WO2025197291A1 - Polyurethane resin and synthetic leather comprising same - Google Patents

Abstract

[Problem] The present invention addresses the problem of developing a polyurethane resin material excellent in low temperature characteristics (in particular, flexibility and strength in a low temperature environment) and suitable for synthetic leather or the like having high flame retardancy.　[Solution] A polyurethane resin comprising at least a structural unit derived from an isocyanate group-terminated prepolymer formed with an isocyanate component and a high molecular weight polyol component, and a structural unit derived from an isocyanurate skeleton-containing polyol, and including a structural unit derived from a long-chain aliphatic polyol having 8-20 carbon atoms in the structure thereof is produced by the reaction of the isocyanate group-terminated prepolymer, the polyol and the isocyanurate-based polyisocyanate compound, and the obtained polyurethane resin is used to form a surface layer on a support to obtain a synthetic leather. <u />

Description

Polyurethane resin and synthetic leather using the same

The present invention relates to a novel flame-retardant polyurethane resin. More specifically, the present invention relates to a polyurethane resin that uses plant-derived ingredients and has a high biomass ratio, and that has excellent flame retardancy, flexibility, and strength (particularly flexibility, flex resistance, and tensile strength in low-temperature environments), as well as synthetic leather made using the same.

Synthetic leather made from polyurethane resin is widely used as a material for automobile seats. Polyurethane resins for such applications generally require high flexibility and flame retardancy. In particular, in applications where the material is exposed to severe temperature changes, it is necessary for flexibility and flame retardancy to be maintained even with temperature changes, but conventional polyurethane resins tend to lose flexibility in low-temperature environments.

A known method of imparting flame retardancy to polyurethane resin is to mix in a flame retardant. However, when using polyurethane resin materials that contain liquid flame retardants, the flame retardant can seep out, a phenomenon known as "bleeding," depending on the product's usage environment.

When such resin materials are used in automotive seating, the bleed-out flame retardant evaporates, causing problems such as clouding of the car's windows. While mixing in solid flame retardants is an option, the resulting polyurethane resin tends to be hard. To maintain high flame retardancy, it is important to impart high flame retardancy to the polyurethane resin itself and reduce the proportion of flame retardant used.

It is already known that flame-retardant polyurethane resins can be obtained by using isocyanurate polyisocyanate components (see, for example, Patent Documents 1 to 5). However, polyurethane resins that use relatively large amounts of multifunctional isocyanate components such as isocyanurates tend to be very hard, and are generally used, for example, as hard boards for building materials, but may not be suitable for materials that require relatively high flexibility, such as automotive seating.

In response to this, means have been proposed for improving flexibility, particularly flexibility in low-temperature environments (Patent Document 6). However, it cannot be said that fully satisfactory performance has been achieved in terms of strength (tensile strength, flex resistance, etc.) in low-temperature environments.

Meanwhile, in recent years, many biomass polyurethane resins have been developed that use plant-derived polyol and polyisocyanate components (Patent Documents 7 and 8), and from the perspective of reducing environmental impact, there is a demand for polyurethane resins with a higher biomass ratio.

There is a need for the development of polyurethane resin materials that are flexible, strong, and highly flame-retardant, while also contributing to carbon neutrality, which aims to combat global warming and reduce environmental impact.

Japanese Patent Application Laid-Open No. 2019-090038 International Publication WO2016/010042 Japanese Patent Application Laid-Open No. 2022-022919 Japanese Patent Application Laid-Open No. 2020-063410 Japanese Patent Application Laid-Open No. 2017-043667 Japanese Patent Application Laid-Open No. 2022-153302 Patent No. 6178541 Japanese Patent Application Laid-Open No. 2022-22226

The objective of this invention is to develop a polyurethane resin material that has excellent low-temperature properties (particularly flexibility and strength in low-temperature environments) and high flame retardancy.

After extensive research, the inventors discovered that a polyurethane resin containing, as constituent components, a segment derived from a prepolymer of a specific polyol and isocyanate, and a segment derived from isocyanurate, could solve the above-mentioned problems, leading to the completion of the present invention.

That is, the present invention relates to the following polyurethane resin, flame-retardant polyurethane resin composition, synthetic leather, and methods for producing them.
(1) A polyurethane resin containing at least a constituent unit derived from an isocyanate group-terminated prepolymer formed from an isocyanate component and a high-molecular-weight polyol component having a number-average molecular weight of 500 or more, and a constituent unit derived from an isocyanurate skeleton-containing polyol, and containing a constituent unit derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms in its structure.

(2) The polyurethane resin according to (1), wherein the isocyanate group content of the structural units derived from the isocyanate group-terminated prepolymer is 1 to 9%.
(3) The polyurethane resin according to (1), wherein the high-molecular-weight polyol component forming the structural unit derived from the isocyanate group-terminated prepolymer is a structural unit derived from a polycarbonate polyol having a number average molecular weight of 500 to 4,000.

(4) The polyurethane resin according to (1), wherein the content of structural units derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms in the structure of the polyurethane resin is 10% by mass or more.
(5) The polyurethane resin according to (1), in which the content of structural units derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms is 10 mol% or more relative to the total amount of structural units derived from aliphatic polyols contained in the structure of the polyurethane resin.

(6) The polyurethane resin according to (1), wherein the long-chain aliphatic polyol having 8 to 20 carbon atoms is a linear long-chain aliphatic polyol having 8 to 20 carbon atoms.
(7) The polyurethane resin according to (1), wherein the polyurethane resin contains 10 mol% or more of a long-chain aliphatic polyol having 8 to 20 carbon atoms relative to the total amount of aliphatic polyols constituting the high-molecular-weight polyol component that forms the structural units derived from the isocyanate group-terminated prepolymer.

(8) The polyurethane resin according to (1), wherein the proportion of structural units derived from an isocyanurate-type polyisocyanate compound in the structure of the polyurethane resin is 1 to 15 mass%.
(9) The polyurethane resin according to (1), wherein the isocyanate component constituting the isocyanate group-terminated prepolymer contains a structural unit derived from 1,5-pentamethylene diisocyanate.

(10) The polyurethane resin according to (1), wherein the structural unit derived from the isocyanurate skeleton-containing polyol includes a structural unit derived from an isocyanurate-type polyisocyanate compound derived from 1,5-pentamethylene diisocyanate.
(11) The polyurethane resin according to (1), wherein the long-chain aliphatic polyol having 8 to 20 carbon atoms includes a plant-derived polyol compound.

(12) A flame-retardant polyurethane resin composition comprising the polyurethane resin according to any one of (1) to (11) and having a glass transition temperature of −30° C. or lower.
(13) The flame-retardant polyurethane resin composition according to (12), which contains 0 to 20% by mass of a flame retardant.

(14) Synthetic leather comprising a support and a surface layer, characterized in that at least the surface layer is made of the flame-retardant polyurethane resin composition according to (12).
(15) The synthetic leather according to (14), which is an interior material for a vehicle.

The polyurethane resin of the present invention contains structural units derived from specific polyol compounds and polyisocyanate compounds in its structure, and has excellent flame retardancy while maintaining high flexibility and strength, including flex resistance and tensile strength, even in low-temperature environments. Furthermore, not only can the content of flame retardants be kept low, but in some cases high flame retardancy is achieved even without the use of flame retardants, eliminating the problem of bleeding. The polyurethane resin and flame-retardant polyurethane resin composition of the present invention can be suitably used in synthetic leather and other automotive seating materials that are used in harsh environments.

Furthermore, by using plant-derived polyisocyanate and polyol components as raw materials for polyurethane resin, environmentally friendly polyurethane resin materials and synthetic leather with a high biomass ratio can be obtained.

I. Polyurethane Resin The polyurethane resin of the present invention contains at least a structural unit derived from an isocyanate group-terminated prepolymer and a structural unit derived from an isocyanurate skeleton-containing polyol.

1. Structural units derived from isocyanate-terminated prepolymers The structural units derived from the isocyanate-terminated prepolymers include structural units formed from an isocyanate component and a high-molecular-weight polyol component. Specifically, they include structural units derived from an isocyanate component (isocyanate units in prepolymers; hereinafter, "PP-isocyanate units") and structural units derived from a high-molecular-weight polyol component having a number-average molecular weight of 500 or more (high-molecular-weight polyol units in prepolymers; hereinafter, "PP-high-molecular-weight polyol units"). In the following description, "polyol" preferably refers to a diol (glycol).

(1) PP-Isocyanate Unit The isocyanate compound capable of forming the PP-isocyanate unit is not particularly limited as long as it is an isocyanate compound used in conventional polyurethane resins. Specific examples include diisocyanates such as aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates.

Aliphatic or alicyclic diisocyanates that can be used are preferably those with 4 to 30 carbon atoms. Examples of aliphatic diisocyanates include tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), 2,2,4- (or 2,4,4-) trimethyl-1,6-hexamethylene diisocyanate, and lysine diisocyanate.

Examples of alicyclic diisocyanates include isophorone diisocyanate, hydrogenated xylene diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, 1,4-diisocyanatocyclohexane, 1,3-bis(diisocyanatomethyl)cyclohexane, and 4,4'-dicyclohexylmethane diisocyanate.

Aromatic diisocyanates include 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, dimethyldiphenylmethane diisocyanate, triphenylmethane triisocyanate, naphthalene diisocyanate, and polymethylene polyphenyl polyisocyanate.

These diisocyanates may be used alone or in combination. Aliphatic diisocyanate compounds with 4 to 6 carbon atoms are more preferred. Of these, 1,6-hexamethylene diisocyanate is preferred due to its weather resistance and ease of industrial availability. Furthermore, considering the impact on the environment, it is preferable to use environmentally friendly 1,5-pentamethylene diisocyanate, which is a plant-derived isocyanate.

(2) PP-High Molecular Weight Polyol Unit A PP-high molecular weight polyol capable of forming a PP-high molecular weight polyol unit is a compound having two or more hydroxyl groups in one molecule and having a number average molecular weight of 500 or more. Preferably, the number average molecular weight is 1,000 or more, more preferably 1,500 or more, and particularly preferably 1,800 or more. A number average molecular weight of 500 or more has the advantage of providing a cured product with excellent low-temperature flexibility.

There is no particular upper limit to the number average molecular weight of the PP-high molecular weight polyol, but it is preferably 10,000 or less, more preferably 8,000 or less, even more preferably 6,000 or less, particularly preferably 4,000 or less, and most preferably 3,000 or less. The number average molecular weight can be determined by measurement using gel permeation chromatography (GPC) using polystyrene as a standard substance.

The PP-high molecular weight polyol is not particularly limited as long as it is a relatively high molecular weight polyol used in conventional polyurethane resins, and examples include polyether polyols, polyester polyols, polycarbonate polyols, polyurethane polyols, epoxy polyols, vegetable oil polyols, polyolefin polyols, acrylic polyols, fluorine polyols, and vinyl monomer-modified polyols. These can be used alone or in combination of two or more. More preferred PP-high molecular weight polyols include polyether polyols, polyester polyols, and polycarbonate polyols, with polycarbonate polyols being particularly preferred. A preferred polycarbonate polyol is polycarbonate diol.

PP-Polycarbonate polyol, a high molecular weight polyol, contains a polycondensate of a relatively low molecular weight aliphatic polyol (a polyol that constitutes polycarbonate polyol; hereinafter referred to as "PC-polyol compound") and a carbonate compound.

The number-average molecular weight of the polycarbonate polyol should be 500 or more, but is preferably 1,200 or more, more preferably 1,500 or more, and even more preferably 1,800 or more. When the number-average molecular weight of the polycarbonate polyol capable of forming an isocyanate-terminated prepolymer is within this range, the cured product has the advantage of excellent flexibility at low temperatures. There is no particular upper limit for the number-average molecular weight of the polycarbonate polyol, but it is preferably 8,000 or less, more preferably 6,000 or less, even more preferably 4,000 or less, and particularly preferably 3,000 or less.

The carbonate compound contains one type of carbonate or two or more types of carbonates. The carbonate may be any compound that can condense with a polyol to produce a polycarbonate polyol. Examples of carbonate compounds include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, and dipropyl carbonate; alkylene carbonates such as ethylene carbonate and propylene carbonate; and diaryl carbonates such as diphenyl carbonate, dinaphthyl carbonate, dianthryl carbonate, diphenanthryl carbonate, diindanyl carbonate, and bistetrahydronaphthyl carbonate.

The PC-polyol compound is a relatively low molecular weight aliphatic polyol (preferably a diol). The relatively low molecular weight aliphatic polyol preferably has a molecular weight of less than 500, more preferably less than 400, and particularly preferably less than 350. Specific examples include aliphatic polyols having 1 to 20 carbon atoms.

Such aliphatic polyols include short-chain aliphatic polyols having 7 or less carbon atoms, and long-chain aliphatic polyols having 8 or more carbon atoms. Furthermore, when using a PP-high molecular weight polyol other than polycarbonate polyol, it is preferable to use a similar aliphatic polyol compound.

The aliphatic hydrocarbons that make up the aliphatic polyol may be either chain aliphatic hydrocarbons or cyclic aliphatic hydrocarbons, but chain aliphatic hydrocarbons are preferred from the perspective of superior flexibility in low-temperature environments. Chain aliphatic hydrocarbons may be either linear or branched, but linear chain aliphatic hydrocarbons are preferred from the perspective of superior strength in low-temperature environments.

Short-chain aliphatic polyols preferably have 1 to 7 carbon atoms, more preferably 2 to 6, and most preferably 3 to 6. Specific examples include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, and 1,4-cyclohexanediol.

In particular, from the standpoint of strength in low-temperature environments, it is more preferable to use unbranched linear aliphatic diols. Even more preferable are linear aliphatic diols having 4 to 6 carbon atoms. Specifically, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol are used. 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol are particularly preferable. These short-chain aliphatic polyols may be used alone or in combination of two or more.

The proportion of branched short-chain aliphatic polyols relative to the total amount of short-chain aliphatic polyols is preferably 20 mol% or less, more preferably 10 mol% or less, and particularly preferably 5 mol% or less, and it is most desirable that no branched short-chain aliphatic polyols are contained.

The long-chain aliphatic polyol is preferably an aliphatic polyol having 8 to 20 carbon atoms, more preferably an aliphatic polyol having 8 to 12 carbon atoms, and particularly preferably an aliphatic polyol having 8 to 10 carbon atoms. Furthermore, these long-chain aliphatic polyols are preferably linear long-chain aliphatic diols.

Examples of linear long-chain aliphatic polyols include linear aliphatic diols such as 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, 1,18-octadecanediol, and 1,20-eicosanediol. These long-chain aliphatic polyols may be used alone or in combination of two or more.

Among these, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol are more preferred. Furthermore, in order to increase the biomass ratio, plant-derived 1,10-decanediol is particularly preferred.

In particular, from the standpoint of strength in low-temperature environments, it is preferable to keep the proportion of branched long-chain aliphatic polyols low. The proportion of branched long-chain aliphatic polyols relative to the total amount of long-chain aliphatic polyols is preferably 5 mol% or less, more preferably 3 mol% or less, and particularly preferably 1 mol% or less, and it is most preferable that no branched long-chain aliphatic polyols are included.

The short-chain aliphatic polyol and the long-chain aliphatic polyol may be used alone. They can also be used in combination. When used in combination, the ratio is not particularly limited, but preferably the long-chain aliphatic polyol:short-chain aliphatic polyol (molar ratio) is 5:95 to 50:50, more preferably 10:90 to 45:55, even more preferably 15:85 to 40:60, particularly preferably 20:80 to 40:60, and most preferably 25:75 to 35:65.

Furthermore, the content of long-chain aliphatic polyols having 8 to 20 carbon atoms relative to the total amount of aliphatic polyols constituting the PP-high molecular weight polyol is preferably 5 mol% or more, more preferably 10 mol% or more, particularly preferably 15 mol% or more, and most preferably 25 mol% or more. There is no particular upper limit, but it is preferably 50 mol% or less, more preferably 40 mol% or less, and particularly preferably 35 mol% or less.

From the standpoint of strength in low-temperature environments, the proportion of branched polyol relative to the total amount of PC-polyol compounds is preferably 5 mol% or less, more preferably 3 mol% or less, and particularly preferably 1 mol% or less, and it is most desirable that no branched polyol is included.

Polycarbonate polyols are obtained by polycondensing the above-mentioned PC-polyol compounds with carbonate compounds using conventional methods.

(3) Method for Producing Isocyanate-Terminated Prepolymers The constitutional units derived from the isocyanate-terminated prepolymers are incorporated into the structure of the polyurethane resin by reacting an isocyanate-terminated prepolymer, which has been produced in advance as a raw material component, with other raw material components during the production of the polyurethane resin.

An isocyanate-terminated prepolymer is a reaction product obtained, for example, by blending the above-mentioned isocyanate component and polyol component in a specified ratio and allowing the mixture to undergo a prepolymerization reaction.

The blending ratio in the prepolymerization reaction is adjusted so that the equivalent ratio (first equivalent ratio, NCO/OH) of the isocyanate groups of the isocyanate component to the hydroxyl groups of the polyol component falls within a specified range. Specifically, for isocyanate-terminated prepolymers, it is desirable to blend the isocyanate component and polyol component so that the NCO/OH ratio is preferably 1.1 or greater, more preferably 1.2 or greater, and particularly preferably 1.5 or greater.

There are no particular restrictions on the molecular weight of the constituent units derived from the isocyanate-terminated prepolymer, but from the perspective of flexibility and strength in low-temperature environments, the isocyanate group content (NCO%), which serves as a guide to molecular weight, is preferably 9% or less, more preferably 6% or less, and especially preferably 4.5% or less. There is no particular restriction on the lower limit of NCO%, but it is preferably 1% or more, more preferably 1.2% or more, and especially preferably 1.5% or more.

If the NCO% is too low (the molecular weight of the constituent units derived from the isocyanate group-terminated prepolymer is too high), the isocyanurate skeleton of the entire polyurethane resin structure may become sparse, resulting in poor flammability.If the NCO% is too high (the molecular weight of the constituent units derived from the isocyanate group-terminated prepolymer is too low), flexibility and strength at low temperatures may be impaired.
The isocyanate group content (%) is given as the amount (g) of isocyanate groups contained in 100 g of a sample, and can be measured by a conventionally known method.

2. Structural Units Derived from Isocyanurate Skeleton-Containing Polyols The polyurethane resin of the present invention contains structural units derived from isocyanurate skeleton-containing polyols. The structural units derived from isocyanurate skeleton-containing polyols consist of structural units derived from an isocyanurate-type polyisocyanate compound ("isocyanurate units") and structural units derived from a polyol ("NU-polyol units") bonded to at least a portion of the isocyanate groups possessed by the isocyanurate rings.

(1) Isocyanurate-Type Polyisocyanate Compounds Isocyanurate-type polyisocyanate compounds capable of forming an isocyanurate skeleton are compounds having one or more isocyanurate rings in one molecule.

The isocyanurate polyisocyanate compound having one or more isocyanurate rings per molecule is preferably primarily an isocyanurate polyisocyanate having one isocyanurate ring per molecule. However, this does not exclude the possibility of a small amount of isocyanurate polyisocyanate having two or more isocyanurate rings per molecule being contained as a by-product during the production of isocyanurate polyisocyanate.

The above-mentioned isocyanurate polyisocyanates can be synthesized from diisocyanates such as aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates.

Aliphatic or alicyclic diisocyanates that can be used are preferably those with 4 to 30 carbon atoms. Examples of aliphatic diisocyanates include tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), 2,2,4- (or 2,4,4-) trimethyl-1,6-hexamethylene diisocyanate, and lysine diisocyanate.

Examples of alicyclic diisocyanates include isophorone diisocyanate, hydrogenated xylene diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, 1,4-diisocyanatocyclohexane, 1,3-bis(diisocyanatomethyl)cyclohexane, and 4,4'-dicyclohexylmethane diisocyanate.

Aromatic diisocyanates include 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, dimethyldiphenylmethane diisocyanate, triphenylmethane triisocyanate, naphthalene diisocyanate, and polymethylene polyphenyl polyisocyanate.

These diisocyanates may be used alone or in combination. Of these, 1,6-hexamethylene diisocyanate is preferred due to its weather resistance and ease of industrial availability. Furthermore, considering the impact on the environment, it is preferable to use environmentally friendly 1,5-pentamethylene diisocyanate, which is a plant-derived isocyanate.

Isocyanurate-type polyisocyanate compounds can be obtained by subjecting diisocyanate to an isocyanuration reaction in the presence of an isocyanuration catalyst. The NCO% of the resulting isocyanurate-type polyisocyanate compound is not particularly limited, but is preferably 20 to 30%.

Specific examples of isocyanurate-type polyisocyanate compounds (having one isocyanurate ring) used in the present invention include the following. Each of the following triisocyanurates may be used alone or in combination of two or more.

HDI3N: an isocyanurate triisocyanate synthesized from 1,6-hexamethylene diisocyanate,
HTMDI3N: isocyanurate-type triisocyanate synthesized from trimethylhexamethylene diisocyanate,
PDI3N: an isocyanurate triisocyanate synthesized from 1,5-pentamethylene diisocyanate,
IPDI3N: isocyanurate triisocyanate synthesized from isophorone diisocyanate,
HTDI3N: isocyanurate triisocyanate synthesized from hydrogenated tolylene diisocyanate,
HXDI3N: isocyanurate triisocyanate synthesized from hydrogenated xylene diisocyanate,
NBDI3N: an isocyanurate triisocyanate synthesized from norbornane diisocyanate, and HMDI3N: an isocyanurate triisocyanate synthesized from hydrogenated diphenylmethane diisocyanate;
MDI3N: isocyanurate triisocyanate synthesized from diphenylmethane diisocyanate,
TDI3N: isocyanurate triisocyanate synthesized from tolylene diisocyanate,
XDI3N: Isocyanurate triisocyanate synthesized from xylene diisocyanate

Among the above, particularly preferred are structural units derived from isocyanurate-type polyisocyanate compounds derived from 1,5-pentamethylene diisocyanate, or structural units derived from isocyanurate-type polyisocyanate compounds derived from 1,6-hexamethylene diisocyanate.

(2) NU-Polyol Examples of polyols capable of forming NU-polyol units include high-molecular-weight polyols ("NU-high-molecular-weight polyols") similar to PP-high-molecular-weight polyols capable of forming isocyanate-terminated prepolymers.

The number average molecular weight of the NU-high molecular weight polyol is preferably 300 or more, more preferably 400 or more, and particularly preferably 500 or more. There is no upper limit, but it is preferably 1,500 or less, more preferably 1,200 or less. It is also preferable that the molecular weight of the NU-high molecular weight polyol is lower than that of the PP-high molecular weight polyol. When the molecular weight of the PP-high molecular weight polyol is higher than that of the NU-high molecular weight polyol, the advantage of excellent mechanical strength and flexibility tends to be obtained. The number average molecular weight is the polystyrene equivalent molecular weight measured by gel permeation chromatography (GPC).

The NU-high molecular weight polyol is not particularly limited as long as it is a relatively high molecular weight polyol used in conventional polyurethane resins, and examples include polyether polyols, polyester polyols, polycarbonate polyols, polyurethane polyols, epoxy polyols, vegetable oil polyols, polyolefin polyols, acrylic polyols, fluorine polyols, and vinyl monomer-modified polyols. These can be used alone or in combination of two or more. More preferred NU-high molecular weight polyols include polyether polyols, polyester polyols, and polycarbonate polyols, with polycarbonate polyols being particularly preferred. A preferred polycarbonate polyol is polycarbonate diol.

Polycarbonate polyols that can form NU-high molecular weight polyols contain polycondensates of relatively low molecular weight aliphatic polyol compounds (PC-polyol compounds) and carbonate compounds.

The carbonate compound can be the same as the carbonate compounds that can be used for the polycarbonate polyols that can form the isocyanate-terminated prepolymers described above.

As the PC-polyol compound, the same PC-polyol compounds that can be used for the polycarbonate polyols that can form the above-mentioned isocyanate-terminated prepolymers can be used.

The PC-polyol compound is preferably a relatively low molecular weight aliphatic polyol (preferably a diol), specifically an aliphatic polyol having 1 to 20 carbon atoms.
Examples of such aliphatic polyols include short-chain aliphatic polyols having 7 or less carbon atoms and long-chain aliphatic polyols having 8 or more carbon atoms. When a NU-high molecular weight polyol other than polycarbonate polyol is used, it is also preferable to use a similar aliphatic polyol compound.

The aliphatic hydrocarbons that make up the aliphatic polyol may be either chain aliphatic hydrocarbons or cyclic aliphatic hydrocarbons, but chain aliphatic hydrocarbons are preferred from the perspective of superior flexibility in low-temperature environments. Chain aliphatic hydrocarbons may be either linear or branched, but linear chain aliphatic hydrocarbons are preferred from the perspective of superior strength in low-temperature environments.

Specific examples of short-chain aliphatic polyols include the same diols listed above as short-chain aliphatic polyols that can form the polycarbonate polyols used in the isocyanate-terminated prepolymer.

In particular, from the viewpoint of strength in low-temperature environments, unbranched linear aliphatic diols are more preferred. Even more preferred are linear aliphatic diols having 2 to 6 carbon atoms. Specific examples include 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. 1,3-propanediol or 1,4-butanediol is particularly preferred. These short-chain aliphatic polyols may be used alone or in combination of two or more.

The proportion of branched short-chain aliphatic polyols relative to the total amount of short-chain aliphatic polyols is preferably 20 mol% or less, more preferably 10 mol% or less, and particularly preferably 5 mol% or less, and it is most desirable that no branched short-chain aliphatic polyols are contained.

The long-chain aliphatic polyol can be the same as the long-chain aliphatic polyol that can form the polycarbonate polyol used in the isocyanate-terminated prepolymer. Preferably, it is an aliphatic polyol having 8 to 20 carbon atoms, more preferably an aliphatic polyol having 8 to 12 carbon atoms, and particularly preferably an aliphatic polyol having 8 to 10 carbon atoms. Furthermore, it is preferable that these long-chain aliphatic polyols be linear long-chain aliphatic diols.

Specific examples of long-chain aliphatic polyols include the same diols listed above as long-chain aliphatic polyols that can form the polycarbonate polyols used in the isocyanate-terminated prepolymer.

Among these, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol are more preferred. Furthermore, in order to increase the biomass ratio, plant-derived 1,10-decanediol is particularly preferred.

In particular, from the standpoint of strength in low-temperature environments, it is preferable to keep the proportion of branched long-chain aliphatic polyols low. The proportion of branched long-chain aliphatic polyols relative to the total amount of long-chain aliphatic polyols is preferably 5 mol% or less, more preferably 3 mol% or less, and particularly preferably 1 mol% or less, and it is most preferable that no branched long-chain aliphatic polyols are included.

The short-chain aliphatic polyol and the long-chain aliphatic polyol may be used alone. Alternatively, the short-chain aliphatic polyol and the long-chain aliphatic polyol may be used in combination. When used in combination, the ratio is not particularly limited, but preferably the long-chain aliphatic polyol:short-chain aliphatic polyol (molar ratio) is 5:95 to 50:50, more preferably 15:85 to 40:60, and particularly preferably 25:75 to 35:65.

From the standpoint of strength in low-temperature environments, the proportion of branched polyol relative to the total amount of PC-polyol compounds is preferably 5 mol% or less, more preferably 3 mol% or less, and particularly preferably 1 mol% or less, and it is most desirable that no branched polyol is included.

Polycarbonate polyols are obtained by polycondensing the above-mentioned PC-polyol compounds with carbonate compounds using conventional methods.

The polycarbonate polyols that can be used for the isocyanurate skeleton-containing polyols are the same as the polycarbonate polyols that can be used for the isocyanate group-terminated prepolymers.

It is preferable that the number average molecular weight (n-NU) of the polycarbonate polyol used in the isocyanurate skeleton-containing polyol is smaller than the number average molecular weight (n-PP) of the polycarbonate polyol that can be used in the isocyanate group-terminated prepolymer. Furthermore, it is even more preferable that n-NU/n-PP = 500/3,000 to 1,000/1,500. When the molecular weight of the polycarbonate polyol that can be used in the isocyanate group-terminated prepolymer is higher than that of the polycarbonate polyol used in the isocyanurate skeleton-containing polyol, the advantages of superior mechanical strength and flexibility tend to be obtained.

The structural units derived from the isocyanurate skeleton-containing polyol in the present invention are formed by reacting the above-mentioned isocyanurate-type polyisocyanate compound with a polyol compound (NU-high molecular weight polyol).

3. Structure of Polyurethane Resin The polyurethane resin of the present invention contains at least a structural unit derived from the isocyanate group-terminated prepolymer and a structural unit derived from an isocyanurate skeleton-containing polyol. The isocyanurate skeleton-containing polyol contains a structural unit derived from an isocyanurate-type polyisocyanate compound (isocyanurate unit) and a structural unit derived from a NU-high molecular weight polyol (NU-polyol unit).

The polyurethane resin of the present invention is thought to have a high-molecular-weight three-dimensional structure in which relatively linear, high-molecular-weight urethane chains called isocyanate-terminated prepolymers and isocyanurate rings are linked by NU-polyol units. The length of the prepolymer maintains the spacing between the isocyanurate rings, preventing them from becoming too dense, which is thought to enable the resin to maintain flexibility and strength (toughness such as tensile strength) even at low temperatures.

In addition to connecting isocyanate-terminated prepolymers and isocyanurate rings, NU-high molecular weight polyols can also connect isocyanate-terminated prepolymers together or isocyanurate-type polyisocyanates together.

In the structure of the polyurethane resin, the constituent units derived from the isocyanate group-terminated prepolymer are contained in an amount of preferably 40 to 90% by mass, more preferably 50 to 85% by mass.
In the structure of the polyurethane resin, the constituent unit (isocyanurate unit) derived from the isocyanurate type polyisocyanate compound is contained in an amount of preferably 1 to 20% by mass, more preferably 1.5 to 15% by mass.

The polyurethane resin of the present invention has an isocyanurate skeleton within its structure, forming three-dimensional crosslinks. There are no particular restrictions on the final molecular weight range, but it is preferable that the thermal softening point, measured by dynamic viscoelasticity measurement (DMA measurement), be 160°C or higher, and more preferably 180°C or higher.

In the polyurethane resin structure, polyol-derived structural units include structural units derived from the high-molecular-weight polyol component that constitutes the isocyanate-terminated prepolymer (PP-high-molecular-weight polyol unit) and polyol-derived structural units that constitute the isocyanurate skeleton-containing polyol (NU-polyol unit).

Furthermore, the PP-high molecular weight polyol units and NU-polyol units each contain low molecular weight aliphatic polyol units that constitute them. For example, if the PP-high molecular weight polyol and NU-high molecular weight polyol that respectively form the PP-high molecular weight polyol units and NU-polyol units are both polycarbonate polyols, each polycarbonate polyol contains constituent units derived from the aliphatic polyol (PC-polyol compound) that constitutes it.

In other words, the aliphatic polyol-derived structural units contained in the structure of the polyurethane resin of the present invention include both the aliphatic polyol-derived structural units that form PP-high molecular weight polyol and NU-high molecular weight polyol.

The aliphatic polyol (for example, the PC-polyol compound that forms it in the case of polycarbonate polyol) may be a short-chain aliphatic polyol having 7 or fewer carbon atoms, or a long-chain aliphatic polyol having 8 or more carbon atoms, but the polyurethane resin of the present invention contains in its structure at least structural units derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms. Preferably, structural units derived from a linear long-chain aliphatic polyol having 8 to 20 carbon atoms are included.

There are no particular restrictions on the content of structural units derived from long-chain aliphatic polyols having 8 to 20 carbon atoms, but the content of structural units derived from long-chain aliphatic polyols having 8 to 20 carbon atoms in the structure of the polyurethane resin of the present invention (the total amount of long-chain aliphatic polyols having 8 to 20 carbon atoms in the aliphatic polyols that constitute the PP-high molecular weight polyol and the NU-high molecular weight polyol) is preferably 10% by mass or more, more preferably 15% by mass or more, and especially preferably 20% by mass or more. There are no particular restrictions on the upper limit, but it is preferably 50% by mass or less, more preferably 40% by mass or less, and especially preferably 30% by mass or less.

In this case, the constituent unit derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms is typically a unit formed from the long-chain aliphatic polyol and a carbonate compound, which corresponds to one unit constituting a polycarbonate polyol, and this unit is primarily used as the basis for calculating the mass.

Among the polyol-derived structural units constituting the polyurethane resin of the present invention, the content of structural units derived from long-chain aliphatic polyols having 8 to 20 carbon atoms relative to the total amount of structural units derived from low-molecular-weight aliphatic polyols is preferably 5 mol% or more, more preferably 10 mol% or more, and particularly preferably 20 mol% or more. There is no particular upper limit, but it is preferably 60 mol% or less, more preferably 50 mol% or less, and particularly preferably 40 mol% or less. If the content of long-chain aliphatic polyol is too low, the strength in low-temperature environments may be insufficient.

The proportion of structural units derived from isocyanurate-type polyisocyanate compounds in the polyurethane resin structure is not particularly limited, but is preferably 1% by mass or more, more preferably 1.5% by mass or more, and especially preferably 2% by mass or more. There is no particular upper limit, but it is preferably 20% by mass or less, more preferably 15% by mass or less, and especially preferably 10% by mass or less.

In the polyurethane resin structure, the content of constituent components derived from isocyanurate polyisocyanates relative to the total amount of constituent units derived from isocyanate compounds is not particularly limited, but is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and particularly preferably 30 to 50% by mass.

The polyurethane resin of the present invention preferably has a glass transition temperature of -20°C or lower, more preferably -25°C or lower, and even more preferably -30°C or lower. This can sometimes provide the advantage of excellent flexibility at low temperatures.

The polyurethane resin of the present invention possesses high flame retardancy in itself, and also possesses excellent flexibility and strength (flexural resistance and tensile strength) in low-temperature environments. Because the polyurethane resin itself is flame retardant, it is possible to obtain a flame-retardant polyurethane resin composition with a low flame retardant content.

4. Method for Producing Polyurethane Resin The polyurethane resin of the present invention is a reaction product obtained by reacting raw material components including an isocyanate-terminated prepolymer, an isocyanurate-type polyisocyanate compound, and a polyol component (NU-high molecular weight polyol). Therefore, it can be produced by a method including a step of reacting these raw material components. Specifically, it can be obtained by subjecting these raw material components to treatments such as heating, drying, and curing.

The isocyanate-terminated prepolymer is obtained by blending the above-mentioned prepolymer isocyanate compound and PP-polyol compound in a specified ratio and carrying out a prepolymerization reaction. The blending ratio in the prepolymerization reaction is adjusted so that the equivalent ratio (first equivalent ratio, NCO/OH) of the isocyanate groups of the isocyanate component to the hydroxyl groups of the PP-polyol component falls within a specified range.

More specifically, the equivalent ratio (NCO/OH) of the isocyanate groups of the isocyanate compound to the hydroxyl groups of the PP-polyol component is preferably 1.1 or greater, more preferably 1.2 or greater, and particularly preferably 1.5 or greater. There is no upper limit to this equivalent ratio (NCO/OH), but it is preferably 5.0 or less, more preferably 4.0 or less, and particularly preferably 3.0 or less.

The reaction conditions for the prepolymerization reaction are not particularly limited and may be set appropriately. Specifically, the reaction can be carried out by bulk polymerization or solution polymerization under an inert gas atmosphere and normal (atmospheric) pressure, at a reaction temperature of, for example, 20°C or higher, preferably 50°C or higher, more preferably 70°C or higher, and 150°C or lower, preferably 120°C or lower, and more preferably 100°C or lower, for a reaction time of, for example, 30 minutes or longer, preferably 1 hour or longer, and 12 hours or shorter, preferably 6 hours or shorter.

In the prepolymerization reaction, known organic solvents, prepolymerization catalysts, known additives, etc. can be added as needed. Examples of additives include antioxidants, heat stabilizers, light stabilizers, and co-catalysts. These can be used alone or in combination of two or more. This results in an isocyanate-terminated prepolymer as the reaction product of the prepolymerization reaction.

Isocyanurate-type polyisocyanate compounds can be obtained by subjecting diisocyanate to an isocyanuration reaction in the presence of an isocyanuration catalyst. Examples of isocyanuration catalysts include trimerization catalysts that react and trimerize the isocyanate groups contained in diisocyanate, promoting the formation of isocyanurate rings.

Examples of isocyanurate catalysts that can be used include nitrogen-containing aromatic compounds such as tris(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol, and 2,4,6-tris(dialkylaminoalkyl)hexahydro-S-triazine; alkali metal salts of carboxylic acids such as potassium acetate, potassium 2-ethylhexanoate, and potassium octoate; tertiary ammonium salts such as trimethylammonium salt, triethylammonium salt, and triphenylammonium salt; and quaternary ammonium salts such as tetramethylammonium salt, tetraethylammonium, and tetraphenylammonium salt. These can be used alone or in combination of two or more.

The amount of isocyanurate catalyst added is preferably in the range of 0.001 to 0.1 parts by mass per 100 parts by mass of diisocyanate, and most preferably in the range of 0.005 to 0.05 parts by mass.

The isocyanate-terminated prepolymer obtained by the above method, an isocyanurate-type polyisocyanate compound, and an NU-polyol are reacted using a conventional polyurethane production method to obtain a polyurethane resin.

By producing polyurethane resin using a pre-prepared isocyanate-terminated prepolymer, the spacing between isocyanurate rings is maintained by the isocyanate-terminated prepolymer structural units, which have a specified molecular weight, preventing the resin from becoming too dense, which is thought to enable the resin to maintain flexibility and strength (toughness such as tensile strength) even at low temperatures.

The content of isocyanate-terminated prepolymer in the raw material components used to produce polyurethane resin is preferably 40 to 90% by mass, more preferably 50 to 85% by mass, and particularly preferably 60 to 80% by mass.

Among the raw materials used to produce polyurethane resins, the content of isocyanurate-type polyisocyanate compounds is preferably 1 to 20% by mass, more preferably 1.5 to 15% by mass, and particularly preferably 2 to 10% by mass.

The content of NU-high molecular weight polyol in the raw material components used to produce polyurethane resin is preferably 10 to 60% by mass, more preferably 15 to 50% by mass, and particularly preferably 20 to 40% by mass.

The content of isocyanurate-type polyisocyanate compounds relative to the total amount of isocyanate compounds in the raw material components used to produce polyurethane resin is not particularly limited, but is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and particularly preferably 30 to 50% by mass. The total amount of isocyanate compounds refers to the sum of isocyanate compounds for the isocyanate-terminated prepolymer and isocyanurate-type polyisocyanate compounds.

Low molecular weight aliphatic polyols used in the production of polyurethane resins include the aliphatic polyols used to form PP-high molecular weight polyols and NU-high molecular weight polyols. The content of long-chain aliphatic polyols having 8 to 20 carbon atoms in the raw material components used to produce polyurethane resins is preferably 10% by mass or more, more preferably 15% by mass or more, and particularly preferably 20% by mass or more. There is no particular upper limit, but it is preferably 50% by mass or less, more preferably 40% by mass or less, and particularly preferably 30% by mass or less.

The content ratio of this long-chain aliphatic polyol having 8 to 20 carbon atoms is calculated based on one unit formed by the long-chain aliphatic polyol and a carbonate compound when polycarbonate polyol is used as the PP-high molecular weight polyol and NU-high molecular weight polyol.

Furthermore, the content of the long-chain aliphatic polyol having 8 to 20 carbon atoms relative to the total amount of the aliphatic polyol is preferably 5 mol% or more, more preferably 10 mol% or more, and particularly preferably 20 mol% or more. There is no particular upper limit, but it is preferably 60 mol% or less, more preferably 50 mol% or less, and particularly preferably 40 mol% or less. If the amount of long-chain aliphatic polyol used is too small, the strength may be insufficient in low-temperature environments.

II. Flame-Retardant Polyurethane Resin Composition The flame-retardant polyurethane resin composition of the present invention contains a reaction product of polyurethane resin raw material components including the above-described isocyanate-terminated prepolymer, an isocyanurate-type polyisocyanate compound, and a NU-high molecular weight polyol, and optionally a flame retardant.

(1) Other Raw Material Components In addition to the raw material components of the polyurethane resin described above, the flame-retardant polyurethane resin composition of the present invention may further contain, as necessary, a crosslinking agent, a chain extender, a curing accelerator (catalyst component), an organic solvent, etc. It may also contain a foaming agent, an antifoaming agent, a thickener, a surface conditioner, a surfactant, a filler, a weather resistance improver, an ultraviolet absorber, water, a dispersant, a color pigment, a pH adjuster, etc.

The chain extender is not particularly limited, but generally a relatively low molecular weight diol is used. Examples include petroleum-derived diols such as ethylene glycol, diethylene glycol, propanediol, butanediol, hexanediol, and PEG, as well as plant-derived diols such as 1,3-propanediol and 1,2-hexanediol. These diols may be used alone, or two or more may be used in combination as needed. Diamines and the like can also be used as needed. There are no particular restrictions on the amount of chain extender used, but it is generally about 1 to 5 parts by mass per 100 parts by mass of the flame-retardant polyurethane resin composition of the present invention.

A curing accelerator (catalyst component) can also be used. Specific examples include metal catalysts such as titanium diisopropoxybis(ethylacetoacetate), amine catalysts, and DBU catalysts. There are no particular restrictions on the amount of curing accelerator used, but it is generally about 0.01 to 1 part by mass per 100 parts by mass of the flame-retardant polyurethane resin composition of the present invention.

The organic solvent is not particularly limited, but examples include polar solvents that are inactive to isocyanate groups, such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), as well as organic solvents such as methyl ethyl ketone (MEK), toluene, and xylene.

(2) Flame Retardant Examples of flame retardants that may be contained in the flame-retardant polyurethane resin composition of the present invention include known flame retardants. For example, organic phosphorus compounds include phosphate esters and their salts, phosphite esters and their salts, phosphonic acid and its derivatives (including salts), phosphinic acid and its derivatives (including salts), phosphine, phosphine oxide, biphosphine, phosphonium salts, and phosphazene. Examples of inorganic phosphorus compounds include phosphates, such as ammonium polyphosphate. In addition to the above compounds, simple red phosphorus may also be used.

Examples of flame retardants other than phosphorus compounds include melamine compounds such as melamine cyanurate and melamine, metal hydrates such as aluminum hydroxide and magnesium hydroxide, and antimony compounds such as antimony trioxide and antimony pentoxide.
Among these, phosphinates are preferred because they have good flame retardancy and have little effect on physical properties.

The content of the flame retardant is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 12.5% by mass or less, and particularly preferably 10% by mass or less, based on the total amount of the flame-retardant polyurethane resin composition of the present invention. There is no particular lower limit, and it is not necessary to add a flame retardant. The content is preferably 0% by mass or more, more preferably 2.5% by mass or more, and particularly preferably 5% by mass or more.

(3) Other Additives Additives such as foaming agents, antifoaming agents, thickeners, surface conditioners, surfactants, fillers, weather resistance improvers, ultraviolet absorbers, organic solvents, water, dispersants, color pigments, and pH adjusters may be blended into the flame-retardant polyurethane resin composition of the present invention, as needed, within limits that do not impair the physical properties of the polyurethane resin obtained by curing.

In addition, optional components such as urethanization catalysts, silane coupling agents, thixotropy-imparting agents, tackifiers, waxes, heat stabilizers, light resistance stabilizers, fluorescent brighteners, thermoplastic resins, thermosetting resins, dyes, pigments, conductivity-imparting agents, antistatic agents, moisture permeability improvers, water repellents, oil repellents, hollow foams, compounds containing crystal water, water absorbing agents, moisture absorbing agents, deodorizing agents, foam stabilizers, antifungal agents, preservatives, anti-algae agents, pigment dispersants, inert gases, antiblocking agents, and hydrolysis inhibitors may also be used as needed.
These additives can be used alone or in combination of two or more.

(4) Method for Producing Flame-Retardant Polyurethane Resin Composition The flame-retardant polyurethane resin composition of the present invention is obtained by mixing polyurethane resin raw material components including the above-mentioned isocyanate group-terminated prepolymer, isocyanurate-type polyisocyanate compound, and NU-high molecular weight polyol, as well as other raw material components used as needed, with other additives such as a flame retardant used as needed, to obtain a flame-retardant polyurethane resin blend, which is then molded as needed and then heat-cured.

The content of isocyanate-terminated prepolymer per 100 parts by mass of the flame-retardant polyurethane resin formulation is 40 to 90% by mass, more preferably 50 to 85% by mass, and particularly preferably 60 to 80% by mass.

The content of the isocyanurate-type polyisocyanate compound per 100 parts by mass of the flame-retardant polyurethane resin formulation is preferably 1 to 20% by mass, more preferably 1.5 to 15% by mass, and particularly preferably 2 to 10% by mass.

The content of NU-high molecular weight polyol per 100 parts by mass of the flame-retardant polyurethane resin formulation is preferably 10 to 60% by mass, more preferably 15 to 50% by mass, and particularly preferably 20 to 40% by mass.

The heat curing conditions are preferably a temperature of 80 to 140° C. and a time of 1 to 10 minutes.
If necessary, a step of drying and removing liquid components such as organic solvents may also be included. For example, polyurethane resin raw material components, flame retardants, and other additives may be blended, followed by molding, drying, and heat curing. Drying and heat curing may be performed in a single step or separately.

For example, as described below, when forming a layer made of a flame-retardant polyurethane resin composition on a support (such as a base fabric) of the synthetic leather of the present invention, the flame-retardant polyurethane resin blend can be applied to the support, followed by treatments such as drying and heat curing.

Alternatively, it can be obtained by pre-reacting some or all of the above raw material components, preferably in the presence of a chain extender, and then mixing in a flame retardant and other additives. An organic solvent can also be added when pre-reacting some or all of the above raw material components before mixing in the flame retardant and other additives.

When applying a flame-retardant polyurethane resin formulation to a substrate, it is preferable to adjust the formulation so that it has a viscosity that allows application without the addition of a solvent. However, if necessary, it is not excluded to add an organic solvent to achieve a viscosity suitable for application.

III. Synthetic Leather The synthetic leather of the present invention comprises at least a support (base fabric) and a surface layer. The synthetic leather of the present invention has excellent flexibility and flame retardancy, and does not suffer from bleeding problems. Therefore, the synthetic leather or artificial leather that combines flexibility and flame retardancy can be suitably used as a material for automobile seats, etc.

(1) Support The support (base fabric) used in the synthetic leather of the present invention can be any conventionally known synthetic leather substrate, and is not particularly limited. Examples include fibrous fabrics such as woven or knitted fabrics made of twill or plain weave, raised fabrics obtained by mechanically raising the cotton fabric of such woven fabrics, rayon fabric, nylon fabric, polyester fabric, Kevlar fabric ("Kevlar" is a registered trademark), nonwoven fabrics (polyester, nylon, various latexes, etc.), various synthetic resin films and sheets, natural leather, etc. These may be selected appropriately depending on the purpose. Preferred examples include fibrous fabrics such as woven fabrics, knitted fabrics, and nonwoven fabrics.

The thickness of the support can be set appropriately taking into consideration the material, structure, texture of the resulting synthetic leather, and intended use, but is preferably 100 to 2,000 μm, and particularly preferably 200 to 1,000 μm.

(2) Surface Layer The synthetic leather of the present invention has a surface layer containing the flame-retardant polyurethane resin composition on at least one surface of a support. The surface layer may be either a porous layer or a non-porous layer.

The thickness of the skin layer can be set appropriately taking into consideration the texture and intended use of the resulting synthetic leather, the material and shape of the support, etc., but is preferably between 5 and 300 μm.

In the present invention, the surface layer may be colored, gloss adjusted, or textured with an uneven pattern, for the purpose of improving the surface strength and design of the synthetic leather. Furthermore, the synthetic leather may be composed of two or more layers, if necessary. When the synthetic leather is composed of two or more layers, examples of layers other than the layer made of the flame-retardant polyurethane resin composition of the present invention include a heat-insulating layer and a foam layer.

(3) Method for Producing Synthetic Leather The synthetic leather of the present invention is produced by a method including the steps of laminating the above-mentioned compound for a flame-retardant polyurethane resin on a support and heat-treating it to form a surface layer.

The skin layer can be formed, for example, by applying a flame-retardant polyurethane resin formulation capable of forming the flame-retardant polyurethane resin composition to at least one surface of a support using a coating method. Examples of coating methods include using a knife coater, comma coater, roll coater, die coater, or lip coater to coat the flame-retardant polyurethane resin formulation directly onto the fabric. There are no particular restrictions on the thickness of the polyurethane resin formulation, but it is preferably 5 to 300 μm.

It is preferable to adjust the formulation of the polyurethane resin compound so that it has a viscosity that allows it to be applied without the addition of a solvent, but if necessary to adjust the viscosity, a solvent can be added. Examples of solvents include well-known organic solvents such as DMF, DMSO, MEK, toluene, and xylene. In this case, it is preferable to use a solution in which the solids concentration is approximately 60 to 100% by mass.

After the coating process, the formed coating layer is dried and heat-treated, and the flame-retardant polyurethane resin compound is heat-cured to form a layer made of a flame-retardant polyurethane resin composition. Drying and heat-curing can be performed in one step or in separate steps. For example, after forming the coating layer, it is preferable to perform treatment at a temperature of 80 to 140°C for 1 to 10 minutes.

It can also be produced by a dipping method in which a support is impregnated with the polyurethane resin compound.

Furthermore, it can also be manufactured by a lamination method in which a separately formed surface layer is laminated to a support. For example, a surface layer is formed by coating the polyurethane resin formulation on a releasable substrate, and the surface layer is then laminated to the support, after which the releasable substrate is peeled off.

Methods of lamination include using an adhesive, or laminating the flame-retardant polyurethane resin formulation of the present invention to a support in a semi-cured, adhesive state by heating, and then heating the flame-retardant polyurethane resin formulation again to fully cure it.

Coating methods include known methods such as comma coating, knife coating, roll coating, gravure coating, die coating, and spray coating. After the film is formed, it is dried appropriately to form a skin layer. Fabric is either directly pressed onto this skin layer, or an adhesive is applied using a known method, and then the skin layer is applied and pressed onto the support. The resulting layer is then heat-cured (by drying or heating) and peeled off from the releasable substrate to obtain synthetic leather.

Preferred conditions for compression bonding are a temperature of 20 to 140°C, a pressure of 0.1 to 10 MPa, and a time of 0.0005 to 3 minutes. Preferred conditions for heat treatment are a temperature of 80 to 140°C and a time of 1 to 10 minutes.

When the surface layer is bonded to the support via an adhesive, examples of adhesives that can be used include the flame-retardant polyurethane resin composition described above, as well as conventional adhesives such as polyurethane resins made from petroleum-based raw materials, acrylic resins, and epoxy resins. The adhesive may be applied to either the surface layer side or the support side.

The releasable substrate is not particularly limited, and examples include a film made of a resin (such as an olefin resin or silicone resin; hereinafter referred to as a release agent) that has releasability against polyurethane resin, and release paper, release cloth, or release film in which a release layer made of a release agent is laminated onto a substrate such as paper, fabric, or film.

The release substrate may have an uneven pattern. By using such a release substrate, a resin film having an uneven pattern on its surface can be formed, preventing blocking between film surfaces and producing synthetic leather that feels good to the touch.

Among the methods mentioned above, the lamination method is preferred in terms of the physical properties and texture of the resulting synthetic leather. However, the present invention is not limited to these methods.

The synthetic leather of the present invention as described above is suitable for shoes, clothing, bags, furniture, vehicle interior materials (e.g., instrument panels, doors, consoles, seats), etc.

The synthetic leather obtained in this manner can be further subjected to post-processing such as surface treatment and kneading, as needed. Furthermore, in addition to the support and surface layer described above, an adhesive layer and a surface protective layer can also be provided. The adhesive layer is provided between the support and the surface layer, for example. The surface protective layer can be provided on the outside of the surface layer. Examples of surface protective layers include layers formed from known polyurethane resins.

For example, a polyurethane resin that will form the surface protective layer (outermost layer) is applied to a releasable substrate and dried, and then the flame-retardant polyurethane resin formulation of the present invention is applied on top of that. It is then semi-cured by heating until it becomes tacky, and the layer made of the flame-retardant polyurethane resin formulation is then laminated to the substrate. The flame-retardant polyurethane resin formulation layer is then heat-treated for full curing, resulting in a synthetic leather that has a surface protective layer as the outermost layer in addition to the substrate and skin layer.

The physical properties of the coating that forms the surface layer made of the flame-retardant polyurethane resin composition preferably satisfy a 100% modulus of 0.4 MPa to 2.0 MPa, a strength at break of 2.0 to 6.0 MPa, and an elongation at break of 150 to 500%. Furthermore, the flame retardancy measured in accordance with the test method of the U.S. automobile safety standard FMVSS 302 preferably has a maximum burning rate of 80 mm/min or less.
By providing a surface layer whose film properties satisfy the above ranges, it is possible to obtain synthetic leather that has good mechanical strength, texture (flexibility), and high flame retardancy.

The flame retardancy of synthetic leather formed from a surface layer made of the flame-retardant polyurethane resin composition and a support is preferably such that the maximum burning rate is 80 mm/min or less, as measured in accordance with the test method of the US automobile safety standard FMVSS 302. Synthetic leather whose various physical properties satisfy the above ranges has high flame retardancy and also has good mechanical strength and texture (flexibility).

The present invention will be explained below using examples, but the present invention is not limited in any way by these examples. Evaluations in the examples were carried out according to the following methods. Note that the amounts used in the following examples, including those shown in Tables 1 and 2, are in parts by mass unless otherwise specified.

[Flame retardancy]
Evaluation was performed in accordance with the test method of the US automobile safety standard FMVSS 302. A test piece (synthetic leather; thickness: 1,000 μm) cut to a width of 100 mm and a length of 350 mm was ignited by applying a flame from a gas burner to the edge of the piece for 15 seconds, and the distance and time from when the ignited flame crossed a marked line 38 mm from the edge until it went out were measured. The burning rate was calculated and evaluated according to the following criteria.

◯: The test piece did not ignite, or the ignited flame was extinguished before the marked line, or the maximum burning rate was less than 50 mm/min. △: The maximum burning rate was between 50 mm/min and 80 mm/min. ×: The maximum burning rate was more than 80 mm/min.

[Glass transition temperature]
The glass transition temperature was evaluated by DMA measurement of the polyurethane. Specifically, a measurement sample (test piece) measuring 200 mm x 5 mm x 0.15 mm thick was first prepared. Next, using a dynamic viscoelasticity measuring device (manufactured by UBM Co., Ltd., product name "Rheogel E-4000"), the peak temperature (glass transition temperature) of the loss modulus (E") was determined under conditions of -100°C to 200°C, a heating rate of 3°C/min, and a frequency of 10 Hz. The results are shown in Table 2.

[Cold resistance]
The resulting synthetic leather was subjected to a bending test (-30°C, 100 bendings per minute) using a flexometer ("Flexometer with Low-Temperature Bath," manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in which the leather was bent 10,000 times. N=2 measurements were taken for each sample, and the occurrence of cracks on the surface of the synthetic leather was observed and evaluated as follows.
◯: No cracks occurred on the surface of either of the two. △: Cracks occurred on the surface of only one of the two. ×: Cracks occurred on the surface of both of the two.

<Synthesis Example 1; PP-1 to 3>
Isocyanate group-terminated prepolymers (PP-1, PP-2, PP-3) were each produced as follows.
A four-necked flask equipped with a thermometer, a stirrer, an inert gas inlet, and a reflux condenser was purged with nitrogen gas, and then polyol 1 and/or polyol 2 were added in the proportions (parts by mass) shown in Table 1.

Next, the flask was heated to 60°C and Polyol 1 and/or Polyol 2 were thoroughly mixed, after which Isocyanate 1 was added in the proportion (parts by mass) shown in Table 1. The mixture was allowed to react at 80°C for approximately 4 hours under a nitrogen atmosphere until the isocyanate group content (NCO%) reached a constant level, yielding isocyanate-terminated prepolymers (PP-1 to PP-3). The NCO% and NCO/OH of the resulting prepolymers are shown in Table 1.

The polyol 1, polyol 2 and isocyanate 1 used were as follows:
[Polyol 1]
Polycarbonate polyol (product name "NL2030DS", number average molecular weight: 2,000, manufactured by Mitsubishi Chemical Corporation) with a 1,10-decanediol:1,4-butanediol ratio of 3:7
[Polyol 2]
Polycarbonate polyol of 1,6-hexanediol (product name "UH-200", number average molecular weight: 2,000, manufactured by UBE Corporation)
[Isocyanate 1]
1,5-Pentamethylene diisocyanate (product name "Stabio PDI", NCO%=54.5%, manufactured by Mitsui Chemicals, Inc.)

<Examples 1 to 6, Comparative Examples 1 to 3>
(Synthetic leather production)
A mixture of 100 parts of an aqueous urethane resin (trade name "Hydran WLS286BP" manufactured by DIC Corporation), 20 parts of a black pigment (trade name "P39-611 Black" manufactured by Stahl), and 4 parts of a carbodiimide crosslinking agent (trade name "CL-7070" manufactured by Seiko Chemicals Corporation) was applied to a textured release paper (trade name "R-86M" manufactured by Lintec Corporation) and dried to form a surface protection layer with a thickness of 40 μm.

A polyurethane surface layer was formed on the formed surface protection layer using the components shown in Table 2 in the amounts shown in Table 2. Specifically, the components were thoroughly mixed until uniform, and then applied to the surface protection layer with an applicator to a wet film thickness of 200 μm.

Then, a polyester tricot fabric (support; thickness 800 μm) was placed on top of the polyurethane surface layer obtained after curing in a dryer at 100°C for 1.5 minutes, and after curing in a dryer at 130°C for 10 minutes, the release paper was peeled off to obtain the synthetic leather of the present invention (thickness 1,000 μm).

Table 2 shows the evaluation results for the above examples and comparative examples. Note that the numerical values for components in the table represent parts by mass.

The materials used in Tables 1 to 3 are as follows:
(1) Polyol 1
Polycarbonate polyol (product name "NL2030DS", number average molecular weight: 2,000, manufactured by Mitsubishi Chemical Corporation) with a 1,10-decanediol:1,4-butanediol ratio of 3:7
(2) Polyol 2
Polycarbonate polyol of 1,6-hexanediol (product name "UH-200", number average molecular weight: 2,000, manufactured by UBE Corporation)
(3) Polyol 3
Polycarbonate polyol (product name "NL1030DS", number average molecular weight: 1,000, manufactured by Mitsubishi Chemical Corporation) with a 1,10-decanediol:1,4-butanediol ratio of 3:7 (4) Polyol 4
Polycarbonate polyol of 1,3-propanediol (number average molecular weight: 1,000, manufactured by Toyokuni Oil Mills Co., Ltd.)
(5) Isocyanate 1
1,5-Pentamethylene diisocyanate (product name "Stabio PDI", NCO%=54.5%, manufactured by Mitsui Chemicals, Inc.)
(6) Isocyanate 2 (isocyanurate-type polyisocyanate compound)
Isocyanurate-modified 1,5-pentamethylene diisocyanate (product name "STABIO D-370N", NCO%=25.0%, manufactured by Mitsui Chemicals, Inc.)

The polyurethane resin of the present invention contains structural units derived from specific polyol compounds and polyisocyanate compounds in its structure, and has excellent flame retardancy while maintaining high flexibility and strength, including flexural resistance and tensile strength, even in low-temperature environments. Furthermore, not only can the flame retardant content be kept low, but in some cases high flame retardancy is achieved without the use of flame retardants, eliminating bleeding problems. Furthermore, by using plant-derived polyisocyanate and polyol components as raw material components, an environmentally friendly polyurethane resin material with a high biomass ratio can be obtained.

Therefore, a flame-retardant polyurethane resin composition suitable for synthetic leather, artificial leather, etc., which require strength and flame retardancy in low-temperature environments, can be obtained, and the composition can be used in various fields such as clothing, bags, shoes, vehicle interior materials, etc. In particular, the composition can be suitably used for vehicle interior materials, including automobile seats, ceiling materials, dashboards, door linings, and steering wheels.

Claims (15)

A polyurethane resin containing at least structural units derived from an isocyanate-terminated prepolymer formed from an isocyanate component and a high-molecular-weight polyol component with a number-average molecular weight of 500 or more, and structural units derived from an isocyanurate skeleton-containing polyol, and containing structural units derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms within its structure. The polyurethane resin according to claim 1, wherein the isocyanate group content of the structural units derived from the isocyanate group-terminated prepolymer is 1 to 9%. The polyurethane resin according to claim 1, wherein the high-molecular-weight polyol component forming the structural units derived from the isocyanate-terminated prepolymer is a structural unit derived from a polycarbonate polyol having a number-average molecular weight of 500 to 4,000. The polyurethane resin according to claim 1, wherein the content of structural units derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms in the polyurethane resin structure is 10% by mass or more. The polyurethane resin according to claim 1, wherein the content of structural units derived from a long-chain aliphatic polyol having 8 to 20 carbon atoms is 10 mol % or more of the total amount of structural units derived from aliphatic polyols contained in the polyurethane resin structure. The polyurethane resin according to claim 1, wherein the long-chain aliphatic polyol having 8 to 20 carbon atoms is a linear long-chain aliphatic polyol having 8 to 20 carbon atoms. The polyurethane resin according to claim 1, wherein the long-chain aliphatic polyol having 8 to 20 carbon atoms accounts for 10 mol% or more of the total amount of aliphatic polyols constituting the high-molecular-weight polyol component that forms the structural units derived from the isocyanate-terminated prepolymer. The polyurethane resin according to claim 1, wherein the proportion of structural units derived from isocyanurate-type polyisocyanate compounds in the polyurethane resin structure is 1 to 15 mass%. The polyurethane resin according to claim 1, wherein the isocyanate component constituting the isocyanate group-terminated prepolymer contains structural units derived from 1,5-pentamethylene diisocyanate. The polyurethane resin according to claim 1, wherein the structural units derived from the isocyanurate skeleton-containing polyol include structural units derived from an isocyanurate-type polyisocyanate compound derived from 1,5-pentamethylene diisocyanate. The polyurethane resin according to claim 1, wherein the long-chain aliphatic polyol having 8 to 20 carbon atoms includes a plant-derived polyol compound. A flame-retardant polyurethane resin composition comprising the polyurethane resin described in any one of claims 1 to 11 and having a glass transition temperature of -30°C or lower. The flame-retardant polyurethane resin composition according to claim 12, containing 0 to 20 mass% of a flame retardant. Synthetic leather comprising a support and a surface layer, wherein at least the surface layer is composed of the flame-retardant polyurethane resin composition described in claim 12. The synthetic leather according to claim 14, which is an interior material for a vehicle.