US20150315741A1

US20150315741A1 - Sheet-shaped material and process for producing said sheet-shaped material (as amended)

Info

Publication number: US20150315741A1
Application number: US14/647,923
Authority: US
Inventors: Gen Koide; Makoto Nishimura; Takahiro Tsuchimoto
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2012-11-30
Filing date: 2013-11-27
Publication date: 2015-11-05
Also published as: CN104838063A; EP2927368A1; KR102090355B1; EP2927368A4; TW201439398A; KR20150090122A; TWI580840B; EP2927368B1; JP6225917B2; WO2014084253A1; CN104838063B; JPWO2014084253A1

Abstract

The present invention provides a process including: (i) dissolving, in water, a polyvinyl alcohol having a degree of saponification of 98% or more and a degree of polymerization of 800 to 3500 to prepare a polyvinyl alcohol aqueous solution in which the concentrations of methyl acetate, acetic acid and methanol are 50 ppm or less, (ii) adding the polyvinyl alcohol aqueous solution to a fibrous substrate having microfiber-generating fibers as its main constituent, so that the fibrous substrate has the polyvinyl alcohol in an amount of 0.1 to 50% by mass based on the mass of the fibers contained in the fibrous substrate, (iii) generating microfibers having an average single fiber diameter of 0.3 to 7 μm from the microfiber-generating fibers contained in the fibrous substrate as its main constituent, (iv) adding a waterborne polyurethane to the fibrous substrate comprising the microfibers as its main constituent and having the added polyvinyl alcohol, and (v) removing the polyvinyl alcohol from the fibrous substrate comprising the microfibers as its main constituent and having the added waterborne polyurethane.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Phase application of PCT/JP2013/081891, filed Nov. 27, 2013, which claims priority to Japanese Patent Application No. 2012-261805, filed Nov. 30, 2012, the disclosures of each of these applications being incorporated herein by reference in their entireties for all purposes.

FIELD OF THE INVENTION

The present invention relates to a sheet-shaped material having both good softness and a high-quality appearance and exhibiting a good abrasion resistance, the sheet-shaped material being produced by using a waterborne polyurethane as a binder resin to reduce the amount of organic solvents used in the production process and thereby to reduce the burden on the environment; and also relates to a process for producing the sheet-shaped material.

BACKGROUND OF THE INVENTION

Sheet-shaped materials comprised primarily of a fibrous substrate and polyurethane have excellent characteristics that cannot be found in natural leather, and are widely used in various applications. Among them, leather-like sheet-shaped materials using a polyester fibrous substrate have excellent light resistance, and thus have been increasingly applied to clothing, chair upholstery, automobile interior materials and others.
Such sheet-shaped materials are typically produced by a wet coagulation process involving impregnating a fibrous substrate with a polyurethane solution in an organic solvent and then immersing the resulting fibrous substrate in a solvent that does not dissolve the polyurethane (i.e., water or a mixed solution of an organic solvent and water) to coagulate the polyurethane. The organic solvent used to dissolve the polyurethane is a water-miscible organic solvent such as N,N-dimethylformamide (hereinafter, also called “DMF”). There has been proposed, for example, a process for producing a sheet-shaped material, the process comprising impregnating a nonwoven fabric with a polyvinyl alcohol (hereinafter, also called “PVA”) aqueous solution to prepare a fibrous sheet-shaped material, immersing the fibrous sheet-shaped material in a polyurethane-impregnating solution, subjecting the polyurethane to wet coagulation in a 45% DMF aqueous solution at 20° C., and removing the polyvinyl alcohol and the DMF in hot water at 85° C. (see Patent Literature 1). However, typically, organic solvents are highly harmful to human bodies and the environment, and therefore there has been a strong demand for a production process for a sheet-shaped material not using organic solvents.
In order to provide a specific solution to meet the demand, there has been proposed, for example, a process using a waterborne polyurethane (a polyurethane dispersed in water) in place of a conventional polyurethane in an organic solvent. However, a sheet-shaped material produced by impregnating a waterborne polyurethane into a fibrous substrate has a hard texture. This problem is mainly caused by strong adhesion of the polyurethane to the fibers in the fibrous substrate. To solve the problem, there has been proposed a process comprising, as in the case of a production process using a conventional polyurethane in an organic solvent, the following steps: first adding a PVA to a fibrous substrate for the purpose of partially inhibiting the adhesion between the fibers and a polyurethane to be added later and thereby of forming voids between the fibers and the polyurethane, adding the polyurethane, and removing the PVA (see Patent Literature 2).
However, PVAs are water soluble, and therefore when a fibrous substrate having a PVA added is wetted with water, the PVA is dissolved away and lost in the water. In order to prevent the dissolution and loss of the PVA in such an operation involving wetting with water, the process in Patent Literature 2 employs particular strategies in (i) the step of ultra-fining fibers with an aqueous alkaline solution and (ii) the step of impregnating a waterborne polyurethane. That is, in the former step of ultra-fining fibers, the dissolution of the PVA is inhibited by the addition of borax to the aqueous alkaline solution, and in the latter step of impregnating a waterborne polyurethane, the dissolution of the PVA in water is inhibited by using a PVA having a degree of saponification of 98% and a degree of polymerization of 500. However, the effect of the addition of borax in the step of ultra-fining fibers is limited because the duration of the immersion in the aqueous alkaline solution should be long enough to ultra-fine fibers. Hence, the addition of borax to the aqueous alkaline solution cannot completely prevent the dissolution of the PVA in water. On the other hand, in the step of impregnating a waterborne polyurethane, the degree of polymerization of the PVA is too low to completely prevent the dissolution of the PVA in water. Hence, the dissolution of the PVA in the waterborne polyurethane dispersion cannot be prevented, and the PVA dissolved in the waterborne polyurethane dispersion becomes an obstacle to stable control over the adhesion of the polyurethane to the fibers, resulting in a sheet-shaped material having a hard texture.
In order to solve the problems in the above steps (i) and (ii), there has been proposed a process comprising adding a PVA having a degree of saponification of 90% or more to a nonwoven fabric sheet, and heating the sheet at 150 to 195° C., thereby reducing the solubility of the PVA in water (see Patent Literature 3). The heating at high temperature strengthens the intermolecular hydrogen bonds in the PVA, leading to reduction in the solubility in water. However, if the heating temperature is too high or the heating time is too long, the PVA becomes insoluble and difficult to redissolve in water. Therefore, there is a problem of difficulty in the optimization and stabilization of the conditions.

PATENT LITERATURE

Patent Literature 1: JP 2002-30579 A
Patent Literature 2: JP 2003-096676 A
Patent Literature 3: JP patent No. 4644971

SUMMARY OF THE INVENTION

An object of the present invention is to provide a process for producing a sheet-shaped material having both an elegant, napped appearance and a soft texture and exhibiting a good abrasion resistance, the process using a reduced amount of organic solvents, thereby reducing the burden on the environment; and a sheet-shaped material produced by the production process.
That is, the process according to an aspect of the present invention for producing a sheet-shaped material comprises the successive steps of:
(i) dissolving, in water, a polyvinyl alcohol having a degree of saponification of 98% or more and a degree of polymerization of 800 to 3500 to prepare a polyvinyl alcohol aqueous solution in which the concentrations of methyl acetate, acetic acid and methanol are 50 ppm or less,
(ii) adding the polyvinyl alcohol aqueous solution to a fibrous substrate comprising microfiber-generating fibers as its main constituent, so that the fibrous substrate has the polyvinyl alcohol in an amount of 0.1 to 50% by mass based on the mass of the fibers contained in the fibrous substrate,
(iii) generating microfibers having an average single fiber diameter of 0.3 to 7 μm from the microfiber-generating fibers contained in the fibrous substrate as its main constituent,
(iv) adding a waterborne polyurethane to the fibrous substrate comprising the microfibers as its main constituent and having the added polyvinyl alcohol, and
(v) removing the polyvinyl alcohol from the fibrous substrate comprising the microfibers as its main constituent and having the added waterborne polyurethane.
In a preferred embodiment of the process of the present invention for producing a sheet-shaped material, the process comprises the step of preparing a polyvinyl alcohol aqueous solution in which the concentrations of methyl acetate, acetic acid and methanol are 0.1 to 50 ppm.
In another preferred embodiment of the process of the present invention for producing a sheet-shaped material, the step of generating the microfibers is performed by treatment with an alkaline aqueous solution.
In another preferred embodiment of the process of the present invention for producing a sheet-shaped material, the process further comprises the step of performing heating at 80 to 170° C. after the addition of the polyvinyl alcohol.
In another preferred embodiment of the process of the present invention for producing a sheet-shaped material, the fibrous substrate comprising microfiber-generating fibers as its main constituent is integrated with a woven fabric and/or a knitted fabric by entanglement.
A resulting sheet-shaped material preferably has a density of 0.2 to 0.7 g/cm³.
The production process of the present invention is environmentally friendly and yet provides a sheet-shaped material having both an elegant appearance and a soft texture, which qualities the conventional art could not achieved concurrently, and also exhibiting a good abrasion resistance.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The process according to an aspect of the present invention for producing a sheet-shaped material comprises the successive steps of:
(i) dissolving, in water, a polyvinyl alcohol having a degree of saponification of 98% or more and a degree of polymerization of 800 to 3500 to prepare a polyvinyl alcohol aqueous solution in which the concentrations of methyl acetate, acetic acid and methanol are 50 ppm or less,
(ii) adding the polyvinyl alcohol aqueous solution to a fibrous substrate comprising microfiber-generating fibers as its main constituent, so that the fibrous substrate has the polyvinyl alcohol in an amount of 0.1 to 50% by mass based on the mass of the fibers contained in the fibrous substrate,
(iii) generating microfibers having an average single fiber diameter of 0.3 to 7 μm from the microfiber-generating fibers contained in the fibrous substrate as its main constituent,
(iv) adding a waterborne polyurethane to the fibrous substrate comprising the microfibers as its main constituent and having the added polyvinyl alcohol, and
(v) removing the polyvinyl alcohol from the fibrous substrate comprising the microfibers as its main constituent and having the added waterborne polyurethane.
A preferred feature of the process of the present invention for producing a sheet-shaped material is that the steps (i) to (v) are performed in the above order. That is, the following steps are successively performed: adding an aqueous solution of a polyvinyl alcohol (also called PVA) having a degree of saponification of 98% or more and a degree of polymerization of 800 to 3500 to a fibrous substrate comprising microfiber-generating fibers as its main constituent, generating microfibers from the microfiber-generating fibers (the removal of a sea component), adding a waterborne polyurethane dispersion to the fibrous substrate comprising the microfibers as its main constituent and having the added PVA, and removing the PVA from the fibrous substrate. As a result of these successive steps, large voids derived from the PVA and the sea component are formed between the fibers and the polyurethane, and the microfibers are partially in direct contact with and held by the polyurethane. Consequently, the resulting product has an elegant appearance and soft texture and exhibits good physical properties such as a good abrasion resistance.
In cases where the fibrous substrate to which a PVA aqueous solution has been added is dried under heating, the PVA in water migrates along with the migration of the water toward the surface and the PVA concentrates in the surface region of the fibrous substrate (migration phenomenon). As a result, a large amount of the PVA adheres to the surface region of the fibrous substrate and a small amount of the PVA adheres to the inside. Such migration of the PVA allows the waterborne polyurethane to be added later to mainly adhere to the inside of the fibrous substrate. Then, after the PVA is removed, large voids are formed between the fibers and the polyurethane in the surface region, where a large amount of the PVA once adhered. The sheet-shaped material with such voids, after napping treatment, can give an elegant appearance with a napped surface on which the raised fibers are not bundled but uniformly separated.
In cases where the removal of the sea component is performed after removing the PVA, voids derived by the removal of the EVA and voids derived by the removal of the sea component are formed between the polyurethane and the microfibers. These voids further efficiently reduces the area where the microfibers are in direct contact with and held by the polyurethane. As a result, the texture of the resulting sheet-shaped material is soft, but the physical properties such as abrasion resistance tend to be deteriorated.

Step (i)

The step (i) of dissolving, in water, a EVA having a degree of saponification of 98% or more and a degree of polymerization of 800 to 3500 to prepare a PVA aqueous solution in which the concentrations of methyl acetate, acetic acid and methanol are 50 ppm or less will be described below.
Methyl acetate, acetic acid and methanol are generated as the degree of saponification increases during the saponification of polyvinyl acetate, which is a precursor used in the synthesis of a PVA. Methyl acetate, acetic acid and methanol are also generated by the decomposition of the residual polyvinyl acetate that has not undergone sufficient saponification. When the concentrations of methyl acetate, acetic acid and methanol in the PVA aqueous solution are 50 ppm or less, the formation of the intermolecular hydrogen bonds in the PVA is facilitated at the time of heat-drying, and thereby the dissolution of the PVA in water (including hot water), an acid aqueous solution, or an alkaline aqueous solution is inhibited. The facilitated formation of the intermolecular hydrogen bonds in the PVA also allows the heat-drying temperature to be set at a relatively low level, for example, at 80 to 140° C., and thereby the thermal decomposition of the PVA is inhibited. The concentrations of methyl acetate, acetic acid and methanol in the PVA aqueous solution are more preferably 0.1 to 50 ppm. When methyl acetate, acetic acid and methanol are present in such small quantities, they are weakly bonded to the PVA molecules via hydrogen bonding and thereby decreases the intermolecular distance in the PVA, and as a result, the formation of the intermolecular hydrogen bonds in the PVA is facilitated. Too high concentrations of methyl acetate, acetic acid and methanol inhibit the formation of the intermolecular hydrogen bonds in the PVA, and therefore the concentrations are more preferably 0.3 to 40 ppm, even more preferably 5 to 40 ppm.
The concentrations of methyl acetate, acetic acid and methanol in the PVA aqueous solution are analyzed as follows. In a 24-mL test tube or flask for heating is placed 1 g of a PVA aqueous solution, and the solution is heated at 90° C. for 1 hour. The generated gas in an amount of 0.1 mL is taken with a gas-tight syringe from the test tube or flask for heating. The gas is introduced into a GC/MS (a mass spectrometer directly connected to a gas chromatograph), and the concentrations are analyzed.
The above-described low concentrations of methyl acetate, acetic acid and methanol in the PVA aqueous solution can be achieved by either using a PVA that generates small amounts of methyl acetate, acetic acid and methanol when heated alone without the addition of water, or by prolonging the length of time for heating to rise the temperature at the time of dissolving a PVA in water for preparing the PVA aqueous solution. In the former case, a higher degree of saponification leads to the generation of smaller amounts of methyl acetate, acetic acid and methanol. Therefore, preferred is a PVA with a high degree of saponification, as high as 98% or more. In the latter case, when the temperature to which the PVA in water is heated is too low, the methyl acetate, acetic acid and methanol cannot be sufficiently removed. Therefore, the temperature is preferably 80 to 100° C. Further, also when the heating time is too short, the methyl acetate, acetic acid and methanol cannot be sufficiently removed. Therefore, the heating time is preferably 1 hour or more. The methyl acetate, acetic acid and methanol may be completely removed from the PVA aqueous solution.
In one embodiment of the present invention, the PVA to be added to the fibrous substrate has a degree of saponification of 98% or more and a degree of polymerization of 800 to 3500. When the degree of saponification of the PVA is 98% or more, the PVA does not dissolved away in the waterborne polyurethane dispersion during the addition of the waterborne polyurethane. If the PVA is dissolved away in the waterborne polyurethane dispersion, the PVA cannot exhibit a sufficient effect of protecting the surface of the nap-forming microfibers. In addition, if a waterborne polyurethane dispersion in which the PVA has been dissolved is added to the fibrous substrate, the PVA is incorporated into the polyurethane and the PVA then becomes difficult to be removed. Consequently, the adhesion between the polyurethane and the fibers cannot be stably controlled, resulting in a hard texture.
In general, the solubility of a PVA in water varies with its degree of polymerization. Thus, a smaller degree of polymerization of the PVA leads to a larger amount of the PVA dissolved away in the waterborne polyurethane dispersion during the addition of the waterborne polyurethane. On the other hand, a higher degree of polymerization of the PVA leads to a higher viscosity of an aqueous solution of the PVA. As a result, when the fibrous substrate is impregnated with the PVA aqueous solution, the PVA cannot infiltrate the inside of the fibrous substrate. Therefore, the degree of polymerization of the PVA is preferably 1000 to 3000, more preferably 1200 to 2500.
In the present invention, the viscosity of an aqueous solution of 4% by mass of the PVA at 20° C. is preferably 10 to 70 mPa·s. When the viscosity of the PVA aqueous solution is within this range, an appropriate migration structure is formed in the fibrous substrate at the time of the drying, and the resulting sheet-shaped material will exhibit balanced physical properties including softness, surface appearance, and abrasion resistance. When the viscosity is 10 mPa·s or more, more preferably 15 mPa·s or more, formation of an excessive migration structure can be prevented. When the viscosity is 70 mPa·s or less, more preferably 50 mPa·s or less, even more preferably 40 mPa·s or less, the PVA readily infiltrates the fibrous substrate.
In the present invention, the glass transition temperature (Tg) of the PVA is preferably 70 to 100° C. When the glass transition temperature of the PVA is 70° C. or higher, more preferably 75° C. or higher, the softening of the PVA during the drying step is prevented, and the fibrous substrate thereby can maintain dimensional stability and the resulting sheet-shaped material will not have a poor surface appearance. When the glass transition temperature is 100° C. or lower, more preferably 95° C. or lower, the fibrous substrate is prevented from becoming excessively hard and difficult to handle.
In the present invention, the melting point of the PVA is preferably 200 to 250° C. When the melting point of the PVA is 200° C. or higher, more preferably 210° C. or higher, the softening of the PVA during the drying step is prevented, and thereby the fibrous substrate can maintain dimensional stability and the resulting sheet-shaped material will not have a poor surface appearance. When the melting point of the PVA is 250° C. or lower, more preferably 240° C. or lower, the fibrous substrate is prevented from becoming excessively hard and difficult to handle.
In the present invention, the tensile strength of the PVA in the form of a film is preferably 400 to 800 kg/cm². When the tensile strength of the PVA film is 400 kg/cm²or more, more preferably 450 kg/cm²or more, deformation of the fibrous substrate during handling is prevented, and the resulting sheet-shaped material will not have a poor surface appearance. When the tensile strength of the PVA film is 800 kg/cm²or less, more preferably 750 kg/cm²or less, the sheet having the added PVA is prevented from becoming excessively hard, and thereby the formation of wrinkles by buckling or other defects during handling is prevented. The tensile strength herein is determined using a film of the PVA with a thickness of 100 μm at a temperature of 20° C. and a humidity of 65%.

Step (ii)

The step (ii) of adding the PVA aqueous solution to a fibrous substrate comprising microfiber-generating fibers as its main constituent, so that the fibrous substrate has the polyvinyl alcohol in an amount of 0.1 to 50% by mass based on the mass of the fibers contained in the fibrous substrate will be described below.
The fibrous substrate in the present invention typically comprises microfiber-generating fibers as its main constituent. The microfiber-generating fibers are used to generate microfibers through the step of ultra-fining the microfiber-generating fibers, and the generated microfibers provide an elegant appearance on the surface of the sheet-shaped material.
In a preferred embodiment of the present invention, the average single fiber diameter of the microfibers generated from the microfiber-generating fibers through the step of ultra-fining is 0.3 to 7 μm. When the average single fiber diameter is 7 μm or less, more preferably 6 μm or less, even more preferably 5 μm or less, the resulting sheet-shaped material will have excellent softness and an excellent nap quality. When the average single fiber diameter is 0.3 μm or more, more preferably 0.7 μm or more, even more preferably 1 μm or more, the resulting sheet-shaped material will exhibit an excellent chromogenic property for dyeing, an excellent separability of fibers aggregated into bundles during napping treatment by, for example, grinding with a sandpaper or the like, and an excellent loosening property of fibers.
The microfiber-generating fibers may be (a) islands-in-the-sea fibers, which are prepared using two types of thermoplastic resins having different solvent solubilities as the sea and island components and which can generate microfibers from the island component through the dissolution and removal of the sea component with a solvent or the like; or (b) splitting composite fibers, which are prepared by alternately arranging two types of thermoplastic resins in radial segments or multi-layered segments in the cross-section and which can generate microfibers through splitting the fibers by peeling and separating the segments. Of the two types, the islands-in-the-sea fibers can give voids in an appropriate size between the island components, i.e., between the microfibers, through the removal of the sea component, and thus are preferred for achieving softness and good texture of the sheet-shaped material.
Examples of the islands-in-the-sea fibers include islands-in-the-sea composite fibers, which are prepared by spinning two types of alternately aligned components (sea and island components) from a spinneret for islands-in-the-sea composite spinning; and blended-spun fibers, which are prepared by blending two types of components (sea and island components) and spinning them into fibers. Preferred are islands-in-the-sea composite fibers because the fibers can generate microfibers having uniform fineness and sufficient length, which sufficient length contributes to the strength of the sheet-shaped material.
The island component of the islands-in-the-sea fibers is not particularly limited and may be a thermoplastic resin capable of being subjected to melt spinning, including polyesters such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polylactic acid; polyamides such as 6-nylon and 66-nylon; acrylics; polyethylenes; polypropylenes; and thermoplastic celluloses. Among them, polyester fibers are preferred because of their strength, dimensional stability, and light resistance. Due to environmental concerns, the fibers are preferably made from recycled materials or plant-derived materials. The fibrous substrate may comprise mixed fibers made from different materials.
The sea component of the islands-in-the-sea fibers is not particularly limited, and may be, for example, polyethylenes; polypropylenes; polystyrenes; copolymerized polyesters prepared by copolymerizing sodium sulfoisophthalate, polyethylene glycol, or the like, and polylactic acid; or PVAs. Among them, due to environmental concerns, preferred are copolymerized polyesters prepared by copolymerizing sodium sulfoisophthalate, polyethylene glycol, or the like, and polylactic acid, because these polymers are alkali-degradable and can be degraded without any organic solvent. Also preferred is a PVA because it is soluble in hot water.
The cross-sectional shape of the fibers constituting the fibrous substrate is not particularly limited, and may be a circular shape, an oval shape, a flat shape, a polygonal shape such as a triangular shape, or a modified cross-sectional shape such as fan and cross shapes.
In the present invention, the average single fiber diameter of the fibers constituting the fibrous substrate is preferably 0.3 to 20 μm. A smaller value of the average single fiber diameter results in a sheet-shaped material having more excellent softness and a more excellent nap quality. On the other hand, a larger value of the average single fiber diameter results in a sheet-shaped material exhibiting a more excellent chromogenic property for dyeing, a more excellent separability of fibers aggregated into bundles during napping treatment by, for example, grinding with a sandpaper or the like, and a more excellent loosening property of fibers. The average single fiber diameter is thus more preferably 0.7 to 15 μm and particularly preferably 1 to 7 μm.
The fibrous substrate in the present invention may be a woven fabric, a knitted fabric, a nonwoven fabric, or the like. Among them, preferred is a nonwoven fabric because it gives a sheet-shaped material having a good surface appearance after napping treatment on the surface.
The nonwoven fabric may be a staple nonwoven fabric or a filament nonwoven fabric. A filament nonwoven fabric has a smaller amount of fibers which lie in the thickness direction of a resulting sheet-shaped material and which is to form a nap by napping, as compared with a staple nonwoven fabric. A filament nonwoven fabric thus tends to give a less dense nap, resulting in a poor surface appearance. Therefore preferred is a staple nonwoven fabric.
The fiber length of the staples in the staple nonwoven fabric is preferably 25 to 90 mm. When the fiber length is 25 mm or more, the fibers can be entangled to yield a sheet-shaped material having an excellent abrasion resistance. When the fiber length is 90 mm or less, the fibers can yield a sheet-shaped material having excellent texture and quality. The fiber length is more preferably 30 to 80 mm.
The method for entangling the fibers or fiber bundles to yield a nonwoven fabric may be needle punching or water-jet punching.
In the present invention, when the fibrous substrate comprising microfibers is a nonwoven fabric, a preferred embodiment of the nonwoven fabric is a nonwoven fabric having a structure in which bundles of microfibers (microfiber bundles) are entangled. The entangled bundles of microfibers improve the strength of the sheet-shaped material. Such a nonwoven fabric can be obtained by entangling microfiber-generating fibers and then generating microfibers therefrom.
When the nonwoven fabric is made of microfibers or bundles of microfibers, a woven fabric or a knitted fabric may be integrated inside the nonwoven fabric by entanglement for the purpose of improving the strength and other properties. Examples of the woven fabric include plain woven fabrics, twill woven fabrics, and satin woven fabrics, and preferred is plain woven fabrics in view of the cost. Examples of the knitted fabric include circular knitted fabrics, tricot fabrics, and raschel fabrics. The fibers constituting such woven and knitted fabrics preferably have an average single fiber diameter of 0.3 to 20 μm.
In a preferred embodiment of the present invention, in cases where a woven fabric and/or a knitted fabric is integrated inside the fibrous substrate comprising microfiber-generating fibers as its main constituent by entanglement, the addition of the PVA reduces the area where the woven fabric and/or the knitted fabric is in direct contact with and held by the waterborne polyurethane that is to be added later, thereby softening the texture of the resulting sheet-shaped material. This softening effect is significant especially in cases where the woven fabric and/or the knitted fabric is made of fibers other than microfiber-generating fibers.
The amount of the PVA to be added to the fibrous substrate is 0.1 to 50% by mass and preferably 1 to 45% by mass based on the total mass of the fibers in the fibrous substrate. When the amount of the PVA to be added is 0.1% by mass or more, the resulting sheet-shaped material has good softness and texture. When the amount of the PVA to be added is 50% by mass or less, the resulting sheet-shaped material has good processability and good physical properties including abrasion resistance.
In the present invention, the method for adding the PVA to the fibrous substrate is not particularly limited, and may be any method commonly used in the art. Preferred is a method involving dissolving the PVA in water, impregnating the fibrous substrate with the PVA solution, and heat-drying the substrate, so that the PVA can be uniformly added. If the drying temperature is too low, a longer drying time is required. On the other hand, if the drying temperature is too high, the PVA becomes completely insoluble and cannot be dissolved and removed later. Hence, the drying temperature is preferably 80 to 140° C., and more preferably 110 to 130° C. The drying time is usually 1 to 20 minutes, and is preferably 1 to 10 minutes and more preferably 1 to 5 minutes in view of the processability. In order to make the PVA more insoluble, heat treatment may be performed after the drying. The heating treatment is preferably performed at 80 to 170° C. By the heat treatment, insolubilization of the PVA proceeds simultaneously with thermal degradation thereof, and thus the heating temperature is more preferably 80° C. to 140° C.
Step (iii)
The step (iii) of generating microfibers having an average single fiber diameter of 0.3 to 7 μm from the microfiber-generating fibers contained in the fibrous substrate as its main constituent will be described below.
The ultra-fining treatment (the removal of the sea component) of the fibrous substrate comprising microfiber-generating fibers as its main constituent can be performed by immersing the fibrous substrate in a solvent and wringing out the solvent. In cases where the microfiber-generating fibers are islands-in-the-sea fibers and where the sea component is polyethylene, polypropylene or polystyrene, the solvent for dissolving the sea component may be an organic solvent such as toluene and trichloroethylene. In cases where the sea component is a copolymerized polyester or polylactic acid, the solvent may be an aqueous solution of alkali such as sodium hydroxide. When the sea component is a PVA, the solvent may be hot water. Due to environmental concerns regarding the process, the removal of the sea component is preferably performed with an aqueous solution of alkali such as sodium hydroxide or with hot water.

Step (iv)

The step (iv) of adding a waterborne polyurethane to the fibrous substrate comprising the microfibers as its main constituent and having the added PVA will be described below.
The waterborne polyurethane includes (I) forcibly emulsified polyurethanes, which have been forced to be stably dispersed in water with use of a surfactant, and (II) self-emulsifying polyurethanes, which have hydrophilic structures in their molecular structures and are capable of being dispersed and then stabilized in water without use of any surfactant. Both types of polyurethanes can be used in the present invention.
The method for adding the waterborne polyurethane to the fibrous substrate is not particularly limited, but preferred is a method in which the waterborne polyurethane is impregnated into or applied to the fibrous substrate, then coagulated and heat-dried, because the waterborne polyurethane is uniformly added by this method.
The concentration of the waterborne polyurethane dispersion (the amount of the polyurethane contained in the waterborne polyurethane dispersion) is preferably 10 to 50% by mass and more preferably 15 to 40% by mass in view of storage stability of the waterborne polyurethane dispersion.
The waterborne polyurethane dispersion used in the present invention may contain a water-soluble organic solvent in an amount of 40% by mass or less based on the total amount of the polyurethane dispersion for the purpose of improving the storage stability of the polyurethane dispersion and the productivity of the sheet. However, the amount of the organic solvent is preferably 1% by mass or less in view of the environmental safety at the production site for the sheet, and the like.
The waterborne polyurethane dispersion used in the present invention preferably has a heat-sensitive coagulation property. When the waterborne polyurethane dispersion has a heat-sensitive coagulation property, the polyurethane can be added uniformly in the thickness direction of the fibrous substrate.
The term “heat-sensitive coagulation property” herein refers to a property that, when the polyurethane dispersion is heated and reaches a certain temperature (heat-sensitive coagulation temperature), reduces the flowability of the polyurethane dispersion and then coagulates the polyurethane. In the production of the sheet-shaped material having the polyurethane added, the waterborne polyurethane is added to the fibrous substrate, then coagulated by dry coagulation, wet-heat coagulation, wet coagulation, or any combination thereof, and dried to give the fibrous substrate having the added polyurethane. In industrial production, a realistic method for coagulating a waterborne polyurethane not exhibiting a heat-sensitive coagulation property is dry coagulation. In this method, the polyurethane tends to migrate toward and concentrate in the surface region of the fibrous substrate and then to harden the texture of the resulting sheet-shaped material having the polyurethane added. Such migration can be prevented by adjusting the viscosity of the waterborne polyurethane dispersion by the addition of a thickener. In cases where a waterborne polyurethane exhibiting a heat-sensitive coagulation property is used, the migration can be prevented by the addition of a thickener before the subsequent dry coagulation.
The heat-sensitive coagulation temperature of the waterborne polyurethane in the present invention is preferably 40 to 90° C. When the heat-sensitive coagulation temperature is 40° C. or higher, the polyurethane dispersion has good storage stability and the adhesion of the polyurethane to the machines during operation is prevented. When the heat-sensitive coagulation temperature is 90° C. or lower, the migration of the polyurethane toward the surface of the fibrous substrate is prevented.
In one embodiment of the present invention, in order to achieve the above heat-sensitive coagulation temperature, a heat-sensitive coagulant may be added to the polyurethane dispersion, as appropriate. Examples of the heat-sensitive coagulant include inorganic salts such as sodium sulfate, magnesium sulfate, calcium sulfate, and calcium chloride; and radical initiators such as sodium persulfate, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, and benzoyl peroxide.
In a preferred embodiment of the present invention, the polyurethane dispersion can be added to the fibrous substrate by impregnation, application, or other methods, and the polyurethane can be coagulated by dry coagulation, wet-heat coagulation, wet coagulation, or any combination thereof.
The temperature for the wet-heat coagulation is preferably equal to or higher than the heat-sensitive coagulation temperature of the polyurethane and is preferably 40 to 200° C. When the temperature for the wet-heat coagulation is 40° C. or higher, more preferably 80° C. or higher, the polyurethane can coagulate in a shorter period of time and the migration phenomenon is more efficiently prevented. When the temperature for the wet-heat coagulation is 200° C. or lower, more preferably 160° C. or lower, thermal degradation of the polyurethane and of the PVA is prevented.
The temperature for the wet coagulation is preferably equal to or higher than the heat-sensitive coagulation temperature of the polyurethane and is preferably 40 to 100° C. When the temperature for the wet coagulation in hot water is 40° C. or higher, more preferably 80° C. or higher, the polyurethane can coagulate in a shorter period of time and the migration phenomenon is more efficiently prevented.
The temperature for the dry coagulation and the drying temperature are preferably 80 to 140° C. When the temperature for the dry coagulation and the drying temperature are 80° C. or higher, more preferably 90° C. or higher, the productivity is excellent. When the temperature for the dry coagulation and the drying temperature are 140° C. or lower, more preferably 130° C. or lower, thermal degradation of the polyurethane and of the PVA is prevented.
In the present invention, after being subjected to the coagulation, the polyurethane may be subjected to heat treatment. The heat treatment reduces the number of the interfaces between the polyurethane molecules, thereby strengthening the polyurethane. In a more preferred embodiment, the heat treatment is preferably performed after removing the PVA from a sheet having the waterborne polyurethane added. The temperature for the heat treatment is preferably 80 to 170° C.
The polyurethane used in the present invention is preferably obtained by reaction of a polymer diol and an organic diisocyanate with a chain extender.
Examples of the polymer diol include, but are not particularly limited to, polycarbonate diols, polyester diols, polyether diols, silicone diols, and fluorine diols, and copolymers obtained by combining them. In view of hydrolysis resistance, preferred are polycarbonate diols and polyether diols. In view of light resistance and heat resistance, preferred are polycarbonate diols and polyester diols. In view of the balance among hydrolysis resistance, heat resistance and light resistance, more preferred are polycarbonate dials and polyester diols, and particularly preferred are polycarbonate diols.
The polycarbonate diols can be produced by, for example, transesterification of an alkylene glycol and a carbonate or reaction of phosgene or a chloroformate with an alkylene glycol.
Examples of the alkylene glycol include, but are not particularly limited to, linear alkylene glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, and 1,10-decanediol; branched alkylene glycols such as neopentyl glycol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, and 2-methyl-1,8-octanediol; alicyclic diols such as 1,4-cyclohexanediol; aromatic dials such as bisphenol A; glycerin; trimethylolpropane; and pentaerythritol. The polycarbonate diol may be either a polycarbonate diol obtained from a single type of alkylene glycol or a copolymerized polycarbonate diol obtained from two or more types of alkylene glycols.
The polyester diols are exemplified by polyester diols obtained by condensation of various low molecular weight polyols and polybasic acids.
Examples of the low molecular weight polyols include, but are not particularly limited to, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,8-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, cyclohexane-1,4-diol, and cyclohexane-1,4-dimethanol. These polyols may be used singly or in combination of two or more of them. Adducts prepared by adding various alkylene oxides to bisphenol A are also usable.
Examples of the polybasic acids include, but are not particularly limited to, succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, and hexahydroisophthalic acid. These acids may be used singly or in combination of two or more of them.
Examples of the polyether diols include, but are not particularly limited to, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymerized diols obtained by combining them.
The number average molecular weight of the polymer diol used in the present invention is preferably 500 to 4000. When the number average molecular weight is 500 or more, more preferably 1500 or more, the texture of the sheet-shaped material is prevented from becoming excessively hard. When the number average molecular weight is 4000 or less, more preferably 3000 or less, the polyurethane can maintain its strength.
Examples of the organic diisocyanate include, but are not particularly limited to, aliphatic diisocyanates such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and xylylene diisocyanate; and aromatic diisocyanates such as diphenylmethane diisocyanate and tolylene diisocyanate. These diisocyanates may be used in combination. Among them, in view of light resistance, preferred are aliphatic diisocyanates such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate.
Examples of the chain extender include, but are not particularly limited to, amine chain extenders such as ethylenediamine and methylenebisaniline; and diol chain extenders such as ethylene glycol. Polyamines prepared by reacting a polyisocyanate with water may also be used as the chain extender.
The polyurethane, if desired, may be used in combination with a crosslinking agent for the purpose of improving water resistance, abrasion resistance, hydrolysis resistance, and other characteristics. The crosslinking agent may be an external crosslinking agent, which is added to the polyurethane as a third component, or an internal crosslinking agent, which previously introduces reaction points into the molecular structure of the polyurethane to form crosslinked structure. In the present invention, preferred is an internal crosslinking agent because it can form crosslinking points uniformly throughout the molecular structure of the polyurethane and alleviates the reduction in softness.
The crosslinking agent may be a compound having an isocyanate group, an oxazoline group, a carbodiimide group, an epoxy group, a melamine resin, a silanol group, or the like. Excessive crosslinking tends to harden the polyurethane, resulting in a sheet-shaped material with a hard texture. Therefore preferred is a crosslinking agent having a silanol group in view of the balance between reactivity and softness.
The polyurethane used in the present invention preferably has a hydrophilic group in its molecular structure. When a hydrophilic group exists in the molecular structure of the polyurethane, the polyurethane, when dispersed in water, will have higher dispersibility and stability.
The hydrophilic group may be any hydrophilic group including cationic groups such as quaternary amine groups; anionic groups such as a sulfonate group and a carboxylate group; nonionic groups such as a polyethylene glycol group; combinations of a cationic group and a nonionic group; and combinations of an anionic group and a nonionic group. Among them, particularly preferred are the nonionic hydrophilic groups, which are free from concerns of yellowing by light or harmful effects by a neutralizer.
In cases where the polyurethane has an anionic hydrophilic group, a neutralizer is required. For example, when the neutralizer used is a tertiary amine such as ammonia, triethylamine, triethanolamine, triisopropanolamine, trimethylamine, and dimethylethanolamine, the amine is volatilized by heating during the sheet production or drying and is released outside the system. In order to prevent the emission to the atmosphere or the deterioration of working environment, a device for recovering the volatilized amine is required to be installed. If the amine is not volatilized by the heating but remains in a sheet-shaped material as the end product, the amine may be released in the environment when, for example, the product is burned. On the other hand, in cases where the polyurethane has a nonionic hydrophilic group, no neutralizer is required and thus the installment of an amine-recovering device is also not required. In addition, there is no need for concerns about a remaining amine in the sheet-shaped material. Therefore, the polyurethane having a nonionic hydrophilic group is preferred.
In cases where the neutralizer for the anionic hydrophilic group is required and the neutralizer is a hydroxide of an alkali metal or an alkaline earth metal, such as sodium hydroxide, potassium hydroxide, and calcium hydroxide, the polyurethane wetted with water shows a shift to alkaline pH. On the other hand, since the polyurethane having a nonionic hydrophilic group requires no neutralizer, there is no need for concerns about the deterioration of the polyurethane by hydrolysis.
The waterborne polyurethane used in the present invention, if desired, may contain various additives, including pigments such as carbon black; flame retardants such as phosphoric flame retardants, halogen flame retardants, silicone flame retardants, and inorganic flame retardants; antioxidants such as phenol antioxidants, sulfur-containing antioxidants, and phosphorus-containing antioxidants; ultraviolet absorbers such as benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, salicylate ultraviolet absorbers, cyanoacrylate ultraviolet absorbers, and oxalic acid anilide ultraviolet absorbers; light stabilizers such as hindered amine light stabilizers and benzoate light stabilizers; hydrolysis inhibitors such as polycarbodiimide; plasticizers; antistatic agents; surfactants; softening agents; water repellents; coagulation modifiers; viscosity modifiers; dyes; antiseptics; antimicrobials; deodorants; fillers such as cellulose particles and microballoons; and inorganic particles such as silica particles and titanium oxide particles. The waterborne polyurethane may also contain inorganic foaming agents such as sodium hydrogen carbonate and organic foaming agents such as 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] in order to form large voids between the fibers and the polyurethane.
The amount of the polyurethane contained in the fibrous substrate comprising microfiber-generating fibers as its main constituent in the present invention is preferably 1 to 80% by mass based on the total mass of the sheet-shaped material. When the amount of the polyurethane contained in the sheet-shaped material is 1% by mass or more, more preferably 5% by mass or more, the sheet-shaped material will have high strength and the fibers are prevented from falling off from the sheet-shaped material. When the amount of the polyurethane contained in the sheet-shaped material is 80% by mass or less, more preferably 70% by mass or less, the texture of the sheet-shaped material is prevented from becoming excessively hard and the sheet-shaped material will have a nap of good quality.

Step (v)

The step (v) of removing the PVA from the fibrous substrate comprising the microfibers as its main constituent and having the added PVA and waterborne polyurethane will be described below.
In a preferred embodiment of the present invention, the PVA is removed from the fibrous substrate having the added polyurethane, and a soft sheet-shaped material is obtained. The method for removing the PVA is not particularly limited, but in a preferred embodiment, the PVA is dissolved and removed by, for example, immersing the sheet in hot water at 60 to 100° C., and wringing out the water from the sheet with a mangle or the like.
The process of the present invention for producing a sheet-shaped material may comprise, after at least the addition of the waterborne polyurethane to the fibrous substrate having the PVA added is performed, the step of cutting the fibrous substrate in half thickness-wise. In the step of adding the PVA, the PVA migrates toward the surface, and thus a large amount of the PVA adheres in the surface region of the fibrous substrate, whereas a small amount of the PVA adheres to the inside of the fibrous substrate. Subsequently the waterborne polyurethane is added and the fibrous substrate is cut in half thickness-wise to give a sheet-shaped material having a structure in which a small amount of the waterborne polyurethane adheres to the side to which a large amount of the PVA has adhered, whereas a large amount of the waterborne polyurethane adheres to the side to which a small amount of the PVA has adhered. In cases where the side to which a large amount of the PVA once adhered (i.e., the side to which a small amount of the waterborne polyurethane has adhered) is used as a nap face of the sheet-shaped material, the previous presence of the large amount of the PVA allows the formation of large voids between the polyurethane and the nap-forming microfibers, such large voids give the freedom of movement to the nap-forming fibers, and as a result the sheet-shaped material will have soft surface texture, an appearance of good quality and soft-touch texture. On the other hand, in cases where the side to which a small amount of the PVA once adhered (i.e., the side to which a large amount of the waterborne polyurethane has adhered) is used as a nap face of the sheet-shaped material, the nap-forming fibers are strongly held by the polyurethane, which provides a high-quality appearance with a short nap with a more density and also provides a good abrasion resistance. When the process comprises the step of cutting the sheet in half thickness-wise, the production efficiency is also improved.
At least one face of the sheet-shaped material may be subjected to napping treatment to raise a nap on the surface. The napping method is not particularly limited, and may be any conventional napping method in the art, such as buffing with a sandpaper or the like. An excessively short nap is unlikely to provide an elegant appearance, whereas an excessively long nap is likely to cause pilling. The length of the nap is thus preferably 0.2 to 1 mm.
In one embodiment of the present invention, before the napping treatment, silicone or the like may be added as a lubricant to the sheet-shaped material. The addition of a lubricant is preferred because it facilitates napping by surface grinding and provides the surface with excellent quality. An antistatic agent may also be added before the napping treatment. The addition of an antistatic agent is preferred because it prevents the dust generated during grinding of the sheet-shaped material from depositing on the sandpaper.
In one embodiment of the present invention, the sheet-shaped material can be dyed. The dyeing can be performed by various methods commonly used in the art. Preferred is a method using a jet dyeing machine because the machine softens the sheet-shaped material by kneading at the same time as the dyeing.
The dyeing temperature varies with the type of the fibers but is preferably 80 to 150° C. When the dyeing temperature is 80° C. or higher, more preferably 110° C. or higher, the attachment of a dye to the fibers is efficiently performed. When the dyeing temperature is 150° C. or lower, more preferably 130° C. or lower, deterioration of the polyurethane is prevented.
The dye used in the present invention is not particularly limited as long as the dye is appropriately selected depending on the type of the fibers constituting the fibrous substrate. For example, when the fibers are polyester fibers, a disperse dye can be used. When the fibers are polyamide fibers, an acid dye, a metal complex dye, or a combination thereof may be used. In cases where the sheet-shaped material is dyed with a disperse dye, the sheet-shaped material may be subjected to reduction cleaning after the dyeing.
In a preferred embodiment, a dyeing aid is used during the dyeing. The dyeing aid improves the uniformity of the dyeing and the reproduction of the color. Simultaneously with the dyeing or after the dyeing, finishing treatment can be performed using a fabric softener such as silicone, an antistatic agent, a water repellent, a flame retardant, a light stabilizer, an antimicrobial agent, or other finishing agents.
The density of the thus obtained sheet-shaped material of the present invention is preferably 0.2 to 0.7 g/cm³. When the density is 0.2 g/cm³or more, more preferably 0.3 g/cm³or more, the sheet-shaped material is provided with a dense and high quality surface appearance. When the density is 0.7 g/cm³or less, more preferably 0.6 g/cm³or less, the sheet-shaped material is prevented from having a hard texture.

EXAMPLES

The process of the present invention for producing a sheet-shaped material will be described in further detail with reference to examples, but the present invention is not limited to these examples. Various modifications can be made within the technical idea of the present invention by a person skilled in the art.

Evaluation Methods

(1) Concentrations of Organic Solvents in PVA Aqueous Solution

In a 24-mL test tube or flask for heating was placed 1 g of a PVA aqueous solution, and the solution was heated at 90° C. for 1 hour. The generated gas in an amount of 0.1 mL was taken with a gas-tight syringe from the test tube or flask for heating. The gas was introduced into a GC/MS, and the concentrations of methyl acetate, acetic acid and methanol were analyzed. The detection limit of GC/MS is less than 0.1 ppm.

(2) Viscosity of PVA Aqueous Solution

In accordance with 3.11.1 Rotational viscometer method specified in JIS K6726 (1994) Testing methods for polyvinyl alcohol, the viscosity of an aqueous solution of 4% by mass of a PVA was determined at 20° C.

(3) Tensile Strength of PVA

A dispersion of 10% by mass of a PVA in water was poured in a polyethylene tray with a size of 5 cm in length, 10 cm in width and 1 cm in height. The dispersion was air-dried at 25° C. for 8 hours, and then heat-treated in a hot-air drier at 120° C. for 2 hours to give a dried film of the PVA with a thickness of 100 μm. The tensile strength of the dried film of the PVA was determined with a tensile tester in accordance with Method A (Strip method) specified in JIS L1096 (2010) 8.14.1.

(4) Average Single Fiber Diameter

An average single fiber diameter was determined as follows. A photograph of the surface of a fibrous substrate or a sheet-shaped material was taken in a scanning electron microscope (SEM) at a magnification of 2000. The diameters of randomly selected 100 fibers were measured, and the average was calculated to determine the average single fiber diameter.
In cases where the fibers constituting the fibrous substrate or the sheet-shaped material had a modified cross section, the diameter of the circumcircle of the modified cross section was measured as a single fiber diameter. In cases where fibers with a circular cross section were mixed with fibers with a modified cross section, or where fibers with greatly varying single fiber diameters were mixed, 100 fibers were selected so that the ratio of each type of fibers is equal to the actual existence ratio, and the average single fiber diameter was determined. In cases where a woven fabric or a knitted fabric was inserted into the fibrous substrate for the purpose of reinforcement, the fibers in the woven fabric or knitted fabric for reinforcement were excluded from the sampling for the determination of the average single fiber diameter.

(5) Bending Stiffness of Sheet-Shaped Material

In accordance with Method A (45° cantilever method) specified in JIS L1096 (2010) 8.21.1, 2 cm×15 cm test pieces long in the longitudinal direction or long in the transverse direction were cut out from the sheet (5 pieces each), and each of the test pieces was placed on a horizontal platform with a 45° sloped surface and was slid. When the center point of the leading edge of the test piece touches the sloped surface, the position of the other end was read by the scale. The bending stiffness is expressed as the distance (mm) that the test piece was slid. The distance slid was measured for each test piece and the average of the five test pieces was calculated to determine the bending stiffness.

(6) Surface Appearance of Sheet-Shaped Material

The surface appearance of a sheet-shaped material was evaluated by 20 panelists including 10 healthy adult males and 10 healthy adult females. Visual evaluation and sensory evaluation were performed and scored based on the following criteria with 5 grades. The grade which had the largest number of the panelists was taken as the grade for the surface appearance of the sheet-shaped material. Grades 3 to 5 were regarded as good surface appearance.
Grade 5: a uniform nap of the fibers were observed, the fibers were well separated, and the appearance was good.
Grade 4: the material was evaluated as between Grade 5 and Grade 3.
Grade 3: some of the fibers were not well separated, but the fibers were napped and the appearance was rather good.
Grade 2: the material was evaluated as between Grade 3 and Grade 1.
Grade 1: the fibers were very poorly separated throughout the whole surface or the napped fibers had a long length, and the appearance was poor.

(7) Evaluation of Abrasion Resistance of Sheet-Shaped Material

Nylon fibers being made of nylon 6 and having a diameter of 0.4 mm were cut perpendicularly to the longitudinal direction of the fibers into a length of 11 mm, and 100 cut fibers were aligned and bundled. Next, 97 bundles were arranged in a concentric circle pattern of 110 mm diameter having 6 circles of increasing diameter (one bundle was placed at the center, 6 bundles were arranged along the circumference of a circle of 17 mm diameter, 13 bundles. were arranged along the circumference of a circle of 37 mm diameter, 19 bundles were arranged along the circumference of a circle of 55 mm diameter, 26 bundles were arranged along the circumference of a circle of 74 mm diameter, and 32 bundles were arranged along the circumference of a circle of 90 mm diameter; the bundles along the circumference of each circle were arranged at equal intervals). The arranged bundles were used as a circular brush (the number of nylon yarns was 9700 in total). A circular sample (diameter: 45 mm) was taken from a sheet-shaped material and the surface was abraded with the circular brush under the conditions of a load of 8 pounds (about 3629 g), a rotation speed of 65 rpm, and a rotation of 50 times. The difference in the mass before and after the abrasion was determined. The average of five samples was calculated to determine the abrasion loss (mg), and the abrasion loss was used to evaluate the abrasion resistance.

Example 1

Preparation of PVA Aqueous Solution

To water at 25° C. was added a PVA (NM-14 produced by The Nippon Synthetic Chemical Industry Co., Ltd.) having a degree of saponification of 99% and a degree of polymerization of 1400, and the mixture was heated to 90° C. The mixture was stirred for 2 hours while the temperature was maintained at 90° C. to give a PVA aqueous solution with a solid content of 10% by mass. The concentrations of methyl acetate, acetic acid, and methanol in the PVA aqueous solution were 10.2 ppm, 0.8 ppm, and 5.2 ppm, respectively.

Nonwoven Fabric as Fibrous Substrate

A polyethylene terephthalate copolymerized with 8 mol % of sodium 5-sulfoisophthalate was used as the sea component, and a polyethylene terephthalate was used as the island component. The sea and island components were used at a ratio of 45% to 55% by mass to give islands-in-the-sea composite fibers with 36 islands per filament and an average single fiber diameter of 17 μm. The obtained islands-in-the-sea composite fibers were cut into a length of 51 mm to prepare staples. The staples were subjected to carding and cross lapping to form a fibrous web. The fibrous web was needle punched to give a nonwoven fabric. The thus obtained nonwoven fabric was shrunk by being immersed in hot water at a temperature of 98° C. for 2 minutes and was dried at a temperature of 100° C. for 5 minutes to give a nonwoven fabric as a fibrous substrate.

Addition of PVA

The nonwoven fabric as a fibrous substrate was impregnated with the PVA aqueous solution, and dried under heating at 140° C. for 10 minutes to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 30% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

The sheet having the added PVA was immersed in a 10 g/L aqueous sodium hydroxide solution at 95° C. for 30 minutes for the removal of the sea component from the islands-in-the-sea composite fibers to give a sea component-removed sheet. The average single fiber diameter of the fibers on the surface of the sea component-removed sheet was 3 μm.

Preparation of Polyurethane Dispersion

Polyhexamethylene carbonate was used as a polyol and dicyclohexylmethane diisocyanate was used as an isocyanate to give a self-emulsifying polycarbonate polyurethane liquid. To the self-emulsifying polycarbonate polyurethane liquid, ammonium persulfate (APS) as a heat-sensitive coagulant was added in an amount of 2 parts by mass based on 100 parts by mass of the solid content of the polyurethane liquid. Water was then added to adjust the overall solid content to 20% by mass to give a waterborne polyurethane dispersion. The heat-sensitive coagulation temperature was 72° C.

Addition of Polyurethane

The sea component-removed sheet having the added PVA was impregnated with the polycarbonate polyurethane dispersion. The sheet was treated in a wet-heat atmosphere at a temperature of 100° C. for 5 minutes, then dried with hot air at a drying temperature of 120° C. for 5 minutes, and dry-heated at a temperature of 140° C. for 2 minutes to give a sheet to which the polyurethane was added so that the amount of the polyurethane adhering to the sheet was 30% by mass based on the total mass of the fibers in the nonwoven fabric.

Removal of PVA

The sheet having the added polyurethane was immersed in hot water at 95° C. for 10 minutes to give a sheet from which the added PVA was removed.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

The PVA-removed sheet was cut in half thickness-wise. The surfaces opposite to the cut surfaces were subjected to napping treatment by grinding with a 240-mesh abrasive belt. The sheet was then dyed with a disperse dye by using a circular dyeing machine and subjected to reduction cleaning to give a sheet-shaped material. The obtained sheet-shaped material had a good surface appearance, a soft texture, and a good abrasion resistance.

Example 2

Preparation of PVA Aqueous Solution

In the same manner as in Example 1, a PVA aqueous solution was prepared.

Nonwoven Fabric as Fibrous Substrate

In the same as in Example 1, a nonwoven fabric as a fibrous substrate was produced.

Addition of PVA

The nonwoven fabric as a fibrous substrate was treated with the PVA aqueous solution in the same manner as in Example 1 except that the amount of the PVA adhering to the nonwoven fabric was adjusted by controlling the degree of wringing after the impregnation, to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 20% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

In the same manner as in Example 1, a sea component-removed sheet was produced.

Preparation of Polyurethane Dispersion

In the same manner as in Example 1, a waterborne polyurethane dispersion was prepared.

Addition of Polyurethane

In the same manner as in Example 1, a sheet having the polyurethane added was produced.

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

In the same manner as in Example 1, a sheet-shaped material was produced. The obtained sheet-shaped material had a good surface appearance, a soft texture, and a good abrasion resistance.

Example 3

Preparation of PVA Aqueous Solution

In the same manner as in Example 1, a PVA aqueous solution was prepared.

Nonwoven Fabric as Fibrous Substrate

A polyethylene terephthalate copolymerized with 8 mol % of sodium 5-sulfoisophthalate was used as the sea component, and a polyethylene terephthalate was used as the island component. The sea and island components were used at a ratio of 20% to 80% by mass to give islands-in-the-sea composite fibers with 16 islands per filament and an average single fiber diameter of 30 μm. The obtained islands-in-the-sea composite fibers were cut into a length of 51 mm to prepare staples. The staples were subjected to carding and cross lapping to form a fibrous web. The fibrous web was needle punched to give a nonwoven fabric. The thus obtained nonwoven fabric was shrunk by being immersed in hot water at a temperature of 98° C. for 2 minutes and was dried at a temperature of 100° C. for 5 minutes to give a nonwoven fabric as a fibrous substrate.

Addition of PVA

The nonwoven fabric as a fibrous substrate was treated with the PVA aqueous solution in the same manner as in Example 1 to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 30% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

The nonwoven fabric as a fibrous substrate was treated for the removal of the sea component from the islands-in-the-sea composite fibers in the same manner as in Example 1 to give a sea component-removed sheet. The average single fiber diameter of the fibers on the surface of the sea component-removed sheet was 4.4 μm.

Preparation of Polyurethane Dispersion

A waterborne polyurethane dispersion prepared in the same manner as in Example 1 was used.

Addition of Polyurethane

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

Example 4

Preparation of PVA Aqueous Solution

To water at 25° C. was added a PVA (NM-11 produced by The Nippon Synthetic Chemical Industry Co., Ltd.) having a degree of saponification of 99% and a degree of polymerization of 1100, and the mixture was heated to 90° C. The mixture was stirred for 2 hours while the temperature was maintained at 90° C. to give a PVA aqueous solution with a solid content of 10% by mass. The concentrations of methyl acetate, acetic acid, and methanol in the PVA aqueous solution were 7.2 ppm, 0.4 ppm, and 2.4 ppm, respectively.

Nonwoven Fabric as Fibrous Substrate

A nonwoven fabric produced in the same manner as in Example 1 was used as a fibrous substrate.

Addition of PVA

Ultra-Fining of Fibers (Removal of Sea Component)

In the same manner as in Example 1, a sea component-removed sheet was produced from the nonwoven fabric as a fibrous substrate.

Preparation of Polyurethane Dispersion

Addition of Polyurethane

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

Example 5

Preparation of PVA Aqueous Solution

To water at 25° C. was added a PVA (NH-26 produced by The Nippon Synthetic Chemical Industry Co., Ltd.) having a degree of saponification of 99% and a degree of polymerization of 2600, and the mixture was heated to 90° C. The mixture was stirred for 2 hours while the temperature was maintained at 90° C. to give a PVA aqueous solution with a solid content of 10% by mass. The concentrations of methyl acetate, acetic acid, and methanol in the PVA aqueous solution were 32.2 ppm, 8.3 ppm, and 20.1 ppm, respectively.

Nonwoven Fabric as Fibrous Substrate

Addition of PVA

The nonwoven fabric as a fibrous substrate was impregnated with the PVA aqueous solution, and dried under heating at 140° C. for 10 minutes to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 10% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

Preparation of Polyurethane Dispersion

Addition of Polyurethane

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

Example 6

Preparation of PVA Aqueous Solution

In the same manner as in Example 1, a PVA aqueous solution was prepared.

Nonwoven Fabric as Fibrous Substrate

A polyethylene terephthalate copolymerized with 8 mol % of sodium 5-sulfoisophthalate was used as the sea component, and a polyethylene terephthalate was used as the island component. The sea and island components were used at a ratio of 20% to 80% by mass to give islands-in-the-sea composite fibers with 16 islands per filament and an average single fiber diameter of 30 μm. The obtained islands-in-the-sea composite fibers were cut into a length of 51 mm to prepare staples. The staples were subjected to carding and cross lapping to form a fibrous web. On each face of the web, a plain woven fabric using a polyethylene terephthalate (PET) hard twist yarn of 84 dtex and 72 filaments with a twist of 2000 T/m was stacked, and the fibrous web and the plain woven fabrics were needle punched together to give a nonwoven fabric. The thus obtained nonwoven fabric was shrunk by being immersed in hot water at a temperature of 98° C. for 2 minutes and was dried at a temperature of 100° C. for 5 minutes to give a nonwoven fabric as a fibrous substrate.

Addition of PVA

The nonwoven fabric as a fibrous substrate was impregnated with the PVA aqueous solution, and dried under heating at 140° C. for 10 minutes to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 15% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

Preparation of Polyurethane Dispersion

Addition of Polyurethane

Removal of PVA

In the same manner as in Example.1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

Example 7

Preparation of PVA Aqueous Solution

In the same manner as in Example 1, a PVA aqueous solution was prepared.

Nonwoven Fabric as Fibrous Substrate

Addition of PVA

The nonwoven fabric as a fibrous substrate was treated in the same manner as in Example 1 to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 30% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

In the same manner as in Example 1, a sea component-removed sheet was produced.

Preparation of Polyurethane Dispersion

Polyhexamethylene carbonate was used as a polyol and dicyclohexylmethane diisocyanate was used as an isocyanate to give a self-emulsifying polycarbonate polyurethane liquid. To the self-emulsifying polycarbonate polyurethane liquid, a thickener (SN-THICKENER 627N produced by San Nopco Limited) was added in an amount of 5 parts by mass based on 100 parts by mass of the solid content of the polyurethane liquid. Water was then added to adjust the overall polyurethane solid content to 20% by mass to give a waterborne polyurethane dispersion.

Addition of Polyurethane

The sea component-removed sheet having the added PVA was impregnated with the polyurethane dispersion. The sheet was dried with hot air at a drying temperature of 100° C. for 30 minutes to give a sheet to which the polyurethane was added so that the amount of the polyurethane adhering to the sheet was 30% by mass based on the total mass of the fibers in the nonwoven fabric.

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

Example 8

Preparation of PVA Aqueous Solution

In the same manner as in Example 5, a PVA aqueous solution was prepared.

Nonwoven Fabric as Fibrous Substrate

Addition of PVA

Ultra-Fining of Fibers (Removal of Sea Component)

Preparation of Polyurethane Dispersion

Addition of Polyurethane

The sea component-removed sheet having the added PVA was impregnated with the polyurethane dispersion. The polyurethane was coagulated in hot water at 80° C. and was dried with hot air at a drying temperature of 100° C. for 15 minutes to give a sheet to which the polyurethane was added so that the amount of the polyurethane adhering to the sheet was 30% by mass based on the total mass of the fibers in the nonwoven fabric.

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

Comparative Example 1

Preparation of PVA Aqueous Solution

In the same manner as in Example 1, a PVA aqueous solution was prepared.

Nonwoven Fabric as Fibrous Substrate

Ultra-Fining of Fibers (Removal of Sea Component)

The above-obtained nonwoven fabric as a fibrous substrate was immersed in a 10 g/L aqueous sodium hydroxide solution at 95° C. for 10 minutes for the removal of the sea component from the islands-in-the-sea composite fibers to give a sea component-removed sheet. The average single fiber diameter of the fibers on the surface of the sea component-removed sheet was 3 μm.

Addition of PVA

The sea component-removed sheet was impregnated with the PVA aqueous solution prepared in the same manner as in Example 1, and dried under heating at 140° C. for 10 minutes to give a sheet to which the PVA was added so that the amount of the PVA adhering to the sea component-removed sheet was 30% by mass based on the total mass of the fibers in the sea component-removed sheet.

Preparation of Polyurethane Dispersion

Addition of Polyurethane

The sea component-removed sheet having the added PVA was impregnated with the polycarbonate polyurethane dispersion. The sheet was treated in a wet-heat atmosphere at a temperature of 100° C. for 5 minutes, then dried with hot air at a drying temperature of 120° C. for 5 minutes, and dry-heated at a temperature of 140° C. for 2 minutes to give a sheet to which the polyurethane was added so that the amount of the polyurethane adhering to the sheet was 30% by mass based on the total mass of the microfibers.

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

In the same manner as in Example 1, a sheet-shaped material was produced. The obtained sheet-shaped material had a good surface appearance and a soft texture, but the abrasion loss was relatively large.

Comparative Example 2

Preparation of PVA Aqueous Solution

To water at 25° C. was added a PVA (GL-05 produced by The Nippon Synthetic Chemical Industry Co., Ltd.) having a degree of saponification of 87% and a degree of polymerization of 500, and the mixture was heated to 90° C. The mixture was stirred for 2 hours while the temperature was maintained at 90° C. to give a PVA aqueous solution with a solid content of 10% by mass. The concentrations of methyl acetate, acetic acid, and methanol in the PVA aqueous solution were 70.1 ppm, 40.1 ppm, and 100.3 ppm, respectively.

Nonwoven Fabric as Fibrous Substrate

Addition of PVA

The nonwoven fabric as a fibrous substrate was impregnated with the PVA aqueous solution in the same manner as in Example 1 except that the amount of the PVA adhering to the nonwoven fabric was adjusted by controlling the degree of wringing after the impregnation, to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 10% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

Preparation of Polyurethane Dispersion

Addition of Polyurethane

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

In the same manner as in Example 1, a sheet-shaped material was produced. To the obtained sheet-shaped material, the polyurethane did not uniformly adhere due to partial dissolution of the PVA into the aqueous alkaline solution and the waterborne polyurethane dispersion. As a result, the sheet-shaped material had a poor surface appearance with a poor separability of the fibers and with no dense nap and had a hard texture.

Comparative Example 3

Preparation of PVA Aqueous Solution

To water at 25° C. was added a PVA (NL-05 produced by The Nippon Synthetic Chemical Industry Co., Ltd.) having a degree of saponification of 99% and a degree of polymerization of 500, and the mixture was heated to 90° C. The mixture was stirred for 2 hours while the temperature was maintained at 90° C. to give a PVA aqueous solution with a solid content of 10% by mass. The concentrations of methyl acetate, acetic acid, and methanol in the PVA aqueous solution were 6.1 ppm, 0.4 ppm, and 1.1 ppm, respectively.

Nonwoven Fabric as Fibrous Substrate

Addition of PVA

Ultra-Fining of Fibers (Removal of Sea Component)

Preparation of Polyurethane Dispersion

Addition of Polyurethane

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

Comparative Example 4

Preparation of PVA Aqueous Solution

In the same manner as in Example 1, a PVA aqueous solution was prepared.

Nonwoven Fabric as Fibrous Substrate

Addition of PVA

The nonwoven fabric as a fibrous substrate was treated with the PVA aqueous solution in the same manner as in Example 1 except that the amount of the PVA adhering to the nonwoven fabric was adjusted by controlling the degree of wringing after the impregnation, to give a sheet to which the PVA was added so that the amount of the PVA adhering to the nonwoven fabric was 55% by mass based on the total mass of the fibers in the nonwoven fabric as a fibrous substrate.

Ultra-Fining of Fibers (Removal of Sea Component)

Preparation of Polyurethane Dispersion

Addition of Polyurethane

Removal of PVA

In the same manner as in Example 1, a PVA-removed sheet was produced.

Cutting in Half, Napping, Dyeing, and Reduction Cleaning

In the same manner as in Example 1, a sheet-shaped material was produced. The obtained sheet-shaped material had a soft texture. However, the excess amount of the PVA resulted in insufficient holding of the fibers by the polyurethane. As a result, the sheet-shaped material had a poor surface appearance with an excessively long nap and had a poor abrasion resistance.

Comparative Example 5

A sheet-shaped material was produced in the same manner as in Example 1 except that no PVA aqueous solution was prepared and that no PVA was added or removed. The obtained sheet-shaped material had a hard texture and had a poor surface appearance with no nap.
Tables 1 and 2 show the test conditions in Examples and Comparative Examples and the evaluation results for the sheet-shaped materials.

	TABLE 1

	Average single
	fiber diameter of	Polyvinyl alcohol (PVA)

fibers in fibrous	Degree of	Degree of				Tensile strength
substrate	saponification	polymerization	Viscosity	Tg	Melting point	in film form
μm	%	—	mPa · s	° C.	° C.	kg/cm²

Example 1	3	99	1400	22	85	230	550
Example 2	3	99	1400	22	85	230	550
Example 3	4.4	99	1400	22	85	230	550
Example 4	3	99	1100	14	80	210	480
Example 5	3	99	2600	64	88	235	600
Example 6	4.4	99	1400	22	85	230	550
Example 7	3	99	1400	22	85	230	550
Example 8	3	99	2600	64	88	235	600
Comparative	3	99	1400	22	85	230	550
Example 1
Comparative	3	87	500	5	58	180	330
Example 2
Comparative	3	99	500	5	83	225	520
Example 3
Comparative	3	99	1400	22	85	230	550
Example 4
Comparative	3	—	—	—	—	—	—
Example 5

	TABLE 2

	Amount of
	adhering PVA

PVA aqueous solution

based on mass of

Sheet-shaped material

Concentrations of organic solvents (ppm)

fibers in fibrous

Density of

Abrasion

Surface

	Acetic	Methyl	substrate	sheet	Texture	resistance	appearance
Methanol	acid	acetate	(% by mass)	g/cm³	mm	mg	Grade

Example 1	5.2	0.8	10.2	30	0.4	28	24	5
Example 2	5.2	0.8	10.2	20	0.4	40	20	5
Example 3	5.2	0.8	10.2	30	0.4	30	22	4
Example 4	2.4	0.4	7.2	30	0.4	36	25	4
Example 5	20.1	8.3	32.2	10	0.45	50	14	4
Example 6	5.2	0.8	10.2	15	0.45	32	24	5
Example 7	5.2	0.8	10.2	30	0.4	56	27	4
Example 8	20.1	8.3	32.2	10	0.45	65	29	4
Comparative	5.2	0.8	10.2	30	0.4	20	54	4
Example 1
Comparative	100.3	40.1	70.1	10	0.3	140	32	2
Example 2
Comparative	1.1	0.4	6.1	10	0.4	150	26	2
Example 3
Comparative	5.2	0.8	10.2	55	0.15	15	80	1
Example 4
Comparative	—	—	—	0	0.4	190	10	1
Example 5

The sheet-shaped materials obtained in Examples 1 to 8 had a good surface appearance, a soft texture, and a good abrasion resistance. On the other hand, the sheet-shaped materials obtained in Comparative Examples 1 and 4 had a poor abrasion resistance, and the sheet-shaped materials obtained in Comparative Examples 2 to 5 had a poor surface appearance. The sheet shaped materials of Comparative Examples 2, 3 and 5 had a hard texture.
The sheet-shaped material obtained according to the present invention is suitable as interior materials having a very elegant appearance, such as surface materials of furniture, chairs, walls, seats in vehicles including automobiles, trains, and aircrafts, ceiling, and interior decoration; clothing materials, such as shirts, jackets, upper and trim and the like of shoes including casual shoes, sports shoes, men's shoes and ladies' shoes, bags, belts, wallets, and a part of them; and industrial materials such as wiping cloth, abrasive cloth and CD curtains.

Claims

1. A process for producing a sheet-shaped material, the process comprising the successive steps of:

(i) dissolving, in water, a polyvinyl alcohol having a degree of saponification of 98% or more and a degree of polymerization of 800 to 3500 to prepare a polyvinyl alcohol aqueous solution in which the concentrations of methyl acetate, acetic acid and methanol are 50 ppm or less,

(ii) adding the polyvinyl alcohol aqueous solution to a fibrous substrate comprising microfiber-generating fibers as its main constituent, so that the fibrous substrate has the polyvinyl alcohol in an amount of 0.1 to 50% by mass based on the mass of the fibers contained in the fibrous substrate,

(iii) generating microfibers having an average single fiber diameter of 0.3 to 7 μm from the microfiber-generating fibers contained in the fibrous substrate as its main constituent,

(iv) adding a waterborne polyurethane to the fibrous substrate comprising the microfibers as its main constituent and having the added polyvinyl alcohol, and

(v) removing the polyvinyl alcohol from the fibrous substrate comprising the microfibers as its main constituent and having the added waterborne polyurethane.

2. The process for producing a sheet-shaped material according to claim 1, wherein the concentrations of methyl acetate, acetic acid and methanol in the polyvinyl alcohol aqueous solution are 0.1 to 50 ppm.

3. The process for producing a sheet-shaped material according to claim 1 or 2, wherein the step of generating the microfibers is performed by treatment with an alkaline aqueous solution.

4. The process for producing a sheet-shaped material according to claim 1 or 2, further comprising the step of performing heating at 80 to 170° C. after the addition of the polyvinyl alcohol.

5. The process for producing a sheet-shaped material according to claim 1 or 2, wherein the fibrous substrate comprising microfiber-generating fibers as its main constituent is integrated with a woven fabric and/or a knitted fabric by entanglement.

6. A sheet-shaped material produced by the process for producing a sheet-shaped material according to claim 1 or 2, the sheet-shaped material having a density of 0.2 to 0.7 g/cm³.

7. The process for producing a sheet-shaped material according to claim 3, further comprising the step of performing heating at 80 to 170° C. after the addition of the polyvinyl alcohol.

8. The process for producing a sheet-shaped material according to claim 3, wherein the fibrous substrate comprising microfiber-generating fibers as its main constituent is integrated with a woven fabric and/or a knitted fabric by entanglement.

9. A sheet-shaped material produced by the process for producing a sheet-shaped material according to claim 3, the sheet-shaped material having a density of 0.2 to 0.7 g/cm³.