A multilayer fiber-reinforced composite material and a method for producing the same

Abstract

The application provides a multilayer fiber reinforced composite material and a preparation method thereof. The multilayer fiber reinforced composite material is prepared by hot pressing and curing a prepreg stack, and the prepreg stack comprises: an alumina fiber plain cloth prepreg located at the center, and high-modulus poly-p-phenylene benzobisoxazole fiber unidirectional cloth prepregs, alumina fiber unidirectional cloth prepregs and high-strength glass fiber plain cloth prepregs symmetrically distributed on both sides of the alumina fiber plain cloth prepreg from inside to outside. The alumina fiber plain cloth prepreg, the high-modulus poly-p-phenylene benzobisoxazole fiber unidirectional cloth prepreg, the alumina fiber unidirectional cloth prepreg and the high-strength glass fiber plain cloth prepreg are all combined by corresponding fiber cloth and epoxy resin adhesive film through hot pressing. The multilayer fiber reinforced composite material is super-thin, has strong impact resistance and puncture resistance, and is environmentally friendly in process.

Description

Technical Field

[0001] This invention relates to the field of fiber-reinforced composite materials technology, and in particular to a multilayer fiber-reinforced composite material and its preparation method. Background Technology

[0002] In the field of consumer electronics devices such as mobile phones, tablets, laptops, and foldable display terminals, products are rapidly developing towards thinner, lighter, more portable, and higher-performance designs. This places stringent requirements on structural components, demanding thinner thickness, lighter weight, and higher impact and puncture resistance. In particular, external structural components such as the back cover of a mobile phone and the support structure for foldable screens, as well as internal support components such as the battery compartment bracket and screen backing, not only need to be thinner to improve the overall texture and grip, but also need to effectively protect critical components such as the internal battery, motherboard, and screen under complex scenarios such as drops, compression, and impacts from sharp objects. This places extremely high demands on the matching of thinness and toughness in materials.

[0003] Currently, traditional structural materials generally have significant shortcomings: glass and ceramic materials are brittle, have poor impact resistance, and are prone to breakage; metal materials experience a significant strength reduction as their thickness decreases, and also suffer from signal shielding issues, which contradicts the development trend of 5G communication and wireless technology. These materials are no longer adequate for the comprehensive requirements of terminal devices for ultra-thinness, high strength, and high impact resistance.

[0004] Glass fiber reinforced composite materials, represented by epoxy glass cloth laminates, possess specific strength and specific modulus comparable to metals, while also offering advantages such as light weight and no signal shielding. In recent years, they have become a preferred solution for structural components of consumer electronic devices such as mobile phone back covers. Current manufacturing processes mostly involve solution impregnation: glass fiber cloth is impregnated in a resin solution, heat-treated to bring the resin to a semi-cured state to create a prepreg, which is then cut, laminated, and hot-pressed to form sheet products.

[0005] However, with the rise of foldable screen devices, the shortcomings of traditional single glass fiber reinforced composite materials and solution impregnation methods have become increasingly apparent: on the one hand, as the thickness of existing glass fiber reinforced composite materials decreases, their puncture resistance and impact resistance drop sharply, making it difficult to effectively protect critical internal components under ultra-thin specifications; on the other hand, traditional solution impregnation methods have problems such as low precision in controlling the adhesive content, high product porosity, and environmental pollution from solvent evaporation, resulting in poor product quality consistency and unstable mechanical properties, further limiting their application in the field of consumer electronics devices.

[0006] In summary, there is an urgent need to develop an ultrathin composite material that combines excellent impact and puncture resistance, while optimizing the preparation process to address the many shortcomings of existing technologies. Summary of the Invention

[0007] In view of this, the present invention provides a multilayer fiber reinforced composite material and a method for preparing the same, aiming to solve the technical problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A multilayer fiber composite material is formed by hot-pressing and curing a prepreg laminate, wherein the prepreg laminate comprises: The alumina fiber plain weave prepreg is located at the center, and the high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg, alumina fiber unidirectional prepreg and high strength glass fiber plain weave prepreg are symmetrically distributed on both sides of the alumina fiber plain weave prepreg from the inside to the outside. The alumina fiber plain weave prepreg, the high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg, the alumina fiber unidirectional prepreg, and the high strength glass fiber plain weave prepreg are all formed by hot pressing the corresponding fiber cloth with an epoxy resin film.

[0009] Optionally, the epoxy resin system accounts for 45% of the content in the alumina fiber plain weave prepreg; The epoxy resin system accounts for 38% of the content of the high-modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric prepreg. The epoxy resin system accounts for 40% of the content of the alumina fiber unidirectional fabric prepreg. The epoxy resin system accounts for 45% of the content of the high-strength glass fiber plain weave prepreg.

[0010] Optionally, the epoxy resin system comprises 90-95 parts epoxy resin and 5-10 parts dicyandiamide by weight.

[0011] Optionally, the alumina fiber plain weave prepreg comprises alumina fiber plain weave fabric with a thickness of 0.08-0.12 mm and a unit area mass of 85-115 g / m². The high-modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric prepreg comprises a high-modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric with a thickness of 0.018-0.022 mm and a unit area mass of 19-21 g / m². The alumina fiber unidirectional fabric prepreg comprises alumina fiber unidirectional fabric with a thickness of 0.04-0.06 mm and a unit area mass of 23-27 g / m². The high-strength glass fiber plain weave prepreg comprises high-strength glass fiber plain weave fabric with a thickness of 0.023-0.033 mm and a unit area mass of 28-32 g / m².

[0012] Optionally, the fiber orientations of the high-modulus poly(p-phenylene benzodioxazole) unidirectional prepreg located on both sides of the alumina fiber plain weave prepreg are 0° and 90°, respectively. The fiber directions of the alumina fiber unidirectional prepreg located on both sides of the alumina fiber plain weave prepreg are 0° and 90°, respectively.

[0013] Furthermore, to achieve the above objectives, the present invention also provides a method for preparing a multilayer fiber composite material, wherein the multilayer fiber composite material is any of the multilayer fiber composite materials described in the preceding claims. The method includes the following steps: S1. Film preparation: Based on the unit area mass of each fiber cloth and the preset epoxy resin system content, prepare epoxy resin films corresponding to each fiber cloth. S2. Prepreg preparation: The epoxy resin films obtained in step S1 are matched with the corresponding fiber cloths one by one, and composite impregnation is carried out by hot pressing to obtain alumina fiber plain weave prepreg, high modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric prepreg, alumina fiber unidirectional fabric prepreg, and high strength glass fiber plain weave prepreg. S3. Lamination: Using alumina fiber plain weave prepreg as the central layer, high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg, alumina fiber unidirectional prepreg, and high-strength glass fiber plain weave prepreg are symmetrically stacked on both sides from the inside to the outside to obtain a prepreg laminate. S4. Curing and molding: The prepreg laminate is placed in a mold of a hot press, the mold is closed for pre-curing, and then pressure is applied and the temperature is raised for curing. S5. Cooling and demolding: After curing, cool and demold to obtain the multilayer fiber composite material.

[0014] Optionally, step S4 includes: The hot press mold is heated to 120°C; The prepreg laminate is placed into a heated hot press mold and pre-cured for 600-700 seconds. Apply pressure of 0.3-1.0 MPa and heat to 140-160℃; Insulate and cure for 25-35 minutes.

[0015] Optionally, the heating rate to 140-160°C is 3°C / min.

[0016] Optionally, step S1 includes the following steps: S11. Calculate the target areal density and thickness of the corresponding epoxy resin film based on the unit area mass of each fiber cloth and the preset epoxy resin system content. S12. Adjust the parameters of the glue applicator, and set the melting temperature to 75℃ and the application temperature to 80℃; S13. The epoxy resin system is heated and melted, and then coated by the coating machine to prepare an epoxy resin film with the target areal density and thickness.

[0017] Optionally, after step S3 and before step S4, the method further includes: applying a PET release film to the upper and lower surfaces of the prepreg laminate. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings. In the following description, the same reference numerals denote the same parts.

[0020] Figure 1 This is a schematic diagram of a prepreg laminate structure of a multilayer fiber-reinforced composite material described in an embodiment of this application; Figure 2 This is a schematic flowchart illustrating a method for preparing a multilayer fiber composite material according to an embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0022] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0024] Example 1: This invention provides a multilayer fiber composite material suitable for the preparation of structural components in various fields, such as consumer electronics and precision instruments.

[0025] This multilayer fiber composite material is integrally formed by hot-pressing and curing a prepreg laminate. The prepreg is an intermediate product used in the manufacture of composite materials, made of filaments or fabrics impregnated with a thermosetting or thermoplastic resin matrix. In this embodiment, the prepreg is specifically made of fiber cloth impregnated with a thermosetting epoxy resin system. Hot-pressing and curing refers to the process of applying pressure while heating to melt and flow the resin matrix, promoting tight adhesion between layers and initiating a resin cross-linking reaction, thereby forming an integral structure. This invention does not limit the specific implementation method of hot-pressing and curing. Various hot-pressing molding processes can be adopted according to the product structure characteristics and production needs, such as flatbed hot-pressing molding, compression molding, or continuous hot-pressing molding using a flatbed vulcanizing machine. Flatbed hot-pressing molding using a flatbed vulcanizing machine is suitable for sheet-like products such as mobile phone back covers, compression molding is suitable for complex irregular structures, and continuous hot pressing is suitable for batch continuous production. This embodiment addresses the application characteristics of the multilayer fiber composite material, which is mainly used for flat structural parts. Specifically, it uses a flat vulcanizing machine for hot pressing and curing. This method applies temperature and pressure evenly to the prepreg laminate by heating the upper and lower plates, which can achieve synchronous heating of the upper and lower mold surfaces, ensuring that each layer of the prepreg laminate is heated evenly and avoiding warping and deformation.

[0026] refer to Figure 1 , Figure 1 This is a schematic diagram of the prepreg laminate structure of the multilayer fiber composite material provided in this embodiment. Figure 1 As shown, the prepreg laminate adopts a symmetrical layered structure design, including an alumina fiber plain weave prepreg 1 located at the center, and high modulus poly(p-phenylenebenzobisoxazole) (HM-PBO) unidirectional fiber prepreg 2, alumina fiber unidirectional fiber prepreg 3, and high strength (S) glass fiber plain weave prepreg 4 symmetrically distributed from the inside to the outside on both sides of the alumina fiber plain weave prepreg. The aforementioned "from the inside to the outside" specifically refers to the arrangement from the layer closest to the center of the laminate to the layer furthest away from the center.

[0027] The alumina fiber plain weave prepreg is made by hot-pressing alumina fiber plain weave fabric and epoxy resin film; the HM-PBO fiber unidirectional fabric prepreg is made by hot-pressing HM-PBO fiber unidirectional fabric and epoxy resin film; the alumina fiber unidirectional fabric prepreg is made by hot-pressing alumina fiber unidirectional fabric and epoxy resin film; and the S glass fiber plain weave prepreg is made by hot-pressing S glass fiber plain weave fabric and epoxy resin film.

[0028] The only difference between plain weave fabric and unidirectional fabric is that plain weave fabric has fibers interwoven in multiple directions to form an interwoven mesh structure; unidirectional fabric has no interwoven structure, and the fibers are arranged in parallel in a single direction.

[0029] The epoxy resin film mentioned above is a sheet-like thin film material made of epoxy resin system. It serves as an intermediate carrier for bonding various fiber cloths with the epoxy resin system, unlike the liquid adhesive of the traditional solution impregnation method.

[0030] The hot pressing method described above can be selected from processes such as hot roller pressing composite, flat plate hot pressing composite, and vacuum hot pressing composite. In this embodiment, hot roller pressing composite is preferred. This method applies linear pressure to the fiber cloth and epoxy resin film through a continuously rotating hot roller, which allows the epoxy resin to quickly and uniformly impregnate the fiber cloth in a molten state. It has the advantages of good impregnation effect and high production efficiency.

[0031] Unlike the division of labor in hot pressing and curing of prepreg laminates described above, hot rolling is mainly used to achieve full impregnation and bonding of each fiber cloth with the epoxy resin film to produce each single layer of prepreg; while hot pressing and curing is used to integrally mold the multi-layer prepregs into composite material boards.

[0032] The beneficial effects of this embodiment are: 1. This embodiment employs a multi-layer fiber composite structure, formed by hot-pressing and curing a prepreg laminate. The central alumina fiber plain weave prepreg is formed by hot-pressing alumina fiber plain weave fabric and an epoxy resin film. The alumina fiber plain weave fabric has bidirectional interwoven fibers with uniform mechanical properties in all directions, providing stable core support for the entire composite material. The HM-PBO fiber unidirectional fabric prepregs located on both sides of the central core layer are formed by hot-pressing HM-PBO fiber unidirectional fabric and an epoxy resin film. The unidirectional fabric fibers are interwoven along the direction of the fiber. One-way directional arrangement maximizes the high impact resistance of that direction, enhancing the impact and puncture resistance of the composite material. The alumina fiber unidirectional prepreg, located outside the HM-PBO fiber unidirectional prepreg, is formed by hot-pressing alumina fiber unidirectional fabric with an epoxy resin film, further strengthening the overall material strength. The outermost S-glass fiber plain weave prepreg, also formed by hot-pressing S-glass fiber plain weave with an epoxy resin film, leverages the directional stability of the plain weave to balance lightweight design and signal shielding characteristics. The synergistic effect of each prepreg layer avoids the brittleness and fragility of glass and ceramic materials, and solves the strength attenuation and signal shielding defects associated with thinning metal materials, adapting to the trends of 5G communication and wireless technology. Meanwhile, this embodiment adopts a symmetrical multi-layer stacked design, which can offset the internal stress of hot pressing and ensure the stability of the ultra-thin structure. The high impact resistance of HM-PBO fiber combined with the strength advantage of alumina fiber, through hot roll pressing composite, realizes the composite impregnation of each fiber cloth with epoxy resin film, improves the interface bonding strength, and makes up for the shortcomings of the traditional single glass fiber material after the thickness is reduced, which has a sharp decline in impact resistance and puncture resistance.

[0033] 2. This embodiment solves the defects of the traditional solution impregnation method. Instead of soaking the fiber cloth in the adhesive solution, the epoxy resin film is directly laminated with each fiber cloth. The adhesive content of the epoxy resin film can be controlled, avoiding the problems of uneven adhesive concentration and difficulty in controlling the content of the adhesive solution in the traditional solution impregnation method. The epoxy resin film is impregnated and bonded to each fiber cloth by hot roller pressing, which can make the epoxy resin film melt evenly and fully wet the fiber cloth, reduce the porosity of the product, and solve the defect of high porosity in the traditional process. At the same time, the use of epoxy resin film eliminates the need for solvents, avoiding the environmental pollution caused by solvent evaporation from the source, making it more environmentally friendly.

[0034] Based on Example 1, in the multilayer fiber composite material provided in this application, the epoxy resin system content in the alumina fiber plain weave prepreg is 45%; the epoxy resin system content in the high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg is 38%; the epoxy resin system content in the alumina fiber unidirectional prepreg is 40%; and the epoxy resin system content in the high strength glass fiber plain weave prepreg is 45%.

[0035] Both alumina fiber plain weave fabric and S-glass fiber plain weave fabric use 45% epoxy resin content. This is because the warp and weft interlacing structure of plain weave fabric has many fiber cross gaps. This content ensures that the epoxy resin system fully fills the fiber gaps, achieving a tight coating between the fiber and the epoxy resin system, thereby improving the interfacial bonding strength between the fiber and the epoxy resin system. At the same time, this ratio can avoid the increase in porosity caused by insufficient epoxy resin system or the increase in weight caused by excessive epoxy resin system, ensuring structural density while taking into account the requirements of lightweight.

[0036] HM-PBO fiber unidirectional fabric uses a relatively low epoxy resin content of 38%. On the one hand, because its fibers are oriented in a single direction with uniform spacing, the lower epoxy resin content helps to fully utilize the directional reinforcement effect of the unidirectional fibers and avoids the mechanical property degradation caused by the redundancy of the epoxy resin system. On the other hand, HM-PBO fiber has a smooth surface and strong chemical inertness. This content can ensure that the epoxy resin system fully wets the fiber bundle, while avoiding the increase in curing internal stress and material brittleness caused by excessive epoxy resin content, thus improving the impact and puncture resistance of the composite material.

[0037] The alumina fiber unidirectional fabric has a content of 40%, which is between that of plain weave fabric and HM-PBO unidirectional fabric. It can achieve a tight bond with adjacent layers through a sufficient epoxy resin system, and can also enhance the overall structural support of the composite material by relying on the high strength characteristics of alumina fiber.

[0038] Based on the foregoing embodiments, the multilayer fiber composite material provided in this application, by weight, comprises 90-95 parts epoxy resin and 5-10 parts dicyandiamide. Epoxy resin, as the core component, provides the composite material with an interfacial bonding base, environmental stability, and mechanical load-bearing capacity. Dicyandiamide, as a latent curing agent, is stable when mixed with epoxy resin at room temperature, facilitating the storage of the prepreg. The 5-10 parts dicyandiamide, in synergy with epoxy resin, slowly release active groups during hot rolling and subsequent hot pressing curing, initiating a cross-linking reaction to achieve complete curing. This avoids problems such as excessively rapid curing leading to internal stress accumulation, increased porosity, or incomplete curing resulting in insufficient strength and toughness. This formulation system balances curing efficiency and quality, enhancing the composite material's impact and puncture resistance.

[0039] Based on Example 1, the multilayer fiber composite material provided in this application includes: alumina fiber plain weave prepreg with a thickness of 0.08-0.12 mm and a unit area mass of 85-115 g / m²; high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg with a thickness of 0.018-0.022 mm and a unit area mass of 19-21 g / m²; alumina fiber unidirectional prepreg with a thickness of 0.04-0.06 mm and a unit area mass of 23-27 g / m²; and high-strength glass fiber plain weave prepreg with a thickness of 0.023-0.033 mm and a unit area mass of 28-32 g / m². By designing the thickness and unit area mass of each fiber cloth, the full function of each layer of prepreg is ensured, achieving a synergy of ultrathinness, lightweight and toughness in composite materials.

[0040] Based on Example 1, in the multilayer fiber composite material provided in this application, the prepregs and fiber directions in the prepreg laminate are arranged in the following order: with alumina fiber plain weave prepreg as the central layer, one side of it is arranged from the inside to the outside as HM-PBO fiber unidirectional prepreg with fiber direction of 0° and alumina fiber unidirectional prepreg with fiber direction of 90°; the other side of it is arranged from the inside to the outside as HM-PBO fiber unidirectional prepreg with fiber direction of 90° and alumina fiber unidirectional prepreg with fiber direction of 0°, and the outermost layer is high-strength glass fiber plain weave prepreg.

[0041] This embodiment adopts a cross-arrangement structure of 0° and 90° fiber directions, which can improve the impact resistance, tensile strength and puncture resistance of the composite material, avoid the local mechanical weakness caused by unidirectional fiber arrangement, give full play to the high impact resistance of HM-PBO fiber and the high strength advantage of alumina fiber, thereby enhancing the overall balance of the mechanical properties of the composite material.

[0042] Example 2: refer to Figure 2 The present invention also provides a method for preparing a multilayer fiber composite material, wherein the multilayer fiber composite material is the multilayer fiber composite material in the above embodiments, and the method specifically includes the following steps: S1. Film preparation: Based on the unit area mass of each fiber cloth and the preset epoxy resin system content, prepare epoxy resin films corresponding to each fiber cloth.

[0043] The preset epoxy resin system content refers to the percentage of epoxy resin system in the total mass of each prepreg, which is a pre-determined process ratio based on different fiber characteristics and target performance requirements. Because different fiber fabrics have different unit area mass, fiber structure (plain weave / unidirectional), and surface properties (e.g., HM-PBO fiber has strong chemical inertness), their requirements for epoxy resin system and wetting requirements vary. Therefore, it is necessary to prepare epoxy resin films corresponding to each fiber fabric. In this embodiment, the epoxy resin system includes 90-95 parts by weight of epoxy resin and 5-10 parts by weight of dicyandiamide.

[0044] Preferably, step S1 includes the following steps: S11. Calculate the target areal density and thickness of the corresponding epoxy resin film based on the unit area mass of each fiber cloth and the preset epoxy resin system content.

[0045] First, determine the unit area mass of the selected fiber fabrics: 85-115 g / m² for alumina fiber plain weave fabric, 19-21 g / m² for HM-PBO fiber unidirectional fabric, and 23-27 g / m² for alumina fiber unidirectional fabric. Also, determine the pre-defined epoxy resin content in each prepreg: 45% in alumina fiber plain weave fabric and high-strength glass fiber plain weave fabric prepregs, 38% in HM-PBO fiber unidirectional fabric prepregs, and 40% in alumina fiber unidirectional fabric prepregs. Then, calculate the target areal density and thickness of the corresponding epoxy resin film using the formula. Target film surface density = (mass per unit area of ​​fiber cloth × preset epoxy resin content) ÷ (1 - preset epoxy resin content). Target film thickness = target film surface density ÷ density of epoxy resin system.

[0046] Meanwhile, the calculated values ​​can be fine-tuned based on the structural characteristics of each fiber fabric to ensure that the epoxy resin film parameters match the impregnation requirements of the fiber fabric. For example, for plain weave fabrics with many warp and weft interlacing gaps, the film thickness can be appropriately increased based on the calculated values, such as by 5%-10%, to ensure that the epoxy resin can fully fill the fiber gaps and avoid the formation of pores.

[0047] Step S11 converts the preset epoxy resin system content into the areal density and thickness parameters of the film, ensuring that an epoxy resin film that precisely matches each fiber cloth can be prepared in the subsequent coating process.

[0048] S12. Adjust the parameters of the glue applicator, and set the melting temperature to 75℃ and the coating temperature to 80℃.

[0049] Based on the target areal density and thickness of the epoxy resin film calculated and fine-tuned in step S11, the parameters of the coating machine are set to ensure that the actual areal density and thickness of the epoxy resin film meet the design requirements. Simultaneously, considering the melting characteristics of the epoxy resin system, the melt temperature is set to 75℃ and the coating temperature to 80℃. This temperature parameter design is based on the following considerations: a melt temperature of 75℃ allows the epoxy resin system to fully melt and maintain a suitable viscosity, which is beneficial for the uniform flow of the epoxy resin and avoids premature reaction of the dicyandiamide curing agent due to excessively high temperatures, thus ensuring the storage stability and subsequent processing performance of the epoxy resin film; a coating temperature of 80℃ effectively prevents the epoxy resin from solidifying due to cooling during coating, ensuring the continuity of coating and the uniformity of film thickness, while reducing defects such as bubbles and insufficient adhesive.

[0050] S13. The epoxy resin system is heated and melted, and then coated by the coating machine to prepare an epoxy resin film with the target areal density and thickness.

[0051] Under the process parameters set in S12, this step performs the actual epoxy resin coating operation. First, the prepared epoxy resin system is added to the coating machine and heated to 75°C to completely melt it into a uniform fluid. Then, the molten resin is fed to the coating head, where it is evenly coated onto the release paper or release film to form a continuous film of consistent thickness. During the coating process, the film thickness is monitored in real time using an online thickness gauge and compared with the target thickness calculated in S11. If necessary, the coating parameters are fine-tuned to ensure accuracy. The resulting epoxy resin film with the target areal density and thickness is cooled and then wound up for later use.

[0052] Step S13 prepares an epoxy resin film that matches each fiber cloth, providing an intermediate material for subsequent composite preparation of prepreg with the fiber cloth.

[0053] In this embodiment, based on the unit area mass of each fiber cloth and the preset epoxy resin system content, an epoxy resin film corresponding to each fiber cloth is prepared. During subsequent hot roll lamination, it can be directly used as needed without on-site mixing of adhesive and control of coating amount, effectively reducing parameter fluctuations in the production process and providing a stable and controllable supply of epoxy resin system for prepreg preparation. This avoids the problem of increased porosity caused by insufficient resin due to universal adhesive film, and also prevents excessive resin from diluting the mechanical properties of the composite material and increasing the overall weight.

[0054] S2. Prepreg preparation: Each epoxy resin film obtained in step S1 is matched with the corresponding fiber cloth, and composite impregnation is carried out by hot pressing to obtain alumina fiber plain weave prepreg, high modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric prepreg, alumina fiber unidirectional fabric prepreg, and high strength glass fiber plain weave prepreg.

[0055] The epoxy resin film obtained in step S1 is laminated with the corresponding fiber cloth, and the epoxy resin film is melted and fully impregnated with the fiber bundle through a hot-pressing composite process, thereby obtaining each prepreg with a preset epoxy resin system content.

[0056] Specifically, the epoxy resin film prepared in step S1 is peeled off from the release film or release paper and then laminated with the corresponding fiber fabrics—alumina fiber plain weave fabric, HM-PBO fiber unidirectional fabric, alumina fiber unidirectional fabric, and S glass fiber plain weave fabric—one by one. The lamination method can be selected according to the structure of the fiber fabric: for plain weave fabrics with large unit area mass and dense structure, a double-sided lamination method can be used, that is, a layer of film is covered on the top and bottom to ensure that the epoxy resin is simultaneously impregnated from both sides; for unidirectional fabrics with uniform fiber arrangement, a single-sided lamination method can be used, relying on hot pressing pressure to make the resin penetrate unidirectionally along the thickness direction, which can meet the impregnation requirements and avoid excessive resin.

[0057] After lamination, the epoxy resin film and fiber cloth assembly are fed into a hot roller press or flat plate hot press for composite impregnation. The hot pressing temperature is controlled at 80-100℃ (preferably 90℃) to allow the epoxy resin film to remelt and form a low-viscosity fluid. Under external pressure, the molten epoxy resin system fully penetrates into the fiber bundle and fills the fiber gaps to achieve uniform wetting.

[0058] Through the above process, alumina fiber plain weave prepreg, HM-PBO fiber unidirectional fabric prepreg, alumina fiber unidirectional fabric prepreg, and S glass fiber plain weave prepreg were respectively prepared. In each of the prepared prepregs, the epoxy resin system is uniformly distributed inside and on the surface of the fiber bundles. The epoxy resin system is in a semi-cured (B-stage) state, which has good lay-up operability and storage stability, and requires low-temperature storage.

[0059] Step S2 achieves full impregnation and composite of epoxy resin film and corresponding fiber cloth, producing prepregs with the same content as the preset epoxy resin system, providing intermediate products for subsequent multilayer composite material lamination and hot-press curing.

[0060] S3. Lamination: Using alumina fiber plain weave prepreg as the central layer, high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg, alumina fiber unidirectional prepreg, and high-strength glass fiber plain weave prepreg are symmetrically stacked on both sides from the inside to the outside to obtain a prepreg laminate.

[0061] Alumina fiber plain weave prepreg possesses high strength, high modulus, and excellent heat resistance. Its plain weave structure provides reinforcement in both warp and weft directions. Placing it as the central layer provides a reference for symmetrical laying on both sides and ensures uniform shrinkage during hot-pressing curing of the laminate, preventing warping and deformation. HM-PBO fiber unidirectional prepreg possesses ultra-high specific strength, high modulus, and excellent impact resistance, serving as the main load-bearing and impact-resistant layer of the composite material. Placing it adjacent to the central layer maximizes its tensile and impact resistance. Preferably, the HM-PBO fiber unidirectional prepreg on both sides is laid at 0° and 90° directions respectively, forming an orthogonal reinforcement network, giving the laminate excellent tensile and impact resistance in both principal directions. The alumina fiber unidirectional prepreg has high rigidity and good temperature resistance. As a transition layer, it is placed between the HM-PBO fiber unidirectional prepreg layer and the outermost layer to form a rigid gradient transition and avoid stress concentration at the interface caused by excessive difference in modulus between adjacent layers. The outermost S glass fiber plain weave prepreg, in which S glass fiber has high strength, good weather resistance and surface smoothness, can protect the internal layers from environmental erosion and mechanical damage. During the stacking process, the prepreg can be cut into 200mm*120mm sizes for easy layering.

[0062] Step S3 constructs a prepreg laminate with a symmetrical structure and functional partitions, laying the structural foundation for subsequent hot-pressing curing to prepare high-performance ultrathin composite materials.

[0063] S4. Curing and molding: The prepreg laminate is placed in a mold of a hot press, the mold is closed for pre-curing, and then pressure is applied and the temperature is raised for curing. In this step, the prepreg laminate obtained in step S3 is cured in a hot press, which causes the epoxy resin system in each layer of prepreg to undergo a cross-linking reaction, forming a three-dimensional network structure. At the same time, the interlayer interfaces are tightly fused, and finally a multilayer fiber-reinforced composite material is obtained.

[0064] Specifically, the hot-pressing equipment mold is preheated to 120°C. In this embodiment, a flat vulcanizing machine mold is used. The prepreg laminate is placed into the mold, and after mold closing, a pre-curing treatment is performed. The purpose of the pre-curing stage is that, at 120°C, the dicyandiamide curing agent begins to slowly decompose and initiates the initial cross-linking of the epoxy resin, causing the resin system to transition from the B-stage (semi-cured) state to the gel state, achieving initial adhesion between the prepreg layers. If the pre-curing time is too short, the epoxy resin will not flow sufficiently, resulting in insufficient interlayer bonding; if the time is too long, the epoxy resin may be over-cross-linked, making it difficult to further compact during subsequent pressurization. Therefore, the pre-curing time is 600-700 seconds, preferably 650 seconds.

[0065] After pre-curing, apply a pressure of 0.3-1.0 MPa, preferably 0.5 MPa, to the laminate and raise the temperature to 140-160°C at a rate of 3°C / min. For example, 140°C, 150°C, or 160°C can be selected as needed. Maintain this temperature for curing for 25-35 minutes, preferably 30 minutes. The purpose of applying pressure is to further compact the interlayer structure, eliminate residual air bubbles, and ensure tight adhesion between layers. The pressure range of 0.3-1.0 MPa effectively compacts the laminate while avoiding excessive pressure that could damage fibers or cause excessive extrusion of the epoxy resin. Controlling the heating rate at 3°C / min prevents stress buildup and concentrated heat release during curing caused by rapid heating, ensuring uniform curing. The curing temperature of 140-160°C ensures complete activation of dicyandiamide, promoting full cross-linking of the epoxy resin and forming a high-density three-dimensional network structure. Below 140℃, the dicyandiamide curing agent is insufficiently activated, resulting in incomplete cross-linking of the epoxy resin. This easily leads to insufficient curing degree, decreased mechanical properties, and weakened interlayer bonding in the composite material. Above 160℃, the epoxy resin is prone to overheating and decomposition, and the fibers may be damaged by heat. At the same time, the excessively concentrated heat release during curing can easily cause internal stress, warping deformation, and surface defects in the product. Holding at this temperature for 25-35 minutes ensures that the cross-linking reaction is completely completed, guaranteeing the stability of the composite material's mechanical properties.

[0066] As a preferred embodiment, before placing the prepreg laminate into the mold, a PET release film can be applied to the upper and lower surfaces of the laminate to prevent the resin from sticking to the mold during the curing process and to ensure smooth demolding; at the same time, it provides a smooth and clean surface quality for the finished product, which is especially suitable for applications with high appearance requirements.

[0067] Through step S4, the epoxy resin system in the prepreg laminate is fully cured, and the interfaces of each layer are fused together, ultimately forming a multilayer fiber-reinforced composite material board with stable structure and qualified performance.

[0068] S5. Cooling and demolding: After curing, cool and demold to obtain the multilayer fiber composite material.

[0069] This step involves cooling the mold after curing to allow the composite material to cool to a suitable temperature before demolding, thus avoiding warping and surface damage caused by thermal stress.

[0070] Specifically: After curing and heat preservation, stop heating and allow the mold to cool naturally or via circulating water to 50-70℃. For example, 50℃, 60℃, or 70℃ can be selected as needed, with 60℃ being preferred. The selection of cooling temperature must consider the following factors: if the demolding temperature is too high, the composite material may generate internal stress due to uneven shrinkage during subsequent cooling, leading to warping or microcracks; if the cooling temperature is too low, it will prolong the production cycle and reduce efficiency. When the mold is cooled to 50-70℃, the composite material has basically completed its volume shrinkage, resulting in less internal stress, which facilitates demolding and avoids scalding operators or damaging the mold.

[0071] After cooling, the mold is opened, and the cured multilayer fiber composite material sheet is removed. At this point, the multilayer fiber composite material is fully cured, with tight fusion between the layers, exhibiting excellent puncture resistance, impact resistance, and dimensional stability in ultra-thin dimensions. Its properties are shown in the table below:

[0072] This embodiment has the same beneficial effects as Embodiment 1 described above, and will not be repeated here.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; under the concept of the present invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the present invention as described above, which are not provided in detail for the sake of brevity; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A multilayer fiber composite material, characterized by It is formed by hot pressing and curing of a prepreg laminate, the prepreg laminate comprising: The alumina fiber plain weave prepreg is located at the center, and the high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg, alumina fiber unidirectional prepreg and high strength glass fiber plain weave prepreg are symmetrically distributed on both sides of the alumina fiber plain weave prepreg from the inside to the outside. The alumina fiber plain weave prepreg, the high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg, the alumina fiber unidirectional prepreg, and the high strength glass fiber plain weave prepreg are all formed by hot pressing the corresponding fiber cloth with an epoxy resin film.

2. The multilayer fiber composite material as described in claim 1, characterized in that, The epoxy resin system accounts for 45% of the content of the alumina fiber plain weave fabric prepreg. The epoxy resin system accounts for 38% of the content of the high-modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric prepreg. The epoxy resin system accounts for 40% of the content of the alumina fiber unidirectional fabric prepreg. The epoxy resin system accounts for 45% of the content of the high-strength glass fiber plain weave prepreg.

3. The multilayer fiber composite material as described in claim 2, characterized in that, The epoxy resin system comprises 90-95 parts epoxy resin and 5-10 parts dicyandiamide by weight.

4. The multilayer fiber composite material as described in claim 1, characterized in that, The alumina fiber plain weave prepreg comprises alumina fiber plain weave fabric with a thickness of 0.08-0.12 mm and a unit area mass of 85-115 g / m². The high-modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric prepreg comprises a high-modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric with a thickness of 0.018-0.022 mm and a unit area mass of 19-21 g / m². The alumina fiber unidirectional fabric prepreg comprises alumina fiber unidirectional fabric with a thickness of 0.04-0.06 mm and a unit area mass of 23-27 g / m². The high-strength glass fiber plain weave prepreg comprises high-strength glass fiber plain weave fabric with a thickness of 0.023-0.033 mm and a unit area mass of 28-32 g / m².

5. The multilayer fiber composite material as described in claim 1, characterized in that, The fiber orientations of the high-modulus poly(p-phenylenebenzodioxazole) unidirectional prepreg located on both sides of the alumina fiber plain weave prepreg are 0° and 90°, respectively. The fiber directions of the alumina fiber unidirectional prepreg located on both sides of the alumina fiber plain weave prepreg are 0° and 90°, respectively.

6. A method for preparing a multilayer fiber composite material as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Film preparation: Based on the unit area mass of each fiber cloth and the preset epoxy resin system content, prepare epoxy resin films corresponding to each fiber cloth. S2. Prepreg preparation: The epoxy resin films obtained in step S1 are matched with the corresponding fiber cloths one by one, and composite impregnation is carried out by hot pressing to obtain alumina fiber plain weave prepreg, high modulus poly(p-phenylene benzodioxazole) fiber unidirectional fabric prepreg, alumina fiber unidirectional fabric prepreg, and high strength glass fiber plain weave prepreg. S3. Lamination: Using alumina fiber plain weave prepreg as the central layer, high modulus poly(p-phenylene benzodioxazole) fiber unidirectional prepreg, alumina fiber unidirectional prepreg, and high-strength glass fiber plain weave prepreg are symmetrically stacked on both sides from the inside to the outside to obtain a prepreg laminate. S4. Curing and molding: The prepreg laminate is placed in a mold of a hot press, the mold is closed for pre-curing, and then pressure is applied and the temperature is raised for curing. S5. Cooling and demolding: After curing, cool and demold to obtain the multilayer fiber composite material.

7. The method for preparing the multilayer fiber composite material as described in claim 6, characterized in that, Step S4 includes: The hot press mold is heated to 120°C; The prepreg laminate is placed into a heated hot press mold and pre-cured for 600-700 seconds. Apply pressure of 0.3-1.0 MPa and heat to 140-160℃; Insulate and cure for 25-35 minutes.

8. The method for preparing the multilayer fiber composite material as described in claim 7, characterized in that, The heating rate to 140-160℃ is 3℃ / min.

9. The method for preparing the multilayer fiber composite material as described in claim 6, characterized in that, Step S1 includes the following steps: S11. Calculate the target areal density and thickness of the corresponding epoxy resin film based on the unit area mass of each fiber cloth and the preset epoxy resin system content. S12. Adjust the parameters of the glue applicator, and set the melting temperature to 75℃ and the application temperature to 80℃; S13. The epoxy resin system is heated and melted, and then coated by the coating machine to prepare an epoxy resin film with the target areal density and thickness.

10. The method for preparing the multilayer fiber composite material as described in claim 6, characterized in that, After step S3 and before step S4, the method further includes: applying PET release film to the upper and lower surfaces of the prepreg laminate.

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