Moisture-curable polyurethane hot melt resin composition, adhesive, and synthetic leather

Abstract

The present invention provides a moisture-curable polyurethane hot melt resin composition which contains an isocyanate group-containing hot melt urethane prepolymer (A) and a sulfonic acid group-containing compound (B), and which is characterized in that the hot melt prepolymer (A) contains, as a raw material, a polyol (a) containing 50 mass% or more of a polyether polyol (a1), and that the content of the compound (B) is 0.01-1 parts by mass relative to 100 parts by mass of the hot melt urethane prepolymer (A). The present invention also provides an adhesive characterized by containing the moisture-curable polyurethane hot melt resin composition. The present invention also provides a synthetic leather characterized by having at least a thermoplastic resin layer and a layer of the adhesive.

Description

[Technical field]

[0001] The present invention relates to a moisture-curable polyurethane hot-melt resin composition, an adhesive, and an artificial leather. [Background technology]

[0002] Synthetic leather uses polyurethane (PU), polyvinyl chloride (PVC), olefin-based thermoplastic elastomer (TPO), etc. as the skin material, and these skin materials are generally bonded to a base fabric such as cloth or nonwoven fabric with an adhesive (see, for example, Patent Document 1). Among these, solvent-based adhesives have been widely used and have been the most commonly used up until now, but as part of environmental efforts, regions, countries, and companies are calling for a reduction in VOCs, and it is becoming necessary to replace solvent-based with water-based or solvent-free adhesives.

[0003] Water-based systems, which are one of the VOC reduction systems, are coated on the surface layer with a low-viscosity compound liquid, then dried to remove the solvent, and if necessary, aged to obtain a strong coating. The low viscosity of these systems allows them to wet well with the surface material, making it easy to obtain adhesion. However, the drying process requires more drying energy than solvent-based systems, making production efficiency an issue. On the other hand, polyurethane-based reactive hot melt adhesives (RHM) are being actively studied as a solvent-free system, which is another VOC reduction system. However, RHMs generally have low wettability with adherends such as PVC surface materials, which is one of the coating substrates, making it difficult to achieve sufficient performance in terms of adhesion, even when using conventional RHMs. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2008-514403 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a moisture-curable polyurethane hot-melt resin composition that is excellent in adhesion, low-temperature flexibility, and durability. [Means for solving the problem]

[0006] The present invention provides a moisture-curable polyurethane hot-melt resin composition containing a hot-melt urethane prepolymer (A) having an isocyanate group and a compound (B) having a sulfonic acid group, wherein the hot-melt prepolymer (A) is made from a polyol (a) containing 50 mass% or more of a polyether polyol (a1), and the content of the compound (B) is in the range of 0.01 to 1 part by mass per 100 mass parts of the hot-melt urethane prepolymer (A).

[0007] The present invention also provides an adhesive comprising the moisture-curable polyurethane hot melt resin composition. The present invention also provides synthetic leather having at least a thermoplastic resin layer and the adhesive layer. Effect of the Invention

[0008] The moisture-curable polyurethane hot-melt resin composition of the present invention is excellent in adhesion (particularly adhesion to polyvinyl chloride), low-temperature flexibility, and durability. Therefore, the moisture-curable polyurethane hot-melt resin composition of the present invention can be particularly suitably used in the production of synthetic leather using a thermoplastic resin as a skin material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The moisture-curable polyurethane hot-melt resin composition of the present invention contains a hot-melt urethane prepolymer (A) having an isocyanate group, which is made from a specific polyol (a), and a specific amount of a specific compound (B).

[0010] In order to obtain excellent low-temperature flexibility, the hot melt urethane prepolymer (A) having an isocyanate group must be made from a polyol (a) containing 50% by mass or more of a polyether polyol (a1). By designing in this way, the glass transition temperature of the adhesive can be lowered, and therefore excellent low-temperature flexibility can be obtained. The amount of the polyether polyol (a1) used is preferably 50 to 90% by mass, more preferably 55 to 70% by mass, of the polyol (a) in order to obtain even better low-temperature flexibility.

[0011] Examples of the polyether polyol (a1) include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxyethylene polyoxytetramethylene glycol, and polyoxypropylene polyoxytetramethylene glycol. These polyols may be used alone or in combination of two or more. Among these, polypropylene glycol and / or polytetramethylene glycol are preferred because they provide better low-temperature flexibility, and polytetramethylene glycol is more preferred because they provide better heat resistance and wet heat resistance. The polyether polyol may be derived from a plant. Examples of the plant-derived polyether polyol include commercially available products such as "Bio PTMG" manufactured by Mitsubishi Chemical Corporation, "Bio PTG" manufactured by Hodogaya Chemical Co., Ltd., and biomass polypropylene glycol manufactured by Vithal Castor Polyols.

[0012] As the polyol (a), other polyols can be used in combination with the polyether polyol (a). As the other polyols, for example, commercially available polyols such as polyester polyols, polycarbonate polyols, polybutadiene polyols, silicon diols, and acrylic diols can be used. These polyols may be used alone or in combination of two or more, and may be derived from petroleum or plants. As the other polyols, polyester polyols are preferred because they provide even better adhesion.

[0013] The number average molecular weight of the polyol (a) is preferably 200 to 10,000, more preferably 500 to 6,000, from the viewpoint of obtaining even better adhesiveness, low-temperature flexibility, durability, and mechanical strength. The number average molecular weight of the polyol (a) is a value measured by gel permeation chromatography (GPC).

[0014] The hot-melt urethane prepolymer (A) having an isocyanate group can be, for example, a reaction product of the polyol (a) and the polyisocyanate (b).

[0015] As the polyisocyanate (b), for example, aromatic polyisocyanates such as polymethylene polyphenyl polyisocyanate, diphenylmethane diisocyanate, carbodiimide-modified diphenylmethane diisocyanate isocyanate, phenylene diisocyanate, tolylene diisocyanate, and naphthalene diisocyanate; aliphatic or alicyclic polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate can be used. These polyisocyanates may be used alone or in combination of two or more, and may be derived from petroleum or plants. Among these, aromatic polyisocyanates are preferred, and diphenylmethane diisocyanate is more preferred, in view of obtaining even better reactivity and adhesion.

[0016] The hot-melt urethane prepolymer (A) has isocyanate groups at the polymer terminals or within the molecule, which are capable of forming a crosslinked structure upon reaction with moisture present in the air or in the substrate or adherend to which the urethane prepolymer is applied.

[0017] The hot-melt urethane prepolymer (A) can be produced, for example, by adding the polyol (a) dropwise to a reaction vessel containing the polyisocyanate (b), followed by heating and reacting under conditions in which the isocyanate groups of the polyisocyanate (b) are in excess of the hydroxyl groups of the polyol (a).

[0018] When the polyol (a) and the polyisocyanate (b) are reacted, the molar ratio [NCO / OH] of the hydroxyl groups in the polyol (a) to the isocyanate groups in the polyisocyanate (b) is preferably 1.3 to 2.5, and more preferably 1.5 to 2.0, in order to obtain even better hot melt properties, adhesion, durability, and low-temperature flexibility.

[0019] The isocyanate group content (hereinafter abbreviated as "NCO%") of the hot-melt urethane prepolymer (A) is preferably 1.2 to 5.0 mass%, more preferably 1.7 to 3.5 mass%, in order to obtain even more excellent hot-melt properties, adhesion, durability, and low-temperature flexibility. The NCO% of the hot-melt urethane prepolymer (A) is a value measured by potentiometric titration in accordance with JIS K1603-1:2007.

[0020] The compound (B) having a sulfonic acid group is an essential component for obtaining excellent adhesiveness, and its content must be in the range of 0.01 to 1 part by mass relative to 100 parts by mass of the hot-melt urethane prepolymer (A) in order to achieve both excellent adhesiveness and durability. The content of the compound (B) is preferably 0.05 to 0.6 parts by mass relative to 100 parts by mass of the hot-melt urethane prepolymer (A) in order to maintain high levels of adhesiveness and durability.

[0021] As the compound (B), for example, methanesulfonic acid, ethanesulfonic acid, methanedisulfonic acid, 2-hydroxy-1-ethanesulfonic acid, sulfoacetic acid, 2-amino-1-ethanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, alkylbenzenesulfonic acid, etc. can be used. These compounds may be used alone or in combination of two or more. Among these, methanesulfonic acid is particularly preferred from the viewpoint of further improving adhesion to polyvinyl chloride.

[0022] The moisture-curable polyurethane hot-melt resin composition of the present invention contains the hot-melt urethane prepolymer (A) and the compound (B) as essential components, and may contain other additives as necessary.

[0023] Examples of the other additives that can be used include urethanization catalysts, neutralizing agents, crosslinking agents, silane coupling agents, thickeners, fillers, thixotropic agents, tackifiers, waxes, heat stabilizers, light resistance stabilizers, fluorescent whitening agents, foaming agents, pigments, dyes, conductivity-imparting agents, antistatic agents, moisture permeability enhancers, water repellents, oil repellents, hollow foams, water absorbents, moisture absorbents, deodorants, foam stabilizers, plasticizers, antiblocking agents, hydrolysis inhibitors, etc. These additives may be used alone or in combination of two or more.

[0024] As described above, the moisture-curable polyurethane hot-melt resin composition of the present invention has excellent adhesion, low-temperature flexibility, and durability. Therefore, the moisture-curable polyurethane hot-melt resin composition of the present invention can be particularly suitably used for the production of synthetic leather using a thermoplastic resin as a skin material.

[0025] Next, the synthetic leather of the present invention will be described.

[0026] The synthetic leather has at least a thermoplastic resin layer and an adhesive layer containing the moisture-curable polyurethane hot-melt resin composition, and can be, for example, a layer obtained by sequentially laminating a substrate, the adhesive layer, and a thermoplastic resin layer.

[0027] Examples of the substrate that can be used include nonwoven fabrics, woven fabrics, knitted fabrics, and the like made of polyester fibers, polyethylene fibers, nylon fibers, acrylic fibers, polyurethane fibers, acetate fibers, rayon fibers, polylactic acid fibers, cotton, hemp, silk, wool, glass fibers, carbon fibers, and blends thereof.

[0028] The thermoplastic resin layer can be formed of, for example, known polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polystyrene, TPO (Thermoplastic Olefinic Elastomer), thermoplastic ester-based elastomer, thermoplastic polyurethane, etc. In the present invention, even when polyvinyl chloride is used as the thermoplastic resin, excellent adhesion is obtained.

[0029] The adhesive layer is formed from the moisture-curable polyurethane hot-melt resin composition of the present invention. Examples of a method for forming the adhesive layer include a method in which the moisture-curable polyurethane hot-melt resin composition is melted at 100 to 140°C, and then coated onto the thermoplastic resin layer or the substrate using a coater method such as a roll coater, spray coater, T-die coater, knife coater, or comma coater; a precision method such as a dispenser, inkjet printing, screen printing, or offset printing; or a nozzle coater, and then the layers are bonded together.

[0030] After the two layers are bonded together with the adhesive, the adhesive can be dried and cured as necessary by a known method.

[0031] The synthetic leather may further include a surface treatment layer on the thermoplastic resin layer. The surface treatment layer may be made of, for example, a known solvent-based urethane resin, water-based urethane resin, solvent-based acrylic resin, water-based acrylic resin, or the like. EXAMPLES

[0032] The present invention will now be described in more detail with reference to examples.

[0033] [Example 1] A four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet, and a reflux condenser was charged with 122 parts by mass of polytetramethylene glycol (number average molecular weight: 2,000, hereinafter abbreviated as "PEt-1"), 73 parts by mass of polyester polyol (a reaction product of 1,6-hexanediol and orthophthalic acid, number average molecular weight: 2,000, hereinafter abbreviated as "PEs-1"), and 49 parts by mass of polyester polyol (a reaction product of 1,6-hexanediol and sebacic acid, number average molecular weight: 3,500, hereinafter abbreviated as "PEs-2"), mixed, and heated under reduced pressure at 100°C to dehydrate the water in the flask until the water content was 0.05% by mass or less. Next, the flask was cooled to 90°C, and 57 parts by mass of 4,4'-diphenylmethane diisocyanate (hereinafter abbreviated as "MDI") melted at 70°C was added, and the mixture was reacted at 110°C for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot-melt urethane prepolymer. 0.45 parts by mass of methanesulfonic acid (hereinafter abbreviated as "compound (B1)") was mixed with 100 parts by mass of this hot-melt urethane prepolymer to obtain a moisture-curable polyurethane hot-melt resin composition (1).

[0034] [Example 2] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 119 parts by mass of PEt-1, 50 parts by mass of PEs-1 and 30 parts by mass of PEs-2 were put, mixed and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 44 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.1 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (2).

[0035] [Example 3] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 188 parts by mass of polypropylene glycol (number average molecular weight: 2,000, hereinafter abbreviated as "PEt-2"), 68 parts by mass of PEs-1, and 85 parts by mass of polyester polyol (ethylene glycol, neopentyl glycol, 16-hexanediol, and adipic acid reacted, number average molecular weight: 5,500, hereinafter abbreviated as "PEs-3") were added, mixed, and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 69 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.3 parts by mass of compound (B1) was mixed with 100 parts by mass of this hot-melt urethane prepolymer to obtain a moisture-curable polyurethane hot-melt resin composition (3).

[0036] [Example 4] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 52 parts by mass of PEt-1, 22 parts by mass of PEs-1, and 13 parts by mass of PEs-2 were put, mixed, and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 19 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.25 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (4).

[0037] [Example 5] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 83 parts by mass of PEt-2, 19 parts by mass of PEs-1, and 26 parts by mass of PEs-3 were put, mixed, and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 28 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.85 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (5).

[0038] [Example 6] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 208 parts by mass of PEt-1, 48 parts by mass of PEs-1, and 64 parts by mass of PEs-3 were put, mixed, and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 66 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.3 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (6).

[0039] [Example 7] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 29 parts by mass of PEt-1, 29 parts by mass of PEt-2, 19 parts by mass of PEs-1 and 19 parts by mass of PEs-2 were put, mixed and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 21 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.1 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (7).

[0040] [Example 8] A moisture-curable polyurethane hot-melt resin composition (8) was obtained in the same manner as in Example 1, except that PEt-1 was replaced with biomass polytetramethylene glycol ("Bio PTMG" manufactured by Mitsubishi Chemical Corporation, number average molecular weight: 2,000).

[0041] [Comparative Example 1] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 67 parts by mass of PEt-1, 24 parts by mass of PEs-1 and 18 parts by mass of PEs-2 were put, mixed and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 24 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.005 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (R1).

[0042] [Comparative Example 2] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 139 parts by mass of PEt-2, 58 parts by mass of PEs-1, and 35 parts by mass of PEs-2 were put, mixed, and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 52 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 2 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (R2).

[0043] [Comparative Example 3] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 58 parts by mass of PEt-1, 58 parts by mass of PEs-1 and 50 parts by mass of PEs-3 were placed, mixed and heated under reduced pressure at 100°C to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90°C, 32 parts by mass of MDI melted at 70°C was added, and the mixture was reacted at 110°C for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot-melt urethane prepolymer and a moisture-curable polyurethane hot-melt resin composition (R3).

[0044] [Comparative Example 4] In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet and a reflux condenser, 54 parts by mass of PEt-1, 81 parts by mass of PEs-1, and 45 parts by mass of PEs-3 were put, mixed, and heated under reduced pressure at 100 ° C. to dehydrate the water content in the flask to 0.05% by mass or less. Next, the flask was cooled to 90 ° C., 37 parts by mass of MDI melted at 70 ° C. was added, and the mixture was reacted at 110 ° C. for about 3 hours under a nitrogen atmosphere until the isocyanate group content became constant, to obtain a hot melt urethane prepolymer. 0.3 parts by mass of compound (B1) was blended with 100 parts by mass of this hot melt urethane prepolymer to obtain a moisture-curable polyurethane hot melt resin composition (R4).

[0045] [Method of measuring number average molecular weight and weight average molecular weight] The number average molecular weights of the polyols used in the examples and comparative examples are values ​​measured by gel permeation column chromatography (GPC) under the following conditions.

[0046] Measurement equipment: High-speed GPC equipment (Tosoh Corporation "HLC-8220GPC") Column: The following columns manufactured by Tosoh Corporation were used, connected in series. "TSKgel G5000" (7.8mm I.D. x 30cm) x 1 "TSKgel G4000" (7.8mm I.D. x 30cm) x 1 "TSKgel G3000" (7.8mm I.D. x 30cm) x 1 "TSKgel G2000" (7.8mmI.D. x 30cm) x 1 Detector: RI (differential refractometer) Column temperature: 40℃ Eluent: tetrahydrofuran (THF) Flow rate: 1.0mL / min Injection volume: 100 μL (sample concentration 0.4% by mass in tetrahydrofuran solution) Standard sample: A calibration curve was prepared using the following standard polystyrene.

[0047] (Standard polystyrene) "TSKgel Standard Polystyrene A-500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-1000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-2500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-5000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-1" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-2" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-4" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-10" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-20" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-40" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-80" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-128" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-288" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-550" manufactured by Tosoh Corporation

[0048] [How to make synthetic leather] In a constant temperature and humidity room adjusted to a temperature of 23°C and a humidity of 50±5%, the moisture-curable polyurethane hot melt resin compositions obtained in the examples and comparative examples were applied to a polyvinyl chloride sheet at a rate of 40±5 g / m using a gravure coater. 2 The mixture was then laminated to a polyester fabric and left to mature for 24 hours at a temperature of 23°C and a humidity of 50±5% to obtain synthetic leather.

[0049] [Method of evaluating adhesion] The peel strength of each of the obtained synthetic leathers was measured using a Tensilon (Tensilon universal testing machine "RTC-1210A" manufactured by Orientec Co., Ltd.) at a crosshead speed of 200 mm / min, and a value of 6 N / cm or more was evaluated as "○", and a value of less than 6 N / cm was evaluated as "×".

[0050] [Evaluation method for low temperature bending properties] Each of the obtained synthetic leathers was subjected to a bending test using a flexometer (-10°C, 100 times per minute) to measure the number of times it was bent until cracks appeared on the surface of the synthetic leather. 20,000 times or more was evaluated as "○", and less than 20,000 times was evaluated as "×".

[0051] [Durability evaluation method] The moisture-curable polyurethane hot melt resin composition obtained in the examples and comparative examples was applied to a thickness of 30 microns using a roll coater, and then aged for 24 hours or more under conditions of a temperature of 23 ° C. and a humidity of 50 ± 5% to produce a film. Next, the obtained film was cut into strips with a width of 5 mm and a length of 50 mm, and pulled at a crosshead speed of 10 mm / sec under an atmosphere of a temperature of 23 ° C. using a tensile tester "Autograph AG-i" (manufactured by Shimadzu Corporation), and the 100% modulus (MPa) of the test piece was measured. The chuck distance at this time was 40 mm. Furthermore, the film strength of the film prepared was measured after leaving it for 5 weeks under conditions of a temperature of 70 ° C. and a humidity of 95 ± 5% as a durability test, and the value of the 100% modulus (MPa) at that time was measured, and the value divided by the value of the 100% modulus (MPa) of the test piece before the durability test was taken as the retention rate of the 100% modulus. A retention rate of 30% or more was marked as "○", a retention rate of 10% or more but less than 30% was marked as "△", and a retention rate of less than 10% was marked as "×".

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] It was found that Examples 1 to 8, which are moisture-curable polyurethane hot-melt resin compositions of the present invention, were excellent in adhesion, low-temperature flexibility, and durability.

[0056] On the other hand, in Comparative Example 1, the content of compound (B) was below the range specified in the present invention, but the adhesion was poor.

[0057] In Comparative Example 2, the content of compound (B) exceeded the range specified in the present invention, but the durability was poor.

[0058] Comparative Example 3 is an embodiment in which the amount of polyether polyol (a1) used was below the range specified in the present invention and no compound (B) was used, but the adhesion and low-temperature flexibility were poor.

[0059] In Comparative Example 4, the amount of polyether polyol (a1) used was below the range specified in the present invention, but the low-temperature flexibility was poor.

Claims

[Claim 1] A synthetic leather having at least a thermoplastic resin layer and an adhesive layer formed of an adhesive containing a moisture-curable polyurethane hot melt resin composition, the thermoplastic resin is polyvinyl chloride, The moisture-curable polyurethane hot-melt resin composition contains a hot-melt urethane prepolymer (A) having an isocyanate group and a compound (B) having a sulfonic acid group, the hot melt prepolymer (A) is made from a polyol (a) including a polyether polyol (a1) and a polyester polyol, and is not made from an acrylic polyol; the amount of the polyether polyol (a1) used is in the range of 50 to 90 mass% in the polyol (a); The synthetic leather is characterized in that the compound (B) is methanesulfonic acid, and the content of the compound (B) is in the range of 0.05 to 1 part by mass per 100 parts by mass of the hot-melt urethane prepolymer (A).

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