CA2249569A1 - Bonded polyolefin sheet - Google Patents
Bonded polyolefin sheet Download PDFInfo
- Publication number
- CA2249569A1 CA2249569A1 CA002249569A CA2249569A CA2249569A1 CA 2249569 A1 CA2249569 A1 CA 2249569A1 CA 002249569 A CA002249569 A CA 002249569A CA 2249569 A CA2249569 A CA 2249569A CA 2249569 A1 CA2249569 A1 CA 2249569A1
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- Canada
- Prior art keywords
- sheet
- roll
- heated
- cooling
- preheating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
- D04H3/08—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating
- D04H3/16—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating with bonds between thermoplastic filaments produced in association with filament formation, e.g. immediately following extrusion
-
- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
- D04H3/08—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating
- D04H3/14—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating with bonds between thermoplastic yarns or filaments produced by welding
-
- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
- D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
- D04H1/72—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged
- D04H1/724—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged forming webs during fibre formation, e.g. flash-spinning
Abstract
A process is provided for producing a bonded nonwoven sheet from a lightly consolidated fibrous polyolefin sheet wherein the sheet is preheated on one or more preheating rolls, is bonded in one or more calendering nips, and is cooled on one or more cooling rolls. The process is used to make bonded polyolefin fibrous sheets that are smooth, are substantially impermeable to air and water, and are moisture vapor permeable.
Description
CA 02249~69 1998-09-16 BONDED POLYOLEFIN
Field of the Invention This invention relates to a bonded nonwoven sheet made 5 from a fibrous polyolefin material. More particularly, the invention relates to a bonded nonwoven sheet that is smooth, permeable to moisture vapor, and substantially impermeable to air and water. The invention also relates to a bonding process for producing such a sheet.
Background of the Invention Processes for manufacturing fibrous nonwoven sheets from polyolefin polymers are known in the art. Blades et al., U.S. Patent No.
3,0~1,519 (assigned to E.I. DuPont de Nemours & Company (hereinafter "DuPont")), discloses flash-spinning of plexifilamentary 15 polyethylene film-fibrils. Steuber, U.S. Patent No. 3,169,899 (assigned to DuPont), discloses depositing a flash-spun polyethylene plexifilamentary film-fibril web onto a moving belt and compressing the deposited web to form a lightly consolidated nonwoven sheet.
The term "plexifilamentary" means a three-dimensional integral network ~0 of a multitude of thin, ribbon-like, film-fibril elements of random length and with a mean thickness of less than about 20 microns. In plexifilamentary structures, the film-fibril elements are generally coextensively aligned with the longitudinal axis of the structure and they interrnittently unite and separate at irregular intervals in various places 25 throughout the length, width and thickness of the structure to form the three--limen~ional network.
In order to produce sheets with the strength and barrier properties required for many applications, such as air infiltration barrier sheet material used in home construction (housewrap), the film-fibrils or 30 other fibers of the lightly consolidated sheet material must be bonded together. Lightly consolidated nonwoven sheets made from polyolefin fibers have been bonded by calendering and hot air treatments.
However, sheets so bonded have tended to shrink and curl, resulting in CA 02249~69 1998-09-16 WO 97/40224 PCTrUSg7/OS859 sheets with irregular thickness, opacity, strength and permeability propert~es.
A process for bonding polyolefinic plexifilamentary, film-fibril sheets with properties sufficiently uniform for commercial applications is disclosed in David, U.S. Patent No. 3,532,589 (assigned to DuPont) and is shown in Figure 1. The thermal bonding process disclosed in the David patent requires that the unconsolidated film-fibril sheet 5 from supply roll 6 be subjected to light compression d-lring heating in order to prevent shrinkage and curling of the bonding sheet.
A flexible belt 2 is used to compress a sheet being bonded against a large heated drum 1 that is made of a heat-conducting material. Tension in the belt is m~int~ined by the rolls 3. The belt is preheated by a heating roll 9 and a heated plate 10. The drum 1 is m~int~ined at a temperature substantially equal to or greater than the upper limit of the melting range of the film-fibril elements of the sheet being bonded. The rotating heated drum 1 is large (about 2 m in diameter) so as to permit the film-fibril sheet to be heated long enough to allow the face of the sheet ~in~t the roll to reach a lell~c.alllre within 7~ C ofthe upper limit of the melting range of the film-fibril elementc, but not substantially above said upper limit, and to allow the second face of the sheet to reach a temperature between 0.8~ to 10~ C lower than the temperature of the first face of the sheet. The heated sheet 5 is removed from the heated drum 1 without removing the belt lc~int and the sheet is then transferred to a cooling roll 4 where the temperature of the film-fibril sheet throughout its thickness is rec~llce(l to a temperature less than that at which the sheet will distort or shrink when unlesl~ined. Roll 7 removes the bonded sheet from the belt 2 before the sheet is collected on a collection roll 8. The sheet may be run through another thermal bonding device like that shown in Figure 1 with the second surface facing the heated drum in order to produce a hard bonded surface on the opposite side of the sheet.
For the past twenty-five years, a thermal bonding process similar to that shown in Figure 1 has been applied to the commercial production of hard-surfaced spunbonded polyolefin sheet material, such CA 02249~69 1998-09-16 as TYVEKX spunbonded polyethylene sheet sold by DuPont. TYVEK~
is a registered tr~dern~rk of DuPont. This experience has demonstrated that the bonding a~u~aial.ls shown in Figure 1 is costly to construct, operate and maintain. The large heating drums are expensive to 5 construct, they require large amounts of energy to heat, and their surfaces are difficult to keep clean. The flexible belt 2 used in the prior art process is similarly expensive to heat and m~int~in In addition, the bonding process shown in Figure 1 offers little flexibility for altering the degree of bonding in a sheet product or for producing sheet structures 10 that are extra highly impermeable to air and water, while m~int~ining good moisture vapor tr~n~micsibility. Finally, the bonding process shown in Figure 1 cannot be used to produce an embossed, point bonded, or otherwise patterned sheet without additional processing steps. Accordingly, there is a need for a lower cost process for bonding 15 plexifilamentary film-fibril sheet material that also offers the flexibilitv to produce a variety of bonded sheet products including sheet structures that have excellent strength yet are also very smooth and printable, and sheet structures that are highly impermeable to air and water, but demonstrate good moisture vapor tr~n~mi~sibility.
Sl-mm~ry of t~le Tnve~tion There is provided by this invention a process for producing a bonded nonwoven sheet from a lightly consolidated fibrous polyolefin sheet. According to the process, the lightly consolidated polyolefin 25 sheetis provided to a first preheating roll, the first prehe~tin~ roll havinga rotating outer surface that is heated to a telllp~lal~lre within 25~ C of the melting temperature of the sheet. At least one face of the sheet is contacted with the heated surface of the first preheating roll to heat the sheet. The sheet is transferred from the first pr~he~ting roll to a rotating 30 first heated calender roll, the first heated calender roll having an outer heated surface with a linear surface speed not less than the linear surface speed of the first preheating roll. The outer heated surface of the first heated calender roll is m~int~ined at a te~ cldL~lre within 25~ C of the melting te,ll~erdl~lre of the sheet material and the surface of the sheet is CA 02249~69 1998-09-16 W O 97/40224 PCT~US97/0S859 contacted with the outer heated surface of the first heated calender roll.
While the sheet is in contact with the first heated calender roll, the sheet is passed through a first nip forrned between the first heated calender roll and a back-up roll, the first nip ilnp~ Ling an average nip pressure of at S least 8.75 N/linear cm on the sheet. The calendered sheet is transferred from the first heated calender roll to a first cooling roll, the first cooling roll having an outer cooling surface rotating at a linear surface speed not less than the linear surface speed of the first heated calender roll. The outer cooling surface of the cooling roll is m~int~ine(l at a te~ .eralllre at 10 least 15~ C below the melting point of the sheet material, and the calendered sheet is contaceed with the outer cooling surface of the first cooling roll for a period sufficient to cool the sheet to a telnpe1al~lre below the melting temperature of the sheet material, which stabilizes the sheet material. Finally, the bonded sheet is removed from the cooling 1 5 roll.
The fibrous sheet material used in the process of the invention may be comprised of plexifilamentary film-fibrils.
Preferably, the outer heated surface of the first calender roll has a linear surface speed at least 0.2% faster than the linear surface speed of 20 the first preheating roll. It is also plefelled that the outer cooling surface of said first cooling roll have a linear surface speed at least 0.2% faster than the linear surface speed of the first calender roll. It is also preferred that each of the plurality of free spans between the sheet's first contact with the first preheating roll and the sheet's removal from the cooling 25 roll where the sheet is not in contact with any roll be less than 20 cm.
When the shcct is ~ansferred from the first heated calender roll to the first cooling roll, thc sheet may be first transferred to a second heated calender roll, said second heated calender roll having an outer heated surface rotating at a lincar surface speed not less than the linear surface 30 speed of the first heated calender roll. The outer heated surface of the second calender roll is maintained at a lempcldl~ e within 25~ C of the melting temperature of the film-fibrils of the plexifil~mentary sheet.
The outer heated surface the second calender roll is cont~cted with the surface of the sheet opposite the sheet surface that cont~cte~l the first CA 02249~69 1998-09-16 heated calender roll. While the sheet is in contact with the second heated calender roll, the sheet is passed through a second nip that imparts an average nip pressure of at least 8.75 N/linear cm on the sheet.
The calendered sheet is transferred from the second heated calender roll 5 to said first cooling roll.
The process of the invention may be used to make a bonded polyolefin fibrous sheet having a basis weight in the range of 17 to 270 gtm2, an average thickness in the range of 0.025 to 1.0 mm, a low air permeability expressed as Gurley-Hill porosity of at least 70 seconds, 10 a low li~uid water permeability ex~l~ssed by a hydrostatic head pressure of greater than 170 cm according to AATCC standard 127, and a moderate moisture vapor tr~ mi~sion rate of at least l O0 g/m2 in 24 hours according to ASTM standard E96, method B. The process of the invention may also be used to make a bonded polyolefin l S plexifilamentary bonded film-fibril sheet having a basis weight of about 50 to 120 g/m2, an average thickness in the range of 0.05 to 0.5 mm, with thickness standard deviation of less than 0.02, and a thermal transfer printing grade, according to ANSI Standard X3.182-1990, of at least "C".
Rrief T)escription of the r~rawir~,~
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the presently ~refelled embodiment of the invention and, together with the description, serve to 25 explain the principles of the invention.
Figure 1 is a schem~tic diagram of a prior art process for bonding nonwoven plexifilamentary film-fibril sheet material.
Figure 2 is a schematic diagram of a process according to the invention for bonding nonwoven fibrous sheet material.
n~t~iled nescr~tion of the rr~f~ll ed Fmbodim~nt Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated below.
CA 02249~69 1998-09-16 The nonwoven, polyolefin sheet used in the process of the invention can be plepaled by the process of Steuber, U.S. Pat. No 3,169,899. Preferred polyloefins include polyethylene and polypropylene, but it is anticipated that the process of the invention could be applied to other polyolefin-based fibrous sheets including sheets made from blends of polyolefins and other polymers. In the Steuber process, a solution,of a desired polyolefin is flash-spun from a line of spinnerets to obtain continuous fibrillated plexifilarnentary strands that are spread into a thin web by means of a rotating or osci~l~tin~ baffle. The web is subsequently laid down onto a moving belt. The amount of spreading accomplished by each baffle and the degree of overlap of plexifilamentary material deposited on the belt by adjacent spinnerets is carefully controlled to give as uniforrn a distribution of fibers on the collecting belt as possible. The collected sheet of fibers is lightly consolidated by passing the fibers on the belt under a roll which applies a loading of less than 18 k~/linear cm ( 100 lbs/linear inch) to obtain a sheet that is subsequently passed through a fixed nip to provide the lightly consolidated sheet used as the starting material in the process of the present invention.
The starting sheet material for the process of the invention should have a basis weight of between about 30.5 and 271.2 g/m2 (0.5 and 8.0 oz/yd2). The edges of the unconsolidated sheet 11 are preferably trimmed by an edge trimmer prior to the start of the bonding process. A conventional edge trimming device may be used in conjunction with the feed roll 14 shown in Figure 2. Preferably, the edges of the bonded sheet are trimmed again after bonding is complete.
Alternatively, the sheet edges may be trimmed only after bonding of the sheet is completed.
The bonding process of the invention is shown in Figure 2.
30 The bonding process takes place in three general operations. First, rolls 16 and 18 preheat the sheet. Second, rolls 24 and 26 c~l~nd~r bond one side of the sheet and rolls 30 and 32 calender bond the opposite side of the sheet. Third, rolls 36 and 38 cool and stabilize the sheet. The relative speeds of each of the rolls is controlled such that a desired level CA 02249~69 1998-09-16 W O 97/40224 PCTrUS97/OS859 of tension is m~in~ined in the sheet as it is being bonded. The bonding proces~ is complete by the time the bonded sheet 44 comes off the cooling roll 38.
According to the sheet bonding process of the invention, the S lightly consolidated sheet is first heated ~g~in~t one or more preheating rolls. According to the ~refcll ed embodiment of the invention, sheet 1 1 is guided by one or more fixed rolls 15 as the sheet travels from a feeder roll 14 to the first of two prehe~ting rolls. A fixed roll 17 guides the sheet 1 1 to a position on the heated roll 16 such that the sheet contacts a 10 substantial portion of the circumference of roll 16. Fixed rolls 15 and 17 preferably have a diameter of about 20 cm. The sheet p~fc~bly travels from the first prel e~ting roll 16 to second preheating roll 18. An adjustable wrap roll 20 is provided that is positioned close to the surface of roll 18, but that can be moved relative to the surface of roll 18 so as to 15 permit adjustment of the distance over which the sheet and the preheating roll 18 is in direct contact. The position of wrap roll 20 relative to the surface of roll 18 is e~rcssed in the examples below as the angle formed between a line passing through the centers of rolls 18 and 20 and a horizontal line passing through the center of roll 18. Fixed 20 roll 17 could likewise be replaced by an adjustable ~vrap roll to perrnit additional ad3ustment of the distance over which the sheet contacts preheatingroll 16.
Prehe~ting rolls 16 and 18 p~fefably have a diameter that is large enough to provide good preheating of the sheet, even at relatively 25 high sheet travel speeds. At the same time, it is desirable that rolls 16 and 18 be small enough such that the force of the sheet ~in~t the surface of the roll, in a direction normal to the roll surface, is great enough to generate a frictional force sufficient to resist sheet shrinkage.
The force of the sheet against the roll in the direction normal to the roll 30 surface is a function of the tension in the sheet and the diameter of the roll. As roll size increases, a greater sheet tension is required to m~int~in the same normal force. The frictional force that helps resist sheet shrinkage during bonding is proportional to the sheet force against the roll in the direction normal to the surface ofthe roll. The prefe.led . . .
CA 02249~69 1998-09-16 diameter for the preheating rolls is in the range of 0.15 to O.9lm (6 to 36 in), and more plefel~bly about 0.53 m (21 in).
Preferably rolls l 6 and 18 are heated by hot oil pumped through an annular space under the surface of each roll. Alternatively, 5 rolls 16 and 18 could be heated by other means such as electric, dielectric or steam heating. When a hard sheet structure is desired, the roll surfaces are p~ fc.ably heated to a temperature within 25~ C of the melting point of the sheet material being bonded. For example, when the sheet being bonded is flash-spun polyethylene, the ~iefelled range of 10 operating temperatures for the pre~e~tin~ rolls is 121~ to 143~ C (250~
to 290~ F). When a soft structure product with low internal bonding is desired, preheating rolls 16 and 18 are maintained at a telllpe,~ re well below the sheet's melting temperature or even at ambient temperature.
By ad~usting the preheating roll temperature and the residence time of 15 the sheet on the preheating rolls (by adjusting the roll speed and the position of the wrap roll 20), the tempeldLule of the sheet going into the calendering operation can be carefully controlled.
The surface finish of preheating rolls 16 and 18 must be selected such that the coefficient of friction between the rolls and the 20 heated sheet is high enough to resist sheet shrinkage. At the same time, the roll surface must readily release ~he sheet without sticking or picking of fibers, both of which can damage a sheet surface. In the ~refelled embodiment of the invention, preheating rolls 16 and 18 have polished chrome surfaces with a Teilon(~ release coating. Rolls having a chrome 25 surface finished with a Teflon~ release coating, m~nl-f~c~lred by HFW
Industries, Inc. of Buffalo, New York, have been sllcce~sfully used for preheating the sheet according to the process of the invention. Teflont~
is a registered trademark of DuPont.
The sheet tension and the friction between the sheet and rolls 30 (which is a function of the sheet tension and roll size, as discussed above) combine to minimi~ç sheet shrinkage or curling during the preheating step. Sheet curling arises when a sheet is not uniformly heated such that one side of a sheet shrinks more than the opposite side.
Sheet tension arises from sheet shrinkage that occurs with he~ting and from increasing the linear surface speed of subsequent rolls. The roll speed d~rr~,e..tials may be adjusted so as to achieve a desired sheet tension. The linear surface speed of rotating preheating roll 16 is preferably slightly faster than the speed at which sheet l l passes over 5 feed ro}l 14. This small differential in roll surface speeds helps to m~intAin the sheet tension during prehe~tin~. Likewise, the surface of preheating roll 18 preferably moves at a linear speed slightly faster than the surface speed of roll 16 to help m~int~in sheet tension on and between the prehe~ting rolls. Preferably, the linear surface speed of roll lO 16 is about 0.5% faster than the linear surface speed of feed roll 14.
Similarly, the linear surface speed of the second preheating roll 18 is preferably about 0.5% faster than the surface speed of the first preheatingroll 16.
Shrinkage and curling of the sheet, as the sheet passes 15 between rolls, are minimi7~rl by keeping the spans between rolls where the sheet is free of a roll surface to a minimum. Shrinkage and curling are also controlled by maintaining the sheet under tension in such free sheet spans. The sm~ller the ~ metçr of preheating rolls 16 and 18, and wrap roll 20, and the closer the spacing of the rolls, the shorter are the 20 free spans of the sheet between the rolls. The free sheet span between two rolls can be calc~ te~ as follows: Span = ~(Gap+Rt)2-Rt2 where "Gap" is the distance between the roll surfaces and "Rt" is the combined radii of the two rolls. Preferably, the free span of the sheet being bonded between prlohe~ting rolls 16 and 18 is less than about 20 cm (7.9 in), and 25 more pief~r~bly less than about 8 cm (3.2 in). For example, the free span between two 0.5 m diarneter rolls spaced 0.6 cm from each other would be 7.8 cm.
According to thc invention, the preheated sheet is next transferred to a thermal c~ er roll 24. In m~kin~ the transfer from 30 prehe~tin~ roll 18 to c~ n~er roll 24, the sheet passes over two adjustable wrap rolls 20 and 22. The free sheet spans between rolls 18 and 20, rolls 20 and 22, and rolls 22 and 24 should be kept to a minimum in order to control sheet shrinkage and curling. The use of small diameter wrap rolls 20 and 22, with diameters in the range of 15 to CA 02249~69 1998-09-16 25 cm (6 to 10 in), helps to minimi7e free sheet spans. Preferably, each of the free sheet spans between rolls 18 and 24 is less than 20 cm (7.9 in), and more preferably less than about 8 cm (3.2 in). The tension in the sheet must be maintained as the sheet passes from preheating roll 5 18 to calender roll 24. Preferably, the linear surface speed of calender roll 24 is slightly faster than the surface speed of preheating roll 18 to help m~int~in sheet tension in the free sheet spans between the preheating roll 18 and the calender roll 24, to m~int~in the sheet tension on the flexible wrap rolls 20 and 22, and to help m~int~in the sheet 10 tension on the heated calender roll 24. The pl~fell.,d linear surface speed of calender roll 24 is about 0.5% faster than the surface speed of feed roll 18. The position of the wrap roll 22 is adjustable along the surface of roll 24 for adjusting the degree of contact between the sheet being bonded and the heated calender roll 24. The position of wrap roll 15 22 relative to the surface of calender roll 24 is e~l. ssed in the examples below as the angle formed between a line passing between the centers of rolls 22 and 24 and a horizontal line passing through the center of roll 24. The surfaces of the wrap rolls used in the process of the invention (as well as the small fixed rolls) may each be m~ ined with two spiral 20 grooves that are oppositely directed away from the middle of the roll toward the opposite edges of the roll. The spiral grooves help keep the sheet spread in the cross direction which reduces cross-directional sheet shrinkage.
E'~fel~bly, calender roll 24 is heated by hot oil that is 25 pumped through an annular space under the surface of the roll, but it may be heated by any of the means discussed above with regard to the preheating rolls. The roll surface is preferably heated to a temperature within 25~ C of the melting temperature of the sheet material being bonded. When the sheet being bonded is flash-spun polyethylene, the 30 preferred range of opela~ing temp~_,al~. s for the surface of roll 24 is from 132~ to 146~ C (270~ to 295~ F). Because the sheet has been preheated before reaching the calender roll 24, it is not necess~ry to use excessive c~len~er roll temperatures to force high energy fluxes into the sheet, which is frequently undesirable in the bonding of web structures CA 02249~69 1998-09-16 W O 97/40224 PCTrUS97/05859 because high energy fluxes tend to cause excessive melting on the web surface.
The sheet being bonded is passed through a nip formed between the heated calender roll 24 and a back-up roll 26. In the S preferred embodiment, the back-up roll 26 is an tmh~te~l roll with a resilient surface. However, it is conte~ lated that back-up roll 26 could have a hard surface and it is also contemplated that roll 26 could be a heated roll. The surface of back-up roll 26 moves at the same speed as roll 24. The hardness of the resilient surface is selected in accordance 10 with the desired nip size and pressure. A harder surface on roll 26 results in a smaller nip area. The amount of bonding in the nip is a function of the nip size and nip pressure. If a lightly bonded soft product is desired, the pressure in the nip between rolls 24 and 26 is kept low or roll 26 can be lowered to open up the nip altogether. Where it is 15 desired to obtain a harder, more highly bonded product, the nip pressure can be increased. For example, when a lightly consolidated sheet of flash-spun polyethylene is being bonded to form a hard sheet product suitable for use as an air infiltration barrier housewrap material, a nip pressure in the range of 18 - 54 kg/linear cm (100 -300 Ibs/linear inch) is 20 ~lefell~d.
Heated calender roll 24 and back-up roll 26 should have a diarneter large enough to give them the strength to resist bending. In addition, roll 24 should be large enough that the sheet being bonded will be in contact with the roll surface for a desired period of time before 25 entering the nip. On the other hand, smaller diameter rolls have the advantages that they are less expensive, they are easier to change out if a dir~, ent embossing pattern is desired, and they generate a greater shrinkage resisting force normal to the roll surface (as discussed above).
Preferably, calender roll 24 and back-up roll 26 have a diameter between 30 about 0.15 and 0.91 m (6 and 36 in). In the examples below, 0.61 m (24 in) diameter rolls were used for calendar roll 24 and back-up roll 26.
The surface of heated calender roll 24 is selected such that the coefficient of friction between the roll and the heated sheet is high enough to resist sheet shrinkage. At the same time, the roll surface must CA 02249~69 1998-09-16 readily release the sheet without sticking or picking of fibers. In the preferred embodiment of the invention, heated calender roll 24 has a smooth surface of a Teflon(E~-filled chrome material. If a bonding pattern is desired for the top surface of the sheet being bonded, the 5 smooth calender roll may be replaced by a patterned roll. Chrome and Teflon(~ coated rolls finished by Mirror Polishing and Plating Company of Waterbury, Connecticut, have been successfully used in the calendar operation of the invention. Back-up roll 24 is ~refelably a hard rubber-surfaced roll with a surface hardness in the range of 60 on the Shore A
10 Hardness Scale to 90 on the Shore D Harness Scale, as measured on an ASTM Standard D2240 Type A or D durometer. More ~urefe.ably, back-up roll 24 has a surface hardness of 80 to 95 on the Shore A
Hardness Scale.
The process of the invention includes the step of passing the 15 sheet through a second calender nip for bonding the side of the sheet opposite to the side bonded in the first nip associated with roll 24. Of course, if a sheet product is desired that has just one bonded side, then one of the two nips can be operated in an open position or elimin~te-l entirely. When a second nip is ~ltili7e~1, the sheet is transferred from 20 the first calender roll 24 to a second heated calender roll 32. In making the transfer from roll 24 to roll 32, the sheet passes over a fixed roll 28 and an adjustable wrap roll 29. The free sheet spans between rolls 24 and 28, rolls 28 and 29, and rolls 29 and 32 are kept to a minimum in order to control sheet shrinkage and curling. The use of a small 25 diameter fixed roll 28 and wrap roll 29, in the range of 15 to 25 cm (6 to 10 in), help to keep the free sheet spans to a minimllm ~f~ably, each of the free sheet spans between rolls 24 and 32 is less than about 13 cm (5.1 in), and more pl~fe~dbly less than about 8 cm (3.2 in). It is important that tension be maintained in the sheet between rolls 24 and 30 32. ~lefe~dbly, the linear surface speed of calender roll 32 is slightly faster than the surface speed of calender roll 24 to help m~int~in sheet tension in the free sheet spans between the first and second calendering operations, to m~int~in the sheet tension on the fixed roll 28 and wrap roll 29, and to help m~int~in the sheet tension on the heated calender roll CA 02249~69 1998-09-16 W O 97/40224 PCTnUS97/OS8S9 32. The ~u~cfe~l~ d linear surface speed of roll 32 is about 0.5% faster than the linear surface speed of feed roll 24. The surface speed of back-up roll 30 is substantially equal to the surface speed of calender roll 32.
The position of the wrap roll 29 is adjustable along the surface of roll 3 for adjusting the degree of contact between the sheet being bonded and the heated calender roll 32. The position of wrap roll 29 relative to the surface of calendar roll 32 is expressed in the examples below as the angle between a line passing through the centers of rolls 29 and 32 and a horizontal line passing through the center of roll 32. Again, the surface of fixed roll 28 and wrap roll 29 may each be m~chinç~ with two spiral surface grooves directed away from the middle of the rolls to help m~int~in cross-directional sheet tension.
Heated calender roll 32 is ~rcfe~ably similar to the heated calender roll 24 and the back-up roll 30 is preferably similar to the resilient-surfaced back-up roll 26, as described above. The temperature of the rolls 24 and 32, the finish on the surface of the rolls 24 and 32, the pressure of the corresponding nips, the hardness of back-up rolls 26 and 30, and the degree of sheet wrap on the heated calender rolls can all be adjusted in order to achieve a desired type and degree of sheet bonding.
For example, if hard smooth-surfaced sheets are desired, both of the rolls 24 and 32 should be smooth heated calender rolls operated within the melting temperature range for the sheet material being bonded and relatively high nip pressures should be applied at both nips. If a textured sheet is desired, one or both of the smooth surfaced heated calender rolls could be replaced with patterned embossing rolls. If a soft product is desired, the temperature of the preheating rolls and the calendering rolls can be reduced, the degree of sheet wrap on the preheating and calender rolls can be re~ ce~l and the nip pressures can be re~ ce~ in order to decrease the degree of bonding in the sheet.
In order to stabilize the bonded sheet (i.e., prevent curling or any additional shrinkage), the sheet is transferred from calender roll 3 and corresponding back-up roll 30 to a set of one or more cooling rolls.
The cooling operation rapidly reduces the sheet temperature so as to stabilize the bonded sheet. In the preferred embodiment of the invention CA 02249~69 1998-09-16 W O 97/40224 P ~ nUS97105859 shown in Figure 2, two cooling rolls 36 and 38 are used to quench the heated sheet. In making the transfer from calender roll 32 to cooling roll 36, the sheet passes over two small fixed transfer rolls 34 and 35. The free sheet spans between rolls 30 and 34, between rolls 34 and 35, and 5 between rolls 35 and 36 are kept to a minimum in order to control sheet shrinkage and curling. Preferably, small transfer rolls of 15 to 25 cm in diameter are used in order to reduce the free sheet spans between rolls 32 and 36 to less than about 20 cm (7.9 in). The surface speed of cooling roll 36 is preferably slightly faster than the surface speed of 10 calender roll 32 and back-up roll 30 to help m~int~in sheet tension in the free sheet spans between the calendering operation and the cooling operation, to m~int~in sheet tension on the fixed rolls 34 and 35, and to help m~int~in the sheet tension on the cooling roll 36. The plefellcd surface speed of cooling roll 36 is about 0.5% faster than the surface 15 speed of calender roll 32. Again, the surface of fixed rolls 34 and 35 may each be machined with two spiral surface grooves directed away from the middle of the rolls to help m~int~in cross-directional sheet tension.
Cooling rolls 36 and 38 are plefelably of a rli~mPter similar to 20 that of the prç~e~tin~ rolls 16 and 18. The rolls must be large enough to have the strength to resist bending and to provide a residence time for the sheet on the rolls sufficient for adequate cooling. On the other hand, it is desirable for the rolls to be small enough that the force of the sheet against the rolls is sufficient to generate shrinkage resisting friction 25 between the sheet and cooling rolls (as discussed above). In addition, smaller rolls are less costly to manufacture and install, and they are easier to move when desired. The cooling rolls should be close enough that the free sheet span between the rolls is as small as possible. The cooling rolls used in the examples below had a diameter of about 0.53 m 30 (21 in). It is also important to m~in~in the sheet tension on and between cooling rolls, as for example by operating roll 38 at a surface speed slightly faster than the surface speed of roll 36.
The rolls 36 and 38 cool opposite sides ofthe sheet. The rolls are prefel~bly cooled by cooling water that passes through an annular CA 02249~69 1998-09-16 W O 97/40224 PCT~US97/OS859 space under the surface of each roll. The temperature of the cooling water pumped into the rolls is preferably between about 10 and 43~ C
(50 and l l O~ F). If the sheet being bonded is a polyethylene plexifilamentary sheet, it is desirable for the temperature of the sheet to S be re~ ce~l to a temperature below about 100~ C (212~ F) before coming off the cooling rolls. The cooling rolls prefelably have a non-sticky surface such as a smooth polished chrome finish from which the bonded sheet 44 is easily removed.
The bonded sheet 44 is transferred to a take-up roll or to 10 subsequent downstream processing steps, such as printing, by means of transfer rolls, such as the fixed rolls 40 and 42 shown in Figure 2. After the sheet comes off the cooling rolls 36 and 38 and sheet bonding is complete, it is no longer necessary to keep free sheet spans to an absolute minimum or to maintain sheet tension in order to resist sheet 15 shrinkage and curling.
The process described above is suited for m~kin~ a broad range of nonwoven olefin bonded sheet products with a single set of process equipment. By carefully controlling the tempe~alule ofthe rolls, the speed of the rolls, the sheet residence time on the rolls, the tension in 20 the sheet, the texture of the calender rolls, and the pressure of the calender nips, a wide variety of bonded products can be made. Great process flexibility is attained when each of the rolls is equipped with an independent drive and an individual speed controller. It has been found that with the process of the invention, wherein sheet tension is 25 maintained during bonding, a higher degree of bonding can be achieved because the sheet can be subjected to bonding ten~p~,laL lres that are 1~ to
Field of the Invention This invention relates to a bonded nonwoven sheet made 5 from a fibrous polyolefin material. More particularly, the invention relates to a bonded nonwoven sheet that is smooth, permeable to moisture vapor, and substantially impermeable to air and water. The invention also relates to a bonding process for producing such a sheet.
Background of the Invention Processes for manufacturing fibrous nonwoven sheets from polyolefin polymers are known in the art. Blades et al., U.S. Patent No.
3,0~1,519 (assigned to E.I. DuPont de Nemours & Company (hereinafter "DuPont")), discloses flash-spinning of plexifilamentary 15 polyethylene film-fibrils. Steuber, U.S. Patent No. 3,169,899 (assigned to DuPont), discloses depositing a flash-spun polyethylene plexifilamentary film-fibril web onto a moving belt and compressing the deposited web to form a lightly consolidated nonwoven sheet.
The term "plexifilamentary" means a three-dimensional integral network ~0 of a multitude of thin, ribbon-like, film-fibril elements of random length and with a mean thickness of less than about 20 microns. In plexifilamentary structures, the film-fibril elements are generally coextensively aligned with the longitudinal axis of the structure and they interrnittently unite and separate at irregular intervals in various places 25 throughout the length, width and thickness of the structure to form the three--limen~ional network.
In order to produce sheets with the strength and barrier properties required for many applications, such as air infiltration barrier sheet material used in home construction (housewrap), the film-fibrils or 30 other fibers of the lightly consolidated sheet material must be bonded together. Lightly consolidated nonwoven sheets made from polyolefin fibers have been bonded by calendering and hot air treatments.
However, sheets so bonded have tended to shrink and curl, resulting in CA 02249~69 1998-09-16 WO 97/40224 PCTrUSg7/OS859 sheets with irregular thickness, opacity, strength and permeability propert~es.
A process for bonding polyolefinic plexifilamentary, film-fibril sheets with properties sufficiently uniform for commercial applications is disclosed in David, U.S. Patent No. 3,532,589 (assigned to DuPont) and is shown in Figure 1. The thermal bonding process disclosed in the David patent requires that the unconsolidated film-fibril sheet 5 from supply roll 6 be subjected to light compression d-lring heating in order to prevent shrinkage and curling of the bonding sheet.
A flexible belt 2 is used to compress a sheet being bonded against a large heated drum 1 that is made of a heat-conducting material. Tension in the belt is m~int~ined by the rolls 3. The belt is preheated by a heating roll 9 and a heated plate 10. The drum 1 is m~int~ined at a temperature substantially equal to or greater than the upper limit of the melting range of the film-fibril elements of the sheet being bonded. The rotating heated drum 1 is large (about 2 m in diameter) so as to permit the film-fibril sheet to be heated long enough to allow the face of the sheet ~in~t the roll to reach a lell~c.alllre within 7~ C ofthe upper limit of the melting range of the film-fibril elementc, but not substantially above said upper limit, and to allow the second face of the sheet to reach a temperature between 0.8~ to 10~ C lower than the temperature of the first face of the sheet. The heated sheet 5 is removed from the heated drum 1 without removing the belt lc~int and the sheet is then transferred to a cooling roll 4 where the temperature of the film-fibril sheet throughout its thickness is rec~llce(l to a temperature less than that at which the sheet will distort or shrink when unlesl~ined. Roll 7 removes the bonded sheet from the belt 2 before the sheet is collected on a collection roll 8. The sheet may be run through another thermal bonding device like that shown in Figure 1 with the second surface facing the heated drum in order to produce a hard bonded surface on the opposite side of the sheet.
For the past twenty-five years, a thermal bonding process similar to that shown in Figure 1 has been applied to the commercial production of hard-surfaced spunbonded polyolefin sheet material, such CA 02249~69 1998-09-16 as TYVEKX spunbonded polyethylene sheet sold by DuPont. TYVEK~
is a registered tr~dern~rk of DuPont. This experience has demonstrated that the bonding a~u~aial.ls shown in Figure 1 is costly to construct, operate and maintain. The large heating drums are expensive to 5 construct, they require large amounts of energy to heat, and their surfaces are difficult to keep clean. The flexible belt 2 used in the prior art process is similarly expensive to heat and m~int~in In addition, the bonding process shown in Figure 1 offers little flexibility for altering the degree of bonding in a sheet product or for producing sheet structures 10 that are extra highly impermeable to air and water, while m~int~ining good moisture vapor tr~n~micsibility. Finally, the bonding process shown in Figure 1 cannot be used to produce an embossed, point bonded, or otherwise patterned sheet without additional processing steps. Accordingly, there is a need for a lower cost process for bonding 15 plexifilamentary film-fibril sheet material that also offers the flexibilitv to produce a variety of bonded sheet products including sheet structures that have excellent strength yet are also very smooth and printable, and sheet structures that are highly impermeable to air and water, but demonstrate good moisture vapor tr~n~mi~sibility.
Sl-mm~ry of t~le Tnve~tion There is provided by this invention a process for producing a bonded nonwoven sheet from a lightly consolidated fibrous polyolefin sheet. According to the process, the lightly consolidated polyolefin 25 sheetis provided to a first preheating roll, the first prehe~tin~ roll havinga rotating outer surface that is heated to a telllp~lal~lre within 25~ C of the melting temperature of the sheet. At least one face of the sheet is contacted with the heated surface of the first preheating roll to heat the sheet. The sheet is transferred from the first pr~he~ting roll to a rotating 30 first heated calender roll, the first heated calender roll having an outer heated surface with a linear surface speed not less than the linear surface speed of the first preheating roll. The outer heated surface of the first heated calender roll is m~int~ined at a te~ cldL~lre within 25~ C of the melting te,ll~erdl~lre of the sheet material and the surface of the sheet is CA 02249~69 1998-09-16 W O 97/40224 PCT~US97/0S859 contacted with the outer heated surface of the first heated calender roll.
While the sheet is in contact with the first heated calender roll, the sheet is passed through a first nip forrned between the first heated calender roll and a back-up roll, the first nip ilnp~ Ling an average nip pressure of at S least 8.75 N/linear cm on the sheet. The calendered sheet is transferred from the first heated calender roll to a first cooling roll, the first cooling roll having an outer cooling surface rotating at a linear surface speed not less than the linear surface speed of the first heated calender roll. The outer cooling surface of the cooling roll is m~int~ine(l at a te~ .eralllre at 10 least 15~ C below the melting point of the sheet material, and the calendered sheet is contaceed with the outer cooling surface of the first cooling roll for a period sufficient to cool the sheet to a telnpe1al~lre below the melting temperature of the sheet material, which stabilizes the sheet material. Finally, the bonded sheet is removed from the cooling 1 5 roll.
The fibrous sheet material used in the process of the invention may be comprised of plexifilamentary film-fibrils.
Preferably, the outer heated surface of the first calender roll has a linear surface speed at least 0.2% faster than the linear surface speed of 20 the first preheating roll. It is also plefelled that the outer cooling surface of said first cooling roll have a linear surface speed at least 0.2% faster than the linear surface speed of the first calender roll. It is also preferred that each of the plurality of free spans between the sheet's first contact with the first preheating roll and the sheet's removal from the cooling 25 roll where the sheet is not in contact with any roll be less than 20 cm.
When the shcct is ~ansferred from the first heated calender roll to the first cooling roll, thc sheet may be first transferred to a second heated calender roll, said second heated calender roll having an outer heated surface rotating at a lincar surface speed not less than the linear surface 30 speed of the first heated calender roll. The outer heated surface of the second calender roll is maintained at a lempcldl~ e within 25~ C of the melting temperature of the film-fibrils of the plexifil~mentary sheet.
The outer heated surface the second calender roll is cont~cted with the surface of the sheet opposite the sheet surface that cont~cte~l the first CA 02249~69 1998-09-16 heated calender roll. While the sheet is in contact with the second heated calender roll, the sheet is passed through a second nip that imparts an average nip pressure of at least 8.75 N/linear cm on the sheet.
The calendered sheet is transferred from the second heated calender roll 5 to said first cooling roll.
The process of the invention may be used to make a bonded polyolefin fibrous sheet having a basis weight in the range of 17 to 270 gtm2, an average thickness in the range of 0.025 to 1.0 mm, a low air permeability expressed as Gurley-Hill porosity of at least 70 seconds, 10 a low li~uid water permeability ex~l~ssed by a hydrostatic head pressure of greater than 170 cm according to AATCC standard 127, and a moderate moisture vapor tr~ mi~sion rate of at least l O0 g/m2 in 24 hours according to ASTM standard E96, method B. The process of the invention may also be used to make a bonded polyolefin l S plexifilamentary bonded film-fibril sheet having a basis weight of about 50 to 120 g/m2, an average thickness in the range of 0.05 to 0.5 mm, with thickness standard deviation of less than 0.02, and a thermal transfer printing grade, according to ANSI Standard X3.182-1990, of at least "C".
Rrief T)escription of the r~rawir~,~
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the presently ~refelled embodiment of the invention and, together with the description, serve to 25 explain the principles of the invention.
Figure 1 is a schem~tic diagram of a prior art process for bonding nonwoven plexifilamentary film-fibril sheet material.
Figure 2 is a schematic diagram of a process according to the invention for bonding nonwoven fibrous sheet material.
n~t~iled nescr~tion of the rr~f~ll ed Fmbodim~nt Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated below.
CA 02249~69 1998-09-16 The nonwoven, polyolefin sheet used in the process of the invention can be plepaled by the process of Steuber, U.S. Pat. No 3,169,899. Preferred polyloefins include polyethylene and polypropylene, but it is anticipated that the process of the invention could be applied to other polyolefin-based fibrous sheets including sheets made from blends of polyolefins and other polymers. In the Steuber process, a solution,of a desired polyolefin is flash-spun from a line of spinnerets to obtain continuous fibrillated plexifilarnentary strands that are spread into a thin web by means of a rotating or osci~l~tin~ baffle. The web is subsequently laid down onto a moving belt. The amount of spreading accomplished by each baffle and the degree of overlap of plexifilamentary material deposited on the belt by adjacent spinnerets is carefully controlled to give as uniforrn a distribution of fibers on the collecting belt as possible. The collected sheet of fibers is lightly consolidated by passing the fibers on the belt under a roll which applies a loading of less than 18 k~/linear cm ( 100 lbs/linear inch) to obtain a sheet that is subsequently passed through a fixed nip to provide the lightly consolidated sheet used as the starting material in the process of the present invention.
The starting sheet material for the process of the invention should have a basis weight of between about 30.5 and 271.2 g/m2 (0.5 and 8.0 oz/yd2). The edges of the unconsolidated sheet 11 are preferably trimmed by an edge trimmer prior to the start of the bonding process. A conventional edge trimming device may be used in conjunction with the feed roll 14 shown in Figure 2. Preferably, the edges of the bonded sheet are trimmed again after bonding is complete.
Alternatively, the sheet edges may be trimmed only after bonding of the sheet is completed.
The bonding process of the invention is shown in Figure 2.
30 The bonding process takes place in three general operations. First, rolls 16 and 18 preheat the sheet. Second, rolls 24 and 26 c~l~nd~r bond one side of the sheet and rolls 30 and 32 calender bond the opposite side of the sheet. Third, rolls 36 and 38 cool and stabilize the sheet. The relative speeds of each of the rolls is controlled such that a desired level CA 02249~69 1998-09-16 W O 97/40224 PCTrUS97/OS859 of tension is m~in~ined in the sheet as it is being bonded. The bonding proces~ is complete by the time the bonded sheet 44 comes off the cooling roll 38.
According to the sheet bonding process of the invention, the S lightly consolidated sheet is first heated ~g~in~t one or more preheating rolls. According to the ~refcll ed embodiment of the invention, sheet 1 1 is guided by one or more fixed rolls 15 as the sheet travels from a feeder roll 14 to the first of two prehe~ting rolls. A fixed roll 17 guides the sheet 1 1 to a position on the heated roll 16 such that the sheet contacts a 10 substantial portion of the circumference of roll 16. Fixed rolls 15 and 17 preferably have a diameter of about 20 cm. The sheet p~fc~bly travels from the first prel e~ting roll 16 to second preheating roll 18. An adjustable wrap roll 20 is provided that is positioned close to the surface of roll 18, but that can be moved relative to the surface of roll 18 so as to 15 permit adjustment of the distance over which the sheet and the preheating roll 18 is in direct contact. The position of wrap roll 20 relative to the surface of roll 18 is e~rcssed in the examples below as the angle formed between a line passing through the centers of rolls 18 and 20 and a horizontal line passing through the center of roll 18. Fixed 20 roll 17 could likewise be replaced by an adjustable ~vrap roll to perrnit additional ad3ustment of the distance over which the sheet contacts preheatingroll 16.
Prehe~ting rolls 16 and 18 p~fefably have a diameter that is large enough to provide good preheating of the sheet, even at relatively 25 high sheet travel speeds. At the same time, it is desirable that rolls 16 and 18 be small enough such that the force of the sheet ~in~t the surface of the roll, in a direction normal to the roll surface, is great enough to generate a frictional force sufficient to resist sheet shrinkage.
The force of the sheet against the roll in the direction normal to the roll 30 surface is a function of the tension in the sheet and the diameter of the roll. As roll size increases, a greater sheet tension is required to m~int~in the same normal force. The frictional force that helps resist sheet shrinkage during bonding is proportional to the sheet force against the roll in the direction normal to the surface ofthe roll. The prefe.led . . .
CA 02249~69 1998-09-16 diameter for the preheating rolls is in the range of 0.15 to O.9lm (6 to 36 in), and more plefel~bly about 0.53 m (21 in).
Preferably rolls l 6 and 18 are heated by hot oil pumped through an annular space under the surface of each roll. Alternatively, 5 rolls 16 and 18 could be heated by other means such as electric, dielectric or steam heating. When a hard sheet structure is desired, the roll surfaces are p~ fc.ably heated to a temperature within 25~ C of the melting point of the sheet material being bonded. For example, when the sheet being bonded is flash-spun polyethylene, the ~iefelled range of 10 operating temperatures for the pre~e~tin~ rolls is 121~ to 143~ C (250~
to 290~ F). When a soft structure product with low internal bonding is desired, preheating rolls 16 and 18 are maintained at a telllpe,~ re well below the sheet's melting temperature or even at ambient temperature.
By ad~usting the preheating roll temperature and the residence time of 15 the sheet on the preheating rolls (by adjusting the roll speed and the position of the wrap roll 20), the tempeldLule of the sheet going into the calendering operation can be carefully controlled.
The surface finish of preheating rolls 16 and 18 must be selected such that the coefficient of friction between the rolls and the 20 heated sheet is high enough to resist sheet shrinkage. At the same time, the roll surface must readily release ~he sheet without sticking or picking of fibers, both of which can damage a sheet surface. In the ~refelled embodiment of the invention, preheating rolls 16 and 18 have polished chrome surfaces with a Teilon(~ release coating. Rolls having a chrome 25 surface finished with a Teflon~ release coating, m~nl-f~c~lred by HFW
Industries, Inc. of Buffalo, New York, have been sllcce~sfully used for preheating the sheet according to the process of the invention. Teflont~
is a registered trademark of DuPont.
The sheet tension and the friction between the sheet and rolls 30 (which is a function of the sheet tension and roll size, as discussed above) combine to minimi~ç sheet shrinkage or curling during the preheating step. Sheet curling arises when a sheet is not uniformly heated such that one side of a sheet shrinks more than the opposite side.
Sheet tension arises from sheet shrinkage that occurs with he~ting and from increasing the linear surface speed of subsequent rolls. The roll speed d~rr~,e..tials may be adjusted so as to achieve a desired sheet tension. The linear surface speed of rotating preheating roll 16 is preferably slightly faster than the speed at which sheet l l passes over 5 feed ro}l 14. This small differential in roll surface speeds helps to m~intAin the sheet tension during prehe~tin~. Likewise, the surface of preheating roll 18 preferably moves at a linear speed slightly faster than the surface speed of roll 16 to help m~int~in sheet tension on and between the prehe~ting rolls. Preferably, the linear surface speed of roll lO 16 is about 0.5% faster than the linear surface speed of feed roll 14.
Similarly, the linear surface speed of the second preheating roll 18 is preferably about 0.5% faster than the surface speed of the first preheatingroll 16.
Shrinkage and curling of the sheet, as the sheet passes 15 between rolls, are minimi7~rl by keeping the spans between rolls where the sheet is free of a roll surface to a minimum. Shrinkage and curling are also controlled by maintaining the sheet under tension in such free sheet spans. The sm~ller the ~ metçr of preheating rolls 16 and 18, and wrap roll 20, and the closer the spacing of the rolls, the shorter are the 20 free spans of the sheet between the rolls. The free sheet span between two rolls can be calc~ te~ as follows: Span = ~(Gap+Rt)2-Rt2 where "Gap" is the distance between the roll surfaces and "Rt" is the combined radii of the two rolls. Preferably, the free span of the sheet being bonded between prlohe~ting rolls 16 and 18 is less than about 20 cm (7.9 in), and 25 more pief~r~bly less than about 8 cm (3.2 in). For example, the free span between two 0.5 m diarneter rolls spaced 0.6 cm from each other would be 7.8 cm.
According to thc invention, the preheated sheet is next transferred to a thermal c~ er roll 24. In m~kin~ the transfer from 30 prehe~tin~ roll 18 to c~ n~er roll 24, the sheet passes over two adjustable wrap rolls 20 and 22. The free sheet spans between rolls 18 and 20, rolls 20 and 22, and rolls 22 and 24 should be kept to a minimum in order to control sheet shrinkage and curling. The use of small diameter wrap rolls 20 and 22, with diameters in the range of 15 to CA 02249~69 1998-09-16 25 cm (6 to 10 in), helps to minimi7e free sheet spans. Preferably, each of the free sheet spans between rolls 18 and 24 is less than 20 cm (7.9 in), and more preferably less than about 8 cm (3.2 in). The tension in the sheet must be maintained as the sheet passes from preheating roll 5 18 to calender roll 24. Preferably, the linear surface speed of calender roll 24 is slightly faster than the surface speed of preheating roll 18 to help m~int~in sheet tension in the free sheet spans between the preheating roll 18 and the calender roll 24, to m~int~in the sheet tension on the flexible wrap rolls 20 and 22, and to help m~int~in the sheet 10 tension on the heated calender roll 24. The pl~fell.,d linear surface speed of calender roll 24 is about 0.5% faster than the surface speed of feed roll 18. The position of the wrap roll 22 is adjustable along the surface of roll 24 for adjusting the degree of contact between the sheet being bonded and the heated calender roll 24. The position of wrap roll 15 22 relative to the surface of calender roll 24 is e~l. ssed in the examples below as the angle formed between a line passing between the centers of rolls 22 and 24 and a horizontal line passing through the center of roll 24. The surfaces of the wrap rolls used in the process of the invention (as well as the small fixed rolls) may each be m~ ined with two spiral 20 grooves that are oppositely directed away from the middle of the roll toward the opposite edges of the roll. The spiral grooves help keep the sheet spread in the cross direction which reduces cross-directional sheet shrinkage.
E'~fel~bly, calender roll 24 is heated by hot oil that is 25 pumped through an annular space under the surface of the roll, but it may be heated by any of the means discussed above with regard to the preheating rolls. The roll surface is preferably heated to a temperature within 25~ C of the melting temperature of the sheet material being bonded. When the sheet being bonded is flash-spun polyethylene, the 30 preferred range of opela~ing temp~_,al~. s for the surface of roll 24 is from 132~ to 146~ C (270~ to 295~ F). Because the sheet has been preheated before reaching the calender roll 24, it is not necess~ry to use excessive c~len~er roll temperatures to force high energy fluxes into the sheet, which is frequently undesirable in the bonding of web structures CA 02249~69 1998-09-16 W O 97/40224 PCTrUS97/05859 because high energy fluxes tend to cause excessive melting on the web surface.
The sheet being bonded is passed through a nip formed between the heated calender roll 24 and a back-up roll 26. In the S preferred embodiment, the back-up roll 26 is an tmh~te~l roll with a resilient surface. However, it is conte~ lated that back-up roll 26 could have a hard surface and it is also contemplated that roll 26 could be a heated roll. The surface of back-up roll 26 moves at the same speed as roll 24. The hardness of the resilient surface is selected in accordance 10 with the desired nip size and pressure. A harder surface on roll 26 results in a smaller nip area. The amount of bonding in the nip is a function of the nip size and nip pressure. If a lightly bonded soft product is desired, the pressure in the nip between rolls 24 and 26 is kept low or roll 26 can be lowered to open up the nip altogether. Where it is 15 desired to obtain a harder, more highly bonded product, the nip pressure can be increased. For example, when a lightly consolidated sheet of flash-spun polyethylene is being bonded to form a hard sheet product suitable for use as an air infiltration barrier housewrap material, a nip pressure in the range of 18 - 54 kg/linear cm (100 -300 Ibs/linear inch) is 20 ~lefell~d.
Heated calender roll 24 and back-up roll 26 should have a diarneter large enough to give them the strength to resist bending. In addition, roll 24 should be large enough that the sheet being bonded will be in contact with the roll surface for a desired period of time before 25 entering the nip. On the other hand, smaller diameter rolls have the advantages that they are less expensive, they are easier to change out if a dir~, ent embossing pattern is desired, and they generate a greater shrinkage resisting force normal to the roll surface (as discussed above).
Preferably, calender roll 24 and back-up roll 26 have a diameter between 30 about 0.15 and 0.91 m (6 and 36 in). In the examples below, 0.61 m (24 in) diameter rolls were used for calendar roll 24 and back-up roll 26.
The surface of heated calender roll 24 is selected such that the coefficient of friction between the roll and the heated sheet is high enough to resist sheet shrinkage. At the same time, the roll surface must CA 02249~69 1998-09-16 readily release the sheet without sticking or picking of fibers. In the preferred embodiment of the invention, heated calender roll 24 has a smooth surface of a Teflon(E~-filled chrome material. If a bonding pattern is desired for the top surface of the sheet being bonded, the 5 smooth calender roll may be replaced by a patterned roll. Chrome and Teflon(~ coated rolls finished by Mirror Polishing and Plating Company of Waterbury, Connecticut, have been successfully used in the calendar operation of the invention. Back-up roll 24 is ~refelably a hard rubber-surfaced roll with a surface hardness in the range of 60 on the Shore A
10 Hardness Scale to 90 on the Shore D Harness Scale, as measured on an ASTM Standard D2240 Type A or D durometer. More ~urefe.ably, back-up roll 24 has a surface hardness of 80 to 95 on the Shore A
Hardness Scale.
The process of the invention includes the step of passing the 15 sheet through a second calender nip for bonding the side of the sheet opposite to the side bonded in the first nip associated with roll 24. Of course, if a sheet product is desired that has just one bonded side, then one of the two nips can be operated in an open position or elimin~te-l entirely. When a second nip is ~ltili7e~1, the sheet is transferred from 20 the first calender roll 24 to a second heated calender roll 32. In making the transfer from roll 24 to roll 32, the sheet passes over a fixed roll 28 and an adjustable wrap roll 29. The free sheet spans between rolls 24 and 28, rolls 28 and 29, and rolls 29 and 32 are kept to a minimum in order to control sheet shrinkage and curling. The use of a small 25 diameter fixed roll 28 and wrap roll 29, in the range of 15 to 25 cm (6 to 10 in), help to keep the free sheet spans to a minimllm ~f~ably, each of the free sheet spans between rolls 24 and 32 is less than about 13 cm (5.1 in), and more pl~fe~dbly less than about 8 cm (3.2 in). It is important that tension be maintained in the sheet between rolls 24 and 30 32. ~lefe~dbly, the linear surface speed of calender roll 32 is slightly faster than the surface speed of calender roll 24 to help m~int~in sheet tension in the free sheet spans between the first and second calendering operations, to m~int~in the sheet tension on the fixed roll 28 and wrap roll 29, and to help m~int~in the sheet tension on the heated calender roll CA 02249~69 1998-09-16 W O 97/40224 PCTnUS97/OS8S9 32. The ~u~cfe~l~ d linear surface speed of roll 32 is about 0.5% faster than the linear surface speed of feed roll 24. The surface speed of back-up roll 30 is substantially equal to the surface speed of calender roll 32.
The position of the wrap roll 29 is adjustable along the surface of roll 3 for adjusting the degree of contact between the sheet being bonded and the heated calender roll 32. The position of wrap roll 29 relative to the surface of calendar roll 32 is expressed in the examples below as the angle between a line passing through the centers of rolls 29 and 32 and a horizontal line passing through the center of roll 32. Again, the surface of fixed roll 28 and wrap roll 29 may each be m~chinç~ with two spiral surface grooves directed away from the middle of the rolls to help m~int~in cross-directional sheet tension.
Heated calender roll 32 is ~rcfe~ably similar to the heated calender roll 24 and the back-up roll 30 is preferably similar to the resilient-surfaced back-up roll 26, as described above. The temperature of the rolls 24 and 32, the finish on the surface of the rolls 24 and 32, the pressure of the corresponding nips, the hardness of back-up rolls 26 and 30, and the degree of sheet wrap on the heated calender rolls can all be adjusted in order to achieve a desired type and degree of sheet bonding.
For example, if hard smooth-surfaced sheets are desired, both of the rolls 24 and 32 should be smooth heated calender rolls operated within the melting temperature range for the sheet material being bonded and relatively high nip pressures should be applied at both nips. If a textured sheet is desired, one or both of the smooth surfaced heated calender rolls could be replaced with patterned embossing rolls. If a soft product is desired, the temperature of the preheating rolls and the calendering rolls can be reduced, the degree of sheet wrap on the preheating and calender rolls can be re~ ce~l and the nip pressures can be re~ ce~ in order to decrease the degree of bonding in the sheet.
In order to stabilize the bonded sheet (i.e., prevent curling or any additional shrinkage), the sheet is transferred from calender roll 3 and corresponding back-up roll 30 to a set of one or more cooling rolls.
The cooling operation rapidly reduces the sheet temperature so as to stabilize the bonded sheet. In the preferred embodiment of the invention CA 02249~69 1998-09-16 W O 97/40224 P ~ nUS97105859 shown in Figure 2, two cooling rolls 36 and 38 are used to quench the heated sheet. In making the transfer from calender roll 32 to cooling roll 36, the sheet passes over two small fixed transfer rolls 34 and 35. The free sheet spans between rolls 30 and 34, between rolls 34 and 35, and 5 between rolls 35 and 36 are kept to a minimum in order to control sheet shrinkage and curling. Preferably, small transfer rolls of 15 to 25 cm in diameter are used in order to reduce the free sheet spans between rolls 32 and 36 to less than about 20 cm (7.9 in). The surface speed of cooling roll 36 is preferably slightly faster than the surface speed of 10 calender roll 32 and back-up roll 30 to help m~int~in sheet tension in the free sheet spans between the calendering operation and the cooling operation, to m~int~in sheet tension on the fixed rolls 34 and 35, and to help m~int~in the sheet tension on the cooling roll 36. The plefellcd surface speed of cooling roll 36 is about 0.5% faster than the surface 15 speed of calender roll 32. Again, the surface of fixed rolls 34 and 35 may each be machined with two spiral surface grooves directed away from the middle of the rolls to help m~int~in cross-directional sheet tension.
Cooling rolls 36 and 38 are plefelably of a rli~mPter similar to 20 that of the prç~e~tin~ rolls 16 and 18. The rolls must be large enough to have the strength to resist bending and to provide a residence time for the sheet on the rolls sufficient for adequate cooling. On the other hand, it is desirable for the rolls to be small enough that the force of the sheet against the rolls is sufficient to generate shrinkage resisting friction 25 between the sheet and cooling rolls (as discussed above). In addition, smaller rolls are less costly to manufacture and install, and they are easier to move when desired. The cooling rolls should be close enough that the free sheet span between the rolls is as small as possible. The cooling rolls used in the examples below had a diameter of about 0.53 m 30 (21 in). It is also important to m~in~in the sheet tension on and between cooling rolls, as for example by operating roll 38 at a surface speed slightly faster than the surface speed of roll 36.
The rolls 36 and 38 cool opposite sides ofthe sheet. The rolls are prefel~bly cooled by cooling water that passes through an annular CA 02249~69 1998-09-16 W O 97/40224 PCT~US97/OS859 space under the surface of each roll. The temperature of the cooling water pumped into the rolls is preferably between about 10 and 43~ C
(50 and l l O~ F). If the sheet being bonded is a polyethylene plexifilamentary sheet, it is desirable for the temperature of the sheet to S be re~ ce~l to a temperature below about 100~ C (212~ F) before coming off the cooling rolls. The cooling rolls prefelably have a non-sticky surface such as a smooth polished chrome finish from which the bonded sheet 44 is easily removed.
The bonded sheet 44 is transferred to a take-up roll or to 10 subsequent downstream processing steps, such as printing, by means of transfer rolls, such as the fixed rolls 40 and 42 shown in Figure 2. After the sheet comes off the cooling rolls 36 and 38 and sheet bonding is complete, it is no longer necessary to keep free sheet spans to an absolute minimum or to maintain sheet tension in order to resist sheet 15 shrinkage and curling.
The process described above is suited for m~kin~ a broad range of nonwoven olefin bonded sheet products with a single set of process equipment. By carefully controlling the tempe~alule ofthe rolls, the speed of the rolls, the sheet residence time on the rolls, the tension in 20 the sheet, the texture of the calender rolls, and the pressure of the calender nips, a wide variety of bonded products can be made. Great process flexibility is attained when each of the rolls is equipped with an independent drive and an individual speed controller. It has been found that with the process of the invention, wherein sheet tension is 25 maintained during bonding, a higher degree of bonding can be achieved because the sheet can be subjected to bonding ten~p~,laL lres that are 1~ to
2~ C higher than could be applied with the prior art bonding process without c~-~cing excessive melting of the sheet surface.
The l rocess of the p~esenl invention has been found to be 30 especially suitable for producing nonwoven olefin sheet products that are highly in~cJ .lle~ble to air and water yet retain a subst~nti~l degree of moisture vapor tr~ncmi~sibility. The process described above has also been found to have great utility in bonding a fibrous nonwoven olefin sheet material to produce a bonded sheet that is strong and also has a smooth highly printable surface finish. The following non-limi~ing examples are intended to illustrate the process and products of the invention and not to limit the invention in any manner.
EXAMPLES
In the description above and in the non-limiting examples that follow, the following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society of Testing Materials, TAPPI refers to the Technical Association of the Pulp and Paper Industry, and AATTC refers to the American Association of Textile Chemists and Colorists.
R~ Wei~ht was determined by AS~M D-3776, which is hereby incorporated by reference, and is reported in g/m2. The basis weights reported for the examples below are each based on an average of at least twelve measurements made on the sheet.
Ten~ile Strengtll ~nd Flor~tion were determined by ASTM
D 1682, Section 19, which is hereby incorporated by refe,~.lce, with the following modifications. In the test a 2.54 cm by 20.32 cm (1 inch by 8 inch) sample was clarnped at opposite ends of the sample. The clamps were attached 12.7 cm (5 in) from each other on the sample. The sample was pulled steadily at a speed of 5.08 cm/min (2 in/min) until the sample broke. The force at break was recorded Newtons/cm as the breaking tensile strength. The elongation at break is recorded as a percent of the original sample length. The tensile strength and elongation values reported for the examples below are each an average of at least twelve me~sllren~ tc made on the sheet.
Flmen-~orf T~o~r ~trer~ is a measure of the force required to propagate a tear cut in a sheet. The average force required to continue a tongue-type tear in a sheet is deterrnined by measuring the work done in tearing it through a fixed distance. The tester consists of a sector-shaped pendulum carrying a clamp that is in alignrnent with a fixed clamp when the pendulum is in the raised starting position, with maximum potential energy. The specimen is fastened in the clamps and the tear is started by a slit cut in the specimen between the clamps. The pendulum is released and the specimen is torn as the moving clamp moves away from the W O 97/40224 PCTrUS97/05859 fixed clamp. Elmendorf tear strength is measured in Newtons in accordance with the following standard methods: TAPPI-T-414 om-88 and ASTM D 1424, which are hereby incorporated by reference. The tear strength values reported for the examples below are each an average 5 of at least twelve measurements made on the sheet.
~ ydrost~tic Head measures the resistance of a sheet to the penetration by liquid water under a static load. A 316 cm2 sarnple is mounted in an SDL Shirley Hydrostatic Head Tester (m~nl1f~ctured by Shirley Developments Limited, Stockport, England). Water is pumped l 0 ~g~inct one side of a 102.6 cm2 section of the sample until the sample is penetrated by water. The measured hydrostatic pressure is reported in centimeters of water. The test generally follows AATTC 127-1985, which is hereby incorporated by l~,ferellce. The hydrostatic head values reported for the examples below are each based on an average of at least 15 six measurements made on the sheet.
Gl-rley-Hill Porosity is a measure of the time required for 100 cm3 of air to pass through a sample under standard conditions and is measured by TAPPI T-460 om-8, which is hereby incorporated by reference. The porosity values reported for the examples below are each 20 based on an average of at least twelve measurements made on the sheet.
Moi~hlre Vapor Tr~n.cmi~ion l~t~ (MVTR) was determined by ASTM E96-B, which is hereby incorporated by reference, and is reported in g/m2/24hr. The MVTR values reported for the examples below are each based on an average o f at- least four measurements made 25 on the sheet.
.~heet thickness ~nd lmiformity were determined by ASTM
method D 1777-64, which is hereby incorporated by reference. The thickness values reported for the examples below are each based on an average of at least 80 measurements taken on the sheet. The uniformity 30 value (cs) represents the statistical standard deviation of the measured thiclcness values. A lower standard deviation is indicative of a more uniformly thick sheet.
nel~rnin~tion ~trer~ll of a sheet sample is measured using a constant rate of extension tensile testing machine such as an Instron CA 02249~69 1998-09-16 W O 97/40224 PCTrUS97/05859 table m~del tester. A 1.0 in. (2.54 cm) by 8.0 in. (20.32 cm) sample is del~nlin~tecl approximately 1.25 in. (3.18 cm) by inserting a pick into the cross-section of the sample to initiate a separation and del~rnin~tion by hand. The delaminated sample faces are mounted in the clamps of 5 the tester which are set 1.0 in. (2.54 cm) apart. The tester is started and run at a cross-head speed of 5.0 in./min. (12.7 cm/min.). The computer starts picking up re~ ngs after the slack is removed in about 0.5 in. of crosshead travel. The sample is del~min~te~l for about 6 in. (15.24 cm) during which 3000 readings are taken and averaged. The average 10 del~min~tion strength is given in N/cm. The test generally follows the method of ASTM D 2724-87, which is hereby incorporated by reference. The del~min~tion strength values reported for the examples below are each based on an average of at least twelve measurements made on the sheet.
Opaci~y is measured according to TAPPI T-5 19 om-86, which is hereby incorporated by referellce. The opacity is the reflectance from a single sheet ~in~t a black background compared to the reflectance from a white background standard and is expressed as a percent. The opacity values reported for the examples below are each 20 based on an average of at least twelve measurements made on the sheet.
Print Q~ ity is measured according to ANSI X3.182-1990, which is hereby incorporated by reference. The test measures the print quality of a bar code for purposes of code readability. The test evaluates the print quality of a bar code symbol for contrast, modulation, defects, 25 and decodability and assigns a grade of A, B, C, D or F(fail) for each category. The additional categories of reflect~nce, edge contrast and decodability are evaluated on a pass/fail basis. The overall grade of a sample is the lowest grade received in any of the above categories.
Testing was done on a Code 39 symbology bar code wim the narrow bar 30 width of 0.0096 inch that was printed on an Intermec 400 Printer m~nllf~ctllred by Intermec Inc. of Cincinnati, Ohio. Verification was done with a PSC quick check 200 scanner (660 nm wavelength and 6 mil aperture) manufactured by Photographic Sciences Corporation Inc.
of Webster, New York. Print quality is generally depen-l~nt on the 35 smoothness ofthe printing surface.
, . ...
CA 02249~69 1998-09-16 W O 97/40224 PCTnUS97/058~9 The non-woven flash-spun polyethylene plexifilamentary film-fibril sheet that was used in the examples is the same sheet material that when bonded is sold by DuPont as TYVEK~ spunbonded polyolefin sheet. Four versions of the unbonded plexifilamentary polyethylene sheet material were 5 used as the starting sheet material in the examples. Type A had a basis weightof 49.4 g/m2 and an average thickness of 0.171 mm. Type B had a basis weight of 66.4 g/m2 and an average thickness of 0.244 mm. Type C had a basis weight of 72.5 g/m2 and an average thickness of 0.264 mm. Type D had a basis weight of 53.2 g/m2 and an average thickness of 0.151 mm.
Several bonding patterns were used in the examples below. Samples identified as having a "smooth" pattern have a flat smooth finish on both sides of the sheet. Samples identified as having a "bar" pattern have one side bonded with a smooth finish and the opposite side bonded with an array of alternating vertically oriented and horizontally oriented bar-shaped bonded 15 sections in which each bonded bar section is about 0.5 m~n wide and about 2.6mm long, and in which the end of each bar is spaced about 1 mm from the side of an adjacent bar. Samples identified as having a "linen" pattern have one side bonded with a smooth finish and the opposite side bonded with a pat~ern having the appearance of a linen weave.
In this example, a lightly consolidated flash-spun polyethylene Type A
sheet was bonded according the prior art process described above and shown in 25 Figure 1. The bonded sheet had the following properties:
Basis weight 51.53 g/m2 Tensile strength-MD 42.9 N/cm Tensile strength-CD 53.3 N/cm F.lmentlQrf tear-MD 9.70 N
Elmendorf tear-CD 8.35 N
Elon~tion-MD 1 6%
Elongation-CD 21.1 %
Thickness 0.151 mm W O 97/40224 PCTrUS97/OS859 Thickness Std. Deviation .021 Hydrohead 164.1 cm Gurley Hill 57.5 sec MVTR 856 g/m2-24hr Del~min~tion strength 0.91 N
EXAMP~ES 1-9 In the following examples, lightly consolidated flash-spun polyethylene 10 sheets were bonded according the process shown in Figure 2. Processing conditions and product properties are reported in Table 1 below.
In the following examples, lightly consolidated flash-spun polyethylene sheets were bonded according the prior art process described above and shown in Figure 1. The bonded sheet had the following properties:
Con~. Fx ? Comp. Fx 3 Starting Sheet Type Type C Type B
Basis weight 75 g/m2 68 g/m2 Tensile strength-MD 77 N/cm 64 N/cm Tensile strength-CD 87N/cm 71 N/cm Elmendorf tear-MD 4.4 N 4.9 N
Elmendorf tear-CD 4.2 N 4.9 N
Elongation-MD 20 % 17%
Elongation-CD 24 % 21%
ThirL-ness 0.193 mm 0.191 mm Thickness Std.Deviation(~) 0.023 0.023 Del~min~tion Strength 0.74 N/cm 0.56 N/cm Opacity 94% 97%
PrintQuality F F
W O 97/40224 PCTrUS97/05859 Itl the following example, a lightly consolidated flash-spun polyethylene sheet was bonded according the process shown in Figure 2. Processing conditions and product properties are reported in Table 2 below.
It will be ~,u~ent to those skilled in the art that modifications and variations can be made in bonded polyolefin sheet products of the invention and in the process for making such products. The invention in its broader 10 aspects is, therefore, not limited to the specific details or the illustrative exarnples described above. Thus, it is int~n~led that all matter contained in the foregoing description, drawings and examples shall be hltelpfe~ed as illustrative and not in a limiting sense.
W O 97/40224 22 PCT~US97/05859 Example 1 2 3 4 5 Sheel Type A A A A A
i ine Speed (mpm) 61.0 121.9 61.0 106.7 91.4 Preheat Bottom Roll .~ .' .~ ~'. .' Top Roll .~ ~ .~ . ' alender Roll (Top) .~ . ~ .
mbosser Roll (i3Ot) . ~ " . ' ~
_ ooiing Top Roll 61.3 122.5 61.3 107.3 92.1 Sottom Roll 61.6 123.1 61.6 107.9 92.4 T~mp. (~C) reheat _ _ ~
alender vA ~ ,L ~v vL v mbosser A~ ~ L' ' L' ' Al " ' ooling Water Calender Nip ip Position dosed closed closed closeci open res (kg/iinearcm) 21.48 24.16 21.48 31.86 Embosser Nip Nip Position ciosed closed closed ciosed closed Pres. (kg/iinear cm) 35.80 36.52 38.48 38.31 57.28 ap Angle (degrees) reheat ~45 -45 -45 -45 ~5 alender 35 35 35 35 4 mbosser 0 0 0 0 1 ~
Pattëm srnoo~h smooth bar bar bar Properties Sas Weight (gr/mZ) ' _ 5t-' 50.2 5;. 51.
Thic~ness, ~mm) .~ .104 ~' .13 Thic~nessS~d.Dev.~ C. ~-98 0.) 51 - .0 1 0.0_56 ~ensile, (Nlcm) 1D 44.1 36.81 37.98 35.14 41.38 D 49.4 40.24 41.82 38.80 44.75 Elongation (%) MD 19.19 10.53 10.8 11.1 12.5 CD 13.94 16.36 18.66 18.95 20.71 Imendori Tear (N) ~iD 7.57 12.06 11.93 11.57 10.86 ,D 9.34 11.26 8.19 9.92 9.52 Hydrohead (cm) 254.25 237.34 262.99 278.66 170.66 Guriey Hill (sec) ~300 ~300 9832 7299 211.8 MVTR (gm/mZ-24 hrs) 384 324 434 405 901 C~'i , . (N/cm) CA 02249~69 1998-09-16 W 097/40224 PCT~US97/OS859 Table 1 Cont'd Example 6 7 8 9 Sheet Type B B B D
Une Speed (mpm) 91,4 91.4 99,1 Preheat Bottr n Roll Top oll ~. . .
alenc er Roll (Top) ~ s . 0.
mbosser Roll ~Bot) .. ' .~ -~,ooling rOp Roll 91.7 91.7 91.8 99.5 Bottom Roll 93.0 92.7 92.8 100.5 Temp. (~C) teheat ' ~ ~ ~
alender L' ' ' A ' L ,.
mbosser ~~ L~
oolin,cJ Water ~ .3 . - C
C lender Nip ip Position open open open closed res. ~kgllinear cm) 35 7 smc~oth Embosser Nip Nip Position closed closecl dosed closed Pres. (kg/linear cm) 57.28 57.28 62.86 45.72 V' -ap Anqle (deo,rees) reheat 5 45 5 alender 4 4 3 3 mbosser Pattem bar bar linen linen Properties Bas - Weic ht (c rlm~) 65.8 ~' . 68. 52.
Thic~ness nm .203 .16 .12.
Thic~ness td. ~ev.~ - . 6 0Ø6 0.0 6 ~ensile (Nlcm) ~D 53.21 41.75 56.08 47.88 CD 50.68 42.05 58.90 46.90 Elonqation (%) MD 9.77 7.46 8.B3 8.66 CD 13.49 11.3 15.7 13.83 Elmendorf Tear (N) MD 9.92 13.93 8.19 6.85 CD 10.10 13.93 9.03 6.50 Hydrohead (cm) 226.85 216.15 212.5 287.2 Gurley Hill (sec) 80.83 88.67 455 455 MVTR (qm/m~-24 hrs) 1076 1081 nla nla C ' " . (N/cm) ' 1.71 1.61 Example 10 Sheel Type Type C
UneSpeed (mpm) Pteheat Bottom Roll ~ L, -Top oll alenr er Roll (Top) mhsser Roll (Bot) .
ooling rOp Roll t5.33 BoKom Roll 15.36 Temp. (~C) neheat 3' alender ~ 5 mbosser L~
ooling Water Calender Nip ip Position Closed res. (kg/linear cm) 49.65 Embosser Nip Nip Position Closed Pres, ( kg/linear cm) 66.79 ~'-ap Angle (degnoes) reheat 45 alender 0 mhsser 35 Panem Smooth Propertles Basi Wei~rht(g/rn~) 74.6 Thic~ness nm.) 0.107 Thic~ness td. Dev.~ 0.011 ~ensile (N/cm~
I~ID 71.8 CD 84.1 Elmendorf Tear (NJcm) MD 4.9 CO 5.3 Delam. Strength (N/cm) 0.858 Opacity (%) 86 Print auality (ANSI) C
The l rocess of the p~esenl invention has been found to be 30 especially suitable for producing nonwoven olefin sheet products that are highly in~cJ .lle~ble to air and water yet retain a subst~nti~l degree of moisture vapor tr~ncmi~sibility. The process described above has also been found to have great utility in bonding a fibrous nonwoven olefin sheet material to produce a bonded sheet that is strong and also has a smooth highly printable surface finish. The following non-limi~ing examples are intended to illustrate the process and products of the invention and not to limit the invention in any manner.
EXAMPLES
In the description above and in the non-limiting examples that follow, the following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society of Testing Materials, TAPPI refers to the Technical Association of the Pulp and Paper Industry, and AATTC refers to the American Association of Textile Chemists and Colorists.
R~ Wei~ht was determined by AS~M D-3776, which is hereby incorporated by reference, and is reported in g/m2. The basis weights reported for the examples below are each based on an average of at least twelve measurements made on the sheet.
Ten~ile Strengtll ~nd Flor~tion were determined by ASTM
D 1682, Section 19, which is hereby incorporated by refe,~.lce, with the following modifications. In the test a 2.54 cm by 20.32 cm (1 inch by 8 inch) sample was clarnped at opposite ends of the sample. The clamps were attached 12.7 cm (5 in) from each other on the sample. The sample was pulled steadily at a speed of 5.08 cm/min (2 in/min) until the sample broke. The force at break was recorded Newtons/cm as the breaking tensile strength. The elongation at break is recorded as a percent of the original sample length. The tensile strength and elongation values reported for the examples below are each an average of at least twelve me~sllren~ tc made on the sheet.
Flmen-~orf T~o~r ~trer~ is a measure of the force required to propagate a tear cut in a sheet. The average force required to continue a tongue-type tear in a sheet is deterrnined by measuring the work done in tearing it through a fixed distance. The tester consists of a sector-shaped pendulum carrying a clamp that is in alignrnent with a fixed clamp when the pendulum is in the raised starting position, with maximum potential energy. The specimen is fastened in the clamps and the tear is started by a slit cut in the specimen between the clamps. The pendulum is released and the specimen is torn as the moving clamp moves away from the W O 97/40224 PCTrUS97/05859 fixed clamp. Elmendorf tear strength is measured in Newtons in accordance with the following standard methods: TAPPI-T-414 om-88 and ASTM D 1424, which are hereby incorporated by reference. The tear strength values reported for the examples below are each an average 5 of at least twelve measurements made on the sheet.
~ ydrost~tic Head measures the resistance of a sheet to the penetration by liquid water under a static load. A 316 cm2 sarnple is mounted in an SDL Shirley Hydrostatic Head Tester (m~nl1f~ctured by Shirley Developments Limited, Stockport, England). Water is pumped l 0 ~g~inct one side of a 102.6 cm2 section of the sample until the sample is penetrated by water. The measured hydrostatic pressure is reported in centimeters of water. The test generally follows AATTC 127-1985, which is hereby incorporated by l~,ferellce. The hydrostatic head values reported for the examples below are each based on an average of at least 15 six measurements made on the sheet.
Gl-rley-Hill Porosity is a measure of the time required for 100 cm3 of air to pass through a sample under standard conditions and is measured by TAPPI T-460 om-8, which is hereby incorporated by reference. The porosity values reported for the examples below are each 20 based on an average of at least twelve measurements made on the sheet.
Moi~hlre Vapor Tr~n.cmi~ion l~t~ (MVTR) was determined by ASTM E96-B, which is hereby incorporated by reference, and is reported in g/m2/24hr. The MVTR values reported for the examples below are each based on an average o f at- least four measurements made 25 on the sheet.
.~heet thickness ~nd lmiformity were determined by ASTM
method D 1777-64, which is hereby incorporated by reference. The thickness values reported for the examples below are each based on an average of at least 80 measurements taken on the sheet. The uniformity 30 value (cs) represents the statistical standard deviation of the measured thiclcness values. A lower standard deviation is indicative of a more uniformly thick sheet.
nel~rnin~tion ~trer~ll of a sheet sample is measured using a constant rate of extension tensile testing machine such as an Instron CA 02249~69 1998-09-16 W O 97/40224 PCTrUS97/05859 table m~del tester. A 1.0 in. (2.54 cm) by 8.0 in. (20.32 cm) sample is del~nlin~tecl approximately 1.25 in. (3.18 cm) by inserting a pick into the cross-section of the sample to initiate a separation and del~rnin~tion by hand. The delaminated sample faces are mounted in the clamps of 5 the tester which are set 1.0 in. (2.54 cm) apart. The tester is started and run at a cross-head speed of 5.0 in./min. (12.7 cm/min.). The computer starts picking up re~ ngs after the slack is removed in about 0.5 in. of crosshead travel. The sample is del~min~te~l for about 6 in. (15.24 cm) during which 3000 readings are taken and averaged. The average 10 del~min~tion strength is given in N/cm. The test generally follows the method of ASTM D 2724-87, which is hereby incorporated by reference. The del~min~tion strength values reported for the examples below are each based on an average of at least twelve measurements made on the sheet.
Opaci~y is measured according to TAPPI T-5 19 om-86, which is hereby incorporated by referellce. The opacity is the reflectance from a single sheet ~in~t a black background compared to the reflectance from a white background standard and is expressed as a percent. The opacity values reported for the examples below are each 20 based on an average of at least twelve measurements made on the sheet.
Print Q~ ity is measured according to ANSI X3.182-1990, which is hereby incorporated by reference. The test measures the print quality of a bar code for purposes of code readability. The test evaluates the print quality of a bar code symbol for contrast, modulation, defects, 25 and decodability and assigns a grade of A, B, C, D or F(fail) for each category. The additional categories of reflect~nce, edge contrast and decodability are evaluated on a pass/fail basis. The overall grade of a sample is the lowest grade received in any of the above categories.
Testing was done on a Code 39 symbology bar code wim the narrow bar 30 width of 0.0096 inch that was printed on an Intermec 400 Printer m~nllf~ctllred by Intermec Inc. of Cincinnati, Ohio. Verification was done with a PSC quick check 200 scanner (660 nm wavelength and 6 mil aperture) manufactured by Photographic Sciences Corporation Inc.
of Webster, New York. Print quality is generally depen-l~nt on the 35 smoothness ofthe printing surface.
, . ...
CA 02249~69 1998-09-16 W O 97/40224 PCTnUS97/058~9 The non-woven flash-spun polyethylene plexifilamentary film-fibril sheet that was used in the examples is the same sheet material that when bonded is sold by DuPont as TYVEK~ spunbonded polyolefin sheet. Four versions of the unbonded plexifilamentary polyethylene sheet material were 5 used as the starting sheet material in the examples. Type A had a basis weightof 49.4 g/m2 and an average thickness of 0.171 mm. Type B had a basis weight of 66.4 g/m2 and an average thickness of 0.244 mm. Type C had a basis weight of 72.5 g/m2 and an average thickness of 0.264 mm. Type D had a basis weight of 53.2 g/m2 and an average thickness of 0.151 mm.
Several bonding patterns were used in the examples below. Samples identified as having a "smooth" pattern have a flat smooth finish on both sides of the sheet. Samples identified as having a "bar" pattern have one side bonded with a smooth finish and the opposite side bonded with an array of alternating vertically oriented and horizontally oriented bar-shaped bonded 15 sections in which each bonded bar section is about 0.5 m~n wide and about 2.6mm long, and in which the end of each bar is spaced about 1 mm from the side of an adjacent bar. Samples identified as having a "linen" pattern have one side bonded with a smooth finish and the opposite side bonded with a pat~ern having the appearance of a linen weave.
In this example, a lightly consolidated flash-spun polyethylene Type A
sheet was bonded according the prior art process described above and shown in 25 Figure 1. The bonded sheet had the following properties:
Basis weight 51.53 g/m2 Tensile strength-MD 42.9 N/cm Tensile strength-CD 53.3 N/cm F.lmentlQrf tear-MD 9.70 N
Elmendorf tear-CD 8.35 N
Elon~tion-MD 1 6%
Elongation-CD 21.1 %
Thickness 0.151 mm W O 97/40224 PCTrUS97/OS859 Thickness Std. Deviation .021 Hydrohead 164.1 cm Gurley Hill 57.5 sec MVTR 856 g/m2-24hr Del~min~tion strength 0.91 N
EXAMP~ES 1-9 In the following examples, lightly consolidated flash-spun polyethylene 10 sheets were bonded according the process shown in Figure 2. Processing conditions and product properties are reported in Table 1 below.
In the following examples, lightly consolidated flash-spun polyethylene sheets were bonded according the prior art process described above and shown in Figure 1. The bonded sheet had the following properties:
Con~. Fx ? Comp. Fx 3 Starting Sheet Type Type C Type B
Basis weight 75 g/m2 68 g/m2 Tensile strength-MD 77 N/cm 64 N/cm Tensile strength-CD 87N/cm 71 N/cm Elmendorf tear-MD 4.4 N 4.9 N
Elmendorf tear-CD 4.2 N 4.9 N
Elongation-MD 20 % 17%
Elongation-CD 24 % 21%
ThirL-ness 0.193 mm 0.191 mm Thickness Std.Deviation(~) 0.023 0.023 Del~min~tion Strength 0.74 N/cm 0.56 N/cm Opacity 94% 97%
PrintQuality F F
W O 97/40224 PCTrUS97/05859 Itl the following example, a lightly consolidated flash-spun polyethylene sheet was bonded according the process shown in Figure 2. Processing conditions and product properties are reported in Table 2 below.
It will be ~,u~ent to those skilled in the art that modifications and variations can be made in bonded polyolefin sheet products of the invention and in the process for making such products. The invention in its broader 10 aspects is, therefore, not limited to the specific details or the illustrative exarnples described above. Thus, it is int~n~led that all matter contained in the foregoing description, drawings and examples shall be hltelpfe~ed as illustrative and not in a limiting sense.
W O 97/40224 22 PCT~US97/05859 Example 1 2 3 4 5 Sheel Type A A A A A
i ine Speed (mpm) 61.0 121.9 61.0 106.7 91.4 Preheat Bottom Roll .~ .' .~ ~'. .' Top Roll .~ ~ .~ . ' alender Roll (Top) .~ . ~ .
mbosser Roll (i3Ot) . ~ " . ' ~
_ ooiing Top Roll 61.3 122.5 61.3 107.3 92.1 Sottom Roll 61.6 123.1 61.6 107.9 92.4 T~mp. (~C) reheat _ _ ~
alender vA ~ ,L ~v vL v mbosser A~ ~ L' ' L' ' Al " ' ooling Water Calender Nip ip Position dosed closed closed closeci open res (kg/iinearcm) 21.48 24.16 21.48 31.86 Embosser Nip Nip Position ciosed closed closed ciosed closed Pres. (kg/iinear cm) 35.80 36.52 38.48 38.31 57.28 ap Angle (degrees) reheat ~45 -45 -45 -45 ~5 alender 35 35 35 35 4 mbosser 0 0 0 0 1 ~
Pattëm srnoo~h smooth bar bar bar Properties Sas Weight (gr/mZ) ' _ 5t-' 50.2 5;. 51.
Thic~ness, ~mm) .~ .104 ~' .13 Thic~nessS~d.Dev.~ C. ~-98 0.) 51 - .0 1 0.0_56 ~ensile, (Nlcm) 1D 44.1 36.81 37.98 35.14 41.38 D 49.4 40.24 41.82 38.80 44.75 Elongation (%) MD 19.19 10.53 10.8 11.1 12.5 CD 13.94 16.36 18.66 18.95 20.71 Imendori Tear (N) ~iD 7.57 12.06 11.93 11.57 10.86 ,D 9.34 11.26 8.19 9.92 9.52 Hydrohead (cm) 254.25 237.34 262.99 278.66 170.66 Guriey Hill (sec) ~300 ~300 9832 7299 211.8 MVTR (gm/mZ-24 hrs) 384 324 434 405 901 C~'i , . (N/cm) CA 02249~69 1998-09-16 W 097/40224 PCT~US97/OS859 Table 1 Cont'd Example 6 7 8 9 Sheet Type B B B D
Une Speed (mpm) 91,4 91.4 99,1 Preheat Bottr n Roll Top oll ~. . .
alenc er Roll (Top) ~ s . 0.
mbosser Roll ~Bot) .. ' .~ -~,ooling rOp Roll 91.7 91.7 91.8 99.5 Bottom Roll 93.0 92.7 92.8 100.5 Temp. (~C) teheat ' ~ ~ ~
alender L' ' ' A ' L ,.
mbosser ~~ L~
oolin,cJ Water ~ .3 . - C
C lender Nip ip Position open open open closed res. ~kgllinear cm) 35 7 smc~oth Embosser Nip Nip Position closed closecl dosed closed Pres. (kg/linear cm) 57.28 57.28 62.86 45.72 V' -ap Anqle (deo,rees) reheat 5 45 5 alender 4 4 3 3 mbosser Pattem bar bar linen linen Properties Bas - Weic ht (c rlm~) 65.8 ~' . 68. 52.
Thic~ness nm .203 .16 .12.
Thic~ness td. ~ev.~ - . 6 0Ø6 0.0 6 ~ensile (Nlcm) ~D 53.21 41.75 56.08 47.88 CD 50.68 42.05 58.90 46.90 Elonqation (%) MD 9.77 7.46 8.B3 8.66 CD 13.49 11.3 15.7 13.83 Elmendorf Tear (N) MD 9.92 13.93 8.19 6.85 CD 10.10 13.93 9.03 6.50 Hydrohead (cm) 226.85 216.15 212.5 287.2 Gurley Hill (sec) 80.83 88.67 455 455 MVTR (qm/m~-24 hrs) 1076 1081 nla nla C ' " . (N/cm) ' 1.71 1.61 Example 10 Sheel Type Type C
UneSpeed (mpm) Pteheat Bottom Roll ~ L, -Top oll alenr er Roll (Top) mhsser Roll (Bot) .
ooling rOp Roll t5.33 BoKom Roll 15.36 Temp. (~C) neheat 3' alender ~ 5 mbosser L~
ooling Water Calender Nip ip Position Closed res. (kg/linear cm) 49.65 Embosser Nip Nip Position Closed Pres, ( kg/linear cm) 66.79 ~'-ap Angle (degnoes) reheat 45 alender 0 mhsser 35 Panem Smooth Propertles Basi Wei~rht(g/rn~) 74.6 Thic~ness nm.) 0.107 Thic~ness td. Dev.~ 0.011 ~ensile (N/cm~
I~ID 71.8 CD 84.1 Elmendorf Tear (NJcm) MD 4.9 CO 5.3 Delam. Strength (N/cm) 0.858 Opacity (%) 86 Print auality (ANSI) C
Claims
WHAT IS CLAIMED IS:
1. A bonded plexifilamentary film-fibril sheet characterized in that the sheet is comprised of at least 50% by weight of palyolefin polymer, said sheet having a basis weight in the range of 17 to 270 g/m2, an average thickness in the range of 0.025 to 1.0 mm, a low air permeability expressed as Gurley-Hill porosity of at least 70 seconds, low liquid water permeability expressed by a hydrostatic head pressure of greater than 170 cm according to AATCC standard 127, and a moderate moisture vapor transmission rate of at least 100 g/m2 in 24 hours according to ASTM standard E96, method B.
3. The sheet of claim 1 wherein the sheet has a tensile strength of at least 12.5 N/cm.
4. The sheet of claim 3 wherein the surface on at least one side of the sheet is embossed with a textured pattern.
5. The sheet of claim 1 having a basis weight of about 50 to 120 g/m2, an average thickness in the range of 0.05 to 0.5 mm, with thickness standard deviation of less than 0.02, and a thermal transfer printing grade, according to ANSI Standard X3.182-1990, of at least "C".
6. The sheet of claim wherein the sheet has a delamination strength of at least 0.5 N/cm, a tensile strength of at least 20 N/cm, and an opacity of at least 75%.
7. A process for producing a highly bonded nonwoven sheet from a lightly consolidated fibrous sheet comprised of at least 50% by weight of polyolefin polymer, characterized by the steps of:
providing the lightly consolidated polyolefin sheet to a first preheated roll, said first preheating roll having a rotating outer surface that is heated to a temperature within 25°C of the melting temperature of the sheet;
contacting at least one face of the sheet with the heated surface of the first preheating roll and heating the sheet;
transferring said heated sheet from the first preheating roll to a rotating first heated calender roll, said first heated calender roll having an outer heated surface with a linear surface speed not less than the linear surface speed of the first preheating roll, said outer heated surface of said first heated calender roll being maintained at a temperature within 25°C of the melting temperature of the sheet material;
contacting a surface of the sheet with said outer heated surface of the first heated calender roll;
while said sheet is in contact with said first heated calender roll, passing said sheet through a first nip formed between said first heated calender roll and a back-up roll, said first nip imparting an average nip pressure of at least 8.75 N/linear cm on the sheet;
transferring said calendered sheet from the first heated calender roll to a first cooling roll, said first cooling roll having an outer cooling surface rotating at a linear surface speed not less than the linear surface speed of the first heated calender roll, said outer cooling surface of said cooling roll being maintained at a temperature at least 15°C below the melting point of the sheet material;
contacting the calendered sheet with the outer cooling surface of the first cooling roll for a period sufficient to cool the sheet to a temperature below the melting temperature of the sheet material and stabilize the sheet material, and removing said bonded sheet from said cooling roll.
8. The process for producing a bonded nonwoven sheet according to claim 7 wherein the sheet is comprised of plexifilamentary film-fibrils.
9. The process of claim 8 wherein the outer heated surface of said first calender roll has a linear surface speed at least 0.2% faster than the linear surface speed of the first preheating roll, and wherein the outer cooling surface of said first cooling roll has a linear surface speed at least 0.2% faster than the linear surface speed of the first calender roll.
10. The process for producing a bonded nonwoven sheet according to claim 9 wherein the sheet passes through a plurality of free spans between the sheet's first contact with the first preheating roll and the sheet's removal from the cooling roll where the sheet is not in contact with any roll, and wherein the length of each of said free spans is less than 20 cm.
11. The process for producing a bonded nonwoven sheet according to claim 8 wherein the step of transferring said sheet from the first heated calender roll to the first cooling roll further includes the steps of transferring said sheet from the first heated calender roll to a second heated calender roil, said second heated calender roll having an outer heated surface rotating at a linear surface speed not less than the linear surface speed of the first heated calender roll, said outer heated surface of said second calender roll being maintained at a temperature within 25°C of the melting temperature of the film-fibrils of the plexifilamentary sheet;
contacting the outer heated surface the second calender roll with the surface of the sheet opposite the sheet surface that contacted the first heated calender roll;
while said sheet is in contact with said second heated calender roll, passing said sheet through a second nip formed between said second heated calender roll and a back-up roll, said second nip imparting an average nip pressure of at least 8.75 N/linear cm on the sheet; and transferring said calendered sheet from the second heated calender roll to said first cooling roll.
12. The process for producing a bonded nonwoven sheet according to claim 11 wherein the outer heated surfaces of said first and second calender rolls are smooth and the surface of the resilient back-up roll of said first nip and the resilient back-up roll of said second nip are each made of a smooth resilient material.
13. The process for producing a bonded nonwoven sheet according to claim 11 wherein the outer heated surface of said first heated calender roll is smooth, the outer heated surface of said second heated calender roll has a textured-embossing pattern, and the surface of the resilient back-up roll of said first nip and the resilient back-up roll of said second nip are each made of a smooth resilient material.
14. The process for producing a bonded nonwoven sheet according to claim 10 comprising the additional steps of:
transferring said heated sheet from said first preheating roll to a second preheating roll, said second preheating roll having a rotating outer heated surface moving at a linear surface speed at least 0.2 %
faster than the linear surface speed of the first preheating roll;
contacting a surface of said sheet that is opposite the surface of the sheet contacted with the first preheating roll with the heated surface of said second preheating roll to heat the contacted surface of the sheet, the heated surface of said second preheating roll being maintained at a temperature within 25° C of the melting temperature of the sheet;
transferring said heated sheet from the second preheating roll to the first heated calender roll, the outer heated surface of said first heated calender roll having an outer heated surface rotating at a linear surface speed at least 0.2 %faster than the linear surface speed of the second preheating roll.
15. The process for producing a bonded nonwoven sheet according to claim 14 further comprising the steps of passing the sheet over a first adjustable wrap roll means for adjusting the length of the surface of said second preheating rolls over which the sheet passes, and passing the sheet over a second adjustable wrap roll means for adjusting the length of the first heated calendering roll surface over which the sheet passes.
16. The process for producing a bonded nonwoven sheet according to claim 14 wherein the diameter of said first and second preheating rolls is in the range of 15 to 91 cm and wherein the diameter of said calender roll is within the range of 15 to 91 cm.
17. The process for producing a bonded nonwoven sheet according to claim 10 comprising the additional steps of:
transferring said heated sheet from said first cooling roll to a second cooling roll, said second cooling roll having an outer cooled surface rotating at a linear surface speed at least 0.2 % faster than the outer surface speed of the first cooling roll;
contacting a surface of said sheet that is opposite the surface of the sheet contacted with the first cooling roll with the cooling surface of said second cooling roll and cooling the contacted second surface of the sheet to a temperature less than the melting temperature of the sheet; and removing said cooled sheet from the second cooling roll.
18. The process for producing a bonded nonwoven sheet according to claim 12 wherein the outer heated surfaces of said first and second calender rolls are each maintained at a temperature within 15° C of the melting temperature of the film-fibrils of the plexifilamentary sheet.
1. A bonded plexifilamentary film-fibril sheet characterized in that the sheet is comprised of at least 50% by weight of palyolefin polymer, said sheet having a basis weight in the range of 17 to 270 g/m2, an average thickness in the range of 0.025 to 1.0 mm, a low air permeability expressed as Gurley-Hill porosity of at least 70 seconds, low liquid water permeability expressed by a hydrostatic head pressure of greater than 170 cm according to AATCC standard 127, and a moderate moisture vapor transmission rate of at least 100 g/m2 in 24 hours according to ASTM standard E96, method B.
3. The sheet of claim 1 wherein the sheet has a tensile strength of at least 12.5 N/cm.
4. The sheet of claim 3 wherein the surface on at least one side of the sheet is embossed with a textured pattern.
5. The sheet of claim 1 having a basis weight of about 50 to 120 g/m2, an average thickness in the range of 0.05 to 0.5 mm, with thickness standard deviation of less than 0.02, and a thermal transfer printing grade, according to ANSI Standard X3.182-1990, of at least "C".
6. The sheet of claim wherein the sheet has a delamination strength of at least 0.5 N/cm, a tensile strength of at least 20 N/cm, and an opacity of at least 75%.
7. A process for producing a highly bonded nonwoven sheet from a lightly consolidated fibrous sheet comprised of at least 50% by weight of polyolefin polymer, characterized by the steps of:
providing the lightly consolidated polyolefin sheet to a first preheated roll, said first preheating roll having a rotating outer surface that is heated to a temperature within 25°C of the melting temperature of the sheet;
contacting at least one face of the sheet with the heated surface of the first preheating roll and heating the sheet;
transferring said heated sheet from the first preheating roll to a rotating first heated calender roll, said first heated calender roll having an outer heated surface with a linear surface speed not less than the linear surface speed of the first preheating roll, said outer heated surface of said first heated calender roll being maintained at a temperature within 25°C of the melting temperature of the sheet material;
contacting a surface of the sheet with said outer heated surface of the first heated calender roll;
while said sheet is in contact with said first heated calender roll, passing said sheet through a first nip formed between said first heated calender roll and a back-up roll, said first nip imparting an average nip pressure of at least 8.75 N/linear cm on the sheet;
transferring said calendered sheet from the first heated calender roll to a first cooling roll, said first cooling roll having an outer cooling surface rotating at a linear surface speed not less than the linear surface speed of the first heated calender roll, said outer cooling surface of said cooling roll being maintained at a temperature at least 15°C below the melting point of the sheet material;
contacting the calendered sheet with the outer cooling surface of the first cooling roll for a period sufficient to cool the sheet to a temperature below the melting temperature of the sheet material and stabilize the sheet material, and removing said bonded sheet from said cooling roll.
8. The process for producing a bonded nonwoven sheet according to claim 7 wherein the sheet is comprised of plexifilamentary film-fibrils.
9. The process of claim 8 wherein the outer heated surface of said first calender roll has a linear surface speed at least 0.2% faster than the linear surface speed of the first preheating roll, and wherein the outer cooling surface of said first cooling roll has a linear surface speed at least 0.2% faster than the linear surface speed of the first calender roll.
10. The process for producing a bonded nonwoven sheet according to claim 9 wherein the sheet passes through a plurality of free spans between the sheet's first contact with the first preheating roll and the sheet's removal from the cooling roll where the sheet is not in contact with any roll, and wherein the length of each of said free spans is less than 20 cm.
11. The process for producing a bonded nonwoven sheet according to claim 8 wherein the step of transferring said sheet from the first heated calender roll to the first cooling roll further includes the steps of transferring said sheet from the first heated calender roll to a second heated calender roil, said second heated calender roll having an outer heated surface rotating at a linear surface speed not less than the linear surface speed of the first heated calender roll, said outer heated surface of said second calender roll being maintained at a temperature within 25°C of the melting temperature of the film-fibrils of the plexifilamentary sheet;
contacting the outer heated surface the second calender roll with the surface of the sheet opposite the sheet surface that contacted the first heated calender roll;
while said sheet is in contact with said second heated calender roll, passing said sheet through a second nip formed between said second heated calender roll and a back-up roll, said second nip imparting an average nip pressure of at least 8.75 N/linear cm on the sheet; and transferring said calendered sheet from the second heated calender roll to said first cooling roll.
12. The process for producing a bonded nonwoven sheet according to claim 11 wherein the outer heated surfaces of said first and second calender rolls are smooth and the surface of the resilient back-up roll of said first nip and the resilient back-up roll of said second nip are each made of a smooth resilient material.
13. The process for producing a bonded nonwoven sheet according to claim 11 wherein the outer heated surface of said first heated calender roll is smooth, the outer heated surface of said second heated calender roll has a textured-embossing pattern, and the surface of the resilient back-up roll of said first nip and the resilient back-up roll of said second nip are each made of a smooth resilient material.
14. The process for producing a bonded nonwoven sheet according to claim 10 comprising the additional steps of:
transferring said heated sheet from said first preheating roll to a second preheating roll, said second preheating roll having a rotating outer heated surface moving at a linear surface speed at least 0.2 %
faster than the linear surface speed of the first preheating roll;
contacting a surface of said sheet that is opposite the surface of the sheet contacted with the first preheating roll with the heated surface of said second preheating roll to heat the contacted surface of the sheet, the heated surface of said second preheating roll being maintained at a temperature within 25° C of the melting temperature of the sheet;
transferring said heated sheet from the second preheating roll to the first heated calender roll, the outer heated surface of said first heated calender roll having an outer heated surface rotating at a linear surface speed at least 0.2 %faster than the linear surface speed of the second preheating roll.
15. The process for producing a bonded nonwoven sheet according to claim 14 further comprising the steps of passing the sheet over a first adjustable wrap roll means for adjusting the length of the surface of said second preheating rolls over which the sheet passes, and passing the sheet over a second adjustable wrap roll means for adjusting the length of the first heated calendering roll surface over which the sheet passes.
16. The process for producing a bonded nonwoven sheet according to claim 14 wherein the diameter of said first and second preheating rolls is in the range of 15 to 91 cm and wherein the diameter of said calender roll is within the range of 15 to 91 cm.
17. The process for producing a bonded nonwoven sheet according to claim 10 comprising the additional steps of:
transferring said heated sheet from said first cooling roll to a second cooling roll, said second cooling roll having an outer cooled surface rotating at a linear surface speed at least 0.2 % faster than the outer surface speed of the first cooling roll;
contacting a surface of said sheet that is opposite the surface of the sheet contacted with the first cooling roll with the cooling surface of said second cooling roll and cooling the contacted second surface of the sheet to a temperature less than the melting temperature of the sheet; and removing said cooled sheet from the second cooling roll.
18. The process for producing a bonded nonwoven sheet according to claim 12 wherein the outer heated surfaces of said first and second calender rolls are each maintained at a temperature within 15° C of the melting temperature of the film-fibrils of the plexifilamentary sheet.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US63644796A | 1996-04-23 | 1996-04-23 | |
| US08/636,447 | 1996-04-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2249569A1 true CA2249569A1 (en) | 1997-10-30 |
Family
ID=24551948
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002249569A Abandoned CA2249569A1 (en) | 1996-04-23 | 1997-04-10 | Bonded polyolefin sheet |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5972147A (en) |
| EP (1) | EP0895551B1 (en) |
| JP (1) | JP2000510198A (en) |
| KR (1) | KR20000010588A (en) |
| CA (1) | CA2249569A1 (en) |
| DE (1) | DE69706973T2 (en) |
| ES (1) | ES2163758T3 (en) |
| WO (1) | WO1997040224A1 (en) |
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|---|---|---|---|---|
| NL271149A (en) * | 1960-11-08 | 1900-01-01 | ||
| US3081519A (en) * | 1962-01-31 | 1963-03-19 | Fibrillated strand | |
| DE1164643B (en) * | 1962-03-02 | 1964-03-05 | Dornbusch & Co | Method and device for hot stamping webs of material, in particular thermoplastic plastic films |
| US3442740A (en) * | 1965-04-12 | 1969-05-06 | Du Pont | Process for producing a bonded non-woven sheet |
| US3532589A (en) * | 1965-04-12 | 1970-10-06 | Du Pont | Differentially bonded non-woven sheet |
| US3536552A (en) * | 1966-12-19 | 1970-10-27 | Du Pont | Finishing process for non-woven sheets of strand material |
| NL6712632A (en) * | 1967-09-15 | 1967-11-27 | ||
| IT1012052B (en) * | 1972-03-20 | 1977-03-10 | Du Pont | NON-WOVEN FIBROUS SHEET PRODUCT AND METHOD FOR ITS PREPA RATION |
| US4069078A (en) * | 1976-08-23 | 1978-01-17 | E. I. Du Pont De Nemours And Company | Process for finishing a nonwoven film-fibril sheet |
| US4554207A (en) * | 1984-12-10 | 1985-11-19 | E. I. Du Pont De Nemours And Company | Stretched-and-bonded polyethylene plexifilamentary nonwoven sheet |
| US4652322A (en) * | 1986-02-28 | 1987-03-24 | E. I. Du Pont De Nemours And Company | Process for bonding and stretching nonwoven sheet |
| KR910005573B1 (en) * | 1986-10-13 | 1991-07-31 | 아사히 가세이 고오교 가부시끼가이샤 | High-density polyethylene net-like fiber nonwoven fabric made of the fiber and production of them |
| DE3751793T2 (en) * | 1986-10-13 | 1997-01-09 | Asahi Chemical Ind | NETWORKED HIGH DENSITY POLYETHYLENE FIBER AND WOVEN FABRIC THEREOF AND THEIR PRODUCTION THEREOF |
| JPH01280061A (en) * | 1988-04-30 | 1989-11-10 | Asahi Chem Ind Co Ltd | Nonwoven cloth of net-like polyolefin fiber having soft feeling |
| US4999222A (en) * | 1989-07-10 | 1991-03-12 | E. I. Du Pont De Nemours And Company | Metallized polyethylene plexifilamentary film-fibril sheet |
| US5085817A (en) * | 1989-07-10 | 1992-02-04 | E. I. Du Pont De Nemours And Company | Process for preparing a metallized polyethylene plexfilamentary film-fibril sheet |
| US5122412A (en) * | 1989-07-10 | 1992-06-16 | E. I. Du Pont De Nemours And Company | Polyethylene plexifilamentary film-fibril sheet |
| US5057351A (en) * | 1989-07-10 | 1991-10-15 | E. I. Du Pont De Nemours And Company | Metallized polyethylene plexifilamentary film-fibril sheet |
| US5308691A (en) * | 1993-10-04 | 1994-05-03 | E. I. Du Pont De Nemours And Company | Controlled-porosity, calendered spunbonded/melt blown laminates |
| US5863639A (en) * | 1995-09-13 | 1999-01-26 | E. I. Du Pont De Nemours And Company | Nonwoven sheet products made from plexifilamentary film fibril webs |
-
1997
- 1997-04-10 JP JP09538113A patent/JP2000510198A/en not_active Ceased
- 1997-04-10 ES ES97920249T patent/ES2163758T3/en not_active Expired - Lifetime
- 1997-04-10 WO PCT/US1997/005859 patent/WO1997040224A1/en not_active Application Discontinuation
- 1997-04-10 EP EP97920249A patent/EP0895551B1/en not_active Expired - Lifetime
- 1997-04-10 DE DE69706973T patent/DE69706973T2/en not_active Expired - Lifetime
- 1997-04-10 CA CA002249569A patent/CA2249569A1/en not_active Abandoned
- 1997-04-10 KR KR1019980708464A patent/KR20000010588A/en not_active Application Discontinuation
-
1998
- 1998-07-22 US US09/120,482 patent/US5972147A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JP2000510198A (en) | 2000-08-08 |
| EP0895551B1 (en) | 2001-09-26 |
| US5972147A (en) | 1999-10-26 |
| EP0895551A1 (en) | 1999-02-10 |
| DE69706973T2 (en) | 2002-04-04 |
| DE69706973D1 (en) | 2001-10-31 |
| WO1997040224A1 (en) | 1997-10-30 |
| KR20000010588A (en) | 2000-02-15 |
| ES2163758T3 (en) | 2002-02-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |