Process for the preparation of a medium temperature curing epoxy resin material for carbon fibre prepregs

Abstract

The application relates to the field of high polymer composite materials, in particular to a method for preparing a medium-temperature curing epoxy resin material for carbon fiber pre-impregnation, which comprises the steps of raw material preparation, resin dispersion premixing system and medium-temperature curing resin material preparation; the process carries out constant-temperature high-shear dispersion of an epoxy resin matrix and core-shell structure toughening particles at 50-60 DEG C; the core is that through physical shearing and thermodynamic swelling cooperation, the resin penetrates into the shell layer of the toughening particles, the toughening phase is introduced in a semi-stable state, and the core-shell active groups are utilized to realize co-curing reaction during curing; the application does not need high-temperature pre-reaction, breaks through the technical obstacles of high viscosity and particle filtration caused by traditional toughening and impregnation failure, and significantly improves the interlayer fracture toughness and shear strength of the composite material under the premise of maintaining the heat resistance and modulus of the system.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials, specifically to a method for preparing medium-temperature curing epoxy resin materials for carbon fiber prepreg. Background Technology

[0002] Medium-temperature curing epoxy resin prepregs are widely used in aerospace, wind turbine blades, and high-end industrial fields due to their wide molding process window and low energy consumption. However, epoxy resin cured products with high crosslinking density usually have defects such as high brittleness and poor impact resistance. Existing toughening technologies mainly have the following technical defects: For example, patent CN103113716A uses dimer acid modified epoxy resin for toughening. This method requires a complex chemical pre-reaction under high temperature and catalyst to prepare the modified resin. Moreover, due to the introduction of a large number of flexible segments, the heat resistance and modulus of the system are often significantly reduced. For example, patent CN111087756B uses thermoplastic resin for toughening. The addition of thermoplastic resin will significantly increase the viscosity of the resin system. Moreover, during the preparation of prepreg, large-molecule thermoplastic resin or large-size particles are very likely to have a filtration effect on the surface of carbon fiber bundles, blocking the capillary resin penetration channels between fiber bundles, resulting in poor impregnation of carbon fibers, generating internal pores, and seriously affecting the interlaminar shear strength and overall mechanical properties of the composite material. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a medium-temperature curing epoxy resin material for carbon fiber prepreg, aiming to solve the problems in the prior art where dimer acid modification leads to a significant reduction in resin heat resistance and modulus, and where toughening of thermoplastic resins results in poor fiber impregnation, internal porosity, and damage to interlayer mechanical properties due to a significant increase in viscosity and particle filtration effect. Specifically, the technical solution of this invention is as follows: A method for preparing a medium-temperature curing epoxy resin material for carbon fiber prepreg includes the following steps: Step S1, Raw material preparation: Provide raw materials, by weight, including: 100 parts epoxy resin matrix, 5-15 parts core-shell toughening particles, 5-10 parts medium-temperature latent curing agent, and 1-5 parts accelerator; the core-shell toughening particles have a particle size distribution of 0.5-5 μm, and their core layer is a cross-linked rubber elastomer, and their shell layer is a polymer containing active epoxy groups; Step S2, preparation of resin dispersion premix system: The epoxy resin matrix is ​​heated to 50-60℃, and the core-shell toughening particles are added; at 50-60℃, a high shear dispersion device is used to perform shear dispersion treatment at a speed of 1500-3000 rpm for 1-2 hours, so that the epoxy resin matrix penetrates into the shell layer of the core-shell toughening particles and swells, to obtain the resin dispersion premix system; Step S3, Preparation of medium-temperature curing resin material: Adjust the temperature of the resin dispersion premix system to 40-50℃, add the medium-temperature latent curing agent and the accelerator, and perform vacuum mixing and degassing treatment under a vacuum degree of not less than 0.09MPa to obtain the medium-temperature curing epoxy resin material for carbon fiber prepreg.

[0004] Preferably, in step S1, the median volume diameter of the core-shell toughening particles is 1.0-1.5 μm.

[0005] Preferably, in step S1, the crosslinked rubber elastomer is selected from at least one of polybutadiene rubber, polyacrylate rubber, or siloxane rubber; the polymer containing active epoxy groups is methyl methacrylate-glycidyl methacrylate copolymer.

[0006] Preferably, in step S3, the medium-temperature latent curing agent is micronized dicyandiamide; and the accelerator is an organic urea derivative.

[0007] Preferably, in step S1, the epoxy resin matrix is ​​a blend of bisphenol A type epoxy resin and linear phenolic epoxy resin.

[0008] Preferably, the method for preparing the medium-temperature curing epoxy resin material for carbon fiber prepreg according to any one of claims 1 to 5 is required, and after obtaining the epoxy resin material, the method further includes a step of preparing the prepreg using a hot-melt method: Step S4, film coating: The carbon fiber prepreg medium-temperature curing epoxy resin material is coated onto double-sided release paper to form a resin film. Step S5, hot-press composite impregnation: Provide reinforcing fibers, and perform hot-press composite impregnation of the resin film and the reinforcing fibers at 70-90°C to obtain a medium-temperature curing prepreg.

[0009] Preferably, in step S5, the reinforcing fiber is unidirectional carbon fiber or plain weave carbon fiber fabric; when the reinforcing fiber is unidirectional carbon fiber, the impregnation temperature is 80°C; when the reinforcing fiber is plain weave carbon fiber fabric, the impregnation temperature is 85°C.

[0010] The present invention has the following beneficial effects: Overcoming the traditional high-temperature pre-reactor synthesis process of dimer acids, the toughening phase is introduced into the matrix in a semi-stable form in a one-step method through the synergistic effect of physical shear and thermodynamic swelling at 50-60℃, simplifying the process route; during the curing process, the core-shell particles are uniformly distributed in the resin; the core layer rubber phase acts as a stress concentration point when under stress, inducing shear yielding and crazes in the matrix, absorbing a large amount of impact energy; Simultaneously, the active epoxy groups carried by the shell undergo a co-curing reaction with the dicyandiamide curing agent and epoxy network, forming strong interfacial covalent bonds. This multi-scale synergistic effect produces crack passivation and deflection effects, improving the material's type I fracture toughness without reducing the system's glass transition temperature and modulus; it also improves the high viscosity and filtration effect caused by the toughening of thermoplastic resin; the specific particle size distribution combined with the swollen and softened semi-stable dispersion structure ensures the effective penetration of resin into the capillary channels between carbon fiber bundles; the resulting prepreg exhibits no fiber fuzzing, dry spots, or obvious fiber gaps. Detailed Implementation

[0011] The technical solutions in the embodiments of the present invention will be clearly and completely described below; the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0012] Example 1: This embodiment provides a method for preparing a multi-scale toughened network medium-temperature curing prepreg and its resin material, the specific steps of which are as follows: S1 Raw material preparation: By weight, take 100 parts of a blend of bisphenol A type epoxy resin and linear phenolic epoxy resin, 10 parts of core-shell structure toughening particles, 8 parts of micronized dicyandiamide, and 3 parts of aryl substituted urea accelerator; the core layer of the core-shell structure toughening particles is cross-linked polybutadiene rubber, the shell layer is methyl methacrylate-glycidyl methacrylate copolymer, the particle size distribution is 0.5-3.0 μm, and the median volume particle size is 1.2 μm; Preparation of S2 resin dispersion premix system: 100 parts of epoxy resin matrix were added to a dispersion vessel with a temperature control jacket, heated to 55℃ and kept at that temperature for 20 min to stabilize the resin viscosity; 10 parts of core-shell toughening particles were slowly added to the system, with the feeding time controlled at 15 min; after the feeding was completed, the system was subjected to constant temperature shear dispersion at 2500 rpm for 1.5 h using a high shear disperser; after dispersion, the resulting system had a uniform appearance and no visible particle agglomeration; in this step, small epoxy resin molecules entered the shell polymer and caused moderate swelling, forming a stable solvation layer on the particle surface, suppressing the static aggregation tendency between particles, and maintaining the system viscosity within a range suitable for subsequent processing; Preparation of S3 medium-temperature curing resin material: Cool the system obtained from S2 to 45℃, add 8 parts of micronized dicyandiamide and 3 parts of aryl substituted urea accelerator, mix with a planetary mixer for 45 minutes under a vacuum of not less than 0.095MPa, and continue to degas for 15 minutes to obtain medium-temperature curing epoxy resin material. S4 film coating: The resin material obtained in S3 is used to form two layers of resin film on double-sided release paper. The surface density of a single layer of film is controlled to be 96g / m². S5 Hot-Pressure Composite Impregnation: T300-12K unidirectional carbon fiber is selected as the reinforcing fiber; the upper and lower resin films are combined with the unrolled carbon fiber on a hot-melt prepreg machine, the impregnation temperature is controlled at 80℃, and the impregnation pressure is controlled at 0.30MPa to obtain unidirectional medium-temperature curing prepreg; the prepreg has a uniform appearance at room temperature and no obvious dry spots or fiber fuzzing defects.

[0013] Example 2: This embodiment provides a method for preparing a multi-scale toughened network medium-temperature curing prepreg and its resin material, the specific steps of which are as follows: S1 Raw material preparation: By weight, take 100 parts of a blend of bisphenol A type epoxy resin and linear phenolic epoxy resin, 5 parts of core-shell toughening particles, 5 parts of micronized dicyandiamide, and 1 part of organic urea accelerator; the core layer of the core-shell toughening particles is cross-linked polyacrylate rubber, the shell layer is methyl methacrylate-glycidyl methacrylate copolymer, the particle size distribution is 0.5-2.5μm, and the median volume particle size is 1.0μm; Preparation of S2 resin dispersion premix system: The epoxy resin matrix was heated to 50°C, core-shell toughening particles were added, and the mixture was sheared and dispersed at 1500 rpm for 1 h at 50°C to obtain a uniform resin dispersion premix system. In this step, small epoxy resin molecules entered the shell polymer and caused moderate swelling. A stable solvation layer was formed on the particle surface, the static aggregation tendency between particles was suppressed, and the viscosity of the system was maintained within a range suitable for subsequent processing. Preparation of S3 medium-temperature curing resin material: Cool the resin dispersion premix system obtained from S2 to 40℃, add micronized dicyandiamide and organic urea accelerator, stir and degas for 40 min under a vacuum degree of not less than 0.090MPa to obtain medium-temperature curing epoxy resin material. S4 film coating: The medium-temperature curing epoxy resin material obtained in S3 is used to form a resin film on double-sided release paper; S5 Hot-press Composite Impregnation: T300-12K unidirectional carbon fiber is selected as the reinforcing fiber, and hot-melt composite impregnation is carried out at 80℃ and 0.30MPa to obtain unidirectional medium-temperature curing prepreg.

[0014] Example 3: This embodiment provides a method for preparing a multi-scale toughened network medium-temperature curing prepreg and its resin material, the specific steps of which are as follows: S1 Raw material preparation: By weight, take 100 parts of a blend of bisphenol A type epoxy resin and linear phenolic epoxy resin, 15 parts of core-shell toughening particles, 10 parts of micronized dicyandiamide, and 5 parts of organic urea accelerator; the core layer of the core-shell toughening particles is cross-linked siloxane rubber, the shell layer is methyl methacrylate-glycidyl methacrylate copolymer, the particle size distribution is 0.8-5.0 μm, and the median volume particle size is 1.5 μm; Preparation of S2 resin dispersion premix system: The epoxy resin matrix was heated to 60°C, core-shell toughening particles were added, and the mixture was sheared and dispersed at 3000 rpm for 2 hours at 60°C to obtain the resin dispersion premix system. In this step, small epoxy resin molecules entered the shell polymer and caused moderate swelling. A stable solvation layer was formed on the particle surface, the static aggregation tendency between particles was suppressed, and the viscosity of the system was maintained within a range suitable for subsequent processing. Preparation of S3 medium-temperature curing resin material: Cool the resin dispersion premix system obtained from S2 to 50℃, add micronized dicyandiamide and organic urea accelerator, mix and degas for 60 min under a vacuum degree of not less than 0.090MPa to obtain medium-temperature curing epoxy resin material. S4 film coating: The medium-temperature curing epoxy resin material obtained in S3 is used to form a resin film on double-sided release paper; S5 Hot-press Composite Impregnation: T300-12K unidirectional carbon fiber is selected as the reinforcing fiber, and hot-melt composite impregnation is carried out at 80℃ and 0.30MPa to obtain unidirectional medium-temperature curing prepreg.

[0015] Example 4: This embodiment provides a method for preparing a multi-scale toughened network medium-temperature curing prepreg and its resin material, the specific steps of which are as follows: S1 Raw material preparation: By weight, take 100 parts of a blend of bisphenol A type epoxy resin and linear phenolic epoxy resin, 12 parts of core-shell structure toughening particles, 8 parts of micronized dicyandiamide, and 3 parts of organic urea accelerator; the core layer of the core-shell structure toughening particles is cross-linked polybutadiene rubber, the shell layer is methyl methacrylate-glycidyl methacrylate copolymer, the particle size distribution is 0.6-3.5μm, and the median volume particle size is 1.3μm; Preparation of S2 resin dispersion premix system: The epoxy resin matrix was heated to 58℃, core-shell toughening particles were added, and the mixture was sheared and dispersed at 2200 rpm for 1.5 h at 58℃ to obtain the resin dispersion premix system. In this step, small epoxy resin molecules entered the shell polymer and caused moderate swelling. A stable solvation layer was formed on the particle surface, the static aggregation tendency between particles was suppressed, and the viscosity of the system was maintained within a range suitable for subsequent processing. Preparation of S3 medium-temperature curing resin material: Cool the resin dispersion premix system obtained from S2 to 45℃, add micronized dicyandiamide and organic urea accelerator, mix and degas for 45 min under a vacuum degree of not less than 0.092MPa to obtain medium-temperature curing epoxy resin material; S4 film coating: The medium-temperature curing epoxy resin material obtained in S3 is used to form a resin film on double-sided release paper; S5 Hot-press Composite Impregnation: T300-3K plain weave carbon fiber fabric was selected as the reinforcing fiber and hot-melt composite impregnation was carried out at 85℃ and 0.32MPa to obtain plain weave medium-temperature curing prepreg; after cross-section observation, no obvious resin depletion area was found in the interlacing area of ​​the fabric.

[0016] Comparative Example 1: The difference between this comparative example and Example 1 is that the high-shear isothermal dispersion treatment in step S2 is omitted, and the core-shell toughening particles are directly added to the epoxy resin matrix at 45°C and mixed at 600 rpm for 20 minutes using a planetary mixer. Other operating steps and process parameters are exactly the same as in Example 1.

[0017] Comparative Example 2: The difference between this comparative example and Example 1 is that the core-shell toughening particles in Example 1 are replaced with core-shell toughening particles with a particle size distribution of 3.0-9.0 μm and a median volume particle size of 6.0 μm. Other operating steps and process parameters are exactly the same as in Example 1.

[0018] Comparative Example 3: The difference between this comparative example and Example 1 is that the core-shell toughening particles in Example 1 are replaced with polymethyl methacrylate particles with a core layer of cross-linked polybutadiene rubber and a shell layer of polymethyl methacrylate without glycidyl methacrylate. The particle size distribution and the median volume particle size are kept the same as in Example 1. Other operating steps and process parameters are exactly the same as in Example 1.

[0019] Comparative Example 4: The difference between this comparative example and Example 1 is that the dispersion temperature in step S2 of Example 1 is increased from 55°C to 70°C, while the other operating steps and process parameters are exactly the same as in Example 1.

[0020] Comparative Example 5: The difference between this comparative example and Example 1 is that the immersion temperature in step S5 of Example 1 is adjusted from 80°C to 65°C, while the other operating steps and process parameters are exactly the same as in Example 1.

[0021] Performance Testing and Datasheets All samples were prepared as prepregs and composite laminates were fabricated using the same layup method. The viscosity of the resin system at 50°C was measured using a rotational rheometer, the porosity of the prepreg was measured using ultrasonic C-scan combined with the density method, the interlaminar shear strength was measured using the short beam method, the type I interlaminar fracture toughness was measured using the double cantilever beam method, and the glass transition temperature was measured using DSC. Performance test data are shown in Table 1: Table 1. Performance test results of each embodiment and comparative example. Example 1 8.6 0.38 86 560 131 No dry spots, no fuzzing, and no obvious inter-fiber gaps. Example 2 6.9 0.52 78 470 129 Uniform appearance Example 3 11.4 0.64 82 535 130 The appearance is uniform, with slight local resin enrichment. Example 4 9.1 0.46 84 548 130 Uniform impregnation in the interlacing areas of the fabric Comparative Example 1 13.8 1.62 69 395 130 A small amount of particle aggregation and dry spots are visible. Comparative Example 2 10.7 1.85 66 412 130 Resin accumulation at the edges of fiber bundles Comparative Example 3 8.4 0.91 73 438 128 The appearance is basically uniform Comparative Example 4 12.2 1.08 71 421 126 The surface is uniform, and it thickens slightly after storage. Comparative Example 5 9.5 1.47 68 448 131 There are localized un-impregnated areas. As can be seen from the comparison of the test results of Example 1 and Comparative Example 1 in Table 1, after omitting the high shear isothermal dispersion treatment in step S2, the interlaminar shear strength, type I interlaminar fracture toughness and impregnation quality all decreased. The underlying mechanism is that without high shear dispersion at 50-60℃, epoxy resin cannot fully penetrate the shell polymer and form a stable solvation layer, and secondary agglomeration is more likely to occur between particles. Agglomerated particles form local accumulation on the fiber bundle surface, which increases local flow resistance and hinders the resin from entering the interfilament gaps, resulting in increased porosity. At the same time, the toughening phase is unevenly distributed in the matrix, and it is difficult to form a continuous and uniform energy dissipation zone during crack propagation. Therefore, the type I interlaminar fracture toughness and interlaminar shear strength are significantly reduced. As can be seen from the comparison of the test results of Example 1 and Comparative Example 2 in Table 1, after changing the median volumetric particle size of the toughening particles from 1.2 μm to 6.0 μm, the porosity of the prepreg increased significantly, and the interlaminar shear strength and fracture toughness decreased. The underlying mechanism is that particles with larger diameters are less likely to enter the micro-channels between carbon fiber monofilaments synchronously with the resin, and are more likely to remain on the periphery of the fiber bundle and cause filtration. This local enrichment will compress the effective resin diffusion path, resulting in insufficient wetting inside the fiber bundle, forming resin-depleted areas and micropore defects. Particles with a diameter larger than the capillary channel size of the fiber bundle will also cause discontinuous stress transmission and a discrete distribution of the plastic energy dissipation zone near the crack front, so the interlaminar performance is lower than that of Example 1. As can be seen from the comparison of the test results of Example 1 and Comparative Example 3 in Table 1, after replacing the shell layer with a polymer containing epoxy functional groups with polymethyl methacrylate without glycidyl methacrylate structure, the type I interlaminar fracture toughness and interlaminar shear strength both decreased, and the glass transition temperature also decreased slightly. The underlying mechanism is that the shell lacks epoxy functional groups that can participate in the curing reaction. The particles and the epoxy curing network mainly rely on physical compatibility and entanglement, resulting in a decrease in the degree of interfacial chemical bonding. When the crack extends to the vicinity of the particles, the particle-matrix interface is more prone to debonding. Although it can still provide some energy dissipation, it is difficult to form a stable load transfer interface. Therefore, the interlaminar shear strength and type I interlaminar fracture toughness are lower than those in Example 1. The weakened interfacial bonding also reduces the local network constraint, resulting in a slight decrease in the glass transition temperature. As can be seen from the comparison of the test results of Example 1 and Comparative Example 4 in Table 1, after increasing the dispersion temperature of step S2 to 70°C, the viscosity of the resin system increases, the porosity increases, and the glass transition temperature, interlaminar shear strength and type I interlaminar fracture toughness all decrease. The underlying mechanism is that when the temperature exceeds the specified range, the probability of early reaction between the active epoxy groups on the shell and the trace active components in the system increases, the stability of the solvation layer on the particle surface decreases, and the system is more prone to thickening during mixing and storage. This early structuring weakens the fluidity of the subsequent impregnation stage, reduces the resin penetration efficiency inside the fiber bundle, and worsens the uniformity of the cured network. Therefore, the interlayer performance and heat resistance are lower than those of Example 1. As can be seen from the comparison of the test results of Example 1 and Comparative Example 5 in Table 1, when the impregnation temperature is reduced from 80°C to 65°C, the porosity of the prepreg increases and the interlaminar shear strength and type I interlaminar fracture toughness decrease. The underlying mechanism is that the lower impregnation temperature is insufficient to fully soften the solvation layer on the outer layer of the particles, which weakens the overall rheological compliance of the system and reduces the ability of the particles and resin to enter the gap between the monofilaments under pressure. Insufficient wetting inside the fiber bundle will result in local unimpregnated areas and micropores, thereby weakening the interfacial bonding and interlaminar crack resistance. Therefore, the interlaminar shear strength and type I interlaminar fracture toughness are lower than those in Example 1, while the glass transition temperature does not change significantly, indicating that the difference mainly comes from the impregnation quality rather than the cured network itself. The results from Examples 1 to 4 show that, within the range of components and processes defined by the present invention, the resin processability, prepreg impregnation quality, and interlaminar properties of the composite material can all be balanced. In Example 2, the amount of toughening particles and curing components are at a low level, the system viscosity is low, and the impregnation is good, but the volume fraction of the toughening phase is relatively insufficient, so the fracture toughness is slightly low. In Example 3, the toughening particles and curing components were at a high level, and the material toughness remained at a high level, but the resin viscosity increased, resulting in a slightly higher porosity than in Example 1. In Example 4, plain weave fabric was used as the reinforcing material, which could meet the wetting requirements of the interwoven area of ​​the fabric at 85°C. The resulting composite material still had high interlaminar properties, indicating that the method has good applicability to different carbon fiber reinforcement forms.

[0022] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may use the above-disclosed technical content to make changes or substitutions to equivalent embodiments with equivalent effects and apply them to other fields. However, any simple modifications, equivalent changes and substitutions made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a medium-temperature curing epoxy resin material for carbon fiber prepreg, characterized in that, Includes the following steps: Step S1, Raw material preparation: Provide raw materials, by weight, including: 100 parts epoxy resin matrix, 5-15 parts core-shell toughening particles, 5-10 parts medium-temperature latent curing agent, and 1-5 parts accelerator; the core-shell toughening particles have a particle size distribution of 0.5-5 μm, and their core layer is a cross-linked rubber elastomer, and their shell layer is a polymer containing active epoxy groups; Step S2, preparation of resin dispersion premix system: The epoxy resin matrix is ​​heated to 50-60℃, and the core-shell toughening particles are added; at 50-60℃, a high shear dispersion device is used to perform shear dispersion treatment at a speed of 1500-3000 rpm for 1-2 hours, so that the epoxy resin matrix penetrates into the shell layer of the core-shell toughening particles and swells, to obtain the resin dispersion premix system; Step S3, Preparation of medium-temperature curing resin material: Adjust the temperature of the resin dispersion premix system to 40-50℃, add the medium-temperature latent curing agent and the accelerator, and perform vacuum mixing and degassing treatment under a vacuum degree of not less than 0.09MPa to obtain the medium-temperature curing epoxy resin material for carbon fiber prepreg.

2. The method for preparing medium-temperature curing epoxy resin material for carbon fiber prepreg according to claim 1, characterized in that, In step S1, the median volumetric diameter of the core-shell toughening particles is 1.0-1.5 μm.

3. The method for preparing medium-temperature curing epoxy resin material for carbon fiber prepreg according to claim 1, characterized in that, In step S1, the crosslinked rubber elastomer is selected from at least one of polybutadiene rubber, polyacrylate rubber, or siloxane rubber; the polymer containing active epoxy groups is methyl methacrylate-glycidyl methacrylate copolymer.

4. The method for preparing medium-temperature curing epoxy resin material for carbon fiber prepreg according to claim 1, characterized in that, In step S3, the medium-temperature latent curing agent is micronized dicyandiamide; the accelerator is an organic urea derivative.

5. The method for preparing medium-temperature curing epoxy resin material for carbon fiber prepreg according to claim 1, characterized in that, In step S1, the epoxy resin matrix is ​​a blend of bisphenol A type epoxy resin and linear phenolic epoxy resin.

6. A method for preparing a medium-temperature curing prepreg, characterized in that, The method includes all the steps of the method for preparing medium-temperature curing epoxy resin material for carbon fiber prepreg as described in any one of claims 1 to 5, and after obtaining the epoxy resin material, it further includes the step of preparing the prepreg by a hot-melt method: Step S4, film coating: The carbon fiber prepreg medium-temperature curing epoxy resin material is coated onto double-sided release paper to form a resin film. Step S5, hot-press composite impregnation: Provide reinforcing fibers, and perform hot-press composite impregnation of the resin film and the reinforcing fibers at 70-90°C to obtain a medium-temperature curing prepreg.

7. The method for preparing the medium-temperature curing prepreg according to claim 6, characterized in that, In step S5, the reinforcing fiber is unidirectional carbon fiber or plain weave carbon fiber fabric; when the reinforcing fiber is unidirectional carbon fiber, the impregnation temperature is 80°C; when the reinforcing fiber is plain weave carbon fiber fabric, the impregnation temperature is 85°C.