A hot-melt halogen-free flame-retardant epoxy resin composition, a preparation method thereof, a prepreg and a fiber-reinforced composite material

Abstract

The present invention discloses a hot-melt halogen-free flame-retardant epoxy resin composition, a preparation method thereof, a prepreg and a fiber-reinforced composite material, belonging to the technical field of composite materials. The hot-melt halogen-free flame-retardant epoxy resin composition comprises the following components in parts by weight: 30-80 parts of liquid bisphenol A epoxy resin, 20-50 parts of solid bisphenol A epoxy resin, 5-35 parts of benzoxazine resin containing groups, 3-10 parts of curing agent, 1-6 parts of accelerator, 5-45 parts of additive halogen-free flame retardant, 3-50 parts of reactive halogen-free flame retardant, 1-8 parts of toughening agent, 3-20 parts of porcelain-forming filler, 1-10 parts of flaky inorganic filler, and 1-5 parts of small molecule capturer. The hot-melt halogen-free flame-retardant epoxy resin composition provided by the present invention has good molding process performance. The flame-retardant grade of the fiber-reinforced composite material prepared therefrom reaches above EN45545-2 HL2, and at the same time has good low-toxic and low-smoke performance and mechanical properties, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a hot-melt type halogen-free flame-retardant epoxy resin composition, prepreg, composite material and their preparation methods. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Epoxy resin composites have excellent comprehensive properties and are widely used in the fields of rail transit, aerospace, electronics and electrical appliances, automobiles, ships, etc. At present, the preparation of epoxy resin composites mostly adopts the prepreg layup process. The production of prepregs mainly uses the wet process. The wet-process prepregs have disadvantages such as high volatile content, low production efficiency, unstable resin content, and serious environmental pollution, and it is difficult to meet the increasing application requirements and the increasingly strict environmental protection requirements. The hot-melt method for preparing prepregs has high production efficiency and does not use solvents, alleviating the environmental pollution problems brought by the solution-process prepregs.

[0004] Epoxy resin belongs to flammable materials and is extremely easy to cause fires, which limits its application scope. In order to meet the flame-retardant grade requirements above EN45545-2 HL2 for rail transit, many researchers have developed flame-retardant products. For example, Patent CN115197537 A (Publication Date: October 18, 2022) discloses a flame-retardant epoxy resin composition, prepreg and fiber-reinforced composite material. The cured composite material of the prepared carbon fiber prepreg not only meets the flame-retardant standard requirements of FAR25.853 for aircraft interior materials, but also meets the flame-retardant grade requirements above R1 category HL2 of the EN 45545-2 standard for rail transit.

[0005] Since the hot-melt method for preparing prepregs does not use solvents, if the amount of halogen-free flame retardant added is large, it will inevitably make the molding processability of the fiber-reinforced epoxy resin composite material poor, resulting in a significant decline in mechanical properties; if the amount of halogen-free flame retardant added is small, the composite material will be difficult to meet the flame-retardant requirements. Therefore, how to prepare hot-melt prepregs and composite materials with high heat resistance and a flame retardancy reaching the EN45545-2 HL2 grade with the smallest possible amount of halogen-free flame retardant added is an urgent problem to be solved. Summary of the Invention

[0006] In view of this, the present invention provides a hot-melt halogen-free flame-retardant epoxy resin composition, prepreg, composite material and preparation method thereof. The hot-melt halogen-free flame-retardant epoxy resin composition has good molding process performance, and the prepared fiber-reinforced composite material has good heat resistance, the flame retardancy reaches the HL2 level of the EN45545-2 standard, and it is not easy to produce toxic substances during combustion.

[0007] In the first aspect, the present invention provides a hot-melt halogen-free flame-retardant epoxy resin composition, comprising the following components in parts by weight: 30-80 parts of liquid bisphenol A epoxy resin, 20-50 parts of solid bisphenol A epoxy resin, 5-35 parts of benzoxazine resin containing a group, 3-10 parts of curing agent, 1-6 parts of accelerator, 20-40 parts of additive halogen-free flame retardant, 10-20 parts of reactive halogen-free flame retardant, 1-8 parts of toughening agent, 3-20 parts of porcelain-forming filler, 1-10 parts of flaky inorganic filler, 1-5 parts of small molecule capturer.

[0008] Preferably, the epoxy value of the liquid bisphenol A epoxy resin is 0.23-0.56, and the epoxy value of the solid bisphenol A epoxy resin is 0.04-0.22. The combined use of liquid bisphenol A epoxy resin and solid bisphenol A epoxy resin makes the hot-melt halogen-free flame-retardant epoxy resin composition have appropriate viscosity, so that the system still has good film-forming property and certain toughness under the condition of no solvent and the addition of a large amount of flame retardant and other substances, does not stick to hands or films at room temperature, and presents a semi-solid state; at the same time, the amount of epoxy resin used is large, and using bisphenol A epoxy resin as the resin matrix has a low cost.

[0009] Preferably, the benzoxazine resin containing a group is selected from one or more of cyanobenzoxazine resin, propargylbenzoxazine resin, maleimide group-containing benzoxazine resin or aldehyde group-containing benzoxazine resin. The benzoxazine resin containing a group and the liquid bisphenol A epoxy resin together reduce the viscosity of the system, so that the viscosity adjustable range of the halogen-free flame-retardant epoxy resin system is wide, and it is very easy to meet the special requirements of the hot-melt prepreg process for viscosity, drapability and wettability. In addition, the benzoxazine resin containing a group has intrinsic flame retardant properties, and at the same time, the cross-linking reaction between it and the epoxy resin will increase the cross-linking density of the product, thereby improving the thermal stability and flame retardancy, and no migration will occur. There are also a large number of intermolecular hydrogen bond interactions in the benzoxazine resin containing a group, so the mechanical properties can be greatly improved, and the mechanical properties of the resin system can be improved.

[0010] Specifically, the cyanobenzoxazine resin is polymerized from the benzoxazine monomer represented by formula (I), the propargylbenzoxazine resin is polymerized from the benzoxazine monomer represented by formula (II), the maleimide group-containing benzoxazine resin is polymerized from the benzoxazine monomer represented by formula (III), and the aldehyde group-containing benzoxazine resin is polymerized from the benzoxazine monomer represented by formula (IV).

[0011]

[0012] Preferably, the additive type of halogen-free flame retardant includes one or more of aluminum hydroxide, magnesium hydroxide, silicon dioxide, zinc borate, ammonium polyphosphate, DOPO, aluminum hypophosphite, and antimony dioxide. Additive type flame retardants are generally solids and have relatively low prices.

[0013] Preferably, the reactive type of halogen-free flame retardant is selected from DOPO type flame retardants modified with amino, carboxyl, hydroxyl or epoxy groups. For example, it can be selected from one or more of DOPO-CA (Formula V), DOPO-ITA (Formula VI), DOPO-HQ (Formula VII), and DOPO-EP (Formula VIII). Reactive type halogen-free flame retardants have good compatibility with resins and contain groups that react with epoxy resins, and can play a flame retardant role persistently.

[0014]

[0015] Preferably, the porcelain-forming filler is selected from one or more of muscovite, montmorillonite, wollastonite, kaolin, or diatomite. The dense ceramic protective layer formed by the pyrolysis transformation of the porcelain-forming filler at high temperature has good high temperature resistance and impact resistance, thereby protecting the internal structure of the material from being damaged by fire.

[0016] Preferably, the flaky inorganic filler is selected from one or more of graphene, MXene, boron nitride, and molybdenum disulfide, which can increase the volatilization path of small molecules after combustion, thereby shortening the flame spread time and further improving the flame retardant performance.

[0017] Preferably, the small molecule capturer is selected from one or two of boron carbide or phosphotungstic acid. Boron carbide (B4C) can convert CO, H2O and other small molecule volatile components generated by the thermal decomposition of the resin into amorphous carbon and retain it inside the matrix. B4C is converted into B2O3 to form a dense antioxidant layer on the surface of the carbide, thereby inhibiting the oxidative decomposition of the carbide. Phosphotungstic acid is a heteropolyacid with a relatively large size, and its molecule combines phosphorus element with good flame retardant effect and tungsten element with smoke suppression effect. Therefore, it has both flame retardant and smoke suppression effects. At high temperature, the active sites of phosphotungstic acid crosslink with small molecules after the resin combustion breaks, and then can delay the thermal decomposition process of epoxy resin, improving the flame retardant performance of the composite material. When the addition amount of the small molecule capturer is large, it will affect the forming process performance. Adding a small amount can cooperate with other flame retardants to play a flame retardant effect.

[0018] Preferably, the curing agent is selected from one or more of dicyandiamide, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone or 3,3'-diaminodiphenylsulfone; the accelerator is selected from imidazole compounds or urea compounds; the imidazole compounds are selected from one or more of 1-methylimidazole, 1-ethylimidazole, 2-methyl-5-nitroimidazole, 2-methylimidazole, 2-mercapto-5-methoxybenzimidazole, 4-methylimidazole, N-methylimidazole, N-vinylimidazole, tolylimidazole, imidazole, carbonyldiimidazole. The urea compounds are selected from one or more of 3-phenyl-1,1-dimethylurea, N,N'-dimethyl diphenylurea, N,N'-diethyl diphenylurea or N-(p-chlorophenyl)-N,N'-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea.

[0019] Preferably, the toughening agent is selected from one or more of hydroxyl-terminated acrylonitrile-butadiene rubber, polyvinyl butyral, carboxyl-terminated acrylonitrile-butadiene rubber, chloroprene rubber, ethylene propylene diene monomer rubber, polyamide resin, polyetherimide resin, polyvinyl acetal resin, polyethersulfone resin, carboxyl-containing acrylic resin or amino-terminated polyether resin.

[0020] In a second aspect, the present invention provides a method for preparing the above-mentioned hot-melt halogen-free flame-retardant epoxy resin composition, comprising the following steps:

[0021] Crush the solid bisphenol A epoxy resin into powder, stir and heat it at 70-100 °C until the solid bisphenol A epoxy resin is completely melted, cool it down to 50-70 °C, and add the liquid bisphenol A epoxy resin and the group-containing benzoxazine resin in proportion, and mix evenly to obtain liquid component one;

[0022] Weigh the additive halogen-free flame retardant, toughening agent, porcelain-forming filler, flaky inorganic filler and small molecule scavenger in proportion, add them to the liquid component one, mix evenly at 50-70 °C, and pass through a three-roll mill twice to obtain mixture two;

[0023] Add the reactive halogen-free flame retardant, curing agent and accelerator to the mixture two together, and pass through a three-roll mill twice to obtain the product.

[0024] The hot-melt halogen-free flame-retardant epoxy resin composition provided by the present invention presents a semi-solid state, has good film-forming property and certain toughness, does not stick to hands or films at room temperature, and has good molding process performance.

[0025] In a third aspect, the present invention provides a prepreg, which is formed by laminating reinforcing fibers with a hot-melt halogen-free flame-retardant epoxy resin composition or a hot-melt halogen-free flame-retardant epoxy resin composition prepared by the above-mentioned preparation method.

[0026] Preferably, the mass percentage of the reinforcing fiber in the prepreg is 50-70%; the reinforcing fiber includes one or more of glass fiber, carbon fiber, quartz fiber, basalt fiber, aramid fiber, SiC fiber or mullite fiber; the lamination temperature is 60-90°C.

[0027] In a fourth aspect, the present invention provides a fiber-reinforced composite material cured from the above prepreg.

[0028] Preferably, the curing temperature is 110-140°C.

[0029] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0030] (1) The present invention provides a hot-melt halogen-free flame-retardant epoxy resin composition, which has a low viscosity by introducing a benzoxazine resin containing a group and a liquid bisphenol A epoxy resin, and can meet the special requirements of the hot-melt prepreg process for viscosity, drapability and wettability;

[0031] (2) In the present invention, the introduction of the benzoxazine resin containing a group and the reactive halogen-free flame retardant makes the prepared composite material have intrinsic flame retardancy, avoiding the decline of flame retardancy caused by the migration of the flame retardant;

[0032] (3) In the present invention, the benzoxazine resin containing a group, the reactive halogen-free flame retardant, the additive halogen-free flame retardant and the small molecule scavenger synergistically exert flame retardancy, and the flame retardancy grade of the prepared composite material reaches above EN45545-2 HL2, and at the same time has good low-toxic and low-smoke properties and mechanical properties, with broad application prospects;

[0033] (4) The present invention uses a hot-melt method to prepare a fiber-reinforced composite material, which has high production efficiency and does not require the use of solvents, and is environmentally friendly and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The schematic diagram of the specification drawings forming a part of the present invention is used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 It is a schematic diagram of the preparation process of the fiber-reinforced composite material of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains.

[0037] The technical solution of the present invention will be further elaborated below in conjunction with specific embodiments.

[0038] Examples 1 - 8

[0039] A hot-melt halogen-free flame-retardant epoxy resin composition, the components and ratios (by weight) are shown in Table 1.

[0040] Table 1 Formulations of the hot-melt halogen-free flame-retardant epoxy resin compositions for Examples 1 - 8 (S1 - S8)

[0041]

[0042]

[0043]

[0044] Comparative Example 1

[0045] Compared with Example 1, the difference is that in this comparative example, cyanobenzoxazine resin is not added, and the amounts of the other substances remain unchanged.

[0046] Comparative Example 2

[0047] Compared with Example 1, the difference is that in this comparative example, DOPO-CA is not added, the amount of aluminum hydroxide is 50 parts, and the amounts of the other substances remain unchanged.

[0048] Comparative Example 3

[0049] Compared with Example 1, the difference is that in this comparative example, montmorillonite is not added, and the amounts of the other substances remain unchanged.

[0050] Comparative Example 4

[0051] Compared with Example 1, the difference is that in this comparative example, boron nitride is not added, and the amounts of the other substances remain unchanged.

[0052] Comparative Example 5

[0053] Compared with Example 1, the difference is that in this comparative example, boron carbide is not added, and the amounts of the other substances remain unchanged.

[0054] Comparative Example 6

[0055] Compared with Example 1, the difference is that in this comparative example, the added amount of aluminum hydroxide is 40 parts, and the amounts of the other substances remain unchanged.

[0056] Comparative Example 7

[0057] Compared with Example 2, the difference is that phosphotungstic acid is not added in this comparative example, and the amounts of other substances remain unchanged.

[0058] The preparation methods of the hot-melt halogen-free flame-retardant epoxy resin compositions of Examples 1 to 8 and Comparative Examples 1 to 7 are as follows (if a certain substance is not included in the formula, it is not added):

[0059] (1) Crush solid bisphenol A epoxy resin into powder, stir and heat it at 80 °C until the solid bisphenol A epoxy resin is completely melted, cool it down to 60 °C, and add liquid bisphenol A epoxy resin and benzoxazine resin containing groups in proportion, and mix evenly to obtain Liquid Component 1;

[0060] (2) Weigh the additive halogen-free flame retardant, toughening agent, porcelain-forming filler, flaky inorganic filler and small molecule scavenger in proportion, add them to Liquid Component 1, mix evenly at 60 °C, and pass through a three-roll mill twice to obtain Mixture 2;

[0061] (3) Add the reactive halogen-free flame retardant, curing agent and accelerator to Mixture 2 together, and pass through a three-roll mill twice to obtain the product.

[0062] Preparation of prepreg:

[0063] Heat the hot-melt halogen-free flame-retardant epoxy resin compositions of Examples 1 to 8 and Comparative Examples 1 to 7 at 65 - 70 °C for 1 h to soften, pour them between the two rollers (roller temperature 65 - 70 °C) of a film coater to make a hot-melt halogen-free flame-retardant epoxy resin film. Adjust the temperature of the prepreg machine to 70 °C, laminate the upper and lower layers of resin films with the middle T300-12K carbon fiber cloth. The resin matrix melts and impregnates in the carbon fiber, and then it is cooled to obtain a hot-melt halogen-free flame-retardant epoxy prepreg, which is coated with a release film and release paper and wound for standby.

[0064] The preparation process of the fiber-reinforced composite material is as follows:

[0065] Cut the carbon fiber / hot-melt halogen-free flame-retardant epoxy prepreg into 300 mm × 300 mm, with 18 layers of layup and a laminate thickness of 3 ± 0.2 mm. Apply a release agent evenly on both sides of the stainless steel plate. Place the stacked prepreg between two stainless steel plates coated with the release agent, and then place the whole in a hot press. Close the hot press, slowly raise the temperature to 90 ± 5 °C, keep it warm for 60 min and then apply pressure to 0.4 ± 0.1 MPa, raise the temperature to 130 ± 5 °C and keep it warm for 100 min for lamination molding. After that, turn off the hot press, let it cool naturally to room temperature and then open the press to remove the composite material plate.

[0066] The schematic diagram of the preparation process is as Figure 1 shown.

[0067] Test Examples

[0068] The performance of the hot-melt halogen-free flame-retardant epoxy resin compositions and fiber-reinforced composites of Examples 1 to 8 (S1 to S8) and Comparative Examples 1 to 7 (D1 to D7) was measured, and the results are shown in Tables 2 and 3.

[0069] Table 2 Performance Data of Hot-Melt Halogen-Free Flame-Retardant Epoxy Resin Compositions

[0070]

[0071] Note: The weight ratio of the flame retardant refers to the percentage of the total weight of the additive halogen-free flame retardant, reactive halogen-free flame retardant, and small molecule scavenger in the total weight of all substances; the char yield at 700 °C was measured under a nitrogen atmosphere; the test standard for tensile strength is ASTM D3039; the test standard for impact strength is GBT1043.1.

[0072] Table 3 Performance Data of Fiber-Reinforced Composites

[0073]

[0074] Note: The test standard for the flame retardancy rating is EN45545; the test standards for the smoke rating and the drip rating are DIN5510-2; the test standard for tensile strength is ASTM D3039.

[0075] In Example S1 of the present invention, with the synergistic cooperation of the optimal flame retardant, filler, and small molecule scavenger, the mechanical properties and flame retardant properties reached the optimum. Compared with Comparative Example D1, the flame retardancy rating, smoke rating, and mechanical properties of S1 are higher, indicating that the benzoxazine resin containing groups has intrinsic flame retardancy, high mechanical strength, and can improve the flame retardancy and mechanical properties of the epoxy resin system. Compared with Comparative Example D7, the flame retardancy rating and drip rating of S2 are higher, indicating that the small molecule scavenger can capture the small molecules generated during the combustion of the resin system and slow down the combustion rate.

[0076] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A hot-melt halogen-free flame-retardant epoxy resin composition, characterized in that, It comprises the following components in parts by weight: 30 - 80 parts of liquid bisphenol A epoxy resin, 20 - 50 parts of solid bisphenol A epoxy resin, 5 - 35 parts of group-containing benzoxazine resin, 3 - 10 parts of curing agent, 1 - 6 parts of accelerator, 20 - 40 parts of additive halogen-free flame retardant, 10 - 20 parts of reactive halogen-free flame retardant, 1 - 8 parts of toughening agent, 3 - 20 parts of porcelain-forming filler, 1 - 10 parts of flaky inorganic filler, 1 - 5 parts of small molecule capturer; The group-containing benzoxazine resin is selected from one or more of cyano-containing benzoxazine resin, propargyl-containing benzoxazine resin, maleimide group-containing benzoxazine resin or aldehyde group-containing benzoxazine resin; The additive halogen-free flame retardant includes one or more of aluminum hydroxide, magnesium hydroxide, silicon oxide, zinc borate, ammonium polyphosphate, aluminum hypophosphite; The small molecule capturer is selected from one or two of boron carbide or phosphotungstic acid; The reactive halogen-free flame retardant is selected from DOPO-type flame retardants modified with amino group, carboxyl group, hydroxyl group or epoxy group.

2. The hot-melt halogen-free flame-retardant epoxy resin composition according to claim 1, wherein The epoxy value of the liquid bisphenol A epoxy resin is 0.23 - 0.56, and the epoxy value of the solid bisphenol A epoxy resin is 0.04 - 0.

22.

3. The hot-melt halogen-free flame-retardant epoxy resin composition according to claim 1, characterized in that, The porcelain-forming filler is selected from one or more of muscovite, montmorillonite, wollastonite, kaolin or diatomite; the flaky inorganic filler is selected from one or more of graphene, MXene, boron nitride, molybdenum disulfide.

4. The hot-melt halogen-free flame-retardant epoxy resin composition according to claim 1, wherein The curing agent is selected from one or more of dicyandiamide, 4',4-diaminodiphenylmethane, 4',4-diaminodiphenylsulfone or 3',3-diaminodiphenylsulfone; The accelerator is selected from imidazole compounds or urea compounds; The toughening agent is selected from one or more of carboxyl-terminated nitrile rubber, chloroprene rubber, ethylene propylene diene monomer rubber, polyamide resin, polyetherimide resin, polyvinyl acetal resin, polyethersulfone resin, carboxyl-containing acrylic resin or amino-terminated polyether resin.

5. The preparation method of the hot-melt halogen-free flame-retardant epoxy resin composition according to any one of claims 1 to 4, characterized in that, It includes the following steps: Crush the solid bisphenol A epoxy resin into powder, stir and heat it at 70 - 100 °C until the solid bisphenol A epoxy resin is completely melted, cool it down to 50 - 70 °C, and add the liquid bisphenol A epoxy resin and the group-containing benzoxazine resin in proportion, and mix evenly to obtain liquid component one; Weigh the additive halogen-free flame retardant, toughening agent, porcelain-forming filler, flaky inorganic filler and small molecule capturer in proportion, add them to the liquid component one, mix evenly at 50 - 70 °C, and pass through a three-roll mill twice to obtain mixture two; Add the reactive halogen-free flame retardant, curing agent and accelerator to the mixture two together, and pass through a three-roll mill twice to obtain the product.

6. A prepreg, characterized in that, The prepreg is formed by laminating a reinforcing fiber and a film made of the halogen-free flame-retardant hot-melt epoxy resin composition according to any one of claims 1 - 4.

7. The prepreg according to claim 6, wherein The mass percentage of the reinforcing fiber in the prepreg is 50 - 70%; the reinforcing fiber includes one or more of glass fiber, carbon fiber, quartz fiber, basalt fiber, aramid fiber, SiC fiber or mullite fiber; the laminating temperature is 60 - 90 °C.

8. A fiber-reinforced composite material, characterized in that, It is cured from the prepreg according to claim 6.

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