Wash durable fabric laminates

A delamination problem in fabric laminates made of a fabric laminated to a nonporous, hydrophilic organic polymer film, such as a breathable polyurethane film, was found to be caused by the hydrophilic nature of the polymer. A particular adhesive pattern was devised to overcome the delamination problem. More specifically, a wash-durable fabric laminate of a continuous, non-porous hydrophilic polymer, e.g., a breathable polyurethane, layer and a fabric layer were bonded together by a discontinuous, but interconnected pattern of an adhesive layer. The fabric laminate is water-vapor-permeable, air-impermeable and liquid water impermeable.

FIELD OF THE INVENTION 
This invention relates to laminates of a fabric material adhered by 
adhesive to a layer of a non-porous hydrophilic organic polymer. 
BACKGROUND OF THE INVENTION 
Hydrophilic non-porous organic polymers, such as polyurethanes, transport 
water vapor molecules through them by a molecular transport mechanism. 
Thus, these polymers "breathe", i.e., allow water vapor, as in 
perspiration, to pass through them even though they are not porous, i.e., 
do not contain voids running from one side to the other. Because they are 
non-porous, they are liquid water impervious and air-impermeable 
(windproof and contamination resistant). 
These qualities make them useful as continuous coatings on fabrics, such as 
cotton, wool, nylon, polyester or the like, that are used in garment 
constructions. Alternatively, continuous films of such "breathable" 
polymers are adhesively bonded to these fabrics to create fabric laminates 
useful in making clothing articles. These fabric laminates "breathe" 
thereby keeping the wearer comfortable while providing protection from the 
environment by keeping out rain, wind, snow, viruses, particulates, etc. 
It is well known in the art that breathable fabric laminates are created by 
bonding a continuous film of a hydrophilic polymer to a fabric substrate 
by using a hydrophobic adhesive deposited in a discontinuous, 
non-interconnected pattern. U.S. Pat. No. 4,935,287 to Johnson and U.S. 
Pat. No. 4,761,324 to Rautenberg, for example, describe such lamination 
methods. 
It is a common practice to use engraved gravure rolls to deposit such 
discontinuous, non-interconnected adhesive patterns on a substrate. 
Details of such patterns can be found in standard books like "Modern 
Coating and Drying Technology", p. 103, E. D. Cohen and E. B. Gutoff 
(editors), VCH Publishers, Inc., New York, 1992 and "Handbook of Pressure 
Sensitive Adhesive Technology", p. 789, D. Satas (editor), Van Nostrand 
Reinhold, New York, 1989, as well as in U.S. Pat. No. 4,761,324 by 
Rautenberg. However, no reference was found directed to the use of 
engraved gravure rolls to deposit discontinuous, but interconnected 
adhesive pattern to laminate a hydrophilic polymer film to a fabric layer 
to create a breathable fabric laminate. 
A problem with these breathable fabric laminates is their poor durability 
during washing. Owing to the hydrophilic nature of the breathable polymer 
film, it is difficult to get the film to remain bonded to the fabric 
during continuous washing. This is a serious deficiency in these laminates 
as these are used to construct garments that are subjected to laundering. 
SUMMARY OF THE INVENTION 
This low wash durability has now been found to be due to the hydrophilic 
nature of the non-porous hydrophilic polymer layer. During washing the 
wash water is absorbed to some extent by the polymer causing it to swell, 
deform and thereby create stresses which adversely affect laminate 
adhesion. It is a first aspect of this invention that this delamination 
problem was found to be caused by the hydrophilic nature of the polymer, 
which property is the very property making the polymer useful with 
fabrics. 
It was also observed that the thicker the hydrophilic polymer layer, the 
more severe the delamination problem during washing cycles. This is 
apparently due to the thicker bulk of the polymer, which absorbs 
increasing amounts of wash water and magnifies the effect of internal 
stresses during washing. 
It is a second aspect of this invention that once the cause of the problem 
was found, a particular adhesive pattern was devised to overcome the 
delamination problem. 
Accordingly, this invention includes a wash-durable fabric laminate 
comprising: 
(a) a continuous, non-porous layer of a hydrophilic polymer, e.g., a 
breathable polyurethane, layer; 
(b) a fabric layer; 
wherein the polymer layer is bonded to the fabric layer by a discontinuous, 
but interconnected pattern of an adhesive layer in between; 
said fabric laminate being water-vapor-permeable, air-impermeable and 
liquid water impermeable.

DETAILED DESCRIPTION OF THE INVENTION 
By the term "continuous" is meant that the hydrophilic polymer continuously 
covers the fabric surface. 
By the term "non-porous" is meant that there are no voids in the 
hydrophilic polymer extending from one side of the layer to the other. 
By the term "hydrophilic" is meant that the polymer has the ability to 
transport individual water molecules through it by molecular diffusion. 
Polymers exhibiting this phenomena are referred to sometimes as 
"breathable" polymers. In polyurethanes, such polymers have repeating 
ethylene oxide units in them (--CH.sub.2 --CH.sub.2 --O--). 
The discontinuous, but interconnected adhesive pattern 20, is depicted by 
the grid configuration of adhesive 21 shown in FIG. 2. It is discontinuous 
because it does not completely cover a surface. But, as seen, the 
configuration is interconnected. In contrast the prior art configuration 
10 of FIG. 1 shows the adhesive 11 in a "dot" configuration where the 
adhesive pattern is discontinuous but not interconnected. It is understood 
that the "dots" can be elongated to the point where they "join" and in 
that event the grid pattern of FIG. 2 will be obtained. Therefore, this 
invention includes such intermediate configurations of adhesive. At what 
point these intermediate configurations become a part of this invention 
can easily be determined by the wash-cycle durability test described 
following. 
Wash durability is determined by continuously washing a piece of laminated 
fabric/hydrophilic polymer in an automatic washing machine (AATCC approved 
Kenmore washer) using ambient tap water and visually noting the time it 
takes for the laminate to develop a delaminated area that is 0.5 inches or 
more in width. 
Determination of the Cause of the Problem 
To determine why lamination failure was occurring in laminates in which the 
layers were adhesively bonded by an adhesive applied in a "dot" 
configuration using engraved gravure rolls that deposited a discrete dot 
pattern as shown in FIG. 1. Two gravure patterns were used, but both 
delivered the FIG. 1 adhesive dot pattern. The difference was that one 
gravure pattern has 35 pyramidal cells per inch at a cell depth of 130 
micrometers, while the other pattern had 35 pyramidal cells per inch with 
a cell depth of 160 micrometers. Owing to its increased depth, the 160 
.mu.m pattern deposited about 7-9 gm/yd.sup.2 adhesive while the 130 .mu.m 
pattern deposited 3-4 gm/yd.sup.2. The breathable polymer films used were 
of different thicknesses obtained by extrusion casting of a thermoplastic 
polyurethane polymer made from diphenylmethane diissocyanate, 
polyoxyethylene glycol 1450 and 1,4-butanediol in a mole ratio of 4:1:3. 
These films constituted the continuous, non-porous, hydrophilic polymer 
layer. 
Specifically, the adhesive used was a prepolymer of diphenylmethane 
dissocyanate, polytetramethylene ether glycol 1000, and pentanediol. 
Adhesives of this type are described more fully in U.S. Pat. No. 4,532,316 
to Henn, incorporated herein by reference. These adhesives do not transmit 
any appreciable amount of moisture vapor through them and are considered 
hydrophobic. 
The laminates were prepared by preheating the adhesive to 105.degree. C. 
and applying it to the hydrophilic polyurethane film in a "dot" pattern 
using a gravure roll heated at 105.degree. C. A textile fabric, 
specifically a woven nylon (2.8 oz./yd..sup.2 supplex Taslite.RTM.) 
fabric, was then applied by feeding it along a moving belt of the adhesive 
printed film and pressing the fabric between two rolls maintained at 
40.degree. C. The same method was used to create laminates using other 
fabrics like 1.5 oz./yd..sup.2 nylon Tricot knitted fabric and 5.3 
oz./yd..sup.2 (83% nylon/17% Lycra.RTM.) knitted fabric. 
Fabric laminates prepared as described immediately above were tested for 
wash durability as described above. Results were as follows: 
______________________________________ 
Gravure** 
Breathable 
Cell Polyurethane Wash Hours 
Depth Film Fabric Avg. before 
(.mu.m) 
Thickness Type MVTR Delamination 
______________________________________ 
130 2 mil Woven Taslite 
-- 1.5 
160 2 mil Woven Taslite 
-- 24 
160 0.5 mil Woven Taslite 
-- 1300 
160 2 mil Woven Taslite 
5202 101-300 
160 0.5 mil Woven Taslite 
9860 &gt;2171 
160 2 mil Tricot Knit 
4837 48 
160 1 mil Tricot Knit 
5925 302* 
160 0.5 mil Tricot Knit 
9813 701 
160 2 mil Lycra .RTM. Knit 
4351 96 
160 1 mil Lycra .RTM. Knit 
5682 326 
160 0.5 mil Lycra .RTM. Knit 
8291 801 
______________________________________ 
*Stopped due to disintegration of the Tricot Knit. 
**Gravure pattern consists of 35 pyramidal cells per linear inch. 
These data confirmed that everything else being equal, wash durability of 
the laminate depends on the film thickness of the breathable polymer with 
the durability decreasing as the thickness increases. This is believed to 
be a result of the hydrophilic nature of the film. Unlike conventional 
polyurethane films that are not hydrophilic, these films swell in contact 
with water which in turn creates stresses on the discrete adhesive dots 
leading to delamination during continuous washing. As thickness increases, 
the magnitude of these stresses also increases which in turn leads to 
earlier delamination or reduced wash durability. The data also confirmed 
that the 160 .mu.m deep pattern gives better wash durability than the 130 
.mu.m deep pattern due to higher amounts of adhesive printed onto the 
film. 
MVTR is Moisture Vapor Transmission Rate and records the degree to which 
the initial sample (i.e. before washing) transmits water vapor. 
MVTR was Determined as Follows 
A potassium acetate solution, having a paste like consistency, was prepared 
from potassium acetate and distilled water. (Such a paste may be obtained 
by combining 230 g potassium acetate with 100 g of water, for example). 
This solution was placed into a 133 ml. polypropylene cup, having inside 
diameter of 6.5 cm. at its mouth. An expanded polytetrafluoroethylene 
(ePTFE) membrane was provided having a minimum MVTR of approximately 
85,000 g/m.sup.2 -24 hr. as tested by the method described in U.S. Pat. 
No. 4,862,730 to Crosby. The ePTFE was heat sealed to the lip of the cup 
to create a taut, leakproof, microporous barrier containing the solution. 
A similar ePTFE membrane was mounted to the surface of a water bath. The 
water bath assembly was controlled at 23.degree. C..+-.0.2.degree. C. 
utilizing a temperature controlled room and a water circulating bath. 
Prior to performing the MVTR test procedure, a sample to be tested was 
allowed to condition at a temperature of 23.degree. C. and a relative 
humidity of 50%. The sample to be tested was placed directly on the ePTFE 
membrane mounted to the surface of the water bath and allowed to 
equilibrate for 15 minutes prior to the introduction of the cup assembly. 
The cup assembly was weighed to the nearest 1/1000 g and was placed in an 
inverted manner onto the center of the test sample. 
Water transport was provided by a driving force defined by the difference 
in relative humidity existing between the water in the water bath and the 
saturated salt solution of the inverted cup assembly. The sample was 
tested for 10 minutes and the cup assembly was then removed and weighed 
again within 1/1000 g. 
The MVTR of the sample was calculated from the weight gain of the cup 
assembly and was expressed in grams of water per square meter of sample 
surface area per 24 hours. Five areas within a sample were tested and the 
average value is reported here. 
Overcoming the Problem 
After understanding the failure mechanism of the 2 mil laminates during 
washing, a pattern of adhesive that is still discontinuous (for 
breathability) but interconnected (vs. discrete as in the dots above) was 
used. This pattern is anticipated to distribute the stresses that lead to 
delamination. Experiments were conducted with a gravure roll engraved in a 
grid pattern as shown in FIG. 2. In addition to printing the adhesive in a 
grid pattern, the roll also deposited more adhesive (16-18 g/yd.sup.2). 
The results are as follows: 
______________________________________ 
Breathable 
Type of 
Polyurethane Wash Hours 
Gravure 
Film Fabric Avg. before 
Pattern 
Thickness Type MVTR Delamination 
______________________________________ 
GRID 2 mil Woven Taslite 
2436 &gt;1717 hours 
GRID 0.5 mil Woven Taslite 
4160 &gt;1717 hours 
GRID 2 mil Tricot Knit 
2193 111 hours 
GRID 2 mil Lycra .RTM. Knit 
2673 &gt;2151 hours 
______________________________________ 
The test was halted at the number of hours listed. No delamination had 
occurred. 
The data indicate an order of magniture increase in wash durability by the 
use of this gravure pattern. Note that this significant improvement in 
wash durability is most likely due to the discontinuous, interconnected 
pattern of adhesive which allows more uniform distribution of the stresses 
created by the swelling of the hydrophilic polymer film. Even though the 
grid pattern has been used here to demonstrate the concept, any other 
adhesive pattern that meets this requirement of being discontinuous and 
interconnected is expected to provide similar improvement in wash 
durability. 
Examples of nonporous hydrophilic films include various polyurethane 
polymers with ethylene oxide units, as well as, polyetheresters, such as 
are available under Sympatex.RTM. and Hytrel.RTM. trademarks and 
polyetheresteramides available under Pebax.RTM. trademark, and the like. 
Suitable fabrics include ones made from cotton, wool, polyamide, polyester, 
or the like or blends of these materials. These fabrics may be woven, 
non-woven, knit, or the like. 
The foregoing data was obtained on adhesively bonded laminates of a 
hydrophilic polymer film and a fabric substrate. Once such a wash durable 
laminate is formed using the novel adhesive pattern; the same lamination 
method can be repeated to attach another fabric layer to the other side of 
the polymer film to create a tri-laminate.