US20140212676A1

US20140212676A1 - Leather-like sheet and method for manufacturing the same

Info

Publication number: US20140212676A1
Application number: US14/239,669
Authority: US
Inventors: Tomohiro Tetsui; Naotaka Gotoh
Original assignee: DIC Corp
Current assignee: DIC Corp
Priority date: 2011-08-22
Filing date: 2012-06-29
Publication date: 2014-07-31
Also published as: TW201309865A; JP5196088B1; JPWO2013027489A1; TWI547618B; WO2013027489A1; CN103764899A; CN103764899B

Abstract

An object of the present invention is to provide a urethane resin composition for forming a skin layer of a leather-like sheet having a sufficient level of durability, including perspiration resistance and oil resistance, not to result in a poor appearance of the leather-like sheet or peeling of the skin layer from the support over time, for example, when perspiration or oil adheres thereto. The present invention is a leather-like sheet including a skin layer (C) formed from a urethane resin composition containing a urethane resin (A) having two or more hydroxyl groups on at least one end thereof and an aqueous medium (B); an adhesive layer (D); and a support layer (E).

Description

TECHNICAL FIELD

The present invention relates to leather-like sheets such as synthetic leather and artificial leather.

BACKGROUND ART

Leather-like sheets such as synthetic leather and artificial leather have as good a feel as natural leather and are used in various fields, including clothing, furniture, car interior materials, shoes, and bags.
A typical leather-like sheet includes a support such as a fibrous substrate and a skin layer made of a material such as urethane resin on the surface of the support, optionally with an intermediate layer such as a porous layer therebetween. Each layer has its own requirements. For example, the intermediate layer often requires a soft feel, whereas the skin layer often requires durability, including perspiration resistance and oil resistance, as well as softness.
In particular, as leather-like sheets find more applications, the durability, including perspiration resistance, which is required for the skin layer, is considered important to maintain high quality over an extended period of time without a change in appearance or degradation of the skin layer or a decrease in the adhesion of the skin layer to the support when perspiration or oil adheres to the surface of the skin layer.
As an example of a method for manufacturing such a leather-like sheet including a skin layer, there is a known method for manufacturing a fiber laminate by bonding together a fiber substrate and a skin layer made of a synthetic resin film by dry lamination using an adhesive. The fiber substrate (A layer) is treated with a water-based polyurethane resin having one or more of hydroxyl, amino, and imino groups in the molecular backbone thereof (see, for example, PTL 1).
The skin layer used for the manufacture of the fiber laminate, however, may suffer swelling (become larger), cracking, or a significant decrease in adhesion strength after extended exposure to perspiration or oil, which may result in a poor appearance of the leather-like sheet and peeling of the skin layer from the support over time.

CITATION LIST

Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2005-206970

SUMMARY OF INVENTION

Technical Problem

An object of the present invention is to provide a leather-like sheet including a skin layer having a sufficient level of durability, including perspiration resistance and oil resistance, not to result in a poor appearance of the leather-like sheet or peeling of the skin layer from the support over time, for example, when perspiration or oil adheres thereto.

Solution to Problem

The inventors have conducted research in order to achieve the foregoing object and have found that the use of a urethane resin having two or more hydroxyl groups on the ends present in the urethane resin provides a solution to achieve the foregoing object.
Specifically, the present invention relates to a leather-like sheet including a skin layer (C) formed from a urethane resin composition containing a urethane resin (A) having two or more hydroxyl groups on at least one end thereof and an aqueous medium (B); an adhesive layer (D); and a support layer (E).

Advantageous Effects of Invention

Because the leather-like sheet according to the present invention has a sufficient level of perspiration resistance not to result in a poor appearance of the leather-like sheet or peeling of the skin layer from the support over time, for example, when perspiration, oil, or solvent adheres to the skin layer, it can be used for the manufacture of, for example, clothing, furniture, car interior materials, shoes, and bags.

DESCRIPTION OF EMBODIMENTS

A leather-like sheet according to the present invention includes a skin layer (C) formed from a urethane resin composition containing a urethane resin (A) having two or more hydroxyl groups on at least one end thereof and an aqueous medium (B); an adhesive layer (D); and a support layer (E).
The urethane resin composition that can be used to form the skin layer (C) may be a urethane resin composition containing a urethane resin (A) having two or more hydroxyl groups on the ends thereof, an aqueous medium (B), and optionally other materials such as additives.
In the present invention, the use of a urethane resin (A) having two or more hydroxyl groups on at least one end thereof as the urethane resin is essential to achieve the foregoing object. Specifically, the urethane resin (A) is a urethane resin having two or more hydroxyl groups on at least one of two or more resin ends that can be present in the urethane resin. For example, if the urethane resin is prepared by reacting a diol with a diisocyanate and has two ends therein, it has two or more hydroxyl groups on at least one of the two ends thereof. The urethane resin may have two or more hydroxyl groups on each of the two ends thereof. If the urethane resin is multi-branched and has three or more ends therein, it has two or more hydroxyl groups on at least one of the three ends thereof.
If the urethane resin (A) is replaced with a urethane resin having one hydroxyl group on one end thereof, it cannot form a skin layer having high durability, including perspiration resistance and oil resistance, which may result in a poor appearance of the leather-like sheet and peeling of the skin layer (C) from the adhesive layer (D) and the support (E) over time. If the urethane resin (A) is replaced with a urethane resin having hydroxyl groups on the urethane main chain thereof, rather than on the ends thereof, it cannot form a skin layer having high durability, including perspiration resistance and oil resistance, which may result in a poor appearance of the leather-like sheet and peeling of the skin layer (C) from the adhesive layer (D) and the support (E) over time.
The urethane resin (A) preferably has two or three hydroxyl groups, more preferably two hydroxyl groups, on one end thereof. The urethane resin (A) may have two or more hydroxyl groups on each of all ends present therein. The urethane resin (A) preferably has a hydroxyl value of 10 to 50.
For example, the urethane resin (A) is preferably a linear urethane resin prepared using a diol as the polyol (a1) and a diisocyanate as the polyisocyanate (a2) and having two or more hydroxyl groups, preferably two hydroxyl groups, on each of the two ends thereof. The use of such a urethane resin allows a skin layer (C) having particularly high bending resistance to be formed without degrading the heat (water) resistance or the durability, including perspiration resistance and oil resistance.
The urethane resin (A) preferably has a hydrophilic group so that it can be stably dispersed in the aqueous medium (B).
Examples of hydrophilic groups include anionic, cationic, and nonionic groups. In particular, anionic groups are preferred to quickly increase the viscosity of the urethane resin composition used in the present invention when forming the skin layer (C).
Examples of anionic groups include carboxyl, carboxylate, sulfonic acid, and sulfonate groups. In particular, carboxylate and sulfonate groups partially or completely neutralized with basic compounds are preferred for the manufacture of a composite resin having good water dispersibility.
Examples of basic compounds that can be used to neutralize the anionic groups include organic amines such as ammonia, triethylamine, pyridine, and morpholine; alkanolamines such as monoethanolamine, and basic compounds containing metals such as sodium, potassium, lithium, and calcium.
If anionic groups such as carboxylate and sulfonate groups are used, they are preferably present in an amount of 50 to 1,000 mmol/kg based on the entire urethane resin (A) so that the urethane resin (A) has good dispersion stability in water.
Examples of cationic groups include tertiary amino groups.
Examples of acids that can be used to partially or completely neutralize the tertiary amino groups include organic acids such as acetic acid, propionic acid, lactic acid, and maleic acid; organic sulfonic acids such as sulfonic acid and methanesulfonic acid; and inorganic acids such as hydrochloric acid, sulfuric acid, orthophosphoric acid, and orthophosphorous acid. These acids may be used alone or in a combination of two or more.
Examples of quaternizing agents that can be used to partially or completely quaternize the tertiary amino groups include dialkylsulfuric acids such as dimethylsulfuric acid and diethylsulfuric acid; alkyl halides such as methyl chloride, ethyl chloride, and benzyl chloride; alkyls such as methyl methanesulfonate and methyl paratoluenesulfonate; and epoxies such as ethylene oxide, propylene oxide, and epichlorohydrin. These quaternizing agents may be used alone or in a combination of two or more.
Examples of nonionic groups include polyoxyalkylene groups such as polyoxyethylene, polyoxypropylene, polyoxybutylene, poly(oxyethylene-oxypropylene), and polyoxyethylene-polyoxypropylene groups. In particular, polyoxyalkylene groups having oxyethylene units are preferred to further improve the hydrophilicity.
To form a skin layer having high durability, including perspiration resistance, the urethane resin (A) used in the present invention preferably has a weight average molecular weight of 10,000 to 50,000, more preferably 20,000 to 50,000.
The urethane resin (A) can be prepared, for example, through a step (step 1) of reacting the polyol (a1), the polyisocyanate (a2), and optionally a chain extender (a3) to manufacture an isocyanate-terminated urethane prepolymer and a step (step 2) of reacting the urethane prepolymer with a polyalkanolamine.
Step 1 will be described first.
Step 1 is a step of reacting the polyol (a1), the polyisocyanate (a2), and optionally the chain extender (a3) to manufacture an isocyanate-terminated urethane prepolymer. Specifically, the urethane prepolymer can be manufactured by mixing and reacting the polyol (a1), the polyisocyanate (a2), and optionally the chain extender (a3) at 50° C. to 100° C. for about 3 to 10 hours in the absence of a solvent or in the presence of an organic solvent. Alternatively, the target isocyanate-terminated urethane prepolymer can be manufactured by reacting the polyol (a1) and the polyisocyanate (a2) in the same manner as described above and then mixing and further reacting the reaction product with the chain extender (a3).
Examples of polyols (a1) that can be used in step 1 include polycarbonate polyols, polyester polyols, and polyether polyols. In particular, polycarbonate polyols are preferred to further improve the properties, such as perspiration resistance, of the skin layer (C).
Examples of polycarbonate polyols include those prepared by reacting a carbonate ester with a polyol having a low molecular weight, i.e., about 100 to 500.
Examples of carbonate esters include methyl carbonate, dimethyl carbonate, ethyl carbonate, diethyl carbonate, cyclocarbonates, and diphenyl carbonate.
Examples of low-molecular-weight polyols that can react with the carbonate esters include dihydroxy compounds with relatively low molecular weights, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,5-hexanediol, 2,5-hexanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethylpropanoldiol, 2-methyl-1,8-octanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydroquinone, resorcinol, bisphenol A, bisphenol F, and 4,4′-biphenol; polyether polyols such as polyethylene glycol, polypropylene glycol, and polyoxytetramethylene glycol; and polyester polyols such as polyhexamethylene adipate, polyhexamethylene succinate, and polycaprolactone.
It is preferred to use polycarbonate polyols having number average molecular weights of 500 to 3,000. In particular, it is preferred to use polycarbonate polyols having number average molecular weights of 500 to 1,500 to further improve the heat (water) resistance and perspiration resistance of the skin layer (C). To form a skin layer (C) having high bending resistance as well as good heat (water) resistance and durability, including perspiration resistance and oil resistance, it is preferred to use polycarbonate polyols having number average molecular weights of more than 1,500 to 3,000, more preferably 1,600 to 2,500.
Such polycarbonate polyols are preferably used in an amount of 20% to 95% by mass of the total amount of polyol (a1).
Examples of polyester polyols include those prepared by esterifying a polyol having a low molecular weight, i.e., about 100 to 500, with a polycarboxylic acid.
Examples of low-molecular-weight polyols include aliphatic polyols such as 1,6-hexanediol, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,5-hexanediol, 2,5-hexanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 2-methyl-1,3-propanediol; and alicyclic polyols such as cyclobutanediol, cyclopentanediol, 1,4-cyclohexanediol, cycloheptanediol, cyclooctanediol, cyclohexanedimethanol, and hydroxypropylcyclohexanol.
Examples of polycarboxylic acids that can be used for esterification with the low-molecular-weight polyols include aliphatic polycarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and maleic acid; aromatic polycarboxylic acids such as fumaric acid, terephthalic acid, isophthalic acid, phthalic acid, and 1,4-naphthalenedicarboxylic acid; and anhydrides and ester-forming derivatives thereof.
Examples of polyether polyols include those prepared by addition polymerization of an alkylene oxide using one or more compounds having two or more active hydrogen atoms as an initiator.
Examples of initiators include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolethane, and trimethylolpropane.
Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, and tetrahydrofuran.
As the polyol (a1), polyols having a hydrophilic group are also preferred to introduce a hydrophilic group into the urethane resin (A).
Examples of polyols having a hydrophilic group include polyols having a carboxyl group, such as 2,2′-dimethylolpropionic acid, 2,2′-dimethylolbutanoic acid, 2,2′-dimethylolbutyric acid, and 2,2′-dimethylolvaleric acid; and polyols having a sulfonic acid group, such as 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfophthalic acid, and 5[4-sulfophenoxy]isophthalic acid. Other examples of polyols having a hydrophilic group include polyester polyols having a hydrophilic group that are prepared by reacting the above low-molecular-weight polyols having a hydrophilic group with various polycarboxylic acids such as adipic acid.
Such polyols having a hydrophilic group are preferably used in an amount of 0.5% to 10% by mass, more preferably 1% to 5% by mass, of the total amount of polyol (a1).
Examples of polyisocyanates (a2) that can react with the polyol (a1) include aromatic polyisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, polymethylenepolyphenyl polyisocyanate, and carbodiimidized diphenylmethane polyisocyanate; and aliphatic and alicyclic polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate. These polyisocyanates may be used alone or in a combination of two or more. In particular, alicyclic polyisocyanates are preferred, and isophorone diisocyanate and dicyclohexylmethane diisocyanate are more preferred to prevent yellowing of the skin layer (C) over time.
The polyol (a1) is preferably reacted with the polyisocyanate (a2) such that the equivalent ratio (isocyanate/hydroxyl) of the isocyanate groups of the polyisocyanate (a2) to the hydroxyl groups of the polyol (a1) is 1.0 to 2.0, more preferably 1.1 to 1.9.
Examples of chain extenders (a3) include polyamines and hydroxyl-containing compounds.
Examples of polyamines include diamines such as ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4′-dicyclohexylmethanediamine, 3,3′-dimethyl-4,4′-dicyclohexylmethanediamine, and 1,4-cyclohexanediamine; diamines having one primary amino group and one secondary amino group, such as N-hydroxymethylaminoethylamine, N-hydroxyethylaminoethylamine, N-hydroxypropylaminopropylamine, N-ethylaminoethylamine, and N-methylaminopropylamine; polyamines such as diethylenetriamine, dipropylenetriamine, and triethylenetetramine; hydrazines such as hydrazine, N,N′-dimethylhydrazine, and 1,6-hexamethylene-bishydrazine; dihydrazides such as succinic acid dihydrazide, adipic acid dihydrazide, glutaric acid dihydrazide, sebacic acid dihydrazide, and isophthalic acid dihydrazide; and semicarbazides such as β-semicarbazidopropionic acid hydrazide, 3-semicarbazido-propyl-carbazate ester, and semicarbazido-3-semicarbazidomethyl-3,5,5-trimethylcyclohexane.
Examples of hydroxyl-containing compounds include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, saccharose, methylene glycol, glycerol, and sorbitol; phenols such as bisphenol A, 4,4′-dihydroxydiphenyl, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxydiphenylsulfone, hydrogenated bisphenol A, and hydroquinone; and water. These hydroxyl-containing compounds may be used alone or in a combination of two or more provided that they do not decrease the storage stability of the urethane resin composition used in the present invention.
To introduce an urea bond into the skin layer to be formed and thereby further improve the durability of the skin layer for improved perspiration resistance, the chain extender (a3) is preferably used in an amount of 1% to 10% by mass, more preferably 1% to 5% by mass, of the total amount of raw materials used for the manufacture of the urethane resin (A).
Examples of organic solvents that can be used to react the polyol (a1), the polyisocyanate (a2), and optionally the chain extender (a3) in step 1 include ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; acetate esters such as ethyl acetate and butyl acetate; nitriles such as acetonitrile; and amides such as dimethylformamide and N-methylpyrrolidone. These organic solvents may be used alone or in a combination of two or more.
The urethane prepolymer prepared in step 1 preferably has a functional group that can react with the amino group of the polyalkanolamine in step 2 on a molecular end thereof. The functional group is preferably an isocyanate group.
Although the urethane prepolymer prepared in step 1 may be solvent-free, it is preferably dissolved in an organic solvent for ease of handling.
Next, step 2 will be described. Step 2 is a step of mixing and reacting the isocyanate-containing urethane prepolymer or a solution thereof in an organic solvent prepared in step 1 with a polyalkanolamine to introduce two or more hydroxyl groups into one or more ends present in the urethane resin (A) to be prepared.
Specifically, the desired urethane resin (A) can be manufactured by mixing and reacting the isocyanate-containing urethane prepolymer, a solution thereof in an organic solvent, or a dispersion thereof in water with a polyalkanolamine, for example, at room temperature, i.e., 25° C. In this step, the amount of hydroxyl group introduced into the urethane resin (A) to be prepared can be adjusted depending on the amount of polyalkanolamine.
Examples of polyalkanolamines (a4) include amines having a plurality of hydroxyl groups on one amino group, such as diethanolamine, 2-amino-1,3-propanediol, (R)-3-amino-1,2-propanediol, tris(hydroxymethyl)aminoethane, and 1-amino-1-deoxy-D-glucitol. These amines may be used alone or in a combination of two or more provided that they do not decrease the storage stability of the urethane resin composition used in the present invention.
Although the urethane resin composition used to form a skin layer in the present invention may be a solvent-free composition containing the urethane resin (A), it preferably contains a solvent, for example, for ease of application. Examples of solvents include aqueous media and various organic solvents.
If the urethane resin composition for forming a skin layer contains the urethane resin (A) and the aqueous medium (B), it is preferred to manufacture the urethane resin (A) or a solution thereof in an organic solvent in steps 1 and 2, optionally neutralize the hydrophilic group, such as an anionic group, in the urethane resin, and mix and disperse the urethane resin (A) in an aqueous medium. The urethane resin (A) may be mixed with the aqueous medium using a machine such as a homogenizer where necessary.
Examples of aqueous media (B) include water, organic solvents miscible with water, and mixtures thereof. Examples of organic solvents miscible with water include alcohols such as methanol, ethanol, n-propanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol, and propylene glycol; alkyl ethers of polyalkylene glycols; and lactams such as N-methyl-2-pyrrolidone. In the present invention, it is possible to use water alone, a mixture of water and an organic solvent miscible with water, or an organic solvent miscible with water alone. For safety and environmental concerns, it is preferred to use water alone or a mixture of water and an organic solvent miscible with water, more preferably water alone.
The aqueous medium (B) is preferably used in an amount of 40% to 85% by mass, more preferably 50% to 80% by mass, of the total amount of urethane resin composition for forming a skin layer.
Examples of organic solvents include ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; acetate esters such as ethyl acetate and butyl acetate; nitriles such as acetonitrile; and amides such as dimethylformamide and N-methylpyrrolidone.
The urethane resin composition used to form a skin layer in the present invention preferably contains the urethane resin (A) in an amount of 10% to 50% by mass, more preferably 20% to 50% by mass, of the total amount of urethane resin composition for improved ease of application.
The urethane resin composition used in the present invention may contain a crosslinking agent to form a skin layer (C) having particularly high heat (water) resistance and durability, including perspiration resistance, oil resistance, and hydrolysis resistance.
Examples of crosslinking agents include known crosslinking agents such as carbodiimide crosslinking agents, oxazoline crosslinking agents, epoxy crosslinking agents, isocyanate crosslinking agents, and melamine crosslinking agents. In particular, carbodiimide crosslinking agents and oxazoline crosslinking agents are preferred.
Such crosslinking agents are preferably used in an amount of 1 to 10 parts by mass based on 100 parts by mass of the urethane resin (A) to further improve the heat (water) resistance and the durability, including perspiration resistance and oil resistance.
The urethane resin composition used to form a skin layer in the present invention may optionally contain various other additives. Examples of additives that can be used in combination include associative thickeners, urethanization catalysts, silane coupling agents, fillers, thixotropic agents, tackifiers, waxes, heat stabilizers, light stabilizers, fluorescent brighteners, foaming agents, thermoplastic resins, thermosetting resins, pigments, dyes, conductors, antistatic agents, moisture permeability improvers, water repellents, oil repellents, hollow foams, crystallization-water containing compounds, flame retardants, water absorbents, moisture absorbents, deodorants, foam stabilizers, defoamers, fungicides, preservatives, algaecides, pigment dispersants, antiblocking agents, and hydrolysis inhibitors.
Examples of associative thickeners include cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose, polyacrylic acid salts, polyvinylpyrrolidone, urethane associative thickeners, and polyether associative thickeners. In particular, urethane associative thickeners are preferred because they have good miscibility with the urethane resin (A). Such associative thickeners are preferably used in an amount of 0.5% to 5% by mass based on the total amount of the urethane resin (A).
Because the urethane resin composition can form a coating having a sufficient level of perspiration resistance not to result in a poor appearance of the leather-like sheet or peeling of the skin layer from the support over time, for example, when perspiration adheres thereto, the urethane resin composition is suitable for use as a coating for forming a topcoat layer on various substrates. In particular, the urethane resin composition is suitable for forming the skin layer (C) of the leather-like sheet.
The urethane resin composition for forming a skin layer can be used as a material for forming the skin layer (C) of the leather-like sheet. Typically, the leather-like sheet has the skin layer (C) laminated on the surface of the support layer (E), which is made of a fibrous substrate optionally impregnated with a resin, with the adhesive layer (D) therebetween, and the urethane resin composition used in the present invention is suitable for forming the skin layer (C). The leather-like sheet may include a porous layer (foamed layer) for providing properties such as softness. Alternatively, the adhesive layer (D) may be a foamed layer that functions practically as the porous layer.
Examples of supports that can be used to form the support layer (E) include nonwoven fabrics, woven fabrics, and knitting. Examples of materials that form such substrates include polyester fiber, nylon fiber, acrylic fiber, polyurethane fiber, acetate fiber, rayon fiber, polylactic acid fiber, cotton, hemp, silk, wool, and mixtures thereof.
The surface of the support may optionally be treated with a finish such as an antistatic finish, release finish, water-repellent finish, water-absorbent finish, antibacterial/deodorizing finish, bacteriostatic finish, or UV protective finish.
The leather-like sheet having the skin layer (C) laminated on the surface of the support with the adhesive layer (D) therebetween can be manufactured, for example, by applying and drying the urethane resin composition for forming a skin layer on a sheet treated with a release finish to form the skin layer (C) and then laminating the support on the skin layer (C) with an adhesive (d).
Examples of methods for applying the urethane resin composition to the sheet include gravure coating, knife coating, pipe coating, and comma coating. The urethane resin composition applied in the above manner may be dried and cured, for example, by leaving it standing at room temperature for about 1 to 10 days or by heating it at a temperature of 50° C. to 250° C. for about 1 to 600 seconds.
The adhesive (d) used to bond the skin layer (C) to the support layer (E) is preferably an adhesive containing a compound (d-1) having hydroxyl groups and a compound (d-2) having isocyanate groups.
The adhesive (d) preferably contains an excess of the compound (d-2) having isocyanate groups relative to the amount of compound (d-1) having hydroxyl groups. In this case, the hydroxyl groups of the compound (d-1) react with the isocyanate groups of the compound (d-2) to form the adhesive layer (D), and the isocyanate groups of the compound (d-2) remaining after the reaction react with some or all of the hydroxyl groups of the urethane resin (A) that forms the skin layer (C). This provides a leather-like sheet including a skin layer having a sufficient level of durability, including perspiration resistance, not to result in a poor appearance of the leather-like sheet or peeling of the skin layer from the support over time, for example, when perspiration adheres thereto.
Specifically, an excess of the compound (d-2) is preferably used such that the equivalent ratio (isocyanate/hydroxyl) of the isocyanate groups of the compound (d-2) to the hydroxyl groups of the compound (d-1) contained in the adhesive (d) is more than 1.0.
Specifically, the adhesive (d) may be a two-component adhesive containing a urethane resin having hydroxyl groups and a crosslinking agent having isocyanate groups.
Examples of urethane resins having hydroxyl groups that can be used in the adhesive (d) include reaction products of materials such as the polyols (a1), polyisocyanates (a2), and chain extenders (a3) illustrated as the materials that can be used for the manufacture of the urethane resin (A).
To provide hydroxyl groups that can react with the isocyanate groups of the crosslinking agent, the polyol and the polyisocyanate used for the manufacture of the urethane resin having hydroxyl groups are preferably mixed and reacted such that the equivalent ratio (isocyanate/hydroxyl) of the isocyanate groups of the polyisocyanate to the hydroxyl groups of the polyol is less than 1.0.
The thus-manufactured urethane resin having hydroxyl groups preferably has a weight average molecular weight of about 10,000 to 50,000 to provide high adhesion strength.
Alternatively, the adhesive (d) may be a two-component adhesive containing a polyol and a polyisocyanate.
The two-component adhesive can be used to form an adhesive layer (D) having urethane bonds formed therein by mixing the polyol and the polyisocyanate and then quickly applying the mixture to the surface of the support.
Examples of polyols that can be used in the two-component adhesive include those such as the polyols (a1) illustrated as the materials that can be used for the manufacture of the urethane resin (A). Specific examples include polycarbonate polyols.
Examples of polyisocyanates that can be used in the two-component adhesive include those such as the polyisocyanates (a2) illustrated as the materials that can be used for the manufacture of the urethane resin (A).
To react the two-component adhesive with the hydroxyl groups of the urethane resin (A) that forms the skin layer (C) and thereby form a skin layer (C) having a sufficient level of durability, including perspiration resistance, not to result in a poor appearance of the leather-like sheet or peeling of the skin layer from the support over time, for example, when perspiration adheres thereto, the polyol and the polyisocyanate are preferably mixed such that the equivalent ratio (isocyanate/hydroxyl) of the isocyanate groups of the polyisocyanate to the hydroxyl groups of the polyol is more than 1.0.
Examples of adhesives (d) include dispersions and solutions of the curable components as described above, including urethane resins having hydroxyl groups, crosslinking agents having isocyanate groups, polyols, and polyisocyanates, in media such as water and solvents, as well as solvent-free adhesives.
The adhesive (d) can be applied to the surface of the support (C) or the skin layer (C) by methods such as gravure coating, knife coating, pipe coating, and comma coating. To form a porous layer by foaming the adhesive layer (D), it may be formed by a method generally called mechanical foaming or by adding an additive such as microballoons or a blowing agent when applying the adhesive (d) to the surface of the support.
With the skin layer (C) laminated on the surface to which the adhesive (d) is applied, it may be, for example, heated at 40° C. to 120° C. to react the isocyanate groups present in the adhesive (d) with the hydroxyl groups present in the skin layer (C) in the interface between the adhesive layer (D) and the skin layer (C). This provides a leather-like sheet including a skin layer having a sufficient level of durability, including perspiration resistance and oil resistance, not to result in a poor appearance of the leather-like sheet or peeling of the skin layer from the support over time, for example, when perspiration adheres thereto.
A leather-like sheet including an intermediate layer such as a porous layer in addition to the adhesive layer (D) can be manufactured, for example, by applying and drying the urethane resin composition for forming a skin layer on a sheet treated with a release finish to form the skin layer (C), applying and curing a resin composition, for forming a porous layer, foamed by a known process such as mechanical foaming or water foaming on the skin layer (C) to form a porous layer, and laminating the support (C) on the porous layer with the adhesive (d).
The skin layer (C) of the thus-manufactured leather-like sheet preferably has a thickness of about 10 to 300 μm. Also, the adhesive layer (D) preferably has a thickness of 10 to 300 μm.
The leather-like sheet manufactured in the above manner has high durability, including perspiration resistance and oil resistance, and high bending resistance and can therefore be used for various applications, including bags, shoes, clothing, and car interior materials.

EXAMPLES

The present invention is further illustrated by the following examples and comparative examples.

Preparation Example 1

Preparation of Adhesive (d1-1)

In the presence of 1,221 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N980R from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 2,000), 34 g of dimethylolpropionic acid, and 187 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until the isocyanate groups disappeared to yield a solution of a hydroxyl-terminated urethane resin in methyl ethyl ketone.
After 2,462 g of the solution of the urethane resin in methyl ethyl ketone was mixed with 25 g of triethylamine, it was mixed with 2,442 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
The methyl ethyl ketone was then distilled off from the emulsion to yield a urethane resin composition (d1-1-1) having a nonvolatile content of 45% by mass.
To 100 g of the resulting urethane resin composition (d1-1-1) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, 1.0 g of a urethane associative thickener, and 5.0 g of an isocyanate crosslinking agent. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a water-based adhesive (d1-1).

Preparation Example 2

Preparation of Adhesive (d1-2)

In the presence of 0.1 g of stannous octoate, 100 g of a polycarbonate diol (NIPPOLAN N980R from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 2,000) and 14 g of dicyclohexylmethane diisocyanate (HMDI) heated to 80° C. were stirred using a mechanical mixer at 2,000 rpm in a nitrogen atmosphere for 2 minutes and was then deaerated using a vacuum deaerator to yield a solvent-free adhesive (d1-2).

Example 1

Fabrication of Leather-Like Sheet

In the presence of 710 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N981 from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 1,000), 67 g of dimethylolpropionic acid, and 590 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.7% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone. NCO % refers to the mass percentage of the isocyanate groups of the polyisocyanate to the total mass of the raw materials used for the manufacture of the polyurethane.
After 2,367 g of the solution of the isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone was mixed with 50 g of triethylamine, it was mixed with 2,367 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 1,310 g of an aqueous chain extender solution containing 36 g of ethylenediamine and 95 g of diethanolamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (I) having a nonvolatile content of 35% by mass (weight average molecular weight of 42,000 and hydroxyl value of 56.7).
To 100 g of the resulting urethane resin composition (I) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (I-1) for forming a skin layer.
To release paper (155T Flat from Dai Nippon Printing Co., Ltd.), 100 parts by mass of the urethane resin composition (I-1) for forming a skin layer was applied to a thickness of 150 μm.
The coating was immediately predried at 70° C. using a Werner Mathis (drier) for 2 minutes and was then dried at 120° C. for 2 minutes to completely evaporate moisture from the coating, thus forming a polyurethane resin film.
To the polyurethane resin film formed in the above manner, 100 parts by mass of the adhesive (d1-1) prepared in Preparation Example 1 was applied to a thickness of 150 and was dried at 70° C. using a Werner Mathis (drier) for 2 minutes.
After drying, a polyester fiber nonwoven fabric support was placed on the surface to which the adhesive (d1-1) was applied, was pressed using a roller adjusted to 120° C., and was aged at 80° C. for 24 hours. After aging, the release paper was removed to obtain a leather-like sheet (I-2).

Example 2

Fabrication of Leather-Like Sheet

To release paper (155T Flat from Dai Nippon Printing Co., Ltd.), 100 parts by mass of the urethane resin composition (I-1), for forming a skin layer, used in Example 1 was applied to a thickness of 150 μm.
The coating was immediately predried at 70° C. using a Werner Mathis (drier) for 2 minutes and was then dried at 120° C. for 2 minutes to completely evaporate moisture from the coating, thus forming a polyurethane resin film.
To the polyurethane resin film formed in the above manner, 100 parts by mass of the adhesive (d1-2) prepared in Preparation Example 2 was applied to a thickness of 150 and was dried at 70° C. using a Werner Mathis (drier) for 2 minutes. A polyester fiber nonwoven fabric support was placed on the surface to which the adhesive (d1-2) was applied, was pressed using a roller adjusted to 120° C., and was aged at 80° C. for 24 hours. After aging, the release paper was removed to obtain a leather-like sheet (II-2).

Example 3

Fabrication of Leather-Like Sheet

In the presence of 710 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polyester diol (PRACCEL 210 from Daicel Corporation, molecular weight of about 1,000), 67 g of dimethylolpropionic acid, and 590 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.7% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-2) in methyl ethyl ketone.
After 2,367 g of the solution of the urethane prepolymer (A′-2) in methyl ethyl ketone was mixed with 50 g of triethylamine, it was mixed with 2,367 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 1,310 g of an aqueous chain extender solution containing 36 g of ethylenediamine and 95 g of diethanolamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (II) having a nonvolatile content of 35% by mass (weight average molecular weight of 41,000 and hydroxyl value of 56.7).
To 100 g of the resulting urethane resin composition (II) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (II-2) for forming a skin layer.
A leather-like sheet (III-2) was fabricated in the same manner as in Example 1 except that the urethane resin composition (I-1) for forming a skin layer was replaced with 100 parts by mass of the urethane resin composition (II-1) for forming a skin layer.

Example 4

Fabrication of Leather-Like Sheet

In the presence of 710 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N981 from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 1,000), 50 g of polyethylene glycol (PEG-1000 from NOF CORPORATION), 50 g of polyethylene glycol monomethyl ether (UNIOX M1000 from NOF CORPORATION), and 590 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.7% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-3) in methyl ethyl ketone.
After 2,400 g of the solution of the isocyanate-terminated urethane prepolymer (A′-3) in methyl ethyl ketone was mixed with 2,400 g of an aqueous 10% by mass emulsifier solution prepared in advance (Newcol 2314 from Nippon Nyukazai Co., Ltd.), it was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 1,310 g of an aqueous chain extender solution containing 36 g of ethylenediamine and 95 g of diethanolamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (III) having a nonvolatile content of 35% by mass (weight average molecular weight of 43,000 and hydroxyl value of 55.7).
To 100 g of the resulting urethane resin composition (III) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (III-1) for forming a skin layer.
A leather-like sheet (IV-2) was fabricated in the same manner as in Example 1 except that the urethane resin composition (I-1) for forming a skin layer was replaced with 100 parts by mass of the urethane resin composition (III-1) for forming a skin layer.

Example 5

Fabrication of Leather-Like Sheet

In the presence of 630 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N980R from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 2,000), 67 g of dimethylolpropionic acid, and 390 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.0% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-4) in methyl ethyl ketone.
After 2,087 g of the solution of the isocyanate-terminated urethane prepolymer (A′-4) in methyl ethyl ketone was mixed with 50 g of triethylamine, it was mixed with 2,367 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 770 g of an aqueous chain extender solution containing 24 g of ethylenediamine and 53 g of diethanolamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (IV) having a nonvolatile content of 35% by mass (weight average molecular weight of 42,000 and hydroxyl value of 36.8).
To 100 g of the resulting urethane resin composition (IV) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (IV-1) for forming a skin layer.
A leather-like sheet (V-2) was fabricated in the same manner as in Example 1 except that the urethane resin composition (I-1) for forming a skin layer was replaced with 100 parts by mass of the urethane resin composition (IV-1) for forming a skin layer.

Example 6

Fabrication of Leather-Like Sheet

In the presence of 710 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N981 from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 1,000), 67 g of dimethylolpropionic acid, and 590 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.7% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone.
After 2,367 g of the solution of the isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone was mixed with 50 g of triethylamine, it was mixed with 2,367 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 530 g of an aqueous chain extender solution containing 42 g of ethylenediamine and 11 g of diethanolamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (V) having a nonvolatile content of 35% by mass (weight average molecular weight of 42,000 and hydroxyl value of 6.9).
To 100 g of the resulting urethane resin composition (V) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (V-1) for forming a skin layer.
A leather-like sheet (V-2) was fabricated in the same manner as in Example 1 except that the urethane resin composition (I-1) for forming a skin layer was replaced with 100 parts by mass of the urethane resin composition (V-1) for forming a skin layer.

Comparative Example 1

Fabrication of Leather-Like Sheet

In the presence of 710 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N981 from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 1,000), 67 g of dimethylolpropionic acid, and 590 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.7% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone.
After 2,367 g of the solution of the isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone was mixed with 50 g of triethylamine, it was mixed with 2,367 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 910 g of an aqueous chain extender solution containing 36 g of ethylenediamine and 55 g of monoethanolamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (I′) having a nonvolatile content of 35% by mass (weight average molecular weight of 39,000 and hydroxyl value of 28.9).
To 100 g of the resulting urethane resin composition (I′) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (I′-1) for forming a skin layer.
A leather-like sheet (I′-2) was fabricated in the same manner as in Example 1 except that the urethane resin composition (I-1) for forming a skin layer was replaced with 100 parts by mass of the urethane resin composition (I′-1) for forming a skin layer.

Comparative Example 2

Fabrication of Leather-Like Sheet

In the presence of 710 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N981 from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 1,000), 67 g of dimethylolpropionic acid, and 590 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.7% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone.
After 2,367 g of the solution of the isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone was mixed with 50 g of triethylamine, it was mixed with 2,367 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 520 g of an aqueous chain extender solution containing 21 g of N-(aminoethyl)ethanolamine and 31 g of monoethanolamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (II′) having a nonvolatile content of 35% by mass (weight average molecular weight of 40,000 and hydroxyl value of 23.2).
To 100 g of the resulting urethane resin composition (II′) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (II′-1) for forming a skin layer.
A leather-like sheet (II′-2) was fabricated in the same manner as in Example 1 except that the urethane resin composition (I-1) for forming a skin layer was replaced with 100 parts by mass of the urethane resin composition (II′-1) for forming a skin layer.

Comparative Example 3

Fabrication of Leather-Like Sheet

In the presence of 710 g of methyl ethyl ketone and 0.1 g of stannous octoate, 1,000 g of a polycarbonate diol (NIPPOLAN N981 from Nippon Polyurethane Industry Co., Ltd., number average molecular weight of 1,000), 67 g of dimethylolpropionic acid, and 590 g of dicyclohexylmethane diisocyanate (HMDI) were reacted at 70° C. until NCO % reached 2.7% by mass to yield a solution of an isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone.
After 2,367 g of the solution of the isocyanate-terminated urethane prepolymer (A′-1) in methyl ethyl ketone was mixed with 50 g of triethylamine, it was mixed with 2,367 g of pure water and was subjected to phase inversion emulsification to yield an emulsion.
To the resulting emulsion was added 1,400 g of an aqueous chain extender solution containing 36 g of ethylenediamine and 116 g of dibutylamine, and it was mixed to run a chain extension reaction.
The methyl ethyl ketone was then distilled off from the reaction mixture to yield a urethane resin composition (III′) having a nonvolatile content of 35% by mass (weight average molecular weight of 39,000 and hydroxyl value of 0.0).
To 100 g of the resulting urethane resin composition (III′) were added 0.2 g of a silicone leveling agent, 0.1 g of a silicone defoaming agent, and 1.0 g of a urethane associative thickener. The mixture was stirred using a mechanical mixer at 2,000 rpm for 2 minutes and was then deaerated using a vacuum deaerator to yield a urethane resin composition (III′-1) for forming a skin layer.
A leather-like sheet (III′-2) was fabricated in the same manner as in Example 1 except that the urethane resin composition (I-1) for forming a skin layer was replaced with 100 parts by mass of the urethane resin composition (III′-1) for forming a skin layer.

[Adhesion Evaluation Method]

A 1 inch wide hot-melt cloth tape (from San Chemicals, Ltd.) was bonded to the surface of the skin layer of each of the leather-like sheets fabricated in the Examples and Comparative Examples at 130° C. for 5 seconds. The peel strength was measured at a temperature of 23° C. and a relative humidity of 65% using a Tensilon (head speed=200 mm/min) in accordance with JIS K6854-2. A skin layer having a peel strength of 3.0 kg/cm or more was determined to have sufficient adhesion to the support of the leather-like sheet for practical use.

[Perspiration Resistance Evaluation Method 1 (Perspiration Resistance 1)]

A piece of filter paper impregnated with the mass of oleic acid equal to the dry mass of the filter paper was placed on the skin layer of each of the leather-like sheets fabricated in the Examples and Comparative Examples, and it was heated at 80° C. for 24 hours.
After heating, the filter paper was removed, and the oleic acid remaining on the surface of the skin layer was wiped off with cloth.
The wiped surface of the skin layer was visually inspected and was rated according to the following criteria.
A: The skin layer remained the same in appearance as before oleic acid was applied thereto and did not peel off.
B: A limited portion of the skin layer became slightly larger in appearance (swelling in the skin layer) than before oleic acid was applied thereto, although it was acceptable for practical use and did not peel off.
C: The skin layer became clearly larger in appearance (swelling in the skin layer) than before oleic acid was applied thereto, although it did not peel off.
D: The skin layer became clearly larger in appearance (swelling in the skin layer) than before oleic acid was applied thereto and partially peeled off.
E: Most of the skin layer peeled off or dissolved.

[Perspiration Resistance Evaluation Method 2 (Perspiration Resistance 2)]

Each of the leather-like sheets fabricated in the Examples and Comparative Examples was dipped in oleic acid and was left standing at 25° C. for 3 days.
Thereafter, the gauze was removed, and the oleic acid remaining on the surface of the skin layer was wiped off with cloth.
After the wiped leather-like sheet was dried at 90° C. for 1 hour, the leather-like sheet was fixed horizontally, and a piece of canvas was placed thereon. The surface of the skin layer was repeatedly rubbed with the canvas under a load of 500 g.
Based on the number of rubbing cycles and the appearance of the skin layer, the skin layer was rated according to the following criteria. Grade “C” or higher is preferred for practical use, and Grade “B” or higher is particularly preferred.
The specific numbers of rubbing cycles are not available (because they were checked for each 1,000 cycles).
A: The skin layer of the leather-like sheet did not peel off after 5,000 rubbing cycles.
B: The skin layer of the leather-like sheet peeled off and the substrate was exposed after 5,000 rubbing cycles.
C: The skin layer of the leather-like sheet peeled off and the substrate was exposed after 4,000 rubbing cycles.
D: The skin layer of the leather-like sheet peeled off and the substrate was exposed after 3,000 rubbing cycles.
E: The skin layer of the leather-like sheet peeled off and the substrate was exposed before rubbing or within 5 rubbing cycles.

[Oil Resistance Evaluation Method]

A piece of filter paper impregnated with the mass of a suntan lotion (BUG SUN from Coppertorn) equal to the dry mass of the filter paper was placed on the skin layer of each of the leather-like sheets fabricated in the Examples and Comparative Examples, and it was heated at 70° C. for 24 hours.
After heating, the filter paper was removed, and the suntan lotion remaining on the surface of the skin layer was wiped off with cloth.
The wiped surface of the skin layer was visually inspected and was rated according to the following criteria.
A: The skin layer remained the same in appearance as before suntan lotion was applied thereto and did not peel off.
B: A limited portion of the skin layer became slightly larger in appearance (swelling in the skin layer) than before suntan lotion was applied thereto, although it was acceptable for practical use and did not peel off.
C: The skin layer became clearly larger in appearance (swelling in the skin layer) than before suntan lotion was applied thereto, although it did not peel off.
D: The skin layer became clearly larger in appearance (swelling in the skin layer) than before suntan lotion was applied thereto and partially peeled off.
E: Most of the skin layer peeled off or dissolved.

[Bending Resistance Evaluation Method]

A bending tester (flexometer) was used to count the number of bending cycles at −10° C. until the surfaces of the leather-like sheets cracked.
The specific numbers of bending cycles are not available (because they were checked for each predetermined number of cycles).
A: The surface of the leather-like sheet did not crack after 100,000 bending cycles.
B: The surface of the leather-like sheet cracked after 75,000 bending cycles.
C: The surface of the leather-like sheet cracked after 50,000 bending cycles.
D: The surface of the leather-like sheet cracked after 25,000 bending cycles.
E: The surface of the leather-like sheet cracked after 10,000 bending cycles.

TABLE 1

Example 1	Example 2	Example 3	Example 4

Leather-like sheet	I-2	II-2	III-2	IV-2
Urethane resin composition for	I-1	I-1	II-1	III-1
forming skin layer (numbers in	(2)	(2)	(2)	(2)
parentheses are numbers of
hydroxyl groups on one end)
Adhesive (d)	d1-1	d1-2	d1-1	d1-1
Support	Polyester	Polyester	Polyester	Polyester
	fiber	fiber	fiber	fiber
	nonwoven	nonwoven	nonwoven	nonwoven
	fabric	fabric	fabric	fabric
Adhesion (kg/cm)	5.3	5.5	5.4	5.2
Perspiration resistance 1	A	A	A	A
Perspiration resistance 2	A	A	C	B
Oil resistance	A	A	A	A
Bending resistance	B	B	B	B

	TABLE 2

	Example 5	Example 6

Leather-like sheet	V-2	V-2
Urethane resin composition for	IV-1	V-1
forming skin layer (numbers in	(2)	(2)
parentheses are numbers of
hydroxyl groups on one end)
Adhesive (d)	d1-1	d1-1
Support	Polyester	Polyester
	fiber	fiber
	nonwoven	nonwoven
	fabric	fabric
Adhesion (kg/cm)	5.0	5.2
Perspiration resistance 1	A	B
Perspiration resistance 2	B	B
Oil resistance	A	B
Bending resistance	A	B

TABLE 3

Comparative	Comparative	Comparative
Example 1	Example 2	Example 3

Leather-like sheet	I′-2	II′-2	III′-2
Urethane resin composition	I′-1	II′-1	III′-1
for forming skin layer	(1)	(1)	(0)
(numbers in parentheses are
numbers of hydroxyl groups
on one end)
Adhesive (d)	d1-1	d1-1	d1-1
Support	Polyester	Polyester	Polyester
	fiber	fiber	fiber
	nonwoven	nonwoven	nonwoven
	fabric	fabric	fabric
Adhesion (kg/cm)	5.2	5.1	5.3
Perspiration resistance 1	D	D	E
Perspiration resistance 2	E	E	E
Oil resistance	D	D	D
Bending resistance	B	B	B

The leather-like sheets fabricated in Examples 1 and 2 had skin layers with high perspiration resistance and oil resistance and did not crack when bent. The leather-like sheets fabricated in Examples 3 and 4, which had little or no polycarbonate structure, were slightly lower in perspiration resistance 2, although they had good perspiration resistance and high oil resistance and bending resistance. The leather-like sheet fabricated in Example 5 was slightly lower in the hydroxyl value of the urethane resin that formed the skin layer, although it had good perspiration resistance, oil resistance, and bending resistance.
In contrast, the leather-like sheets fabricated in Comparative Examples 1 and 2, which used a urethane resin having one hydroxyl group on one end thereof as the urethane resin that formed the skin layer, had significantly lower perspiration resistance and oil resistance. The leather-like sheet fabricated in Comparative Example 3, which used a urethane resin having no hydroxyl group on the ends thereof as the urethane resin that formed the skin layer, had significantly lower perspiration resistance and oil resistance.

Claims

1. A leather-like sheet comprising:

a skin layer (C) formed from a urethane resin composition containing a urethane resin (A) having two or more hydroxyl groups on at least one end thereof and an aqueous medium (B);

an adhesive layer (D); and

a support layer (E).

2. The leather-like sheet according to claim 1, wherein the urethane resin (A) is prepared by reacting a polyol (a1) including a polycarbonate polyol, a polyisocyanate (a2), and optionally a chain extender (a3) to prepare a urethane prepolymer having an isocyanate group on each end thereof and then reacting the isocyanate group of the urethane prepolymer with an amino group of a polyalkanolamine.

3. The leather-like sheet according to claim 1, wherein the adhesive layer (D) is formed from an adhesive (d) containing a compound (d-1) having hydroxyl groups and a compound (d-2) having isocyanate groups.

4. The leather-like sheet according to claim 3, wherein some or all of the isocyanate groups of the compound (d-2) react with the hydroxyl groups of the urethane resin (A) contained in the skin layer (C) to form urethane bonds.

5. A method for manufacturing a leather-like sheet comprising:

applying and drying a urethane resin composition containing a urethane resin (A) having two or more hydroxyl groups on at least one end thereof and an aqueous medium (B) on a release paper;

applying the adhesive (d) to the surface to which the urethane resin composition is has been applied;

placing a support on the surface to which the adhesive (d) has been applied; and

then heating the adhesive (d).