JP2003096676A - Method for producing leather-like sheet-like article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a leather-like sheet-like article having a good surface nap grade, a soft touch and good physical properties, without applying a treatment for deteriorating the mechanical properties and color-developing property of fibers, such as a thermal treatment. SOLUTION: This method for producing the leather-like sheet-like article, comprising impregnating a fibrous substrate with a polyurethane, is characterized by carrying out a processing treatment containing at least the following processes 1 to 3 in the order. 1. a process for producing a sheet from ultra fine fiber-developable fibers comprising two kinds of polymers having different dissolving properties, respectively, in an alkali aqueous solution, 2. a process for imparting polyvinyl alcohol to the sheet and then thermally treating the sheet, and 3. a process for treating the sheet in an alkali aqueous solution containing an agent for lowering the dissolution of the polyvinyl alcohol to develop the ultra fine fibers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a leather-like sheet material having excellent physical properties, texture and quality. More specifically, the present invention relates to a method for producing a leather-like sheet material by applying polyvinyl alcohol to a fibrous base material and then subjecting it to an ultrafine fiber expression treatment with an alkaline aqueous solution to which a poorly soluble agent for polyvinyl alcohol is added. . The leather-like sheet material obtained by the present invention has excellent coloring properties, has flexibility and texture of texture, is extremely close to natural leather, has a high-grade graceful quality, and has good physical properties. have.

[0002]

2. Description of the Related Art A leather-like sheet made of fibers and a polymer elastic material is widely used for clothing and materials. In particular, a leather-like sheet material using ultrafine fibers of 0.5 dtex or less has a texture and touch similar to natural leather, and its use has been expanding in recent years.

As a means for obtaining the ultrafine fibers, a method of producing sea-island type composite fibers or polymer blend fibers using a plurality of polymer substances, and removing at least one component of the composite fibers with an organic solvent is obtained. It is widely used due to its thinness and the appropriate space between the fibers, and its excellent flexibility. At that time, a method of applying polyvinyl alcohol for the purpose of morphological stability of ultrafine fiber expression treatment and protection of the napped layer from polyurethane is widely adopted because of its texture and easy control of quality and physical properties.

However, in recent years, there is a concern that the use of an organic solvent may adversely affect the human body and the environment. Therefore, it is necessary to produce the leather-like sheet material without using an organic solvent. It started to come.

For this reason, various studies have been made to shift from an organic solvent to an aqueous solution as a solvent for removing at least one component in the composite fiber, but still satisfactory coloring property, texture, and No suede-like artificial leather with physical properties and excellent nap quality has been obtained. The reason is that since polyvinyl alcohol is water-soluble, it will be eluted in an aqueous type solvent during the treatment of expressing ultrafine fibers, and cannot be used, and it is difficult to adjust the nap quality and physical properties. Further, as a means for preventing the elution of polyvinyl alcohol into an aqueous type solvent, it is considered that the polyvinyl alcohol becomes hardly soluble by heat treatment, but the heat treatment at high temperature lowers the physical properties and / or promotes crystallization of the fiber to lower the color developability. There is a problem of doing.

[0006]

In order to obtain a leather-like sheet-like material by applying polyvinyl alcohol to a fibrous base material and then subjecting it to ultrafine fiber expression treatment, an aqueous solvent is used from the viewpoint of effects on the human body and the environment. To use. For this reason, it is essential to make polyvinyl alcohol difficult to dissolve, but it does not have to be treated to reduce the mechanical and physical properties of the fiber by heat treatment, etc., and it has a leather-like surface finish quality, a soft texture and good physical properties. It is to provide a method for manufacturing a sheet-shaped material.

[0007]

The present invention employs the following means in order to solve the problems of the prior art.

That is, in producing a leather-like sheet material in which a fibrous base material is impregnated with polyurethane, a leather-like sheet characterized by performing a processing treatment including at least the following steps 1 to 3 in this order: It is a manufacturing method of the object. 1. A step of producing a sheet using ultrafine fiber-expressing fibers composed of a combination of two or more kinds of polymer substances having different solubilities in an alkaline aqueous solution. 2. A step of applying polyvinyl alcohol to the sheet and subjecting it to heat treatment. 3. A step of treating the above-mentioned sheet with an alkaline aqueous solution to which a poorly soluble agent for polyvinyl alcohol is added to express ultrafine fibers.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has been earnestly studied on the above problems, and in the production of a leather-like sheet-like product, after adding polyvinyl alcohol to a fibrous base material, an alkaline solution containing a polyvinyl alcohol poorly soluble agent is added. It has been found that the surface nap quality, soft texture and good physical properties can be achieved without subjecting the physical properties such as heat treatment and / or the treatment for deteriorating the color development by applying the ultrafine fiber expression treatment with It is a thing.

The material of the ultrafine fiber-expressing fiber is not particularly limited as long as it can be used for a normal leather-like sheet material, but it must be a composite fiber composed of polymer substances having different solubilities in alkaline aqueous solutions. . The polymer substances referred to here have different solubilities in an alkaline aqueous solution because the dissolution rate in a 10% sodium hydroxide aqueous solution heated to 70 ° C. with the same surface area is 5 times or more, It is more preferable that the difference is 20 times or more in that the polymer substance is stably dissolved under the condition of not being dissolved. In addition, although there is no particular limitation as to the polymer substance having high solubility in such an alkaline aqueous solution, from the viewpoint of alkali dissolution rate and spinning stability,
A copolyester obtained by copolymerizing 5-sodium sulfoisophthalic acid, polyethylene glycol, sodium dodecylbenzenesulfonate, bisphenol A compound, isophthalic acid, adipic acid, dodecadioic acid, cyclohexylcarboxylic acid and the like is preferable.

The copolymerization ratio is preferably 5 mol% or more because polyvinyl alcohol needs to be dissolved under the condition that the shape is maintained, and 20 mol% or less because it is not dissolved in the stretching step and / or the shrinking step.
From the viewpoint of heat resistance and alkali solubility, it is more preferable to use a polyethylene terephthalate copolymer obtained by copolymerizing 5-sodium sulfoisophthalic acid in an amount of 5 to 20 mol%. On the other hand, polyesters such as polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, and copolymerized polyesters and nylon-
6, polyamides such as nylon-6,6 and copolyamides can be used, but durability, wet fastness,
Polyethylene terephthalate is preferred from the viewpoints of light fastness and wrinkle resistance. In addition, the density of polyethylene terephthalate after the treatment for expressing ultrafine fibers using polyethylene terephthalate is preferably 1.385 or less from the viewpoint of color developability, and more preferably 1.380 or less. The density of polyethylene terephthalate here is a value measured by the density gradient tube method.

The ultrafine fibers are those spun by ordinary wet, dry and melt spinning methods, and further by the melt blow method, the method of extracting and removing one component from the sea-island type fiber and the polymer blend fiber, the split fiber method and the like. What is obtained can be used. The form of the ultrafine fiber-expressing fiber is shown in Japanese Patent Publication No. 48-22126, etc., polymer mutual array fibers, Japanese Patent Publication No. 51-21041, Japanese Patent Publication No. 60-21904, and the like. It is preferable to appropriately select and use the mixed spun fiber or the like according to the purpose.

The alkaline aqueous solution used for expressing the ultrafine fibers in the present invention is not particularly limited, and examples thereof include sodium hydroxide aqueous solution, potassium hydroxide aqueous solution and ammonia salt, but they are easy to handle. From the viewpoint of, a sodium hydroxide aqueous solution is preferable. The temperature at this time is preferably 40 to 80 ° C. from the viewpoint of easy operation and processing speed. The fineness of the ultrafine fibers obtained from such fibers is 0.
It is preferably 5 dtex or less from the viewpoint of texture such as flexibility, but it is not always necessary that all the single fibers contained in the nonwoven fabric be 0.5 dtex or less, and the surface layer of the fibrous base material is substantially It may be in a state of being composed of single fibers of 0.5 dtex or less. In the present invention, a fibrous base material having a surface fiber layer mainly composed of ultrafine fibers having a single fiber fineness of 0.5 dtex or less obtained by the above method is applied. When the monofilament fineness is 0.5 dtex or less, the rigidity of the fiber is small and the surface nap is weak, so that high-quality surface quality, touch feeling, and writing effect peculiar to suede-like artificial leather can be obtained.

As a method for obtaining a fibrous base material, the above-mentioned various ultrafine fibers and / or ultrafine fiber-expressing fibers are used as a card /
A nonwoven web is produced by a dry method such as a cross layer / random webber method, or by dispersing a ultrafine fiber and / or a fiber expressing an ultrafine fiber in a liquid by a wet method, so-called a papermaking method. It is obtained by entangled and integrating a laminated pair in which non-woven webs of the same kind or different kinds are laminated on at least one surface of the web by needle punching, fluid entanglement treatment or the like.

Further, a needle-punching layered pair obtained by laminating a nonwoven web obtained from the ultrafine fibers and / or the ultrafine fiber-expressing fibers on one side or both sides of a woven or knitted fabric in the same manner,
A fibrous base material can be obtained by entanglement and integration with a fluid entanglement device or the like. The production method according to the present invention can be applied to the fibrous base material obtained by the method as described above.

In the case where the nonwoven web made of the ultrafine fibers and / or the ultrafine fiber-expressing fibers is a fibrous base material which is disposed so as to cover at least one entire surface of the woven or knitted fabric and is three-dimensionally entangled with the woven or knitted fabric, Since the fibrous base material is reinforced by the woven or knitted fabric, it can be selected in a wide range, such as by reducing the amount of polyurethane to be applied, and as a result, it is easy to obtain a supple and soft texture and fine surface nap quality. In addition, the physical properties can be satisfied together, and the effects of the manufacturing method according to the present invention can be maximized.

The polyvinyl alcohol provided as a reinforcing agent during the protection of the napped layer and the treatment for expressing the ultrafine fibers preferably has the following characteristics. (1) The weight reduction rate after immersing in a 10 wt% sodium hydroxide aqueous solution at 50 ° C. for 60 minutes is 50% or less. (2) The weight reduction rate after immersion in hot water of 98 ° C. for 30 minutes is 95% or more. The saponification degree is 90 because the above characteristics must be satisfied.
% Or more of polyvinyl alcohol is preferable, and the saponification degree is 9
More preferably, it is 5% or more of polyvinyl alcohol.

In order to satisfy the above-mentioned characteristics, the treatment for making polyvinyl alcohol difficult to dissolve in alkali is 80-1.
Heat treatment at 60 ° C. can be performed. Further, heat treatment at 110 to 150 ° C. is more preferable from the viewpoint of insolubilization effect.

In the present invention, the polyvinyl alcohol aqueous solution may be applied by a conventional impregnation method, spray method, coating method or the like. In consideration of workability and ease of pickup control, the impregnation method of squeezing with a mangle or the like is preferable.

As a specific method for heat-drying and heat-treating the polyvinyl alcohol of the present invention, hot air heating, infrared heating, high-frequency overheating, etc. can be applied, but polyvinyl alcohol is applied more to the surface layer of the non-woven sheet material during drying. From the standpoint of protecting more napped layers, it is more preferable to use hot air drying with a pin tenter, clip tenter or the like. Further, the drying and the heat treatment may be performed in each step, or may be performed simultaneously.

The term “hardly soluble” in the present invention means that polyvinyl alcohol is less likely to be eluted into an alkaline aqueous solution.
Here, as the poorly-solubilizing agent for polyvinyl alcohol, borax, boric acid, sodium hydroxide, etc. which are generally used may be used, but borax is preferably used from the viewpoint of the effect of making it difficult to dissolve and the toxicity. The amount of the hardly-solubilizing agent can be appropriately selected, but it is preferably 0.004 g to 2.2 g per 1 g of polyvinyl alcohol from the viewpoint of concentration control. Furthermore, 0.004 g to 0.4 g is preferable from the viewpoint of waste liquid treatment.

The polyurethane which can be used in the method of the present invention is not particularly limited, but is known to have at least one kind of polymer diol such as polyester polyol, polyether polyol, polycarbonate polyol and polyester polycarbonate polyol and an isocyanate group. An aliphatic diisocyanate,
For example, alicyclic diisocyanate, aromatic diisocyanate, specifically isophorone diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, 1,
5-naphthylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, 4,4 '
-Dicyclohexylmethane diisocyanate, 3,3 '
-A low-molecular compound having at least one kind of dichloro-4,4'-diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate and the like and two or more active hydrogen groups capable of reacting with an isocyanate group as a chain extender in the molecule, such as ethylene. Glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanediol, bis- (β-hydroxyethyl) terephthalate ,
Xylene glycol, diols such as 1,4-bis (β-hydroxyethoxy) benzene, hydrazine, ethylenediamine, propylenediamine, isophoronediamine, piperazine and its derivatives, phenylenediamine, tolylenediamine, xylylenediamine, adipic acid dihydrazide, Isophthalic acid dihydrazide, hexamethylenediamine, 4,4′-diaminophenylmethane,
It is obtained by reacting at least one of diamines such as 4,4′-dicyclohexylmethanediamine, triamines such as diethylenetriamine, amino alcohols such as aminoethyl alcohol and aminopropyl alcohol at a predetermined molar ratio. This polyurethane can be used as a polyurethane solution or a polyurethane aqueous dispersion which is dissolved in a solvent such as toluene, methyl ethyl ketone, N, N'-dimethylformamide or isopropyl alcohol. The concentration of these polyurethane solutions or aqueous polyurethane dispersions can be appropriately selected from the amount of polyurethane attached to obtain the desired suede-like artificial leather, texture, and physical properties, but the concentration range of 1-40%, The amount of adhesion to the woven sheet material is preferably 2 to 140% by weight of fiber. In the case where the non-woven sheet material provided has high-strength physical properties such as reinforced by the woven or knitted material, the concentration of the polyurethane solution or polyurethane dispersion is in the range of 1 to 30%,
The amount of polyurethane attached to the non-woven sheet is preferably in the range of 2 to 80% by weight of fiber.

That is, if the amount of polyurethane adhered to the non-woven sheet is less than 1%, the binder effect of polyurethane is remarkably reduced, and the peel strength of the intended artificial leather,
If the physical properties of dimensional stability cannot be obtained and the amount of adhesion is 140% or more, it becomes hard and has a rough feel, which is not preferable.

In the present invention, the method of applying the polyurethane solution or polyurethane dispersion can be carried out by a conventional impregnation method, spray method, coating method or the like. In consideration of workability and ease of pickup control, the impregnation method of squeezing with a mangle or the like is preferable. The method for coagulating polyurethane is not particularly limited, but for example, a dry method for coagulating polyurethane by drying and removing the solvent or water,
A wet method in which the solvent is replaced with a non-solvent to solidify the polyurethane, a wet heat method in which the polyurethane is solidified by heating with steam or the like can be appropriately selected.

Subsequently, a suede-like artificial leather excellent in nap quality can be obtained by subjecting it to hot water treatment with open soap, wince or the like to extract and remove polyvinyl alcohol and raising treatment. The polyurethane dispersion may cause a so-called migration phenomenon in which it migrates to both front and back surface layers. In that case, if necessary, a method of destroying the emulsion before drying by steam treatment, a method of uniformly removing water from the inner and outer layers of the substrate by microwave heating, a method of wet coagulation in a salt water bath, a thickener It is also possible to adjust the degree of migration, for example, by adding a migration inhibitor such as a heat-sensitive poorly soluble agent.

In the ultrafine fiber expression treatment, heating is performed if necessary,
Perform operations such as stirring and squeezing. In this case, a polymer substance having a lower solubility may be partially dissolved and a polymer substance having a higher solubility may remain.

The method for raising the non-woven sheet-like material is as follows:
Although it is possible to use a brush, buffing, or the like, buffing with sandpaper is preferable because the length and length of the napped hair and the fineness of the sandpaper can be easily adjusted by the count, rotation speed, and the like of the sandpaper.

The dyeing method is not particularly limited, but it is preferable to use a circular dyeing machine because the texture is softened by being rubbed by the liquid flow during the treatment.

The polyvinyl alcohol aqueous solution and the polyurethane solution or polyurethane dispersion of the present invention may contain a small amount of organic solvents, various stabilizers such as weathering agents, pigments, migration inhibitors and the like. .

By the above manufacturing method, a suede-like artificial leather satisfying the physical properties and texture and excellent in nap quality is obtained, but the surface is further brushed, antistatic processed, water-repellent processed and other finishing processing is carried out to further increase the commercial value. Can be increased.

[0031]

The present invention will be described with reference to the following examples.

The parts in the examples mean parts by weight. Further, the dissolution rate and the weight loss rate in the present invention were measured by the following methods. (1) Dissolution rate: It was determined from the weight ratio obtained by setting the treatment time to 1 hour according to the chemical resistance test of JIS K6911 method. (2) Weight reduction rate: (a) W ₀ g was obtained by impregnating 2 g of polypropylene nonwoven fabric with a total weight of about 5 g and applied as W ₀ g. The weight after immersing in 300 mL of a 10 wt% sodium hydroxide aqueous solution kept at 50 ° C. for 60 minutes was W ₁ g, and the weight was determined by the following equation.

Weight reduction rate = (W ₀ −W ₁ ) / (W ₀ −2)
× 100 (%) (b) W ₀ g was obtained by impregnating 2 g of polypropylene non-woven fabric with a total weight of about 5 g to give W ₀ g, and keeping this at 98 ° C. in a constant temperature bath. The weight after soaking in the hot water soaked for 30 minutes was W ₂ g, and the weight was determined by the following equation.

Weight reduction rate = (W ₀ -W ₂ ) / (W ₀ -2)
× 100 (%) (3) Tensile strength: Tensile strength measuring instrument (Toyo Instruments
2 cm width sample with a distance between chucks of 100 mm, crosshead speed of 100 mm /
Measured in minutes.

The values shown in Table 1 are expressed as (vertical value + horizontal value) / 2 for ease of expression. (4) Tear strength: measured by the Elemendorff tear strength measuring method.

The values shown in Table 1 are expressed as (vertical value + horizontal value) / 2 for ease of expression.

Example 1 Polyethylene terephthalate copolymerized with 5.5 mol% of 5-sodium sulfoisophthalic acid was used as a sea component.
Part, and the island component is 70 parts of polyethylene terephthalate as a component, and 36 islands are contained in one filament, and the average fineness is 3.8 dtex. A web was formed, and after that, needle punching was performed to create a nonwoven fabric.

This sheet has a degree of polymerization of 500 and a degree of saponification of 98%.
30 parts of the polyvinyl alcohol aqueous solution was impregnated into the island fiber and dried at 150 ° C. The weight reduction rate after immersing the above-mentioned polyvinyl alcohol in a 10 wt% sodium hydroxide aqueous solution at 50 ° C. for 60 minutes is 20%,
Weight loss rate after immersion in hot water at 98 ℃ for 30 minutes is 1
It was 00%.

Next, the sea component of this sheet was removed with a 10% aqueous sodium hydroxide solution at 60 ° C. to which 1 g / L of borax was added. At this time, the density of polyethylene terephthalate was 1.3790. This sheet was impregnated with 30 parts of polycarbonate-based polyurethane dispersed in water.
After the drying and curing treatment, polyvinyl alcohol was extracted and removed with hot water.

Next, this sheet was sliced and buffed, and then dyed with a disperse dye in a circular dyeing machine.

The leather-like sheet material thus obtained exhibited excellent coloring properties as shown in the table, and had an elegant nap quality and a soft texture. Comparative Example 1 A leather-like sheet was obtained in the same manner as in Example 1 except that the ultrafine fiber expressing treatment was carried out without adding borax.

The obtained leather-like sheet material was inferior in process passability due to the elution of polyvinyl alcohol during the treatment for expressing ultrafine fibers, had a paper-like texture as shown in the table, and had polyurethane on the surface, showing a high quality. It was inferior. Comparative Example 2 A leather-like sheet material was obtained in the same manner as in Example 1 except that an aqueous polyvinyl alcohol solution was heat-treated at 180 ° C. and then an ultrafine fiber expression treatment without addition of borax was performed. Also,
The density of polyethylene terephthalate at this time is 1.3.
It was 865.

The leather-like sheet thus obtained had a good texture as shown in Table 1, but the color development of the fiber was low and the quality was poor. Comparative Example 3 Polyethylene terephthalate copolymerized with 5.5 mol% of 5-sodium sulfoisophthalic acid was used as a sea component.
Part, and the island component is 70 parts of polyethylene terephthalate as a component, and 36 islands are contained in one filament, and the average fineness is 3.8 dtex. A web was formed, and after that, needle punching was performed to create a nonwoven fabric.

Next, the non-woven fabric was removed of sea components with a 10% aqueous sodium hydroxide solution heated to 60 ° C. At this time, the density of polyethylene terephthalate was 1.3731.

This sheet has a degree of polymerization of 500 and a degree of saponification of 98%.
30 parts of the polyvinyl alcohol aqueous solution was impregnated into the fibers and dried at 100 ° C. The weight loss rate after dipping the above polyvinyl alcohol in a 10 wt% sodium hydroxide aqueous solution at 50 ° C. for 60 minutes was 50%, 9%.
The weight reduction rate after immersion in hot water at 8 ° C for 30 minutes is 10
It was 0%.

This sheet was impregnated with 30 parts of a polycarbonate polyurethane dispersed in water. After the drying and curing treatment, polyvinyl alcohol was extracted and removed with hot water.

Next, after slicing and buffing this sheet, it was dyed with a disperse dye in a circular dyeing machine.

The leather-like sheet thus obtained exhibited excellent color development as shown in Table 1 and had an elegant nap quality, but it had a dull texture and weak physical properties. It was Example 2 Polyethylene terephthalate copolymerized with 5.5 mol% of 5-sodium sulfoisophthalic acid was used as a sea component.
Part, and the island component is 70 parts of polyethylene terephthalate as a component, and 36 islands are contained in one filament, and the average fineness is 3.8 dtex. A web was formed, and after that, needle punching was performed to create a nonwoven fabric. This non-woven fabric has a degree of polymerization of 500,
30 parts of an island fiber was impregnated with a polyvinyl alcohol aqueous solution having a saponification degree of 98%, and dried at 150 ° C. The weight reduction rate of the above-mentioned polyvinyl alcohol after being immersed in a 10 wt% sodium hydroxide aqueous solution at 50 ° C for 60 minutes was 20%, and the weight reduction rate after being immersed in hot water of 98 ° C for 30 minutes was 100%. there were. This sheet was impregnated with 30 parts of a polycarbonate-based polyurethane dispersed in water, dried, and cured.

Next, the sea component was removed from this sheet with a 10% aqueous sodium hydroxide solution at 60 ° C. to which 1 g / L of borax was added. At this time, the density of polyethylene terephthalate was 1.3790. Next, polyvinyl alcohol was subjected to extraction removal treatment with hot water.

Next, this sheet was sliced and buffed, and then dyed with a disperse dye in a circular dyeing machine.

The leather-like sheet material thus obtained exhibited excellent color-forming properties as shown in Table 1, and had an elegant nap quality and a soft texture. Comparative Example 4 A leather-like sheet was obtained in the same manner as in Example 2 except that the ultrafine fiber expressing treatment was performed without adding borax. The obtained leather-like sheet was inferior in process passability as shown in the table because of the elution of polyvinyl alcohol during the ultrafine fiber expression treatment. . Comparative Example 5 A leather-like sheet was obtained in the same manner as in Example 2 except that the polyvinyl alcohol aqueous solution was heat-treated at 180 ° C. and then the ultrafine fiber expression treatment without adding borax was performed. Also,
The density of polyethylene terephthalate at this time is 1.3.
It was 865. The obtained leather-like sheet had a good texture as shown in Table 1, but the color development of the fiber was low and the quality was poor.

[0052]

[Table 1]

[0053]

EFFECTS OF THE INVENTION According to the production method of the present invention, an artificial leather having excellent coloring properties, soft texture, graceful quality and good physical properties, which reduces the load on the environment without using an organic solvent, is produced. It can be manufactured.

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Claims (8)

[Claims] 1. When producing a leather-like sheet material in which a fibrous base material is impregnated with polyurethane, at least the following 1
A method for producing a leather-like sheet material, which is characterized by performing processing including all of steps 3 to 3 in this order. 1. A step of producing a sheet using ultrafine fiber-expressing fibers composed of a combination of two or more kinds of polymer substances having different solubilities in an alkaline aqueous solution. 2. A step of applying polyvinyl alcohol to the sheet and subjecting it to heat treatment. 3. A step of treating the above-mentioned sheet with an alkaline aqueous solution to which a poorly soluble agent for polyvinyl alcohol is added to express ultrafine fibers. 2. The method for producing a leather-like sheet material according to claim 1, wherein the temperature of the heat treatment applied to polyvinyl alcohol is 80 to 160 ° C. 3. A polyvinyl alcohol satisfying the characteristics of (1) and (2) at the time of ultrafine fiber developing treatment using an alkaline aqueous solution containing a polyvinyl alcohol sparingly soluble agent. The method for producing a leather-like sheet material according to item 1. (1) The weight reduction rate after immersing in a 10 wt% sodium hydroxide aqueous solution at 50 ° C. for 20 minutes is 50% or less. (2) The weight reduction rate after immersion in hot water of 98 ° C. for 30 minutes is 95% or more. 4. The polyvinyl alcohol poorly-solubilizing agent is borax and / or boric acid.
4. The method for producing a leather-like sheet material according to any one of 3 above. 5. The step of expressing ultrafine fibers is carried out using an alkaline aqueous solution at 40 to 80 ° C. to which a poorly soluble agent for polyvinyl alcohol is added.
4. The method for producing a leather-like sheet material according to any one of 4 above. 6. When applying polyurethane to a fibrous base material,
The method for producing a leather-like sheet material according to any one of claims 1 to 5, wherein the method is carried out by impregnating with a polyurethane aqueous dispersion obtained by dispersing polyurethane in water. 7. The method for producing a leather-like sheet according to claim 1, wherein the ultrafine fibers are made of polyethylene terephthalate and have a fineness of 0.5 dtex or less. 8. The method for producing a leather-like sheet material according to claim 7, wherein the ultrafine fibers have a density of 1.385 or less.