Modified epoxy vinyl sizing agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of sizing agents, in particular to a modified epoxy vinyl sizing agent and a preparation method and application thereof, and the modified epoxy vinyl sizing agent comprises modified epoxy resin and water; based on the total weight of the sizing agent, the content of the modified epoxy resin is 1-1.5 wt%; the modified epoxy resin is selected from at least one of polymers with a structure as shown in a formula (1), and in the formula (1), n is an integer of 3-10. The structure of the modified epoxy vinyl sizing agent simultaneously contains a functional group capable of being cross-linked and cured with matrix resin and a functional group capable of being combined with carbon fibers, so that the interface performance of vinyl ester resin and the carbon fibers is improved, and the vinyl ester resin and the carbon fibers are tightly combined together by the sizing agent in the processing and forming process of a composite material; the composite material performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sizing agent, in particular to a modified epoxy vinyl sizing agent and a preparation method and application thereof. BACKGROUND

[0002] Carbon fiber composite materials are widely used in the field of marine vessels. Due to the requirement of long-term contact with seawater, the composite material is required to be resistant to water erosion, mainly manifested as good water resistance of the resin matrix. Different types of resin matrix have large differences in water resistance, and epoxy vinyl ester resin has excellent mechanical properties, high heat resistance, corrosion resistance and fast curing characteristics, and becomes the first choice of matrix material. The epoxy vinyl ester resin is the reaction of epoxy resin and methyl acrylic acid, which retains the skeleton structure of epoxy resin, and introduces unsaturated double bonds into the molecular structure, which can realize free radical curing. The methyl in methyl acrylic acid protects the ester group in the molecular structure, thereby improving the water resistance.

[0003] Sizing agent is a crucial link in the production process of carbon fiber, which protects the internal structure of carbon fiber, reduces the hairiness, improves the bundling, fibrillation and wear resistance, improves the matrix resin wettability, and improves the interface performance of the composite material. The vinyl ester resin and the carbon fiber resin surface lack chemical bond connection, and the interface bonding effect of the carbon fiber and the vinyl resin matrix is poor. SUMMARY

[0004] One of the purposes of the present application is to overcome the problem that the existing bisphenol A epoxy vinyl ester resin cannot form a stable emulsion with water, which limits its application.

[0005] The second purpose of the present application is to overcome the problem that the interface bonding effect of the carbon fiber and the vinyl resin matrix is poor in the prior art, and to provide a modified epoxy vinyl sizing agent, a preparation method and application thereof. The modified epoxy vinyl sizing agent has a structure containing a cross-linkable functional group with the matrix resin and a functional group combined with the carbon fiber, which helps to improve the interface performance of the vinyl ester resin and the carbon fiber. The sizing agent makes the two closely combined together during the processing and molding of the composite material, thereby improving the performance of the composite material.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a modified epoxy vinyl sizing agent, which comprises a modified epoxy resin and water;

[0007] The content of the modified epoxy resin is 1-1.5% by weight based on the total weight of the sizing agent;

[0008] The modified epoxy resin is selected from at least one of the polymers with the structure as shown in formula (1),

[0009]

[0010] In formula (1), n is an integer of 3-10.

[0011] The second aspect of the present application provides a preparation method of a modified epoxy vinyl sizing agent, which comprises:

[0012] (1) contacting and reacting an epoxy vinyl resin represented by formula (2) with a modified monomer in the presence of an initiator;

[0013]

[0014] In formula (2), n is an integer of 3-10;

[0015] The modified monomer is maleic anhydride;

[0016] (2) performing decarboxylation on the product obtained in step (1) with a solubilizing agent and a neutralizing agent to obtain a modified epoxy resin;

[0017] (3) mixing the product obtained in step (2) with water to obtain a sizing agent.

[0018] The third aspect of the present application provides a sizing agent prepared by the preparation method described in the present application.

[0019] The fourth aspect of the present application provides an application of the sizing agent described in the present application to surface modification of fibers.

[0020] Through the above technical solution, the sizing agent described in the present application contains both functional groups capable of cross-linking and curing with the base resin and functional groups capable of binding with carbon fibers in the structure of the modified epoxy resin, which helps to improve the interfacial properties of the vinyl ester resin and the carbon fibers, and the sizing agent makes the two closely combined together during the processing and molding of the composite material.

[0021] In the sizing agent described in the present application, the polar functional groups (such as carboxyl groups) contained in the modified epoxy resin can form a stable emulsion dispersion system with water, so that the sizing agent has the advantages of small particle size and good stability; these polar functional groups can also form rich hydrogen bonds and chemical bonds with the surface of the carbon fibers, establishing strong interaction connections, effectively improving the interfacial bonding of the composite material; at the same time, the unsaturated double bond structure in the polymer chain segment can form strong interactions with the vinyl ester resin through "similar compatibility", further improving the interfacial properties of the composite material.

[0022] In the preparation method of the modified epoxy vinyl sizing agent described in this invention, under the action of an initiator, epoxy vinyl resin segments are introduced into carboxylic acid functional groups through free radical polymerization, forming a stable emulsion dispersion system in water through self-emulsification. Studies have shown that, compared with several existing epoxy vinyl sizing agents, the self-emulsifying emulsion-type modified epoxy vinyl sizing agent exhibits better stability, better film-forming properties on carbon fiber surfaces, and better interfacial bonding performance with vinyl resin. This characteristic will meet the processing and molding requirements of carbon fiber and vinyl resin, expanding the application fields of carbon fiber / vinyl resin composite materials. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these 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.

[0024] A first aspect of the present invention provides a modified epoxy vinyl sizing agent comprising a modified epoxy resin and water;

[0025] Based on the total weight of the sizing agent, the content of the modified epoxy resin is 1-1.5% by weight;

[0026] The modified epoxy resin is selected from at least one of polymers with the structure shown in formula (1).

[0027]

[0028] In formula (1), n ​​is an integer from 3 to 10. In the sizing agent of the present invention, the polar functional groups (e.g., carboxyl groups) contained in the modified epoxy resin can form a stable emulsion dispersion system with water, giving the sizing agent the advantages of small particle size and good stability; these polar functional groups can also form abundant hydrogen bonds and chemical bonds with the carbon fiber surface, establishing strong interaction connections and effectively improving the interfacial bonding of the composite material; at the same time, the unsaturated double bond structure in the polymer chain segment can form a strong interaction with the vinyl resin through "like dissolves like", further improving the interfacial performance of the composite material.

[0029] According to a preferred embodiment of the present invention, in formula (1), n ​​is an integer from 4 to 8.

[0030] According to a preferred embodiment of the present invention, the water content is 98-99% by weight, for example, it can be 98.1% by weight, 98.2% by weight, 98.3% by weight, 98.4% by weight, 98.5% by weight, 98.6% by weight, 98.7% by weight, 98.8% by weight, 98.9% by weight, or 99.0% by weight.

[0031] Any sizing agent possessing the aforementioned characteristics of this invention can be prepared; the preparation method of the sizing agent is not particularly required. This is an illustrative example and does not limit the scope of this invention. According to a preferred embodiment of this invention, this invention provides a method for preparing the modified epoxy vinyl sizing agent of this invention, the method comprising:

[0032] (1) In the presence of an initiator, the epoxy vinyl resin shown in formula (2) is contacted with the modified monomer for reaction;

[0033]

[0034] In equation (2), n is an integer from 3 to 10;

[0035] The modified monomer is maleic anhydride;

[0036] (2) The product obtained in step (1) is subjected to a decarboxylation reaction with a catalytic solvent and a neutralizing agent to obtain a modified epoxy resin;

[0037] (3) The product obtained in step (2) is mixed with water to obtain a sizing agent. Under the action of an initiator, epoxy vinyl resin segments are introduced into carboxylic acid functional groups through free radical polymerization, forming a stable emulsion dispersion system in water through self-emulsification. Studies have shown that, compared with several existing epoxy vinyl sizing agents, the self-emulsifying emulsion-type modified epoxy vinyl sizing agent has better stability, better film-forming properties on the carbon fiber surface, and better interfacial bonding performance with vinyl resin. This feature will meet the processing and molding requirements of carbon fiber and vinyl resin, expanding the application field of carbon fiber / vinyl resin composite materials.

[0038] According to a preferred embodiment of the present invention, in formula (2), n is an integer from 4 to 8.

[0039] In this invention, the range of initiators that can be selected is relatively wide. According to a preferred embodiment of this invention, the initiator is one or more organic peroxides, preferably benzoyl peroxide.

[0040] In this invention, the co-solvent is ethylene glycol monobutyl ether.

[0041] In this invention, the range of neutralizing agents is relatively wide, as long as they contain organic amines. The neutralizing agent is selected from one or more organic amine compounds. According to a preferred embodiment of this invention, the neutralizing agent is selected from one or both of N,N'-dimethylethanolamine and N,N'-dimethylethanolamine.

[0042] In this invention, the epoxy vinyl resin shown in formula (2) can be softened by heating and then reacted with the modified monomer. Preferably, it is softened by heating at 80-90°C.

[0043] According to a preferred embodiment of the present invention, the epoxy vinyl resin and the modified monomer shown in formula (2) are both dehydration raw materials, for example, the water-containing components therein are removed by benzoyl peroxide.

[0044] In this invention, the range of selectable contact reaction conditions in step (1) is relatively wide. According to a preferred embodiment of this invention, the contact reaction conditions include: a reaction temperature of 100-110℃; and a reaction time that can be determined according to actual needs. Preferably, the reaction time is 8-9h.

[0045] In this invention, the amount of initiator in step (1) can be selected from a wide range. According to a preferred embodiment of this invention, the amount of initiator is 0.8-2.7 wt% of the mass of the epoxy vinyl resin.

[0046] In this invention, in step (1), the modified monomer is used to introduce carboxylic acid functional groups into the epoxy vinyl resin chain segment. The amount of modified monomer can be selected from a wide range. According to a preferred embodiment of this invention, in step (1), the mass ratio of the epoxy vinyl resin to the modified monomer is 2-7:1.

[0047] In this invention, the contact reaction conditions in step (2) can be selected from a wide range. According to a preferred embodiment of this invention, the decarboxylation reaction conditions include: a decarboxylation temperature of 25-50°C; and a decarboxylation time that can be determined according to actual needs. Preferably, the decarboxylation time is 2-16 hours.

[0048] In this invention, in step (2), the co-solvent is used to encapsulate the modified resin molecular chain segments to form an emulsion in water; the amount of co-solvent can be selected from a wide range. According to a preferred embodiment of this invention, the amount of co-solvent is 12-30 wt% of the mass of the epoxy vinyl resin.

[0049] In this invention, in step (2), the neutralizing agent is used to neutralize the acidity of the carboxyl group and adjust the pH of the sizing agent system to be neutral; the amount of neutralizing agent can be selected from a wide range. According to a preferred embodiment of this invention, the amount of neutralizing agent is 3-10 mL relative to 100 g of the epoxy vinyl resin.

[0050] According to a preferred embodiment of the present invention, in step (3), the amount of water used is such that the solid content of the sizing agent is 1-1.5 wt%.

[0051] In this invention, in step (3), the sizing agent can be prepared by adding water in steps. First, water is added to prepare the sizing agent stock solution, and then the sizing agent stock solution is mixed with water to prepare the sizing agent. According to a preferred embodiment of this invention, water is added to the product obtained in step (2) to prepare the sizing agent stock solution, such that the content of the modified epoxy resin in the sizing agent stock solution is 8-35% by weight, preferably 12-28% by weight.

[0052] According to a preferred embodiment of the present invention, the water content in the sizing agent stock solution is 65-92% by weight, preferably 72-88% by weight.

[0053] A third aspect of the present invention provides a sizing agent prepared by the preparation method described above; preferably, the solid content of the sizing agent is 1-1.5 wt%.

[0054] A fourth aspect of this invention provides an application of the sizing agent described herein in fiber surface modification. The sizing agent described herein is used to modify fiber surfaces, exhibiting good film-forming properties on fiber (e.g., carbon fiber) surfaces and good interfacial bonding with vinyl ester resins, thereby improving the interfacial properties of fiber composite materials.

[0055] In this invention, the range of fiber types that can be selected is relatively wide. According to a preferred embodiment of the invention, the fiber includes carbon fiber and / or graphite fiber, preferably carbon fiber. Preferably, the carbon fiber includes, but is not limited to, one or more of SCF-35S-12K, SCF-35S-24K, and SCF-35S-48K carbon fibers. In this embodiment of the invention, SCF-35S-48K carbon fiber is used as an example to illustrate the advantages of the invention, but the invention is not limited thereto.

[0056] According to a preferred embodiment of the present invention, the amount of fiber used is 1000-2000g relative to 100mL of the sizing agent.

[0057] According to a preferred embodiment of the present invention, a method for surface modification of carbon fibers using the sizing agent of the present invention includes:

[0058] The sizing agent of the present invention is placed in the sizing tank. Unsized carbon fibers are immersed in the sizing agent and pass through the sizing tank at a speed of 4 m / min-8 m / min for 0.05-0.1 min. Excess sizing agent is squeezed out of the carbon fibers exiting the tank. The sized carbon fibers are then dried at 120℃-180℃. Preferably, the drying is carried out by a three-stage temperature gradient of 140℃-160℃-180℃.

[0059] Sizing carbon fibers can be used to prepare composite materials at high temperatures, which improves the compatibility of the carbon fiber / resin matrix interface and enhances the wear resistance, stiffness, and interlaminar shear strength of the composite materials.

[0060] In the context of this invention specification, including the following embodiments, the method for testing the solid content in the slurry is as follows: weigh the bottle mass W0, add the sizing agent and the mass W1, dry in a forced-air drying oven at 120°C for 3 hours, the mass of the bottle and the dried sizing agent after drying is W2, and the solid content = (W2-W0) / (W1-W0)*100%.

[0061] In the context of this invention specification, including the following embodiments, the method for testing the stability of the sizing agent is as follows: the sizing agent is centrifuged at 3000 rpm for 5 min; after centrifugation, the sizing agent does not separate into layers, indicating excellent stability.

[0062] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0063] In the following embodiments, the abrasion resistance test method is as follows: Take approximately 30cm of carbon fiber to be tested, protect both ends of the carbon fiber with labels, and fix both ends of the carbon fiber bundle to the clamp of the abrasion tester. A certain weight is loaded onto one end of the clamp. After the counter is zeroed, the rotation speed is adjusted to 300 r / min, the motor is turned on, and the carbon fiber begins to rub against the friction roller (stainless steel rod). After the fiber breaks, the machine automatically stops and records the cumulative number of reciprocating frictions until breakage. The average value of 10 tests is taken as the analysis result.

[0064] In the following embodiments, the stiffness test method is as follows: Three 1m long strands of the fiber sample to be tested are cut and placed in a standard temperature and humidity environment, and allowed to stand for at least 16 hours to reach moisture equilibrium. Then, a 1m long fiber bundle is suspended at its midpoint, with knots at both ends, and a certain load is hung from the lower end to correct the bending and twisting of the fiber bundle. It is then allowed to stand for 30 minutes under standard temperature and humidity conditions. The load is removed, and two 40cm long strands are cut from each fiber bundle. The midpoint of the 40cm sample is suspended on the hook of the stiffness tester. After 60 seconds of standing, the distance between the two ends of the suspended sample is quickly read and the data (L1, L2) are recorded. The stiffness is calculated according to Equation 1-1.

[0065] Stiffness = L2 - L1 (1-1)

[0066] In the formula: L - the length readings at both ends of the carbon fiber, in centimeters (cm).

[0067] The arithmetic mean of the six samples was used as the reported value for carbon fiber stiffness, in cm.

[0068] In the following embodiments, the interlaminar shear strength test method is as follows:

[0069] (1) Mix vinyl resin (MERICAN 30-200P) and curing agent (Akzo LPT system) at a mass ratio of 1:1 to prepare vinyl resin matrix;

[0070] (2) Apply resin evenly to the unidirectional carbon fiber bundle, lay it flat in the mold with a size of 200*10*2mm, and fix it firmly with a clamp so that the resin can fully wet the carbon fiber and remove air bubbles in the mold.

[0071] (3) Place the sample strip in an oven and cure it at 120℃ for 2 hours;

[0072] (4) After cooling to room temperature, demold to obtain composite material specimens;

[0073] (5) The interlaminar shear strength of the composite material strip was determined using the short beam method of ISO 14130:1991 on a bundled wire strength tester (5566A).

[0074] In the following examples, unless otherwise specified, the bisphenol A epoxy vinyl ester resin is Huachang MFE-2 bisphenol A epoxy vinyl ester resin, with the structural formula shown in formula (2), where n = 5.

[0075] All other chemical reagents are commercially available.

[0076] Example 1

[0077] (1) Take 100g of bisphenol A epoxy vinyl ester resin and add it to a three-necked flask. Preheat at 80℃ for 1.5h to soften the epoxy resin.

[0078] (2) Heat to 110℃, add 24g maleic anhydride and 2.2g benzoyl peroxide, and stir mechanically for 8h.

[0079] (3) After cooling to room temperature, add 25g of ethylene glycol monobutyl ether and 8mL of N,N'-dimethylethanolamine, and stir mechanically for 6h.

[0080] (4) After the reaction is complete, add 550 mL of water and stir at high speed to disperse it evenly to obtain the original slurry of the sizing agent;

[0081] (5) Dilute the original sizing agent with water to a solid content of 1.3wt% to obtain the sizing agent.

[0082] Example 2

[0083] (1) Take 100g of bisphenol A epoxy vinyl ester resin and add it to a three-necked flask. Preheat at 80℃ for 1.5h to soften the epoxy resin.

[0084] (2) Heat to 100℃, add 36g maleic anhydride and 2.7g benzoyl peroxide, and stir mechanically for 9h.

[0085] (3) After cooling to room temperature, add 30g of ethylene glycol monobutyl ether and 10mL of N,N'-dimethylethanolamine, and stir mechanically for 5h.

[0086] (4) After the reaction is complete, add 600 mL of water and stir at high speed to disperse it evenly to obtain the original slurry of the sizing agent;

[0087] (5) Dilute the original sizing agent with water to a solid content of 1.5wt% to obtain the sizing agent.

[0088] Example 3

[0089] The method of Example 1 is the same, except that the amount of bisphenol A epoxy vinyl ester resin used is 150g, and the other conditions are the same as in Example 1.

[0090] Example 4

[0091] (1) Take 150g of bisphenol A epoxy vinyl ester resin and add it to a three-necked flask. Preheat at 80℃ for 1.5h to soften the epoxy resin.

[0092] (2) Heat to 110℃, add 30g maleic anhydride and 1.5g benzoyl peroxide, and stir mechanically for 9h.

[0093] (3) After cooling to room temperature, add 20g of ethylene glycol monobutyl ether and 5mL of N,N'-dimethylethanolamine, and stir mechanically for 6h.

[0094] (4) After the reaction is complete, add 500 mL of water and stir at high speed to disperse it evenly to obtain the original slurry of the sizing agent;

[0095] (5) Dilute the original sizing agent with water to a solid content of 1.0 wt% to obtain the sizing agent.

[0096] Example 5

[0097] (1) Take 150g of bisphenol A epoxy vinyl ester resin and add it to a three-necked flask. Preheat at 80℃ for 1.5h to soften the epoxy resin.

[0098] (2) Heat to 110℃, add 36g maleic anhydride and 1.5g benzoyl peroxide, and stir mechanically for 9h.

[0099] (3) After cooling to room temperature, add 20g of ethylene glycol monobutyl ether and 5mL of N,N'-dimethylethanolamine, and stir mechanically for 6h.

[0100] (4) After the reaction is complete, add 500 mL of water and stir at high speed to disperse it evenly to obtain the original slurry of the sizing agent;

[0101] (5) Dilute the original sizing agent with water to a solid content of 1.0 wt% to obtain the sizing agent.

[0102] Example 6

[0103] The method of Example 1 is different in that the bisphenol A epoxy vinyl ester resin has the structural formula shown in Formula (2), where n = 10; the other conditions are the same as in Example 1, and the sizing agent is prepared.

[0104] Test Example 1

[0105] Preparation of sized carbon fibers:

[0106] The amount of carbon fiber used was 1200g relative to 100mL of sizing agent. The sizing agents of Examples 1-6 were placed in the sizing tank. The unsized SCF-35S-48K carbon fiber was immersed in the sizing agent and passed through the sizing tank at a speed of 6m / min for 120min. The excess sizing agent of the carbon fiber exiting the tank was squeezed out. Then the sized carbon fiber was dried by heating in three temperature gradients of 140℃-160℃-180℃ to obtain sized carbon fiber.

[0107] The sized carbon fiber was tested according to the wear resistance test method, stiffness test method and interlaminar shear strength test method of the present invention, and the test results are shown in Table 1.

[0108] Test Example 2

[0109] Take the sizing agents from Examples 1-6 and place them in centrifuge tubes. Centrifuge at 3000 rpm for 5 min. Observe the state of the sizing agents. The test results are shown in Table 1.

[0110] Comparative Example 1

[0111] According to the abrasion resistance test method, stiffness test method, and interlaminar shear strength test method of this invention, the unsized SCF-35S-48K carbon fiber and the sized carbon fiber were tested respectively, and the test results are shown in Table 1.

[0112] Comparative Example 2

[0113] Epoxy sizing agent was obtained by dissolving bisphenol A type epoxy resin in water with a solid content of 1.3 wt%. The unsized SCF-35S-48K carbon fiber and the sized carbon fiber were tested according to the abrasion resistance test method, stiffness test method and interlaminar shear strength test method of this invention. The test results are shown in Table 1.

[0114] Table 1

[0115]

[0116] As shown in Table 1, emulsion-type modified epoxy vinyl sizing agent can effectively improve the interfacial bonding performance of sized carbon fiber / vinyl resin composites. This is because the main polymer chain segments of the emulsion-type modified epoxy vinyl sizing agent contain polar oxygen-containing functional groups and unsaturated carbon-carbon double bonds, which can form abundant hydrogen bonds and chemical bonds with the carbon fiber surface, and can also form strong interactions with the vinyl resin matrix, thereby improving the interlaminar shear strength of sized carbon fiber / vinyl resin composites.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified epoxy vinyl sizing agent, characterized in that, The sizing agent comprises modified epoxy resin and water; Based on the total weight of the sizing agent, the content of the modified epoxy resin is 1-1.5% by weight; The modified epoxy resin is selected from at least one of polymers with the structure shown in formula (1). In equation (1), n ​​is an integer from 3 to 10.

2. The sizing agent according to claim 1, wherein, In equation (1), n ​​is an integer from 4 to 8; and / or The water content is 98-99% by weight.

3. A method for preparing a modified epoxy vinyl sizing agent, characterized in that, The method includes: (1) In the presence of an initiator, the epoxy vinyl resin shown in formula (2) is contacted with the modified monomer for reaction; In equation (2), n is an integer from 3 to 10; The modified monomer is maleic anhydride; (2) The product obtained in step (1) is subjected to a decarboxylation reaction with a catalytic solvent and a neutralizing agent to obtain a modified epoxy resin; (3) The product obtained in step (2) is mixed with water to obtain a sizing agent.

4. The preparation method according to claim 3, wherein, In equation (2), n is an integer from 4 to 8; and / or The initiator is one or more organic peroxides, preferably benzoyl peroxide; and / or The co-solvent is ethylene glycol monobutyl ether; The neutralizing agent is selected from one or more organic amine compounds, preferably one or both of N,N'-dimethylethanolamine and N,N'-dimethylethanolamine.

5. The preparation method according to claim 3 or 4, wherein, In step (1), the contact reaction conditions include: a reaction temperature of 100-110℃; and / or a reaction time of 8-9 h; and / or The amount of initiator used is 0.8-2.7 wt% of the mass of the epoxy vinyl resin; The mass ratio of the epoxy vinyl resin to the modified monomer is 2-7:

1.

6. The preparation method according to any one of claims 3-5, wherein, In step (2), Decarboxylation reaction conditions include: a decarboxylation temperature of 25-50℃; and / or a decarboxylation time of 2-16 h; and / or The amount of solvent used is 12-30 wt% of the mass of the epoxy vinyl resin; and / or The amount of neutralizing agent used is 3-10 mL relative to 100 g of the epoxy vinyl resin.

7. The preparation method according to any one of claims 3-6, wherein, In step (3), the amount of water used makes the solid content of the sizing agent 1-1.5 wt%.

8. The sizing agent prepared by the preparation method according to any one of claims 3-7; preferably, the solid content of the sizing agent is 1-1.5 wt%.

9. The application of the sizing agent according to claim 1 or 2, or the sizing agent according to claim 8, in fiber surface modification.

10. The application according to claim 9, wherein, The fibers include carbon fibers and / or graphite fibers, preferably carbon fibers; and / or The amount of fiber used is 1000-2000g relative to 100mL of the sizing agent.

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