Modified epoxy resin, preparation method thereof and sizing agent

Abstract

According to the modified epoxy resin provided by the invention, a hydrophilic group and a flexible chain segment are introduced into the main chain of the epoxy resin, so that the intrinsic water solubility of the epoxy resin is realized. The invention also provides a preparation method of the modified epoxy resin. The method is simple, the solvent used in the synthesis process is environment-friendly, and the method is suitable for industrial production. The sizing agent provided by the invention can be stably dispersed in a water phase without an emulsifier, and solves the problems of poor stability and emulsifier migration of a traditional physical phase inversion emulsification method. After the surface of the carbon fiber is coated with the sizing agent provided by the invention, agglomeration of the carbon fiber in a water phase can be effectively avoided, and the water-phase dispersion uniformity of the sizing agent in application of a paper-based composite material is greatly improved. The method can be used for preparing the carbon fiber paper-based composite material.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber material application technology, specifically relating to a modified epoxy resin and its preparation method, as well as a sizing agent comprising the modified epoxy resin, its preparation method, and its application. Background Technology

[0002] Carbon fiber, as a high-performance reinforcing material, is widely used in aerospace, automotive manufacturing, electronics and electrical engineering, new energy and other fields due to its excellent properties such as high specific strength, high specific modulus and corrosion resistance.

[0003] Carbon fiber paper-based composites, as one of the important applications of carbon fiber, are prepared by wet papermaking process. They combine the performance advantages of carbon fiber with the molding flexibility of paper-based composites and have significant application potential in battery electrode substrates, filter materials, thermal insulation materials and other scenarios.

[0004] Because carbon fibers are prepared from organic precursors through processes such as carbonization and graphitization, their surfaces lack active groups, exhibit strong hydrophobicity, and are highly inert. Industrially, carbon fibers are typically subjected to surface oxidation treatment, introducing oxygen-containing polar groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH) onto their surface through gas-phase, liquid-phase, or electrochemical methods, and constructing microscopic roughness to improve the surface energy and wettability of the carbon fibers, laying the foundation for interfacial bonding in subsequent composite materials. Furthermore, sizing agents are applied during carbon fiber production to protect the carbon fiber surface and enhance its interfacial bonding properties.

[0005] Currently, most mainstream sizing agents on the market contain a significant amount of surfactants such as emulsifiers and dispersants. While sizing agents themselves possess good stability and meet the bonding requirements between carbon fibers and the resin matrix, in the wet-process papermaking process for preparing carbon fiber paper-based composites, traditional sizing agents, after reducing or eliminating surfactants such as emulsifiers and dispersants, result in film-forming substances on the carbon fiber surface that exhibit strong hydrophobicity or insufficient hydrophilicity. This leads to easy aggregation and poor dispersion uniformity of carbon fibers in the aqueous dispersion system. This not only results in uneven pore distribution and decreased mechanical properties in the carbon fiber paper-based composites but also reduces production efficiency and increases process costs, severely restricting the performance and preparation efficiency of carbon fiber paper-based composites. Therefore, the inappropriate use of sizing agents has become a major obstacle to the uniform dispersion of carbon fibers in the aqueous phase.

[0006] Epoxy resin is a commonly used matrix resin for carbon fiber sizing agents due to its adhesive properties and chemical stability. However, its inherent strong hydrophobicity prevents its direct application in aqueous systems. Traditional methods for waterborne epoxy resin mainly involve physical phase transformation emulsification, which disperses epoxy resin in water to form an emulsion by adding emulsifiers. However, this method suffers from problems such as easy migration of emulsifiers, poor emulsion stability, and a significant decrease in hydrophilicity after film formation on the carbon fiber surface, failing to meet the requirements for the preparation of carbon fiber paper-based composite materials.

[0007] For example, CN116535452A discloses a water-soluble sizing agent applied in the field of carbon fiber surface modification technology. The sizing agent comprises the following raw materials in parts by weight: 0.1 to 10 parts of water-based epoxy-modified naringin, 0.2 to 10 parts of surfactant, 0.1 to 5 parts of lubricant, 0.1 to 5 parts of adhesive, 0.2 to 5 parts of antistatic agent, and 100 parts of deionized water. The water-based epoxy-modified naringin is purified by fully reacting naringin, allyl bromide, anhydrous potassium carbonate, benzyltriethylammonium chloride, and ethanol. The purified product is then fully reacted with m-chloroperoxybenzoic acid and post-treated to obtain the final product. This patent provides a method for water-soluble modification of epoxy resin, solving the problems of complex application methods and organic solvent residues in water-soluble sizing agents, and improving stability.

[0008] For example, CN116837633A discloses a water-soluble sizing agent with self-emulsifying function for use in the field of carbon fiber sizing agents. This sizing agent first undergoes a modification and grafting reaction of polyethylene glycol and phthalic anhydride in an acidic environment, and then the phthalic anhydride-modified polyethylene glycol and epoxy resin undergo a grafting reaction under the action of a catalyst to obtain a water-soluble epoxy resin sizing agent with self-emulsifying properties. This water-soluble sizing agent has good self-emulsifying function, can solve the stability problem of emulsion-type sizing agents, and is easy to use.

[0009] The above patents, through different water-soluble modification methods of epoxy resin, can improve the stability and ease of application of sizing agents, but they do not address the uniform dispersion performance of carbon fibers in the aqueous phase, nor do they achieve the inherent water solubility of the sizing agent. To achieve uniform dispersion of carbon fibers in the aqueous phase during the wet papermaking process of carbon fiber paper-based composite materials, a new technological direction for preparing water-soluble epoxy resin sizing agents is to introduce permanent hydrophilic groups into the epoxy resin skeleton through molecular structure design, achieving inherent water solubility without the addition of emulsifiers or dispersants. Summary of the Invention

[0010] The first objective of this invention is to provide a modified epoxy resin for improving the dispersibility of carbon fibers in an aqueous dispersion system and enhancing the interfacial bonding performance between carbon fibers and the composite matrix.

[0011] A second objective of this invention is to provide a method for preparing the modified epoxy resin.

[0012] A third object of the present invention is to provide a sizing agent comprising the modified epoxy resin.

[0013] A fourth objective of this invention is to provide a method for preparing the sizing agent.

[0014] A fifth object of the present invention is to provide an application of the sizing agent.

[0015] This invention is achieved through the following technical solution: A modified epoxy resin has the following structure: ; Where 2≤m≤10, 3≤n≤6.

[0016] The method for preparing the modified epoxy resin includes the following steps: Compound 1 was obtained by dissolving bisphenol A, bisphenol A-type epoxy resin monomer, and catalyst in an organic solvent and carrying out a chain extension reaction. Compound 1 was reacted with diethanolamine and a catalyst in an organic solvent to undergo an amine-addition reaction to obtain compound 2; Compound 2 is subjected to a polyetheramine grafting reaction with a catalyst in an organic solvent to obtain the product; The structure of compound 1 is as follows: ; The structure of compound 2 is as follows: ; The chain extension reaction is carried out at a temperature of 120~160℃; The chain extension reaction takes 120-240 minutes; The temperature for the amine-addition reaction is 100~120℃; The time for the amine-addition reaction is 120-180 min; The temperature for the polyetheramine grafting reaction is 120~140℃; The time for the polyetheramine grafting reaction is 120~240 min.

[0017] The catalyst is selected from one of quaternary ammonium salts, quaternary phosphorus salts, or tertiary amine compounds; The quaternary ammonium salts include tetraethylammonium bromide and tetrabutylammonium iodide; The quaternary phosphorus salt includes tetraphenylphosphine bromide; The tertiary amine compounds include at least one of N,N-dimethylbenzylamine and N-methyldiethanolamine.

[0018] The bisphenol A type epoxy resin monomer is selected from at least one of E-51, CYD-128, NPEL-128, EPLC-828 / 828A, YD-825GS, GELR-128 / 128E, and LER850. Since the molecular weights of E-51, CYD-128, NPEL-128, EPLC-828 / 828A, YD-825GS, GELR-128 / 128E, and LER850 are too low, a chain extension reaction can be used to obtain the target structure or a polymeric structure with the desired molecular weight.

[0019] The polyetheramine is selected from one of EDR-148, EDR-176, M-600, D-230, and D-400.

[0020] The organic solvent is selected from at least one of propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, ethylene glycol monobutyl ether, methyl isobutyl ketone, methyl ethyl ketone, and methyl propyl ketone.

[0021] A sizing agent, by weight, comprises 30-40 parts of the modified epoxy resin as described in claim 1, 1.5-2.5 parts of a neutralizing agent, and 60-70 parts of water.

[0022] The neutralizing agent is selected from at least one of formic acid, acetic acid, lactic acid, oxalic acid, and citric acid.

[0023] The preparation method of the sizing agent includes the following steps: The modified epoxy resin and neutralizing agent are mixed and reacted at 50-60℃ for at least 60 minutes, and then water is added and stirred at 35-40℃ for at least 30 minutes to obtain the final product.

[0024] One application of the sizing agent is in the preparation of carbon fiber paper-based composite materials using wet papermaking.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: The modified epoxy resin provided by this invention introduces hydrophilic groups and flexible segments into the main chain of the epoxy resin through molecular design, thereby achieving the inherent water solubility of the epoxy resin.

[0026] The modified epoxy resin preparation method provided by this invention is simple, uses environmentally friendly solvents in the synthesis process, and is suitable for industrial production. Furthermore, by precisely controlling the epoxy value during the synthesis process, a template-based modified epoxy resin synthesis technology route with reproducible synthesis pathways and customizable molecular structures is achieved for waterborne applications.

[0027] The sizing agent provided by this invention can be stably dispersed in the aqueous phase without emulsifier, solving the problems of poor stability and emulsifier migration in traditional physical phase-to-emulsification methods; The sizing agent provided by this invention, when coated on the surface of carbon fiber, will change the surface properties of the carbon fiber. Combined with the steric hindrance effect of the polyetheramine chain segment, the sizing agent can effectively prevent the agglomeration of carbon fiber in the aqueous phase and greatly improve its aqueous phase dispersion uniformity in paper-based composite material applications.

[0028] The sizing agent application method provided by this invention retains the excellent mechanical and adhesive properties of epoxy resin during the preparation process, protecting carbon fibers from damage. It can also form a stable bond with carbon fibers and matrix resin through active groups, enhancing the interfacial bonding performance. It is suitable for the production process of carbon fiber paper-based composite materials and provides a new direction for the waterborne application of epoxy resin.

[0029] The sizing process for adapting carbon fiber paper-based composite materials provided by this invention simplifies the process, reduces costs, and has broad application prospects in various paper-based product fields.

[0030] This invention utilizes the high reactivity of epoxy groups on the epoxy resin backbone to inherently hydrophilize the epoxy resin molecular design. Active amine compounds with specific molecular structures are selected as modifiers. Through precise amine ring-opening reactions, hydrophilic segments are covalently grafted onto the resin backbone, simultaneously achieving molecular-level control over hydrophilicity, flexibility, and adhesion. This allows the synthesized modified epoxy resin to be directly and stably dispersed in the aqueous phase, completely eliminating the need for added emulsifiers or dispersants. This fundamentally solves the drawbacks of traditional sizing agents, such as poor stability and easy migration of additives, providing an excellent and durable aqueous dispersion environment for carbon fibers. This preparation method is highly efficient, and the product structure has a high degree of determinism and designability, forming a template-based modified synthesis route for aqueous epoxy resin with a replicable synthetic path and customizable molecular structure. It can prepare sizing agents suitable for the production process of carbon fiber paper-based composite materials. Detailed Implementation

[0031] The invention will be further described in detail below through specific implementation examples. It should be noted that the following implementation examples are descriptive only and are not restrictive, and should not be used to limit the scope of protection of the invention. Unless otherwise specified, the experimental instruments, equipment, materials and reagents used in the invention are all commercially available.

[0032] This invention provides a modified epoxy resin with the following structure: ; Wherein, 2≤m≤10, 3≤n≤6. This modified epoxy resin is prepared from bisphenol A and epoxy resin monomers (epoxy equivalent between 180 and 190) through a three-step reaction involving chain extension, amine addition, and polyetheramine grafting. After acidification, this epoxy resin contains quaternary ammonium salts, hydroxyl groups, and flexible polyetheramine segments, thus exhibiting excellent solubility and direct, stable dispersion in the aqueous phase without the need for external emulsifiers or dispersants. Simultaneously, the highly polar molecules of this acidified modified epoxy resin allow for stable and uniform coating onto the carbon fiber surface. Furthermore, during the dispersion of carbon fibers coated with a sizing agent including the acidified modified epoxy resin in the aqueous system, the excellent water solubility, electrostatic repulsion, and steric hindrance effect of the alkyl branches make this modified epoxy resin an effective surface modifier to prevent carbon fiber agglomeration or clustering, achieving uniform dispersion of carbon fibers in the aqueous system.

[0033] Specifically, the preparation method of the modified epoxy resin includes the following steps: Bisphenol A, epoxy resin monomer, and catalyst were dissolved in an organic solvent and subjected to a chain extension reaction to obtain compound 1; the structure of compound 1 is as follows: , The reaction equation for this step is as follows: .

[0034] Compound 1 was reacted with diethanolamine and a catalyst in an organic solvent via an amine-addition reaction to yield compound 2; the structure of compound 2 is as follows. , The reaction equation for this step is as follows: Compound 2 is subjected to a polyetheramine grafting reaction with a catalyst in an organic solvent to obtain the product; The reaction equation for this step is as follows: .

[0035] The present invention also provides a sizing agent, comprising, by weight, 30-40 parts of the modified epoxy resin as described in claim 1, 1.5-2.5 parts of a neutralizing agent and 60-70 parts of water.

[0036] The neutralizing agent is selected from at least one of formic acid, acetic acid, lactic acid, oxalic acid, and citric acid.

[0037] The preparation method of the sizing agent includes the following steps: The modified epoxy resin and neutralizing agent are mixed and reacted at 50-60℃ for at least 60 minutes, and then water is added and stirred at 35-40℃ for at least 30 minutes to obtain the final product.

[0038] The equation for this reaction is as follows: The sizing agent provided by this invention can be applied to the preparation of carbon fiber paper-based composite materials in wet papermaking.

[0039] The present invention will be further described below with reference to specific embodiments.

[0040] Example 1 In this embodiment, the proportions of the substances are as follows: epoxy resin E51, bisphenol A, diethanolamine, polyetheramine EDR-176, tetrabutylammonium bromide, and propylene glycol methyl ether are in a mass ratio of 60:15:6:7:0.2:10. The catalyst used in this embodiment is tetrabutylammonium bromide.

[0041] In this embodiment, the organic solvent is propylene glycol methyl ether. The neutralizing agent is acetic acid.

[0042] The specific steps are as follows: In step (1), the bisphenol A and epoxy resin monomer are premixed at 100°C and 40 rpm / min. After uniform mixing, the reaction is carried out at 150°C and 150 rpm / min for 240 min.

[0043] Before adding the diethanolamine and tetrabutylammonium bromide, the reaction system temperature in step (2) is controlled below 120°C. After adding the reactants and tetrabutylammonium bromide, the reaction is carried out at 120°C and 300 rpm / min for 180 min.

[0044] The reaction in step (3) was carried out at 140°C and 200 rpm for 240 min.

[0045] The reaction in step (4) was carried out for 60 min at 50 °C and 1500 rpm / min after the addition of acetic acid, and then carried out for 30 min at 40 °C and 1500 rpm / min after the addition of deionized water.

[0046] The carbon fiber sizing agent prepared in Example 1 was diluted with deionized water to a solids content of 3%. An appropriate amount of the sizing agent was placed in a sizing tank and used to sizing mesophase pitch-based carbon fibers with a tow specification of 2K. Subsequently, the carbon fiber tow was dried at 170°C. The mechanical properties and fuzz content of the dried carbon fibers were measured. Simultaneously, the carbon fibers were chopped to 5 mm, and the dispersibility of the chopped carbon fibers in deionized water was tested. The test results are shown in Table 1.

[0047] Example 2 In this embodiment, the proportions of the substances are as follows: epoxy resin E51, bisphenol A, diethanolamine, polyetheramine EDR-176, tetrabutylammonium bromide, and propylene glycol methyl ether are in a mass ratio of 55:15:5.5:8:0.2:10. The catalyst in this embodiment is tetrabutylammonium bromide. The organic solvent in this embodiment is propylene glycol methyl ether. The neutralizing agent in this embodiment is acetic acid.

[0048] The preparation steps are the same as in Example 1.

[0049] The carbon fiber sizing agent prepared in Example 2 was diluted with deionized water to a solids content of 3%. An appropriate amount of the sizing agent was placed in a sizing tank and used to sizing mesophase pitch-based carbon fibers with a tow specification of 2K. Subsequently, the carbon fiber tow was dried at 170°C. The mechanical properties and fuzz content of the dried carbon fibers were measured. At the same time, the carbon fibers were chopped to 5 mm, and the dispersibility of the chopped carbon fibers in deionized water was tested. The test results are shown in Table 1.

[0050] Example 3 In this embodiment, the proportions of each substance are as follows: epoxy resin E51, bisphenol A, diethanolamine, polyetheramine (EDR-148 to M-600 in a mass ratio of 6:4), tetrabutylammonium bromide, and propylene glycol methyl ether in a mass ratio of 60:15:6:7:0.2:10. The catalyst used in this embodiment is tetrabutylammonium bromide.

[0051] In this embodiment, the organic solvent is propylene glycol methyl ether. The neutralizing agent is acetic acid.

[0052] The preparation steps are the same as in Example 1.

[0053] The carbon fiber sizing agent prepared in Example 3 was diluted with deionized water to a solids content of 3%. An appropriate amount of the sizing agent was placed in a sizing tank and used to sizing mesophase pitch-based carbon fibers with a tow specification of 2K. Subsequently, the carbon fiber tow was dried at 170°C. The mechanical properties and fuzz content of the dried carbon fibers were measured. At the same time, the carbon fibers were chopped to 5 mm, and the dispersibility of the chopped carbon fibers in deionized water was tested. The test results are shown in Table 1.

[0054] Comparative Example 1 A commercially available water-based emulsion carbon fiber sizing agent (emulsion sizing agent A) was diluted with deionized water to a solids content of 3%. An appropriate amount of the sizing agent was placed in a sizing tank and used to sizing mesophase pitch-based carbon fibers with a tow specification of 2K. Subsequently, the carbon fiber tow was dried at 170℃. The mechanical properties and fuzz content of the dried carbon fibers were measured. Simultaneously, the carbon fibers were chopped to 5 mm, and the dispersibility of the chopped carbon fibers in deionized water was tested. The test results are shown in Table 1.

[0055] Comparative Example 2 A commercially available water-soluble carbon fiber sizing agent (solution-type sizing agent B) was diluted with deionized water to a solids content of 3%. An appropriate amount of the sizing agent was placed in a sizing tank and used to sizing mesophase pitch-based carbon fibers with a tow specification of 2K. The carbon fiber tow was then dried at 170℃. The mechanical properties and fuzz content of the dried carbon fibers were measured. Simultaneously, the carbon fibers were chopped to 5 mm, and the dispersibility of the chopped carbon fibers in deionized water was tested. The test results are shown in Table 1.

[0056] Table 1. Test results of carbon fiber performance Based on the test results in Table 1, comparing Examples 1, 2, and 3 with Comparative Examples 1 and 2, it can be seen that, in terms of carbon fiber interfacial shear strength, the carbon fiber sizing agent provided by this invention significantly improves the interfacial shear strength of carbon fibers; in terms of controlling the amount of carbon fiber filaments, the carbon fiber sizing agent provided by this invention can also improve the filament state of the carbon fiber bundles; overall, the advantages of the sizing agent provided by this invention in these two aspects can greatly improve the composite effect of carbon fiber paper-based composite materials, ultimately improving the performance of the composite materials. Meanwhile, regarding the most prominent issue of carbon fiber dispersion in the aqueous phase in the production of carbon fiber paper-based composite materials, compared with the emulsion-type sizing agent A in Comparative Example 1 and the solution-type sizing agent B in Comparative Example 2, the sizing agent provided by this invention solves the compatibility problem between the carbon fiber sizing agent and the aqueous phase system in wet papermaking, achieving uniform dispersion of carbon fibers in the aqueous phase system.

[0057] The embodiments described above are preferred embodiments, but not all embodiments that can be implemented with respect to this invention. Those skilled in the art should understand that further optimizations or combinations of this invention based on its technical principles, including changes in raw material types, proportions, and process conditions, should all be considered within the scope of protection of this invention.

Claims

1. A modified epoxy resin, characterized in that: The structure of the modified epoxy resin is as follows: ； Where 2≤m≤10, 3≤n≤6.

2. The method for preparing the modified epoxy resin as described in claim 1, characterized in that: Includes the following steps: Compound 1 was obtained by dissolving bisphenol A, bisphenol A type epoxy resin monomer with an epoxy equivalent between 180 and 190, and a catalyst in an organic solvent and carrying out a chain extension reaction. Compound 1 was reacted with diethanolamine and a catalyst in an organic solvent to undergo an amine-addition reaction to obtain compound 2; Compound 2 is subjected to a polyetheramine grafting reaction with a catalyst in an organic solvent to obtain the product; The structure of compound 1 is as follows: ； The structure of compound 2 is as follows: 。 3. The method for preparing the modified epoxy resin as described in claim 2, characterized in that: The chain extension reaction is carried out at a temperature of 120~160℃; The chain extension reaction takes 120-240 minutes; The temperature for the amine additional reaction is 100~120℃; The time for the amine-addition reaction is 120-180 min; The temperature for the polyetheramine grafting reaction is 120~140℃; The time for the polyetheramine grafting reaction is 120~240 min.

4. The method for preparing the modified epoxy resin as described in claim 2, characterized in that: The catalyst is selected from one of quaternary ammonium salts, quaternary phosphorus salts, or tertiary amine compounds; The quaternary ammonium salts include tetraethylammonium bromide and tetrabutylammonium iodide; The quaternary phosphorus salt includes tetraphenylphosphine bromide; The tertiary amine compounds include at least one of N,N-dimethylbenzylamine and N-methyldiethanolamine.

5. The method for preparing the modified epoxy resin as described in claim 2, characterized in that: The bisphenol A type epoxy resin monomer is selected from at least one of E-51, CYD-128, NPEL-128, EPLC-828 / 828A, YD-825GS, GELR-128 / 128E, and LER850; The polyetheramine is selected from one of EDR-148, EDR-176, M-600, D-230, and D-400.

6. The method for preparing the modified epoxy resin according to claim 2, characterized in that: The organic solvent is selected from at least one of propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, ethylene glycol monobutyl ether, methyl isobutyl ketone, methyl ethyl ketone, and methyl propyl ketone.

7. A sizing agent, characterized in that: By weight, it comprises 30 to 40 parts of the modified epoxy resin as described in claim 1, 1.5 to 2.5 parts of the neutralizing agent, and 60 to 70 parts of water.

8. The sizing agent as described in claim 7, characterized in that: The neutralizing agent is selected from at least one of formic acid, acetic acid, lactic acid, oxalic acid, and citric acid.

9. The method for preparing the sizing agent as described in claim 7, characterized in that: Includes the following steps: The modified epoxy resin and neutralizing agent are mixed and reacted at 50-60℃ for at least 60 minutes, and then water is added and stirred at 35-40℃ for at least 30 minutes to obtain the final product.

10. An application of the sizing agent as described in claim 7, characterized in that: It is applied to the preparation of carbon fiber paper-based composite materials in wet papermaking.

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