A medium temperature curing high heat resistant epoxy prepreg and a preparation method thereof

Abstract

The application discloses a medium-temperature curing high-heat-resistance epoxy prepreg and a preparation method thereof. Linear phenolic resin and liquid epoxy resin prepolymer are introduced into rigid benzene rings, and then react with aromatic ring-containing diisocyanate to form a double-multiple rigid structure of 'benzene ring+oxazolidone ring', which can significantly improve the high-temperature resistance of the cured product. In addition, the process route of 'linear phenolic prepolymer+oxazolidone modification' step-by-step prepolymerization can avoid the formation of too rigid crosslinking structure in the early stage, and can effectively reduce the viscosity of the prepreg resin system, so that the epoxy resin composition for the prepreg is finally prepared, which has excellent processing process performance, medium-temperature curing and excellent high-temperature performance.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and specifically relates to a medium-temperature curing high heat-resistant epoxy prepreg and its preparation method. Background Technology

[0002] Advanced resin-based composite materials, due to their superior properties such as high specific strength, high specific modulus, and strong designability, have become key materials in high-end equipment manufacturing fields such as aerospace and rail transportation. Epoxy resin, as the most widely used matrix resin, generally has a glass transition temperature (Tg) of less than 150℃, making it difficult to meet the requirements of long-term high-temperature service. Existing technologies mainly employ phenolic resin modification or oxazolidinone ring modification. The former utilizes the rigid structure of multiple benzene rings to increase crosslinking density, but the Tg improvement is limited; for example, the Tg of the CN103958561A system is only around 170℃. The latter introduces a heat-resistant structure through the reaction of isocyanate and epoxy, but conventional isocyanates lack rigidity; for example, the Tg improvement of the CN118702889A system is less than 20℃. Direct blending of the two leads to problems such as poor system compatibility, poor processability, and phase separation due to polarity differences. More importantly, large aerospace components require medium-temperature curing (130-150℃) to reduce internal stress, but traditional medium-temperature curing systems have insufficient crosslinking density, making it difficult to improve heat resistance. Therefore, existing technologies cannot simultaneously achieve the requirements of "medium-temperature curing, high Tg (≥180℃), and good processability". Summary of the Invention

[0003] To address at least some of the technical problems in the prior art, this invention provides a medium-temperature curing, high-heat-resistant epoxy prepreg and its preparation method. The main technical solution of this invention is as follows: (1) Epoxy resin A is added to a reaction vessel, linear phenolic resin is slowly added, and catalyst is added at the same time. The mixture is prepolymerized at 90-110℃ for 60-120 min to obtain phenolic modified epoxy prepolymer. The amount of linear phenolic resin added is 10%-25% of the mass of epoxy resin A, the amount of catalyst added is 0.1%-1.0% of the mass of epoxy resin A, and the viscosity of the phenolic modified epoxy prepolymer at room temperature at the end of the reaction is controlled to be 1500~3500 mPa·s. (2) Cool the phenolic modified epoxy prepolymer obtained in step (1) to 70-80°C, and under nitrogen protection, slowly add aromatic isocyanate. Stir and react at 80-110°C for 120-240 min to obtain oxazolidinone-phenolic modified epoxy prepolymer; wherein the amount of aromatic isocyanate added is 10%-20% of the mass of epoxy resin A. (3) Cool the oxazolidinone-phenolic modified epoxy prepolymer obtained in step (2) to 75~85℃, add epoxy resin B and a latent curing system to obtain an epoxy resin composition for medium-temperature curing high-temperature resistant prepreg; wherein, the amount of epoxy resin B added is 20-40% of the mass of the oxazolidinone-phenolic modified epoxy prepolymer, and the latent curing system is 5-10% of the total mass of epoxy resin B and oxazolidinone-phenolic modified epoxy prepolymer; (4) Coat the medium-temperature curing high heat-resistant prepreg obtained in step (3) with an epoxy resin composition and then prepreg it with reinforcing fibers or fabrics to obtain the medium-temperature curing high heat-resistant epoxy prepreg. The epoxy resin A is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol AD ​​epoxy resin. The linear phenolic resin is at least one of phenol-formaldehyde linear phenolic resin, o-cresol-formaldehyde linear phenolic resin, and cashew phenol modified linear phenolic resin. The catalyst is at least one of imidazole, imidazole derivatives, Lewis acids, and base complexes. The aromatic isocyanate is at least one selected from diphenylmethane diisocyanate, toluene diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, and 1,4-phenyl diisocyanate. The epoxy resin B is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, liquid phenolic epoxy resin, and alicyclic epoxy resin. The latent curing system is at least one of dicyandiamide, dicyandiamide derivatives, and substituted urea derivatives. The reinforcing fiber includes at least one of carbon fiber, glass fiber, PBO fiber, polyimide fiber, aramid fiber, and basalt fiber. The advantages of this invention lie in its two-step reaction of linear phenolic resin and isocyanate synergistic modification of epoxy resin. First, the phenolic hydroxyl groups react with the epoxy ring to form a rigid network and generate active hydroxyl groups. Subsequently, the isocyanate reacts with the hydroxyl groups to introduce flexible segments for toughening. Second, the aromatic ring structure of the phenolic resin reacts with the aromatic isocyanate to generate an oxazolidinone ring, synergistically improving heat resistance. This synergistic effect of "rigid crosslinking - flexible toughening - heat resistance enhancement" achieves simultaneous improvement in the heat resistance and mechanical properties of the epoxy resin. Furthermore, the two-step prepolymerization process effectively reduces the viscosity of the system by controlling the degree of prepolymerization, significantly improving the processing performance of prepreg and the molding performance of composite materials. Detailed Implementation The present application will be further described in detail below with reference to preferred embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application. The purpose of providing these embodiments is to enable a more thorough and comprehensive understanding of the disclosure of the present application. Example 1 The following presents a method for preparing medium-temperature curing, high-heat-resistant epoxy prepreg. 1. Preparation method (1) Add 55 parts by weight of bisphenol A epoxy resin and 45 parts by weight of bisphenol AD ​​epoxy resin to a reaction vessel, slowly add 15 parts by weight of o-cresol formaldehyde linear phenolic resin, and simultaneously add 0.3 parts by weight of 2-ethyl-4-methylimidazolium. After stirring evenly, heat to 110°C and keep warm for 60 min to prepolymerize to obtain phenolic modified epoxy prepolymer. The viscosity of the prepolymer at room temperature at the end of the reaction is 2470 mPa·s. (2) Cool the phenolic modified epoxy prepolymer obtained in step (1) to 80°C, and under nitrogen protection, slowly add 10 parts by weight of diphenylmethane diisocyanate and 5 parts by weight of 1,4-phenyl diisocyanate. After stirring evenly, heat to 110°C and stir for 120 min to obtain oxazolidinone-phenolic modified epoxy prepolymer. (3) Cool the oxazolidinone-phenolic modified epoxy prepolymer obtained in step (2) to 85°C, add 20 parts by weight of 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester and 18 parts by weight of bisphenol F type epoxy resin, mix evenly, add 10 parts by weight of dicyandiamide and 0.6 parts by weight of 1,1-dimethyl-3-phenylurea, stir until completely dissolved, and obtain a medium-temperature curing high heat-resistant prepreg epoxy resin composition; (4) Coating the epoxy resin composition obtained in step (3) with unidirectional carbon fiber (T700S, surface density 160 / m²) and prepreg composite to obtain medium temperature curing high heat resistance epoxy prepreg. Example 2 The following presents a method for preparing medium-temperature curing, high-heat-resistant epoxy prepreg. 1. Preparation method (1) 100 parts by weight of bisphenol A epoxy resin were added to a reaction vessel, and 15 parts by weight of phenol-formaldehyde linear phenolic resin and 10 parts by weight of cashew phenol modified linear phenolic resin were slowly added. At the same time, 0.3 parts by weight of 2-methylimidazole were added. After stirring evenly, the temperature was raised to 100°C and kept at the temperature for 90 min to obtain phenolic modified epoxy prepolymer. The viscosity of the prepolymer at 25°C at the end of the reaction was 2980 mPa·s. (2) Cool the phenolic modified epoxy prepolymer obtained in step (1) to 75°C, and under nitrogen protection, slowly add 10 parts by weight of 3,3'-dimethyl-4,4'-biphenyl diisocyanate. After stirring evenly, heat to 95°C and stir for 180 min to obtain oxazolidinone-phenolic modified epoxy prepolymer. (3) Cool the oxazolidinone-phenolic modified epoxy prepolymer obtained in step (2) to 80°C, add 8 parts by weight of bisphenol AD ​​type epoxy resin, 12 parts by weight of phenolic epoxy resin and 20 parts by weight of tetraglycidyl diaminodiphenylmethane, mix evenly, add 11.5 parts by weight of aromatic modified dicyandiamide and 1.0 parts by weight of didimethylureatoluene diamine accelerator, stir until completely dissolved, and obtain a medium-temperature curing high heat-resistant prepreg epoxy resin composition; (4) Coating the epoxy resin composition obtained in step (3) with unidirectional high-strength glass fiber (area density 210g / m²) and prepreg to obtain medium-temperature curing high heat-resistant epoxy prepreg. Example 3 The following presents a method for preparing medium-temperature curing, high-heat-resistant epoxy prepreg. 1. Preparation method (1) 65 parts by weight of bisphenol A epoxy resin and 35 parts by weight of bisphenol F epoxy resin were added to a reaction vessel, and 10 parts by weight of phenol-formaldehyde linear phenolic resin were slowly added. At the same time, 1.0 parts by weight of boron trifluoride-diethylamine complex was added. After stirring evenly, the temperature was raised to 90°C and prepolymerized for 120 min to obtain phenolic modified epoxy prepolymer. The viscosity of the prepolymer at 25°C at the end of the reaction was 2030 mPa·s. (2) Cool the phenolic modified epoxy prepolymer obtained in step (1) to 70°C, and under nitrogen protection, slowly add 10 parts by weight of toluene diisocyanate. After stirring evenly, heat to 80°C and stir for 240 min to obtain oxazolidinone-phenolic modified epoxy prepolymer. (3) Cool the oxazolidinone-phenolic modified epoxy prepolymer obtained in step (2) to 70°C, add 20 parts by weight of tetraglycidyl diaminodiphenylmethane and 20 parts by weight of bisphenol F epoxy resin, mix evenly, add 8 parts by weight of dicyandiamide and 0.5 parts by weight of 1,1-dimethyl-3-phenylurea accelerator, stir until completely dissolved, and obtain a medium-temperature curing high heat-resistant prepreg epoxy resin composition; (4) Coating the epoxy resin composition obtained in step (3) with unidirectional aramid fiber (area density 200g / m²) and prepreg to obtain medium temperature curing high heat resistance epoxy prepreg. Comparative Example 1 (1) Add 55 parts by weight of bisphenol A epoxy resin and 45 parts by weight of bisphenol AD ​​epoxy resin to a reaction vessel, slowly add 15 parts by weight of o-cresol formaldehyde linear phenolic resin, and simultaneously add 0.3 parts by weight of 2-ethyl-4-methylimidazolium. After stirring evenly, heat to 110°C and keep warm for 60 min to prepolymerize to obtain phenolic modified epoxy prepolymer. The viscosity of the prepolymer at 25°C at the end of the reaction is 2510 mPa·s. (2) Cool the phenolic modified epoxy prepolymer obtained in step (1) to 85°C, add 20 parts by weight of 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester and 18 parts by weight of bisphenol F type epoxy resin, mix evenly, add 10 parts by weight of dicyandiamide and 0.6 parts by weight of 1,1-dimethyl-3-phenylurea, stir until completely dissolved, and obtain the epoxy resin composition for prepreg; (3) The epoxy resin composition obtained in step (2) is coated and prepreg-composite with unidirectional carbon fiber (T700S, surface density 160g / m²) to obtain epoxy prepreg. Comparative Example 2 (1) 55 parts by weight of bisphenol A epoxy resin and 45 parts by weight of bisphenol AD ​​epoxy resin were added to a reaction vessel. Under nitrogen protection, 0.3 parts by weight of 2-ethyl-4-methylimidazolium was added, and 10 parts by weight of diphenylmethane diisocyanate (MDI) and 5 parts by weight of 1,4-phenyl diisocyanate (PPDI) were slowly added. After stirring evenly, the temperature was raised to 110°C and the reaction was stirred for 120 min to obtain oxazolidinone modified epoxy prepolymer. (2) Cool the oxazolidinone-modified epoxy prepolymer obtained in step (1) to 85°C, add 20 parts by weight of 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester and 18 parts by weight of bisphenol F type epoxy resin, mix evenly, add 10 parts by weight of modified dicyandiamide and 0.6 parts by weight of 1,1-dimethyl-3-phenylurea, stir until completely dissolved, and obtain epoxy resin composition; (4) Coating the epoxy resin composition obtained in step (3) with unidirectional carbon fiber (T700S, surface density 160g / m²) to obtain epoxy prepreg. Comparative Example 3 (1) Add 55 parts by weight of bisphenol A epoxy resin and 45 parts by weight of bisphenol AD ​​epoxy resin to a reaction vessel. Under nitrogen protection, slowly add 15 parts by weight of o-cresol formaldehyde linear phenolic resin, 10 parts by weight of diphenylmethane diisocyanate (MDI) and 5 parts by weight of 1,4-phenyl diisocyanate (PPDI), and add 0.3 parts by weight of 2-ethyl-4-methylimidazolium. After stirring evenly, heat to 110°C and keep the temperature for 120 min to obtain a mixed modified epoxy prepolymer. (2) Cool the mixed modified epoxy prepolymer obtained in step (1) to 85°C, add 20 parts by weight of 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester and 18 parts by weight of bisphenol F type epoxy resin, mix evenly, add 10 parts by weight of modified dicyandiamide and 0.6 parts by weight of urea latent accelerator, stir until completely dissolved, and obtain epoxy resin composition; (3) Coating the epoxy resin composition obtained in step (2) with unidirectional carbon fiber (T700S, surface density 160g / m²) to obtain epoxy prepreg. Compared with traditional methods of modifying epoxy resin systems with linear phenolic resin (Comparative Example 1) and using isocyanate to modify epoxy resin (Comparative Example 2), the resin compositions prepared in the embodiments of the present invention exhibit excellent heat resistance. Compared with the conventional process route of simultaneously adding linear phenolic resin and isocyanate to directly blend and modify epoxy resin (Comparative Example 3), the embodiments of the present invention control the prepolymerization degree of the prepolymer through stepwise reactions, resulting in resin compositions with lower viscosity, excellent processability, and benefits for prepreg production and composite material molding. As can be seen from the above embodiments and comparative examples, the present invention, through the synergistic effect of linear phenolic resin prepolymerization and modification with benzene ring-containing diisocyanate oxazolidinone, not only achieves the unity of medium-temperature curing and high-temperature resistance, but also completely solves the problems of poor system compatibility and easy phase separation in existing blending modification processes through stepwise prepolymerization reactions, significantly reducing the viscosity of the system and improving the processability of hot-melt prepregs. Its performance advantages are significantly superior to existing conventional modification methods, demonstrating significant technological innovation and industrial application value.

Claims

1. A medium-temperature curing, high-heat-resistant epoxy prepreg and its preparation method, characterized in that, Includes the following steps: (1) Epoxy resin A is added to a reaction vessel, linear phenolic resin is slowly added, and catalyst is added at the same time. The mixture is prepolymerized at 90-110℃ for 60-120 min to obtain phenolic modified epoxy prepolymer. The amount of linear phenolic resin added is 10%-25% of the mass of epoxy resin A, the amount of catalyst added is 0.1%-1.0% of the mass of epoxy resin A, and the viscosity of the phenolic modified epoxy prepolymer at room temperature at the end of the reaction is controlled to be 1500~3500 mPa·s. (2) Cool the phenolic modified epoxy prepolymer obtained in step (1) to 70-80°C, and under nitrogen protection, slowly add aromatic isocyanate. Stir and react at 80-110°C for 120-240 min to obtain oxazolidinone-phenolic modified epoxy prepolymer; wherein the amount of aromatic isocyanate added is 10%-20% of the mass of epoxy resin A. (3) Cool the oxazolidinone-phenolic modified epoxy prepolymer obtained in step (2) to 75~85℃, add epoxy resin B and a latent curing system to obtain an epoxy resin composition for medium-temperature curing high-temperature resistant prepreg; wherein, the amount of epoxy resin B added is 20-40% of the mass of the oxazolidinone-phenolic modified epoxy prepolymer, and the latent curing system is 5-10% of the total mass of epoxy resin B and oxazolidinone-phenolic modified epoxy prepolymer; (4) Coat the medium-temperature curing high heat-resistant prepreg obtained in step (3) with an epoxy resin composition and then prepreg it with reinforcing fibers or fabrics to obtain the medium-temperature curing high heat-resistant epoxy prepreg.

2. The preparation method according to claim 1, characterized in that, The epoxy resin A is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol AD ​​epoxy resin.

3. The preparation method according to claim 1, characterized in that, The linear phenolic resin is at least one of phenol-formaldehyde linear phenolic resin, o-cresol-formaldehyde linear phenolic resin, and cashew phenol modified linear phenolic resin.

4. The preparation method according to claim 1, characterized in that, The catalyst is at least one of imidazole, imidazole derivatives, Lewis acids, and base complexes.

5. The preparation method according to claim 1, characterized in that, The aromatic isocyanate is at least one selected from diphenylmethane diisocyanate, toluene diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, and 1,4-phenyl diisocyanate.

6. The preparation method according to claim 1, characterized in that, The epoxy resin B is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, liquid phenolic epoxy resin, and alicyclic epoxy resin.

7. The preparation method according to claim 1, characterized in that, The latent curing system is at least one of dicyandiamide, dicyandiamide derivatives, and substituted urea derivatives.

8. The method for preparing the medium-temperature curing high heat-resistant epoxy prepreg according to claim 1, characterized in that, The reinforcing fiber includes at least one of carbon fiber, glass fiber, PBO fiber, polyimide fiber, aramid fiber, and basalt fiber.