Ultrathin broadening polyimide fabric as well as preparation method and application thereof

Abstract

The invention relates to an ultrathin broadening polyimide fabric and a preparation method thereof. The fabric is formed by weaving warp-wise and weft-wise broadening polyimide fibers or weaving the warp-wise and weft-wise broadening polyimide fibers with broadening fibers such as aramid fibers and carbon fibers in a mixed mode, the surface density is 20-200 g / m, the thickness is 20-200 microns, the length-width ratio of the section of the broadening polyimide fibers is 10: 1-100: 1, and the width is 0.5-10 mm. The preparation method comprises the steps of polyimide precursor hot roller broadening, fiber pre-shaping, weaving forming, after-finishing and the like, and the fabric is ultrathin, high in strength, good in resin wettability and high-temperature stability by accurately controlling the broadening temperature, tension, weaving parameters and a surface treatment process. The technical blank of the polyimide broadening fabric is filled, and the polyimide broadening fabric can be widely applied to the fields of aerospace, high-temperature protection, new energy automobiles and the like and has important industrial application value.

Description

Technical Field

[0001] This invention relates to the field of high-performance textile materials technology, and in particular to a polyimide fabric, its preparation method, and its application. Background Technology

[0002] Polyimide materials, due to their excellent high-temperature resistance, high strength, and chemical corrosion resistance, play an irreplaceable role in aerospace, high-end equipment, and high-temperature protection. However, with the increasing demands of modern industry for lightweight and high-performance materials, traditional polyimide fabrics suffer from problems such as excessive thickness, insufficient resin impregnation, and incomplete mechanical property development, limiting their application in high-end fields.

[0003] Currently, the technology for spreading fabrics mainly focuses on carbon fiber. For example, Chinese patent document CN118306032A discloses a thermoplastic sheet of PA6 low-basis-weight carbon fiber spread woven fabric and its manufacturing method. However, this technology is only applicable to carbon fiber and has drawbacks such as high resin content and poor flexibility. Polyimide fibers, due to their structural characteristics, face numerous technical challenges in spreading processes and fabric preparation: firstly, polyimide fibers have high rigidity, and conventional spreading methods easily lead to fiber breakage or uneven spreading; secondly, the morphological stability of the spread fibers is poor, making them prone to springback during weaving; and thirdly, the fabric surface is highly inert, resulting in poor compatibility with the matrix resin and affecting the overall performance of the composite material. To date, there are no reports on the preparation process of polyimide spread fabrics. Developing polyimide spread fabrics that combine ultra-thinness, high strength, morphological stability, and good resin wettability is of significant practical importance and urgent need. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the primary objective of this invention is to provide an ultra-thin, widened polyimide fabric with advantages such as ultra-thinness, high strength, high temperature stability and good resin wettability, which can meet the application requirements of high-end fields such as aerospace.

[0005] Another objective of this invention is to provide a method for preparing the above-mentioned ultrathin stretched polyimide fabric, which achieves efficient and stable preparation of polyimide stretched fabric by precisely controlling the stretching process, pre-setting parameters and finishing technology.

[0006] Another objective of this invention is to provide applications for the aforementioned ultrathin, widened polyimide fabrics, expanding their application scenarios in aerospace, high-temperature protection, new energy vehicles, and other fields.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: an ultra-thin stretched polyimide fabric, woven from warp and weft fibers, wherein the fabric has an areal density of 20-200 g / m² and a thickness of 20-200 μm; wherein the warp and / or weft fibers include stretched polyimide fibers, wherein the stretched polyimide fibers are obtained by processing polyimide precursor yarns through a hot roller stretching process, and its cross-section is flat, with an aspect ratio of 10:1-100:1, a width of 0.5-10 mm, and a thickness of 20-150 μm.

[0008] Preferably, the fabric surface is plasma-treated with a power of 50-200W for 1-10 minutes, resulting in a contact angle ≤60° to improve resin wettability. It should be noted that in the technical scenario of plasma treatment of fabrics to improve resin wettability, there is no fixed lower limit for the contact angle; it is mainly determined by two factors. First, the contact angle essentially reflects the degree of matching between the surface energy of the solid and the surface tension of the liquid (resin). When the fabric surface is plasma-treated, polar groups such as hydroxyl and carboxyl groups are introduced, significantly increasing the surface energy and causing the contact angle to continuously decrease. Theoretically, when the fabric surface energy is much higher than the resin surface tension, the resin can spread completely on the fabric surface, at which point the contact angle approaches 0° (i.e., fully wetted). However, in practice, due to the microstructure of the fabric fibers (such as pores and roughness) and the uniformity of the plasma treatment, it is difficult to achieve an absolute 0°. Secondly, from the perspective of improving resin wettability, a contact angle of ≤60° can meet the interfacial bonding requirements of most resin-based composite materials (generally, a contact angle <90° is considered wetting, and the smaller the angle, the better the wetting effect).

[0009] Preferably, the fabric is a blended and expanded fabric, which is made of expanded polyimide fibers and other expanded fibers; the other expanded fibers are selected from at least one of aramid expanded fibers, carbon fiber expanded fibers, glass fiber expanded fibers, aramid III expanded fibers, and PBO (poly-p-phenylenebenzodioxazole) expanded fibers; by mass percentage, the proportion of expanded polyimide fibers in the blended fibers is 50%-90%, and the proportion of other expanded fibers is 10%-50%, and the fiber ratio can be adjusted according to application requirements to optimize fabric performance.

[0010] Preferably, the expanded polyimide fiber and other expanded fibers are treated with a setting agent, which is a polyamic acid solution containing active groups; the active groups are selected from at least one of hydroxyl, amino, carboxyl, and epoxy groups; the solid content of the polyamic acid solution is 1%-10wt%, and the solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. By introducing the active groups, the bonding force between the fiber and the resin is further enhanced.

[0011] Preferably, the tensile strength of the expanded polyimide fiber is ≥2.5GPa, the strength retention rate at 200℃ for 100h is ≥75%, and the resin wetting rate is ≥80%, ensuring the stability of the fabric in high-temperature environments and the molding quality of the composite material.

[0012] Preferably, the aspect ratio of the expanded polyimide fiber is 20:1 to 80:1, ensuring multi-dimensional optimization in terms of morphological stability, mechanical properties, resin wettability, and processing adaptability.

[0013] The preparation method of the above-mentioned ultrathin expanded polyimide fabric includes the following steps: (1) Polyimide filament stretching treatment: The polyimide filament is placed in a stretching device and stretched at a temperature of 80-150℃ and a tension of 5-20N. The stretching rate is controlled at 0.5-4m / min. After stretching, a setting agent is sprayed or impregnated to form a stretched polyimide fiber with a width of 0.5-10mm and a thickness of 20-150μm. If it is a blended fabric, other fibers are simultaneously subjected to differentiated stretching treatment to control the thickness deviation of different fibers ≤7% to ensure the compatibility of fibers during weaving.

[0014] (2) Fiber pre-forming: The expanded fibers are pre-formed by hot air. The pre-forming temperature of polyimide expanded fibers is 70-350℃, the time is 5-15min, and the tension is 1-3N; the pre-forming temperature of other expanded fibers is 80-350℃, the time is 5-20min, and the tension is 1-2.5N. The pre-forming process fixes the fiber expansion shape and prevents rebound during weaving.

[0015] (3) Weaving: The pre-shaped fibers are installed on the warp yarn release frame system of the loom, and the weaving parameters are set: the weaving speed is 10-100 revolutions / minute, and plain weave, twill weave or satin weave is used to weave to obtain the initial product of the fabric.

[0016] (4) Finishing: The initial fabric is surface treated, including plasma treatment or coupling agent coating, to obtain ultra-thin expanded polyimide fabric.

[0017] In step (1), the "thickness deviation" is defined as: (the difference in thickness between the two fibers ÷ the thickness of the reference fiber) × 100% (the reference fiber is a spread polyimide fiber). The thickness deviation of different fibers is preferably ≤5%, and more preferably ≤3%.

[0018] Preferably, in step (1), the stretching equipment is a pressure roller-hot air synergistic stretching device or an airflow stretching machine; the polyimide precursor has a single filament diameter of 10-20μm, a breaking strength ≥3.0GPa, and a glass transition temperature ≥280℃, providing raw material guarantee for the high performance of the fabric.

[0019] Preferably, in step (4), the coupling agent is selected from at least one of KH550 and KH560, and the coating amount is 2%-5%; if the coupling agent and nanoparticle composite coating is used, the nanoparticles are selected from at least one of nano SiO2 and nano Al2O3, and the addition amount is 1%-2%, which can further improve the wear resistance of the fabric and the interfacial bonding force with the resin.

[0020] It should be noted that in this invention, the polyimide precursor fiber refers to the initial fiber form obtained from polyimide polymer through a spinning process (polymer fines are extruded from the spinneret and then solidified in the spinning field), without subsequent processing such as widening or pre-shaping, and usually exists in the form of continuous filaments. This polyimide precursor fiber serves as the basic raw material for preparing widened polyimide fibers, fabrics, or composite materials, retaining the basic characteristics of the polyimide polymer; the single filament diameter is mostly 10-20 μm, the linear density is 55D-3000D (D is a unit of linear density), the tensile strength is ≥1.5 GPa (some high-performance models ≥2.5 GPa), and the glass transition temperature is ≥280℃; its morphological characteristics are that the cross-section is mostly circular, without flattening or widening treatment, and in the bundled state, morphological modification needs to be achieved through specific processes.

[0021] In addition, in step (1), during the widening process, a suitable setting agent can be selected for spraying or impregnation after widening, depending on the application scenario. The setting agent described in this invention is used to fix the widening morphology of polyimide precursor fibers (or other blended fibers), improving the structural stability of the fiber and its compatibility with the matrix resin. The setting agent is selected from at least one of polyurethane setting agents, epoxy resin setting agents, polyamic acid setting agents, polyimide setting agents, and polyetheretherketone setting agents, preferably with a solid content of 1wt% to 10wt%, and preferably a polyamic acid setting agent. Among them, polyamic acid setting agents use polyamic acid containing active groups (at least one of hydroxyl, amino, carboxyl, and epoxy groups) as the core component, and the solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. The solid content is, for example, 1.5wt%-2wt%. By spraying or impregnating, it treats the spread fibers, fixing their flattened shape and enhancing the interfacial bonding between the fiber and the resin through the active groups. Polyurethane setting agents are preferably water-based polyurethane systems with a solid content of, for example, about 3wt%. They have good film-forming properties and flexibility, suitable for spreading and setting blended fibers such as aramid, preventing fiber rebound or breakage during pre-setting and weaving. Epoxy resin setting agents are preferably water-based epoxy resins with a solid content of, for example, about 4wt%. After curing, they have strong structural stability and are suitable for blended fibers such as glass fiber that require increased rigidity. When combined with spread fibers, they can enhance the overall mechanical properties of the fabric. For epoxy resin-based setting agents, water-based epoxy resins are preferred, with a solid content of approximately 4 wt%. These agents exhibit strong structural stability after curing and are suitable for blended fibers such as glass fiber that require increased rigidity. When combined with expanded fibers, they can enhance the overall mechanical properties of the fabric. In addition, polyimide and polyetheretherketone (PEEK) setting agents must be in low-viscosity fluid form (suitable for spraying / impregnation processes). Their chemical properties must be compatible with polyimide fibers, with no significant corrosion or compatibility issues, and they must not affect the high-temperature stability of the fibers after setting (strength retention rate ≥75% at 200℃ for 100 hours). The setting agent used must meet the following requirements: fiber thickness variation coefficient ≤1% after treatment; no damage to the original tensile strength of the fiber (retention rate ≥90%); compatibility with subsequent pre-setting processes (70-350℃); and no excessive volatiles or thermal degradation.

[0022] This invention also protects the application of the aforementioned ultrathin, widened polyimide fabric in aerospace, high-temperature protection, new energy vehicles, or high-end composite materials, as well as composite materials containing the fabric as a reinforcement. The composite material further comprises a matrix resin, which is at least one selected from epoxy resins, polyurethane resins, polyimide resins, bismaleimide resins, and polyetheretherketone resins.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) Filling the technological gap: For the first time, ultra-thin stretched polyimide fabric was developed, breaking through the technical bottleneck of polyimide fiber stretching and weaving, solving the problems of large thickness and poor resin impregnation of traditional polyimide fabrics, and expanding the application scenarios of polyimide materials.

[0024] (2) Excellent product performance: The fabric surface density is only 20~200g / m², the thickness is 20~200μm, and it has high strength (fiber tensile strength ≥2.0GPa), high temperature stability (strength retention rate ≥75% at 200℃ for 100h) and good resin wettability (contact angle ≤60°), which can meet the needs of high-end fields for lightweight and high-performance materials.

[0025] (3) Stable and controllable process: Through differentiated widening, precise pre-forming and optimized weaving parameters, stable control of the widened fiber morphology and efficient fabric preparation are achieved. The process has good repeatability and is suitable for industrial production.

[0026] (4) Wide adaptability: It can prepare pure or mixed knitted fabrics. By adjusting the fiber ratio, weaving structure and finishing process, it can meet the personalized needs of different fields such as aerospace, high temperature protection, and new energy vehicles. Attached Figure Description

[0027] Figure 1 This is a photograph of the appearance of the ultrathin stretched polyimide fabric prepared in Example 1. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. The polyimide precursor used in the embodiments was provided by Jiangsu Xiannuo New Material Technology Co., Ltd., and other raw materials were all commercially available conventional products.

[0029] The performance testing methods in the following examples and comparative examples are described below.

[0030] Areal density: Tested according to GB / T4669-2008 "Textiles - Determination of mass per unit length and mass per unit area of ​​woven fabrics".

[0031] Fabric thickness: The thickness was measured using a thickness gauge. Ten measuring points were taken at different locations on the fabric, and the average value was calculated.

[0032] Tensile strength: Tested according to GB / T3923.1-2013 "Textiles - Tensile properties of fabrics - Part 1: Determination of breaking strength and elongation at break (strip method)".

[0033] High-temperature strength retention rate: The fabric was placed in a 200℃ oven for 100 hours and then cooled to room temperature. The tensile strength was then tested and the ratio to the initial strength was calculated.

[0034] Surface contact angle: Measured using a contact angle meter with a water droplet volume of 5 μL, and the average value of 3 different measuring points was taken.

[0035] Resin impregnation rate: The mass method is used. After the fabric is fully impregnated with epoxy resin, excess resin on the surface is removed, and the fabric is dried. The proportion of resin mass to fabric mass is then calculated.

[0036] Example 1: Pure woven ultra-thin spreadable polyimide fabric (1000D) (1) Polyimide precursor fiber stretching treatment: Polyimide precursor fiber with a single filament diameter of 15μm, a breaking strength of 3.5GPa, and a glass transition temperature of 300℃ was selected. A pressure roller-hot air co-stretching device was used, with the stretching temperature set at 80℃, tension at 5N, and stretching rate at 0.5m / min. The stretched fiber was treated with a 2wt% polyamic acid solution containing epoxy groups (synthetic dianhydride monomer: pyromellitic dianhydride PMDA; diamine monomer: 4,4'-diaminodiphenyl ether ODA + 4,4'-diaminodiphenyl ether glycidyl ether; solvent: N,N-dimethylacetamide DMAc) to obtain stretched polyimide fiber with a width of 4mm and a thickness of 61μm and a cross-sectional aspect ratio of 65:1.

[0037] (2) Fiber pre-forming: The stretched polyimide fiber is placed in a hot air oven and pre-formed at 300°C for 5 minutes. A tension of 2N is applied. The fiber heat shrinkage rate after pre-forming is 0.8%.

[0038] (3) Weaving: A rapier loom with a plain weave is used. The warp tension is 15N and the weaving speed is 30 revolutions / minute to obtain the initial fabric.

[0039] (4) Post-treatment: Low-temperature oxygen plasma treatment is adopted, with a treatment power of 100W and a treatment time of 5min.

[0040] Tests showed that the fabric has a surface density of 60 g / m², a thickness of 125 μm, a tensile strength at break of 1000 N / 25 mm, a strength retention rate of 100% after 100 hours at 200°C, a surface contact angle of 55°, and a resin wetting rate of 92%. Additionally, Figure 1 This is a photograph of the appearance of the ultrathin stretched polyimide fabric prepared in Example 1.

[0041] Example 2: Polyimide / aramid blended ultrathin spreadable fabric (mass ratio 7:3) (1500D) (1) Fiber broadening treatment: Polyimide precursor: Same as in Example 1, with a spreading temperature of 100℃, a tension of 8N, and a spreading rate of 1m / min, to obtain a spread polyimide fiber with a width of 5mm and a thickness of 105μm, and a cross-sectional aspect ratio of 38:1; Aramid precursor: monofilament diameter 12μm, breaking strength 3.0GPa, alkali resistance 92%, using an airflow spreading machine, spreading temperature 60℃, tension 6N, spreading rate 0.8m / min, the spread fiber is treated with 3wt% aqueous polyurethane solution to obtain spread aramid fiber with a width of 5mm and a thickness of 104.5μm, with a thickness deviation of 0.48% from polyimide fiber.

[0042] (2) Fiber pre-type: Expanding polyimide fibers: pre-shaped at 320℃ for 8 minutes, with a tension of 2.5N, resulting in a heat shrinkage rate of 0.7%; Stretched aramid fibers: pre-shaped at 80℃ for 10 min, with a tension of 1.5N, resulting in a heat shrinkage rate of 0.6%.

[0043] (3) Weaving: A dual-system tension-controlled rapier loom is used with a twill weave, a warp ratio of 3:1, a weft ratio of 2:1, and a weaving speed of 50 rpm.

[0044] (4) Finishing: Coating with 1.5% KH550 coupling agent + 2% nano SiO2, coating amount 3%.

[0045] The fabric was tested and found to have a surface density of 85 g / m², a thickness of 170 μm, a tensile strength at break of 1200 N / 25 mm, a strength retention rate of 82% at 200℃ for 100 h, a surface contact angle of 58°, and a resin wetting rate of 90%.

[0046] Example 3: Polyimide / carbon fiber blended ultrathin spreadable fabric (mass ratio 8:2) (1700D) (1) Fiber broadening treatment: Polyimide precursor fiber: spreading temperature 120℃, tension 10N, spreading rate 1.5m / min. The spread fiber is then treated with a 1.5wt% polyamic acid solution containing carboxyl groups (synthetic dianhydride monomers: 3,3',4,4'-biphenyltetracarboxylic dianhydride BPDA + pyromellitic dianhydride trimellitic anhydride ester; diamine monomer: p-phenylenediamine PDA; solvent: N,N-dimethylformamide DMF) to obtain spread polyimide fibers with a width of 5mm and a thickness of 100μm, and a cross-sectional aspect ratio of 50:1. Carbon fiber precursor: single filament diameter 10μm, tensile strength 3.5GPa, thermal conductivity 12W / (m K) was used as an airflow stretching machine with a stretching temperature of 100℃, a tension of 8N, and a stretching rate of 1m / min. The stretched fibers were then treated with a 2wt% polyamic acid solution containing hydroxyl groups (dianhydride monomers used in synthesis: diphenyl ether tetracarboxylic dianhydride ODPA; diamine monomers: m-phenylenediamine MPD + 2,2-bis(4-aminophenyl)-1,3-propanediol; solvent: N-methylpyrrolidone NMP) to obtain stretched carbon fibers with a width of 5mm and a thickness of 99.8μm, with a thickness deviation of 0.2% from that of polyimide fibers.

[0047] (2) Fiber pre-type: Expanding polyimide fibers: pre-shaped at 350℃ for 10 min, with a tension of 2.5N, resulting in a heat shrinkage rate of 0.5%; Stretched carbon fiber: pre-shaped at 350℃ for 15 minutes, with 2N tension applied, resulting in a heat shrinkage rate of 0.4%.

[0048] (3) Machine-woven: satin weave, warp ratio 4:1, weft ratio 3:1, weaving speed 30 revolutions / minute.

[0049] (4) Finishing: Coating with 4% KH560 coupling agent + 1.5% nano Al2O3, coating amount 4%.

[0050] The fabric was tested and found to have a surface density of 80 g / m², a thickness of 180 μm, a tensile strength at break of 1300 N / 25 mm, a surface contact angle of 52°, and a resin wetting rate of 95%.

[0051] Example 4: High areal density pure woven ultrathin spread polyimide fabric (2000D) (1) Polyimide precursor fiber stretching treatment: Polyimide precursor fiber with a single filament diameter of 18μm and a breaking strength of 3.2GPa was selected. The stretching temperature was 150℃, the tension was 20N, and the stretching rate was 4m / min. The stretched fiber was treated with 1.5wt% polyamic acid solution containing epoxy groups (dianhydride monomer used for synthesis: pyromellitic dianhydride PMDA; diamine monomer: 4,4'-diaminodiphenyl ether ODA + 4,4'-diaminodiphenyl ether glycidyl ether; solvent: N,N-dimethylacetamide DMAc) to obtain stretched polyimide fiber with a width of 3mm and a thickness of 120μm and a cross-sectional length-to-width ratio of 27:1.

[0052] (2) Fiber pre-forming: Pre-forming at 300℃ for 15 min, applying 3N tension, heat shrinkage rate 0.9%.

[0053] (3) Machine-woven: plain weave, warp tension 20N, weaving speed 40 rpm.

[0054] (4) Post-treatment: plasma treatment, power 200W, treatment time 10min.

[0055] The fabric was tested and found to have a surface density of 200 g / m², a thickness of 200 μm, a tensile strength at break of 2500 N / 25 mm, a surface contact angle of 48°, and a resin wetting rate of 93%.

[0056] Example 5: Polyimide / glass fiber blended ultrathin spreadable fabric (mass ratio 6:4) (500D) (1) Fiber broadening treatment: Polyimide precursor fibers: spreading temperature 90℃, tension 7N, spreading rate 0.7m / min. The spread fibers are then treated with a 1.5wt% polyamic acid solution containing epoxy groups (synthetic dianhydride monomer: pyromellitic dianhydride PMDA; diamine monomer: 4,4'-diaminodiphenyl ether ODA + 4,4'-diaminodiphenyl ether glycidyl ether; solvent: N,N-dimethylacetamide DMAc) to obtain spread polyimide fibers with a width of 2mm and a thickness of 53μm, with a cross-sectional aspect ratio of 37:1. Glass fiber precursor: monofilament diameter 14μm, tensile strength 2.8GPa, using an airflow spreading machine, spreading temperature 70℃, tension 5N, spreading rate 0.6m / min, the spread fiber is sprayed with 4wt% water-based epoxy resin to obtain spread glass fiber with a width of 2mm and a thickness of 52.8μm, with a thickness deviation of 0.38% from polyimide fiber.

[0057] (2) Fiber pre-type: Expanding polyimide fibers: pre-shaped at 280℃ for 7 minutes, with 2N tension applied, resulting in a heat shrinkage rate of 0.6%; Fiberglass stretching: pre-shape at 120℃ for 5 minutes, apply 1.8N tension, heat shrinkage rate 0.5%.

[0058] (3) Machine-woven: Twill weave, warp ratio 2:1, weft ratio 2:1, weaving speed 20 revolutions / minute.

[0059] (4) Finishing: Coat with 2% KH550 coupling agent, coating amount 2%.

[0060] The fabric was tested and found to have a surface density of 60 g / m², a thickness of 90 μm, a tensile strength at break of 900 N / 25 mm, a strength retention rate of 100% at 200℃ for 100 h, a surface contact angle of 59°, and a resin wetting rate of 88%.

[0061] Comparative Example 1: Polyimide fabric (1000D) without stretching treatment Using the same polyimide precursor yarn as in Example 1, without any stretching treatment, the fabric was prepared directly according to the weaving parameters and finishing process of Example 1.

[0062] The fabric was tested and found to have a surface density of 200 g / m², a thickness of 290 μm, a tensile strength at break of 2300 N / 25 mm, a surface contact angle of 75°, and a resin wetting rate of 65%. Compared with Example 1, the unstretched fabric has a significantly increased thickness and poor resin wetting, which fails to meet the requirements for ultra-thin, high-performance applications.

[0063] Comparative Example 2: No pre-design processing performed (1500D) Except for omitting the fiber pre-forming process in step (2), the remaining steps are exactly the same as in Example 2.

[0064] Tests showed that the fabric had a surface density of 86 g / m², a thickness of 200 μm, a tensile strength at break of 1200 N / 25 mm, and that the fibers exhibited rebound during weaving, the fabric surface wrinkled, and the resin impregnation rate was 78%. Pre-setting treatment is a crucial step in fixing the fiber spread shape; omitting it leads to a significant decrease in the fabric's appearance quality.

[0065] Comparative Example 3: Plasma processing parameters exceeded the limit (power 300W) (1700D) Except for the plasma processing power of 300W (higher than the upper limit of 200W) in step (4), the other steps are exactly the same as in Example 3.

[0066] Tests showed the fabric had a surface density of 80 g / m², a thickness of 185 μm, a tensile strength at break of 1080 N / 25 mm, and a surface contact angle of 45°. However, the fabric surface fibers showed damage, resulting in a 16.7% decrease in tensile strength and a reduction in high-temperature strength retention to 72%. Excessive plasma treatment power can damage the fiber structure, leading to a deterioration in mechanical properties.

[0067] This invention successfully prepared ultra-thin, high-strength, high-temperature stable, and resin-wetting polyimide fabrics by precisely controlling the spreading process, pre-forming parameters, and finishing techniques of polyimide fibers. Comparison results between the examples and comparative examples show that spreading temperature, pre-forming treatment, and surface treatment parameters have a significant impact on fabric performance. Only by strictly controlling each process parameter within the range defined by this invention can products with excellent performance be obtained. This invention fills the technological gap in polyimide spread fabrics and can provide a new type of high-performance material for high-end fields such as aerospace, high-temperature protection, and new energy vehicles, possessing broad application prospects and significant industrial value.

[0068] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An ultra-thin broadloom polyimide fabric, characterized in that, The fabric is woven from warp and weft fibers, with an areal density of 20-200 g / m² and a thickness of 20-200 μm. The warp and / or weft fibers include expanded polyimide fibers, which are obtained by hot-rolling expanded polyimide filaments. The expanded polyimide fibers have a flat cross-section with an aspect ratio of 10:1-100:1, a width of 0.5-10 mm, and a thickness of 20-150 μm.

2. The ultra-thin, widened polyimide fabric according to claim 1, characterized in that, The fabric surface is treated with plasma at a power of 50-200W for 1-10 minutes, resulting in a surface contact angle of ≤60°.

3. The ultra-thin, widened polyimide fabric according to claim 1, characterized in that, The fabric is a mixed-woven, expanded fabric, which is made of expanded polyimide fibers and other expanded fibers. The other expanded fibers are selected from at least one of aramid expanded fibers, carbon fiber expanded fibers, glass fiber expanded fibers, aramid triterpenoid expanded fibers, and PBO expanded fibers; and / or By weight percentage, expanded polyimide fibers account for 50%-90% of the blended fibers, while other expanded fibers account for 10%-50%.

4. The ultrathin, widened polyimide fabric according to claim 1 or 3, characterized in that, The expanded polyimide fibers and other expanded fibers are treated with a setting agent, which is a polyamic acid solution containing active groups; the active groups are selected from at least one of hydroxyl, amino, carboxyl, and epoxy groups; the solid content of the polyamic acid solution is 1%-10wt%, and the solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

5. The ultra-thin, widened polyimide fabric according to claim 1, characterized in that, The stretched polyimide fiber has a tensile strength ≥2.5 GPa, a strength retention rate ≥75% after 100 h at 200℃, and a resin wetting rate ≥80%; and / or The aspect ratio of the cross section of the stretched polyimide fiber is 20:1 to 80:

1.

6. A method for preparing the ultrathin, widened polyimide fabric according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Polyimide precursor fiber stretching treatment: The polyimide precursor fiber is placed in a stretching device and stretched under the conditions of 80-150℃ and tension of 5-20N. The stretching rate is controlled at 0.5-4m / min. After stretching, a setting agent is sprayed or impregnated to form a stretched polyimide fiber with a width of 0.5-10mm and a thickness of 20-150μm. If it is a blended fabric, other fibers are simultaneously subjected to differentiated stretching treatment to control the thickness deviation of different fibers to ≤7%. (2) Fiber pre-forming: The expanded fibers are pre-formed by hot air. The pre-forming temperature of polyimide expanded fibers is 70-350℃, the time is 5-15min, and the tension is 1-3N; the pre-forming temperature of other expanded fibers is 80-350℃, the time is 5-20min, and the tension is 1-2.5N. (3) Weaving: The pre-shaped fibers are installed on the warp yarn release frame system of the loom, and the weaving parameters are set: the weaving speed is 10-100 revolutions / minute, and plain weave, twill weave or satin weave is used to weave to obtain the initial product of the fabric; (4) Finishing: The initial fabric is subjected to surface treatment, including plasma treatment or coupling agent coating, to obtain ultra-thin expanded polyimide fabric.

7. The preparation method according to claim 6, characterized in that, In step (1), the stretching equipment is a pressure roller-hot air co-stretching device or an airflow stretching machine; the polyimide precursor fiber has a single filament diameter of 10-20 μm, a tensile strength ≥3.0 GPa, and a glass transition temperature ≥280℃; and / or The setting agent is selected from at least one of polyurethane setting agents, epoxy resin setting agents, polyamic acid setting agents, polyimide setting agents, and polyetheretherketone setting agents.

8. The preparation method according to claim 6, characterized in that, In step (4), the coupling agent is selected from at least one of KH550 and KH560, and the coating amount is 2%-5%; if the coupling agent and nanoparticles are used for composite coating, the nanoparticles are selected from at least one of nano SiO2 and nano Al2O3, and the addition amount is 1%-2%.

9. The application of the ultrathin expanded polyimide fabric according to any one of claims 1-5 or the ultrathin expanded polyimide fabric prepared by the preparation method according to any one of claims 6-8 in the fields of aerospace, high temperature protection, new energy vehicles or high-end composite materials.

10. A composite material, characterized in that, The product comprises a reinforcing agent and a matrix resin, wherein the reinforcing agent is an ultrathin, broadened polyimide fabric as described in any one of claims 1-5 or an ultrathin, broadened polyimide fabric prepared by the preparation method as described in any one of claims 6-8, and the matrix resin is at least one selected from epoxy resins, polyurethane resins, polyimide resins, bismaleimide resins, and polyetheretherketone resins.

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