A solvent-free polyurethane resin, its preparation method and application

Abstract

The present application discloses a solvent-free polyurethane resin, its preparation method and application. The solvent-free polyurethane resin is prepared from component A and component B in a mass ratio of 100:(15-25); component A is a carboxyl-terminated polyurethane prepolymer formed by reacting 70-90 parts by mass of polyester polyol acid, 10-20 parts by mass of diisocyanate and 0.2-1 part by mass of a catalyst; component B is an epoxy resin; wherein, the polyester polyol acid is an intermediate with an acid value of 50-80 mgKOH / g and a hydroxyl value of 60-100 mgKOH / g obtained by polycondensation of a dibasic acid and a diol. By crosslinking and curing component A of the carboxyl-terminated polyurethane prepolymer formed by using a polyester polyol acid with specific acid value and hydroxyl value and component B of the epoxy resin, and embedding the epoxy resin in the polyurethane system, a solvent-free polyurethane resin with excellent comprehensive properties is obtained. The solvent-free polyurethane resin has excellent heat resistance and is suitable for product fields with heat resistance requirements such as automotive instrument panels.

Description

Technical Field

[0001] This application belongs to the technical field of polyurethane materials, and specifically relates to a solvent-free polyurethane resin, its preparation method and application. Background Art

[0002] Traditional automotive instrument panels mostly use materials such as PC and ABS. Although these materials have certain strength and rigidity and can meet the basic structural requirements of automotive instrument panels, their texture is hard and it is difficult to create a comfortable driving atmosphere. In contrast, polyurethane materials (PU) offer the possibility of creating soft interiors due to their excellent softness and delicate touch, making them one of the ideal choices for automotive interior materials.

[0003] However, PU materials have deficiencies in heat resistance. Existing research shows that under high-temperature environments, the mechanical properties and peel strength of PU materials will both decrease significantly. This defect limits the application of polyurethane in components with high heat resistance requirements such as automotive instrument panels.

[0004] Therefore, it is very necessary to research and develop polyurethane materials with excellent heat resistance, in order to enable polyurethane materials to be more widely applied in fields such as automotive instrument panels and outdoor products. Summary of the Invention

[0005] In view of this, the primary objective of this application is to provide a solvent-free polyurethane resin. By crosslinking and curing the A component of the terminal carboxyl polyurethane prepolymer formed by polyester polyol acid with specific acid value and hydroxyl value and the B component of epoxy resin, the epoxy resin is embedded in the polyurethane system to obtain a solvent-free polyurethane resin with excellent heat resistance, providing the possibility for the application of polyurethane materials in product fields with heat resistance requirements such as automotive instrument panels.

[0006] One aspect of this application discloses a solvent-free polyurethane resin, which is prepared from the A component and the B component according to a mass ratio of 100:(15 - 25);

[0007] The A component is a terminal carboxyl polyurethane prepolymer formed by reacting 70 - 90 parts by mass of polyester polyol acid, 10 - 20 parts by mass of diisocyanate and 0.2 - 1 part by mass of catalyst; the B component is epoxy resin;

[0008] Among them, the polyester polyol acid is an intermediate obtained by polycondensation reaction of dibasic acid and diol with an acid value of 50 - 80 mgKOH / g and a hydroxyl value of 60 - 100 mgKOH / g.

[0009] Another aspect of this application discloses a method for preparing the above-mentioned solvent-free polyurethane resin, including the following steps:

[0010] Using a dibasic acid and a diol as raw materials, a polyester polyol acid is prepared through a polycondensation reaction.

[0011] After mixing the polyester polyol acid, diisocyanate, and catalyst, the temperature is raised to 70 - 100 °C and reacted for 3 - 5 hours to obtain a carboxyl - terminated polyurethane prepolymer, which is Component A.

[0012] After uniformly mixing Component A and Component B according to a mass ratio of 100:(15 - 25), the mixture is reacted at 130 - 150 °C for 10 - 15 minutes to prepare a solvent - free polyurethane resin.

[0013] Another aspect of the present application discloses the use of the solvent - free polyurethane resin as described above in the preparation of polyurethane synthetic leather.

[0014] Another aspect of the present application discloses a polyurethane synthetic leather, which contains a polyurethane surface layer and a solvent - free polyurethane layer. The solvent - free polyurethane layer is made of the solvent - free polyurethane resin as described above. The specific process includes the following steps:

[0015] Coat Component A and Component B on the polyurethane surface layer according to a mass ratio of 100:(15 - 25), pre - react at 100 °C for 70 - 90 seconds, and bond with the base fabric; then react and cure at 130 - 150 °C to form a polyurethane synthetic leather.

[0016] Advantages of the present application:

[0017] In the present application, a dibasic alcohol and a dibasic acid are used to prepare a polyester polyol acid with specific acid value and hydroxyl value through a polycondensation reaction; it is reacted with diisocyanate to synthesize a carboxyl - terminated polyurethane prepolymer as Component A. Due to the high reactivity of the carboxyl group, it can undergo a cross - linking curing reaction with the epoxy resin in Component B, embedding the epoxy resin into the polyurethane system. Thus, the heat - resistant performance of the solvent - free polyurethane resin and the polyurethane synthetic leather is significantly improved.

[0018] After testing, the polyurethane synthetic leather made of this solvent - free polyurethane resin has excellent comprehensive performance; after continuous aging at a high temperature of 120 °C for 200 hours, the leather surface remains intact, without cracks or stickiness, and the retention rate of the peel strength is above 80%, showing excellent heat - resistant performance. Detailed Embodiments

[0019] The following will clearly and completely describe the embodiments of the present application. The technical solutions in the following described embodiments are exemplary and only possible technical implementations of the present application, not all possible implementations. Those skilled in the art can fully combine the embodiments of the present application to obtain other embodiments without creative labor, and these embodiments are also within the protection scope of the present application.

[0020] The first aspect of the present application discloses a solvent-free polyurethane resin, which is prepared from component A and component B in a mass ratio of 100:(15 - 25).

[0021] Component A in the present application is a carboxyl-terminated polyurethane prepolymer obtained by reacting a polyester polyol acid with specific acid value and hydroxyl value and a diisocyanate. Utilizing the high reactivity of the carboxyl group, it undergoes a crosslinking and curing reaction with component B of epoxy resin, embedding the epoxy resin into the polyurethane system to obtain a solvent-free polyurethane resin with significantly improved heat resistance.

[0022] <Component A>

[0023] Component A described in the present application is a carboxyl-terminated polyurethane prepolymer formed by reacting 70 - 90 parts by mass of polyester polyol acid, 10 - 20 parts by mass of diisocyanate, and 0.2 - 1 part by mass of a catalyst.

[0024] Among them, the polyester polyol acid is an intermediate obtained by polycondensation of a dibasic acid and a diol, with an acid value of 50 - 80 mgKOH / g and a hydroxyl value of 60 - 100 mgKOH / g.

[0025] In the present application, the dibasic acid is an organic dibasic acid, which is a class of organic compounds containing two carboxyl groups (—COOH) in the molecular structure, and the structural general formula is as follows:

[0026] HOOC-R1-COOH.

[0027] In the present application, R1 is one of —(CH2) n —, —C6H4—, and n is 2 - 8. In some examples, specific examples of the dibasic acid that can be mentioned include but are not limited to at least one of succinic acid, adipic acid, sebacic acid, isophthalic acid, and terephthalic acid.

[0028] In the present application, the diol is a class of aliphatic organic compounds containing two hydroxyl groups (—OH) in the molecular structure and containing 2 to 8 carbon atoms. Specific examples that can be mentioned include but are not limited to at least one of ethylene glycol, 1,2 - propanediol, 1,3 - propanediol, 2 - methyl - 1,3 - propanediol, 1,4 - butanediol, 1,5 - pentanediol, neopentyl glycol, and diethylene glycol.

[0029] In the present application, the diisocyanate is any conventional raw material component in the art that can be used to prepare polyurethanes. Specific examples that can be mentioned include but are not limited to at least one of 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0030] In the present application, the catalyst refers to a reagent used to increase the reaction rate or the degree of reaction, and those skilled in the art can select it according to needs. In some examples, the catalyst is selected from at least one of dimethylaminophenol, triethylamine, benzyldimethylamine, and tetrabutylammonium bromide, but is not limited thereto.

[0031] It can be understood that in the present application, the amounts of the dibasic acid, the diol, and the catalyst can be adjusted according to the acid value and hydroxyl value of the target polyester polyol acid, and these can all be determined by experiments without special limitations.

[0032] <Component B>

[0033] In the present application, the Component B is an epoxy resin, and there are no special requirements for its specific type. In some examples, it is preferably a bisphenol A type epoxy resin, such as at least one of E-42, E-44, E-51, and E-55, but is not limited thereto.

[0034] The second aspect of the present application provides a method for preparing the solvent-free polyurethane resin, including the following steps:

[0035] Using a dibasic acid and a diol as raw materials, through a polycondensation reaction, a polyester polyol acid is prepared;

[0036] After mixing the polyester polyol acid, the diisocyanate, and the catalyst, the temperature is raised to 70 - 100 °C and reacted for 3 - 5 hours to obtain a carboxyl-terminated polyurethane prepolymer, i.e., Component A;

[0037] After uniformly mixing Component A and Component B according to a mass ratio of 100:(15 - 25), the mixture is reacted at 130 - 150 °C for 10 - 15 minutes to prepare the solvent-free polyurethane resin.

[0038] As described above, in the preparation of the polyester polyol acid, a polycondensation reaction well-known in the art is used, and those skilled in the art can adjust the amounts of the raw material dibasic acid and diol and the specific conditions, etc., according to the target acid value and hydroxyl value, without special limitations.

[0039] In some specific examples, the preparation of the polyester polyol acid includes the following steps:

[0040] Gradually raise the temperature of the dibasic acid and the diol to 240 °C under a protective atmosphere for dehydration polycondensation reaction; when the acid value is detected to be 70 - 100 mgKOH / g, add tetra-isopropyl titanate and continue the reaction, and gradually increase the vacuum degree to 0.095 MPa to obtain a polyester polyol acid with an acid value of 50 - 80 mgKOH / g and a hydroxyl value of 60 - 100 mgKOH / g.

[0041] Among them, the dibasic acid, dibasic alcohol and tetra-isopropyl titanate can be determined by experimental methods as needed. In some examples, the dibasic acid is 170-215 parts by mass, the dibasic alcohol is 120-230 parts by mass, and the tetra-isopropyl titanate is 0.01 part by mass.

[0042] After the A component and the B component are mixed, the A component has a carboxyl group with high reactivity at the end, and the B component is an epoxy resin. The two crosslink and cure to embed the epoxy resin into the polyurethane system, and a solvent-free polyurethane resin can be prepared.

[0043] The third aspect of the present application discloses the application of the described solvent-free polyurethane resin in the preparation of polyurethane synthetic leather.

[0044] The fourth aspect of the present application discloses a polyurethane synthetic leather, which contains a polyurethane surface layer and a solvent-free polyurethane layer, and the solvent-free polyurethane layer is made of the described solvent-free polyurethane resin.

[0045] The described polyurethane synthetic leather has a conventional composition in the art, including but not limited to a polyurethane surface layer, a solvent-free polyurethane layer, a base fabric layer, etc., and can be specifically set according to performance requirements. Among them, there are no special requirements for the selection of the surface layer and the base fabric layer, and corresponding selections can be made according to the specific application fields of the synthetic leather.

[0046] Among them, the specific preparation process of the solvent-free polyurethane layer includes the following steps:

[0047] Coat the A component and the B component on the polyurethane surface layer according to a mass ratio of 100:(15-25), pre-react at 100°C for 70-90 seconds, and bond the base fabric; then react and cure at 130-150°C to form a polyurethane synthetic leather.

[0048] The polyurethane synthetic leather prepared based on the solvent-free polyurethane resin in the present application has excellent comprehensive performance and excellent heat resistance. After being treated at high temperature, the retention rate of the peel strength is above 80%, which is very suitable for fields with high requirements for the heat resistance of synthetic leather such as automotive instrument panels and outdoor products.

[0049] The following are specific examples of the present application. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of the present application in any way.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0051] In addition, unless otherwise specified, the methods without specific conditions or steps recorded are conventional methods, and the reagents and materials used can be obtained from commercial sources.

[0052] Raw materials used in the following examples:

[0053] HMDI, MDI, and IPDI are diisocyanates produced by Yantai Wanhua Company; tetra-isopropyl titanate is a catalyst of Auspicious Material Technology Co., Ltd.; the surface layer resin LT-95 is a polyurethane resin produced by Hefei Anli Polyurethane New Materials Co., Ltd.

[0054] Example 1

[0055] In this example, a preparation method of a solvent-free polyurethane resin is disclosed, and the specific steps are as follows:

[0056] 1. Preparation of polyester polyol acid

[0057] A four-necked flask equipped with a magnetic stirrer, a constant pressure burette, a thermometer, an N2 inlet tube, and an air-cooled condenser was installed in a jacketed resistance heater. Adipic acid (190 g) and 1,3-propanediol (120 g) were added to the four-necked flask; then, under nitrogen protection, the temperature was gradually raised for dehydration polycondensation reaction, and the top temperature of the condenser was controlled below 100 °C during the temperature rise; when the acid value was detected to be 70 mgKOH / g, tetra-isopropyl titanate (0.01 g) as the catalyst was added and the reaction continued for 30 min, and then the temperature was gradually raised to 240 °C and the vacuum degree was ≥0.095 MPa. After removing part of 1,3-propanediol, a polyester polyol acid with an acid value of 50 mgKOH / g and a hydroxyl value of 60 mgKOH / g was obtained.

[0058] 2. Preparation of solvent-free polyurethane resin

[0059] (1) Component A: Take polyester polyol acid (90 g) and add it to the reaction kettle, then add isophorone diisocyanate (10 g) and catalyst benzyldimethylamine (0.5 g), and stir and react at 90 °C for 5 h to obtain a terminal carboxyl polyurethane prepolymer, which is Component A.

[0060] (2) Component B: Epoxy resin E-55.

[0061] (3) Preparation of solvent-free polyurethane resin: Mix Component A and Component B in a mass ratio of 100:15 in a low-pressure casting machine and mix well, and react at 130 °C for 15 minutes to obtain a solvent-free polyurethane resin.

[0062] In this example, a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin is further disclosed, and the specific preparation process is as follows:

[0063] The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained;

[0064] Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:15, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 70 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 130°C for 15 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0065] Example 2

[0066] This embodiment discloses a method for preparing a solvent-free polyurethane resin, and the specific steps are as follows:

[0067] 1. Preparation of polyester polyol acid

[0068] A four-necked flask equipped with a magnetic stirrer, a constant pressure burette, a thermometer, a N2 inlet tube and an air-cooled condenser was installed in a mantle-type resistance heater, and sebacic acid (215 g) and 1,5-pentanediol (150 g) were added to the four-necked flask; then, the temperature was gradually increased under nitrogen protection to carry out a dehydration polycondensation reaction, and the top temperature of the condenser was controlled to be lower than 100°C during the heating process; when the acid value was detected to be 80 mgKOH / g, a catalyst tetraisopropyl titanate (0.01 g) was added and the reaction was continued for 30 minutes, and then the temperature was gradually increased to 240°C, and the vacuum degree was ≥0.095 MPa, and after removing part of 1,5-pentanediol, a polyester polyol acid with an acid value of 60 mgKOH / g and a hydroxyl value of 80 mgKOH / g was obtained.

[0069] 2. Preparation of solvent-free polyurethane resin

[0070] (1) Component A: Take polyester polyol acid (80 g) and add it into a reactor. Then add 4,4'-diphenylmethane diisocyanate (14.5 g) and catalyst triethylamine (0.2 g). Stir and react at 70°C for 3 h to obtain a carboxyl-terminated polyurethane prepolymer, i.e., component A.

[0071] (2) Component B: epoxy resin E-51.

[0072] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:19, mixed thoroughly, and reacted at 140° C. for 13 minutes to obtain a solvent-free polyurethane resin.

[0073] This embodiment further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows:

[0074] The surface layer resin slurry LT-95 was coated on the release paper and dried at 130°C for 2 minutes to form a polyurethane surface layer with a thickness of 0.05 mm.

[0075] Component A and component B were placed in a low-pressure casting machine and fully mixed in a mass ratio of 100:19, then coated on the surface layer with a coating gap of 0.3 mm. After entering the oven and reacting at 100°C for 80 seconds, it was laminated with a base cloth (a single-sided special fiber velvet base cloth with a thickness of 0.7 mm and a weight of 270 g). Subsequently, it continued to react at 140°C for 13 minutes, and the solvent-free polyurethane resin was fully cured. After forming, it was wound up and the release paper was peeled off to obtain the polyurethane synthetic leather.

[0076] Example 3

[0077] In this example, a preparation method of solvent-free polyurethane resin is disclosed, and the specific steps are as follows:

[0078] 1. Preparation of polyester polyol acid

[0079] A four-necked flask equipped with a magnetic stirrer, a constant pressure burette, a thermometer, an N2 inlet tube, and an air-cooled condenser was installed in a jacketed resistance heater. Isophthalic acid (170 g) and 2-methyl-1,3-propanediol (230 g) were added to the four-necked flask. Then, under nitrogen protection, it was gradually heated and raised to carry out dehydration polycondensation reaction, and the top temperature of the condenser was controlled below 100°C during the heating process. When the acid value was detected to be 100 mgKOH / g, tetra-isopropyl titanate (0.01 g) as a catalyst was added and the reaction continued for 30 min. Then, it was gradually heated and raised to 240°C and the vacuum degree ≥ 0.095 MPa. After removing part of 2-methyl-1,3-propanediol, polyester polyol acid with an acid value of 80 mgKOH / g and a hydroxyl value of 100 mgKOH / g was obtained.

[0080] 2. Preparation of solvent-free polyurethane resin

[0081] (1) Component A: Polyester polyol acid (70 g) was added to the reaction kettle, and then 4,4'-dicyclohexylmethane diisocyanate (20 g) and catalyst tetrabutylammonium bromide (1 g) were added. It was stirred and reacted at 100°C for 4 h to obtain a terminal carboxyl polyurethane prepolymer, that is, component A.

[0082] (2) Component B: Epoxy resin E-44.

[0083] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine and fully mixed in a mass ratio of 100:25, and reacted at 150°C for 10 minutes to prepare the solvent-free polyurethane resin.

[0084] In this example, a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin is further disclosed, and the specific preparation process is as follows:

[0085] After coating the release paper with the surface layer resin slurry LT-95 and drying at 130°C for 2 minutes to form it, a polyurethane surface layer with a thickness of 0.05 mm is obtained.

[0086] The component A and component B are placed in a low-pressure casting machine and fully mixed according to the mass ratio of 100:80, and then coated on the surface layer with a coating gap of 0.3 mm. After entering the oven and reacting at 100°C for 90 seconds, it is laminated with a base fabric (a single-sided special fiber velvet base fabric with a thickness of 0.7 mm and a weight of 270 g). Subsequently, it continues to react at 150°C for 10 minutes, and the solvent-free polyurethane resin fully cures and reacts. After forming, it is wound up and the release paper is peeled off to obtain the polyurethane synthetic leather.

[0087] Comparative Example 1

[0088] In order to verify the effect of introducing epoxy resin, in this comparative example, a solvent-free polyurethane resin is prepared by curing a hydroxyl-terminated polyurethane prepolymer A component with isocyanate, and other raw materials, as well as the preparation processes of the solvent-free polyurethane resin and the synthetic leather, all refer to Example 1. The specific steps are as follows:

[0089] 1. Preparation of polyester polyol

[0090] Using adipic acid and 1,3-propanediol, a commercially available conventional polyester polyol is synthesized, with an acid value of 0.3 mg KOH / g and a hydroxyl value of 60 mg KOH / g.

[0091] 2. Preparation of solvent-free polyurethane resin

[0092] (1) Component A: Take the above-mentioned polyester polyol (90 g), isophorone diisocyanate (5 g), and catalyst benzyl dimethylamine (0.5 g), and stir and react at 90°C for 5 h to obtain a hydroxyl-terminated polyurethane prepolymer, that is, component A.

[0093] (2) Component B: Take the above-mentioned polyester polyol (90 g) and isophorone diisocyanate (34 g) to react to obtain a terminal isocyanate prepolymer with an isocyanate content of 10%, that is, component B.

[0094] (3) Preparation of solvent-free polyurethane resin: Place component A and component B in a low-pressure casting machine and fully mix them according to the mass ratio of 100:22, and react at 130°C for 15 minutes to prepare the solvent-free polyurethane resin.

[0095] In this comparative example, a polyurethane synthetic leather prepared based on the above-mentioned solvent-free polyurethane resin is further disclosed. The specific preparation process is as follows:

[0096] After coating the release paper with the surface layer resin slurry LT-95 and drying at 130°C for 2 minutes to form it, a polyurethane surface layer with a thickness of 0.05 mm is obtained.

[0097] The component A and component B are placed in a low-pressure casting machine and fully mixed according to a mass ratio of 100:22, then coated on the surface layer with a coating gap of 0.3 mm. After entering the oven and reacting at 100 °C for 70 seconds, it is laminated with a base fabric (a single-sided special fiber velvet base fabric with a thickness of 0.7 mm and a weight of 270 g); then it continues to react at 130 °C for 15 minutes, and the solvent-free polyurethane resin fully cures. After forming, it is wound up and the release paper is peeled off to obtain the polyurethane synthetic leather.

[0098] Comparative Example 2

[0099] In order to compare the acid value of polyester polyol acid, that is, the influence of the addition amount of epoxy resin on the heat resistance, polyester polyol acids with different acid values were prepared in this comparative example. Other raw materials, as well as the preparation processes of the solvent-free polyurethane resin and the synthetic leather, were all referred to Example 1. The specific steps are as follows:

[0100] 1. Preparation of polyester polyol acid

[0101] Referring to Example 1, the acid value of the obtained polyester polyol acid is 120 mgKOH / g and the hydroxyl value is 60 mgKOH / g.

[0102] 2. Preparation of solvent-free polyurethane resin

[0103] (1) Component A: Refer to Example 1.

[0104] (2) Component B: Epoxy resin E-55.

[0105] (3) Preparation of solvent-free polyurethane resin: The component A and component B are placed in a low-pressure casting machine and fully mixed according to a mass ratio of 100:35, and reacted at 130 °C for 15 minutes to obtain the solvent-free polyurethane resin.

[0106] This comparative example further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin. The specific preparation process is as follows:

[0107] Coat the surface layer resin slurry LT-95 on the release paper, and after drying at 130 °C for 2 minutes to form, a polyurethane surface layer with a thickness of 0.05 mm is obtained;

[0108] The component A and component B are placed in a low-pressure casting machine and fully mixed according to a mass ratio of 100:35, then coated on the surface layer with a coating gap of 0.3 mm. After entering the oven and reacting at 100 °C for 70 seconds, it is laminated with a base fabric (a single-sided special fiber velvet base fabric with a thickness of 0.7 mm and a weight of 270 g); then it continues to react at 130 °C for 15 minutes, and the solvent-free polyurethane resin fully cures. After forming, it is wound up and the release paper is peeled off to obtain the polyurethane synthetic leather.

[0109] Comparative Example 3

[0110] In order to compare the hydroxyl value of polyester polyol acid, that is, the effect of the content of carbamate group formed by reaction with isocyanate on heat resistance, polyester polyol acids with different hydroxyl groups were prepared in this comparative example, and other raw materials, as well as the preparation process of solvent-free polyurethane resin and synthetic leather were all referred to Example 1, and the specific steps were as follows:

[0111] 1. Preparation of polyester polyol acid

[0112] Referring to Example 1, the acid value of the prepared polyester polyol acid was 50 mgKOH / g and the hydroxyl value was 30 mgKOH / g.

[0113] 2. Preparation of solvent-free polyurethane resin

[0114] (1) Component A: Take the above polyester polyol acid (90 g), isophorone diisocyanate (4 g), and catalyst benzyl dimethylamine (0.5 g), and stir and react at 90°C for 5 h to obtain a carboxyl-terminated polyurethane prepolymer, i.e., component A.

[0115] (2) Component B: epoxy resin E-55.

[0116] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:15, mixed thoroughly, and reacted at 130° C. for 15 minutes to obtain a solvent-free polyurethane resin.

[0117] This comparative example further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows:

[0118] The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained;

[0119] Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:15, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 70 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 130°C for 15 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0120] Comparative Example 4

[0121] In order to compare the performance of the carboxyl / epoxy resin curing system with the hydroxyl / epoxy resin curing system commonly used on the market, the terminal hydroxyl group was used to cure the epoxy resin in this comparative example. The other raw materials, as well as the preparation process of the solvent-free polyurethane resin and the synthetic leather were all referred to Example 1. The specific steps are as follows:

[0122] 1. Preparation of polyester polyols

[0123] Adipic acid and 1,3-propanediol were used to synthesize a conventional polyester polyol on the market, with an acid value of 0.3 mg KOH / g and a hydroxyl value of 60 mg KOH / g.

[0124] 2. Preparation of solvent-free polyurethane resin

[0125] (1) Component A: Polyester polyol (90 g), isophorone diisocyanate (5 g), and catalyst benzyl dimethylamine (0.5 g) were stirred and reacted at 90 °C for 5 h to obtain a hydroxyl-terminated polyurethane prepolymer, i.e., Component A.

[0126] (2) Component B: Epoxy resin E-55.

[0127] (3) Preparation of solvent-free polyurethane resin: Component A and Component B were mixed thoroughly in a low-pressure casting machine at a mass ratio of 100:9 and reacted at 130 °C for 15 minutes to obtain the solvent-free polyurethane resin.

[0128] This comparative example further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin. The specific preparation process is as follows:

[0129] The surface layer resin slurry LT-95 was coated on the release paper and dried at 130 °C for 2 minutes to form a polyurethane surface layer with a thickness of 0.05 mm.

[0130] Component A and Component B were placed in a low-pressure casting machine at a mass ratio of 100:9, mixed thoroughly and coated on the surface layer with a coating gap of 0.3 mm, then entered an oven and reacted at 100 °C for 70 seconds and then laminated with a base fabric (a single-sided special fiber velvet base fabric with a thickness of 0.7 mm and a weight of 270 g); subsequently, it continued to react at 130 °C for 15 minutes, and the solvent-free polyurethane resin was fully cured; after forming, it was wound up and the release paper was peeled off to obtain the polyurethane synthetic leather.

[0131] Performance testing

[0132] The polyurethane synthetic leathers prepared in Examples 1-3 and Comparative Examples 1-4 were tested for peel strength according to the standard of 5.9 in GB / T 8949-2008 and for 100,000 times at room temperature and 30,000 times at -10 °C for flexure according to QB / T 2714-2018. In addition, in order to further reflect the difference in the heat resistance performance of the polyurethane synthetic leather, the polyurethane synthetic leather was placed in a constant temperature oven at 120 °C for high-temperature aging for 200 hours, and then the peel strength was detected and the peel strength retention rate was calculated. The test results are shown in Table 1.

[0133] Table 1 Test results of the performance of polyurethane synthetic leather

[0134]

[0135] Note: The retention rate of peel strength in Table 1 = (Peel strength before aging - Peel strength after aging) / Peel strength before aging × 100%.

[0136] As can be seen from the above table, the peel strength of the polyurethane synthetic leather in Examples 1 - 3 of this application all reaches above 90 N / 3 cm, and it passes the flexing test of 100,000 times at room temperature and 30,000 times at -10°C, with good comprehensive performance. After heat resistance testing, the retention rate of the peel strength of the synthetic leather in Examples 1 - 3 is all above 80%, showing excellent heat resistance performance.

[0137] Among them, compared with Example 1, Comparative Example 1 is a polyurethane system without introducing epoxy resin with relatively high rigidity, and its peel strength is 52 N / 3 cm, which is relatively low.

[0138] Compared with Example 1, in Comparative Example 2, the acid value of the polyester polyol acid is too high, and more epoxy resin is required for curing. Although it can obtain relatively high peel strength and heat resistance performance, the excessive epoxy resin reduces the flexibility of the polymer, and the flexing is unqualified.

[0139] Compared with Example 1, in Comparative Example 3, the hydroxyl value of the polyester polyol acid is relatively low, and the amount of isophorone diisocyanate required for preparing Component A is less, resulting in a relatively low content of urethane groups in the polymer. Therefore, the peel strength of the final synthetic leather is 83 N / 3 cm, which is inferior to that of Example 1.

[0140] Compared with Example 1, in Comparative Example 4, hydroxyl groups are used to cure with epoxy resin to form epoxy resin - modified polyurethane. Although this method can also enable the synthetic leather to obtain relatively good peel strength, after heat resistance testing, the retention rate of the peel strength is lower than 70%. This is mainly because the ester bonds and other structures formed by the reaction of carboxyl groups and epoxy groups are relatively stable and can maintain the performance of the material at relatively high temperatures; while the ether bonds and other structures formed by the reaction of hydroxyl groups and epoxy groups have certain flexibility, so their heat resistance performance is not good.

[0141] Based on the above - mentioned examples and performance test results, it can be known that the solvent - free polyurethane resin provided in this application has excellent performance. The prepared solvent - free polyurethane resin and polyurethane synthetic leather have excellent heat resistance performance. After high - temperature aging treatment at 120°C for 200 h, the retention rate of the peel strength is above 80%, and at the same time, they have good flexibility. This solvent - free polyurethane resin can be applied to synthetic leather with high heat - resistance requirements such as automotive interiors, instrument panels, and outdoor products.

[0142] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are only examples, and embodiments having the same constitution in essence as the technical idea and achieving the same effects within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some of the constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A solvent-free polyurethane resin, characterized in that, The solvent-free polyurethane resin is prepared from component A and component B in a mass ratio of 100:(15 - 25); Component A is a carboxyl-terminated polyurethane prepolymer formed by reacting 70 - 90 parts by mass of polyester polyol acid, 10 - 20 parts by mass of diisocyanate, and 0.2 - 1 part by mass of catalyst; Component B is an epoxy resin; Among them, the polyester polyol acid is an intermediate obtained by polycondensing dibasic acid and diol, with an acid value of 50 - 80 mgKOH / g and a hydroxyl value of 60 - 100 mgKOH / g. The preparation of the polyester polyol acid includes the following steps: Gradually heat the dibasic acid and diol to 240°C under a protective atmosphere for dehydration polycondensation reaction; when the acid value is detected to be 70 - 100 mgKOH / g, add tetra-isopropyl titanate and continue the reaction, and gradually increase the vacuum degree to 0.095 MPa to obtain the polyester polyol acid; The dosage of each raw material is: 170 - 215 parts by mass of dibasic acid, 120 - 230 parts by mass of diol, and 0.01 part by mass of tetra-isopropyl titanate; The dibasic acid is at least one of adipic acid, sebacic acid, and isophthalic acid; The diol is at least one of 1,3-propanediol, 2-methyl-1,3-propanediol, and 1,5-pentanediol.

2. The solvent-free polyurethane resin according to claim 1, wherein, The diisocyanate is at least one of 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate; And / or, the catalyst is at least one of dimethylaminophenol, triethylamine, benzyldimethylamine, and tetrabutylammonium bromide.

3. The solventless polyurethane resin according to claim 1, characterized in that, The epoxy resin is bisphenol A type epoxy resin.

4. The solventless polyurethane resin according to claim 3, characterized in that, The bisphenol A type epoxy resin is at least one of E-42, E-44, E-51, and E-55.

5. A method for preparing a solvent-free polyurethane resin as described in any one of claims 1-4, characterized in that, Including the following steps: Using dibasic acid and diol as raw materials, through polycondensation reaction, polyester polyol acid is prepared; After mixing the polyester polyol acid, diisocyanate, and catalyst, heat to 70 - 100°C and react for 3 - 5 hours to obtain a carboxyl-terminated polyurethane prepolymer, that is, component A; After uniformly mixing component A and component B in a mass ratio of 100:(15 - 25), react at 130 - 150°C for 10 - 15 minutes to prepare the solvent-free polyurethane resin.

6. The application of the solvent-free polyurethane resin according to any one of claims 1 - 4 in the preparation of polyurethane synthetic leather.

7. A polyurethane synthetic leather, comprising a polyurethane surface layer and a solvent-free polyurethane layer, characterized in that, The solvent-free polyurethane layer is made of the solvent-free polyurethane resin according to any one of claims 1 - 4, and its preparation process includes the following steps: Coat component A and component B on the polyurethane surface layer in a mass ratio of 100:(15 - 25), pre-react at 100°C for 70 - 90 seconds, and bond with the base fabric; then react and cure at 130 - 150°C to form the polyurethane synthetic leather.

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