Synthetic leather and vehicle interior material

Abstract

Provided is easily recyclable synthetic leather having excellent durability and bendability.　This synthetic leather has an adhesive layer between a base material layer and a skin layer, wherein: the base material layer, the skin layer, and the adhesive layer each contain a polyester-based resin; and the polyester-based resin forming the adhesive layer has a glass transition temperature (Tg) of -20°C or lower. This synthetic leather has an adhesive layer between a base material layer and a skin layer, wherein: the base material layer, the skin layer, and the adhesive layer each contain a polyester-based resin; the polyester-based resin forming the skin layer has a glass transition temperature (Tg) of -10°C or lower; and the number of flex cycles exhibited by the synthetic leather at -20°C exceeds 6000.

Description

Synthetic leather and vehicle interior materials

[0001] This disclosure relates to synthetic leather with excellent recyclability, durability, and flexibility, and to vehicle interior materials containing said synthetic leather.

[0002] Synthetic leather has long been widely used in automotive applications, such as for interior materials like car headliners, door trims, instrument panels, and car seat upholstery. Historically, PVC leather was commonly used as a synthetic leather due to its superior leather-like appearance, price, abrasion resistance, and moldability. However, because PVC leather is composed of polyvinyl chloride, there are concerns about dioxin generation during incineration after disposal, and its use is being restricted. As an alternative to PVC leather, various synthetic leathers have been developed, such as those made by impregnating or laminating polyurethane resin onto a fibrous base material. The synthetic leathers described in Patent Documents 1 to 3 are known examples of synthetic leather made by impregnating or laminating polyurethane resin onto a fibrous base material.

[0003] Patent Document 1 describes synthetic leather that has high flame retardancy due to the inclusion of a flame retardant in the adhesive layer. In this synthetic leather, a surface layer containing polyurethane is formed on a polyester tricot knitted fabric used as a base layer via a polyurethane adhesive. Patent Document 2 describes a surface material that has high moisture permeability and breathability and excellent appearance by providing the surface material with multiple ventilation holes that penetrate in the thickness direction. In this surface material, a surface layer containing polyurethane is formed on a base fabric containing polyester fibers via an adhesive layer containing polyurethane. Patent Document 3 describes synthetic leather having a layer made of synthetic resin and a fibrous fabric base material. This synthetic leather maintains mechanical strength despite the high concentration of additives that are solid at room temperature in the layer made of synthetic resin. An example in Patent Document 3 describes synthetic leather in which a surface layer containing polycarbonate polyurethane resin, a reinforcing layer containing polycarbonate polyurethane resin, an adhesive layer containing polycarbonate polyurethane resin, and a polyester fabric (base material) are laminated together.

[0004] Furthermore, Patent Documents 4 to 6 describe artificial leather that includes at least a surface fiber layer constituting a first surface. This surface fiber layer includes at least one type of main fiber and a thermoplastic resin.

[0005] Japanese Patent Publication No. 5731086, Japanese Unexamined Patent Publication No. 2016-129994, Japanese Unexamined Patent Publication No. 2022-72684, Japanese Unexamined Patent Publication No. 2022-179173, Japanese Unexamined Patent Publication No. 2022-179174, Japanese Unexamined Patent Publication No. 2022-179195

[0006] The synthetic leathers described in Patent Documents 1 to 3 use nonwoven or woven fabrics made of polyester resins such as polyethylene terephthalate for the base layer, but the surface layer uses polyurethane resin, polyamide resin, polyacrylate resin, vinyl acetate resin, polyacrylonitrile resin, etc., either alone or in combination of two or more, and a polyurethane adhesive is used as the adhesive layer to bond the surface layer and the base layer. However, because a variety of resins are used, the materials are usually incinerated after use, and it is currently difficult to recover and reuse them.

[0007] Incidentally, synthetic leather is required to have durability such as resistance to delamination between the base layer and the surface layer, and flexibility such as resistance to cracking even after repeated bending. However, no synthetic leather was known that was excellent in durability and flexibility, as well as recyclability.

[0008] The artificial leathers described in Patent Documents 4 to 6 had poor flexibility because the surface fiber layer contained the main fiber.

[0009] The problem addressed by this disclosure is to provide synthetic leather that is easily recyclable and also possesses excellent durability and flexibility.

[0010] The first synthetic leather and first vehicle interior material of this disclosure are as follows: [1-1] A synthetic leather having an adhesive layer between a base layer and a surface layer, wherein the base layer, the surface layer, and the adhesive layer all contain a polyester resin, and the polyester resin constituting the adhesive layer has a glass transition temperature (Tg) of -20°C or lower. [1-2] The synthetic leather according to [1-1], wherein the polyester resin constituting the surface layer has a glass transition temperature (Tg) of -10°C or lower. [1-3] The synthetic leather according to [1-1] or [1-2], wherein the polyester resin constituting the adhesive layer is amorphous. [1-4] The adhesive layer contains a flame retardant at a concentration of 16 g / m². ２ Synthetic leather as described in any of [1-1] to [1-3] below. [1-5] Synthetic leather as described in [1-4], wherein the amount of the flame retardant is 27 parts by mass or less per 100 parts by mass of the polyester resin constituting the adhesive layer. [1-6] Vehicle interior material containing the synthetic leather as described in any of [1-1] to [1-5].

[0011] The second synthetic leather and second vehicle interior material of this disclosure are as follows: [2-1] A synthetic leather having an adhesive layer between a base layer and a surface layer, wherein the base layer, the surface layer, and the adhesive layer all contain a polyester resin, the polyester resin constituting the surface layer has a glass transition temperature (Tg) of -10°C or lower, and the synthetic leather has more than 6,000 bending cycles at -20°C. [2-2] The adhesive layer contains 16 g / m of flame retardant. ２Synthetic leather as described in [2-1], which contains the following: [2-3] Synthetic leather as described in [2-2], wherein the amount of the flame retardant is 27 parts by mass or less per 100 parts by mass of the polyester resin constituting the adhesive layer. [2-4] Synthetic leather as described in any of [2-1] to [2-3], wherein the polyester resin constituting the surface layer has a glass transition temperature (Tg) of -30°C or lower. [2-5] Synthetic leather as described in any of [2-1] to [2-4], wherein the polyester resin constituting the adhesive layer is amorphous. [2-6] Synthetic leather as described in any of [2-1] to [2-5], wherein the polyester resin constituting the adhesive layer has a glass transition temperature (Tg) of -5°C or lower. [2-7] Synthetic leather as described in any of [2-1] to [2-6], wherein the polyester resin constituting the adhesive layer has a glass transition temperature (Tg) of -20°C or lower. [2-8] Vehicle interior material containing synthetic leather as described in any of [2-1] to [2-7].

[0012] The first synthetic leather of this disclosure has an adhesive layer between a base layer and a surface layer, and the base layer, surface layer, and adhesive layer all contain a polyester resin. Because the base layer, adhesive layer, and surface layer are made of polyester resin, it has excellent recyclability. Furthermore, because the glass transition temperature (Tg) of the polyester resin constituting the adhesive layer is -20°C or lower, it has excellent durability and flexibility. The first synthetic leather can be suitably used as an interior material for vehicles.

[0013] The second synthetic leather of this disclosure has an adhesive layer between a base layer and a surface layer, and the base layer, surface layer, and adhesive layer all contain a polyester resin. Because the base layer, adhesive layer, and surface layer are made of polyester resin, it has excellent recyclability. Furthermore, the glass transition temperature (Tg) of the polyester resin constituting the surface layer is -10°C or lower, and the synthetic leather can withstand more than 6,000 flexures at -20°C, thus it has excellent durability and flexibility. The second synthetic leather can be suitably used as an interior material for vehicles.

[0014] The first and second embodiments of synthetic leather will be described in detail below.

[0015] In the embodiment, the first synthetic leather has an adhesive layer between the base layer and the surface layer. The base layer, surface layer, and adhesive layer all contain a polyester resin, and the polyester resin constituting the adhesive layer has a glass transition temperature (Tg) of -20°C or lower. In the embodiment, the second synthetic leather has an adhesive layer between the base layer and the surface layer. The base layer, surface layer, and adhesive layer all contain a polyester resin, and the polyester resin constituting the surface layer has a glass transition temperature (Tg) of -10°C or lower. The synthetic leather can withstand more than 6,000 flexing cycles at -20°C. Note that common parts of the first and second synthetic leathers will be described without distinguishing between them to avoid redundant explanations.

[0016] 1. Base Layer The base layer contains a polyester resin. This makes it easier to recycle the synthetic leather. It is preferable that the base layer be formed using a composition containing a polyester resin (hereinafter sometimes referred to as a base layer forming composition).

[0017] The base layer is preferably made of a polyester resin. Being made of a polyester resin means, for example, that the polyester resin in 100 parts by mass of the base layer is 60 parts by mass or more, preferably 70 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, and particularly preferably 95 parts by mass or more.

[0018] The base layer may be a nonwoven fabric or a woven or knitted fabric, and may be a nonwoven fabric or woven or knitted fabric composed of fibers containing a polyester resin.

[0019] The polyester resin constituting the base layer is not particularly limited as long as it has fiber-forming ability. For example, thermoplastic resins such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, as well as polyester resins such as low-melting-point polyesters mainly composed of these and further using isophthalic acid as a copolymer component, or mixtures or copolymers thereof can be used. The synthetic fibers obtained from the thermoplastic resin may be single-component systems, or multi-component systems such as core-sheath type, eccentric core-sheath type, parallel type, or sea-island type. The cross-sectional shape of the fibers is not particularly limited.

[0020] Fibers containing polyester resins may be, for example, fibers made from a blend of multiple resins, such as copolymerized polyester.

[0021] The polyester resin fibers may contain or be impregnated with additives such as matting agents, pigments, antioxidants, UV absorbers, light stabilizers, crystal nucleating agents, and mite repellents, in addition to the flame retardants described later, as needed. In particular, with regard to flame retardants, as described later, the flame retardancy of synthetic leather can be further improved by including or impregnating them not only in the surface layer but also in the base layer. However, from the viewpoint of recyclability, it is preferable to use as little flame retardant as possible.

[0022] The base layer may be a single layer or may have a multilayer structure. If the base layer has a multilayer structure, different types of nonwoven fabrics may be laminated, different types of woven or knitted fabrics may be laminated, or nonwoven fabrics and woven or knitted fabrics may be laminated.

[0023] The base layer may be napped, and the napping may be on one side or both sides of the base layer. By napping the side of the base layer that faces the surface layer, adhesion to the surface layer is increased, improving peel resistance. By napping the side of the base layer that faces the surface layer, the volume of the synthetic leather can be improved.

[0024] When using woven or knitted fabrics as the base layer, there are no particular limitations on the weaving method or knitting method. Examples of knitted fabrics include weft knitting, circular knitting, and warp knitting. Woven and knitted fabrics are thin and lightweight, and woven fabrics have the advantage of excellent strength and abrasion resistance, while knitted fabrics have the advantage of stretchability and a soft texture.

[0025] When using a nonwoven fabric as the base layer, the nonwoven fabric may be either a short-fiber nonwoven fabric or a long-fiber nonwoven fabric, but a long-fiber nonwoven fabric is preferred in order to ensure better mechanical properties.

[0026] The method for manufacturing nonwoven fabrics is not particularly limited, but for example, for long-fiber nonwoven fabrics, methods such as the spunbond method and the melt-blown method can be used, and for short-fiber nonwoven fabrics, methods such as the carding method and the air-lay method can be used. As for the nonwoven fabric, those having a two-layer structure in which the fiber structure constituting the upper layer and the fiber structure constituting the lower layer are laminated by mechanical entanglement are particularly preferred.

[0027] 2. Epidermal layer The epidermal layer contains a polyester resin. This makes it easier to recycle the synthetic leather. It is preferable that the epidermal layer be formed using a composition containing a polyester resin (hereinafter sometimes referred to as an epidermal layer forming composition).

[0028] The epidermal layer may contain, for example, polyamide resin, polyurethane resin, polyacrylate resin, vinyl acetate resin, polyacrylonitrile resin, and the like.

[0029] The surface layer is preferably composed of a polyester resin. Composed of a polyester resin means, for example, that the polyester resin in 100 parts by mass of the surface layer is 60 parts by mass or more, preferably 70 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, and particularly preferably 95 parts by mass or more.

[0030] The type of polyester resin that constitutes the surface layer is not particularly limited. Examples include polyesters formed by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, and polyesters formed by copolymerization of hydroxycarboxylic acids and lactones.

[0031] In the case of a polyester resin constituting the surface layer being a polyester formed by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, it is preferable that at least one of the polycarboxylic acid component or the polyhydric alcohol component is a copolymerized polyester consisting of two or more components. This improves adhesion to the adherend. It is preferable that the polycarboxylic acid component mainly consists of a dicarboxylic acid component and the polyhydric alcohol component mainly consists of a glycol component in the copolymerized polyester.

[0032] Examples of polycarboxylic acid components include aromatic polycarboxylic acids, alicyclic polycarboxylic acids, or aliphatic polycarboxylic acids, with aromatic dicarboxylic acids, alicyclic dicarboxylic acids, or aliphatic dicarboxylic acids being preferred, and aromatic dicarboxylic acids or aliphatic dicarboxylic acids being more preferred.

[0033] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, and naphthalenedicarboxylic acid. Examples of alicyclic dicarboxylic acids include hexahydrophthalic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Examples of aliphatic dicarboxylic acids include saturated aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, and dodecanedicarboxylic acid; and unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid. These dicarboxylic acids may be used individually or in combination of two or more. In addition, tricarboxylic acids or tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid, as well as their anhydrides, may be used as needed.

[0034] When the polycarboxylic acid component contains trifunctional or higher-functioning components, the amount of trifunctional or higher-functioning components is preferably 3 mol% or less relative to 100 mol% of the total amount of polycarboxylic acid components. By keeping the amount of trifunctional or higher-functioning components below the upper limit, gelation during polymerization can be suppressed, and a resin with high molecular weight and excellent flexural resistance can be obtained.

[0035] Examples of the polyhydric alcohol component include aromatic polyhydric alcohols, alicyclic polyhydric alcohols, and aliphatic polyhydric alcohols. Aromatic dihydric alcohols, alicyclic dihydric alcohols, and aliphatic dihydric alcohols are preferred, and aliphatic glycols are more preferred.

[0036] Examples of the aliphatic glycol include ethylene glycol, propylene glycol, 1,3 - propanediol, 2,2 - dimethyl - 1,3 - propanediol (neopentyl glycol), 2 - methyl - 1,3 - propanediol (hereinafter also referred to as 2MG), 1,4 - butanediol, 1,5 - pentanediol, 1,6 - hexanediol, 3 - methyl - 1,5 - pentanediol, diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. These aliphatic glycols may be used alone or in combination of two or more.

[0037] Examples of the polyhydric alcohol component include alicyclic polyhydric alcohols such as 1,2 - cyclohexanedimethanol, 1,3 - cyclohexanedimethanol, 1,4 - cyclohexanedimethanol, tricyclodecanediol; alkylene oxide adducts such as ethylene oxide adduct and propylene oxide adduct of bisphenol A, ethylene oxide adduct and propylene oxide adduct of hydrogenated bisphenol A; and the like may also be used. These polyhydric alcohol components may be used alone or in combination of two or more. Further, if necessary, triols or tetrols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used.

[0038] The copolymerization amount of the aliphatic glycol may be, for example, 70 mol% or more, preferably 75 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, and may be 100 mol% based on 100 mol% of the total amount of the polyhydric alcohol component. When the copolymerization amount of the aliphatic glycol is at least the lower limit value, it is easy to adhere to the base material layer and can be suitably used as an adhesive.

[0039] When the polyester resin constituting the skin layer is a polyester copolymerized with a hydroxycarboxylic acid or a lactone, examples of the hydroxycarboxylic acid include glycolic acid, lactic acid, tartaric acid, etc., and examples of the lactone include ε-caprolactone, γ-butyrolactone, etc., and ε-caprolactone is preferred.

[0040] As a method for introducing a carboxylic acid group into the polyester resin constituting the skin layer, for example, after polymerizing the polyester resin, an acid anhydride compound is added under normal pressure and in a nitrogen atmosphere for an addition reaction, or an acid anhydride compound is introduced into the oligomer before polycondensing the polyester, and then the molecular weight is increased by a polycondensation reaction under reduced pressure. Examples of the acid anhydride compound include phthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, itaconic anhydride, citraconic anhydride, 5-(2,5-dioxotetrahydrofurfuryl)-3-cyclohexene-1,2-dicarboxylic acid monoanhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, pyromellitic anhydride, 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, ethylene glycol bistrimellitate dianhydride, 2,2',3,3'-diphenyltetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, ethylenetetracarboxylic dianhydride, the dianhydride of 4,4'-oxydiphthalic acid, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, etc. These acid anhydride compounds may be used alone or in combination of two or more. When controlling the acid value of the polyester resin constituting the skin layer, the former method is preferred, and as the acid anhydride compound for the addition reaction, it is preferable to use trimellitic anhydride from the viewpoints of versatility and economy.

[0041] Methods for introducing sulfonic acid groups into polyester resins constituting the epidermal layer include copolymerization of dicarboxylic acids having sulfonic acid groups, such as 5-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and 5-[4-sulfophenoxy]isophthalic acid; glycols having sulfonic acid groups, such as 2-sulfo-1,4-butanediol and 2,5-dimethyl-3-sulfo-2,5-hexanediol; and metal salts thereof. Among these, sodium 5-sulfoisophthalate is preferred because it is inexpensive and can be applied to a wide range of uses.

[0042] The polyester resin constituting the epidermal layer may have an ionic group concentration of, for example, less than 30 mg KOH / g, preferably less than 25 mg KOH / g, and more preferably less than 20 mg KOH / g. By keeping the ionic group concentration below the upper limit, it is possible to improve water resistance while maintaining the mechanical strength of the epidermal layer, thereby improving adhesion.

[0043] The method for producing the polyester resin constituting the surface layer is not particularly limited and known methods can be employed. For example, the polycarboxylic acid component and polyhydric alcohol component described above may be esterified at 150 to 250°C, and then polycondensed at 230 to 300°C under reduced pressure. In addition, compounds such as hindered phenols or hindered amines may be added as heat stabilizers. When introducing hydrophilic ionic groups into the polyester resin, monovalent inorganic salts such as sodium acetate or potassium acetate may be added as polymerization stabilizers.

[0044] Additives may be incorporated into the surface layer to the extent that they do not impede recyclability. The type of additive is not particularly limited, and additives commonly used when molding thermoplastic resins can be used. Examples of additives include colorants; flame retardants; and agents having antibacterial, deodorizing, antifouling, abrasion-resistant, conductive, antistatic, lubricating, and hygroscopic properties.

[0045] The type of flame retardant is not particularly limited, and examples include brominated flame retardants such as tetrabromobisphenol A, decabromodiphenyl ether, octabromodiphenyl ether, hexabromocyclododecane, decabromodiphenylethane, bistribromophenoxyethane, polydibromphenyl oxide, tetrabromophthalic anhydride, TBA carbonate oligomer, and bromide polystyrene, as well as chlorinated flame retardants such as chlorinated polyphenyls, perchlorpentacyclodecane, and hexachlorocyclopentadiene derivatives. Flame retardants; triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, triethyl phosphate, cresyl diphenyl phosphate, xylenyl diphenyl phosphate, cresyl bis(2,6-xylenyl) phosphate, 2-ethylhexyl phosphate, dimethylmethyl phosphate, resorcinol bis(diphenyl) phosphate, bisphenol A bis(diphenyl) phosphate, bisphenol A bis(dicresyl) phosphate, Phosphorus-based flame retardants such as diethyl-N,N-bis(2-hydroxyethyl)aminomethyl phosphate, phosphate amides, organophosphorus oxides, and red phosphorus; ammonium polyphosphate, phosphazene, cyclophosphazene, 9,10-dihydro-9-oxa-10-phosphahenanthrene-10-oxide, 9,10-dihydro-9-oxa-10-phosphahenanthrene-10-oxide derivatives, triazine, melamine cyanurate, succinoguanamine, ethylenedimelamine, triguanamine, cyanoguanamine Nitrogen-based flame retardants such as triazinyl anurate, melem, melam, tris(β-cyanoethyl) isocyanurate, acetoganamine, guanylmamine sulfate, melem sulfate, melam sulfate; metal salt-based flame retardants such as potassium diphenylsulfon-3-sulfonate, aromatic sulfonimide metal salts, and alkali metal salts of polystyrene sulfonate; hydrated metal-based flame retardants such as aluminum hydroxide, magnesium hydroxide, dolomite, hydrotalcite, barium hydroxide, basic magnesium carbonate, zirconium hydroxide, and tin oxide;Examples of flame retardants include inorganic flame retardants such as silica, aluminum oxide, iron oxide, titanium oxide, manganese oxide, magnesium oxide, zirconium oxide, zinc oxide, molybdenum oxide, cobalt oxide, bismuth oxide, chromium oxide, tin oxide, antimony oxide, nickel oxide, copper oxide, tungsten oxide, zinc borate, zinc metaborate, barium metaborate, zinc carbonate, magnesium carbonate, calcium carbonate, and zinc barium stannate; and silicone-based flame retardants such as silicone powder. These flame retardants may be used individually or in combination of two or more. Among these, phosphorus-based flame retardants are preferred.

[0046] The reduced viscosity of the polyester resin constituting the surface layer is preferably 0.3 dl / g or more, more preferably 0.5 dl / g or more, even more preferably 0.8 dl / g or more, particularly preferably 0.95 dl / g or more, and most preferably 1.0 dl / g or more. A reduced viscosity above the above lower limit improves the elongation at break of the polyester resin and enhances the flexural resistance of the synthetic leather. The upper limit of the reduced viscosity of the polyester resin constituting the surface layer is not particularly limited; for example, it is preferably 1.7 dl / g or less, more preferably 1.5 dl / g or less, even more preferably 1.4 dl / g or less, and particularly preferably 1.3 dl / g or less. Specifically, the reduced viscosity of the polyester resin constituting the surface layer is preferably, for example, 0.3 to 1.7 dl / g, more preferably 0.5 to 1.5 dl / g, even more preferably 0.8 to 1.4 dl / g, particularly preferably 0.95 to 1.3 dl / g, and most preferably 1.0 to 1.3 dl / g.

[0047] The reduced viscosity of the polyester resin constituting the surface layer can be measured at 30°C using an Ubbelohde viscometer.

[0048] The polyester resin constituting the surface layer of the first synthetic leather may have a glass transition temperature (Tg) of, for example, -10°C or lower, preferably -20°C or lower, more preferably -25°C or lower, even more preferably -30°C or lower, even more preferably -40°C or lower, particularly preferably -45°C or lower, and most preferably -50°C or lower. If the Tg of the polyester resin constituting the surface layer is too high, the texture of the synthetic leather will become hard and deteriorate, and cracks may occur, especially when bent at low temperatures. If the Tg of the polyester resin constituting the surface layer is particularly -25°C or lower, the texture of the synthetic leather will be good, and the flexibility of the synthetic leather may be good. The glass transition temperature (Tg) of the polyester resin constituting the surface layer can be, for example, -80°C or higher, may be -70°C or higher, may be -65°C or higher, or may be -60°C or higher. That is, the glass transition temperature (Tg) of the polyester resin constituting the surface layer of the first synthetic leather may be -80°C to -10°C, -70°C to -20°C, -65°C to -25°C, -60°C to -30°C, -60°C to -40°C, -60°C to -45°C, or -60°C to -50°C.

[0049] The polyester resin constituting the surface layer of the second synthetic leather has a glass transition temperature (Tg) of -10°C or lower, preferably -20°C or lower, more preferably -25°C or lower, even more preferably -30°C or lower, even more preferably -40°C or lower, particularly preferably -45°C or lower, and most preferably -50°C or lower. If the Tg of the polyester resin constituting the surface layer is too high, the texture of the synthetic leather will become hard and deteriorate, and cracks may occur, especially when bent at low temperatures. If the Tg of the polyester resin constituting the surface layer is particularly -25°C or lower, the texture of the synthetic leather will be good and the flexibility of the synthetic leather may be good. The glass transition temperature (Tg) of the polyester resin constituting the surface layer can be, for example, -80°C or higher, may be -70°C or higher, may be -65°C or higher, or may be -60°C or higher. That is, the glass transition temperature (Tg) of the polyester resin constituting the surface layer of the second synthetic leather may be -80°C to -10°C, -70°C to -20°C, -65°C to -25°C, -60°C to -30°C, -60°C to -40°C, -60°C to -45°C, or -60°C to -50°C.

[0050] To achieve a Tg of -10°C or lower for the polyester resin constituting the surface layer, it is preferable to use aliphatic dicarboxylic acids, aromatic dicarboxylic acids, and aliphatic glycols as copolymerization components. In particular, it is more preferable to include at least one polycarboxylic acid selected from the group consisting of terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, sodium 5-sulfisoisophthalate, adipic acid, and trimellitic anhydride, and at least one polyhydric alcohol component selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and polytetramethylene glycol. Furthermore, a polyester resin having a desired Tg can also be obtained by copolymerizing polycaprolactone.

[0051] As a polyester resin with a Tg of -10°C or lower, for example, a crystalline polyester resin can be used. Examples of crystalline polyester resins include "Byron 30P (Tg = -28°C, melting point = 125°C)", "Byron GM-913 (Tg = -70°C, melting point = 123°C)", "Byron GM-915 (Tg = -70°C, melting point = 139°C)", "Byron GM-920 (Tg = -60°C, melting point = 108°C)", "Byron GM-950 (Tg = -65°C, melting point = 190°C)", "Byron GM-955 (Tg = -65°C, melting point = 160°C)", "Byron GM-960 (Tg = -65°C, melting point = 160°C)", and "Byron GM-962 (Tg = -65°C, melting point = 160°C)", all manufactured by Toyobo MC Co., Ltd.

[0052] The polyester resin constituting the surface layer is preferably crystalline. Since the surface layer may be the outermost layer of synthetic leather, its crystalline nature can enhance the durability of the synthetic leather. Whether the polyester resin constituting the surface layer is crystalline can be determined by whether the polyester resin constituting the surface layer has a melting point.

[0053] The melting point of the polyester resin constituting the surface layer is not particularly limited, but for example, in order to enable room temperature distribution without the need for a release film, the melting point is preferably 70°C or higher, more preferably 80°C or higher, even more preferably 90°C or higher, preferably 210°C or lower, more preferably 170°C or lower, and even more preferably 130°C or lower. That is, the melting point of the polyester resin constituting the surface layer is preferably 70°C to 210°C, more preferably 80°C to 170°C, and even more preferably 90°C to 130°C.

[0054] Examples of crystalline polyester resins include "Byron 30P (Tg = -28°C, melting point 125°C)" manufactured by Toyobo MC Corporation.

[0055] When the polyester resin constituting the surface layer is crystalline, the degree of crystallinity is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more, and may be 100%. When the degree of crystallinity is 50% or more, crystalline material is quickly formed after the surface layer is prepared, improving resistance to the solvent contained in the adhesive layer-forming composition when applying the composition after the surface layer is prepared, resulting in excellent workability. In addition, because a suitable amount of stable crystals are formed, the heat resistance of the synthetic leather is improved.

[0056] The thickness of the surface layer is not particularly limited, but if it is too thin, durability such as abrasion resistance may be insufficient. For example, it is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. On the other hand, if the thickness of the surface layer is too thick, handling and lightness during post-processing may be impaired. For example, it is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and particularly preferably 150 μm or less. That is, the thickness of the surface layer may be, for example, 10 to 500 μm, 20 to 300 μm, 30 to 200 μm, or 10 to 150 μm.

[0057] The epidermal layer can be formed by preparing an epidermal layer-forming composition containing a resin including a polyester resin and additives such as a colorant and solvent, which are optionally added, and then molding the obtained epidermal layer-forming composition. The epidermal layer-forming composition can be prepared by dissolving the resin including the polyester resin in a solvent or by dispersing it in an aqueous medium.

[0058] Examples of solvents for dissolving resins, including polyester resins, include methyl ethyl ketone, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, 1,3-dioxane, 1,3-dioxolane, 1,2-hexanediol, methyl cellosolve, n-butyl cellosolve, t-butyl cellosolve, ethyl carbitol, butyl carbitol, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and triethylene glycol monobutyl ether. Using these solvents as cosolvents during aqueous dispersion facilitates the dispersion of crystalline polyester resins.

[0059] The method for forming the epidermal layer is not particularly limited, and the epidermal layer can be formed by depositing the epidermal layer-forming composition using known film formation methods such as calendering, paste processing, or melt extrusion. Alternatively, the epidermal layer can be formed by applying the epidermal layer-forming composition onto release paper, allowing it to react and solidify. For application, for example, knife coating, command coater, roll coater, reverse roll coater, rotary screen coater, gravure coater, or other appropriate means can be used. Either mold transfer release paper or smooth release paper can be used as the release paper, and by using mold transfer release paper, an uneven pattern called a molded pattern can be formed on the surface of the epidermal layer.

[0060] 3. Adhesive Layer: The adhesive layer is used to bond the base material layer and the epidermis layer, and has the effect of preventing the base material layer and the epidermis layer from separating. However, it is important that it does not hinder the flexibility of the synthetic leather.

[0061] The adhesive layer contains a polyester resin. This makes it easier to recycle the synthetic leather. It is preferable that the adhesive layer be formed using a composition containing a polyester resin (hereinafter sometimes referred to as an adhesive layer forming composition).

[0062] The adhesive layer may contain, for example, polyamide resin, polyurethane resin, polyacrylate resin, vinyl acetate resin, polyacrylonitrile resin, and the like.

[0063] The adhesive layer is preferably composed of a polyester resin. Composed of a polyester resin means, for example, that the polyester resin in 100 parts by mass of the adhesive layer is 60 parts by mass or more, preferably 70 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, and particularly preferably 95 parts by mass or more.

[0064] The type of polyester resin that constitutes the adhesive layer is not particularly limited. Examples include polyesters formed by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, and polyesters formed by copolymerization of hydroxycarboxylic acids and lactones.

[0065] In the case where the polyester resin constituting the adhesive layer is a polyester formed by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, it is preferable that at least one of the polycarboxylic acid component or the polyhydric alcohol component is a copolymerized polyester consisting of two or more components. This can improve adhesion to the adherend. The polycarboxylic acid component and the polyhydric alcohol component are preferably copolymerized polyesters mainly consisting of a dicarboxylic acid component and a glycol component.

[0066] Examples of polycarboxylic acid components include aromatic polycarboxylic acids, alicyclic polycarboxylic acids, or aliphatic polycarboxylic acids, with aromatic dicarboxylic acids, alicyclic dicarboxylic acids, or aliphatic dicarboxylic acids being preferred, and aromatic dicarboxylic acids being more preferred.

[0067] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, and naphthalenedicarboxylic acid. Examples of alicyclic dicarboxylic acids include hexahydrophthalic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Examples of aliphatic dicarboxylic acids include saturated aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, and dodecanedicarboxylic acid; and unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid. These dicarboxylic acids may be used individually or in combination of two or more. In addition, tricarboxylic acids or tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid, as well as their anhydrides, may be used as needed.

[0068] When the polycarboxylic acid component contains trifunctional or higher-functioning components, the amount of trifunctional or higher-functioning components is preferably 3 mol% or less relative to 100 mol% of the total amount of polycarboxylic acid components. By keeping the amount of trifunctional or higher-functioning components below the upper limit, gelation during polymerization can be suppressed, and a resin with high molecular weight and excellent flexural resistance can be obtained.

[0069] Examples of polyhydric alcohol components include aromatic polyhydric alcohols, alicyclic polyhydric alcohols, and aliphatic polyhydric alcohols, with aromatic dihydric alcohols, alicyclic dihydric alcohols, and aliphatic dihydric alcohols being preferred, and aliphatic glycols being more preferred.

[0070] Examples of aliphatic glycols include ethylene glycol, propylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-methyl-1,3-propanediol (hereinafter also referred to as 2MG), 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. These aliphatic glycols may be used individually or in combination of two or more.

[0071] Examples of polyhydric alcohol components include alicyclic polyhydric alcohols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and tricyclodecanediol; alkylene oxide adducts such as ethylene oxide adducts and propylene oxide adducts of bisphenol A, and ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A; and others. These polyhydric alcohol components may be used individually or in combination of two or more. In addition, triols or tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used as needed.

[0072] The copolymerization amount of aliphatic glycol may be, for example, 70 mol% or more, preferably 75 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and may also be 100 mol%, based on 100 mol% of the total amount of polyhydric alcohol components. A copolymerization amount of aliphatic glycol above the lower limit allows for easy adhesion to the substrate layer, making it suitable for use as an adhesive.

[0073] When the polyester resin constituting the adhesive layer is a polyester copolymerized with hydroxycarboxylic acid or lactone, examples of hydroxycarboxylic acid include glycolic acid, lactic acid, and tartaric acid, and examples of lactone include ε-caprolactone and γ-butyrolactone.

[0074] Methods for introducing carboxylic acid groups into polyester resins constituting the adhesive layer include, for example, adding an acid anhydride compound under normal pressure and a nitrogen atmosphere after polymerization of the polyester resin to carry out an addition reaction, or adding an acid anhydride compound to an oligomer before polycondensation of polyester, followed by a polycondensation reaction under reduced pressure to increase the molecular weight. Examples of acid anhydride compounds include phthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, itaconic anhydride, citraconic anhydride, monoanhydride of 5-(2,5-dioxotetrahydrofurfuryl)-3-cyclohexene-1,2-dicarboxylic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, pyromelitic anhydride, 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and cyclopentanetetracarboxylic dianhydride. Examples include carboxylic acid dianhydrides, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, ethylene glycol bistrimellitate dianhydride, 2,2',3,3'-diphenyltetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, ethylenetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, and 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride. These acid anhydride compounds may be used individually or in combination of two or more. When controlling the acid value of the polyester resin constituting the adhesive layer, the former method is preferred, and trimellitic anhydride is preferred as the acid anhydride compound to be added, from the viewpoint of versatility and economy.

[0075] Methods for introducing sulfonic acid groups into the polyester resin constituting the adhesive layer include copolymerization of dicarboxylic acids having sulfonic acid groups, such as 5-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and 5-[4-sulfophenoxy]isophthalic acid; glycols having sulfonic acid groups, such as 2-sulfo-1,4-butanediol and 2,5-dimethyl-3-sulfo-2,5-hexanediol; and metal salts thereof. Among these, sodium 5-sulfoisophthalate is preferred because it is inexpensive and can be applied to a wide range of uses.

[0076] The polyester resin constituting the adhesive layer may have an ionic group concentration of less than 30 mg KOH / g, preferably less than 25 mg KOH / g, and more preferably less than 20 mg KOH / g. By keeping the ionic group concentration below the upper limit, the water resistance of the adhesive layer can be increased while maintaining its mechanical strength, thereby improving adhesion.

[0077] The method for producing the polyester resin constituting the adhesive layer is not particularly limited and known methods can be employed. For example, the polycarboxylic acid component and polyhydric alcohol component described above may be esterified at 150 to 250°C, and then polycondensed at 230 to 300°C under reduced pressure. In addition, compounds such as hindered phenols or hindered amines may be added as heat stabilizers. When introducing hydrophilic ionic groups into the polyester resin, monovalent inorganic salts such as sodium acetate or potassium acetate may be added as polymerization stabilizers.

[0078] In the first synthetic leather, the glass transition temperature (Tg) of the polyester resin constituting the adhesive layer is -20°C or lower. When the Tg of the polyester resin constituting the adhesive layer is -20°C or lower, the peel strength is increased and the flexibility of the synthetic leather is improved. The glass transition temperature (Tg) of the polyester resin constituting the adhesive layer is preferably -25°C or lower, and more preferably -30°C or lower. The glass transition temperature (Tg) of the polyester resin constituting the adhesive layer can be -80°C or higher, and can be -70°C or higher, -65°C or higher, or -60°C or higher. That is, the glass transition temperature (Tg) of the polyester resin constituting the adhesive layer may be, for example, -80°C to -20°C, -70°C to -25°C, or -65°C to -30°C.

[0079] In the first synthetic leather, to achieve a Tg of -20°C or lower for the polyester resin constituting the adhesive layer, it is preferable to use aliphatic dicarboxylic acids, aromatic dicarboxylic acids, and aliphatic glycols as copolymerization components. In particular, it is more preferable to include at least one polycarboxylic acid selected from the group consisting of terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, sodium 5-sulfisoisophthalate, adipic acid, and trimellitic anhydride, and at least one polyhydric alcohol component selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and polytetramethylene glycol. Furthermore, a polyester resin having a desired Tg can also be obtained by copolymerizing polycaprolactone.

[0080] In the first synthetic leather, the polyester resin constituting the adhesive layer may be amorphous. The peel strength is increased by the inclusion of an amorphous polyester resin in the adhesive layer. Whether the polyester resin constituting the adhesive layer is amorphous can be determined by whether or not the polyester resin constituting the adhesive layer has a melting point.

[0081] In the first synthetic leather, when forming an adhesive layer containing an amorphous polyester resin, for example, an aqueous dispersion of a polyester resin with a Tg of -20°C or lower may be used. Examples of aqueous dispersions of polyester resin with a Tg of -20°C or lower include "Vylonal MD-1984 (Tg = -20°C)" and "Vylonal MD-1985 (Tg = -20°C)" manufactured by Toyobo MC Co., Ltd.

[0082] In the second synthetic leather, the glass transition temperature (Tg) of the polyester resin constituting the adhesive layer may be -5°C or lower. When the Tg of the polyester resin constituting the adhesive layer is -5°C or lower, the peel strength becomes higher and the flexibility of the synthetic leather improves. The glass transition temperature (Tg) of the polyester resin constituting the adhesive layer is preferably -10°C or lower, more preferably -20°C or lower, even more preferably -25°C or lower, and particularly preferably -30°C or lower. The glass transition temperature (Tg) of the polyester resin constituting the adhesive layer can be -80°C or higher, and can be -70°C or higher, -65°C or higher, or -60°C or higher. That is, the glass transition temperature (Tg) of the polyester resin constituting the adhesive layer may be, for example, -80°C to -5°C, -70°C to -10°C, -65°C to -20°C, -65°C to -25°C, or -65°C to -30°C.

[0083] In the second synthetic leather, to achieve a Tg of -5°C or lower (particularly -20°C or lower) for the polyester resin constituting the adhesive layer, it is preferable to use aliphatic dicarboxylic acids, aromatic dicarboxylic acids, and aliphatic glycols as copolymerization components. More preferably, the copolymerization components include at least one polycarboxylic acid selected from the group consisting of terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, sodium 5-sulfisoisophthalate, adipic acid, and trimellitic anhydride, and at least one polyhydric alcohol component selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and polytetramethylene glycol. Furthermore, a polyester resin having the desired Tg can also be obtained by copolymerizing polycaprolactone.

[0084] In the second synthetic leather, the polyester resin constituting the adhesive layer may be amorphous. The peel strength is increased by the inclusion of an amorphous polyester resin in the adhesive layer. Whether the polyester resin constituting the adhesive layer is amorphous can be determined by whether or not the polyester resin constituting the adhesive layer has a melting point.

[0085] In the second synthetic leather, an amorphous polyester resin can be used as the polyester resin constituting the adhesive layer. Examples of amorphous polyester resins that can be used include "Byron GK-680 (Tg = 10°C)", "Byron 557 (Tg = -11°C)", "Byron 553 (Tg = -12°C)", "Byron 554 (Tg = -12°C)", "Byron 516 (Tg = -14°C)", "Byron BX-1001 (Tg = -15°C)", "Byron 550 (Tg = -15°C)", and "Byron 559 (Tg = -17°C)" manufactured by Toyobo MC Co., Ltd. Among these, it is preferable that the Tg is -5°C or lower.

[0086] In the second synthetic leather, when forming an adhesive layer containing an amorphous polyester resin, for example, an aqueous dispersion of a polyester resin with a Tg of -5°C or lower may be used. Examples of aqueous dispersions of polyester resins with a Tg of -5°C or lower include "Vylonal MD-1930 (Tg = -10°C)", "Vylonal MD-1984 (Tg = -20°C)", and "Vylonal MD-1985 (Tg = -20°C)" manufactured by Toyobo MC Co., Ltd. In particular, examples of aqueous dispersions of polyester resins with a Tg of -20°C or lower include "Vylonal MD-1984 (Tg = -20°C)" and "Vylonal MD-1985 (Tg = -20°C)".

[0087] The adhesive layer does not need to contain a flame retardant, but it may contain one to the extent that it does not impede recyclability. The type of flame retardant is not particularly limited, and those exemplified as flame retardants for the surface layer can be used. When a flame retardant is incorporated into both the adhesive layer and the surface layer, the type of flame retardant incorporated into the adhesive layer and the type of flame retardant incorporated into the surface layer may be the same or different.

[0088] If the adhesive layer contains a flame retardant, the flame retardant content is 1 m of synthetic leather. ２ The amount may be 16g or less per square meter (excluding 0g). The flame retardant content is 16g / m². ２ The following conditions ensure that the flame retardancy of synthetic leather is not hindered by the recyclability of the synthetic leather. The flame retardant content is more preferably 15 g / m². ２ More preferably, 14 g / m ２ The following applies:

[0089] When the adhesive layer constituting the synthetic leather contains a flame retardant, the amount of the flame retardant is preferably 27 parts by mass or less (not 0 parts by mass) per 100 parts by mass of the polyester resin constituting the adhesive layer. By having a flame retardant content of 27 parts by mass or less, the flame retardancy of the synthetic leather can be ensured without hindering the recyclability of the synthetic leather. The amount of the flame retardant is more preferably 22 parts by mass or less, and even more preferably 17 parts by mass or less.

[0090] The absolute value of the difference between the glass transition temperature (Tg) of the adhesive layer and the glass transition temperature (Tg) of the epidermal layer (epidermal layer - adhesive layer) is preferably 40°C or less, more preferably 30°C or less, even more preferably 25°C or less, and particularly preferably 23°C or less, from the viewpoint of improving recyclability, durability, and flexibility.

[0091] The reduced viscosity of the polyester resin constituting the adhesive layer is preferably 0.3 dl / g or higher, more preferably 0.5 dl / g or higher, even more preferably 0.8 dl / g or higher, and most preferably 1.0 dl / g or higher. A reduced viscosity above the above lower limit improves the elongation at break of the polyester resin, thereby improving the flexural resistance of the synthetic leather. Furthermore, a higher reduced viscosity of the polyester resin increases the cohesive force, increasing the peel strength between the base layer and the surface layer, resulting in better durability of the synthetic leather. The upper limit of the reduced viscosity of the polyester resin constituting the adhesive layer is not particularly limited; for example, it is preferably 2.0 dl / g or lower, more preferably 1.5 dl / g or lower, even more preferably 1.3 dl / g or lower, most preferably 1.2 dl / g or lower, and most preferably 1.1 dl / g or lower. Specifically, the reduced viscosity of the polyester resin constituting the adhesive layer is preferably, for example, 0.3 to 2.0 dl / g, more preferably 0.5 to 1.5 dl / g, even more preferably 0.8 to 1.3 dl / g, particularly preferably 1.0 to 1.2 dl / g, and most preferably 1.0 to 1.1 dl / g.

[0092] The reduced viscosity of the polyester resin constituting the adhesive layer can be measured at 30°C using an Ubbelohde viscometer.

[0093] The polyester resin constituting the adhesive layer and the polyester resin constituting the surface layer preferably have a high ester group concentration. The ester group concentration should be similar to that of polyethylene terephthalate (10,000 eq / t), which is used as a tricot base material, to ensure excellent recyclability. The ester group concentration is preferably 2,000 eq / t or higher, more preferably 3,000 eq / t or higher, and even more preferably 4,000 eq / t or higher.

[0094] The ratio of the ester group concentration of the polyester resin constituting the surface layer to the ester group concentration of the polyester resin constituting the base layer (surface layer / base layer) is not particularly limited, but is preferably 0.4 or higher, more preferably 0.5 or higher, and even more preferably 0.6 or higher, as this improves recyclability. Furthermore, the ratio of ester group concentrations is preferably 2.2 or lower, more preferably 2.1 or lower, and even more preferably 2.0 or lower. That is, the ratio of ester group concentrations is preferably 0.4 to 2.2, more preferably 0.5 to 2.1, and even more preferably 0.6 to 2.0.

[0095] The ratio of the ester group concentration of the polyester resin constituting the adhesive layer to the ester group concentration of the polyester resin constituting the base layer (adhesive layer / base layer) is not particularly limited, but is preferably 0.4 or higher, more preferably 0.5 or higher, and even more preferably 0.6 or higher, as this improves recyclability. Furthermore, the ratio of ester group concentrations is preferably 2.2 or lower, more preferably 2.1 or lower, and even more preferably 2.0 or lower. That is, the ratio of ester group concentrations is preferably 0.4 to 2.2, more preferably 0.5 to 2.1, and even more preferably 0.6 to 2.0.

[0096] The ratio of the ester group concentration of the polyester resin constituting the surface layer to the ester group concentration of the polyester resin constituting the adhesive layer (surface layer / adhesive layer) is not particularly limited, but is preferably 0.2 or higher, and more preferably 0.3 or higher, as this improves recyclability. Furthermore, the ratio of ester group concentrations is preferably 3.5 or lower, and more preferably 3.3 or lower. That is, the ratio of ester group concentrations is preferably 0.2 to 3.5, and more preferably 0.3 to 3.3.

[0097] The aromatic group concentration of the polyester resin constituting the surface layer is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 23% by mass or less, even more preferably 22% by mass or less, particularly preferably 20% by mass or less, and most preferably 18% by mass or less.

[0098] The aromatic group concentration of the polyester resin constituting the adhesive layer is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 23% by mass or less, even more preferably 22% by mass or less, particularly preferably 20% by mass or less, and most preferably 18% by mass or less.

[0099] The aromatic group concentration of the polyester resin constituting the adhesive layer or the polyester resin constituting the surface layer is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 23% by mass or less, even more preferably 22% by mass or less, particularly preferably 20% by mass or less, and most preferably 18% by mass or less. It is preferable that the aromatic group concentrations of both the polyester resin constituting the adhesive layer and the polyester resin constituting the surface layer are within the above range.

[0100] The aromatic group concentration (mass%) of polyester resins can be calculated by dividing the total molecular weight derived from benzene rings by the total molecular weight of the units. The molecular weight derived from benzene rings refers to the molecular weight calculated based on the benzene ring contained in a unit formed by the bonding of one polycarboxylic acid component and one polyhydric alcohol component. The unit molecular weight refers to the molecular weight of a unit formed by the bonding of one polycarboxylic acid component and one polyhydric alcohol component.

[0101] The adhesive layer may be formed by applying an adhesive layer-forming composition to the surface of the epidermal layer. The method of applying the adhesive layer-forming composition to the surface of the epidermal layer is not particularly limited and may be by coating or by transfer. A synthetic leather having an epidermal layer / adhesive layer / base layer layer structure can be manufactured by overlapping a base layer onto the adhesive layer side of a laminate obtained by forming an adhesive layer on the surface of the epidermal layer and applying pressure in the thickness direction. Heating may be applied when overlapping the base layer onto the adhesive layer side of the laminate and applying pressure, or heat treatment may be applied after overlapping the base layer onto the adhesive layer side of the laminate and applying pressure. The heating method is not particularly limited and examples include heating using a hot roll, hot air heating, and heating in a heating furnace (especially a heating and drying furnace).

[0102] The thickness of the adhesive layer is not particularly limited, but if it is too thin, the durability, such as abrasion resistance, may be insufficient. For example, it is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. On the other hand, if the thickness of the adhesive layer is too thick, the handling and lightness during post-processing may be impaired. For example, it is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and particularly preferably 150 μm or less. In other words, the thickness of the adhesive layer may be, for example, 10 to 500 μm, 20 to 300 μm, 30 to 200 μm, or 30 to 150 μm.

[0103] The first synthetic leather has good flexibility, particularly low-temperature flexibility. Flexibility can be evaluated based on the results of a bending resistance test. In the embodiment, the first synthetic leather preferably has a bending count of more than 6,000 times at -20°C, more preferably 7,000 times or more, even more preferably 8,000 times or more, particularly preferably 9,000 times or more, and most preferably 10,000 times or more. The number of bending count refers to the number of times damage is observed in the test piece when a bending resistance test is performed in accordance with JIS K6542.

[0104] The second synthetic leather has good flexibility, particularly low-temperature flexibility. Flexibility can be evaluated based on the results of a bending resistance test. In the embodiment, the second synthetic leather has a bending count of more than 6,000 times at -20°C, preferably 7,000 times or more, more preferably 8,000 times or more, even more preferably 9,000 times or more, and particularly preferably 10,000 times or more. The bending count refers to the number of times damage is observed in the test piece when a bending resistance test is performed in accordance with JIS K6542.

[0105] The surface of the epidermal layer constituting the synthetic leather may have a surface treatment layer. The surface treatment layer is a layer that improves the durability of the synthetic leather or improves the gloss of the surface of the synthetic leather to give it a good appearance. The surface treatment layer may be composed of a synthetic resin, and polyester resin is preferred as the synthetic resin. The surface treatment layer may also contain, to the extent that it does not impede recyclability, synthetic resins such as polyurethane resin, acrylic resin, fluororesin, and polyvinyl chloride resin. The surface of the epidermal layer constituting the synthetic leather may be embossed, for example, to give it a patterned design.

[0106] The synthetic leather in the embodiments can be used in fields such as clothing, gloves, shoes, bags, furniture, waterproof fabrics, light-blocking fabrics, and vehicle interior materials, but is particularly preferred for use as vehicle interior materials. Embodiments of this disclosure also include vehicle interior materials containing the above-mentioned synthetic leather. Examples of vehicle interior materials include vehicle seats, door trims, console boxes, instrument panels, ceiling materials, steering wheels, tonneau covers, and the like.

[0107] This application claims the benefit of priority based on Japanese Patent Application No. 2024-230882, filed on 26 December 2024, Japanese Patent Application No. 2024-230883, filed on 26 December 2024, Japanese Patent Application No. 2025-086438, filed on 23 May 2025, and Japanese Patent Application No. 2025-086439, filed on 23 May 2025. The entire contents of the specifications of the above Japanese Patent Application No. 2024-230882, Japanese Patent Application No. 2024-230883, Japanese Patent Application No. 2025-086438, and Japanese Patent Application No. 2025-086439 are incorporated herein by reference.

[0108] The contents of this disclosure will be explained in more detail below with reference to examples, but the contents of this disclosure are not limited by the examples below, and it is of course possible to implement modifications to the extent that are consistent with the spirit described above and below, and all such modifications are included in the technical scope of this disclosure. Unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0109] Each measured value described in the examples was measured by the following method.

[0110] (Measurement of the composition of the polyester resin) The measurement sample (copolyester) was dissolved in deuterated chloroform, and 1H-NMR analysis was performed using a nuclear magnetic resonance (NMR) apparatus 400-MR manufactured by VARIAN. From the integral value ratio, the composition (molar ratio) of the polyester resin was determined. １

[0111] (Measurement of glass transition temperature and melting point) 5 mg of the measurement sample was placed in an aluminum pan, covered and sealed, and using a differential scanning calorimeter "DSC220 type" manufactured by Seiko Instruments Inc., it was held at 250 °C for 5 minutes to completely melt the measurement sample, then rapidly cooled using liquid nitrogen, and then heated from -150 °C to 250 °C at a heating rate of 20 °C / min for measurement. In the endothermic curve obtained during heating from -150 °C to 250 °C, the temperature at the intersection of the baseline before the endothermic peak appears and the tangent line towards the endothermic peak was defined as the glass transition temperature (Tg, unit: °C). Also, the maximum peak temperature of the heat of fusion was defined as the melting point (Tm, unit: °C).

[0112] (Measurement of reduced viscosity) The reduced viscosity was measured at 30 °C using an Ubbelohde viscometer by dissolving 0.10 g of the sufficiently dried measurement sample in 25 ml of a mixed solvent of phenol / tetrachloroethane (mass ratio = 6 / 4).

[0113] (Solubility parameter) The solubility parameter was calculated from the formula of Fedors δ = (E ｃｏｈ / V) １／２ (Fedors, R.F., Polymer Eng. Sci. 14 (1974) 147). Here, δ represents the solubility parameter, E ｃｏｈ represents the cohesive energy, V represents the molar volume, and by substituting the values reported by Fedors for E ｃｏｈ and V, the solubility parameter of the polyester resin was calculated.

[0114] (Ester group concentration) The ester group concentration (Es group concentration) of the polyester resin was calculated based on the following formula and Tables 1 to 6 (resins A to F), and the theoretical value was calculated by determining the unit molecular weight. Tables 1 to 6 correspond to resins A to F, respectively. The molar ratio of each monomer in the polyester resin is as follows: １ The results were calculated from the 1H-NMR analysis. In addition, the distillate in the following refers to the amount of volatile components separated by esterification (condensation reaction). For example, in the first row of Table 1 (esterification of DMT and EG), it refers to the molecular weight of methanol (32.04 g / mol).

[0115]

[0116] The theoretical values ​​of the ester group concentration in resins A, C, D, and F were calculated based on the following formula: Ester group concentration (Es group concentration) = 2,000,000 / Total molecular weight of units. Resins A, C, D, and F are composed of dialcohols and dicarboxylic acids. Since the dialcohols and dicarboxylic acids react, the number of ester groups per unit is "2". In addition, to convert the units from g / mol to ton / mol, the theoretical value of the ester group concentration was calculated based on the above formula by multiplying by 1,000,000.

[0117] The theoretical value of the ester group concentration in resin B was calculated based on the following formula: Ester group concentration (Es group concentration) = 1333333 / Total molecular weight of units. Since resin B contains ε-caprolactone in addition to dialcohols and dicarboxylic acids, the number of ester groups per unit is "2 × molar ratio (sum of molar ratios of DMT, DMI, and TMA) + 1 × molar ratio (molar ratio of ε-caprolactone)". Furthermore, to convert g / mol to ton, the theoretical value of the ester group concentration was calculated based on the above formula by multiplying by 1,000,000.

[0118] The theoretical value of the ester group concentration in resin E was calculated based on the following formula: Ester group concentration (Es group concentration) = 1,416,667 / Total molecular weight of the unit. Since resin E contains ε-caprolactone in addition to dialcohols and dicarboxylic acids, the number of ester groups per unit is "2 × molar ratio (sum of molar ratios of TPA, IPA, and TMA) + 1 × molar ratio (molar ratio of ε-caprolactone)". Furthermore, to convert g / mol to ton, the theoretical value of the ester group concentration was calculated based on the above formula by multiplying by 1,000,000.

[0119] (Aromatic group concentration) The aromatic group concentration (mass%) of polyester resin is: １ Based on the H-NMR analysis results, it was calculated by dividing the total molecular weight derived from the benzene ring by the total unit molecular weight.

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126] (Crystallization) The degree of crystallinity was measured using a differential scanning calorimetry analyzer "DSC220" manufactured by Seiko Electronics Industries, Ltd. Two g of crystalline polyester resin was dissolved in eight g of chloroform, and the solution was applied to the non-corona treated surface of a polypropylene film (manufactured by Toyobo Co., Ltd., P2162) to a dry film thickness of 10 μm. The film was then aged at 50°C for 10 minutes or 30 hours. The treated coating was peeled off the polypropylene film, 5 mg of the coating was placed in an aluminum container with a retaining lid and sealed, and cooled to -50°C using liquid nitrogen. The temperature was then raised to 200°C at a rate of 20°C / min. For all endothermic peaks obtained during this process, the sum of the integral values ​​obtained by subtracting the baseline from the endothermic peak was calculated as the total heat of fusion (J / g). The degree of crystallinity (%) of the polyester resin was then determined from the obtained total heat of fusion using the following formula. Crystallinity of polyester resin (%) = Sum of the heat of fusion of all endothermic peaks after aging treatment at 50°C for 10 minutes / Sum of the heat of fusion of all endothermic peaks after aging treatment at 50°C for 30 hours × 100

[0127] In manufacturing synthetic leather, a knitted fabric was prepared to form the base layer, a composition for forming the surface layer to form the surface layer, and a composition for forming the adhesive layer to form the adhesive layer.

[0128] (Base Layer) A polyester circular knit fabric was prepared as the base layer. The prepared polyester circular knit fabric had the following yarn composition: front 84T / 72F, back 110T / 48F, gauge: 26, knit composition: 38W / inch, 78C / inch, and thickness of 1200 μm. The base layer was a single layer. The basis weight of the base layer was 300 g / m ２ That was the case.

[0129] (Compositions for forming epidermal layers and adhesive layers) The following polyester resins A to F were prepared to form an epidermal layer or an adhesive layer. The amounts used are shown when the total amount of polycarboxylic acid components is assumed to be 100 mol%, and when the total amount of polyhydric alcohol components is assumed to be 100 mol%. If ε-caprolactone is included as an adduct, the amount used is shown when the total amount of polycarboxylic acid components is assumed to be 100 mol%.

[0130] (Polyester Resin A) In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and distillation tube, 353 parts (55 mol%) of dimethyl terephthalate, 193 parts (40 mol%) of adipic acid, 49 parts (5 mol%) of dimethyl sodium 5-sulfoisophthalate, 123 parts (24.5 mol%) of ethylene glycol, 521 parts (71.4 mol%) of 1,4-butanediol, 330 parts (4.1 mol%) of polytetramethylene glycol (molecular weight 1000), and 0.03 mol% of tetra-n-butyl titanate (hereinafter sometimes abbreviated as TBT) as a catalyst were charged based on 100 mol% of the total acid components. A transesterification reaction was carried out while raising the temperature from 160°C to 240°C over 4 hours. Next, the pressure in the system was gradually reduced to 5 mmHg over 20 minutes, and then a polycondensation reaction was carried out at 260°C for 90 minutes under a vacuum of 0.3 mmHg or less to obtain polyester resin A.

[0131] (Polyester Resin B) In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and distillation tube, 246 parts (49 mol%) of dimethyl terephthalate, 246 parts (49 mol%) of dimethyl isophthalate, 10 parts (2 mol%) of trimellitic anhydride, 129 parts (57 mol%) of ethylene glycol, 162 parts (43 mol%) of neopentyl glycol, and 0.03 mol% of tetra-n-butyl titanate (TBT) as a catalyst (based on 100 mol%) of the total acid components were charged, and the transesterification reaction was carried out while raising the temperature from 160°C to 240°C over 4 hours. Next, the pressure in the system was gradually reduced to 5 mmHg over 20 minutes, and then the polycondensation reaction was carried out at 260°C for 90 minutes under a vacuum of 0.3 mmHg or less. The mixture was cooled to 230°C under a nitrogen stream, 591 parts (200 mol%) of ε-caprolactone were added, and the reaction was carried out for 30 minutes to obtain polyester resin B.

[0132] (Polyester Resin C) In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and distillation tube, 204 parts (65 mol%) of dimethyl terephthalate, 110 parts (35 mol%) of dimethyl isophthalate, 194 parts (89 mol%) of 1,4-butanediol, 269 parts (11 mol%) of polytetramethylene glycol (molecular weight 1000), and 0.03 mol% of tetra-n-butyl titanate (TBT) as a catalyst based on 100 mol% of the total acid components were charged, and the transesterification reaction was carried out while raising the temperature from 160°C to 240°C over 4 hours. Next, the pressure in the system was gradually reduced to 5 mmHg over 20 minutes, and then a polycondensation reaction was carried out at 260°C for 90 minutes under a vacuum of 0.3 mmHg or less to obtain polyester resin C.

[0133] (Polyester Resin D) In ​​a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and distillation tube, 218 parts (56.7 mol%) of terephthalic acid, 24 parts (3.5 mol%) of dimethyl sodium 5-sulfoisophthalate, 135 parts (39.8 mol%) of adipic acid, 16 parts (7 mol%) of ethylene glycol, 291 parts (91 mol%) of 1,4-butanediol, 69 parts (2 mol%) of polytetramethylene glycol (molecular weight 1000), and 0.03 mol% of tetra-n-butyl titanate (TBT) as a catalyst based on 100 mol% of the total acid components were charged, and the transesterification reaction was carried out while raising the temperature from 160°C to 240°C over 4 hours. Next, the pressure in the system was gradually reduced to 5 mmHg over 20 minutes, and then a polycondensation reaction was carried out at 260°C for 90 minutes under a vacuum of 0.3 mmHg or less to obtain polyester resin D.

[0134] (Polyester Resin E) In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and distillation tube, 157 parts (49 mol%) of terephthalic acid, 157 parts (49 mol%) of isophthalic acid, 7.4 parts (2 mol%) of trimellitic anhydride, 111 parts (62 mol%) of ethylene glycol, 114 parts (38 mol%) of neopentyl glycol, and 0.03 mol% of tetra-n-butyl titanate (TBT) as a catalyst (based on 100 mol%) of the total acid components were charged, and the transesterification reaction was carried out while raising the temperature from 160°C to 240°C over 4 hours. Next, the pressure in the system was gradually reduced to 5 mmHg over 20 minutes, and then the polycondensation reaction was carried out at 260°C for 90 minutes under a vacuum of 0.3 mmHg or less. The mixture was cooled to 230°C under a nitrogen stream, 308 parts (140 mol%) of ε-caprolactone were added, and the reaction was carried out for 30 minutes to obtain polyester resin E.

[0135] (Polyester resin F) In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and distillation tube, 265 parts (49.5 mol%) of terephthalic acid, 246 parts (46 mol%) of isophthalic acid, 28.6 parts (3 mol%) of dimethyl sodium 5-sulfisophthalate, 9.3 parts (1.5 mol%) of trimellitic anhydride, 226 parts (44 mol%) of diethylene glycol, 320 parts (56 mol%) of 1,6-hexanediol, and 0.03 mol% of tetra-n-butyl titanate (TBT) as a catalyst based on 100 mol% of the total acid components were charged, and the transesterification reaction was carried out while raising the temperature from 160°C to 240°C over 4 hours. Next, the pressure in the system was gradually reduced to 5 mmHg over 20 minutes, and then a polycondensation reaction was carried out at 260°C for 90 minutes under a vacuum of 0.3 mmHg or less to obtain polyester resin F.

[0136] Composition of the obtained polyester resins A to F ( １ The H-NMR analysis values ​​are shown in Table 7 below. Also, the composition of polyester resins A to F is as follows: １ Based on the 1H-NMR analysis values, the ester group concentration and aromatic group concentration were calculated and are shown in Table 7 below. In addition, the glass transition temperature, melting point, reduced viscosity, and solubility parameter (SP value) of the obtained polyester resins A to F were measured and are shown in Table 7 below.

[0137]

[0138] Next, synthetic leather was manufactured using the knitted fabric for forming the prepared base layer and polyester resins A to F.

[0139] (Example 1) 337.5 parts of polyester resin A and 112.5 parts of n-butyl cellosolve were placed in a reaction vessel equipped with a stirrer, condenser, and thermometer, and the resin was dissolved at 130°C for 3 hours. After dissolution, the temperature was lowered to 97°C, 800 parts of warm water were added, and the mixture was stirred for 1 hour. Then, the internal temperature was lowered to room temperature to obtain an aqueous dispersion of polyester resin A (NV 27%). The obtained aqueous dispersion of polyester resin A was used as an adhesive layer forming composition and an epidermal layer forming composition. The epidermal layer forming composition was applied to release paper with a comma coater, and the temperature was gradually increased from 70°C to 120°C. After reaching 120°C, it was held for 2 minutes to dry and produce an epidermal layer with a thickness of 40 μm. Subsequently, the adhesive layer forming composition was applied on the epidermal layer with a comma coater, and then heated to 100°C to dry and form an adhesive layer with a thickness of 100 μm. The adhesive layer was bonded to the base material layer (polyester circular knit fabric) at the moment when the adhesive properties had developed in the adhesive layer. The laminate, consisting of the base material layer, adhesive layer, and surface layer in this order, was wound into a roll and held at 60°C for 48 hours. After that, the release paper was peeled off to produce synthetic leather 1.

[0140] (Example 2) An aqueous dispersion of polyester resin A (NV 27%) described in Example 1 was prepared as a composition for forming the surface layer. In addition, an adhesive layer composition was prepared by dissolving 40% polyester resin B in ethyl acetate. The surface layer composition was applied onto release paper with a comma coater, and the temperature was gradually increased from 70°C to 120°C. After reaching 120°C, it was held for 2 minutes to dry and produce a surface layer with a thickness of 40 μm. Subsequently, the adhesive layer composition was applied onto the surface layer with a comma coater, and then heated to 100°C to dry and form an adhesive layer with a thickness of 100 μm. At the moment when the adhesive layer exhibited adhesive properties, it was bonded to the base material layer (polyester circular knit fabric). The laminate, in which the base material layer, adhesive layer, and surface layer were laminated in this order, was wound into a roll, held at 60°C for 48 hours, and then the release paper was peeled off to produce synthetic leather 2.

[0141] (Example 3) A skin layer forming composition was prepared by dissolving 40% polyester resin B in ethyl acetate. In addition, an aqueous dispersion of polyester resin A (NV 27%) described in Example 1 was prepared as an adhesive layer forming composition. The skin layer forming composition was applied to release paper with a comma coater, and the temperature was gradually increased from 70°C to 120°C. After reaching 120°C, it was held for 2 minutes to dry and a skin layer with a thickness of 40 μm was produced. Subsequently, the adhesive layer forming composition was applied on top of the skin layer with a comma coater, and then heated to 100°C to dry and form an adhesive layer with a thickness of 100 μm. At the moment when the adhesive layer exhibited adhesive properties, it was bonded to the base layer (polyester circular knit fabric). The laminate, in which the base layer, adhesive layer, and skin layer were laminated in this order, was wound into a roll, held at 60°C for 48 hours, and then the release paper was peeled off to produce synthetic leather 3.

[0142] (Comparative Example 1) A skin layer forming composition was prepared by dissolving 10% polyester resin C in 1,3-dioxolane, and an adhesive layer forming composition was prepared by dissolving 40% polyester resin E in ethyl acetate. The skin layer forming composition was applied to release paper with a comma coater, and the temperature was gradually increased from 70°C to 120°C. After reaching 120°C, it was held for 2 minutes to dry and produce a skin layer with a thickness of 40 μm. Subsequently, the adhesive layer forming composition was applied to the skin layer with a comma coater, and then heated to 100°C to dry and form an adhesive layer with a thickness of 100 μm. At the moment when the adhesive layer exhibited adhesive properties, it was bonded to a base layer (polyester circular knit fabric). The laminate, in which the base layer, adhesive layer, and skin layer were stacked in this order, was wound into a roll, held at 60°C for 48 hours, and then the release paper was peeled off to produce comparative synthetic leather 1.

[0143] (Comparative Example 2) A skin layer forming composition was prepared by diluting 100 parts of DIC's "Crisbon S-703" with 45 parts of dimethylformamide (DMF), and an adhesive layer forming composition was prepared by diluting 100 parts of DIC's "Crisbon TA-230FT" with 60 parts of DMF. Both "Crisbon S-703" and "Crisbon TA-230FT" are polyurethane resins. Polyurethane resins are denoted as PU in Table 8 below. The skin layer forming composition was applied to release paper with a comma coater, and the temperature was gradually increased from 70°C to 120°C. After reaching 120°C, it was held for 2 minutes to dry and produce a skin layer with a thickness of 40 μm. Subsequently, the adhesive layer forming composition was applied on top of the skin layer with a comma coater, and then heated to 100°C to dry and form an adhesive layer with a thickness of 100 μm. The adhesive layer was bonded to the base material layer (polyester circular knit fabric) at the moment when the adhesive properties had developed in the adhesive layer. The laminate, consisting of the base material layer, adhesive layer, and surface layer in this order, was wound into a roll and held at 60°C for 48 hours. After that, the release paper was peeled off to produce comparative synthetic leather 2.

[0144] (Comparative Example 3) 337.5 parts of polyester resin F and 112.5 parts of n-butyl cellosolve were placed in a reaction vessel equipped with a stirrer, condenser, and thermometer, and the resin was dissolved at 130°C for 3 hours. After dissolution, the temperature was lowered to 97°C, 800 parts of warm water were added, and the mixture was stirred for 1 hour. Then, the internal temperature was lowered to room temperature to obtain an aqueous dispersion of polyester resin F (NV 27%). The aqueous dispersion of polyester resin F (NV 27%) was prepared as a composition for forming an adhesive layer. In addition, a composition for forming a skin layer was prepared by dissolving 15% polyester resin D in 1,3-dioxolane. The composition for forming a skin layer was applied onto release paper with a comma coater, the temperature was gradually raised from 70°C to 120°C, and after reaching 120°C it was held for 2 minutes to dry, producing a skin layer with a thickness of 40 μm. Next, the adhesive layer-forming composition was applied to the surface layer using a comma coater, then heated to 100°C and dried to form an adhesive layer with a thickness of 100 μm. At the moment the adhesive layer developed its adhesive properties, it was bonded to the base layer (polyester circular knit fabric). The laminate, in which the base layer, adhesive layer, and surface layer were stacked in this order, was wound into a roll, held at 60°C for 48 hours, and then the release paper was peeled off to produce comparative synthetic leather 3.

[0145] The thickness of the obtained synthetic leathers 1-3 and comparative synthetic leathers 1-3 was measured in accordance with JIS-L1913 (2010) and was found to be 1.2 mm. Furthermore, the obtained synthetic leathers 1-3 and comparative synthetic leathers 1-3 were cut along the thickness direction, and the cross-sections were observed with a scanning electron microscope (SEM) to measure the thickness of the epidermal layer and adhesive layer. The thickness of the epidermal layer was found to be 40 μm, and the thickness of the adhesive layer was found to be 100 μm.

[0146] For the obtained synthetic leathers 1-3 and comparative synthetic leathers 1-3, the absolute value of the difference (epidermal layer - adhesive layer) between the glass transition temperature (Tg) of the adhesive layer and the glass transition temperature (Tg) of the epidermal layer was calculated, and the results are shown in Table 8 below.

[0147] For the obtained synthetic leathers 1-3 and comparative synthetic leathers 1-3, the ratio of the ester group concentration of the polyester resin constituting the surface layer to the ester group concentration of the polyester resin constituting the base layer (surface layer / base layer), the ratio of the ester group concentration of the polyester resin constituting the adhesive layer to the ester group concentration of the polyester resin constituting the base layer (adhesive layer / base layer), and the ratio of the ester group concentration of the polyester resin constituting the surface layer to the ester group concentration of the polyester resin constituting the adhesive layer (surface layer / adhesive layer) were calculated, and the results are shown in Table 8 below.

[0148] The peel strength, low-temperature flexibility, and recyclability of the obtained synthetic leathers 1-3 and comparative synthetic leathers 1-3 were evaluated, and the evaluation results are shown in Table 8 below.

[0149] (Peel Strength) An adhesive tape (2.0 cm wide) having a hot-melt resin layer on the back of a polyester substrate was prepared. The hot-melt resin layer of the adhesive tape was brought into contact with the surface of the surface layer of synthetic leather and bonded using an iron (low temperature 120°C). Then, one end of the adhesive tape was slightly peeled off, and the peeled portion was pulled at a speed of 200 mm / min using an Autograph AG-LS (manufactured by Shimadzu Corporation). The tensile load (peel strength) at which the polyester substrate peeled off from the surface layer was measured, and the durability of the synthetic leather was evaluated.

[0150] (Cold-temperature flexibility) Cold-temperature flexibility was evaluated based on the number of times damage was observed in the test specimen during a flexion resistance test. The flexion resistance test was performed using the following procedure: A test specimen measuring 45 mm wide x 70 mm long was cut from synthetic leather and set in a flexion resistance test apparatus (Yasuda Seiki's "Flexiometer (with low-temperature chamber)"). The setting method was as follows: Step 1: Open the upper and lower clamps. Step 2: Ensure that the lower end of the upper clamp is parallel to the upper end of the lower clamp. Step 3: With the surface layer of the test specimen facing inward, fold the test specimen in half so that the two long sides overlap. Step 4: Secure one end of the folded test specimen to the upper clamp. Step 5: Fold the test specimen, which is clamped in place, downward with the surface layer facing outward, and secure it with the lower clamp. After setting up as described above, a flexural resistance test (flexible leather, size: 45 mm x 70 mm) was conducted in accordance with JIS K6542 under the conditions of flexion angle: 22.5° ± 0.5°, speed: 100 ± 5 times / min, and temperature: -20°C. After removing the test piece, the presence or absence of damage to the surface layer was checked. The presence or absence of damage was checked for the obtained synthetic leather every 2000 flexures. Flexure tests were performed up to a maximum of 10,000 times, and the low-temperature flexure performance was evaluated based on the number of flexures until damage was observed. Table 8 below shows the number of flexures at which damage was observed. If no damage was observed even after 10,000 flexures, it was indicated as "10000<" in Table 8 below.

[0151] (Recyclability) If the base layer and the surface layer are made of the same type of resin, or if the base layer, adhesive layer, and surface layer are made of the same type of resin, the recyclability is evaluated as excellent and indicated as A in Table 8. If the base layer and the surface layer are made of different types of resin, or if the base layer, adhesive layer, and surface layer are made of different types of resin, the recyclability is evaluated as poor and indicated as B in Table 8.

[0152]

[0153] From Tables 7 and 8, the following can be considered. Examples 1 to 3 are first synthetic leathers having an adhesive layer between the base layer and the surface layer, and the base layer, adhesive layer, and surface layer all contain polyester resin. Since the base layer, adhesive layer, and surface layer are all composed of the same type of resin, they have excellent recyclability. In addition, the polyester resin constituting the adhesive layer has a glass transition temperature (Tg) of -20°C or lower, so it has high peel strength and excellent durability. It also has excellent flexibility (especially low-temperature flexibility). Examples 1 to 3 are also second synthetic leathers having an adhesive layer between the base layer and the surface layer, and the base layer, adhesive layer, and surface layer all contain polyester resin. Since the base layer, adhesive layer, and surface layer are all composed of the same type of resin, they have excellent recyclability. In addition, they have high peel strength and excellent durability. They also have excellent flexibility (especially low-temperature flexibility). On the other hand, Comparative Example 1 is inferior in flexibility (especially low-temperature flexibility). Comparative Example 2 has a base layer made of polyester resin, and adhesive and surface layers made of polyurethane resin. Because the base layer and adhesive and surface layers are made of different types of resin, it is difficult to recycle. Comparative Example 3 has low peel strength and poor durability. It also has poor flexibility (especially low-temperature flexibility).

[0154] Next, the flame retardancy of the synthetic leather was evaluated when a flame retardant was incorporated into the adhesive layer of the first and second synthetic leathers.

[0155] (Flame Retardancy) (Example 11) Synthetic leather 11 was manufactured under the same conditions as in Example 1, except that Marubishi Oil & Chemical Industries Co., Ltd.'s phosphorus-based flame retardant "Non-nen DE-1" was added to the adhesive layer forming composition as a flame retardant. The amount of flame retardant added to the adhesive layer forming composition was 18.8 parts by mass per 100 parts by mass of polyester resin contained in the adhesive layer forming composition. The amount of flame retardant contained in the adhesive layer was 11.5 g / m². ２ This is the result.

[0156] (Example 12) Synthetic leather 12 was manufactured under the same conditions as in Example 1, except that Marubishi Oil & Chemical Industries Co., Ltd.'s phosphorus-based flame retardant "Non-nen DE-1" was added to the adhesive layer forming composition as a flame retardant. The amount of flame retardant added to the adhesive layer forming composition was 37.5 parts by mass per 100 parts by mass of polyester resin contained in the adhesive layer forming composition. The amount of flame retardant contained in the adhesive layer was 20.9 g / m². ２ This is the result.

[0157] Using test pieces cut from synthetic leather 11 and 12, a test according to FMVSS (Fast Motor Vehicle Safety Standards) No. 302 was performed, and the burning distance (mm), burning time (seconds), and burning rate (mm / min) were measured. The test was performed three times, and the results when the burning rate was maximum are shown in Table 9 below.

[0158] (Reference Example 1) Using a test piece cut from synthetic leather 1 described in Example 1, the above test No. 302 was performed to evaluate flame retardancy. The results are shown in Table 9 below.

[0159] (Comparative Example 4) Using test pieces cut from comparative synthetic leather 2 obtained in Comparative Example 2, the flame retardancy was evaluated by performing the test described in No. 302 above. The results are shown in Table 9 below.

[0160]

[0161] From Table 9, the following can be considered: The synthetic leathers 11 and 12 obtained in Examples 11 and 12 have a burning rate of 50 mm / min or less and exhibit excellent flame retardancy.

Claims

1. A synthetic leather having an adhesive layer between a base layer and a surface layer, wherein the base layer, the surface layer, and the adhesive layer all contain a polyester resin, and the polyester resin constituting the adhesive layer has a glass transition temperature (Tg) of -20°C or lower.

2. The synthetic leather according to claim 1, wherein the polyester resin constituting the surface layer has a glass transition temperature (Tg) of -10°C or lower.

3. The synthetic leather according to claim 1, wherein the polyester resin constituting the adhesive layer is amorphous.

4. A vehicle interior material comprising synthetic leather as described in any one of claims 1 to 3.

5. A synthetic leather having an adhesive layer between a base layer and a surface layer, wherein the base layer, the surface layer, and the adhesive layer all contain a polyester resin, the polyester resin constituting the surface layer has a glass transition temperature (Tg) of -10°C or lower, and the synthetic leather has more than 6,000 bending cycles at -20°C.

6. The adhesive layer contains 16 g / m² of flame retardant. ２ The synthetic leather according to claim 5, which contains the following:

7. The synthetic leather according to claim 6, wherein the amount of the flame retardant is 27 parts by mass or less per 100 parts by mass of the polyester resin constituting the adhesive layer.

8. The synthetic leather according to claim 5, wherein the polyester resin constituting the surface layer has a glass transition temperature (Tg) of -30°C or lower.

9. The synthetic leather according to claim 5, wherein the polyester resin constituting the adhesive layer is amorphous.

10. The synthetic leather according to claim 5, wherein the polyester resin constituting the adhesive layer has a glass transition temperature (Tg) of -5°C or lower.

11. A vehicle interior material comprising synthetic leather according to any one of claims 5 to 10.

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