CA1178139A - Impregnated non-woven sheet material and products produced therewith - Google Patents
Impregnated non-woven sheet material and products produced therewithInfo
- Publication number
- CA1178139A CA1178139A CA000452138A CA452138A CA1178139A CA 1178139 A CA1178139 A CA 1178139A CA 000452138 A CA000452138 A CA 000452138A CA 452138 A CA452138 A CA 452138A CA 1178139 A CA1178139 A CA 1178139A
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- Prior art keywords
- sheet material
- polymer
- density
- layer
- split
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Abstract
ABSTRACT OF THE DISCLOSURE
A simulated leather sheet material is comprised of a polymer impregnated fibrous mass with a grain layer forming one surface and a split layer forming the opposing surface. The grain layer has an actual density equal to its bulk density and the split layer has a bulk density less than its actual density. The sheet material has a density decreasing from the grain layer to the split layer. A method of forming the simulated leather sheet material is also disclosed.
A simulated leather sheet material is comprised of a polymer impregnated fibrous mass with a grain layer forming one surface and a split layer forming the opposing surface. The grain layer has an actual density equal to its bulk density and the split layer has a bulk density less than its actual density. The sheet material has a density decreasing from the grain layer to the split layer. A method of forming the simulated leather sheet material is also disclosed.
Description
3~t7~3~
This application is divided out of copending parent application Serial No. 385,081 and relates to a simulated leather sheet material and a process for making same.
The above parent invention relates to resin impregnated fibrous webs and more particularly to resin impregnated fibrous webs having a uniform density throughout and products produced therefrom.
Resin impregnated sheet materials such as cloth, batts, water-leaves, and the like are well known in the art. These resin impregnated sheet materials are useful for a plurality of purposes including imitation leather in the form of vinyls and the like, structural sheet materials such as co-nveyor belts and similar products.
Prior art methods of impregnating a particular web involve the impregnation or coating of a porous material with a polymeric resin such as a polyurethane, vinyl or a similar material. Polyurethanes have met with wide acceptance as a coating or impregnating composition due to their capability of wide variation in chemical and physical properties, particularly their flexi-bility and chemical resistance. In impregnating the porous sheet material with a polymeric resin several techniques have been employed. One such prior art method involves the use of the polymeric resin in an organic solvent system wherein the sheet material is dipped in the solution and the solvent is removed therefrom. These solvent systems are undesirable since the solvent; in many cases, is toxic and must either be recovered for reuse or discarded. These solvent systems are expensive and do not necessarily provide a desirable product since upon evaporation of the solvent from the impregnated porous sheet material the resin tends to migrate to provide a non-homogeneous impregnation of the porous sheet material resulting in resin richness toward the surface of the ~7~3~3~
sheet material rather than uniform impregnation.
In order to alleviate the proklems with solvent systems, certain aqueous polymeric systems have been proposed. In forming impregnated sheet materials by impregnation with aqueous polymers the aqueous portion must be removed. Again heat is required and migration of the polymer to the surfaces of the impregnated sheet material is encountered.
In one method of combining polyurethane solutions with porous substrates the polymer is applied in an organic solvent to a substrate, such as a needle punched polyester batt. The polymer-substrate composite is subse-quently bathed with a mixture of organic solvent for the polymer and a non-solvent for the polymer that is at least partially miscible with the solvent until the layer is coagulated into a cellular structure of interconnected micro-pores. The solvent is removed from the coating layer along with the non-solvent to produce a solvent free microporous layer. Although this process yields acceptable properties for a polyurethane impregnated fabric, it has the dis-advantage of an organic solvent system partially when high performance poly-urethanes are utilized which require relatively toxic and high boiling solvents.
An example of this method is disclosed in United States Patent No. 3,208,875.
In another method, polyurethane dispersions in organic vehicles have been proposed and used to coat porous substrates such as is disclosed in United States Patent No. 3,100,721. In this system, a dispersion is applied to a substrate, and coagulated by further addition of a non-solvent. Although this approach has been used with some success, it involves two major limitations:
(1) the vehicle of the dispersion is substantially organic since relatively small amounts of non-solvent, preferably water~ are needed to form a dispersion;
and (2) there is a narrow useful range of added non-solvent so that reproducible results are difficult to obtain.
3,s~
One particularly useful method of preparing composite sheet material by impregnating a porous substrate is disclosed in United States Patent No. 4,171,391. In this system a porous sheet material is impregnated with an aqueous ionic dispersion of a polyurethane and the impregnant is coagulated therein. The composite is then dried to form a composite sheet material.
The present invention and that of the abovementioned parent application is an improvement over this basic process and in some instances is broader in scope.
Impregnated porous substrates and similar materials have been proposed as leather substitutes with the goal of preparing a product having the same characteristics as natural leather.
Natural leather, appropriately finished, is valued for its dura-bility and aesthetic characteristics for a plurality of uses. Due to the scarcity of leather and the increased cost of processing leather for particular applications, economics have dictated that synthetic materials be substituted in certain applications where leather goods had been used. Such synthetic materials have been proposed and used in the`areas of shoe uppers, upholstery, clothing, luggage making, book binding and similar applications. Because these various applications require differing physical, chemical, and aesthetic qualities, different processes using differing materials must be used to
This application is divided out of copending parent application Serial No. 385,081 and relates to a simulated leather sheet material and a process for making same.
The above parent invention relates to resin impregnated fibrous webs and more particularly to resin impregnated fibrous webs having a uniform density throughout and products produced therefrom.
Resin impregnated sheet materials such as cloth, batts, water-leaves, and the like are well known in the art. These resin impregnated sheet materials are useful for a plurality of purposes including imitation leather in the form of vinyls and the like, structural sheet materials such as co-nveyor belts and similar products.
Prior art methods of impregnating a particular web involve the impregnation or coating of a porous material with a polymeric resin such as a polyurethane, vinyl or a similar material. Polyurethanes have met with wide acceptance as a coating or impregnating composition due to their capability of wide variation in chemical and physical properties, particularly their flexi-bility and chemical resistance. In impregnating the porous sheet material with a polymeric resin several techniques have been employed. One such prior art method involves the use of the polymeric resin in an organic solvent system wherein the sheet material is dipped in the solution and the solvent is removed therefrom. These solvent systems are undesirable since the solvent; in many cases, is toxic and must either be recovered for reuse or discarded. These solvent systems are expensive and do not necessarily provide a desirable product since upon evaporation of the solvent from the impregnated porous sheet material the resin tends to migrate to provide a non-homogeneous impregnation of the porous sheet material resulting in resin richness toward the surface of the ~7~3~3~
sheet material rather than uniform impregnation.
In order to alleviate the proklems with solvent systems, certain aqueous polymeric systems have been proposed. In forming impregnated sheet materials by impregnation with aqueous polymers the aqueous portion must be removed. Again heat is required and migration of the polymer to the surfaces of the impregnated sheet material is encountered.
In one method of combining polyurethane solutions with porous substrates the polymer is applied in an organic solvent to a substrate, such as a needle punched polyester batt. The polymer-substrate composite is subse-quently bathed with a mixture of organic solvent for the polymer and a non-solvent for the polymer that is at least partially miscible with the solvent until the layer is coagulated into a cellular structure of interconnected micro-pores. The solvent is removed from the coating layer along with the non-solvent to produce a solvent free microporous layer. Although this process yields acceptable properties for a polyurethane impregnated fabric, it has the dis-advantage of an organic solvent system partially when high performance poly-urethanes are utilized which require relatively toxic and high boiling solvents.
An example of this method is disclosed in United States Patent No. 3,208,875.
In another method, polyurethane dispersions in organic vehicles have been proposed and used to coat porous substrates such as is disclosed in United States Patent No. 3,100,721. In this system, a dispersion is applied to a substrate, and coagulated by further addition of a non-solvent. Although this approach has been used with some success, it involves two major limitations:
(1) the vehicle of the dispersion is substantially organic since relatively small amounts of non-solvent, preferably water~ are needed to form a dispersion;
and (2) there is a narrow useful range of added non-solvent so that reproducible results are difficult to obtain.
3,s~
One particularly useful method of preparing composite sheet material by impregnating a porous substrate is disclosed in United States Patent No. 4,171,391. In this system a porous sheet material is impregnated with an aqueous ionic dispersion of a polyurethane and the impregnant is coagulated therein. The composite is then dried to form a composite sheet material.
The present invention and that of the abovementioned parent application is an improvement over this basic process and in some instances is broader in scope.
Impregnated porous substrates and similar materials have been proposed as leather substitutes with the goal of preparing a product having the same characteristics as natural leather.
Natural leather, appropriately finished, is valued for its dura-bility and aesthetic characteristics for a plurality of uses. Due to the scarcity of leather and the increased cost of processing leather for particular applications, economics have dictated that synthetic materials be substituted in certain applications where leather goods had been used. Such synthetic materials have been proposed and used in the`areas of shoe uppers, upholstery, clothing, luggage making, book binding and similar applications. Because these various applications require differing physical, chemical, and aesthetic qualities, different processes using differing materials must be used to
2~ obtain an acceptable product which is comparable to natural leather; although in most instances these synthetics are readily distinguishable from natural leather.
Natural leather from animal hides is composed of two surfaces:
one surface defining the grain layer, which in most instances is the most aesthetically desirable and the opposing surface defining tlle split layer.
The grain layer is the epidermis of the animal and is very smooth whereas the the split layer in most instances is rough and fibrous.
One method of preparing a synthetic as a substitute for leather involves impregnating and/or coating of porous material, for example, cloth, with a polyurethane, vinyl or a similar material. Polyurethanes have met with wide acceptance as a coating or impregnating composition due to their capability of wide variation in chemical and physical properties, particularly their flexibility and chemical resistance.
Objectives in preparing the synthetic substi-tutes for leather are that they provide: (1) sheets especially suitable for leather-like and uphol-stery uses; (2~ sheets of uniform width as commonly used in the textile indus-try (unlike natural products which sustain substantial weight and area losses in cutting and finishing); (3) end use versatility, for example, under a variety of exposure conditions where certain chemical treatments will assist maintenance and useful lifetime of properties; and most importantly, ~4) a product with the strength, hand, drape and softness comparable to natural leather.
Further, a simulated leather sheet material when used for shoe uppers should be characterized by a leather appearance, with no undesirable fabric show through, good water vapor permeation into the uncoated side of the upper, and a leather grain break (minimal gross wrinkling). "Leather-like grain break", as recognized in leather and upholstery industries, is manifested in the behavior of well finished leather when folded or crumpled. The leather fold is characterized by a smooth curved contour, frequently with numerous fine wrinkles in the compressed region of the fold area. This is contrasted with sharp creases or gross wrinkles formed when papers or films are folded;
this kind of undesirable appearance is known as "pin wrinkling."
~he "hand" of leather is highly distinctive and synthetics normally have a rubbery feel which is contrasted with leather.
~7~L3~
Polyurethane polymers as coatings or impregnants for fabric to provide substitutes for leather have long been recognized. For example, polyurethanes can be made which are highly resistant to solvents and abrasion, conferring dry cleanability and outstanding durability to coated fabrics. The basic chemistry of polyurethanes, involving reactions between the isocyanate groups and molecules with multiply reactive hydrogen, such as polyols and polyamines, afford great versatility and variability in final chemical and physical properties by the selection of intermediates to achieve processibility and the desired balance of end use performance requirements.
There are various methods for applying polyurethane solutions or other post curable liquid polymers to porous substrates which are well known to those skilled in the art. An article in J r al of Coated Fabrics, Vol.7 (July 1977), pages 43 through 57 describe some of the commercial coating systems, e.g. reverse roll coating, pan ed coater, gravure and the like.
Brushing and spraying may also be used to coat polyurethanes on porous sub-strates~ These polyurethane solutions, after impregnation or coating on the porous substrate, are dried or cured by a method such as heated air, infrared radiation and the like. Characteristic of these processes is the deposition of a polymer and a film-like layer which tends to produce a coated fabric which folds in undesirable sharp creases rather than leather-like grain break.
Other me~hods of combining polymeric solutions and particularly polyurethane solutions with porous substrates are exemplified by United States Patent No.
Natural leather from animal hides is composed of two surfaces:
one surface defining the grain layer, which in most instances is the most aesthetically desirable and the opposing surface defining tlle split layer.
The grain layer is the epidermis of the animal and is very smooth whereas the the split layer in most instances is rough and fibrous.
One method of preparing a synthetic as a substitute for leather involves impregnating and/or coating of porous material, for example, cloth, with a polyurethane, vinyl or a similar material. Polyurethanes have met with wide acceptance as a coating or impregnating composition due to their capability of wide variation in chemical and physical properties, particularly their flexibility and chemical resistance.
Objectives in preparing the synthetic substi-tutes for leather are that they provide: (1) sheets especially suitable for leather-like and uphol-stery uses; (2~ sheets of uniform width as commonly used in the textile indus-try (unlike natural products which sustain substantial weight and area losses in cutting and finishing); (3) end use versatility, for example, under a variety of exposure conditions where certain chemical treatments will assist maintenance and useful lifetime of properties; and most importantly, ~4) a product with the strength, hand, drape and softness comparable to natural leather.
Further, a simulated leather sheet material when used for shoe uppers should be characterized by a leather appearance, with no undesirable fabric show through, good water vapor permeation into the uncoated side of the upper, and a leather grain break (minimal gross wrinkling). "Leather-like grain break", as recognized in leather and upholstery industries, is manifested in the behavior of well finished leather when folded or crumpled. The leather fold is characterized by a smooth curved contour, frequently with numerous fine wrinkles in the compressed region of the fold area. This is contrasted with sharp creases or gross wrinkles formed when papers or films are folded;
this kind of undesirable appearance is known as "pin wrinkling."
~he "hand" of leather is highly distinctive and synthetics normally have a rubbery feel which is contrasted with leather.
~7~L3~
Polyurethane polymers as coatings or impregnants for fabric to provide substitutes for leather have long been recognized. For example, polyurethanes can be made which are highly resistant to solvents and abrasion, conferring dry cleanability and outstanding durability to coated fabrics. The basic chemistry of polyurethanes, involving reactions between the isocyanate groups and molecules with multiply reactive hydrogen, such as polyols and polyamines, afford great versatility and variability in final chemical and physical properties by the selection of intermediates to achieve processibility and the desired balance of end use performance requirements.
There are various methods for applying polyurethane solutions or other post curable liquid polymers to porous substrates which are well known to those skilled in the art. An article in J r al of Coated Fabrics, Vol.7 (July 1977), pages 43 through 57 describe some of the commercial coating systems, e.g. reverse roll coating, pan ed coater, gravure and the like.
Brushing and spraying may also be used to coat polyurethanes on porous sub-strates~ These polyurethane solutions, after impregnation or coating on the porous substrate, are dried or cured by a method such as heated air, infrared radiation and the like. Characteristic of these processes is the deposition of a polymer and a film-like layer which tends to produce a coated fabric which folds in undesirable sharp creases rather than leather-like grain break.
Other me~hods of combining polymeric solutions and particularly polyurethane solutions with porous substrates are exemplified by United States Patent No.
3,208,875 and United States Patent ~o. 3,100,721.
An improved process for impregnating fabrics is disclosed in United States Patent No. 4,171,391 which includes certain steps which are necessary in forming simulated leather sheet material in accordance with the invention.
~ 5 . .
3~
In accordance with the present invention, a simulated leather sheet material is formed which has the appearance and properties of natural leather and further has certain physical similarities therewith.
In accordance with the invention of the parent application, a method of impregnating porous sheet materials and particularly needled batts is disclosed wherein uniform impregnation is provided in an aqueous system forrning a product with high tear strength and integrity.
Further, in accordance with the invention of the parent application, an impregnated fibrous web is provided which has a novel and unusual useful structure adapted to be used as formed or subsequently processed to provide further advantage.
According to one aspect of the present invention there is provided a simulated leather sheet material comprising:
a polymer impregnated fibrous mass with a grain layer forming one surface, the grain layer having an actual density equal to its bulk density and a split layer forming the opposing surface, the grain layer being a composite of fibers in a continuous resin matrix, the split layer having a bulk density less than its actual density, the split layer having coated and uncoated fibers, masses of polymer and voids, said sheet material having a density de-creasing from the grain layer to the split layer, wherein the ratio of fiber to polymer is uniform tl-roughout said sheet material.
According to a further aspect of the present invention there is provided a method of forming a simulated leather sheet material comprising:
uniformly impregnating a fibrous mass with a polymer to form a porous sheet material;
heating the porous sheet material under heat and pressure, said heat and pressure being applied to at least one surface thereof, to develop a simulated leather sheet material having a grain layer on the surface to which the heat has ~een applied, the grain layer having a bulk density equal to the actual density, said grain layer being a composite of fibers in a continuous resin matrix, a split layer having a bulk density less than its actual densityJ
said split layer having coated and uncoated fibers, masses of polymer and voids, the sheet material having a density decreasing from the grain layer to the split layer and wherei.n the ratio of :Eiber to polymer is uniform throughout said sheet material.
According to one aspect of the invention of the parent application there is provided a resin impregnated fibrous web comprised of:
a needled fibrous batt;
a polymeric resin distributed throughout said batt forming a resin impregnated fibrous web;
the density of said impregnated fibrous web being uniform throughout;
the bulk density of said web being less than the actual density of said web, whereby the web is porous; and said impregnated web having filaments which are both coated and uncoated with polymeric resin and concentrations of polymeric resin.
According to a further aspect of the invention of the parent application there is provided a method of forming an impregnated fibrous web comprising:
fully saturating a needled fibrous batt with an aqueous dispersion or emulsion of ionically solubilized polymeric resin;
contacting the fully saturated needled batt with an ionic coagu-lating agent to coagulate the polymeric resin from the aqueous dispersion and deposit the polymeric resin within said needled batt; and drying the needled batt and polymeric resin to form an impregnated fibrous web having a uniform density throughout.
"Bulk density" as used herein means and refers to the density of the material including air space. "Actual density" as used herein means and refers to the density of the material not including air space, i.e. specific gravity.
The fibrous mass includes woven and knit fabrics, felt and non-wovens, such a~spun bonded sheets, needled batts and waterleaves. Suitable substrate fibers are the natural fibers3 particularly cotton and wool; synthetic fibers such as polyester, nylon, acrylics, modacrylics, and rayon. Most preferably, the fibrous mass is needled fibrous batts formed of such natural and synthetic fibers. Preferably, the fibers have a denier of 1 to 5 and a length which is suitable for carding which is typically one to six inches and more preferably one and one-half to three inches.
The necdled fibrous batts can be either of high, intermediate or low density. The high density batts have a maximum density of 0.5 grams/cc.
These high density batts are typically composed of wool. ~hen synthetic fibers are used in forming the batts, the high density batts are up to 0.25 grams/cc.
Preferably the fibrous batts have a density of 0.08 grams/cc to 0.5 grams/cc.
The thickness of the batts may be up to 0.5 inch and preferably between 0.12 inch and 0.4 inch with a minimum thickness of 0.030 inch. Additionally, the batts are characterized as "saturating batts" which have~high integrity due to the needle punching operation as opposed to lightly bonded batts having few needle punches with little or no integrity.
The polymeric resins useful in the practice of the invention are preferably those polymeric resins which are capable of solubilization, disper-sion, or emulsification in water and subsequent coagulation from the water system with an ionic coagulating agent.
~'7~L3~
~ preferred polymer system is one which is synthesized from acrylic monomers such as the alkyl acrylates and methylacrylates, acrylonitrile, methylacrylonitrile and other well known acrylic monomers. These acrylic monomers may be polymerized by emulsion polymerization to form a latex or by other free radical polymerization mechanisms and subsequently solubilized or emulsified in water. The emulsification or solubilizing system must be such that when the emulsion is contacted with concentrated acid or base the polymer coagulates from the aqueous system and is rendered substantially insoluble.
Most preferably, emulsified or aqueously dispersed polyurethanes are utilized. Exemplary of the emulsified polyurethanes are those disclosed in United States Patent No. 2,968,575 prepared and dispersed in water with the aid of detergents under the action of powerful shearing forces. ~hen these polyurethane emulsions are formed, the emulsifying agent or detergent must be one which is ionic in nature so that a counter ion may be added to the aqueous system to coagulate the polymer Most preferably, the polyurethanes are those recognized in the art as ionically water dispersible.
The preferred system for preparing ionic aqueous polurethane dis-persions is to prepare polymers that have free acid groups, preferably carboxylic acid groups covalently bonded to the polymer backbone. Neutralization of these carboxyl groups with an amine, preferably a water soluble mono-amine, affords water dilutability. Careful selection of the compound bearing the carboxylic group must be made ~ecause isocyanates, necessary components in any poly-urethane system, are generally reactive with carboxylic groups. However, as disclosed in United States Patent No. 3,412,05~, 2,2-hydroxymethyl-substituted carboxylic acids can be reacted with organic polyisocyanates without significant reaction ~etween the acid and isocyanate groups due to the stearic hinderance 3~
of the carboxyl by the adjacent alkyl groups. This approach provides the desired carboxyl containing polymer with the carboxylic groups being neutralized with the tertiary mono-amine to provide an internal quaternary alnmonium salt and hence, water dilutability.
Suitable carboxylic acids and preferably the stearically hindered carboxylic acids, are well known and readily available. For example, they may be prepared from an aldehyde that contains at least two hydrogens in the alpha position which are reacted in the presence of a base with two equivalents of formaldehyde to form a 2~2-hydroxymethyl aldehyde. The aldehyde is then oxidized to the acid by procedures known to those skilled in the art. Such acids are represented by the structural formula, Cl H20~1 R - C - COOH
wherein R represents hydrogen, or alkyl of up to 20`-carbon atoms, and preferably, up to eight carbon atoms. A pre~erred acid is 2,2-di-(hydroxymethyl)propionic acid. The polymers with the pendant carboxyl groups are characterized as anionic polyurethane polymers.
Further, an alternate route to confer water dilutability is to use a cationic polyurethane having pendant amino groups. Such cationic polyurethanes are disclosed in United States Patent ~o. 4,066,591, and particularly, in Example XVII. It is pre~erred that the anionic polyurethane be used.
The polyurethanes useful more particularly involve the reaction of di-or polyisocyanates and compounds with multiple reactive hydrogens suitable for the preparation of polyurethanes. Such diisocyanates and reactive hydrogen compounds are more fully disclosed in United States Patent Nos. 3,412,034 and
An improved process for impregnating fabrics is disclosed in United States Patent No. 4,171,391 which includes certain steps which are necessary in forming simulated leather sheet material in accordance with the invention.
~ 5 . .
3~
In accordance with the present invention, a simulated leather sheet material is formed which has the appearance and properties of natural leather and further has certain physical similarities therewith.
In accordance with the invention of the parent application, a method of impregnating porous sheet materials and particularly needled batts is disclosed wherein uniform impregnation is provided in an aqueous system forrning a product with high tear strength and integrity.
Further, in accordance with the invention of the parent application, an impregnated fibrous web is provided which has a novel and unusual useful structure adapted to be used as formed or subsequently processed to provide further advantage.
According to one aspect of the present invention there is provided a simulated leather sheet material comprising:
a polymer impregnated fibrous mass with a grain layer forming one surface, the grain layer having an actual density equal to its bulk density and a split layer forming the opposing surface, the grain layer being a composite of fibers in a continuous resin matrix, the split layer having a bulk density less than its actual density, the split layer having coated and uncoated fibers, masses of polymer and voids, said sheet material having a density de-creasing from the grain layer to the split layer, wherein the ratio of fiber to polymer is uniform tl-roughout said sheet material.
According to a further aspect of the present invention there is provided a method of forming a simulated leather sheet material comprising:
uniformly impregnating a fibrous mass with a polymer to form a porous sheet material;
heating the porous sheet material under heat and pressure, said heat and pressure being applied to at least one surface thereof, to develop a simulated leather sheet material having a grain layer on the surface to which the heat has ~een applied, the grain layer having a bulk density equal to the actual density, said grain layer being a composite of fibers in a continuous resin matrix, a split layer having a bulk density less than its actual densityJ
said split layer having coated and uncoated fibers, masses of polymer and voids, the sheet material having a density decreasing from the grain layer to the split layer and wherei.n the ratio of :Eiber to polymer is uniform throughout said sheet material.
According to one aspect of the invention of the parent application there is provided a resin impregnated fibrous web comprised of:
a needled fibrous batt;
a polymeric resin distributed throughout said batt forming a resin impregnated fibrous web;
the density of said impregnated fibrous web being uniform throughout;
the bulk density of said web being less than the actual density of said web, whereby the web is porous; and said impregnated web having filaments which are both coated and uncoated with polymeric resin and concentrations of polymeric resin.
According to a further aspect of the invention of the parent application there is provided a method of forming an impregnated fibrous web comprising:
fully saturating a needled fibrous batt with an aqueous dispersion or emulsion of ionically solubilized polymeric resin;
contacting the fully saturated needled batt with an ionic coagu-lating agent to coagulate the polymeric resin from the aqueous dispersion and deposit the polymeric resin within said needled batt; and drying the needled batt and polymeric resin to form an impregnated fibrous web having a uniform density throughout.
"Bulk density" as used herein means and refers to the density of the material including air space. "Actual density" as used herein means and refers to the density of the material not including air space, i.e. specific gravity.
The fibrous mass includes woven and knit fabrics, felt and non-wovens, such a~spun bonded sheets, needled batts and waterleaves. Suitable substrate fibers are the natural fibers3 particularly cotton and wool; synthetic fibers such as polyester, nylon, acrylics, modacrylics, and rayon. Most preferably, the fibrous mass is needled fibrous batts formed of such natural and synthetic fibers. Preferably, the fibers have a denier of 1 to 5 and a length which is suitable for carding which is typically one to six inches and more preferably one and one-half to three inches.
The necdled fibrous batts can be either of high, intermediate or low density. The high density batts have a maximum density of 0.5 grams/cc.
These high density batts are typically composed of wool. ~hen synthetic fibers are used in forming the batts, the high density batts are up to 0.25 grams/cc.
Preferably the fibrous batts have a density of 0.08 grams/cc to 0.5 grams/cc.
The thickness of the batts may be up to 0.5 inch and preferably between 0.12 inch and 0.4 inch with a minimum thickness of 0.030 inch. Additionally, the batts are characterized as "saturating batts" which have~high integrity due to the needle punching operation as opposed to lightly bonded batts having few needle punches with little or no integrity.
The polymeric resins useful in the practice of the invention are preferably those polymeric resins which are capable of solubilization, disper-sion, or emulsification in water and subsequent coagulation from the water system with an ionic coagulating agent.
~'7~L3~
~ preferred polymer system is one which is synthesized from acrylic monomers such as the alkyl acrylates and methylacrylates, acrylonitrile, methylacrylonitrile and other well known acrylic monomers. These acrylic monomers may be polymerized by emulsion polymerization to form a latex or by other free radical polymerization mechanisms and subsequently solubilized or emulsified in water. The emulsification or solubilizing system must be such that when the emulsion is contacted with concentrated acid or base the polymer coagulates from the aqueous system and is rendered substantially insoluble.
Most preferably, emulsified or aqueously dispersed polyurethanes are utilized. Exemplary of the emulsified polyurethanes are those disclosed in United States Patent No. 2,968,575 prepared and dispersed in water with the aid of detergents under the action of powerful shearing forces. ~hen these polyurethane emulsions are formed, the emulsifying agent or detergent must be one which is ionic in nature so that a counter ion may be added to the aqueous system to coagulate the polymer Most preferably, the polyurethanes are those recognized in the art as ionically water dispersible.
The preferred system for preparing ionic aqueous polurethane dis-persions is to prepare polymers that have free acid groups, preferably carboxylic acid groups covalently bonded to the polymer backbone. Neutralization of these carboxyl groups with an amine, preferably a water soluble mono-amine, affords water dilutability. Careful selection of the compound bearing the carboxylic group must be made ~ecause isocyanates, necessary components in any poly-urethane system, are generally reactive with carboxylic groups. However, as disclosed in United States Patent No. 3,412,05~, 2,2-hydroxymethyl-substituted carboxylic acids can be reacted with organic polyisocyanates without significant reaction ~etween the acid and isocyanate groups due to the stearic hinderance 3~
of the carboxyl by the adjacent alkyl groups. This approach provides the desired carboxyl containing polymer with the carboxylic groups being neutralized with the tertiary mono-amine to provide an internal quaternary alnmonium salt and hence, water dilutability.
Suitable carboxylic acids and preferably the stearically hindered carboxylic acids, are well known and readily available. For example, they may be prepared from an aldehyde that contains at least two hydrogens in the alpha position which are reacted in the presence of a base with two equivalents of formaldehyde to form a 2~2-hydroxymethyl aldehyde. The aldehyde is then oxidized to the acid by procedures known to those skilled in the art. Such acids are represented by the structural formula, Cl H20~1 R - C - COOH
wherein R represents hydrogen, or alkyl of up to 20`-carbon atoms, and preferably, up to eight carbon atoms. A pre~erred acid is 2,2-di-(hydroxymethyl)propionic acid. The polymers with the pendant carboxyl groups are characterized as anionic polyurethane polymers.
Further, an alternate route to confer water dilutability is to use a cationic polyurethane having pendant amino groups. Such cationic polyurethanes are disclosed in United States Patent ~o. 4,066,591, and particularly, in Example XVII. It is pre~erred that the anionic polyurethane be used.
The polyurethanes useful more particularly involve the reaction of di-or polyisocyanates and compounds with multiple reactive hydrogens suitable for the preparation of polyurethanes. Such diisocyanates and reactive hydrogen compounds are more fully disclosed in United States Patent Nos. 3,412,034 and
4,046,729. Further, the processes to prepare such polyurethanes are well lo-~7i~3~
recognized as exemplified by the aforementioned patents. Aromatic, aliphatic andcyclo-aliphatic diisocyanates or mixtures thereof can be used in forming the polymer. Such diisocyanates, for example, are tolylene-2,4-diisocyanate;
tolylene-2,6-diisocyanate; meta-phenylene diisocyanate; biphenylene-4,4'-diisocyanate; methylene-bis(4-phenyl isocyanate); 4-chloro-1,3-phenylene diisocyanate; naphthylene-1,5-diisocyanate; tetramethylene-l J 4-diisocyanate;
hexamethylene-1,6-diisocyanate; decamethylene-l,10-diisocyanate; cyclohexylene-1,4-diisocyana-te; methylene-bis~4-cyclohexyl isocyanate); tetrahydronaphthy-lene diisocyanate; isophorone diisocyanate and the like. Preferably, the arylene and cyclo-aliphatic diisocyanates are used most advantageously.
Characteristically, the arylene diisocyanates encompass those in which the isocyanate group is attached to the aromatic ring. The most preferred isocyanates are the 2,4 and 2,6 isomers of tolylene diisocyanate and mixtures thereof, due to their ready availability and their reactivity. Further, the cyclo-aliphatic diisocyanates used most advantageously are 4,4'-methylene-bis(cyclohexyl isocyanate) and isophorone diisocyanate.
Selection of the aromatic or aliphatic diisocyanates is predicated upon the final end use of the particular material. As is well recogniæed by those skilled in the art, the aromatic isocyanates may be used where the final product is not excessively exposed to ultraviolet radiation which ~ends to yellow such polymeric compositions; whereas the aliphatic diisocyanates may be more advantageously used in exterior applications and have less tendency to yellow upon exposure to ultraviolet radiation. Although these principles form a general basis for the selection of the particular isocyanate to be used, the aromatic diisocyanates may be further stabilized by well known ultraviolet stabilizers to enhance the final properties of the polyurethane impregnated sheet material. In addition, antioxidants may be added in art recogniæed levels 3~
to improve the characteristics of the final product. Typical antioxidants are the thioethers and phenolic antioxidants such as ~,4'-butylidine bis-meta-cresol and 2,6-ditert-butyl-para-cresol.
The isocyanate is reacted with the multiple reactive hydrogen compounds such as diols, diamines, or triols. In the case of diols or triols, they are typically either polyalkylene ether or polyester polyols. A polyalky-lene ether polyol is the preferred active hydrogen containing polymeric materialfor formulation of the polyurethane. The most useful polyglycols have a molecular weight of 50 to 10,000 and the most preferred is from about 400 to 7,000. Further,the polyether polyols improve flexibility proportionally with the increase in their molecular weight.
Examples of the polyether polyols are, but not limited to, poly-ethylene ether glycol, polypropylene-ether glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, polyoctamethylene ether glycol, poly-decamethylelle ether glycol, polydodecamethylene ether glycol and mixtures thereof. Polyglycols containing several different radicals in the molecular chain, such as, for example, the compound HO(CH20C2H~O)nH wherein n is an integer greater than one, can also be used.
The polyol may also be a hydroxy terminated or hydroxy pendant polyester which can be used instead or in combination with the polyalkylene ether glycols. Examplary of such polyesters are thus formed by reacting acids, esters or acid halides with glycols. Suitable glycols are polymethylene glycols such as ethylene, propylene~ tetramethylene or decamethylene glycol; substitutedmethylene glycols such as 2,2-dimethyl-1,3-propane diol, cyclic glycols such as cyclohexanediol and aromatic glycols. Aliphatic glycols are genera:Lly preferred when flexibility is desired. These glycols are reacted with aliphatic 3~
cyclo-aliphatic or aromatic dicarboxylic acids or lower alkyl esters or -ester forming derivatives to produce relatively low molecular weight polymers, - f preferably having a melting point of less than about 70C, and a molecular weight like those indicated for the polyalkylene ether glycols. Acids for preparing such polyesters are, for example, phthalic, maleic, succinic, adipic, suberic, sebacic, terephthalic and hexahydrophthalic acids and the alkyl and halogen substituted derivativesof these acids. In addition, polycaprolactone terminated with hydroxyl groups may also be used.
One particularly useful polyurethane system is the crosslinked polyurethane system which is more fully disclosed in Canadian Patent No.
l,154,191 of Andrea Russiello entitled "Crosslinked Polyurethane Dispersions".
When used herein, "ionic dispersing agent" means an ionizable 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-ethyl piperidine, and the like; also, acid and preferc~bly water soluble acids such as acetic, propionic, lactic, and the like.
Naturally, an acid or amine will be selected contingent on the solubilizing group pendant on the polymer chain.
The desired elastomeric behavior would generally require about 25-80% by weight of long chain polyol ~i.e. 700 to 2,000 eq. wt.) in the polymer.
The degree of elongation and elasticity may vary widely from product to product depending upon the desired properties of the final product.
In forming the polyurethanes, the polyol and a molar excess of diisocyanate are reacted to form isocyanate terminated polymer. Although suitable reaction conditions and reaction times and temperatures are variable within the context of the particular isocyanate and polyol utilized, those _ 13 _ ~L:3L7~35~
skill0d in the art well recognize these variations. Such skilled artisans recognize that reactivity o:E the ingredients involved requires the balance of reaction rate with undesirable secondary reactions leading to color and molecular weight degradation. Typically, the reaction is carried out with stirring at about 50C. to about 120C. for about one to four hours. To proùide pendant carboxyl groups the isocyanate terminated polymer is reacted with a molar deficiency of dihydroxy acid, for one to four hours at 50C. to 120C. to form isocyanate terminated prepolymer. The acid is desirably added as a solution, for example, in N-methyl-1,2-pyrrolldone or N-N-dimethylformamide. The solvent for the acid will typically be no more than about 5% of the total charge in order to minimize the organic solvent concentration in the polyurethane composi-tion. After the dihydroxy acid is reacted into the polymer chain, the pendant carboxyl groups are neutralized with an amine at about 58-75C. for about twenty minutes and chain extension and dispersion are accomplished by addition to water with stirring. A water soluble diamine may be added to the water as an additional chain extender. The chain extension involves the reaction of the remaining isocyanate groups with water to form urea groups and further polymerize the polymeric material with the result that all the isocyanate groups are reacted by virtue of the addition to a large stoichiometric excess of water.
It is to be noted that the polyurethanes are thermoplastic in nature, i.e., not capable of extensive further curing after formation except by the addition of an external curing agent. Preferably, no such curing agent is added to form the composite sheet material.
Sufficient water is used to disperse the polyurethane at a concen-tration of about 10-40% by weight solids and a dispersion viscosity in the range of 10-1,000 centipoise. Viscosity may be adjusted in accordance with the 3~
particular impregnation properties desired and by the particular dispersion composition which are all dictated by the final product characteristics. It should be noted that no emulsifiers or thickeners are required for the stability of the dispersions.
Those of ordinary skill in the art recognize ways to modify the primary polyurethane dispersion according to end product uses, for example, by the addition of coloring agents, compatible vinyl polymer dispersions, ultra-violet filtering compounds, stabili~ers against oxidation alld the like.
The characterization of the dispersions is done by measurements of non-volatile content, particle si~e, viscosity measurements and by stress strain properties on strips of cast film.
The concentration range useful in practice is governed by the desirable percent add on of polymer into the needled batt.
The dispersion viscosi~y is generally in the range from 10-1,000 centipoise. The low viscosity, relative to that of identical polymers at the same solids level in organic solvent polymer solutions~ assists rapid and complete penetration of the aqueous dispersion and subsequent penetration of the coagulant. Useful solutions of polyurethanes will, in contrast, generally have viscosities of several thousand centipoise, ranging as high as 50,000 centipoise at concentrations of 20-30%.
The polymers should be impregnated into the fibrous batt at a level of at least 70 percent by weight add on based upon the weight of the fibrous batt and up to about 400 percent by weight. Preferably, the polymeric resin is impregnated at a level of about 200 to 300 percent by weight add on based upon the weight of the fibrous batt.
Coagulation is accomplished by contacting the impregnated substrate ~7~3L3~
with an aqueous solution of an ionic media designed to ionically replace the solubilizing ion. In theoryJ although not intended to be bound by such theory, in the case of an anionically solubilized polymer, the amine whicll neutralizes the carboxyl containing polyurethane is replaced with a hydrogen ion which reverts the anionic carboxyl ion thus reverting the polymer to its original, "non-dilutable" condition. This causes coagulation of the pol~er ~ithin the substrate structure.
In the case of the anionic polymer, aqueous acetic acid solutions at concentrations of 0.5% to about 75% are suitable ionic coagulant for the anionic dispersions and are preferred over stronger acids because of the relative ease of handling, low corrosion potential and disposability.
"Salting out" to coagulate the dispersion by the addition of the neutral salt is feasible but is not favored because of the large amounts of salt needed, about 10 times the concentration of acid, and attendant problems of product contamination.
In impregnating the needled batt with the polymeric resin as contemplated herein, the batt is immersed in an aqueous ionic emulsion or dispersion at a concentration level sufficient to provide an add on of at least 70% by weight. Upon immersion of the batt in the aqueous emulsion or ZO dispersion, the katt may be squeezed to remove air to provide full impregnation of the emulsion or dispersion within the batt. The batt, now fully impregnated with the aqueous dispersion or emulsion, is passed through wiping rolls or the like to remove excess dispersion or emulsion on the surface of the impregnated batt. The batt is then immersed in a bath containing the counter ion to provide coagulation with the counter ion containing material permeating the batt through diffusion and providing coagulation of the resin within the fibrous structure.
~7~i~L3~
After coagulation, the batt is squeezed to remove excess water and dried to form the impregnated web.
This process is a further improvement over the process described in United States Patent No. 4,171,391 in respect of providing particular products. The differences between the referenced patent and the present process is that the batt is fully saturated, i e. no retained air space with the aqueous dispersion or emulsion providing an ultimate add on of at least 70 percent by weight of polymeric resin based upon the weight of the batt.
Because of these differences, a novel structure is obtained wherein the batt has a uniform density throughout and the bulk density of the web is less than the actual density of the web.
After the impregnated web has been formed, a density gradient is imported hereto to form a simulated leather sheet material. When forming the simulated leather sheet material the impregnant for the web is preferably polymers which in particulate form are capable of fusion with themselves under conditions of heat and pressure. Normally, these polymers are thermoplastic;
however, some crosslinked polymers capable of coalescense may also be used.
More particularly, polyurethanes described in Canadian Patent No. 1,154,191, by Andrea Russiello entitled "Crosslinked Polyurethane Dispersions" have been found to be particularly useful to develop the desired density gradient through the thickness of the material.
The characterizing features of the simulated sheet material are primarily physical features wherein a density gradient is provided from one side of the sheet material to the opposing side of the sheet material. Prefer-ably, the density gradient is uniform. One surface of the impregnated fibrous mass defines a grain layer with this grain layer having an actual density equal to its bulk density.
This grain layer closely simulates the grain layer of natural leather. On the opposing side of the sheet material, there is a surface which defines the split layer which has a bulk density less than its actual density with there being ~preferably uniform density gradient throughout the material.
The split layer is somewhat fibrous and simulates the split layer of natural leather.
The polymer is present in the simulated leather sheet material at a level of at least 70% by weight add on based upon the weight of the fibrous mass.
Typically, the split layer is up to about 75% of the density of the grain layer to provide a porous grain layer simulating the grain layer of the leather. Also it must be noted that the polymer is uniformly distributed throughout the fibrous mass in a manner wherein the ratio of fiber to polymer is uniform throughout.
The simulated leather sheet matèrial is produced by processing the impregnated fibrous mass and preferably an impregnated non-woven sheet material as previously described.
Most preferably, the polymer used as the impregnant is one of those ~O or of the type disclosed in Canadian Patent No. 1,15~,191 previously cited.
In one method of processing, the impregnated non-woven sheet material to form the simulated leather sheet, the impregnated non-woven sheet material is placed in a press and heat and pressure are applied to both sides thereof. The heat and pressure is suffient to fuse the polymer to itself within the impregnant at the surfaces of the material, but yet insufficient to completely fuse the polymer at the interior of the sheet material. This process 3~
develops a density gradient from the interior of the non-woven sheet material to the two exterior surfaces. The dimensions of the gauge of the heated and pressed sheet material can be regulated by the pressure applied during the heating and pressing operations or by the insertion of spacers between the press plates or by use of a dead load press.
Further, the plates of the press can be embossed to provide a specific surface finish design to the material. After pressing, the sheet material is split dohn the middle to provide two simulated leather sheets each having a grain layer and a split layer.
In another process for forming the simulated leather sheet material, the impregnated non-woven starting material previously discussed can be placed in a press with only one of the plates heated to form the grain layer while having the opposing side on the cool plate forming the split layer.
In yet another process for forming the s-imulated leather sheet material, two pieces of the impregnated non-woven starting material previously discussed can be mounted upon each other in à press and heat and pressure applied sufficient to fuse the polymer to itself within the impregnant at the outer surface of each piece. After pressing, the individual pieces are separated resulting in two sheets of simulated leather.
Subsequent to ~ormation, the simulated leather may be buffed, coated or further processed in accordance with known leather ~inishing techniques.
In still another process, grain layer development may be accom-plished on unwound strips of impregnated non-woven starting material unwound from packages and passed through a pair of rolls in a calendering operation.
Preferably one of the rolls is metal, heated to 300 to 400F., smooth or -g~
suitably embossed; and the other roll is a sof~er, resilient material, such as rubber. The grain layer will be developed on the metal roll side of the sheek.
E.ffective calendering may be accomplished generally with a load of 5-15 tons/
yard width of the sheet passing through the rolls. Wetting the sheetJ prior to calendering, to 50 to 100 percent by weight added water may assist calendering.
The structures of the impregnated web and simulated leather sheet material are more fully shown in the accompanying drawings which are photo-micrographs of cross sections of an impregnated web and simulated leather sheet material prepared in accordance with the present invention and that of the parent application.
Figure l is a plan view of the resin impregnated web prepared in accordance with Example 1 prior to splitting;
Figure 2 i5 a photomicrograph taken through the thickness of the web of Figure 1 through the II-II line;
Figure 3 is a lOOx photomicrograph of the III section of Figure 2;
Figure 4 is a lOOx photomicrograph of the IV section of Figure 2;
Figure 5 is a lOOx photomicrograph of the V section of Figure 2;
; Figure 6 is a lOOx photomicrograph of a resin impregnated batt prepared in accordance with Example I after splitting; and Figure 7 is a lOOx photomicrograph of a cross section through the thickness of a simulated leather sheet material produced ~rom the batt of Figure 6.
Referring now to Figures 1 through 5, wherein like reference numerals refer to like parts there is shown a resin impregnated web 10 prepared in accordance with Example I. More particularly, Figures 2-5 show a cross section through the thickness of the web lQ. The web lQ is composed of a top surface 12 and a bottom surface 14. Throughout the web 10 there are a substan-_ 20 -3~
tial number of uncoated fibers 16, concentrations of resin 20, voids 18 and resin coated fibers 22. The struc~ure and hence its bulk density is substan-tially uniform throughout the thickness of the material, although on a micro-scopic scale~ the structure is non-homogeneous.
The structure shotvn in Figures 2_5 is believed to ~e attributable to the full impregnation of the needled batt with the aqueous emulsion or dispersion with subsequent coagulation of the polymer while the batt is fully impregnated with the aqueous resin system.
Referring now to Figure 6 which is a lOOx photomicrograph, there is shown a split impregnated needled batt 24 having a uniform density through-out such as is shown in Figures 1-5. The impregnated batt 24 has a substantial amount of uncoated fibers 26, masses of polymer 28, coated fibers 32, and voids 30. It is to be noted that although the impregnated batt is non-homogeneous on a microscopic scale it has a uniform bulk density throughout.
Referring now to Figure 7 which is a 100~ photomicrograph, there is shown the simulated leather sheet material 32 in accordance with Example IV.
The material 32 has a grain layer 34 which has minimalvoid space and the bulk density at the grain layer 34 is equal to the actual density. At the grain layer 34, there is formed a composite 36 of fibers in a continuous resin matrix as a result of the application of heat and pressure. Moving along the A direc-tion, it is shown that the voids 30 increase along the direction approaching the split layer 38. At the split layer 38, there are a substantial number of voids 30, uncoated fibers 26, and masses of polymer 28. The structure at the split layer 38 approximates the structure shown in Figure 6.
The following examples are illustrative of the products prepared in accordance with the present invention and that of the parent application.
~~~
~7~3~
EXA~IPLE I
A needled batt which was heat set and ilad a density of 1,200 grams/sq. meter composed of polyester, polypropylene and rayon fibers and a thickness of 0.3 inch with a bulk density of 0.16 grams/cm was immersed in a polyurethane prepared in accordance with Example III of Canadian Patent No.
1,15~ 1 of Andrea Russiello previously cited herein. The polymeric dispersion had a 22o total solids content to provide an add on of 120 percent based upon the weight of the batt. The batt was immersed in the polyurethane disper-sion for 10 minutes at room temperature until all of the air was expelled from within the batt and the batt was fully impregnated. The surface of the batt was wiped with a straight edge on both sides to remove excess aqueous dispersion ; and immersed in a 10 percent acetic acid bath for 10 minutes at room temperature.
Immersion in the acid completely coagulated the polyurethane within the fiber struçture. The excess acetic acid was washed from the batt and the resin im-pregnated batt was squeezed to remove excess water. The resin impregnated batt was split into four slices through its thickness and each split was dried at 300 to 350F. in a circulating air oven to form four resin impregnated webs having a bulk density of 0.~1 g/cc. The final product had a photomicrograph as shown in the drawings.
; 20 EX~MPLE II
Example I was repeated except that a 100 percent polyester batt `- having a density of 0.13 grams/cc and 0.2 inch thick was impregnated with 22 percent solids dispersion of Example I. The resulting impregnated web had a uniform density throughout, high integrity and a bulk density of 0.38 grams/cm~.
EXAMPLE III
Example I was repeated except that a 100% polyester needled batt of 0.22 inch thickness and a density of 0.23 grams/cc was impregnated with 32 , ~. ~....
. . . .
percent solids dispersion to form a needled impregnated resin fibrous web having a bulk density of 0.56 grams/cm . The product in accordance with Example III
was used as a polishing pad and had toughness, high tear strength, resilience and complete recovery upon compression.
Thus the process and product provides an impregnated fibrous web of high integrity and useful as a product in and of itself and useful in forming other products. Further, the impregnated fibrous web may be buffed to provide a desirable finish.
EXAMPLE IV
~wo 0.07-inch thick splits of the non~woven impregnated web pre-pared in accordance with Example I were superposed upon each other and placed between plates of a press heated to 300 F. at a pressure of 500 psi for 30 seconds. The two splits were then peeled apart, thus obtaining two sheets of simulated leather sheet material. The grain layer of the sheets correspond to the surfaces~which were in contact with the hot press plates. The interior sides of the sheets retained their fibrous tèxture similar to the unpressed sheet. Microscopic examination showed that the simulated leather sheet material had a density gradient from the grain layer to the split layer as is shown in Figure 7.
The simulated leather sheet material, subsequent to formation can be post treated with other polymers for surface finishing in accordance with known techniques.
Although the invention has been described with reference to parti-cular materials and particular processes, the invention is only to be limited so far as is set forth in the accompanying claims.
recognized as exemplified by the aforementioned patents. Aromatic, aliphatic andcyclo-aliphatic diisocyanates or mixtures thereof can be used in forming the polymer. Such diisocyanates, for example, are tolylene-2,4-diisocyanate;
tolylene-2,6-diisocyanate; meta-phenylene diisocyanate; biphenylene-4,4'-diisocyanate; methylene-bis(4-phenyl isocyanate); 4-chloro-1,3-phenylene diisocyanate; naphthylene-1,5-diisocyanate; tetramethylene-l J 4-diisocyanate;
hexamethylene-1,6-diisocyanate; decamethylene-l,10-diisocyanate; cyclohexylene-1,4-diisocyana-te; methylene-bis~4-cyclohexyl isocyanate); tetrahydronaphthy-lene diisocyanate; isophorone diisocyanate and the like. Preferably, the arylene and cyclo-aliphatic diisocyanates are used most advantageously.
Characteristically, the arylene diisocyanates encompass those in which the isocyanate group is attached to the aromatic ring. The most preferred isocyanates are the 2,4 and 2,6 isomers of tolylene diisocyanate and mixtures thereof, due to their ready availability and their reactivity. Further, the cyclo-aliphatic diisocyanates used most advantageously are 4,4'-methylene-bis(cyclohexyl isocyanate) and isophorone diisocyanate.
Selection of the aromatic or aliphatic diisocyanates is predicated upon the final end use of the particular material. As is well recogniæed by those skilled in the art, the aromatic isocyanates may be used where the final product is not excessively exposed to ultraviolet radiation which ~ends to yellow such polymeric compositions; whereas the aliphatic diisocyanates may be more advantageously used in exterior applications and have less tendency to yellow upon exposure to ultraviolet radiation. Although these principles form a general basis for the selection of the particular isocyanate to be used, the aromatic diisocyanates may be further stabilized by well known ultraviolet stabilizers to enhance the final properties of the polyurethane impregnated sheet material. In addition, antioxidants may be added in art recogniæed levels 3~
to improve the characteristics of the final product. Typical antioxidants are the thioethers and phenolic antioxidants such as ~,4'-butylidine bis-meta-cresol and 2,6-ditert-butyl-para-cresol.
The isocyanate is reacted with the multiple reactive hydrogen compounds such as diols, diamines, or triols. In the case of diols or triols, they are typically either polyalkylene ether or polyester polyols. A polyalky-lene ether polyol is the preferred active hydrogen containing polymeric materialfor formulation of the polyurethane. The most useful polyglycols have a molecular weight of 50 to 10,000 and the most preferred is from about 400 to 7,000. Further,the polyether polyols improve flexibility proportionally with the increase in their molecular weight.
Examples of the polyether polyols are, but not limited to, poly-ethylene ether glycol, polypropylene-ether glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, polyoctamethylene ether glycol, poly-decamethylelle ether glycol, polydodecamethylene ether glycol and mixtures thereof. Polyglycols containing several different radicals in the molecular chain, such as, for example, the compound HO(CH20C2H~O)nH wherein n is an integer greater than one, can also be used.
The polyol may also be a hydroxy terminated or hydroxy pendant polyester which can be used instead or in combination with the polyalkylene ether glycols. Examplary of such polyesters are thus formed by reacting acids, esters or acid halides with glycols. Suitable glycols are polymethylene glycols such as ethylene, propylene~ tetramethylene or decamethylene glycol; substitutedmethylene glycols such as 2,2-dimethyl-1,3-propane diol, cyclic glycols such as cyclohexanediol and aromatic glycols. Aliphatic glycols are genera:Lly preferred when flexibility is desired. These glycols are reacted with aliphatic 3~
cyclo-aliphatic or aromatic dicarboxylic acids or lower alkyl esters or -ester forming derivatives to produce relatively low molecular weight polymers, - f preferably having a melting point of less than about 70C, and a molecular weight like those indicated for the polyalkylene ether glycols. Acids for preparing such polyesters are, for example, phthalic, maleic, succinic, adipic, suberic, sebacic, terephthalic and hexahydrophthalic acids and the alkyl and halogen substituted derivativesof these acids. In addition, polycaprolactone terminated with hydroxyl groups may also be used.
One particularly useful polyurethane system is the crosslinked polyurethane system which is more fully disclosed in Canadian Patent No.
l,154,191 of Andrea Russiello entitled "Crosslinked Polyurethane Dispersions".
When used herein, "ionic dispersing agent" means an ionizable 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-ethyl piperidine, and the like; also, acid and preferc~bly water soluble acids such as acetic, propionic, lactic, and the like.
Naturally, an acid or amine will be selected contingent on the solubilizing group pendant on the polymer chain.
The desired elastomeric behavior would generally require about 25-80% by weight of long chain polyol ~i.e. 700 to 2,000 eq. wt.) in the polymer.
The degree of elongation and elasticity may vary widely from product to product depending upon the desired properties of the final product.
In forming the polyurethanes, the polyol and a molar excess of diisocyanate are reacted to form isocyanate terminated polymer. Although suitable reaction conditions and reaction times and temperatures are variable within the context of the particular isocyanate and polyol utilized, those _ 13 _ ~L:3L7~35~
skill0d in the art well recognize these variations. Such skilled artisans recognize that reactivity o:E the ingredients involved requires the balance of reaction rate with undesirable secondary reactions leading to color and molecular weight degradation. Typically, the reaction is carried out with stirring at about 50C. to about 120C. for about one to four hours. To proùide pendant carboxyl groups the isocyanate terminated polymer is reacted with a molar deficiency of dihydroxy acid, for one to four hours at 50C. to 120C. to form isocyanate terminated prepolymer. The acid is desirably added as a solution, for example, in N-methyl-1,2-pyrrolldone or N-N-dimethylformamide. The solvent for the acid will typically be no more than about 5% of the total charge in order to minimize the organic solvent concentration in the polyurethane composi-tion. After the dihydroxy acid is reacted into the polymer chain, the pendant carboxyl groups are neutralized with an amine at about 58-75C. for about twenty minutes and chain extension and dispersion are accomplished by addition to water with stirring. A water soluble diamine may be added to the water as an additional chain extender. The chain extension involves the reaction of the remaining isocyanate groups with water to form urea groups and further polymerize the polymeric material with the result that all the isocyanate groups are reacted by virtue of the addition to a large stoichiometric excess of water.
It is to be noted that the polyurethanes are thermoplastic in nature, i.e., not capable of extensive further curing after formation except by the addition of an external curing agent. Preferably, no such curing agent is added to form the composite sheet material.
Sufficient water is used to disperse the polyurethane at a concen-tration of about 10-40% by weight solids and a dispersion viscosity in the range of 10-1,000 centipoise. Viscosity may be adjusted in accordance with the 3~
particular impregnation properties desired and by the particular dispersion composition which are all dictated by the final product characteristics. It should be noted that no emulsifiers or thickeners are required for the stability of the dispersions.
Those of ordinary skill in the art recognize ways to modify the primary polyurethane dispersion according to end product uses, for example, by the addition of coloring agents, compatible vinyl polymer dispersions, ultra-violet filtering compounds, stabili~ers against oxidation alld the like.
The characterization of the dispersions is done by measurements of non-volatile content, particle si~e, viscosity measurements and by stress strain properties on strips of cast film.
The concentration range useful in practice is governed by the desirable percent add on of polymer into the needled batt.
The dispersion viscosi~y is generally in the range from 10-1,000 centipoise. The low viscosity, relative to that of identical polymers at the same solids level in organic solvent polymer solutions~ assists rapid and complete penetration of the aqueous dispersion and subsequent penetration of the coagulant. Useful solutions of polyurethanes will, in contrast, generally have viscosities of several thousand centipoise, ranging as high as 50,000 centipoise at concentrations of 20-30%.
The polymers should be impregnated into the fibrous batt at a level of at least 70 percent by weight add on based upon the weight of the fibrous batt and up to about 400 percent by weight. Preferably, the polymeric resin is impregnated at a level of about 200 to 300 percent by weight add on based upon the weight of the fibrous batt.
Coagulation is accomplished by contacting the impregnated substrate ~7~3L3~
with an aqueous solution of an ionic media designed to ionically replace the solubilizing ion. In theoryJ although not intended to be bound by such theory, in the case of an anionically solubilized polymer, the amine whicll neutralizes the carboxyl containing polyurethane is replaced with a hydrogen ion which reverts the anionic carboxyl ion thus reverting the polymer to its original, "non-dilutable" condition. This causes coagulation of the pol~er ~ithin the substrate structure.
In the case of the anionic polymer, aqueous acetic acid solutions at concentrations of 0.5% to about 75% are suitable ionic coagulant for the anionic dispersions and are preferred over stronger acids because of the relative ease of handling, low corrosion potential and disposability.
"Salting out" to coagulate the dispersion by the addition of the neutral salt is feasible but is not favored because of the large amounts of salt needed, about 10 times the concentration of acid, and attendant problems of product contamination.
In impregnating the needled batt with the polymeric resin as contemplated herein, the batt is immersed in an aqueous ionic emulsion or dispersion at a concentration level sufficient to provide an add on of at least 70% by weight. Upon immersion of the batt in the aqueous emulsion or ZO dispersion, the katt may be squeezed to remove air to provide full impregnation of the emulsion or dispersion within the batt. The batt, now fully impregnated with the aqueous dispersion or emulsion, is passed through wiping rolls or the like to remove excess dispersion or emulsion on the surface of the impregnated batt. The batt is then immersed in a bath containing the counter ion to provide coagulation with the counter ion containing material permeating the batt through diffusion and providing coagulation of the resin within the fibrous structure.
~7~i~L3~
After coagulation, the batt is squeezed to remove excess water and dried to form the impregnated web.
This process is a further improvement over the process described in United States Patent No. 4,171,391 in respect of providing particular products. The differences between the referenced patent and the present process is that the batt is fully saturated, i e. no retained air space with the aqueous dispersion or emulsion providing an ultimate add on of at least 70 percent by weight of polymeric resin based upon the weight of the batt.
Because of these differences, a novel structure is obtained wherein the batt has a uniform density throughout and the bulk density of the web is less than the actual density of the web.
After the impregnated web has been formed, a density gradient is imported hereto to form a simulated leather sheet material. When forming the simulated leather sheet material the impregnant for the web is preferably polymers which in particulate form are capable of fusion with themselves under conditions of heat and pressure. Normally, these polymers are thermoplastic;
however, some crosslinked polymers capable of coalescense may also be used.
More particularly, polyurethanes described in Canadian Patent No. 1,154,191, by Andrea Russiello entitled "Crosslinked Polyurethane Dispersions" have been found to be particularly useful to develop the desired density gradient through the thickness of the material.
The characterizing features of the simulated sheet material are primarily physical features wherein a density gradient is provided from one side of the sheet material to the opposing side of the sheet material. Prefer-ably, the density gradient is uniform. One surface of the impregnated fibrous mass defines a grain layer with this grain layer having an actual density equal to its bulk density.
This grain layer closely simulates the grain layer of natural leather. On the opposing side of the sheet material, there is a surface which defines the split layer which has a bulk density less than its actual density with there being ~preferably uniform density gradient throughout the material.
The split layer is somewhat fibrous and simulates the split layer of natural leather.
The polymer is present in the simulated leather sheet material at a level of at least 70% by weight add on based upon the weight of the fibrous mass.
Typically, the split layer is up to about 75% of the density of the grain layer to provide a porous grain layer simulating the grain layer of the leather. Also it must be noted that the polymer is uniformly distributed throughout the fibrous mass in a manner wherein the ratio of fiber to polymer is uniform throughout.
The simulated leather sheet matèrial is produced by processing the impregnated fibrous mass and preferably an impregnated non-woven sheet material as previously described.
Most preferably, the polymer used as the impregnant is one of those ~O or of the type disclosed in Canadian Patent No. 1,15~,191 previously cited.
In one method of processing, the impregnated non-woven sheet material to form the simulated leather sheet, the impregnated non-woven sheet material is placed in a press and heat and pressure are applied to both sides thereof. The heat and pressure is suffient to fuse the polymer to itself within the impregnant at the surfaces of the material, but yet insufficient to completely fuse the polymer at the interior of the sheet material. This process 3~
develops a density gradient from the interior of the non-woven sheet material to the two exterior surfaces. The dimensions of the gauge of the heated and pressed sheet material can be regulated by the pressure applied during the heating and pressing operations or by the insertion of spacers between the press plates or by use of a dead load press.
Further, the plates of the press can be embossed to provide a specific surface finish design to the material. After pressing, the sheet material is split dohn the middle to provide two simulated leather sheets each having a grain layer and a split layer.
In another process for forming the simulated leather sheet material, the impregnated non-woven starting material previously discussed can be placed in a press with only one of the plates heated to form the grain layer while having the opposing side on the cool plate forming the split layer.
In yet another process for forming the s-imulated leather sheet material, two pieces of the impregnated non-woven starting material previously discussed can be mounted upon each other in à press and heat and pressure applied sufficient to fuse the polymer to itself within the impregnant at the outer surface of each piece. After pressing, the individual pieces are separated resulting in two sheets of simulated leather.
Subsequent to ~ormation, the simulated leather may be buffed, coated or further processed in accordance with known leather ~inishing techniques.
In still another process, grain layer development may be accom-plished on unwound strips of impregnated non-woven starting material unwound from packages and passed through a pair of rolls in a calendering operation.
Preferably one of the rolls is metal, heated to 300 to 400F., smooth or -g~
suitably embossed; and the other roll is a sof~er, resilient material, such as rubber. The grain layer will be developed on the metal roll side of the sheek.
E.ffective calendering may be accomplished generally with a load of 5-15 tons/
yard width of the sheet passing through the rolls. Wetting the sheetJ prior to calendering, to 50 to 100 percent by weight added water may assist calendering.
The structures of the impregnated web and simulated leather sheet material are more fully shown in the accompanying drawings which are photo-micrographs of cross sections of an impregnated web and simulated leather sheet material prepared in accordance with the present invention and that of the parent application.
Figure l is a plan view of the resin impregnated web prepared in accordance with Example 1 prior to splitting;
Figure 2 i5 a photomicrograph taken through the thickness of the web of Figure 1 through the II-II line;
Figure 3 is a lOOx photomicrograph of the III section of Figure 2;
Figure 4 is a lOOx photomicrograph of the IV section of Figure 2;
Figure 5 is a lOOx photomicrograph of the V section of Figure 2;
; Figure 6 is a lOOx photomicrograph of a resin impregnated batt prepared in accordance with Example I after splitting; and Figure 7 is a lOOx photomicrograph of a cross section through the thickness of a simulated leather sheet material produced ~rom the batt of Figure 6.
Referring now to Figures 1 through 5, wherein like reference numerals refer to like parts there is shown a resin impregnated web 10 prepared in accordance with Example I. More particularly, Figures 2-5 show a cross section through the thickness of the web lQ. The web lQ is composed of a top surface 12 and a bottom surface 14. Throughout the web 10 there are a substan-_ 20 -3~
tial number of uncoated fibers 16, concentrations of resin 20, voids 18 and resin coated fibers 22. The struc~ure and hence its bulk density is substan-tially uniform throughout the thickness of the material, although on a micro-scopic scale~ the structure is non-homogeneous.
The structure shotvn in Figures 2_5 is believed to ~e attributable to the full impregnation of the needled batt with the aqueous emulsion or dispersion with subsequent coagulation of the polymer while the batt is fully impregnated with the aqueous resin system.
Referring now to Figure 6 which is a lOOx photomicrograph, there is shown a split impregnated needled batt 24 having a uniform density through-out such as is shown in Figures 1-5. The impregnated batt 24 has a substantial amount of uncoated fibers 26, masses of polymer 28, coated fibers 32, and voids 30. It is to be noted that although the impregnated batt is non-homogeneous on a microscopic scale it has a uniform bulk density throughout.
Referring now to Figure 7 which is a 100~ photomicrograph, there is shown the simulated leather sheet material 32 in accordance with Example IV.
The material 32 has a grain layer 34 which has minimalvoid space and the bulk density at the grain layer 34 is equal to the actual density. At the grain layer 34, there is formed a composite 36 of fibers in a continuous resin matrix as a result of the application of heat and pressure. Moving along the A direc-tion, it is shown that the voids 30 increase along the direction approaching the split layer 38. At the split layer 38, there are a substantial number of voids 30, uncoated fibers 26, and masses of polymer 28. The structure at the split layer 38 approximates the structure shown in Figure 6.
The following examples are illustrative of the products prepared in accordance with the present invention and that of the parent application.
~~~
~7~3~
EXA~IPLE I
A needled batt which was heat set and ilad a density of 1,200 grams/sq. meter composed of polyester, polypropylene and rayon fibers and a thickness of 0.3 inch with a bulk density of 0.16 grams/cm was immersed in a polyurethane prepared in accordance with Example III of Canadian Patent No.
1,15~ 1 of Andrea Russiello previously cited herein. The polymeric dispersion had a 22o total solids content to provide an add on of 120 percent based upon the weight of the batt. The batt was immersed in the polyurethane disper-sion for 10 minutes at room temperature until all of the air was expelled from within the batt and the batt was fully impregnated. The surface of the batt was wiped with a straight edge on both sides to remove excess aqueous dispersion ; and immersed in a 10 percent acetic acid bath for 10 minutes at room temperature.
Immersion in the acid completely coagulated the polyurethane within the fiber struçture. The excess acetic acid was washed from the batt and the resin im-pregnated batt was squeezed to remove excess water. The resin impregnated batt was split into four slices through its thickness and each split was dried at 300 to 350F. in a circulating air oven to form four resin impregnated webs having a bulk density of 0.~1 g/cc. The final product had a photomicrograph as shown in the drawings.
; 20 EX~MPLE II
Example I was repeated except that a 100 percent polyester batt `- having a density of 0.13 grams/cc and 0.2 inch thick was impregnated with 22 percent solids dispersion of Example I. The resulting impregnated web had a uniform density throughout, high integrity and a bulk density of 0.38 grams/cm~.
EXAMPLE III
Example I was repeated except that a 100% polyester needled batt of 0.22 inch thickness and a density of 0.23 grams/cc was impregnated with 32 , ~. ~....
. . . .
percent solids dispersion to form a needled impregnated resin fibrous web having a bulk density of 0.56 grams/cm . The product in accordance with Example III
was used as a polishing pad and had toughness, high tear strength, resilience and complete recovery upon compression.
Thus the process and product provides an impregnated fibrous web of high integrity and useful as a product in and of itself and useful in forming other products. Further, the impregnated fibrous web may be buffed to provide a desirable finish.
EXAMPLE IV
~wo 0.07-inch thick splits of the non~woven impregnated web pre-pared in accordance with Example I were superposed upon each other and placed between plates of a press heated to 300 F. at a pressure of 500 psi for 30 seconds. The two splits were then peeled apart, thus obtaining two sheets of simulated leather sheet material. The grain layer of the sheets correspond to the surfaces~which were in contact with the hot press plates. The interior sides of the sheets retained their fibrous tèxture similar to the unpressed sheet. Microscopic examination showed that the simulated leather sheet material had a density gradient from the grain layer to the split layer as is shown in Figure 7.
The simulated leather sheet material, subsequent to formation can be post treated with other polymers for surface finishing in accordance with known techniques.
Although the invention has been described with reference to parti-cular materials and particular processes, the invention is only to be limited so far as is set forth in the accompanying claims.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A simulated leather sheet material comprising:
a polymer impregnated fibrous mass with a grain layer forming one surface the grain layer having an actual density equal to its bulk density and a split layer forming the opposing surface, the grain layer being a com-posite of fibers in a continuous resin matrix, the split layer having a bulk density less than its actual density, the split layer having coated and uncoated fibers, masses of polymer and voids, said sheet material having a density decreasing from the grain layer to the split layer, wherein the ratio of fiber to polymer is uniform throughout said sheet material.
a polymer impregnated fibrous mass with a grain layer forming one surface the grain layer having an actual density equal to its bulk density and a split layer forming the opposing surface, the grain layer being a com-posite of fibers in a continuous resin matrix, the split layer having a bulk density less than its actual density, the split layer having coated and uncoated fibers, masses of polymer and voids, said sheet material having a density decreasing from the grain layer to the split layer, wherein the ratio of fiber to polymer is uniform throughout said sheet material.
2. The sheet material of claim 1 wherein the fibrous mass is a needled batt.
3. The sheet material of claim 1 wherein said polymer is a poly-urethane.
4. The sheet material of claim 3 wherein said polyurethane is cross-linked.
5. The sheet material of claim 1 wherein said polymer is present at a level of at least 75 percent by weight add on based upon the weight of said fibrous mass.
6. The sheet material of claim 5 wherein said polymer is present at a level of up to 400 percent by weight based upon the weight of said fibrous mass.
7. The sheet material of claim 6 wherein said polymer is present at a level of 200 to 300 percent by weight add on based upon the weight of said fibrous mass.
8. The sheet material of claim 1 wherein the split layer is up to 75 percent of the density of the grain layer.
9. The sheet material of claim 1 wherein the polymer is uniformly distributed throughout said fibrous mass.
10. The sheet material of claim 1 wherein the density of said sheet material has a uniform gradient from the split side to the grain side.
11. A method of forming a simulated leather sheet material comprising:
uniformly impregnating a fibrous mass with a polymer to form a porous sheet material;
heating the porous sheet material under heat and pressure, said heat and pressure being applied to at least one surface thereof, to develop a simulated leather sheet material having a grain layer on the surface to which the heat has been applied, the grain layer having a bulk density equal to the actual density, said grain layer being a composite of fibers in a continuous resin matrix, a split layer having a bulk density less than its actual density said split layer having coated and uncoated fibers, masses of polymer and voids, the sheet material having a density decreasing from the grain layer to the split layer and wherein the ratio of fiber to polymer is uniform throughout said sheet material.
uniformly impregnating a fibrous mass with a polymer to form a porous sheet material;
heating the porous sheet material under heat and pressure, said heat and pressure being applied to at least one surface thereof, to develop a simulated leather sheet material having a grain layer on the surface to which the heat has been applied, the grain layer having a bulk density equal to the actual density, said grain layer being a composite of fibers in a continuous resin matrix, a split layer having a bulk density less than its actual density said split layer having coated and uncoated fibers, masses of polymer and voids, the sheet material having a density decreasing from the grain layer to the split layer and wherein the ratio of fiber to polymer is uniform throughout said sheet material.
12. The method of Claim 11 wherein heat and pressure is applied to both surfaces of said sheet material to develop a density gradient from the exterior of said sheet material to the interior of said sheet material and splitting the sheet material in half, the exterior surfaces forming the grain layer and the interior surfaces forming the split layers.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000452138A CA1178139A (en) | 1980-09-18 | 1984-04-16 | Impregnated non-woven sheet material and products produced therewith |
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US188,330 | 1980-09-18 | ||
| US06/188,330 US4342805A (en) | 1980-09-18 | 1980-09-18 | Simulated leather sheet material |
| US188,329 | 1980-09-18 | ||
| US06/188,329 US4376148A (en) | 1980-09-18 | 1980-09-18 | Impregnated non-woven sheet material with ionically solubilized resin |
| CA000385081A CA1178138A (en) | 1980-09-18 | 1981-09-02 | Impregnated non-woven sheet material and products produced therewith |
| CA000452138A CA1178139A (en) | 1980-09-18 | 1984-04-16 | Impregnated non-woven sheet material and products produced therewith |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000385081A Division CA1178138A (en) | 1980-09-18 | 1981-09-02 | Impregnated non-woven sheet material and products produced therewith |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1178139A true CA1178139A (en) | 1984-11-20 |
Family
ID=27426327
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000452138A Expired CA1178139A (en) | 1980-09-18 | 1984-04-16 | Impregnated non-woven sheet material and products produced therewith |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1178139A (en) |
-
1984
- 1984-04-16 CA CA000452138A patent/CA1178139A/en not_active Expired
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