LU83641A1 - RESIN-IMPREGNATED FIBROUS TABLECLOTH, PROCESS FOR PRODUCING THE SAME, APPLICATION TO THE PRODUCTION OF ARTIFICIAL LEATHER SHEET AND PRODUCT OBTAINED - Google Patents

Description

·%; The present invention relates to fibrous webs impregnated with resin and it relates more particularly to fibrous webs impregnated with resin of uniform specific gravity at all points, as well as products obtained from these webs.

Resin-impregnated sheet materials such as canvas, mats, primed paper, etc. are well known in practice. These resin-impregnated sheet materials are useful for a variety of purposes, for example for producing imitation leather in the form of vinyls, etc., carrier sheets such as conveyor belts, and the like.

Known methods of impregnating a particular sheet involve impregnating or coating a porous material with a polymeric resin such as a polyurethane, a vinyl material or the like. Polyurethanes have been widely adopted as a coating or impregnating composition due to the wide variety of their chemical and physical properties, including their flexibility and resistance to chemical agents. Several techniques have been used for impregnating the porous sheet material with a polymeric resin. One of these prior art methods involves the use of the polymeric resin in an organic solvent system, in which the sheet material is immersed in the solution and the solvent is removed therefrom. These solvent systems are undesirable because in many cases the solvent is toxic and must be recovered for re-use, or else discarded, these solvent systems are expensive and do not necessarily yield a suitable product, because that when the solvent is evaporated from the impregnated porous sheet material, the resin tends to migrate, producing an inhomogeneous impregnation of the porous sheet material by producing a resin enrichment towards the surface of the sheet material, rather than giving a uniform impregnation.

To overcome the problems associated with solvent systems, certain aqueous polymer systems have been proposed.

Λ 2: In the formation of sheet materials impregnated by impregnation with aqueous polymers, the aqueous portion must be eliminated. Again, heat is required and migration of the polymer to the surfaces of the impregnated sheet material is observed.

In a process in which polyurethane solutions are combined with porous substrates, the polymer is applied in an organic solvent to a substrate such as a polyester mat stitched using needles. The polymer-substrate composite is then immersed in a bath of a mixture of organic solvent for the polymer and of a non-solvent for the polymer which is at least partially miscible with the solvent, until the layer is coagulated. by forming a cellular structure 15. of anastomosed micropores. The solvent is removed from the coating layer along with the non-solvent to produce a microporous layer containing no solvent. While this method gives acceptable methods for polyurethane impregnated fabric, it has the disadvantage of an organic solvent system, in part when using high performance polyurethanes which require relatively toxic solvents and high boiling point. An example of such a process is given in U.S. Patent No. 3,208,875.

In another method, polyurethane dispersions in organic vehicles have been proposed and used to coat porous substrates as described in U.S. Patent No. 3,100,721. In this system, a dispersion is applied to a substrate and coagulated by the subsequent addition of a non-solvent. Although this approach has been used with some success, it involves two main limitations: (1) the vehicle of the dispersion is substantially organic since relatively small amounts of non-solvent, preferably water, are required to form a dispersion; and (2) there is a narrow useful range of non-solvent addition, so that reproducible results are difficult to obtain.

A particularly useful process for the preparation of a composite sheet material by impregnation of a porous substrate is described in US Pat. No. 4,171,391 cited in reference herein. In this system, a porous sheet material is impregnated with an aqueous ionic dispersion of a polyurethane and the impregnation material is coagulated in place. The composite is then dried to form a composite sheet material. The present invention is an improvement made to this basic process and the framework is enlarged in some cases.

Porous substrates and similar impregnated materials have been proposed as substitutes for leather for the preparation of a product having the same characteristics as natural leather.

Natural leather, having received the correct finishing, is appreciated for its durability and its aesthetic characteristics for various applications. Because of the shortage of leather and the high cost of treating leather for particular applications, economic considerations have dictated the possible replacement of leather with plastics in certain applications in which leather articles have been used. . These synthetic materials have been proposed and used in the production of shoe uppers, in upholstery, clothing, the manufacture of travel articles, bookbinding and similar applications. Since these various applications require different physical, chemical and aesthetic qualities, different methods using different materials must be used to obtain an acceptable product which is comparable to natural leather; however, in some cases, these synthetic materials are easy to distinguish from natural leather.

Natural leather obtained from the skins of large animals consists of two surfaces: a surface defining the flower, which is in most cases the

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: 4? most appreciated surface from the aesthetic point of view, and the opposite surface defining the crust. The flower is the skin of the animal and is very smooth, while the crust is in most cases rough and fibrous.

A method of preparing a synthetic material as a leather substitute involves impregnating and / or coating a porous material, for example a canvas, with a polyurethane, a vinyl material or. a similar matter. Polyurethanes have been widely adopted as coating or impregnating compositions because of their great ability to vary with respect to chemical and physical properties, especially their flexibility and chemical resistance.

The objectives of the preparation of synthetic leather substitutes lie in the fact that these substitutes must give (1) sheets usable especially for imitation leather and upholstery; (2) sheets of uniform width as is commonly used in the textile industry (unlike natural products which undergo significant losses of weight and surface during cutting and finishing); (3) "end use flexibility, for example under various exposure conditions where certain chemical treatments facilitate maintenance and improve the longevity of the properties; and, most importantly, (4) a product whose mechanical resistance, hand, drape and softness are comparable to those of natural leather.

In addition, a sheet material simulating leather should be characterized, when used for shoe uppers, by its resemblance to leather, without any undesirable fabric transparency, good penetration of vapor water by the uncoated side of the stem, and a "break" of the leather-like flower (minimum formation of coarse wrinkles). A "leather-like flower break", as is well known in the leather industry and in the upholstery industry, manifests itself in the behavior of properly finished leather when it is folded or crumpled. The fold of the leather is characterized by a smoothly curved profile, often with many fine wrinkles in the compressed region of the fold-forming area. This is in contrast to the accentuated folds or coarse wrinkles which are formed when papers or films are folded; this type of undesirable aspect constitutes what is called "hairpin wrinkle formation".

The "hand" of leather is very distinctive 10 and synthetic leathers normally have a rubbery feel which is in contrast to that of leather.

Polymers of the polyurethane type have long been used as coating layers or impregnating materials for a fabric for the production of leather substitutes. For example, polyurethanes having high resistance to solvents and abrasion can be prepared, imparting dry cleaning ability and remarkable durability to coated fabrics. The basic chemistry of polyurethanes, involving reactions between isocyanate groups and molecules with multiple reactive hydrogen atoms, such as polyols and polyamines, offers great flexibility and great variability in the final chemical and physical properties by choice of intermediate compounds to achieve processability and the advantageous balance of conditions required for final performance.

There are various ways of applying polyurethane or other post-curing liquid polymer solutions to porous substrates, which are well known to those of skill in the art. An article in the Journal of Coated Fabrics, volume 7 (July 1977), pages 43 to 57, describes some of the industrial coating systems, for example inverted roller coating, applicator powered by a reservoir, engraving, etc. Polyurethanes can also be applied by brush and spray on porous substrates. These polyurethane solutions, after impregnation or application to the porous substrate, are dried or cured, for example with hot air, 6% infrared rays, etc. The feature of these processes is the deposition of a polymer and a film-like layer which tends to produce a coated fabric which, when folded, forms undesirable sharp edge folds instead of a break resembling the leather flower. Other methods of mixing polymer solutions and in particular polyurethane solutions with porous substrates are illustrated in US Patents 3,208,875 and 3,100,721.

An improved process for impregnating fabrics is disclosed in United States Patent No. 4,171,391; this process involves certain steps which are necessary to form artificial leather sheet in accordance with the invention.

According to the present invention, there is provided a method of impregnating porous sheet materials and in particular needle-quilted mats, method in which uniform impregnation is accomplished in an aqueous system giving a product of high resistance to tear and great integrity.

The invention further provides an impregnated fibrous web with a new and original structure, suitable for use as formed or improved by a subsequent treatment.

According to another of its particularities, the invention proposes a sheet material simulating leather which has the appearance and properties of natural leather and which also has certain physical similarities with leather.

A resin-impregnated fibrous web is formed from a needle-stitched fibrous mat and a polymeric resin distributed over this mat. The specific weight of the impregnated sheet is uniform at all points, the apparent density of the sheet being less than the real density of the sheet, so that the latter is porous. The impregnated web comprises filaments which are coated and not coated with the polymeric resin. The invention also describes a method for forming an impregnated fibrous web.

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A sheet material simulating leather is produced from the impregnated tablecloth. The sheet material simulating leather is formed of a fibrous mass impregnated with a polymer, with a "flower" layer forming a surface and a "crust" layer forming the opposite surface. The "flower" layer has an actual density equal to its apparent density and the "crust" layer has an apparent density lower than its actual density. The sheet material has a density which decreases from the "flower" layer to the "crust" layer.

- The expression "apparent density" used in the present specification designates the specific weight of the material including the spaces filled with air. The term "actual density" used herein refers to the density of the non-air-containing material, that is, its specific gravity.

The fibrous mass useful in practicing the present invention includes woven and knitted fabrics, felt and non-woven fabrics, for example, spunbonded sheets, needle-quilted mats and papers without sizing. Suitable support fibers are natural fibers, especially cotton and wool; synthetic fibers such as polyester, "Nylon", acrylic materials, modacrylic materials and rayon.

The fibrous mass very advantageously consists of needle-pricked fibrous mats formed from these natural and synthetic fibers. Preferably, the fibers have a denier of 1 to 5 and a length which is suitable for carding, for example 2.54 to 15.24 cm and in particular 3.81 to 7.62 cm.

30 Needle-stitched fibrous mats can • have a high, intermediate or low specific weight.

High specific weight mats have a maximum specific weight of 0.5 g / cm3. These high specific weight mats are normally made of wool. When synthetic fibers are used for making the mats, the mats of high specific gravity reach 0.25 g / cm 3. Preferably, in the practice of the invention, the fibrous mats have a specific weight of 0.08 to 0.5 g / cm 3.

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8 The thickness of the mats can reach 1.27 cm and is preferably between 3.05 and 10.16 mm, with a minimum thickness of 0.76 mm. In addition, the mats are characterized as "saturation mats", which have great integrity due to the needle pricking operation as opposed to lightly bound mats, having some needle and needle bites. little or no integrity.

The polymeric resins useful for practicing the present invention are preferably polymeric resins which are capable of solubilization, dispersion or emulsification in water and subsequent coagulation in the aqueous system with an agent ionic coagulant.

A preferred polymeric system is one which is synthesized from acrylic monomers such as alkyl acrylates and methylacrylates, acrylonitrile, methylacrylonitrile and other well known acrylic monomers. These acrylic monomers can be polymerized by emulsion polymerization to form a latex or by other free radical polymerization mechanisms and they can then be solubilized or emulsified in water. The emulsion or solubilization system should be chosen such that when the emulsion is contacted with a concentrated acid or a concentrated base, the polymer coagulates in the aqueous system and is made substantially insoluble.

Polyurethanes emulsified or dispersed in water are very advantageously used. Examples of the emulsified polyurethanes include those disclosed in U.S. Patent No. 2,968,575, prepared and dispersed in water using detergents under the action of large shear forces. When these polyurethane emulsions are formed, the emulsifying agent or detergent must be a substance which is ionic in nature, so that a complementary ion can be added to the aqueous system to coagulate the polymer.

The polyurethanes useful for the implementation of the invention are very advantageously those which are known to be capable of ionic dispersion in water.

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The system of choice for the preparation of aqueous ionic dispersions of polyurethanes consists in preparing polymers which carry free acid groups, preferably carboxylic acid groups in covalent bond with the backbone of the polymer.

By neutralizing these carboxyl groups with an amine, preferably a water-soluble mono-amine, the ability to dilute with water is obtained. The compound bearing the carboxylic group should be suitably chosen because the isocyanates, necessary components of any polyurethane system, are generally reactive towards carboxyl groups. However, as described in U.S. Patent No. 3,412,054, which may be consulted, 2,2-hydroxymethyl substituted carboxylic acids can be reacted with organic polyisocyanates without significant reaction between the acid and the isocyanate groups because of the steric hindrance of the carboxyl group by the adjacent alkyl groups. This approach makes it possible to obtain the desired carboxylic polymer, the carboxyl groups of which are neutralized with the tertiary mono-amine, in order to obtain an internal quaternary ammonium salt and, consequently, the ability to dilute with water.

Suitable carboxylic acids and, for example,

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In particular, sterically hindered carboxylic acids are well known and readily available. For example, they can be prepared from an aldehyde which carries in the alpha position at least 2 hydrogen atoms which are reacted in the presence of a base with 2 equivalents of formaldehyde to form 2,2-hydroxymethylaldehyde . The aldehyde is then oxidized to the acid by operations well known to those skilled in the art. These acids are represented by the general formula:

CHo0H

I 2

35 R - C - COOH

CH 2 OH

in which R represents hydrogen or an alkyl radical having up to 20 carbon atoms and preferably up to 10 8 carbon atoms. A preferred acid is 2,2-di- (hydroxymethyl) -propionic acid. The polymers carrying the carboxyl groups are characterized as being anionic polymers of the polyurethane type.

Furthermore, in accordance with the present invention, another way of imparting the dilutability with water is to use a cationic polyurethane carrying two amino groups. Such cationic polyurethanes are described in the patent of the United States of America 10 as No. 4,066,591, of which one can consult in particular Example XVII. In the context of the present invention, it is preferable to use the anionic polyurethane.

The polyurethanes useful in the practice of the present invention more particularly involve the reaction of di- or polyisocyanates and of compounds bearing multiple reactive hydrogen atoms, which are suitable for the preparation of polyurethanes. These diiso-cyanates and compounds carrying reactive hydrogen are described in detail in US Pat. Nos. 3,412,034 and 4,046,729. In addition, the processes for preparing these polyurethanes are well known and described for example in the patents mentioned above. In accordance with the present invention, aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used in the formation of the polymer. These diisocyanates are, for example, 2,4-diiso-cyanatotoluene; 2,6-diisocyanatotoluene; meta-phenylene diisocyanate, biphenylene-4,4-diisocyanate; methylene-bis- (4-phenylisocyanate); 4-chloro-1,3-30 phenylene diisocyanate, naphthylene-1,5-diisocyanate, ‘tetramethylene-1,4-diisocyanate; Hexamethylene-1,6-diisocyanate; decamethylene-1,10-diisocyanate; cyclohexylene-1,4-diisocyanate, methylene-bis- (4-cyclo-hexylisocyanate); tetrahydronaphthylene diisocyanate, isophorone diisocyanate, etc. In the implementation of the present invention, arylene diisocyanates and cycloaliphatic diisocyanates are very advantageously used.

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Arylene diisocyanates typically include those in which the iso-cyanato group is attached to the aromatic ring. The most preferred isocyanates are the 2,4 and 2,6 isomers of diisocyanatotoluene and mixtures thereof, due to the ease with which they are obtained and their reactivity. In addition, the cycloaliphatic diisocyanates used most advantageously in the implementation of the pre-; The invention is 4,4'-methylene-bis- (cyclohexylisocyanate) and isophorone diisocyanate.

The choice of aromatic or aliphatic diisocyanates is based on the final application for which the particular material is intended. As is well known to those skilled in the art, aromatic isocyanates can be used when the final product is not excessively exposed to ultraviolet rays, which tends to yellow such polymeric compositions; while aliphatic diisocyanates can be more advantageously used in exterior applications and are less likely to turn yellow upon exposure to ultraviolet rays. Although these principles form a general basis for the choice of the particular isocyanate to be used, the aromatic diisocyanates can still be stabilized by well known ultraviolet light stabilizers, in the interest of the final properties of the material. sheet impregnated with polyurethane. In addition, antioxidants can be added in the proportions accepted in practice to improve the characteristics of the final product. Examples of antioxidants are thioethers and phenolic antioxidants such as 4,4-butylidene-bis-meta-cresol and 2,6-di-tertio-butyl-para-cresol.

The isocyanate is reacted with compounds carrying more than one reactive hydrogen atom such as diols, diamines or triols. In the case of diols or triols, these are normally polyalkylene ether-polyols or polyester polyols. A polyalkylene ether polyol is the polymeric material containing 12 of the preferred active hydrogen for the formulation of the polyurethane. The most useful polyglycols have a molecular weight of 50-10,000 and for the purposes of the present invention the most preferred have a molecular weight of about 400-7000. In addition, polyether polyols improve flexibility in proportion to increase in their molecular weight.

Examples of polyether polyols include, but are not limited to, a polyethylene ether glycol, a polypropylene ether glycol, a polytetramethylene ether glycol, a polyhexamethylene ether glycol, a polyethylene methyl ether- glycol, a polydecamethylene-ether-glycol, a polydodecamethylene-ether-glycol and mixtures thereof. Polyglycols containing several different radicals in the molecular chain, such as for example the compound of formula HOÎCE ^ CX ^ H ^ O) nH where n is an integer greater than 1, can also be used.

The polyol can also be a polyester terminated with a hydroxy group or a side hydroxy group, which can be used in place of or in combination with polyalkylene ether glycols. Examples of these polyesters are those which are formed by the reaction of acids, esters or acid halides with glycols. Suitable glycols are polymethylene glycols such as ethylene, propylene, tetramethylene or decamethylene glycol; substituted methylene glycols such as 2,2-dimethyl-1,3-propane diol, cyclic glycols, such as cyclohexane diol and aromatic glycols. Aliphatic glycols are generally preferred when flexibility is a desired property. These glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or lower alkyl esters or ester-forming derivatives to produce polymers of relatively low molecular weight, preferably having a melting point below about 70 ° C. and a molecular weight such as those indicated for polyalkylene ether glycols. Acids useful in the preparation of these polyesters are, for example, phthalic, maleic, succinic, adipic, suberic, sebacic, terephthalic and hexahydrophthalic acids and the alkylated and halogenated derivatives of these acids. It is also possible to use, in addition, a polycaprolactone terminated with hydroxyl groups.

A particularly useful polyurethane is the crosslinked polyurethane which is described in detail in United States patent application No. 947,544 filed October 2, 1978 in the name of Andrea Russiello and entitled "Crosslinked Polyurethane Dispersions".

The expression "ionic dispersing agent" used in the present specification designates an ionisable acid or base capable of forming a salt with the solubilizing agent.

These "ionic dispersing agents" are amines and preferably water-soluble amines such as triethylamine, tripropylamine, N-ethylpiperidine, etc. ; as well as preferably water-soluble acids such as acetic, propionic, lactic, etc. Naturally, an acid or an amine is chosen depending on the solubilizing group attached to the polymer chain.

The desired elastomeric behavior would generally require about 25-80% by weight of long chain polyol (i.e., an equivalent weight of 700 to 2000) in the polymer. The degree of elongation and elasticity can vary widely from one product to another depending on the desired properties of the final product.

To form the polyurethanes useful for carrying out the invention, the polyol and a molar excess of diisocyanate are reacted to form an isocyanate-terminated polymer. Although suitable reaction conditions and reaction times and temperatures will vary depending on the particular isocyanate and polyol that is used, those skilled in the art are well aware of these variations. Those skilled in the art are aware that the reactivity of the ingredients involved necessitates the equilibrium of the reaction rate with undesirable side reactions leading to an alteration in color and molecular weight. Normally, the reaction is carried out with stirring between about 50 and about 120 ° C for about 1 to 4 hours. To create side carboxyl groups, the isocyanate-terminated polymer is reacted with an insufficient molar amount of a dihydroxy acid for 1 to 4 hours at a temperature of 50 to 120 ° C to form an isocyanate-terminated prepolymer. The acid is advantageously added in the form of a solution, for example in N-methyl-1,2-pyrrolidone and N, N-dimethylformamide. The acid solvent normally does not exceed about 5% of the total charge, in order to minimize the concentration of organic solvent in the polyurethane composition. When the dihydroxy acid has been incorporated by reaction into the polymer chain, the side carboxyl groups are neutralized with an amine at approximately 58-75 ° C for approximately 20 minutes and the chain extension and the dispersion are carried out by addition of water with stirring. A water-soluble diamine can be added to water as an additional chain extender. Chain extension involves the reaction of the remaining 20 isocyanato groups with water to form urea groups and to further polymerize the polymeric material and as a result all of the isocyanato groups have reacted due to the addition to a large excess water stoichiometric. It should be noted that the poly-urethanes of the invention are of a thermoplastic nature, that is to say that they are not capable of prolonged post-maturation after their formation, except by addition of an external ripening agent. Preferably, no such agent is added to form the composite sheet.

Sufficient water is used to disperse the polyurethane at a concentration of about 10 to 40% by weight of solids and with a viscosity in dispersion in the range of 10 to 1000 mPa.s. The viscosity can be adjusted in accordance with the particular impregnation properties desired and by the particular composition in dispersion, as dictated in each case by the characteristics of the final product. It should be noted that no emulsifier or thickener is desired for the stability of the dispersions.

Those skilled in the art are aware of means of modifying the primary dispersion of polyurethane in accordance with the uses for which the final product is intended, for example the addition of coloring agents, dispersions of compatible vinyl polymers, compounds filtering the rays. UV stabilizers, stabilizers against oxidation, etc.

The characterization of the dispersions prepared in accordance with the invention is carried out by measurements of the content of non-volatile substances, of the diameter of the particles, by measurements of viscosity and by the stress-strain properties determined on strips of 'a cast film.

The range of concentrations which is useful for practicing the invention is governed by the desired percentage of polymer addition to the needle quilted mat.

The viscosity in dispersion is generally in the range of 10 to 1000 mPa.s. The low viscosity compared to that of polymers identical to the same solids content in solutions of these polymers in an organic solvent, facilitates rapid and total penetration of the aqueous dispersion and subsequent penetration of the coagulant. Useful solutions of polyurethanes generally have, on the other hand, viscosities of several thousand mPa.s, which can reach 50,000 mPa.s at concentrations of 20 to 30%.

The polymers should be impregnated into the fiber mat in a proportion of at least 70% by weight of added material based on the weight of the fibrous mat, this proportion being up to about 400% by weight. Preferably, the polymeric resin is impregnated in a proportion of about 200 to 300% by weight based on the weight of the fibrous mat.

Coagulation is carried out by contact of the impregnated substrate with an aqueous solution of an ionic medium intended to ionically replace the solubilizing ion.

5 16 'Theoretically, although no such theory is desired, in the case of an anionically solubilized polymer, the amine which neutralizes the polyurethane carrying carboxyl groups is replaced by a hydrogen ion which restores the anionic carboxyl ion, thereby bringing the polymer back to its initial "not susceptible to dilution" state. This causes the polymer to coagulate in the structure of the substrate.

In the case of the anionic polymer, aqueous solutions of acetic acid at concentrations of 0.5 to about 75% constitute an ionic coagulant suitable for anionic dispersions and are preferable to stronger acids because of the relative ease of handling, low corrosiveness and the possibility of elimination.

A "release" intended to coagulate the dispersion by the addition of the neutral salt is achievable, but is not appreciated because of the large amount of salt required, about 10 times the concentration of the acid, and the problems of contamination of the resulting product.

To impregnate the sewn mat with the polymeric resin as indicated in the present specification, the mat is immersed in an aqueous ionic emulsion or dispersion at a concentration sufficient for there to be an introduction of at least 70% by weight. . When the mat is immersed in the emulsion or aqueous dispersion, the mat can be pressed to expel the air so that the emulsion or dispersion is completely impregnated in the mat. The latter, now fully impregnated with the dispersing agent or the aqueous emulsion, passes between wiping rollers or the like which remove the excess dispersion or emulsion on the surface of the impregnated mat.

The mat is then immersed in a bath containing the complementary ion to produce coagulation, the material containing the complementary ion penetrating into the mat by diffusion and producing the coagulation of the resin in the fibrous structure. After coagulation, the mat is wrung out to remove excess water and it is dried "= 17 to form the impregnated sheet.

This process constitutes an improvement compared to the process described in the aforementioned patent of the United States of America No. 4,171,391, as regards the obtaining of particular products. The differences which exist between the process of the said patent and the process of the present invention reside in the fact that the mat is completely saturated, that is to say that it does not retain air, the aqueous dispersion or emulsion being thus finally added in proportion of at least 70% by weight of polymeric resin based on the weight of the mat. Owing to these differences, a new structure is obtained in which the mat has a uniform specific gravity at all points and the apparent density of the sheet is less than its actual density.

When the impregnated sheet has been formed, a specific weight gradient is imparted thereto so as to form a sheet material simulating leather. When forming the sheet material simulating leather, the impregnation composition of the web preferably consists of polymers which, in the form of particles, are capable of being welded to each other under working conditions heat and pressure. Normally, these polymers are thermoplastic. However, certain crosslinked polymers capable of coalescence can also be used. More particularly, the polyurethanes described in the aforementioned United States patent application No. 947,544 have been found to be especially useful in the practice of the present invention for developing the desired density gradient throughout the material thickness.

The characteristics of the leather-like sheet material in accordance with the present invention are mainly physical features whereby a density gradient is created from one side of the sheet material to the opposite side of that material. Preferably, the specific gravity gradient is uniform. An area of the impregnated fibrous mass 4 18 defines a "flower" layer, which has an actual density equal to its apparent density.

This "flower" layer closely simulates the "flower" layer of natural leather. On the opposite side of the sheet material is a surface which defines the "crust" layer whose bulk density is less than the actual density, a density gradient, preferably uniform, existing at all points of the material. The "crust" layer is a little more fibrous and simulates the "crust" layer 10 of natural leather.

The polymer is present in the sheet simulating the leather in a proportion of at least 70% by weight relative to the weight of the fibrous mass.

Normally, the density of the "crust" layer is up to about 75% of that of the "flower" layer to create a porous "flower" layer simulating the "flower" layer of leather. Likewise, it should be noted that the polymer is uniformly distributed throughout the fibrous mass so that the fiber: polymer ratio is uniform in all respects.

The sheet material simulating leather is produced by treating the impregnated fibrous mass and preferably an impregnated nonwoven sheet, as indicated above.

The polymer used as impregnation material is very advantageously one of those or of the type described in the aforementioned United States patent application No. 947,544.

In a method of treating the impregnated non-woven sheet material to form the leather-like sheet, the impregnated non-woven sheet material is placed in a press and is heat treated and pressurized thereon. two sides. The heat and pressure are sufficient to weld the polymer to itself in the impregnation composition at the surfaces of the material, but still insufficient to completely weld the polymer to the interior of the sheet material. This method develops a specific weight gradient from the interior of the nonwoven sheet material to the two exterior surfaces. The thickness dimensions of the heat treated sheet and the pressure can be adjusted by the pressure applied during the heating and pressing operations or by the insertion of spacers between the platens of the press or by the use of a dead load press.

In addition, the press platens can be embossed to give the surface of the material a particular final pattern. After the pressure treatment, the sheet material is split through the middle to form two sheets simulating leather, each having a flower layer and a crust layer.

In another method of forming a sheet simulating leather, the impregnated nonwoven starting material discussed above can be introduced into a press in which only one of the platens is heated to form the flower layer, while that the opposite side resting on the cold plate forms the crust layer.

In another variant of forming the sheet material simulating leather, two pieces of the impregnated nonwoven starting material discussed above can be arranged one on top of the other in a press and one can causing the heat and pressure to act to an extent sufficient to weld the polymer to itself in the impregnation composition on the outer surface of each piece. After the pressure has been applied, the individual pieces are separated and two sheets of imitation leather are thus obtained.

3 ° After training, the simulated leather can be sanded, coated or otherwise treated in accordance with well-known techniques for finishing leather.

In another method, the development of the flower layer can be carried out on unwound strips of impregnated nonwoven starting material which is unrolled from their packages and passed between two rollers in a calendering operation. Preferably, one of the rollers is metallic, smooth or suitably embossed, heated to a temperature of 145 to 204 ° C; the other roller is made of a softer elastic material, for example rubber. The flower layer is developed on the side of the sheet in contact with the metal roller. Effective calendering can generally be carried out with a load of 5.6 to 16.7 tonnes / m of width of the sheet passing between the rollers. Wetting the sheet, before calendering, until the addition of 50 to 100% by weight of water, can promote calendering.

The structures of the impregnated sheet and of the leather-like sheet material are illustrated in greater detail in the appended drawings which represent micrographs of sections of an impregnated sheet and of a leather-like sheet material, prepared. in accordance with the present invention.

Figure 1 is a plan view of the resin-impregnated web prepared according to Example 1, before slitting; Figure 2 is a photomicrograph of the thickness of the web of Figure 1 taken along line II-II; Figure 3 is a photomicrograph at 100x magnification of section III of Figure 2; Figure 4 is a photomicrograph at 100x magnification of section IV of Figure 2; Figure 5 is a 100x magnification photomicrograph of section V of Figure 2; Figure 6 is a photomicrograph at 100x magnification of a resin-impregnated mat prepared according to Example 1 after slitting; and Figure 7 is a 100x magnification photomicrograph of a cross section through the thickness of a sheet material simulating leather made from the mat according to Figure 6.

Figures 1 to 5 show a sheet 10 impregnated with resin prepared in accordance with Example 1. More particularly, Figures 2 to 5 show a cross section through the thickness of the sheet 10. The latter comprises a upper surface 12 and a lower surface * 21 14. The ply 10 as a whole has a large number of uncoated fibers 16, resin concentrations 20, voids 18 and fibers 22 coated with resin. The structure and therefore the bulk density are substantially uniform throughout the thickness of the material, although at the microscopic scale the structure is not homogeneous.

The structure shown in FIGS. 2 to 5 is considered to be attributable to the total impregnation of the mat sewn with the emulsion or aqueous dispersion, with subsequent coagulation of the polymer, while the mat is completely impregnated with the aqueous resin-based composition.

Figure 6 shows a photomicrograph at 100x magnification :, which shows a sewn mat 24 impregnated and slit having a uniform specific weight at all points, such as that shown in Figures 1 to 5. The impregnated mat 24 contains a significant quantity of uncoated fibers 26, masses of polymer 28, coated fibers 32 and voids 30.

It should be noted that although the impregnated mat is not homogeneous on the microscopic scale, it has in all points a uniform apparent density.

Figure 7 shows a photomicrograph at 100x magnification, which shows a sheet material 32 simulating leather in accordance with Example 4.

The material 32 has a flower layer 34 comprising a minimum of voids and the apparent density at the flower layer 34 is equal to the actual density. At level 30 of the flower layer 34, a composite 36 of fibers is formed in a continuous matrix of resin as a result of the application of heat and pressure. In the direction of arrow A, it can be seen that the voids 30 increase as we approach the crust layer 35 38. At the crust layer 38, there are a large number of voids 30, fibers 26 not coated and with polymer masses 28. The structure of the crust layer 38 approximates the structure which is shown in% 22 * Figure 6.

The following examples illustrate the products prepared in accordance with the invention.

EXAMPLE 1 A quilted mat which has been heat formed and which has a surface weight of 1200 g / m2, composed of polyester, polypropylene and rayon fibers and which has a thickness of 7.62 mm, with a density apparent of 0.16 g / cm3, is immersed in a polyurethane prepared con-10 formally in Example III of the aforementioned US patent application No. 947,544. The polymer dispersion has a total solids content of 22%, which makes an addition of 120% based on the weight of the mat. The latter is immersed in the polyurethane dispersion for -10 minutes at room temperature until all the air has been expelled from the interior of the mat and has been completely impregnated. The surface of the mat is wiped with a ruler on both sides to remove excess aqueous dispersion, and the mat is immersed in a 10% acetic acid bath for 10 minutes at room temperature. Immersion in the acid completely coagulates the polyurethane in the fiber structure. The excess acetic acid is removed by washing the mat and the resin impregnated mat is wrung out to remove excess water. The resin-impregnated mat is split into four thick slices and each part is dried at a temperature of 149 to 177 ° C. in an air circulation oven to form four layers impregnated with resin having an apparent density 30 of 0, 41 g / cm3. The micrograph of the final product is reproduced on the drawings.

Example 2

The procedure of Example 1 is repeated, except that a 100% polyester mat having a specific gravity of 0.13 g / cm 3 and a thickness of 5.08 mm is impregnated with the dispersion at 22 % solids of Example 1. The resulting impregnated sheet has a uniform density at all points, great integrity and an apparent density of 0.38 g / cm 3.

Example 3

The procedure of Example 1 is repeated, with the difference that a quilted mat made of 100% polyester, 5 with a thickness of 5.59 mm and a density equal to 0.23 g / cm 3, is impregnated with a 32% solids dispersion to form a sewn fibrous web impregnated with resin having an apparent density of 0.56 g / cm3. The product according to Example 3 is used as a pad 10 to be polished and it is tenacious, it has a high resistance to tearing, a high impact resistance and a total recovery after compression.

Consequently, the process and the product according to the present invention provide an impregnated fibrous web of great integrity and useful as a product as it is and for the formation of other products. In addition, the impregnated fibrous web can be sanded to acquire an appreciable finish.

EXAMPLE 4 Two 1.78 mm thick slits of the nonwoven impregnated sheet prepared in accordance with Example 1 are superimposed and placed between the plates of a press heated to 149 ° C. under pressure of 3.5 MPa for 30 seconds. The two slits are then separated from each other, which gives two sheets of a material simulating leather. The flower layer of the leaves corresponds to the surfaces which were in contact with the heated plates of the press. The inner sides of the sheets retain a fibrous texture similar to that of the unpressed sheet. Microscopic examination shows that the sheet material simulating leather has a density gradient from the flower layer to the crust layer as shown in Figure 7.

The leather-like sheet material, after its formation, can be subjected to a subsequent treatment with other polymers for the finishing of its surface in accordance with known techniques.

Claims (23)

24 T CLAIMS 1. Fibrous tablecloth impregnated with resin, characterized in that it comprises: a sewn fibrous mat? 5 a polymeric resin distributed throughout the mat to form a fibrous web (10) impregnated with resin; the density of said impregnated fibrous sheet being uniform at all points; the apparent density of said sheet being inferior to the actual density of the latter, which is thus porous; and the impregnated web having filaments which are both coated and uncoated with polymeric resin. 2. Resin impregnated fibrous sheet according to claim 1, characterized in that the sewn fibrous mat has an apparent density of less than 0.5 g / cm3 and preferably less than 0.25 g / cm3. 3. Resin impregnated fibrous web according to claim 1, characterized in that the sewn fibrous mat has a thickness of between 3.048 and about 10.16 mm, preferably at least equal to 0.762 mm. 4. Resin impregnated fibrous web according to claim 1, characterized in that the sewn fibrous mat is composed of substantially non-fusible fibers. 5. fibrous web impregnated with resin according to claim 1, characterized in that the polymeric resin is a polyurethane, preferably a water-dispersible polyurethane, in particular a crosslinked polyurethane. 6. Resin impregnated fibrous web according to claim 1, characterized in that said polymeric resin is a polyacrylate. 7. Resin impregnated fibrous sheet according to claim 1, characterized in that the polymeric resin is present in proportion representing an addition of at least 70% by weight based on the weight of the fibrous mat, preferably a proportion of less than about 400% by weight and in particular a proportion of about 200 to 300% by weight based on the weight of the fibrous mat. 8. Fibrous tablecloth impregnated with resin according to claim 1, characterized in that it has a specific weight of approximately 0.75 g / cm3, in particular approximately 0.4 5. approximately 0.75 g / cm3. 9. A method of forming an impregnated fibrous web, characterized in that it consists in: completely saturating a sewn fibrous mat with an aqueous dispersion or emulsion of an ionically dissolved polymeric resin, to be brought in the fully saturated sewn mat * in contact with an ionic coagulating agent to coagulate the polymeric resin in the aqueous dispersion and to deposit the polymeric resin in the sewn mat; and drying the sewn mat and the polymeric resin to form an impregnated fibrous web having at all points a uniform apparent density. 10. The method of claim 9, characterized in that the sewn mat has an apparent density of less than 0.5 to 0.5 g / cm3, preferably less than 0.25 g / cm3. 11. The method of claim 9, characterized in that the sewn fibrous mat has a thickness between 3.048 and 10.16 mm, preferably at least equal to 0.762 mm. 12. The method of claim 9, character ized in that the sewn fibrous mat is composed of substantially non-fusible fibers. 13. The method of claim 9, characterized in that the polymeric resin is a polyurethane, preferably crosslinked. 14. The method of claim 9, characterized in that the aqueous dispersion or emulsion has a solids content of about 5 to 60% by weight. 15. The method of claim 9, character-ized in that the polymeric resin is present in said web in proportion, added relative to the weight of the fibrous mat, of at least 70% by weight, preferably less than 'about 400% by weight and in particular about 200 to c 26' 300% by weight. 16. The method of claim 9, characterized in that the impregnated fibrous web has a specific gravity of up to about 0.75 g / cm3, preferably between about 0.4 and about 0.75 g / cm3. 17. The product obtained by the process according to claim 9. 18. Sheet material simulating leather, characterized in that it comprises a fibrous mass impregnated with polymer having a flower layer forming a surface, the flower layer having a real density equal to its apparent density, and a crust layer. forming the opposite surface, the crust layer having an apparent density less than its actual density, said sheet material 15 having a decreasing specific weight from the flower layer to the crust layer, the ratio of the fiber to the polymer being uniform in all respects of said sheet material, the fibrous mass preferably being a sewn mat. 19. Sheet material according to claim 20 18, characterized in that the polymer is a polyurethane, preferably crosslinked. 20. Sheet material according to claim 18, characterized in that the polymer is present in a proportion, added relative to the weight of said fibrous mass, of at least 75% by weight, which can range up to 400% by weight. weight and in particular between 200 and 300% by weight. 21. Sheet material according to claim 18, characterized in that the crust layer has up to 75% of the density of the flower layer, the polymer being * uniformly distributed in all points of the fibrous mass and the density of said leaf having a uniform gradient from the flower side to the crust side. 22. A method of producing a sheet material simulating leather, characterized in that it consists in: uniformly impregnating a fibrous mass with a polymer to form a porous sheet material; heating the porous sheet material under pressure, the heat and pressure being applied to at least one surface of the sheet, to develop a sheet material simulating leather having a grain layer on the surface to which the heat has been applied, the flower layer having an apparent density equal to the actual density, and a crust layer having an apparent density lower than its actual density, the sheet material having a density decreasing from the flower layer to the crust layer and the ratio of the fiber to the polymer being uniform at all points of said material * 10 in sheet form. 23. The method of claim 22, characterized in that heat and pressure are applied to both surfaces of the sheet material to develop a density gradient from the outside of the sheet inward and the sheet material is split into two halves, the outer surfaces forming the flower layer and the inner surfaces forming the crust layers. »K