A carbon fiber prepreg, a carbon fiber composite plate and a preparation method thereof

Abstract

This invention relates to a carbon fiber prepreg, a carbon fiber composite sheet, and a method for preparing the same, falling within the technical field of carbon fiber and its composite materials. The main technical solution is as follows: the method for preparing the carbon fiber prepreg includes the following steps: mixing 50-70 parts by weight of solid epoxy resin, 10-20 parts by weight of chopped fibers, 20-40 parts by weight of curing agent, and 1-5 parts by weight of coupling agent to obtain a resin matrix; preparing the resin matrix into a film of a predetermined thickness; and impregnating the carbon fiber with the film to obtain the carbon fiber prepreg. A designed detachable mold, combined with a corresponding molding process, is used to prepare carbon fiber composite sheets from the carbon fiber prepreg. This invention is mainly used to reduce the internal porosity of carbon fiber composite sheets, improve interlaminar shear and in-plane shear properties, and enhance the appearance quality of the carbon fiber composite sheets.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber and its composite materials, and in particular to a carbon fiber prepreg, a carbon fiber composite sheet, and a method for preparing the same. Background Technology

[0002] Carbon fiber sheets are composite material sheets made of carbon fiber as reinforcement and resin as the matrix. During processing, the performance of carbon fiber sheets can be customized to a certain extent by adjusting the weaving method, layup direction, and resin composition, giving them high flexibility. However, their manufacturing cost is high, and the molding process is mostly for small-batch production, requiring specialized equipment and operating methods. Due to their high strength and low density, carbon fiber sheets are widely used in aerospace, automotive, and sporting goods industries.

[0003] The quality of the carbon fiber prepreg used in the preparation of carbon fiber composite sheets affects the internal porosity of the sheets, which in turn affects their appearance. Currently, carbon fiber composite sheets are mostly formed using autoclaves or hot presses. For large-sized sheets, autoclave forming is the primary method. Autoclaves are a common and widely used piece of equipment for forming carbon fiber products. However, in the forming of carbon fiber sheets, due to operator errors (lack of pressing during the fabric laying process), sheets of varying thicknesses often have high internal porosity. The thicker the sheet, the more easily air bubbles are formed inside, resulting in defects in the appearance of the formed sheet. These defects require sanding and painting, increasing production costs.

[0004] In summary, there is an urgent need to improve carbon fiber prepregs to reduce the internal porosity of the sheets, improve interlaminar and in-plane shear properties, and enhance the appearance quality of the sheets. Furthermore, the manufacturing process of carbon fiber composite sheets urgently needs improvement to increase production efficiency. Summary of the Invention

[0005] In view of this, the present invention provides a carbon fiber prepreg, a carbon fiber composite material sheet and a method for preparing the same, the main purpose of which is to reduce the internal porosity of the sheet, improve shear performance and enhance the appearance quality of the sheet.

[0006] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0007] On one hand, embodiments of the present invention provide a method for preparing carbon fiber prepreg, which includes the following steps:

[0008] Preparation of resin matrix: Mix 50-70 parts by weight of solid epoxy resin, 10-20 parts by weight of chopped fibers, 20-40 parts by weight of curing agent, and 1-5 parts by weight of coupling agent to obtain resin matrix.

[0009] Preparation steps of the adhesive film: Prepare an adhesive film of a set thickness from the resin matrix;

[0010] Impregnation step: The carbon fiber is impregnated with the aforementioned adhesive film to obtain carbon fiber prepreg.

[0011] Preferably, in the step of preparing the resin matrix:

[0012] The chopped fibers are 2-4 mm in length; and / or

[0013] The chopped fibers are chopped carbon fibers; and / or

[0014] The curing agent is selected from dicyandiamide curing agent; and / or

[0015] The coupling agent is selected from aminosilane coupling agents; and / or

[0016] First, solid epoxy resin and chopped fibers are mixed in a mixing tank. Then, curing agent and coupling agent are added and stirred evenly to obtain the resin matrix.

[0017] Preferably, in the step of preparing the adhesive film: the resin matrix is ​​heated to 70-90°C and then conveyed to the impregnation roller to prepare an adhesive film of 100-200μm.

[0018] Preferably, in the impregnation step: the fiber bundle is drawn out on the unwinding device, and the corresponding number of fibers are matched according to the required quality requirements of the carbon fiber prepreg. The fibers are flattened by a flattening roller, and then the adhesive film is attached to the flattened fiber bundle. The resin matrix is ​​melted by a heating roller and impregnated in the fibers. After cooling, adding a release film, trimming the edges, and winding, the carbon fiber prepreg is obtained. Preferably, the heating temperature of the heating roller is 70-90℃.

[0019] On the other hand, embodiments of the present invention provide a carbon fiber prepreg, wherein the carbon fiber prepreg is prepared by the carbon fiber prepreg preparation method described in any one of the above claims; wherein short-cut fibers are adhered to the surface of the carbon fiber prepreg.

[0020] In another aspect, embodiments of the present invention provide a method for preparing a carbon fiber composite material sheet, wherein the method for preparing the carbon fiber composite material sheet includes the following steps:

[0021] Lamination steps: Cut the above-mentioned carbon fiber prepreg into prepreg layers of a set size; lay up multiple prepreg layers to obtain a laminated block;

[0022] Mold assembly steps: Assemble the mold and fix the stacked material blocks in place by the mold to obtain the loading mold;

[0023] Curing step: The filling mold is cured to obtain a cured filling mold;

[0024] Post-processing: The mold after curing is disassembled to obtain carbon fiber composite material sheets.

[0025] Preferably, in the layup step: when laying up multiple prepreg layers: the fiber orientation of the prepreg layers is alternately set at 0° and 90°;

[0026] When the total number of prepreg layers is odd, the prepreg layer in the middle is taken as the axis of symmetry, and the prepreg layers on both sides of the axis of symmetry are mirror symmetrical, and the fiber directions of the symmetrical layers are the same.

[0027] When the total number of prepreg layers is even, the prepreg layers on both sides of the center plane between the two middle prepreg layers are mirror-symmetrical, and the fiber orientation of the two middle prepreg layers is the same.

[0028] Preferably, in the assembly mold step: a first release film is laid on the surface of the bottom plate; the stacked material blocks are confined within a confining frame coated with a release agent, and the confining frame is placed on the first release film; a second release film is laid on the stacked material blocks; the top plate is placed on the second release film to obtain the first loading mold;

[0029] Preferably, the limiting frame is a frame structure formed by multiple limiting strips being snapped together end to end;

[0030] Preferably, each limiting strip includes a limiting strip unit or each limiting strip includes multiple overlapping limiting strip units to increase the thickness of each limiting strip;

[0031] Preferably, the loading mold includes only a first loading mold; or when producing carbon fiber composite material sheets in batches: there are multiple loading molds; wherein, the multiple loading molds are stacked, and the bottommost loading mold is the first loading mold; more preferably, for two adjacent loading molds, the loading mold located above uses the upper panel of the loading mold located below as the lower panel.

[0032] Preferably, in the curing process: the filling mold is wrapped with a breathable felt and a vacuum bag and then placed in an autoclave; the autoclave is evacuated, and when the vacuum level drops by ≤ 1 kPa within 5 minutes, the autoclave is closed, and heating and pressurization curing begins; wherein, the curing process is as follows: first, pressurize to 0.1-0.3 MPa, heat to 70-90°C at a rate of 2-5°C / min, and hold for 10-30 minutes; then pressurize to 0.4-0.6 MPa, heat to 90-120°C at a rate of 2-5°C / min, and hold for 10-30 minutes; subsequently, pressurize to 0.5-0.7 MPa, heat to 130-150°C at a rate of 1-2°C / min, and hold for 20-60 minutes; finally, cool down and depressurize at a rate of 2-5°C / min, and when the temperature drops to room temperature, begin depressurization to atmospheric pressure.

[0033] In the post-processing step: the mold after curing is disassembled, the carbon fiber composite material sheet is removed, and the surrounding film is cleaned.

[0034] In another aspect, embodiments of the present invention provide a carbon fiber composite material sheet, wherein the carbon fiber composite material sheet is prepared by any of the above-described methods for preparing carbon fiber composite material sheets; preferably, after ultrasonic non-destructive testing, the carbon fiber composite material sheet has no shadow in the middle and no pore defects; preferably, the shear strength of the carbon fiber composite material sheet is 65-75 MPa.

[0035] Compared with the prior art, the carbon fiber prepreg, carbon fiber composite material sheet and preparation method of the present invention have at least the following beneficial effects:

[0036] On one hand, embodiments of the present invention provide a carbon fiber prepreg and its preparation method. The preparation method of the carbon fiber prepreg includes the following steps: mixing 50-70 parts by weight of solid epoxy resin, 10-20 parts by weight of chopped fibers, 20-40 parts by weight of curing agent, and 1-5 parts by weight of coupling agent to obtain a resin matrix; preparing the resin matrix into a film of a set thickness; and impregnating the carbon fiber with the film to obtain the carbon fiber prepreg. The above scheme is explained as follows: Embodiments of the present invention prepare a film by uniformly mixing a certain proportion of chopped fibers into the resin matrix, and then uniformly impregnating it onto the carbon fiber using an impregnation device to produce a carbon fiber prepreg. This achieves the purpose of adding a certain amount of chopped fibers between the fibers in each layer of fiber when subsequently laying the carbon fiber prepreg. Wherein, there are gaps between the fibers of the carbon fiber fabric, and its surface can be well wetted by resin after treatment. The negative pressure formed by vacuuming will create a pressure difference within the system. On the one hand, bubbles expand under negative pressure, and the carbon fiber surface becomes the path for bubble movement. On the other hand, resin flows along the fiber texture and impregnates the fibers. The flowing resin carries surrounding bubbles towards the vacuum extraction port, where they gradually converge and are discharged outwards along the narrow channels on the fiber surface and between fibers. This reduces porosity defects in the molded composite material, improving the stability of the molding quality of large-size sheets, reducing quality fluctuations caused by differences in manual layup, resulting in a smooth product surface with no residual bubbles. Especially for sheets thicker than 10mm, the vacuum curing stage allows for the complete removal of internal gas, reducing internal porosity and enhancing the density of the sheet. Carbon fiber sheets prepared using this process exhibit better structural integrity and fatigue resistance, enabling them to withstand a wider range of stress environments during subsequent use, thus improving durability.

[0037] On the other hand, the carbon fiber composite material sheet and its preparation method provided in this embodiment of the invention are designed with a combined mold consisting of a top panel, a bottom panel, and a limiting frame. The limiting frame is formed by connecting the limiting strips through a snap-fit ​​structure, which can fix the position of the material block, prevent deformation, and ensure the dimensional accuracy of the sheet after curing. Furthermore, it is easy to assemble and disassemble, can be adjusted according to production needs, and is easy to clean, maintain, and store after disassembly. Existing technologies conventionally use integrated molds, which are cumbersome to remove, highly specialized, and have high mold opening costs. Therefore, compared with conventional integrated pressure plate molds, the combined mold proposed in this embodiment of the invention is lighter, lower in cost, and can be stacked in multiple sets for production, thus adapting to the batch processing and molding of sheets of various sizes. The sheet forming thickness can be controlled within ±0.10mm. Through this process, the appearance quality of the sheet is easy to control, which is beneficial for the mass production and processing of the sheet.

[0038] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the prepreg layer being laid up;

[0040] Figure 2 This is a diagram showing the limiting frame and its assembly;

[0041] Figure 3 This is a schematic diagram of the loading mold assembly;

[0042] Figure 4 This is a schematic diagram of the loading mold assembly during the mass production of sheet metal;

[0043] Figure 5 This is a schematic diagram showing that a high-thickness limiting strip is formed by stacking multiple limiting strip units;

[0044] Figure 6 This is a schematic diagram of the assembly process of the general mold in Comparative Example 1;

[0045] Figure 7 These are ultrasonic non-destructive testing (NDT) scan results of the molded plates in Experimental Example 1 and Comparative Example 1. Figure 7 Figure (1) shows the detection results of Experimental Example 1, and Figure (2) shows the detection results of Comparative Example 1. Detailed Implementation

[0046] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0047] This invention optimizes the composition of carbon fiber prepreg, which helps to reduce the internal porosity of the sheet, improves the interlayer shear and in-plane shear performance, and enhances the appearance quality of the sheet. At the same time, it is equipped with an easy-to-assemble molding die, which can be assembled according to production needs and equipment size, effectively improving production efficiency.

[0048] The following detailed description uses specific examples:

[0049] Example 1

[0050] This embodiment provides a method for preparing carbon fiber prepreg, which includes the following steps:

[0051] Preparation of the resin matrix: 50-70 parts by weight of solid epoxy resin, 10-20 parts by weight of chopped fibers (chopped carbon fibers, 2-4 mm in length), 20-40 parts by weight of curing agent, and 1-5 parts by weight of coupling agent are mixed to obtain the resin matrix. Specifically, the solid epoxy resin and chopped fibers are first mixed in a stirred tank, and then the curing agent and coupling agent are added and stirred evenly to obtain the resin matrix. Preferably, the curing agent is a dicyandiamide curing agent; the coupling agent is an aminosilane coupling agent.

[0052] Preparation steps of the adhesive film: Prepare an adhesive film of a set thickness from the resin matrix. Specifically, heat the well-mixed resin matrix to a certain temperature (70-90℃), then feed it onto the impregnation rollers. Adjust the speed of the release paper and the gap between the impregnation rollers to produce an adhesive film of a certain thickness (100-200μm).

[0053] Impregnation Step: The carbon fiber is impregnated with the aforementioned adhesive film to obtain carbon fiber prepreg. Specifically, the fiber bundle is drawn out on the unwinding device, and the corresponding number of fibers are matched according to the prepreg weight requirements. The fibers are flattened by a flattening roller, and then the adhesive film is attached to the flattened fiber bundle. The resin matrix is ​​melted by a heating roller and impregnated into the fibers. The resin temperature is controlled at 70-90℃. After cooling, a release film is added (the release film is a PE film, which is non-adhesive; the prepreg has resin glue on it, and the release film separates the fibers to prevent them from sticking together), the edges are trimmed and the fibers are wound up to form the prepreg, which is then sealed and packaged.

[0054] The following explanation is needed regarding the above-mentioned scheme in this embodiment: This embodiment prepares a film by uniformly mixing a certain proportion of chopped fibers into a resin matrix, and then uniformly impregnating it onto carbon fibers using an impregnation device to produce carbon fiber prepreg. This achieves the purpose of adding a certain amount of chopped fibers between each layer of fibers when subsequently laying the carbon fiber prepreg. During the curing process of the prepreg, the flowing resin will carry the surrounding air bubbles towards the vacuum extraction port. The air bubbles will gradually converge and be discharged outward along the narrow channels on the fiber surface and between the fibers, allowing the air bubbles to be discharged more smoothly along the fiber-related channels, reducing porosity defects after the composite material is formed. This will help improve the stability of the forming quality of large-size plates, reduce the quality fluctuations of the plates caused by differences in manual layup, and produce a smooth product surface with no residual air bubbles inside. Especially for plates with a thickness of 10mm or more, it can fully exhaust internal gas during the vacuum curing stage, reduce the internal voids of the plate, and enhance the density of the plate. The carbon fiber plates prepared under this process have better structural integrity and better fatigue resistance. In subsequent use, they can adapt to more stress environments, that is, they have a certain improvement in durability.

[0055] Example 2

[0056] This embodiment provides a carbon fiber prepreg; wherein, the carbon fiber prepreg provided in this embodiment is prepared by the preparation method of the carbon fiber prepreg in Example 1. The carbon fiber prepreg prepared in this embodiment has a certain amount of chopped fibers added to its surface, which helps to reduce the internal voids of the board and improve the interlaminar shear properties of the board.

[0057] The carbon fiber prepreg provided in this embodiment is prepared using the method of Example 1, which results in short-cut fibers between the fibers of the carbon fiber prepreg in this embodiment. This is beneficial to improve the stability of the molding quality of large-size boards, reduce the quality fluctuation of boards caused by differences in manual layup, and produce a smooth product surface with no residual air bubbles inside. Especially for boards with a thickness of 10mm or more, it can fully exhaust internal gas during the vacuum curing stage, reduce the internal voids of the board, and enhance the density of the board.

[0058] Example 3

[0059] This embodiment provides a method for preparing a carbon fiber composite material sheet, wherein the method for preparing the carbon fiber composite material sheet includes the following steps:

[0060] Lamination steps: Cut the above-mentioned carbon fiber prepreg into prepreg layers of a set size; lay up multiple prepreg layers to obtain a laminated block.

[0061] In this step, such as Figure 1 As shown, when multiple prepreg layers are stacked, the fiber orientations of the prepreg layers are alternated between 0° and 90°. When the total number of prepreg layers is odd, the prepreg layers on both sides of the axis of symmetry are mirror-symmetrical, with the middle prepreg layer as the axis of symmetry, and the fiber orientations of the symmetrical layers are the same. When the total number of prepreg layers is even, the prepreg layers on both sides of the center plane between the two middle prepreg layers are mirror-symmetrical, with the fiber orientations of the two middle prepreg layers being the same.

[0062] Mold assembly steps: Assemble the mold and fix the stacked material blocks by the mold to obtain the loading mold.

[0063] Among them, such as Figure 3 As shown, in this step, a first release film is laid on the surface of the bottom plate 3; the stacked material blocks are placed in the limiting frame 1 coated with release agent, and the limiting frame 1 is placed on the first release film; a second release film is laid on the stacked material blocks; the top plate 2 is placed on the second release film to obtain the first loading mold.

[0064] Among them, see Figure 2The limiting frame 1 is formed by multiple limiting strips being snapped together end to end; preferably, it is formed by four limiting strips being snapped together end to end to form a square structure.

[0065] Among them, such as Figure 2 and Figure 5 As shown, each limiting strip includes one limiting strip unit 11. Alternatively, each limiting strip includes multiple overlapping limiting strip units 11 to increase the thickness of each limiting strip. Here, to achieve the overlapping of multiple limiting strip units 11, a pin hole 112 is provided on each limiting strip unit 11, and multiple limiting strip units 11 are stacked together using positioning pins 113 (stacking limiting strip units of different thicknesses is used to control the accuracy of the overall thickness of the sheet after molding). Preferably, to achieve the first and last ends of multiple limiting strips being connected, a snap-fit ​​structure 111 (e.g., a slot) is provided at the end of each limiting strip unit, so that the snap-fit ​​structures at the ends of two limiting strip units snap together.

[0066] Preferably, the loading mold includes only the first loading mold (e.g., Figure 3 (As shown). Or as... Figure 4 As shown, when mass-producing carbon fiber composite material sheets: there are multiple loading molds; wherein, the multiple loading molds are stacked, and the bottommost loading mold is the first loading mold; more preferably, for two adjacent loading molds, the loading mold located above uses the upper panel of the loading mold located below as the lower panel. Figure 4 The illustration uses a filling mold comprising a first filling mold, a second filling mold, and a third filling mold as an example. The first filling mold is located at the bottom. The second filling mold uses the upper panel 2 of the first filling mold as its lower panel, and a first release film is laid on its surface. The stacked material blocks are placed within a limiting frame 1 coated with a release agent, and the limiting frame 1 is placed on the first release film. A second release film is then laid on top of the stacked material blocks. The upper panel 2 is placed on the second release film, resulting in the second filling mold (the second filling mold is stacked on top of the first filling mold). Further, the third filling mold uses the upper panel 2 of the second filling mold as its lower panel, and a first release film is laid on its surface. The stacked material blocks are placed within a limiting frame 1 coated with a release agent, and the limiting frame 1 is placed on the first release film. A second release film is then laid on top of the stacked material blocks. The upper panel 2 is placed on the second release film, resulting in the third filling mold (the third filling mold is stacked on top of the first filling mold).

[0067] Curing step: The filling mold is cured to obtain a cured filling mold.

[0068] In the curing process: the filling mold is wrapped with breathable felt and a vacuum bag and then placed in an autoclave; the autoclave is evacuated, and when the vacuum level drops by ≤ 1 kPa within 5 minutes, the autoclave is closed, and heating and pressurization curing begins; the curing procedure is as follows: first, pressurize to 0.1-0.3 MPa, heat to 70-90℃ at a rate of 2-5℃ / min, and hold for 10-30 minutes; then pressurize to 0.4-0.6 MPa, heat to 90-120℃ at a rate of 2-5℃ / min, and hold for 10-30 minutes; then pressurize to 0.5-0.7 MPa, heat to 130-150℃ at a rate of 1-2℃ / min, and hold for 20-60 minutes; finally, depressurize by cooling at a rate of 2-5℃ / min until the temperature reaches room temperature, and then depressurize to atmospheric pressure.

[0069] Post-processing: The cured filling mold is disassembled to obtain the carbon fiber composite material sheet. Specifically, the cured filling mold is disassembled, the carbon fiber composite material sheet is removed, and the surrounding film is cleaned.

[0070] The above plan is explained as follows: Figures 2-5 This embodiment provides a method for preparing carbon fiber composite material sheets. A combined mold consisting of an upper panel 2, a lower panel 3, and a limiting frame 1 is designed. The limiting frames are connected by a snap-fit ​​structure 111, which fixes the position, prevents deformation, and ensures the dimensional accuracy of the sheet after curing. Furthermore, it is easy to assemble and disassemble, allowing for adjustments according to production needs. After disassembly, it is easy to clean, maintain, and store. Compared to conventional integrated pressure plate molds, it is lighter, lower in cost, and can accommodate batch processing of sheets of various sizes. The sheet thickness can be controlled within ±0.10mm. This process makes it easy to control the appearance quality of the sheet, which is beneficial for mass production.

[0071] Furthermore, this embodiment also provides a carbon fiber composite material sheet, wherein the carbon fiber composite material sheet is prepared by the preparation method of carbon fiber composite material sheet described in any of the above embodiments; wherein the carbon fiber composite material sheet has no shading in the middle; and wherein the shear strength of the carbon fiber composite material sheet is 65-75 MPa. The above-described solution of the present invention can meet the requirements of batch and same-tank production of sheets of different thicknesses.

[0072] The present invention will be further illustrated below through experimental examples:

[0073] Experimental Example 1

[0074] The preparation of carbon fiber composite material plates in this experimental example mainly includes the following steps:

[0075] Preparation steps of resin matrix: Add 58 parts by weight of solid epoxy resin and 10 parts by weight of 2-4mm short chopped fiber into a mixing tank and mix evenly. Then add 30 parts by weight of curing agent (dicyandiamide curing agent) and 2 parts by weight of coupling agent (aminosilane coupling agent). After stirring evenly again, the resin matrix is ​​obtained.

[0076] Preparation steps of the adhesive film: Heat the well mixed resin matrix to 80°C, feed it onto the impregnation roller, adjust the speed of the release paper and the gap between the impregnation rollers to make the adhesive film.

[0077] Impregnation steps: After cooling to 30°C, the fiber bundle is drawn out on the unwinding device. The number of fiber bundles is matched according to the weight requirement. The bundles are flattened by the flattening roller and then attached to the prepared adhesive film. The resin matrix is ​​melted by the heating roller and impregnated in the fiber. The impregnation resin temperature is controlled at 80°C. After cooling, adding a release film, trimming the edges and winding, carbon fiber prepreg is made and stored in a cold storage.

[0078] Laying steps: Take the carbon fiber prepreg stored after impregnation out of the cold storage and place it in a constant temperature and humidity room (temperature 20~24℃, humidity 45~55%) until there is no water vapor on the surface. Cut the prepreg into 1000×1000 mm pieces. Lay 60 sheets of 1000×1000 mm prepreg on each board. The laying method is [0°90°]15s, that is, lay the material alternately at 0° and 90° 15 times, and then lay it symmetrically 15 times [0°90°]. This completes the laying of carbon fiber board material blocks and obtains the laid material blocks.

[0079] Mold assembly steps: as follows Figure 3 As shown, remove panel 3 and place it on the workbench. Cut a 1100×1100 mm release film and lay it flat on panel 3, ensuring the release film is flat and free of scratches. Peel off the release paper from one side of the stacked material block and place that side on the release film. Take a limiting strip (1060×30×10 mm), apply the release agent evenly to the limiting strip, and then assemble the limiting strip around the stacked material block to form a limiting strip frame. Peel off the release paper from the other side of the stacked material block, cut another 1100×1100 mm release film and lay it flat on the surface of the material block. After smoothing the release film with a scraper, take the upper panel 3 and place it on the release film, ensuring that the upper panel 2 and the lower panel 3 are aligned. This completes the molding and closing of the carbon fiber plate material block.

[0080] Curing steps: Lay the vacuum film and breathable felt on the trolley platform in sequence. Place the entire loading mold on the breathable felt and wrap the upper and lower panels tightly with the breathable felt. Attach sealing strips to the vacuum film and insert the vacuum nozzle. After ensuring there are no sharp foreign objects on the vacuum film, wrap it with a vacuum bag and evacuate. After evacuating for 1 minute, close the vacuum valve and observe the change in vacuum level. If the vacuum level drops by ≤1 kPa within 5 minutes, close the autoclave. The curing procedure is as follows: Initially, pressurize to 0.2 MPa and heat at a rate of 2℃ / min. When the temperature reaches 80℃, hold for 20 minutes. Then pressurize to 0.3 MPa and heat at a rate of 2℃ / min. When the temperature reaches 100℃, hold for 10 minutes. Pressurize to 0.5 MPa and heat at a rate of 2℃ / min. When the temperature reaches 135℃, hold for 60 minutes. When cooling and depressurizing, cool at a rate of 4℃ / min. When the temperature drops to room temperature, begin depressurizing to atmospheric pressure.

[0081] Post-processing involves cutting open the vacuum membrane, removing the vacuum nozzle, opening the internal breathable felt, separating the upper and lower glass plates, removing the middle-formed carbon fiber plate, cleaning away excess material around the edges, and completing the forming of a 1000×1000×10mm carbon fiber sheet.

[0082] Comparative Example 1

[0083] Comparative Example 1 uses existing conventional methods to prepare carbon fiber sheets (1000×1000×10mm), mainly including the following steps:

[0084] Take carbon fiber prepreg (without added short fibers), place it in a constant temperature and humidity room (temperature 20-24℃, humidity 45-55%) until there is no water vapor on the surface, then cut the prepreg into 1000×1000 mm pieces. Lay 64 sheets of 1000×1000 mm prepreg on each board. The layup method is [0°, 90°] 17s, that is, lay up 17 times in [0°, 90°], and then lay up 17 times symmetrically in [0°, 90°]. This completes the laying up of the carbon fiber board material block, that is, the laid up material block.

[0085] like Figure 6 As shown, the stacked material block 5 is placed in the mold (including the mold base plate 4 and the mold cover plate 6). After the mold is closed, it is placed in the molding equipment and pressed and cured. After the board is cured, the mold is removed and the board is taken out to complete the molding of a 1000×1000×10mm carbon fiber composite material board.

[0086] Figure 7 These are ultrasonic non-destructive testing (NDT) scan results of the carbon fiber composite plates prepared in Experimental Example 1 and Comparative Example 1. Figure 7 Figure (1) shows the detection results of Experimental Example 1, and Figure (2) shows the detection results of Comparative Example 1. Figure 7As shown, the carbon fiber sheet prepared in Experimental Example 1 has no shadow in the middle, and the overall continuity of the sheet is relatively high. The carbon fiber sheet prepared in Comparative Example 1 has a large shadow in the middle, indicating that there are certain pores inside. During the molding process, the gas inside the sheet was not fully discharged, which has a certain impact on subsequent use. The long strip shadow in the test result image is the label, not a defect image.

[0087] Compared with Comparative Example 1, the shear strength of the carbon fiber composite sheet prepared in Experimental Example 1 is 65-75 MPa, while the interlaminar shear strength in Comparative Example 1 is between 55-65 MPa. This shows that the present invention increases the shear strength of the carbon fiber composite sheet by approximately 15%. During the layup process of carbon fiber prepreg, the manual layup method and techniques have a certain impact on the mechanical properties of the fiber laminate. Especially in mass production, human negligence often leads to defects in the sheet. The process scheme involved in this invention can effectively improve the appearance, dimensions, and performance of the sheet, and helps in quality control during mass production.

[0088] In summary, this invention provides a carbon fiber prepreg, carbon fiber composite sheet, and their preparation method. By adding a certain amount of chopped fibers during the prepreg preparation stage, resin particles and chopped fibers are uniformly mixed and melted to form a uniformly distributed resin matrix. This completes the addition of chopped fibers between the layers of the unidirectional or woven prepreg. The chopped fibers between the carbon fiber layers facilitate the extraction of internal gas during sheet molding, reduce interlayer voids, and improve the interlayer shear properties within the sheet. The invention also includes usage instructions and curing parameters for the prepreg, providing a complete production process from raw materials to finished products. Furthermore, in the preparation of carbon fiber composite sheets, this invention designs a freely clampable mold, which can flexibly process sheets of various specifications. The mold features detachable and assembleable limiting strips with uniform specifications, convenient use and maintenance, and interlocking structures at both ends of the limiting strips that can be connected to fix the position, preventing movement during molding and affecting sheet precision. Simultaneously, based on production needs, combined with the characteristics of the prepreg and the mold assembly quantity, a matching molding and curing regime is set, effectively ensuring processing efficiency and the quality of the molded sheets.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing carbon fiber prepreg, characterized in that, It includes the following steps: Preparation of resin matrix: Mix 50-70 parts by weight of solid epoxy resin, 10-20 parts by weight of chopped fibers, 20-40 parts by weight of curing agent, and 1-5 parts by weight of coupling agent to obtain resin matrix. Preparation steps of the adhesive film: Prepare an adhesive film of a set thickness from the resin matrix; Impregnation step: The carbon fiber is impregnated with the aforementioned adhesive film to obtain carbon fiber prepreg.

2. The carbon fiber prepreg according to claim 1, characterized in that, In the step of preparing the resin matrix: The chopped fibers are 2-4 mm in length; and / or The chopped fibers are chopped carbon fibers; and / or The curing agent is selected from dicyandiamide curing agent; and / or The coupling agent is selected from aminosilane coupling agents; and / or First, solid epoxy resin and chopped fibers are mixed in a mixing tank. Then, curing agent and coupling agent are added and stirred evenly to obtain the resin matrix.

3. The carbon fiber prepreg according to claim 1 or 2, characterized in that, In the step of preparing the adhesive film: The resin matrix is ​​heated to 70-90℃ and then conveyed to the impregnation roller to prepare a 100-200μm film.

4. The carbon fiber prepreg according to any one of claims 1-3, characterized in that, In the impregnation step: The fiber bundle is drawn out on the unwinding device. According to the required quality requirements of the carbon fiber prepreg, the corresponding number of fibers are matched and flattened by the flattening roller. Then, the adhesive film is attached to the flattened fiber bundle. The resin matrix is ​​melted by the heating roller and impregnated in the fiber. After cooling, adding a release film, trimming the edges, and winding, the carbon fiber prepreg is obtained. Preferably, the heating temperature of the heating roller is 70-90℃.

5. A carbon fiber prepreg, characterized in that, The carbon fiber prepreg is prepared by the method for preparing carbon fiber prepreg according to any one of claims 1-4; wherein, short-cut fibers are adhered to the surface of the carbon fiber prepreg.

6. A method for preparing a carbon fiber composite material plate, characterized in that, The preparation method of the carbon fiber composite material plate includes the following steps: Lamination step: Cut the carbon fiber prepreg as described in claim 5 into prepreg layers of a set size; lay up multiple prepreg layers to obtain a laminated block; Mold assembly steps: Assemble the mold and fix the stacked material blocks in place by the mold to obtain the loading mold; Curing step: The filling mold is cured to obtain a cured filling mold; Post-processing: The mold after curing is disassembled to obtain carbon fiber composite material sheets.

7. The method for preparing carbon fiber composite material plates according to claim 6, characterized in that, In the said layup step: When multiple prepreg layers are stacked: the fiber orientation of the prepreg layers is set alternately at 0° and 90°; When the total number of prepreg layers is odd, the prepreg layer in the middle is taken as the axis of symmetry, and the prepreg layers on both sides of the axis of symmetry are mirror symmetrical, and the fiber directions of the symmetrical layers are the same. When the total number of prepreg layers is even, the prepreg layers on both sides of the center plane between the two middle prepreg layers are mirror-symmetrical, and the fiber orientation of the two middle prepreg layers is the same.

8. The method for preparing carbon fiber composite material plates according to claim 6 or 7, characterized in that, In the assembly mold step: A first release film is laid on the surface of the bottom plate; the stacked material blocks are confined within a confining frame coated with a release agent, and the confining frame is placed on the first release film; a second release film is laid on the stacked material blocks; the top plate is placed on the second release film to obtain the first loading mold; Preferably, the limiting frame is a frame structure formed by multiple limiting strips being snapped together end to end; Preferably, each limiting strip includes a limiting strip unit or each limiting strip includes multiple overlapping limiting strip units to increase the thickness of each limiting strip; Preferably, the loading mold includes only a first loading mold; or when producing carbon fiber composite material sheets in batches: there are multiple loading molds; wherein, the multiple loading molds are stacked, and the bottommost loading mold is the first loading mold; more preferably, for two adjacent loading molds, the loading mold located above uses the upper panel of the loading mold located below as the lower panel.

9. The method for preparing carbon fiber composite material plates according to any one of claims 6-8, characterized in that, In the curing process: the filling mold is wrapped with breathable felt and a vacuum bag and then placed in an autoclave; the autoclave is evacuated, and when the vacuum level drops ≤ 1 kPa within 5 minutes, the autoclave is closed, and heating and pressurization curing begins; the curing procedure is as follows: first, pressurize to 0.1-0.3 MPa, heat to 70-90℃ at a rate of 2-5℃ / min, and hold for 10-30 minutes; then pressurize to 0.4-0.6 MPa, heat to 90-120℃ at a rate of 2-5℃ / min, and hold for 10-30 minutes; then pressurize to 0.5-0.7 MPa, heat to 130-150℃ at a rate of 1-2℃ / min, and hold for 20-60 minutes; finally, depressurize by cooling at a rate of 2-5℃ / min until the temperature reaches room temperature, and then depressurize to atmospheric pressure. In the post-processing step: the mold after curing is disassembled, the carbon fiber composite material sheet is removed, and the surrounding film is cleaned.

10. A carbon fiber composite material plate, characterized in that, The carbon fiber composite material sheet is prepared by the method for preparing carbon fiber composite material sheet according to any one of claims 6-9; Preferably, after ultrasonic non-destructive testing, the carbon fiber composite material sheet has no shadow in the middle and no pore defects. Preferably, the shear strength of the carbon fiber composite plate is 65-75 MPa.

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