US3510344A - Vapour permeable sheet materials - Google Patents

Description

May 5, 1970 DUNDERDALE 4 VAPQURPERMEABLE simm- MATERIALS med June 23, 1967 T HIGH MODULUS LOW MODULUS REGION REGION v 2 5 p 2 2 FIG. 2 /i COATING FIG. 4

MODULUS (Kq/cm LAYER Z l E I D IC l B IA COATING THICKNESS (THOU INCH) NON WOVEN FABRJC/ COATING COATING INTERFACE SURFACE j/vVflv/ae United States Patent Otficc 3,510,344 Patented May 5, 1970 3,510,344 VAPOUR PERMEABLE SHEET MATERIALS Keith Frederick Dunderdale, Harrogate, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain 7 Filed June 23, 1967, Ser. No. 648,270 Claims priority, application Great Britain, July 11, 1966, 30,976/ 66 Int. Cl. D04h 1/48; D06n 3/08; B32h 27/40 US. Cl. 117-76 4 Claims ABSTRACT OF THE DISCLOSURE A Water-vapour permeable poromeric material having a fibrous base and a polymeric coating which has a modulus which varies through its thickness, is made by a method in which several coating layers of different moduli are built up on the fibrous base and then the coating is rendered microporous.

The present invention relates to water vapour permeable sheet materials particularly suitable for use in the manufacture of upholstery products and shoe uppers.

It is known that useful breathable (water vapour permeable) sheet materials can be made by coating certain nonwoven fabrics comprising entangled fibres with a flexible layer of polymeric material having a microporous open-cell structure. The more durable grades of these sheet materials are made with a relatively dense, yet porous, fibre-interlocked fabric, the fibre-interlocking being accomplished by needle-punching, hot-pressing and/or by incorporating a porous polymeric binder. Unfortunately, the nonwoven fabrics of this type which provide the best combination of durability and water vapour permeability, when coated with the microporous layer at optimum thickness, often do not provide the degree of surface smoothness desired in certain products, particularly when the material is stretched. For example, in smooth-finish products for shoe uppers and upholstery, the surface tends to appear rough in areas of the product applied under tension suflicient to stretch it. This occurs, for example, on the toe areas of shoes and along the edges of upholstered articles.

At least two techniques are known which can be used to substantially overcome the surface roughening of the polymeric coating on the nonwoven fabric when stretched. One such technique is to apply a polymeric coating of increased thickness to the nonwoven fabric, but it has been found that the thickness of the polymeric coating has to be increased to a point where other properties, such as leather-like handle, and flex and fold properties suffer. Another technique comprises incorporating a woven fabric in the sheet material between the nonwoven fabric and the polymeric coating, but this can result in a product having inadequate extensibility.

The object of the present invention is to provide a water vapour permeable sheet material which has an im proved surface smoothness when stretched, and which also has a leather-like handle and good flex and fold properties.

FIG. 1 shows an unstretched nonwoven fabric having regions of high and low modulus.

FIG. 2 shows a stretched nonwoven fabric having regions of high and low modulus.

FIG. 3 shows a stretched nonwoven fabric having regions of high and low modulus with a coating thereon.

FIG. 4 is a graph illustrating the modulus profiles of coatings on nonwoven fabric.

According to the present invention a water vapour permeable sheet material comprises a water vapour permeable nonwoven fabric comprising interlocked and entangled fibres, and a vapour permeable coating of flexible polymeric material in superposed adherence with the nonwoven fabric, said coating having a microporous structure and having a modulus that varies through its thickness in such a manner that, on moving through the thickness of the coating from the surface adjacent the fabric to the exposed surface of the coating, the modulus increases to a maximum and then decreases in value towards the exposed surface.

The nonwoven fabric may be formed Wholly or partly of synthetic fibres such as, for example, polyesters, polyolefines or polyamides. Part at least of the synthetic fibres may be shrinkable and increased consolidation of the fabric may be achieved by a shrinkage treatment. Polyethylene terephthalate fibres are suitable for such processes. Especially good results are obtained by using at least a proportion of fibres of high shrinkage/ high shrinkage force, i.e., the ability to shrink when under restraint. Fibres of such high shrinkage force may be prepared from polypropylene.

A preferred nonwoven fabric for use in the material of the present invention is in the form of a needle-punched batt of fibres containing at least 20% and less than 50% by weight of in situ retracted fibres, said batt having been shrunk by about 35% of its original planar area and impregnated with a resinous or elastomeric filling agent.

The present invention also includes a method for the production of a water-vapour permeable sheet material which comprises (a) applying to a water-vapour permeable nonwoven fabric comprising interlocked and entangled fibres, a coating of polymeric material and a filler in particle form in a liquid which is a solvent for the polymeric material and a nonsolvent for the filler, (b) removing substantially all the solvent fiom the coating and (c) rendering the coating microporous, the coating in step (a) being applied in the form of a plurality of coating layers having different compositions so that after steps (b) and (c) the microporous coating has a modulus which varies through its thickness in such a manner that, on moving through the thickness of the coating from the surface adjacent the fabric to the exposed surface of the coating, the modulus increases to a maximum and then decreases in value towards the exposed surface.

The flexible (nonrigid) polymeric material of which the coating is formed can consist entirely of a polymer, or polymers, or blends thereof. The polymeric material is selected having properties suited to the intended application, such as flexibility, toughness and cold flow resistance. A large number of polymers, either individually or in combination, can be used, for example, including polyurethanes, polyvinyl derivatives, polyesters, polyethers, polyamides, polyesteramides, polyacetals, etc., etc.

Preferably, the polyurethane elastomer from which the coating layer is made is prepared by reacting isocyanurate polymers of diisocyanates with a polyesteramide.

The modulus of the coating is made to vary throughout its thickness, according to a preferred process of the invention, by building up the coating from a plurality of layers of polymeric material, each of which has a different modulus from that of its neighboring layer(s). The different moduli of the layers forming the coating can be achieved, for example, by forming the layers of a polymeric material incorporating a soluble filler in particle form, the filler content being different in neighbouring layers. The filler particles can subsequently be leached out using a suitable solvent to render the coating microporus and water vapour permeable. Another method of achieving the modulus variation of the coating is to incorporate a reinforcing filler into at least some of the polymeric material in differing amounts, which filler is preferably hydrophilic in nature.

Using the latter method, the microporosity of the layers of the coating may be obtained for example by a coagulation technique. One such technique comprises treating each coating layer of the polymeric material in a liquid which is a solvent therefor with a nonsolvent for the polymeric material which is at least Partially miscible with the solvent whereby the layer is coagulated. into an intercommunicating microporous structure. The solvent is then substantially all removed from the layer and substantially all of the nonsolvent is subsequently removed from the substantially solvent-free layer.

Alternatively, the reinforcing filler may be mixed with an agent in particle form which will decompose upon heating into one or more gases to form micropores in the coating. As in the case of the soluble salt particles described above the gas-evolving agent may be used alone, both as a filler to achieve the different moduli of the coating layers and as the means of obtaining microporosity.

Suitable soluble fillers for use in the method of the invention include, for example, sodium chloride, sodium sulphate, polyvinyl alcohol and Dispersol LN (Dispersol is a registered trademark). Useful reinforcing fillers include Solka-Floc B.W. 200 (a finely divided Wood pulp derivative containing 99.5% cellulose available from Brown Company, Solka-Floc Division, N.Y., U.S.A.), wood flour, silica, china clay, titanium dioxide, calcium carbonate, alumina and talc. A particularly suitable gas-evolving agent is ammonium bicarbonate.

In a preferred embodiment of the invention, use is made of a mixture of soluble filler and reinforcing filler such that by varying the proportions of the reinforcing filler and the soluble filler (prior to leaching), water vapour permeable layers of the coating can subsequently be obtained having a range of values of modulus for a given polymeric material. Using this technique to obtain the desired modulus variation and water vapour permeability of the coating, it has also been found that the flex life of the product formed by the nonwoven fabric with the multi-layered coating is improved as the salt and filler particle sizes are reduced. The reinforcing filler may have a maximum particle size of about 150 microns (largest dimension), but preferred particle size is 75 microns or less, and the most preferable particle size less than about 50 microns. The particle size of the soluble filler is preferably less than about 50 microns average diameter. Under such conditions, products have been made which have flex-lites which exceed 1.0 flexes and a water-vapour permeability of at least 0.5 mg./cm. /hr. The flex-life was measured on the S.A.T.R.A. shoe upper material flexing machine designated S.T.M. 101, and the water-vapour permeability was measured by the method designated British Standard 3177:1959 using a standard vapour pressure of 11.44 mm. of mercury Although the success of the present invention, in providing a vapour permeable material which has an improved surface smoothness when stretched, is not dependent upon any theory, it nevertheless may be worthwhile considering how the tendency to surfacing roughening of the material when stretched is substantially overcome. The phenomenon of surface roughening which occurs when a coated nonwoven fabric is stretched may be attributed to the following mechanism. Due to the microscopic nonuniformity of the elastic properties of the nonwoven fabric, the application of stress (during stretching) results in strains being developed which vary in magnitude and direction, from point to point, within the fabric. Thus in regions of high modulus, for a given applied stress, the strains are small; whereas in regions of low modulus the strains are relatively large. This behaviour is exemplified in FIGS. 1 and 2 of the accompanying drawings which represent an idealised nonwoven fabric prior to, and during, stretching. When such anonwoven fabric is coated with a polymeric material, the nonuniform strains developed in the nonwoven fabric on stretching are transmitted through the polymer coating so that it exhibits a surface roughening (FIG. 3). v

The material of the present invention, however, has a coating structure which prevents the nonuniform strains developed in the nonwoven fabric being transmitted to the exposed surface of the coating in the following manner. The layer or layers of the coating adjacent to the nonwoven fabric have a low modulus and have superimposed thereon layers of higher modulus. On stretching of the material the low modulus layer(s) acts as a stress distributing agent and consequently the unequal strains developed in the nonwoven fabric are not transmitted through the higher modulus layers. Thus the low modulus layer(s) serves as a buffer between the nonwoven fabric and the higher modulus layers. Furthermore, the higher modulus layers contribute to the suppression of surface roughening by confining the irregu-. larities developed in the nonwoven fabric to the low modulus layer(s), that is, the high modulus layers effectively increase the efliciency with which the low modulus layer(s) absorbs the irregular strains developed in the nonwoven fabric. Thus, when the material of the invention is stretched, the surface of the coating, being isolated from the nonwoven fabric by the low modulus buffer. layer(s) and the higher modulus layers, acquires the configuration of the least energy and consequently remains smooth.

For most applications, the total thickness of the coat-v ing should not exceed 0.04 inch and should preferably be less than 0.03 inch, although the thickness will be dependent on the modulus of each layer of the coating and also on the magnitude and variability of the elastic properties of the nonwoven fabric. Preferably, the coating comprises at least three coating layers of which the one adjacent the nonwoven fabric has a-thickness of at least 0.002 inch, and preferably about 0.004 inch, and each remaining coating layer has a thickness of at least 0.001 inch, and preferably 0.002 to 0.003 inch. For reasons of economy and ease of production, the coating should be no thicker than is necessary to provide the desired degree of product smoothness and durability.

In order to improve the appearance of the coating on the nonwoven fabric and to render it liquid water impermeable, a thin pigmented top-coat may be applied thereto. This top-coat may also be embossed, if'desired, in a pattern which resembles the grain of natural leather. Such top-coated product of the invention has a liquid water impermeability, measured as an initial liquid water penetration value, of at least 1000 flexes. The initial liquid water penetration is determined by a method (A.S.T.M. Designation D.2099-62T, issued 1962) which utilizes the Maeser Water Penetration Tester which is described in method E56 of the American Leather Chemists Association. The invention will now be further described by of the following examples.

EXAMPLE I way fibre 1% inch staple length, 1% denier per filament) and 55% by weight of substantially heat stable polyethylene terephthalate fibre (l /2 inch staple length, 1% denier per filament), and which Weighed 10 ounces per square yard. The polypropylene fibres were high shrinkage/ high shrinkage force fibres having a shrinkage force of at least 0.005 gm./denier for 10% shrinkage at 150 C.

The batt was passed through a needle-loom and needlepunched to a level of 1500 punches per square centimetre to initially consolidate the batt. Final consolidation of the batt was carried out by passing it through an oven with high pressure steam (55 p.s.i.g.; 154 C.) for about 5 minutes, during which treatment the batt underwent an area shrinkage of about 35% The consolidated batt Was calendered and then impregnated with 25%'by weight of Butakon ML520 as a filling agent (Butakon ML520 is a butadiene-acrylonitrile copolymer available from Imperial Chemical Industries Limited and Butakon is a registered trademark). After curing of the filling agent, the nonwoven fabric was coated on one surface with a multilayered coating of polymeric material having the composition and structure shown in Table 1.

TABLE 1 Thick- Constituents (parts by weight) ness, Coating layer No. inch (A) (B) (C) (D) (E) (F) The constituents of the coating composition were as follows:

(A) Wood flour having particles of a size less than 50 microns.

(B) Sodium chloride having a particle size less than 50 microns average diameter.

(C) A polyurethane elastomer which is the reaction product of a 65:35 mixture of tolylene-2:4- and -2:6-diisocyanates with an ethylene glycol/ethanolamine adipate. Its method of preparation is as follows: A mixture of 433 parts of adipic acid, 1820 parts of ethylene glycol, 177 parts of diethylene glycol and 113 parts of monoethanolamine is heated at 240 C. under reflux until an acid value of 2 to 3 mg. KOH per gm. is obtained. The acid value and hydroxyl value of the polymer so formed are determined and equimolecular amounts of this polymer and a 65 :35 mixture of tolylene-2:4- and -2:6-diisocyamates are mixed at 80 C. and then heated at 130 C. for four hours, to give the final product.

(D) A 40% solution in butyl acetate of isocyanurate polymers of tolylene diisocyanates, the solution containing 5.8% of isocyanate groups, and which is prepared as follows: A solution of 89 parts of an 80/20 mixture of tolylene-2:4- and -2:6-diisocyanates in 134 parts of dry butyl acetate, is stirred in an atmosphere of ntirogen at 55 C., and 0.47 part of calcium naphthanate and 0.15 part of phenol added. The mixture is stirred until the isocyanate value has dropped to 5.8%; 0.05 part of phosphoric acid is then added; and the mixture is then stirred at 55 C. for 30 minutes. The term isocyanate value means the percentage weight of the mixture present as isocyanate groups.

(E) Methyl ethyl ketone as solvent.

(F) Dimethylphenylethylamine as catalyst.

The individual layers of the coating composition were applied to the nonwoven fabric using a doctor knife technique. Layer No. 2 was applied directly to the nonwoven fabric and layer Nos. 1A to IE were built up on a layer No. 2 such that layer No. 1A formed the outermost layer of the coating. The methyl ethyl ketone was initially removed from the coating by heating in air at 50 C. Thereafter the coated fabric was cured by heating to 55 C. for

TABLE 2 Extension at Coating layer No. Modulus, kgJcrn. break, percent The modulus of each coating layer is most easily obtained by casting a film of the coating composition of each layer. A sample of each film measuring 10 cm. by 2.5 cm. is then extended at a rate of 5 cm. per minute in an 'Instron Tester. The term modulus used throughout the specification and claims is defined as the slope of the load-extension curve at Zero extension, obtained using the above procedure.

The extensibility, extension at break is the extension of the sample, expressed as a percentage of its original length, at which the sample breaks when being extended at a rate of 5 cm. per minute.

EXAMPLE II TABLE 3 Thick- Constituents (parts by weight) ness, Coating layer No. inch (A) (B) (C) (D) (E) (F) The constituents (B) to (F) were the same as for Example I, but constituent A was Solka-Floc B.W. 200 having maximum sized particles of less than microns. The coating structure had the same modulus profile as the coating structure of Example I.

EXAMPLE III A nonwoven fabric was prepared according to Example I. The nonwoven fabric was coated on one surface with a multilayered coating of polymeric material having the composition and structure shown in Table 4.

TABLE 4 Thick- Constituents (parts by weight) ness, Coating layer No. inch (A) (B) (C) (D) (E) (F) 1A- 0.003 0 57. 0 14.2 7.1 21. 2 0.46 0. 002 0 34. 1 l6. 9 8. 5 40. 5 0. 53 0.002 7. 6 25. 6 l7. 2 8.6 40.0 0. 53 0. 002 11.4 22. 8 l7. 2 8. 6 40.0 0. 53 0.002 13. 7 20. 5 17. 2 8. 6 40.0 0. 53 0. 004 O 57. 0 14.2 7.1 21.2 0. 46

The constituents (B) to (F) were the same as for Example I, -but constituent A was talc (Norwegian dolomite) having maximum sized particles less than 50 microns. The coating structure had the same modulus profile as the coating structure of Example I.

EXAMPLE IV A nonwoven fabric was prepared according to Example I. The nonwoven fabric was coated on one surface with 7 a multilayered coating of polymeric material having the composition and structure shown in Table 5.

TABLE 5 Thick- Constituents (parts by weight) ness Coating layer No. 111011 (A) (B) o) (D) (E) (E) The constituents (A) to (F) were the same as for Example II. The modulus profile of the coating structure was of the same general shape as the profile of the coating of Example I, but the modulus of the individual layers was lower.

The products made according to the examples were smooth-surfaced, water-vapour permeable sheet materials which were useful for most of the same applications as smooth-finished natural leather, such as shoe uppers and upholstery.

These products can be coloured by incorporating colouring agents in the coating compositions and/ or by coatting with a coloured top coat composition. The latter may also be embossed to resemble the grain of leather and may serve to render the products impermeable to liquid water, while remaining permeable to liquid water.

The coated surface of the product of the invention is surprisingly smooth whether it is in a relaxed condition or subjected to an area stretch of several percent.

For the purposes of comparison, a water vapour permeable sheet material was made according to Example I, except that the coating had the same composition as that described for layer 2 (Table 1). On stretching this control material and a sample of the material made according to each example by several percent, it was found that each of the latter samples had a much smoother surface appearance than the control material. The material of each example had a leather-like handle, a good flex-life, and was water vapour permeable.

What we claim is:

1. A water-vapour permeable sheet material comprising: a water-vapour permeable nonwoven fabric in the form of a needle-punched batt containing in situ retracted fibres; and a water-vapour permeable coating of flexible polymeric material selected from the group consisting of a polyurethane elastomer, a vinyl chloride polymer, and a combination thereof in superposed adherence with said nonwoven fabric, said coating being a microporous multilayered structure of which neighbouring layers have different moduli, Which layers are arranged so that the layer of lowest modulus is adjacent said nonwoven fabric and each other layer has an increased modulus with increased distance from said nonwoven fabric, except for the final layer which has a modulus at least equal to that of the layer adjacent said nonwoven fabric and less than that of each of said other layers.

2. A sheet material according to claim 1, wherein th coating comprises six layers of which the moduli in kg./ cm. are 25, 50, 280, 400, 600, 25, respectively, beginning with the layer nearest said fabric.

3. A sheet material according to claim 1, in which at least some of the layers of the coating incorporate a reinforcing filler in particle form.

4. A sheet material according to claim 1, in which a thin, liquid water impermeable top coat is applied to the microporous coating.

References Cited UNITED STATES PATENTS 2,826,509 3/1958 Sarbach 117135.5 X 2,839,479 6/1958 Caldwell et al. 1 117135.5 X 2,983,960 5/1961 Jilge 117135.5 X 3,000,757 9/1961 Johnston et al 11763 3,100,721 8/1963 Holden 117161 X 3,180,853 4/1965 Peters 11763 X 3,190,765 6/1965 Yuan 1171355 X 3,136,655 6/1964 Wolinski 117138.8 X 3,208,875 9/1965 Holden 11763 X 3,238,055 3/1966 Brightwell 117135.5 X 3,413,179 11/1968 Goy et al. 117161 FOREIGN PATENTS 893,637 4/ 1912 Great Britain.

WILLIAM D. MARTIN, Primary Examiner M. R. P. PERRONE, 111., Assistant Examiner US. 01. X.R. 11763, 135.5, 138.8, 140, 161; 161-159, 154

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