Method for improving cloth lines after hot pressing of epoxy glass fiber composite material

Abstract

The invention discloses a method for improving cloth lines after hot pressing of an epoxy glass fiber composite material, and the method comprises the steps of resin glue solution blending, glass fiber cloth presoaking, gradient pre-drying, hot pressing molding, cooling demolding and the like. The volume expansion rate is accurately matched with the resin curing shrinkage rate, interface stress caused by shrinkage difference is directly counteracted, meanwhile, gradient pre-drying and staged hot pressing processes are combined, and the resin fluidity and interface bonding strength are optimized. The resin conversion rate is controlled in two stages through gradient pre-drying, and flow blocking caused by premature curing is avoided; and secondly, through the chemical compensation mechanism of the expansion monomer, the mechanical property of the material is maintained while the cloth lines are eliminated.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically a method for improving the texture of epoxy fiberglass composites after hot pressing. Background Technology

[0002] Epoxy resin / glass fiber composites are widely used in aerospace, automotive, and consumer electronics fields due to their high strength, lightweight, and corrosion resistance. However, during the hot pressing process, the difference between the curing shrinkage of epoxy resin (2%-7%) and the thermal expansion coefficient of glass fiber leads to interfacial stress, causing surface texture issues that severely affect the product's appearance and performance. Existing technologies attempt to address this issue through the following methods, but all have significant drawbacks.

[0003] Chinese patent literature discloses a modified glass fiber reinforced epoxy resin composite material and its preparation method [Application No.: 202411043803.5, Publication No.: CN119019813A], proposing to reduce the resin shrinkage rate by adding inorganic fillers such as calcium carbonate and silica. Although this method reduces the overall volume shrinkage of epoxy resin through physical filling, the interfacial compatibility between the filler and the resin matrix is ​​insufficient, resulting in impaired resin flow and uneven microstructure. This unevenness exacerbates the shrinkage difference between the resin and glass fiber during hot pressing, failing to effectively eliminate interfacial stress concentration, and ultimately still forming obvious textured patterns. In addition, although the introduction of fillers partially alleviates shrinkage, the resin-glass fiber interfacial bonding force decreases after curing, further weakening the texture suppression effect, and surface defects remain significant. Summary of the Invention

[0004] A method for improving the texture of epoxy fiberglass composites after hot pressing, characterized by comprising the following steps:

[0005] (a) Preparation of resin solution: The resin solution comprises the following components by weight:

[0006] Bisphenol A type epoxy resin E51: 50-100 parts;

[0007] Anhydride-based curing agent or amine-based curing agent: 10-20 parts;

[0008] Expanded monomer: 10-30 parts;

[0009] Silane coupling agent: 1-5 parts;

[0010] (b) Impregnate the fiberglass cloth in the resin solution of step (a) for 3-10 minutes to form a prepreg with a resin content of 35%-50%.

[0011] (c) Perform gradient pre-drying treatment on the prepreg:

[0012] The first stage involves preheating at 70-100℃ for 5-15 minutes;

[0013] The second stage involves pre-baking at 100-120℃ for 10-30 minutes to allow the resin solution to enter stage B and achieve a volatile content of ≤1.5%.

[0014] (d) Cool the pre-baked prepreg to 25-40℃ to obtain a semi-cured sheet;

[0015] (e) The pre-baked semi-cured sheets are stacked and hot-pressed at 140-180℃ and 5-15MPa for 60-120 minutes to allow the epoxy resin curing reaction and the ring-opening polymerization of the expanding monomer to proceed simultaneously. The volume expansion of the expanding monomer compensates for the curing shrinkage of the epoxy resin and eliminates the stress difference at the resin-glass fiber interface.

[0016] Preferably, the expanding monomer includes one or more of spirocyclic orthoesters, bicyclic orthoesters, spirocyclic orthocarbonates, and benzoxazine monomers.

[0017] Through the above technical solutions, the introduction of expanding monomers effectively compensates for the volume shrinkage of epoxy resin during the curing process, significantly reducing the fabric texture caused by shrinkage differences during hot pressing. The expansion effect generated by the ring-opening polymerization reaction of spirocyclic orthoesters, bicyclic orthoesters, spirocyclic orthocarbonates, and benzoxazine monomers during the curing process can offset the shrinkage of epoxy resin, thereby balancing the volume difference between the resin and glass fiber, improving the appearance quality of the composite material, and making the surface smoother.

[0018] This technical solution avoids the curing rate variations and performance losses associated with the use of fillers in traditional methods, providing a more stable and efficient solution. Furthermore, the use of expanded monomers reduces the need for subsequent finishing processes, improving production efficiency and reducing costs. Overall, this invention not only solves the problem of textured surfaces during the hot pressing of composite materials but also improves their appearance and structural stability, demonstrating significant industrial application value.

[0019] Preferably, the silane coupling agent includes one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

[0020] The above technical solutions can effectively improve the interfacial bonding between resin and glass fiber. These silane coupling agents, in conjunction with epoxy resin and expanding monomers in the resin solution, enhance the compatibility between the resin and glass fiber, promote resin wetting and full penetration of the glass fiber cloth during curing, thereby improving the mechanical properties and stability of the composite material.

[0021] Furthermore, the use of silane coupling agents not only enhances the interfacial bonding of the composite material but also helps control the dispersion of the expanding monomers, ensuring their uniform action within the resin and further reducing the textured appearance caused by shrinkage differences. This approach effectively improves the overall performance of the composite material, particularly in terms of appearance quality and service life, demonstrating broad application potential and value.

[0022] Preferably, the amount of silane coupling agent added to the resin solution is 1-5 parts, and the expanding monomer is added after premixing with epoxy resin E51 at 25-40°C for 20-40 minutes.

[0023] Through the above technical solution, this premixing process ensures that the silane coupling agent reacts fully with the epoxy resin, thereby improving the bonding force between the resin and glass fiber and enhancing the interfacial properties of the composite material. Simultaneously, the addition of the silane coupling agent helps improve the resin's wettability, allowing the glass fiber cloth to be more evenly penetrated by the resin adhesive, thus reducing fabric wrinkles caused by insufficient interfacial bonding. The expanded monomers can be more evenly distributed in the resin, ensuring that the expansion effect generated during curing effectively compensates for the shrinkage of the epoxy resin, thereby reducing fabric wrinkles during hot pressing. Furthermore, the introduction of the silane coupling agent also enhances the mechanical properties and stability of the composite material, resulting in a final product that not only has a smooth appearance but also better structural strength and durability.

[0024] Preferably, the amount of the expanding monomer added is 10-30 parts by weight, and the ratio of its ring-opening expansion rate to the curing shrinkage rate of the epoxy resin is 0.9-1.1.

[0025] Through the above technical solution, this design allows the expanding monomer to exert the best expansion effect during the epoxy resin curing process, which can effectively compensate for the volume shrinkage of the epoxy resin, thereby reducing the fabric texture caused by the difference in the expansion coefficients of resin and glass fiber during hot pressing.

[0026] The appropriate addition of expanded monomers not only ensures a smoother and more even surface of the composite material but also maintains the mechanical properties of the resin, avoiding the performance degradation caused by filler addition in traditional methods. This technical solution significantly improves the appearance quality of the composite material while enhancing its overall stability and service life, providing an effective solution for manufacturing high-quality composite materials in industrial production.

[0027] Preferably, the impregnated prepreg needs to be left to stand for 10-30 minutes at 25-30°C and ≤40% humidity to balance the resin distribution.

[0028] Through the above technical solution, this settling process can ensure the uniform distribution of resin in the fiberglass cloth, thereby improving the quality of the prepreg and enabling the resin to fully penetrate each fiberglass, avoiding performance differences caused by uneven resin distribution.

[0029] This treatment method not only improves the stability of the prepreg but also provides a good foundation for subsequent gradient pre-drying and hot pressing. By ensuring the uniform bonding between the resin and the fiberglass cloth, the generation of fabric wrinkles is further reduced, resulting in a smoother and more even surface of the final composite material, thus improving the overall appearance quality and mechanical properties of the material. This solution optimizes the production process, reduces quality problems caused by uneven resin distribution, and has good application prospects.

[0030] Preferably, gradient pre-curing includes:

[0031] First stage: Treat at 80-100℃ for 3-8 minutes to remove solvent and control resin conversion rate ≤20%;

[0032] Second stage: Treat at 110-120℃ for 2-5 minutes to achieve a resin conversion rate of 40-60% and enter stage B.

[0033] Through the above technical solution, this gradient pre-curing process can ensure that the resin gradually transforms during the pre-baking process, thereby optimizing the curing state of the resin.

[0034] During pre-curing, the resin maintains appropriate fluidity and wettability, ensuring full penetration of the fiberglass cloth during subsequent hot pressing. Simultaneously, proper control of the resin conversion rate prevents premature curing, thereby reducing stress accumulation and fiber texture during hot pressing. This not only improves the appearance quality of the composite material but also ensures its mechanical properties and dimensional stability. Ultimately, the gradient pre-curing process provides effective technical support for the production of high-quality composite materials.

[0035] Preferably, the expanding monomer is a mixture of spirocyclic orthoester and bicyclic orthoester, with a mixing mass ratio of 1:1 to 3:1.

[0036] Through the above technical solution, the expansion monomer ratio can achieve the best expansion effect, effectively compensate for the volume shrinkage of epoxy resin during the curing process, and thus reduce the fabric texture phenomenon generated during hot pressing.

[0037] The mixed use of spirocyclic orthocyanins and bicyclic orthocyanins balances the expansion characteristics of the two expanding monomers, ensuring effective regulation of the difference in expansion and shrinkage rates during curing, and avoiding performance problems caused by excessive or insufficient expansion. This formulation results in a smoother surface for the composite material while maintaining its mechanical properties, significantly improving its appearance quality and enhancing its stability and service life. Therefore, this approach provides an effective solution for improving the appearance and performance of composite materials.

[0038] Preferably, the pressure during hot pressing is applied in stages:

[0039] Initial stage: Maintain pressure at 5-8 MPa for 20-30 minutes;

[0040] Final stage: Maintain pressure at 10-15 MPa for 40-60 minutes.

[0041] Through the above technical solution, this method of applying pressure in stages can effectively control the resin curing process and ensure that the composite material obtains a uniform pressure distribution throughout the hot pressing process, thereby avoiding the fabric texture caused by uneven pressure.

[0042] In the initial stage, lower pressure allows the resin to fully penetrate the fiberglass cloth and begin curing, while reducing interfacial stress between the resin and fiberglass. In the final stage, higher pressure ensures complete resin curing and compaction of the composite material, further eliminating stress differences caused by resin shrinkage and ensuring the smoothness and mechanical properties of the composite. This staged pressure application technique effectively improves the appearance quality and mechanical properties of the composite material, making it more suitable for high-precision and high-strength industrial applications.

[0043] Preferably, the heating rate of hot pressing is 1-3℃ / min, and after the pressure holding is completed, the temperature is cooled to below 80℃ at a rate of 0.5-2℃ / min for demolding.

[0044] Through the above technical solution, the control of heating and cooling rates can effectively avoid thermal stress caused by excessive temperature changes during hot pressing, and ensure the uniformity and stability of the composite material during the molding process.

[0045] Controlling the heating rate within the range of 1-3℃ / min ensures that the resin gradually enters the curing stage, avoiding premature curing or bubble formation due to excessively rapid temperature rise. The cooling rate after pressure holding is 0.5-2℃ / min, effectively reducing internal stress caused by excessive temperature differences and ensuring that the composite material does not deform during cooling, thus maintaining good surface smoothness and mechanical properties. This technical solution makes the hot pressing process more stable, further improving the overall quality of the composite material.

[0046] Compared with the prior art, the present invention has the following advantages:

[0047] 1. This invention introduces an expanding monomer to simultaneously trigger a ring-opening polymerization reaction during the epoxy resin curing process. The volume expansion rate precisely matches the resin curing shrinkage rate, directly offsetting the interfacial stress caused by shrinkage differences. Compared to traditional filler methods that only reduce shrinkage through physical filling, this invention solves the shrinkage compensation problem at the level of chemical bond recombination, avoiding uneven resin flow and microscopic defects caused by fillers, and significantly improving the smoothness and uniformity of the composite material.

[0048] 2. This invention combines gradient pre-drying and staged hot pressing processes to optimize resin flowability and interfacial bonding strength. Gradient pre-drying controls resin conversion rate in two stages to avoid flow obstruction caused by premature curing; staged hot pressing ensures that the resin fully impregnates the glass fiber and forms a dense mold. In addition, the introduction of expanded monomers does not require complex equipment modifications, is compatible with existing production lines, and has the potential for industrial-scale promotion.

[0049] 3. This invention utilizes the chemical compensation mechanism of expanded monomers to eliminate fabric texture while maintaining the material's mechanical properties. This characteristic makes it particularly suitable for applications requiring both strength and surface quality, such as aerospace structural components and battery casings for new energy vehicles. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the process of this invention;

[0051] Figure 2 This is a schematic diagram illustrating the expansion polymerization principle of this invention;

[0052] Figure 3 This is a schematic diagram of the detection process in Embodiment 2 of the present invention;

[0053] Figure 4 This is a schematic diagram of the detection process in Embodiment 2 of the present invention;

[0054] Figure 5 This is a schematic diagram of the detection process in Embodiment 2 of the present invention;

[0055] Figure 6 This is a schematic diagram of the detection process in Embodiment 2 of the present invention; Detailed Implementation

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0057] A method for improving the texture of epoxy fiberglass composites after hot pressing, characterized by comprising the following steps:

[0058] (a) Preparation of resin solution: The resin solution comprises the following components by weight:

[0059] Bisphenol A type epoxy resin E51: 50-100 parts;

[0060] Anhydride-based curing agent or amine-based curing agent: 10-20 parts;

[0061] Expanded monomer: 10-30 parts;

[0062] Silane coupling agent: 1-5 parts;

[0063] (b) Impregnate the fiberglass cloth in the resin solution of step (a) for 3-10 minutes to form a prepreg with a resin content of 35%-50%.

[0064] (c) Perform gradient pre-drying treatment on the prepreg:

[0065] The first stage involves preheating at 70-100℃ for 5-15 minutes;

[0066] The second stage involves pre-baking at 100-120℃ for 10-30 minutes to allow the resin solution to enter stage B and achieve a volatile content of ≤1.5%.

[0067] (d) Cool the pre-baked prepreg to 25-40℃ to obtain a semi-cured sheet;

[0068] (e) The pre-baked semi-cured sheets are stacked and hot-pressed at 140-180℃ and 5-15MPa for 60-120 minutes to allow the epoxy resin curing reaction and the ring-opening polymerization of the expanding monomer to proceed simultaneously. The volume expansion of the expanding monomer compensates for the curing shrinkage of the epoxy resin and eliminates the stress difference at the resin-glass fiber interface.

[0069] refer to Figures 1 to 6 .

[0070] This invention relates to the polymerization reaction of epoxy resins. During the polymerization of epoxy resins, some degree of volume shrinkage inevitably occurs. One important reason is that the distance between liquid monomer molecules is the van der Waals force distance, while the distance between structural units in a polymer is the covalent bond distance. Clearly, the covalent bond distance is smaller than the van der Waals force distance, so volume shrinkage occurs when liquid monomers transform into polymers. Particularly in some fiber-reinforced composite materials, when monomers polymerize into polymer compounds, thermosetting resins undergo curing shrinkage. This shrinkage can generate harmful internal stresses, causing internal deformation, fiber deformation, premature aging of the substrate resin, and fiber-resin debonding, among other problems. Currently, commonly used thermosetting resins shrink by 3%-15% during curing, and even epoxy resins with the lowest shrinkage rate still have a curing shrinkage rate of 2%-7%. Curing shrinkage of adhesives can cause residual stress and lead to detachment of the resin substrate from the filler material.

[0071] The principle of expansion polymerization: Taking the ring-opening polymerization of spirocyclic monomers as an example, when the cation R and oxygen atom approach each other and form a single bond, the van der Waals force distance transforms into a covalent bond distance, and the other carbon-oxygen single bond transforms into a carbonyl double bond, causing volume shrinkage. However, the ring-opening process is also accompanied by the breaking of two carbon-oxygen bonds, and the distance between the two carbon-oxygen covalent bonds transforms into a van der Waals force distance, causing volume expansion. The shrinkage and expansion cancel each other out, so the volume remains essentially unchanged during polymerization.

[0072] A schematic diagram of the expansion polymerization principle is shown below. Figure 2 As shown.

[0073] Example 1: Comparison of the process of the present invention with the traditional process

[0074] Experimental Group 1 (Process of this Invention)

[0075] (a) Preparing the resin solution

[0076] Formula composition:

[0077] Bisphenol A type epoxy resin E51: 80 parts;

[0078] Methyltetrahydrophthalic anhydride curing agent: 15 parts;

[0079] Spirocycloorthoester: 15 parts;

[0080] γ-aminopropyltriethoxysilane: 2 parts.

[0081] (b) Mixing process:

[0082] Premix epoxy resin E51 with silane coupling agent at 25°C for 30 minutes;

[0083] Add curing agent and expanding monomer, stir under vacuum at 50°C for 30 minutes, and the viscosity of the adhesive is 1200±50mPa·s.

[0084] Pre-impregnation of fiberglass cloth:

[0085] Material: E-glass fiberglass cloth (200g / m²) 2 12×12 warp / cm 2 );

[0086] Soaking time: 8 minutes;

[0087] Resin content: 40%;

[0088] Standing conditions: Let stand for 20 minutes at 25℃ and humidity ≤40%.

[0089] (c) Gradient pre-baking:

[0090] First stage: Preheat at 80℃ for 10 minutes, solvent evaporation ≤0.5%;

[0091] Second stage: Pre-dry at 110℃ for 20 minutes, resin conversion rate 50%, then proceed to stage B.

[0092] (d) Cool the pre-baked prepreg to 25-40℃ to obtain a semi-cured sheet;

[0093] (e) Hot pressing

[0094] Phased pressure application:

[0095] Initial stage: Maintain pressure of 6 MPa for 25 minutes;

[0096] Final stage: Maintain 12 MPa pressure for 50 minutes;

[0097] Temperature control: 160℃, heating rate 2℃ / min;

[0098] Cooling and demolding: Cool to below 80°C at a rate of 1°C / min.

[0099] Experimental Group 2 (Traditional Process)

[0100] (a) Preparing the resin solution

[0101] Formula composition:

[0102] Bisphenol A type epoxy resin E51: 80 parts;

[0103] Methyltetrahydrophthalic anhydride curing agent: 15 parts;

[0104] Calcium carbonate filler (replacement for expanded monomer): 15 parts;

[0105] γ-aminopropyltriethoxysilane: 2 parts.

[0106] (b) Mixing process:

[0107] The resin and filler were premixed in a high-speed disperser (3000 rpm) for 15 minutes, then the curing agent and coupling agent were added, and stirring was continued for 30 minutes. The viscosity of the adhesive was 1800±100 mPa·s.

[0108] Pre-impregnation of fiberglass cloth:

[0109] Material: E-glass fiberglass cloth (200g / m²) 2 12×12 warp / cm 2 );

[0110] Soaking time: 8 minutes;

[0111] Resin content: 40%;

[0112] Standing conditions: Let stand for 20 minutes at 25℃ and humidity ≤40%.

[0113] Due to filler settling, additional adjustments to the scraper pressure are needed to ensure a resin content of 40%.

[0114] (c) Gradient pre-baking:

[0115] First stage: Preheat at 80℃ for 10 minutes, solvent evaporation ≤0.5%;

[0116] Second stage: Pre-dry at 110℃ for 20 minutes, resin conversion rate 45%, then proceed to stage B.

[0117] (d) Cool the pre-baked prepreg to 25-40℃ to obtain a semi-cured sheet;

[0118] (e) Hot pressing

[0119] Single-stage pressurization: hot-pressed at 12MPa pressure for 75 minutes (160℃), without staged optimization.

[0120] Cooling and demolding: Cool to below 80°C at a rate of 1°C / min.

[0121] Test results: See Table 1

[0122] Table 1

[0123] parameter Experimental Group 1 (Process of this Invention) Experimental Group 2 (Traditional Process) Fabric texture depth (μm) 0.9 4.8 Surface roughness (Ra) 0.8 3.0 Tensile strength (MPa) 320 290 Degumming rate 0.3％ 2.5％ Process efficiency 75 minutes in stages 75 minutes per stage

[0124] The experimental results show that:

[0125] 1. The ring-opening expansion rate of the expanding monomer matches the curing shrinkage rate of the epoxy resin, eliminating interfacial stress differences at the source.

[0126] 2. Staged hot pressing and gradient pre-drying ensure resin flowability and interfacial compactness, avoiding performance loss caused by fillers in traditional processes.

[0127] 3. In terms of key indicators such as fabric texture depth, surface roughness, tensile strength, and degumming rate, the present invention is superior to the traditional solution in all aspects.

[0128] Example 2: Comparison of Optimized Expanded Monomer Addition Amount

[0129] (a) Preparing the resin solution

[0130] Formula composition:

[0131] Fixed parameters

[0132] Bisphenol A type epoxy resin E51: 80 parts;

[0133] Methyltetrahydrophthalic anhydride curing agent: 15 parts;

[0134] γ-aminopropyltriethoxysilane: 2 parts.

[0135] Variable parameters

[0136] Spirocyclic orthoesters: 0 parts; 10 parts; 15 parts; 20 parts; four groups in total.

[0137] (b) Mixing process:

[0138] Premix epoxy resin E51 with silane coupling agent at 25°C for 30 minutes;

[0139] Add curing agent and expanding monomer, stir under vacuum at 50°C for 30 minutes, and the viscosity of the adhesive is 1200±50mPa·s.

[0140] Pre-impregnation of fiberglass cloth:

[0141] Material: E-glass fiberglass cloth (200g / m²) 2 12×12 warp / cm 2 );

[0142] Soaking time: 8 minutes;

[0143] Resin content: 40%;

[0144] Standing conditions: Let stand for 20 minutes at 25℃ and humidity ≤40%.

[0145] (c) Gradient pre-baking:

[0146] First stage: Preheat at 80℃ for 10 minutes, solvent evaporation ≤0.5%;

[0147] Second stage: Pre-dry at 110℃ for 20 minutes, resin conversion rate 50%, then proceed to stage B.

[0148] (d) Cool the pre-baked prepreg to 25-40℃ to obtain a semi-cured sheet;

[0149] (e) Hot pressing

[0150] Phased pressure application:

[0151] Initial stage: Maintain pressure of 6 MPa for 25 minutes;

[0152] Final stage: Maintain 12 MPa pressure for 50 minutes;

[0153] Temperature control: 160℃, heating rate 2℃ / min;

[0154] Cooling and demolding: Cool to below 80°C at a rate of 1°C / min.

[0155] Test results: See Table 2

[0156] Table 2

[0157]

[0158] When the spirocyclic orthoester content is 0 parts, the detection chart is shown below. Figure 3 ;

[0159] When the number of spirocyclic orthoester esters is 10, the detection chart is shown below. Figure 4 ;

[0160] When the number of spirocyclic orthoester esters is 15, the detection chart is shown below. Figure 5 ;

[0161] When the number of spirocyclic orthoester esters is 20, the detection chart is shown below. Figure 6 ;

[0162] The experimental results show that:

[0163] When the spirocyclic orthoester content is 15 parts, the fabric texture depth is the smallest, and other parameters are better than those of other content. The performance of laser + color inspection and 3D inspection is also the best.

[0164] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for improving the fabric texture of epoxy fiberglass composites after hot pressing, characterized in that, Includes the following steps: (a) Preparation of resin solution: The resin solution comprises the following components by weight: Bisphenol A type epoxy resin E51: 50-100 parts; Anhydride-based curing agent or amine-based curing agent: 10-20 parts; Expanded monomer: 10-30 parts; Silane coupling agent: 1-5 parts; (b) Impregnate the fiberglass cloth in the resin solution of step (a) for 3-10 minutes to form a prepreg with a resin content of 35%-50%. (c) Perform gradient pre-drying treatment on the prepreg: The first stage involves preheating at 70-100℃ for 5-15 minutes; The second stage involves pre-baking at 100-120℃ for 10-30 minutes to allow the resin solution to enter stage B and achieve a volatile content of ≤1.5%. (d) Cool the pre-baked prepreg to 25-40℃ to obtain a semi-cured sheet; (e) The pre-baked semi-cured sheets are stacked and hot-pressed at 140-180℃ and 5-15MPa for 60-120 minutes to allow the epoxy resin curing reaction and the ring-opening polymerization of the expanding monomer to proceed simultaneously. The volume expansion of the expanding monomer compensates for the curing shrinkage of the epoxy resin and eliminates the stress difference at the resin-glass fiber interface.

2. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, The expanding monomers include one or more of spirocyclic orthoesters, bicyclic orthoesters, spirocyclic orthocarbonates, and benzoxazine-type monomers.

3. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, The silane coupling agent includes one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

4. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, The silane coupling agent is added to the resin solution in an amount of 1-5 parts, and is premixed with epoxy resin E51 at 25-40°C for 20-40 minutes before the expanding monomer is added.

5. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, In step (a), the amount of expanded monomer added is 10-30 parts by weight, and the ratio of its ring-opening expansion rate to the curing shrinkage rate of epoxy resin is 0.9-1.

1.

6. The method according to claim 1, characterized in that, In step (b), the prepreg after impregnation needs to be left to stand for 10-30 minutes at 25-30℃ and ≤40% humidity to balance the resin distribution.

7. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, The gradient pre-curing in step (c) includes: First stage: Treat at 80-100℃ for 3-8 minutes to remove solvent and control resin conversion rate ≤20%; Second stage: Treat at 110-120℃ for 2-5 minutes to achieve a resin conversion rate of 40-60% and enter stage B.

8. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, The expanding monomer is a mixture of spirocyclic orthoester and bicyclic orthoester, with a mixing mass ratio of 1:1 to 3:

1.

9. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, In step (e), the pressure for hot pressing is applied in stages: Initial stage: Maintain pressure at 5-8 MPa for 20-30 minutes; Final stage: Maintain pressure at 10-15 MPa for 40-60 minutes.

10. The method for improving the fabric texture of epoxy fiberglass composite materials after hot pressing according to claim 1, characterized in that, In step (e), the heating rate of hot pressing is 1-3℃ / min, and after holding the pressure, it is cooled to below 80℃ at a rate of 0.5-2℃ / min for demolding.

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