EP4079962A1

EP4079962A1 - Sheet-like article and method for producing same

Info

Publication number: EP4079962A1
Application number: EP20903475.0A
Authority: EP
Inventors: Takuya SHIBANO; Ryuji SHIKURI; Koki ISHII
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2019-12-20
Filing date: 2020-12-10
Publication date: 2022-10-26
Also published as: CN114729501B; CN114729501A; JPWO2021125032A1; JP6904493B1; TW202129118A; WO2021125032A1; EP4079962A4; KR20220113689A; US20220380976A1

Abstract

The purpose of the present invention is to provide: a sheet-like article which has a good balance between soft texture and excellent light resistance; and a method for producing this sheet-like article. In order to achieve this purpose, a sheet-like article according to the present invention has the following configuration. Specifically, a sheet-like article which contains a polymer elastic body in a fibrous base material, wherein: the fibrous base material is composed of ultrafine fibers that have an average single fiber diameter of from 0.1 µm to 10 µm; the polymer elastic body has a hydrophilic group, while containing a polyether diol as a constituent; the polymer elastic body internally has an N-acylurea bond and/or an isourea bond; and the condition 1 and the condition 2 described below are satisfied. Condition 1: The bending resistance in the lengthwise direction as determined in accordance with specific standards is from 40 mm to 140 mm. Condition 2: The abrasion weight loss after 20,000 cycles of a Martindale abrasion test set forth in JIS L 1096 (2005) after a light resistance test as performed under the conditions defined in accordance with specific standards is 25 mg or less.

Description

TECHNICAL FIELD

The present invention relates to a sheet material and a method for producing the sheet material, and particularly to a sheet material superior in flexibility and light resistance and a method for producing the sheet material.

BACKGROUND ART

Sheet materials mainly including a fibrous base material such as a nonwoven fabric and polyurethane have superior characteristics not shared with natural leather, and are widely used for various applications such as artificial leather. In particular, sheet materials using a polyester-based fibrous base material have superior moldability, so that their usage as clothing, chair covering, and automobile interior material has increasingly been extended year by year.
In order to produce such a sheet material, a combination of steps has been generally adopted, including: impregnating a fibrous base material with a polyurethane-containing organic solvent solution; and then immersing the resulting fibrous base material in an aqueous solution containing water or an organic solvent in which polyurethane is not dissolved, thereby subjecting the polyurethane to wet coagulation. In this case, a water-miscible organic solvent such as N,N-dimethylformamide is used as the organic solvent that is a solvent for polyurethane. However, since the organic solvents are highly harmful to the environment in general, a procedure without using any organic solvent has been strongly sought in producing the sheet material.
As a specific solution, a method of using a water-dispersed polyurethane obtained by dispersing a polyurethane resin in water instead of a conventional organic solvent-based polyurethane has been studied. However, a problem arises in that a sheet material coagulated by using a water-dispersed polyurethane generally tends to have a hard texture.
One of main reasons is a difference between two coagulation methods. That is, the coagulation method of an organic solvent-applied polyurethane is a so-called wet coagulation method in which polyurethane molecules dissolved in an organic solvent are coagulated by solvent substitution with water, and a porous film having a low density is formed in terms of a polyurethane film. Therefore, it is considered that, even when a polyurethane is impregnated inside a fibrous base material and is coagulated, the adhesion area between the fiber and the polyurethane is small, and thus a soft sheet material is obtained.
Meanwhile, as for a water-dispersed polyurethane, there is an often used method, i.e., a so-called wet coagulation method including disintegrating the hydration state of a water-dispersed polyurethane dispersion mainly by heating to cause polyurethane emulsions to be aggregated to one another for coagulation, and the obtained polyurethane film structure is a non-porous film having a high density. This enhances the adhesion between the fibrous base material and the polyurethane, thereby strongly retaining entangled portions of fibers. Accordingly, it is considered that this makes the texture hard.
So far, in order to obtain a sheet material with a soft texture by using a water-dispersed polyurethane, for example, a method has been proposed in which a thickener is added to a solution containing a water-dispersed polyurethane, and a fibrous substrate impregnated with the solution is treated with hot water, thereby reducing the coating film of polyurethane covering the fibrous base material so as to obtain a soft texture (Patent Document 1).
As a method of using a coagulation method by the same hot water treatment, there have been proposed a method in which a curing treatment is performed after dyeing to prevent deterioration in physical properties due to polyurethane swelling during dyeing and to obtain a sheet material superior in moist-heat resistance (Patent Document 2) and a method in which a water-dispersed polyurethane containing a hindered amine compound is applied to obtain a sheet material superior in light resistance, such as photo-yellowing resistance or light fastness, and flexibility (Patent Document 3).
A method has been proposed in which an inorganic salt is dissolved and mixed in a forcedly emulsified nonionic water-dispersed polyurethane to adjust a thermosensitive gelation temperature that is a temperature at which the water-dispersed polyurethane is gelled, and a soft texture is obtained by suppressing a phenomenon that particles of a polymer emulsion dispersed in water intensively adhere to a surface layer of a sheet material due to the movement of water, i.e., a so-called migration phenomenon (Patent Document 4).
A method has been proposed in which a sheet material is impregnated with a water-dispersed polyurethane added with a polysaccharide, and a polymer elastic body is heated and dried at two stages of temperatures to form a porous structure, so that the texture is softened (Patent Document 5). In this method, the polymer elastic body is completely coagulated in a state where a polysaccharide retains moisture in the first state of drying, and the moisture retained by the polysaccharide contained in the polymer elastic body is evaporated in a state where the polymer elastic body is completely coagulated in the second stage of drying. Thus, portions where the moisture retained by the polysaccharide is present become spaces, and a porous structure can be formed.
Alternatively, a method has been proposed in which a crosslinker is imparted to a sheet material with a coagulated water-dispersed polyurethane, and the sheet material is heated to cause a reaction, thereby maintaining the texture before the addition of the crosslinker (Patent Document 6). In this method, regardless of the coagulation methods of polyurethane, the water-dispersed polyurethane and the crosslinker can be reacted, and a state close to the original aggregated structure of polyurethane can be maintained.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: WO 2015/129602 A
Patent Document 2: Japanese Patent Laid-open Publication No. 2017-172074
Patent Document 3: Japanese Patent Laid-open Publication No. 2000-265052
Patent Document 4: Japanese Patent Laid-open Publication No. H6-316877
Patent Document 5: Japanese Patent Laid-open Publication No. 2019-112742
Patent Document 6: WO 2016/052189 A

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

However, in the case of using a sheet material outdoors for automobile interior materials and the like, a problem arises in that polyurethane retaining fibers in the sheet material is decomposed by ultraviolet rays included in sunlight to deteriorate the sheet material.
In general, a water-dispersed polyurethane is obtained by a reaction of a polymeric polyol, an organic polyisocyanate, and a chain extender and exhibits various properties depending on components of the polymeric polyol. As typical polymeric polyols, there are two types of a polyether-based polyol and a polycarbonate-based polyol. However, a sheet material using a polyether-based applied polyurethane has a soft texture as compared with a polycarbonate-based applied polyurethane, but is inferior in light resistance. To achieve both of a soft texture and light resistance, it is necessary to improve light resistance using polyether-based applied polyurethane in order to withstand practical use.
In the methods disclosed in Patent Documents 1 to 3, although the hardness of the texture can be improved by coagulation in hot water to obtain a soft texture to some extent, polyurethane does not sufficiently function as a binder, and the wear resistance is insufficient. In the method disclosed in Patent Document 2, since heating is performed at a high temperature after dyeing, the dye sublimates, and thus there is a concern of color loss in practical use, so that light resistance is not sufficient. In the method disclosed in Patent Document 3, the hindered amine compound is contained, as a result of which light resistance is improved. However, the film properties are deteriorated since this compound is contained in the polymeric polyol, and the retaining force with respect to fibers is weak, so that the wear resistance of the sheet material is not sufficient. Flexibility is also not sufficient.
Further, in the method disclosed in Patent Document 4, a soft texture can be achieved by suppressing migration. However, the polyurethane resin is not three-dimensionally crosslinked so that fibers cannot be sufficiently retained, and thus wear resistance and light resistance are not sufficient.
On the other hand, in the method disclosed in Patent Document 5, the porous structure can be obtained through two-stage drying, but the migration phenomenon cannot be completely suppressed, and the texture is not sufficient. In addition, the polyurethane resin is not three-dimensionally crosslinked so that fibers cannot be sufficiently retained, and thus wear resistance and light resistance are not sufficient.
Alternatively, in the method disclosed in Patent Document 6, the crosslinker is impregnated after coagulation of polyurethane. However, the reaction between polyurethane and the crosslinker does not proceed so much, and thus a three-dimensional structure by polyurethane and the crosslinker cannot be sufficiently formed, so that wear resistance and light resistance are not sufficient.
Therefore, in view of the background of the related art described above, an object of the present invention is to provide a sheet material having a good balance between soft texture and superior light resistance, and a method for producing the sheet material.

SOLUTIONS TO THE PROBLEMS

As a result of repeated studies by the present inventors to achieve the above object, the inventors have found that a drying temperature is adjusted in coagulation of a polymer elastic body containing a polyether diol as a constituent and using a specific amount of a monovalent positive ion-including inorganic salt and a crosslinker in combination, whereby it is possible to produce not only a sheet material in consideration of the environment, but also a sheet material having superior texture and light resistance as compared with a conventional sheet material. Thus, the present invention has been completed.
That is, the present invention is intended to solve the above-described problems, and the sheet material of the present invention is a sheet material containing a polymer elastic body in a fibrous base material, in which the fibrous base material includes ultrafine fibers having an average single fiber diameter of 0.1 µm or more and 10 µm or less, the polymer elastic body has a hydrophilic group and contains a polyether diol as a constituent, the polymer elastic body internally has an N-acylurea bond and/or an isourea bond, and the following condition 1 and condition 2 are satisfied:

condition 1: A bending resistance in a lengthwise direction as determined in accordance with Method A (45° cantilever method) described in JIS L 1096:2010 "Testing methods for woven and knitted fabrics" is 40 mm or more and 140 mm or less; and
condition 2: An abrasion weight loss after 20, 000 cycles of a Martindale abrasion test set forth in JIS L 1096:2005 after a light resistance test as performed under the conditions that a xenon arc amount as measured by a light fastness measurement method of JIS L 0843:2006 is 110 MJ/m², is 25 mg or less.

According to a preferred embodiment of the sheet material of the present invention, the abrasion weight loss after 20, 000 cycles of the Martindale abrasion test set forth in JIS L 1096:2010 of the sheet material before the light resistance test is 20 mg or less.
According to a preferred embodiment of the sheet material of the present invention, the sheet material contains 10% by mass or more of the polymer elastic body.
According to a preferred embodiment of the sheet material of the present invention, the sheet material further satisfies the following condition 3:
condition 3: An L value retention when a napped surface of the sheet material is placed on a hot plate heated to 150°C and pressed at a pressing load of 2.5 kPa for 10 seconds, is 90% or more and 100% or less.
A method for producing a sheet material of the present invention is a method for producing a sheet material, including steps (1) to (4) shown below, in this order:

(1) a polymer elastic body impregnating step of impregnating a fibrous base material including ultrafine fiber-generating fibers with an aqueous dispersion containing a polymer elastic body, a monovalent positive ion-including inorganic salt, and a crosslinker and then performing a heating treatment at a temperature of 120°C or higher and 180°C or lower, the polymer elastic body having a hydrophilic group and containing a polyether diol as a constituent, a content of the monovalent positive ion-including inorganic salt in the aqueous dispersion being 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polymer elastic body;
(2) an ultrafine fiber generating step of subjecting the ultrafine fiber-generating fibers to an alkali treatment to generate ultrafine fibers;
(3) a drying step of performing a thermal treatment at a temperature of 120°C or higher and 180°C or lower; and
(4) a nap raising step of subjecting at least one surface of an unnapped sheet material to a nap raising treatment to form a nap on the surface.

According to a preferred embodiment of the method for producing a sheet material of the present invention, the method further includes a dyeing step of dyeing the unnapped sheet material or the sheet material after the drying step.
According to a preferred embodiment of the method for producing a sheet material of the present invention, the monovalent positive ion-including inorganic salt is sodium chloride and/or sodium sulfate.
According to a preferred embodiment of the method for producing a sheet material of the present invention, the crosslinker is a carbodiimide-based crosslinker.

EFFECTS OF THE INVENTION

According to the present invention, a sheet material having a good balance between soft texture and superior light resistance is obtained.

EMBODIMENTS OF THE INVENTION

A sheet material of the present invention is a sheet material containing a polymer elastic body in a fibrous base material, in which the fibrous base material includes ultrafine fibers having an average single fiber diameter of 0.1 µm or more and 10 µm or less, the polymer elastic body has a hydrophilic group and contains a polyether diol as a constituent, the polymer elastic body internally has an N-acylurea bond and/or an isourea bond, and the following condition 1 and condition 2 are satisfied:

condition 1: A bending resistance in a lengthwise direction as determined in accordance with Method A (45° cantilever method) described in JIS L 1096:2010 "Testing methods for woven and knitted fabrics" is 40 mm or more and 140 mm or less; and
condition 2: An abrasion weight loss after 20, 000 cycles of a Martindale abrasion test set forth in JIS L 1096:2005 after a light resistance test as performed under the conditions that a xenon arc amount as measured by the light fastness measurement method of JIS L 0843:2006 is 110 MJ/m², is 25 mg or less.

Hereinafter, this constituent element will be described in detail, but the present invention is not limited to the scope described below at all as long as it is not beyond the gist of the present invention.

[Ultrafine Fibers]

Examples of a resin that can be used for ultrafine fibers used in the present invention include a polyester-based resin and a polyamide-based resin, from the viewpoint of superior durability, particularly, mechanical strength, heat resistance, and light resistance. Specific examples of the polyester-based resin include polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate. The polyester-based resin can be obtained from, for example, a dicarboxylic acid and/or an ester-forming derivative thereof and a diol.
Examples of the dicarboxylic acid and/or the ester-forming derivative thereof used for the polyester-based resin include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, and an ester-forming derivative thereof. Note that the ester-forming derivative referred in the present invention is a lower alkyl ester of a dicarboxylic acid, an acid anhydride, an acyl chloride, and the like. Specifically, a methyl ester, an ethyl ester, a hydroxyethyl ester, and the like are preferably used. A more preferred embodiment of a dicarboxylic acid and/or an ester-forming derivative thereof used in the present invention is a terephthalic acid and/or a dimethyl ester thereof.
Examples of the diol used in the polyester-based resin include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and cyclohexanedimethanol. Among them, ethylene glycol is preferably used.
In the case of using a polyamide-based resin as a resin used for ultrafine fibers, polyamide 6, polyamide 66, polyamide 56, polyamide 610, polyamide 11, polyamide 12, copolymerized polyamide, and the like can be used.
The resin used for ultrafine fibers can contain inorganic particles such as titanium oxide particles, a lubricant, a pigment, a thermal stabilizer, an ultraviolet absorber, an electrically conductive agent, a heat storage agent, an antibacterial agent, and the like in accordance with various purposes.
The resin used for ultrafine fibers preferably contains components derived from biomass resources.
As for components derived from biomass resources in the case of using a polyester-based resin as the resin used for ultrafine fibers, components derived from biomass resources may be used as a dicarboxylic acid, which is a constituent thereof, or an ester-forming derivative thereof or components derived from biomass resources may be used as a diol. However, from the viewpoint of reducing the environmental load, components derived from biomass resources are preferable used for both of a dicarboxylic acid or an ester-forming derivative thereof and a diol.
As components derived from biomass resources in the case of using a polyamide resin as the resin used for ultrafine fibers, from the viewpoint of economically advantageously obtaining raw materials derived from biomass resources and viewpoint of properties of fibers, polyamide 56, polyamide 610, and polyamide 11 are preferably used.
As the cross-sectional shape of the ultrafine fiber, either a round cross section or a modified cross section can be adopted. Specific examples of the modified cross section include an elliptical shape, a flat shape, a polygonal shape such as a triangular shape, a fan-like shape, and a cross shape.
In the present invention, it is important that the average single fiber diameter of the ultrafine fibers is 0.1 µm or more and 10 µm or less. When the average single fiber diameter of the ultrafine fibers is 10 µm or less, preferably 7 µm or less, and more preferably 5 µm or less, it is possible to cause the sheet material to be more flexible. Furthermore, the quality of the nap can be improved. Meanwhile, when the average single fiber diameter of the ultrafine fibers is 0.1 µm or more, preferably 0.3 µm or more, and more preferably 0.7 µm or more, it is possible to obtain a sheet material superior in color developability after dyeing in the case of performing dyeing. Further, when performing a nap raising treatment by buffing, bundled ultrafine fibers can be easy to disperse and handle.
The average single fiber diameter described in the present invention is measured by the following method. Specifically,

(1) A cross section of the sheet material cut in the thickness direction is observed with a scanning electron microscope (SEM).
(2) The fiber diameters of any 50 ultrafine fibers in the observation plane with respect to 3 sites on each ultrafine fiber cross section are measured. Provided that in the case of utilizing ultrafine fibers with a modified cross section, the cross-section area of single fiber is measured and the diameter of a circle corresponding to the cross-section area is calculated using the following equation. The resulting diameter is defined as the single fiber diameter of the single fiber.
- $Single fiber diameter (μm) = {(4 \times (\begin{array}{l} Cross - section area \\ ({μm}^{2}) of single fiber \end{array}) / π)}^{1 / 2}$
(3) The total of the diameters obtained at 150 points is averaged and the arithmetic mean value (µm) is rounded off to the first decimal place.

[Fibrous Base Material]

The fibrous base material used in the present invention includes the above ultrafine fiber. In this regard, it is allowed that ultrafine fibers of different raw materials are mixed in the fibrous base material.
As a specific form of the above fibrous base material, it is possible to use a nonwoven fabric in which the above ultrafine fibers are interlaced or a nonwoven fabric in which fiber bundles of ultrafine fibers are interlaced. Among them, a nonwoven fabric in which fiber bundles of ultrafine fibers are interlaced is preferably used, from the viewpoints of the strength and texture of a sheet material. From the viewpoints of flexibility and texture, it is particularly preferable to use a nonwoven fabric in which ultrafine fibers constituting fiber bundles of ultrafine fibers are appropriately spaced from one another to form spaces. As described above, the nonwoven fabric, in which fiber bundles of ultrafine fibers are interlaced, can be obtained by, for example, beforehand interlacing ultrafine fiber-generating fibers and then generating ultrafine fibers. Further, the nonwoven fabric, in which ultrafine fibers constituting fiber bundles of ultrafine fibers are appropriately spaced from one another to form spaces, can be obtained by, for example, using sea-island composite fibers in which a sea component may be removed to make a space between island components.
The nonwoven fabric may be either a short fiber nonwoven fabric or a long fiber nonwoven fabric. From the viewpoint of the texture and quality of the sheet material, the short fiber nonwoven fabric is more preferably used.
The fiber length of the short fibers in the case of using the short fiber nonwoven fabric is in a range of 25 mm or more and 90 mm or less. When the fiber length is set to 25 mm or more, more preferably 35 mm or more, and still more preferably 40 mm or more, a sheet material with superior wear resistance is easy to obtain by interlacing. Further, when the fiber length is set to 90 mm or less, more preferably 80 mm or less, and still more preferably 70 mm or less, it is possible to obtain a sheet material having more superior texture and quality.
In the present invention, when a nonwoven fabric is used as the fibrous base material, a woven fabric or a knitted fabric can also be inserted into or laminated on the nonwoven fabric, or the nonwoven fabric can also be lined with a woven fabric or a knitted fabric, for the purpose of improving strength or the like. The average single fiber diameter of the fibers constituting the woven fabric and the knitted fabric is more preferably 0.3 µm or more and 10 µm or less, because damage during needle punching can be reduced and the strength can be maintained.
As the fibers constituting the woven fabric and the knitted fabric, it is possible to use a polyester such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, or polylactic acid, a synthetic fiber such as a polyamide such as 6-nylon or 66-nylon, a regenerated fiber such as cellulosic polymer, and a natural fiber such as cotton or hemp.

[Polymer Elastic Body]

In the sheet material of the present invention, examples of the polymer elastic body include water-dispersible silicone resins, water-dispersible acrylic resins, water-dispersible urethane resins, and copolymers thereof. Among them, water-dispersed polyurethane resins are preferably used from the viewpoint of texture.
As the water-dispersed polyurethane resin, a resin obtained by a reaction of a polymeric polyol having a number average molecular weight of preferably 500 or more and 5,000 or less, an organic polyisocyanate, and a chain extender is preferably used. Further, in order to enhance the stability of the water-dispersed polyurethane dispersion, it is preferable to use a hydrophilic group-containing active hydrogen component in combination. When the number average molecular weight of the polymeric polyol is set to 500 or more, and more preferably 1,500 or more, it is possible to easily prevent the texture from becoming hard. Further, when the number average molecular weight is set to 5,000 or less, and more preferably 4, 000 or less, it is possible to easily maintain the strength of the polyurethane as a binder. Hereinafter, a case where a water-dispersed polyurethane resin is used as the polymer elastic body will be described.

(1) Reaction Components of Water-Dispersed Polyurethane Resin

First, reaction components of the water-dispersed polyurethane resin will be described.

(1-1) Polymeric Polyol

In the sheet material of the present invention, the polymer elastic body contains a polyether diol as a constituent. The content of the polyether diol in the polymeric polyol is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more of the whole polymeric polyol. Examples of the polyether diol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and a copolymerized polyether diol combining these. In the present specification, the term "contain as a constituent" refers to containing as a monomer component or an oligomer component constituting the polymer elastic body. The polyether diol has a high degree of freedom of the ether bond, and thus has a low glass transition temperature and a weak cohesive force. Accordingly, a polyurethane having superior flexibility is easily obtained.

(1-2) Organic Diisocyanate

Examples of the organic diisocyanate used in the present invention include a C6-20 aromatic diisocyanate (excluding carbon atoms in an NCOgroup; the same applies to the following), a C2-18 aliphatic diisocyanate, a C4-15 alicyclic diisocyanate, a C8-15 aroaliphatic diisocyanate, a modified product of these diisocyanates (e.g., a carbodiimide-modified product, a urethane-modified product, a uretdione-modified product), and a mixture of two or more kinds thereof.
Specific examples of the C6-20 aromatic diisocyanate include 1,3- and/or 1,4-phenylene diisocyanate, 2,4- and/or 2,6-tolylene diisocyanate, 2,4'- and/or 4,4'-diphenylmethane diisocyanate (hereinafter, abbreviated as MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane, and 1,5-naphthylene diisocyanate.
Specific examples of the C2-18 aliphatic diisocyanate include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylcaproate, bis(2-isocyanatoethyl)carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexaate.
Specific examples of the C4-15 alicyclic diisocyanate include isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis(2-isocyanatoethyl)-4-cyclohexylene-1,2-dicarboxylate, and 2,5- and/or 2,6-norbornane diisocyanate.
Specific examples of the C8-15 aroaliphatic diisocyanate include m- and/or p-xylylene diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.
Among them, a preferred organic diisocyanate is an alicyclic diisocyanate. A particularly preferred organic diisocyanate is dicyclohexylmethane-4,4'-diisocyanate.

(1-3) Chain Extender

Examples of the chain extender used in the present invention include water, a low-molecular-weight diol such as "ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, or neopentyl glycol", an alicyclic diol such as "1,4-bis(hydroxymethyl)cyclohexane", an aromatic diol such as "1,4-bis(hydroxyethyl)benzene", an aliphatic diamine such as "ethylenediamine", an alicyclic diamine such as "isophoronediamine", an aromatic diamine such as "4-4-diaminodiphenylmethane", an aroaliphatic diamine such as "xylenediamine", an alkanolamine such as "ethanolamine", hydrazine, a dihydrazide such as "adipic acid dihydrazide", and a mixture of two or more kinds thereof.
Among them, preferred chain extenders are water, low molecular weight diols, and aromatic diamines, and more preferred examples thereof include water, ethylene glycol, 1,4-butanediol, 4,4'-diaminodiphenylmethane, and a mixture of two or more kinds thereof.

(2) Additives of Water-Dispersed Polyurethane Resin

In the present invention, for the reasons described later, it is important to add a monovalent positive ion-including inorganic salt to a solution containing water-dispersed polyurethane. In addition, a colorant such as titanium oxide, various stabilizers such as a UV absorber (e.g., a benzophenone-based or benzotriazole-based UV absorber) and an antioxidant [e.g., a hindered phenol such as 4,4-butylidene-bis(3-methyl-6-1-butylphenol); an organic phosphite such as triphenylphosphite or trichloroethylphosphite], an inorganic filler (e.g., calcium carbonate), and the like may be added, if necessary.

(3) Structure of Water-Dispersed Polyurethane Resin

In the water-dispersed polyurethane used in the present invention, examples of the component for imparting a hydrophilic group to polyurethane include a hydrophilic group-containing active hydrogen component. Examples of the hydrophilic group-containing active hydrogen component include a compound containing a nonionic group and/or an anionic group and/or a cationic group and active hydrogen.
Examples of the compound having a nonionic group and active hydrogen include compounds containing two or more active hydrogen components or two or more isocyanate groups and having a polyoxyethylene glycol group with a molecular weight of 250 to 9,000 or the like in a side chain, and triols such as trimethylol propane and trimethylol butane.
Examples of the compound having an anionic group and active hydrogen include carboxyl group-containing compounds such as 2,2-dimethylol propionic acid, 2,2-dimethylol butanoic acid and 2,2-dimethylol valeric acid and derivatives thereof, sulfonic group-containing compounds such as 1,3-phenylenediamine-4,6-disulfonic acid and 3-(2,3-dihydroxypropoxy)-1-propanesulfonic acid and derivatives thereof, and salts obtained by neutralizing these compounds with a neutralizer.
Examples of the compound containing a cationic group and active hydrogen include tertiary amino group-containing compounds such as 3-dimethylaminopropanol, N-methyldiethanolamine, and N-propyldiethanolamine, and derivatives thereof.
The hydrophilic group-containing active hydrogen component can also be used in the form of salt neutralized with a neutralizer.
As the hydrophilic group-containing active hydrogen component used in the polyurethane molecule, 2,2-dimethylol propionic acid, 2,2-dimethylol butanoic acid, and neutralized salts thereof are preferably used from the viewpoints of the mechanical strength and dispersion stability of the water-dispersed polyurethane resin.
In the present invention, the hydrophilic group in the polymer elastic body is a group having active hydrogen. Specific examples of the hydrophilic group include a hydroxyl group, a carboxyl group, a sulfonic acid group, and an amino group.
In the present invention, the polymer elastic body internally has an N-acylurea bond and/or an isourea bond. Here, the expression "the polymer elastic body internally has an N-acylurea bond and/or an isourea bond" means that the polymer elastic body has an N-acylurea bond and/or an isourea bond. When a water-dispersed polyurethane resin is used as the polymer elastic body, the N-acylurea bond and/or the isourea bond can be formed, for example, by reacting a hydroxyl group and/or a carboxyl group present as the hydrophilic group-containing active hydrogen component with a carbodiimide-based crosslinker. As a result, a three-dimensional crosslinked structure by the N-acylurea bond and/or the isourea bond, which is superior in physical properties, such as light resistance, heat resistance, and wear resistance, and flexibility, is imparted into the molecule of the polymer elastic body, and physical properties such as wear resistance can be dramatically improved while maintaining the flexibility of the sheet material.
The presence of the N-acylurea group or the isourea group described above in the polymer elastic body can be analyzed, for example, by subjecting the cross section of the sheet material to a mapping treatment such as time-of-flight type secondary ion mass spectrometry (TOF-SIMS) (as an analytical instrument, for example, "TOF.SIMS 5" manufactured by ION-TOF GmbH, or the like) or infrared spectroscopic analysis (as an analytical instrument, for example, "FT/IR 4000 series" manufactured by JASCO Corporation, or the like).
The number average molecular weight of the polymer elastic body used in the present invention is preferably 20, 000 or more from the viewpoint of resin strength, and is preferably 500,000 or less from the viewpoint of viscosity stability and workability. The number average molecular weight is more preferably 30,000 or more and 150,000 or less.
The number average molecular weight of the polymer elastic body can be determined by gel permeation chromatography, and is measured under, for example, the following conditions.

Instrument: HLC-8220, manufactured by Tosoh Corporation
Column: TOSOH TSKgel α-M
Solvent: N,N-dimethylformamide (DMF)
Temperature: 40°C
Calibration: polystyrene

The polymer elastic body used in the present invention can suitably retain fibers in the sheet material. Preferably, from the viewpoint of providing at least one napped surface of the sheet material, the polymer elastic body is present in an inside of the fibrous base material in a preferable embodiment.

[Sheet material]

It is important for the sheet material of the present invention that a bending resistance in a lengthwise direction as determined in accordance with Method A (45° cantilever method) described in JIS L 1096:2010 "Testing methods for woven and knitted fabrics" is 40 mm or more and 140 mm or less. The bending resistance is set in the above range, as a result of which moderate flexibility and repulsive property can be attained. The bending resistance is preferably 50 mm or more and more preferably 55 mm or more from the viewpoint that a sheet material having repulsive property can be obtained, and the bending resistance is preferably 120 mm or less and more preferably 110 mm or less from the viewpoint of obtaining a sheet material having flexibility.
The lengthwise direction in the sheet material of the present invention refers to a direction in which the sheet material is subjected to the nap raising treatment. As a method of searching the direction in which the nap raising treatment has been performed, methods such as visual confirmation when tracing the sheet material with a finger and SEM photographing can be appropriately adopted according to the constituents of the sheet material. That is, a direction in which the napped fibers can be laid or raised when traced with a finger is the lengthwise direction. Further, a direction in which most of the laid napped fibers are directed when the surface of the sheet material traced with a finger is photographed by SEM is the lengthwise direction. On the other hand, as for the traverse direction in the sheet material of the present invention, a direction perpendicular to the lengthwise direction refers to the traverse direction.
It is important for the sheet material of the present invention that the abrasion weight loss after 20, 000 cycles of a Martindale abrasion test set forth in JIS L 1096:2005 after a light resistance test as performed under the conditions that a xenon arc amount as measured by the light fastness measurement method of JIS L 0843:2006 is 110 MJ/m², is 25 mg or less. The abrasion weight loss after the light resistance test is set in the above range, as a result of which deterioration of the polymer elastic body can be suppressed even in the case of using the sheet material for a long period of time in a severe environment exposed to sunlight, and the appearance of the sheet material can be maintained. The abrasion weight loss is preferably 23 mg or less and more preferably 20 mg or less from the viewpoint that deterioration of the appearance of the sheet material can be suppressed.
It is preferable for the sheet material of the present invention that the abrasion weight loss after 20, 000 cycles of the Martindale abrasion test set forth in JIS L 1096:2010 of the sheet material before the light resistance test is 20 mg or less. The abrasion weight loss before the light resistance test is set in the above range, as a result of which it is easy to suppress fall-off of raised fibers in practical use, deterioration of appearance, and the like. The abrasion weight loss is preferably 18 mg or less and more preferably 15 mg or less from the viewpoint that fall-off of raised fibers in practical use can be further suppressed.
The sheet material of the present invention preferably contains 10% by mass or more of the polymer elastic body. The contain of the polymer elastic body is preferably 12% by mass or more and more preferably 15% by mass or more from the viewpoint that breakage due to tension in the production processes, fall-off of raised fibers in practical use, and the like can be suppressed. The upper limit of the content is not particularly limited, and is usually 50% by mass or less, preferably 40% by mass or less, and more preferably 35% by mass or less.
The sheet material of the present invention preferably further satisfies the following condition 3:
condition 3: An L value retention when a napped surface of the sheet material is placed on a hot plate heated to 150°C and pressed at a pressing load of 2.5 kPa for 10 seconds (hereinafter, sometimes simply abbreviated as L value retention), is 90% or more and 100% or less.
In particular, when the L value retention is 90% or more, more preferably 92% or more, and still more preferably 95% or more, the sheet material has high heat resistance.
In the present invention, the "napped surface of the sheet material" refers to a surface obtained by subjecting the sheet material to the nap raising treatment. In addition, the L value is an L value defined by the International Commission on Illumination (CIE). The L value retention in the present invention is an index indicating that a rate of change in brightness under heating and pressing conditions is small, that is, to what extent a sheet material having a dark color before heating and pressing does not become bright after heating and pressing.
In the present invention, the L value retention refers to a value measured and calculated by the following procedure.

(1) The sheet material is cut, and the L value of the cut test piece is measured using a color difference meter (e.g., "CR-410", manufactured by KONICA MINOLTA, INC.).
(2) The test piece is placed on a hot plate (e.g., "CHP-250 DN", manufactured by AS ONE Corporation) heated to 150°C with the napped surface of the test piece facing down.
(3) An indenter adjusted to have a pressing load of 2.5 kPa is placed on the test piece, and held for 10 seconds.
(4) The indenter on the test piece is removed, and the L value of the napped surface of the test piece is measured with the color difference meter.
(5) The L value retention is calculated by the following equation.

L value retention (%) = (L value measured by (1)) / (\begin{array}{l} L value \\ measured by (4) \end{array}) \times 100

To set the bending resistance, the abrasion weight loss before the light resistance test or after the light resistance test, and the L value retention in the above ranges, for example, a sheet material is produced through a polymer elastic body impregnating step, an ultrafine fiber generating step, and a drying step described below. The ultrafine fiber generating step is performed after impregnation of the polymer elastic body, as a result of which the ultrafine fiber can be formed in a gap between the ultrafine fibers and the polymer elastic body, and thus a soft texture is easily obtained. For example, in the drying step, the thermal treatment (curing treatment) is performed at a temperature of 120°C or higher and 180°C or lower, as a result of which particles of the polymer elastic body are aggregated, and light resistance, wear resistance, and heat resistance can be easily improved. The thermal coagulation temperature of the aqueous dispersion is set in the range described below, as a result of which uneven distribution (migration) of polyurethane on the sheet material surface due to moisture evaporation can be suppressed, and the L value retention can be increased.

[Method for Producing Sheet material]

Next, a method for producing a sheet material of the present invention will be described.
The method for producing a sheet material of the present invention includes steps (1) to (4) shown below, in this order:

In the present invention, the term "unnapped sheet material" refers to a sheet material, which has not been subjected to the nap raising treatment, obtained by the method including at least the above steps (1) to (3) in this order
In a preferred embodiment of the present invention, as a means for obtaining the ultrafine fibers, ultrafine fiber-generating fibers are used. A nonwoven fabric including ultrafine fiber bundles entangled with one another can be obtained by beforehand interlacing ultrafine fiber-generating fibers to form a nonwoven fabric, and then making the fibers ultrafine.
As the ultrafine fiber-generating fibers, it is preferable to use a sea-island composite fiber in which two components (two or three components when the island fiber is a core-sheath composite fiber) of thermoplastic resins having different solvent solubility are used as a sea component and an island component, the sea component is dissolved and removed using a solvent or the like so as to form the island component as an ultrafine fiber, from the viewpoint of the texture and the surface appearance of the sheet material, since appropriate spaces can be imparted between the island components, that is, between the ultrafine fibers inside the fiber bundle when the sea component is removed.
As for the sea-island composite fiber, a method of using a spinneret for sea-island composite and using a mutually aligned polymer in which two components, namely, a sea component and an island component (three components when the island fiber is core-sheath composite fiber) are spun in an aligned manner is preferred from the viewpoint of obtaining ultrafine fibers with an uniform single fiber diameter.
As the sea component of the sea-island composite fiber, polyethylene, polypropylene, polystyrene, a copolymerized polyester obtained by copolymerizing sodium sulfoisophthalic acid, polyethylene glycol, and the like, polylactic acid, and the like can be used, and from the viewpoint of yarn-making property, easy elutability, and the like, polystyrene or a copolymerized polyester is preferably used.
In a preferred embodiment, the sea component is preferably dissolved and removed after imparting the polymer elastic body. The details thereof are as described below.
It is preferable that the mass ratio between the sea component and the island component in the sea-island composite fibers used in the present invention is in a range of the sea component : the island component = 10 : 90 to 80 : 20. When the mass ratio of the sea component is 10% by mass or more, the island component tends to be made sufficiently ultrafine. When the mass ratio of the sea component is 80 mass or less, the proportion of the eluted component is small and the productivity is thus improved. The mass ratio between the sea component and the island component is more preferably in a range of the sea component : the island component = 20 : 80 to 70 : 30.
A fiber interlaced body is preferably in the form of a nonwoven fabric, and both of a short fiber nonwoven fabric and a long fiber nonwoven fabric can be used as described above. However, in the case of using the short fiber nonwoven fabric, the number of fibers facing the thickness direction of the fibrous base material is larger than that of the long fiber nonwoven fabric, and a high dense feeling can be obtained on the surface of the fibrous base material when nap-raised, which is preferred.
If a short fiber nonwoven fabric is used as the fiber interlaced body, it is preferable for the resulting ultrafine fiber-generating fibers to be crimped and then cut to required length to provide raw stock. Generally known methods may be used for the crimping and cutting.
Then, the resulting raw stock is processed by, for example, a cross lapper to produce a fiber web, which is then subjected to interlacing to provide a short fiber nonwoven fabric. As methods for producing a short fiber nonwoven fabric by interlacing a fiber web, a needle punching treatment, a water jet punching treatment, and the like can be used.
The obtained short fiber nonwoven fabric and the woven fabric are laminated and integrated by interlacing. For integration of the short fiber nonwoven fabric and the woven fabric by interlacing, the woven fabric is laminated on one surface or both surfaces of the short fiber nonwoven fabric. Alternatively, the woven fabric is sandwiched between a plurality of sheets of short fiber nonwoven fabric webs, and then fibers of the short fiber nonwoven fabric and the woven fabric can be interlaced by a needle punching treatment, a water jet punching treatment, or the like.
The apparent density of the short fiber nonwoven fabric including composite fibers (ultrafine fiber-generating fibers) after a needle punching treatment or a water jet punching treatment is preferably 0.15 g/cm³ or more and 0.45 g/cm³ or less. When the apparent density is preferably set to 0.15 g/cm³ or more, the fibrous base material attains sufficient shape stability and dimension stability. Meanwhile, when the apparent density is preferably set to 0.45 g/cm³ or less, a sufficient space can be kept such that the polymer elastic body is imparted.
From the viewpoint of compactness, the nonwoven fabric thus obtained may be contracted and further highly compacted by dry heat or wet heat or by both in a preferred embodiment. Further, the nonwoven fabric can also be compressed in the thickness direction by a calendaring treatment or the like.
The method for producing a sheet material of the present invention includes (1) a polymer elastic body impregnating step of impregnating a fibrous base material including ultrafine fiber-generating fibers with an aqueous dispersion containing a polymer elastic body, a monovalent positive ion-including inorganic salt, and a crosslinker and then performing a heating treatment at a temperature of 120°C or higher and 180°C or lower, the polymer elastic body having a hydrophilic group and containing a polyether diol as a constituent, a content of the monovalent positive ion-including inorganic salt in the aqueous dispersion being 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polymer elastic body.
In the method for producing a sheet material of the present invention, a polymer elastic body having a hydrophilic group and containing a polyether diol as a constituent is imparted to a fibrous base material. When a nonwoven fabric is used as the fibrous base material, the polymer elastic body can be imparted to both a nonwoven fabric including composite fibers and a nonwoven fabric in which fibers are made ultrafine.
In the method for producing a sheet material of the present invention, the polymer elastic body contains a polyether diol as a constituent. The reason is as described in the section of (1-1) Polymeric Polyol.
In the method for producing a sheet material of the present invention, a dry-heat coagulation method in which a heating treatment is performed at a temperature of 120°C or higher and 180°C or lower is used for coagulation after imparting the polymer elastic body. In another coagulation method, for example, a hot water coagulation method in which the polymer elastic body is coagulated in hot water, the polymer elastic body is diffused into hot water and partially falls off, whereby there is a concern about processability. Further, in an acid coagulation method in which the polymer elastic body is coagulated by an acid, it is necessary to neutralize an acidic solution remaining in the sheet, which is not preferable in processing operability. Meanwhile, the dry-heat coagulation method used in the present invention is a very simple procedure of subjecting a sheet impregnated with the polymer elastic body to a heating treatment using a hot-air dryer or the like, and is a procedure superior in processability without concern of falling off of the polymer elastic body.
In the method for producing a sheet material of the present invention, the heating temperature in dry-heat coagulation is 120°C or higher and 180°C or lower. The heating temperature is more preferably 140°C or higher. This is because it is possible to cause the polymer elastic body to rapidly coagulate, and reduce uneven distribution of the polymer elastic body on the lower surface of the sheet due to its own weight. Further, in the present invention, it is necessary to use a crosslinker in combination. The temperature is set to the above temperature, so that the crosslinking reaction can be sufficiently promoted, a three-dimensional network structure can be formed, and the physical properties, light resistance, and heat resistance can be improved. The heating temperature is more preferably 175°C or lower. This is because the thermal degradation of the polymer elastic body can be suppressed.
From the viewpoint of storage stability of the aqueous dispersion, the concentration of the polymer elastic body in the aqueous dispersion (i.e., the content of the polymer elastic body in 100% by mass of the aqueous dispersion) is preferably 10% by mass or more and 50% by mass or less and more preferably from 15% by mass or more and 40% by mass or less.
To improve the storage stability and film-forming potential, the content of water-soluble organic solvent in the aqueous dispersion used in the present invention may be 40% by mass or less in 100% by mass of the aqueous dispersion. The content of the organic solvent is preferably 1% by mass or less in view of, for instance, protecting a film-forming environment.
In the method for manufacturing a sheet material of the present invention, the aqueous dispersion contains a monovalent positive ion-including inorganic salt. The monovalent positive ion-including inorganic salt is contained, thereby making it possible to impart thermal coagulation characteristic to the aqueous dispersion. In the present invention, the thermal coagulation characteristic refers to a characteristic of decreasing the fluidity of aqueous dispersion and coagulating the aqueous dispersion after a certain temperature (thermal coagulation temperature) is reached at the time of heating the polyurethane liquid.
In the method for producing a sheet material of the present invention, the aqueous dispersion is imparted to the fibrous base material, and the resulting product is dry-heat coagulated by a heating treatment at a temperature of 120°C or higher and 180°C or lower so as to impart the polymer elastic body to the fibrous base material.
In a case where the polymer elastic body does not have thermal coagulation characteristic, migration occurs in which the polymer elastic body migrates to the sheet surface along with evaporation of moisture. Further, coagulation proceeds in a state in which the polymer elastic body is unevenly distributed around the fiber as moisture evaporates, whereby the polymer elastic body covers the periphery of the fiber and strongly restricts the movement. As a result, the texture of the sheet material becomes significantly hard.
The thermal coagulation temperature of the aqueous dispersion is preferably 55°C or higher and 80°C or lower. The thermosensitive temperature is more preferably set to 60°C or higher, since the stability of the aqueous dispersion during storage is improved, and the adhesion of the polymer elastic body to a machine during operation or the like can be suppressed. The thermal coagulation temperature is more preferably set to 70°C or lower, since the migration phenomenon of the polymer elastic body to the surface layer of the fibrous base material can be suppressed. Further, the coagulation of the polymer elastic body proceeds before moisture evaporates from the fibrous base material, so that a structure similar to that obtained by wet coagulation of a solvent-based polymer elastic body, i.e., a structure in which the polymer elastic body does not strongly retain fibers can be formed, thereby achieving favorable flexibility and repulsive feeling.
In the present invention, regarding an inorganic salt used as a thermosensitive coagulant, it is important to use a monovalent positive ion-including inorganic salt. The monovalent positive ion-including inorganic salt is preferably sodium chloride and/or sodium sulfate. In the conventional procedure, a divalent positive ion-including inorganic salt such as magnesium sulfate or calcium chloride has been preferably used as the thermosensitive coagulant. These inorganic salts greatly affect the stability of the aqueous dispersion even when added in a small amount. Depending on the kind of the polymer elastic body, it is difficult to strictly control the thermosensitive gelation temperature by adjusting the additive amount of the polymer elastic body. In addition, there has been a problem such as concern about gelation at the time of adjusting or storing the aqueous dispersion. Meanwhile, the monovalent positive ion-including inorganic salt having a small ionic valence has a small influence on the stability of the aqueous dispersion. Thus, the additive amount is adjusted, as a result of which the thermal coagulation temperature of the aqueous dispersion can be strictly controlled while ensuring the stability of the aqueous dispersion.
Further, in the present invention, it is important that the content of the monovalent positive ion-including inorganic salt in the aqueous dispersion is 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polymer elastic body. When the content is set to 10 parts by mass or more, ions present in a large amount in the aqueous dispersion uniformly act on the polymer elastic body particles, as a result of which coagulation can be rapidly completed at a specific thermal coagulation temperature. Thus, a more remarkable effect can be obtained by allowing the coagulation of the polymer elastic body to proceed in a state where a large amount of moisture is contained in the fibrous base material as described above. As a result, it is possible to form a structure very similar to that obtained by wet coagulation of the solvent-based polymer elastic body and to achieve favorable flexibility and repulsive feeling. Furthermore, the additive amount is set as described above, as a result of which the inorganic salt serves as an inhibitor in the fusion of the polymer elastic body particles, and it is also possible to prevent the polymer elastic body from being hardened due to the continuous film formation. Meanwhile, the content is set to 50 parts by mass or less, as a result of which it is possible to cause a continuous film structure of an appropriate polymer elastic body to be remained, and suppress a decrease in physical properties. The stability of the aqueous dispersion can also be maintained.
In the method for manufacturing a sheet material of the present invention, it is important that the aqueous dispersion contains a crosslinker. By introducing a three-dimensional network structure into the polymer elastic body by the crosslinker, physical properties such as wear resistance can be improved. Further, when the coagulation of the polymer elastic body and the reaction between the polymer elastic body and the crosslinker are allowed to proceed at the same time by using the monovalent positive ion-including inorganic salt described above in combination, the sheet material is made flexible by forming a dense three-dimensional network structure and controlling the adhesive structure of the fibers, and at the same time, high physical properties, high light resistance, and high heat resistance of the sheet material can also be achieved. That is, to improve physical properties, light resistance, and heat resistance of the sheet material, it is essential to concurrently perform use of the monovalent positive ion-including inorganic salt and the crosslinker and control of the heating temperature in dry-heat coagulation.
The crosslinker is preferably a carbodiimide-based crosslinker since the polymer elastic body obtained after the reaction is superior in light resistance, heat resistance, and wear resistance, and also has favorable flexibility.
The method for producing a sheet material of the present invention includes (2) an ultrafine fiber generating step of subjecting the ultrafine fiber-generating fibers to an alkali treatment to generate ultrafine fibers. When the alkali treatment is performed after the polymer elastic body is imparted, a space caused by a component, which is dissolved by the alkali treatment, occurs between the polymer elastic body and the ultrafine fibers. Accordingly, the polymer elastic body does not directly retain the ultrafine fibers, so the texture of the sheet material becomes softer.
An ultrafine fiber-generating treatment (sea-removing process) in the case of using sea-island composite fibers as the ultrafine fiber-generating fibers can be performed, for example, by immersing the sea-island composite fiber in a solvent and by squeezing them. As the solvent for dissolving the sea component, it is possible to use an alkaline aqueous solution such as sodium hydroxide, or hot water.
The ultrafine fiber generating step can be implemented by using a machine such as a continuous dyeing machine, a vibro washer type sea remover, a jet dyeing machine, a wins dyeing machine, or a jigger dyeing machine.
After the ultrafine fiber generating step, it is preferable to perform a sufficient washing step after the alkali treatment. Through the washing step, the sheet material can be processed without remaining alkali or the monovalent positive ion-including inorganic salt adhering to the sheet material in the sheet, and processing can be performed without affecting the production facilities. Water is preferably used as a cleaning solution in consideration of environmental aspects and safety.
The method for producing a sheet material of the present invention includes (3) a drying step of performing a thermal treatment at a temperature of 120°C or higher and 180°C or lower. During the ultrafine fiber generating step, the bonding of the polymer elastic body is partially decomposed by a solvent that dissolves a component other than the ultrafine fibers in the ultrafine fiber-generating fibers. Thus, particles of the polymer elastic body are aggregated by performing a curing treatment by drying, and physical properties such as light resistance, wear resistance, and heat resistance can be further improved.
In the method for producing a sheet material of the present invention, the heating temperature in the curing treatment by drying is 120°C or higher and 180°C or lower. To enhance the effect of the curing treatment and enhance physical properties such as light resistance, wear resistance, and heat resistance, the heating temperature is preferably 140°C or higher and more preferably 150°C or higher. To suppress thermal degradation of the polymer elastic body, the heating temperature is preferably 175°C or lower and more preferably 170°C or lower.
The method for producing a sheet material of the present invention preferably includes a dyeing step of dyeing the unnapped sheet material or the sheet material after the drying step. As the dyeing treatment, vacuum methods usually used in the art can be employed. For example, it is possible to use a jet dyeing treatment using a jigger dyeing machine or a jet dyeing machine, a dip dyeing treatment such as thermosol dyeing treatment using a continuous dyeing machine, a printing treatment to the napped surface, such as roller printing, screen printing, inkjet printing, sublimation printing, and vacuum sublimation printing, and the like. Among them, since the unnapped sheet material or the sheet material can be made flexible by adding a softening effect at the same time of dyeing of the unnapped sheet material or the sheet material, a method using a jet dyeing machine is preferable. If necessary, the sheet material may be subjected to various kinds of resin finishing after the dyeing.
Although depending on the kind of fiber, the dyeing temperature is preferably set to 80°C or higher and 150°C or lower. The dyeing temperature is set to 80°C or higher, and more preferably 110°C or higher, so that it is possible to efficiently dye the fiber. Meanwhile, the dyeing temperature is set to 150°C or lower, and more preferably 130°C or lower, so that it is possible to prevent deterioration of the polymer elastic body.
A dye used in the present invention may be selected according to the kind of fibers included in the fibrous base material, and is not particularly limited. For example, any disperse dye can be used in the case of a polyester-based fiber. In the case of a polyamide-based fiber, an acidic dye or a gold-containing dye can be used, and further, a combination thereof can be used. In the case of dyeing with a disperse dye, reduction cleaning may be performed after the dyeing.
A dyeing auxiliary is used during dyeing in a preferred embodiment. The dyeing auxiliary is used, so that the evenness and reproducibility of dyeing can be improved. Further, in the same bath during dyeing or after dyeing, it is possible to perform treatment using a finishing agent such as a softener such as silicone, an antistatic agent, a water repellent, a flame retardant, a lightfast agent, and an antimicrobial agent.
Regardless of before or after the dyeing step, from the viewpoint of production efficiency, cutting in half in the thickness direction is also a preferred embodiment of the present invention.
The method for producing a sheet material of the present invention includes, regardless of before or after the dyeing step, (4) a nap raising step of subjecting at least one surface of an unnapped sheet material to a nap raising treatment to form a nap on the surface. The method for forming a nap is not particularly limited, and various methods usually performed in the art such as buffing with sandpaper or the like can be used. When the length of the nap is too short, it is difficult to obtain an elegant appearance, and when the length of the nap is too long, pilling tends to occur. Therefore, the length of the nap is preferably 0.2 mm or more and 1.0 mm or less.
Further, in one embodiment of the present invention, prior to the nap raising treatment, a lubricant such as silicone may be imparted to an unnapped sheet material. When a lubricant is imparted, nap raising can be made easy by surface grinding. This is preferable because the surface appearance is very favorable. In addition, an antistatic agent may be imparted before the nap raising treatment. When an antistatic agent is imparted, grinding powder generated from the sheet material by grinding is unlikely to be deposited on a sandpaper. This is thus a preferred embodiment.
In one embodiment of the present invention, designability can be imparted to the surface thereof as necessary. For example, the sheet material can be subjected to post processing including boring such as perforation, embossing, laser processing, pin-sonic processing, and printing processing.

EXAMPLES

Next, the sheet material of the present invention will be described more specifically using Examples, but the present invention is not limited to these Examples.

[Evaluation method]

(1) Average Single Fiber Diameter of sheet material:

A cross section including the fibers of the sheet material, the cross section being perpendicular to the thickness direction, was observed at a magnification of 3000 times using a scanning electron microscope (SEM, VE-7800, manufactured by KEYENCE CORPORATION), and the single fiber diameters of 50 single fibers randomly extracted in a field of view of 30 µm × 30 µm were measured in µm units up to the first decimal place.
This operation was performed at 3 locations, the diameters of 150 single fibers in total were measured, and the average value was calculated up to the first decimal place. When fibers with a fiber diameter of more than 50 µm were mixed in, these fibers were determined not to fall under ultrafine fibers and were excluded from subjects for the average fiber diameter measurement. In addition, when ultrafine fibers had a modified cross section, the cross-section area of each single-fiber was first measured as described above, and the diameter when the cross section was assumed to be circular was estimated to determine the diameter of the single fiber. Each diameter-containing mother population was averaged to define the average single fiber diameter.

(2) Coagulation Temperature of Aqueous Dispersion

Into a test tube with an inner diameter of 12 mm, 20 g of the aqueous dispersion containing the polymer elastic body prepared in each Example and each Comparative Example was put; a thermometer was inserted such that the tip was below the liquid level; and the test tube was then sealed and immersed in a hot water bath at a temperature of 95°C such that the liquid level of the aqueous dispersion was below the liquid level of the hot water bath. While the temperature rise inside the test tube was checked by the thermometer, the test tube was lifted, if appropriate, and was swung for 5 seconds or less per check so as to examine the presence or absence of fluidity of the aqueous dispersion at its surface. Then, the temperature at which the aqueous dispersion at its surface lost fluidity was defined as the coagulation temperature. This measurement was triplicated per kind of aqueous dispersion, and then averaged.

(3) Flexibility Evaluation of Sheet material:

Based on Method A (45° cantilever method) described in section 8.21.1 of the chapter 8.21 "Bending Resistance" in JIS L 1096:2010 "Testing methods for woven and knitted fabrics", five test pieces of 2 × 15 cm were prepared in the lengthwise direction. Each test piece was placed on a horizontal table having a slope at an angle of 45 degrees, and was made to glide. Next, when a middle point at one end of the test piece was in contact with the slope, the scale was read. Then, the values for the five test pieces were averaged.

(4) Evaluation of Wear of Sheet material

Evaluation of wear was performed based on JIS L 1096:2010. Model 406, manufactured by James H. Heal & Co. Ltd., was used as a Martindale abrasion tester, and ABRASTIVE CLOTH SM 25, manufactured by James H. Heal & Co. Ltd., was used as a standard friction cloth. A load of 12 kPa was applied to the sheet material before and after the light resistance test described below, and the number of times of wear was set to 20,000. The mass of the sheet material before and after abrasion was used, and the abrasion weight loss was calculated by the following equation.
$\begin{array}{l} Abrasion weight loss (mg) = Mass before abrasion (mg) - \\ Mass after abrasion (mg) \end{array}$
As for the abrasion weight loss, a value obtained by rounding off the first decimal place was regarded as the abrasion weight loss.

(5) Light Resistance Test of Sheet material

In accordance with the light fastness measurement method of JIS L 0843:2006 (Method B, fifth exposure method), the sheet material was irradiated with a xenon arc lamp under conditions where the measurement time was adjusted so that the xenon arc intensity might be 110 MJ/m².

(6) Identification of Bonded Species in Polymer Elastic Body

Regarding the polymer elastic body separated from the sheet material, the bonded species were identified by infrared spectroscopic analysis using FT/IR 4000 series, manufactured by JASCO Corporation.

(7) L value retention

Measurement and calculation were performed by the above method using "CHP-250 DN" manufactured by AS ONE Corporation as a hot plate and "CR-410" manufactured by KONICA MINOLTA, INC. as a color difference meter.

(8) Kind of Inorganic Salt Contained in Sheet material and Content Measurement:

The sheet material was immersed in N,N-dimethylformamide overnight, and the solution from which the polymer elastic body and the inorganic salt had been eluted was concentrated by heating and drying at 140°C for solidification. Distilled water was added to the resulting solid, and only the inorganic salt was eluted. The aqueous solution containing the inorganic salt was heated and dried, and then the amount of the inorganic salt contained in the sheet material was measured. In addition, the mass of the solidified polymer elastic body was also measured after heating and drying, and the mass of the inorganic salt with regard to the mass of the polymer elastic body was calculated. Provided that, from the viewpoint of the effectiveness of the numerical value, the content of less than 0.1% by mass with regard to the polymer elastic body is set to be less than the detection lower limit.
The kind of the inorganic salt in the aqueous solution containing the inorganic salt was identified using an ion chromatograph system of "ICS-3000 type", manufactured by Dionex Corporation.

[Method for Producing Nonwoven Fabric A for Fibrous Base Material]

A copolymerized polyester containing 8 mol% SSIA (sodium 5-sulfoisophthalate) was used as a sea component, and polyethylene terephthalate was used as an island component to obtain sea-island composite fibers with an average single fiber diameter of 20 µm in which the composite ratio of the sea component : the island component was 20% by mass : 80% by mass and the number of islands was 16 islands/1 filament. The resulting sea-island composite fibers were cut into a fiber length of 51 mm to obtain a staple, which went through a carding machine and a cross wrapper to form a fiber web. This fiber web was subjected to a needle punching treatment to produce a nonwoven fabric with a basis weight of 700 g/m² and a thickness of 3.0 mm. The nonwoven fabric thus obtained was immersed and contracted in hot water at a temperature of 98°C for 2 minutes, and was then dried at a temperature of 100°C for 5 minutes to obtain a nonwoven fabric A for fibrous base material.

[Method for Producing Nonwoven Fabric B for Fibrous Base Material]

A copolymerized polyester containing 8 mol% SSIA (sodium 5-sulfoisophthalate) was used as a sea component, and polyethylene terephthalate was used as an island component to obtain sea-island composite fibers with an average single fiber diameter of 20 µm in which the composite ratio of the sea component : the island component was 43% by mass : 57% by mass and the number of islands was 16 islands/1 filament. The resulting sea-island composite fibers were cut into a fiber length of 51 mm to obtain a staple, which went through a carding machine and a cross wrapper to form a fiber web. This fiber web was subjected to a needle punching treatment to produce a nonwoven fabric with a basis weight of 550 g/m² and a thickness of 2.9 mm. The nonwoven fabric thus obtained was immersed and contracted in hot water at a temperature of 98°C for 2 minutes, and was then dried at a temperature of 100°C for 5 minutes to obtain a nonwoven fabric B for fibrous base material.

[Method for Producing Polymer Elastic Body]

A prepolymer was prepared in a toluene solvent using polytetramethylene ether glycol (described as PTMG in the table) having a number average molecular weight (Mn) of 2,000 as a polyol, MDI as an isocyanate, and 2,2-dimethylol propionic acid as a component for imparting a hydrophilic group. Ethylene glycol and ethylenediamine as chain extenders, polyoxyethylene nonylphenyl ether as an external emulsifier, and water were added and stirred. Toluene was removed under reduced pressure to obtain an aqueous dispersion of a polymer elastic body.

[Example 1]

(Nonwoven Fabric)

The nonwoven fabric A for a fibrous base material was used as a nonwoven fabric.

(Impartment of Polymer Elastic Body)

An aqueous dispersion containing a polymer elastic body was obtained by adding 20 parts by mass of sodium sulfate (described as "Na₂SO₄" in Table 1) as a thermosensitive coagulant and 3 parts by mass of a carbodiimide-based crosslinker with respect to 100 parts by mass of the polymer elastic body, and entirely adjusting the mixture to a solid content of 12% by mass using water. The thermal coagulation temperature was 70°C. The obtained nonwoven fabric A for a fibrous base material was immersed in the aqueous dispersion and then dried by hot air at a temperature of 160°C for 20 minutes, thereby obtaining a polymer elastic body-imparted nonwoven fabric having a thickness of 2.10 mm to which the polymer elastic body was imparted so that the content of the polymer elastic body was 20% by mass in 100% by mass of the sheet material when obtaining a sheet material.

(Ultrafine Fiber Generating Treatment)

The resulting polymer elastic body-imparted nonwoven fabric was immersed and treated for 5 minutes in a sodium hydroxide aqueous solution heated to a temperature of 95°C and having a concentration of 8 g/L, and the sea component of the sea-island composite fiber was removed. Thereafter, the sodium hydroxide aqueous solution adhering to the nonwoven fabric was immersed in water and washed for 30 minutes, and dried for 30 minutes by a dryer at 160°C, thereby obtaining a sheet including ultrafine fibers (polymer elastic body-imparted sheet).

(Dyeing/Finishing)

The resulting sea-removed, polymer elastic body-imparted sheet was cut in half in a direction perpendicular to the thickness direction. The side opposite to the half-cutting surface was subjected to grinding with an endless sandpaper of sandpaper count No. 180 to obtain a sheet material having a nap with a thickness of 0.75 mm.
The resulting sheet material having a nap was dyed with a black dye by using a jet dyeing machine under conditions at a temperature of 120°C. Then, drying was performed with a dryer to obtain a sheet material having ultrafine fibers with an average single fiber diameter of 4.4 µm. The bending resistance of the obtained sheet material was 80 mm, the abrasion weight loss before the light resistance test was 7 mg, the abrasion weight loss after the light resistance test was 9 mg, and the sheet material had soft texture and superior light resistance and wear resistance. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 93%, superior heat resistance was attained, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Example 2]

(Nonwoven Fabric)

As in Example 1, the nonwoven fabric A for a fibrous base material was used as a nonwoven fabric.

(Impartment of Polymer Elastic Body)

The thermosensitive coagulant was changed to sodium chloride (described as "NaCl" in Table 1). A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 1, except that the additive amount of the thermosensitive coagulant, the heating temperature by hot air, and the imparted amount of the polymer elastic body were changed.

(Ultrafine Fiber Generating Treatment)

The ultrafine fiber generating treatment was performed in the same manner as in Example 1, except that the drying temperature was changed.

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was 90 mm, the abrasion weight loss before the light resistance test was 6 mg, the abrasion weight loss after the light resistance test was 8 mg, and the sheet material had soft texture and superior light resistance and wear resistance. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 91%, superior heat resistance was attained, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Example 3]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 1, except that the additive amount of the thermosensitive coagulant, the heating temperature by hot air, and the imparted amount of the polymer elastic body were changed.

(Ultrafine Fiber Generating Treatment)

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was 55 mm, the abrasion weight loss before the light resistance test was 12 mg, the abrasion weight loss after the light resistance test was 18 mg, and the sheet material had soft texture and superior light resistance and wear resistance. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 97%, superior heat resistance was attained, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Example 4]

(Nonwoven Fabric)

The nonwoven fabric B for a fibrous base material was used as a nonwoven fabric.

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric having a thickness of 2.05 mm was obtained in the same manner as in Example 2, except that the heating temperature by hot air and the imparted amount of the polymer elastic body were changed.

(Ultrafine Fiber Generating Treatment)

The resulting polymer elastic body-imparted nonwoven fabric was immersed and treated for 10 minutes in a sodium hydroxide aqueous solution heated to a temperature of 95°C and having a concentration of 8 g/L, and the sea component of the sea-island composite fiber was removed. Thereafter, the sodium hydroxide aqueous solution adhering to the nonwoven fabric was immersed in water and washed for 30 minutes, and dried for 30 minutes by a dryer at 170°C, thereby obtaining a sheet including ultrafine fibers (polymer elastic body-imparted sheet).

(Dyeing/Finishing)

The resulting sea-removed, polymer elastic body-imparted sheet was cut in half in a direction perpendicular to the thickness direction. The side opposite to the half-cutting surface was subjected to grinding with an endless sandpaper of sandpaper count No. 120 to obtain a sheet material having a nap with a thickness of 0.75 mm.
The resulting sheet material having a nap was dyed with a black dye by using a jet dyeing machine under conditions at a temperature of 120°C. Then, drying was performed with a dryer to obtain a sheet material having ultrafine fibers with an average single fiber diameter of 3.0 µm. The bending resistance of the obtained sheet material was 75 mm, the abrasion weight loss before the light resistance test was 7 mg, the abrasion weight loss after the light resistance test was 10 mg, and the sheet material had soft texture and superior light resistance and wear resistance. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 96%, superior heat resistance was attained, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Example 5]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 1, except that the thermosensitive coagulant, the additive amount of the thermosensitive coagulant, and the imparted amount of the polymer elastic body were changed.

(Ultrafine Fiber Generating Treatment)

The ultrafine fiber generating treatment was performed in the same manner as in Example 1.

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was 100 mm, the abrasion weight loss before the light resistance test was 6 mg, the abrasion weight loss after the light resistance test was 8 mg, and the sheet material had soft texture and superior light resistance and wear resistance. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 94%, superior heat resistance was attained, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Example 6]

(Nonwoven Fabric)

As in Example 4, the nonwoven fabric B for a fibrous base material was used as a nonwoven fabric.

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 4.

(Ultrafine Fiber Generating Treatment)

The ultrafine fiber generating treatment was performed in the same manner as in Example 4.

(Dyeing/Finishing)

The both surfaces of the resulting sea-removed, polymer elastic body-imparted sheet were subjected to grinding with an endless sandpaper of sandpaper count No. 180 to obtain a sheet material having a nap with a thickness of 1.50 mm.
The resulting sheet material having a nap was dyed with a black dye by using a jet dyeing machine under conditions at a temperature of 120°C. Then, the sheet material was dried with a dryer and then cut in half in the thickness direction to obtain a sheet material having ultrafine fibers with an average single fiber diameter of 3.0 µm.
The bending resistance of the obtained sheet material was 80 mm, the abrasion weight loss before the light resistance test was 6 mg, the abrasion weight loss after the light resistance test was 9 mg, and the sheet material had soft texture and superior light resistance and wear resistance. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 96%, superior heat resistance was attained, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 1]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

An aqueous dispersion containing a polymer elastic body was obtained by adding 10 parts by mass of magnesium sulfate (described as "MgSO₄" in Table 1) as a thermosensitive coagulant and 3 parts by mass of a carbodiimide-based crosslinker with respect to 100 parts by mass of the polymer elastic body, and entirely adjusting the mixture to a solid content of 12% by mass using water. However, the aqueous dispersion was gelled in the nonwoven fabric surface during processing, and thus, it was not possible to impart the polymer elastic body to the nonwoven fabric.

[Comparative Example 2]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 1, except that the additive amount of the thermosensitive coagulant was changed.

(Ultrafine Fiber Generating Treatment)

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was larger than 150 mm. Thus, the bending resistance was not measurable and a hard texture was obtained. The abrasion weight loss before the light resistance test was 15 mg, and the abrasion weight loss after the light resistance test was 25 mg. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 87%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 3]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

(Ultrafine Fiber Generating Treatment)

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was larger than 150 mm. Thus, the bending resistance was not measurable and a hard texture was obtained. The abrasion weight loss before the light resistance test was 16 mg, the abrasion weight loss after the light resistance test was 28 mg, and light resistance was poor. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 89%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 4]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 2, except that no crosslinker was imparted.

(Ultrafine Fiber Generating Treatment)

The ultrafine fiber generating treatment was performed in the same manner as in Example 2.

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was larger than 150 mm. Thus, the bending resistance was not measurable and a hard texture was obtained. The abrasion weight loss before the light resistance test was 21 mg, the abrasion weight loss after the light resistance test was 32 mg, and light resistance and wear resistance were poor. An N-acylurea bond and an isourea bond were not present inside the polymer elastic body. The L value retention was 88%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 5]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 1, except that the heating temperature was changed.

(Ultrafine Fiber Generating Treatment)

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was 120 mm, the abrasion weight loss before the light resistance test was 13 mg, the abrasion weight loss after the light resistance test was 29 mg, and light resistance was poor. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 88%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 6]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 1.

(Ultrafine Fiber Generating Treatment)

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was 130 mm, the abrasion weight loss before the light resistance test was 16 mg, the abrasion weight loss after the light resistance test was 30 mg, and light resistance was poor. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 88%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 7]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

An aqueous dispersion containing a polymer elastic body was obtained by adding 3 parts by mass of a carbodiimide-based crosslinker with respect to 100 parts by mass of the polymer elastic body, adding a nonionic thickener (guar gum) ["NEOSOFT G" manufactured by Taiyo Kagaku Co., Ltd.] so that the active ingredient was 1 part by mass with respect to 100 parts by mass of the polymer elastic body, and entirely adjusting the mixture to a solid content of 13% by mass using water. The obtained nonwoven fabric was immersed in the aqueous dispersion, treated in hot water at a temperature of 90°C for 3 minutes, and then dried by hot air at a temperature of 160°C for 30 minutes, thereby obtaining a polymer elastic body-imparted nonwoven fabric having a thickness of 2.10 mm to which the polymer elastic body was imparted so that the content of the polymer elastic body was 20% by mass in 100% by mass of the sheet material when obtaining a sheet material.

(Ultrafine Fiber Generating Treatment)

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was 90 mm, the abrasion weight loss before the light resistance test was 20 mg, the abrasion weight loss after the light resistance test was 33 mg, and light resistance and wear resistance were poor. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 87%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 8]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

(Ultrafine Fiber Generating Treatment)

The resulting polymer elastic body-imparted nonwoven fabric was immersed and treated for 5 minutes in a sodium hydroxide aqueous solution heated to a temperature of 95°C and having a concentration of 8 g/L, and the sea component of the sea-island composite fiber was removed. Next, the sodium hydroxide aqueous solution adhering to the nonwoven fabric was immersed in water and washed for 30 minutes, and dried for 30 minutes by a dryer at 120°C. Thereafter, water was added to the carbodiimide-based crosslinker, the crosslinker entirely adjusted to a solid content of 2% by mass was impregnated and imparted to the sheet, and drying was performed for 30 minutes by a dryer at 160°C, thereby obtaining a sheet including ultrafine fibers (polymer elastic body-imparted sheet).

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was larger than 150 mm. Thus, the bending resistance was not measurable and a hard texture was obtained. The abrasion weight loss before the light resistance test was 20 mg, the abrasion weight loss after the light resistance test was 30 mg, and light resistance and wear resistance were poor. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 86%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Comparative Example 9]

(Nonwoven Fabric)

(Impartment of Polymer Elastic Body)

The above nonwoven fabric was impregnated with an aqueous solution containing 10% by mass of PVA (NM-14, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) with a saponification degree of 99% and a polymerization degree of 1400, and heated and dried at a temperature of 140°C for 10 minutes to obtain a PVA-imparted sheet in which the amount of PVA imparted with respect to 100 parts by mass of the fiber mass of the nonwoven fabric for a fibrous base material was 30 parts by mass.
The resulting PVA-imparted sheet was immersed and treated for 30 minutes in a sodium hydroxide aqueous solution heated to a temperature of 95°C and having a concentration of 8 g/L, thereby obtaining a sheet (PVA-imparted ultrafine fiber nonwoven fabric) including ultrafine fibers from which the sea component of the sea-island composite fiber had been removed.
An aqueous dispersion containing a polymer elastic body was obtained by adding 15 parts by mass of sodium chloride (described as "NaCl" in Table 1) as a thermosensitive coagulant and 3 parts by mass of a carbodiimide-based crosslinker with respect to 100 parts by mass of the polymer elastic body, and entirely adjusting the mixture to a solid content of 12% by mass using water. The thermal coagulation temperature was 68°C. The obtained nonwoven fabric A for a fibrous base material was immersed in the aqueous dispersion and then dried by hot air at a temperature of 160°C for 20 minutes, thereby obtaining a polymer elastic body-imparted sheet having a thickness of 2.05 mm to which the polymer elastic body was imparted so that the content of the polymer elastic body was 38% by mass in 100% by mass of the sheet material when obtaining a sheet material.
The resulting polymer elastic body-imparted sheet was immersed and treated for 10 minutes in water heated to 95°C and dried for 30 minutes by a dryer at 120°C, thereby obtaining a sheet from which the imparted PVA had been removed.

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 1. The bending resistance of the obtained sheet material was 90 mm, the abrasion weight loss before the light resistance test was 11 mg, the abrasion weight loss after the light resistance test was 26 mg, and light resistance was poor. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 91%, superior heat resistance was attained, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was 1.2% by mass.

[Comparative Example 10]

(Nonwoven Fabric)

As in Example 6, the nonwoven fabric B for a fibrous base material was used as a nonwoven fabric.

(Impartment of Polymer Elastic Body)

A polymer elastic body-imparted nonwoven fabric was obtained in the same manner as in Example 6, except that the heating temperature was changed.

(Ultrafine Fiber Generating Treatment)

The ultrafine fiber generating treatment was performed in the same manner as in Example 6, except that the drying temperature was changed.

(Dyeing/Finishing)

The dyeing/finishing was performed in the same manner as in Example 6. The bending resistance of the obtained sheet material was 85 mm, the abrasion weight loss before the light resistance test was 21 mg, the abrasion weight loss after the light resistance test was 31 mg, and light resistance and wear resistance were poor. An N-acylurea bond and an isourea bond were present inside the polymer elastic body. The L value retention was 85%, heat resistance was not sufficient, and the amount of the monovalent positive ion-including inorganic salt inside the polymer elastic body was less than the detection lower limit.

[Table 1]

	Aqueous dispersion containing hydrophilic group-having polymer elastic body			Processing condition
	Thermosensitive coagulant		Crosslinker	Polymer elastic body imparting step	Drying step
	Type	Additive amount (parts by mass)	Crosslinker	Heating temperature (°C)	Drying temperature (°C)
Example 1	Na₂SO₄	20	Carbodiimide-based	160	160
Example 2	NaCl	15	Carbodiimide-based	150	155
Example 3	Na₂SO₄	15	Carbodiimide-based	170	170
Example 4	NaCl	15	Carbodiimide-based	160	170
Example 5	NaCl	40	Carbodiimide-based	160	160
Example 6	NaCl	15	Carbodiimide-based	160	170
Comparative Example 1	MgSO₄	10	Carbodiimide-based	-	-
Comparative Example 2	Na₂SO₄	1	Carbodiimide-based	160	160
Comparative Example 3	Na₂SO₄	55	Carbodiimide-based	160	160
Comparative Example 4	NaCl	15	-	150	155
Comparative Example 5	Na₂SO₄	20	Carbodiimide-based	110	160
Comparative Example 6	Na₂SO₄	20	Carbodiimide-based	160	110
Comparative Example 7	-	-	Carbodiimide-based	160	160
Comparative Example 8	NaCl	15	-	150	160
Comparative Example 9	NaCl	15	Carbodiimide-based	160	-
Comparative Example 10	NaCl	15	Carbodiimide-based	110	110

[Table 2]

	Average single fiber diameter (µm)	PU-imparted amount (mass%)	Presence or absence of N-acylurea bond/isourea bond	Bending resistance (mm)	Abrasion weight loss (mg)		L value retention (%)
	Average single fiber diameter (µm)	PU-imparted amount (mass%)	Presence or absence of N-acylurea bond/isourea bond	Bending resistance (mm)	Before light resistance test	After light resistance test	L value retention (%)
Example 1	4.4	20	Presence	80	7	9	93
Example 2	4.4	30	Presence	90	6	8	91
Example 3	4.4	16	Presence	55	12	18	97
Example 4	3.0	38	Presence	75	7	10	96
Example 5	4.4	32	Presence	100	6	8	94
Example 6	3.0	38	Presence	80	6	9	96
Comparative Example 1
Comparative Example 2	4.4	20	Presence	> 150	15	25	87
Comparative Example 3	4.4	20	Presence	> 150	16	28	89
Comparative Example 4	4.4	30	Absence	> 150	21	32	88
Comparative Example 5	4.4	20	Presence	120	13	29	88
Comparative Example 6	4.4	20	Presence	130	16	30	88
Comparative Example 7	4.4	20	Presence	90	20	33	87
Comparative Example 8	4.4	20	Absence	> 150	20	30	86
Comparative Example 9	3.0	38	Presence	90	11	26	91
Comparative Example 10	3.0	38	Presence	85	21	31	85

"PU" in Table 2 represents polyurethane.

INDUSTRIAL APPLICABILITY

The sheet material obtained according to the present invention can be suitably used 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

A sheet material comprising a polymer elastic body in a fibrous base material,
wherein the fibrous base material includes ultrafine fibers having an average single fiber diameter of 0.1 µm or more and 10 µm or less, the polymer elastic body has a hydrophilic group and contains a polyether diol as a constituent, the polymer elastic body internally has an N-acylurea bond and/or an isourea bond, and the following condition 1 and condition 2 are satisfied:
condition 1: A bending resistance in a lengthwise direction as determined in accordance with Method A (45° cantilever method) set forth in JIS L 1096:2010 "Testing methods for woven and knitted fabrics" is 40 mm or more and 140 mm or less; and

condition 2: An abrasion weight loss after 20,000 cycles of a Martindale abrasion test set forth in JIS L 1096:2005 after a light resistance test as performed under the conditions that a xenon arc amount as measured by a light fastness measurement method of JIS L 0843:2006 is 110 MJ/m², is 25 mg or less.
The sheet material according to claim 1, wherein the abrasion weight loss after 20,000 cycles of the Martindale abrasion test set forth in JIS L 1096:2010 of the sheet material before the light resistance test is 20 mg or less.
The sheet material according to claim 1 or 2, wherein the sheet material contains 10% by mass or more of the polymer elastic body.
The sheet material according to any one of claims 1 to 3, wherein
the sheet material further satisfies the following condition 3:
condition 3: An L value retention when a napped surface of the sheet material is placed on a hot plate heated to 150°C and pressed at a pressing load of 2.5 kPa for 10 seconds, is 90% or more and 100% or less.
A method for producing a sheet material, comprising steps (1) to (4) shown below, in this order:
(1) a polymer elastic body impregnating step of impregnating a fibrous base material including ultrafine fiber-generating fibers with an aqueous dispersion containing a polymer elastic body, a monovalent positive ion-including inorganic salt, and a crosslinker and then performing a heating treatment at a temperature of 120°C or higher and 180°C or lower, the polymer elastic body having a hydrophilic group and containing a polyether diol as a constituent, a content of the monovalent positive ion-including inorganic salt in the aqueous dispersion being 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polymer elastic body;

(2) an ultrafine fiber generating step of subjecting the ultrafine fiber-generating fibers to an alkali treatment to generate ultrafine fibers;

(3) a drying step of performing a thermal treatment at a temperature of 120°C or higher and 180°C or lower; and

(4) a nap raising step of subjecting at least one surface of an unnapped sheet material to a nap raising treatment to form a nap on the surface.
The method for producing a sheet material according to claim 5, further comprising a dyeing step of dyeing the unnapped sheet material or the sheet material after the drying step.
The method for producing a sheet material according to claim 5 or 6, wherein the monovalent positive ion-including inorganic salt is sodium chloride and/or sodium sulfate.
The method for producing a sheet material according to any one of claims 5 to 7, wherein the crosslinker is a carbodiimide-based crosslinker.