A polyimide hot melt prepreg, composite material and preparation method thereof

Abstract

The application discloses a kind of polyimide hot melt prepreg, composite material and preparation method thereof, belong to composite material technical field.The application is prepared by polyimide and single solvent, mixed solvent and is obtained polyimide resin solution for impregnated fiber and self-adhesive surface layer;Based on the two kinds of polyimide resin solution preparation impregnated fiber and semi-solid polyimide prepreg for surface layer self-adhesion, then with fiber cloth by film preparation and first and after compounding obtains fiber prepreg;Based on fiber prepreg preparation obtains polyimide hot melt prepreg.The application is first to reinforcing fiber is fully infiltrated, then after impregnation reinforcing fiber surface is compounded toughening, and the resin layer of tackifying is obtained resin content controllable, and the polyimide hot melt prepreg of good laying and bonding, and accordingly prepared high-quality fiber reinforced composite material of low porosity, greatly reduce the difficulty of forming process control, improve production efficiency.

Description

Technical Field

[0001] This invention relates to a polyimide hot-melt prepreg, a composite material, and a method for preparing the same, belonging to the field of composite material technology. Background Technology

[0002] Polyimide is a high-performance, heat-resistant polymer material with imide rings as its core structural unit. Its unique molecular design endows it with excellent heat resistance, enabling stable operation under extreme conditions. It can withstand temperatures up to 600°C and operate continuously within a temperature range of 200–500°C. In particular, thermosetting polyimides, through their three-dimensional network structure, exhibit extremely high heat resistance, excellent mechanical strength, and superior dielectric properties. These characteristics hold a crucial position in the field of advanced composite materials. As a matrix, this type of material is widely used in high-performance engine cold-end components in the aerospace field, thermal protection structures of advanced strategic defense systems, and key components of cruise and tactical missiles, demonstrating its irreplaceable application value.

[0003] Currently, the preparation of high-temperature resistant polyimide resin-based composites mainly falls into two categories: one is the PMR (polymeric mesophase resin) method, which first prepares an imide oligomer solution containing active end groups, followed by imidization crosslinking in a layered structure to form the final network structure. However, this process involves vigorous imidization, accompanied by the release of small molecules, making process control complex and prone to problems such as fiber buckling and increased porosity; at the same time, unreacted monomers and solvent residues shorten the material's storage stability, limiting the efficiency of large-scale production. The other approach is the imidization soluble resin method, which completes imidization in the early stages of resin synthesis, resulting in oligomers with good solubility, facilitating subsequent processing. This method avoids additional imidization steps during the composite material curing process, improving production efficiency, reducing porosity, and achieving long-term stable storage of the material. However, in practical applications, such as using solution impregnation to prepare prepregs, challenges remain, including uneven resin content distribution, difficulty in controlling volatile matter, and environmental pollution.

[0004] To overcome the aforementioned challenges, the hot-melt coating method, with its ability to precisely control resin content and volatile matter, has become the preferred solution for the large-scale preparation of prepregs. However, for fully imidized polyimide resins, their insoluble and infusible properties significantly reduce fiber wetting efficiency, requiring stringent control of the film solids content, affecting the prepreg's viscosity and storage stability, and thus hindering the balance between the coating process and volatile matter control. This has become a key technical bottleneck that urgently needs to be addressed in this field. Currently, systematic research on improving this problem is insufficient, and new solutions are urgently needed to promote the widespread application of imidized polyimide resins in high-end composite materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polyimide hot-melt prepreg, a composite material, and a method for preparing the same.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a polyimide hot-melt prepreg, the steps of which include:

[0008] 1) The polyimide is mechanically stirred with a single solvent to obtain a polyimide resin solution for impregnating fibers;

[0009] 2) The polyimide and the mixed solvent are mechanically stirred to obtain a polyimide resin solution for self-adhesive surface layer;

[0010] 3) The two polyimide resin solutions obtained in steps 1) and 2) are subjected to vacuum distillation to obtain semi-solid polyimide prepregs for impregnating fibers and for surface self-adhesion.

[0011] 4) After the semi-solid polyimide prepreg for impregnating fibers is hot-melted in a hot-melt three-roll mill, it is coated onto release paper to obtain an impregnated fiber resin film. The impregnated fiber resin film is then laminated with fiber cloth through multiple hot-pressing rollers to obtain an impregnated fiber prepreg.

[0012] 5) After the semi-solid polyimide prepreg for self-adhesive surface layer is hot-melted in a hot melt three-roll mill, it is coated onto release paper to obtain a self-adhesive surface resin film; the self-adhesive surface resin film is then double-sided laminated with the fiber cloth impregnated with fiber prepreg obtained in step 4) through multiple hot press rollers to obtain fiber prepreg.

[0013] 6) The fiber prepreg obtained in step 5) is processed by a heating plate, hot press roller and cooling plate, the upper release paper is peeled off and covered with PE film to obtain polyimide hot melt prepreg.

[0014] Furthermore, in steps 1) and 2), the polyimide is an acetylene-terminated, allyl norbornene-terminated, or phenylacetylene-terminated polyimide resin, specifically one or more of NPI-550, NPI-550-2, KH-360A / B, PMR-15, PMR-Ⅱ-50, PETI-5, LARC-160, LARC-13, etc.

[0015] Further, in step 1), the single solvent is selected from one of N,N-dimethylacetamide (DMAC), dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0016] Further, in step 2), the mixed solvent includes a low-boiling-point solvent and a high-boiling-point solvent. The low-boiling-point solvent is selected from one or more of dioxane, n-butanol, isopropanol, cyclopentanone, and sec-butanol, and the high-boiling-point solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0017] Furthermore, in step 2), the polyimide resin solution used for the self-adhesive surface layer contains a toughening agent and a tackifying modifier. The toughening agent is a high-temperature resistant thermoplastic polyimide resin with a concentration of 5-20 wt%. The tackifying modifier is one or more of a high-temperature resistant uniminated thermosetting polyimide and a high-temperature resistant PMR resin with a concentration of 5-10 wt%.

[0018] Furthermore, the stirring conditions for steps 1) and 2) are: mechanical stirring for 60 to 240 minutes at a temperature 30 to 60°C lower than the boiling point of the solvent.

[0019] Furthermore, the solid content of the two polyimide resin solutions obtained in steps 1) and 2) is 20% to 50%, and the melt viscosity at 50°C is 20 to 100 Pa·s.

[0020] Furthermore, in step 3), the distillation temperature is 50–100°C and the time is 0.5–5 h.

[0021] Furthermore, in step 3), the solid content of the semi-solid polyimide prepreg used to impregnate the fibers is 75-90%, and the gelation time of the adhesive solution at 120°C is 10-15 minutes.

[0022] Furthermore, in step 3), the solid content of the semi-solid polyimide prepreg used for the self-adhesive surface layer is 65-75%, and the gel time of the adhesive at 120°C is 10-15 minutes.

[0023] Further, in step 4), the fiber cloth accounts for 50-75 wt% of the total weight of the impregnated fiber prepreg, and the impregnated fiber resin film accounts for 20-40 wt% of the total weight of the impregnated fiber prepreg.

[0024] Further, in step 4), the fiber cloth is selected from one of the following: high modulus carbon fiber (such as T300, T700, T800, T1000, T1100 grade, etc.), high strength glass fiber, aramid fiber, quartz fiber, and ultra-high molecular weight polyethylene fiber, and the fiber form is unidirectional or plain weave fabric.

[0025] Furthermore, in step 4), the heating and melting temperature of the semi-solid polyimide prepreg used for impregnating the fibers is 50–80°C, the coating speed is 2–6 m / min, the thickness of the single-layer impregnated fiber resin film is 0.05–0.2 mm, the composite temperature of the fiber cloth and the impregnated fiber resin film is 60–90°C, the composite pressure is 0.2–0.4 MPa, and the cooling table temperature of the hot press roller is 5–10°C.

[0026] Furthermore, in step 4), the viscosity of the impregnated fiber resin film is 12–400 Pa·s.

[0027] Furthermore, in step 5), the self-adhesive surface resin film accounts for 5 to 20 wt% of the total weight of the fiber prepreg.

[0028] Furthermore, in step 5), the heating and melting temperature of the semi-solid polyimide prepreg used for the self-adhesive surface layer is 50–80°C, the coating speed is 2–6 m / min, and the thickness of a single layer of adhesive film is 0.05–0.2 mm.

[0029] Furthermore, in step 5), the composite temperature of the self-adhesive surface resin film and the impregnated fiber prepreg is 60-90℃, the composite pressure is 0.2-0.4 MPa, and the cooling table temperature is 5-10℃.

[0030] Furthermore, the polyimide hot melt prepreg obtained in step 6) is vacuum-packed in one of PE, PA, PET or aluminum foil bags and stored in a refrigerator at low temperature.

[0031] Secondly, the present invention provides a polyimide hot-melt prepreg prepared by the above method.

[0032] Thirdly, the present invention also provides a polyimide thermal composite material, which is prepared by the following steps:

[0033] Solvent is sprayed onto the surface of the polyimide hot melt prepreg to soften it, and then it is laid up according to the design specifications. Finally, it is heated and cured to obtain the polyimide thermal composite material.

[0034] Furthermore, the softening solvent is one or more of ethanol, methanol, petroleum ether, dichloromethane, dichloroethane, and tetrahydrofuran.

[0035] This invention improves the dissolution and concentration process by using a double-layer impregnation gradient prepreg technology. By adjusting the composite temperature and pressure of the imidized resin matrix and reinforcing fibers, a gradient distribution of the resin system's viscosity and solid content is achieved on the prepreg cross-section. First, the reinforcing fibers are fully impregnated with a resin system that has high resin content and good flexibility. Then, a toughening and tackifying resin layer is composited onto the surface of the reinforcing fibers after impregnation. This results in an imidized polyimide hot-melt prepreg with controllable resin content and good adhesion. Finally, the impregnated preform is processed through molding and other processes to obtain a high-quality fiber-reinforced composite material with low porosity. This significantly reduces the difficulty of controlling the molding process and improves production efficiency.

[0036] The beneficial effects of this invention compared to the prior art are as follows:

[0037] (1) Compared with the traditional wet process using PMR polyimide resin solution, the present invention directly heat-melts the resin into a film and then impregnates it with fibers to prepare prepreg. This completely eliminates the need for multiple impregnations and cumbersome drying and solvent removal steps, which not only greatly simplifies the continuous preparation process of prepreg, but also significantly shortens the preparation cycle. At the same time, it avoids the buckling phenomenon that easily occurs in the wet process of fibers, effectively reduces the porosity of the composite material, and improves the molding quality of the final product.

[0038] (2) This invention achieves precise control of the solid content of polyimide prepreg, ensuring that the solvent content is maintained within an extremely low range of 5-20 wt%. Furthermore, the effective evaporation of the solvent during the hot-melt stage further reduces solvent residue in the prepreg. This not only significantly reduces the release of volatile small molecules during subsequent composite material molding, reducing potential environmental impact, but also ensures that the prepreg maintains appropriate viscosity while facilitating interlayer bonding, laying a solid foundation for achieving low porosity, low defects, and high-quality molding of large-size or irregularly shaped composite parts.

[0039] (3) The prepreg of this invention adopts a unique double-layer gradient impregnation structure. By constructing a self-adhesive high-toughness resin film layer on the surface of the prepreg, the layup process of the prepreg is significantly improved, making the layup operation more efficient and convenient, thereby effectively reducing the overall manufacturing cost of the composite material. In addition, the self-adhesive layer also plays a positive role in interlayer toughening, working synergistically with the resin matrix of the internal impregnation layer to give the composite material better comprehensive mechanical properties, including but not limited to strength, toughness and fatigue resistance, further broadening its application fields and market prospects. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the cross-sectional structure of a polyimide hot-melt prepreg proposed in this invention.

[0041] Figure 2The images show a comparison of the porosity of the composite materials in Example 1 and Comparative Example 1. Detailed Implementation

[0042] To make the various technical features, advantages, or effects of the present invention more apparent and understandable, detailed descriptions are provided below in conjunction with embodiments and accompanying drawings.

[0043] In the following embodiments, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, apparatus, instruments, equipment, etc., used in the following embodiments are commercially available.

[0044] Example 1

[0045] (1) In a reaction vessel containing a heating and mechanical stirring device, add polyimide NPI-550-2 / DMAc (mass ratio of 30 / 50), heat to 140°C, stir for 80 min to obtain a uniform solution, and obtain a polyimide resin solution for impregnating fibers.

[0046] (2) In a reaction vessel containing a heating and mechanical stirring device, add polyimide NPI-550-2 / Vespel toughening agent / adhesive modifier / DMF / dioxane (mass ratio of 30 / 8 / 5 / 30 / 30), heat to 100℃, stir for 80 min to obtain a uniform solution, and obtain a polyimide resin solution for self-adhesive surface layer;

[0047] (3) The resin solutions obtained in steps (1) and (2) are placed in a vacuum distillation apparatus, the temperature is set to 60°C and the time is 5h, respectively, to obtain 85% solid content impregnated polyimide prepreg (gel time of 12min at 120°C) and 70% solid content self-adhesive surface polyimide prepreg (gel time of 13min at 120°C). The aluminum foil is collected and sealed for freezing at -18°C.

[0048] (4) The frozen impregnating resin is taken out and placed in a hot melt three-roll mill at 70°C for hot melting. The film speed is 4 m / min, and the thickness of the single-layer impregnated fiber resin film is 0.15 mm. It is then coated onto release paper to obtain a resin film (viscosity 150 Pa·s). Then, unidirectional T800 grade carbon fiber is combined with the impregnated resin film, and a pressure of 0.3 MPa is applied at 75°C using a pressure roller to obtain an impregnated prepreg. The cooling table temperature of the hot press roller is 8°C.

[0049] (5) Set the heating and melting temperature of the self-adhesive polyimide prepreg to 750℃, the coating speed to 4.0m / min, and the thickness of a single layer of adhesive film to 0.15mm to prepare a surface self-adhesive resin film (viscosity 120Pa.s). Double-sided composite of the impregnated T800 continuous unidirectional carbon fiber from step (4) at a composite temperature of 70℃ to obtain fiber prepreg. After further processing by a heating plate, hot press roller, and cooling plate, peel off the upper release paper and cover it with a PE film to obtain polyimide hot melt prepreg, i.e., T800 carbon fiber prepreg.

[0050] (6) Cut T800 carbon fiber prepreg into appropriate size, lay it in the design direction and place it in the mold. After gradient heating to 335℃, heat cure it under 2.2MPa pressure for 3h, then keep the pressure and cool down, and open the mold to obtain fiber reinforced composite material.

[0051] Example 2

[0052] (1) In a reaction vessel containing a heating and mechanical stirring device, add polyimide NPI-550-2 / DMAc (mass ratio of 35 / 60), heat to 140°C, stir for 60 min to obtain a uniform solution, and obtain a polyimide resin solution for impregnating fibers.

[0053] (2) In a reaction vessel containing a heating and mechanical stirring device, add polyimide NPI-550-2 / polyimide toughening agent / PMR-350 / DMAc / dioxane (mass ratio of 30 / 10 / 8 / 30 / 50), heat to 120°C, stir for 60 min to obtain a uniform solution, and obtain a polyimide resin solution for self-adhesive surface layer;

[0054] (3) The resin solutions obtained in steps (1) and (2) are placed in a vacuum distillation apparatus, the temperature is set to 100°C and the time is 0.5h, respectively, to obtain 75% solid content impregnated polyimide prepreg (gel time of 15min at 120°C) and 65% solid content self-adhesive surface polyimide prepreg (gel time of 15min at 120°C). The aluminum foil is collected and sealed for freezing at -18°C.

[0055] (4) The frozen impregnating resin is taken out and placed in a hot melt three-roll mill at 50°C for hot melting. The coating speed is 2m / min, and the thickness of a single-layer impregnated fiber resin film is 0.2mm. The resin film (viscosity 400Pa·s) is then coated onto the release paper. The quartz fiber cloth is then combined with the impregnated resin film, and a pressure of 0.4MPa is applied at 60°C using a pressure roller to obtain the impregnated prepreg. The cooling table temperature of the hot press roller is 10°C.

[0056] (5) Set the heating and melting temperature of the self-adhesive polyimide prepreg to 50℃, the coating speed to 2m / min, and the thickness of a single layer of adhesive film to 0.2mm to prepare a surface self-adhesive resin film (viscosity 15Pa·s). This film is then double-sided laminated with the quartz fiber cloth impregnated with resin from step (4) at a lamination temperature of 50℃ to obtain a fiber prepreg. After further processing with a heating plate, hot press roller, and cooling plate, the upper release paper is peeled off and covered with a PE film to obtain a polyimide hot melt prepreg, i.e., a quartz fiber cloth prepreg.

[0057] (6) Cut the quartz fiber cloth prepreg into appropriate size, lay it in the design direction and place it in the mold. After gradient heating to 320℃, heat cure it under 2MPa pressure for 3.5h, then keep the pressure and cool down, and open the mold to obtain the fiber reinforced composite material.

[0058] Example 3

[0059] (1) In a reaction vessel containing a heating and mechanical stirring device, add polyimide KH-360 / DMAc (mass ratio of 30 / 50), heat to 120°C, stir for 240 min to obtain a uniform solution, and obtain a polyimide resin solution for impregnating fibers.

[0060] (2) In a reaction vessel containing a heating and mechanical stirring device, add polyimide NPI-550-2 / polyimide toughening agent / PMR-370 / DMAc / n-butanol (mass ratio of 30 / 10 / 8 / 30 / 50), heat to 80°C, stir for 240 min to obtain a uniform solution, and obtain a polyimide resin solution for self-adhesive surface layer;

[0061] (3) The resin solutions obtained in steps (1) and (2) are placed in a vacuum distillation apparatus, the temperature is set to 80°C and the time is 2.5h, respectively, to obtain 90% solid content (gel time of 10min at 120°C) impregnated polyimide prepreg and 75% solid content self-adhesive surface polyimide prepreg (gel time of 10min at 120°C). The aluminum foil is collected and sealed for freezing at -18°C.

[0062] (4) The frozen impregnating resin is removed and placed in a hot-melt three-roll mill at 80°C for hot melting. The coating speed is 6 m / min, and the thickness of a single-layer impregnated fiber resin film is 0.1 mm. This film is then coated onto release paper to obtain a resin film (viscosity 12 Pa·s). T700 carbon fiber is then composited with the impregnated resin film, and a pressure of 0.2 MPa is applied using a pressure roller at 90°C to obtain an impregnated prepreg. The cooling table temperature of the hot pressure roller is 5°C.

[0063] (5) Set the heating and melting temperature of the self-adhesive polyimide prepreg to 80℃, the coating speed to 3.0m / min, and the thickness of a single layer of adhesive film to 0.10mm to prepare a surface self-adhesive resin film (viscosity 12Pa·s). This film is then double-sided laminated with the T700 carbon fiber impregnated with resin from step (4) at a lamination temperature of 90℃ to obtain a fiber prepreg. After further processing with a heating plate, hot press roller, and cooling plate, the upper release paper is peeled off and covered with a PE film to obtain a polyimide hot melt prepreg, i.e., a T700 carbon fiber prepreg.

[0064] (6) Cut T700 carbon fiber prepreg into appropriate size, lay it in the design direction and place it in the mold. After gradient heating to 330℃, heat cure it under 5.0MPa pressure for 3h, then keep the pressure and cool down, and open the mold to obtain fiber reinforced composite material.

[0065] Comparative Example 1

[0066] The selected material system and process are the same as in Example 1, except that:

[0067] (1) In the prepreg preparation process, no self-adhesive surface resin prepreg was prepared, and the prepreg had no self-adhesive surface resin film. Other process parameters were the same as in Example 1.

[0068] (2) In the composite material preparation process, no solvent was sprayed onto the surface of the polyimide carbon fiber prepreg for softening. The molding and curing process was the same as in Example 1.

[0069] The properties of the polyimide resin and hot-melt prepreg used in the above embodiments and comparative examples are shown in Table 1, and the interlaminar shear and porosity of the prepared composite materials are shown in Table 2.

[0070] Table 1 Summary of Properties of Polyimide Resins and Hot-Melt Prepregs

[0071]

[0072] *The viscosity, resin content, and volatile matter of the prepreg were determined according to standards HB7736.3-2004, HB7736.5-2004, and HB7736.4-2004, respectively.

[0073] Table 2 Summary of the properties of polyimide composite materials

[0074]

[0075] *Porosity was determined according to national standard GB / T3365-2008, and interlaminar shear strength was determined according to JC / T773-1996.

[0076] As can be seen from the data in Tables 1 and 2, compared with Comparative Example 1, the prepregs of Examples 1-3 have good adhesion, controllable resin content and volatile matter, and meet the process parameter requirements for hot melt prepreg layup. The obtained polyimide composite materials have high fiber straightness, no obvious internal defects, porosity of less than 1%, and unidirectional fiber interlaminar shear strength of 112 MPa (Example 1), which is significantly higher than Comparative Example 1, showing excellent internal quality and mechanical properties.

[0077] Figure 2 These are comparison images of the internal quality of the composite materials in Example 1 and Comparative Example 1, obtained using Scan C-scan. Figure 2 It can be seen that the composite material obtained in Example 1 has no defects such as porosity or delamination, has a smooth surface, and good internal quality. In contrast, the composite material in Comparative Example 1 shows obvious porosity and delamination, fiber buckling, uneven thickness, and poor internal quality. This indicates that under the same curing conditions, the prepreg in Comparative Example 1 has a low resin content and poor lay-up properties, which is not conducive to the preparation of high-quality composite materials.

[0078] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention should be covered within the protection scope of the present invention, which is defined by the claims.

Claims

1. A method for preparing a polyimide hot-melt prepreg, characterized in that the steps include... include: 1) Mechanically stir the polyimide with a single solvent. The polyimide is an acetylene-terminated, allyl norbornene-terminated, or phenylacetylene-terminated polyimide resin. The single solvent is selected from N,N-dimethylacetamide, dimethylformamide, and N-methylpyrrolidone to obtain a polyimide resin solution for impregnating fibers. 2) The polyimide is mechanically stirred with a mixed solvent. The polyimide is an acetylene-terminated, allyl norbornene-terminated, or phenylacetylene-terminated polyimide resin. The mixed solvent includes a low-boiling-point solvent and a high-boiling-point solvent. The low-boiling-point solvent is selected from one or more of dioxane, n-butanol, isopropanol, cyclopentanone, and sec-butanol. The high-boiling-point solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone to obtain a polyimide resin solution for self-adhesive surface layer. The polyimide resin solution for self-adhesive surface layer contains a toughening agent and a tackifying modifier. The toughening agent is a high-temperature resistant thermoplastic polyimide resin with a concentration of 5-20 wt%. The tackifying modifier is one or more of a high-temperature resistant uniminated thermosetting polyimide and a high-temperature resistant PMR resin with a concentration of 5-10 wt%. 3) The two polyimide resin solutions obtained in steps 1) and 2) are subjected to vacuum distillation to obtain semi-solid polyimide prepregs for impregnating fibers and for surface self-adhesion. 4) After the semi-solid polyimide prepreg for impregnating fibers is hot-melted in a hot-melt three-roll mill, it is coated onto release paper to obtain an impregnated fiber resin film. The impregnated fiber resin film is then laminated with fiber cloth through multiple hot-pressing rollers to obtain an impregnated fiber prepreg. 5) After the semi-solid polyimide prepreg for self-adhesive surface layer is hot-melted in a hot melt three-roll mill, it is coated onto release paper to obtain a self-adhesive surface resin film; the self-adhesive surface resin film is then double-sided laminated with the fiber cloth impregnated with fiber prepreg obtained in step 4) through multiple hot press rollers to obtain fiber prepreg. 6) The fiber prepreg obtained in step 5) is processed by a heating plate, hot press roller and cooling plate, the upper release paper is peeled off and covered with PE film to obtain polyimide hot melt prepreg.

2. The method as described in claim 1, characterized in that, The stirring conditions for steps 1) and 2) are: mechanical stirring for 60 to 240 minutes at a temperature 30 to 60°C lower than the boiling point of the solvent; the solid content of the two polyimide resin solutions obtained is 20% to 50%, and the melt viscosity at 50°C is 20 to 100 Pa·s.

3. The method as described in claim 1, characterized in that, In step 3), the distillation temperature is 50~100℃ and the time is 0.5~5h; the solid content of the semi-solid polyimide prepreg used for impregnating fibers is 75~90%, and the gel time of the adhesive solution at 120℃ is 10~15min; the solid content of the semi-solid polyimide prepreg used for self-adhesive surface layer is 65~75%, and the gel time of the adhesive solution at 120℃ is 10~15min.

4. The method as described in claim 1, characterized in that, In step 4), the fiber cloth is selected from one of the following: high modulus carbon fiber, high strength glass fiber, aramid fiber, quartz fiber, and ultra-high molecular weight polyethylene fiber. The fiber form is unidirectional or plain weave fabric. The fiber cloth accounts for 50-75 wt% of the total weight of the impregnated fiber prepreg, and the impregnated fiber resin film accounts for 20-40 wt% of the total weight of the impregnated fiber prepreg.

5. The method as described in claim 1, characterized in that, In step 4), the heating and melting temperature of the semi-solid polyimide prepreg used for impregnating the fibers is 50~80℃, the coating speed is 2~6m / min, the thickness of the single-layer impregnated fiber resin film is 0.05~0.2mm, the composite temperature of the fiber cloth and the impregnated fiber resin film is 60~90℃, the composite pressure is 0.2~0.4MPa, and the cooling table temperature of the hot press roller is 5~10℃.

6. The method as described in claim 1, characterized in that, In step 5), the self-adhesive surface resin film accounts for 5~20wt% of the total weight of the fiber prepreg; the heating and melting temperature of the semi-solid polyimide prepreg used for the self-adhesive surface is 50~80℃, the coating speed is 2~6m / min, and the thickness of a single layer of film is 0.05~0.2mm; the composite temperature of the self-adhesive surface resin film and the impregnated fiber prepreg is 60~90℃, the composite pressure is 0.2~0.4Mpa, and the cooling table temperature is 5~10℃.

7. A polyimide hot-melt prepreg, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. A polyimide thermal composite material, characterized in that, It is prepared through the following steps: A solvent is sprayed onto the surface of the polyimide hot melt prepreg prepared by any one of claims 1-6 to soften it, and then the layers are laid up according to the design specifications. Finally, the layers are heated and cured to obtain a polyimide thermal composite material. The solvent used for softening is one or more of ethanol, methanol, petroleum ether, dichloromethane, dichloroethane, and tetrahydrofuran.

Images