JP2024046144A - Polyurethane and synthetic leather for synthetic leather - Google Patents

Abstract

[Problem] To provide a polyurethane for synthetic leather which is excellent in mechanical properties and chemical resistance and does not easily adsorb odorous components. [Solution] A polyurethane for synthetic leather containing a structural unit (A) derived from a polycarbonate diol (A) and a structural unit (B) derived from an isocyanate compound (B). The polycarbonate diol (A) has a structural unit (I) derived from a compound represented by the following formula (1) and a structural unit (II) derived from at least one diol selected from isosorbide, isomannide and isoidide, and in the polycarbonate diol (A), the molar ratio ((I)/(II)) of the structural unit (I) to the structural unit (II) is in the range of 45/55 to 75/25. HO-R1-OH ... (1) (In formula (1), R1 is a substituted or unsubstituted alkylene group having 3 to 10 carbon atoms. The carbon atoms in the alkylene group of R1 are primary, secondary and tertiary carbon atoms.) [Selected Figure] None

Description

The present invention relates to a polyurethane for synthetic leather and to synthetic leather.
More specifically, the present invention relates to a polyurethane for synthetic leather which contains structural units derived from a polycarbonate diol having a specific structure, is resistant to adsorption of odorous components, and has excellent mechanical properties and chemical resistance, and to a synthetic leather produced using the polyurethane.

As polyurethanes produced on an industrial scale, polycarbonate-type polyurethanes that use polycarbonate diol as the raw material for the soft segment portion have been proposed (Patent Document 1). Furthermore, in recent years, synthetic leathers with high chemical resistance that use this polycarbonate-type polyurethane have been proposed (Patent Documents 2 and 3).

Synthetic leather products using polyurethane are used in furniture parts such as exterior materials and protective covers for sofas; vehicle parts such as seat covers and interior materials for automobiles; clothing parts such as leather shoes, jumpers, and belts; bags, etc. It is used for decorative parts such as bags, watch belts, and wallets.

In the above applications, synthetic leather products are required to be less likely to adsorb odors such as cigarettes and cosmetics, odors of food such as grilled meat, and odors from the human body such as sweat and sebum. In other words, polyurethanes for synthetic leather are required to be less likely to adsorb odorous components.
In addition, since the synthetic leather products are used in the above applications under conditions where they are subjected to weight or load such as the weight of the human body or external resistance, the synthetic leather products are required to have excellent mechanical properties, i.e., polyurethane for synthetic leather is required to have excellent mechanical properties such as tensile strength.
Furthermore, in the above applications, since the synthetic leather products are washed or disinfected with ethanol or isopropanol, the synthetic leather products are required to have excellent chemical resistance, i.e., polyurethane for synthetic leather is required to have excellent chemical resistance.

Japanese Patent Application Publication No. 2013-108196 JP2019-044280A Japanese Patent Application Publication No. 2012-072350

For polyurethanes for synthetic leather, it is particularly desirable that they have excellent mechanical properties and chemical resistance, as well as being resistant to the adsorption of odorous components, for their intended use. However, it was difficult for the polyurethanes disclosed in Patent Documents 1 to 3 to simultaneously achieve these three properties: excellent mechanical properties and chemical resistance, and being resistant to the adsorption of odorous components. In particular, Patent Documents 1 to 3 make no mention whatsoever of the structure or composition of polyurethanes that are resistant to the adsorption of odorous components.

The purpose of the present invention is to solve the problems of the prior art described above, and to provide a polyurethane for synthetic leather that has excellent mechanical properties and chemical resistance and is difficult to absorb odor components, and a synthetic leather using this polyurethane. shall be.

As a result of intensive research into solving the above problems, the present inventors have discovered that the above problems can be solved by producing polyurethane using a polycarbonate diol having a specific structure as a raw material.

The present invention was achieved based on these findings and is summarized as follows:

[1] A polyurethane for synthetic leather containing a structural unit (A) derived from a polycarbonate diol (A) and a structural unit (B) derived from an isocyanate compound (B),
The polycarbonate diol (A) contains a structural unit (I) derived from a compound represented by the following formula (1), and a structural unit (II) derived from at least one diol selected from isosorbide, isomannide, and isoidide. have,
In the polycarbonate diol (A), the molar ratio ((I)/(II)) of the structural unit (I) to the structural unit (II) is within the range of 45/55 or more and 75/25 or less. Characteristic polyurethane for synthetic leather.
HO-R ¹ -OH...(1)
(In formula (1), R ¹ is a substituted or unsubstituted alkylene group having 3 to 10 carbon atoms, and the carbon atoms in the alkylene group of R ¹ are primary to tertiary carbon atoms.)
[2] The polyurethane for synthetic leather according to [1], wherein the number average molecular weight determined from the hydroxyl value of the polycarbonate diol (A) is 500 or more and 3,000 or less.
[3] The polyurethane for synthetic leather according to [1] or [2], wherein R ¹ in the formula (1) is a substituted or unsubstituted alkylene group having 4 to 6 carbon atoms.
[4] The molar ratio ((A)/(B)) of the structural unit (A) to the structural unit (B) is within the range of 1.0/5.0 or more and 1.0/0.5 or less. The polyurethane for synthetic leather according to any one of [1] to [3].
[5] Synthetic leather produced using the polyurethane for synthetic leather according to any one of [1] to [4].

According to the present invention, by using a polycarbonate diol with a specific structure as a raw material, it is possible to provide polyurethane for synthetic leather that has excellent mechanical properties and chemical resistance and is less likely to adsorb odorous components, and synthetic leather made from this polyurethane.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following description, and can be implemented with arbitrary modifications within the scope of the gist of the present invention.

As used herein, the term "structural unit" refers to a unit derived from the raw material compound used in the production of polyurethane, which is formed by polymerization of the raw material compound, and which is a unit derived from the raw material compound used in the production of polyurethane, and which has any linking group in the resulting polymer. It also includes partial structures in which one end of the polymer is a linking group and the other is a polymerization-reactive group. The structural unit may be a unit directly formed by a polymerization reaction, or a part of the unit may be converted into another structure by treating the obtained polymer.
In this specification, "repeating unit" has the same meaning as "structural unit".

In this specification, unless otherwise specified, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits, and "A~B" means greater than or equal to A and less than or equal to B.

In this specification, "mass %" indicates the content ratio of a given component contained in a total amount of 100 mass %.
In this specification, "mass%" and "weight%", "ppm by mass" and "ppm by weight", and "parts by mass" and "parts by weight" are synonymous. In addition, when simply written as "ppm", it means "ppm by weight".

[Polyurethane for synthetic leather]
The polyurethane for synthetic leather of the present invention is a polyurethane containing a structural unit (A) derived from a polycarbonate diol (A) described below and a structural unit (B) derived from an isocyanate compound (B) described below.
The polyurethane for synthetic leather of the present invention can be produced according to a conventional method using at least a polycarbonate diol (A) and an isocyanate compound (B) described below as production raw materials.

<Molar ratio of structural unit (A) to structural unit (B) ((A)/(B))>
In the polyurethane for synthetic leather of the present invention, the lower limit of the molar ratio ((A)/(B)) of the structural unit (A) to the structural unit (B) is determined from the viewpoint of the texture of the synthetic leather finally obtained. , preferably 1.0/5.0 or more, more preferably 1.0/4.0 or more, and even more preferably 1.0/3.0 or more. On the other hand, the upper limit of the molar ratio ((A)/(B)) is preferably 1.0/0.5 or less, more preferably 1.0/1.0 or less, from the viewpoint of the strength of the polyurethane obtained. More preferably, it is 1.0/1.5 or less.
The above upper and lower limits can be arbitrarily combined. That is, in the polyurethane for synthetic leather of the present invention, the molar ratio of the structural unit (A) to the structural unit (B) ((A)/(B)) is not particularly limited, but is 1.0. /5.0 or more and 1.0/0.5 or less, more preferably 1.0/4.0 or more and 1.0/1.0 or less, and 1.0/3.0 or more and 1.0/1. More preferably 5 or less.
The value of the molar ratio ((A)/(B))) of the structural unit (A) to the structural unit (B) is the value of the molar ratio ((A)/(B))) of the polycarbonate diol (A) and the isocyanate compound ( It can be calculated from the blending ratio of B). This is because the blending ratio is substantially the same as the composition ratio of the structural unit (A) and the structural unit (B) in the finally obtained polyurethane for synthetic leather.

<Polycarbonate diol (A)>
The polycarbonate diol (A) in the present invention is a raw material for forming the structural unit (A) constituting the polyurethane for synthetic leather of the present invention.
The polycarbonate diol in the present invention can be produced by carrying out transesterification and polycondensation in the presence of a transesterification catalyst using at least a compound represented by the following formula (1) described below, at least one diol selected from isosorbide, isomannide, and isoidide, and a carbonate ester as raw materials.
Examples of the carbonate ester include alkyl carbonates, aryl carbonates, and alkylene carbonates, and more specific examples include ethylene carbonate, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, and diphenyl carbonate.

The polycarbonate diol (A) in the present invention has a structural unit (I) derived from a compound represented by the following formula (1) and a structural unit (II) derived from at least one diol selected from isosorbide, isomannide, and isoidide.
HO-R ¹ -OH ... (1)
(In formula (1), R ¹ is a substituted or unsubstituted alkylene group having 3 to 10 carbon atoms, and the carbon atoms in the alkylene group of R ¹ are primary, secondary, or tertiary carbon atoms.)

When the alkylene group of R ¹ in formula (1) has a substituent, examples of the substituent include an ether group, a thioether group, and an alkyl group-substituted amino group.

From the viewpoints of the strength of the resulting polyurethane and low odor adhesion, R ¹ in the formula (1) is preferably a substituted or unsubstituted alkylene group having 4 to 6 carbon atoms.

Examples of the compound represented by formula (1) include diols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 2-ethyl-1,6-hexanediol. These may be used alone or in combination of two or more.
Among these, 1,4-butanediol and 1,6-hexanediol are preferred from the viewpoints of the bending strength and heat resistance of the resulting polyurethane.

As the diol providing the structural unit (II), at least one selected from isosorbide, isomannide, and isoidide is used from the viewpoint that odor components are difficult to adsorb in the obtained polyurethane and can be obtained industrially in large quantities at low cost. Among them, isosorbide is preferred from the viewpoint that odor components are particularly difficult to adsorb in the obtained polyurethane.

In the polycarbonate diol (A) of the present invention, the lower limit of the molar ratio ((I)/(II)) of the structural unit (I) to the structural unit (II) is determined by the strength and chemical resistance of the resulting polyurethane, and From the viewpoint of excellent handling of the polyol and excellent feel of the synthetic leather finally obtained, the ratio is 45/55 or more, preferably 50/50 or more, and more preferably 55/45 or more. On the other hand, the upper limit of the molar ratio ((I)/(II)) is 75/25 or less, preferably 70/30 or less, and 65/35 from the viewpoint of low odor adhesion and excellent strength of the polyurethane obtained. The following are more preferred.
The above upper and lower limits can be arbitrarily combined. That is, in the polycarbonate diol (A) of the present invention, the molar ratio ((I)/(II)) of the structural unit (I) to the structural unit (II) is 45/55 or more and 75/25 or less, The ratio is preferably 50/50 or more and 70/30 or less, and more preferably 55/45 or more and 65/35 or less.
A specific method for measuring the molar ratio ((I)/(II)) of the structural unit (I) to the structural unit (II) will be described in detail in the Examples section below.

The lower limit of the hydroxyl value of the polycarbonate diol (A) in the present invention is not particularly limited, but is preferably 37 mgKOH/g or more, more preferably 44 mgKOH/g or more, and even more preferably 56 mgKOH/g or more, from the viewpoint of maintaining good handleability without excessively increasing the viscosity of the polycarbonate diol. On the other hand, the upper limit of the hydroxyl value is not particularly limited, but is preferably 225 mgKOH/g or less, more preferably 187 mgKOH/g or less, and even more preferably 161 mgKOH/g or less, from the viewpoint of maintaining good flexibility and low-temperature properties of the finally obtained polyurethane.
The upper and lower limits can be combined in any combination. That is, the hydroxyl value of the polycarbonate diol (A) in the present invention is not particularly limited, but is preferably from 37 mgKOH/g to 225 mgKOH/g, more preferably from 44 mgKOH/g to 187 mgKOH/g, and even more preferably from 56 mgKOH/g to 161 mgKOH/g.

The lower limit of the number average molecular weight determined from the hydroxyl value of the polycarbonate diol (A) in the present invention is not particularly limited, but from the viewpoint of the texture of the final polyurethane, it is preferably 500 or more, and 600 or more. More preferably, it is 700 or more. On the other hand, the upper limit of the number average molecular weight is not particularly limited, but from the viewpoint of handling of the polycarbonate diol (A) and strength of the obtained polyurethane, it is preferably 3000 or less, more preferably 2500 or less, and 2000 or less. is even more preferable.
The above upper and lower limits can be arbitrarily combined. That is, the number average molecular weight determined from the hydroxyl value of the polycarbonate diol (A) in the present invention is not particularly limited, but is preferably 500 or more and 3000 or less, more preferably 600 or more and 2500 or less, and 700 or more and 2000 or less. More preferred.

Note that specific methods for measuring the hydroxyl value and number average molecular weight will be explained in detail in the Examples section below.

Only one kind of polycarbonate diol (A) as a raw material for producing the polyurethane for synthetic leather of the present invention may be used, or two or more kinds having different repeating units, molar ratios thereof, physical properties, etc. may be used.

<Isocyanate compound (B)>
The isocyanate compound (B) used as a raw material for producing the polyurethane for synthetic leather of the present invention may have two or more isocyanate groups, and examples thereof include various known aromatic, aliphatic, and alicyclic isocyanate compounds. It will be done.

For example, aromatic diisocyanate compounds such as xylylene diisocyanate, 4,4'-diphenyl diisocyanate, toluene diisocyanate (2,4-toluene diisocyanate, 2,6-toluene diisocyanate), m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, polymethylene polyphenyl isocyanate, phenylene diisocyanate, and m-tetramethylxylylene diisocyanate; tetramethylene Aliphatic diisocyanate compounds such as diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and dimer diisocyanate in which the carboxyl groups of dimer acid are converted to isocyanate groups; alicyclic diisocyanate compounds such as 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate, 1-methyl-2,6-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, and 1,5-pentamethylene diisocyanate. These may be in the form of an isocyanurate as appropriate.
These may be used alone or in combination of two or more.

Among these, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl diisocyanate, and toluene diisocyanate (2,4-toluene diisocyanate, 2,6-toluene diisocyanate) are preferred, and 4,4'-diphenylmethane diisocyanate is particularly preferred. Alternatively, 4,4'-dicyclohexylmethane diisocyanate, 1,6-hexamethylene diisocyanate, and isophorone diisocyanate may be mentioned from the viewpoint of excellent weather resistance of the resulting polyurethane. Note that these may be isocyanurates.

<Polyols other than polycarbonate diol (A)>
In the polyurethane-forming reaction in producing the polyurethane for synthetic leather of the present invention, a polyol other than the polycarbonate diol (A) of the present invention may be used in combination within a range that does not affect the physical properties.
Here, the polyol other than the polycarbonate diol (A) in the present invention is not particularly limited as long as it is one that is used in the production of ordinary polyurethanes, and examples thereof include polyester polyols, polycaprolactone polyols, polyalkylene ether glycols, and polycarbonate polyols other than the polycarbonate diol (A). When a polyol other than the polycarbonate diol (A) is used as the polyol component in the production of the polyurethane for synthetic leather of the present invention, the mass ratio of the polycarbonate diol (A) in the total polyol components is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more, from the viewpoint of effectively obtaining the effects of using the polycarbonate diol (A).

<Chain extender>
A chain extender may be used in the polyurethane forming reaction when producing the polyurethane for synthetic leather of the present invention.
The chain extender is a low molecular weight compound having at least two active hydrogen atoms that react with isocyanate groups, and is selected from at least one compound selected from the group consisting of polyols and polyamines.

Specific examples of such polyols include linear diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol; 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,4-heptanediol, 1,4-dimethylolhexane, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, and the like. branched chain diols such as hexanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, and dimer diol; ether group-containing diols such as diethylene glycol and propylene glycol; alicyclic structure-containing diols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and 1,4-dihydroxyethylcyclohexane, aromatic group-containing diols such as xylylene glycol, 1,4-dihydroxyethylbenzene, and 4,4'-methylenebis(hydroxyethylbenzene); polyols such as glycerin, trimethylolpropane, and pentaerythritol.
Examples of polyamines include hydroxyamines such as N-methylethanolamine and N-ethylethanolamine; and polyamines such as ethylenediamine, 1,3-diaminopropane, hexamethylenediamine, triethylenetetramine, diethylenetriamine, isophoronediamine, 4,4'-diaminodicyclohexylmethane, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine, di-2-hydroxypropylethylenediamine, 4,4'-diphenylmethanediamine, methylenebis(o-chloroaniline), xylylenediamine, diphenyldiamine, tolylenediamine, hydrazine, piperazine, and N,N'-diaminopiperazine.

These chain extenders may be used alone or in combination of two or more.

Among these, linear diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol are preferred from the viewpoints of excellent flexibility and stress relaxation due to excellent phase separation between the soft and hard segments of the resulting polyurethane, and of being industrially available in large quantities at low cost. If a diol having a side chain is used, the cohesive force of the polyurethane hard segments may decrease, resulting in a decrease in various physical properties such as mechanical properties. Of these linear diols, 1,4-butanediol is the most preferred from the viewpoint of an excellent balance of physical properties.

<Chain Terminator>
In the polyurethane-forming reaction in producing the polyurethane for synthetic leather of the present invention, a small amount of a chain terminator having one active hydrogen group can be added as necessary for the purpose of controlling the molecular weight of the resulting polyurethane.
Examples of these chain terminators include aliphatic mono-ols having one hydroxyl group, such as methanol, ethanol, propanol, butanol, and hexanol.
These may be used alone or in combination of two or more.

<Catalyst>
In the polyurethane-forming reaction when producing the polyurethane for synthetic leather of the present invention, a urethane-forming reaction catalyst may be used for the urethane-forming reaction. Examples of the urethanization reaction catalyst include organic tin compounds, organic zinc compounds, organic bismuth compounds, organic titanium compounds, organic zirconium compounds, and amine compounds. The urethanization reaction catalyst may be used alone or in combination of two or more.
When using a urethanization reaction catalyst, the amount of the catalyst is not particularly limited, but is usually within the range of 0.1 to 100 ppm by mass based on the mass of polyurethane to be produced. Its usage can be adjusted.

Among the urethane reaction catalysts, organotin compounds are preferred. Examples of organotin compounds include tin-containing acylate compounds and tin-containing mercaptocarboxylates. Specific examples of organotin compounds include compounds disclosed in WO 2020/218507, such as tin octylate, monomethyltin mercaptoacetate, monobutyltin triacetate, monobutyltin monooctylate, monobutyltin monoacetate, and monobutyltin maleate.

When using aliphatic and/or alicyclic isocyanate compounds as the isocyanate compound raw material, it is preferable to use a tin-based catalyst or the like because they have lower reactivity than aromatic isocyanate compounds, and it is even more preferable to use a catalyst when using 4,4'-dicyclohexylmethane diisocyanate, which has particularly low reactivity.

In particular, when using 4,4'-dicyclohexylmethane diisocyanate, which has low reactivity, the onset of curing after polymerization is slow even when a catalyst is used. It is more preferable to ripen at ~120°C for 10 hours or more. If the aging is not carried out sufficiently, the degree of polymerization of the polyurethane may not be sufficiently increased, and various physical properties may deteriorate.

<Production method of polyurethane for synthetic leather>
As a method for producing the polyurethane for synthetic leather of the present invention, production methods generally used experimentally or industrially can be used, and specific examples include the one-stage method described below or the two-stage method described below.

In producing the polyurethane for synthetic leather of the present invention, a solvent may or may not be used. However, since a process for removing the solvent is required during molding, using a solvent is not industrially advantageous. In addition, since solvents have a large environmental impact, it is more preferable to carry out the reaction without a solvent (in the absence of a solvent).

As an example of a method for producing polyurethane, for example, as disclosed in International Publication No. 2018/088575, a polyol component containing a polycarbonate diol (A) and an isocyanate compound (B) are continuously reacted by a one-shot method (one-step method), whereby the polyurethane for synthetic leather of the present invention can be efficiently produced.
As another example of the production method, as disclosed in International Publication No. 2018/088575, a polyol component containing a polycarbonate diol (A) is first reacted with an excess of an isocyanate compound (B) to produce a prepolymer having an isocyanate group at its terminal, and the prepolymer is then reacted with a chain extender (two-stage method) to increase the degree of polymerization, thereby producing the polyurethane for synthetic leather of the present invention.

<One-step method>
The one-stage method in the production of the polyurethane for synthetic leather of the present invention is also called a one-shot method, and the industrial production method is not particularly limited, but examples thereof include a method in which the polycarbonate diol (A) and the isocyanate compound (B), as polyurethane raw materials, and other components as necessary, are continuously supplied simultaneously or almost simultaneously to a single- or multi-screw type extruder or a static mixer, and continuously melt-polymerized within a range of 40 to 300° C., preferably within a range of 80 to 220° C., to produce the polyurethane.
Also included is a method in which the polycarbonate diol (A), the isocyanate compound (B), and, if necessary, other components are mixed together, the mixture is cast onto a release sheet, and cured by heating.

When producing the polyurethane for synthetic leather of the present invention, the polycarbonate diol (A) and the isocyanate compound (B) are mixed thoroughly in a solvent system by rapid stirring, and then the mixture is continuously fed to the single-screw or multi-screw extruder or static mixer to continuously produce the polyurethane. This method is effective in the case of aliphatic isocyanate compounds and/or alicyclic isocyanate compounds with low reactivity.

The one-stage method is preferable because the desired polyurethane can be continuously produced extremely simply by simply feeding all of the reaction components to the extruder at the same time or almost at the same time.

<Two-step method>
The two-stage method for producing the polyurethane for synthetic leather of the present invention is also called a prepolymer method, and the industrial production method is not particularly limited, but the following method can be mentioned.
(a) A method for producing a polyurethane by reacting a polycarbonate diol (A) with an excess of an isocyanate compound (B) in advance at a reaction equivalent ratio of the isocyanate compound (B)/polycarbonate diol (A) of more than 1 to 10.0, thereby producing a prepolymer having an isocyanate group at the molecular chain terminal, and then adding a known chain extender described later to this prepolymer.
(b) A method of producing a polyurethane by reacting an isocyanate compound (B) with an excess of a polycarbonate diol (A) in a reaction equivalent ratio of the isocyanate compound (B)/polycarbonate diol (A) of 0.1 or more and less than 1.0 to produce a prepolymer having a hydroxyl group at the molecular chain end, and then reacting this with an isocyanate compound (B) having an isocyanate group at the end as a chain extender.

The two-step method can be carried out without a solvent or in the presence of a solvent.
As a more specific method for producing polyurethane using a two-stage method, any of the methods (1) to (3) described below can be used.
Method (1): Without using a solvent, first, isocyanate compound (B) and polycarbonate diol (A) are directly reacted to synthesize a prepolymer, and a chain extension reaction is directly performed to obtain polyurethane.
Method (2): The prepolymer synthesized by method (1) is dissolved in a solvent, and then a chain extension reaction is performed to obtain polyurethane.
Method (3): Isocyanate compound (B) and polycarbonate diol (A) are reacted in the presence of a solvent to synthesize a prepolymer, and then a chain extension reaction is performed in the presence of a solvent to obtain polyurethane.

In the case of the two-stage method, the above-mentioned methods (2) and (3) are suitable for producing polyurethanes to be used in paints and coatings, since polyurethane can be obtained in the presence of a solvent by dissolving a known chain extender, which will be described later, in the solvent or by simultaneously dissolving the prepolymer and the chain extender in the solvent during the chain extension reaction.

In the case of the two-stage method, the above-mentioned method (1) is suitable for producing polyurethanes to be used in melt molding. In the above-mentioned method (1), from the viewpoint of producing polyurethanes having excellent melt moldability and mechanical properties, it is preferable to carry out melt polymerization substantially in the absence of a solvent, and a continuous melt polymerization method using a multi-screw extruder is more preferable. Polyurethanes obtained by the continuous melt polymerization method are generally superior in strength to polyurethanes obtained by solid-phase polymerization at polymerization temperatures in the range of 40 to 300°C. The polyurethanes obtained by method (1) can be dissolved in a solvent and used as a polyurethane solution to be used for paint applications or coating applications.

<Reaction molar ratio>
In both the one-stage method and the two-stage method described above, the urethanization reaction when producing the polyurethane for synthetic leather of the present invention involves the addition of polycarbonate diol (A) to the structural unit (B) derived from the isocyanate compound (B). After making sure that the molar ratio ((A)/(B)) of the structural unit (A) derived from is within the aforementioned preferred range, the molar ratio of the polycarbonate diol (A) and the isocyanate compound (B) is The polycarbonate diol (A) of the obtained polyurethane: isocyanate compound (B): diol as a chain extender is reacted in a molar ratio of 1:2 to 6:1 to 5. At this time, the molar ratio of the raw materials is reflected in the molar ratio of the product.

In the molar ratio of the raw materials, the ratio of the molar amount (Mc) of the isocyanate compound (B) to the sum (Ma + Mb) of the molar amount (Ma) of the polycarbonate diol (A) and the molar amount (Mb) of the diol as a chain extender, It is preferable to use these so that (Mc)/(Ma+Mb) is in the range of 0.95 to 1.10.
If the (Mc)/(Ma+Mb) molar ratio is at least the above-mentioned lower limit, the resulting polyurethane will have sufficient strength, and if it is below the above-mentioned upper limit, the obtained polyurethane will have sufficient flexibility, which is preferable.

<Molecular weight>
The molecular weight of the polyurethane for synthetic leather of the present invention is appropriately adjusted depending on the application and is not particularly limited, but is preferably 50,000 to 500,000, and more preferably 100,000 to 300,000, in terms of polystyrene equivalent weight average molecular weight (Mw) measured by gel permeation chromatography (GPC). If the weight average molecular weight (Mw) is less than the lower limit, sufficient strength and hardness may not be obtained, while if it is more than the upper limit, handling properties such as processability tend to be impaired.

<Additives>
The polyurethane for synthetic leather of the present invention can be used as a polyurethane composition for synthetic leather by adding or mixing known additives such as fillers, plasticizers, colorants (dyes, pigments), stabilizers (e.g., antioxidants, UV stabilizers, heat stabilizers, etc.), flame retardants, crosslinking agents, reaction accelerators, reinforcing agents, etc., within the range that does not impair the properties of the polyurethane for synthetic leather of the present invention.
As specific additives, for example, additives disclosed in JP-A-2021-152239 can be used.

The amount of these additives added, as a mass ratio to the polyurethane for synthetic leather of the present invention, is preferably 0.01 mass% at the lower limit, more preferably 0.05 mass%, and even more preferably 0.1 mass%, and preferably 10 mass%, more preferably 5 mass%, and even more preferably 1 mass% at the upper limit. If the amount of additives added is too small, the effect of adding the additives cannot be fully obtained, and if the amount is too large, precipitation or turbidity may occur during the processing of the polyurethane for synthetic leather.

[Synthetic leather]
The method for manufacturing the synthetic leather of the present invention using the polyurethane for synthetic leather of the present invention can be performed using a known method, for example, as described in "Artificial Leather/Synthetic Leather Japan Textile Products and Consumer Science Society (2010)". Manufactured in such a way that Generally, synthetic leather refers to woven fabric or knitted fabric as a base material, and is sometimes distinguished as a different structure from artificial leather, which uses nonwoven fabric as a base material. However, in recent years, this distinction has become less strict, as woven fabrics and knitted fabrics are attached to nonwoven fabrics to give them strength. The polyurethane for synthetic leather in the present invention can be equally applied to polyurethane for artificial leather, and also includes compositions that can be distinguished from synthetic leather and artificial leather, and the effects of the present invention can be applied to both. do.

Synthetic leather using the polyurethane for synthetic leather of the present invention is produced, for example, by forming a microporous layer containing a polyurethane resin on a base fabric as a substrate, and laminating a polyurethane resin for a surface layer via an adhesive layer, or by impregnating a substrate filled with a resin such as polyurethane with a polyurethane resin, and further laminating a microporous layer on top of that. The polyurethane for synthetic leather of the present invention may be applied to or impregnated into the substrate, may be contained in an adhesive layer, may be used as a surface layer, or may be used in other layers. For the purpose of enhancing the effect of bacteria repellency, it is particularly preferable to use the polyurethane for synthetic leather of the present invention in a surface layer.

Examples of embodiments of synthetic leather using the polyurethane for synthetic leather of the present invention include the following (1) or (2) synthetic leather laminate.
(1) A synthetic leather laminate in which a base fabric, an adhesive layer, an intermediate layer, and a skin layer containing the polyurethane for synthetic leather of the present invention are laminated in this order (2) A base fabric, an adhesive layer, and a main layer A synthetic leather laminate in which an intermediate layer containing the polyurethane for synthetic leather of the invention and a skin layer are laminated in this order.

<Base material>
As the base material, base fabrics can be used, and specifically, synthetic fibers such as polyester, polyamide, polyacrylonitrile, polyolefin, polyvinyl alcohol, natural fibers such as cotton and hemp, recycled rayon, cotton wool, acetate, etc. Knitted fabrics, woven fabrics, non-woven fabrics, etc., made of single fibers, blended fibers, or multicomponent fibers modified into ultrafine fibers by dissolving at least one component or splitting bicomponent fibers. can be used.
This base fabric may be raised. The nap may be raised on one side or on both sides. Further, the base fabric is not limited to a single layer, and may have a multilayer structure consisting of a plurality of fibers. Furthermore, a knitted fabric having a raised surface may be used as the base fabric.

<Microporous layer>
The substrate may have a microporous layer. The wet microporous layer is produced by a general substrate impregnation method. For example, the substrate is immersed in a dimethylformamide solution containing the polyurethane for synthetic leather of the present invention, or the solution is applied to the substrate, coagulated in water, desolvated, and dried under hot air at about 120°C to form a wet microporous layer having excellent surface smoothness.
The thickness of the wet microporous layer is preferably 50 to 400 μm, and more preferably 100 to 300 μm, in which range of thickness provides optimal flexibility and volume for synthetic leather.

<Adhesive layer>
When the skin layer is bonded to the base material via an adhesive, conventional adhesives such as polyurethane resin, acrylic resin, and epoxy resin can be used as the adhesive for the adhesive layer. The polyurethane for synthetic leather of the present invention can also be used in the adhesive layer. A crosslinking agent and, if necessary, a crosslinking accelerator may be added to the adhesive used for this adhesive layer.

<Middle class>
The intermediate layer can be appropriately set in consideration of the texture or use of the synthetic leather to be obtained. The intermediate layer is formed, for example, from a foaming layer mixture liquid containing a polyurethane resin having a terminal isocyanate group and water. The polyurethane resin having a terminal isocyanate group can be obtained by reacting a polyisocyanate component such as diphenylmethane diisocyanate (MDI) and a polyol component such as polycarbonate polyol or polyether polyol. The intermediate layer mixture liquid constituting the intermediate layer may contain, for example, a foam stabilizer, a foam catalyst, a foam nucleating agent, etc., as necessary. The polyurethane for synthetic leather of the present invention can also be used for the intermediate layer.

<Epidermal layer>
The polyurethane for synthetic leather of the present invention can also be used for the skin layer. The skin layer can be formed to a desired thickness by applying a skin layer formulation containing the polyurethane for synthetic leather of the present invention onto a mold release material and drying by heating. After that, an adhesive is further applied to form an adhesive layer, a base fabric such as a raised cloth is laminated on top of the adhesive layer, and it is dried. After aging at room temperature for several days, the release material is peeled off to obtain synthetic leather. It will be done.
In the present invention, the synthetic leather (or artificial leather) produced in this manner may be subjected to a rubbing process using a jet dyeing machine or the like to create wrinkles similar to natural leather.

<Applications>
Synthetic leather (or artificial leather) using the polyurethane for synthetic leather of the present invention can be used for automobile interior materials, furniture, clothing, shoes, bags, decorations, etc.

EXAMPLES The present invention will be described in more detail by way of Examples below, but the present invention is not limited by the Examples unless the gist thereof is exceeded.

[Evaluation method]
In the following examples and comparative examples, various physical properties were measured by the following methods.

<Solution viscosity>
The polyurethane solutions obtained in Examples and Comparative Examples were measured at 25° C. using an E-type viscometer (device name: TV-100EH, cone: 3°×R14, manufactured by Toki Sangyo Co., Ltd.). The viscosity of this solution is not particularly limited, but from the viewpoint of maintaining good handling and processability of the polyurethane solution during production and the tendency for the obtained polyurethane to exhibit sufficient mechanical properties, the viscosity of the solution is 10,000. It is preferably in the range of ~500,000 mPa·S.

<Number average molecular weight (Mn) of polycarbonate diol>
The polycarbonate diol used in the Examples and Comparative Examples was dissolved in CDCl ₃ (tetramethylsilane internal standard) and subjected to a nuclear magnetic resonance spectrometer (device name: ECZ-400, manufactured by JEOL Ltd., resonance frequency: 400 MHz). ¹ H-NMR measurements were carried out using the following conditions: measurement temperature: 30° C., and number of integration: 64 times.

From the ¹ H-NMR measurement results obtained, integral values a to f of the peaks observed at the following signal positions were obtained.
Integral value of the peak present at δ 5.207 to 4.973 ppm = a
Integral value of the peak present at δ 4.697 to 4.599 ppm = b
Integral value of the peak present at δ 4.599 to 4.464 ppm = c
δ Integral value of the peak present at 3.686 to 3.501 ppm = d
δ Integral value of the peak present at 2.764 to 2.717 ppm = e
δ Integral value of the peak present at 1.493 to 1.295 ppm = f

As the diol forming the structural unit (II), there are two types of polycarbonate diol terminal structural units derived from isosorbide (hereinafter abbreviated as "ISB"), and the integral value of the peak derived from each structural unit is calculated. "ISB _m1 " and "ISB _m2 ". Moreover, the integral value of the peak derived from the structural unit derived from ISB in the polycarbonate diol other than the polycarbonate diol terminal was defined as "ISB _o ".
Similarly, as a compound represented by the above formula (1) forming structural unit (I), the structural unit at the terminal of polycarbonate diol derived from 1,6-hexanediol (hereinafter abbreviated as "16HD") The integral value of the derived peak was defined as "16HD _m ", and the integral value of the peak derived from the structural unit derived from 16HD in the polycarbonate diol other than the polycarbonate diol terminal was defined as "16HD _o ".

Using the following formula, the molar ratios of the structural units at the polycarbonate diol terminals derived from hydroxyl groups and the repeating structural units of the polycarbonate diol derived from carbonate groups were calculated.
Based on the number of protons in the structural unit derived from ISB and the structural unit derived from 16HD, the integral value of the peak derived from each of the structural units described above was calculated using the following formula.
ISB _m1 = b - e
ISB _o = c - ISB _m1
ISB _m2 = a - ISB _m1 - ISB _o x 2
16HD _m = (d-e-ISB _m1 ) ÷ 2
_16HDo = (f- _16HDm x 4) ÷ 4

Next, the number average molecular weight (Mn) of the polycarbonate diol was calculated from the ratio of the repeating structural unit to the terminal structural unit (number of diol units) using the following formula.

In the formula (I), the molar ratio (I) refers to the content (mol %) of the structural unit (I) in the polycarbonate diol calculated from the obtained ¹ H-NMR measurement result, M(16HD _o ) refers to the molecular weight of the structural unit derived from 16HD in the polycarbonate diol other than the polycarbonate diol terminal (=100), M(ISB _o ) refers to the molecular weight of the structural unit derived from ISB in the polycarbonate diol other than the polycarbonate diol terminal (=128), M(carbonyl group) refers to the molecular weight of the carbonyl group (=28), and M(hydroxyl group) refers to the molecular weight of the hydroxyl group (=17).

<Molar ratio of structural unit (I) to structural unit (II): (I)/(II)>
From the ¹ H-NMR measurement results obtained by the method for measuring the "number average molecular weight (Mn) of polycarbonate diol" described above, the mole of structural unit (I) relative to structural unit (II) is calculated using the following formula (II). The ratio ((I)/(II)) was determined.

<Molar ratio of structural unit (A) to structural unit (B): (A)/(B)>
The molar ratio ((A)/(B)) of the structural unit (A) to the structural unit (B) is determined from the composition ratio (molar ratio) of the polycarbonate diol (A) and the isocyanate compound (B) used in the production of polyurethane. I calculated it.

<Weight average molecular weight (Mw) of polyurethane>
The polyurethanes obtained in Examples and Comparative Examples were dissolved in dimethylacetamide containing lithium bromide to a concentration of 0.14% by mass, and this was used as a sample for GPC measurement.
Using a gel permeation chromatography (GPC) measurement device (device name: HPLC-8220GPC, manufactured by Tosoh Corporation), the weight average molecular weight (Mw) in terms of polystyrene was measured under the following GPC measurement conditions.
(GPC measurement conditions)
Column: TSKgel GMHxL-L
(7.8mm ID x 300mmL x 2 (series connection))
Sample charge amount: 100μL
Eluent: THF (tetrahydrofuran)
Flow rate: 0.8mL/min
Column temperature: 40℃
Detector: RI (differential refractometer)

<Mechanical property test>
As an index of the mechanical properties of polyurethane, the tensile breaking strength of the polyurethane was measured using the following method.
The polyurethane solutions obtained in the Examples and Comparative Examples were applied to a 0.1 mm thick fluororesin sheet (product name: fluoro tape "Nitoflon 900", manufactured by Nitto Denko Corporation) using an applicator with a clearance of 500 μm, and dried at a temperature of 80° C. for 5 hours to dry and remove the solvent (DMF), and then left to stand at a constant temperature and humidity of 23° C. and 55% RH for 12 hours or more to obtain a laminated film in which a polyurethane layer was formed on the surface of the fluororesin sheet. The thickness of the polyurethane layer after drying was 50 μm.
After peeling the polyurethane layer from the obtained laminated film, a rectangular polyurethane film (length 70 mm, width 10 mm, thickness 50 μm) was cut out to prepare a sample piece for a tensile test.

(Measurement of Tensile Breaking Strength)
The above tensile test specimens were subjected to a tensile test in accordance with JIS K6301 (2010) using a universal benchtop testing machine (manufactured by Shimadzu Corporation, product name "Universal benchtop testing machine AGX-1kNX") at a chuck distance of 30 mm, a tensile speed of 200 mm/min, and a temperature of 23°C (relative humidity of 55%). The stress (tensile breaking strength) at the time when the test specimen broke was measured and evaluated according to the following criteria.
(Judgment criteria)
◎: 60 MPa or more 〇: 40 MPa or more, less than 60 MPa ×: Less than 40 MPa

<Chemical resistance test>
As an index of the chemical resistance of polyurethane, the mass change rate when the polyurethane was immersed in oleic acid or ethanol was measured using the method described below.
The polyurethane solutions obtained in the Examples and Comparative Examples were applied to a 0.1 mm thick fluororesin sheet (product name: fluorotape "Nitoflon 900", manufactured by Nitto Denko Corporation) using an applicator with a clearance of 500 μm, and dried at a temperature of 80° C. for 5 hours to dry and remove the solvent (DMF), thereby obtaining a laminated film in which a polyurethane layer was formed on the surface of the fluororesin sheet. The thickness of the polyurethane layer after drying was 50 μm.
After peeling the polyurethane layer from the obtained laminated film, a square polyurethane film (3 cm long, 3 cm wide, 50 μm thick) was cut out and used as a sample piece for chemical resistance testing.

(oleic acid resistance test)
After measuring the mass of the above chemical resistance test specimen using a precision balance, the test specimen was immersed in a 250 mL glass bottle containing 50 mL of oleic acid as a test solvent, and placed in a constant temperature bath under a nitrogen atmosphere. The mixture was left standing at a temperature of 80° C. for 16 hours. After the test, take out the test piece and wipe the front and back sides lightly with a paper wiper, then measure the mass with a precision balance, calculate the mass change rate (increase rate) from the change in the mass of the test piece before and after the test, and meet the following criteria. Judgment was made according to the following.
(Judgment criteria)
◎: Mass change rate is less than 2.5% ○: Mass change rate is 2.5% or more and less than 15% ×: Mass change rate is 15% or more

(Ethanol resistance test)
After measuring the weight of the above chemical resistance test specimen using a precision balance, it was placed in a glass petri dish with an inner diameter of 10 cm and containing 50 mL of ethanol as a test solvent, and immersed for 1 hour at room temperature of about 23 ° C. . After the test, take out the test piece and wipe the front and back sides lightly with a paper wiper, then measure the mass with a precision balance, calculate the mass change rate (increase rate) from the change in the mass of the test piece before and after the test, and meet the following criteria. Judgment was made according to the following.
(Judgment criteria)
◎: Mass change rate is less than 2.5% ○: Mass change rate is 2.5% or more and less than 15% ×: Mass change rate is 15% or more

<Odor component adsorption test>
As an indicator of the adsorption of odor components of polyurethane, the reduction rate of odor components was measured according to the method described below using ammonia, trimethylamine, and acetaldehyde as the odor components.
The polyurethane solutions obtained in the examples and comparative examples were applied onto a 0.1 mm thick fluororesin sheet (trade name: fluorine tape "Nitoflon 900", manufactured by Nitto Denko Corporation) using an applicator with a clearance of 500 μm. A laminated film in which a polyurethane layer was formed on the surface of the fluororesin sheet was obtained by coating and drying at a temperature of 80° C. for 5 hours to remove the solvent (DMF).
After peeling off the urethane layer from the obtained laminated film, a square urethane film (length 10 cm, width 10 cm, thickness 50 μm) was cut out, and this was used as a sample piece for an adsorption test.

(Evaluation of Adsorption of Odor Components)
In accordance with the detector tube method of ISO 17299-2, the obtained sample piece for the adsorption test was left for 3 hours in an atmosphere containing an ammonia gas concentration of 100 ppm, a trimethylamine gas concentration of 28 ppm, and an acetaldehyde gas concentration of 14 ppm at a temperature of 25° C., and the odor component reduction rate was calculated from the change in gas concentration before and after the test, and judged according to the following criteria.
(Judgment criteria)
◎: Odor component reduction rate is 3.0% or less. ◯: Odor component reduction rate is more than 3.0% and 5.0% or less. ×: Odor component reduction rate is more than 5.0%.

[raw materials]
The abbreviations of compounds used in Examples and Comparative Examples are as follows.
PCDI: Copolymerized polycarbonate diol containing 1,6-hexanediol units and isosorbide units (number average molecular weight 804), hydroxyl value 139.6 mgKOH/g, 1,6-hexanediol units/isosorbide units = 60/40 [mole ratio ]) (manufactured by Mitsubishi Chemical Corporation)
PCD2: Polycarbonate diol having only 1,6-hexanediol units (number average molecular weight 2,029, hydroxyl value 55.3 mgKOH/g, 1,6-hexanediol units/isosorbide units = 100/0 [molar ratio]) ( Product name: Duranol T6002, manufactured by Asahi Kasei Corporation)
PCD3: Polytetramethylene glycol (number average molecular weight 1,948, hydroxyl value 57.6 mgKOH/g) (product name: PTMG #2000, manufactured by Mitsubishi Chemical Corporation)
MDI: 4,4'-diphenylmethane diisocyanate (manufactured by Tosoh Corporation)
1,4BG: 1,4-butanediol (manufactured by Mitsubishi Chemical Corporation)
DMF: N,N-dimethylformamide (super dehydrated grade) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
U-830: Dioctyltin monodecanate (product name: Neostan U-830, manufactured by Nitto Kasei Co., Ltd.)

[Example 1]
A separable flask (reaction vessel) equipped with a thermocouple, a cooling tube and a stirring device was placed on a 60 ° C. oil bath, and 59.8 g of PCD1, 6.7 g of 1,4BG, and 253.7 g of DMF as a reaction solvent were placed in advance to 80 ° C., and then the inside of the reaction vessel was replaced with nitrogen, and 33.5 g of MDI was added, and the reaction vessel was heated to 70 ° C. in about 1 hour while stirring at 60 rpm under a nitrogen atmosphere. After reaching 70 ° C., 0.025 g of U-830 was added as a urethane reaction catalyst, and the mixture was stirred for another 2 hours while maintaining the liquid temperature at 70 ° C. Then, MDI was added little by little to adjust the viscosity of the solution in the reaction vessel. At this time, the amount of MDI added was 3.7 g. After the addition of MDI, the mixture was further stirred at 70 ° C. for 1 hour to obtain a polyurethane solution with a solution viscosity of 145,900 mPa s. This was designated polyurethane solution “U-1.” The properties and physical properties of this polyurethane solution were evaluated and are shown in Table 1.

[Comparative Example 1 and Comparative Example 2]
Polyurethane solutions having the solution viscosities shown in Table 1 were obtained under the same conditions as in Example 1, except that the type and amount of polycarbonate diol (A) and the amounts of other raw materials in Example 1 were changed as shown in Table 1. These were named polyurethane solutions "U-2" and "U-3". The properties and physical property evaluation results of the obtained polyurethane solutions are shown in Table 1.

The following can be seen from Table 1.
It can be seen that the polyurethane of Example 1 has excellent mechanical properties and chemical resistance, and also has low adsorption of odor components. That is, it can be said that the synthetic leather products containing the polyurethane of the present invention have excellent mechanical properties and chemical resistance, and are difficult to be stained by the smell of foodstuffs, cigarettes, etc.

On the other hand, the polyurethanes of Comparative Examples 1 and 2 had high adsorption of odorous components because the molar ratio ((I)/(II)) of the structural unit (I) to the structural unit (II) in the polycarbonate diol (A) was outside the range of 45/55 to 75/25. Furthermore, the polyurethane of Comparative Example 2 had insufficient chemical resistance.

The polyurethane for synthetic leather of the present invention has excellent mechanical properties and chemical resistance, and further has the characteristic of being less likely to adsorb odorous components.
Therefore, synthetic leather products containing the polyurethane for synthetic leather of the present invention can be suitably used for furniture components such as exterior materials for sofas and the like and protective covers; vehicle components such as seat covers and interior materials for automobiles and the like; clothing components such as leather shoes, jackets, and belts; and decorative components such as bags, purses, watch straps, and wallets.

Claims (5)

A polyurethane for synthetic leather comprising a structural unit (A) derived from a polycarbonate diol (A) and a structural unit (B) derived from an isocyanate compound (B),
The polycarbonate diol (A) has a structural unit (I) derived from a compound represented by the following formula (1) and a structural unit (II) derived from at least one diol selected from isosorbide, isomannide, and isoidide,
A polyurethane for synthetic leather, characterized in that in the polycarbonate diol (A), the molar ratio ((I)/(II)) of the structural unit (I) to the structural unit (II) is within the range of 45/55 or more and 75/25 or less.
HO-R ¹ -OH ... (1)
(In formula (1), R ¹ is a substituted or unsubstituted alkylene group having 3 to 10 carbon atoms, and the carbon atoms in the alkylene group of R ¹ are primary, secondary, or tertiary carbon atoms.) The polyurethane for synthetic leather according to claim 1, wherein the number average molecular weight of the polycarbonate diol (A) calculated from the hydroxyl value is 500 or more and 3,000 or less. The polyurethane for synthetic leather according to claim 1, wherein R ¹ in the formula (1) is a substituted or unsubstituted alkylene group having 4 to 6 carbon atoms. A molar ratio ((A)/(B)) of the structural unit (A) to the structural unit (B) is within the range of 1.0/5.0 or more and 1.0/0.5 or less. Item 1. Polyurethane for synthetic leather according to item 1. A synthetic leather produced using the polyurethane for synthetic leather according to any one of claims 1 to 4.