Waterproof and moisture-conducting fabric coated with hydrophilic polymer

A waterproof and moisture-conducting fabric comprising a base permeable to water vapor and sealed with a closed coating of a hydrophilic polymer. The sealing coating is advantageously a compressed foam of an acrylic resin modified with polyvinyl chloride or polyurethane. A second base may be laminated onto the sealing layer. Protective fillers such as lead compounds and carbon may be included in or on the coating. The fabric is suited for protective clothing articles such as rescue-at-sea garments and shoe uppers, and sleeping bags.

The invention is a waterproof and moisture-conducting fabric. 
The most effective way of getting rid of excess human-body heat is the 
evaporation of water. This normally occurs in the skin, which keeps it 
dry. This mechanism, however, can function only when the resulting water 
vapor can be eliminated. Clothing can be comfortable, therefore, only when 
it allows water vapor to permeate through it from the skin. Usually this 
is accompanied by a more or less high level of air permeability. This has 
led to the basically erroneous concept that the skin "breathes." Actually 
the skin does not breath, but only releases moisture. 
There are conditions in which it is demanded that a fabric not only allow 
water vapor to permeate but also be satisfactorily waterproof and 
airtight. Such fabrics are employed for protective garments like 
antiweather, occupational, and military safety clothing and for 
recreational clothing and equipment like parkas, tents, and sleeping bags. 
Attempts have been made to remove water vapor from the skin by introducing 
hydrophilic bodies, based on starch for example, that swell up with water 
into coatings that do not permit water vapor to permeate. The most 
significant result however was to diminish the mechanical properties of 
the coating. It has also been attempted to laminate fabrics to a 
microporous film, of polytetrafluorethylene for example. Such products, 
however, also have drawbacks as well as being complicated and extremely 
expensive to manufacture. 
The present invention is intended as a fabric that is not only waterproof 
and airtight but that also stores a significant amount of moisture, 
conducts it, and releases it from both sides in the form of water vapor. 
It is desirable for a fabric to store moisture in this manner because, 
since the body does not perspire at a rate that is constant over time, 
clothing must be able to deal like a "buffer" with a temporary surplus 
production of moisture that can not be rapidly enough expelled. It is also 
important to combine this buffer effect, which contributes so much to 
comfort, with moisture transport in a way that will not adversely affect 
the mechanical properties of the fabric. It should also be possible, for 
special purposes, to accompany all these properties with the specific 
ability to protect the wearer against aggressive chemicals, bacteria, or 
radiation, etc. 
The invention achieves these objectives because it is a waterproof and 
moisture-conducting fabric consisting of a base that allows water vapor to 
permeate and that is sealed with a closed layer of a hydrophilic polymer. 
The sealing layer is in particular a layer of foam that can subsequently be 
compressed. The application and subsequent compression of layers of foam 
are conventional in the fabric industry. Another possibility is the 
application of a coating of foam followed by the application of another 
layer and of a layer of paste, solution, dispersion, or melt. 
The base of the fabric may be a woven or knit or even a felt or nonwoven 
fabric. It may be composed of natural fibers like cotton, wool, or silk, 
of synthetic fibers based on polyesters, polyamides, polyacrylonitrile, 
polyurethanes, polyolefins, polyvinyl chloride, or aramides, or even of 
mineral fibers like glass or carbon fibers. Whether the base itself is 
hydrophobic or hydrophilic is not decisive. It must, however, be permeable 
to water vapor. The hydrophilicity of the fibers themselves may also 
contribute to permeability when the fabric is very dense and only slightly 
permeable to air, whereas a hydrophobic base should be open enough to 
permit enough water vapor to permeate. 
A base that is permeable to water vapor can be sealed as desired by the 
application of a closed layer of hydrophilic polymer. Appropriate 
hydrophilic polyers are known or can be prepared or compounded by fabric 
chemists from conventional components. The properties of absorbing water 
vapor at points of high partial pressure, effecting its migration within 
the layer in the form of water molecules to points of low partial 
pressure, and releasing it in the form of water vapor again at the surface 
of the fabric can be obtained by introducing enough hydrophilic groups, 
especially hydroxyl-ether-amine or carboxyl groups. These hydrophilic 
groups can be produced, on the bases of the copolymerization or 
cocondensation of monomers that effect chain formation or cross-linkage, 
with hydrophilic monomers. It is also possible to prepare polymerization 
with very high water-absorption capabilities together with polymers that, 
although they contribute other desirable properties, are themselves not, 
or only slightly, hydrophilic. 
Hydroxyalkylacrylates and the acrylic or methacrylic esters of polyalkylene 
oxides or polyalkylenimides are examples of monomers with hydrophilic 
groups. Acrylic- or methacrylic-acid derivatives of this type can 
subsequently be copolymerized with the acrylic or methacrylic ester that 
forms the basic polymerizate and with cross-linking monomers. Dispersions 
of hydrophilic resins of this type are known, from German OS No. 2 749 386 
for example. The commercially available Plextrol 4871D, manufactured by 
the firm of Rohm, as well as modified vinyl-alcohol resins or regenerated 
cellulose are also practical for a moisture-conducting sealing layer. 
Copolymerizates of vinyl chloride and vinyl acetate in which the acetate 
groups have been hydrolyzed into OH groups or polyurethanes with excess OH 
or NH and NH.sub.2 groups are also appropriate. It is also possible, in 
the same way that the hydrophilic monomers themselves are copolymerized, 
to blend dispersions obtained from them with dispersions that have 
properties that are desirable for other reasons. Polyurethanes, for 
example, have very satisfactory mechanical properties, while polyvinyl 
chloride improves flame resistance. A polyvinyl chloride with built-in 
monomers that have powerfully hydrophilic groups can also be employed. The 
desired properties can also be introduced into polyurethanes by using 
starting materials that have enough hydrophilic groups, especially ether 
or imine groups. 
It is easy to test a coating to determine whether its moisture absorption 
and conduction are as satisfactory as those claimed for the invention. 
Layers in accordance with the invention will in practical terms store 200 
to 400% of their weight in moisture and allow at least 500 g/m.sup.2 /24 
hours of water vapor to permeate through them in accordance with DIN 53 
122. 
As long as these results are confirmed, the coating may also contain such 
conventional additives as dyes, adhesion enhancers, antioxidants, 
antistatics, pigments, thermal stability agents, fillers, etc. 
The coating is usually applied in the form of 5-500 g/m.sup.2 in terms of 
the dry weight of a dispersion or foam (which can subsequently be 
compressed). When it is necessary for the coating to be airtight as well 
and a thick fabric, especially a woven fabric, that is only slightly 
air-permeable is accordingly employed as a base, a dry layer weighing more 
than 50 g/m.sup.2 is recommended. For many purposes, especially in 
conjunction with a base that is not very thick or air-permeable, a very 
light coating of a hydrophilic polymer that is still air-permeable is very 
practical. Such thin coatings can be obtained by abrading away a dry layer 
of 5-50, and especially 10-30, g/cm.sup.2. Such a waterproof but still 
more or less air-permeable and in any event moisture-conducting fabric has 
for example been demonstrated to be very satisfactory for permeable, 
meaning active-breathing, ABC-protection suits, which usually contain an 
outer coating and, underneath it, a filter layer that absorbs gaseous but 
not liquid chemical-warfare agents. One function of the outer coating is 
accordingly to keep liquid agents away from the filter layer. Oleophobic 
finishes are used for this purpose. Drops of a chemical agent, like those 
deriving from an aerosol or spray for example, that fall from greater 
heights may have enough kinetic energy to penetrate the outer coating and 
soak the filter layer. This will result in penetration of the locally 
overstressed filter layer. It has however been demonstrated that even the 
thin layer of hydrophilic polymers in question, which, although it 
slightly decreases the air-permeability of the fabric, does allow water 
vapor to permeate, will impede the penetration of the drops of chemical 
agent without significantly affecting the wearing properties of the 
protective clothing. 
The vapor-permeable coating is also practical as a binder for laminating 
fabrics when another layer of vapor-permeable textile is applied to the 
coating of hydrophilic polymers. This results in a double-layered 
material, the outside of which can if desired be additionally hydrophobed. 
A sealing layer of hydrophilic polymer can be applied not only to one side 
but also to both sides of the base of the invention. 
Substances with specific protective properties--lead sulfate against 
radiation, activated carbon against chemical-warfare agents, and 
antimony(III) oxide or halogenated aromatic compounds for flame 
resistance, for example--can be introduced into the coating. These or 
other substances with specific protective properties can also be applied 
to the coating, which will simultaneously function as a binder for them: 
A porous hydrophobing of the outer surface of the material that will not 
affect vapor permeability is also recommended for later use with respect 
to the base itself, to a laminated material, or to the sealing layer. 
Whereas the water-repellent action of hydrophobing does not last very long 
because from a microscopic standpoint it is applied in points or clusters, 
the water uptake of the sealing layer in the invention makes the layer 
swell up, augmenting its sealing action. This is a particular advantage 
when impermeability is essential, in rescue-at-sea suits for aviators for 
instance, which must be comfortable when worn under normal circumstances 
but waterproof in emergencies to protect aviators from the incursion of 
water and hence hypothermia for a certain length of time when they have to 
parachute over frigid seas. This is one of the applications for which the 
waterproof, moisture-conducting fabric in accordance with the invention is 
especially appropriate. Other examples are protective clothing for various 
fields like ABC warfare, civil defence, and atomic power plants. The 
vapor-permeable coating can block the penetration of water, dust, and gas. 
The polyurethane, when emloyed, may be applied as a dispersion or other 
liquid form, e.g. a melt of 100% binder. 
The vapor-permeable double-layer materials in accordance with the invention 
and described above are appropriate for high-quality and comfortable 
rainwear, sleeping bags, sportswear, shoe uppers, etc.

In the drawing 1 is a support base fabric, 2' is an acrylate foam layer, 2 
is the acrylate layer after compression and setting, i.e. condensation, 3 
is solid particles of filler in the foam, and 4 is solid particles of 
filler applied on top of the still-wet foam 2. 
In FIG. 5, 6 is a layer of bonding agent, 7 is an acrylate dispersion and 8 
is another textile fabric. 
The invention will be further described in the following illustrative 
examples: 
EXAMPLE 1 
A cotton twill 1 (FIG. 1) weighing 140 g/m.sup.2 is coated with an acrylate 
foam 2 weighing 300 g/l and manufactured by Rohm GmbH (Test Code 
65/33/15). The dried coating weighs 35 g/m.sup.2. The dry foam is 
compressed and recondensed (FIG. 2). The water column in a DIN 35 886 test 
is more than 100 mm high and water-vapor permeability as demonstrated by a 
DIN 53 122 test greater than 1000 g/m.sup.2 /24 hours. 
EXAMPLE 2 
The process in Example 1 is followed except that the dried coating weighs 
300 g/m.sup.2 and contains 50% by weight of finely ground lead sulfate 3 
(FIG. 3). This fabric is especially effective for protection against 
radiation. 
EXAMPLE 3 
The process in Example 1 is followed except that finely ground activated 
carbon 4 (FIG. 4) is scattered over and forced into wet acrylate foam 2, 
which is then dried and condensed. This waterproof and moisture-conducting 
fabric is effective for protection against chemical-warfare agents. 
EXAMPLE 4 
A coated textile 1, 2 (FIG. 5) is produced by the process specified in FIG. 
1. An acrylate dispersion 7 with a dry weight of 10 g/m.sup.2 is 
subsequently applied to its coated side 6. Another textile 8 is then 
laminated on. The fabric is condensed out and hot calendered. This double 
fabric allows 1000 g/m.sup.2 /24 hours of vapor to permeate and is 
especially effective when hydrophobed for protection against rain. It is a 
good sportswear fabric. 
EXAMPLE 5 
A cotton twill is coated as in Example 1 except that a dispersion of 
self-crosslinking polyvinyl alcohol extended with 40% of a dispersion of 
soft polyurethane is employed. Although the vapor permeability of this 
fabric is slightly lower than that of the fabric in Example 1, it is much 
higher than that of any known product. 
It will be understood that the specification and examples are illustrative 
but not limitative of the present invention and that other embodiments 
within the spirit and scope of the invention will suggest themselves to 
those skilled in the art.