Preparation method of two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol

Abstract

The application discloses a preparation method of a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol, and comprises the following steps: (1) preparing a repairing agent microcapsule and a curing agent microcapsule by using an emulsion polymerization method; (2) mixing the prepared repairing agent microcapsule and the curing agent microcapsule, obtaining a two-component microcapsule solution, and adding the two-component microcapsule solution into treated paper pulp; and (3) performing papermaking, drying and calendering on the paper pulp added with the two-component microcapsule solution, so that the insulating paper is obtained. The two-glycerol ether type bisphenol F epoxy resin (DGEBF) stabilized by an emulsifier is used as a repairing agent core, the polythiol (PETMP) stabilized by the emulsifier is used as a curing agent core, and the emulsifier is cellulose nanofiber, so that the insulating paper with the self-repairing performance is prepared, the dielectric constant, the breakdown field strength, the tensile strength, the elongation at break and the thermal stability of the insulating paper are all superior to those of a traditional cellulose insulating paper, and the overall performance and the service life of the insulating paper can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of high voltage and insulation technology, and in particular to a method for preparing two-component microcapsule self-repairing insulation paper based on epoxy resin and polythiol. Background Art

[0002] Large oil-immersed transformers are the core hub for the transportation and distribution of electrical energy within power systems. Their healthy operation is crucial for the reliable power supply of the power grid. Failure of the transformer's internal insulation system is one of the main causes of failure. According to statistics and analysis of transformer accidents conducted by relevant departments, transformer insulation failures account for the vast majority of failures, with oil-paper insulation failure being the primary factor. Over the course of long-term service, the cellulose insulation paper within the transformer is subject to numerous factors, including electrical and thermal stresses and the environment, which can easily lead to aging and failure. Therefore, the performance of the insulation paper directly determines the reliability and lifespan of the transformer.

[0003] In recent years, considerable progress has been made in improving the performance of cellulose insulating paper through chemical modification and physical doping, but completely eliminating mechanical and electrical damage has been a bottleneck. Inspired by the self-repairing abilities of organisms, self-healing technologies have recently attracted considerable attention, with microcapsules showing particular promise in repairing mechanical and electrical damage to insulating materials. Composite materials obtained by mixing two-component microcapsules containing a healing agent and a curing agent can self-heal cracks. Applying microcapsule self-healing technology to cellulose-based composites has important engineering value. Summary of the Invention

[0004] To address the above shortcomings, the present invention provides a method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol, which can improve the dielectric constant, breakdown field strength, tensile strength and elongation at break compared to traditional cellulose insulating paper under the same conditions, effectively improve the overall performance and service life of the insulating paper, and can release the repair agent and curing agent in the microcapsule to achieve rapid repair when the insulating paper is damaged. The method comprises:

[0005] The prepared two-component microcapsule solution is added during the pulping and papermaking process of insulating paper. The two-component microcapsules contain repair agent microcapsules and curing agent capsules. The repair agent in the repair agent microcapsules is diglycerol ether type bisphenol F epoxy resin (DGEBF) stabilized by an emulsifier, and the curing agent in the curing agent microcapsules is polythiol (PETMP) stabilized by an emulsifier. The emulsifier is cellulose nanofiber (CNF).

[0006] A method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol, specifically comprising the following steps:

[0007] (1) Preparation of curing agent microcapsules

[0008] 1.1) Preparation of microcapsule walls: Melamine was dissolved in a 30-40 wt% formaldehyde solution and reacted at room temperature to obtain a melamine-formaldehyde prepolymer (PMF). Deionized water was added to the prepolymer at a concentration of 40-48 wt%. Triethanolamine was added to adjust the pH to 8.0-9.0, and the mixture was heated and stirred to obtain a microcapsule wall prepolymer solution.

[0009] 1.2) Preparing a core material emulsion: Dissolve CNF in deionized water, homogenize at 600-800W for 7-15 minutes, and then sonicate for 10-30 minutes to prepare a CNF aqueous suspension. Then, add polythiol to the CNF aqueous suspension and emulsify using a high-speed emulsifier to obtain a CNF-stabilized polythiol core material emulsion.

[0010] 1.3) Microcapsules are prepared by emulsion polymerization. A polythiol core material emulsion is diluted with deionized water. An acid solution is added to the polythiol core material emulsion to adjust the pH to 3-4. The emulsion is then transferred to a three-necked flask. The microcapsule wall prepolymer solution is then slowly added dropwise. The reaction is carried out at 65-75°C for 1-3 hours. After the reaction is completed, heating is stopped and stirring is continued until the solution cools to obtain a curing agent microcapsule solution. The repair agent microcapsule solution is then separated by suction filtration using a Büchner funnel, and the solution is alternately rinsed with deionized water and ethanol, and dried at room temperature to obtain melamine-formaldehyde resin-coated polythiol curing agent microcapsules as a white powder.

[0011] (2) Preparation of repair agent microcapsules

[0012] 2.1) Prepare microcapsule wall, same as step 1.1);

[0013] 2.2) Preparing an epoxy resin core material emulsion: CNF was dissolved in deionized water, homogenized at 600-800W for 7-15 minutes, and then sonicated for 10-30 minutes to prepare a CNF aqueous suspension. DGEBF was diluted and then added to the CNF aqueous suspension to obtain a mixed solution. The mixed solution was heated to 50-55°C and stirred for 5-20 minutes to promote the dispersion of DGEBF in water, thereby obtaining a CNF-stabilized DGEBF core material emulsion.

[0014] 2.3) Microcapsules were prepared by emulsion polymerization. A DGEBF core material emulsion was diluted with deionized water. An acid solution was added to the DGEBF core material emulsion to adjust the pH to 3-4. The solution was then transferred to a three-necked flask. The microcapsule wall prepolymer solution was then slowly added dropwise. The reaction was carried out at 65-75°C for 1-3 hours. After the reaction was completed, heating was stopped and stirring was continued until the solution cooled to obtain a repair agent microcapsule solution. The repair agent microcapsule solution was then separated by suction filtration using a Buchner funnel and rinsed alternately with deionized water and ethanol. The solution was dried at room temperature to obtain repair agent capsules containing diglycerol ether type bisphenol F epoxy resin coated with melamine-formaldehyde resin.

[0015] (3) preparing a 2-5 wt% solution of the prepared repair agent microcapsules and curing agent capsules in a mass ratio of 1:1 to obtain a two-component microcapsule solution;

[0016] (4) Weigh the pulp board, tear the pulp into pulp board fragments, and then soak them in deionized water for 20-30 hours to soften them for later use; then add deionized water to the beater, start the beater, and slowly add the pulp board fragments softened by deionized water into the beater and start beating. Beat until the SR reaches 38-42°, open the water valve, use a special cloth bag to catch the pulp, repeatedly knead to remove excess water, separate the kneaded blocks into small pulp blocks, let them stand for 20-36 hours to balance the moisture in the pulp, and the humidity of the pulp after moisture balance is 75-85%, thus obtaining the processed pulp;

[0017] (5) Using an electronic balance, weigh the mass of the processed pulp required for preparing the insulating paper sheet, set the dissociator to dissociate 3-4 times, with an interval of 1 minute between each dissociation, and set each dissociation to 9000-11000 revolutions. Place the weighed pulp into a dissociation container, add deionized water to one-half of the dissociation container, turn on the power, and allow the undissociated pulp to sink so that the pulp is completely dissociated by the high-speed rotating blades. After the dissociation is completed, add the prepared two-component microcapsule solution and stir manually for 5-10 minutes to obtain a fiber suspension for preparing the insulating paper sheet;

[0018] (6) The two-component microcapsule solution prepared in step (3) is added to the fiber suspension prepared in step (5), and the mixture is stirred for 3-6 minutes and then subjected to a paper former for papermaking and forming. The drying process is then performed to obtain a dried and formed insulating paper hand sheet, which is then calendered to obtain the insulating paper of the present invention.

[0019] Preferably, the particle size of the curing agent microcapsules and the repairing agent microcapsules are both 0.3-0.6 μm.

[0020] Preferably, the material of the microcapsule wall is melamine-formaldehyde resin.

[0021] Preferably, in the preparation of the microcapsule wall of step 1.1), the molar ratio of melamine to formaldehyde is 2-4:6-8, and the reaction temperature is 65-75℃.

[0022] Further preferably, in the preparation of the microcapsule wall of step 1.1), the molar ratio of melamine to formaldehyde is 3:7, and the reaction temperature is 70℃.

[0023] Preferably, in step (2), the curing agent is diluted with 10-20wt% of benzyl glycidyl ether diluent, and the mass ratio of 10-20wt% of benzyl glycidyl ether diluent to curing agent is 0.8-1.3:9-11.

[0024] Preferably, the doping concentration of the two-component microcapsule is 1-8wt%.

[0025] Further preferably, the doping concentration of the two-component microcapsule is 5wt%.

[0026] Preferably, in step 1.3), the mass ratio of the polythiol core material emulsion to deionized water is 1.8-2.5:1.

[0027] Preferably, in step 1.3), the volume ratio of the polythiol core material emulsion to the microcapsule wall prepolymer solution is 3-5.5:1; and in step 2.3), the volume ratio of the diglycidyl ether type bisphenol F epoxy resin core material emulsion to the microcapsule wall prepolymer solution is 2.5-4:1.

[0028] Preferably, in step 1.2), the mass concentration of CNF is 0.5-2wt%, and the mass ratio of polythiol to CNF is 2.5-3.5:6.5-8; and in step 2.2), the mass concentration of CNF is 1wt%, and the mass ratio of diglycidyl ether type bisphenol F epoxy resin to CNF is 2.5-3.5:6.5-8.

[0029] Preferably, the curing agent microcapsule wall thickness is 0.55μm, and the microcapsule diameter is 7.5±2μm; and the repair agent microcapsule wall thickness is 0.75μm, and the microcapsule diameter is 8.4±1.5μm.

[0030] The beneficial effects of the present application are:

[0031] 1. The present invention provides a method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol. The two-component microcapsule solution is prepared by emulsion polymerization using an emulsifier CNF, a curing agent PETMP, and a repairing agent DGEBF. The solution is then applied to the insulating paper. When microcracks are generated locally on the insulating paper, the microcapsule wall ruptures under the stress of the crack tip and fills the microcracks after curing by releasing DGEBF and PETMP. Compared with single-component repairing agent microcapsules, the present invention circumvents the defects of the microcapsule wall not being 100% resistant to penetration and slow penetration by separately microencapsulating the repairing agent and the curing agent, further improving the stability of the microcapsules in the insulating paper. The dielectric constant, breakdown field strength, tensile strength, and elongation at break of the insulating paper of the present invention are all superior to those of traditional cellulose insulating paper under the same conditions, and can effectively improve the overall performance and service life of the insulating paper.

[0032] 2. The microcapsule technology of the present invention isolates the core material from the outside world through a core-shell structure, which allows the two reactive components to be blended in the same system for stable storage, and allows the wall material to rupture under specific stress conditions, and the core material to flow out and come into contact with each other to react. Compared with the commonly used diglycerol ether type bisphenol A epoxy resin (DGEBA), diglycerol ether type bisphenol F epoxy resin (DGEBF) generally has better toughness and impact resistance. The cured product of DGEBF can exhibit more superior mechanical properties, and DGEBF has better thermal stability and chemical resistance. Therefore, in self-repair applications, DGEBF may provide better fluidity and filling capacity, which helps to repair microcracks more effectively when they appear.

[0033] 3. The present invention uses CNF as an emulsifier. CNF is known for its excellent emulsifying ability, renewability, biodegradability, biocompatibility, mechanical properties, good water dispersibility, and large specific surface area. Surfactants used in traditional emulsion polymerization methods are harmful to the environment and can sometimes remain in the core and wall materials, affecting the properties of the microcapsules. CNF also serves as a reinforcing agent for the microcapsule polymer shell. When the melamine capsule wall is formed through in-situ polymerization of the precursor using a CNF emulsion, some CNF is also incorporated into the capsule wall. However, compared to traditional surfactants, CNF is more environmentally friendly, more compatible, and less expensive, and poses no environmental pollution. The CNF-incorporated capsule wall can also significantly improve the mechanical properties of the insulating paper.

[0034] 4. The CNF-stabilized DGEBF of the present invention also undergoes a cross-linking reaction with PETMP. This cross-linking structure improves the thermal stability of the material, making it less susceptible to deformation or degradation in high-temperature environments. Furthermore, cross-linking reduces expansion and contraction of the material under changes in humidity or temperature, stabilizes the material's relative crystallinity, and enhances the thermal aging stability of the insulating paper. The cross-linking structure also improves the material's electrical insulation properties, enhancing its performance in electrical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0036] Figure 1 This is a production flow chart of the two-component microcapsule self-repairing insulation paper of the present invention;

[0037] Figure 2 This is a comparison chart of the tensile strength of the insulating paper with different doping concentrations, DGEBA insulating paper, and pure cellulose insulating paper without microcapsules added;

[0038] Figure 3 This is a comparison chart of the elongation at break of the insulating paper with different doping concentrations, DGEBA insulating paper, and pure cellulose insulating paper without microcapsules added;

[0039] Figure 4 This is a comparison chart of the breakdown field strength of the insulating paper with different doping concentrations, DGEBA insulating paper, and pure cellulose insulating paper without adding microcapsules;

[0040] Figure 5 This is a comparison chart of the dielectric constants of the insulating paper with different doping concentrations, DGEBA insulating paper, and pure cellulose insulating paper without microcapsules added;

[0041] Figure 6 It is the relative crystallinity of the insulating paper with different doping concentrations, DGEBA insulating paper, and pure cellulose insulating paper without adding microcapsules in the present invention; wherein, the horizontal axis time represents the aging time. DETAILED DESCRIPTION

[0042] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Unless otherwise defined, all technical terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

[0043] Example 1

[0044] The method for preparing the two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol in this embodiment specifically comprises the following steps:

[0045] (1) Preparation of repair agent microcapsules

[0046] 1.1) Preparation of microcapsule wall: 3.5 g of melamine was dissolved in 5.86 g of a 37 wt% formaldehyde solution and reacted at room temperature to obtain a melamine-formaldehyde prepolymer. 20 ml of deionized water was added, followed by 0.5 mol / L NaOH to adjust the pH to 8.5. The mixture was heated and stirred to obtain a microcapsule wall prepolymer solution.

[0047] 1.2) Preparation of a core material emulsion: CNFs were dissolved in deionized water, homogenized at 700 W for 10 min, and then sonicated for 20 min to obtain a 1 wt% CNF aqueous suspension. Subsequently, 30 g of polythiol was added to 75 g of the CNF aqueous suspension and emulsified using a high-speed emulsifier to obtain a CNF-stabilized polythiol core material emulsion.

[0048] 1.3) Microcapsules were prepared by emulsion polymerization. 100 g of the polythiol core material emulsion was diluted with 50 g of deionized water. 0.5 mol / L HCl was added to the polythiol core material emulsion to adjust the pH to 3.5. The solution was then transferred to a three-necked flask. The microcapsule wall prepolymer solution was then slowly added dropwise. The reaction was maintained at 70° C. for 2 h. After the reaction was complete, heating was stopped and stirring was continued until the solution cooled to obtain a curing agent microcapsule solution. The repair agent microcapsule solution was then separated by suction filtration using a Büchner funnel and rinsed alternately with deionized water and ethanol three times. The solution was dried at room temperature for 48 h to obtain melamine-formaldehyde resin-coated polythiol curing agent microcapsules as a white powder.

[0049] (2) Preparation of curing agent microcapsules

[0050] 2.1) Preparation of microcapsule wall: 3.5 g of melamine was dissolved in 5.86 g of a 37 wt% formaldehyde solution and reacted at room temperature to obtain a melamine-formaldehyde prepolymer. 20 ml of deionized water was added, followed by 0.5 mol / L NaOH to adjust the pH to 8.5. The mixture was heated and stirred to obtain a microcapsule wall prepolymer solution.

[0051] 2.2) Preparation of a core material emulsion: CNF was dissolved in deionized water, homogenized at 700 W for 10 min, and then ultrasonicated for 20 min to obtain a 1 wt% CNF aqueous suspension. DGEBF was diluted with benzyl glycidyl ether at a ratio of 1:10, and 35 g of the diluted DGEBF was added to 75 g of the CNF aqueous suspension. After emulsification using a high-speed emulsifier, the mixed solution was heated to 50°C and stirred for 10 min to promote the dispersion of DGEBF in water, thereby obtaining a CNF-stabilized DGEBF core material emulsion.

[0052] 2.3) Microcapsules were prepared by emulsion polymerization. 100 g of the prepared DGEBF core material emulsion was diluted with 50 g of deionized water. 0.5 mol / L HCl solution was added to the DGEBF core material emulsion to adjust the pH to 3.5. The mixture was then transferred to a three-necked flask. The microcapsule wall prepolymer solution was then slowly added dropwise. The mixture was kept at 70° C. for 2 h. After the reaction was complete, heating was stopped and stirring was continued until the solution cooled to obtain a repair agent microcapsule solution. The repair agent microcapsule solution was then separated by suction filtration using a Buchner funnel and rinsed alternately with deionized water and ethanol three times. The solution was then dried at room temperature for 48 h to obtain repair agent capsules containing diglycerol ether-type bisphenol F epoxy resin coated with melamine-formaldehyde resin.

[0053] (3) preparing a 3 wt % solution of the prepared repair agent microcapsules and curing agent capsules at a mass ratio of 1:1 to obtain a two-component microcapsule solution;

[0054] (4) Weigh the pulp board and tear the pulp into 1cm 2 The pulp board fragments are then soaked in deionized water for 24 hours and softened for 15 hours for standby use; deionized water is then added to the beater, the beater is started, and the pulp board fragments softened by deionized water are slowly added to the beater and beating is started. The pulping is completed when the SR reaches 38-42°. The water valve is opened, and the pulp is caught with a special cloth bag. The pulp is repeatedly kneaded to remove excess water, and the kneaded lumps are separated into small pulp pieces. The pulp is allowed to stand for 24 hours to balance the moisture in the pulp. After the moisture balance, the humidity of the pulp is 80%, and the processed pulp is obtained;

[0055] (5) Weigh 20 g of the treated pulp using an electronic balance, set the dissociator to dissociate 3 times, with an interval of 1 minute between each dissociation, and set each dissociation to 10,000 revolutions. Place the weighed pulp in a dissociation container, add deionized water to half of the dissociation container, turn on the power, and allow the undissociated pulp to sink so that the pulp is completely dissociated by the high-speed rotating blades. After the dissociation is completed, add the prepared two-component microcapsule solution and stir manually for 5-10 minutes to obtain a fiber suspension for preparing insulating paper sheets.

[0056] (6) The two-component microcapsule solution prepared in step (3) was added to the fiber suspension prepared in step (5) to a total concentration of 5 wt %. After stirring for 5 min, the mixture was subjected to papermaking and forming treatment using a paper former, and then dried at 90° C. for 10 min to obtain a dried and formed insulating paper hand sheet. The dried and formed insulating paper hand sheet was then calendered with a calendering pressure of 3 MPa and a calendering temperature of 100° C. After calendering, the insulating paper of the present invention was obtained.

[0057] Example 2: This example is different from Example 1 in that no repair agent microcapsules and curing agent microcapsules are added to the pulp, thereby preparing traditional cellulose insulation paper.

[0058] Example 3: This example is different from Example 1 in that the doping concentration of the two-component microcapsules is 1 wt%.

[0059] Example 4: This example is different from Example 1 in that the doping concentration of the two-component microcapsules is 3 wt%.

[0060] Example 5: This example is different from Example 1 in that the doping concentration of the two-component microcapsules is 8 wt%.

[0061] Example 6: This example is different from Example 1 in that the doping concentration of the two-component microcapsules is 10 wt%.

[0062] Comparative Example 1: This comparative example differs from Example 1 in that diglyceryl ether type bisphenol F epoxy resin (DGEBF) is replaced by diglyceryl ether type bisphenol A epoxy resin (DGEBA).

[0063] Comparative Example 2:

[0064] The difference between this comparative example and Example 1 is that the preparation method of the curing agent microcapsules and the repairing agent microcapsules in this comparative example is:

[0065] (1) Preparation of curing agent microcapsules

[0066] 1.1) preparing microcapsule walls, following the same steps as step 1.1) of Example 1;

[0067] 1.2) Prepare a core material emulsion by dissolving 5 g of styrene-maleic anhydride copolymer pellets in 45 g of standard NaOH solution and stirring at 85°C for 3 h to obtain a polystyrene-maleic anhydride sodium salt solution. Then, 7 g of polythiol was mixed with 55 g of the polystyrene-maleic anhydride sodium salt solution and emulsified using a high-speed emulsifier for 60 min to obtain a stable polythiol emulsion.

[0068] 1.3) Microcapsules were prepared by in situ polymerization. 0.5 mol / L HCl was added to a polythiol emulsion to adjust the pH to 3.5, which was then transferred to a three-necked flask. The microcapsule wall prepolymer solution was then slowly added dropwise. The reaction was maintained at 70°C for 2 h. After the reaction, heating was stopped and stirring was continued until the solution cooled. 21 wt% Na2CO3 was added to adjust the pH to 9.5 to obtain a microcapsule solution. The microcapsule solution was then separated by suction using a Büchner funnel and rinsed alternately with deionized water and ethanol three times. The solution was then dried at room temperature for 48 h to obtain curing agent microcapsules.

[0069] (2) Preparation of repair agent microcapsules

[0070] 2.1) preparing microcapsule walls, following the same steps as step 1.1) of Example 1;

[0071] 2.2) preparing a core material emulsion, following the same steps as step 1.2) of this comparative example;

[0072] 2.3) DGEBF was diluted with 15 wt.% benzyl glycidyl ether at a ratio of 1:10, and microcapsules were prepared by in situ polymerization. 0.5 mol / L HCl was added to the DGEBF emulsion to adjust the pH to 3.5, and the mixture was transferred to a three-necked flask. The microcapsule wall prepolymer solution was then slowly added dropwise. The mixture was kept at 70°C for 2 h. After the reaction, heating was stopped and stirring was continued until the solution cooled. 21 wt.% Na2CO3 was added to adjust the pH to 9.5 to obtain a microcapsule solution. The microcapsule solution was then separated by suction using a Buchner funnel, rinsed three times alternately with deionized water and ethanol, and dried at room temperature for 48 h to obtain the repair agent capsules.

[0073] The remaining mixing, dissociation, papermaking, drying and calendering procedures are the same as in Example 1.

[0074] Comparing the self-healing cellulose insulating paper in the above examples with conventional cellulose insulating paper reveals that the insulating paper produced by the present invention exhibits self-healing capabilities compared to unmodified paper, significantly improving the performance, safety, and reliability of the insulating paper. The test results after aging experiments are shown in the accompanying figures.

[0075] As can be seen from the above embodiments and accompanying drawings, the present invention provides a method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol. When microcracks are generated locally in the insulating paper, the microcapsule wall breaks under the stress of the crack tip, and the microcracks are filled by releasing the DGEBF repair agent and PETMP curing agent stabilized by CNF. Compared with single-component repair agent microcapsules, the present invention avoids the defects of the microcapsule wall not being 100% anti-penetration and slow penetration by respectively microencapsulating the repair agent and the curing agent, further improving the stability of the microcapsules in the insulating paper, and the dielectric constant, breakdown field strength, tensile strength and elongation at break of the insulating paper of the present invention are better than traditional cellulose insulating paper under the same conditions, which can effectively improve the overall performance and service life of the insulating paper. Compared to commonly used diglycerol ether type bisphenol A epoxy resin (DGEBA), diglycerol ether type bisphenol F epoxy resin (DGEBF) generally has better toughness and impact resistance, and the cured product of DGEBF can show more superior mechanical properties, and DGEBF has better thermal stability and chemical resistance. The present invention uses CNF as an emulsifier. CNF has excellent emulsifying ability, reproducibility, biodegradability, biocompatibility, mechanical properties, good water dispersibility and large specific surface area. In traditional emulsion polymerization, surfactants are harmful to the environment. At the same time, surfactants sometimes remain in the core material and wall material, affecting the properties of microcapsules. When the melamine capsule wall is formed by in-situ polymerization of the CNF emulsion precursor, some CNF is also mixed in the capsule wall. However, compared with traditional surfactants, it is more environmentally friendly, more compatible, and has lower cost, and does not pollute the environment. At the same time, the capsule wall mixed with CNF can significantly improve the tensile strength and elongation at break of the insulating paper. Under the operating temperature of the transformer, the DGEBF stabilized by CNF in the present invention also produces a cross-linking reaction with cellulose when reacting with polythiol (PETMP). The cross-linked structure improves the thermal stability of the material, making it less likely to deform or degrade in a high temperature environment. The relative crystallinity of the material is stable, and the thermal aging stability of the insulating paper is enhanced. In addition, cross-linking can reduce the expansion and contraction of the material under humidity changes or temperature changes, thereby enhancing the dimensional stability of the material. The cross-linked structure can also improve the material's power frequency breakdown field strength.

[0076] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol, characterized by comprising: adding a prepared two-component microcapsule solution to the pulping and papermaking process of the insulating paper, wherein the two-component microcapsules contain a repair agent microcapsule and a curing agent capsule; the repair agent in the repair agent microcapsule is a diglycerol ether type bisphenol F epoxy resin treated with an emulsifier, and the curing agent in the curing agent microcapsule is a polythiol treated with an emulsifier; and the emulsifier is cellulose nanofiber; The material of the microcapsule wall is melamine-formaldehyde resin; The specific preparation method comprises the following steps: (1) Preparation of curing agent microcapsules 1.1) Preparing a microcapsule wall: dissolving melamine in a formaldehyde solution to obtain a melamine-formaldehyde prepolymer; adding deionized water to the melamine-formaldehyde prepolymer; and adjusting the pH to 8.0-9.0 by adding triethanolamine. The mixture was stirred to obtain a microcapsule wall prepolymer solution. 1.2) preparing a polythiol core material emulsion by dissolving cellulose nanofibers in deionized water, homogenizing, and then ultrasonicating to prepare a cellulose nanofiber aqueous suspension, then adding polythiol to the cellulose nanofiber aqueous suspension and performing high-speed emulsification to obtain a polythiol core material emulsion stabilized by the cellulose nanofibers; 1.3) preparing curing agent microcapsules by emulsion polymerization, diluting the prepared polythiol core material emulsion with deionized water, adding an acid solution to the polythiol core material emulsion to adjust the pH to 3-4, then slowly adding a microcapsule wall prepolymer solution, keeping the temperature to react, cooling to obtain a curing agent microcapsule solution, and then filtering, separating, rinsing, and drying to obtain melamine-formaldehyde resin-coated polythiol curing agent microcapsules; (2) Preparation of repair agent microcapsules 2.1) Prepare microcapsule wall, same as step 1.1); 2.2) preparing a diglyceryl ether type bisphenol F epoxy resin core material emulsion, dissolving cellulose nanofibers in deionized water, homogenizing at a power of 600-800W for 7-15 minutes, and then ultrasonically treating for 10-30 minutes to prepare a cellulose nanofiber aqueous suspension, diluting the diglyceryl ether type bisphenol F epoxy resin, and adding the diluted diglyceryl ether type bisphenol F epoxy resin to the cellulose nanofiber aqueous suspension to obtain a mixed solution, and heating the mixed solution to 50-55°C to promote dispersion of the diglyceryl ether type bisphenol F epoxy resin in water to obtain a diglyceryl ether type bisphenol F epoxy resin core material emulsion stabilized by the cellulose nanofibers; 2.3) preparing repair agent microcapsules by emulsion polymerization, diluting the prepared diglycerol ether type bisphenol F epoxy resin core material emulsion with deionized water, adding an acid solution to the diglycerol ether type bisphenol F epoxy resin core material emulsion to adjust the pH to 3-4, then slowly adding a microcapsule wall prepolymer solution, keeping the temperature to react, cooling to obtain a repair agent microcapsule solution, and then filtering, separating, rinsing, and drying to obtain repair agent capsules of diglycerol ether type bisphenol F epoxy resin coated with melamine-formaldehyde resin; (3) mixing the prepared repair agent microcapsules and curing agent capsules to form a solution to obtain a two-component microcapsule solution; (4) soaking and beating the pulp board to obtain processed pulp; (5) dissociating the treated pulp, adding the two-component microcapsule solution prepared in step (3) after dissociation, and manually stirring for 5-10 minutes; (6) The paper pulp to which the two-component microcapsule solution is added is subjected to papermaking, drying, and calendering to obtain the insulating paper.

2. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 1, characterized in that: The particle sizes of the curing agent microcapsules and the repairing agent microcapsules are both 0.3-0.6 μm.

3. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 1, characterized in that: In the process of preparing the microcapsule wall in step 1.1), the molar ratio of melamine to formaldehyde is 2-4:6-8, and the reaction temperature is 65-75°C.

4. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 1, characterized in that: In the step (5), the doping concentration of the two-component microcapsules in the treated pulp is 1-8 wt%.

5. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 1, characterized in that: In the step 2.2), the diglyceryl ether type bisphenol F epoxy resin is diluted with benzyl glycidyl ether diluent.

6. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 1, characterized in that: In the step (3), the weight ratio of the repair agent microcapsules and the curing agent capsules in the two-component microcapsules is 1:

1.

7. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 1, characterized in that: In the step 1.3), the mass ratio of the polythiol core material emulsion to the microcapsule wall prepolymer solution is 3-5.5:1; in the step 2.3), the mass ratio of the diglyceryl ether type bisphenol F epoxy resin core material emulsion to the microcapsule wall prepolymer solution is 2.5-4:

1.

8. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 1, characterized in that: In the step 1.2), the mass concentration of the cellulose nanofiber aqueous suspension is 0.5-2wt%, and the mass ratio of polythiol to cellulose nanofiber is 2.5-3.5:6.5-8; in the step 2.2), the mass concentration of the cellulose nanofiber aqueous suspension is 0.5-2wt%, and the mass ratio of diglycerol ether type bisphenol F epoxy resin to cellulose nanofiber is 2.5-3.5:6.5-8.

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