Halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors

Abstract

This invention relates to the field of prepreg technology, specifically to a halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim. It comprises: halogen-free flame-retardant epoxy resin, an active ester curing agent, a low-temperature curing accelerator, a halogen-free flame-retardant additive, a silane coupling agent, a defoamer, a leveling agent, and glass fiber material. In this invention, a flame-retardant phosphated epoxy resin is used as the matrix, compounded with a halogen-free synergistic flame retardant. The curing temperature is lowered by the combination of the active ester curing agent and glass fiber, while ensuring the mechanical strength of the material. This avoids the problems of existing halogen-containing prepregs for rail transit interior trim, such as the release of large amounts of smoke during combustion, high curing temperatures, and low interlaminar shear strength, thus meeting the safety, efficiency, and structural performance requirements of rail transit interior trim.

Description

Technical Field

[0001] This invention relates to the field of prepreg technology, and more specifically, to halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors. Background Technology

[0002] In recent years, my country's rail transit industry has developed rapidly, with the operating mileage of high-speed trains and urban rail transit vehicles continuously increasing, and the number of vehicles in operation also rising steadily. As people's demands for travel quality increase, higher requirements are being placed on the aesthetics, comfort, and safety of rail transit vehicle interiors.

[0003] Prepreg, as an advanced composite material, has been widely used in the interior decoration of rail transit vehicles. It possesses advantages such as high strength, lightweight, and good formability, meeting various material performance requirements for rail transit vehicle interiors. However, several key technical bottlenecks remain in the currently widely used prepregs: on the one hand, halogenated flame retardants added to meet fire safety standards release large amounts of toxic fumes during combustion, threatening passenger safety; on the other hand, conventional epoxy resin systems require long curing times at high temperatures (usually above 120°C), resulting in high energy consumption and long curing cycles.

[0004] Furthermore, the industry often uses phenolic resin-based prepregs or modified polyester prepregs to meet flame retardant requirements. The drawback is that although phenolic resin prepregs have excellent flame retardant properties, they are brittle and have a rough surface after curing, which is not aesthetically pleasing and is prone to cracking. Although modified polyester prepregs can achieve low-temperature curing, their mechanical properties, especially interlaminar shear strength, are low and cannot withstand the vibration and impact loads during the operation of rail vehicles. Summary of the Invention

[0005] The purpose of this invention is to avoid the problems of existing halogenated prepregs for rail transit interiors, such as the release of large amounts of smoke during combustion, high curing temperature, and low interlaminar shear strength.

[0006] The purpose of this invention is to provide a halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors. It uses flame-retardant phosphated epoxy resin as the matrix and is compounded with a halogen-free synergistic flame retardant. The curing temperature is reduced by combining an active ester curing agent and glass fiber, while ensuring the mechanical strength of the material.

[0007] To achieve the above objectives, the present invention aims to provide a halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim, comprising the following raw materials in the following mass percentages:

[0008] The composition includes 20-35% halogen-free flame-retardant epoxy resin, 15-25% reactive ester curing agent, 0.1-0.8% low-temperature curing accelerator, 5-10% halogen-free flame-retardant additive, 0.1-0.5% silane coupling agent, 0.02-0.15% defoamer, 0.02-0.15% leveling agent, and the balance being glass fiber material.

[0009] The active ester curing agent is an adduct of p-toluenesulfonyl isocyanate and bisphenol A benzoate or phenyl ester-functionalized phenolic resin.

[0010] The low-temperature curing accelerator is a microencapsulated imidazole derivative or a Lewis acid-amine complex.

[0011] As a further improvement to this technical solution, the halogen-free flame-retardant epoxy resin is a DOPO modified epoxy resin or a phosphorus-containing phenolic epoxy resin.

[0012] As a further improvement to this technical solution, the halogen-free flame retardant is composed of microencapsulated red phosphorus and aluminum hydroxide or magnesium hydroxide in a mass ratio of 1:2-4.

[0013] As a further improvement to this technical solution, the silane coupling agent is γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane.

[0014] As a further improvement to this technical solution, the defoamer is a non-silicone polymer type defoamer.

[0015] As a further improvement to this technical solution, the non-silicone polymer defoamer is a copolymer of acrylate and propylene oxide.

[0016] As a further improvement to this technical solution, the leveling agent is a modified silicone leveling agent or a fluorocarbon modified acrylate leveling agent.

[0017] As a further improvement to this technical solution, the glass fiber material has a unit weight of 100-300 g / m³. 2 Short-cut fiberglass mat or plain weave biaxial fiberglass fabric.

[0018] As a further improvement to this technical solution, the active ester curing agent accounts for one of the following mass percentages in the prepreg: 18%, 22%, or 23%.

[0019] As a further improvement to this technical solution, the low-temperature curing accelerator accounts for one of the following mass percentages in the prepreg: 0.3%, 0.4%, or 0.7%.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] In this halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors, DOPO modified epoxy resin is used as the intrinsic flame-retardant matrix. Through the chemically bonded phosphorus-phenanthroline structure, it decomposes and promotes char formation in the early stage of combustion. Simultaneously, it undergoes a cross-linking reaction with the active ester curing agent under the low-temperature activation of the latent accelerator, thus constructing a three-dimensional network skeleton that combines flame retardancy and rigidity.

[0022] Furthermore, the crosslinking density is further increased by using high-functionality curing agents such as phenyl ester-functionalized phenolic resin, and a synergistic effect is generated with the microencapsulated red phosphorus-hydroxide compound flame retardant system, which inhibits combustion through both gas and condensed phase pathways. At the same time, the glass fiber fabric treated with γ-glycidyl etheroxypropyltrimethoxysilane forms a strong interfacial chemical bond with the resin during the impregnation process. Its reinforced skeleton effectively disperses stress and avoids the decline in interlayer performance due to low-temperature curing, thereby meeting the safety, efficiency production and structural performance requirements of rail transit interiors. Attached Figure Description

[0023] Figure 1 A schematic diagram showing the tensile strength of prepregs with different mass percentages of reactive ester curing agent;

[0024] Figure 2 A schematic diagram showing the interlaminar shear strength of prepregs with different mass percentages of low-temperature curing accelerator. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In recent years, my country's rail transit industry has developed rapidly, and the number of vehicles has continued to grow, placing higher demands on the lightweight, safety, and comfort of interior materials. Prepregs, as key composite materials, are widely used in interior manufacturing due to their high strength and ease of molding; however, their performance still needs further improvement to meet more demanding application environments.

[0027] Currently, most common prepreg materials used in rail transit interiors have significant shortcomings: halogenated flame-retardant types release toxic fumes during combustion, resulting in low safety; traditional epoxy resin-based prepregs require high-temperature curing, which easily leads to component deformation and high energy consumption; while some low-temperature curing systems suffer from insufficient flame retardancy or poor interfacial adhesion. From a materials processing perspective, the above materials still have significant deficiencies in the synergy between halogen-free flame retardancy, low-temperature curing processes, and mechanical properties, making it difficult to simultaneously meet the requirements of safe and efficient production and structural performance.

[0028] Therefore, the present invention aims to provide a halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim, comprising the following raw materials in the following mass percentages:

[0029] The composition includes 20-35% halogen-free flame-retardant epoxy resin, 15-25% reactive ester curing agent, 0.1-0.8% low-temperature curing accelerator, 5-10% halogen-free flame-retardant additive, 0.1-0.5% silane coupling agent, 0.02-0.15% defoamer, 0.02-0.15% leveling agent, and the balance being glass fiber material.

[0030] Among them, the halogen-free flame-retardant epoxy resin is DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) modified epoxy resin or phosphorus-containing phenolic epoxy resin, with its phosphorus content controlled between 1.5-3.0%. The phosphorus element is introduced into the epoxy resin backbone through chemical bonding, giving the resin intrinsic flame retardancy and avoiding the addition of halogen-containing flame retardants from the source.

[0031] The active ester curing agent is an adduct of p-toluenesulfonyl isocyanate (P-TSA) and bisphenol A benzoate or phenyl ester-functionalized phenolic resin. This type of curing agent has high activity and can react with the hydroxyl groups of epoxy resin, avoiding the use of traditional amine or acid anhydride curing agents, thereby significantly reducing the curing reaction temperature.

[0032] Low-temperature curing accelerators are microencapsulated imidazole derivatives or Lewis acid-amine complexes. These accelerators are in a "dormant" state at room temperature and have good storage stability. When heated to a specific temperature range (80-100℃), the microcapsules rupture or the complexes dissociate, releasing the active ingredients and rapidly catalyzing the cross-linking reaction between the resin and the curing agent.

[0033] The halogen-free flame retardant is composed of microencapsulated red phosphorus and aluminum hydroxide or magnesium hydroxide in a mass ratio of 1:2-4. The microencapsulated red phosphorus effectively solves the problem of red phosphorus's easy moisture absorption and migration, and produces a synergistic flame retardant effect with metal hydroxides, exerting its flame retardant effect in both the gas phase and the condensed phase.

[0034] The silane coupling agent is γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane. It is used to pretreat reinforced glass fiber materials. The alkoxy group at one end of the molecule binds to the glass fiber surface, while the epoxy group or amino group at the other end reacts chemically with the resin matrix, which greatly improves the interfacial bonding performance.

[0035] The defoamer is a non-silicone polymer defoamer. In this invention, a copolymer of acrylate and propylene oxide is preferred to be used to eliminate air bubbles in the resin mixture during the prepreg preparation process, thereby avoiding defects in the final product.

[0036] The leveling agent is a modified silicone leveling agent or a fluorocarbon modified acrylate leveling agent, used to reduce the surface tension of the resin liquid, ensuring that it can uniformly impregnate the reinforcing material and obtain a smooth surface.

[0037] Fiberglass material has a unit weight of 100-300g / m² 2 Short-cut fiberglass mats or plain-weave biaxial fiberglass fabrics, whose fiber surfaces are treated with the aforementioned silane coupling agent, serve as a reinforcing skeleton for the prepreg, primarily providing mechanical strength and dimensional stability.

[0038] In this invention, by selecting DOPO-modified epoxy resin and other materials as the matrix, the environmental friendliness and intrinsic high flame retardancy of the material are ensured from the source. A highly reactive specific active ester curing agent, combined with a latent accelerator, successfully lowers the curing temperature to 80-100℃, effectively preventing deformation of interior parts caused by high temperatures and significantly reducing energy consumption. Through specific silane coupling agent treatment of glass fiber and compounding with halogen-free flame retardant additives, interfacial bonding strength and comprehensive mechanical properties are maintained even under low-temperature curing conditions, with high flame retardant efficiency and low smoke production. This combined approach effectively solves the contradiction between traditional materials' difficulty in simultaneously achieving environmental protection and flame retardancy, low-temperature processing, and high performance.

[0039] First, the above-mentioned halogen-free flame-retardant epoxy resin, reactive ester curing agent, low-temperature curing accelerator, halogen-free flame-retardant additive, silane coupling agent, defoamer, and leveling agent are dissolved in an acetone / butanone mixed solvent according to the specified ratio, and the mixture is stirred at high speed to form a homogeneous resin solution. Then, the glass fiber material pretreated with the silane coupling agent is passed through the impregnation tank at a constant rate to fully absorb the resin solution. Next, the impregnated material is passed through a temperature-controlled drying tunnel to gradually evaporate and remove the solvent and achieve pre-curing. Finally, the prepreg product is obtained by winding and cutting.

[0040] The following specific embodiments will further illustrate the halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors provided by the present invention.

[0041] Example 1

[0042] This embodiment provides a halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim, comprising the following raw materials by mass percentage:

[0043] The composition consists of 20% halogen-free flame-retardant epoxy resin, 25% reactive ester curing agent, 0.1% low-temperature curing accelerator, 10% halogen-free flame-retardant additive, 0.1% silane coupling agent, 0.15% defoamer, 0.02% leveling agent, and the remainder is glass fiber material.

[0044] Among them, the halogen-free flame-retardant epoxy resin is a DOPO modified epoxy resin.

[0045] The active ester curing agent is an adduct of p-toluenesulfonyl isocyanate and bisphenol A benzoate;

[0046] The low-temperature curing accelerator is a microencapsulated imidazole derivative;

[0047] The halogen-free flame retardant additive is composed of microencapsulated red phosphorus and aluminum hydroxide in a mass ratio of 1:3.

[0048] The silane coupling agent is γ-glycidoxypropyltrimethoxysilane;

[0049] The defoamer is a non-silicone polymer defoamer, and in this invention, a copolymer of acrylate and propylene oxide is preferred.

[0050] The leveling agent is a modified organosilicon leveling agent;

[0051] The fiberglass material has a unit weight of 300g / m². 2 Short-cut fiberglass mat.

[0052] First, the above-mentioned halogen-free flame-retardant epoxy resin, reactive ester curing agent, low-temperature curing accelerator, halogen-free flame-retardant additive, silane coupling agent, defoamer, and leveling agent are dissolved in an acetone / butanone mixed solvent according to the specified ratio, and the mixture is stirred at high speed to form a homogeneous resin solution. Then, the glass fiber material pretreated with the silane coupling agent is passed through the impregnation tank at a constant rate to fully absorb the resin solution. Next, the impregnated material is passed through a temperature-controlled drying tunnel to gradually evaporate and remove the solvent and achieve pre-curing. Finally, the prepreg product is obtained by winding and cutting.

[0053] Example 2

[0054] This embodiment provides a halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim, comprising the following raw materials by mass percentage:

[0055] The composition consists of 25% halogen-free flame-retardant epoxy resin, 20% reactive ester curing agent, 0.5% low-temperature curing accelerator, 8% halogen-free flame-retardant additive, 0.2% silane coupling agent, 0.10% defoamer, 0.10% leveling agent, and the remainder is glass fiber material.

[0056] Among them, the halogen-free flame-retardant epoxy resin is a phosphorus-containing phenolic epoxy resin.

[0057] The active ester curing agent is an adduct of p-toluenesulfonyl isocyanate and bisphenol A benzoate;

[0058] The low-temperature curing accelerator is a microencapsulated imidazole derivative;

[0059] The halogen-free flame retardant additive is composed of microencapsulated red phosphorus and magnesium hydroxide in a mass ratio of 1:2.

[0060] The silane coupling agent is γ-glycidoxypropyltrimethoxysilane;

[0061] The defoamer is a non-silicone polymer defoamer, and in this invention, a copolymer of acrylate and propylene oxide is preferred.

[0062] The leveling agent is a fluorocarbon-modified acrylate leveling agent;

[0063] The fiberglass material has a unit weight of 200g / m². 2 Short-cut fiberglass mat.

[0064] First, the above-mentioned halogen-free flame-retardant epoxy resin, reactive ester curing agent, low-temperature curing accelerator, halogen-free flame-retardant additive, silane coupling agent, defoamer, and leveling agent are dissolved in an acetone / butanone mixed solvent according to the specified ratio, and the mixture is stirred at high speed to form a homogeneous resin solution. Then, the glass fiber material pretreated with the silane coupling agent is passed through the impregnation tank at a constant rate to fully absorb the resin solution. Next, the impregnated material is passed through a temperature-controlled drying tunnel to gradually evaporate and remove the solvent and achieve pre-curing. Finally, the prepreg product is obtained by winding and cutting.

[0065] Example 3

[0066] This embodiment provides a halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim, comprising the following raw materials by mass percentage:

[0067] The composition consists of 35% halogen-free flame-retardant epoxy resin, 15% reactive ester curing agent, 0.8% low-temperature curing accelerator, 5% halogen-free flame-retardant additive, 0.5% silane coupling agent, 0.02% defoamer, 0.15% leveling agent, and the remainder is glass fiber material.

[0068] Among them, the halogen-free flame-retardant epoxy resin is a phosphorus-containing phenolic epoxy resin.

[0069] The active ester curing agent is a phenyl ester-functionalized phenolic resin;

[0070] The low-temperature curing accelerator is a Lewis acid-amine complex;

[0071] The halogen-free flame retardant additive is composed of microencapsulated red phosphorus and magnesium hydroxide in a mass ratio of 1:4.

[0072] The silane coupling agent is γ-aminopropyltriethoxysilane;

[0073] The defoamer is a non-silicone polymer defoamer, and in this invention, a copolymer of acrylate and propylene oxide is preferred.

[0074] The leveling agent is a fluorocarbon-modified acrylate leveling agent;

[0075] Fiberglass material with a unit weight of 100g / m 2 Plain weave bidirectional fiberglass fabric.

[0076] First, the above-mentioned halogen-free flame-retardant epoxy resin, reactive ester curing agent, low-temperature curing accelerator, halogen-free flame-retardant additive, silane coupling agent, defoamer, and leveling agent are dissolved in an acetone / butanone mixed solvent according to the specified ratio, and the mixture is stirred at high speed to form a homogeneous resin solution. Then, the glass fiber material pretreated with the silane coupling agent is passed through the impregnation tank at a constant rate to fully absorb the resin solution. Next, the impregnated material is passed through a temperature-controlled drying tunnel to gradually evaporate and remove the solvent and achieve pre-curing. Finally, the prepreg product is obtained by winding and cutting.

[0077] Prepregs were prepared according to the contents provided in Examples 1-3, and then flame retardant performance, mechanical performance and curing characteristics of the prepregs were tested.

[0078] The flame retardancy performance test was conducted according to EN 45545-2:2020 Railway Applications - Fire Protection for Railway Vehicles - Part 2: Fire Performance Requirements for Materials and Components, using a cone calorimeter. The sample size was 100×100×3mm, ignited under a heat radiation intensity of 50kW / m², and the peak heat release rate (pk-HRR), total heat release (THR), and mean effective heat of combustion (av-EHC) were recorded. Simultaneously, the maximum smoke density (MSD) was determined according to GB / T 8323.2-2008 Plastics Smoke Generation - Part 2: Determination of Smoke Density by Single Chamber Method. The test was terminated when the sample ceased to burn or the back panel temperature dropped to ambient temperature. The final pk-HRR and MSD values ​​were recorded in Table 1.

[0079] Mechanical property testing was conducted using ASTM D3039 / D3039M-14, Standard Test Method for Tensile Properties of Polymer-Based Composites, and ASTM D2344 / D2344M-16, Standard Test Method for Strength of Short Beams of Polymer-Based Composites. After curing at 80℃ for 2 hours, the specimens were processed to the specified dimensions and loaded at a rate of 2 mm / min on a universal testing machine. Tensile strength (MPa) and interlaminar shear strength (ILSS, MPa) were measured. The performance retention rate (%) relative to a conventionally cured reference specimen at 120℃ was calculated and recorded in Table 1.

[0080] Curing characteristics were tested according to GB / T 22567-2008 "Differential Scanning Calorimetry (DSC) for Electrical Insulation Materials – Determination of Curing Properties of Thermosetting Resins". Approximately 10 mg of uncured prepreg resin film was taken and heated from 30 °C to 250 °C at a rate of 10 °C / min under a nitrogen atmosphere. The curing initiation temperature (T0, °C) and peak exothermic temperature (T...) were recorded. p The low-temperature curing activity was evaluated by measuring the heat of curing reaction (ΔH, J / g) at ℃ and the heat of curing reaction (ΔH, J / g), and the data are recorded in Table 1.

[0081] Table 1. Performance comparison of prepregs in Examples 1-3

[0082]

[0083] As shown in Table 1, the flame retardant properties of the prepreg meet the stringent requirements of EN 45545-2 for HL3 (high hazard level) of interior materials for rail transit, especially the low smoke density value, which proves its excellent fire safety.

[0084] Under low-temperature curing conditions of 80℃, both tensile strength and interlaminar shear strength remain high, and the performance retention rate exceeds 90% compared with the conventional high-temperature curing system of 120℃. This fully demonstrates that the prepreg provided by this invention successfully retains the core mechanical properties of the composite material while reducing the curing temperature.

[0085] The curing initiation temperature of this prepreg resin system is below 85℃, and the peak temperature is around 100℃, which is significantly lower than that of traditional epoxy resin systems, verifying its excellent low-temperature curing activity.

[0086] In this invention, DOPO-modified epoxy resin is first used as the intrinsic flame-retardant matrix. Its chemically bonded phosphorus-phenanthrene structure decomposes and promotes char formation in the early stage of combustion. Simultaneously, it undergoes a cross-linking reaction with the active ester curing agent under the low-temperature activation of the latent accelerator, constructing a three-dimensional network skeleton that combines flame retardancy and rigidity. Then, the cross-linking density is further improved by high-functionality curing agents such as phenyl ester-functionalized phenolic resin, and it produces a synergistic effect with the microencapsulated red phosphorus-hydroxide compound flame-retardant system, inhibiting combustion through both gas phase and condensed phase pathways. At the same time, the glass fiber fabric treated with γ-glycidyl etheroxypropyltrimethoxysilane forms a strong interfacial chemical bond with the resin during the impregnation process. Its enhanced skeleton effectively disperses stress and avoids the decline in interlayer performance caused by low-temperature curing.

[0087] Experimental Example 1

[0088] In this invention, the active ester curing agent is an adduct of p-toluenesulfonyl isocyanate and bisphenol A benzoate or a phenyl ester-functionalized phenolic resin. This type of curing agent contains highly active ester (-COO-) functional groups. Its curing mechanism lies in the fact that the active ester groups can undergo transesterification with the hydroxyl groups (-OH) on the epoxy resin molecular chain, thereby initiating the ring-opening polymerization of the epoxy groups to form a three-dimensional network structure. This reaction pathway avoids the problem of traditional amine curing agents readily reacting with carbon dioxide in the air to form carbamates (commonly known as "whitening"), and also overcomes the drawback of anhydride curing agents requiring high-temperature curing (typically >150℃).

[0089] Among them, the adduct of p-toluenesulfonyl isocyanate and bisphenol A benzoate is a compound with a specific structure synthesized by the addition reaction between the isocyanate group (-NCO) of p-toluenesulfonyl isocyanate and the terminal hydroxyl group (-OH) of the bisphenol A benzoate molecule. Its molecular structural characteristics are as follows:

[0090] The molecule incorporates both a rigid bisphenol A backbone and a highly polar p-toluenesulfonyl group. The bisphenol A backbone provides excellent heat resistance and mechanical strength, while the p-toluenesulfonyl group, as a strong electron-withdrawing group, significantly activates the chemical reactivity of adjacent ester groups. Furthermore, due to the strong activating effect of the p-toluenesulfonyl group, this adduct can react efficiently with the hydroxyl groups of epoxy resin at relatively low temperatures (80-100℃), significantly reducing the curing temperature of the system and meeting the requirements of low-temperature curing processes.

[0091] In addition, its molecular structure has excellent compatibility with epoxy resin, the prepreg prepared has good storage stability, and after low-temperature curing, it can form a cured product with high crosslinking density and high glass transition temperature (Tg), which ensures the dimensional stability and mechanical properties of the product under the service environment.

[0092] Phenyl ester-functionalized phenolic resin is a multifunctional reactive ester curing agent prepared by chemically modifying the molecular backbone of phenolic resin by introducing phenyl ester groups (such as benzoyloxy, -OCOC6H5). Based on the multi-benzene ring backbone and high reactive sites of phenolic resin itself, each molecule of this curing agent can contain multiple phenyl ester groups. When cured with epoxy resin, it can form an extremely high crosslinking density, thereby endowing the cured composite material with excellent heat resistance, high modulus, good rigidity, and excellent chemical resistance. The phenyl ester group has moderate reactivity and, in the presence of a latent accelerator, can be activated within a set low-temperature window and complete the curing reaction rapidly. Its cured product not only has good heat resistance, but also exhibits enhanced flame retardant properties due to the multiplicity of the benzene ring structure, showing a synergistic effect with halogen-free flame-retardant epoxy resin systems.

[0093] In summary, the selection of the above two types of reactive ester curing agents is based on a comprehensive consideration of their high reactivity, good compatibility with halogen-free flame-retardant epoxy resins, and ability to achieve low-temperature curing and ultimately form a high-strength, high-heat-resistant cured network.

[0094] In this invention, when the mass percentage of the active ester curing agent is less than 15%, the crosslinking density of the resin system is significantly insufficient, making it difficult for the curing reaction to proceed fully. This results in a decrease in the glass transition temperature and heat resistance of the prepreg after curing. Simultaneously, due to the incomplete crosslinking network, the cohesive strength and interlaminar shear strength of the composite material are difficult to meet design requirements, and interfacial delamination easily occurs under vibration loads. Furthermore, a large amount of unreacted epoxy groups remain, deteriorating the material's long-term aging resistance. Conversely, when the mass percentage of the active ester curing agent exceeds 25%, the excessively high functionality makes the crosslinking network too dense, restricting the mobility of molecular chain segments, leading to a significant increase in material brittleness and a decrease in impact toughness. Additionally, excess curing agent may not fully participate in the reaction and may remain as small molecules, easily migrating and precipitating under high-temperature conditions, affecting the surface properties of the product and accelerating aging. Moreover, excessively high crosslinking density weakens the stress transfer efficiency at the resin-fiber interface, which is detrimental to the optimization of overall mechanical properties.

[0095] To verify that the 15-25% mass proportion of the reactive ester curing agent in the prepreg is one of the important factors contributing to the good mechanical properties of the halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors provided by this invention, this experimental example, based on Example 2 above, only changed the mass proportion of the reactive ester curing agent in the prepreg, setting it to 8%, 10%, 12%, 14%, 15%, 16%, 18%, 22%, 23%, 25%, 28%, or 30%. Prepregs were then prepared, and prepreg products were obtained. Tensile strength tests were performed on the prepreg products according to the test methods provided in the above examples. The test results are as follows: Figure 1 As shown.

[0096] according to Figure 1 It can be seen that when the mass percentage of the active ester curing agent in the prepreg is 8%, 10%, 12%, 14%, 28%, or 30%, rather than 15-25%, the tensile strength of the prepreg product is significantly lower than that of the prepreg product when the mass percentage of the active ester curing agent is 15%, 16%, 18%, 22%, 23%, or 25%.

[0097] This demonstrates that the 15-25% mass ratio of the active ester curing agent in the prepreg is one of the important factors contributing to the good mechanical properties of the halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors provided by this invention.

[0098] In addition, by Figure 1 It can be seen that when the mass percentage of the active ester curing agent in the prepreg is 18%, 22%, or 23%, the tensile strength of the obtained prepreg product is at a relatively high level.

[0099] Experimental Example 2

[0100] In this invention, a low-temperature curing accelerator is used to reduce the activation energy of the crosslinking reaction in the resin matrix, shifting the main exothermic peak temperature of the curing reaction to the low-temperature region. Specifically, the accelerator is in a chemically "dormant" state at room temperature, ensuring that the prepreg has sufficient shelf life and operating window. When heated to the set low-temperature range (80-100℃), the accelerator is rapidly activated, efficiently catalyzing the reaction between the halogen-free flame-retardant epoxy resin and the reactive ester curing agent, enabling the rapid formation of a highly crosslinked three-dimensional network structure at temperatures far lower than those of traditional epoxy systems. This not only significantly reduces production energy consumption, but more importantly, it avoids thermal stress deformation and internal damage caused by high-temperature curing to large or complex-shaped interior parts, fundamentally ensuring the dimensional accuracy and appearance quality of the products.

[0101] It is worth noting that in this invention, when the mass percentage of the low-temperature curing accelerator is less than 0.1%, the number of its catalytic active centers is insufficient, making it difficult to effectively reduce the curing reaction energy barrier of the entire resin system. This will lead to a delayed curing reaction initiation and a slow rate, and even if the curing time is extended at a certain temperature, the resin cannot be fully cross-linked. The consequence is that the glass transition temperature of the cured product is significantly lower, and the heat resistance cannot meet the requirements of the vehicle operating environment; at the same time, due to the imperfect cross-linking network, the mechanical strength of the composite material, especially the interlaminar shear strength and hardness, will be severely reduced, directly affecting the structural reliability and durability of the interior parts; while when the mass percentage of the low-temperature curing accelerator exceeds 0.8%, the excessively high accelerator concentration will cause the reactivity of the resin system to increase sharply, and may even cause local pre-curing during storage or prepreg preparation, resulting in increased prepreg viscosity, poor flowability, shortened pot life, and seriously affecting process operability.

[0102] To verify that the 0.1-0.8% mass ratio of the low-temperature curing accelerator in the prepreg is also one of the important factors contributing to the good mechanical properties of the halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors provided by this invention, this experimental example, based on Example 1 above, only changed the mass ratio of the low-temperature curing accelerator in the prepreg, setting it to 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. Prepregs were then prepared, resulting in prepreg products. Interlaminar shear strength tests were performed on the prepreg products according to the test methods provided in the above examples. The test results are as follows: Figure 2 As shown.

[0103] according to Figure 2It can be seen that when the mass percentage of the low-temperature curing accelerator in the prepreg is 0.1%, 0.2%, 0.9%, or 1.0%, which is not 0.1-0.8%, the interlaminar shear strength of the prepreg product is significantly lower than that of the prepreg product when the mass percentage of the low-temperature curing accelerator is 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%.

[0104] This demonstrates that the 0.1-0.8% mass ratio of the low-temperature curing accelerator in the prepreg is one of the important factors contributing to the good mechanical properties of the halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interiors provided by this invention.

[0105] In addition, by Figure 2 It can be seen that when the mass percentage of the low-temperature curing accelerator in the prepreg is 0.3%, 0.4%, or 0.7%, the interlaminar shear strength of the obtained prepreg product is at a relatively high level.

[0106] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim, characterized in that, Raw materials include the following mass percentages: The composition includes 20-35% halogen-free flame-retardant epoxy resin, 15-25% reactive ester curing agent, 0.1-0.8% low-temperature curing accelerator, 5-10% halogen-free flame-retardant additive, 0.1-0.5% silane coupling agent, 0.02-0.15% defoamer, 0.02-0.15% leveling agent, and the balance being glass fiber material. The active ester curing agent is an adduct of p-toluenesulfonyl isocyanate and bisphenol A benzoate or phenyl ester-functionalized phenolic resin. The low-temperature curing accelerator is a microencapsulated imidazole derivative or a Lewis acid-amine complex. The active ester curing agent is an adduct of p-toluenesulfonyl isocyanate and bisphenol A benzoate. The adduct is synthesized by an addition reaction between the isocyanate group of p-toluenesulfonyl isocyanate and the hydroxyl group at the end of the bisphenol A benzoate molecule.

2. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The halogen-free flame-retardant epoxy resin is a DOPO-modified epoxy resin or a phosphorus-containing phenolic epoxy resin.

3. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The halogen-free flame retardant additive is composed of microencapsulated red phosphorus and aluminum hydroxide or magnesium hydroxide in a mass ratio of 1:2-4.

4. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The silane coupling agent is γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane.

5. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The defoamer is a non-silicone polymer defoamer.

6. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The leveling agent is a modified silicone leveling agent or a fluorocarbon modified acrylate leveling agent.

7. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The fiberglass material has a unit weight of 100-300 g / m³. 2 Short-cut fiberglass mat or plain weave biaxial fiberglass fabric.

8. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The active ester curing agent accounts for one of the following mass percentages in the prepreg: 18%, 22%, or 23%.

9. The halogen-free flame-retardant low-temperature curing glass fiber epoxy resin prepreg for rail transit interior trim according to claim 1, characterized in that: The low-temperature curing accelerator accounts for one of the following mass percentages in the prepreg: 0.3%, 0.4%, or 0.7%.

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