A polyurethane toughened phenolic resin hot melt adhesive film and preparation method thereof

Abstract

The present invention relates to the technical field of hot melt adhesives, and in particular to a polyurethane toughened phenolic resin hot melt adhesive film and a preparation method thereof, wherein the hot melt adhesive film comprises a phenolic resin, a polyurethane and a high temperature resistant filler; the polyurethane is prepared by reacting a polyol, a chain extender and an isocyanate, and according to weight parts, the polyol comprises 100 parts, the chain extender comprises 10-35 parts, and the isocyanate comprises 40-100 parts. The weight ratio of the chain extender to the isocyanate is 1:(4.0-6.0); the total weight ratio of the chain extender and the isocyanate to the weight ratio of the polyol is 1:(0.8-2.0). The polyurethane toughened phenolic resin hot melt adhesive film has the advantages of solvent-free use, environmental friendliness, low viscosity, etc., and has a more excellent impregnation effect on fibers, which is beneficial to improving the mechanical properties of composite materials.

Description

Technical Field

[0001] The invention relates to a polyurethane toughened phenolic resin hot melt adhesive film and a preparation method thereof, belonging to the technical field of hot melt adhesives. Background Art

[0002] Phenolic resin has abundant raw material sources, simple preparation and production process, low cost, and good mechanical properties, heat resistance and dimensional stability. Therefore, it is widely used as the matrix resin of high-performance fiber-reinforced resin-based composite materials. Phenolic resin-based composite materials have the advantages of heat resistance, combustion resistance, light weight and high strength, corrosion resistance and low moisture absorption, and are widely used in rail transportation, wind turbine blades, aerospace and other fields.

[0003] In the preparation process of phenolic resin-based composite materials, the prepreg process and quality have an important influence on the performance of the final product. At present, the preparation of phenolic prepreg mainly adopts the solution impregnation method. During the preparation process, there is a problem of continuous volatilization of the solvent in the glue tank, which leads to a gradual increase in the solution concentration, and then the resin content in the prepreg also increases. In this case, the resin content of the prepreg is difficult to accurately control, the resin is unevenly distributed in the reinforcement material, and the volatile content is high, which directly leads to problems such as high porosity and batch instability of the product. Another production process for prepreg is the hot melt impregnation method, which can be divided into direct hot melt method and hot melt adhesive film method. Because the thickness of the adhesive film is controllable and the resin does not contain solvent, the prepared prepreg resin content has high control accuracy, low volatile matter, little harm to the environment and operator health, good product surface appearance, low porosity of the composite material, and good batch stability. It is currently the mainstream preparation process for prepreg.

[0004] Chinese patent application CN104449434A discloses a method for preparing a high temperature resistant adhesive film, however, the adhesive film is manufactured by a solution coating method, which is cumbersome and pollutes the environment. Chinese patent application CN118440638A discloses a hot melt adhesive film process resin and its preparation method, as well as a hot melt adhesive film preparation method and its application, the adhesive film preparation process is simple and solvent-free; however, the adhesive film prepared by this method does not contain a toughening agent, and the adhesive film is brittle and has poor toughness after curing. Summary of the invention

[0005] The present invention aims to solve the problems of solvent volatilization in the process of preparing phenolic adhesive film by the solution coating method in the prior art and the brittleness and poor toughness of the thermosetting resin after curing, and provides a polyurethane toughened phenolic resin hot melt adhesive film and a preparation method thereof. The hot melt adhesive film has the advantages of solvent-free use, environmental friendliness, low viscosity, etc., has a better impregnation effect on fibers, and is beneficial to improving the mechanical properties of composite materials.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: a polyurethane toughened phenolic resin hot melt adhesive film, the hot melt adhesive film comprising phenolic resin, polyurethane and high temperature resistant filler;

[0007] The polyurethane is prepared by reacting a polyol, a chain extender and an isocyanate. In terms of weight parts, the polyol comprises 100 parts, the chain extender comprises 10-35 parts and the isocyanate comprises 60-130 parts.

[0008] Furthermore, the weight ratio of the chain extender to the isocyanate is 1:(4.0-6.0); the weight ratio of the total weight of the chain extender and the isocyanate to the weight of the polyol is 1:(0.8-2.0).

[0009] Furthermore, the polyol is at least one of polytetramethylene glycol, polypropylene glycol and polyethylene glycol.

[0010] Preferably, the polyol is polytetramethylene ether glycol.

[0011] Furthermore, the chain extender is at least one of 1,4-butanediol, 1,3-propylene glycol, diethylene glycol, 1,8-octanediol, bisphenol A, hydroquinone dihydroxyethyl ether, and resorcinol dihydroxyethyl ether.

[0012] Furthermore, the isocyanate is at least one of MDI-50, MDI-100, hydrogenated MDI, and hexamethylene diisocyanate.

[0013] Preferably, the isocyanate is at least one of MDI-50, hydrogenated MDI, and hexamethylene diisocyanate.

[0014] Furthermore, the high temperature resistant filler is at least one of antimony trioxide, mica powder, quartz powder, white carbon black, and alumina.

[0015] Furthermore, in terms of weight, the hot melt adhesive film comprises 70-100 parts of phenolic resin, 5-35 parts of polyurethane, and 5-20 parts of high temperature resistant filler.

[0016] Furthermore, the preparation method of the polyurethane is as follows: 100 parts of polyol and 40-100 parts of isocyanate, 100-150 parts of solvent and 0.01-0.04 parts of catalyst are weighed and added into a reaction container, and reacted at 60°C-80°C for 2-3h to obtain an isocyanate-terminated polyurethane prepolymer; then 10-35 parts of a chain extender are added into the reaction container, and the reaction is continued at 60°C-80°C for 2-3h, and the polyurethane is obtained after the solvent is removed.

[0017] Furthermore, the catalyst is at least one of dibutyltin dilaurate and dimethyltin glycolate.

[0018] Furthermore, the solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0019] The present invention also discloses a method for preparing a polyurethane toughened phenolic resin hot melt adhesive film, the preparation method comprising:

[0020] The formulated phenolic resin, polyurethane and high temperature resistant filler are mixed on a double-roll mill at a temperature of 70-100°C and a rotation speed of 50-180r / min for 30min-50min, and then the mixed material is calendered at 80-90°C using a double-roll calender to obtain the polyurethane toughened phenolic resin hot melt adhesive film.

[0021] The beneficial effects of the present invention are:

[0022] The present invention uses a polyurethane with a low melting point and excellent processability as a film-forming agent and a toughening agent. The polyurethane can produce a toughening and modification effect on the phenolic resin during the mixing process with the phenolic resin; the polyurethane has good film-forming properties, and after being blended with the phenolic resin, the film-forming property of the phenolic resin can be improved, thereby preparing a phenolic resin adhesive film; in addition, the polyurethane toughened phenolic resin hot-melt adhesive film of the present invention has a low melting point and excellent processability, and can better impregnate fibers during the hot pressing process, thereby improving the performance of the composite material.

[0023] The present invention prepares the polyurethane by controlling the usage ratio between polyol, chain extender and isocyanate, and the reaction is sufficient to obtain a polyurethane with a suitable molecular weight. The polyurethane is applied to the preparation process of the polyurethane toughened phenolic resin hot melt adhesive film, so that the hot melt adhesive film can have a relatively low viscosity, so that it has good processing performance, good impregnation with fibers, so as to be more conducive to obtaining a composite material with high strength performance, and when the polyurethane toughened phenolic resin hot melt adhesive film is bonded to different layered composite materials, it has good bonding strength and shear strength, so that the layered composite material has a higher peel strength. In addition, the present invention adopts suitable polyols and isocyanates, which can break the crystallinity between molecules, help reduce the melting temperature of polyurethane, and improve processing fluidity, so that the final polyurethane toughened phenolic resin hot melt adhesive film has a lower viscosity, which is more conducive to processing, and can maintain higher bonding performance and strength performance, and improve composite material performance. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is described in detail below. The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0026] A polyurethane toughened phenolic resin hot melt adhesive film, the hot melt adhesive film comprising phenolic resin, polyurethane and high temperature resistant filler;

[0027] The polyurethane is prepared by reacting a polyol, a chain extender and an isocyanate, wherein the polyol comprises 100 parts, the chain extender comprises 10-35 parts and the isocyanate comprises 40-100 parts by weight.

[0028] Specifically, the weight ratio of the chain extender to isocyanate is 1:(4.0-6.0); the weight ratio of the total weight of the chain extender and isocyanate to the weight of the polyol is 1:(0.8-2.0).

[0029] Specifically, the polyol is at least one of polytetramethylene glycol, polypropylene glycol, and polyethylene glycol.

[0030] Preferably, the polyol is polytetramethylene ether diol, which has low crystallinity and is beneficial to improving the processing fluidity of the resin.

[0031] Specifically, the chain extender is at least one of 1,4-butanediol, 1,3-propylene glycol, diethylene glycol, 1,8-octanediol, bisphenol A, hydroquinone dihydroxyethyl ether, and resorcinol dihydroxyethyl ether.

[0032] Specifically, the isocyanate is at least one of MDI-50, MDI-100, hydrogenated MDI, and hexamethylene diisocyanate.

[0033] Preferably, the isocyanate is at least one of MDI-50, hydrogenated MDI, and hexamethylene diisocyanate. Applying these isocyanates to the preparation of polyurethane can help lower the melting temperature and improve processing fluidity, so that the final polyurethane toughened phenolic resin hot melt adhesive film can maintain high strength at lower viscosity performance, which is more conducive to processing operations.

[0034] Specifically, the high temperature resistant filler is at least one of antimony trioxide, mica powder, quartz powder, white carbon black, and alumina.

[0035] Specifically, in terms of weight, the hot melt adhesive film comprises 70-100 parts of phenolic resin, 5-35 parts of polyurethane, and 5-20 parts of high temperature resistant filler.

[0036] Specifically, the preparation of the polyurethane is carried out according to a two-step prepolymer method, and the preparation method of the polyurethane is as follows: 100 parts of polyol and 40-100 parts of isocyanate, 100-150 parts of solvent and 0.01-0.04 parts of catalyst are weighed and added into a reaction container, and reacted at 60°C-80°C for 2-3h to obtain an isocyanate-terminated polyurethane prepolymer; then 10-35 parts of a chain extender are added into the reaction container, and the reaction is continued at 60°C-80°C for 2-3h, and the polyurethane is obtained after the solvent is removed.

[0037] Specifically, the catalyst is at least one of dibutyltin dilaurate and dimethyltin glycolate.

[0038] Specifically, the solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0039] A method for preparing a polyurethane toughened phenolic resin hot melt adhesive film, the preparation method comprising:

[0040] The phenolic resin, polyurethane and high temperature resistant filler in the formula are mixed on a double-roll open mill at a temperature of 70-100°C and a rotation speed of 50-180r / min. The mixing time is 30min-50min. During the mixing process, the polyurethane film-forming agent with excellent processability and low viscosity can be blended with the phenolic resin, so that the phenolic resin that originally does not have film-forming properties has good film-forming properties after processing. After the mixing is completed, the mixed material is calendered at 80-90°C using a double-roll calender to obtain the polyurethane toughened phenolic resin hot melt adhesive film. The prepared polyurethane toughened phenolic resin hot melt adhesive film has excellent processing fluidity and low viscosity within the processing temperature range, can better impregnate fibers, and improve the performance of composite materials.

[0041] More specifically, the phenolic resin used in the embodiments of the present invention has Mw=7000 g / mol, Mn=1000 g / mol (Tiancheng Resin Co., Ltd.).

[0042] Example 1

[0043] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0044] 100 g of polytetrahydrofuran ether diol (number average molecular weight of 1000 g / mol), 55 g of MDI-50, 0.01 g of dibutyltin dilaurate and 100 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 70°C for 2.5 h for prepolymerization. Afterwards, 10 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2.5 h to obtain polyurethane.

[0045] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0046] 100 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler antimony trioxide were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 120 r / min for 40 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0047] Example 2

[0048] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0049] 100 g of polytetramethylene glycol (number average molecular weight of 1000 g / mol), 75 g of MDI-50, 0.04 g of dibutyltin dilaurate and 150 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 60°C for 3 h for prepolymerization. Afterwards, 15 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 3 h to obtain polyurethane.

[0050] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0051] 100 parts of phenolic resin, 35 parts of polyurethane and 20 parts of high-temperature resistant filler mica powder were mixed on a double-roll open mill at a temperature of 70°C and a rotation speed of 180 r / min for 50 min; the mixed material was calendered at 90°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0052] Example 3

[0053] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0054] 100 g of polytetramethylene glycol (number average molecular weight of 1000 g / mol), 100 g of MDI-50, 0.02 g of dibutyltin dilaurate and 120 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 80°C for 2 h for prepolymerization. Afterwards, 25 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2 h to obtain polyurethane.

[0055] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0056] 100 parts of phenolic resin, 25 parts of polyurethane, and 10 parts of high-temperature resistant filler quartz powder were mixed on a double-roll mill at a temperature of 100°C and a rotation speed of 50 r / min for 30 minutes; the mixed material was calendered at 90°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0057] Example 4

[0058] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0059] 100 g of polyethylene glycol 1000, 45 g of hydrogenated MDI, 0.02 g of dimethyltin glycolate and 120 g of N-methylpyrrolidone were added to a three-necked flask equipped with a mechanical stirrer, and reacted at 75° C. for 2.0 h to perform prepolymerization. Afterwards, 10 g of hydroquinone dihydroxyethyl ether was added to the three-necked flask for chain extension, and the reaction was continued for 2.0 h to obtain polyurethane.

[0060] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0061] 70 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler white carbon black were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 100 r / min for 45 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0062] Example 5

[0063] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0064] 100 g of polypropylene glycol 1000, 40 g of hexamethylene diisocyanate, 0.03 g of dibutyltin dilaurate and 120 g of N,N-dimethylacetamide were added to a three-necked flask equipped with a mechanical stirrer, and reacted at 80°C for 2.0 h for prepolymerization. Afterwards, 10 g of diethylene glycol and 5 g of 1,3-propylene glycol were added to the three-necked flask for chain extension, and the reaction was continued for 2.0 h to obtain polyurethane.

[0065] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0066] 100 parts of phenolic resin, 35 parts of polyurethane and 20 parts of high-temperature resistant filler alumina were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 100 r / min for 45 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0067] Example 6

[0068] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0069] 100 g of polytetramethylene glycol (number average molecular weight of 1000 g / mol), 55 g of MDI-100, 0.01 g of dibutyltin dilaurate and 100 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 70°C for 2.5 h for prepolymerization. Afterwards, 10 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2.5 h to obtain polyurethane.

[0070] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0071] 100 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler antimony trioxide were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 120 r / min for 40 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0072] Example 7

[0073] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0074] 100 g of polyethylene glycol 1000, 55 g of MDI-50, 0.01 g of dibutyltin dilaurate and 100 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 70°C for 2.5 h for prepolymerization. Afterwards, 10 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2.5 h to obtain polyurethane.

[0075] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0076] 100 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler antimony trioxide were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 120 r / min for 40 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0077] Comparative Example 1

[0078] The polyurethane toughened phenolic resin hot melt adhesive film was prepared by the same method as in Example 1, except that the amount of the chain extender in step (1) was increased so that the weight ratio of the chain extender to the isocyanate was 1:2.5 (not within the ratio range specified in the present invention). The specific preparation process is as follows:

[0079] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0080] 100 g of polytetramethylene glycol (number average molecular weight of 1000 g / mol), 55 g of MDI-50, 0.01 g of dibutyltin dilaurate and 100 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 70°C for 2.5 h for prepolymerization. Afterwards, 20 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2.5 h to obtain polyurethane.

[0081] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0082] 100 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler antimony trioxide were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 120 r / min for 40 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0083] Comparative Example 2

[0084] The polyurethane toughened phenolic resin hot melt adhesive film was prepared by the same method as in Example 1, except that the amount of isocyanate in step (1) was increased so that the weight ratio of the chain extender to the isocyanate was 1:8.0 (not within the ratio range specified in the present invention). The specific preparation process is as follows:

[0085] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0086] 100 g of polytetrahydrofuran ether diol (number average molecular weight of 1000 g / mol), 80 g of MDI-50, 0.01 g of dibutyltin dilaurate and 100 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 70°C for 2.5 h for prepolymerization. Afterwards, 10 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2.5 h to obtain polyurethane.

[0087] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0088] 100 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler antimony trioxide were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 120 r / min for 40 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0089] Comparative Example 3

[0090] The polyurethane toughened phenolic resin hot melt adhesive film was prepared by the same method as in Example 1, except that the amount of polyol used in step (1) was reduced so that the total weight ratio of the chain extender and the isocyanate to the weight ratio of the polyol was 1:0.6 (not within the ratio range specified in the present invention). The specific preparation process is as follows:

[0091] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0092] 40g of polytetrahydrofuran ether diol (number average molecular weight of 1000g / mol), 55g of MDI-50, 0.01g of dibutyltin dilaurate and 100g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 70°C for 2.5h for prepolymerization. Afterwards, 10g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2.5h to obtain polyurethane.

[0093] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0094] 100 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler antimony trioxide were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 120 r / min for 40 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0095] Comparative Example 4

[0096] The polyurethane toughened phenolic resin hot melt adhesive film was prepared by the same method as in Example 1, except that the amount of polyol in step (1) was increased so that the total weight ratio of the chain extender and the isocyanate to the weight ratio of the polyol was 1:3.19 (not within the ratio range specified in the present invention). The specific preparation process is as follows:

[0097] (1) The polyurethane film former and toughener with low melting point and excellent processability are synthesized as follows:

[0098] 200 g of polytetramethylene glycol (number average molecular weight of 1000 g / mol), 55 g of MDI-50, 0.01 g of dibutyltin dilaurate and 100 g of N,N-dimethylformamide were added to a three-necked flask equipped with a mechanical stirrer and reacted at 70°C for 2.5 h for prepolymerization. Afterwards, 10 g of 1,4-butanediol was added to the three-necked flask for chain extension and the reaction was continued for 2.5 h to obtain polyurethane.

[0099] (2) The preparation process of polyurethane toughened phenolic resin hot melt adhesive film is as follows:

[0100] 100 parts of phenolic resin, 5 parts of polyurethane and 5 parts of high-temperature resistant filler antimony trioxide were mixed on a double-roll mill at a temperature of 80°C and a rotation speed of 120 r / min for 40 min; the mixed material was calendered at 80°C using a double-roll calender to obtain a polyurethane toughened phenolic resin hot melt adhesive film.

[0101] The performance indexes of the hot melt adhesive films prepared in the above embodiments and comparative examples were measured, and the hot melt adhesive films were applied to two composite materials for performance testing. The specific operations were as follows:

[0102] 1. Applied between polyimide film and 45# steel sheet

[0103] Place a 100mm thick hot melt adhesive film between a polyimide film and a 45# steel sheet, and heat press for 30 minutes at 140°C and 4MPa to obtain the sample required for the test. Test the shear strength of the hot melt adhesive film (reference standard: GB / T7124-2008) and the interlayer peel strength of the sample to be tested (reference standard: GB / T 2790-1995).

[0104] 2. Application in aramid fiber

[0105] The hot melt adhesive film and aramid fabric (model: TH51081) were placed in a metal mold in a cross-layered manner. After that, the mold was placed in a vacuum hot press for hot pressing to obtain an aramid composite material sheet. The flexural strength (reference standard: ASTM D790) and interlaminar shear strength (reference standard: ASTM D2344) of the aramid composite material sheet were tested.

[0106] The specific test results are shown in Table 1.

[0107] Table 1 Hot melt adhesive film performance test results

[0108]

[0109] It can be seen from the above table data that the hot melt adhesive film prepared by the preparation method of the present invention has a low melting point and excellent processability, can better impregnate fibers during the hot pressing process, and is beneficial to improving the mechanical properties of the composite material. Moreover, compared with the traditional phenolic resin adhesive film, the present invention has the advantages of solvent-free use, environmental friendliness, and low viscosity. In addition, it can be seen from the experimental conditions and data comparison of Example 1 and Example 6 that when MDI-50 is used as an isocyanate to prepare polyurethane, the polyurethane can have a relatively low melting temperature, which is more conducive to processing fluidity, and can also ensure that the hot melt adhesive film has higher strength performance. It can be seen from the experimental conditions and data comparison of Example 1 and Example 7 that when polytetrahydrofuran ether diol is used as a polyol to prepare polyurethane, the polyurethane can have a relatively low melting temperature, which is more conducive to processing fluidity, and can also ensure that the hot melt adhesive film has higher strength performance.

[0110] From the comparison of the data of Example 1 and Comparative Example 1, it can be seen that when the usage ratio of the chain extender and the isocyanate is too high, the strength performance of the hot melt adhesive film and the mechanical properties of the composite material will be affected. This is because when the usage ratio of the chain extender and the isocyanate is too high, the molecular weight of the polyurethane will be reduced, resulting in a decrease in the bonding performance of the polyurethane, which will cause a decrease in the mechanical properties of the adhesive film, and further reduce the mechanical properties of the composite material.

[0111] From the data comparison of Example 1 and Comparative Example 2, it can be seen that when the ratio of the amount of chain extender to isocyanate is too low, the R value of the polyurethane will be too high and the hard segment ratio will increase. Although the tensile strength of the polyurethane can be improved, the processing fluidity of the polyurethane is reduced, resulting in an increase in the viscosity of the film, a decrease in the wettability of the film, and a decrease in the mechanical properties of the composite material.

[0112] From the data comparison of Example 1 and Comparative Examples 3-4, it can be seen that when the ratio of the total weight of the chain extender and the isocyanate to the amount of the polyol is too low, it will also cause changes in the R value, molecular weight and mechanical properties of the polyurethane, thereby affecting the processing fluidity and wettability of the prepreg, thereby causing a decrease in the mechanical properties of the aramid composite material.

[0113] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0114] For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, all of which belong to the protection scope of the present invention. The protection scope of the present invention shall be based on the attached claims.

Claims

1. A polyurethane toughened phenolic resin hot melt adhesive film, characterized in that: The hot melt adhesive film comprises phenolic resin, polyurethane and high temperature resistant filler; The polyurethane is prepared by reacting a polyol, a chain extender and an isocyanate, wherein the weight ratio of the chain extender to the isocyanate is 1:(4.0-6.0); the total weight ratio of the chain extender and the isocyanate to the weight ratio of the polyol is 1:(0.8-2.0); The polyol is at least one of polytetramethylene glycol, polypropylene glycol and polyethylene glycol; The isocyanate is at least one of MDI-50, MDI-100, hydrogenated MDI, and hexamethylene diisocyanate; In terms of weight, the hot melt adhesive film comprises 70-100 parts of phenolic resin, 5-35 parts of polyurethane, and 5-20 parts of high temperature resistant filler.

2. The polyurethane toughened phenolic resin hot melt adhesive film according to claim 1, characterized in that: The chain extender is at least one of 1,4-butanediol, 1,3-propylene glycol, diethylene glycol, 1,8-octanediol, bisphenol A, hydroquinone dihydroxyethyl ether, and resorcinol dihydroxyethyl ether.

3. The polyurethane toughened phenolic resin hot melt adhesive film according to claim 1, characterized in that: The high temperature resistant filler is at least one of antimony trioxide, mica powder, quartz powder, white carbon black and alumina.

4. A polyurethane toughened phenolic resin hot melt adhesive film according to any one of claims 1 to 3, characterized in that: The preparation method of the polyurethane is as follows: 100 parts of polyol, 40-100 parts of isocyanate, 100-150 parts of solvent and 0.01-0.04 parts of catalyst are weighed and added into a reaction container, reacted at 60-80°C for 2-3h to obtain an isocyanate-terminated polyurethane prepolymer; 10-35 parts of a chain extender are added into the reaction container, reacted at 60-80°C for 2-3h, and the polyurethane is obtained after the solvent is removed.

5. The polyurethane toughened phenolic resin hot melt adhesive film according to claim 4, characterized in that: The catalyst is at least one of dibutyltin dilaurate and dimethyltin glycolate; The solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

6. A method for preparing a polyurethane toughened phenolic resin hot melt adhesive film according to any one of claims 1 to 5, characterized in that: The preparation method is: The formulated phenolic resin, polyurethane and high temperature resistant filler are mixed on a double-roll mill at a temperature of 70-100°C and a rotation speed of 50-180r / min for 30min-50min, and then the mixed material is calendered at 80-90°C using a double-roll calender to obtain the polyurethane toughened phenolic resin hot melt adhesive film.

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