Solvent-free polyurethane synthetic leather bonding layer and preparation method thereof

Abstract

The invention belongs to the technical field of polyurethane materials, and particularly relates to a solvent-free polyurethane synthetic leather bonding layer and a preparation method thereof. The bonding layer is formed by mixing a component A and a component B according to the mass ratio of 100: (80-100); the component A comprises the following components in percentage by mass: 40-50% of polyether polyol a; 30% to 40% of polyether polyol b; 8%-12% of polyether polyol c; 3%-5% of a hardening agent; 0.2%-0.4% of a foaming agent; 0.3%-0.6% of a composite catalyst; 0.5%-1.0% of a foam stabilizer; 3%-5% of a surfactant; the component B comprises 40%-55% of polyester polyol; and liquefying 45%-60% of MDI (methylene diphenyl diisocyanate). The peeling strength of the water-based surface layer and the solvent-free bonding layer is improved, and the low-temperature flexibility, the hydrolysis resistance, the hydrophobicity and the aging resistance are remarkably improved. The invention also provides a preparation method thereof.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane materials, and in particular relates to a solvent-free polyurethane synthetic leather adhesive layer and a preparation method thereof. Background Art

[0002] Polyurethane synthetic leather is a kind of artificial leather, which is made by coating polyurethane resin on the base fabric and undergoing a series of processing steps. It is widely used in many fields such as clothing, shoes, home decoration and automobile interior due to its wear resistance, softness and breathability. It is the most ideal substitute for natural leather.

[0003] In recent years, with the continuous development of the synthetic leather industry, new environmentally friendly synthetic leathers such as TPU synthetic leather, water-based synthetic leather, and solvent-free synthetic leather have emerged rapidly, bringing new opportunities for the environmentally friendly and clean road of the synthetic leather industry. Among them, the technology with water-based polyurethane as the surface layer and solvent-free synthetic leather as the adhesive layer is the most prominent. Since this technology combines the advantages of water-based and solvent-free synthetic leathers, the performance has also been significantly improved, with better wear resistance, softness and breathability, further broadening the application field of synthetic leather, and therefore has attracted much attention.

[0004] However, most of the waterborne polyurethanes used in the waterborne surface layer are carboxylic acid type, and their preparation method mainly uses dimethylol propionic acid (DMPA) as a hydrophilic group. The solvent-free adhesive layer is usually connected only by hydrogen bonds and van der Waals forces, and the peel strength is poor. In addition, waterborne / solvent-free synthetic leather products also have the disadvantages of poor low-temperature compliance, poor hydrophobicity, and poor aging resistance. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a solvent-free polyurethane synthetic leather adhesive layer, which generates no solvent during production and use, improves the peel strength of the water-based surface layer and the solvent-free adhesive layer, and significantly improves the low-temperature compliance, hydrolysis resistance, hydrophobicity and aging resistance. The present invention also provides a preparation method thereof.

[0006] The solvent-free polyurethane synthetic leather adhesive layer of the present invention is composed of a mixture of component A and component B in a mass ratio of 100:(80-100); In terms of mass percentage, component A is: Polyether polyol a, 40%~50%; Polyether polyol b, 30%~40%; Polyether polyol c, 8%~12%; Hardener, 3%~5%; Foaming agent, 0.2%~0.4%; Composite catalyst, 0.3%~0.6%; Foam stabilizer, 0.5%~1.0%; Surfactant, 3%~5%; Group B is composed of: Polyester polyol, 40%~55%; Liquefied MDI, 45%~60%.

[0007] The polyether polyol a is polytetramethylene ether diol, with a functionality of 2 and a number average molecular weight of 3000. PTMG3000 produced by BASF (China) Co., Ltd. is preferred.

[0008] The polyether polyol b is prepared by ring-opening polymerization of propylene oxide using hydroxy polysiloxane and trimethylolpropane as composite initiators and KOH as a catalyst, and has a functionality of 2 and a number average molecular weight of 1000-1500. The hydroxy polysiloxane is preferably hydroxy-terminated polydimethylsiloxane, and has a CAS number of 70131-67-8.

[0009] The preparation method of polyether polyol b comprises the following steps: (1) Add terminal hydroxyl polydimethylsiloxane, trimethylolpropane and KOH into a high-pressure reactor, and after nitrogen replacement twice, start to evacuate to -0.95~-0.1MPa, maintain vacuum, raise the temperature to 120~130℃, keep it warm for 3~4h, then cool it down to 110℃, continuously introduce propylene oxide, and control the pressure in the reactor to be less than 0.2MPa. After the introduction, keep it warm at 120℃ until negative pressure appears, and then cool it down to discharge the material to obtain crude ether; (2) Pour the crude ether into a container equipped with a stirrer and a thermometer, add distilled water, raise the temperature to 90-95°C, and stir for 2-3 hours; add phosphoric acid, stir for 1-1.5 hours, add the refining agent magnesium silicate, and stir for another 1-2 hours; vacuum dehydrate at 110-120°C to a moisture content of ≤0.05%, filter out the refining agent, and obtain polyether polyol b.

[0010] The polyether polyol c is polyoxypropylene triol terminated with ethylene oxide, having a functionality of 3 and a number average molecular weight of 7000 to 8000. CHE-2901L produced by Changhua Chemical Technology Co., Ltd. is preferred.

[0011] The hardener is 1,4-butanediol.

[0012] The blowing agent is water.

[0013] The composite catalyst is a composite of a delayed amine catalyst and a thermosensitive catalyst, and the mass ratio of the delayed amine catalyst to the thermosensitive catalyst is 1: 1. The delayed amine catalyst is preferably SA-102 from Evonik Specialty Chemicals Co., Ltd., and the thermosensitive catalyst is preferably MP608 from Evonik Specialty Chemicals Co., Ltd.

[0014] The foam stabilizer is a polysiloxane-olefin oxide block copolymer, preferably 8835 from The Dow Chemical Company.

[0015] The surfactant is a fluorinated polysiloxane copolymer, preferably (3,3,3-trifluoropropyl)trimethoxysilane, with a CAS number of 429-60-7.

[0016] The polyester polyol is a bio-based polyester polyol, which is polymerized from castor oil, 1,4-butanediol and a small molecular weight polyacid, and has a hydroxyl value of 85-90 mgKOH / g. The small molecular weight polyacid is preferably 1,6-hexanoic acid.

[0017] The preparation method of polyester polyol is as follows: add 1,6-hexanedioic acid, 1,4-butanediol and castor oil into a reaction kettle, start stirring, and when the temperature rises to 135-140°C, water begins to be discharged, and the condensation reflux temperature is controlled to be 100-105°C, and then the temperature is gradually increased to 220-240°C, and vacuum is gradually drawn until the hydroxyl value is 85-90 mgKOH / g and the moisture content is ≤0.05%, and then the temperature is reduced to 80°C to discharge the material.

[0018] The liquefied MDI is carbodiimide modified MDI, preferably MM103C produced by BASF (China) Co., Ltd.

[0019] The method for preparing the solvent-free polyurethane synthetic leather adhesive layer of the present invention comprises the following steps: (1) Component A: First, add polyether polyol a, polyether polyol b, polyether polyol c, hardener, foaming agent, composite catalyst, foam stabilizer and surfactant based on the formula amount into an autoclave and stir. Heat to 40-50°C, rotate at 30-40 r / min, and stir for 1-2 hours to obtain component A. (2) Component B: Add polyester polyol into a reactor, heat to 110-120°C and perform vacuum dehydration for 3-4 hours, then cool to 45-50°C, add liquefied MDI, heat to 75-80°C and keep warm for 1-2 hours, take samples for testing, and when the mass percentage of -NCO reaches 9.5%-15%, cool down, discharge the material, and seal for storage.

[0020] The component A and the component B are mixed evenly in a mass ratio of 100:(80-100), and placed in an oven at 120-150° C. for aging for 5-8 minutes to obtain the solvent-free polyurethane synthetic leather adhesive layer.

[0021] The invention is adopted to prepare solvent-free polyurethane synthetic leather: firstly, a water-based polyurethane surface layer is roller-coated on release paper, and the surface layer is placed in an oven at 120-150°C for curing for 5-8 minutes to form a water-based coating, and the surface layer is taken out for standby; component A and component B are mixed evenly at a mass ratio of 100:(80-100), and then coated on the surface of the water-based coating to form an adhesive layer coating, and the surface layer is placed in an oven at 120-150°C, and when the adhesive layer coating begins to turn milky white, the surface layer is taken out from the oven and covered with a non-woven fabric, and the surface layer is placed in an oven at 120-150°C for curing for 5-8 minutes to obtain the solvent-free polyurethane synthetic leather.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The B component of the present invention adopts carbodiimide isocyanate to introduce the carbodiimide structure into the main chain of the polyurethane molecule of the adhesive layer. The carbodiimide group can react with the carboxyl group in the water-based surface layer to form a covalent bond, thereby improving the peel strength of the water-based surface layer and the solvent-free adhesive layer; 2. The present invention introduces polysiloxane polyether polyol and fluorinated polysiloxane copolymer into component A, and castor oil-modified polyester polyol into component B, so that the low-temperature compliance, hydrolysis resistance, hydrophobicity and aging resistance of the product are significantly improved; 3. The present invention adopts a thermosensitive catalyst to increase the operating time of the combined material; 4. The preparation method of the present invention has simple process and high production efficiency. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below in conjunction with embodiments.

[0024] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0025] Example 1 The solvent-free polyurethane synthetic leather adhesive layer is prepared by mixing component A and component B in a mass ratio of 100:100, wherein component A includes the following raw materials: PTMG3000, 50kg; Polyether polyol b, 32.5 kg; CHE-2901L, 8kg; Hardener 1,4-butanediol, 4.5 kg; Foaming agent water, 0.2kg; Composite catalyst (SA-102 and MP608 in a mass ratio of 1:1), 0.3 kg; Foam stabilizer 8835, 0.5kg; Surfactant (3,3,3-trifluoropropyl)trimethoxysilane, 4 kg; The raw materials of component B are: Polyester polyol, 55 kg; MM103C, 45kg.

[0026] Among them, the polyether polyol b has a functionality of 2 and a number average molecular weight of 1500. The specific preparation method comprises the following steps: (1) Add 1 mol of hydroxy-terminated polydimethylsiloxane, 1 mol of trimethylolpropane and 0.05 g of KOH into a high-pressure reactor, and after nitrogen replacement twice, start to evacuate to -0.1 MPa, maintain vacuum, raise the temperature to 130°C, keep it warm for 4 hours, then cool it down to 110°C, continuously introduce 16.7 mol of propylene oxide, and control the pressure in the reactor to be less than 0.2 MPa. After the introduction, keep it warm at 120°C until negative pressure appears, and then cool it down and discharge the material to obtain crude ether; (2) Pour the crude ether into a container equipped with a stirrer and a thermometer, add distilled water, raise the temperature to 95°C, and stir for 3 hours; add 0.06 g of phosphoric acid, stir for 1.5 hours, add 7 g of the refining agent magnesium silicate, and stir for another 2 hours; vacuum dehydrate at 110°C to a moisture content of ≤0.05%, filter out the refining agent, and obtain polyether polyol b.

[0027] The polyester polyol is a bio-based polyester polyol with a hydroxyl value of 88 mgKOH / g. The specific preparation method is as follows: Add 6.85 mol 1,6-hexanedioic acid, 6.13 mol 1,4-butanediol and 6.13 mol castor oil into the reactor and start stirring. When the temperature rises to 138°C, water begins to come out. Control the condensation reflux temperature at 102°C, then gradually increase the temperature to 230°C, start to gradually evacuate until the hydroxyl value is 88 mgKOH / g and the moisture content is ≤0.05%, then cool to 80°C and discharge the material.

[0028] The method for preparing the solvent-free polyurethane synthetic leather adhesive layer comprises the following steps: (1) Preparation of component A: first, PTMG3000, polyether polyol b, CHE-2901L, hardener 1,4-butanediol, foaming agent water, composite catalyst, foam stabilizer 8835 and surfactant (3,3,3-trifluoropropyl) trimethoxysilane were put into an autoclave and stirred, the temperature was raised to 45°C, the speed was 35 r / min, and the stirring was carried out for 1.5 h to obtain component A; (2) Preparation of component B: Add polyester polyol into a reactor, heat to 115°C and vacuum dehydrate for 3.5 hours, then cool to 48°C, add MM103C, heat to 78°C and keep warm for 1.5 hours, take samples for testing, and when the mass percentage of -NCO reaches 9.5%, cool down, discharge the material, and seal for storage.

[0029] The component A and the component B were mixed evenly at a mass ratio of 100:100, and placed in an oven at 140° C. for aging for 7 minutes to obtain the solvent-free polyurethane synthetic leather adhesive layer sample.

[0030] Preparation of solvent-free polyurethane synthetic leather: first, a water-based polyurethane surface layer (anionic water-based polyurethane KL-718, Hefei Amway Polyurethane New Materials Co., Ltd.) was roller-coated onto release paper, placed in a 140°C oven for aging for 7 minutes to form a water-based coating, and then taken out for use; component A and component B were evenly mixed in a mass ratio of 100:100, and then coated on the surface of the water-based coating to form an adhesive layer coating, which was placed in a 140°C oven. When the adhesive layer coating began to turn milky white, it was taken out of the oven and covered with non-woven fabric, and then continued to be placed in a 130°C oven for aging for 7 minutes to obtain solvent-free polyurethane synthetic leather.

[0031] Example 2 The solvent-free polyurethane synthetic leather adhesive layer is prepared by mixing component A and component B in a mass ratio of 100:90, wherein component A includes the following raw materials: PTMG3000, 49kg; Polyether polyol b, 30 kg; CHE-2901L, 9.5kg; Hardener 1,4-butanediol, 5kg; Foaming agent water, 0.3kg; Composite catalyst (SA-102 and MP608 in a mass ratio of 1:1), 0.4 kg; Foam stabilizer 8835, 0.8kg; Surfactant (3,3,3-trifluoropropyl)trimethoxysilane, 5 kg; The raw materials of component B are: Polyester polyol, 50 kg; MM103C, 50kg.

[0032] Among them, the polyether polyol b has a functionality of 2 and a number average molecular weight of 1200. The specific preparation method comprises the following steps: (1) Add 1 mol of hydroxy-terminated polydimethylsiloxane, 1 mol of trimethylolpropane and 0.03 g of KOH into a high-pressure reactor, and after nitrogen replacement twice, start to evacuate to -0.98 MPa, maintain vacuum, raise the temperature to 125°C, keep it warm for 3.5 hours, then cool it down to 110°C, continuously introduce 11.5 mol of propylene oxide, and control the pressure in the reactor to be less than 0.2 MPa. After the introduction, keep it warm at 120°C until negative pressure appears, and then cool it down and discharge the material to obtain crude ether; (2) Pour the crude ether into a container equipped with a stirrer and a thermometer, add distilled water, raise the temperature to 92°C, and stir for 2.5 hours; add 0.06 g of phosphoric acid, stir for 1.2 hours, add 5 g of the refining agent magnesium silicate, and stir for another 1.5 hours; vacuum dehydrate at 110°C to a moisture content of ≤0.05%, filter out the refining agent, and obtain polyether polyol b.

[0033] The polyester polyol is a bio-based polyester polyol with a hydroxyl value of 90 mgKOH / g. The specific preparation method is as follows: Add 6.85 mol 1,6-hexanedioic acid, 7.13 mol 1,4-butanediol and 3.65 mol castor oil into the reaction kettle, start stirring, and when the temperature rises to 140°C, water begins to come out. Control the condensation reflux temperature at 105°C, then gradually raise the temperature to 240°C, start to gradually evacuate until the hydroxyl value is 90 mgKOH / g and the moisture content is ≤0.05%, then cool to 80°C and discharge the material.

[0034] The method for preparing the solvent-free polyurethane synthetic leather adhesive layer comprises the following steps: (1) Preparation of component A: first, PTMG3000, polyether polyol b, CHE-2901L, hardener 1,4-butanediol, foaming agent water, composite catalyst, foam stabilizer 8835 and surfactant (3,3,3-trifluoropropyl) trimethoxysilane were put into an autoclave and stirred, the temperature was raised to 50°C, the speed was 40r / min, and the stirring was carried out for 2h to obtain component A; (2) Preparation of component B: Add polyester polyol into a reactor, heat to 120°C and vacuum dehydrate for 4 h, then cool to 50°C, add MM103C, heat to 80°C and keep warm for 2 h, take samples for testing, and the mass percentage of -NCO reaches 11.3%. Cool down, discharge, and seal for storage.

[0035] The component A and the component B were mixed evenly in a mass ratio of 100:90, and placed in an oven at 150° C. for aging for 8 minutes to obtain the solvent-free polyurethane synthetic leather adhesive layer sample.

[0036] Preparation of solvent-free polyurethane synthetic leather: first, a water-based polyurethane surface layer (anionic water-based polyurethane KL-718, Hefei Amway Polyurethane New Materials Co., Ltd.) was roller-coated onto release paper, placed in a 150°C oven for aging for 8 minutes to form a water-based coating, and then taken out for use; component A and component B were evenly mixed in a mass ratio of 100:90, and then coated on the surface of the water-based coating to form an adhesive layer coating, which was placed in a 150°C oven. When the adhesive layer coating began to turn milky white, it was taken out of the oven and covered with non-woven fabric, and then continued to be placed in a 150°C oven for aging for 8 minutes to obtain solvent-free polyurethane synthetic leather.

[0037] Example 3 The solvent-free polyurethane synthetic leather adhesive layer is prepared by mixing component A and component B in a mass ratio of 100:80, wherein component A includes the following raw materials: PTMG3000, 40kg; Polyether polyol b, 40 kg; CHE-2901L, 12kg; Hardener 1,4-butanediol, 3kg; Foaming agent water, 0.4kg; Composite catalyst (SA-102 and MP608 in a mass ratio of 1:1), 0.6 kg; Foam stabilizer 8835, 1.0kg; Surfactant (3,3,3-trifluoropropyl)trimethoxysilane, 3 kg; The raw materials of component B are: Polyester polyol, 40 kg; MM103C, 60kg.

[0038] Among them, the polyether polyol b has a functionality of 2 and a number average molecular weight of 1000. The specific preparation method comprises the following steps: (1) Add 1 mol of hydroxy-terminated polydimethylsiloxane, 1 mol of trimethylolpropane and 0.04 g of KOH into a high-pressure reactor, and after nitrogen replacement twice, start to evacuate to -0.95 MPa, maintain vacuum, raise the temperature to 120°C, keep it warm for 3 hours, then cool it down to 110°C, continuously introduce 8.1 mol of propylene oxide, and control the pressure in the reactor to be less than 0.2 MPa. After the introduction, keep it warm at 120°C until negative pressure appears, and then cool it down and discharge the material to obtain crude ether; (2) Pour the crude ether into a container equipped with a stirrer and a thermometer, add distilled water, raise the temperature to 90°C, and stir for 2 hours; add 0.03 g of phosphoric acid, stir for 1 hour, add 4 g of the refining agent magnesium silicate, and stir for another 1 hour; vacuum dehydrate at 110°C to a moisture content of ≤0.05%, filter out the refining agent, and obtain polyether polyol b.

[0039] The polyester polyol is a bio-based polyester polyol with a hydroxyl value of 85 mgKOH / g. The specific preparation method is as follows: Add 6.85 mol 1,6-hexanedioic acid, 4.46 mol 1,4-butanediol and 8.91 mol castor oil into the reaction kettle, start stirring, and when the temperature rises to 135°C, water begins to come out. Control the condensation reflux temperature at 100°C, then gradually increase the temperature to 220°C, start to gradually evacuate until the hydroxyl value is 85 mgKOH / g and the moisture content is ≤0.05%, then cool to 80°C and discharge the material.

[0040] The method for preparing the solvent-free polyurethane synthetic leather adhesive layer comprises the following steps: (1) Preparation of component A: first, PTMG3000, polyether polyol b, CHE-2901L, hardener 1,4-butanediol, foaming agent water, composite catalyst, foam stabilizer 8835 and surfactant (3,3,3-trifluoropropyl) trimethoxysilane were put into an autoclave and stirred, the temperature was raised to 40°C, the speed was 30 r / min, and the stirring was carried out for 1 hour to obtain component A; (2) Preparation of component B: Add polyester polyol into a reactor, heat to 110°C and vacuum dehydrate for 3 h, then cool to 45°C, add MM103C, heat to 75°C and keep warm for 1 h, take samples for testing, and when the mass percentage of -NCO reaches 15%, cool down, discharge the material, and seal for storage.

[0041] The component A and the component B were mixed evenly in a mass ratio of 100:80, and placed in an oven at 120° C. for aging for 5 minutes to obtain the solvent-free polyurethane synthetic leather adhesive layer sample.

[0042] Preparation of solvent-free polyurethane synthetic leather: first, a water-based polyurethane surface layer (anionic water-based polyurethane KL-718, Hefei Amway Polyurethane New Materials Co., Ltd.) was roller-coated onto release paper, placed in a 120°C oven for aging for 5 minutes to form a water-based coating, and then taken out for use; component A and component B were evenly mixed in a mass ratio of 100:80, and then applied to the surface of the water-based coating to form an adhesive layer coating, which was placed in a 120°C oven. When the adhesive layer coating began to turn milky white, it was taken out of the oven and covered with non-woven fabric, and then continued to be placed in a 120°C oven for aging for 5 minutes to obtain solvent-free polyurethane synthetic leather.

[0043] Comparative Example 1 The only difference between this comparative example 1 and example 3 is that the polyether polyol b in component A is completely replaced by DL1000 (functionality 2, number average molecular weight 1000). DL1000, produced by Sinochem Dongda (Zibo) Co., Ltd., is a polyether polyol using propylene glycol as the initiator.

[0044] Comparative Example 2 The only difference between Comparative Example 2 and Example 3 is that all (3,3,3-trifluoropropyl)trimethoxysilane in component A is replaced with trimethoxysilane (CAS No. 2487-90-3) of the same mass.

[0045] Comparative Example 3 The only difference between Comparative Example 3 and Example 3 is that the composite catalyst in component A is completely replaced with delayed catalyst MP608 (Evonik Specialty Chemicals Co., Ltd.) of equal mass.

[0046] Comparative Example 4 The only difference between this comparative example 4 and example 3 is that in the preparation of the polyester polyol of component B, castor oil is replaced with MN1000 (functionality 3, number average molecular weight 1000) of the same mass. MN1000, from Sinochem Dongda (Zibo) Co., Ltd., is a polyether polyol using glycerol as the initiator.

[0047] Comparative Example 5 The only difference between Comparative Example 5 and Example 3 is that MM103C in component B is replaced by pure MDI of equal mass.

[0048] Comparative Example 6 The only difference between Comparative Example 6 and Example 3 is that the 1,4-butanediol used in the preparation of the polyester polyol in component A and component B is replaced by ethylene glycol of the same mass.

[0049] The adhesive layer samples and synthetic leather prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests, and the results are shown in Table 1.

[0050] Among them, the peel strength test standard is GB / T8949-2008; The hydrolysis resistance test standard is QB / T4671-2014; High temperature aging resistance: after baking at 150℃ for 300h and returning to normal temperature, the surface does not crack when bent at 90℃; Hydrophobicity test: The contact angle of water is tested using the method in ASTM D7490-2013; Low temperature compliance test: Test the flexural performance of the product at 30°C. The flexural performance test standard is GB / T20991-2007. Water absorption rate: conditions are 90℃, 95%RH, 200h; Working time: The time from when components A and B are mixed to when the viscosity increases to the point where coating is impossible.

[0051] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-6

[0052] As can be seen from Table 1, the adhesive layers prepared in Examples 1-3 of the present invention not only have high bonding strength with the aqueous surface layer, but also have good low-temperature compliance, hydrolysis resistance, hydrophobicity and aging resistance. Comparative Examples 1, 2, 4, and 6 replace the polyether polyol b, fluorinated polysiloxane copolymer in component A, castor oil in component B, and 1,4-butanediol in components A and B, and the prepared products cannot have good low-temperature compliance, hydrolysis resistance, hydrophobicity and aging resistance; Comparison between Example 3 and Comparative Example 3 shows that the use of a thermosensitive catalyst greatly prolongs the operation time; Comparison between Example 3 and Comparative Example 5 shows that the introduction of a carbodiimide structure in component B greatly improves the peel strength of the aqueous surface layer and the solvent-free adhesive layer.

Claims

1. A solvent-free polyurethane synthetic leather adhesive layer, characterized in that: It is composed of component A and component B mixed in a mass ratio of 100: (80~100); In terms of mass percentage, component A is: Polyether polyol a, 40%~50%; Polyether polyol b, 30%~40%; Polyether polyol c, 8%~12%; Hardener, 3%~5%; Foaming agent, 0.2%~0.4%; Composite catalyst, 0.3%~0.6%; Foam stabilizer, 0.5%~1.0%; Surfactant, 3%~5%; Group B is composed of: Polyester polyol, 40%~55%; Liquefied MDI, 45%~60%; Polyether polyol a is polytetramethylene ether diol; Polyether polyol b is prepared by ring-opening polymerization of propylene oxide using hydroxy polysiloxane and trimethylolpropane as composite initiators and KOH as a catalyst; Polyether polyol c is polyoxypropylene triol terminated with ethylene oxide; The hardener is 1,4-butanediol; The surfactant is a fluorinated polysiloxane copolymer; Polyester polyols are bio-based polyester polyols, which are polymerized from castor oil, 1,4-butanediol and small molecule polyacids.

2. The solvent-free polyurethane synthetic leather adhesive layer according to claim 1, characterized in that: Polyether polyol a, functionality is 2, number average molecular weight is 3000.

3. The solvent-free polyurethane synthetic leather adhesive layer according to claim 1, characterized in that: Polyether polyol b, functionality is 2, number average molecular weight is 1000-1500.

4. The solvent-free polyurethane synthetic leather adhesive layer according to claim 1, characterized in that: Polyether polyol c, functionality is 3, number average molecular weight is 7000~8000.

5. The solvent-free polyurethane synthetic leather adhesive layer according to claim 4, characterized in that: The foaming agent is water; the composite catalyst is a composite of a delayed amine catalyst and a thermosensitive catalyst, and the mass ratio of the delayed amine catalyst to the thermosensitive catalyst is 1:

1.

6. The solvent-free polyurethane synthetic leather adhesive layer according to claim 1, characterized in that: The foam stabilizer is a polysiloxane-olefin oxide block copolymer.

7. The solvent-free polyurethane synthetic leather adhesive layer according to claim 1, characterized in that: The hydroxyl value of polyester polyol is 85~90mgKOH / g.

8. The solvent-free polyurethane synthetic leather adhesive layer according to claim 1, characterized in that: Liquefied MDI is carbodiimide modified MDI.

9. A method for preparing the solvent-free polyurethane synthetic leather adhesive layer according to claims 1 to 8, characterized in that: The steps include: (1) Component A: First, add polyether polyol a, polyether polyol b, polyether polyol c, hardener, foaming agent, composite catalyst, foam stabilizer and surfactant based on the formula amount into an autoclave and stir. Heat to 40-50°C, rotate at 30-40 r / min, and stir for 1-2 hours to obtain component A. (2) Component B: Add polyester polyol into a reactor, heat to 110-120°C and perform vacuum dehydration for 3-4 hours, then cool to 45-50°C, add liquefied MDI, heat to 75-80°C and keep warm for 1-2 hours, take samples for testing, and when the mass percentage of -NCO reaches 9.5%-15%, cool down, discharge the material, and seal for storage.

Images