Preparation method of carbon fiber bismaleimide resin composite material

Abstract

The invention relates to the technical field of composite material preparation and curing molding, in particular to a preparation method of a carbon fiber bismaleimide resin composite material. The method comprises the following steps: curing a carbon fiber bismaleimide resin prepreg under vacuum and pressure conditions, wherein the carbon fiber bismaleimide resin prepreg is prepared from a resin system containing an allyl compound, bismaleimide resin and a thermoplastic toughening agent; the curing procedure comprises the following steps: (1) raising the temperature to 130-150 DEG C and keeping the temperature; (2) continuously raising the temperature to 180 + / -5 DEG C and keeping the temperature; (3) continuously raising the temperature to 200-220 DEG C and keeping the temperature to complete the curing reaction; and cooling and demolding. The structure prepared by the method has relatively good energy dissipation capability when bearing an impact load, so that the damage expansion trend of the material is effectively controlled, and a relatively small damage area after impact is shown.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation and curing technology, and in particular to a method for preparing carbon fiber bismaleimide resin composite material. Background Technology

[0002] With continuous technological advancements, the application of carbon fiber composites in high-performance structural materials has been steadily increasing. Their excellent processability, along with their comprehensive mechanical properties of high modulus and high strength at relatively high temperatures, makes them extremely widely used, particularly in aerospace and electronics industries. However, the impact resistance of current carbon fiber composite laminates is relatively poor. Aircraft are subjected to impacts from tools, hail, birds, and other foreign objects during manufacturing, service, and maintenance. Some damage is difficult to observe on the product surface but can cause matrix cracking, delamination, and fiber breakage within the material. This leads to a significant decrease in the load-bearing capacity of structural components. The more pronounced the damage and the larger the damaged area, the more drastically the impact resistance and damage tolerance decrease, further jeopardizing equipment and personal safety. Therefore, evaluating the post-impact performance and damage area of ​​composite materials is of great significance for their application in the aerospace field.

[0003] Currently, methods to reduce the impact damage area of ​​carbon fiber composites mainly include optimizing ply design, material modification, and optimizing the composite material preparation process. Existing research shows that when the composite ply thickness is the same, the closer the ply design is to isotropic, the lower its compressibility, or in other words, the greater its stiffness. Quasi-isotropic ply designs can reduce the damage area by nearly 20% compared to orthogonal ply designs, but can still generate damage areas as high as nearly 2000 mm² under low-velocity impacts. 2 Even for larger damaged areas, the reduction effect is not significant. Material modification often refers to toughening the resin matrix, which may not only increase the complexity of the process and thus increase production costs, but may also affect the bonding effect with the fiber interface, further hindering the improvement of composite material performance. Summary of the Invention

[0004] This invention covers the following technical solutions:

[0005] One aspect of the present invention relates to a method for preparing a carbon fiber bismaleimide resin composite material, comprising:

[0006] The carbon fiber bismaleimide resin prepreg is cured under vacuum and pressure conditions, wherein the carbon fiber bismaleimide resin prepreg is made of a resin system containing allyl compounds, bismaleimide resin and thermoplastic toughening agents.

[0007] The curing process includes:

[0008] (1) Raise the temperature to 130℃~150℃ and maintain it;

[0009] (2) Continue to raise the temperature to 180±5℃ and maintain it;

[0010] (3) Continue to raise the temperature to 200℃~220℃ and maintain it to complete the curing reaction;

[0011] Then cool down and demold.

[0012] Another aspect of the present invention relates to a carbon fiber bismaleimide resin composite material, which is prepared by the method described above.

[0013] Another aspect of the present invention relates to a load-bearing structural member, which is at least partially composed of a carbon fiber bismaleimide resin composite material as described above.

[0014] This invention employs a staged curing process on a resin system containing allyl compounds, bismaleimide resin, and thermoplastic toughening agents. This process allows the system to complete flow regulation, crosslinking reaction, and structural stabilization at different temperature zones, resulting in a relatively uniform and stable microstructure. This structure exhibits good energy dissipation capacity under impact loads, effectively controlling the damage propagation trend and demonstrating a smaller post-impact damage area. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 : Process flow diagram.

[0017] Figure 2 The results of the damage area comparison between the embodiments of the present invention and the comparative examples under the same impact energy conditions.

[0018] Figure 3 Microscopic images of the curing behavior of the BMI system at different temperatures (left: 130℃ 30min, middle: 150℃ 30min, right: 180℃ 60min). Detailed Implementation

[0019] Reference will now be made to detailed embodiments of the present invention, one or more of which are described below. Each example is provided for explanation and not for limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0020] In this invention, unless otherwise stated, the scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, the terms and procedures related to composite materials engineering, polymer chemistry, thermosetting resin curing science, and aerospace materials engineering used herein are all widely used terms and routine procedures in their respective fields. To better understand this invention, definitions and explanations of relevant terms are provided below.

[0021] The terms “containing,” “comprising,” and “including” as used in this invention are synonyms and are inclusive or open-ended, and do not exclude additional, uncited members, elements, or method steps.

[0022] In this invention, the numerical range represented by endpoints includes all numerical values ​​and fractions contained within that range, as well as the endpoints mentioned.

[0023] Furthermore, in describing representative embodiments of the invention, this specification may present the methods and / or processes of the invention as a specific sequence of steps. However, the method or process should not be limited to the specific order of the steps described herein, to the extent that the method or process does not depend on the specific order of the steps presented herein. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps presented in the specification should not be construed as a limitation of the claims. Additionally, the claims relating to the methods and / or processes of the invention should not be limited to the execution of their steps in the order they are written, and those skilled in the art will readily recognize that the sequence can be changed while still remaining within the spirit and scope of the invention.

[0024] As used in this invention, unless otherwise stated, the singular forms of the articles “a,” “an,” and “the” include plural referents.

[0025] In this invention, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity of 2 or more.

[0026] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0027] In this invention, terms such as "preferred," "better," "more suitable," and "ideal" merely describe implementation methods or embodiments with better effects and should be understood not to limit the scope of protection of this invention. In this invention, terms such as "optionally," "optionally," and "optional" mean that something is optional, that is, selected from either "with" or "without" a parallel solution. If multiple "optional" statements appear in a technical solution, unless otherwise specified and without contradiction or mutual constraint, each "optional" statement is independent.

[0028] In this invention, "carbon fiber bismaleimide resin prepreg" refers to a prepreg material obtained by compounding carbon fiber reinforcement with a resin system containing allyl compounds, bismaleimide resin and thermoplastic toughening agents. It can be a prepreg material formed by combining unidirectional, woven, chopped strip or other forms of carbon fiber reinforcement with the resin system, and is not limited by its form or preparation method.

[0029] In this invention, "thermoplastic toughening agent" refers to a polymeric material that can undergo curing-induced phase separation and form a toughening phase structure during the curing process of bismaleimide resin. The thermoplastic toughening agent exists in a dispersed manner in the resin system and undergoes swelling, phase separation, and phase structure stabilization during the curing process to improve the interlaminar toughness and damage tolerance of the composite material.

[0030] In this invention, "resin system" refers to a curable resin composition mainly composed of bismaleimide resin and allyl compounds, containing the above-mentioned resin components and a thermoplastic toughening agent for improving toughness. It may also contain curing accelerators, flow regulators, antioxidants or other additives known in the art for improving processability and curing performance, and their types and contents do not affect the basic concept of this invention.

[0031] In this invention, the "curing process" generally refers to a curing process path in which the temperature applied to carbon fiber bismaleimide resin prepreg varies over time. In this invention, it includes steps of sequentially heating the prepreg to different temperature zones and maintaining the temperature within each zone to ensure that the resin system undergoes a pre-reaction, gradual cross-linking, and final curing process. The curing process is not limited to a specific heating device or pressure method and can be completed using an autoclave, a flatbed press, or other equipment capable of controlling heating and pressure.

[0032] In this invention, "holding" refers to maintaining a preset temperature range after heating to the target temperature, allowing the resin system to reach thermal equilibrium within that range and complete the required curing or pre-reaction process. The holding time can be determined by those skilled in the art through conventional process optimization based on differences in equipment, material system, and product thickness, and is not limited to the specific time in the embodiments of the specification, nor is it limited to a specific detection method.

[0033] In this invention, "allylic compound" refers to a compound containing an allyl functional group that can undergo a co-curing reaction with bismaleimide resin. It can act as a chain extender or co-curing monomer for bismaleimide resin, improving the processing performance and toughness of the cured system. The allyl compound may include, but is not limited to, dielyl esters, allyl ethers, or oligomers containing an allyl structure. The specific type can be selected by those skilled in the art as needed and is not limited to a specific chemical structure.

[0034] In this invention, "bismaleimide resin" refers to a thermosetting resin based on bismaleimide, capable of undergoing an addition crosslinking reaction with allyl compounds or other co-curing monomers under heating conditions to form a crosslinked network with high glass transition temperature, high rigidity, and excellent heat resistance. The specific structure or source of the bismaleimide resin is not limited; it can be commercially available bismaleimide resin, its modified system, or a resin composition containing bismaleimide functional groups.

[0035] In this invention, a "load-bearing structural component" refers to a part that bears mechanical loads, provides structural support, or ensures stability during use. The form of the load-bearing structural component is not limited; it can be a plate, shell, beam, integral component, or assembly, as long as it is at least partially composed of the composite material of this invention.

[0036] This invention provides a method for preparing carbon fiber bismaleimide resin composite material, comprising:

[0037] The carbon fiber bismaleimide resin prepreg is cured under vacuum and pressure conditions, wherein the carbon fiber bismaleimide resin prepreg is made of a resin system containing allyl compounds, bismaleimide resin and thermoplastic toughening agents.

[0038] The curing process includes:

[0039] (1) Raise the temperature to 130℃~150℃ and maintain it;

[0040] (2) Continue to raise the temperature to 180±5℃ and maintain it;

[0041] (3) Continue to raise the temperature to 200℃~220℃ and maintain it to complete the curing reaction;

[0042] Then cool down and demold.

[0043] The curing process of this invention includes three consecutively set heating and holding stages. In the first stage, the prepreg is heated to 130–150°C and held, allowing the resin system to complete the pre-reaction and flow conditioning process within this temperature range, reducing the system viscosity and forming an initial phase structure suitable for subsequent curing reactions. In the second stage, the temperature is further increased to 180±5°C and held, significantly increasing the reaction rate between the bismaleimide resin and the allyl compound and entering the main curing stage, thereby promoting the gradual formation of a continuous cross-linked network structure in the resin system and stabilizing the existing phase distribution. In the third stage, the temperature is further increased to 200–220°C and held to promote the final completion of the curing reaction, enabling the system to reach a highly cross-linked state and locking in the microstructure of the material. The temperature settings and holding processes for the three stages can be determined by those skilled in the art through conventional process experiments based on the product thickness, equipment capacity, and resin reaction characteristics. After curing, the molded composite material part is obtained by cooling and demolding.

[0044] Through the aforementioned staged curing process, the resin system undergoes a gradual reaction under temperature gradient control during curing, forming a more uniform and stable phase structure. This enhances the material's energy dissipation capacity under impact loads, thereby significantly reducing the post-impact damage area. The curing procedure of this invention is particularly suitable for bismaleimide resin systems containing thermoplastic toughening agents. Such systems are significantly affected by temperature control during curing. By implementing the three-stage heating and holding process described in this invention, the system's flowability, reaction rate, and microstructure can be effectively optimized, resulting in a final material with higher mechanical properties and damage tolerance.

[0045] The resin system can be prepared by conventional methods in the field, such as mixing, kneading, homogenizing and dispersing. The toughening agent exists in a dispersed state in the resin, and the prepreg can be in the form of unidirectional, woven or other common composite reinforcement configurations.

[0046] Furthermore, as is well known to those skilled in the art, the carbon fiber bismaleimide resin composite material may contain at least one additive, such as catalysts, antioxidants, heat stabilizers, UV stabilizers, light stabilizers, lubricants, fillers, plasticizers, flame retardants, nucleating agents, chain extenders, and dyes or mixtures thereof.

[0047] In some embodiments, the heating rate in the curing process is preferably controlled to be 1°C / min to 3°C / min.

[0048] This heating rate allows the resin system to gradually heat up during the heating process, maintaining suitable flowability and reactivity within the predetermined temperature range. This reduces the premature occurrence of localized reactions caused by excessively rapid heating and avoids phenomena such as decreased flowability due to excessively slow heating. For bismaleimide resin systems containing thermoplastic toughening agents, a gentler heating method typically allows different components to maintain a relatively stable dispersion state during temperature changes, gradually forming a more uniform microstructure in the subsequent curing stage. Controlling the heating rate within the above range helps the resin system sequentially undergo flow conditioning, crosslinking reaction, and structural stabilization stages according to the curing procedure, resulting in composite materials exhibiting excellent comprehensive performance in terms of interfacial bonding, overall structural stability, and damage propagation behavior under impact loads.

[0049] In some implementations, the cooling rate for demolding is ≤ 2℃ / min.

[0050] In some embodiments, the holding time of each temperature zone in the curing process of the present invention can be appropriately selected by those skilled in the art based on the resin content of the prepreg, the thickness of the product, the reaction rate of the resin system, and the heat transfer characteristics of the curing equipment. For example, in some embodiments, the holding time in (1) is 0.3 h to 0.7 h (optional 0.4 h, 0.5 h, 0.6 h); the holding time in (2) is 1 h to 3 h (optional 1.5 h, 2 h, 2.5 h); and the holding time in (3) is 3 h to 6 h (optional 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h).

[0051] The first temperature zone is mainly used to bring the resin system to a stable thermal equilibrium state and complete the initial flow regulation and pre-reaction, so that the toughening agent will swell moderately and form an initial dispersion structure. The second temperature zone corresponds to the main curing stage of the resin system. An appropriate holding time is conducive to the formation of a more continuous cross-linking network and to gradually stabilize the curing-induced phase separation process. The third temperature zone is used to allow the cross-linking reaction in the system to proceed fully and to stabilize the microstructure under medium and high temperature conditions, which helps to obtain a dense cured structure with good interlayer bonding performance.

[0052] In some embodiments, the vacuum degree during the curing process of the curing procedure is ≥0.095 MPa, and the applied pressure is 0.6 MPa to 0.7 MPa.

[0053] This vacuum condition maintains a low ambient gas content during the pre-curing heating stage, which positively impacts the reduction of micropores formed during resin flow and cross-linking, while also facilitating better wetting of the resin system between fiber bundles. The pressurized condition maintains stable interfacial contact throughout the curing process, and the coordination of pressure and resin viscosity changes with temperature results in tighter adhesion between prepreg layers. For bismaleimide resin systems containing thermoplastic toughening agents, curing under the combined effects of vacuum and pressure allows the resin to maintain suitable spreading capacity at each insulation stage, resulting in a denser cured structure. This is beneficial for the material to exhibit better mechanical response and damage propagation characteristics under subsequent impact loads. Those skilled in the art can adjust the vacuum and pressure appropriately according to actual equipment conditions and product thickness without deviating from the overall curing concept of this invention.

[0054] In some embodiments, the thermoplastic toughening agent is one or more of polyetherketone, polyethersulfone, polyetherimide, and polyimide resins. Regarding polyetherketone resins, selectable materials include polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetherketoneketoneketone (PEKKT), polyetherketoneetherketone (PEKEKK), and polyetherketone c (PEKc) with meta-structure characteristics. PEKc typically refers to polyetherketone modified materials with meta-substituted structures or special configurations in the main chain, which maintain high heat resistance while possessing relatively good solubility and processing adaptability, making them suitable for phase separation toughening requirements in bismaleimide resin systems. For polyethersulfone resins, selectable materials include polyethersulfone (PES), polyphenylene sulfone (PPSU), polyphenylene sulfone (PPES), modified polyethersulfone copolymers, and end-functionalized polyethersulfone resins. These materials exhibit high glass transition temperatures and excellent heat resistance, and readily form stable dispersed phases in thermosetting resin systems. For polyetherimide resins, selectable materials include polyetherimide (PEI), modified polyetherimide, amino-terminated polyetherimide, carboxyl-terminated polyetherimide, and copolymer polyetherimide materials containing flexible segments. These materials combine the heat resistance of imide structures with the flexibility of ether structures, making them suitable for participating in interface regulation and toughening structure construction during the curing process. In the field of polyimide resins, selectable materials include aromatic polyimides (PI), soluble polyimides, thermoplastic polyimides (TPI), bisphenol-type polyimides, fluorinated polyimides, and modified copolymer polyimides. These materials typically possess extremely high heat resistance and mechanical stability, and can be used to synergistically improve the toughness and structural stability of composite materials under high-temperature service environments. These thermoplastic resins can be used alone or in combination with bismaleimide resin systems through blending, copolymerization, or end-group modification. During the curing-induced phase separation process, they form toughening phase structures of different sizes and morphologies, thereby achieving control over the interlaminar toughness and damage tolerance of the composite material.

[0055] These types of thermoplastic materials typically exhibit good thermal stability and compatibility during the curing process of bismaleimide resin. Under heating conditions, they can form a uniformly dispersed state in the resin system and undergo certain phase structure evolution with temperature changes during curing, resulting in a microstructure with a certain degree of toughness after cross-linking and molding. When these toughening agents work together with bismaleimide resin, the resin system can exhibit suitable viscosity changes and phase behavior at different stages of curing, which is beneficial for the spreading and wetting of the prepreg during the heating stage and the formation of a relatively stable interfacial bond and interlayer structure after final curing.

[0056] Those skilled in the art can select one or more of the above toughening agents to combine according to actual needs, so as to adjust the rheological properties of the resin system at different curing stages and the mechanical properties of the cured material, so that the resulting composite material exhibits good damage propagation characteristics and comprehensive performance when subjected to impact loads.

[0057] In some embodiments, the mass ratio of the thermoplastic toughening agent to the bismaleimide resin is 3-6:17-19.

[0058] This ratio helps the toughening agent to form a suitable dispersion in the resin system and exhibit viscosity and phase changes that are compatible with bismaleimide resin during curing. It also helps the resin system maintain appropriate flowability during the heating phase and form a relatively stable microstructure during the gradual temperature increase curing process. Within the above ratio range, the toughening agent content can typically improve the interlaminar toughness of the composite material while maintaining its mechanical strength, resulting in a final cured system with both good rigidity and damage propagation inhibition capabilities.

[0059] In some embodiments, the molar ratio of the allyl compound to the bismaleimide resin is 0.8:1 to 1.1:1.

[0060] By adjusting the amount of allyl compound added, the crosslinking density, reaction rate, and viscosity changes during curing of the resin system can be controlled, resulting in more suitable processing and molding characteristics at each stage of curing. Those skilled in the art can routinely adjust the above proportions based on the prepreg content, product thickness, and required curing window to achieve an overall balance in mechanical properties, heat resistance, and damage tolerance of the resulting composite material.

[0061] In some embodiments, the preparation of the resin system includes homogenizing and dispersing a mixture of allyl compound, bismaleimide resin, and thermoplastic toughening agent using a three-roll mill. Three-roll milling allows the toughening agent in the resin system to exhibit a finer and more uniform dispersion under shear action, maintaining a relatively stable phase evolution during subsequent curing and heating. This results in more stable viscosity changes across different temperature zones, providing suitable flowability and wetting characteristics for prepreg layering and curing. The roller gap of the three-roll mill can be adjusted according to the viscosity and dispersion requirements of the actual material system. In a preferred embodiment, the roller gap is less than 80 μm. A roller gap of less than 80 μm typically provides strong shear action, further improving the dispersion of the toughening agent in the resin and facilitating the acquisition of a more uniform cured microstructure. Those skilled in the art can routinely optimize the milling conditions based on equipment type, material viscosity, and target dispersion effect to ensure the resin system exhibits stable processing performance during prepreg preparation and subsequent curing.

[0062] In the implementation of this invention, the prepreg can take various forms, including woven prepregs with plain weave, twill weave, or warp-knitted fabrics as reinforcements, strip prepregs based on chopped strands or laid-out strips, unidirectional prepregs based on continuous fibers, or other prepreg forms that can be uniformly compounded with the resin system and are suitable for thermosetting resin curing. These different forms of prepregs have their own characteristics in terms of layup formation, flow behavior, and post-curing structural features, and can be flexibly selected according to the stress direction, thickness design, and molding process conditions of the structural component. Among these optional prepreg types, unidirectional carbon fiber prepregs, due to their consistent fiber arrangement, clear reinforcement direction, and relatively controllable interfacial wetting behavior, can usually obtain a relatively stable wetting and crosslinking environment under the three-stage curing process of this invention, resulting in the cured composite material exhibiting good mechanical properties in the load-bearing direction and a smaller damage propagation tendency under impact loads. Therefore, in a preferred embodiment of this invention, the prepreg can be a unidirectional carbon fiber prepreg.

[0063] The method described in this invention can be used to reduce the damage area of ​​high-strength carbon fiber bismaleimide resin composites after impact. In a bismaleimide resin system containing a thermoplastic toughening agent, by heating and curing the prepreg according to a set three-stage curing procedure, the resin system undergoes a continuous process of flow, dispersion, crosslinking, and structural shaping in each temperature zone, resulting in a relatively uniform and stable microstructure after curing. When the material is subjected to external impact loads, the energy transfer mode between the resin matrix and the fiber interface, the local phase characteristics, and the structural density have a significant impact on the initiation and propagation of damage. Under the curing conditions of this invention, the material often exhibits good interlayer bonding and energy dissipation capacity, resulting in a relatively small damage area after impact. Those skilled in the art can select appropriate prepregs and curing conditions according to the stress environment of different structural components, making this method applicable to the preparation of composite material products that require improved damage tolerance or control of damage range.

[0064] In one embodiment of the present invention, the resin film used to prepare the carbon fiber bismaleimide resin prepreg can be obtained by a coating process. The coating process can be carried out at a temperature of about 80-100°C, so that the resin system is uniformly coated on the substrate surface in a state with suitable fluidity. As the temperature gradually increases, the viscosity of the resin system changes in a controllable manner, which is conducive to the formation of a uniform resin distribution on the surface of the film, thereby creating favorable conditions for subsequent composite with carbon fiber reinforcement. The thickness of the film can be adjusted according to the required resin content and fiber volume fraction of the product, so as to obtain a suitable resin content during the preparation of the prepreg.

[0065] In the prepreg preparation process, carbon fiber reinforcements pass through a resin film at a certain speed on heated rollers, allowing the resin to penetrate into the gaps between the fiber bundles under heat and pressure. The prepreg temperature of the carbon fibers can be selected, for example, at approximately 100–130°C. Within this temperature range, the resin system exhibits good fluidity, facilitating easier wetting of the fiber bundles. The prepreg speed can be adjusted to approximately 2–5 m / min based on equipment capacity and resin viscosity, ensuring sufficient resin penetration as the fiber bundles pass through the coating and heating zones, thereby forming a uniform prepreg structure. Those skilled in the art can conduct routine experiments and optimizations of the prepreg temperature, speed, and resin content based on the thickness of the target product, fiber type, and resin characteristics to obtain a prepreg with stable processing properties.

[0066] During the prepreg layup stage, the layup sequence, layup angles, and overlap patterns between different layers can be adjusted according to the stress direction and design requirements of the structural component. For example, combinations of layup angles of 0°, ±45°, or 90° can be selected to enhance the load-bearing capacity of the structural component in different directions, while controlling interlayer shear properties and overall damage resistance. The layup process can be carried out on a heated table to give the prepreg suitable flexibility, facilitating laying and molding, and reducing the generation of interlayer voids.

[0067] During the preparation process before curing, the prepreg preform can be evacuated to reduce the gas content within the cavity, which helps to reduce porosity formation in the early stages of heating. An isolation membrane, breathable felt, and vacuum bag material can be applied to the periphery of the preform to form a stable encapsulation system, maintaining the predetermined molding pressure and media environment throughout the curing process. This type of encapsulation is a common technique in the art and can be used in conjunction with the three-stage curing process of this invention.

[0068] After the curing process is complete and cooling is finished, the resulting composite material can be machined, trimmed, drilled, or surface-treated to meet the assembly and usage requirements of specific structural components. The cooling rate can be adjusted according to the equipment characteristics and material thickness, allowing the material to complete the thermal shrinkage process after curing under relatively stable temperature drop conditions, thereby obtaining molded parts that maintain structural integrity.

[0069] According to another aspect of the present invention, there is a carbon fiber bismaleimide resin composite material prepared by the method described above.

[0070] The present invention also relates to a load-bearing structural member, which is at least partially composed of the carbon fiber bismaleimide resin composite material as described above.

[0071] The carbon fiber bismaleimide resin composite material prepared by this invention can be used to construct various load-bearing structural components. These components are those that bear structural support, mechanical loads, or stability functions during use. Commercial forms include aircraft and spacecraft skin panels, wingtip components, door structures, fairings, radomes, and beams, frames, stiffeners, or covers for structural connections. They can also include external structures, aerodynamic components, control surface assemblies, and thermal insulation supports for high-temperature environments in high-speed aircraft. Furthermore, this material can also be applied to local load-bearing sections or reinforced parts of blades in wind power generation equipment, as well as structural support plates or packaging substrates in high-temperature electronic devices. When the composite material obtained by this invention is used in load-bearing structural components, it can provide good mechanical support capacity with a relatively light weight and exhibits relatively stable damage propagation behavior under impact or cyclic loading, thereby meeting the requirements for structural safety and service life in different engineering scenarios.

[0072] The embodiments of the present invention will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this invention, or follow experimental manuals or conventional conditions in the art, or other experimental methods known in the art, or follow the conditions recommended by the manufacturer.

[0073] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0074] Example

[0075] In this embodiment, the mass ratio of allyl compound: bismaleimide resin: toughening agent is 87:100:40.

[0076] Reference Figure 1 The process flow, preparation of modified bismaleimide resin, carbon fiber bismaleimide resin prepreg and composite material in this embodiment, and the performance testing of the composite material are as follows:

[0077] (1) The preparation of the modified bismaleimide resin includes the following steps:

[0078] 1) Add the allyl compound to the kneader according to the mass ratio, set the kneader to (120±5)℃ for 15 min, and stir at 70 r / min for 50 min to obtain molten resin;

[0079] 2) Set the kneader temperature to (80±5)℃. After the kneader temperature reaches the required level, add diphenylmethane bismaleimide compound to the above molten resin. The mass ratio of diphenylmethane bismaleimide compound to molten resin is 100:87. Knead at (80±5)℃. Set the kneader rotor speed to 6r / min. After stirring for 10min, increase the kneader rotor speed to 25r / min and stir for 10min to obtain an allyl compound / bismaleimide resin mixture.

[0080] 3) Add a toughening agent to the above allyl compound / bismaleimide resin mixture. The toughening agent is a polyether ketone (such as PEK). The mass ratio of the polyether ketone to the bismaleimide resin in the above allyl compound / bismaleimide resin mixture is 40:100. Knead at (80±5)℃. The initial rotor speed is set to 15 r / min. After stirring for 10 min, the rotor speed is increased to 50 r / min. After stirring for 10 min, the rotor speed is increased to 70 r / min. Stir for 10 min to obtain the allyl compound / bismaleimide resin / toughening agent mixture.

[0081] 4) The above allyl compound / bismaleimide resin / toughening agent mixture was added to a three-roll mill for grinding. The measured gap of the three-roll mill was 80 μm. The grinding was carried out 3 times to obtain the well-ground allyl compound / bismaleimide resin / toughening agent mixture, i.e., modified bismaleimide resin.

[0082] (2) Preparation of high-toughness carbon fiber bismaleimide resin prepreg, including the following steps:

[0083] 1) Preheat the prepared modified bismaleimide resin: Each tray of modified bismaleimide resin weighs 5~6 kg and is preheated at (85±5)℃ for 45 min to obtain molten modified bismaleimide resin.

[0084] 2) Transfer the molten modified bismaleimide resin into the resin tank of the coating machine and coat it at (85±5)℃. The coating width is >1000mm, the coating speed is (2~5)m / min, and the standard coating weight is (33±3)g / m. 2 , to prepare a bismaleimide resin film;

[0085] 3) Place one layer of the above-mentioned bismaleimide resin film on the top and bottom, and place a layer of carbon fiber reinforcement material in the middle. Use a hot melt prepreg machine to prepreg and composite the above-mentioned bismaleimide resin film and carbon fiber reinforcement material together by heating and pressurizing. The prepreg temperature is (105±5)℃ and the prepreg speed is (2~5)m / min to prepare carbon fiber bismaleimide resin prepreg, namely high toughness carbon fiber bismaleimide resin prepreg.

[0086] (3) Preparation of high-toughness carbon fiber bismaleimide resin composite material:

[0087] Randomly select the above-mentioned high-toughness carbon fiber bismaleimide resin prepreg and cut and lay it according to the [45 / 0 / 90 / -45] 5s laying angle direction; after laying, use a thermostatic precipitator for curing and molding:

[0088] The sample was placed on a flat mold in an autoclave at room temperature. A release cloth, a release film, and a breathable felt were then sequentially applied to the surface. Finally, the sample was sealed in a vacuum bag and evacuated to a vacuum level ≥ -0.095 MPa. The temperature was increased to 150±5℃ at a rate of 1~2℃ / min and held for 0.5 h. Then, the temperature was increased to 180±5℃ at a rate of 1~2℃ / min and held for 2 h. Finally, the temperature was increased to 200±5℃ at a rate of 1~2℃ / min and held for 4 h. The pressure system was required to be 0.6~0.7 MPa. The temperature was then reduced to 60℃ at a rate of 1~2℃ / min to release the pressure. After curing, the autoclave was opened to obtain the carbon fiber bismaleimide resin composite material.

[0089] (4) Carbon fiber composite material CAI performance test:

[0090] The carbon fiber composite material was cut into 150×100mm specimens and tested according to the requirements of ASTM D7136 / D7137 standards. The impact compressive strength and damage area data of the composite material were recorded.

[0091] Comparative Example 1

[0092] In this comparative example, the mass ratio of allyl compound: bismaleimide resin: toughening agent is 87:100:40.

[0093] Reference Figure 1 The process flow, preparation of modified bismaleimide resin, carbon fiber bismaleimide resin prepreg and composite material in this embodiment, and the performance testing of the composite material are as follows:

[0094] (1) The preparation of the modified bismaleimide resin includes the following steps:

[0095] 1) Add the allyl compound to the kneader according to the mass ratio, set the kneader to (120±5)℃ for 15 min, and stir at 70 r / min for 50 min to obtain molten resin;

[0096] 2) Set the kneader temperature to (80±5)℃. After the kneader temperature reaches the required level, add diphenylmethane bismaleimide compound to the above molten resin. The mass ratio of diphenylmethane bismaleimide compound to molten resin is 100:87. Knead at (80±5)℃. Set the kneader rotor speed to 6r / min. After stirring for 10min, increase the kneader rotor speed to 25r / min and stir for 10min to obtain an allyl compound / bismaleimide resin mixture.

[0097] 3) Add a toughening agent to the above allyl compound / bismaleimide resin mixture. The toughening agent is a polyether ketone (such as PEK). The mass ratio of the polyether ketone to the bismaleimide resin in the above allyl compound / bismaleimide resin mixture is 40:100. Knead at (80±5)℃. The initial rotor speed is set to 15 r / min. After stirring for 10 min, the rotor speed is increased to 50 r / min. After stirring for 10 min, the rotor speed is increased to 70 r / min. Stir for 10 min to obtain the allyl compound / bismaleimide resin / toughening agent mixture.

[0098] 4) The above allyl compound / bismaleimide resin / toughening agent mixture was added to a three-roll mill for grinding. The measured gap of the three-roll mill was 80 μm. The grinding was carried out 3 times to obtain the well-ground allyl compound / bismaleimide resin / toughening agent mixture, i.e., modified bismaleimide resin.

[0099] (2) Preparation of high-toughness carbon fiber bismaleimide resin prepreg, including the following steps:

[0100] 1) Preheat the prepared modified bismaleimide resin: Each tray of modified bismaleimide resin weighs 5~6 kg and is preheated at (85±5)℃ for 45 min to obtain molten modified bismaleimide resin.

[0101] 2) Pour the molten modified bismaleimide resin into the resin tank of the coating machine and coat it at (85±5)℃. The coating width is >1000mm, the coating speed is (2~5)m / min, and the standard coating weight is (33±3)g / m. 2 , to prepare a bismaleimide resin film;

[0102] 3) Place one layer of the above-mentioned bismaleimide resin film on the top and bottom, and place a layer of carbon fiber reinforcement material in the middle. Use a hot melt prepreg machine to prepreg and composite the above-mentioned bismaleimide resin film and carbon fiber reinforcement material together by heating and pressurizing. The prepreg temperature is (105±5)℃ and the prepreg speed is (2~5)m / min to prepare carbon fiber bismaleimide resin prepreg, namely high toughness carbon fiber bismaleimide resin prepreg.

[0103] (3) Preparation of high-toughness carbon fiber bismaleimide resin composite material:

[0104] Randomly select the above-mentioned high-toughness carbon fiber bismaleimide resin prepreg and cut and lay it according to the [45 / 0 / 90 / -45] 5s laying angle direction; after laying, use a thermostatic precipitator for curing and molding:

[0105] The sample was placed on a flat mold in an autoclave at room temperature. A release cloth, a release film, and a breathable felt were then sequentially applied to the surface. Finally, the sample was sealed in a vacuum bag, and a vacuum of ≥-0.095 MPa was applied. The temperature was increased to 130±5℃ at a rate of 1~2℃ / min and held for 0.5 h. Then, the temperature was increased to 180±5℃ at a rate of 1~2℃ / min and held for 2 h. Finally, the temperature was increased to 200±5℃ at a rate of 1~2℃ / min and held for 4 h. The pressure system was required to be 0.6~0.7 MPa. The temperature was then reduced to 60℃ at a rate of 1~2℃ / min to release the pressure. After curing, the autoclave was opened to obtain the carbon fiber bismaleimide resin composite material.

[0106] (4) Carbon fiber composite material CAI performance test:

[0107] The carbon fiber composite material was cut into 150×100mm specimens and tested according to the requirements of ASTM D7136 / D7137 standards. The impact compressive strength and damage area data of the composite material were recorded.

[0108] Comparative Example 2

[0109] In this comparative example, the mass ratio of allyl compound: bismaleimide resin: toughening agent is 87:100:40.

[0110] Reference Figure 1 The process flow, preparation of modified bismaleimide resin, carbon fiber bismaleimide resin prepreg, and composite material in this embodiment, as well as the performance testing of the composite material, are as follows:

[0111] (1) The preparation of the modified bismaleimide resin includes the following steps:

[0112] 1) Add the allyl compound to the kneader according to the mass ratio, set the kneader to (120±5)℃ for 15 min, and stir at 70 r / min for 50 min to obtain molten resin;

[0113] 2) Set the kneader temperature to (120±5)℃. After the kneader temperature reaches the required level, add diphenylmethane bismaleimide compound to the above molten resin. The mass ratio of diphenylmethane bismaleimide compound to molten resin is 100:87. Knead at (80±5)℃. Set the kneader rotor speed to 6r / min. After stirring for 10min, increase the kneader rotor speed to 25r / min and stir for 10min to obtain an allyl compound / bismaleimide resin mixture.

[0114] 3) Add a toughening agent to the above allyl compound / bismaleimide resin mixture. The toughening agent is a polyether ketone (such as PEK). The mass ratio of the polyether ketone to the bismaleimide resin in the above allyl compound / bismaleimide resin mixture is 40:100. Knead at (80±5)℃. The initial rotor speed is set to 15 r / min. After stirring for 10 min, the rotor speed is increased to 50 r / min. After stirring for 10 min, the rotor speed is increased to 70 r / min. Stir for 10 min to obtain the allyl compound / bismaleimide resin / toughening agent mixture.

[0115] 4) The above allyl compound / bismaleimide resin / toughening agent mixture was added to a three-roll mill for grinding. The measured gap of the three-roll mill was 80 μm. The grinding was carried out 3 times to obtain the well-ground allyl compound / bismaleimide resin / toughening agent mixture, i.e., modified bismaleimide resin.

[0116] (2) Preparation of high-toughness carbon fiber bismaleimide resin prepreg, including the following steps:

[0117] 1) Preheat the prepared modified bismaleimide resin: Each tray of modified bismaleimide resin weighs 5~6 kg and is preheated at (85±5)℃ for 45 min to obtain molten modified bismaleimide resin.

[0118] 2) Transfer the molten modified bismaleimide resin into the resin tank of the coating machine and coat it at (85±5)℃. The coating width is >1000mm, the coating speed is (2~5)m / min, and the standard coating weight is (33±3)g / m. 2 , to prepare a bismaleimide resin film;

[0119] 3) Place one layer of the above-mentioned bismaleimide resin film on the top and bottom, and place a layer of carbon fiber reinforcement material in the middle. Use a hot melt prepreg machine to prepreg and composite the above-mentioned bismaleimide resin film and carbon fiber reinforcement material together by heating and pressurizing. The prepreg temperature is (105±5)℃ and the prepreg speed is (2~5)m / min to prepare carbon fiber bismaleimide resin prepreg, namely high toughness carbon fiber bismaleimide resin prepreg.

[0120] (3) Preparation of high-toughness carbon fiber bismaleimide resin composite material:

[0121] Randomly select the above-mentioned high-toughness carbon fiber bismaleimide resin prepreg and cut and lay it according to the [45 / 0 / 90 / -45] 5s laying angle direction; after laying, use a thermostatic precipitator for curing and molding:

[0122] The sample was placed on a flat mold in an autoclave at room temperature. A release cloth, release film, and breathable felt were then sequentially applied to the surface. Finally, the sample was sealed in a vacuum bag and evacuated to a vacuum level ≥ -0.095 MPa. The temperature was increased to 130±5℃ at a rate of 1~2℃ / min and held for 2 h. Then, the temperature was increased to 200±5℃ at a rate of 1~2℃ / min and held for 4 h. The pressure system was required to be 0.6~0.7 MPa. Finally, the temperature was reduced to 60℃ at a rate of 1~2℃ / min to release the pressure. After curing, the autoclave was opened to obtain the carbon fiber bismaleimide resin composite material.

[0123] (4) Carbon fiber composite material CAI performance test:

[0124] The carbon fiber composite material was cut into 150mm×100mm specimens and tested according to the requirements of ASTM D7136 / D7137 standards. The impact compressive strength and damage area data of the composite material were recorded.

[0125] Comparative Example 3

[0126] Comparative Example 3 was set up based on Example 1 to investigate the effect of increasing the final curing temperature on the post-impact damage area under the same resin system and prepreg process conditions.

[0127] Specifically, Comparative Example 3 and Example 1 were identical in raw material ratios, resin system preparation methods, prepreg preparation conditions, layup methods, and sample preparation and post-impact / compression testing methods, with only the curing procedure adjusted: Comparative Example 3 employed the same first, second, and third curing steps as Example 1. After holding at 200–220°C in the third stage, the temperature was further increased to 280°C and held for 2.5 h, with the same heating rate (1–3°C / min). Afterward, it was cooled and demolded as in Example 1. By comparing the post-impact damage areas obtained in Comparative Example 3 and Example 1 under the same impact load conditions, the effect of adding a 280°C high-temperature final curing stage on the material's impact damage behavior can be evaluated.

[0128] Comparative Example 4

[0129] It does not contain thermoplastic toughening agents, and all other conditions are the same as in Example 1.

[0130] Experimental results

[0131] The relevant experimental data of the above embodiments and comparative examples are shown in the following table and Figure 2 As shown:

[0132] project Post-impact compressive strength (MPa) <![CDATA[Injury area (mm 2 )]]> Indentation depth (mm) Example 1 265 675 0.286 Comparative Example 1 261 1065 0.28 Comparative Example 2 239 1907 0.268 Comparative Example 3 203 2199 0.298 Comparative Example 4 239 777 0.294

[0133] like Figure 2 As shown, under the same impact energy conditions, the post-impact compressive strength of Example 1 is 265 MPa, the damage area is 675 mm², and the pit depth is 0.286 mm. The pit depths of each group are generally close (approximately 0.268–0.298 mm), which can be considered as consistent impact input, thus better reflecting the differences in damage propagation within the material.

[0134] Regarding the influence of the curing regime, under the premise that the resin system formulations of Example 1, Comparative Examples 1, 2, and 3 are the same (all containing thermoplastic toughening agents), significant differences can be caused by only the curing path: Comparative Example 1, by adjusting the first temperature zone to 130℃ and holding it at that temperature for 0.5 h, saw its damaged area increase to 1065 mm². 2 Comparative Example 2 further eliminated the low-temperature stage and directly entered the main curing stage at 180℃, resulting in a significant increase in the damaged area to 1907 mm². 2 Comparative Example 3, based on the three-stage curing of Example 1, added a high-temperature final curing at 280℃ for 2.5 h, further increasing the damaged area to 2199 mm. 2 Furthermore, the compressive strength decreased to 203 MPa after impact. These results indicate that in this system, the degree of matching between the three-stage heating and holding windows and the "flow regulation—crosslinking advancement—structural shaping" process directly determines whether damage will rapidly propagate in the plane, and the curing regime has a significantly greater impact on the damage area than any other single factor.

[0135] Regarding the impact of thermoplastic toughening agents, Figure 2 As can be seen from the comparison between "Comparative Example 4" and the Example 1, when the curing conditions are kept consistent with those of Example 1, simply removing the thermoplastic toughening agent can reduce the post-impact compressive strength from 265 MPa to 239 MPa and the damage area from 675 mm². 2 Increased to 777 mm 2 The results show that thermoplastic toughening agents can further suppress impact damage propagation and improve post-impact load-bearing capacity under the same curing path. However, the increase in damage area compared with comparative examples 1 to 3 also shows that within the data range shown in this application, "reasonable design of the curing regime" is still the dominant factor determining the damage area level, and the toughening agent and curing regime working together can achieve the optimal damage tolerance performance.

[0136] Combination Figure 3The microstructure can explain the above-mentioned patterns: the system undergoes a structural evolution process of "nucleation-growth-destabilization and phase separation" during temperature-curing. The thermoplastic toughening agent particles gradually swell and form initial island structures at low and medium temperatures. Further temperature increases can lead to fine bicontinuous structures that evolve into droplet-like phase regions during subsequent curing. The three-stage curing regime in Example 1 can limit fluidity, reaction rate, and phase separation behavior within a suitable window, resulting in a stable and uniform microstructure, which is beneficial for crack deflection and energy dissipation. Figure 2 Smaller damage area. In contrast, when the curing path deviates, it is difficult to form or stabilize the aforementioned favorable phase structure, and Comparative Example 4, lacking thermoplastic toughening agent, cannot undergo phase separation toughening process, thus being more prone to larger damage propagation.

[0137] The embodiments described above are merely illustrative 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 patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for preparing a carbon fiber bismaleimide resin composite material, characterized in that, include: The carbon fiber bismaleimide resin prepreg is cured under vacuum and pressure conditions, wherein the carbon fiber bismaleimide resin prepreg is made of a resin system containing allyl compounds, bismaleimide resin and thermoplastic toughening agents. The curing process includes: (1) Raise the temperature to 130℃~150℃ and maintain it; (2) Continue to raise the temperature to 180±5℃ and maintain it; (3) Continue to raise the temperature to 200℃~220℃ and maintain it to complete the curing reaction; Then cool down and demold.

2. The method according to claim 1, characterized in that, The heating rate of the curing process is 1℃ / min to 3℃ / min; Optionally, the holding time in (1) is 0.3 h ~ 0.7 h; in (2) the holding time is 1 h ~ 3 h; and in (3) the holding time is 3 h ~ 6 h.

3. The method according to claim 1, characterized in that, The vacuum degree during the curing process of the curing procedure is ≥-0.095 MPa, and the applied pressure is 0.6 MPa to 0.7 MPa.

4. The method according to claim 1, characterized in that, The thermoplastic toughening agent is one or more of polyetherketone, polyethersulfone, polyetherimide, and polyimide resins.

5. The method according to claim 1, characterized in that, The mass ratio of the thermoplastic toughening agent to the bismaleimide resin is 3-6: 17-19; Optionally, the molar ratio of the allyl compound to the bismaleimide resin is 0.8:1 to 1.1:

1.

6. The method according to any one of claims 1 to 5, characterized in that, The preparation of the resin system includes homogenizing and dispersing a mixture of allyl compound, bismaleimide resin and thermoplastic toughening agent using a three-roll mill. Optionally, the gap between the rollers of the three-roll mill is less than 80 μm.

7. The method according to any one of claims 1 to 5, characterized in that, The prepreg is a unidirectional carbon fiber prepreg.

8. The method according to any one of claims 1 to 5, characterized in that, The method is used to reduce the damage area of ​​high-strength carbon fiber bismaleimide resin composite material after impact.

9. A carbon fiber bismaleimide resin composite material, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. A load-bearing structural member, at least in part composed of the carbon fiber bismaleimide resin composite material as described in claim 9.

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