Microporous waterproof and moisture vapor permeable structures, processes of manufacture and useful articles thereof

Microporous waterproof and moisture vapor permeable products are described which are formed from a matrix having an internal microstructure which is coated with a hydrophobic material. A process is described including the steps of (1) applying to the surface of the matrix a liquid hydrophobic material, (2) allowing the liquid to penetrate into the microstructure and then (3) drying, vulcanizing or curing the product.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improved microporous waterproof and moisture 
vapor permeable structures, and more particularly it relates to such 
structures which primarily comprise known microporous 
polytetrafluoroethylene (PTFE) or microporous interpenetrating matrices of 
PTFE and polydiorganosiloxane, and which have been treated in accordance 
with the process of this invention with either a curable or a non-curable 
hydrophobic silicone composition, or mixtures thereof, to produce 
microporous waterproof and moisture vapor permeable structures having 
improved physical characteristics and having resistance to surfactant 
activity. 
2. Background Information 
In U.S. Pat. No. 4,187,390 to Gore, there is disclosed a process of 
producing microporous PTFE membranes which are waterproof yet moisture 
vapor permeable. Such membranes are characterized by a microstructure 
consisting of nodes interconnected by fibrils. 
In our copending application (Ser. No. 000,389 filed Jan. 5, 1987, U.S. 
Pat. No. 4,945,125, the disclosure of which is hereby incorporated by 
reference) there is disclosed a process of producing a fibrillated (having 
nodes interconnected by fibrils) semi-interpenetrating polymer network 
(SIN) of PTFE and silicone, and shaped products thereof. 
In the production of microporous PTFE membranes according to the Gore 
('390) process, or the production of microporous PTFE/silicone SIN 
membranes according to our ('389) process, linearly oriented extrudate of 
a biaxial fibrillation process is further biaxially oriented by use of 
equipment such as tenter frames or the like. The microporous membranes 
thus produced are then normally heated to above 327.degree. C. and 
subsequently cooled to effect sintering of the PTFE, the resulting films 
having waterproof and moisture vapor permeable characteristics. 
In U.S. Pat. No. 3,325,434 to Tully, there is disclosed an extrudable PTFE 
composition containing 0.6% to 12.5% by weight of uncured silicone rubber, 
said silicone principally serving to fill the voids created as the organic 
processing aid is volatilized after wire extrusion, thereby rendering a 
structure which has outstanding electrical properties. 
In U.S. Pat. No. 4,194,041 to Gore, there is disclosed a layered article 
comprising a microporous membrane of PTFE having one surface in contact 
with a layer of hydrophilic materials so as to maintain moisture vapor 
diffusion while preventing contamination of the PTFE membrane from 
surfactants or the like. Articles produced according to this process have 
been found to have substantially less moisture vapor permeability in 
comparison to conventional microporous PTFE membranes. 
In U.S. Pat. No. 4,613,544 to Burleigh, there is disclosed a unitary sheet 
of microporous polymeric matrix having continuous pores, said pores being 
sufficiently filled with a hydrophilic material so that moisture vapor is 
enabled to permeate the structure only by molecular diffusion. 
In U.S. Pat. No. 4,500,688 to Arkles there is disclosed a melt processable 
pseudo-interpenetrating polymer network of silicone in thermoplastic 
matrices. 
In U.S. Pat. No. 4,764,560 to Mitchell there is disclosed polymeric 
structures having interpenetrating matrices in cured form, comprising a 
PTFE network and a polydiorganosiloxane network. 
The disclosures of each of the foregoing patents are incorporated herein by 
reference. 
SUMMARY OF THE INVENTION 
We have unexpectedly discovered that both substrates formed of microporous 
PTFE and those formed of microporous PTFE/silicone interpenetrating 
matrices having improved resistance to surfactant activity, such as 
conventional laundering, are produced by the process of applying to said 
substrates an effective amount of either a curable or non-curable 
hydrophobic silicone composition, or mixtures thereof, wherein the 
silicone composition at least partially penetrates into the pores of the 
microstructure, thereby coating nodes and fibriles. Upon vulcanization, 
curing or drying of the silicone composition, the treated substrates have 
been found to have superior resistance to contamination by surfactants 
while maintaining waterproofness and a substantially unchanged rate of 
moisture vapor permeability in comparison to conventional microporous PTFE 
membranes.

DETAILED DESCRIPTION OF THE SEVERAL EMBODIMENTS 
The several embodiments of this invention are shown in the following 
illustrative examples. 
EXAMPLE 1 
The following ingredients are mixed to form a curable silicone composition: 
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Parts by 
Weight 
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Vinyl N-stopped polydimethylisiloxane 
68.2 
(3500 cps at 25.degree. C.) 
MDQ silicone resin blend 
22.7 
Dimethyl vinylsiloxane resin blend 
8.2 
bis(trimethoxysilylpropyl) maleate 
0.9 
Lamoreaux platinum catalyst 
10 ppm 
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This silicone composition was supplied by General Electric Company as a two 
part system consisting of the polydimethylsiloxane, MDQ, and catalyst 
components as part (A) and Dimethyl vinylsiloxane, and 
trimethoxysilylpropyl components as part (B). The two part system was then 
mixed in a high sheer blender at a ratio of 10 parts (A) to 1 part (B), as 
taught by the manufacturer to affect the above proportions by weight. 
This curable silicone composition was then blended using a liquid-solids 
blender as follows: 
2955.5 grams of dispersion grade Fluon.RTM. CD123 PTFE resin 
222.5 grams curable silicone composition 
580.3 grams of kerosene 
The resultant blend was compacted into a preform, biaxially extruded 
through a die, linearly stretched 84 percent, transversely stretched 1278 
percent in a tenter frame, and sintered at above 327.degree. C. according 
to the process described in our co-pending application ('389). 
Five pieces of the resultant microporous film were then affixed to a flat 
21".times.20" chrome plated surface by means of adhesive applied around 
the perimeter of the material. Each piece was surface coated by spraying 
continuously for 15 seconds through a pressure atomizer with various 
kerosene mixtures of the hydrophobic curable silicone composition set 
forth above (2.5, 5.0, 10.0, 15.0 and 20.0 percent by weight silicone), 
whereupon each mixture spontaneously wicked into the microporous 
structure. The treated samples where then placed in an external exhaust 
oven and heated to 150.degree. C. for 15 minutes to evaporate the solvent 
and cure the silicone elastomer. The scanning electron micrograph of FIG. 
2 when compared with that of FIG. 1 shows that the nodes and fibrils of 
the internal microstructure of a conventional microporous PTFE membrane 
are partially masked with a surface coating of hydrophobic silicone 
composition leaving porous interstices. Table 1 shows the surprising 
effect on the physical characteristics of the original hydrophobic 
microporous film by coating the microstructure with the hydrophobic 
curable silicone elastomer. 
EXAMPLE 2 
Several samples of conventional microporous PTFE film were laminated to a 
woven fabric by conventional adhesive-dot bonding techniques. The curable 
silicone composition used in Example 1 was diluted to 11 weight percent 
silicone using kerosene, and the liquid applied to the film side of the 
laminate, whereupon it spontaneously wicked into the microporous film. The 
treated material was then placed in an external exhaust oven and heated to 
150.degree. C. for 15 minutes to affect curing of the hydrophobic silicone 
composition and volatilization of the diluent. After cooling, the dried 
material was determined to have 2.91 mg of silicone per square centimeter 
of substrate. The treated sample was then washed according to American 
National Standard laundry method AATCC 135-1987, and found to have passed 
the test by maintaining hydrostatic resistance of 50 psi after five cycles 
of washing. Untreated samples have consistently failed the above 
identified test procedure by having a hydrostatic resistance of less than 
25 psi. 
EXAMPLE 3 
A hydrophobic non-crosslinkable (non-curable) liquid silicone composition 
(62 percent mineral spirits) supplied by Dow Corning under the product 
code C2-0563 was applied to the film side of a piece of the PTFE/fabric 
laminate of Example 2, whereupon the liquid composition spontaneously 
wicked into the microporous film, and the resultant product was allowed to 
thoroughly dry overnight before further analysis. The dried material was 
determined to have 2.71 mg of silicone per square centimeter of substrate. 
After washing in accordance with AATCC 135-1987, the sample was found to 
have maintained a hydrostatic resistance of 63 psi after five cycles of 
washing, thereby passing the test. 
EXAMPLE 4 
The curable silicone composition of Example 1, and the non-curable 
silicone of Example 3 were mixed with mineral spirits in the following 
proportions: 
100 parts Curable Silicone Composition 
261.99 parts Dow Corning C2-0563 
1,638,01 parts Mineral Spirits 
The above proportions were chosen to affect an approximately half 
curable/half non-curable silicone mix in 90 weight percent mineral 
spirits. A piece of laminated substrate as in Examples 2 and 3 was 
similarly treated with the hydrophobic mixture and then placed in an 
external exhaust oven and heated to 150.degree. C. for 15 minutes to 
affect crosslinking of the curable silicone composition and evaporation of 
the volatile components in situ. The sample was determined to have 1.19 mg 
of silicone per square centimeter of material and was found to pass AATCC 
test method 135-1987 with a hydrostatic resistance of 56 psi. 
It is seen from Example 1 and Table 1 that a treated substrate was produced 
comprising a microporous polytetrafluoroethylene/silicone interpenetrating 
polymer network comprising a matrix in which the internal microstructure 
of nodes and fibrils is at least partially coated with a hydrophobic cured 
silicone composition. Increasing weight amounts of applied silicone 
compositions affected increased hydrostatic resistance while maintaining 
moisture vapor permeability. Optical opacity of the microporous film is 
decreased in direct proportion to the increase in the amount of cured 
silicone composition applied. 
In Example 2 the treated substrate comprised conventional PTFE film which 
had been laminated to a breathable and non-water resistant fabric. This 
laminate was rendered resistant to the effects of laundering by forming a 
hydrophobic cured silicone composition around the PTFE microstructure of 
nodes and fibrils. 
The benefits of the process of this invention are also observed from 
Example 3 where a treated substrate was produced which comprised a 
microporous PTFE membrane having a microstructure of nodes and fibrils 
which are at least partially coated with a hydrophobic non-curable 
silicone composition, the substrate being one layer of a laminate with a 
breathable and non-water resistant fabric. The resultant laminated fabric 
had increased resistance to surfactant activity. 
In Example 4, it is shown that curable and noncurable silicone compositions 
may be blended to produce an effective hydrophobic coating formed in situ 
within the microstructure of nodes and fibrils of microporous PTFE 
laminated to a breathable and nonwater resistant fabric, the coating 
effectively increasing the resistance to surfactant activity of the 
laminate. 
Definitions 
The TAPPI opacity value is a quantification of optical opacity expressed in 
percentage form. Optical transparency is the mathematical compliment of 
opacity, and can be expressed by the equation: 
EQU % Transparency=100-% Opacity 
Moisture vapor transmission (ASTM E96, Method B-upright) is a measurement 
of the moisture vapor permeability rate for a given material, and is 
expressed in the form of mass per area per unit time. Hydrostatic 
resistance is a measure of waterproofness (MIL SPEC 5512, Federal Standard 
191) and is expressed as a pressure. Gurley number (ASTM D726-58 Method A) 
is a measurement of the air permeability of a material. The value is the 
amount of time in seconds that it takes a given volume of air to flow 
through a given area of material at a set pressure differential. The lower 
the Gurley number, the higher the air flow rate. 
TABLE 1 
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Moisture 
Amount (1) Hydrostatic 
Vapor TAPPI 
Gurley 
% Solution 
Deposited 
Thickness 
Density 
Resistance 
Transmission 
Opacity 
Number 
Sample # 
Sprayed 
(mg/cm.sup.2) 
(mil) (g/cc) 
(psi) (g/m.sup.2 /24 hrs) 
(%) (seconds) 
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ORIGINAL 
-- -- 1.3 0.33 77 701 73.8 6 
1 2.5 0.11 0.5 0.95 82 736 49.0 44 
2 5 0.26 0.5 1.07 82 755 50.1 64 
3 10 0.33 0.4 1.13 84 764 36.7 90 
4 15 0.38 0.5 1.17 91 720 35.3 116 
5 20 0.70 0.6 1.18 125 638 16.8 1128 
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(1) Net amount of silicone elastomer