Solvent-free toughened phenolic resin for hot-melt prepreg and preparation method of solvent-free toughened phenolic resin

Abstract

The invention discloses a solvent-free toughened phenolic resin for hot-melt prepreg and a preparation method of the solvent-free toughened phenolic resin. The solvent-free toughened phenolic resin comprises the following components in parts by mass: 70-80 parts of thermosetting phenolic resin; 10 to 15 parts of glycidyl ether type epoxy resin; 3-15 parts of a toughening agent; and 2-15 parts of thermoplastic resin. The invention also discloses a preparation method of the solvent-free toughened phenolic resin, and a hot-melt prepreg prepared from the solvent-free toughened phenolic resin. According to the invention, epoxy resin is used as a medium to melt a flexibilizer, and then the mixture and phenolic resin are mixed and stirred uniformly to prepare the hot-melt toughened phenolic resin. The resin system is high in viscosity and can adapt to a hot-melt phenolic resin process system, and the problems that phenolic resin is poor in toughness and low in strength can be solved; the problems of environmental pollution, complex mixing process and the like caused by adopting an organic solvent as a medium for later toughening of the traditional phenolic resin are solved.

Description

Technical Field

[0001] This invention relates to the field of phenolic resin toughening technology, and more specifically, to a solvent-free toughened phenolic resin for hot-melt prepregs and its preparation method. Background Technology

[0002] Phenolic resins possess outstanding advantages such as heat resistance, flame retardancy, low smoke emission, low toxicity, and abrasion resistance. They also exhibit excellent instantaneous high-temperature ablation resistance, making them an irreplaceable material for ablation-type thermal protection in spacecraft, rockets, and missiles. While phenolic resins themselves possess good flame retardancy and low smoke toxicity, the lack of flexibility in the phenolic molecular backbone results in a highly rigid, cross-linked network structure in the cured resin. This structure is brittle, exhibiting poor toughness and fatigue performance. Therefore, effective toughening modification of phenolic resins is necessary. Traditional toughening methods for phenolic resins mainly fall into two categories. One involves introducing toughening groups during the phenolic resin synthesis stage to lengthen the phenolic resin molecular chain and improve toughness. However, this method can only be implemented by the phenolic resin manufacturer during the synthesis process and cannot be modified according to actual needs at the application end. The other method uses organic solvents such as anhydrous ethanol or acetone as a medium to dissolve the toughening material, which is then dissolved into the phenolic resin. However, this method is mostly used for wet-process phenolic resins. Although the solvent can be removed in subsequent preparation processes to produce hot-melt resins, the use of solvents not only causes environmental pollution and poses certain dangers, but also increases the preparation cycle. Chinese invention patent application CN113637286A discloses a toughened, flame-retardant hot-melt phenolic resin, prepreg, composite material, and its preparation method. The raw materials include 0-100 parts of thermoplastic phenolic resin, 0-100 parts of thermosetting phenolic resin, 1-15 parts of flame retardant, 5-100 parts of toughening agent, 0.05-1 part of coupling agent, and 0-20 parts of curing agent. However, the toughening agent in this patent is a mixture of polymer and organic solvent, which affects the flame-retardant properties of the material. Therefore, it is necessary to further add flame retardant to reduce the influence of organic solvent on the flame-retardant properties. At the same time, the addition of flame retardant further affects its mechanical properties. The solvent-free toughened phenolic resin preparation method provided by the present invention introduces the toughening agent into the phenolic resin in a solvent-free state, which not only simplifies the preparation process and solves the environmental pollution problem, but also makes its performance comparable to that of toughened hot melt phenolic resin prepared by solvent method. At the same time, it has excellent flame retardant properties without the addition of flame retardant. Summary of the Invention

[0003] This invention addresses the shortcomings of traditional hot-melt toughening methods for phenolic resins, which suffer from high brittleness, poor toughness, and poor fatigue performance, failing to meet the mechanical requirements of various applications. It solves the problems of complex methods or environmental pollution and high risks associated with organic solvents in traditional hot-melt toughening methods for phenolic resins. The invention provides a solvent-free toughened phenolic resin for hot-melt prepregs and its preparation method. This resin has high viscosity, making it suitable for the preparation of hot-melt prepregs. Furthermore, the absence of organic solvents in the preparation process solves the environmental pollution problem and simplifies the preparation process. Its mechanical properties are comparable to those of traditional phenolic resins toughened with organic solvents, exhibiting excellent toughness.

[0004] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a solvent-free toughened phenolic resin, comprising the following components in parts by weight: 70-80 parts of thermosetting phenolic resin; 10-15 parts of glycidyl ether type epoxy resin; 3-15 parts toughening agent; 2-15 parts of thermoplastic resin.

[0005] As some specific embodiments of the present invention, the thermosetting phenolic resin is selected from any one or more of barium phenolic resin, boron phenolic resin, and aminophenolic resin.

[0006] As some specific embodiments of the present invention, the glycidyl ether type epoxy resin is selected from any one or more of bisphenol A diglycidyl ether and bisphenol F diglycidyl ether. The present invention uses these two glycidyl ether type epoxy resins, both of which have low cost and good solubility for toughening agents and thermoplastic resins at high temperatures, and the mixture is easily soluble in phenolic resin. Therefore, the glycidyl ether type epoxy resin not only undergoes a grafting reaction with phenolic resin to achieve a certain toughening effect, but also acts like an organic solvent to dissolve other toughening agents into the phenolic resin.

[0007] As some specific embodiments of the present invention, the toughening agent is selected from polyvinyl butyral or core-shell particle toughening agents.

[0008] Furthermore, the core-shell particle toughening agent comprises an elastomeric core and a polymer shell encapsulating the core; The elastomer core is selected from either silicone rubber or polybutyl acrylate elastomer. The polymer shell is a copolymer of methyl methacrylate and a monomer containing reactive functional groups, wherein the reactive functional groups are epoxy, hydroxyl, carboxyl, or amino groups, and can react with epoxy resin.

[0009] Furthermore, the copolymer is any one of the following: a copolymer of methyl methacrylate and glycidyl methacrylate P (MMA-co-GMA), a copolymer of methyl methacrylate and hydroxyethyl methacrylate P (MMA-co-HEMA), and a copolymer of methyl methacrylate and methacrylic acid P (MMA-co-MAA).

[0010] As some specific embodiments of the present invention, the thermoplastic resin includes any one or more of thermoplastic phenolic resin (ordinary linear phenolic resin), polysulfone resin, and polyphenylene sulfone resin.

[0011] In a second aspect, the present invention provides a method for preparing the solvent-free toughened phenolic resin according to any one of the above claims, comprising the following steps: S1. Add toughening agent and thermoplastic resin to glycidyl ether type epoxy resin, melt and stir, and cool to obtain mixture A; S2. Add mixture A to thermosetting phenolic resin, heat and stir until uniform, and cool to obtain solvent-free toughened phenolic resin.

[0012] As some specific embodiments of the present invention, in step S1, the melting temperature is 130-160°C and the stirring time is 30-50 min.

[0013] As some specific embodiments of the present invention, in step S2, the heating temperature is 40-60°C and the stirring time is 30-60 min.

[0014] Thirdly, the present invention provides a hot-melt prepreg, which is prepared using the solvent-free toughened phenolic resin described in any of the above-mentioned methods. The preparation method includes: making the solvent-free toughened phenolic resin into a resin film, compounding it with alkali-free glass fiber cloth, and then curing it to obtain the final product.

[0015] As some specific embodiments of the present invention, the coating temperature when solvent-free toughened phenolic resin is made into a resin film is 65~70°C. And / or, the impregnation temperature when compounded with alkali-free glass fiber cloth is 85~90℃.

[0016] As some specific embodiments of the present invention, the curing includes two steps: first, heating to 100~110℃ and holding for 20~40 minutes, and then heating to 120~130℃ and holding for 1.5~2.5 hours.

[0017] This invention uses epoxy resin as a medium to melt the toughening agent, and then mixes the mixture with phenolic resin to form a hot-melt toughened phenolic resin. This resin system has a higher viscosity, making it suitable for hot-melt phenolic resin processes, and can improve the toughness and strength of the phenolic resin. It solves the problems of traditional phenolic resin toughening requiring organic solvents as a medium, which causes environmental pollution and complex mixing processes.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses glycidyl ether type epoxy resin, which can not only react with phenolic resin to play a toughening role, but also can replace organic solvents to introduce toughening agents and thermoplastic resins into phenolic resins, so that toughening agents and epoxy resins can synergistically toughen each other, thereby improving toughness while retaining more modulus strength at room temperature. At the same time, removing organic solvents not only simplifies the preparation process, but also solves the environmental impact and dangers of using organic solvents.

[0019] (2) The present invention selects polyvinyl butyral or core-shell particles as toughening agents, which can not only synergistically toughen epoxy resin, but also be used in conjunction with thermoplastic resin to form a semi-interpenetrating network, enhance interfacial bonding, and coordinate with thermoplastic resin to form phase separation or "island structure", which can retain more resin rigidity and improve the toughness of phenolic resin.

[0020] (3) The thermoplastic resin used in this invention is selected from ordinary linear phenolic resin, polysulfone resin and polyphenylsulfone resin, all of which have a certain toughening effect and can retain more modulus properties at room temperature.

[0021] (4) The solvent-free toughened phenolic resin combination prepared by the present invention not only has excellent toughness, but also excellent flame retardancy. The resin system has high viscosity and good film-forming properties, making it suitable for the preparation of hot melt prepreg. Attached Figure Description

[0022] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A diagram illustrating the preparation process of a solvent-free toughened phenolic resin film; Figure 2 The left image shows the composite process of solvent-free toughened phenolic resin film and alkali-free fiberglass cloth, while the right image shows the hot-melt prepreg after molding. Figure 3 Photographs of some of the composite material samples prepared in Example 1. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0024] Example 1 This embodiment provides a method for preparing a solvent-free toughened phenolic resin prepreg, the specific steps of which are as follows: (1) Add 3 parts of polyvinyl butyral and 2 parts of ordinary linear phenolic resin (thermoplastic phenolic resin) to 15 parts of bisphenol A diglycidyl ether, melt at 150°C and stir for 30 min, and cool to obtain mixture A; (2) Add mixture A to a mixture of 40 parts barium phenolic resin, 20 parts boron phenolic resin and 20 parts aminophenolic resin, heat and stir at 60°C for 30 min, and cool to obtain solvent-free toughened phenolic resin. (3) Add solvent-free toughened phenolic resin to the glue tank, and set the coating temperature to 65℃ to prepare a resin film (e.g. Figure 1 The diagram shows the process of preparing a resin film from solvent-free toughened phenolic resin, which is then laminated with 200 grams of alkali-free glass fiber cloth (the lamination process is as follows). Figure 2 As shown), the impregnation temperature was set to 85℃ to prepare a solvent-free toughened phenolic resin prepreg. Figure 3 The image shown is a photograph of a partial composite material specimen prepared in Example 1.

[0025] Example 2 This embodiment provides a method for preparing a solvent-free toughened phenolic resin prepreg, the specific steps of which are as follows: (1) Five parts of core-shell particles with silicone rubber core and P(MMA-co-GMA) (i.e., copolymer of methyl methacrylate and glycidyl methacrylate) shell, and two parts of polysulfone resin were added to 10 parts of bisphenol F diglycidyl ether, melted at 160°C and stirred for 50 min, and then cooled to obtain mixture A. (2) Add mixture A to a mixture of 50 parts barium phenolic resin and 33 parts aminophenolic resin, heat and stir at 40°C for 40 minutes until uniformly mixed, and then cool to obtain solvent-free toughened phenolic resin. (3) The solvent-free toughened phenolic resin is put into the glue tank, the coating temperature is set to 70°C to make a resin film, and then it is compounded with alkali-free glass fiber cloth, the impregnation temperature is set to 90°C to make a solvent-free toughened phenolic resin prepreg.

[0026] Example 3 This embodiment provides a method for preparing a solvent-free toughened phenolic resin prepreg, the specific steps of which are as follows: (1) Seven parts of core-shell particles with polybutyl acrylate core and P(MMA-co-HEMA) (i.e., copolymer of methyl methacrylate and hydroxyethyl methacrylate) shell, and two parts of polysulfone resin were added to 12 parts of bisphenol F diglycidyl ether, melted at 160°C and stirred for 40 min, and then cooled to obtain mixture A. (2) Add mixture A to a mixture of 50 parts barium phenolic resin and 29 parts boron phenolic resin, heat and stir at 40°C for 60 min until uniformly mixed, and then cool to obtain solvent-free toughened phenolic resin. (3) The solvent-free toughened phenolic resin is put into the glue tank, the coating temperature is set to 70°C to make a resin film, and then it is compounded with alkali-free glass fiber cloth, the impregnation temperature is set to 90°C to make a solvent-free toughened phenolic resin prepreg.

[0027] Comparative Example 1 This comparative example uses only thermosetting phenolic resin to prepare hot-melt prepreg, specifically including the following steps: (1) Mix 60 parts of barium phenolic resin, 20 parts of boron phenolic resin and 20 parts of aminophenolic resin at 60°C for 50 min until homogeneous. After cooling, hot melt phenolic resin is obtained.

[0028] (2) The solvent-free toughened phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a solvent-free toughened phenolic resin prepreg.

[0029] Comparative Example 2 This comparative example uses toughening agents, thermoplastic resins, and thermosetting phenolic resins to prepare hot-melt prepregs under solvent conditions, without involving glycidyl ether type epoxy resins. The specific steps include: (1) Add 3 parts of polyvinyl butyral and 2 parts of ordinary linear phenolic resin to 15 parts of anhydrous ethanol solution and stir at room temperature for 30 min to obtain mixture A; (2) Add mixture A to a mixture of 55 parts barium phenolic resin, 20 parts boron phenolic resin and 20 parts aminophenolic resin, heat at 40°C to dissolve and stir for 30 min to obtain toughened phenolic resin containing anhydrous ethanol solvent. (3) The anhydrous ethanol in the toughened phenolic resin containing anhydrous ethanol solvent is removed by rotary evaporation equipment to obtain solvent-free toughened phenolic resin; (4) The solvent-free toughened phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a solvent-free toughened phenolic resin prepreg.

[0030] Comparative Example 3 This comparative example uses only glycidyl ether type epoxy resin and thermosetting phenolic resin as raw materials to prepare solvent-free toughened phenolic resin, without toughening agents or thermoplastic resin. The preparation steps are as follows: (1) Add 10 parts of bisphenol F diglycidyl ether to a mixture of 50 parts of barium phenolic resin, 20 parts of boron phenolic resin and 20 parts of aminophenolic resin, dissolve and stir at 40°C for 30 min to mix evenly, and toughen the phenolic resin. (2) The toughening phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a toughening phenolic resin prepreg.

[0031] Comparative Example 4 This comparative example provides a hot-melt prepreg, replacing the glycidyl ether type epoxy resin in Example 1 with glycidyl ester type epoxy resin diglycidyl terephthalate, specifically including the following steps: (1) Add 3 parts of polyvinyl butyral and 2 parts of ordinary linear phenolic resin to 15 parts of diglycidyl terephthalate, melt at 150°C and stir for 30 min, and cool to obtain mixture A; (2) Add mixture A to a mixture of 40 parts barium phenolic resin, 20 parts boron phenolic resin and 20 parts aminophenolic resin, heat and stir at 60°C for 30 min, and cool to obtain solvent-free phenolic resin. (3) The solvent-free phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a prepreg.

[0032] Comparative Example 5 This comparative example provides a hot-melt prepreg prepared from thermosetting phenolic resin, glycidyl ether epoxy resin, and toughening agent, without involving thermoplastic resin. The specific steps include: (1) Add 3 parts of polyvinyl butyral to 15 parts of bisphenol A diglycidyl ether, melt at 150°C and stir for 30 min, and then cool to obtain mixture A; (2) Add mixture A to a mixture of 44 parts barium phenolic resin, 20 parts boron phenolic resin and 20 parts aminophenolic resin, heat and stir at 60°C for 30 min, and cool to obtain solvent-free toughened phenolic resin. (3) The solvent-free toughened phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a prepreg.

[0033] Comparative Example 6 This comparative example provides a hot-melt prepreg prepared from thermosetting phenolic resin, glycidyl ether epoxy resin, and thermoplastic resin, without involving toughening agents, and specifically includes the following steps: (1) Add 2 parts of ordinary linear phenolic resin to 15 parts of bisphenol A diglycidyl ether, melt at 150°C and stir for 30 min, and cool to obtain mixture A; (2) Add mixture A to a mixture of 42 parts barium phenolic resin, 20 parts boron phenolic resin and 20 parts aminophenolic resin, heat and stir at 60°C for 30 min, and cool to obtain solvent-free phenolic resin. (3) The solvent-free phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a prepreg.

[0034] Comparative Example 7 This comparative example provides a solvent-free toughened phenolic resin, which, based on Example 1, uses ordinary nitrile rubber as a toughening agent, and specifically includes the following steps: (1) 7 parts of ordinary nitrile rubber, 2 parts of ordinary linear phenolic resin and 12 parts of bisphenol A diglycidyl ether were melted at 150°C and stirred for 30 min. After cooling, mixture A was obtained. (2) Add mixture A to a mixture of 40 parts barium phenolic resin, 20 parts boron phenolic resin and 20 parts aminophenolic resin, heat and stir at 60°C for 30 min, and cool to obtain solvent-free toughened phenolic resin. (3) The solvent-free toughened phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a prepreg.

[0035] Comparative Example 8 This comparative example provides a solvent-free toughened phenolic resin, specifically including the following steps: (1) Add 3 parts of polyvinyl butyral and 40 parts of ordinary linear phenolic resin to 15 parts of bisphenol A diglycidyl ether, melt at 150°C and stir for 30 min, and cool to obtain mixture A; (2) Add mixture A to a mixture of 20 parts barium phenolic resin, 10 parts boron phenolic resin and 10 parts aminophenolic resin, heat and stir at 60°C for 30 min, and cool to obtain solvent-free toughened phenolic resin. (3) The solvent-free toughened phenolic resin is put into the glue tank and the coating temperature is set to 65°C to make a resin film. Then it is compounded with alkali-free glass fiber cloth and the impregnation temperature is set to 85°C to make a prepreg.

[0036] Effect Example The phenolic resin prepregs prepared in the above embodiments and comparative examples were cured, specifically including: raising the room temperature to 105°C, pressing at 0.3 MPa, holding at that temperature for 30 min, and then raising the temperature to 125°C and holding at that temperature for 120 min.

[0037] The cured phenolic resin prepreg was subjected to the following performance tests: (1) Tensile strength test Samples were prepared according to ISO 527-4 standard, and the tensile strength, modulus, and elongation at break of the composite material were tested.

[0038] (2) In-plane shear strength test Samples were prepared according to ISO 14129 standard, and the in-plane shear properties of the composite material were tested.

[0039] (3) Compression strength test Samples were prepared according to ISO 14126 standard, and the surface compression properties of the composite material were tested.

[0040] (4) Porosity test Porosity testing was conducted according to JC 287 and GB / T 1463.

[0041] (5) Limiting oxygen index test The limiting oxygen index of composite materials was tested according to GB / T 8924 standard.

[0042] The performance test results are shown in Table 1 below: Table 1 Performance Comparison

[0043] As shown in Table 1, Examples 1-3 used the solvent-free toughened phenolic resin of the present invention to prepare hot melt prepregs. Without adding flame retardants or curing agents, thermosetting phenolic resin, glycidyl ether epoxy resin, toughening agent and thermoplastic resin were used as raw materials to prepare toughened phenolic resin in a solvent-free system, which obtained excellent mechanical properties and flame retardant properties.

[0044] Comparative Example 1 uses only thermosetting phenolic resin to prepare hot melt prepreg, and its cured product has poor toughness, resulting in a decrease in mechanical properties.

[0045] Compared with Comparative Example 2, the performance of the composite materials prepared by Examples 1-3 is slightly higher than that prepared by using conventional organic solvent-toughened phenolic resin. This is because the organic solvent in Comparative Example 2 cannot be completely removed, resulting in more micropores during the curing process.

[0046] Comparative Example 3 only uses epoxy resin toughening agent to undergo a grafting reaction with phenolic resin, and its toughening effect is limited. The more complex three-dimensional interwoven network in Examples 1-3 shows better mechanical properties.

[0047] Comparative Example 4 uses glycidyl ester type epoxy resin to replace the glycidyl ether type epoxy resin in the examples. The glycidyl ether type epoxy resin used in Examples 1-3 has slightly better flame retardancy and contains ether bonds and methylene chains in the main chain, which makes it more flexible and therefore has better overall performance.

[0048] In Comparative Example 5, the lack of thermoplastic resin resulted in toughening and stress-dispersing effects, leading to a decrease in toughness (elongation at break). The absence of thermoplastic resin also resulted in lower viscosity at high temperatures, making the resin more prone to loss during pressing, thus increasing porosity and slightly reducing strength.

[0049] In Comparative Example 6, the lack of toughening agent meant that the toughening effect of thermoplastic resin and epoxy resin alone was limited, resulting in a decrease in mechanical properties.

[0050] In Comparative Example 7, nitrile rubber was used as a toughening agent. In the absence of solvent, it was difficult to disperse evenly in the phenolic resin matrix, resulting in concentrated stress distribution in the cured product. Moreover, the amount added was relatively large, which had a significant impact on the flame retardant properties.

[0051] In Comparative Example 8, ordinary linear phenolic resin accounted for a large proportion, but no corresponding curing agent was added, and the amount of epoxy resin added was limited. As a result, a large amount of ordinary linear phenolic resin could not be cross-linked and cured. In the end, the cross-linking density of the resin matrix of the cured product decreased, the mechanical properties decreased, and the porosity was high, which also led to a decrease in flame retardant properties.

[0052] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A solvent-free toughened phenolic resin, characterized in that, The components include the following parts by mass: 70-80 parts of thermosetting phenolic resin; 10-15 parts of glycidyl ether type epoxy resin; Toughening agent 3-15 parts; 2-15 parts of thermoplastic resin.

2. The solvent-free toughened phenolic resin as described in claim 1, characterized in that, The thermosetting phenolic resin is selected from any one or more of barium phenolic resin, boron phenolic resin, and aminophenolic resin.

3. The solvent-free toughened phenolic resin as described in claim 1, characterized in that, The glycidyl ether type epoxy resin is selected from any one or more of bisphenol A diglycidyl ether and bisphenol F diglycidyl ether.

4. The solvent-free toughened phenolic resin as described in claim 1, characterized in that, The toughening agent is selected from polyvinyl butyral or core-shell particle toughening agents; The core-shell particle toughening agent comprises an elastomeric core and a polymer shell encapsulating the core; The elastomer core is selected from either silicone rubber or polybutyl acrylate elastomer. The polymer shell is a copolymer of methyl methacrylate and a monomer containing a reactive functional group, wherein the reactive functional group is an epoxy group, a hydroxyl group, a carboxyl group, or an amino group.

5. The solvent-free toughened phenolic resin as described in claim 1, characterized in that, The thermoplastic resin includes any one or more of thermoplastic phenolic resin, polysulfone resin, and polyphenylsulfone resin.

6. A method for preparing a solvent-free toughened phenolic resin as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Add toughening agent and thermoplastic resin to glycidyl ether type epoxy resin, melt and stir, and cool to obtain mixture A; S2. Add mixture A to thermosetting phenolic resin, heat and stir until uniform, and cool to obtain solvent-free toughened phenolic resin.

7. The preparation method according to claim 6, characterized in that, In step S1, the melting temperature is 130-160℃, and the stirring time is 30-50 minutes.

8. The preparation method according to claim 6, characterized in that, In step S2, the heating temperature is 40-60℃ and the stirring time is 30-60 min.

9. A hot-melt prepreg, characterized in that, The resin is prepared using any one of the solvent-free toughened phenolic resins as described in any one of claims 1-5. The preparation method includes: making the solvent-free toughened phenolic resin into a resin film, compounding it with alkali-free glass fiber cloth, and then curing it to obtain the final product.

10. The hot-melt prepreg according to claim 9, characterized in that, It also includes at least one of the following technical features:

1. The coating temperature for preparing solvent-free toughened phenolic resin into resin film is 65~70℃; II. The impregnation temperature when composited with alkali-free glass fiber cloth is 85~90℃; 3. The curing process includes two steps: first, heating to 100~110℃ and holding for 20~40 minutes, then heating to 120~130℃ and holding for 1.5~2.5 hours.

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