20 United States of America) and SUPER 3-1000 (available from ~hree Bond of America, Torr~nce, California). Mixtures of these commercia~ly-available cyano-acrylates may also be used.
Very viscous cyanoacrylate preparations having viscosities in excess of 8D0 cPs. are available commercially for example, Alteco USA, Inc., produce a 25 cyanoacrylate preparation CN-~*having a viscosity of 8û0-120D cPs. Although we do not exclude the possibility of using such very viscous cyanoacrylate preparations in the adhesive compositions of the im/ention, we do not recommend the use of such viscous cyflnoacrylate preparativns for most uses of the instant adhesive compositions. The addition of a vinyl chloride/vinyl acetate copolymer 30 alone or in conj~ction with a plasticizer, to such viscous cyanoacrylate preparstions to form a composition of the invention will resL~t in an adhesive composition having lower skin adhesion than the cyanoacrylate preparation alone, but wi~l resLdt in a viscous composition which forms thick films when used in bonding and hence requires the use of an external catalyst9 for example an amine, to 35 e~f ect f urther cure.

~ trade mark As those skilled in the art are aware, cyanoacrylates are susceptible to both anionic and fre~radical polymerization, and it is therefore advisable to protect cyanoacry~ate compositions againsl both types of polymerization to ensl~re `that premature curing of the cyanoacrylate does not Occul, thereby avoiding 05 difficulties in storage. ~o avoid anionic polymerizationg it is desirable to add to the compositions of the invention an anionic polymerization inhibitor. Any of the anionic polymerization inhibitors used in prior art cyanoacrylate compositions can be used; for example, the anionic polymerization inhibitor may be an acidic gas, a protonic acid, or an anhydride thereof. The preferred anionic polymlerization 10 inhibitor for use in the compositions of the invention is sulfur dioxide, preferably in an amount of from 0.Q0l to 0.596 of the composition. Other possible anionic polymerization inhibitors include nitrous oxide, hydrogen fluoride, hydrochloric acid, sulfuric acid, phosphoric acid, organic sulfonic and carboxylic acids and anhydrides thereof, phosphorus pentoxide and acid chlorides. The compositions of the invention 15 also desirably conLain from 0.0l to 0.05% of a free radical polymerization inhibitor.
Again, any of the free radical polymeri~ation inhibitors hitherto used in cyano-acrylate compositions may be used3 the free-radical polymerization inhibitors are usually phenolic-~ype compounds, for example hydroquinone, t-butylcatechol, pyro-catechol, and E~-methoxyphenol. The commerically-available ethyl 2-cyanoacrylate20 preparations mentioned above are already stabilized; should it be necessary to adjust the concentration of stabilizer }vhen using these commericall~available prepar-ations, those skilled in the art will have no difficulty in adjusting the concentration of anionic and free radical polymerization inhibitors to appropriate values empir-ically.
We believe (although the invention is in no way limited by this belief) that it is the vinyl chloride/vinyl acetate copolymer in the compositions of ~he invention which is responsible for most of the reduction in skin adhesion. Some care must be exercised in selecting an appropriate vinyl chloride/vinyl acetate copolymer since certain vinyl chloride/vinyl acetate copolymers are not compatible with the other 30 components of the adhesive composition. Although it is not known exactly whatf actors are responsible f or rendering certain commercially-available vinyl chloride/vinyl acetate copolymers incompatible with the remaining components of the adhesive composition s~f the invention, in practice incompatible copvlyrmers are not a significant problem since those sldlled in the art can very e~sily discover 35 whether any particular copolymer is compatible by routine empirical tests. Asalready mentioned, the vinyl chloride/vinyl acetate copolymer comprises a major ~ j ,

3~

proportion of vinyl chloride and a minor proportion, but not less than about 5%, of ~inyl acetate. In general, we have found that good results are obtained with copolymers which contain 30 to 90 percent of vinyl chloride and lD to 20 percent by weight vinyl acetate.
05 Care should also be taken to ensure that the vinyl chloride/vinyl acetate copolymer se]ected does not increase the viscosity of the adhesive composition to an excessive extent since we have found Ihat very viscous adhesive compositions do not cure rapidly and the guality of the final bond is adversely affected. Obvio-lsly, there is a continuous variation in rate of cure and quality of the final bond with the19 viscosity of instant adhesive composition of Lhe invention, and thus there is no one fixed upper limit for the viscosity of the adhesive composition; however, in general the properties of the sdhesive compositions are adversely affected if their viscosity exceeds about 3,000 cPs.
Although the copolymer may be a simple vinyl chloride/vinyl acetflte copoly-15 mer, we prefer to use a carbo2yl-modified vinyl chloride/vinyl acetate copolymer, and in particL~ar a vinyl c~oride/vinyl acetate/maleic acid terpolymer, althoughother carboxylating agents, such as itaconic acid, may be employed if desired. The terpolymer desiraMy contains 80 to 90 percent of vinyl chloride, 10 to 2D percent of vinyl acetate and not more than 2% of maleic acid. More specifically, we have 20 found that very good res~dts are obtained using a terpolymer comprising about 83%
vinyl chloride, about 16% vinyl acetate and about 1% maleic acid. A terpolymer having this composition is available commercially under the trade mark UCAR
VMCC (sold by Union C~rbide Corporation, Coating Materials Division, Old Ridge-bury Rd., I)anbury, Connecticut 06817, United States of America). This materi~l has 25 an inherent viscosity of 0.38 when tested by the standard of Arneric~n Society for Testing and Materials (AST3~) test ~1243, a specific graYity according ~o ATSM
792 of 1.34, a glass transition temperature of 72~C, an average molecular weight of 15,000 and a solution viscosity at 25~ of 100cps. at 30% solids concentr~tion inmethyl ethyl ketone. Other resins that can be used in the compositions of the 30 invention but are l~;s desirable because of varying degrees of compatability in the compositions, include those sold commercially as UCAR VMCH*(a c~rboxyl-modified vinyl chloride/vinyl ace~ate copolymer) and VCAR VYHH* VYHD*and VYL~*all ~hree of these being simple vinyl chloride/vinyl acetate copolymers (all the aforementioned resins are available from Union Carbide at the address previously35 given). The use of the Union C~rbide resin UCAR VMCA is not recommended sinceit is incompatible with the other components of the compositions of the invention.

* trade Illark Further details of the pl)ysical properties of the preferred resins nre given in the examples below. The preferred amount of copolymer fcr use in the compositions ofthe in~ention is from about l0 to about 18~360 Among the factors which affect the cornpatibility of the copolyMer with the 05 other components of the Qdhesive compositions of the invention is the molecular weight of the copolymer. The copolymer should have an average molecular weight of not substantially less thnn 8000, and in sorne cases the minimum molecular weight fo~ proper compatibili~y with the o~her components of the adhesive compositions may be even hiKher. For example, the aforementioned UCAR VYLF*a simple vinyl 10 chloride/vinyl acetate copolymer having a molecular weight of about 8000, gives acceptable results in the aàhesive compositions of the invention. On the other hand, when the preferred vinyl chloride/vinyl acetate/maleic acid ~erpolymers are used, the minimum useful molecular weight tends to be higher ~han ~000. The afore-mentioned terpolymer UCAR VMCA* which has a molecular weight of aoout 8000?
15 ten~s to be incompatible with the other components of the ~omposi~ions of theinventiorl, while the similar terpolymer UCAR VMCH*which has a molecL~ar weight of about 21~000, gives very acceptable results.
It sh~uld be noted that, although i~ has previously been proposed to use vinyl chloride and vinyl acetate monomers, and very low molecular weight polymers of 20 such monomers, in cyanoacrylate-based adhesive compositions used for repairing brok~ bones and other ~nimal ti~;ues (see U.S. patent 3,223,083), the relatively high molecular weight copolymers used in ~he adhesive compositions of ehe inven~ion are very different from the very low molecular weight p~lymers used in such prior art compositions. Vinyl acetate monomer ~nd very low molecular weight vinyl chloride~5 and vinyl acetate polymers are low viscosi~y liquids which exert a solvent effect on cyanoacrylatesJ so that in such prior art compositions the monomers o~ low molecular weight polymers ~ct as solvents and/or viscosity reducing agents for the cyanoacrylates. In contrast, the relatively high molecular weight copolymers used in the comp~;itions of the invention serve to incrense the viscosity of the30 ~yanoacrylate s, thereby rendering the adhesive composition less fluid and thus less likely to re~ch ir~ppropriate places, such RS human skin, durin~ use. Thus, the advarltages obtained by the adhesive compositions of the invention are not obtained by the prior art cyanoaeryla~based adhesive compositions wS~ioh employ very low molecular wei~ht vinyl aeetate ~nd vinyl chloride polymers. Moreover, le is 35 surprising that the relatively high molecular weight vinyl chlvride/vinyl acetate '9~-'',is copolymers used in the composition of the invention are oompatible with the other . ~ .

8~

component.s of the compositions since (as those skilled in polymer t~echnology are aware) in general the solubility of polymeric resins decreflses with increasing molecular weight. Indeed, as is shown by the comparative f xamples below, the vinyl chloride/vinyl acetate copolymers used in the compositions of the invention cannot U5 be replaced by either vinyl chloride or vinyl acetate homopolymers since suchhomopolymers are not compatible with cyanoacryl~l:es and thus cannot be used in the cornpositiorls of the in~en~:ion; those sk:illed in the field of polymer technology will of course appreciate that the polymer employed must be compatible with the cyarloacrylate i.e. the copolymer must dissolve in the cyanoacryl~te 10 since a copolymer which is simply suspended as solid particles in the cyan~acrylate will not substantially affect the properties of the ester and thus will not produce the advantages obtained with the compositions of the invention~
It is believed (although the invention is in no way limi~ed by this belief) thatthe mechanism by which the vinyl chloride/vinyl acetate copolymer reduces the skin 1~ adhesion of the comp~sitions o~ the invention is primarily physical. Vinyl chlolide/Yin~l ~ceta~e copolymers themselves have an aIfinity and adhesion prope~
ties for metals, glass, rubber, plastics and other materi~ls,. and are capable of forming fairly strong bonds with these- materials.. It appears that the copolymer serves to provide a physical block which markedly reduces the amount of ethyl ~-20 cyanoecrylate which comes into contact with the skin, thus greatly reducing the skinadhesion of the composition. Although the preferred - vinyl: chloride/Yinyl aceta~e/rnaleic acid terpolymer .poesesses. some c~rboxyl cross-linking î~ctionality, i~ does not re~ct with the moisture present on the skin and bond the skin instantly as does ~modi~ied ethyl 2-cyanoacryiate. -However9 ~lthough the vinyl chloride/vinyl.-25 acetate copolymer does not fo~m strong bonds with ~he skin, its own adhesiveproperties are suf~lciently good tha~ it does not significantly affect the r~te of cure of the ~dhesive compositions or the quality of ~he bond-finally achieved .when ~sing such compositior~s. In fact, as shown in some OI the examples below, at least when the preferred vinyl chloride/vinyl acet~te/m~leic acid terpolymer is employed, the 30 bonds achieved using the adhesive composition of the invention ~re not or~y comparable in strength under normal conditions, but ~re also more- resistant.. to soaking in water and sodillm hydroxide solutian, than-bonds achieved with conven-tional unmodifie~ ethyl 2-cyanoacrylRte; these di~ferences in bond-char~cteristics ~r2 probably due to the cnrboxyl funtionality of the terpo~ymer.
Although it is not ~bsolutely essenti~l, it is preferred that the compasitions of th~ invention contain a plasticizer in the a-mount of from about zero to not , more than 25% by weight. Desirably, the plastici~er comprises from about 3 to about 8% of the composition, and may be any of the liquid and solid plasticizers hitherto useà in cyanoacrylate adhesive composil:ions. Examples of suitable liquid plasticizers include dipropylene glycol dibenzoate (available as Benzoflex, Registered Trademark 9-88 from Velsicol Chemical Corporation, 341 East Ohio 05 Street, Chicago, Illinois 60611), diethylene glycol dibenzoate (available commercially as Benzo~lex 2-45*from Velsicol Chemical Ccrporation)9 butyl benzyl phthalate (available commercially as Santicizer 160 from Monsanto), the polymeric plasticizer available as Resoflex R-296*from Cambridge Industries Company, Inc., 440 ArsenalStreet, Watertown, Massachusetts 02172 and dibutyl phthalate. Dimethyl and diethyl 10 phthalate can also be used but are less desirable because of their higher volatibility.
Exarnples of suitable solid plasticizers include benzoate esters of di- and poly-hydroxy branched aliphatic compounds such as ~hose available commerci~lly as Benzoflex S-312, S-404*arld S-552 (all obtainable from Velsicol Chemicals Corpor-ation of the address previously given). Mixtures of plasticizers may of course be 15 used.
The plasticizer serves to render the cured film of adhesive produced by the adhesive compositions of the invention more flexible; the plastieizer in effect softens the polymerized cyanoacrylate/copolymer mixture in the cured film. Thus,the addition of plasticizer improves the adhesion of the composition to flexible20 substrates and also improves the impact resistanee of the composition when it is used to bond rigid substrates. The plasticizer also assists the vinyl chloride/vinyl acetate copolymer in reducing the skin adhesion of the composition. Experiments we have conducted show that the plasticizer normally serves to fur~her reduce the skin adhesion of the composition, as compared with a composition comprising solely 25 the cyanoacrylate and the vinyl chloride/vinyl acetate copolymer, but that the addition of the plasticizer does not significantly affect the rate of cure of the comp~ition nor does it significantly affect the quality of the bonds produced when the adhesive composition cures.
The incorporation of the plasticizer into the adhesive compocition also serves 30 to lower the viscosity of the cyanoacrylate/copolymer mixture. If the cyano-acrylate/copolymer mixture tends to be too viscous, it is desirable to use a liquid plasticizer, since such a liquid plasticizer usually lowers the viscosity 5-20%
depending upon the amount of plasticizer used. Solid plasticizers have less effect on the viscosity, typically lowering the viscosity only about 2-109~, depending upon the 35 amount oi solid plasticizer employed. Finally, the commercially-available plasti-cizers are much lower in cost than stabilized cyanoacrylates, so that the * trade mark addition of plasticizer to the cyanoacrylate/copolyrner rnixlure "extends" the relatively expensive cyanoacrylate thus producing the cost of the final com posi ti on.
It will thus be seen that the use of a plasticizer in the adhesive composition of 05 the invention gives a number of significant advantagesO Accordingly, although the adhesive compositiorLs of the invention need not contain any plasticizer at all, in general it is recommended that the compositions do include a plasticizer.
In addition to reduced skin adhesion, the compositions of the invention posse.ssadditional advantages. Presumably because of their reduced skin adhesion, the 10 compositions tend to be easier to clean up and to remove from the skin; they are ca~veniently removed from the skin with acetone, al with nail polish remover. The compositions of the invention are also lower in cost per unit weight than prior art compositions which comprise substantially pure ethyl 2-cyanoacrylate m onomer, since in the eompositions of the invention the expensive cyanoacrylate is 15 "extended~' with relatively less expensive copolymers and plasticizers. For example, stabilizeC ethyl 2-cyano~crylate monomer costs approxima~ely 12-15 dollars per pound, whereas the aforementioned UCAR VMCC * vinyl chloride/vinyl acetate/maleic acid terpolymer costs approximately $1.24 per pound and the aforementioned Benzoflex 9-88,*S-312*and S-404*plasticizers range in price from 58 20 cents to $1.65 per pound. Thus, by using a composition comprising approximately 75~ ethyl 2-cyanoacrylate, 17,6 of copolymer and 8~ of paasticizer, the cost per unit weight of the composition can be reduced by more than 20~ as compared with a pure ethyl 2-cyanoacrylate composition. Finally, as shown in more detail in the examples below, at least some of the compositions of the invention have a 25 resistance to hot and cold water and to sodium hydro~de solution which is better than that of prior art pure cyanoacrylate compositions.
The aavanta~es of reduced skin adhesion, easier clean-up and lower cost a~sociated with the adhesive compositions of the invention do not involve any sacrifice in bond strength or rate of curing as the comparative tests below show, the 30 strength of the bonds produced by the compo~sitions of the invention are as good as, and in some cases better than, prior art cyanoacrylate adhesive compositions, and the compositions of the invention also cure as fast as the prior art cs)mpositions.
Moreover, since the presence of ~he vinyl acetate/vinyl chloride copolymer (and,optionally, of the plasticizer~ renders the cured films formed from the compositions 35 of the invention more flexible than those formed from prior art compositions, and this film tlexibility increases the adhesion of the compositiorLs of the invention to ~3 * trade mark flexible substrates, and also increases their impact resistance on rigid substrates. Final~y, although the cured form of the compositions of the invention is more soluble in acetone and nail polish remover than prior art compositions, the tests described below show that the cured form of the compositions of the invention is not more affected by most other solvents than are the cured forms of prior art compositions; indeed, when cured the compositions o-E the invention appear to display resistance to the effects of alkali and boiling water which is noticeably greater than tha~ of prior art compositions.
The compositions of the invention may be prepared by forming a stabili7ed cyanoacrylate composition comprising a 2-cyanoacrylic acid ester and an anionic polymerization inhibitor and dissolving the vinyl chloride/vinyl acetate copolymer in a pulverulent state in the cyano-acrylate composition with a temperature of about 70-85C until the co-polymer is completely dissolved. If a plasticizer is to be added, we prefer to dissolve it in the cyanoacrylate composition at the same temper-ature of about 70 to about 85~C after the copolymer has been dissolved in the composition. Especially where the anionic polymeri~ation inhibitor used in the cyanoacrylate composition is sulfur dioxide, the cyanoacrylate is conveniently prepared with the inhibitor already contained therein. The various stages in the synthesis of the 2-cyanoacrylic acid ester may be conducted with a stream of of sulfur dioxide passing through the system, thus building up a high concentration of inhibitor as the 2-cyanoacrylic acid ester is produced in the last stage of the synthesis. In fact, the concentration of inhibitor which builds up is greater than i5 desirable and it is therefore desirable to remove excess inhibitor by applying a vacuum to the ester after it has been synthesized. This process of stabil-izing the adhesive during synthesis is described in U.S. patent 2,756,251.
Specific preferred compositions and processes of the invention will now be described, though by way of illustration only, to show details of particularly preferred reagents and techniques used in the compositions and processes of the invention.
In the following examples, various commercially-available pro-ducts are referred to by their trade marks. The products thus identified are as follows:
Cyanoacrylates The cyanoacrylates CN-2*, CN-4*, CN-6*, EE* and E-50* used in the examples are all obtainable from Alteco U.S.A., Inc. 23510 Telo Avenue, Unit 9~ Torrance, California 90503, United States of America. The main constituent of all these preparations is ethyl 2-cyanoacrylate. According to ~he manufacturer's data, ; ~ trade mark ~2~

all these cyanacrylate preparations are colorless transparent liquids having a storage life at 25C in excess of one ye~r and being soluble in acetone and nitromethane. The CN-2,*CN-4 'and CN-~ preparations all have a specific gravity of 1.05-1.10 at 25~C/4C and a refractive index ~nD20~ of 1.45; the bonds they produce 05 have excellent impact resistance and high tensile strength. The preparation CN-2 has a viscosity of 3-5cPs., the preparation C~-~*a viscosity of 75-lOOcPs and the preparation CN-6*a viscosity of 1000-1200cPs~ The preparations EE*and E-50*both have specific gravities of 1.05-1.08 at 25C/4~C, and a refractive index (nD ) of 1.48. The preparation EE has a viscosity of 3-5cPs., while the preparation E-50 hss a 10 viscosity of 7 5-lODcPs.
RS40X*and RPNX*are ethyl 2-cyanoacrylic acid esters availa~le from Sumitomo Chemical Company Ltd., Osaka, Japam According to the manufacturer's data, RS40~*is a transparent, colorless liquid having a flash point of 80C and a specific gravity of 1.07, while RPNX ls also a transparent colorless liquid having a flash point of 85C and a specific gravity of 1.05. The manufacturer states that both these cyanoacrylate6 qre soluble in acetone, methyl ethyl ketone, benzene, toluene and nitromethane. RS40~*and RPNX*are similar in properties to CN-4 and CN-~
respecti vely.
_opolymers All the copolymers used are available from Union Carbide Corporation at the aadress previously given and are sold by them as llCA~ resins VMCC, VMCH, VMCA
and VYLF. As previously mentioned, VMCC comprises, according to the man-ufacturer's data, 83% vinyl cl~oride7 16~ vinyl acetate and 1~ maleic acid. Thisresin has an inherent viscosity according to American Society ~or Testing and Materials Standard (ASTM) D-12q~3 of 0.38, a specific gravity according to ASTM ~
792 of 1.34, a glass transition temperature of 72DC and an average molecular weight l~l n 15,000. The solution viscosity a~ 30% solids in methyl ethyl ketone at 25C is lOOcPs. The resin VMCH comprises 869~ vinyl c}doride, 13% vinyl acetate and 1%
maleic acid. This resin has in inherent viscosity of 0.50, a specific gravity of 1.35, a glass transition temper~ture of 74C, an average molecular weight of 21,000 and a solution viscosity of ~50cPs, using the same tests as previously mentioned. The resin VMCA comprises 8196 vinyl chloride, 17% vinyl acetate and 2% maleic acid;
this resin has an inherent viscosity of 0.32, a specific gravity of 1.34, a glass transition temperature of 70~C, an average molecular weight of 8,000 and a solution 35 viscosity of 55cPs. Finally, the resin VYLF,*which is a simple vinyl chloride/vinyl acetate copolymer without modifying groups, comprises 88% vinyl ahloride and 12%
, ~ .
* trade m~rk vinyl acetate. This resin has an inherent viscosity of 0.28, a specific gravity of 1.36, a glass transition temperaturc of fi8~C, an average molecular weight of 8,00n and a soluti on viscosity of 60cPs.
Pl asti ci zers D5 The plasticizers us~d include Benzoflex 9-88;*50* 2-45*, S-312* S-552~nd-S-404 all available from Velsicol Chemical Corporation at thle address previously ~iven.
Benzoflex 9-88*comprises dipropylene glycol dibenzoate, Benzoflex 2-4~*comprisesdiethylene glycol dibenzoate, Benzoflex S-312 comprises neopentyl glycol diber~
zoate~ Benzoflex- S~55?. c~mprises ~ery~hritol tetr~benzoate, ~nd-b~n~oflex-S-10 4û4 glyceryl tribenzoate, all these compositions being at least 97% pure by ester content assay. Benzoflex 50 comprises a 1:1 mixture of Benzoflex 9-88 and Benzoflex 2-45. The other plasticizers that were used were Santicizer 160, available from Monsanto and comprising a butyl benzvl phthalate, Resoilex R-296 available from Cambridge Industries Company, Inc., and comprising an unmodified long chain1~ saturated polyester, and dibutyl phthalate.
Stabilizer In many of the adhesive compositions described below, hydroquinone as a free--radical stabliæer. It is believed that most commercially-available stabilized cyanoacrylates already contain some hydroquinone. However, in many cases 20 we have found it advantageous to add further amounts of hydroquinone to the ins~ant adhesive compositions to provide increased stability. In all cases, the hydroquinone is added to the compasition with the Yinyl chloride/vinyl acetate copolymer and dissolves therewith.
Example I
An ~dhesive comp~sition of the invention was formulated using the following components and proportions.

Reagen~ %
Alteco CN-2*800913 VMCC * 14.279 30 Hydroquinone0.048 ~3enzoflex 9-88*4.760 100.000 The stabilized cyanoacrylate composition, CN-2 was heated to 70-8ljC and the copolymer, VMCC, which was obtained in powdered form, was dissolved in the * traae mark ,~

~2~

lleated cyanoacrylate composition by mixing over a period of approximately 20 minutes within this temperature ran~e. The 20 minute mixing period usually sufficed to complete dissolve the copolymer~ but if the copolymer had not completely dissolved at the end of the mixing, mixing was continued until the resin 05 was completely dissolved. The cyanoacrylate/copolymer mix was then maintainedwithin the same temper~ture range while the plgsticizer, Benzoflex 9-88,* was added thereto, and the mixing was continued at the same temperature for an additional 5-10 minutes until the plasticizer had become completely uniformly mixed into the composition. Finally, the adhesive composition was cooled and passed through a fine 10 polytetrafluoroetllylene filter.
Details of the properties of this composition, and those produeed in the following Examples Il-XXIII are given in the section headed "~est Results" below.
Example Il An adhesive composition of the invention was formulated from the following ~5 components in the same rnanner IlS in Example I above:
ReatJent %
C~-2 76.153 V~qCC* 19.039 Hydroquinone 0.048 20 Benzoflex 9-88 *4.760 100.000 Example III
Another adhesive composition of the invention was formulated from the following components in the same manner as in Example I above:
25 Rea~rent %
CN-2 * 71.394 VMCC 23. 79 8 Hydroquinone 0.043 Benzoflex 9-884.760 100.000 Example IV
Another adhesive composition of the invention was formulated from the following components in the same manner as in Exarnple 1:

~- * trade mark .~.i .~i Rea~ent %
CN-2 * 66.634 VMCC~ 28.558 Hydroquinone 0.048 05 Benzoflex 9-88 4.760 100.~00 Example V
Another Eldhesive composition of t~e invention was formulated from the f~l~win~components in the same manner ~ in Example l:
lD Rea~ent %
CN-2 * 60.843 V.~ICC * 26.076 ~lydroquinone 0.043 Ben~ofle~; 9-88 * 13.038 100.000 Example Vl Another adhesive composition of the invention was formulated from the following components in the same manner as in Example I above, except that the two cyanoacrylate compositions, CN-~*and CN-4*were first mixed with each other 20 at room temperature for five minutes before admixture of the other components as described in Ex~nple I:
Rea~ nt %
CN-2 * 39.266 CN-4 42.837 25 VMCC 13.089 Hyds oquinone 0.048 Benzoflex 9-88 4.760 100. 00~
Examele VII (control) To simulate a typicRl prior art stabilized cy~noacrylate composition, D~8 parts of CN-2 were mixed with 52 parts of GN-4 Rt room temperature to forrn n control com position.
Exam~le Vlll (control) This control composition comprised pure CN-2;~

* trade mark -16~

Exam ple IX (control) This control cornposition cornprised pure CN-4~' ~xample X
To provide an adhesive composition of the invention containing isopropyl 2 O~- -cyanoaerylat~, the-f~}l-owing ~ mponents-Yvere formulated in the- sam~e way as in Example I above:
Reagent Alteco isopropyl 2-cyanoacr~late 82.l03 VMC~ * 13.089 10 Hydroquinone 0.048 Benzoflex 9-88* 4.760 100. 000 This cornposition was considerably less stable than tne compositions of the invention containing etnyl 2-cyanoacrylate described above. As prepared, the cornposition 15 was cloudy Pn~ it gelled upon overni~ht stanàing. Thus, this composition is not suitable for retail sale, where a long shel~life is essential but mi~Ilt be suitable for industrial use where it could be applied shortly after formulation.
Example XI
To provide an adhesive composition of the invention containing methyl 2-2~ yanoacrylate the following component~ were formulated in the same way as in Exarnple I above:
Rea~Jent %
Alteco methyl 2-cyanoacrylate 82.103 V4~CC L3.089 25 Hydroquinone 0.048 Benoflex 9-88* 4.760 10~.000 This composition was considerably less stable than the compositions of the invention containing ethyl 2-cyanoacrylate described above. The product underwent phase 30 separation and thickened a few hours after mixing. Thus, as with the cornposition of Ex~nple X above, the use of this composition is restricted to applications where the composition can be used within a few hours after its manufacture.
The following Examples xn-xIv are similar to Example VI except that various different plasticizers were substituted for the Benzoflex 9-88*used in Example Vl.
35 Examples XII-XVI were formulated in a manner identical to that used in Example Vl.
,,~., .
~.' 'S' * trade mark 7~

EXaMPIe XII
Reagent %
CN-4 42.836 CN-2 39.267 05 VMCC 13.089 Hydroquinone 0.048 Benzoflex S0 4.760 100.000 Examp~e XIII

10 Reagent 9~
CN-4 42.836 *

CN-2 39.267 *

V:~CC 13.089 ~y~oquinone 0.048 15 Benzoflex 2-45 * 4.760 100. 000 Exam ple XIV
eagenl ~
CN 4 * 42.836 20 CN-2 * 39.267 Vl~CC * 13.089 Hydroquinone 0.048 Santicizer 160 * 4.760 100.000 Exam7~1e XV

Reagent %
CN-4 * 42.836 CN-2 * 39.267 VMCC * 13.089 30 Hydroquinone 0.048 Benzoflex S-312 * 4.760 100.000 ~ * trac~e m~rk Example XVI

Reagent %
CN-4 * 42.836 05 CN-2 * 39.267 VMCC * 13. 089 Hydroquinone 0.048 Rezoflex R-296 4.760 100.000 Example XVl:l The following composition is identical to Example VI above and was form-ulated in precisely the same manner, except that Alteco EE WAS substituted for ~lteco ~,N-4 and Alteco E-50 was substituted fo. Alteco CN-2-Reagent ~o 15 EE ~2.~3(;
E-50 39.267 VI~C(~ 13.089 Hydroquinone 0.048 Benzoflex 9-8$ 4.760 20lO0.000 _ ample XVIII
Another adhesive composition of the invention was formulated in the same manner in Example I, but using the following components:
Reagent 96 ~5 CN-2 * 84.957 VMCH* 9 995 Hydroquinone 0.050 Benzoflex 9-88 * 4, 998 1 00. 000 Exampl_ XIX
This exarnple illustrates the effect of omitting the plastici~er from the adhesiYe composition of Example Vl. An adhesive composition of the invention wasformulated in the same manner RS in ExamF~e VI but using the following corn-ponents:
* trad~ mark R ea~ent CN-4 * 44.978 CN-2 * 41.229 VMCC * 13.743 05 Hydroquinone 0.050 100.000 Example XX
Another adhesiYe composition of the invention was formulated in the same manner as in Example VI above but using the following components 10 Rea~ent 9~
CN-4 43. 881 C~-2 * 40.224 ~!MCC * 13.408 }-iycLroqui!~one Benzoflex 9-88 2.438 100.000 The following examples XXI and XXII are simil~r to Example XV above, except that in place of the mixture of Alteco CN-2 and CN-4 used in Exarnple XV, Example XXI uses pure CN-2 while Example XXII uses pure CN-4. Both compositions were 20 for m ulated in the same manner as in Example I above.

Example XXl Rea~ent CN-2* 82.103 VMCC 13.089 25 Hydroquinone 0.048 Benzoflex S-312* 4.760 100.000 * trade mark . ~

Examp1e XXII
Reagent %
_ CN-4 * 82.1û3 VI~ICC * 13.089 05 Hydroquinone 0.048 Benzoflex S-3l2 * 4.760 100.000 _~(C ontrol) Pacer E-40 a commercially-available stabilized cyanoacrylate composition sold 10 by Pacer Technology and Resources, 1550 Dell Avenue, Suite K, Campbell, Cali-f ornia 95Q08, was used as a control composition.

Examplea XXIV and X~V below illustrate adhesive compositions oî the invention l~ithout plasticizers. Both the~e compositions ~.~ere pr-epared in the same manner as in Exainple I above, except of course that the addition of plasticizer was not made.

~;, Ex~mple XXlV
ReaQent ' CN-2 * 85 Vl\ICA *

Examele XXV

Alteco E-50* 85 VllCA 15 The stability of the compositions of both Examp1es XXIV and XXV was very poor;
25 both composition~s gelled while mixing, the composition foaming up and solidifying.
Examples XXVI and XXVII below illustrate adhesive composiitons of the inver~
tion containing the simple vinyl chloride/vinyl acetate copolymer UCAR VYLF in place of the vinyl chloride/vinyl acetate/maleic ncid terpolymers used in the precedirlg examples. The compositions of Examples XXVI and XXVII were prepared 30 by the same method as in Example I above.

* trade ulark Example XXVI
Re~ent E-5û * 80.952 VYl,F * 14.286 05 Benzoflex 9-88* 4.762 1 00~ 000 It will be seen that, unlike most of the preceding exarrlples, this comp~sition did not contain the free radical polymerization inhibi~or hy~roquinone. The ~Ibsence of a free radical polymerization inhibitor greatly reduced the stability of the com-10 position, which gelled nvernight~ although it was stable for a period of a few hours after preparation.

Exa~ple XXVII
Re~-Tent ~
Cl\l-2 * 80.~13 15 VYLF * 1~.279 Hydroquinone 0.048 Benzoflex 9-88 ~ 4.760 100. 000 The presence of hydroquinone in this cornposition rendered it considersbly more 20 stable than the composition of Example XXVI, which i5 similar except for the absence of hydroqllinone. This composition remained stable for several days but increased markedly in viscosity and underwent phase separation after one week.
~ x~nples XXVIII and XXIX are identical to Example Vl above and were preparedin precisely the same rnanner, except that the plasticizer Benzoflex 9-88*used in the 25 composition of Exarnple Vl was replaced by Benzoflex S-55~*in Example XXVIII and Benzoflex S-404 In Exarnple XXIX; also the plasticizer was admixed with the other eom ponen~s at 80C .

Exarn ple XXVIII
_.
Reagent %
30 Cl~-~ 42.836 CN~4 39.267 Vl~CC 13.089 * trade mark Hydroquinone 0.048 *

Benzoflex S-552 4.760 lOO.D00 _X~
05 Rea~ent CN-2 * 420836 CN-4 * 39.267 VMCC * 13.089 Hydro~uinone 0.04~
10 13enzoflex S-404 * 4.760 1 00. 000 Exam ple XXX
This ex;~lnple illustrates a compesition similar to that of Example XXIX, except at the proportion of plasticizer is increaseci. An adhesive composition of the 15 invention was f orrnulated from the following components by the same method described in Ex~nple ~1 above, except that the powdered plasticizer, Benzoflex S-404 *was added at 80DC. This example, and the following Example XXXI represent the presently preferred compositions of the invention:

~ %
CN-4 3g.00 CN-2 38.'15 Vl~lCC * 1~.00 hydroquinone 0.05 Benzoflex S-404 7.50 100.00 Example XXXI
This example illustrates an adhesive composition of the invention similar to that of Exarnple XXX except for the use of different cyanoacrylate compositions;the Alteco CN-4 and CN-~ of Example XXX were replaced with RS-40X and r.PNX
30 respectively. The method of preparation was the same as in Example XXX:

~r~ * trade mark .,,~ I

R ea~ %
RS-4 0X * 39, 0 0 RPNX * 38.45 VMCC * 15.0 0 05 Hydroquinone 0.05 Benæoflex S-404 * 7.5 0 100.00 Example XXXII
Another adhesive composition of the invention was formulated from the 10 following components using the same method as in Example XXX:
Reagent æ
CN -4 * 4;, . oo CN -2 * 41.2 Q
VMC(~ * 13. 5 15 Hy~ oquinone ().05 Benzofle2~ 9-88* 2.50 Benzofle~; S-552* 2.50 100.00 Example XXXIII (Control) 20 Pure Alteco CN-6 was used as a control composition.

Example XXXIV
Another adhesh7e composition of the invention was prepared from the fol-lowing components using the sa;ne technique as in Example I (although sulfur dioxide is shown separa~ely in the fo~lowing list of components, the sulfur dioxide was in 25 f act present in the cyanoacrylate monom er as procured and was not added separ~lely during ~he preparation):
Reas~ent 9~, Ethyl 2-cyanoacrylate monomer 77.488 Sulf ur dioxide 0.0020 30 Hydroquinone 0.0100 Carboxyl-modified vinyl chloride/vinyl acetate copolymer 15.0000 Plasticizer 7.5000 1 00. 0000 . . .
* t, adf~ mark Exam ple XXXV
The iollowing composition is a presently preferred composition of the invention usin~ a liquid plasticizer:
05 Reagent %

CN-2 38.45 VMCC 15.00 Hydroquinone 0.05 13 Dibutyl phthala~e 7.50 100. Q0 TEST RESllLTS
Except where the compositions were unstable as previously noted, each of the colnpositions in Examples ~-~XXI~ and XXX\' above were subjected to the following 15 tests:

Viscosity The viscosity of the adhesive compositions was measured using a Brookfield Synchr~lectric viscometer, l~lodel LVF. The tests were condu^ted using a No. 3 spindle at 60 revolutions per minute and 25~C.

20 Rate of C ure One drop of the adhesive composition was placed between two flat pieces of the substrate5 and then the upper plate was twirled under slight pressure until gelling Dccurred. The ~elling_tim~ v~as r~e~sured in seconds. In all cases, two similar portions of t!~e subsLnate were used, the substrates used being stainless steel, 25 rubber, glass and polyvinyl chloride film (PVC), All rate of cure tests were carried out at 75~ (24~) and 50% relative humidity.

Bond Development:Tensile Strength The adhesive composition was placed between the ends two stainless steel rods and allowed to gel for five minutes, one hour, 24 hours or five days. The rods were 3Q then pulled ap~rt using a Comten 9"2 MT-2QVP p~ling machine using a pLùl rate of six inches/minute (lScm./rnin.). The tensile force neCessQry to break the bond is * trade mark i, ~ ~ `

given in Mega Pascals, and all values given are averaged over 10 specimens. All tests wer~ conducted at 75C(24C) and 50% relatlve humidity.

The results of all the foregoing tests are shown in Table 1 below. The results of the following tests are shown in Table 2 below.

Skin ~dhesion One drop of adhesive was applied between the tips of the thumb and forefinger of a volunteer and the adhesion obtained was checked 1~ 5, 10, 15, 20, 30, 45, and 60 seconds after application. The time and the degree of skin bonding obtained were recorded, the types of skin bonding mentioned in Table 2 being as follows:
1. Weak skin bond(W)-a bond which was easily broken by finger strength with no damage to the skin.
2. Strong bond(S)-a bond which was not easily broken directly by finger strength but which could be separated by peeling; and 3. Very s~rong skin bond (VS)-a bond which was sufficiently strong that skin damage would occur if the skin was separated.

In addition to measuring the strength of the skin bond, the resistance of that bond ~o attack by acetone and Cutex ~registered trademark) nail polish remover was measured. (Cutex* nail polish remover is manufactured by Cheseborough Ponds, Inc. of Greenwich, Connecticut, ~nited States of America and its ingredients are stated by the manufacturer to be acetone, water, PEG-115~' tallow polyamine, fragrance and D&C yellow No. 11.) In Table 2 below, "easy"
(E) indicates that the finger-to-thumb bond could be broken for soaking for less than 90 seconds in either acetone or nail polish remover, while "difficult" (D) indicates that the bond could only be broken by soaking in acetone for more than three minutes or in nall polish remover for more than five minutes.
;~ - 25 -, *trade mark lh/ ^~

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Sk~n Adhes on Ease of Removal Nail Polish E,~ample # Time(secs.) Strength Acetone Remover II 60 S E: E
III 60 W _ _ lo VII(Control) 1 VS D D
VIII(Control) 1 VS D D
IX(Control) 1 VS D D

XVII ................ 45 S E E

XXIII(Control) 1 VS D D

XXXII 45 S E T~
XXXIII(Control) 1 VS D D

'~

lb/~, j The data set forth in Tables 1 and Z above illustrate the dramatic reduction in skin adhesion achieved by the instant compositions. All five of the control compositions formed within one second of application to skin very strong skin bonds which could damage the skin if one attempted to separate them bv force, and these very strong skin bonds were difficult to break with either acetone or nail polish remover~ In contrast, all of the instant compositions took at least thirty seconds to form a skin bond which, although strong, was peelable and would not damage slcin, and these skin bonds were relatively easily removed with either acetone or nail polish remover. Moreover, comparison of the skin adhesion times in Table 2 with the corresponding rate of cure times in Table 1 shows that, at least on rubber, glass and polyvinyl chloride substrates, the skin adhesion time of the instant compositions is considerably greater than their gelling times. Thus, if a user of the adhesive composition is holding two parts of an object together until the adhesive composition gels and thus produces a bond between the two parts, even if ~he person has accidentally applied some of the adhesive to his finger tips, the ewO parts of the object will be held together before the fingers become strongly adhered to the object, and thus there is little possibility of skin adhesions. On the other hand, with the prior art compositions the gel time is considerably longer than the skin adhesion time, so that accidental skin adhesions are very likely when a person is holding two parts of an object together until the adhesive composition gels.
It should also be noted that, with the exception of the composition of Example XXXIII, which is not a typical prior art cyanoacrylate adhesive composition, the prior art compositions have much lower viscosities than the instant compositions and are thus far more likely to run from the desired location. This greater fluidity of the prior art compositions increases the risk of accidental skin adhesions during use.

- 29 ~

" , i~
lb/

Finally, comparison of the composition o~ Example V with those of Ex~mples IIT and IV shows that when the proportion of cyanoacrylate in the instant adhesive compositions falls to about 60%, the final bond strength of the bond formed tends to appreciablv reduced.
Accordingly, we prefer to keep the proportion of cyanoacrylate in the instant compositions above 60% and indeed our tests indicate that the proportion of cyanoacrylate should be from about 75-85% of the composition.
The instant adhesive composition of Example XXXI and the control composition of Example XXIII were also tested for the resistance to solvents and chemicals of the bonds formed. This test was conducted using stainless steel rods bonded together at their ends and allowed to cure for five days at 75F (24C) and 50% relative humidity. The tensile strength of the bond formed was then tested in the same manner as descr~bed above under "Bond Development" except that the results were averaged over five speciments rather than ten. Selected specimens were then allowed to soak for 24 hours in one of various solvents and chemicals and their tensile strength tested in the same manner. Finally, specimens which has been allowed to cure for five days were placed in boiling water for one hour, cooled for two hours at 75F (24C) and then tested. The results are given in Table 3 below.
(The solvent Varsol~ No. 1 used in these tests i& a commercial mixed hydrocarbon solvent available from Exxon Company, U.S.A., of PØ Box 2180, Houston, Texas 77001. According to the manufacturer's, this solvent contains 18% by volume of aromatic hydrocarbons, 1.0%
of olefins, 81.0% of saturated hydrocarbons, 18.0% of C6 and higher aromatics and one part per million of sulfur.
The solvent has a flash point of 41C, an aniline point of 52C and a specific gravity of 0.7~7.) *trade mark ,'~ lb/ lj ~,.

~2~

Tensile Strength(MPa) Soakin~ L~ d IJsed Exa~le XXXIExample XXIII(Control None(5-day cure only) 48.40 45.16 Denatured alcohol 45.51 39.64 l,l,l-Trichloroethane 48.88 39.44 Acetone disassembled while disassembled while soakingsoaking Wa~er 38.15 22.13 Varsol~ No. 1 37.30 43.78 SAE-30 Motor Oil 35.65 33.58 IN HCl 41.30 31.65 IN NaOH 23.51 7.31 Automatic Transmission 42.13 36.96 fluid Nail Polish Remover disassembled while ~.62 soaking Toluene 37.02 44.95 n-Hexane' 38.81 35.23 Boiling Water 31.58 19.99 The data presented in Table 3 above show that not only does the instant composition of Example XXXI produce a bond at least as strong as the bond produced by the prior art composition of Example XXIII, but that, with the exception of the highly desirable lower resis~ance to nail polish remover, the bonds produced by the instant composition are at least as resistant to solvents as those produced by the prior art composition. Indeed the resistance of the instant composition to alkali and boiling water appears to be markedly better than that of the prior art composition.
ATTEMPTED REPLACEMENT OF THE VINYL CHLORIDE/VINYL ACETATE
COPOLYMER IN THE INSTANT COMPOSITIONS WITH POLYVINYL ETHER, POLYVINYL CHLORIDE AND POLYVINYL ACETATE
Experiments were conducted to determine whether the vinyl chloride/vinyl acetate copolymer used in the instant *trade mark ~,, !
~'~ lb/"- , compositions could be replaced with polyvinyl chloride alone, polyvinyl chloride, polyvinyl acetate or a polyvinyl ether. Firstly, pure polyvinyl methyl ether was prepared by evapora~ing Gantrez* ~-154, a 50% solution of pol~vinyl methyl ether in water, to complete dryness.
This polyvinyl methyl ether was then used in an attempt to prepare an adhesive composition having the following formulation:
Rea~ent %
Alteco E-50* 77.45 Polyvinyl methyl ether 15.00 Hydroquinone 0.05 Benzoflex S-40* 7.50 100.00 The technique used in the attempt to prepare this composition was the same as that used in Example l above.
~owever, a homogeneous composition could not be prepared since the polyvinyl methyl ether refused to dissolve in the cyanoacryla~e even after protracted heating to 125C.
To test whether a pure polyvinyl acetate was usable in the instant adhesive compositions, Vinac B-15*, a solid polyvinyl acetate resin manufactured by Air Product & Chemicals, Allentown, Pennsylvania, was used in an attempt to prepare a composition having the following formulation:
Reagent %
Alteco E-50* 77.45 Polyvinyl acetate15.00 Hydroquinone 0.05 Benzoflex S-404* 7.50 100. 00 Again an attempt was made to formulate this composition using the method of Example 1, but the poylvinyl acetate refused to dissolve in the cyanoacrylate composition even after prolonged heating at 120C.

*trade mark lb/' ' ~2~

To determine w~)ether polyvinyl chloride was usable in the instan~ adhesive compositions, VC-lOORE*, a commercially-available polyvinyl chloride resin manu-factured bv Borden, Inc., of 180 East Broad Street, Columbus, Ohio 43215, was used in an attempt to prepare a composition having the following formulation:
Reagent Alteco E-50* 77.45 Polyvinyl chloride15.00 Hydroquinone 0.05 Benzoflex S-404*7.50 100.00 Again, an attempt was made to prepare this formulation using the method of Example 1 above, but the polyvinyl chloride refused to dissolve in the cyanoacrylate even after protracted heating at 120C.
To test whether the results obtained with a mixture of polyvinyl chloride and polyvinyl acetate differed from those with the two resins separately, an attempt was made to prepare a composition having the formulation:
ent %
Alteco E-50* 77.45 Polyvinyl acetate (Vinac B-15~ 7.50 Polyvinyl chloride (VC-lOORE*) 7.50 Hydroquinone 0^05 Benzoflex S-404;~ 7.50 100.00 The results obtained with the mixture of polyvinyl chloride and polyvinyl acetate were no different from those obtained 3~ using the two resins separately; both resins refused to dissolve ln the cyanoacrylate even after protracted heating at 120C.
Finally, an attempt was made to prepare a composition identical to that in Example XXXI above except that instead of using the vinyl chloride/vinyl acetate/maleic *trade mark . .
lb/~ ~

acid terpolymer, VMCC*, polyvinyl chloride, polyvinyl acetate and maleic acid were added as separate compounds.
Thus, the attempted composition would have the following formulati.on:
Reagent RS-40X~- 39.00 RPNX* 38.45 Polyvinyl chloride (VC-lOORE*) 12.45 Polyvinyl acetate (Vinac B-15*) 2,40 Maleic acid 0.15 Hydroquinone 0.05 Benzoflex S~404* 7.50 100.00 When formulation of this composition was attempted by the method described in Example I above, the maleic acid readily dissolved in the cyanacrylate but, as in the previous tests, the vinyl chloride and vinyl acetate refused to dissolve in the cyanoacrylate even after protracted heating at 120DC.
The above tests demonstrate that the vinyl chloride/
vinyl acetate and vinyl chloride/vinyl acetate/~aleic acid copolymers used in the instant adhesive compositions can not be replaced by vinyl chloride, vinyl acetate, polyvinyl ethers, mixtures of polyvinyl chloride and polyvinyl acetate or mixtures of polyvinyl chloride, polyvinyl acetate and maleic acid since these homopolymers and mixtures are not compatible with cyanoacrylates.

*trade mark lb/

Claims (23)

THE EMBODIMENT OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An adhesive composition comprising:
from about 55 to about 92 percent by weight of a 2-cyanoacrylic acid ester;
from about 4 to about 30 percent by weight of a vinyl chloride/vinyl acetate copolymer dissolved in said 2-cyanoacrylic acid ester, said copolymer having a molecular weight of at least about 8,000 and containing a major propor-tion by weight of vinyl chloride and a minor proportion, but not less than 5 percent by weight, of vinyl acetate; and from about zero to not more than about 25 percent by weight of a plasticizer.

2. A composition according to claim 1, wherein said 2-cyanoacrylic acid ester comprises ethyl 2-cyanoacrylate.

3. A composition according to claim 2, wherein said ethyl 2-cyanoacrylate has a viscosity of about 5 to about 50 cPs.

4. A composition according to claim 1, 2 or 3, wherein said 2-cyanoacrylic acid ester comprises from about 75 to about $5 percent by weight of said composition.

5. A composition according to claim 1, 2 or 3, wherein said copolymer comprises about 80 to about 90 percent by weight vinyl chloride and about 10 to about 20 percent by weight vinyl acetate.

6. A composition according to claim 1, wherein said copolymer comprises a carboxyl-modifled vinyl chloride/
vinyl acetate copolymer.

7. A composition according to claim 6, wherein said copolymer comprises a vinyl chloride/vinyl acetate/
maleic acid terpolymer.

8. A composition according to claim 7, wherein said terpolymer comprises about 80 to about 90 percent by weight vinyl chloride, about 10 to about 20 percent by weight vinyl acetate and not more than about 2 percent by weight maleic acid.

9. A composition according to claim 1, 2 or 3,wherein said copolymer comprises from about 10 to about 18 percent by weight of said composition.

10. A composition according to claim 1, 2 or 3, wherein said plasticizer is selected from the group con-sisting of dipropylene glycol dibenzoate, diethylene glycol dibenzoate, butyl benzyl phthalate, dibutyl phthalate and benzoate esters of di- and poly-hydroxy branched alphatic compounds.

11. A composition according to claim 1, 2 or 3, wherein said plasticizer comprises from about 3 to about 8 percent by weight of said composition.

12. A composition according to claim 1, further comprising an anionic polymerization inhibitor.

13. A composition according to claim 12, wherein said anionic polymerization inhibitor comprises sulfur dioxide.

14. A composition according to 13, wherein said sulfur dioxide is present in an amount of from about 0.001 to about 0.5 percent by weight of said composition.

15. A composition according to claim 1, 2 or 3, further comprising from about 0.001 to about 0.05 percent by weight of a free radical polymerization inhibitor.

16. An adhesive composition comprising:
from about 75 to about 85 percent by weight of ethyl 2-cyanoacrylate;
from about 10 to about 18 percent by weight of a vinyl chloride/vinyl acetate copolymer dissolved in said ethyl 2-cyanoacrylate, said copolymer having a molecular weight of at least about 8,000 and comprising about 80 to about 90 percent by weight vinyl chloride and about 10 to about 20 percent by weight vinyl acetate; and from about 3 to about 8 percent by weight of a plasticizer.

17. A composition according to claim 16, wherein said ethyl 2-cyanoacrylate has a viscosity of about 5 to about 50 cPs.

18. A composition according to claim 16 or 17, wherein said copolymer comprises a carboxyl-modified vinyl chloride/vinyl acetate copolymer.
19. An adhesive composition comprising:
from about 75 to about 85 percent by weight of ethyl 2-cyanoacrylate;
from about 10 to about 18 percent by weight of a vinyl chloride/vinyl acetate/maleic acid terpolymer dis-solved in said ethyl 2-cyanoacrylate, said terpolymer hav-ing a molecular weight of at least about 8,000 and comprising about 80 to about 90 percent by weight vinyl chloride, from about 10 to about 20 percent by weight vinyl acetate and

Claim 19 continued...
not more than about 2 percent by weight maleic acid; and from about 3 to about 8 percent by weight of a plasticizer.

20. A composition according to claim 19, wherein said ethyl 2-cyanoacrylate has a viscosity of about 5 to about 50 cPs.

21. A composition according to claim 19 or 20, wherein said terpolymer comprises about 83 percent by weight vinyl chloride, about 16 percent by weight vinyl acetate and about 1 percent by weight maleic acid.

22. A process for forming an adhesive composition, which comprises:
forming a stabilized cyanoacrylate composition comprising a 2-cyanoacrylic acid ester and an anionic poly-merization inhibitor; and dissolving a pulverulent vinyl chloride/vinyl acetate copolymer having a molecular weight of at least about 8,000 in said cyanoacrylate composition at a temperature of about 70 to about 85°C until said copolymer is completely dissolved in said cyanoacrylate composition, such that the adhesive composition formed comprises from about 55 to about 92 percent by weight of said cyanoacrylate and about 4 to about 30 percent by weight of said copolymer.

23. A process according to claim 22, wherein there is also dissolved in said cyanoacrylate composition a plasticizer in such an amount that said plasticizer is present in said adhesive composition in an amount of from greater than zero but not more than about 25 percent by weight.