US2774687A - Process for the manufacture of porous flexible sheet material - Google Patents

Description

Dec. 18, 1956 C. L. NOTTEBOHM ET AL 2,774,687 PROCESS FOR THE MANUEACTURE 0F POROUS FLEXIBLE SHEET MATERIAL Filed Sept. l. 1953 56,9006 fla-Q Wap/m76.

PROCESS FOR THE MANUFACTURE OF POROUSv FLEXIBLE SHEET MATERIAL Carl Ludwig Nottebohm, Weinheim an der Bergstrasse, l

Germany, Werner Jacob, Lowell, Mass., and Wilhelm' Lauppe and Robert Schabert, Weinheim an der Bergstrasse, Germany Application September 1, 1953, Serial No. 377,979

Claims priority, application Germany September 3, 1952 9 Claims. (Cl. 117-120) The present invention relates to the manufacture of porous, flexible sheet material similar to textile or leather which involves impregnating` ber eeces with lm-forming binders, preferably emulsions or dispersions ofv examples, may be mentioned vegetable bers, such V as cotton, ramie, ax, jute,.animal bers, such as wool and j other animal hair or human hair, or synthetic bers, such as viscose bers, acetate bers, superpolyamide bers, polyvinyl bers, polyvinylidene bers, polyethylene bers,

polyester bers, lPolyacryl bers, bers consisting of co-V polymers of several ber-forming monomeric compounds, protein bers, alginate bers, casein bers, mineral bers,

United States Patent such as glassor stone-wool or asbestos bers, or mix- .l

tures of two or more of the above mentioned types of bers. It is essential that the bers are used in cardable 8 cm., preferably about 2 to 6 cm. Fibers such as horsehair, cocoanut bers, etc. which are too long or too thick and which have hard and smooth surfaces, rendering them unsuitable for carding on ordinary carding machines have generally been found unsuitable for use in processesk of..

the type in question.

Suitable binders are, as mentioned heretofore, preferably emulsions or dispersions of natural and/-or synthetic rubber. Excellent results have been obtained, for instance, with polymers of butadiene-acrylonitrile, butadiene-styrene, their derivatives, such as chloroprene,and their copolymers.

additional components, such as wetting agents, dispersing agents, thickening agents, antioxidants, llers, vulcani'zing agents, vulcanization accelerators and the like. The aqueous emulsions or dispersions may contain-about 15 Vto 35% by weight and preferably about 20 'to 29% byl weight of solid binder, such as natural rubber. Wetting agents, such as sodium isobutylene naphthylene sulphonate (Nekal) may be present in an amount up to 60% by weight of the solid binder content of the dispersion. Preferably about 20 to 28 parts by solid weight of'wetting agents are used for each 100 parts by weight of binder solids. ployed in the rubber industry, such as, for instance, paraphenylenediamine derivatives, mercapto benzamidazol or The emulsions or dispersions vused for impregnating the ber fleece may contain one or more.`

The antioxidants used are those commonly ern-l form.` 'Iheir length should be generally about 0.8 to .40

2,774,687 n Patented Dec. 18, 1956 phenyl beta-naphthylamine. A preferred method of manufacturing brous sheet material, as described in the above mentioned copending applications comprises the following steps:

T-he bers or ber mixtures, which may rst have been verse rdircti'om*'the thin webs, the bers of which havey been partially aligned in longitudinal direction by4 the carding o'peratiom are Aplaced uponv one another at an angle inv'such a manner that the bers of adjacent layers crosseach 'other and, thus, a eece is formed in which the' bers extend in various directions, i. e., the bers are v polyposed.` In order to obtain an intimate cohesion be--v tween thesuperposed websv and to produce a light felting, increased densen'es's yand smooth surfaces, the multi-layer eeces are passed through pressure rollers heated to about eece, for instance,` by spraying -or by means of rollers? Advantageously the binder liquid is spreadonl the surface of the eece in the form of a stili foam havinga high air "content When the eece is dried, its surface bers are cemented together at their crossing points undertpreservation of practically all the interstices between the bers rand the surface-of the fleece is coated with athin, spider-web like net of binder. This unilateral surface treatmentstabilizes the fleece sufficiently to permit its through impregnation, for instance by passing it through roller pairs, without dangerof the eece being torn'orserious distorted. n

The unilaterally stabilized eece is now' through impregnated by passing it through a pair of rollers having their axes disposed in a horizontal plane whilev a suitable lm-formingfbinder liquid is pressed through its untreated surface uniformly in such 'a' manner that it penetrates the-entire thickness of the eece.

stepgin-the formofa stableowable foam.

`The impregnated eece or sheetmaterial is driedfor instance, by passing it through a drying chamber heated to about to '120 C. yThis dryingstep may 'also involve avulcanization or-nal vulcanization of the rubberbinder. After-drying, the material may vbe subjected to, the

usual after-treatments, such as calendering, washing, etc.

Subsequent to calendering, nal vulcanization may be effected, for-instance, by heating the material to temperatures of C.' or higher. Dependent upon the typey and composition of the brous material, the type and composition Aofv the binder, the quantity proportions between brous material and binder and the specic' conditions under'which the impregnation is carried out, products can be obtained which have the properties desi-red for the particular purpose for which the material` is intended, such as softness, porosity, elasticity, springiness, creaseresistance, water resistance, and fastness against washing'and cleaning. The material may also be treated -in such away that it can be stitched, padded orsewedon:V

The binderl liquid is preferably used in the through impregnating' 3 sewing machines, and it can be dyed any desired color.

The quantity of the film-forming binder material introduced into the fiber fieece is, preferably, so selected that the fibers are cemented together at their crossing points only and such interstices or pores .are maintained that porous structures are formed which are similar to textiles. Generally, it has been found advantageous to produce sheet material containing about 25 to about 65 percent by weight and ,(preferably about 35 to 55% by Weight) of solid binder particles .and about 75` to 35% by weight of fibrous material. The finished sheet material has a thickness of about 0.15 to 1.5 millimeter and, preferably, ofabout 0.2 to 0.9 millimeter. It is soft, 1iexible and has a textile-like feel and drape', uniformpor'osity and excellent elasticity. lAs compared to ordinary textile fabrics, which have different properties in'the direction of the Woof and of ythe warp, sheet materials prepared by the described process are distinguished by iso-elasticity; that is, they are `resiliently and uniformly resistant to creasing'or folding in'any direction.

If the described process' is usedfor themanufacture of form-'giving and form-retaining"interlinirigs or stiiening materials or as `cold an'dldust protecting interlinings for clothing, it is preferred to use fiber'fieeces which contain wool, possibly mixed with other fibers and toftreat such flee'ces with aqueous dispersions or emulsions of natural or synthetic rubber containing vulcanizing agents, vulcanization accelerators, wetting agents and Aantioxidants. After impregnation, the products are vulcanized, then freed of water-soluble components by washing and finally dried.I The fiber eeces used for these purposes should generally contain at least by Weight, and preferably fromv to 70% by weight, of wool fibers.

Binder liquids which are preferred for use in the described process are emulsions or dispersions of synthetic rubbers or mixtures thereof, therDefo values of which in dry condition .are between 1000 and 8000 degrees Defo. As will be understood by those familiar with the art, the term Defo hardness designates the force in grams which is required to compress a rubber test cylinder of 10 millimeterI height and 10 millimeter diameter at l80v C. in thirtyseconds by 4 millimeter (compare Houwink, page 450). The Defo values determine the` degree of softness and the Idegree of elasticity of the rubber.

For the preparation of softer, still fabric-like products of less springiness, fiber mixtures may be used 'which do not contain `any wool fibers. Thus, a fleece made from a mixture of 30 parts by Weight of polyamide fiber', 30 parts by weight o'f cell wool acetate fiber, 20 parts by weight of ramie fiber combings and 20 parts by weight of cell wool viscose fiber may be impregnated withv a soft, synthetic rubber (Defo valueA between about 800 and 1700).

In some cases it is advantageous to'incorporate into. the fibrous sheet material'water repellant lubricants, such as p'arafiin, wax or the like in quantities of about 2 to 10% by weight. These materials act during sewing, especially sewing on sewing machines, as lubricants for the needles. The waterrepe'llant lubricants can be used in combination with other water repellant materials, such as aluminum salts; preferably the Water repellant lubricants or other water -repellants are incorporated into the solidified and vulcanize'd'sheet material after washing thereof.

While' the products obtainable by the heretofore describedmethods; as particularly set forth and disclosed in the applicants above mentioned copendingpatent applications, produce valuable sheet material having outstanding properties with regard to porosity, elasticity, springiness,l etc., it has now been found that the products can be fur-ther improved, particularly as regards' their springiness, their fastness against dry cleaning and their abrasion resistance. It is the principal objectv of4 4 the present invention to provide methods for attaining such improvements.

In order to accomplish this object, it is proposed, according to the present invention, to incorporate into the fiber fieeces in addition to the above mentioned filmforming binders and previously specified additional cornponents, such as vulcanizing agents, vulcanization accelerators, fillers, water repellants, etc., certain relatively small quantities of synthetic resin condensates. Suitable Synthetic resin condensates are, for instance, condensates of aldehydes, and preferably condensates of formaldehyde with substances which can be condensed with aldehydes, such as phenols `and derivatives thereof,

urea and urea compounds and derivatives, such as cyan` their pre-condensates which are stillrsoluble in water.

Such water soluble pre-condensate may, forinstance, be'

admixed to `a rubber dispersion or emulsion which may also contain other components, such as wetting agents, vulcanizing agents, vulcanization accelerators and the like, and this mixture may be used for the through im'- pregnation of the fiber fleeces. It is preferred to incorporate into the aqueous mixture' additional substances which are capable of promoting or accelerating the conversion of the condensation products to their insoluble final state. Suitable condensation activators are, for instance, alkali compositions,` such as caustic soda solution, earth alkali compositions, such as barium chloride, ammonium salts, such :as ammonium chloride, organic acids, such as lactic acid and sulphonic acids or their salts, such as sodium lauryl sulphonate or soaps of the I type obtainable from fatty acids plus ammonia. Sometimes, certain components of the impregnating dispersion which are present for other purposes, such as vulcanizing agents, vulcanization accelerators, anti-oxidants or emulsifying agents may act as condensation activators. A material which can serve such double purpose is, for instance, hexamethylene tetrarnine.

The most -suitable quantities of poly-condensates to be used can be ascertained by simple tests and ran-ge from about l-15% by weight of the binder solids. In the manufacture of sheet material which is intended as interlining for articles of clothing, the quantities of polycondensates to be employed may be determined on the basis of the Defo values of the rubbers used in the binder liquids, as shown by the following table:

Defo values of Rubber It has been found desirable to use the dispersions orl emulsions which, according to the invention, contain, in"

addition to the rubber binders, also Water soluble precondensates of synthetic resins, such as pre-condensates' of formaldehyde with phenols, urea and thev like, in the in such a manner and quantity into/ the impregnating binder dispersion that they do no't prevent the conversion o f the dispersion into a stable foam suitable for` impregnation vof the lieeces. For this reason, generally, according to the invention, only relatively small quantities of water soluble precondensates of water soluble compounds` capable of condensation are added to the impregnating dispersions. In some cases, it-has also been found advantageous to incorporate into the fibrous eeces or into the impregnating dispersions, softening agents of the type generally used in thesynthetic resin condensate industry. Typical softening agents of this type are, for instance, glycerine, glycols, fatty acid esters and the like.

The impregnation of the ber eeces may be carried out in the manner described above and set forth in detail in the applicants above mentioned co-pending applications by converting the impregnating dispersion containing, in addition to the film-forming binders, also precondensates of synthetic resins, such as formaldehyde with substances condensable therewith, and possibly other desired components, to a stable, owable foam and pressing this foam by means of rollers into the eeces. The stabilization of the impregnation may be eiected by heat agglomeration such as, for instance, simple drying. For this purpose, the impregnated fleeces may be passed through heating chambers. Care must be taken to carry out the after-treatment of the impregnated eeces under such conditions that the precondensates are converted to their Water insoluble and solvent resistant final form. In order to accomplish this result, the drying and vulcanization steps may-be suitably modified withV regard to the temperature and the duration of the heat treat. ment. According to one embodiment of the process according to the invention, the impregnated sheet ma-v terial is subjected, after heat coagulation, to a vulcanizing treatment at temperatures from about 80 to 120 C. which is continued until complete vulcauization of the rubber and simultaneous complete conversion of the synthetic resinv condensate to its final condensed state has taken place. Thereafter, the material may be washed and subjected to any `other desired after treatment.

, The vulcanization and hardening of the synthetic resin condensates may also becarried out in several stages. Thus, the impregnated and dried material may first be prevulcanized at temperatures of 80 to 95 C., then calendered, washed and passed through a paraffin emulsion bath. Thereafter, the rubber components may be finally vulcanized and the synthetic resin condensates may be converted to their final insoluble state or hardened by subjecting the impregnated sheet material for about 24 hours to temperatures between 80 to 100 C. It will be understood that the heat treatments must` be carried out under such conditions that the fibers are not damaged. Generally, it is recommended to use temperatures not exceeding about 135 C.

Due to the incorporation of hardened condensation products of aldehydes, preferably formaldehyde, with substances which can be condensed therewith, such as phenols, ureas, etc., the properties of the products according to the invention are improved in various respects. Thus, the incorporation into a fiber fleece of a quantity of phenol formaldehyde condensate in an amount of about 4% by weight of the film forming elastic rubber solids constituting the primary binder leads to products having substantially improved springiness and abrasion resistance. Such products are particularly suitable for use as interlinings in clothing.

lThe accompanying drawing shows several alternate procedures in accordance with the present invention.

The following examples may serve to illustrate the invention.

' Example 1 A fiber mixture consisting of 30 parts by weight of cotton combings, 30 parts by Weight of ramie combings and'40 parts by weight of cell wool combings was formed into a fiber fleece havinga weight of 135 g. per square millimeter. The vfleece was condensed and streached between pressure rollers heated to C.

A stiff foam was formed from an aqueous dispersion of the following composition:

The foam was spread uniformly in a very thin layer by means -of a doctor blade onto one lsurface of the fiber fleece while the eece was passed under the blade, whereupon the eece was dried.

-The sheet material, stabilized by this unilateral pretreatment, was now passed between a pair of cooperating rollers with smooth surfaces having their axes arranged in a horizontal plane, and a stable, flowable aqueous foam was pressed into the fleece through its untreated surface, so as to penetrate the cutive thickness of the lieece. The foam was prepared from a dispersion of the following composition:

The mixture contained about 22.5% by Weight of the solution of rubber solids and about 25.2% by weight of the solution of total solids.

The impregnated eece lwas now passed through a drying chamber where it was dried at about to 100 C. for twenty minutes and simultaneously pre-vulcanized. The resulting highly porous sheet material, which already exhibited good springiness, was now finally vulcanized and hardened for about twenty-four hours at 75 C. in a drying chamber. Thereafter, it was washed in a washing machine in the manner customary in the textile industry whereby all water soluble `substances were dissolved out. Then, the material was dried again and treated with parafn-wax-aluminum salt dispersion to make it water repellant. The final product had a thickness of .8 to 1 millimeter and a weight of about 220 g. per square millimeter. Its rubber content was labout 42% by weight. The material had the particular advantage that its properties were not significantly impaired by dry cleaning. lt exhibited excellent springiness after dry cleaning.

Example 2 A mixture of 50 parts by weight of cotton combings and 50 parts by weight of cell wool was formed into thin fibrous webs and a number of these webs were superposed upon one another to produce a eece containing bers disposed in all directions and having, after stretching, a weight of about 70 to 100 g. per square meter. One surface of the fleece was pretreated with a foam having the same composition as the pretreatment foam described in Example l.

VAfter drying, the unilaterally prestablized fleece was treated by means of a pair of rollers, as described in Example gl, with a stable, flowable foam obtained from a dispersion of the following composition:

The impregnated material was treated with a saturated sodiumsulphate solution and dried. Thereafter, it was subjected to a second impregnation by passing the sheet material through a pair of rollers with smooth surfaces and pressing into both surfaces of the sheet an aqueous paste of the following composition:

Liquid Solid Parts Parts B. W. B. W.

Butadiene-acrylonitrile dispersion (37%) 270 100 Starch solution (35%) 90 Sodiumsulphate 100 Sulphur dispersion (80 3 Zincoxide dispersion (50%) 12 6 Zinc salt of phcnylethyldithiocarbaminic acid as dispersion (25%) 4 1 Paraphenyldiamine derivative (25%) 8 2 After the second impregnation, the material was vulcanized by passing it over drying .cylinders at a temperature of about 110 C. and final vulcanization and hardening of the synthetic resin components was accomplished by subsequent storing in a drying oven. Thereafter, the finally vulcanized and hardened material was thoroughly washed in washing machines whereby all water soluble components were dissolved out, leaving numerous fine and extra fine pores in the material. The material was then dried. lt was characterized by extremely high porosity and absorptiveness. Generally, it had the properties of chamois leather, but, due to the presence of the phenol-formaldehyde resin, its abrasion resistance was substantially greater than that ofnatural leather.

Further experiments have shown that in some cases it is advantageous to introduce at least part of the synthetic resin condensates into the fibrous sheet material in a second impregnating stage following the impregnation of the sheet material -with the elastic binders, such as natural or synthetic rubber. In these cases, the fiber fleece is treated in a first impregnating stage, preferably in the manner disclosed in the applicants prior copending patent applications 262,941 and 262,942, with a dispersion or emulsion containing the film-forming binder and preferably such additional materials, as wetting agents, vulcanizing agents, antioxidants and the like, and the pre-impregnated sheet material thus obtained is then treated in a second impregnating stage with at least one synthetic resin precondensate, such as a precondensate of an aldehyde with phenols, urea or urea derivatives. Finally, the impregnated sheet material is subjected to a treatment suitable for the hardening of the synthetic resin condensate, for instance by heating in the presence of condensation catalysts.

This two-stage process has the advantage that it permits the introduction into the fibrous sheet material of such precondensates which are incompatible with one or more of the components of the binder liquids used for the principal impregnation of the fibrous material. Certain melamine resins are typical examples of this group of synthetic resins suitable for use in the second impregnating stage of a two-stage impregnation. The secondary impregnation of the fibrous sheet material preimpregnated with film-forming binders may be carried out with emulsions, dispersions or solutions containing the synthetic resin precondensate in crystalloid-dispersed form, in colloid-dispersed form or in hetero-dispersed form. Such emulsions, dispersions or solutions may, in addition to the precondensates used, also contain catalysts capable of promoting the conversion of the precondensates to their insoluble final state. Suitable condensation catalysts are, for instance, ammonium salts, such as ammonium chloride, di-amrnoniurn phosphate or propanolaminehydrochloride, anorganic acids, such as hydrochloric acid or boric acid, anorganic bases, such as caustic soda solution or ammonia and organic bases such as, for instance, triethanolamine. The secondary impregnation may, for instance, be carried out with phenolic plastics in their soluble state, such as, for instance, the known precondensates of formaldehyde with urea or urea derivatives known under the trade names Ka 1525 or GFT 167,

the urea precondensate known under the trade name- Kaurit KW or the dicyandiamide known under the trade name Kaurit DD. Other suitable precondensates are known under the trade names Cassurit (trihydroxymethylmelamine), Lyotix MA (etheried trihydroxymethyl melamine), Lyofix CH (hexahydroxymethyl melamine) or Aerotex (etheried hydroxymethyl melamine).

It is recommended to use such precondensates which, after hardening, are resistant to organic solvents, as they are used in dry cleaning operations and which thus help to preserve the desired properties of the products, especially with regard to elasticity, springiness, feel, etc., even after several dry cleanings. Condensation products of melamine with formaldehyde or other aldehydes have been found to be particularly suitable for this purpose.

According to a further embodiment of the invention, the precondensates to be introduced into the fibrous sheet material are used partly in the first impregnating stage as components of the emulsions or dispersions containing the film-forming binder and partly in the second impregnating stage applied to the fibrous sheet material obtained from the first impregnating stage. It is possible to use in both impregnating stages precondensates of the same type, but, according to a preferred mode of operation, the first impregnating stage is carried out with emulsions or dispersions containing precondensates which are Well compatible with the film-forming binders and other components of the binder liquids employed in this stage, while in the second impregnating stage (final impregnation) precondensates are used which are more or less incompatible with the components of the binder liquids used in the first impregnating stage. As mentioned before, melamine precondensates have been found to be particularly suitable for the second impregnating stage.

Generally, it is desirable to submit the fibrous sheet material after primary impregnation to a stabilizing and, if desired, vulcanizing treatment, for instance by heating, before carrying out the final impregnation by introducing the precondensates into the preimpregnated fibrous sheet material and subsequent hardening. Alternatively, the fibrous material leaving the first impregnating stage may be only lightly dried and submitted in this condition to the final impregnating treatment with synthetic resin precondensates. In the latter case, it is advisable to use for the second stage impregnation emulsions, dispersions or solutions which contain the synthetic resin precondensate in a relatively high concentration. The impregnating products are then subjected to a preferably intense drying and to a treatment, such as a heat treatment, which serves to harden the introduced precondensates. The hardening process may oe carried out in such a manner that simultaneously the vulcanizable filmstage -revulcanized v In thiscase,"v the second stage impregnation may becarried out withfan emulsion,-disper sionorsolution containing, in addition to theffsynthetic resin precondensates and the condensationcatalysts, also vulcanizing agents and possible vvulcanization accelerators.

The second 'stage impregnation of'thelibrous sheet material preimpregn'ated with'lm-.forming binders can be carried out by saturating the material throughout with tiret-emulsion, Idispersion or solution of the syntheticresin precondensate followed by a suitable hardening step, if desired@ after removal of excess precondensate liquid by squeezing outU or the like. vuAlternatively, thek second in ip'regrratingy step maybe so controlled that only one or both surface layers of the d brous sheet material are impregnated to a desired depthwith the synthetic resin precoden'sate liquid, for instance, by spraying or spreading-tof thelat'ter upon one or bothsurfaces ofthe sheet material. `This makes it possible to produce certain desired surface effects.

Finally, it has been found that in some cases it is advantageous to submit the fibrous sheet material into which, according to the present invention, synthetic resins have been introduced to an after-treatment with superheated steam, for instance in a drying room or under a press or on drying cylinders. Such treatment with superheated steam may, if desired, be utilized for the hardening of the synthetic resin condensate introduced into the fibrous material and/or for the vulcanization of the vu1- canizable binders, such as rubber.

Example 3 A fibrous fleece prepared and pre-stabilized by a unilateral surface treatment according to Example 1 was through impregnated in a first impregnating stage by passing it between a pair of rollers and pressing into the untreated surface thereof a stable owable foam obtained from an aqueous dispersion containing the following solid ingredients:

Parts B. W. Butadiene-acrylonitrile polymer 100 Sodiumsulphonate (dispersing agent) 27 Sulphur 3 Active zincoxide 5 vuikazit P extra N (zinc sait of phenyliethyr dithiocarbaminic acid) 1 80 g. etherifled trihydroxymethylmelamne (Lyolix MA) 15 g. diammonium-phosphate l5 g. dicyandiamide The impregnated sheet material was pre-dried at about 80 C. and finally hardened for about ten minutes at 140 C. In a modification, pre-drying was omitted and the impregnated material was dried and hardened by heating it for twenty minutes to about 140 C.

Example 4 A fiber eece was prepared, surface stabilized and through impregnated in a rst impregnating stage as described in Example 3, but in this case the foam used in the first impregnating stage was obtained from an aqueous-*dispersion containing the? following'vsoxlid irl-#f f In this.; case,- dryingM-and .hardeninglwere `effected by heating the impregnated material for'about 21A 'minutesl to 165 Example 5 A surface stabilized fiber eece was treated in a rst impregnating stage, as described in Example 3, with a foam obtained from a dispersion of the following composition:

Llquid Solid Parts Parts B. W. B. W.

Leguvol T (polyester resin) dis ersion 27.1 20. 25 Emulphor FFO (30%) (alkylnap thylpolyglycolether) solution 6 1.8 Benzeneperoxide (Hardener-BPO paste) 0. 72 0. 64 Nekal (alkyl-naphthalinesulphonate) 8 8 Cobaltous chloride solution (20%) 0.9 0. 18 Softened water 48. l

After drying, vulcanization and washing, the material was treated in a second impregnating stage with a solution containing per liter the following solid ingredients:

g. etherilied hydroxymethylmelamine (Aerotex M3) 15 g. of a mixture containing isopropanolamine hydrochloride (UTX) 20 g. dicyandiamide After drying, the product was in this case hardened under a pressure of 0.5 kg. per square centimeter at a temperature of C. It was found that complete conversion of the synthetic resin precondensate to its insoluble state occurred in two to three seconds.

The process according to the present invention makes it possible to produce porous sheet material which, due to the increased condensation of the fiber material, have a relatively high specific weight. The hand, the springiness and other properties are improved. Moreover, the products obtained accordingto the present invention are characterized by particularly smooth surfaces, and high resistance to dry cleaning fluids.

We claim:

1. In the manufacture of porous sheet material similar to textile or leather and containing from about 25-65% by weight of rubber based on the combined wei-gh-ts of fibers and rubber, wherein a fleece of cardable polyposed fibers is impregnated with an aqueous dispersion of a rubber and the impregnated ileece is thereafter dried to deposit the rubberv primarily at the crossing points of the fibers, the improvement which comprises introducing intothe fibrous sheet material, in addition to the rubber, from 1 to 15 parts by weight per 100 parts by weight of rubber solids of a water-soluble condensation product of formaldehyde with a member of the group consisting of ureas, melamines and phenols, and there- ..11 aftenconverting said condensation product' to waterinsoluble form.

2. The process of claim 1, wherein the condensation product is employed in an amount ranging from 2 to 6 parts by weight per 10() parts by weight of rubber solids.

3. The process of claim 1, wherein the condensation product is at leastpartly included in the aqueous dispersion of the rubber solids.

4. The process of claim 3, wherein the aqueous dispersion of rubber solids and condensation product is applied as a foam. Y f i 5. The process of claim 1, wherein the rubber solids have a high Defo value and the condensation product is employed .in an amount ranging from 1 to 2 parts by weight per 100 parts by weight of rubber solids.

6. The process of claim 1, wherein the rubber solids have a low Defo value and the condensation product is employed in an amount ranging from 6 to 8 parts by weight per 1100 parts byweight of rubber solids.

7. The process of claim 1,l wherein the condensation product is at least partly applied as an aqueous dispersion after drying of the sheet material following depositing of the rubber solids.

12 8. The process of claim 1, wherein the-condensation product is a water-soluble melamine formaldehyde.`

9. The process of claim l, wherein the aqueous rubber dispersion also contains a vulcanizingagent and the sheet material is subjected to vulcanization prior to application ofthe water-soluble.condensation product.

References Cited in the le of this patent UNITED STATES PATENTS 1,459,499 Brown et al June 19, 1923 1,766,817 Friedlan-der et al. June 24, 1930 1,899,535 Teague Feb. 28, 1933 1,936,999 Teague Nov. 28, 1933 2,088,227 Battye July 27, 1937 2,267,316 Thompson et a1. Dec. 23, 1941 2,424,923 Edgar July 29, 1947 2,467,233 Rust Apr. l2, 1949 2,536,050 Fluck Jan. 2, 1951 2,563,897 Wilson Aug. 14, 1951 2,716,617 Auestu Aug. 30, 1955

Claims (1)

1. IN THE MANUFACTURE OF POROUS SHEET MATERIAL SIMILAR TO TEXTILE OR LEATHER AND CONTAINING FROM ABOUT 25-65% BY WEIGHT OF RUBBER BASED ON THE COMBINED WEIGHTS OF FIBERS AND RUBBER, WHEREIN A FLEECE OF CARDABLE POLYPOSED FIBERS IS IMPREGNATED WITH AN AQUEOUS DISPERSION OF A RUBBER AND THE IMPREGNATED FLEECE IS THEREAFTER DRIED TO DEPOSIT THE RUBBER PRIMARILY AT THE CROSSING POINTS OF THE FIBERS, THE IMPROVEMENT WHICH COMPRISES INTRODUCING INTO THE FIBROUS SHEET MATERIAL, IN ADDITION TO THE RUBBER, FROM 1 TO 15 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OF RUBBER SOLIDS OF A WATER-SOLUBLE CONDENSATION PRODUCT OF FROMALDEHYDE WITH A MEMBER OF THE GROUP CONSISTING OF UREAS, MELAMINES AND PHENOLS, AND THEREAFTER CONVERTING SAID CONDENSATION PRODUCT TO WATERINSOLUBLE FORM.

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