Polyol Composition

Abstract

To provide a polyol composition usable as raw material for producing synthetic leather without using solvent, a production method of synthetic leather without using solvent, and a polyol composition from which a polyurethane film excellent in flexibility, chemical resistance and moist-heat resistance can be produced, usable as raw material for producing synthetic leather without using solvent.SOLUTION: A polyol composition usable as raw material for producing synthetic leather without using solvent has a carbonate skeleton, a viscosity measured by a method according to JIS K 1557-5(2007) at 50°C of 100 to 1250 mPa s, and a hydroxyl value measured by a method according to JIS K 1557-1(2007) of 40 to 75 mg KOH / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyol composition. [Background technology]

[0002] Synthetic leather made from urethane resin is widely used in the manufacture of vehicle interior materials, furniture, breathable waterproof clothing, and more. Among these, urethane resins made from polycarbonate diol are known as materials with excellent hydrolysis resistance, chemical resistance, resistance to oxidation and degradation, and heat resistance. For urethane resins, solutions of polyurethane in N,N-dimethylformamide (hereinafter abbreviated as "DMF") are commonly used. However, restrictions on the use of DMF are being fully implemented in Europe and China, and there is an urgent need to reduce its use and transition to solvent-free solutions.

[0003] To solve this problem, a surface layer forming composition for fiber laminates is known, in which the base agent is a polycarbonate diol obtained from 1,6-hexanediol and a low molecular weight carbonate, the curing agent is a hexamethylene diisocyanate-modified polyisocyanate and an isocyanurate-modified polyisocyanate, and neither the base agent nor the curing agent contains any organic solvent (see, for example, Patent Document 1). Another known method for eliminating solvents is a method for producing synthetic leather having a cured layer of a moisture-curable urethane hot-melt resin composition (see, for example, Patent Document 2). Another known method for ultrafine fiber nonwoven synthetic leather is a polyurethane dispersion containing an aromatic diisocyanate, a polyurethane prepolymer containing a polyether polyol, and an anionic surfactant (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2009-098841 [Patent Document 2] Patent No. 6485726 [Patent Document 3] Special Publication No. 2019-529614 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the polycarbonate diol used in Patent Document 1, obtained from 1,6-hexanediol and low molecular weight carbonate, has a high viscosity, and therefore the viscosity of the liquid containing the base resin and curing agent is high, which may make it impossible to apply to a release substrate, and even if it can be applied, there is a problem with the surface smoothness of the resulting coating film. Furthermore, the method described in Patent Document 2 has a problem in that the viscosity of the urethane resin is high, and when the resin composition is applied to a substrate, the resulting coating film does not have a uniform thickness. Furthermore, the method described in Patent Document 3 has problems with the chemical resistance and abrasion resistance of the resulting synthetic leather.

[0006] Therefore, an object of the present invention is to provide a polyol composition that can be used as a raw material in the solvent-free production of synthetic leather, and a method for producing synthetic leather in the solvent-free state.Another object of the present invention is to provide a polyol composition that can be used as a raw material in the solvent-free production of synthetic leather, and that can give a polyurethane film that has excellent flexibility, chemical resistance, and moist heat resistance. [Means for solving the problem]

[0007] As a result of extensive research into solving the above problems, the present inventors have found that a polyol composition satisfying predetermined properties can solve the above problems, and have thus completed the present invention.

[0008] That is, the present invention is as follows. [1] It has a carbonate skeleton and has a viscosity of 100 to 1250 mPa s measured at 50°C according to the method of JIS K 1557-5 (2007), A polyol composition for use as a raw material for producing synthetic leather in the absence of solvents, having a hydroxyl value of 40 to 75 mgKOH / g as measured by the method of JIS K 1557-1 (2007). [2] The polyol composition according to [1], which has an ester skeleton and / or an ether skeleton and has a carbonate skeleton content of 1 to 99 mol %. [3] The polyol composition according to [1], which has an ester skeleton and / or an ether skeleton and has a carbonate skeleton content of 1 to 30 mol %. [4] The polyol composition according to any one of [1] to [3], which has a glass transition temperature of −60° C. or lower as measured by a differential scanning calorimeter and an acid value of 2.5 mg KOH / g or lower as determined by the method specified in JIS K 0070 (1992). [5] A urethane prepolymer for producing synthetic leather in the absence of solvent, obtained using the polyol composition according to any one of [1] to [4] and a polyisocyanate. [6] A method for producing synthetic leather, comprising the steps of applying a urethane prepolymer composition containing the urethane prepolymer according to [5] onto a base fabric or a release support in the absence of a solvent, and then moisture-curing the composition. [7] A method for producing synthetic leather, comprising the step of mixing a urethane prepolymer composition containing the urethane prepolymer according to [5] with a crosslinking agent, and applying the resulting mixture onto a base fabric or a release support in the absence of a solvent to cause a reaction. [Effects of the Invention]

[0009] The polyol composition of the present invention can be used, for example, as a raw material for producing synthetic leather in the absence of a solvent. The polyol composition of the present invention can also be used to obtain a polyurethane film having excellent flexibility, chemical resistance, and moist heat resistance, and can be used as a raw material for producing synthetic leather in the absence of a solvent. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "the present embodiment") will be described in detail. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention.

[0011] [Polyol composition] The polyol composition of this embodiment is a polyol composition used as a raw material in the production of synthetic leather in the absence of a solvent (hereinafter also referred to as "polyol composition for use as a raw material in the production of synthetic leather in the absence of a solvent"), and has a carbonate skeleton, a viscosity of 100 to 1250 mPa·s measured at 50°C according to the method of JIS K 1557-5 (2007), and a hydroxyl value of 40 to 75 mgKOH / g measured according to the method of JIS K 1557-1 (2007). The polyol composition of the present invention can be used to obtain, for example, a polyurethane film having excellent flexibility, chemical resistance, and moist heat resistance.

[0012] The polyol composition of the present embodiment preferably contains a polyol having a carbonate skeleton represented by the following formula (A) (hereinafter also simply referred to as "carbonate skeleton") and a terminal hydroxyl group. [ka]

[0013] Furthermore, the polyol composition of this embodiment may have an ester skeleton and / or an ether skeleton in addition to the carbonate skeleton. In this case, the carbonate skeleton content, as evaluated by the method described in the Examples below, is preferably 1 to 99 mol%. If the carbonate skeleton content is 1 mol% or more, the resulting synthetic leather or artificial leather can be expected to have good chemical resistance and hydrolysis resistance. On the other hand, if the carbonate skeleton content is 99 mol% or less, the viscosity of the polyol composition at 50°C can be set within the above-mentioned range by optimizing the composition of the polyol composition. The carbonate skeleton content is more preferably 5 mol% or more, and even more preferably 10 mol% or more, since it provides chemical resistance and hydrolysis resistance sufficient for use in applications requiring high durability, such as automotive applications. The carbonate skeleton content is more preferably 90 mol% or less, even more preferably 80 mol% or less, even more preferably 70 mol% or less, particularly preferably 60 mol% or less, and extremely preferably 30 mol% or less.

[0014] The polyol composition of this embodiment has a viscosity of 100 to 1250 mPa·s as measured at 50°C according to the method of JIS K 1557-5 (2007). If the viscosity of the polyol composition is 100 mPa·s or higher, the required thickness can be obtained when the resulting polyurethane resin composition is applied to a base fabric or release paper. On the other hand, if the viscosity of the polyol composition is 1250 mPa·s or lower, the polyurethane composition obtained from the polyol composition can be applied to a base fabric or release support without using a solvent. It is more preferable that the viscosity of the polyol composition is 100 to 1200 mPa·s. If the viscosity of the polyol composition is 100 to 1000 mPa·s, synthetic leather of the desired thickness tends to be obtained without using a solvent for the polyurethane composition obtained from the polyol composition, regardless of the molecular weight of the polyurethane.

[0015] The method for controlling the viscosity of the polyol composition within the above range is not particularly limited, but for example, a method of selecting a diol used as a raw material in the production of a polycarbonate diol can be mentioned. Usually, the viscosity of the obtained polycarbonate diol tends to decrease as the main chain of the diol becomes longer or the diol has a side chain. Another method can be a method of selecting the structure and amount of the ester compound and / or ether compound to be combined.

[0016] In this embodiment, the viscosity of the polyol composition can be measured by the method described in the examples below.

[0017] The polyol composition of this embodiment preferably has a hydroxyl value of 40 to 75 mgKOH / g, as measured by the method specified in JIS K 1557-1 (2007). If the polyol composition of this embodiment has a hydroxyl value of 40 mgKOH / g or more, the polyurethane composition obtained from the polyol composition tends to be able to be applied to a base fabric or a release support without using a solvent. If the polyol composition of this embodiment has a hydroxyl value of 75 mgKOH / g or more, a flexible synthetic leather or artificial leather tends to be obtained. It is more preferable that the polyol composition of this embodiment has a hydroxyl value of 45 to 70 mgKOH / g, and even more preferably 45 to 65 mgKOH / g.

[0018] The method for controlling the hydroxyl value of the polyol composition within the above range is not particularly limited, but for example, in a method of mixing a polycarbonate diol with an ether compound and / or an ester compound, a method of mixing the polycarbonate diol with the ether compound and / or the ester compound so that the mass average hydroxyl value of the polycarbonate diol and the ether compound and / or the ester compound falls within the above range can be mentioned. In addition, in a case where an ether compound and / or an ester compound is used as a raw material to polymerize a polycarbonate diol, a method of carrying out polymerization until the hydroxyl value falls within the above range can be mentioned.

[0019] In the present embodiment, the hydroxyl value of the polyol composition can be measured by the method described in the examples below.

[0020] It is generally known that increasing the hydroxyl value of a polyol composition reduces the viscosity of the polyol composition, and the flexibility of synthetic leather made using such a polyol composition decreases. The polyol composition of the present embodiment has a low viscosity without increasing the hydroxyl value, which enables the use of less solvent, or even solvent-free methods, when producing synthetic leather, and also enables the production of synthetic leather with flexibility.

[0021] Synthetic leathers used in automobiles and the like are required to maintain flexibility even at temperatures as low as -20°C or lower. To obtain such synthetic leathers, it is preferable that the glass transition temperature (hereinafter also referred to as "Tg") of the polyol composition used as the raw material is low. The polyol composition of this embodiment preferably has a Tg of -50°C or lower as measured by a differential scanning calorimeter. If the Tg is -50°C or lower, synthetic leathers obtained using the polyol composition tend to exhibit little loss in flexibility even at temperatures as low as -20°C or lower. It is more preferable that the polyol composition of this embodiment has a Tg of -55°C or lower, and even more preferable that the Tg is -60°C or lower, since this reduces changes in flexibility at low temperatures regardless of the polyurethane composition. The lower limit of the Tg of the polyol composition of this embodiment is not particularly limited, but is, for example, -90°C.

[0022] The method for controlling the Tg of the polyol composition within the above range is not particularly limited, but examples thereof include a method of selecting a diol used as a raw material in the production of a polycarbonate diol, and a method of controlling the structure and amount of an ester compound and / or an ether compound to be combined with a polycarbonate diol.

[0023] In this embodiment, the Tg of the polyol composition is evaluated by the method described in the examples below.

[0024] Typically, the Tg of a polyurethane obtained from a polyol composition is higher than the Tg of the polyol composition itself (hereinafter, the difference between the Tg of the polyurethane and the Tg of the polyol composition will also be referred to as ΔTg). ΔTg varies depending on the type of polyol composition and the urethane composition, but a small ΔTg tends to reduce the change in flexibility of the synthetic leather between room temperature and low temperature. The polyol composition of this embodiment uses MDI as the isocyanate and 1,4-butanediol as the chain extender, and the ΔTg, as evaluated by the method described in the Examples below, is preferably 50°C or less, and more preferably 45°C or less. The lower limit of ΔTg is not particularly limited, but is, for example, 1°C.

[0025] The method for controlling ΔTg within the above range is not particularly limited, but examples include a method of controlling the structure and amount of the ester compound and / or ether compound combined with the polycarbonate diol.

[0026] The polyol composition of this embodiment preferably has fluidity at room temperature (20±5°C). As used herein, "having fluidity at room temperature" means that the flow time evaluated by the method described in the Examples below is 90 seconds or less. The flow time is preferably 70 seconds or less, and more preferably 50 seconds or less. When the polyol composition of this embodiment has a flow time of 90 seconds or less, it does not need to be heated to dissolve and is easy to handle. Furthermore, the flexibility of the resulting polyurethane tends to be high, which is preferable.

[0027] The polyol composition of the present embodiment may be cloudy, as long as it is fluid at room temperature.

[0028] The polyol composition of this embodiment preferably has an acid value of 2.5 mg KOH / g or less. If the polyol composition of this embodiment has an acid value of 2.5 mg KOH / g or less, the polyol composition tends to less inhibit the action of the catalyst used in the urethane reaction. The acid value is more preferably 1.5 mg KOH / g or less. The lower limit of the acid value of the polyol composition of this embodiment is not particularly limited, but is, for example, 0.05 mg KOH / g.

[0029] The method for controlling the acid value of the polyol composition within the above range is not particularly limited, but includes, for example, a method of adding an acidic compound or a basic compound to the polyol composition.

[0030] In the present embodiment, the acid value of the polyol composition is evaluated by the method described in the examples below.

[0031] The polyol composition of the present embodiment preferably contains a polycarbonate diol. The method for obtaining a polyol composition having an ether skeleton and / or an ester skeleton is not limited, but examples thereof include a method of mixing a polycarbonate diol with an ether compound and / or an ester compound, a method of adding an ether compound and / or an ester compound to a polycarbonate diol and heating and stirring at 130 to 180°C to cause a reaction, and a method of polymerizing a polycarbonate diol using an ether compound and / or an ester compound as a raw material.

[0032] The method for producing the polycarbonate diol used in the polyol composition of the present embodiment is not particularly limited, but it can be produced by various methods described in Schnell, Polymer Reviews, Vol. 9, pp. 9-20 (1994), for example, using a diol and a carbonate as raw materials.

[0033] The diol is not particularly limited, and examples thereof include diols having no side chains, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-dodecanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, and 1,15-pentadecanediol; 2-methyl Examples of diols include diols having side chains such as 1,8-octanediol, 2-ethyl-1,6-hexanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,4-dimethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, and 2,2-dimethyl-1,3-propanediol; and cyclic diols such as 1,4-cyclohexanedimethanol and 2-bis(4-hydroxycyclohexyl)propane. These diols can be used alone or in combination of two or more. Among these, using one or more diols without side chains as raw materials is preferred because it further improves chemical resistance and mechanical strength. Furthermore, two or more (preferably two) diols selected from the group consisting of 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol are preferably used as raw materials for polycarbonate diol.

[0034] In the production of the polycarbonate diol used in this embodiment, when two or more types of diols are used as raw materials, the ratio of these raw materials is not particularly limited, but it is preferable to set the ratio of these raw materials so that the resulting polyol composition has fluidity at room temperature. More specifically, when two types of diols are used as raw materials, it is preferable to set the amount of each diol charged so that the molar ratio is 20 / 80 to 80 / 20. If the molar ratio is within the above range, the resulting polycarbonate diol tends to be liquid at 20°C. The molar ratio is more preferably 30 / 70 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0035] The carbonate is not particularly limited, but examples thereof include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate; diaryl carbonates such as diphenyl carbonate; and alkylene carbonates such as ethylene carbonate, trimethylene carbonate, 1,2-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, and 1,2-pentylene carbonate. These carbonates can be used alone or in combination of two or more. Among these, from the viewpoints of availability and ease of setting conditions during the polymerization reaction, it is preferable to use at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, diphenyl carbonate, dibutyl carbonate, and ethylene carbonate.

[0036] In the production of the polycarbonate diol used in this embodiment, it is preferable to add a catalyst. The catalyst is not particularly limited, but examples thereof include catalysts typically used in transesterification (transesterification catalysts). The transesterification catalyst is not particularly limited, but examples thereof include metal compounds of alkali metals and alkaline earth metals (for example, organometallic compounds such as metal alcoholates (metal alkoxides), metal oxides, and metal amides; inorganic metal compounds such as metal hydrides and metal hydroxides; metal carbonates, nitrogen-containing metal borates, and metal salts such as basic alkali metal salts and alkaline earth metal salts of organic acids). Examples of alkali metals include, but are not limited to, lithium, sodium, and potassium. Examples of alkaline earth metals include, but are not limited to, magnesium, calcium, strontium, and barium. Examples of other metals include, but are not limited to, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, tungsten, rhenium, osmium, iridium, platinum, gold, thallium, lead, bismuth, and ytterbium. These catalysts can be used alone or in combination of two or more. Among these, the use of at least one metal organic compound (particularly a metal alkoxide) and / or salt selected from the group consisting of sodium, potassium, magnesium, potassium, titanium, zirconium, tin, lead, and ytterbium is preferred because it allows the polymerization reaction of polycarbonate diol to proceed smoothly and does not have an adverse effect on the production of resins such as polyurethane resins using the resulting polycarbonate diol. In particular, it is more preferred to use an organic compound (particularly a metal alkoxide) and / or salt of at least one metal selected from the group consisting of titanium, tin, zirconium, magnesium, and ytterbium as the catalyst.

[0037] Specific examples of methods for producing the polycarbonate diol used in this embodiment are shown below. The production of the polycarbonate diol used in this embodiment is not particularly limited, but can be carried out, for example, in two separate stages. Diol and carbonate are mixed in a molar ratio (diol:carbonate) of, for example, 20:1 to 1:10, and the first-stage reaction is carried out at 100 to 250°C under normal pressure or reduced pressure. When dimethyl carbonate is used as the carbonate, the produced methanol can be removed as a mixture with dimethyl carbonate to obtain a low-molecular-weight polycarbonate diol. When diethyl carbonate is used as the carbonate, the produced ethanol can be removed as a mixture with diethyl carbonate to obtain a low-molecular-weight polycarbonate diol. Furthermore, when ethylene carbonate is used as the carbonate, the produced ethylene glycol can be removed as a mixture with ethylene carbonate to obtain a low-molecular-weight polycarbonate diol. Next, in the second-stage reaction, the reaction product of the first stage is heated at 160 to 250°C under reduced pressure to remove unreacted diol and carbonate, and at the same time, the low-molecular-weight polycarbonate diol is condensed to obtain a polycarbonate diol having a predetermined molecular weight.

[0038] The ether compound used in the polyol composition of the present embodiment is not particularly limited, but examples thereof include polyether polyols obtained by adding one or more alkylene oxides such as ethylene oxide and propylene oxide to one or more polyhydric hydroxy compounds (for example, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, pentaerythritol), ring-opening polymers such as tetrahydrofuran, and ethers having two or more OH groups such as diethylene glycol and triethylene glycol.

[0039] The ester compound used in the polyol composition of this embodiment is not particularly limited, and examples thereof include polyester polyols obtained by direct esterification and / or transesterification of a polyhydric alcohol with a polycarboxylic acid or its ester, anhydride, halide, or other ester-forming derivative. Examples of the polyhydric alcohol include, but are not particularly limited to, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, and the like. aliphatic diols such as ethanol, 1,7-heptanediol, 3,5-heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, diethylene glycol, and triethylene glycol; alicyclic diols such as cyclohexanedimethanol and cyclohexanediol; and trihydric or higher alcohols such as trimethylolethane, trimethylolpropane, hexitols, pentitols, glycerin, pentaerythritol, and tetramethylolpropane.The polycarboxylic acid or its ester-forming derivative is not particularly limited, and examples thereof include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid, hydrogenated dimer acid, and dimer acid; aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid; 1,2-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, and 1,3-cyclopentanedicarboxylic acid; Examples of suitable polycarboxylic acids include alicyclic dicarboxylic acids such as cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-dicarboxymethylenecyclohexane, nadic acid, and methylnadic acid; polycarboxylic acids such as tricarboxylic acids such as trimellitic acid, trimesic acid, and the trimer of castor oil fatty acid; acid anhydrides of these polycarboxylic acids; halides such as chlorides and bromides of these polycarboxylic acids; and methyl esters, ethyl esters, propyl esters, isopropyl esters, butyl esters, and isobutyl esters of these polycarboxylic acids. Furthermore, examples of suitable polycarboxylic acid ring-opening polymers include polycaprolactone diol.

[0040] [Urethane prepolymer] The urethane prepolymer of the present embodiment is a urethane prepolymer for use in producing synthetic leather in the absence of a solvent, and is obtained using the above-described polyol composition and polyisocyanate.

[0041] The urethane prepolymer can be obtained by using a polyol composition and a polyisocyanate, and optionally a chain extender in combination. Furthermore, additives such as a urethanization catalyst, a silane coupling agent, a thixotropic agent, an antioxidant, a plasticizer, a filler, and a wax may be used alone or in combination.

[0042] The polyisocyanate is not particularly limited, and examples thereof include aromatic polyisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, polymethylene polyphenyl polyisocyanate, and carbodiimidized diphenylmethane polyisocyanate; and aliphatic or 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 combination of two or more.

[0043] The chain extender is not particularly limited, and examples thereof include chain extenders having an amino group such as ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-4,4'-dicyclohexylmethanediamine, and hydrazine; Examples of chain extenders that can be used include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, sucrose, methylene glycol, glycerin, sorbitol, bisphenol A, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxydiphenyl ether, and trimethylolpropane. These chain extenders may be used alone or in combination of two or more.

[0044] Specifically, the urethane prepolymer of the present embodiment can be produced, for example, by reacting the above-described polyol composition with a polyisocyanate, and optionally a chain extender, under conditions in which the isocyanate groups of the polyisocyanate are in excess relative to the hydroxyl groups of the polyol composition, etc.

[0045] [Manufacturing method for synthetic leather] The method for producing synthetic leather of this embodiment may be a method including a step of applying a urethane prepolymer composition containing the above-mentioned urethane prepolymer onto a base fabric or a release support in the absence of a solvent and allowing it to cure with moisture, or a method including a step of mixing a urethane prepolymer composition containing the above-mentioned urethane prepolymer with a crosslinking agent to obtain a mixed liquid and applying it onto a base fabric or a release support in the absence of a solvent and allowing it to react.

[0046] The method for producing the synthetic leather of this embodiment is not particularly limited, but examples include a method in which the above-mentioned urethane prepolymer having an isocyanate group is made and then moisture-cured, and a method in which the above-mentioned urethane prepolymer is mixed with a crosslinking agent having a hydroxyl group and / or an amino group and then cured.

[0047] More specifically, examples of such methods include a method in which the above-mentioned urethane prepolymer is applied to a release support, and then the applied surface is attached to a substrate (base fabric) and cured to form a cured layer on the substrate (base fabric), and a method in which the above-mentioned urethane prepolymer is applied directly to a substrate (base fabric) and cured to form a cured layer on the substrate.

[0048] Examples of the substrate (base fabric) that can be used include nonwoven fabrics, woven fabrics, and knitted fabrics made from polyester fibers, polyethylene fibers, nylon fibers, acrylic fibers, polyurethane fibers, acetate fibers, rayon fibers, polylactic acid fibers, cotton, linen, silk, wool, glass fibers, carbon fibers, and blends thereof; nonwoven fabrics impregnated with resins such as polyurethane resins; nonwoven fabrics further provided with a porous layer; and resin substrates such as thermoplastic polyurethane (TPU).

[0049] The method for applying the urethane prepolymer is not particularly limited, but examples thereof include methods using an applicator, a roll coater, a spray coater, a T-die coater, a knife coater, a comma coater, and the like.

[0050] Examples of the crosslinking agent include crosslinking agents having a hydroxyl group, such as polyether polyol, polycarbonate polyol, polyester polyol, polyacrylic polyol, dimer diol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, sucrose, methylene glycol, glycerin, sorbitol, bisphenol A, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxydiphenyl ether, and trimethylolpropane; and crosslinking agents having an amino group, such as ethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, hydrazine, piperazine, diaminodiphenylmethane, tolylenediamine, xylylenediamine, isophoronediamine, and norbornanediamine.

[0051] In this embodiment, "solvent-free" refers to producing a urethane prepolymer without using a solvent and producing synthetic leather without adding any solvent to the urethane prepolymer, as well as not using DMF, which has been used conventionally, and reducing the amount of solvent used to less than half, or even one-third, of the amount used conventionally. Furthermore, in this embodiment, artificial leather is also included in the category of synthetic leather. [Example]

[0052] The present embodiment will be described in more detail below with reference to specific examples and comparative examples, but the present embodiment is not limited in any way to the following examples and comparative examples as long as they do not depart from the gist of the present embodiment.

[0053] Various physical properties in the examples and comparative examples described below were measured by the methods shown below.

[0054] 1. Viscosity of the polyol composition The viscosity of the polyol composition was determined by the method using a cone-plate rotational viscometer specified in JIS K 1557-5 (2007), except that the measurement temperature was set to 50°C.

[0055] 2. Determination of the hydroxyl number of the polyol composition The hydroxyl value of the polyol composition was determined by Method A specified in JIS K 1557-1 (2007).

[0056] 3. Determination of the acid number of the polyol composition The acid value of the polyol composition was determined by the potentiometric titration method specified in JIS K 0070 (1992).

[0057] 4. Determination of the Carbonate Backbone Value of the Polyol Composition Polyol composition 1 The H-NMR integral value ratio was determined as follows to determine the carbonate skeleton value of the polyol composition. First, 10 mg of a sample was dissolved in 0.75 mL of deuterated chloroform (manufactured by Aldrich). Tetramethylsilane (TMS) was added to the solution as a chemical shift standard, and the resulting solution was analyzed using an ECZ500 (SC) manufactured by JEOL Ltd. 1 H-NMR was measured. In the measurement, the resonance frequency was 500 MHz, the pulse width was 45°, the waiting time was 5 seconds, the number of accumulations was 5000, and the TMS signal was set at 0 ppm. 1 The H-NMR spectrum was obtained. 1 In the H-NMR spectrum, the carbonate skeleton value of the polyol composition was calculated using the integral values ​​of the methylene and / or methine signals bonded to the oxygen of the carbonate bond, the methylene and / or methine signals bonded to the oxygen of the ether bond, and the methylene and / or methine signals bonded to the carbonyl carbon of the ester bond, according to the following formula (1): Carbonate skeleton value (mol%) = (A / 2 + B) / {(A / 2 + B) / 2 + (C / 2 + D) / 2 + (E / 2 + F)} × 100 (1) A: Integral value of methylene bonded to oxygen of carbonate bond B: Integral value of methine bonded to oxygen of carbonate bond C: Integral value of methylene bonded to oxygen of ether bond D: Integral value of methine bonded to oxygen of ether bond E: Integral value of methylene bonded to carbonyl carbon of ester bond F: Integral value of methine bonded to carbonyl carbon of ester bond

[0058] 5. Determination of the flowability of polyol compositions A flat-bottomed, cylindrical, transparent glass test tube with an inner diameter of 30 mm and a height of 120 mm was used, with marked lines at heights of 55 mm (line A) and 85 mm (line B) from the bottom. A sample (polyol composition) was heated in a 50°C oven for 8 hours, measured up to line A, and then allowed to stand upright at room temperature of 20±5°C for 24 hours. The tube was then immediately tilted horizontally on a table. The time required for the tip of the sample's liquid surface to pass line B after tilting the test tube was taken as the flow time (seconds), which was used as an index of the fluidity of the polyol composition. A flow time of 90 seconds or less was considered to be fluid. During this measurement, it was also confirmed whether the polyol composition was transparent or opaque.

[0059] 6. Determination of the Glass Transition Temperature (Tg) of Polyol Compositions Approximately 10 g of the polyol composition was placed in an aluminum pan, and using a differential scanning calorimeter (DSC7000X, Hitachi High-Technoscience Corporation) under a nitrogen atmosphere, the temperature was raised and lowered from 30°C to 100°C at a rate of 20°C per minute, from 100°C to -100°C at a rate of 5°C per minute, and from -100°C to 100°C at a rate of 5°C per minute, and the inflection point during the second temperature increase was taken as the glass transition temperature (Tg) of the polyol composition.

[0060] 7. Determination of the difference (ΔTg) in glass transition temperature (Tg) between polyurethane and polyol composition A polyurethane film was produced by the method described below using the polyol composition whose Tg was determined in 6 above. A test piece measuring 10 mm in width, 40 mm in length, and 0.4 mm in thickness was cut from the resulting polyurethane film. Using a viscoelasticity measuring device (Hitachi High-Tech Science Corporation, [TA7000 series, DMA7100]), the test piece was set at a chuck distance of 20 mm, and the viscoelasticity was measured while the temperature was raised from -100°C to 100°C at a rate of 5°C / min. The peak of tan δ was read from the measurement results to determine the glass transition temperature (Tg) of the polyurethane. Using the Tg of the polyol composition determined in 6 above and the Tg of a polyurethane using that polyol composition, ΔTg was determined using the following formula (2): ΔTg (°C) = (Tg of polyurethane) - (Tg of polyol composition) (2)

[0061] 8. Flexibility Assessment A rectangular test piece measuring 10 mm wide, 100 mm long, and approximately 0.1 mm thick was prepared from the polyurethane film produced by the method described below. A tensile test was performed on the prepared test piece using a tensile tester (manufactured by Orientec Co., Ltd., product name "Tensilon, Model RTE-1210") at a chuck distance of 20 mm, a tensile speed of 100 mm / min, and a temperature of 23°C (relative humidity of 55%), and the stress at the point when the test piece was 100% elongated (100% modulus) was measured. The lower the 100% modulus, the better the flexibility was evaluated.

[0062] 9. Evaluation of moisture and heat resistance Polyurethane film was used to prepare rectangular samples measuring 10 mm wide, 100 mm long, and approximately 100 μm thick. The samples were heated for 10 days in an Espec Corporation thermo-hygrostat (product name: PL-1J) at 85°C and 85% humidity. The samples before and after heating were subjected to tensile testing using a tensile tester (Orientec Co., Ltd., product name: Tensilon, model RTE-1210) at a chuck distance of 20 mm, a tensile speed of 100 mm / min, and a temperature of 23°C (relative humidity of 55%). The stress at which the test piece broke was measured, and the strength retention (%) was calculated using the following formula (3) as an index of the polyurethane's moist heat resistance. A higher strength retention indicated better moist heat resistance. Strength retention rate (%) = Breaking strength after heating / Breaking strength before heating × 100 (3)

[0063] 10. Chemical resistance test (oleic acid resistance test) As the chemical resistance, the resistance to oleic acid was evaluated. A 1cm x 10cm test piece was cut from the polyurethane film. After measuring the mass of the test piece using a precision balance, it was placed in a 250mL glass tray containing 50mL of oleic acid as the test solvent and left to stand in a constant temperature bath at 80°C under a nitrogen atmosphere for 24 hours. After the test, the test piece was removed and lightly wiped on both sides with a paper wiper. The mass was then measured using a precision balance and the mass change rate (increase rate (swelling rate (%)) from before the test was calculated. A mass change rate closer to 0% indicates better resistance to oleic acid.

[0064] [Polymerization Example 1] A 2-L glass flask equipped with a rectification column packed with structured packing and a stirrer was charged with 680 g (7.6 mol) of dimethyl carbonate, 420 g (4.0 mol) of 1,5-pentanediol, and 480 g (4.1 mol) of 1,6-hexanediol. 0.14 g of titanium tetraisopropoxide was further added as a catalyst to the flask, and the mixture in the flask was stirred and heated at normal pressure to initiate the reaction. The reaction was continued for 20 hours, with the resulting mixture of methanol and dimethyl carbonate being distilled off while the temperature was raised to 90-140°C. The pressure was then reduced to 17 kPa, and the mixture was further reacted at 150°C for 15 hours while the mixture of methanol and dimethyl carbonate was distilled off, yielding polycarbonate diol (hereinafter also referred to as "PC-1").

[0065] [Polymerization Example 2] Polymerization was carried out using the apparatus shown in Polymerization Example 1. 580 g (6.6 mol) of ethylene carbonate, 300 g (3.3 mol) of 1,4-butanediol, and 390 g (3.3 mol) of 1,6-hexanediol were charged. 0.11 g of titanium tetrabutoxide was added as a catalyst, and the mixture was stirred and heated at normal pressure. The reaction temperature was gradually raised to 160°C, and the reaction was carried out for 20 hours while the resulting mixture of ethylene glycol and ethylene carbonate was distilled off. Thereafter, the pressure was reduced to 15 kPa, and the reaction was carried out for an additional 6 hours at 160°C while the diol and ethylene carbonate were distilled off, yielding polycarbonate diol (hereinafter also referred to as "PC-2").

[0066] [Polymerization Example 3] Polymerization was carried out using the apparatus shown in Polymerization Example 1. 820 g (7.0 mol) of diethyl carbonate and 860 g (7.3 mol) of 1,6-hexanediol were charged. 0.14 g of titanium tetrabutoxide was added as a catalyst, and the mixture was stirred at normal pressure. While the temperature was raised to 90 to 160°C, the mixture of ethanol and diethyl carbonate produced was distilled off, and the reaction was carried out for 20 hours. Thereafter, the pressure was reduced to 17 kPa, and the mixture of ethanol and diethyl carbonate was distilled off, and the reaction was carried out for an additional 12 hours at 160°C, to obtain polycarbonate diol (hereinafter also referred to as "PC-3").

[0067] [Comparative Example 1] A 1-liter glass flask (hereinafter also referred to as the "reactor") equipped with a stirrer was charged with 420 g of the polycarbonate diol P-1 obtained in Polymerization Example 1 and 180 g of polyoxypropylene glycol E-1 (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000). The contents were then heated with stirring, and the reactor temperature was maintained at approximately 145°C for 15 hours. Next, 2-ethylhexyl acid phosphate was added in an amount 2.5 times the molar ratio of titanium tetraisopropoxide, and the reactor temperature was heated at 120°C for 5 hours to obtain polyol composition A-21. Regarding the transesterification reaction, gel permeation chromatography (hereinafter sometimes abbreviated as "GPC") was performed over time on the reaction solution to monitor the disappearance of peaks derived from the raw materials and the appearance of peaks derived from the product over time, thereby confirming the progress of the reaction. The polyol composition finally obtained had undergone almost quantitative reaction based on the amount of raw materials charged, and it was confirmed by GPC measurement over time that it had a corresponding structure. The physical properties of the obtained polyol composition A-21 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0068] [Example 1] Polyol composition A-1 was obtained by carrying out the reaction in the same manner as in Comparative Example 1, except that 300 g of polycarbonate diol P-1 obtained in Polymerization Example 1 and 300 g of polyoxypropylene glycol E-1 (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000) were charged. The physical properties of the obtained polyol composition A-1 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0069] [Example 2] Polyol composition A-2 was obtained by carrying out the reaction in the same manner as in Comparative Example 1, except that 150 g of polycarbonate diol P-1 obtained in Polymerization Example 1 and 450 g of polyoxypropylene glycol E-1 (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000) were charged. The physical properties of the obtained polyol composition A-2 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0070] [Example 3] Polyol composition A-3 was obtained by carrying out the reaction in the same manner as in Comparative Example 1, except that 18 g of polycarbonate diol P-1 obtained in Polymerization Example 1 and 582 g of polyoxypropylene glycol E-1 (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000) were charged. The physical properties of the obtained polyol composition A-3 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0071] Comparative Example 2 Polyol composition A-22 was obtained by carrying out the reaction in the same manner as in Example 1, except that 6 g of polycarbonate diol P-1 obtained in Polymerization Example 1 and 594 g of polyoxypropylene glycol E-1 (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000) were charged. The physical properties of the obtained polyol composition A-22 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0072] [Example 4] Using the apparatus used in Example 1, 270 g of the polycarbonate diol P-2 obtained in Polymerization Example 2 and 330 g of polyoxypropylene glycol E-1 (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000) were charged. Next, these were heated with stirring and the reactor temperature was maintained at approximately 145°C for 15 hours. Next, n-butyl acid phosphate was added in an amount 2.5 times the molar ratio of titanium tetraisopropoxide, and the mixture was heat-treated at a reactor temperature of 120°C for 5 hours to obtain polyol composition A-4. The physical properties of the obtained polyol composition A-4 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0073] [Example 5] Using the apparatus used in Example 1, 270 g of the polycarbonate diol P-2 obtained in Polymerization Example 2 and 330 g of polyoxypropylene glycol E-1 (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000) were charged. Next, these were heated with stirring, and the reactor temperature was maintained at approximately 80°C for 30 minutes. Next, n-butyl acid phosphate was added in an amount 2.5 times the molar ratio of titanium tetraisopropoxide, and the mixture was heat-treated at a reactor temperature of 120°C for 5 hours to obtain polyol composition A-5. The physical properties of the obtained polyol composition A-5 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0074] [Example 6] Using the apparatus used in Example 1, 120 g of the polycarbonate diol P-2 obtained in Polymerization Example 2 and 480 g of polyoxytetramethylene glycol E-2 (manufactured by Mitsubishi Chemical Corporation, "PTMG2000" (trade name), number average molecular weight: approximately 2000) were charged. Next, these were heated with stirring, and the reactor temperature was maintained at approximately 145°C for 15 hours. Next, n-butyl acid phosphate was added in an amount 2.5 times the molar ratio of titanium tetraisopropoxide, and the mixture was heat-treated at a reactor temperature of 120°C for 5 hours to obtain polyol composition A-6. The physical properties of the obtained polyol composition A-6 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0075] [Example 7] Using the apparatus used in Example 1, 90 g of the polycarbonate diol P-3 obtained in Polymerization Example 3 and 510 g of polycaprolactone diol E-3 (manufactured by Daicel Corporation, "Placcel 220" (trade name), number average molecular weight: approximately 2000) were charged. Next, these were heated with stirring, and the reactor temperature was maintained at approximately 80°C for 30 minutes. Next, 2-ethylhexyl acid phosphate was added in an amount 2.5 times the molar ratio of titanium tetraisopropoxide, and the mixture was heat-treated at a reactor temperature of 120°C for 5 hours to obtain polyol composition A-7. The physical properties of the obtained polyol composition A-7 were measured by the above-mentioned methods, and the results are shown in Table 1.

[0076] [Table 1]

[0077] The abbreviations used in the tables and text are as follows: E-1: Polyoxypropylene glycol (manufactured by Sanyo Chemical Industries, Ltd., "Newpol PE-61" (trade name), number average molecular weight: approximately 2000) E-2: Polyoxytetramethylene glycol (manufactured by Mitsubishi Chemical Corporation, "PTMG2000" (trade name), number average molecular weight: approximately 2000) E-3: Polycaprolactone diol E-3 (manufactured by Daicel Corporation, "Placcel 220" (trade name), number average molecular weight: approximately 2000)

[0078] [Polyurethane manufacturing] Polyurethane films were produced using the polyol compositions obtained in the Examples and Comparative Examples as follows. A 500 mL separable flask equipped with a thermocouple and a condenser was charged with 38 g of the polyol composition, 224 g of dimethylformamide (hereinafter sometimes abbreviated as DMF), and 0.26 g of a 1% dibutyltin dilaurate toluene solution (50 ppm relative to the total mass of MDI and the polycarbonate diol composition), and heated in a 40°C oil bath. While stirring the solution in the flask at 100 rpm under a nitrogen atmosphere, 14.8 g of MDI (3.09 times [mol] relative to the OH [mol] of the polycarbonate diol composition) was added dropwise, and the solution in the flask was further stirred for approximately 1.5 hours. The isocyanate group concentration was analyzed, confirming that the theoretical amount had been consumed, yielding a prepolymer. Subsequently, 3.2 g of 1,4-butanediol (1,4-BD), the required amount calculated from the remaining isocyanate, was added in portions to the flask. After stirring the solution in the flask for about 1 hour, about 1 g of ethanol was added, and the solution in the flask was further stirred for 30 minutes to obtain a polyurethane solution. Using a 0.8 mm thick applicator, the resulting polyurethane solution was dropped onto the top of a glass plate (JIS R3202, 2 mm x 100 mm x 150 mm) to coat it to a dry film thickness of 50-150 μm. The film was then dried on a hot plate at a surface temperature of 60°C for 2 hours, followed by 12 hours in an oven at 80°C. The film was then left to stand at a constant temperature and humidity of 23°C and 55% RH for at least 12 hours to obtain a polyurethane film. The resulting polyurethane film was evaluated for various physical properties using the methods described above. The evaluation results are shown in Table 2.

[0079] [Table 2]

[0080] [Application Example 1 (Urethane prepolymer)] A 500 mL separable flask equipped with a thermocouple and a condenser was charged with 300 g of Polyol Composition A-1, and the mixture was dehydrated under reduced pressure at 50° C. until the water content reached 0.05% by mass or less. Next, 75 g of MDI was added, and the mixture was heated to 80° C. The mixture was reacted for about 2 hours until the isocyanate group content reached a constant level, yielding urethane prepolymer PP-1-1.

[0081] [Application Examples 2-7 (Urethane Prepolymer)] Urethane prepolymers PP-1-2 to PP-1-7 were obtained by the method of Application Example 1, except that polyol compositions A-2 to A-7 were used instead of polyol composition A-1.

[0082] [Comparative Application Examples 1 and 2 (Urethane Prepolymer)] Urethane prepolymers PP-1-21 and PP-1-22 were obtained by the same method as in Application Example 1, except that polyol compositions A-21 and A-22 were used instead of polyol composition A-1.

[0083] [Application Example 8 (Urethane Prepolymer)] A 500 mL separable flask equipped with a thermocouple and a condenser was charged with 300 g of Polyol Composition A-1, and the mixture was dehydrated under reduced pressure at 50° C. until the water content reached 0.05% by mass or less. Next, 55 g of MDI was added, and the mixture was heated to 80° C. The mixture was reacted for about 2 hours until the isocyanate group content reached a constant value, yielding urethane prepolymer PP-2-1.

[0084] [Application Examples 51-57 (Synthetic Leather)] 100 parts by mass of urethane prepolymers PP-1-1 to PP-1-7 and 3.6 parts by mass of 1,4-butanediol were mixed and applied to release paper using a knife coater to a dry thickness of 30 μm, followed by hot air drying at 100°C for 2 minutes. A polyester tricot was then attached as a base fabric. After drying at 50°C for 48 hours, the release paper was peeled off to obtain synthetic leather.

[0085] [Comparative Application Examples 11 and 12 (Synthetic Leather)] A mixture of 100 parts by weight of urethane prepolymers PP-1-21 and PP-1-22 and 3.6 parts by weight of 1,4-butanediol was applied to release paper using a knife coater to a dry thickness of 30 μm and then dried with hot air at 100°C for 2 minutes. A polyester tricot base was then attached to the mixture. After drying at 50°C for 48 hours, the release paper was peeled off to obtain synthetic leather.

[0086] [Application Example 61 (Synthetic Leather)] Urethane prepolymer PP-2-1 was heated to 110°C and applied at 0.2 kg / m onto a release paper set on a roll coater. 2 After applying the coating in an amount of 100g, the coated layer was attached to a nonwoven fabric impregnated with urethane resin in a tacky state, and left to stand for 3 days in an atmosphere of 25°C and 50% RH to obtain synthetic leather. [Industrial Applicability]

[0087] The polyol composition of the present invention has a low viscosity and can be used in polyurethane resin compositions for synthetic leathers and artificial leathers without using a solvent. Furthermore, the use of the polyol composition of the present invention tends to result in synthetic leathers and artificial leathers with excellent chemical resistance and moist heat resistance. Therefore, the polyol composition of the present invention can be suitably used in polyurethane resin compositions for solvent-free synthetic leathers and artificial leathers.

Claims

1. It has a carbonate skeleton and has a viscosity of 100 to 1250 mPa s measured at 50°C according to the method of JIS K 1557-5 (2007), A polyol composition for use as a raw material for producing synthetic leather in the absence of a solvent, having a hydroxyl value of 40 to 75 mgKOH / g as measured by the method of JIS K 1557-1 (2007).

2. The polyol composition according to claim 1, which has an ester skeleton and / or an ether skeleton and has a carbonate skeleton content of 1 to 99 mol %.

3. The polyol composition according to claim 1, which has an ester skeleton and / or an ether skeleton and has a carbonate skeleton content of 1 to 30 mol %.

4. The polyol composition according to claim 1, wherein the glass transition temperature measured by a differential scanning calorimeter is −60° C. or lower, and the acid value determined by the method specified in JIS K 0070 (1992) is 2.5 mg KOH / g or lower.

5. The polyol composition according to claim 2, wherein the glass transition temperature measured by a differential scanning calorimeter is −60° C. or lower, and the acid value determined by the method specified in JIS K 0070 (1992) is 2.5 mg KOH / g or lower.

6. The polyol composition according to claim 3, wherein the glass transition temperature measured by a differential scanning calorimeter is −60° C. or lower, and the acid value determined by the method specified in JIS K 0070 (1992) is 2.5 mg KOH / g or lower.

7. A urethane prepolymer for producing synthetic leather in the absence of solvent, obtained by using the polyol composition according to any one of claims 1 to 6 and a polyisocyanate.

8. A method for producing synthetic leather, comprising the steps of applying a urethane prepolymer composition containing the urethane prepolymer according to claim 7 onto a base fabric or a release support in the absence of a solvent, and then moisture-curing the composition.

9. A method for producing synthetic leather, comprising a step of mixing a urethane prepolymer composition containing the urethane prepolymer according to claim 7 with a crosslinking agent, and applying the resulting mixture onto a base fabric or a release support in the absence of a solvent to cause a reaction.

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