A sacrificial layer prepreg for composite materials and preparation method thereof

Abstract

The present application discloses a sacrificial layer prepreg for composite materials and a preparation method thereof, which belongs to the field of composite material molding. The preparation method described in the present application comprises: mixing an inorganic filler with a resin and then forming a film to obtain a resin film; coating the resin film on the surface of the fiber to obtain a sacrificial layer prepreg; after the preparation of the sacrificial layer prepreg, the sacrificial layer prepreg, the absorbing prepreg and the structural prepreg are sequentially laid on the surface of the tooling according to the thickening requirements of the tooling, and the co-curing treatment and demoulding treatment are carried out according to the curing process of the structural prepreg to obtain a composite material with a surface coated with a sacrificial layer prepreg. The sacrificial layer prepreg for composite materials prepared in the present application uses aramid fiber with excellent flexibility as a carrier, which can be directly peeled off manually, and the actual number of stacked layers can be adjusted according to the thickness requirements of the tooling. Compared with the traditional CNC cutting method, the peeling efficiency is faster and the thickness control is more precise.

Description

Technical Field

[0001] The present application belongs to the technical field of composite material forming, and specifically relates to a sacrificial layer prepreg for composite materials and a preparation method thereof. Background Art

[0002] Composite material processing equipment (abbreviated as composite material processing equipment or composite tooling) is used to form composite parts for aircraft bodies, primarily using autoclave molding, resin transfer molding (RTM), and compression molding. Lay-up tooling (LM) is widely used in autoclave molding for large composite panels. Composite materials are distinct from metals. Material forming and structural component forming are completed simultaneously. The structural properties of composite materials are highly sensitive to the manufacturing process and the composite tooling structure. The ultimate performance of the material is also determined by the tooling and manufacturing process. These processes and tooling structures directly impact the quality of composite structural parts. Improper processing or any aspect of the composite tooling can lead to manufacturing defects and dimensional deviations in the composite material, severely impacting its performance and even causing component failure. For example, over-milling can lead to manufacturing defects and dimensional deviations in the composite material.

[0003] Over-milling refers to the phenomenon of excessive cutting during the milling process, where the milling cutter's cutting depth exceeds the predetermined value or the milling time is too long. This phenomenon can negatively impact workpiece quality. If the affected tooling is scrapped, re-manufacturing it will incur extremely high tooling costs. Therefore, if over-milling occurs during the actual composite molding process, the tooling needs to be thickened. Similarly, in the actual composite molding process, tooling thickness may also be required due to design requirements.

[0004] Therefore, there is an urgent need for a method that can freely adjust the thickness of the tooling, so that the tooling can be thickened during the composite molding process. Summary of the Invention

[0005] The purpose of the present application is to provide a sacrificial layer prepreg for composite materials and a preparation method thereof, which can solve the problem that the tooling becomes thinner after milling and cannot be reused.

[0006] To achieve the above-mentioned object, the present application provides a method for preparing a sacrificial layer prepreg for composite materials, comprising the following steps:

[0007] Mixing the inorganic filler with the resin and then forming a film to obtain a resin film;

[0008] Applying the resin film on the surface of the fiber to obtain a sacrificial layer prepreg;

[0009] After the sacrificial layer prepreg is prepared, the sacrificial layer prepreg, the absorbing prepreg, and the structural prepreg are sequentially laid on the surface of the tooling according to the tooling thickening requirements, and co-curing and demolding are performed according to the curing process of the structural prepreg to obtain a composite material with a surface coated with the sacrificial layer prepreg; wherein:

[0010] The fiber is an aramid unidirectional tape or an aramid fabric.

[0011] Furthermore, the inorganic filler is inorganic rigid particles, and the filling amount of the inorganic filler in the resin film is 10 wt % to 90 wt %.

[0012] Furthermore, the inorganic filler includes at least one of alumina, glass beads and silica, and the resin includes at least one of epoxy resin, bismaleimide resin and cyanate resin.

[0013] Furthermore, the weight of the resin film is 10 g / m 2 ~200g / m 2 .

[0014] Furthermore, the fiber is an aramid unidirectional tape or an aramid fabric, and the mass ratio of the inorganic filler to the fiber in the sacrificial layer prepreg is (1-2):10.

[0015] Furthermore, the absorbing prepreg is composited by an absorbing resin and a fiber carrier, and the content of the fiber carrier in the absorbing prepreg is 30wt%~90wt%; the raw materials of the absorbing resin include a metal absorber and a resin, and the content of the metal absorber in the absorbing resin is 40wt%~98wt%.

[0016] Furthermore, the structural prepreg is formed by compounding resin and carbon fiber, and the content of the carbon fiber in the structural prepreg is 60wt% to 70wt%.

[0017] Furthermore, paving the sacrificial layer prepreg on the surface of the tooling includes paving at least one layer of the sacrificial layer prepreg, and the thickness after paving is 0.1 mm to 10 mm.

[0018] Furthermore, the curing process includes the following steps:

[0019] The autoclave curing method is adopted, the internal pressure of the autoclave is increased to 3 bar ~ 6 bar, the temperature is increased to 120 ° C ~ 180 ° C, and the constant temperature is maintained for 30 minutes ~ 240 minutes; the temperature is further increased to 190 ° C ~ 260 ° C, and the constant temperature is maintained for 30 minutes ~ 240 minutes; the temperature is reduced to 30 ° C ~ 80 ° C, and the pressure is released.

[0020] The present application also provides a sacrificial layer prepreg for composite materials, which is prepared using the above-mentioned preparation method.

[0021] In summary, this application has the following advantages:

[0022] The sacrificial layer prepreg for composite materials prepared in this application has excellent tooling adaptability and convenience. After the prepreg is laid on the tooling surface, the tooling thickness can be flexibly adjusted according to the specific tooling design requirements, thereby achieving fast and easy tooling preparation. The sacrificial layer prepreg on the surface of the composite material can be removed by a simple tearing operation, thereby achieving the purpose of tooling thickening and composite material forming at the same time during the composite material forming process. In addition, the residual resin film forms a protective layer on the surface of the composite material, which significantly improves the chemical corrosion resistance of the composite material and extends the service life of the tooling.

[0023] Specifically, the sacrificial layer prepreg in the present application is mainly used as a tooling thickening structure, and the tooling thickening thickness is calibrated by the coating thickness of the sacrificial layer prepreg. It can be stacked and laid according to the tooling size and shape requirements to achieve precise control of the tooling thickness; the absorbing prepreg in the present application is mainly used as an absorbing functional layer to provide absorbing performance for the composite material; the structural prepreg in the present application bears the main mechanical properties of the composite material (such as strength, stiffness, etc.), that is, the absorbing prepreg in the present application and the structural prepreg form a composite material, and the sacrificial layer prepreg in the present application is used to thicken the tooling during the composite material molding process, and can be removed from the surface of the composite material after molding, without affecting the structure of the original tooling or the structure of the composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a comparison diagram of the sacrificial layer prepreg for composite materials prepared in Example 1 of the present application after manual tearing; wherein, Figure 1 (a) is a photo of the sacrificial layer prepreg for composite materials before it is torn. Figure 1 (b) is a photo of the sacrificial layer prepreg used in composite materials being torn off. Figure 1 (c) is the photo after tearing is completed.

[0025] Figure 2 These are the results of the salt spray test on the composite materials prepared in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0026] Composite materials are made up of two or more different materials. They have the characteristics of light weight, high strength, corrosion resistance, and good damping properties. They are widely used in aviation, aerospace, automobiles and other fields. In order to produce composite products, it is necessary to design corresponding tooling and equipment to realize the molding, connection and assembly of composite materials. The development of composite materials is of great significance to the performance improvement of aviation equipment. The performance of an aircraft depends half on the design and the other half on the materials selected. Due to their unique physical and chemical properties, composite materials have a profound impact on the speed, altitude, range, maneuverability and other performance of the aircraft. Composite materials are widely used in the aviation field for military aircraft, civil aircraft, helicopters, drones, aircraft engines and other defense and military industries. At present, most of the structural parts of aircraft are made of composite materials.

[0027] Composite molding tooling refers to tooling and equipment designed for the manufacture of composite molded products. It is the tools and equipment used to shape and assemble composite materials during the composite manufacturing process. Its primary function is to ensure that the shape, size, and performance of composite components meet design requirements while improving production efficiency and reducing costs. In the aviation field, composite tooling is primarily used to manufacture key components of aircraft such as rockets and aircraft, such as wings and fuselages. Therefore, tooling design must meet high precision and high strength requirements.

[0028] In composite molding tooling technology, milling is often required for the following reasons: ① Excess material or burrs remain on the tooling, affecting the tooling's precision and surface quality; ② To adjust the tooling's size and shape and correct for dimensional errors; ③ To improve the tooling's surface quality and reduce surface roughness; ④ To process various complex shapes to meet the needs of tooling of varying shapes and sizes. However, during the actual milling process, cutting forces can cause localized deformation and tool deflection in the part, leading to localized deformation and irreversible plastic deformation. Furthermore, factors such as high material removal rates during high-speed cutting and complex cross-sectional shapes can lead to the release and rebalancing of residual stresses, which can also cause workpiece deformation. These deformations can lead to over-milling of the tooling, which can cause the tooling to become thinner and, therefore, scrapped due to its inability to be reused.

[0029] Therefore, the present application proposes a method for preparing a sacrificial layer prepreg for composite materials. The prepared sacrificial layer prepreg for composite materials includes three different functional materials. In the entire composite molding process (including the process of thickening the tooling and the process of preparing the composite material in the thickened tooling), the sacrificial layer prepreg is mainly used as a sacrificial layer after curing. On the one hand, it can directly thicken the tooling that is over-milled or of insufficient thickness. On the other hand, the composite material can be directly molded in the thickened tooling. After molding, the sacrificial layer is easy to peel off and will not have any negative impact on the molded composite material and the tooling after use. After curing, the absorbing prepreg is used as the absorbing functional layer of the composite material, and the structural prepreg provides structural strength for the composite material after curing. Based on this, the sacrificial layer of the present application is very easy to peel off after molding on the tooling surface, and can play the role of support, isolation during the co-curing process, and easy removal in subsequent processing.

[0030] The principles and features of the present invention are described below in conjunction with the examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Where specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0031] The present application provides a method for preparing a sacrificial layer prepreg for composite materials, comprising the following steps:

[0032] Mixing the inorganic filler with the resin and then forming a film to obtain a resin film;

[0033] Applying the resin film on the surface of the fiber to obtain a sacrificial layer prepreg;

[0034] After the sacrificial layer prepreg is prepared, the sacrificial layer prepreg, the absorbing prepreg, and the structural prepreg are sequentially laid on the surface of the tooling according to the tooling thickening requirements, and co-curing and demolding are performed according to the curing process of the structural prepreg to obtain a composite material with a surface coated with the sacrificial layer prepreg; wherein:

[0035] The fiber is an aramid unidirectional tape or an aramid fabric.

[0036] In the sacrificial layer prepreg of this application, an inorganic filler is first mixed with a resin to prepare a resin film. This can reduce the adhesion of the resin and make the sacrificial layer easier to peel. Aramid fiber is then used to provide flexible support to ensure that it does not break during the subsequent tearing process. In the composite structure, an absorbing prepreg is used to impart functional properties to the composite material (for example, an absorbing resin imparts stealth properties), and a structural prepreg is used to provide structural strength to the composite material. Co-curing the three prepregs ensures perfect interface bonding, and co-curing using the curing process of the structural prepreg can avoid delamination or incomplete curing, thereby achieving thickening and forming. The above method can produce a composite material with a surface coated with a sacrificial layer prepreg. The sacrificial layer formed by the sacrificial layer prepreg on the surface of the composite material is easy to peel off and will not affect the other structures of the composite material. At the same time, after the demolding process, the original tooling component will not have any structural changes and can be reused (reuse here means that the original tooling component can be reused without any treatment; it also means that the original tooling component can be coated with the same sacrificial layer prepreg to meet other composite material forming requirements).

[0037] In the present application, aramid fiber is combined with a resin film containing inorganic fillers to solve the problem that traditional thickening methods cannot take into account both easy peeling and precise thickness control. By stacking and co-curing the sacrificial layer prepreg, the absorbing prepreg, and the structural prepreg, functional integration (such as absorption + structural reinforcement) and interface compatibility are achieved, avoiding the defects of the traditional layering process. The composite material prepared by the method of the present application can be manually torn for processing, which improves the peeling efficiency. The sacrificial layer prepreg of the present application is mainly used for tooling thickening and to provide sacrificial points in the later stage. The absorbing prepreg is used to give new functions to the composite material after molding (that is, the material after co-curing and demolding treatment, and the demolding treatment can separate the original tooling from the composite material obtained by molding). The structural prepreg mainly provides structural strength for the composite material. After subsequent curing and demolding, a composite material with a surface covered with a sacrificial layer can be obtained, and the cross-section of the cured sacrificial layer prepreg is then torn to further obtain the final composite material.

[0038] In this application, after stripping the aramid fibers closest to the composite material, a layer of resin film remains on the composite material surface. This residual resin film improves the corrosion resistance of the composite material and provides a high-adhesion base for subsequent spraying. This preparation method also prevents tooling from being scrapped, increases tooling life and reuse, and solves the industry's long-standing problem of tooling thickening.

[0039] In some optional embodiments of the present application, the inorganic filler is an inorganic rigid particle, and the filling amount of the inorganic filler in the resin film is 10wt%~90wt%. The inorganic filler of the present application can reduce the adhesion of the resin, making the sacrificial layer easier to peel off, and the presence of the inorganic filler can reduce the fluidity of the resin, further ensuring the film-forming performance. At the same time, the content of the inorganic filler needs to balance the peelability and film strength. If the content of the inorganic filler is too low (<10wt%), the adhesion will be too strong and it will be difficult to peel off. If the content of the inorganic filler is too high (greater than 90wt%), the resin film will become brittle, making it impossible to form a film.

[0040] In some optional embodiments of the present application, the inorganic filler includes at least one of alumina, glass beads, and silica, and the resin includes at least one of epoxy resin, bismaleimide resin, and cyanate resin. The inorganic filler can reduce the adhesion between the sacrificial layer prepreg and the resin, making the sacrificial layer easy to peel off. The choice of resin system remains consistent with the resin system in the absorbing prepreg and the structural prepreg, meeting the requirements of the co-curing process. For example, when the resin used in the sacrificial layer prepreg is epoxy resin, the resin in the absorbing prepreg and the structural prepreg is also selected from epoxy resin; for example, when the resin used in the sacrificial layer prepreg is bismaleimide resin, the resin in the absorbing prepreg and the structural prepreg is also selected from bismaleimide resin. The preferred resin in this application is a high-temperature epoxy resin.

[0041] In some optional embodiments of the present application, the weight of the resin film is 10g / m 2 ~200g / m 2 . The appropriate gram weight value of the resin film is to ensure that the composite material is intact and qualified, and to avoid the increase in peeling force and difficulty in peeling due to the excessive gram weight of the resin film. However, if the gram weight of the resin film is too low, that is, the resin film is too thin, it will not be able to form a continuous film layer, resulting in an incomplete protective layer and poor corrosion resistance. It is worth mentioning that the final composite material prepared in this application, the resin film containing inorganic fillers remaining on the surface of the composite material after peeling can form a protective layer, and no rust will occur after 7 days of salt spray test. At the same time, the residual resin film can provide a rough interface for the surface of the composite material, thereby improving the surface adhesion.

[0042] In some optional embodiments of the present application, the fiber is an aramid unidirectional tape or an aramid fabric, and the mass ratio of the inorganic filler to the fiber in the sacrificial layer prepreg is (1-2):10. In this application, aramid fiber is used as a carrier. Its flexibility allows the sacrificial layer to be manually torn off, replacing traditional glass fiber (glass fiber is highly brittle and can only be cut using CNC milling). The mass ratio of the inorganic filler to the fiber ensures a balance between the fiber's load-bearing capacity and the resin filling. If the fiber ratio is too low (for example, the mass ratio of the inorganic filler to the fiber is less than 1:10), the thickness of the resin film will be large, making it difficult to peel off. If the fiber ratio is too high (for example, the mass ratio of the inorganic filler to the fiber is greater than 2:10), the sacrificial layer will lack rigidity and will be easily torn.

[0043] In some optional embodiments of the present application, the absorbing prepreg is composed of an absorbing resin and a fiber carrier, wherein the fiber carrier content in the absorbing prepreg is 30wt% to 90wt%. The raw materials of the absorbing resin include at least a metal absorber and resin, and the metal absorber content in the absorbing resin is 40wt% to 98wt%. The absorbing prepreg is used to prepare an absorbing layer, which can impart stealth functional properties to the composite material. The metal absorber includes ferrite, carbonyl iron powder, or silicon carbide, and the particle size of the metal absorber is 1μm to 10μm.

[0044] Specifically, the microwave absorbing prepreg of the present application can be prepared by a hot melt method, including:

[0045] The metal absorber and resin were mixed in accordance with the mass ratio and heated to 80℃. A high-speed stirring device (speed 60r / min~120r / min) was used to mix the mixture evenly to obtain the absorbing resin. The absorbing resin was melted on a hot plate at 80℃ and rolled with a double roller to obtain a weight of 300g / m 2 The two layers of absorbing resin films are placed on both sides of a fiber carrier, and are hot-pressed at 45° C. to prepare an absorbing prepreg.

[0046] In some optional embodiments of the present application, the structural prepreg is composed of a composite of resin and carbon fiber, wherein the carbon fiber content in the structural prepreg is 60wt% to 70wt%. The structural prepreg is prepared into a structural layer, which can provide structural strength to the composite material.

[0047] Specifically, the structural prepreg is prepared by the following method:

[0048] The resin was melted on a hot plate at 80°C and prepared using a double roller to a weight of 62 g / m 2 The two layers of resin film are placed on both sides of a layer of carbon fiber and hot-pressed at 45°C to prepare a structural prepreg.

[0049] In some optional embodiments of the present application, laying a sacrificial layer of prepreg on the surface of the tooling includes laying at least one layer of the sacrificial layer of prepreg, with a thickness of 0.1 mm to 10 mm after laying. The laying thickness determines the thickness of the tooling, and thus the thickness of the sacrificial layer of prepreg can be determined based on the requirements for tooling thickness.

[0050] The preparation method of the present application can adjust the thickness of the tooling thickening (for example, the thickening thickness after laying one layer of sacrificial layer prepreg is 0.1mm, and two layers are 0.2mm). By adjusting the number of laying layers of sacrificial layer prepreg, the tooling thickening requirements can be accurately controlled, avoiding the errors caused by traditional CNC milling, reducing time consumption, and improving processing efficiency and accuracy.

[0051] Furthermore, the curing process includes the following steps:

[0052] The autoclave curing method is adopted, the internal pressure of the autoclave is increased to 3 bar ~ 6 bar, the temperature is increased to 120 ° C ~ 180 ° C, and the constant temperature is maintained for 30 minutes ~ 240 minutes; the temperature is further increased to 190 ° C ~ 260 ° C, and the constant temperature is maintained for 30 minutes ~ 240 minutes; the temperature is reduced to 30 ° C ~ 80 ° C, and the pressure is released.

[0053] In a second aspect, based on a general inventive concept, the present application further provides a sacrificial layer prepreg for composite materials, which is prepared using the above-mentioned preparation method. After curing and demolding the sacrificial layer prepreg for composite materials, a composite material coated with the sacrificial layer prepreg can be obtained. The single layer of fibers in the sacrificial layer structure formed by the sacrificial layer prepreg can be lifted and manually torn off to retain a resin film on the surface of the composite material. The retained resin film can improve the chemical corrosion resistance of the formed composite material.

[0054] As a further improvement of the present application, corresponding functional coatings can be sprayed on the surface of the composite material to achieve functions such as stealth, thermal protection, electrical conductivity and thermal conductivity.

[0055] The method provided in this application is different from the traditional method of directly thickening the tooling. It uses a sacrificial layer prepreg to achieve tooling thickening, which can achieve the purpose of freely adjusting the thickening thickness. It can also give the composite material surface a certain chemical corrosion resistance after peeling off the sacrificial layer prepreg.

[0056] The above technical solutions of the present application are described in detail below with reference to specific embodiments.

[0057] Example 1

[0058] This embodiment provides a method for preparing a sacrificial layer prepreg for composite materials, which requires thickening the tooling by 0.2 mm, and includes the following steps:

[0059] (1) Add silica to epoxy resin and form a film with a weight of 40g / m 2 The resin film has a mass fraction of silicon dioxide of 80%;

[0060] (2) Two layers of resin film are applied to the surface density of 100g / m 2 Aramid fabric surface, and hot pressing at 45 ° C to obtain a sacrificial layer prepreg;

[0061] (3) Laying the sacrificial layer prepreg on the tooling surface to obtain the first sacrificial layer with a single layer thickness of 0.1 mm;

[0062] (4) Laying the sacrificial layer prepreg on the surface of the first sacrificial layer to obtain a total sacrificial layer with a double-layer total thickness of 0.2 mm;

[0063] (5) Prepare the absorbing prepreg. Mix carbonyl iron powder with a particle size of 5 μm and epoxy resin in a mass ratio of 72:28 and heat to 80°C. Use a high-speed stirring device (speed 120 r / min) to mix evenly to obtain the absorbing resin. Melt the absorbing resin on a hot plate at 80°C and use a double roller to prepare a 300 g / m 2 The two layers of absorbing resin films are coated on the surface of a layer of carbon fiber respectively, and hot-pressed at 45° C. to prepare an absorbing prepreg;

[0064] (6) Prepare structural prepreg, melt the epoxy resin on a hot plate at 80℃, and use a double roller to prepare it into a prepreg with a gram weight of 62g / m 2 The two layers of resin film are placed on both sides of a layer of carbon fiber, and hot pressed at 45°C to prepare a structural prepreg.

[0065] (7) Continue to lay and stack 4 layers of absorbing prepreg and 10 layers of structural prepreg on the surface of the total sacrificial layer, and co-cure according to the curing process parameters of the structural prepreg. After completion, demold. The curing process includes: curing in an autoclave, pressurizing the interior of the autoclave to 5 bar, heating the temperature to 135°C, and maintaining the temperature for 60 minutes; continuing to heat the temperature to 160°C and maintaining the temperature for 120 minutes; finally cooling the temperature to 60°C, then releasing the pressure, releasing the vacuum, and removing the material from the autoclave (the following examples and comparative examples all adopt this curing process).

[0066] like Figure 1 As shown, after demoulding, the final composite material can be obtained by tearing along the aramid fabric in the second sacrificial layer. Figure 1 middle, Figure 1 (a) is a photo of the sacrificial layer prepreg for composite materials before it is torn. Figure 1 (b) is a photo of the sacrificial layer prepreg used in composite materials being torn off. Figure 1(c) is the photo after tearing is completed.

[0067] The infrared absorbing coating was directly sprayed on the surface of the composite material, and then the composite material was placed in 5wt% sodium chloride salt spray for salt spray test, and taken out after seven days. Figure 2 Observation revealed no yellow rust on the surface, indicating that the resin film remaining on the composite material significantly enhances its chemical corrosion resistance. Adhesion testing of the molded composite material revealed a surface adhesion of 28 MPa (room temperature, testing standard GB / T5210).

[0068] Example 2

[0069] This embodiment provides a method for preparing a sacrificial layer prepreg for composite materials, requiring the same tooling as in Example 1 to be thickened by 0.8 mm, comprising the following steps:

[0070] (1) Add silica to epoxy resin and form a film with a weight of 40g / m 2 The resin film has a mass fraction of silicon dioxide of 80%;

[0071] (2) Two layers of resin film are applied to the surface density of 100g / m 2 The surface of the aramid fabric is compounded to obtain a sacrificial layer prepreg;

[0072] (3) Laying the sacrificial layer prepreg on the tooling surface to obtain the first sacrificial layer with a single layer thickness of 0.1 mm;

[0073] (4) Continue to lay the sacrificial layer prepreg on the surface of the first sacrificial layer to obtain a total sacrificial layer with a total thickness of 0.8 mm;

[0074] (5) Prepare the absorbing prepreg. Mix carbonyl iron powder with a particle size of 5 μm and epoxy resin in a mass ratio of 72:28 and heat to 80°C. Use a high-speed stirring device (speed 120 r / min) to mix evenly to obtain the absorbing resin. Melt the absorbing resin on a hot plate at 80°C and use a double roller to prepare a 300 g / m 2 The two layers of absorbing resin films are coated on both sides of a layer of carbon fiber, and hot-pressed at 45° C. to prepare an absorbing prepreg;

[0075] (6) Prepare structural prepreg, melt the epoxy resin on a hot plate at 80℃, and use a double roller to prepare it into a prepreg with a gram weight of 62g / m 2 The two layers of resin film are placed on both sides of a layer of carbon fiber, and hot pressed at 45°C to prepare a structural prepreg.

[0076] (7) Continue to lay and stack 4 layers of absorbing prepreg and 10 layers of structural prepreg on the surface of the total sacrificial layer, and co-cure according to the structural prepreg curing process parameters of Example 1, and demold after completion.

[0077] After demolding, the final composite material was obtained by tearing along the aramid fabric in the eighth sacrificial layer. This composite material was then placed in a 5wt% sodium chloride salt spray test and removed after seven days. No yellow rust was observed on the surface.

[0078] Example 3

[0079] This embodiment provides a method for preparing a sacrificial layer prepreg for composite materials, requiring the same tooling as in Example 1 to be thickened by 0.2 mm, comprising the following steps:

[0080] (1) Add silica to epoxy resin and form a film with a weight of 40g / m 2 The resin film has a mass fraction of silicon dioxide of 80%;

[0081] (2) Two layers of resin film are applied to the surface density of 100g / m 2 The surface of the aramid unidirectional tape is compounded to obtain a sacrificial layer prepreg;

[0082] (3) Laying the sacrificial layer prepreg on the tooling surface to obtain the first sacrificial layer with a single layer thickness of 0.1 mm;

[0083] (4) Laying the sacrificial layer prepreg on the surface of the first sacrificial layer to obtain a total sacrificial layer with a double-layer total thickness of 0.2 mm;

[0084] (5) Prepare the absorbing prepreg. Mix carbonyl iron powder with a particle size of 5 μm and epoxy resin in a mass ratio of 72:28 and heat to 80°C. Use a high-speed stirring device (speed 120 r / min) to mix evenly to obtain the absorbing resin. Melt the absorbing resin on a hot plate at 80°C and use a double roller to prepare a 300 g / m 2 The two layers of absorbing resin films are coated on both sides of a layer of carbon fiber, and hot-pressed at 45° C. to prepare an absorbing prepreg;

[0085] (6) Prepare structural prepreg, melt the epoxy resin on a hot plate at 80℃, and use a double roller to prepare it into a prepreg with a gram weight of 62g / m 2 The two layers of resin film are placed on both sides of a layer of carbon fiber, and hot pressed at 45°C to prepare a structural prepreg.

[0086] (7) Continue to lay and stack 4 layers of absorbing prepreg and 10 layers of structural prepreg on the surface of the total sacrificial layer, and co-cure according to the structural prepreg curing process parameters of Example 1, and demold after completion.

[0087] After demolding, the final composite material was obtained by tearing along the aramid unidirectional tape in the second sacrificial layer. This composite material was then placed in a 5wt% sodium chloride salt spray test and removed after seven days to observe that no yellow rust was present on the surface.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing a sacrificial layer prepreg for composite materials, the preparation method comprising the following steps:

[0090] (1) Prepare the absorbing prepreg. Mix carbonyl iron powder with a particle size of 5 μm and epoxy resin in a mass ratio of 72:28 and heat to 80°C. Use a high-speed stirring device (speed 120 r / min) to mix evenly to obtain the absorbing resin. Melt the absorbing resin on a hot plate at 80°C and use a double roller to prepare a 300 g / m 2 The two layers of absorbing resin films are coated on both sides of a layer of carbon fiber, and hot-pressed at 45° C. to prepare an absorbing prepreg;

[0091] (2) Prepare structural prepreg: melt the epoxy resin on a hot plate at 80°C and use a double roller to prepare it into a prepreg with a gram weight of 62g / m 2 The two layers of resin film are placed on both sides of a layer of carbon fiber, and hot pressed at 45°C to prepare a structural prepreg.

[0092] (3) Two layers of absorbing prepreg and 10 layers of structural prepreg are stacked on the surface of the tooling in sequence, and co-cured according to the curing process parameters of the structural prepreg. After completion, demoulding is completed.

[0093] The composite material obtained after demoulding was placed in 5wt% sodium chloride salt spray for salt spray test and taken out after seven days. Figure 2 , it can be seen that the surface of the composite material without sacrificial layer prepreg is covered with yellow rust marks.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing a sacrificial layer prepreg for composite materials, requiring the same tooling as in Example 1 to be thickened by 0.2 mm. The preparation method comprises the following steps:

[0096] (1) Add silica to epoxy resin and form a film with a weight of 40g / m 2 The resin film has a mass fraction of silicon dioxide of 80%;

[0097] (2) Two layers of resin film are applied to the surface density of 100g / m 2 The surface of the glass fiber fabric is compounded to obtain a glass fiber prepreg;

[0098] (3) Laying the glass fiber prepreg on the surface of the tooling to obtain the first sacrificial layer with a single layer thickness of 0.1 mm;

[0099] (4) paving the glass fiber prepreg on the surface of the first sacrificial layer to obtain a double-layer sacrificial layer with a total thickness of 0.2 mm;

[0100] (5) Prepare the absorbing prepreg. Mix carbonyl iron powder with a particle size of 5 μm and epoxy resin in a mass ratio of 72:28 and heat to 80°C. Use a high-speed stirring device (speed 120 r / min) to mix evenly to obtain the absorbing resin. Melt the absorbing resin on a hot plate at 80°C and use a double roller to prepare a 300 g / m 2 The two layers of absorbing resin films are coated on both sides of a layer of carbon fiber, and hot-pressed at 45° C. to prepare an absorbing prepreg;

[0101] (6) Prepare structural prepreg, melt the epoxy resin on a hot plate at 80℃, and use a double roller to prepare it into a prepreg with a gram weight of 62g / m 2 The two layers of resin film are placed on both sides of a layer of carbon fiber, and hot pressed at 45°C to prepare a structural prepreg.

[0102] (7) Continue to lay and stack 4 layers of absorbing prepreg and 10 layers of structural prepreg on the surface of the total sacrificial layer, and co-cure according to the structural prepreg curing process parameters of Example 1, and demold after completion.

[0103] After demolding, the glass fiber fabric in the second sacrificial layer could not be removed by peeling, and the final composite material could not be obtained. This was because the glass fiber is brittle and cannot be removed by tearing, so it can only be removed by CNC milling. Therefore, a CNC machine was used to mill 0.2mm to obtain the final composite material. The composite material was then placed in a 5wt% sodium chloride salt spray test and removed after seven days to observe the presence of yellow rust on the surface.

[0104] The infrared absorbing coating was directly sprayed on the surface of the composite material obtained in Comparative Example 2 (not subjected to the salt spray test), and the surface adhesion was measured by an adhesion tester to be 19 MPa.

[0105] It can be seen from Examples 1-3 that the composite material after demoulding prepared by the preparation method provided by the present application can be easily removed by manually tearing off the layer to be peeled off on the surface, and will not affect the structure and integrity of the composite material. By comparing Example 1 with Comparative Example 1, it can be seen that the final composite material prepared by the present application still has a resin film remaining on the surface, which can play a barrier role and effectively prevent the interior of the composite material from rusting. By comparing Example 1 with Comparative Example 2, it can be seen that the composite material with a sacrificial layer on the surface prepared by the present application uses aramid fiber as a carrier in its preparation process. Therefore, the sacrificial layer on the surface can be manually torn off by the excellent flexibility of aramid fiber, and the peeling effect is excellent, and the surface shape of the composite material itself will not be damaged. By comparing the surface adhesion test of Example 1 with Comparative Example 2, it can be seen that the preparation method provided by the present application can give the composite material a rougher surface compared to the traditional CNC machine tool milling processing method to improve surface adhesion. For example, the surface of the final composite material of the present application is rough (surface adhesion is 28 MPa), while the surface of the final composite material obtained by traditional processing is smooth (surface adhesion is 19 MPa). Therefore, the preparation method of the present application can significantly improve the adhesion of the surface spraying material, that is, by spraying the corresponding functional coating on the surface, stealth, thermal protection, electrical conductivity, and thermal conductivity and other functions can be achieved.

[0106] It is also worth mentioning that traditional processing methods usually remove the thickened part of the tooling by milling, but milling is difficult to remove the narrow area of ​​the thickened tooling. The removal method of this application is simpler, not limited by the depth of the composite material and the narrow area, and is more flexible and controllable.

[0107] Although the specific embodiments of the present application have been described in detail, this should not be construed as limiting the scope of protection of the present application. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of the present application.

Claims

1. A method for preparing a composite material coated with a sacrificial layer prepreg, characterized in that: The following steps are involved: (1) Mixing the inorganic filler with the resin and then forming a film to obtain a resin film; (2) coating the resin film on the surface of the fiber to obtain a sacrificial layer prepreg; (3) After the sacrificial layer prepreg is prepared, the sacrificial layer prepreg, the absorbing prepreg and the structural prepreg are sequentially laid on the surface of the tooling according to the tooling thickening requirements, and co-curing and demoulding are performed according to the curing process of the structural prepreg to obtain a composite material with a surface coated with the sacrificial layer prepreg; wherein: The fiber is an aramid unidirectional tape or an aramid fabric; the inorganic filler is an inorganic rigid particle, and the filling amount of the inorganic filler in the resin film is 10wt% to 90wt%; the inorganic filler includes at least one of alumina, glass beads, and silica, and the resin includes at least one of epoxy resin, bismaleimide resin, and cyanate resin; The sacrificial layer prepreg is used to: retain the resin film on the surface of the composite material by picking up the single layer of fibers in the sacrificial layer structure formed by the sacrificial layer prepreg and tearing it off manually.

2. The method for preparing a composite material coated with a sacrificial layer prepreg according to claim 1, characterized in that: The weight of the resin film in step (1) is 10 g / m 2 ~200g / m 2 .

3. The method for preparing a composite material coated with a sacrificial layer prepreg according to claim 1, wherein: The mass ratio of the inorganic filler to the fiber in the sacrificial layer prepreg is (1-2):

10.

4. The method for preparing a composite material coated with a sacrificial layer prepreg according to claim 1, wherein: The absorbing prepreg is composited with an absorbing resin and a fiber carrier, wherein the content of the fiber carrier in the absorbing prepreg is 30wt% to 90wt%; the raw materials of the absorbing resin include a metal absorber and a resin, wherein the content of the metal absorber in the absorbing resin is 40wt% to 98wt%.

5. The method for preparing a composite material coated with a sacrificial layer prepreg according to claim 1, wherein: The structural prepreg is formed by compounding resin and carbon fiber, and the content of the carbon fiber in the structural prepreg is 60wt% to 70wt%.

6. The method for preparing a composite material coated with a sacrificial layer prepreg according to claim 1, wherein: The paving of the sacrificial layer prepreg on the tooling surface includes paving at least one layer of the sacrificial layer prepreg, and the thickness after paving is 0.1 mm to 10 mm.

7. The method for preparing a composite material coated with a sacrificial layer prepreg according to claim 1, wherein: The curing process comprises the following steps: The autoclave curing method is adopted, the internal pressure of the autoclave is increased to 3 bar ~ 6 bar, the temperature is increased to 120 ° C ~ 180 ° C, and the constant temperature is maintained for 30 minutes ~ 240 minutes; the temperature is further increased to 190 ° C ~ 260 ° C, and the constant temperature is maintained for 30 minutes ~ 240 minutes; the temperature is reduced to 30 ° C ~ 80 ° C, and the pressure is released.

8. A composite material coated with a sacrificial layer prepreg, characterized in that The method according to any one of claims 1 to 7 is used for preparation.

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