High toughness epoxy prepreg and method of making same

Abstract

The application relates to the technical field of high-performance composite materials, and particularly relates to a high-toughness epoxy prepreg. The epoxy prepreg is of a layered structure and sequentially comprises a fiber reinforced layer, an epoxy resin matrix layer and a functional toughening layer from inside to outside; the epoxy resin matrix layer comprises an epoxy resin mixture, a toughening agent A, a curing agent and an accelerator; the epoxy resin mixture is a compound of a liquid epoxy resin and a solid epoxy resin; the toughening agent A is a core-shell structure polymer particle with polybutadiene rubber as a core and polymethyl methacrylate as a shell; and the functional toughening layer comprises an epoxy resin and a toughening agent B; the toughening agent B is a composite of a surface-modified nano-clay and a thermoplastic resin superfine particle. The prepreg provided by the application can greatly improve the interlaminar fracture toughness and the compression damage tolerance after impact of the composite material through the unique'matrix-interlayer double-system synergistic toughening' structure design, while perfectly retaining the basic mechanical properties and heat resistance of the composite material.

Description

Technical Field

[0001] This application relates to the technical field of high-performance composite materials, and in particular to a high-toughness epoxy prepreg and its preparation method. Background Technology

[0002] Epoxy resin-based carbon fiber composites have been widely used in many high-end manufacturing fields such as aerospace, rail transportation, wind power equipment, and high-end electronic packaging due to their excellent high specific strength and high specific modulus characteristics. They have become one of the indispensable core materials in modern industry, especially in the manufacture of main and secondary load-bearing structural components with strict requirements for material lightweighting and high strength.

[0003] However, traditional epoxy resins form a rigid three-dimensional network structure after curing, which has the inherent defect of being brittle. This results in a significant deficiency in its impact resistance and damage tolerance, with the low compressive strength after impact (CAI) being particularly prominent. This defect severely limits the further application of epoxy resin-based carbon fiber composites in fields with stringent toughness requirements, such as aerospace main load-bearing components and key structures of rail transit vehicles, becoming a major bottleneck restricting its upgrading to high-end applications.

[0004] To improve the toughness of epoxy resin and enhance its impact resistance and damage tolerance, the most mainstream and commonly used method in the existing technology is to add various toughening agents to the epoxy resin matrix. The toughening agents that have been reported and applied mainly include rubber elastomers (such as carboxyl-terminated nitrile rubber CTBN), thermoplastic resins (such as polyethersulfone PES and polyetherimide PEI), and inorganic nanoparticles. By adding these toughening agents, it is attempted to alleviate the brittleness problem of epoxy resin after curing.

[0005] However, in practice, it has been found that existing toughening methods of this type always face an irreconcilable dual contradiction, which greatly limits the toughening effect and application value:

[0006] On the one hand, there is a contradiction between processability and toughening effect. To achieve the ideal toughening effect, it is often necessary to add a large amount of toughening agents such as thermoplastic resins. However, the addition of a large amount of these toughening agents will cause the viscosity of the epoxy resin system to rise sharply, which will seriously affect the processability of the prepreg preparation by hot melt method. At the same time, it will hinder the resin from fully impregnating the carbon fiber bundles, which will easily lead to problems such as uneven impregnation and dry filaments. Ultimately, it will damage the molding quality and mechanical properties of the composite material, making it difficult to meet the requirements of industrial production and the preparation of high-end structural components.

[0007] On the other hand, there is a contradiction between toughening efficiency and overall performance. Traditional toughening methods often suffer from the problem of "sacrificing one for another." While improving the toughness and impact resistance of epoxy resin, they inevitably sacrifice the resin's heat resistance (such as a decrease in glass transition temperature Tg), stiffness, or strength. They cannot achieve a simultaneous improvement in toughness and overall performance, making it difficult to meet the multiple stringent requirements of aerospace and other fields for materials with "high toughness, high strength, and high heat resistance."

[0008] In summary, current technologies still cannot effectively resolve the aforementioned dual contradictions. Developing a high-toughness epoxy prepreg that can significantly improve the interlaminar toughness and damage tolerance of epoxy resin prepregs while taking into account the comprehensive properties of resin such as heat resistance, stiffness, and strength has become an urgent technical problem to be solved in this field, and is also the key to promoting the expansion of epoxy resin-based carbon fiber composites into higher-end application areas. Summary of the Invention

[0009] This application provides a high-toughness epoxy prepreg and its preparation method. The prepreg provided in this application, through an original "matrix-interlaminar dual-system synergistic toughening" structural design, significantly improves the interlaminar fracture toughness (GIC, GIIC) and post-impact compression damage tolerance (CAI) of the composite material without significantly increasing the viscosity of the resin system and ensuring adaptability to industrial production using the hot-melt method. Simultaneously, it perfectly preserves the basic mechanical properties and heat resistance of the composite material, solving the long-standing technical challenge of balancing "high toughness, high strength, and high heat resistance" multiple properties. Ultimately, it yields a high-damage-tolerance aerospace-grade epoxy prepreg with excellent comprehensive performance.

[0010] In the first aspect, this application provides a high-toughness epoxy prepreg, which adopts the following technical solution:

[0011] A high-toughness epoxy prepreg, wherein the epoxy prepreg has a layered structure, comprising, from the inside out, a fiber reinforcement layer, an epoxy resin matrix layer, and a functionalized toughening layer;

[0012] The epoxy resin matrix layer comprises the following components in parts by weight: 100 parts epoxy resin mixture, 5-15 parts toughening agent A, 30-50 parts curing agent, and 0.5-3 parts accelerator; the epoxy resin mixture is a compound of liquid epoxy resin and solid epoxy resin, and the weight ratio of liquid epoxy resin to solid epoxy resin is (4-5):1; the toughening agent A is a core-shell structured polymer particle with polybutadiene rubber as the core and polymethyl methacrylate as the shell (PB@PMMA);

[0013] The functionalized toughening layer comprises the following components in parts by weight: 100 parts epoxy resin and 10-30 parts toughening agent B; the toughening agent B is a composite of surface-modified nano-clay and thermoplastic resin ultrafine particles; the weight ratio of the surface-modified nano-clay to the thermoplastic resin ultrafine particles is 1:(2-5).

[0014] The functionalized toughening layer is a continuous coating independently applied to the surface of the epoxy resin matrix layer, and the toughening agent B is not dispersed in the epoxy resin matrix layer.

[0015] In this application, the crosslinking density and melt flowability of the resin system can be precisely controlled by mixing liquid epoxy resin and solid epoxy resin in a ratio of (4-5):1. This ensures both the low viscosity characteristics required for the hot melt impregnation process and provides an excellent heat resistance foundation for the cured composite material. The rubber core layer of the core-shell toughening agent A can achieve resin toughening by inducing crazes and shear bands, while the PMMA shell layer can ensure that the particles are uniformly dispersed in the epoxy resin, avoiding agglomeration, and will not significantly increase the viscosity of the resin system. Within the addition range of 5-15 parts, the best balance between matrix toughening effect and process flowability can be achieved.

[0016] This application completely decouples the interlaminar toughening components from the matrix impregnation resin through an independent functionalized toughening layer design, fundamentally avoiding the industry problem of increased matrix resin viscosity and difficulty in carbon fiber impregnation caused by the addition of interlaminar toughening agents. At the same time, surface-modified nanoclay and thermoplastic resin ultrafine particles can produce a significant synergistic toughening effect at a ratio of 1:(2-5): the thermoplastic resin toughening phase can passivate the interlaminar crack tip and achieve crack bridging, while the nanoclay can achieve crack pinning and deflection. The two work together to greatly improve the interlaminar fracture toughness and impact damage tolerance of the composite material.

[0017] Optionally, the weight ratio of the surface-modified nanoclay to the thermoplastic resin ultrafine particles is 1:(3-4).

[0018] Under the above-mentioned optimal ratio, the synergistic toughening effect of the two is maximized, while ensuring the best coating processability of the functional toughening layer slurry.

[0019] Optionally, the fiber reinforcement layer comprises continuous carbon fibers, glass fibers, or aramid fibers.

[0020] The selected high-strength continuous carbon fiber is T800 grade, which is suitable for the performance requirements of aerospace main load-bearing structural components.

[0021] Optionally, the areal density of the fiber reinforcement layer is 100-200 g / m².

[0022] Optionally, the areal density of the fiber reinforcement layer is 140-160 g / m².

[0023] The above areal density range is a standard specification for general aviation prepregs in the industry, which can guarantee the specific strength, specific modulus and molding process stability of composite materials.

[0024] Optionally, the liquid epoxy resin is TDE-85 with an epoxy value of 0.80-0.90 eq / 100g.

[0025] The rigid ring structure inherent in liquid epoxy resins endows the resin system with excellent heat resistance and mechanical strength.

[0026] Optionally, the solid epoxy resin is bisphenol A type 0191 with an epoxy value of 0.18-0.24 eq / 100g.

[0027] Solid epoxy resins allow for precise adjustment of the melt viscosity and curing crosslinking density of the resin system, balancing processability and post-curing performance.

[0028] Optionally, the toughening agent A has an average particle size of 50-200 nm.

[0029] Optionally, the toughening agent A has an average particle size of 100-150 nm.

[0030] The above particle size range ensures that the toughening agent is uniformly dispersed in the resin without agglomeration, while exerting the best toughening effect on the matrix.

[0031] Optionally, the surface-modified nanoclay is organically modified montmorillonite.

[0032] Organically modified montmorillonite exhibits excellent compatibility with epoxy resin systems, fully leveraging the nano-reinforcement and crack deflection effects.

[0033] Optionally, the thermoplastic resin ultrafine particles are polyethersulfone ultrafine particles.

[0034] The polyethersulfone ultrafine particles have good interfacial bonding with the epoxy resin matrix and excellent heat resistance, which will not cause a decrease in the heat resistance of the composite material after curing.

[0035] Optionally, the particle size of the thermoplastic resin ultrafine particles is 0.1-5 μm.

[0036] Optionally, the particle size of the thermoplastic resin ultrafine particles is 0.5-2 μm.

[0037] The above-mentioned particle size is adapted to the interlayer thickness of the composite material, which can ensure the uniformity and stability of the interlayer toughening effect.

[0038] Optionally, the curing agent is a dicyandiamide-based latent curing agent.

[0039] The aforementioned curing agent can give the prepreg an excellent room temperature storage period, while also being compatible with a medium-temperature curing process at 180°C.

[0040] Optionally, the promoter is a urea derivative.

[0041] The above-mentioned accelerators can be combined with dicyandiamide curing agents to precisely control the curing reaction rate and optimize the curing process window.

[0042] Secondly, this application provides a method for preparing a high-toughness epoxy prepreg, which adopts the following technical solution:

[0043] A method for preparing a high-toughness epoxy prepreg, the method specifically includes the following steps:

[0044] (1) Preparation of epoxy resin matrix layer composition: Liquid epoxy resin and solid epoxy resin are mixed evenly in the required ratio, toughening agent A is added and stirred and dispersed until uniform; then curing agent and accelerator are added, and the mixture is mixed evenly to obtain epoxy resin matrix layer composition;

[0045] (2) Preparation of functionalized toughening layer slurry: Epoxy resin and toughening agent B are mixed in the required ratio, and solvent is added for high-speed shear dispersion to prepare functionalized toughening layer slurry;

[0046] (3) Preparation of prepreg: The fiber reinforcement layer is passed through an impregnation tank containing an epoxy resin matrix layer composition. The resin content of the fiber reinforcement layer is controlled. Then, a functionalized toughening layer slurry is coated on the surface of the epoxy resin matrix layer. After drying and winding, a high-toughness epoxy prepreg is obtained.

[0047] The above preparation method can achieve large-scale stable production; at the same time, through the step-by-step process design of matrix impregnation and interlayer coating, the problem of "toughening and impregnation processability cannot be taken into account" in traditional toughened prepregs is completely solved.

[0048] In summary, this application includes at least one of the following beneficial technical effects:

[0049] (1) Dual-system synergistic toughening significantly improves damage tolerance: Through the dual design of "intrinsic toughening of matrix core-shell particles" and "synergistic toughening of interlayer nano-clay-thermoplastic resin", the toughness of the resin body and the crack propagation resistance of the composite material interlayer are improved at the same time. The compressive strength (CAI) of the composite laminate after impact can reach up to 285MPa, which far exceeds the standard of aerospace-grade high-toughness resin (CAI>255MPa); the type I interlaminar fracture toughness (GIC) can reach up to 350J / m², which is more than 59% higher than the traditional toughening system, and the type II interlaminar fracture toughness (GIIC) can reach up to 920J / m², which is more than 55% higher than the traditional toughening system. The toughening effect is far superior to the single toughening method.

[0050] (2) Excellent processability, fully adaptable to industrial mass production: The core-shell toughening agent A has minimal impact on the viscosity of the resin system, and the interlayer toughening agent B exists as an independent functional layer and does not participate in the impregnation process of the main resin, fundamentally solving the industry pain point of traditional toughening technology that "the addition of toughening agent leads to a surge in resin viscosity and difficulty in impregnating carbon fiber". The viscosity of the epoxy resin matrix composition of this application is only 4500 mPa·s at 80°C, which is completely within the optimal viscosity window for industrial production of hot melt prepreg, and can be directly adapted to existing production lines to achieve large-scale mass production.

[0051] (3) Perfect balance of comprehensive performance with no performance shortcomings: While significantly improving the toughness and damage tolerance of composite materials, thanks to the rigid shell of core-shell particles, the reinforcing effect of nano-clay, and the precise compounding design of epoxy resin system, the bending strength, tensile strength, and interlaminar shear strength of composite materials are all maintained at the industry's best level for T800 grade carbon fiber epoxy composite materials. The glass transition temperature (Tg) reaches up to 182℃ and the heat distortion temperature (HDT) reaches up to 176℃. There is no problem of "toughening inevitably reduces heat resistance and toughening inevitably reduces strength" that is common in traditional toughening technologies. It achieves a balance of high toughness, excellent processability, high strength, and high heat resistance, and can be widely used in the fields of main load-bearing structural components such as aerospace, rail transportation, and high-end equipment. Detailed Implementation

[0052] Before describing the embodiments of this application in detail, it should be understood that the terminology used herein is for the purpose of describing a particular embodiment only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the term pertains.

[0053] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0054] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0055] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0056] This application provides a high-toughness epoxy prepreg. It has a multi-layer structure, comprising, from the inside out, a fiber reinforcement layer, an epoxy resin matrix layer, and a functionalized toughening layer.

[0057] The fiber reinforcement layer includes continuous carbon fibers, glass fibers, or aramid fibers, with a surface density of 100-200 g / m².

[0058] The epoxy resin matrix layer comprises the following components in parts by weight: 100 parts epoxy resin mixture, 5-15 parts toughening agent A, 30-50 parts curing agent, and 0.5-3 parts accelerator.

[0059] The epoxy resin mixture is a blend of liquid epoxy resin (such as TDE-85, epoxy value 0.80-0.90 eq / 100g) and solid epoxy resin (such as bisphenol A type 0191, epoxy value 0.18-0.24 eq / 100g) in a weight ratio of (4-5):1.

[0060] Toughening agent A (matrix toughening agent) consists of polybutadiene rubber core-polymethyl methacrylate (PB@PMMA) core-shell polymer particles with an average particle size of 50-200 nm. These particles are used to induce energy dissipation mechanisms such as crazes and shear banding within the resin matrix, thereby achieving matrix toughening. This polybutadiene rubber core-polymethyl methacrylate core-shell polymer particle is a mature product in existing technology and will not be described in detail here.

[0061] The curing agent is a dicyandiamide-based latent curing agent. The accelerator is a urea derivative.

[0062] The functionalized toughening layer comprises the following components in parts by weight: 100 parts epoxy resin and 10-30 parts toughening agent B;

[0063] Toughening agent B (interlaminar toughening agent) is a composite of surface-modified nanoclay (such as organically modified montmorillonite) and ultrafine thermoplastic resin particles (such as polyethersulfone PES). The weight ratio of the modified nanoclay to the ultrafine thermoplastic resin particles is 1:(2-5). After curing, this layer forms a tough interface that effectively pins, deflects, and bridges interlaminar cracks, absorbing impact energy.

[0064] This application also provides a method for preparing a high-toughness epoxy prepreg. The preparation method specifically includes the following steps:

[0065] (1) Preparation of epoxy resin matrix layer composition: Liquid epoxy resin and solid epoxy resin are heated and stirred at 80-90℃ to mix evenly; toughening agent A is added and stirred to disperse until there are no obvious agglomerates; then dicyandiamide curing agent and urea accelerator are added, the temperature is lowered to 70℃ and mixed evenly to obtain epoxy resin matrix composition.

[0066] (2) Preparation of functionalized toughening layer slurry:

[0067] Preparation of toughening agent B: Polyethersulfone ultrafine particles were added to acetone and dispersed by shearing with a high-speed shear machine at a speed of 2000-3000 r / min to form a uniform dispersion; then, organically modified montmorillonite was slowly added to the dispersion and dispersed by high-speed shearing at a speed of 2000-3000 r / min, while ultrasonic dispersion was assisted by a power of 300-500 W to obtain a composite dispersion; the composite dispersion was placed in a vacuum drying oven at 70-90℃ for vacuum drying, and after drying, it was pulverized and passed through a 100-mesh sieve to obtain powdered toughening agent B;

[0068] Preparation of functionalized toughening layer slurry: Epoxy resin, toughening agent B and acetone are mixed and dispersed by high-speed shearing to prepare a functionalized toughening layer slurry with a solid content of 35-45% and uniform dispersion.

[0069] (3) Preparation of prepreg: The carbon fiber bundles are passed through the impregnation tank containing the epoxy resin matrix composition obtained in step (1) using a hot melt prepreg machine, and the resin content of the carbon fiber bundles is controlled to be 30-40%; then, a layer of functionalized toughening slurry obtained in step (2) is uniformly coated on the surface of the impregnated prepreg using a precision coating machine, and the coating amount is controlled to be 8-12 g / m² dry weight; finally, after drying and winding, a high-toughness epoxy prepreg is obtained.

[0070] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0071] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0072] The present application will be further described in detail below with reference to the embodiments and test results.

[0073] Example 1

[0074] This embodiment provides a high-toughness epoxy prepreg.

[0075] The preparation method of this high-toughness epoxy prepreg specifically includes the following steps:

[0076] (1) Preparation of epoxy resin matrix layer composition

[0077] 80g of liquid TDE-85 epoxy resin (epoxy value 0.85eq / 100g, commercially available) and 20g of solid bisphenol A type 0191 epoxy resin (epoxy value 0.20eq / 100g, commercially available) are heated and stirred at 80℃ to ensure that the two epoxy resins are completely fused.

[0078] Add 10g of toughening agent A (a core-shell polymer particle with polybutadiene rubber as the core and polymethyl methacrylate as the shell, with an average particle size of 100nm, commercially available and directly purchasable), and continue stirring and dispersing for 1 hour to ensure that toughening agent A is uniformly dispersed in the epoxy resin mixture without obvious agglomerates.

[0079] Then add 40g of dicyandiamide curing agent (commercially available and readily purchasable) and 1.5g of urea accelerator (commercially available and readily purchasable), cool to 70℃ and continue mixing until homogeneous to obtain a low-viscosity, uniformly dispersed epoxy resin matrix composition.

[0080] (2) Preparation of functionalized toughening layer slurry:

[0081] ①Preparation of toughening agent B

[0082] Add 15g of thermoplastic resin ultrafine particles (polyethersulfone PES ultrafine particles, particle size 1μm, commercially available) to acetone (commercially available), and shear and disperse them for 20min using a high-speed shear machine with a rotation speed of 2500r / min to prepare a uniform thermoplastic resin ultrafine particle dispersion.

[0083] Then, slowly add 5g of surface-modified nano clay (organic modified montmorillonite, commercially available) to the above dispersion, and continue to shear and disperse at 2500r / min for 30min. At the same time, use 400W power ultrasonic-assisted dispersion for 12min to ensure that the organic modified montmorillonite and polyethersulfone ultrafine particles are uniformly mixed and without agglomeration, thus obtaining a composite dispersion.

[0084] The composite dispersion was placed in an 80℃ vacuum drying oven and vacuum dried for 2.5 h to completely remove the solvent. After drying, it was pulverized and passed through a 100-mesh sieve to obtain powdered toughening agent B.

[0085] ②Preparation of functionalized toughening layer slurry

[0086] 100g of epoxy resin (E-51 type, commercially available) was mixed with 20g of the toughening agent B prepared above and acetone, and dispersed by high-speed shearing for 2 hours to produce a functional toughening layer slurry with a solid content of about 40%, uniform dispersion, and no obvious agglomeration.

[0087] (3) Preparation of prepreg

[0088] T800 grade carbon fiber bundles (area density 145g / m², commercially available) are passed through an impregnation tank containing the epoxy resin matrix composition obtained in step (1) using a hot melt prepreg machine. The resin content of the carbon fiber bundles is controlled to be 35±3%, ensuring that the epoxy resin matrix composition is uniformly impregnated on the surface and inside of the carbon fiber bundles.

[0089] Subsequently, a layer of functionalized toughening slurry obtained in step (2) is uniformly coated on the surface of the prepreg impregnated with epoxy resin matrix composition using a precision coating machine. The coating amount is controlled to be 10 g / m² dry weight to ensure that the coating is uniform, without omissions or accumulation.

[0090] Finally, the coated prepreg is sent to a drying device to dry and remove the solvent and allow the resin to cure initially. After being wound up, a high-toughness epoxy prepreg is obtained.

[0091] Table 1. Specific dosage of each component in the examples and comparative examples.

[0092]

[0093] Example 2

[0094] This embodiment provides a high-toughness epoxy prepreg. The difference between this embodiment and Embodiment 1 lies in the weight ratio of liquid epoxy resin to solid epoxy resin, as shown in Table 1. All other operating steps remain the same as in Embodiment 1.

[0095] Examples 3-5

[0096] The above embodiments each provide a high-toughness epoxy prepreg. The difference between these and Embodiment 1 lies in the addition ratio of surface-modified nanoclay to thermoplastic resin ultrafine particles in toughening agent B, as shown in Table 1. All other operating steps remain consistent with Embodiment 1.

[0097] Examples 6-7

[0098] The above embodiments each provide a high-toughness epoxy prepreg. The difference between them and Embodiment 1 lies in the addition of toughening agent A, as shown in Table 1. All other operating steps remain the same as in Embodiment 1.

[0099] Comparative Example 1

[0100] This comparative example provides a high-toughness epoxy prepreg. It differs from Example 1 in that no functionalized toughening layer is added, and the specific amounts of each component are shown in Table 1. All other operating steps are consistent with Example 1.

[0101] Comparative Example 2

[0102] This comparative example provides a high-toughness epoxy prepreg. It differs from Example 1 in that toughening agent A is not added to the epoxy resin matrix layer; instead, toughening agent B is added only to the functionalized toughening layer. The specific amounts of each component are shown in Table 1. All other operating steps remain the same as in Example 1.

[0103] Comparative Example 3

[0104] This comparative example provides a high-toughness epoxy prepreg. It differs from Example 1 in that toughening agent B is not added to the functionalized toughening layer; toughening agent A is added only to the epoxy resin matrix layer. The specific amounts of each component are shown in Table 1. All other operating steps are consistent with Example 1.

[0105] Comparative Example 4-5

[0106] The above comparative examples each provide a high-toughness epoxy prepreg. The difference between them and Example 1 lies in the weight ratio of liquid epoxy resin to solid epoxy resin, as shown in Table 1. All other operating steps remain the same as in Example 1.

[0107] Comparative Examples 6-7

[0108] The above comparative examples each provide a high-toughness epoxy prepreg. The difference between them and Example 1 lies in the addition ratio of surface-modified nanoclay to thermoplastic resin ultrafine particles in toughening agent B, as shown in Table 1. All other operating steps remain consistent with Example 1.

[0109] Comparative Example 8

[0110] This comparative example provides a high-toughness epoxy prepreg. It differs from Example 1 in that no functionalized toughening layer is added, and toughening agent A is replaced with the same weight of carboxyl-terminated nitrile butadiene rubber (CTBN). The specific amounts of each component are shown in Table 1. All other operating steps are consistent with Example 1.

[0111] Comparative Example 9

[0112] This comparative example provides a high-toughness epoxy prepreg. The difference between this example and Example 1 is that no functionalized toughening layer was added, and the epoxy resin and toughening agent B from the original functionalized toughening layer were incorporated into the epoxy resin matrix layer to prepare a fully-component blended epoxy resin matrix composition. The specific amounts of each component are shown in Table 1. All other operating steps are consistent with Example 1.

[0113] The specific preparation method of the above-mentioned epoxy prepreg is as follows:

[0114] (1) Preparation of a full-component blended epoxy resin matrix composition

[0115] 80g of liquid TDE-85 epoxy resin, 20g of solid bisphenol A type 0191 epoxy resin, and 100g of E-51 epoxy resin were mixed and heated at 80°C with stirring until homogeneous. Toughening agent A and toughening agent B (preparation method as described in Example 1) were added sequentially, and the mixture was stirred and dispersed for 1 hour until a homogeneous state without obvious agglomerates was reached. After cooling to 70°C, 40g of dicyandiamide curing agent and 1.5g of urea accelerator were added, and the mixture was stirred until homogeneous to obtain a full-component blended epoxy resin matrix composition.

[0116] (2) Preparation of prepreg

[0117] A hot-melt prepreg machine was used to pass a T800 grade continuous carbon fiber reinforcement layer (completely consistent with Example 1) through an impregnation tank containing the above-mentioned full-component blended epoxy resin matrix composition. The total resin content of the prepreg was controlled to be 35±3%, which was completely consistent with Example 1. Subsequently, the impregnated prepreg was sent to a drying device and wound up to obtain a comparative epoxy prepreg.

[0118] Performance test results

[0119] The high-toughness epoxy prepregs of the above embodiments and comparative examples were subjected to the following tests. The test results are shown in Table 2.

[0120] (a) Sample preparation

[0121] For different performance test items, the above-mentioned high-toughness epoxy prepreg was laid up according to the layup sequence and number of layups specified in the corresponding test standards. All layups adopted a symmetrical and balanced design, with no risk of curing warping. After the layup was completed, it was placed in an autoclave and cured according to the following curing process: the temperature was increased to 120°C at a heating rate of 2°C / min and held for 1 hour, then increased to 180°C and held for 2 hours. The curing pressure was 0.6 MPa. After curing, the material was allowed to cool naturally to room temperature and demolded to obtain the corresponding composite material laminate for testing. The laminate was then processed into standard size samples according to the requirements of the corresponding test standards.

[0122] The ply rules for each test item are as follows: Compressive strength after impact (CAI) test: [45 / 0 / -45 / 90]4s symmetrical quasi-isotropic ply, with a total of 32 ply layers and a specimen thickness of 4mm after curing; Type I interlaminar fracture toughness (GIC) and Type II interlaminar fracture toughness (GIIC) test: unidirectional [0]16 ply, with the ply direction consistent with the specimen length direction; Tensile properties / flexural strength / interlaminar shear strength test: unidirectional [0]8 ply, with the ply direction consistent with the specimen stress direction.

[0123] (ii) Performance testing

[0124] Part 1: Rotational Viscosity Testing of Epoxy Resin Matrix Systems

[0125] Test objects: epoxy resin matrix layer compositions prepared in step (1) of each embodiment and comparative example.

[0126] The specific testing method is as follows: A Brookfield rotational viscometer is used. The instrument's constant temperature system is preheated to 80°C and kept constant. About 10g of the epoxy resin matrix composition to be tested is placed in the viscometer test sleeve. After the sample temperature stabilizes at 80°C, the appropriate rotor is selected, and the test is performed at the specified speed. After the reading stabilizes, the viscosity value is recorded. Each sample is measured in parallel 3 times. After removing outliers, the arithmetic mean is taken. The final result is expressed in mPa·s.

[0127] Part Two: Interlaminar Toughness and Damage Tolerance Testing

[0128] (1) Type I interlaminar fracture toughness (GIC) test

[0129] The specific testing method is as follows: Double cantilever beam (DCB) specimens are used, with specimen dimensions of 250mm×25mm×3mm. Initial cracks are pre-formed, and the specimens are tested on a universal testing machine at a loading rate of 1mm / min. The load-displacement curves are recorded, and the critical strain energy release rate (GIC) is calculated. Each test group consists of no less than 5 valid specimens.

[0130] (2) Type II interlaminar fracture toughness (GIIC) test

[0131] The specific testing method is as follows: End-notched bending (ENF) specimens with a size of 140mm×25mm×3mm are used. Initial cracks are pre-formed, and three-point bending tests are performed on a universal testing machine at a loading rate of 1mm / min. The load-displacement curve is recorded, and the critical strain energy release rate (GIIC) is calculated. Each test group has no less than 5 valid specimens.

[0132] (3) Post-impact compressive strength (CAI) test

[0133] The specific testing method is as follows: The sample size is 150mm×100mm×4mm. A drop hammer impact tester is used to impact the sample with an impact energy of 6.7J / mm, and the impact damage area is recorded. After impact, the sample is subjected to compression test on a universal testing machine with a loading rate of 1.25mm / min. The compressive strength after impact is measured. Each test group has no less than 5 valid samples.

[0134] Part Three: Basic Mechanical Property Testing

[0135] (1) Tensile property testing

[0136] The specific testing method is as follows: The sample size is 230mm×12.5mm×2mm, with aluminum alloy reinforcing sheets attached. The sample is tested on a universal testing machine at a loading rate of 2mm / min to determine the tensile strength. Each test group shall have no less than 5 valid samples.

[0137] (2) Bending performance test

[0138] The specific testing method is as follows: a three-point bending test is adopted, the sample size is 80mm×15mm×2mm, the span-to-thickness ratio is 16:1, and the test is carried out on a universal testing machine at a loading rate of 2mm / min to determine the bending strength. Each test group shall have no less than 5 valid samples.

[0139] (3) Interlaminar shear strength testing

[0140] Test method: Three-point short beam shear test was adopted. The sample size was 20mm×6mm×2mm with a span-to-thickness ratio of 4:1. The test was carried out on a universal testing machine at a loading rate of 1mm / min to determine the interlaminar shear strength. Each test group had no less than 5 valid samples.

[0141] Fourth aspect: Heat resistance testing

[0142] (1) Glass transition temperature (Tg) detection

[0143] The specific detection method is as follows: Take 5-10 mg of the sample to be tested, and use a differential scanning calorimeter to heat from 30℃ to 250℃ at a heating rate of 10℃ / min under a nitrogen atmosphere. Record the DSC curve and determine the glass transition temperature Tg. Each sample is tested in parallel 3 times, and the arithmetic mean is taken.

[0144] (2) Heat distortion temperature (HDT) test

[0145] The specific testing method is as follows: The sample size is 80mm×10mm×4mm. The three-point bending mode is adopted, the bending stress is 1.82MPa, the heating rate is 2℃ / min, and the temperature corresponding to the sample deformation reaching 0.34mm is determined, which is the heat distortion temperature. Each group of tests shall have no less than 3 valid samples.

[0146] Table 2 Performance Test Results

[0147]

[0148] As shown in Table 2, this application utilizes a dual-system synergistic toughening approach of "an epoxy resin matrix layer containing a core-shell toughening agent A + a functionalized toughening layer containing a montmorillonite-polyethersulfone composite toughening agent B" to completely solve the industry pain point that existing epoxy prepregs cannot simultaneously achieve both toughening effect and industrial processability, heat resistance, and basic mechanical properties.

[0149] Example 1 employs a dual system of matrix toughening and interlaminar toughening, achieving an order-of-magnitude improvement in its core damage tolerance and interlaminar toughness indices: post-impact compressive strength (CAI), Type I interlaminar fracture toughness (GIC), and Type II interlaminar fracture toughness (GIIC) are all significantly improved compared to Comparative Example 1 without functionalized toughening layer, Comparative Example 2 with only interlaminar toughening and no matrix toughening, Comparative Example 3 with only matrix toughening and no interlaminar toughening, and Comparative Example 9 with conventional dual toughening agent full-component blending scheme. The performance improvement far exceeds the combined effect of the two toughening methods alone. In contrast, in Comparative Example 9, when all the toughening agents were blended into the matrix resin, the toughening agents could not be directionally enriched in the interlayer. Not only could they not exert a synergistic toughening effect, but the toughening effect was also greatly reduced due to particle agglomeration. This fully demonstrates that the dual toughening system of this application produces a significant synergistic effect through the synergistic effect of intrinsic matrix toughening and interlayer crack passivation, pinning, and bridging, achieving a breakthrough improvement in the damage tolerance and interlayer toughness of composite materials.

[0150] Meanwhile, the dual toughening system of this application perfectly overcomes the dual contradiction of existing technologies that "toughening inevitably increases viscosity and toughening inevitably decreases heat resistance": the viscosity of the resin system at 80℃ in Example 1 is only 4500 mPa·s, which is completely within the optimal viscosity window (3000-6000 mPa·s) for industrial production of hot-melt aerospace prepregs, and is only 35.7% of the viscosity of the resin in Comparative Example 9, which has the same total amount of raw materials. There is no problem of impregnation difficulties caused by traditional toughening technology and conventional dual toughening blending schemes; the glass transition temperature Tg reaches 182℃ and the heat distortion temperature HDT reaches 176℃, which is basically the same as that of the untoughened Comparative Example 1, with no loss of heat resistance; the flexural strength, tensile strength, and interlaminar shear strength reach 1850 MPa, 2150 MPa, and 68 MPa, respectively, which remain at the industry's best level for T800 grade carbon fiber epoxy composite materials, achieving a comprehensive balance of multiple properties such as "high toughness, excellent processability, strength preservation, and high heat resistance".

[0151] Furthermore, Table 2 shows that the weight ratio of liquid epoxy resin to solid epoxy resin is (4-5):1. In Examples 1 (4:1) and 2 (5:1), the resin viscosities are 4500 mPa·s and 4200 mPa·s, respectively, which are suitable for hot melt impregnation processes. At the same time, the interlayer toughness, basic mechanical properties, and heat resistance are all maintained at an excellent level, achieving a perfect balance among the three. However, in Comparative Example 4 (3:1), where the compounding ratio is lower than the lower limit of the protection range, the proportion of solid epoxy resin is too high, and the resin viscosity soars to 9. The 800 mPa·s ratio is far beyond the acceptable range for industrial production, making it prone to defects such as uneven carbon fiber impregnation, dry filaments, and excessive adhesive, thus making stable mass production impossible. In Comparative Example 5 (6:1), the compounding ratio is higher than the upper limit of the protection range, and the proportion of liquid epoxy resin is too high. Although the resin viscosity is reduced to 2800 mPa·s, the Tg of the composite material after curing is only 168℃ and the HDT is only 160℃, resulting in a significant decrease in heat resistance. At the same time, the basic mechanical properties also show a significant decline, which cannot meet the requirements of high-end fields such as aerospace.

[0152] The addition amount of toughening agent A is 5-15 parts (based on 100 parts of epoxy resin mixture). Examples 6-7 fall within this range. As the addition amount of toughening agent A increases, the interlaminar toughness and CAI value of the composite material show a steady upward trend, while the resin viscosity is consistently controlled below 5000 mPa·s, fully meeting the requirements of the hot-melt process. This range fully covers the adjustable range for industrial production, avoiding both insufficient addition leading to substandard toughening effect and excessive addition leading to uncontrolled resin viscosity and decreased processability.

[0153] The weight ratio of surface-modified nano-clay to thermoplastic resin ultrafine particles is 1:(2-5). Examples 1 and 3-5 are within this range, with CAI values ​​all maintained above 265MPa and GIC values ​​all maintained above 320J / m², showing excellent toughening effect. At the same time, the resin viscosity and heat resistance are not significantly degraded. Among them, Example 1 with a ratio of 1:3 has the best performance, and the synergistic toughening effect of montmorillonite and polyethersulfone is most fully exerted. Comparative Example 6 (1:1), with a ratio lower than the lower limit of this range, had an excessively high proportion of nano-montmorillonite, which easily led to agglomeration in the resin. This not only significantly reduced the toughening effect but also caused the resin viscosity to rise to 6200 mPa·s, exceeding the optimal process window, while the basic mechanical properties showed a significant decline. Comparative Example 7 (1:6), with a ratio higher than the upper limit of this range, had an excessively high proportion of polyethersulfone, resulting in excessively high viscosity of the functionalized toughening layer slurry and a decrease in coating uniformity. At the same time, the Tg of the composite material dropped to 172℃ and the HDT dropped to 165℃, resulting in a significant loss of heat resistance and failing to meet the application requirements.

[0154] Finally, through a direct comparison between Example 1 and Comparative Example 8 (a common carboxyl-terminated nitrile butadiene rubber (CTBN) toughening system), it can be fully demonstrated that: in terms of toughening effect, the CAI value of Example 1 is 39.0% higher than that of Comparative Example 8, the GIC value is 59.1% higher, and the GIIC value is 55.9% higher, with a toughening effect far exceeding that of the traditional CTBN toughening system; in terms of processability, the resin viscosity of Example 1 is only 37.5% of that of Comparative Example 8, perfectly adapting to existing mature hot-melt prepreg industrial production lines, while the resin viscosity of Comparative Example 8 is as high as 12000 mPa·s, which cannot meet the requirements of large-scale hot-melt production; in terms of heat resistance, the Tg and HDT of Example 1 are 12°C and 14°C higher than those of Comparative Example 8, respectively, completely solving the industry pain point of a significant decrease in heat resistance that is inevitably caused by traditional rubber toughening systems; in terms of basic mechanical properties, the bending, tensile, and interlaminar shear strengths of Example 1 are all superior to those of Comparative Example 8, with almost no loss of mechanical properties.

[0155] In summary, this application, through a three-layer structure design of "fiber reinforcement layer - epoxy resin matrix layer - functionalized toughening layer", combines the synergistic effect of matrix toughening and interlayer toughening, and achieves a breakthrough improvement in the interlayer toughness and damage tolerance of epoxy prepreg by precisely limiting the epoxy resin compounding ratio, the amount and ratio of toughening agent, and so on. At the same time, it perfectly balances the industrial processability of prepreg, the basic mechanical properties and heat resistance of composite materials, and solves the dual contradictions of the prior art mentioned in the background.

[0156] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A high-toughness epoxy prepreg, characterized in that, The epoxy prepreg has a layered structure, which includes, from the inside out, a fiber reinforcement layer, an epoxy resin matrix layer, and a functionalized toughening layer. The epoxy resin matrix layer comprises the following components in parts by weight: 100 parts epoxy resin mixture, 5-15 parts toughening agent A, 30-50 parts curing agent, and 0.5-3 parts accelerator. The epoxy resin mixture is a compound of liquid epoxy resin and solid epoxy resin, and the weight ratio of liquid epoxy resin to solid epoxy resin is (4-5):

1. The toughening agent A is a core-shell structured polymer particle with polybutadiene rubber as the core and polymethyl methacrylate as the shell. The functionalized toughening layer comprises the following components in parts by weight: 100 parts epoxy resin and 10-30 parts toughening agent B; The toughening agent B is a composite of surface-modified nanoclay and thermoplastic resin ultrafine particles; the weight ratio of the surface-modified nanoclay to the thermoplastic resin ultrafine particles is 1:(2-5).

2. The high-toughness epoxy prepreg according to claim 1, characterized in that, The weight ratio of the surface-modified nanoclay to the thermoplastic resin ultrafine particles is 1:(3-4).

3. The high-toughness epoxy prepreg according to claim 1, characterized in that, The fiber reinforcement layer includes continuous carbon fibers, glass fibers, or aramid fibers; Optionally, the areal density of the fiber reinforcement layer is 100-200 g / m²; Optionally, the areal density of the fiber reinforcement layer is 140-160 g / m².

4. The high-toughness epoxy prepreg according to claim 1, characterized in that, The liquid epoxy resin is TDE-85, with an epoxy value of 0.80-0.90 eq / 100g.

5. The high-toughness epoxy prepreg according to claim 1, characterized in that, The solid epoxy resin is bisphenol A type 0191, with an epoxy value of 0.18-0.24 eq / 100g.

6. The high-toughness epoxy prepreg according to claim 1, characterized in that, The toughening agent A has an average particle size of 50-200 nm; Optionally, the toughening agent A has an average particle size of 100-150 nm.

7. The high-toughness epoxy prepreg according to claim 1, characterized in that, The surface-modified nanoclay is organically modified montmorillonite.

8. The high-toughness epoxy prepreg according to claim 1, characterized in that, The thermoplastic resin ultrafine particles are polyethersulfone ultrafine particles; Optionally, the particle size of the thermoplastic resin ultrafine particles is 0.1-5 μm; Optionally, the particle size of the thermoplastic resin ultrafine particles is 0.5-2 μm.

9. The high-toughness epoxy prepreg according to claim 1, characterized in that, The curing agent is a dicyandiamide-based latent curing agent; Optionally, the promoter is a urea derivative.

10. A method for preparing a high-toughness epoxy prepreg according to any one of claims 1-9, characterized in that, The preparation method specifically includes the following steps: (1) Preparation of epoxy resin matrix layer composition: Liquid epoxy resin and solid epoxy resin are mixed evenly in the required ratio, toughening agent A is added and stirred and dispersed until uniform; then curing agent and accelerator are added, and the mixture is mixed evenly to obtain epoxy resin matrix layer composition; (2) Preparation of functionalized toughening layer slurry: Epoxy resin and toughening agent B are mixed in the required ratio, and solvent is added for high-speed shear dispersion to prepare functionalized toughening layer slurry; (3) Preparation of prepreg: The fiber reinforcement layer is passed through an impregnation tank containing an epoxy resin matrix layer composition. The resin content of the fiber reinforcement layer is controlled. Then, a functionalized toughening layer slurry is coated on the surface of the epoxy resin matrix layer. After drying and winding, a high-toughness epoxy prepreg is obtained.

Images