Leather surface treatment agent and leather treated with the same

Abstract

To provide a surface treatment agent capable of suppressing yellowing of the leather surface, and leather in which yellowing of the surface is suppressed. [Solution] (A) A resin capable of forming a resin layer on a leather substrate, (B) Water-soluble salt and A leather surface treatment agent containing [specific ingredient].

Description

Technical Field

[0001] The present invention relates to a surface treatment agent for leather and leather treated with the same.

Background Art

[0002] Leathers typified by synthetic leathers having an epidermal layer (PU epidermal layer) made of polyurethane resin and polyvinyl chloride (PVC) leather are laminated with a soft polyurethane foam to form a cushioning composite material, and due to their good touch, they are used in a wide range of fields such as automotive interior materials and furniture. Such a cushioning composite material is manufactured by a so-called frame lamination method in which the surface of the soft polyurethane foam is burned and melted by a flame or the like, and synthetic leather or the like is laminated thereto. However, in the cushioning composite material manufactured by the frame lamination method, there is a problem that the leather surface turns yellow. Conventionally, since dark-colored synthetic leathers such as black and gray were used, the discoloration of the leather surface was not noticeable and was not a major problem. However, in recent years, since light-colored synthetic leathers such as white and beige are often used, the discoloration of the leather surface is noticeable and has become a major problem. For this reason, in the cushioning composite material manufactured by the frame lamination method, a method capable of suppressing the yellowing of the leather surface has been demanded.

[0003] As a method for suppressing the yellowing of the soft polyurethane foam itself, for example, a method of blending a phosphorus-based antioxidant and a hindered amine-based light stabilizer into a foaming raw material containing a polyol, an aromatic polyisocyanate, a foaming agent, and a catalyst (Japanese Patent Application Laid-Open No. 2010-100717 (Patent Document 1)), or a method of manufacturing a non-yellowing soft polyurethane foam using a polyurethane foam raw material containing at least a polyol component, an aliphatic or alicyclic polyisocyanate component, a foam stabilizer, a catalyst, and a foaming agent, and the polyol component containing a specific polyoxyalkylene polyol (Japanese Patent Application Laid-Open No.

Prior Art Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-100717 [Patent Document 2] Japanese Patent Publication No. 2010-150438 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] This invention has been made in view of the problems of the prior art described above, and aims to provide a surface treatment agent capable of suppressing yellowing of the leather surface, and leather in which yellowing of the surface is suppressed. [Means for solving the problem]

[0006] The inventors of this invention have conducted extensive research to achieve the above objectives and have discovered that in a cushioning composite material made by bonding soft polyurethane foam and various types of leather by a frame lamination method, the cause of yellowing of the leather surface is NOx gas contained in the gas generated from the soft polyurethane foam during combustion by flames, etc. Furthermore, they have discovered that yellowing of the leather surface due to NOx gas can be suppressed by forming a surface treatment layer on the leather substrate using a surface treatment agent containing a water-soluble salt, thus completing the present invention.

[0007] In other words, the present invention provides the following embodiments.

[0008] [1] (A) A resin capable of forming a resin layer on a leather substrate, (B) Water-soluble salt and A leather surface treatment agent containing [specific ingredient]. [2] The leather surface treatment agent according to [1], wherein the resin capable of forming a resin layer on the leather substrate (A) is at least one selected from the group consisting of acrylic resins and polyurethane resins. [3] The leather surface treatment agent according to [1] or [2], wherein the water-soluble salt (B) has a solubility in water of 1 g / 100 ml or more at 15 to 25°C. [4] The water-soluble salt (B) is one of the following formulas (1) to (5):

[0009] [ka]

[0010] (R1 is a carboxyl group or a hydrocarbon group having 1 to 7 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R2, R3, R4, and R5 are each independently a hydroxyl group, R6O, or a hydrocarbon group having 1 to 16 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R6 is a hydrocarbon group having 1 to 16 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R4 and R5 may be the same or different.) A leather surface treatment agent according to any one of [1] to [3], which is at least one selected from the group consisting of salts of acids represented by [1]. [5] The water-soluble salt (B) is one of the following formulas (1) to (4):

[0011] [ka]

[0012] (R1 is a carboxyl group or a hydrocarbon group having 1 to 5 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R2, R3, R4, and R5 are each independently a hydroxyl group, R6O, or a hydrocarbon group having 1 to 6 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R6 is a hydrocarbon group having 1 to 6 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R4 and R5 may be the same or different.) A leather surface treatment agent according to [4], which is at least one selected from the group consisting of salts of acids represented by [4]. [6] Leather comprising a leather base material and a surface treatment layer formed on the leather base material with a leather surface treatment agent described in any one of [1] to [5]. [7] A cushioning composite material comprising a soft polyurethane foam and the leather described in [6] bonded to the surface of the soft polyurethane foam. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a surface treatment agent that can suppress yellowing of the leather surface, and leather in which yellowing of the surface is suppressed. [Modes for carrying out the invention]

[0014] The present invention will be described in detail below with reference to its preferred embodiments.

[0015] [Surface treatment agent for leather] First, the surface treatment agent for leather of the present invention will be described. The surface treatment agent for leather of the present invention (hereinafter, also simply referred to as "surface treatment agent") contains (A) a resin capable of forming a resin layer on a leather base material, and (B) a water-soluble salt. Hereinafter, each component will be described.

[0016] (A) Resin The (A) resin used in the present invention is not particularly limited as long as it is a resin capable of forming a resin layer on a leather base material (for example, on the surface of a leather base material or on the surface of various functional layers formed thereon). For example, polyurethane resin, acrylic resin, polyester resin, polyolefin resin, polyvinyl chloride resin, silicone resin, urethane acrylate resin, vinyl acetate resin, ethylene-vinyl acetate resin, styrene-butadiene resin, acrylonitrile-butadiene resin, polyamide resin, epoxy resin, etc. can be mentioned as resins generally used as the base resin when forming a resin layer (resin film). These resins can be appropriately selected according to the material of the surface of the leather base material or the surface of various functional layers formed thereon, and may be used alone or in combination of two or more. Among these resins, when the material of the surface of the leather base material or the surface of various functional layers formed thereon is polyurethane resin, polyvinyl chloride resin, or polyolefin resin, from the viewpoint of the adhesion between the surface treatment layer formed by the surface treatment agent of the present invention and the surface of the leather base material or the surface of various functional layers formed thereon, polyurethane resin and acrylic resin are preferable.

[0017] (Polyurethane resin) The polyurethane resin is not particularly limited. For example, polyurethane resins obtained by reacting at least organic polyisocyanate, polyol, and polyamine having two or more amino groups and / or imino groups can be mentioned. The manufacturing method of such polyurethane resin is not particularly limited, and a conventionally known method can be adopted. In the present invention, both aqueous and solvent-based polyurethane resins can be used.

[0018] Furthermore, among the polyurethane resins, from the viewpoint of abrasion resistance and flexibility of leather, a self-emulsifying aqueous polyurethane resin is preferred, which is a chain extension product of (a) an organic polyisocyanate, (b) a polyol, and (c) a neutralized isocyanate-terminated prepolymer which is a reaction product of a compound having an anionic hydrophilic group and at least two active hydrogens, and (d) a polyamine having two or more amino groups and / or imino groups. In the self-emulsifying aqueous polyurethane resin, "aqueous" means that after emulsifying and dispersing the self-emulsifying polyurethane resin in water to prepare an emulsion dispersion with a resin content of 35% by mass in water, it is possible to maintain a state in which no separation or sedimentation is observed even when this emulsion dispersion is left standing at 20°C for 12 hours.

[0019] (a) Organic polyisocyanates The above (a) organic polyisocyanates are not particularly limited and include aromatic, aliphatic, and alicyclic polyisocyanates that have been commonly used in the past. For example, aromatic polyisocyanates include m-phenylenediisocyanate, p-phenylenediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 4,4'-diphenylmethanediisocyanate, 2,4'-diphenylmethanediisocyanate, 3,3'-dimethyl-4,4'-biphenylenediisocyanate, 3,3'-dichloro-4,4'-biphenylenediisocyanate, 1,5-naphthalenediisocyanate, tolidinediisocyanate, tetramethylenexylylenediisocyanate, xylylenediisocyanate, and the like. Examples of aliphatic polyisocyanates include tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. Examples of alicyclic polyisocyanates include isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate, norbornane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane. These organic polyisocyanates may be used individually or in combination of two or more. Furthermore, among these organic polyisocyanates, aliphatic polyisocyanates and alicyclic polyisocyanates are preferred from the viewpoint that the resulting self-emulsifying aqueous polyurethane resin will not yellow, and alicyclic polyisocyanates are more preferred from the viewpoint of heat resistance.

[0020] (b) Polyol The (b) polyol is not particularly limited and examples include conventionally known polymer polyols such as polyether polyols, polyester polyols, and polycarbonate polyols, conventionally known low molecular weight diols, and polyhydric alcohols having at least three or more active hydrogens. These polyols may be used individually or in combination of two or more. In this specification, the polymer polyols and low molecular weight diols are collectively referred to as "(b1) polyols," and the polyhydric alcohols having at least three or more active hydrogens are referred to as "(b2) polyhydric alcohols." The (b1) polyols may be used alone or in combination with the (b2) polyhydric alcohols. Furthermore, it is preferable to use the (b2) polyhydric alcohols in combination with the (b1) polyols.

[0021] There are no particular restrictions on the polyether polyol, and examples include polymers of alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide. Such polymers may be homopolymers of one type of alkylene oxide or copolymers of two or more types of alkylene oxides. If they are copolymers, they may be random polymers or block polymers. There are no particular restrictions on the weight-average molecular weight of such polyether polyols, but 400 to 5000 is preferred. In addition, compounds obtained by adding one or more alkylene oxides to a low molecular weight dihydric alcohol can also be used as the polyether polyol. Examples of low molecular weight dihydric alcohols include ethylene glycol, propylene glycol, and 1,4-butanediol.

[0022] The aforementioned polyester polyol is not particularly limited and may include, for example, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol with a weight-average molecular weight of 300 to 1000, dipropylene glycol, tripropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanedimethanol, bisphenol A, bisphenol S, hydrogenated bisphenol A, hydroquinone, or alkylene oxide adducts thereof, as well as other diol components. Examples include polyester polyols obtained by dehydration condensation reactions with dicarboxylic acid components such as dimer acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic anhydride, fumaric acid, 1,3-cyclopentanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, 1,2-bisphenoxyethane-p,p'-dicarboxylic acid, anhydrides of dicarboxylic acids, or ester-forming derivatives; polyester polyols obtained by ring-opening polymerization reactions of cyclic ester compounds such as ε-caprolactone; and polyester polyols copolymerized from these.

[0023] There are no particular restrictions on the polycarbonate-based polyols, and examples include polycarbonate-based polyols obtained by the reaction of glycols such as 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,8-octanediol, 1,10-decanediol, and diethylene glycol with diphenyl carbonate, phosgene, etc. There are no particular restrictions on the weight-average molecular weight of such polycarbonate-based polyols, but from the viewpoint of the handling of the polycarbonate-based polyol and the flexural resistance of the resulting leather, 500 to 3000 is preferred, and 800 to 2500 is more preferred.

[0024] The low molecular weight diol is not particularly limited and examples include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, nonanediol, neopentyl glycol, and the like.

[0025] There are no particular restrictions on the (b2) polyhydric alcohol, and examples include trivalent or higher low molecular weight polyhydric alcohols such as trimethylolpropane, pentaerythritol, and sorbitol. Compounds with a molecular weight of 500 or less obtained by adding one or more alkylene oxides to such trivalent or higher low molecular weight polyhydric alcohols or low molecular weight polyalkylene polyamines can also be used as the (b2) polyhydric alcohol. Examples of the low molecular weight polyalkylene polyamines include ethylenediamine, diethylenetriamine, and triethylenetetramine. Examples of the alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide. Among these (b2) polyhydric alcohols, trivalent to tetravalent (b2) polyhydric alcohols are preferred from the viewpoint of abrasion resistance and flexural resistance of leather, and trivalent (b2) polyhydric alcohols are more preferred.

[0026] In the polyurethane resin, when the (b2) polyhydric alcohol is used, the proportion of the (b2) polyhydric alcohol is preferably 0.1 to 1.5% by mass, and more preferably 0.3 to 1.1% by mass, based on the total amount of the (b1) polyol, the (b2) polyhydric alcohol, and the (c) compound having an anionic hydrophilic group and at least two active hydrogens, from the viewpoint of the abrasion resistance and flexibility of the leather.

[0027] (c) Compounds having an anionic hydrophilic group and at least two active hydrogens The compound having the (c) anionic hydrophilic group and at least two active hydrogens is not particularly limited, and is, for example, a compound having an anionic hydrophilic group such as a carboxyl group, carboxylate group, sulfo group, or sulfonate group and two or more active hydrogen-containing groups such as a hydroxyl group. By copolymerizing this compound having the (c) anionic hydrophilic group and at least two active hydrogens, a self-emulsifying aqueous polyurethane resin can be obtained. Examples of the (c) compound include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dihydroxymaleic acid, and 2,6-dihydroxybenzoic acid. These (c) compounds may be used individually or in combination of two or more.

[0028] Furthermore, in the resulting self-emulsifying aqueous polyurethane resin, the content of the anionic hydrophilic group is preferably 0.3 to 3.0% by mass, and more preferably 0.5 to 2.5% by mass, from the viewpoint of emulsification stability, storage stability, and leather flexure resistance.

[0029] (d) Polyamines The (d) polyamine is a compound having two or more amino groups and / or imino groups in one molecule. There are no particular limitations on such (d) polyamines, and examples include diamines such as ethylenediamine, propylenediamine, tetramethylenediamine, hexamethylenediamine, diaminocyclohexylmethane, hydrazine, 2-methylpiperazine, isophoronediamine, norboranediamine, diaminodiphenylmethane, tolylenediamine, xylylenediamine; polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, iminobispropylamine; and primary amines. Examples include amide amines derived from ammonium compounds and monocarboxylic acids; water-soluble amine derivatives such as monokethimine of primary amines; and hydrazine derivatives such as dihydrazide oxalate, dihydrazide malonate, dihydrazide succinate, dihydrazide glutarate, dihydrazide adipic acid, dihydrazide sebacate, dihydrazide maleate, dihydrazide fumarate, dihydrazide itaconic acid, 1,1'-ethylenehydrazine, 1,1'-trimethylenehydrazine, and 1,1'-(1,4-butylene)dihydrazine. These (d) polyamines may be used individually or in combination of two or more. Furthermore, the amount of such (d) polyamine used is preferably an amount containing 0.8 to 1.2 equivalents of amino groups, etc., relative to the free isocyanate groups of the isocyanate-terminated prepolymer described later.

[0030] (Isocyanate-terminated prepolymer) The isocyanate-terminated prepolymer is a reaction product of (a) an organic polyisocyanate, (b) a polyol, and (c) a compound having an anionic hydrophilic group and at least two active hydrogens.

[0031] There are no particular limitations on the method for producing such isocyanate-terminated prepolymers. Examples include the conventionally known one-stage so-called one-shot method and the multi-stage isocyanate polyaddition reaction method. The reaction temperature is preferably 40 to 150°C. In this case, a reaction catalyst such as dibutyltin dilaurate, stanus octoate, dibutyltin di-2-ethylhexoate, triethylamine, triethylenediamine, N-methylmorpholine, or bismastris (2-ethylhexanoate), or a reaction inhibitor such as phosphoric acid, sodium hydrogen phosphate, p-toluenesulfonic acid, adipic acid, or benzoyl chloride may be added as needed.

[0032] Furthermore, an organic solvent that does not react with the isocyanate group may be added during or after the reaction. Examples of such organic solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, dimethylformamide, dimethyl sulfoxide, toluene, xylene, ethyl acetate, butyl acetate, and methylene chloride. Of these organic solvents, methyl ethyl ketone, toluene, and ethyl acetate are particularly preferred. These organic solvents can also be removed by heating and reducing pressure after emulsification, dispersion, and chain extension of the prepolymer.

[0033] In the production of isocyanate-terminated prepolymers, the molar ratio (NCO / OH) of isocyanate groups to hydroxyl groups in the raw material is preferably 2.0 / 1.0 to 1.1 / 1.0, and more preferably 1.7 / 1.0 to 1.25 / 1.0. By adjusting the molar ratio of isocyanate groups to hydroxyl groups in the raw material within the above range, an isocyanate-terminated prepolymer having a desired free isocyanate group content can be obtained. On the other hand, if the molar ratio of isocyanate groups to hydroxyl groups in the raw material falls below the lower limit, the free isocyanate group content tends to decrease too much, while if it exceeds the upper limit, the free isocyanate group content tends to increase too much.

[0034] The free isocyanate group content in the isocyanate-terminated prepolymer obtained in this manner is preferably 0.2 to 3.0% by mass. If the free isocyanate group content falls below the lower limit, the viscosity of the isocyanate-terminated prepolymer during production tends to increase significantly, requiring a large amount of organic solvent, which is disadvantageous in terms of cost and tends to make emulsification and dispersion difficult. On the other hand, if the free isocyanate group content exceeds the upper limit, the balance of water solubility after emulsification and dispersion and after chain extension with (d) polyamine tends to change significantly, which may reduce the storage stability or processing stability of the aqueous polyurethane resin over time. In addition, the flexural resistance of the leather may decrease.

[0035] Furthermore, the (a) organic polyisocyanate, the (b) polyol, and the (c) compound having an anionic hydrophilic group and at least two active hydrogens all have multiple reaction sites. The isocyanate-terminated prepolymer obtained by reacting such (a) organic polyisocyanate, (b) polyol, and (c) compound having an anionic hydrophilic group and at least two active hydrogens has a complex structure and cannot be directly represented by a general formula (structural formula).

[0036] (Neutralized product of isocyanate-terminated prepolymer) The neutralized product of the isocyanate-terminated prepolymer is obtained by neutralizing the anionic hydrophilic groups in the isocyanate-terminated prepolymer. Such a neutralized product of the isocyanate-terminated prepolymer may be produced by (i) reacting the (a) organic polyisocyanate, the (b) polyol, and the (c) compound having an anionic hydrophilic group and at least two active hydrogens, and then neutralizing the anionic hydrophilic groups in the isocyanate-terminated prepolymer by a known method; or (ii) mixing the (a) organic polyisocyanate, the (b) polyol, and the (c) compound having an anionic hydrophilic group and at least two active hydrogens, then neutralizing the anionic hydrophilic groups in the (c) compound by a known method, and then reacting the neutralized (c) compound, the (a) organic polyisocyanate, and the (b) polyol. Furthermore, the neutralized product of the isocyanate-terminated prepolymer can also be produced by reacting (iii) the (a) organic polyisocyanate, the (b) polyol, and the (c) compound, in which the anionic hydrophilic group is a salt of the anionic hydrophilic group.

[0037] In the production methods described in (i) and (ii) above, there are no particular restrictions on the basic compound used for neutralizing the anionic hydrophilic group. Examples include amines such as trimethylamine, triethylamine, tri-n-propylamine, tributylamine, N-methyl-diethanolamine, N,N-dimethylmonoethanolamine, N,N-diethylmonoethanolamine, and triethanolamine; alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; and ammonia. Among these, tertiary amines such as trimethylamine, triethylamine, tri-n-propylamine, and tributylamine are particularly preferred.

[0038] In the neutralization of the anionic hydrophilic group in the manufacturing methods (i) and (ii) described above, the amount of the neutralizing basic compound used is preferably 0.5 to 1.5 equivalents, more preferably 0.6 to 1.4 equivalents, and particularly preferably 0.7 to 1.3 equivalents, relative to the anionic hydrophilic group. If the amount of the neutralizing basic compound used falls below the lower limit, the emulsification and storage stability of the aqueous polyurethane resin tend to decrease. On the other hand, adding an amount of the neutralizing basic compound exceeding the upper limit does not further improve the emulsification and storage stability of the aqueous polyurethane resin, which is economically undesirable.

[0039] (Water-based polyurethane resin) The self-emulsifying aqueous polyurethane resin is obtained by extending the chain of the neutralized isocyanate-terminated prepolymer using the (d) polyamine (chain extension product).

[0040] (emulsification dispersion) In order to extend the chain of the isocyanate-terminated prepolymer neutralized product, the isocyanate-terminated prepolymer neutralized product is first emulsified and dispersed in water. There are no particular restrictions on the method of emulsification and dispersion, and conventionally known methods using homomixers, homogenizers, dispersers, etc., can be used. The isocyanate-terminated prepolymer neutralized product can be emulsified and dispersed in water at a temperature in the range of 0 to 40°C without the addition of any emulsifier. This suppresses the reaction between the isocyanate group and water. Furthermore, when emulsifying and dispersing the isocyanate-terminated prepolymer neutralized product, reaction inhibitors such as phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, p-toluenesulfonic acid, adipic acid, and benzoyl chloride may be added as needed.

[0041] (Chain elongation) Next, the neutralized isocyanate-terminated prepolymer, which has been emulsified and dispersed in water in this manner, is chain-extended using the (d) polyamine to form the self-emulsifying aqueous polyurethane resin.

[0042] There are no particular restrictions on the method of chain elongation, but for example, a method of chain elongation is preferred in which the (d) polyamine is added to an emulsion dispersion of the isocyanate-terminated prepolymer neutralized product, or in which the (d) polyamine is added to an emulsion dispersion of the isocyanate-terminated prepolymer neutralized product to elongate the chain. The reaction between the isocyanate-terminated prepolymer neutralized product and the amine is usually completed at a reaction temperature of 20 to 50°C, within 30 to 120 minutes after mixing the isocyanate-terminated prepolymer neutralized product and the (d) polyamine.

[0043] Such chain elongation may be performed simultaneously with the emulsification and dispersion, after the emulsification and dispersion, or before the emulsification and dispersion. Furthermore, if the obtained aqueous polyurethane resin contains an organic solvent, it is preferable to remove the organic solvent under reduced pressure at a temperature of 30 to 80°C.

[0044] Furthermore, similar to the (a) organic polyisocyanates, the (b) polyols, and the (c) compounds having an anionic hydrophilic group and at least two active hydrogens, the (d) polyamine also has multiple reaction sites. The chain extension of the neutralized isocyanate-terminated prepolymer (a self-emulsifying aqueous polyurethane resin) obtained by extending the chain of the neutralized isocyanate-terminated prepolymer using such a (d) polyamine also has a complex structure, similar to the isocyanate-terminated prepolymer, and cannot be directly represented by a general formula (structural formula).

[0045] The self-emulsifying aqueous polyurethane resin obtained in this manner is preferably used in an emulsified and dispersed state in water. There are no particular restrictions on the resin concentration, but 20 to 60% by mass is preferred. The resin concentration in such an emulsified dispersion of self-emulsifying aqueous polyurethane resin can be adjusted by adding or removing water.

[0046] (Acrylic resin) Examples of the acrylic resin include homopolymers and copolymers of acrylic monomers. Examples of the acrylic monomer include (meth)acrylic acid and its derivatives, such as methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, (meth)acrylic acid, glycidyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate. Here, (meth)acrylic acid refers to acrylic acid or methacrylic acid. Furthermore, these acrylic monomers may be used individually or in combination of two or more.

[0047] Examples of copolymer monomers used in the acrylic resin include aromatic vinyl compounds such as styrene, α-methylstyrene, and p-methylstyrene; acrylamides such as acrylamide, diacetone acrylamide, methacrylamide, and maleamide; heterocyclic vinyl compounds such as vinylpyrrolidone; vinyl compounds such as vinyl chloride, acrylonitrile, vinyl ether, vinyl ketone, and vinylamide; α-olefins such as ethylene and propylene; and maleic acid, fumaric acid, itaconic acid, and their derivatives. These copolymer monomers may be used individually or in combination of two or more.

[0048] The glass transition temperature (Tg) of the acrylic resin is preferably -40 to +50°C, more preferably -20 to +30°C, and most preferably -10 to +20°C. When the Tg of the acrylic resin falls below the lower limit, the abrasion resistance and stain resistance of the leather tend to decrease, while when it exceeds the upper limit, the abrasion resistance and stain resistance of the leather tend to improve, but the flexibility tends to decrease.

[0049] In the surface treatment agent of the present invention, commercially available acrylic resins can be used as the acrylic resin. Examples of commercially available acrylic resins include Saibinol EC-065 (Tg=5℃), Saibinol EC-071 (Tg=-20℃), Saibinol EC-064 (Tg=-40℃), Saibinol UC-6600 (Tg=50℃), Saibinol EC-2020 (Tg=17℃) (all manufactured by Saiden Chemical Co., Ltd.), DURAFLEX 84S (Tg=0℃), ORGAL P036V (Tg=0℃), ORGAL D55HC (Tg=-3℃), ORGAL DCS80 (Tg=-16℃) (all manufactured by ORGANIK Examples include Toktril BCX-8111 (Tg=-30℃), Toktril W-168 (Tg=-10℃), Toktril X-4403 (Tg=-7℃), Toktril W463 (Tg=11℃), Toktril BCX-1160R-2 (Tg=12℃), Toktril BCX-8104 (Tg=29℃), and Toktril X-4402 (Tg=35℃) (all manufactured by Toyo Chem Co., Ltd.).

[0050] (B) Water-soluble salts The (B) water-soluble salt used in the present invention is not particularly limited as long as it is a water-soluble compound consisting of a cation and an anion, but examples include water-soluble compounds produced from acids and alkalis. Furthermore, it is preferable that such a water-soluble salt has a solubility in water of 1 g / 100 ml or more at 15 to 25°C.

[0051] Examples of acids include inorganic acids and organic acids, but from the viewpoint of being able to further suppress yellowing of the leather surface, inorganic acids excluding hydrochloric acid and carbonic acid, or organic acids are preferred. Examples of organic acids include carboxylic acids, alkyl esters of sulfuric acid, sulfonic acid, sulfinic acid, alkyl esters of phosphoric acid, alkyl esters of phosphonic acid, alkylphosphonic acid, alkyl esters of alkylphosphonic acid, alkylphosphinic acid, etc. Examples of inorganic acids include sulfuric acid, sulfurous acid, phosphoric acid, phosphonic acid, phosphinic acid, nitric acid, nitrous acid, etc. The water-soluble salts produced from such acids and alkalis may be used individually or in combination of two or more types.

[0052] Among these acids, carboxylic acids represented by formula (1) below, sulfuric acid, alkyl esters of sulfuric acid and sulfonic acid represented by formula (2) below, sulfites and sulfinic acid represented by formula (3) below, phosphoric acid, alkylphosphonic acid, alkylphosphinic acid, alkyl esters of phosphoric acid and alkyl esters of alkylphosphonic acid represented by formula (4) below, and phosphonic acid represented by formula (5) below are preferred, and carboxylic acids represented by formula (1) below, sulfuric acid, alkyl esters of sulfuric acid and sulfonic acid represented by formula (2) below, sulfites and sulfinic acid represented by formula (3) below, and phosphoric acid, alkylphosphonic acid, alkylphosphinic acid, alkyl esters of phosphoric acid and alkyl esters of alkylphosphonic acid represented by formula (4) below are more preferred.

[0053] [ka]

[0054] (R1 is a carboxyl group or a hydrocarbon group having 1 to 7 carbon atoms (preferably 1 to 5 carbon atoms), and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R2, R3, R4, and R5 are each independently a hydroxyl group, R6O, or a hydrocarbon group having 1 to 16 carbon atoms (preferably 1 to 6 carbon atoms), and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R6 is a hydrocarbon group having 1 to 16 carbon atoms (preferably 1 to 6 carbon atoms), and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. R4 and R5 may be the same or different.)

[0055] Examples of carboxylic acids include acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, oxalic acid, succinic acid, malic acid, malonic acid, tartaric acid, citric acid, salicylic acid, maleic acid, fumaric acid, hydroxyacetic acid, and hydroxypropionic acid. Sulfuric acid, acetic acid, malic acid, and citric acid are particularly preferred from the viewpoint of suppressing yellowing of the leather surface.

[0056] The alkali is not particularly limited, but examples include sodium hydroxide, potassium hydroxide, magnesium hydroxide, ammonia, and amines. Examples of amines include triethanolamine, diethanolamine, triethylamine, and trimethylamine. Sodium hydroxide and potassium hydroxide are particularly preferred from the viewpoint of suppressing yellowing of the leather surface.

[0057] Water-soluble salts include, for example, the normal salts of the aforementioned acids such as sodium acetate, potassium acetate, ammonium acetate, disodium malate, dipotassium malate, diammonium malate, disodium succinate, dipotassium succinate, diammonium succinate, disodium malonate, dipotassium malonate, diammonium malonate, disodium fumarate, dipotassium fumarate, diammonium fumarate, sodium tartrate, potassium tartrate, diammonium tartrate, disodium oxalate, dipotassium oxalate, diammonium oxalate, trisodium citrate, tripotassium citrate, triammonium citrate, sodium sulfate, sodium sulfite, potassium sulfate, ammonium sulfate, magnesium sulfate, sodium phosphate, potassium phosphate, ammonium phosphate, magnesium phosphate, sodium phosphite, triethylammonium acetate, etc.; sodium bicarbonate, potassium bicarbonate, phosphorus Examples of acidic salts of the aforementioned acids include ammonium hydrogen phosphate, sodium hydrogen succinate, potassium hydrogen succinate, ammonium hydrogen succinate, sodium hydrogen malonate, potassium hydrogen malonate, ammonium hydrogen malonate, sodium hydrogen fumarate, potassium hydrogen fumarate, ammonium hydrogen fumarate, ammonium hydrogen tartrate, sodium hydrogen oxalate, potassium hydrogen oxalate, ammonium hydrogen oxalate, disodium hydrogen citrate, dipotassium hydrogen citrate, dipotassium hydrogen citrate, dipotassium hydrogen citrate, diammonium hydrogen citrate, diammonium hydrogen citrate, sodium bisulfite, sodium bisulfite, potassium hydrogen sulfate, ammonium hydrogen sulfate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, dipotassium hydrogen phosphate, diammonium hydrogen phosphate, diammonium hydrogen phosphate, magnesium hydrogen phosphate, and dihydrogen dihydrogen phosphate. These water-soluble salts may be used individually or in combination of two or more. These water-soluble salts may also be used in hydrate form.

[0058] Among these water-soluble salts, the normal salt of the acid is particularly preferred from the viewpoint of having good compatibility with the resin (A), being less prone to agglomeration, obtaining a stable surface treatment agent, and forming a uniform surface treatment layer. Furthermore, from the viewpoint of suppressing yellowing of the leather surface, sodium salts and potassium salts are preferred. Specifically, sodium sulfate, sodium acetate, potassium acetate, trisodium citrate, tripotassium citrate, and disodium malate are preferred, and sodium acetate, potassium acetate, trisodium citrate, tripotassium citrate, and disodium malate are even more preferred.

[0059] <Surface treatment agent> The surface treatment agent of the present invention contains (A) a resin capable of forming a resin layer on a leather substrate and (B) a water-soluble salt. By treating a leather substrate or various functional layers formed thereon with such a surface treatment agent, a surface treatment layer is formed on the leather substrate by the surface treatment agent, and even if the leather substrate is capable of yellowing, this surface treatment layer makes it possible to suppress the yellowing of the leather substrate.

[0060] In the surface treatment agent of the present invention, the mass ratio of the resin (A) to the water-soluble salt (B) can be appropriately set according to the degree of yellowing of the leather surface. However, the content of the water-soluble salt (B) is usually preferably 0.1 to 50 parts by mass, and more preferably 3 to 25 parts by mass, per 100 parts by mass of the resin (A). When the content of the water-soluble salt (B) is above the lower limit, the yellowing of the leather surface tends to be better controlled, while when it is below the upper limit, the quality of the leather surface tends not to deteriorate (for example, the tactile feel does not deteriorate).

[0061] In addition to the resin (A) and the water-soluble salt (B) mentioned above, the surface treatment agent of the present invention may also contain various additives and reaction catalysts, such as water repellents, hydrophilic compounds, matting agents, smoothing agents, thickeners, crosslinking agents, antifouling agents, surfactants, defoaming agents, leveling agents, viscoelastic modifiers, wetting agents, dispersants, preservatives, film-forming agents, plasticizers, penetrating agents, fragrances, bactericides, acaricides, fungicides, ultraviolet absorbers, antioxidants, antistatic agents, flame retardants, dyes, pigments, etc., to the extent that they do not impair the purpose and performance of the present invention.

[0062] (Water repellent) The surface treatment agent of the present invention may contain a water-repellent agent in order to impart SG properties (Soil Guard: the ability to make it difficult for dirt itself to adhere) to the leather surface. Examples of water-repellent agents include fluorine-based water-repellent agents, which are fluorine-containing compounds, and non-fluorine-based water-repellent agents, which do not contain any fluorine-containing compounds.

[0063] In the surface treatment agent of the present invention, commercially available fluorine-based water repellent and non-fluorine-based water repellent can be used, respectively. Examples of commercially available fluorine-based water repellents include NK Guard S-0671, NK Guard S-0543, NK Guard S-740, NK Guard S-0546, NK Guard S-0545, NK Guard S-750, NK Guard S-755, NK Guard S-9020, NK Guard S-33 (all manufactured by Nikka Chemical Co., Ltd.), Unidyne TG-5574, Unidyne TG-4575, Unidyne TG-5543, Unidyne TG-5546, Unidyne TG-5545, Unidyne TG-5601, Unidyne TG-5541, Unidyne TG-4571, Unidyne TG-6071, Unidyne TG-6501, Unidyne TG-5671, Unidyne TG-5672, Unidyne TG-5673, and Unidyne TG-9011 (all manufactured by Daikin Industries, Ltd.). Examples of commercially available non-fluorine water-repellent agents include Neoseed NR-158, Neoseed NR-7080, Neoseed NR-7400, Neoseed NR-7500, Neoseed NR-7600, Neoseed NR-8800 (all manufactured by Nikka Chemical Co., Ltd.), and Unidyne XF-5003, Unidyne XF-5005, Unidyne XF-5007 (all manufactured by Daikin Industries, Ltd.).

[0064] From the viewpoint of SG properties, the amount of such water-repellent agent (content of non-volatile components) is preferably 1 to 50 parts by mass, and more preferably 5 to 30 parts by mass, per 100 parts by mass of the (A) resin.

[0065] (hydrophilic compound) The surface treatment agent of the present invention may contain hydrophilic compounds to impart SR properties (Soil Release: the ability to easily remove dirt by wiping with water, etc.) to the leather surface. Examples of such hydrophilic compounds include polyester-based hydrophilic compounds, urethane-based hydrophilic compounds other than the self-emulsifying aqueous polyurethane resins mentioned above, silicone-based hydrophilic compounds, and water-soluble polymer compounds.

[0066] From the viewpoint of SR properties, the content of such hydrophilic compounds (content of non-volatile components) is preferably 1 to 50 parts by mass, and more preferably 5 to 20 parts by mass, per 100 parts by mass of the (A) resin.

[0067] In the surface treatment agent of the present invention, commercially available hydrophilic compounds can be used as the hydrophilic compound. Examples of commercially available hydrophilic compounds include Nicepole PR-99, Nicepole PR-9000, Nicepole PRK-60 (all manufactured by Nikka Chemical Co., Ltd.), Hydroperm NIOPOs (manufactured by Archroma), and the like.

[0068] (Matte agent) The surface treatment agent of the present invention may contain a matting agent to adjust the gloss and shine of the leather surface. Examples of such matting agents include organic beads, silica particles, talc, aluminum hydroxide, calcium sulfate, calcium silicate, calcium carbonate, magnesium carbonate, barium carbonate, aluminasilicate, kaolin, mica, and other similar substances. These matting agents may be used individually or in combination of two or more.

[0069] Examples of the organic beads include urethane beads, acrylic beads, silicone beads, olefin beads, high-density polyethylene, and low-density polyethylene. Examples of the silica particles include dry silica and wet silica, among which dry silica is preferred from the viewpoint of having a high scattering effect and being able to adjust the gross value with a small amount. The average particle diameter (average secondary particle diameter) of dry silica is preferably 4 to 15 μm, and more preferably 5 to 12 μm.

[0070] The amount of such matting agent (non-volatile content) should be appropriate depending on the matte finish (gloss / sheen) of the leather surface, but generally, 1 to 150 parts by mass, more preferably 5 to 120 parts by mass, and even more preferably 7 to 100 parts by mass per 100 parts by mass of the (A) resin.

[0071] (Smoothing agent) The surface treatment agent of the present invention may contain a smoothing agent to improve the smoothness and abrasion resistance of the leather surface. Examples of such smoothing agents include polydimethyl silicone, hydrogen-modified silicone, vinyl-modified silicone, epoxy-modified silicone, amino-modified silicone, carboxyl-modified silicone, halogenated-modified silicone, methacryloxy-modified silicone, mercapto-modified silicone, fluorine-modified silicone, alkyl-modified silicone, phenyl-modified silicone, and polyether-modified silicone. These smoothing agents may be used individually or in combination of two or more. Among these smoothing agents, polydimethyl silicone and epoxy-modified silicone are preferred from the viewpoint of providing a significant improvement in abrasion resistance.

[0072] The surface treatment agent of the present invention can use commercially available smoothing agents. Examples of commercially available polydimethyl silicone emulsions include DOWSIL SM490EX, DOWSIL SM-8706EX, DOWSIL IE-7046T, DOWSIL FBL-3289, DOWSIL Q2-3238 (all manufactured by Dow-Toray Industries, Inc.), KM-752T, KM-862T, KM-9737A, and POLON MF-33 (all manufactured by Shin-Etsu Chemical Co., Ltd.). Examples of commercially available epoxy-modified silicone emulsions include DOWSIL SM-8701 (manufactured by Dow-Toray Industries, Inc.), POLON MF-18T, and X-51-1264 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0073] The amount of such smoothing agent (content of non-volatile components) should be appropriate depending on the smoothness and abrasion resistance of the leather surface, but generally, 1 to 500 parts by mass, more preferably 5 to 400 parts by mass, and even more preferably 7 to 350 parts by mass per 100 parts by mass of the (A) resin.

[0074] (Thickening agent) The surface treatment agent of the present invention may contain a thickening agent to adjust the viscosity to an appropriate level. Examples of such thickening agents include alkali-thickening acrylic resins, association-type thickening agents, and water-soluble organic polymers. These thickening agents may be used individually or in combination of two or more.

[0075] In the surface treatment agent of the present invention, commercially available alkali-thickened acrylic resins can be used. Examples of commercially available alkali-thickened acrylic resins include Nikazol VT-253A (manufactured by Nippon Carbide Industries, Ltd.), Aron A-20P, Aron A-7150, Aron A-7070, Aron B-300, Aron B-300K, Aron B-500 (all manufactured by Toagosei Co., Ltd.), Julimar AC-10LHP, Julimar AC-10SHP, Leozic 835H, Junron PW-110, Junron PW-150 (all manufactured by Toagosei Co., Ltd.). Examples include Primal ASE-60, Primal TT-615, and Primal RM-5 (all manufactured by Rohm & Haas Japan Co., Ltd.), SN Thickener A-818 and SN Thickener A-850 (both manufactured by Sunopco Corporation), Paragum 500 (manufactured by Parachem Southern Co., Ltd.), Leolate 430 (manufactured by Elementis Japan Co., Ltd.), and NeoSticker V-420 (manufactured by Nikka Chemical Co., Ltd.). Such alkali-thickened acrylic resins are usually commercially available as emulsified dispersions of resins, and it is preferable to use them in an emulsified dispersion state.

[0076] Furthermore, in the surface treatment agent of the present invention, commercially available associative thickeners can be used. Examples of commercially available associative thickeners include Adekanol UH-450, Adekanol UH-540, Adekanol UH-752 (all manufactured by Asahi Denka Kogyo Co., Ltd.), SN Thickener 601, SN Thickener 612, SN Thickener 621N, SN Thickener 623N, SN Thickener 660T (all manufactured by Sunopco Co., Ltd.), Leolate 244, Leolate 278, Leolate 300 (all manufactured by Elementis Japan Co., Ltd.), and DK Thickener SCT-275 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0077] Examples of the aforementioned water-soluble organic polymers include natural water-soluble organic polymers, semi-synthetic water-soluble organic polymers, and synthetic water-soluble organic polymers. Examples of the aforementioned natural water-soluble organic polymers include starches such as potato starch, sweet potato starch, wheat starch, rice starch, tapioca starch, and corn starch; resin polysaccharides such as gum arabic, tragacanth gum, karaya gum, and tororo aoi; seaweed polysaccharides such as sodium alginate, carrageenan, agar (galactan), and funori; microbial fermentation polysaccharides such as xanthan gum, pullulan, curdlan, dextrin, and levan; proteins such as casein, gelatin, arabine, glue, and collagen; and pectin, chitin, and chitosan.

[0078] Examples of the aforementioned semi-synthetic water-soluble organic polymers include cellulose derivatives such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, and sodium cellulose sulfate; starch derivatives such as dextrin, soluble starch, oxidized starch, carboxymethyl starch, hydroxyethyl starch, hydroxypropyl starch, dialdehyde starch, phosphate starch, and acetyl starch; and propylene glycol alginate.

[0079] Examples of the aforementioned synthetic water-soluble organic polymers include polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl alkyl ether, maleic anhydride copolymer, maleic acid copolymer, maleate copolymer, and the like.

[0080] The amount of such thickener (non-volatile content) should be appropriate depending on the viscosity of the surface treatment agent, but generally, 1 to 200 parts by mass, more preferably 1 to 150 parts by mass, and even more preferably 1 to 100 parts by mass per 100 parts by mass of the (A) resin.

[0081] (Crosslinking agent) The surface treatment agent of the present invention may contain a crosslinking agent to improve the water resistance and durability of the leather. Examples of such crosslinking agents include carbodiimide-based crosslinking agents, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, blocked isocyanate-based crosslinking agents, water-dispersible isocyanate-based crosslinking agents, and melamine-based crosslinking agents. These crosslinking agents may be used individually or in combination of two or more. Among these crosslinking agents, carbodiimide-based crosslinking agents are particularly preferred from the viewpoint of texture and stability of the processing solution.

[0082] In the surface treatment agent of the present invention, commercially available crosslinking agents can be used. Examples of commercially available carbodiimide-based crosslinking agents include Carbodilite E-02, Carbodilite SV-02, Carbodilite V02-L2, Carbodilite V-10 (all manufactured by Nisshinbo Chemical Co., Ltd.), and NK Assist CI-02 (manufactured by Nikka Chemical Co., Ltd.).

[0083] From the viewpoint of the abrasion resistance and flexibility of the leather, the amount of such crosslinking agent (content of non-volatile components) is preferably 1 to 50 parts by mass, and more preferably 1 to 30 parts by mass, per 100 parts by mass of the (A) resin.

[0084] 〔leather〕 The leather of the present invention comprises a leather base material and a surface treatment layer formed on the leather base material with the surface treatment agent of the present invention. In addition, in the leather of the present invention, layers having various functions (hereinafter referred to as "functional layers") may be provided between the leather base material and the surface treatment layer and / or on the surface treatment layer. Such functional layers are not particularly limited as long as they do not impair the effects of the present invention, but examples include a primer layer for improving the adhesion between the leather base material and the surface treatment layer.

[0085] (base material for leather) Examples of leather base materials include synthetic leather having a surface layer made of polyurethane resin (PU), polyvinyl chloride (PVC) leather, imitation leather such as polyurethane thermoplastic elastomer (TPU), artificial leather, and natural leather.

[0086] The structure of the leather substrate mentioned above includes a fiber laminate structure comprising a fiber substrate and an epidermal layer. In addition, in a leather substrate of such a structure, an adhesive layer and / or an intermediate layer may be disposed between the fiber substrate and the epidermal layer as needed.

[0087] Examples of the fibrous base material include woven fabrics, nonwoven fabrics, knitted fabrics, etc. Examples of the surface layer include polyurethane resin layers. The thickness of such a surface layer is preferably 5 to 100 μm. Examples of the adhesive layer include adhesive layers formed using known adhesives such as polyurethane adhesives. The thickness of such an adhesive layer is preferably 5 to 100 μm.

[0088] Such leather substrates can be manufactured, for example, by the following method. First, a surface coating agent (e.g., polyurethane resin) is applied to release paper using various coaters such as a gravure coater, bar coater, comma coater, blade coater, or air knife coater, and dried as appropriate to form a surface layer. Next, an adhesive (e.g., polyurethane-based adhesive) is applied to this surface layer using various coaters such as a gravure coater, bar coater, comma coater, blade coater, or air knife coater, and dried to form an adhesive layer. Next, a fiber substrate is placed on the surface of this adhesive layer and pressed down, and then allowed to mature. After that, the release paper is peeled off to obtain a fiber laminate (leather substrate) comprising a fiber substrate, an adhesive layer, and a surface layer.

[0089] (Functional layer) In the leather of the present invention, the functional layer may be formed on the surface (surface of the epidermal layer) (between the leather substrate and the surface treatment layer) and / or on the surface treatment layer of the leather substrate (fiber laminate) prepared in this manner, as needed.

[0090] For example, by forming the primer layer as a functional layer between the leather substrate and the surface treatment layer, the adhesion between the leather substrate and the surface treatment layer can be improved. Such a functional layer is a layer made of resin (a resin capable of forming a resin layer on the leather substrate), and known additives such as matting agents, smoothing agents, thickeners, pigments, antioxidants, and crosslinking agents may be added as needed, or the (B) water-soluble salt may be added.

[0091] These functional layers may be a single layer or a multilayer of two or more layers. Methods for forming the functional layers include applying a functional layer material such as a primer to the surface of the leather substrate using various coaters such as a gravure coater, bar coater, comma coater, blade coater, or air knife coater; spraying a functional layer material such as a primer onto the surface of the leather substrate; or immersing the leather substrate in a functional layer material such as a primer.

[0092] (Surface treatment layer) The leather of the present invention can be obtained by forming a surface treatment layer on the surface of the leather substrate or the functional layer prepared in this manner using the surface treatment agent of the present invention. By forming a surface treatment layer on the leather substrate using the surface treatment agent of the present invention in this way, it is possible to suppress yellowing of the resulting leather surface even if the leather substrate is prone to yellowing. Furthermore, such leather can be bonded to a cushioning composite material by, for example, a soft polyurethane foam and frame lamination, and in this cushioning composite material as well, it is possible to suppress yellowing of the leather surface (especially yellowing caused by NOx generated by frame lamination, etc.).

[0093] There are no particular limitations on the method for forming the surface treatment layer on the leather substrate. For example, the surface treatment layer can be formed by treating the leather substrate with the surface treatment agent and then drying it.

[0094] Examples of treatment methods using the surface treatment agent include applying the surface treatment agent to the surface of the leather substrate using various coaters such as a gravure coater, bar coater, comma coater, blade coater, and air knife coater; spraying the surface treatment agent onto the surface of the leather substrate; and immersing the leather substrate in the surface treatment agent. However, the direct coating method and the reverse coating method using a gravure coater are more preferred. The amount of surface treatment agent applied is 4 to 40 g / m² after drying. 2 A suitable amount is 6-30 g / m². 2 A quantity that results in the above is more preferable. If the amount of coating after drying falls below the lower limit, the abrasion resistance and stain resistance of the leather may become insufficient, while if it exceeds the upper limit, the flexibility of the leather may decrease.

[0095] There are no particular restrictions on the drying method of the coated surface treatment agent. For example, it is preferable to dry it at a temperature in the range of 40 to 160°C for 30 seconds to 10 minutes, and more preferably at a temperature in the range of 80 to 130°C for 30 seconds to 2 minutes. Furthermore, it is preferable to perform an aging treatment at a temperature in the range of 20 to 100°C for 5 to 72 hours after drying.

[0096] Leather products made using leather produced in this manner include vehicle interior materials, motorcycle seats and grips, shoes, bags, clothing, sanitary products, outdoor tents, and furniture. [Examples]

[0097] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples. In the synthesis examples, the free isocyanate group content was measured by the following method.

[0098] (Content of free isocyanate groups) 0.3 g of urethane prepolymer was placed in an Erlenmeyer flask, and 10 ml of 0.1 N dibutylamine toluene solution was added to dissolve the urethane prepolymer. Then, a few drops of bromophenol blue solution were added, and the mixture was titrated with 0.1 N methanol hydrochloric acid solution to obtain the following formula: NCO% = (ab) × 0.42 × f / x (In the above formula, a: titration volume of 0.1N hydrochloric acid methanol solution when only 10 ml of 0.1N dibutylamine toluene solution is titrated, b: titration volume of 0.1N hydrochloric acid methanol solution when the solution containing the dissolved urethane prepolymer is titrated, f: factor of 0.1N hydrochloric acid methanol solution, x: amount of urethane prepolymer) The free isocyanate group content (NCO%) was determined by this method.

[0099] Furthermore, the polyurethane resins used in the examples and comparative examples were synthesized by the following method.

[0100] (Synthesis Example 1) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 71.7 parts by mass of polycarbonate diol (manufactured by Asahi Kasei Chemicals Corporation, trade name "Duranole T6002", average molecular weight 2,000), 0.4 parts by mass of trimethylolpropane, 3.4 parts by mass of dimethylolbutanoic acid, and 32.9 parts by mass of methyl ethyl ketone were charged. After homogeneous mixing of these, 23.5 parts by mass of dicyclohexylmethane diisocyanate and 0.03 parts by mass of bismastris (2-ethylhexanoate) were added, and the mixture was reacted at 80°C for 240 minutes to obtain a methyl ethyl ketone solution of urethane prepolymer with a free isocyanate group content of 2.28% relative to nonvolatile matter.

[0101] To this solution, 2.2 parts by mass of triethylamine was added and mixed uniformly. Then, 185 parts by mass of water was gradually added to emulsify and disperse the mixture. To the resulting emulsified dispersion, 2.2 parts by mass of a 30% aqueous solution of hydrazine hydrate and 1.8 parts by mass of a 20% aqueous solution of diethylenetriamine were added, and the mixture was stirred for 90 minutes to obtain a polyurethane dispersion. Next, this polyurethane dispersion was desolvented under reduced pressure at 40°C to obtain a stable aqueous polyurethane dispersion (PUD-1) with a non-volatile content of 35.0% by mass, a viscosity of 50 mPa·s, and an average particle size of 0.1 μm.

[0102] (Synthesis Example 2) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 61.9 parts by mass of polycarbonate diol (manufactured by Asahi Kasei Chemicals Corporation, trade name "Duranole T6001", average molecular weight 1,000), 0.2 parts by mass of trimethylolpropane, 3.4 parts by mass of dimethylolbutanoic acid, and 32.9 parts by mass of methyl ethyl ketone were charged. After homogeneous mixing of these, 32.7 parts by mass of dicyclohexylmethane diisocyanate and 0.03 parts by mass of bismastris (2-ethylhexanoate) were added, and the mixture was reacted at 80°C for 240 minutes to obtain a methyl ethyl ketone solution of urethane prepolymer with a free isocyanate group content of 3.21% relative to nonvolatile matter.

[0103] To this solution, 2.2 parts by mass of triethylamine was added and mixed uniformly. Then, 185 parts by mass of water was gradually added to emulsify and disperse the mixture. To the resulting emulsified dispersion, 3.0 parts by mass of a 30% aqueous solution of hydrazine hydrate and 2.5 parts by mass of a 20% aqueous solution of diethylenetriamine were added, and the mixture was stirred for 90 minutes to obtain a polyurethane dispersion. Next, this polyurethane dispersion was desolvented under reduced pressure at 40°C to obtain a stable aqueous polyurethane dispersion (PUD-2) with a non-volatile content of 35.0% by mass, a viscosity of 20 mPa·s, and an average particle size of 0.1 μm.

[0104] (Synthesis Example 3) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen blowing tube, 71.7 parts by mass of polycarbonate diol (manufactured by Kuraray Co., Ltd., trade name "Kuraray Polyol C-2090", average molecular weight 2,000), 0.4 parts by mass of trimethylolpropane, 3.4 parts by mass of dimethylolbutanoic acid, and 32.9 parts by mass of methyl ethyl ketone were charged. After homogeneous mixing of these, 23.5 parts by mass of dicyclohexylmethane diisocyanate and 0.03 parts by mass of bismastris (2-ethylhexanoate) were added, and the mixture was reacted at 80°C for 240 minutes to obtain a methyl ethyl ketone solution of urethane prepolymer with a free isocyanate group content of 2.28% relative to nonvolatile matter.

[0105] To this solution, 2.2 parts by mass of triethylamine was added and mixed uniformly. Then, 185 parts by mass of water was gradually added to emulsify and disperse the mixture. To the resulting emulsified dispersion, 2.2 parts by mass of a 30% aqueous solution of hydrazine hydrate and 1.8 parts by mass of a 20% aqueous solution of diethylenetriamine were added, and the mixture was stirred for 90 minutes to obtain a polyurethane dispersion. Next, this polyurethane dispersion was desolvented under reduced pressure at 40°C to obtain a stable aqueous polyurethane dispersion (PUD-3) with a non-volatile content of 40.0% by mass, a viscosity of 40 mPa·s, and an average particle size of 0.1 μm.

[0106] (Synthesis Example 4) 350 parts by mass of polycarbonate diol (manufactured by Asahi Kasei Chemicals Corporation, trade name "Duranole T5652", average molecular weight 2,000) was charged into a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen blowing tube, and dehydrated at a reduced pressure of 0.095 MPa and 120-130°C. After dehydration, 650 parts by mass of N,N-dimethylformamide and 11 parts by mass of ethylene glycol were added and thoroughly mixed while cooling to 30°C. Then, 21 parts by mass of hexamethylene diisocyanate and 54 parts by mass of 4,4'-diphenylmethane diisocyanate were added and mixed at 80°C for 2 hours, after which 0.2 parts by mass of bismastris (2-ethylhexanoate) was added and mixed at 100°C for 8 hours. Next, while cooling to 70°C, 360 parts by mass of methyl ethyl ketone were added and mixed to obtain a urethane resin composition (PU-1) with a non-volatile content of 30.0% by mass.

[0107] (Example 1) As shown in Table 1, a surface treatment agent was obtained by uniformly mixing (A) 10 parts by mass of solids of polyurethane aqueous dispersion (PUD-1) obtained in Synthesis Example 1 as the resin, (B) 2 parts by mass of trisodium citrate dihydrate (purchased from Nacalai Tesque, solubility in water (25℃): 72g / 100ml) as a water-soluble salt, 9 parts by mass of solids of an associative thickener ("SN Thickener 612" manufactured by Sunopco Co., Ltd.), and 3 parts by mass of solids of a water-dispersible carbodiimide crosslinking agent ("Carbodilite SV-02" manufactured by Nisshinbo Chemical Inc.) using a disperser.

[0108] (Examples 2-4) As shown in Table 1, a surface treatment agent was prepared in the same manner as in Example 1, except that, as (A) resin, 10 parts by mass of the polyurethane aqueous dispersion (PUD-2) obtained in Synthesis Example 2, the polyurethane aqueous dispersion (PUD-3) obtained in Synthesis Example 3, or the urethane resin composition (PU-1) obtained in Synthesis Example 4 was used instead of the polyurethane aqueous dispersion (PUD-1) obtained in Synthesis Example 1.

[0109] (Example 5) As shown in Table 1, a surface treatment agent was prepared in the same manner as in Example 1, except that 10 parts by mass of acrylic resin emulsion (Saibinol EC-065, manufactured by Saiden Chemical Co., Ltd.) was used as the resin (A) instead of the polyurethane aqueous dispersion (PUD-1) obtained in Synthesis Example 1.

[0110] (Example 6) As shown in Table 1, a surface treatment agent was prepared in the same manner as in Example 1, except that 20 parts by mass of acrylic resin emulsion (Saibinol EC-065, manufactured by Saiden Chemical Co., Ltd.) was added as (A) resin to the formulation composition of Example 1.

[0111] (Example 7) As shown in Table 1, a surface treatment agent was prepared in the same manner as in Example 1, except that 30 parts by mass of polydimethyl silicone emulsion (KM-862T, manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a smoothing agent to the formulation of Example 1.

[0112] (Example 8) As shown in Table 1, a surface treatment agent was prepared in the same manner as in Example 7, except that 30 parts by mass of polydimethyl silicone emulsion (KM-862T, manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a smoothing agent to the formulation of Example 6.

[0113] (Example 9) As shown in Table 1, a surface treatment agent was prepared in the same manner as in Example 8, except that 8 parts by mass of silica particles manufactured by a dry process (ACEMATT TS 100, manufactured by Evonik Degussa, average particle size: 10 μm) were added as a matting agent to the formulation composition of Example 8.

[0114] (Example 10) As shown in Table 1, a surface treatment agent was prepared in the same manner as in Example 9, except that 8 parts by mass of a non-fluorine-based water-repellent and oil-repellent agent ("Neoseed NR-158" manufactured by Nikka Chemical Co., Ltd.) was added as a water-repellent agent to the formulation composition of Example 9.

[0115] (Examples 11-12) A surface treatment agent was prepared in the same manner as in Example 10, except that the amount of trisodium citrate dihydrate was changed to the amount shown in Table 1.

[0116] (Examples 13-21) As shown in Table 2, (B) as a water-soluble salt, instead of trisodium citrate dihydrate, tripotassium citrate monohydrate (solubility in water (15℃): 167g / 100ml), triammonium citrate (solubility in water (25℃): 5g or more / 100ml), disodium malate 0.5 hydrate (solubility in water (21℃): 10g or more / 100ml), sodium acetate (solubility in water (20℃): 46.5g / 100ml), potassium acetate (solubility in water (20℃): 9.8g / 100ml), A surface treatment agent was prepared in the same manner as in Example 10, except that 2 parts by mass each of ammonium acetate (solubility in water (25℃): 7.7g or more / 100ml), sodium sulfate (solubility in water (20℃): 20g / 100ml) (both purchased from Nacalai Tesque), trisodium phosphate dodecahydrate (solubility in water (20℃): 28.5g / 100ml), and disodium hydrogen citrate pentahydrate (solubility in water (25℃): 5g or more / 100ml) (both purchased from Fujifilm Wako Pure Chemical Industries) were used.

[0117] (Comparative Example 1) As shown in Table 2, a surface treatment agent was prepared in the same manner as in Example 10, except that (B) a water-soluble salt was not included.

[0118] (Comparative Examples 2-4) As shown in Table 2, a surface treatment agent was prepared in the same manner as in Example 10, except that (B) as a water-soluble salt, 2 parts by mass each of citric acid monohydrate (purchased from Nacalai Tesque), a phosphorus-based antioxidant (tris(tridecyl) phosphite, manufactured by Johoku Chemical Industry Co., Ltd. "JP-333E"), and a hindered amine-based light stabilizer (manufactured by Nikka Chemical Co., Ltd. "NK Assist HAL") were used instead of trisodium citrate dihydrate.

[0119] (compatibility) The surface treatment agents obtained in Examples 1-21 and Comparative Examples 1-4 were allowed to stand for 24 hours after preparation. The appearance of the surface treatment agents after standing (presence or absence of aggregates, etc.) was visually observed to confirm the compatibility between the (A) resin, the (B) water-soluble salt, and each additive, and was evaluated according to the following criteria. The results are shown in Tables 1 and 2. [Evaluation Criteria] A: No changes in appearance were observed even after 24 hours of standing, indicating that it could be used industrially without any problems. B: Changes in appearance were observed within 1 to 24 hours after preparation, but the product was still industrially usable. C: Changes in appearance were observed within one hour of preparation, making it difficult to use industrially.

[0120] <Preparation of base materials for leather> A surface coating agent was prepared by applying 100 parts by mass of polyurethane resin (Evaphanol HA-68, manufactured by Nikka Chemical Co., Ltd., with a non-volatile content of 35% by mass), 5 parts by mass of pigment (SB White 11339W, manufactured by Mikuni Pigment Co., Ltd., with a non-volatile content of 67.2% by mass), 1 part by mass of a water-dispersible carbodiimide crosslinking agent (NK Assist CI-02, manufactured by Nikka Chemical Co., Ltd., with a non-volatile content of 40% by mass), and 3 parts by mass of an associative thickener (Neo Sticker S, manufactured by Nikka Chemical Co., Ltd.) to a release paper (Asahi Release AR-148, manufactured by Asahi Roll Co., Ltd.) to a coating thickness of 100 μm (wet coating amount). The coating was pre-dried at 80°C for 2 minutes using a dryer, and then dried at 120°C for 3 minutes to completely evaporate the moisture and obtain a polyurethane resin film (hereinafter referred to as the "surface layer").

[0121] On this surface layer, a polyurethane adhesive mixture was applied to a thickness of 200 μm (WET application amount), comprising 100 parts by mass of a two-component polyurethane resin (Evaphanol HO-38, manufactured by Nikka Chemical Co., Ltd., adhesive main component, non-volatile content 35% by mass), 7 parts by mass of a polyisocyanate-based curing agent (NK Assist NY-27, manufactured by Nikka Chemical Co., Ltd., non-volatile content 100% by mass), and 5 parts by mass of an associative thickener (Neo Sticker N, manufactured by Nikka Chemical Co., Ltd., non-volatile content 30% by mass).

[0122] Next, the material was dried in a dryer at 90°C for 1 minute, and immediately after drying, a polyester knit was laminated on top as a fiber base material. Then, it was cured at 120°C for 3 minutes, followed by aging at 40°C for 72 hours, and the release paper was peeled off to obtain a leather base material (fiber laminate) for evaluation.

[0123] <Leather production> On the surface layer of the leather substrate obtained above, the surface treatment agents obtained in Examples 1-21 and Comparative Examples 1, 3-4 were applied using a 100-mesh gravure coater, with a coating amount of 10-20 g / m² after drying. 2 The leather was coated to achieve the desired surface treatment, and then hot-air dried at 125°C for 3 minutes to produce evaluation leather with a surface treatment layer. The gas discoloration properties of this leather were evaluated by the following method. The results are shown in Tables 1 and 2. Note that for the surface treatment agent obtained in Comparative Example 2, no leather was produced because aggregates were formed during preparation.

[0124] (Gas discoloration) The gas discoloration properties of the leather obtained above (Examples 1-21 and Comparative Examples 1, 3-4) were measured using a nitrogen oxide testing apparatus and nitrogen oxide generator specified in JIS L0855 (1992).

[0125] Specifically, first, the leather obtained as described above was cut into pieces measuring 7 cm in length and 4 cm in width to prepare test specimens. The short side of each test specimen was attached with clips to a radially oriented test holder (capacity: approximately 15 L), and this sample holder was fixed to the frame inside the test container of the nitrogen oxide testing apparatus. Twelve test specimens were used for each test.

[0126] Next, 50 ml of nitrogen oxide was withdrawn from the nitrogen oxide storage unit of the nitrogen oxide generator using a syringe and injected into the inlet of the test container. Immediately after injection, the propeller inside the test container was rotated at approximately 270 rpm to equalize the nitrogen oxide concentration inside the test container. After 60 minutes had elapsed since the injection of nitrogen oxides, the propeller rotation was stopped, the lid of the test apparatus was opened, and each test specimen was removed into the atmosphere. After each test specimen was air-dried, the degree of discoloration due to exposure to nitrogen oxides was measured using a colorimeter as the degree of yellowing, and this degree of yellowing was graded on a 9-level scale from 5 to 1 based on the gray scale for contamination colors in accordance with JIS L0805 (2005). In this grading evaluation, a higher numerical value indicates less discoloration.

[0127] [Table 1]

[0128] [Table 2]

[0129] As shown in Tables 1 and 2, surface treatment agents (Examples 1 to 21) containing (A) a resin capable of forming a resin layer on a leather substrate and (B) a water-soluble salt showed good compatibility and were industrially usable. In particular, surface treatment agents (Examples 1 to 20) containing a normal salt of an acid as the (B) water-soluble salt showed superior compatibility compared to surface treatment agents (Example 21) containing an acidic salt of an acid.

[0130] Furthermore, the surface treatment agent without the aforementioned (B) water-soluble salt (Comparative Example 1), the surface treatment agent with a phosphorus-based antioxidant instead of the (B) water-soluble salt (Comparative Example 3), and the surface treatment agent with an amine-based light stabilizer (Comparative Example 4) also exhibited excellent compatibility.

[0131] On the other hand, the surface treatment agent (Comparative Example 2) which contained a water-soluble acid instead of the water-soluble salt (B) generated aggregates during preparation and was not industrially usable.

[0132] As is clear from comparing Examples 1-21 and Comparative Example 1 shown in Tables 1-2, when a surface treatment agent comprising (A) a resin capable of forming a resin layer on a leather substrate and (B) a water-soluble salt is used to form a surface treatment layer on a leather substrate (Examples 1-21), the discoloration of the leather surface due to NOx gas is less compared to when a surface treatment agent without (B) a water-soluble salt is used (Comparative Example 1), and yellowing of the leather surface due to NOx gas is suppressed. Furthermore, when a metal salt (normal salt) of an organic acid, such as sodium salt or potassium salt, is used as the (B) water-soluble salt (Examples 1-13, 15-17), yellowing of the leather surface is suppressed more effectively compared to when ammonium salts (Examples 14, 18), inorganic salts (Examples 19, 20), or acidic salts (Example 21) of organic acids are used.

[0133] On the other hand, as is clear from comparing Comparative Examples 2-4 and Comparative Example 1 shown in Table 2, when a surface treatment agent containing a phosphorus-based antioxidant (Comparative Example 3) or an amine-based light stabilizer (Comparative Example 4) was used instead of the water-soluble salt (B), the surface of the resulting leather yellowed to the same extent as the leather surface when a surface treatment agent without the water-soluble salt (B) was used (Comparative Example 1).

[0134] From the above results, it was confirmed that in order to suppress the yellowing of the surface of leather substrates due to NOx, it is effective to (A) a resin capable of forming a resin layer on a leather substrate and (B) a water-soluble salt (preferably a metal salt (normal salt) of an organic acid, more preferably trisodium citrate, tripotassium citrate, disodium malate, sodium acetate, potassium acetate) to form a surface treatment layer on the leather substrate.

[0135] Therefore, the leather surface treatment agent of the present invention can suppress yellowing of the leather surface caused by NOx gas contained in the gas generated from the soft polyurethane foam during combustion by flame, etc., in a cushioning composite material in which soft polyurethane foam and various types of leather are bonded by the flame lamination method, for example. Furthermore, it has been confirmed that the leather of the present invention is less prone to yellowing of the surface during combustion by flame, etc., even when bonded with soft polyurethane foam by the flame lamination method. [Industrial applicability]

[0136] As described above, the present invention makes it possible to suppress yellowing of the leather surface. Therefore, leather products using the leather of the present invention are less prone to surface yellowing and can be used as stable and high-quality leather products, and can be suitably used in various industrial fields such as vehicles, furniture, clothing, bags, shoes, pouches, and general merchandise. In particular, the cushioning composite material obtained by bonding the leather of the present invention and soft polyurethane foam by the frame lamination method suppresses yellowing of the leather surface caused by NOx gas contained in the gas generated from the soft polyurethane foam during combustion in the frame lamination method, and can be used as a leather product with excellent surface quality.

Claims

1. (A) A resin capable of forming a resin layer on a leather substrate, (B) Water-soluble salts and A leather surface treatment agent containing [specific ingredient].

2. The leather surface treatment agent according to claim 1, wherein the resin capable of forming a resin layer on the leather substrate (A) is at least one selected from the group consisting of acrylic resins and polyurethane resins.

3. The leather surface treatment agent according to claim 1, wherein the water-soluble salt (B) has a solubility in water of 1 g / 100 ml or more at 15 to 25°C.

4. The aforementioned (B) water-soluble salt is given by the following formulas (1) to (5): 【Chemistry 1】 (R １ is a carboxy group or a hydrocarbon group having 1 to 7 carbon atoms, and the hydrocarbon group may contain a cyclic structure, an unsaturated bond or a branched structure. One or more hydroxy groups and / or one or more carboxy groups may be bonded to the hydrocarbon group. R ２ , R ３ , R ４ , R ５ are each independently a hydroxy group, R ６ O or a hydrocarbon group having 1 to 16 carbon atoms. The hydrocarbon group may contain a cyclic structure, an unsaturated bond or a branched structure. One or more hydroxy groups and / or one or more carboxy groups may be bonded to the hydrocarbon group. R ６ is a hydrocarbon group having 1 to 16 carbon atoms. The hydrocarbon group may contain a cyclic structure, an unsaturated bond or a branched structure. One or more hydroxy groups and / or one or more carboxy groups may be bonded to the hydrocarbon group. R ４ and R ５ may be the same or different. ) The leather surface treatment agent according to claim 1, which is at least one selected from the group consisting of salts of acids represented by .

5. The aforementioned (B) water-soluble salt is given by the following formulas (1) to (4): 【Chemistry 2】 (R １ R is a carboxyl group or a hydrocarbon group having 1 to 5 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. ２ , R ３ , R ４ , R ５ Each of these independently represents a hydroxyl group or R ６ O or a hydrocarbon group having 1 to 6 carbon atoms, the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and the hydrocarbon group may have one or more hydroxyl groups and / or one or more carboxyl groups bonded to it, R ６ R is a hydrocarbon group having 1 to 6 carbon atoms, and the hydrocarbon group may include a cyclic structure, an unsaturated bond, or a branched structure, and one or more hydroxyl groups and / or one or more carboxyl groups may be bonded to the hydrocarbon group. ４ and R ５ They may be the same or they may be different. The leather surface treatment agent according to claim 4, which is at least one selected from the group consisting of salts of acids represented by .

6. Leather comprising a leather base material and a surface treatment layer formed on the leather base material with a leather surface treatment agent according to any one of claims 1 to 5.

7. A cushioning composite material comprising a soft polyurethane foam and the leather described in claim 6, bonded to the surface of the soft polyurethane foam.

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