Adhesive film sealing structure for composite material forming and preparation method and application thereof

Abstract

The invention discloses an adhesive film sealing structure for forming a composite material as well as a preparation method and application of the adhesive film sealing structure. The adhesive film sealing structure comprises a flexible fabric reinforcing body, a silica gel base body and a vacuum valve. The vacuum valve is pre-embedded in the flexible fabric reinforcement body, and the silica gel matrix coats the flexible fabric reinforcement body and coats the joint of the vacuum valve and the flexible fabric reinforcement body to form a co-inlay structure. The adhesive film sealing structure is matched with a forming die to form a composite material part, and excellent sealing performance, puncture resistance and shape follow-up performance under the high-temperature and high-pressure environment are achieved. The adhesive film sealing structure can be repeatedly used, use of auxiliary materials such as isolating films, breathable felts and sealing adhesive strips is reduced, the adhesive film sealing structure can also play a role of a pressure pad, the appearance quality of products is guaranteed, the production cost, the operation difficulty and the environmental pollution risk are remarkably reduced, and the service life is prolonged. The problems that a traditional PE / PA vacuum bag is disposable, prone to air leakage and bag explosion, tedious in operation, poor in product quality and the like are solved.

Description

Technical Field

[0001] This invention relates to the field of composite material molding technology, specifically to a reusable adhesive film sealing structure for composite material molding, its preparation method, and its application. This adhesive film sealing structure can be repeatedly used to mold composite material parts and can also function as a pressure pad during the molding process, ensuring product molding quality. Background Technology

[0002] Composite materials, especially carbon fiber reinforced resin matrix composites, are widely used in aerospace, rail transportation, and high-end sporting goods due to their advantages such as high specific strength, high specific modulus, and strong designability. Current composite material molding processes typically include autoclave molding or oven molding. In these processes, a vacuum bag sealing system needs to be established on the composite prepreg layers to remove interlayer air and volatiles, providing vacuum pressure and external pressure for product molding, while simultaneously completing the resin curing reaction at high temperatures.

[0003] Currently, the vacuum bag sealing system commonly used in the industry is mainly based on thermoplastic plastic bag film, such as polyethylene (PE) or nylon (PA) bag film. In order to ensure the conformability of the vacuum bag, these vacuum bag films are usually thin (about 50-75μm). Therefore, this traditional vacuum bag system has the following defects: (1) Non-reusability: After the PE or PA vacuum bag film has undergone high temperature curing of the composite material (usually above 130°C), it will undergo thermal aging and degradation, which will cause the material to harden and become brittle, lose its flexibility and sealing performance, and cannot be reused. This means that each molding process requires the consumption of brand new vacuum bag material, which is not only costly, but also generates a lot of solid waste, which is not environmentally friendly. (2) Vulnerability and sealing reliability issues: Due to the extremely thin film, it is easily scratched or punctured during handling and laying, leading to vacuum leakage. During the heating and pressurization process in the autoclave, if there are minor defects in the film or improper laying (such as "bridging" at complex curved surfaces), it is very easy to "burst" due to uneven pressure, resulting in product scrap and economic loss. Currently, vacuum bag sealing usually relies on additional sealing strips. The adhesion between the strips and the mold and the film may fail under high temperature and pressure, causing air leakage. (3) Numerous auxiliary materials and complex operation: In order to prevent the vacuum bag film from sticking to the uncured resin, multiple layers of auxiliary materials such as isolation film and breathable felt must be laid between the product and the vacuum bag. Most of these auxiliary materials are also disposable, which further increases the material cost and waste. In addition, the laying process is cumbersome and requires high skill from the operators. Improper laying of any layer of auxiliary materials may affect the quality of the product. In addition, in order to achieve a vacuum passage, it is also necessary to accurately arrange the vacuum pipeline and sealing strips, which is complicated and inefficient. (4) Surface quality and additional costs: For products with extremely high surface quality requirements (such as aircraft skin), wrinkles in the release liner and vacuum bag may be transferred to the product surface under pressure, forming marks. To solve this problem, it is usually necessary to lay an additional layer of special elastic pressure pad (such as silicone rubber pad) on top of the release liner, which undoubtedly further increases material costs and operating procedures.

[0004] In summary, developing a novel sealing system that overcomes the aforementioned shortcomings, possesses reusability, high reliability, ease of operation, and integrates pressure pad functionality, has become a crucial issue urgently needing resolution in the field of composite material molding technology. While attempts have been made to use silicone materials, integrating them with reinforcing structures and vacuum valves to form a stable, durable, and highly process-adaptable systematic solution remains a challenge that current technologies have not yet fully addressed. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a sealing structure for composite material molding, its preparation method, and its application. It aims to solve problems in existing technologies such as the inability to reuse sealing systems, susceptibility to air leakage and bag bursting, the need for large amounts of auxiliary materials, operational difficulties, and the need to use pressure pads to ensure product molding quality.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A composite material molding film sealing structure includes a flexible fabric reinforcement, a silicone matrix, and a vacuum valve. The vacuum valve is embedded in the flexible fabric reinforcement, and the silicone matrix covers the flexible fabric reinforcement and the connection between the vacuum valve and the flexible fabric reinforcement, forming a co-embedded structure.

[0007] In this adhesive film sealing structure, the silicone matrix possesses extremely high elongation at break (≥600%) and extremely low tensile modulus (≤0.01GPa), endowing the sealing structure with excellent flexibility and deformability. This allows it to adhere well to composite materials and molds. Furthermore, the adhesive properties of the silicone matrix enable it to achieve a self-sealing effect by adhering to the mold without the need for sealing strips. Moreover, after sealing, the higher the external pressure, the lower the risk of leakage. The flexible fabric reinforcement provides skeletal support for the silicone matrix, improving the puncture resistance and tear resistance of the adhesive film sealing structure, and further reducing the risk of leakage.

[0008] In another embodiment, the flexible reinforcing fabric is a flexible warp-knitted spacer fabric. The warp-knitted spacer fabric has a certain thickness and a fluffy three-dimensional structure. Its porous structure is conducive to the anchoring of the silicone matrix, forming a strong and tough composite material structure. At the same time, the warp-knitted spacer fabric, together with the silicone matrix, can have sufficient deformation capacity when subjected to pressure or tension, and can rebound after the pressure or tension is removed.

[0009] In another embodiment, the silicon matrix has a temperature resistance of -60°C to 250°C; the flexible fabric reinforcement is woven from high-temperature resistant fibers (above 150°C), wherein the high-temperature resistant fibers are at least one of glass fiber, basalt fiber, aramid fiber, and pre-oxidized filament fiber. Typically, the molding temperature range of composite materials is 120-205°C, and the temperature resistance of the silicone matrix, between -60°C and 250°C, can meet the molding temperature requirements of most composite materials, ensuring long-term repeated use at 200°C, while maintaining good conformability and sealing properties.

[0010] In another embodiment, the thickness of the flexible fabric reinforcement is 1-5 mm, and the overall thickness of the adhesive film seal is 2-6 mm. Unlike PE / PA materials, silicone matrix has excellent flexibility and retains excellent conformability even at a certain thickness. By preparing an adhesive film seal structure of a certain thickness, better puncture resistance can be achieved, reducing the risk of air leakage. Furthermore, in existing processes, to form composite parts with high surface quality requirements, it is usually necessary to cover the product surface with a pressure pad to ensure a smooth surface and avoid wrinkles from the release liner and vacuum bag. In this invention, the silicone sealing film structure of a certain thickness can act as a pressure pad during the part forming process, ensuring a smooth surface is formed during molding.

[0011] In another embodiment, the adhesive film sealing structure is sheet-like or conforms to the shape of the composite material part. Due to the ductility of the silicone matrix and the elasticity of the flexible fabric reinforcement, a sheet-like adhesive film sealing structure can typically adapt to different product profiles and deform under external pressure, continuing to transmit pressure to the composite material part. The extremely high elongation at break ensures that the adhesive film sealing structure will not burst. However, for parts with very complex profiles, the adhesive film sealing structure can be custom-molded to conform to the shape of the composite material part, thereby achieving better conformability.

[0012] The method for preparing the above-mentioned adhesive film sealing structure includes the following steps: S11. Prepare a flexible fabric reinforcement with a thickness of 1-5mm, the size of which is larger than the working surface of the composite material part molding die; S12. Position the vacuum valve and pre-set it to the predetermined position relative to the flexible fabric reinforcement; S13. Apply liquid silicone to the flexible fabric reinforcement by spraying, injection or hand lay-up, so that it fully wets and completely covers the flexible fabric reinforcement, as well as the connection part between the vacuum valve and the flexible fabric reinforcement. S14. The composite obtained in step S3 is cured to form a film sealing structure.

[0013] The curing process can be carried out by allowing the material to cure at room temperature or by curing it in an oven at 60-100°C.

[0014] Secondly, a reusable high-pressure sealing system for molding composite materials is provided, comprising the aforementioned film sealing structure and a composite material molding die.

[0015] Thirdly, a method for molding composite materials is provided, comprising the following steps: S21. Based on the layup design of the composite material part, complete the sheet laying on the composite material molding die; S22. A film sealing structure is directly covered on top of the material sheet, so that the four edges of the film sealing structure are in contact with the mold surface to form a high-pressure sealing system. S23. Vacuum the high-pressure sealing system through the vacuum valve on the film sealing structure; S24. Curing prepares composite material parts.

[0016] The beneficial effects of this invention are as follows: (1) Reusability: The core material, silicone matrix, has excellent heat aging resistance and can maintain its elasticity and sealing performance even after long-term use at 200℃. After testing, this sealing system can be reused dozens or even hundreds of times without significant performance degradation, which greatly reduces the cost of consumables per molding and reduces waste; (2) Extremely high sealing reliability and damage resistance: The inherent flexibility and viscosity of silicone material enable it to produce an excellent "fitting surface sealing" effect under external pressure when in contact with the mold surface. The greater the pressure, the tighter the seal, eliminating the need for easily failed sealing strips; The silicone matrix of a certain thickness combined with the fabric reinforcement gives it excellent puncture resistance and makes it less likely to be scratched or punctured under external force, effectively avoiding the risk of "bag bursting". (3) Significantly reduced auxiliary material consumption: Since the silicone matrix does not adhere to common composite material matrices such as epoxy resin, it can directly contact the product without the need for release films or breathable felts. At the same time, the system itself has an integrated sealing function, eliminating the need to seal the film to the mold surface with sealing strips; this significantly reduces auxiliary material costs, layup time, and waste. (4) Easy to operate and highly adaptable: The extremely high elongation at break and low modulus of the silicone sealing film enable it to adapt well to complex component surfaces. Even in areas with large curvature changes, it can adhere tightly to the product under external pressure, effectively transmit pressure, and avoid quality defects caused by "bridging". For particularly complex surfaces, silicone sealing films can be customized by mold making to obtain perfect conformity. (5) Integrated pressure pad function: The smooth inner surface of the silicone sealing film can be used directly as a pressure pad to uniformly transmit pressure and ensure that the surface of the composite material product is smooth and wrinkle-free, saving the steps and costs of preparing and laying a special pressure pad. Attached Figure Description

[0017] Appendix Figure 1 This is a schematic diagram of a silicone sealing structure; Appendix Figure 2 This is a schematic diagram of the high-pressure sealing structure of Example 1; Appendix Figure 3 This is a schematic diagram of the bag film sealing structure in Comparative Example 1; Appendix Figure 4 This is a schematic diagram illustrating the failure of the bag film sealing structure in Comparative Example 2.

[0018] In the diagram: 1-Silicone sealing structure; 11-Silicone matrix; 12-Flexible fabric reinforcement; 13-Vacuum valve; 2-Molding die; 3-Composite component; 4-Bag film; 5-Pressure pad; 6-Separation membrane; 7-Breathable felt; 8-Sealing strip; 9-Bridging position. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are used to further illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Example 1

[0020] This embodiment uses a molded carbon fiber epoxy resin flat plate component as an example. The preparation method is as follows:

[0021] S1. Prepare a molding mold and fabricate a film sealing structure according to the dimensions of the flat plate component; the film sealing structure is as follows: Figure 1 As shown, the structure is sheet-like, comprising a silicone matrix 11, a flexible fabric reinforcement 12, and a vacuum valve 13. The vacuum valve 13 is embedded in the flexible fabric reinforcement 12. The silicone matrix 11 covers the flexible fabric reinforcement 12 and the connection between the vacuum valve 13 and the flexible fabric reinforcement 12, forming a co-embedded structure. Its fabrication steps are as follows: S11. Prepare a glass fiber warp-knitted spacer fabric, larger than the working surface of the mold, with a thickness of about 0.5 mm, as a flexible fabric reinforcement for the adhesive film sealing structure; S12. Place the vacuum valve at the predetermined position on the glass fiber warp-knitted spacer fabric; S13. Apply liquid silicone matrix to glass fiber warp-knitted spacer fabric using spraying, injection, or hand lay-up methods, ensuring it fully impregnates and completely covers the glass fiber warp-knitted spacer fabric, as well as the connection area between the vacuum valve and the glass fiber warp-knitted spacer fabric. The viscosity of the liquid silicone matrix used to impregnate and cover the glass fiber warp-knitted spacer fabric is controlled to be less than or equal to 6000 mPa·s, and the viscosity of the liquid silicone matrix used to cover the connection area between the vacuum valve and the glass fiber warp-knitted spacer fabric is controlled to be 30000-80000 mPa·s. A glass fiber warp-knitted spacer fabric reinforcement layer is provided around the vacuum valve. S14. The composite obtained in step S13 is cured to form a sheet-like adhesive film sealing structure with an overall thickness of 2mm. S2. Prepare the flat plate component. The specific steps are as follows: S21. Lay epoxy resin carbon fiber prepreg on the molding die according to the layup design of the composite material part; S22. Directly cover the film sealing structure obtained in step S1 over the material sheet, ensuring that the edges of the film sealing structure adhere to the edges of the molding die surface to form a high-pressure sealing system; see attached diagram for specific structural details. Figure 2 ; S23. Evacuate the high-pressure sealing system to ≤-0.085MPa using the vacuum valve on the film sealing structure; S24. The high-pressure sealing system after vacuuming is placed into a hot autoclave for curing. The curing temperature is set to 130℃ / 3h and the pressure is set to 0.6MPa to obtain a carbon fiber epoxy resin flat plate component.

[0022] Example Results: Due to the elimination of the need for auxiliary materials such as isolation membranes, breathable felts, and sealing strips, and the self-absorbing properties of silicone, the entire sealing process is simple and convenient, improving production efficiency. The probability of seal failure or bag bursting is extremely low during sealing and curing in the autoclave. The molded flat components have smooth, wrinkle-free surfaces, improving product yield. After being reused dozens of times, the silicone sealing structure remains intact and shows no signs of aging. Example 2

[0023] This embodiment takes the molding of a part with corners as an example. The preparation method is as follows:

[0024] S1. Prepare the molding mold and fabricate the adhesive film sealing structure according to the shape and dimensions of the part; in this embodiment, the adhesive film sealing structure can be made into a sheet shape as in Embodiment 1, or a conformal adhesive film sealing structure can be fabricated by mold making based on the part; the steps for fabricating the sheet-shaped adhesive film sealing structure are as follows: S11. Prepare a polyester fiber warp-knitted spacer fabric, larger than the working surface of the mold, with a thickness of about 0.5 mm, as a flexible fabric reinforcement for the adhesive film sealing structure; S12. Place the vacuum valve at the predetermined position on the glass fiber warp-knitted spacer fabric; S13. Apply liquid silicone matrix to polyester warp-knitted spacer fabric using spraying, injection, or hand lay-up methods, ensuring it fully impregnates and completely covers the polyester warp-knitted spacer fabric, as well as the connection area between the vacuum valve and the polyester warp-knitted spacer fabric. The viscosity of the liquid silicone matrix used to impregnate and cover the polyester warp-knitted spacer fabric is controlled to be less than or equal to 6000 mPa·s, and the viscosity of the liquid silicone matrix used to cover the connection area between the vacuum valve and the polyester warp-knitted spacer fabric is controlled to be 30000-80000 mPa·s. A glass fiber warp-knitted spacer fabric reinforcement layer is provided around the vacuum valve. S14. The composite obtained in step S3 is cured to form a sheet-like adhesive film sealing structure with an overall thickness of 2 mm. S2. The steps for preparing composite material parts are as follows: S21. Lay epoxy resin carbon fiber prepreg on the molding die according to the layup design of the composite material part; S22. Directly cover the sheet-like adhesive film sealing structure obtained in step S1 on top of the material sheet, so that the four edges of the adhesive film sealing structure are in contact with the edge of the molding die surface to form a high-pressure sealing system. S23. Evacuate the high-pressure sealing system to ≤-0.085MPa using the vacuum valve on the film sealing structure; S24. The high-pressure sealing system after vacuuming is placed into a thermostatic precipitator for curing. The curing temperature is set to 130℃ / 3h and the pressure is set to 0.6MPa to obtain a carbon fiber epoxy resin flat plate component.

[0025] Example Results: Due to the elimination of the need for auxiliary materials such as release membranes, breathable felts, and sealing strips, and the self-absorbing properties of silicone, no special pleating is required at corners, making the entire sealing process simple and convenient, and improving production efficiency; the probability of seal failure or bag bursting is extremely low during sealing and curing in the autoclave; during the vacuuming process of the high-pressure sealing system, the silicone sealing structure can conform well to the shape, and no "bridging" or "bag bursting" occurs at corners, and the surface of the molded composite material component is smooth and wrinkle-free.

[0026] Comparative Example 1 As a comparative example of Example 1, the difference lies in the use of a vacuum bag film of existing technology for bag sealing. A schematic diagram of the sealing structure is shown in the attached diagram. Figure 3 In this embodiment, a release film, a breathable felt, and a vacuum bag need to be sequentially laid on top of the material sheet. The edges of the vacuum bag need to be glued to the mold with sealing strips. For cases where high appearance quality is required, a pressure pad also needs to be placed between the release film and the material sheet.

[0027] As can be seen from the above, compared with Comparative Example 1, Example 1: (1) can save a variety of auxiliary materials, and its reusability can greatly save costs; (2) the reduction of auxiliary materials can make the operation simpler and improve labor efficiency; (3) the silicone sealing film is more reliable than the bag film, which can better guarantee the molding quality of composite material parts.

[0028] Comparative Example 2 As a comparative example of Example 2, the difference lies in the use of a vacuum bag, a technology already in use, for bagging and sealing. In this example, a release film, a breathable felt, and a vacuum bag are sequentially laid on top of the material sheet, and pleats are made at the corners of the release film, the breathable felt, and the vacuum bag. The edges of the vacuum bag are glued to the mold using sealing strips. For cases requiring high surface quality, a pressure pad is also needed between the release film and the material sheet.

[0029] During operation, the installation of the release liner, breathable felt, and vacuum bag is extremely difficult, and bridging is very likely to occur during vacuuming. This can prevent pressure from being transmitted to the composite material, resulting in quality defects, or even cause the bag to burst, rendering the entire product unusable. See the attached diagram for a seal failure illustration. Figure 4 .

[0030] The comparison between the above embodiments and comparative examples fully demonstrates that the reusable composite material molding film sealing structure of the present invention is significantly superior to traditional technologies in terms of repeatability, reliability, economy, environmental protection and ease of operation.

[0031] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A film sealing structure for composite material molding, characterized in that, The device includes a flexible fabric reinforcement, a silicone matrix, and a vacuum valve. The vacuum valve is embedded in the flexible fabric reinforcement, and the silicone matrix covers the flexible fabric reinforcement and the connection between the vacuum valve and the flexible fabric reinforcement, forming a co-embedded structure.

2. The adhesive film sealing structure for composite material molding according to claim 1, characterized in that, The flexible fabric reinforcement is a flexible warp-knitted spacer fabric.

3. The adhesive film sealing structure for composite material molding according to claim 1, characterized in that, The flexible fabric reinforcement is woven from high-temperature resistant fibers, which are selected from at least one of glass fiber, basalt fiber, aramid fiber, and pre-oxidized fiber.

4. The adhesive film sealing structure for composite material molding according to claim 1, characterized in that, The thickness of the flexible fabric reinforcement is 0.5-5 mm; the overall structural thickness of the sealant film is 2-6 mm.

5. The adhesive film sealing structure for composite material molding according to claim 1, characterized in that, The adhesive film seal is in sheet form or conforms to the shape of the composite material part.

6. The adhesive film sealing structure for composite material molding according to claim 1, characterized in that, The temperature resistance of the silicone matrix is ​​from -60°C to 250°C.

7. A film sealing structure for composite material molding according to any one of claims 1-6, characterized in that, The method for preparing the adhesive film seal includes the following steps: S11. Prepare a flexible fabric reinforcement with a thickness of 1-5mm, the size of which is larger than the working surface of the product molding die. S12: Position the vacuum valve and pre-position it at the predetermined location of the flexible fabric reinforcement; S13: Apply liquid silicone matrix to flexible fabric reinforcement by spraying, injection or hand lay-up, so that it fully wets and completely covers the flexible fabric reinforcement, as well as the connection between the vacuum valve and the flexible fabric reinforcement. S14: The composite obtained in step S3 is cured to form a film sealing structure.

8. A high-pressure sealing system for composite material molding, characterized in that, Includes the film sealing structure and composite material part molding die as described in any one of claims 1-6.

9. A method for molding composite materials, characterized in that, The high-pressure sealing system according to claim 8 specifically includes the following steps: S21. Based on the layup design of the composite material part, complete the sheet laying on the composite material molding die; S22. Cover the material sheet directly with the adhesive film sealing structure, so that the four edges of the adhesive film sealing structure are in contact with the mold surface; S23. Vacuum the high-pressure sealing system through the vacuum valve on the film sealing structure; S24. The vacuum-sealed mold is placed into the container to allow the composite material to solidify and form, thus obtaining the composite material part.

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