A fiber-reinforced thermoplastic polyimide laminate and a method for manufacturing and use thereof

Abstract

This invention relates to a fiber-reinforced thermoplastic polyimide laminate, its preparation method, and its application. The preparation method includes the following steps: S1: Prepare a diamine solution, add a dianhydride to the diamine solution to obtain a precursor solution, and prepare a diluent; S2: Add the diluent to the precursor solution to obtain an impregnation resin; S3: Coat the impregnation resin onto the surface of a substrate to form a wet film, and then perform a first drying treatment on the wet film to obtain an adhesive film; impregnate a fiber fabric with the impregnation resin or coat the surface of the fiber fabric with the impregnation resin to obtain an impregnated fabric, and then perform a second drying treatment on the impregnated fabric to obtain a prepreg; S4: Stack m prepreg sheets and n adhesive films alternately along the thickness direction to form a laminate, wherein m≥1, n≥1, and then hot-press the laminate to obtain a thermoplastic polyimide laminate. This invention has a simple process, high preparation efficiency, and the resulting laminate has excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of thermoplastic polyimide composite materials, and in particular to a method for preparing a fiber-reinforced thermoplastic polyimide laminate, the fiber-reinforced thermoplastic polyimide laminate obtained by the method, and the application of the fiber-reinforced thermoplastic polyimide laminate. Background Technology

[0002] Laminates are one of the core structural and functional components in the aerospace field. They are integral products formed by laminating and curing multiple layers of fibers / fabrics impregnated with high-performance resin through high-temperature hot pressing. They can be processed into various components such as fuselage skin structures, insulating supports for avionics equipment, and thermal protection materials for propulsion systems. They are widely used in manned spacecraft, supersonic aircraft, satellites, and other equipment in the extreme service environments of aerospace equipment. Coupled with the core requirement of "lightweighting to improve parameters such as range / load / speed", laminates have been subject to stringent comprehensive performance requirements such as "high long-term heat resistance, ultra-high mechanical strength, and excellent electrical insulation".

[0003] Polyimide (PI) is a high-performance polymer material produced by the polycondensation reaction of dianhydrides and diamines. The rigid imide ring structure in its molecular backbone endows the material with excellent high-temperature resistance, radiation resistance, and beneficial mechanical strength and dielectric properties. In aerospace laminate applications, polyimides are mainly divided into two technical routes based on processing characteristics: thermosetting polyimide (TI) and thermoplastic polyimide (TPI). Thermosetting polyimide undergoes cross-linking of the molecular chains during processing through active end-capping agents (such as acetylene groups), ultimately forming an insoluble and infusible three-dimensional network structure with extremely high cross-linking density. Thermoplastic polyimide, on the other hand, maintains a linear or slightly esterified molecular chain structure, and can be repeatedly plasticized and molded through a physical melt-cooling process without relying on chemical reactions, exhibiting typical crystalline or semi-crystalline behavior.

[0004] Although both types of polyimides meet the basic requirements of the aerospace industry for laminates—namely, high long-term heat resistance, ultra-high mechanical strength, and excellent electrical insulation—traditional processes often favor thermosetting polyimides as the resin matrix, aiming to achieve ideal dimensional stability through their highly cross-linked networks. However, under extreme service environments of long-term high temperature, high pressure, and variable heat loads, thermosetting systems, due to the three-dimensional cross-linked network formed after curing, have significant application limitations: First, they cannot be melt-processed; once a component is damaged, it cannot be repaired by hot pressing or other methods, leading to the complete scrapping of expensive aerospace components and extremely high maintenance costs. Second, the curing reaction cycle is lengthy, and the curing shrinkage rate is difficult to control, easily generating microcracks or participating in stress within thick-walled laminates, affecting structural reliability. Third, the modulus decays rapidly after the glass transition temperature (Tg), and the coefficient of thermal expansion (CTE) is poorly matched with reinforcements such as carbon fibers, limiting its application in high-precision avionics insulation supports and large-size skin structures. In contrast, thermoplastic polyimide, with its linear molecular chain structure, perfectly meets the advanced requirements of the aerospace industry for "reproducible, high toughness, and long lifespan." This material not only retains the inherent high stability and insulation of polyimide but also overcomes the limitations of thermosetting materials: it supports secondary melting and reshaping for on-site repair of damaged components; it possesses superior fatigue resistance and impact toughness, effectively absorbs vibration energy, significantly shortens the molding cycle, and improves interfacial bonding, making it an ideal substrate choice for manufacturing aerospace laminates.

[0005] Currently, the preparation methods for fiber-reinforced thermoplastic polyimide laminates include melt impregnation, powder impregnation, and in-situ polymerization. Melt impregnation involves heating thermoplastic polyimide resin above its melting point to form a melt, which is then forced to penetrate the fiber / fabric under pressure. After cutting and laminating, the laminate is then hot-pressed under high temperature and pressure. Powder impregnation involves heating and melting polyimide resin powder into a melt, which is then penetrated into the reinforcement using vacuum suction or alternating positive and negative pressure. After cooling, the laminate is obtained through hot pressing and thermosetting. In-situ polymerization involves impregnating the fiber fabric with monomer or diammonium phosphate solution, continuously drying to remove the solvent, then heating inside the prepreg to initiate polymerization and imidization reactions, followed by cutting, laminating, and hot pressing to obtain the product. However, these methods all have limitations: melt impregnation, as the mainstream industrial process, has high continuous production efficiency, but the high viscosity of thermoplastic polyimide melt makes it easy for fibers to be insufficiently impregnated; powder impregnation can reduce dependence on melt viscosity and the fiber impregnation effect is better than melt impregnation, but the uniformity of powder is difficult to control, resin enrichment or deficiency is easy to occur, and it is not suitable for complex shaped components; although in-situ polymerization has extremely strong interfacial bonding and excellent comprehensive performance, and can prepare complex shaped components, it requires extremely high molecular weight to achieve good interlayer density and mechanical properties. This requires a more thorough polymerization reaction and is more sensitive to solvent residue and temperature uniformity. Therefore, it is necessary to remove the solvent through continuous long-term drying treatment (usually 10-20 hours), which is complex, has low production efficiency, and is difficult to scale up for mass production. Summary of the Invention

[0006] Based on this, the purpose of the present invention is to overcome the defects or deficiencies of the prior art. On the one hand, it provides a method for preparing fiber-reinforced thermoplastic polyimide laminate, which has a simple process, high preparation efficiency, and produces fiber-reinforced thermoplastic polyimide laminate with good density.

[0007] A method for preparing a fiber-reinforced thermoplastic polyimide laminate includes the following steps:

[0008] S1: Prepare a diamine solution, add a dihydric anhydride to the diamine solution to obtain a precursor solution; And prepare the diluent; S2: Add a diluent to the precursor solution to obtain an impregnating resin; S3: The impregnation resin is coated on the surface of the substrate to form a wet film, and then the wet film is subjected to a first drying treatment to obtain an adhesive film; The reinforcing material is impregnated with the impregnation resin to obtain an impregnated material, and then the impregnated material is subjected to a second drying treatment to obtain a semi-cured sheet; S4: The m semi-cured sheets and n adhesive films are stacked alternately along the thickness direction to form a laminate, wherein m≥1 and n≥1. Then the laminate is hot-pressed to obtain a thermoplastic polyimide laminate.

[0009] Compared to existing technologies, the method for preparing fiber-reinforced thermoplastic polyimide laminates of this invention involves first mixing diamine and dianhydride in a certain proportion to obtain a precursor solution, and then significantly diluting the precursor solution by adding a diluent to reduce its viscosity, thereby improving its fluidity and allowing it to fully wet the reinforcing material. By introducing an adhesive film to increase the resin content on both sides of the prepreg, adjacent prepregs can bond together to form a dense structure after hot-pressing amination, ultimately producing a highly dense fiber-reinforced thermoplastic polyimide laminate. This method overcomes the defects of traditional methods for preparing thermoplastic polyimide laminates, such as melt impregnation, powder impregnation, and in-situ polymerization.

[0010] In one embodiment, in step S1, preparing the diamine solution involves dissolving the diamine monomer in a first solvent, wherein the amount of the first solvent is 70% to 95% of the total mass of the reaction system.

[0011] In one embodiment, in step S2, the viscosity of the impregnating resin is 100 to 1000 cP.

[0012] In one embodiment, in step S3, the temperature of the first drying process is 80–160°C, and the time is 10–30 min.

[0013] In one embodiment, in step S3, the temperature of the second drying process is 80–160°C, and the time is 5–30 min.

[0014] In one embodiment, the diluent includes a second solvent.

[0015] In one embodiment, the diluent further includes a functional filler.

[0016] In one embodiment, in step S1, preparing the diluent involves adding the functional filler to the second solvent and dispersing it.

[0017] On the other hand, the present invention also provides a fiber-reinforced thermoplastic polyimide laminate, which is prepared according to the above-described method for preparing fiber-reinforced thermoplastic polyimide laminate.

[0018] In another aspect, the present invention also provides the application of the fiber-reinforced thermoplastic polyimide laminate as described above in the preparation of components.

[0019] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of an exemplary thermoplastic polyimide laminate prepared by the method of the present invention; Figure 2 This is a schematic diagram of the structure of another exemplary thermoplastic polyimide laminate prepared by the method of the present invention; Figure 3 This is a schematic diagram of the structure of another exemplary thermoplastic polyimide laminate prepared by the method of the present invention; Figure 4 SEM images of the thermoplastic polyimide laminate obtained in Example 1 of the present invention: 4(a) is a SEM image of the thermoplastic polyimide laminate (scale bar: 200 μm); 4(b) is a SEM image of the thermoplastic polyimide laminate (scale bar: 100 μm). Figure 5 SEM images of the thermoplastic polyimide laminate obtained in Example 2 of the present invention: 5(a) is an SEM image of the thermoplastic polyimide laminate (scale bar: 200 μm); 5(b) is an SEM image of the thermoplastic polyimide laminate (scale bar: 100 μm). Figure 6 SEM images of the thermoplastic polyimide laminate obtained in Example 3 of the present invention: 6(a) is an SEM image of the thermoplastic polyimide laminate (scale bar: 200 μm); 6(b) is an SEM image of the thermoplastic polyimide laminate (scale bar: 100 μm). Figure 7 SEM images of the thermoplastic polyimide laminate obtained in Example 4 of the present invention: 7(a) is an SEM image of the thermoplastic polyimide laminate (scale bar: 100 μm); 7(b) is an SEM image of the thermoplastic polyimide laminate (scale bar: 20 μm); Figure 8 SEM images of the thermoplastic polyimide laminate prepared in Comparative Example 1 of the present invention: 8(a) is an SEM image of the thermoplastic polyimide laminate (scale bar: 100 μm); 8(b) is an SEM image of another location of the thermoplastic polyimide laminate (scale bar: 100 μm). Figure 9 SEM images of the thermoplastic polyimide laminate prepared in Comparative Example 2 of the present invention: 9(a) is an SEM image of the thermoplastic polyimide laminate (scale bar: 100 μm); 9(b) is an SEM image of another location of the thermoplastic polyimide laminate (scale bar: 100 μm). Figure 10SEM images of the thermoplastic polyimide laminate prepared in Comparative Example 3 of the present invention are shown below: 10(a) is an SEM image of the thermoplastic polyimide laminate (scale bar: 300 μm); 10(b) is an SEM image of another location of the thermoplastic polyimide laminate (scale bar: 300 μm). Figure 11 This is a photograph of the thermoplastic polyimide laminate prepared in Comparative Example 3 of the present invention.

[0021] Figure label: 10. Prepreg; 20. Adhesive film. Detailed Implementation

[0022] Existing methods for preparing thermoplastic polyimide laminates, such as melt impregnation, powder impregnation, and in-situ polymerization, all have different limitations: melt impregnation is prone to insufficient fiber wetting due to the high viscosity of the thermoplastic polyimide melt; while powder impregnation has better fiber wetting effect than melt impregnation, it is difficult to control the uniformity of the powder, which can easily lead to resin enrichment or deficiency, and it is not suitable for complex shaped components; although in-situ polymerization has excellent overall performance and can prepare complex shaped components, the process is complex, the production efficiency is low, it is difficult to scale up mass production, solvent recovery is difficult, and environmental costs are high.

[0023] Based on this, the present invention provides a method for preparing thermoplastic polyimide that differs from existing melt impregnation, powder impregnation, and in-situ polymerization methods. First, a diamine and a dianhydride are mixed in a certain proportion to obtain a polyamic acid solution. Then, a diluent is added to the polyamic acid solution. Next, the polyamic acid solution is uniformly coated onto the surface of a substrate to form a polyimide wet film of a certain thickness. Then, most of the solvent in the wet film is removed by drying to obtain a polyamic acid adhesive film. Simultaneously, a reinforcing material is impregnated in the polyamic acid solution to obtain an impregnated material. Then, most of the solvent in the impregnated material is removed by drying to obtain a prepreg. Finally, the adhesive film and the prepreg are stacked alternately along the thickness direction to form a laminate. The laminate is then subjected to hot-press imidization treatment under high temperature and high pressure to obtain a fiber-reinforced thermoplastic polyimide laminate.

[0024] Traditional processes produce polyamic acid solutions with high viscosity, making it difficult to completely wet the reinforcing material. Therefore, in the aforementioned preparation process, the polyamic acid solution is significantly diluted with a diluent to achieve low viscosity and good flowability, ensuring complete wetting of the reinforcing material. However, the excessive addition of solvent leads to a decrease in the resin content of the resulting prepreg, resulting in poor adhesion. If the prepregs are directly laminated and hot-pressed for amination, they cannot bond, preventing the formation of the laminate. Therefore, this invention introduces an adhesive film made from the polyamic acid solution onto both sides of the prepreg to increase the resin content on both sides, enabling adjacent prepregs to bond firmly after hot-pressing for amination, ultimately producing a dense, fiber-reinforced thermoplastic polyimide laminate.

[0025] Based on the above-mentioned design concept, the following details the preparation method of the fiber-reinforced thermoplastic polyimide laminate of the present invention: The method for preparing the fiber-reinforced thermoplastic polyimide laminate of this embodiment includes the following steps: S1: Prepare a diamine solution, add a dihydric anhydride to the diamine solution to obtain a precursor solution; and prepare a diluent. Specifically, under an air or nitrogen atmosphere, a diamine monomer and a first solvent are added to a reaction vessel, and the diamine monomer is completely dissolved to obtain a diamine solution. Then, a diacid monomer is slowly added to the diamine solution in batches, and the mixture is mechanically stirred at room temperature. After the diamine monomer and the diacid monomer have completely reacted, a transparent liquid, namely the polyimide precursor—a polyamic acid solution, is obtained. The diamine monomer can be ODA (4,4'-diaminodiphenyl ether) or TPE-Q (1,4-bis(4-aminodiphenyl ether)). p-PDA (p-phenylenediamine) and DDS (4,4'-diaminodiphenyl sulfone), TFMB (2,2'-di(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine), M-Tolidine (4,4'-diamino-2,2'-dimethylbiphenyl), BAP (2,2-bis(4-hydroxy-3-aminophenyl)propane) and BAPP (2,2-bis[4-(4-aminophenoxy)phenyl] Any of the following diamine monomers (propane) or others that can be used to synthesize polyamic acid; the dihydric anhydride monomer may be BPADA (2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride), PMDA (pyromellitic dianhydride), BPDA (biphenyltetracarboxylic dianhydride), BTDA (benzophenone tetracarboxylic dianhydride), ODPA (4,4'-biphenyl ether dianhydride), HQDPA (4,4'-terephthalodioxybisphthalic anhydride), and BPAF (9,9-bis(3,4-dicarboxyphenyl)fluorene). The first solvent is any one of the following: diamine monomers (DAMs) or other dihydric anhydrides that can be used to synthesize polyamic acid; the molar ratio of the diamine monomer to the dihydric anhydride monomer is 1:(1.01 to 1.05), and the total solid content of the two is 5 wt% to 30 wt%; the first solvent is any one of DMF (N,N-dimethylformamide), DMAC (N,N-dimethylacetamide), and NMP (N-methylpyrrolidone) or other organic solvents that can dissolve polyamic acid, and the amount of the first solvent is 70% to 95% of the total mass of the reaction system.

[0026] The functional filler is added to the second solvent and mechanically stirred at room temperature to uniformly disperse the functional filler in the second solvent, thereby obtaining a diluted solution containing the functional filler. The second solvent is any one of DMF, DMAC, and NMP or any other organic solvent that can dissolve polyamic acid. The functional filler is a functionalized inorganic nano-non-metallic powder that can impart special properties to the laminate (such as conductivity, wave absorption and heat generation), such as multi-walled carbon nanotubes, nano-iron oxide, boron nitride, silicon dioxide or hollow silicon dioxide microspheres, but is not limited to these, and its average particle size is 10 nm to 20 μm.

[0027] Of course, you can also omit the functional filler and use only the second solvent as a diluent.

[0028] S2: Add diluent to the precursor solution to obtain impregnating resin; Specifically, a diluent is added to the precursor solution to dilute the viscosity of the precursor solution to 100-1000 cP, thereby obtaining the impregnating resin.

[0029] The first and second solvents added in steps S1 and S2 above can be the same organic solvent or different organic solvents. Adding the organic solvent in stages ensures a higher molecular weight polyamic acid while reducing the viscosity of the polyamic acid solution. Furthermore, the functional filler is pre-dispersed in the second solvent. The inventors of this invention have found in practice that adding the functional filler in powder form to the precursor solution results in significant performance differences and poor stability at different locations on the final laminate. Therefore, the above preparation method pre-disperses the functional filler in the second solvent to ensure uniform dispersion of the functional filler in the impregnating resin, thereby ensuring the overall mechanical properties of the final fiber-reinforced thermoplastic polyimide laminate are stable.

[0030] S3: The impregnation resin is coated on the surface of the substrate to form a wet film, and then the wet film is subjected to a first drying treatment to obtain an adhesive film; The reinforcing material is impregnated in the impregnation resin to obtain the impregnated material, and then the impregnated material is subjected to a second drying treatment to obtain a semi-cured sheet; Specifically, an impregnation resin is uniformly coated on a clean glass substrate to form a polyamic acid wet film with a thickness of 0.05 to 0.2 mm. The wet film is then placed in a forced-air drying oven at 80 to 160°C for 10 to 30 minutes to remove most of the solvent from the wet film, thus obtaining a polyamic acid wet film. Impregnate a reinforcing material with a thickness of 0.05 to 0.2 mm in an impregnation resin or coat the surface of the reinforcing material with the impregnation resin so that the impregnation resin completely wets the reinforcing material to obtain an impregnated material. Then place the impregnated material in a forced-air oven at 80 to 160°C and dry it for 5 to 30 minutes to remove most of the solvent to obtain a semi-cured sheet.

[0031] S4: Stack m semi-cured sheets and n adhesive films alternately along the thickness direction to form a laminate, where m≥1 and n≥1. Then, hot press the laminate to obtain a thermoplastic polyimide laminate. Specifically, such as Figure 1As shown, the semi-cured sheet 10 and adhesive film 20 obtained in step S3 are cut into uniform sizes. Then, the semi-cured sheet 10 and adhesive film 20 are stacked alternately along the thickness direction to form a laminate. The laminate is then subjected to gradient heating and hot-press amination under high temperature and high pressure conditions. After cooling, a reinforced fiber thermoplastic polyimide laminate is obtained. The high temperature and high pressure conditions and hot-pressing time required for hot-press amination can be adjusted according to the reaction system composed of the selected diamine and dianhydride, and are not specifically limited here.

[0032] When m≥2, the number of adhesive films 20 between two adjacent prepreg sheets 10 can be as follows: Figure 1 The layer shown can also be two layers, or as shown in the image. Figure 2 The three layers shown can be further divided into three or more layers. The number of adhesive films 20 between two adjacent prepregs 10 can be adjusted according to the resin content in the prepreg 10. If the resin content in the prepreg 10 is low, the number of adhesive films 20 can be increased accordingly to ensure that the adjacent prepregs 10 can be effectively bonded during the hot-pressing amination process to form a dense laminate.

[0033] It should be noted that, although Figure 1-3 The uppermost and lowermost layers of the laminate shown are both adhesive films 20. However, in other embodiments, the uppermost and lowermost layers of the laminate may both be prepreg sheets 10; or the uppermost layer may be a prepreg sheet 10 and the lowermost layer may be an adhesive film 20; or the uppermost layer may be an adhesive film 20 and the lowermost layer may be a prepreg sheet 10.

[0034] Based on the above-described method for preparing fiber-reinforced thermoplastic polyimide laminates, this invention further conducted experimental operations and verifications on various parameters, which are described in detail below: Example 1 This embodiment provides a method for preparing a fiber-reinforced thermoplastic polyimide laminate containing functional fillers, comprising the following steps: S1: Under air atmosphere, 74.32g ODA and 861ml DMF, the first solvent, were added to the reaction flask. After complete dissolution, a diamine solution was obtained. Then, 81.79g PMDA was slowly added to the diamine solution in batches, and the solution was mechanically stirred at room temperature for 12h. After the diamine unit and the diacid monomer reacted completely, a precursor solution with a mass fraction of 16wt% was obtained. 16.61 g of multi-walled carbon nanotubes were added to 1044 ml of the second solvent DMF and mechanically stirred at room temperature for 12 h to ensure uniform dispersion of the multi-walled carbon nanotubes, thus obtaining a diluted solution. S2: Add diluent to the polyamic acid precursor solution obtained in step S1 and mechanically stir at room temperature for 12 hours to obtain an impregnation resin with a mass fraction of 8 wt%, wherein the resin contains 0.8 wt% multi-walled carbon nanotubes. S3: The impregnation resin obtained in step S2 is coated on a clean glass plate to form a 1 mm thick wet film. The wet film is then placed in a forced-air oven at 150°C for 15 minutes to remove most of the solvent and obtain the adhesive film. The reinforcing fiber fabric (cloth) is impregnated in the impregnation resin obtained in step S2, so that the impregnation resin fully wets the reinforcing fiber fabric to obtain the impregnated fabric. The impregnated fabric is then placed in a forced-air drying oven at 150°C for 10 minutes to remove most of the solvent, resulting in a semi-cured sheet. S4: Die-cut the adhesive film and prepreg obtained in step S3 into 10 pieces. A 10cm-sized sheet is formed by alternately stacking 12 semi-cured sheets and 39 adhesive films along the thickness direction to create a laminate. The top and bottom of the laminate each have three layers of adhesive film, and there are three layers of adhesive film between adjacent semi-cured sheets. The laminate is then hot-pressed under the following conditions to ensure complete amination of the polyamic acid inside the laminate: 150℃ / 60min / 30MPa, 250℃ / 60min / 30MPa, 350℃ / 60min / 30MPa, 380℃ / 60min / 30MPa, 400℃ / 10min / 30MPa. After cooling, a reinforced fiber thermoplastic polyimide / inorganic nanocomposite laminate is obtained.

[0035] Due to the long molecular chains and strong intermolecular forces of polyamic acid, polyamic acid solutions have high viscosity, exceeding 60,000 cP in traditional processes. This high viscosity prevents complete impregnation of reinforcing fiber fabrics. The present invention addresses this by adding a large amount of the second solvent DMF to the prepared polyamic acid solution, thereby reducing its viscosity and giving the impregnating resin good flowability, allowing for thorough impregnation of the reinforcing fiber fabric. Table 1 below shows the viscosity of commercially available polyamic acid solutions and the viscosity of the polyamic acid solution prepared by step S1 of the present invention: Table 1

[0036] As can be seen from Table 1, the viscosity of the polyamic acid solution obtained in step S1 of Example 1 of the present invention is much lower than that of commercial polyamic acid solutions. This characteristic provides excellent flowability assurance for the subsequent impregnation of the resin to fully wet the reinforcing fiber fabric.

[0037] Meanwhile, the preparation method of this invention disperses the functional filler in a second solvent, DMF, and adds the functional filler dispersion to the polyamic acid solution, allowing the functional filler to be uniformly dispersed in the impregnation resin. However, due to the long molecular chain and strong intermolecular forces of polyamic acid, its solubility in the precursor solution is low (typically 10-20%). Combined with the large addition of the second solvent, the resin content of the impregnation resin obtained in step S2 decreases, leading to a decrease in the resin content of the prepreg formed after impregnating the reinforcing fiber fabric. Consequently, after hot-press amination, the prepreg cannot bond, and the laminate cannot be formed. Therefore, this invention introduces an adhesive film formed by the impregnation resin to increase the resin content on both sides of the prepreg, thereby enabling adjacent prepregs to bond firmly after hot-press amination, forming a high-density fiber-reinforced thermoplastic polyimide laminate. Figure 4 (a)-4(b) show the microstructure of the fiber-reinforced thermoplastic polyimide laminate prepared in this embodiment. Figure 4 As can be seen from (a)-4(b), the fiber-reinforced thermoplastic polyimide laminate prepared in this embodiment has a dense internal interlayer structure without any gaps, and there is no interface between the prepreg and the adhesive film.

[0038] To verify the mechanical properties of the fiber-reinforced thermoplastic polyimide laminate prepared in Example 1, five locations were selected from the fiber-reinforced thermoplastic polyimide laminate prepared in Example 1 and marked as locations 1-5. The interlaminar shear strength at locations 1-5 was then measured using an interlaminar shear strength testing device. The measurement results are shown in Table 2 below: Table 2

[0039] As shown in Table 2, the interlaminar shear strength of the thermoplastic laminate obtained in Example 1 of the present invention reaches more than 30 MPa at different locations, which meets the requirements of this technical field for the interlaminar shear strength of thermoplastic polyimide laminate (30-40 MPa), and has high stability.

[0040] The fiber-reinforced thermoplastic polyimide laminate obtained above can be used to manufacture components in the aerospace field (such as aircraft, engines, fairings, etc.), as well as components in the rail transportation field, electronic and electrical fields, and industrial equipment and electronic and electrical fields. The required functions can be achieved by adding corresponding functional fillers according to the specific application scenario.

[0041] Example 2 The only difference between this embodiment and Example 1 is the functional filler used and its dosage in step S2: the functional filler used in this embodiment is nano-ferric oxide (particle size 20nm), and the dosage is 78.06g. All other steps and technical parameters are the same as in Example 1. The total solids content of the impregnating resin obtained in step S2 of this embodiment is 8%, of which nano-ferric oxide accounts for 40wt% of the total mass of polyamic acid.

[0042] Figure 5 Figures (a)-5(b) show the microstructure of the thermoplastic polyimide laminate prepared in this embodiment. Figure 5 As shown in (a)-5(b), the fiber-reinforced thermoplastic polyimide laminate prepared in this embodiment has a dense internal interlayer structure without any gaps, and there is no interface between the prepreg and the adhesive film.

[0043] Example 3 This embodiment provides a method for preparing a fiber-reinforced thermoplastic polyimide laminate without functional fillers, comprising the following steps: S1: Under air atmosphere, 29.739 g MDA and 313 ml DMF solvent were added to the reaction flask and completely dissolved to obtain a diamine solution; then 29.422 g BPDA was slowly added to the diamine solution in batches, and the solution was mechanically stirred at room temperature for 12 h. After the diamine unit and the diacid monomer had completely reacted, a precursor solution with a mass fraction of 20 wt% was obtained. S2: Add 387 ml DMF to a 20 wt% precursor solution and dilute it to 10 wt% to obtain the impregnation resin; S3: The impregnation resin obtained in step S2 is coated on a clean glass plate to form a 1 mm thick wet film. The wet film is then placed in a forced-air oven at 150°C for 15 minutes to remove most of the solvent and obtain the adhesive film. The reinforcing fiber fabric is impregnated with the impregnation resin obtained in step S2, and the impregnation resin fully wets the reinforcing fiber fabric. Then the impregnated fabric is placed in a forced-air drying oven at 150°C for 10 minutes to remove most of the solvent, and a semi-cured sheet is obtained. S4: Die-cut the prepreg and adhesive film obtained in step S3 into 10 pieces. 10cm thick, then 9 layers of prepreg and 30 layers of adhesive film are staggered along the thickness direction to form a laminate. The top and bottom of the laminate each have three layers of adhesive film, and there are three layers of adhesive film between each pair of adjacent prepregs. Then, the laminate is hot-pressed under the following conditions to ensure complete amination of the polyamic acid inside the laminate: 150℃ / 60min / 30MPa, 250℃ / 60min / 30MPa, 350℃ / 60min / 30MPa, 380℃ / 60min / 30MPa, 400℃ / 10min / 30MPa. After cooling, the reinforced fiber thermoplastic polyimide laminate is obtained.

[0044] Figure 6 (a)-6(b) show the microstructure of the thermoplastic polyimide laminate prepared in this embodiment. Figure 6 As shown in (a)-6(b), the thermoplastic polyimide laminate prepared in this embodiment has a dense internal interlayer structure without any gaps, and there is no interface between the prepreg and the adhesive film.

[0045] Example 4 The difference between this embodiment and embodiment 3 is as follows: (1) The atmosphere and reaction system for generating polyamic acid precursor in step S1 of this embodiment are different from those in Example 3: In step S1 of this embodiment, 5.115g of TPE-Q and 60ml of the first solvent DMF are added to the reaction flask under a nitrogen atmosphere. After complete dissolution, a diamine solution is obtained. Then, 9.1075g of BPADA is slowly added to the diamine solution in batches. (2) The amount of the second solvent DMF added in step S2 is different: In this embodiment, step S2 is to add 76 ml of the second solvent DMF to a 20 wt% polyamic acid solution to dilute it to 10 wt% and obtain the impregnation resin; (3) The number of adhesive films stacked between adjacent prepregs and the hot-press amination conditions in step S4 are different from those in Example 3: In the laminate formed in step S4 of this example, the number of adhesive films between adjacent prepregs decreases from bottom to top, and is 12, 8, 4 and 2 layers respectively; the hot-press amination conditions are 150℃ / 30min / 30MPa and 250℃ / 30min / 30MPa. All other steps and the technical parameters in each step are the same as in Example 3.

[0046] Figure 7 Images (a)-7(b) show the microstructure of the thermoplastic polyimide laminate prepared in this embodiment. Figure 7 As shown in (a)-7(b), the thermoplastic polyimide laminate prepared in Example 4 has a dense internal interlayer structure without any gaps, and there is no interface between the prepreg and the adhesive film.

[0047] The following three comparative examples further illustrate the beneficial effects of the fiber-reinforced thermoplastic polyimide laminate preparation method of the present invention.

[0048] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not perform step S2, while the other steps and the technical parameters in each step are the same as in Example 1.

[0049] Figure 8 (a)-8(b) show the internal microstructure of the thermoplastic polyimide laminate prepared in Comparative Example 1. Figure 8 As shown in (a)-8(b), there are a large number of voids in the interlayer of the thermoplastic polyimide laminate prepared in Comparative Example 1. The reason is that the precursor solution prepared in step S1 of Comparative Example 1 has a high viscosity, which makes the impregnation resin prepared in step S2 have poor fluidity and cannot completely wet the reinforcing fiber fabric. The semi-cured sheet is difficult to bond tightly, resulting in a large number of voids in the interlayer.

[0050] Comparative Example 2 Comparative Example 2 uses the same steps as Example 1 of the present invention, the only difference being that in step S1 of Comparative Example 2, the functional filler is added to the polyamic acid solution in powder form.

[0051] Figure 9 (a)-9(b) show the internal microstructure of the fiber-reinforced thermoplastic polyimide laminate prepared in Comparative Example 2. Figure 9 As shown in (a)-9(b), there are voids in the interlayer of the fiber-reinforced thermoplastic polyimide laminate prepared by the method of Comparative Example 2.

[0052] Comparative Example 3 Comparative Example 3 uses the same steps as Example 1 of the present invention, the only difference being that no adhesive film is introduced when forming the laminate in Comparative Example 3 in step S3.

[0053] Figure 10 (a)-10(b) show the internal microstructure of the fiber-reinforced thermoplastic polyimide laminate prepared in Comparative Example 3. Figure 10 As shown in (a)-10(b), the fiber-reinforced thermoplastic polyimide laminate prepared in Comparative Example 3 has a large number of voids between its layers. This is because the resin content in the prepreg is low, and the prepregs cannot bond together after thermo-curing; in fact, the prepregs can be easily broken apart layer by layer (e.g., ...). Figure 11 (As shown).

[0054] Effect verification Five positions corresponding to positions 1-5 in Example 1 were selected on the laminates prepared in Comparative Examples 1-3. The interlaminar shear strength of positions 1-5 in Comparative Examples 1-3 was then measured using an interlaminar shear strength testing device. The measurement results are shown in Table 3 below. Table 3

[0055] As shown in Table 3, the interlaminar shear strength of the laminates prepared in Comparative Example 1 is less than 10 MPa, and the absolute values ​​of the measured values ​​at different locations differ significantly. This is because the polyamic acid solution prepared in step S1 of Comparative Example 1 has a high viscosity and poor fluidity. When the reinforcing fibers are impregnated in the impregnation resin, the impregnation resin hardly flows on the reinforcing fibers, making it difficult to completely wet the reinforcing fibers. Therefore, after the hot-pressing amination treatment of the laminate in step S3, the prepregs are difficult to bond together to form a dense structure. These defects are reflected in the mechanical properties of the final laminate, resulting in an interlaminar shear strength of the laminate that is much lower than that of Example 1, and the interlaminar shear strength fluctuates greatly at different locations, showing poor stability.

[0056] Although the interlaminar shear pressure at position 1 of the laminate obtained in Comparative Example 2 exceeds 34.12, the absolute values ​​of different measurements differ significantly. This is because the functional filler in Comparative Example 2 is directly dispersed in polyamic acid solution in powder form. Even though the viscosity of the polyamic acid solution has been reduced by adding a large amount of the first solvent in the previous steps, the powdered functional filler is still prone to agglomeration after being added to a polyamic acid solution with a certain viscosity. Even with mechanical stirring, it is difficult to ensure that the functional filler is fully dispersed, which leads to a large difference in interlaminar shear strength at different positions of the laminate and poor stability.

[0057] In Comparative Example 3, a large amount of solvent was added to reduce the viscosity of the polyamic acid solution during preparation. Simultaneously, functional fillers were added to the polyamic acid solution in dispersion form to ensure uniform dispersion of the functional fillers in the impregnation resin. However, the addition of a large amount of solvent led to a decrease in the resin content of the prepreg formed by impregnating the fiber fabric with the impregnation resin. Consequently, the laminate formed solely from the prepreg failed to bond after hot-pressing amination, making it impossible to measure the interlaminar shear strength due to its fragility.

[0058] Compared to existing technologies, the method for preparing fiber-reinforced thermoplastic polyimide laminates of this invention involves first mixing diamine and dianhydride in a certain proportion to obtain a precursor solution, and then significantly diluting the precursor solution by adding a diluent to reduce its viscosity, thereby improving its fluidity and allowing it to fully impregnate the reinforcing material. By introducing an adhesive film to increase the resin content on both sides of the prepreg, adjacent prepregs can bond together to form a dense structure after hot-pressing amination, ultimately producing a highly dense fiber-reinforced thermoplastic polyimide laminate with interlaminar shear strength meeting the requirements of this technical field. When it is necessary to prepare fiber-reinforced thermoplastic polyimide laminates containing functional fillers, the functional fillers are dispersed in a solvent beforehand, allowing them to be added to the precursor solution in the form of a dispersion, thus ensuring uniform dispersion of the functional fillers in the impregnating resin. The preparation method of the present invention is simple, efficient, and can be mass-produced. In the obtained fiber-reinforced thermoplastic polyimide laminate, the resin and fiber are well bonded, forming a dense structure inside the laminate.

[0059] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this application are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; the terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description relates to drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this application, those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0060] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. 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, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a fiber-reinforced thermoplastic polyimide laminate, characterized in that, Includes the following steps: S1: Prepare a diamine solution, add a dihydric anhydride to the diamine solution to obtain a precursor solution; And prepare the diluent; S2: Add a diluent to the precursor solution to obtain an impregnating resin; S3: The impregnation resin is coated on the surface of the substrate to form a wet film, and then the wet film is subjected to a first drying treatment to obtain an adhesive film; The reinforcing material is impregnated with the impregnation resin to obtain an impregnated material, and then the impregnated material is subjected to a second drying treatment to obtain a semi-cured sheet; S4: The m semi-cured sheets and n adhesive films are stacked alternately along the thickness direction to form a laminate, wherein m≥1 and n≥1. Then the laminate is hot-pressed to obtain a thermoplastic polyimide laminate.

2. The method for preparing fiber-reinforced thermoplastic polyimide laminate according to claim 1, characterized in that: In step S1, the preparation of the diamine solution involves dissolving the diamine monomer in a first solvent, wherein the amount of the first solvent is 70% to 95% of the total mass of the reaction system.

3. The method for preparing fiber-reinforced thermoplastic polyimide laminate according to claim 1, characterized in that: In step S2, the viscosity of the impregnating resin is 100-1000 cP.

4. The method for preparing fiber-reinforced thermoplastic polyimide laminate according to claim 1, characterized in that: In step S3, the temperature of the first drying treatment is 80-160°C, and the time is 10-30 min.

5. The method for preparing fiber-reinforced thermoplastic polyimide laminate according to claim 1, characterized in that: In step S3, the temperature of the second drying process is 80–160°C, and the time is 5–30 min.

6. The method for preparing the fiber-reinforced thermoplastic polyimide laminate according to any one of claims 1 to 5, characterized in that: The diluent includes a second solvent.

7. The method for preparing fiber-reinforced thermoplastic polyimide laminate according to claim 6, characterized in that: The diluent also includes functional fillers.

8. The method for preparing fiber-reinforced thermoplastic polyimide laminate according to claim 7, characterized in that: In step S1, preparing the diluent involves adding the functional filler to the second solvent and dispersing it.

9. A fiber-reinforced thermoplastic polyimide laminate, characterized in that: The fiber-reinforced thermoplastic polyimide laminate is prepared according to the method described in claim 1.

10. The use of the fiber-reinforced thermoplastic polyimide laminate as described in claim 9 in the preparation of components.

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