Preparation method of bi-component microcapsule self-repairing insulation paper based on epoxy resin and polymercaptan

Abstract

The invention discloses a preparation method of two-component microcapsule self-repairing insulation paper based on epoxy resin and polymercaptan. The preparation method comprises the following steps: (1) preparing a repairing agent microcapsule and a curing agent microcapsule by an emulsion polymerization method; (2) mixing the prepared repairing agent microcapsule and curing agent capsule to obtain a bi-component microcapsule solution, and adding the bi-component microcapsule solution into the treated paper pulp; and (3) performing papermaking, drying and calendaring on the paper pulp added with the bi-component microcapsule solution to obtain the insulation paper. According to the invention, diglycerol ether type bisphenol F epoxy resin (DGEBF) stabilized by an emulsifier is adopted as a core of a repairing agent, polythiol (PETMP) stabilized by the emulsifier is adopted as a core of a curing agent, and the emulsifier is cellulose nanofiber, so that the insulating paper with 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 insulation paper are superior to those of traditional cellulose insulation paper, and the overall performance and the service life of the insulation 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 a two-component microcapsule self-repairing insulation paper based on epoxy resin and polythiol. Background Art

[0002] Large oil-immersed transformers are the core hub of power transportation and distribution in the power system, and their healthy operation plays an important role in the reliable power supply of the power grid. The failure of the insulation system inside the transformer is one of the main causes of its failure. According to the statistics of transformer accidents by relevant departments, transformer insulation failure accounts for the vast majority, among which oil-paper insulation failure is the main factor. The cellulose insulation paper inside the transformer is affected by many factors such as electrical stress, thermal stress, and environment during long-term service, which can easily cause the insulation paper to age and fail. Therefore, the performance of the insulation paper directly determines the reliability and life of the transformer operation.

[0003] In recent years, considerable progress has been made in improving the performance of cellulose insulation paper through chemical modification and physical doping, but completely eliminating its mechanical and electrical damage has always been a bottleneck. Inspired by the self-repairing ability of organisms, self-repairing technology has recently attracted considerable attention, and microcapsules are particularly promising in repairing mechanical and electrical damage to insulating materials. Composite materials obtained by mixing two-component microcapsules containing a repair agent and a curing agent can self-repair cracks. Applying microcapsule self-repairing technology to cellulose-based composite materials has important engineering value. Summary of the invention

[0004] In view of 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 better than traditional cellulose insulating paper under the same conditions, and can effectively improve the overall performance and service life of the insulating paper. When the insulating paper is damaged, the repair agent and curing agent in the microcapsule can be released to achieve rapid repair. The method comprises:

[0005] The prepared two-component microcapsule solution is added during 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 (DGEBF) stabilized by an emulsifier, and the curing agent in the curing agent microcapsule is a polythiol (PETMP) stabilized by an emulsifier; and 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) preparing microcapsule wall, dissolving melamine in a 30-40wt% formaldehyde solution, reacting at room temperature to obtain a melamine-formaldehyde prepolymer (PMF), adding deionized water at a prepolymer concentration of 40-48wt.%, adding triethanolamine to adjust the pH to 8.0-9.0, heating and stirring to obtain a microcapsule wall prepolymer solution;

[0009] 1.2) preparing a core material emulsion, dissolving CNF in deionized water, homogenizing at a power of 600-800W for 7-15min, and then ultrasonically treating for 10-30min to prepare a CNF water suspension, then adding polythiol to the CNF water suspension, and emulsifying with a high-speed emulsifier to obtain a CNF-stabilized polythiol core material emulsion;

[0010] 1.3) preparing microcapsules by emulsion polymerization, diluting the polythiol core material emulsion with deionized water, adding an acid solution to the polythiol core material emulsion to adjust the pH to 3-4, and then transferring to a three-necked flask, and then slowly dripping the microcapsule wall prepolymer solution, and keeping the reaction at 65-75° C. for 1-3 hours. After the reaction is completed, stop heating, and continue stirring until the solution is cooled to obtain a curing agent microcapsule solution; then filter and separate the repair agent microcapsule solution with a Buchner funnel, and rinse it alternately with deionized water and ethanol, and dry it at room temperature to obtain a melamine-formaldehyde resin-coated polythiol curing agent microcapsule, which is a white powder;

[0011] (2) Preparation of repair agent microcapsules

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

[0013] 2.2) preparing an epoxy resin core material emulsion, dissolving CNF in deionized water, homogenizing at a power of 600-800w for 7-15min, and then ultrasonically treating for 10-30min to prepare a CNF water suspension, diluting DGEBF, and adding the diluted DGEBF to the CNF water suspension to obtain a mixed solution, heating the mixed solution to 50-55°C and stirring for 5-20min to promote the dispersion of DGEBF in water, and obtaining a CNF-stabilized DGEBF core material emulsion;

[0014] 2.3) Prepare microcapsules by emulsion polymerization, dilute the DGEBF core material emulsion with deionized water, add acid solution to the DGEBF core material emulsion to adjust the pH to 3-4, transfer to a three-necked flask, and then slowly drip the microcapsule wall prepolymer solution, keep warm at 65-75°C for 1-3 hours, stop heating after the reaction, continue stirring until the solution cools down to obtain a repair agent microcapsule solution, and then separate the repair agent microcapsule solution by suction filtration with a Buchner funnel, and rinse with deionized water and ethanol alternately, and dry at room temperature to obtain a repair agent capsule of 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 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 to start beating, and beat until the SR is 38-42°, open the water valve, catch the pulp with a special cloth bag, repeatedly knead to remove excess water, separate the kneaded lumps into small pulp blocks, and let them stand for 20-36 hours to balance the moisture in the pulp. After the moisture is balanced, the humidity of the pulp is 75-85%, and the treated pulp is obtained;

[0017] (5) Weigh the mass of the processed pulp required for preparing the insulating paper sheet using an electronic balance, set the dissociator to dissociate 3-4 times, with an interval of 1 minute between each dissociation, set each dissociation to 9000-11000 revolutions, put 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) Add the two-component microcapsule solution prepared in step (3) to the fiber suspension prepared in step (5), stir for 3-6 minutes, and then use a paper former to perform papermaking and forming treatment, and then perform a drying process to obtain a dried and formed insulating paper hand sheet, and then perform a calendering treatment to obtain the insulating paper of the present invention.

[0019] Preferably, the particle sizes 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 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.

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

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

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

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

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

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

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

[0030] The beneficial effects of the present invention 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, using emulsifier CNF, curing agent PETMP, and repairing agent DGEBF to prepare a two-component microcapsule solution by emulsion polymerization, and apply it to insulating paper. 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 after the DGEBF and PETMP are released and cured. Compared with the single-component repairing agent microcapsule, the present invention circumvents the defects of the microcapsule wall not being 100% resistant to penetration and slow penetration by microencapsulating the repairing agent and the curing agent separately, further improving the stability of the microcapsule 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 better than those of the 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, so that the two reactive components can be blended in the same system for stable storage, and the wall material can be broken under specific stress conditions, and the core material can flow out and contact 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, and the cured product of DGEBF can show 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 has excellent emulsification ability, renewability, biodegradability, biocompatibility, mechanical properties, good water dispersibility and large specific surface area. Surfactants in traditional emulsion polymerization are harmful to the environment, and surfactants sometimes remain in the core material and wall material, affecting the properties of microcapsules. At the same time, CNF is also used as a reinforcing agent for the microcapsule polymer shell. When the melamine capsule wall is formed by in-situ polymerization of the CNF emulsion precursor, some CNF will also be mixed in the capsule wall. However, compared with traditional surfactants, CNF is more environmentally friendly, more compatible, and has lower cost, and does not pollute the environment. The capsule wall mixed with CNF can also greatly improve the mechanical properties of insulating paper.

[0034] 4. The CNF-stabilized DGEBF of the present invention will also produce a cross-linking reaction with cellulose when reacting with PETMP. The cross-linking structure improves the thermal stability of the material, making it less likely to deform or degrade in a high temperature environment. In addition, cross-linking can reduce the expansion and contraction of the material under humidity changes or temperature changes, stabilize the relative crystallinity of the material, and enhance the thermal aging stability of the insulating paper. The cross-linking structure can also improve the electrical insulation performance of the material, making it perform better in electrical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order 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 for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[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, the DGEBA insulating paper, and the pure cellulose insulating paper without adding microcapsules;

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

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

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

[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 protection scope of the present invention is not limited by the specific embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention, etc. 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) preparing microcapsule wall, dissolving 3.5 g melamine in 5.86 g 37 wt % formaldehyde solution, reacting at room temperature to obtain melamine-formaldehyde prepolymer, adding 20 ml deionized water, and then adding 0.5 mol / L NaOH to adjust the pH to 8.5, heating and stirring to obtain a microcapsule wall prepolymer solution;

[0047] 1.2) preparing a core material emulsion, dissolving CNF in deionized water, homogenizing at a power of 700 W for 10 min, and then ultrasonically treating for 20 min to prepare a 1 wt% CNF aqueous suspension, then adding 30 g of polythiol to 75 g of the CNF aqueous suspension, and emulsifying with a high-speed emulsifier to obtain a CNF-stabilized polythiol core material emulsion;

[0048] 1.3) preparing microcapsules by emulsion polymerization, taking 100g of the polythiol core material emulsion and diluting it with 50g of deionized water, adding 0.5mol / L HCl to the polythiol core material emulsion to adjust the pH to 3.5, and then transferring it to a three-necked flask, and then slowly dripping the microcapsule wall prepolymer solution, keeping the temperature at 70°C for 2h, stopping heating after the reaction, and continuing to stir until the solution cools to obtain a curing agent microcapsule solution; then filtering the repair agent microcapsule solution with a Buchner funnel, and washing it with deionized water and ethanol alternately for 3 times, and drying it at room temperature for 48h, so as to obtain a melamine-formaldehyde resin-coated polythiol curing agent microcapsule, which is a white powder;

[0049] (2) Preparation of curing agent microcapsules

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

[0051] 2.2) Prepare the core material emulsion, dissolve CNF in deionized water, homogenize at a power of 700 W for 10 min, and then ultrasonically treat for 20 min to prepare a 1 wt% CNF water suspension; dilute DGEBF with benzyl glycidyl ether at a ratio of 1:10, add 35 g of the diluted DGEBF to 75 g of the CNF water suspension, emulsify with a high-speed emulsifier, heat the mixed solution to 50 ° C and stir for 10 min to promote the dispersion of DGEBF in water, and obtain a DGEBF core material emulsion stabilized by CNF;

[0052] 2.3) Prepare microcapsules by emulsion polymerization, take 100g of the prepared DGEBF core material emulsion and dilute it with 50g of deionized water, add 0.5mol / L HCl solution to the DGEBF core material emulsion to adjust the pH to 3.5, and then transfer it to a three-necked flask, and then slowly drip the microcapsule wall prepolymer solution, keep it at 70°C for 2h, stop heating after the reaction, continue stirring until the solution cools down, and obtain a repair agent microcapsule solution, and then separate the repair agent microcapsule solution by suction filtration with a Buchner funnel, and rinse it with deionized water and ethanol alternately for 3 times, and dry it at room temperature for 48h, so as to obtain a repair agent capsule of 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 in a mass ratio of 1:1 to obtain a two-component microcapsule solution;

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

[0055] (5) Weigh 20 g of the treated pulp with 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. Put 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 insulating paper sheets;

[0056] (6) The two-component microcapsule solution prepared in step (3) is added to the fiber suspension prepared in step (5) to obtain a total concentration of 5 wt % of the two-component microcapsules. After stirring for 5 min, the mixture is 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 is then subjected to calendering treatment. The calendering pressure is set to 3 MPa and the calendering temperature is set to 100° C. After calendering, the insulating paper of the present invention is 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 to prepare 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 is different 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 wall, the steps are the same as step 1.1) of Example 1;

[0067] 1.2) preparing a core material emulsion, weighing 5 g of styrene-maleic anhydride copolymer particles and dissolving them in 45 g of a standard NaOH solution, stirring at 85° C. for 3 h to obtain a polystyrene-maleic anhydride sodium salt solution, then weighing 7 g of polythiol and mixing it in 55 g of the polystyrene-maleic anhydride sodium salt solution, and emulsifying it with a high-speed emulsifier for 60 min to obtain a stable polythiol emulsion;

[0068] 1.3) preparing microcapsules by in-situ polymerization, adding 0.5 mol / L HCl to the polythiol emulsion to adjust the pH to 3.5, then transferring to a three-necked flask, then slowly dripping the microcapsule wall prepolymer solution, keeping the temperature at 70°C for 2 hours, stopping heating after the reaction, continuing to stir until the solution is cooled, adding 21 wt% Na2CO3 to adjust the pH to 9.5, and obtaining a microcapsule solution; then filtering the microcapsule solution with a Buchner funnel, and washing it alternately with deionized water and ethanol for 3 times, and drying it at room temperature for 48 hours, to obtain a curing agent microcapsule;

[0069] (2) Preparation of repair agent microcapsules

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

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

[0072] 2.3) After diluting DGEBF with 15wt.% benzyl glycidyl ether diluent at a ratio of 1:10, microcapsules were prepared by in-situ polymerization, 0.5mol / L HCl was added to the DGEBF emulsion to adjust the pH to 3.5, and then transferred to a three-necked flask, and then the microcapsule wall prepolymer solution was slowly dripped, and the reaction was kept at 70°C for 2h. After the reaction was completed, heating was stopped, and stirring was continued until the solution was cooled, and 21wt% Na2CO3 was added to adjust the pH to 9.5 to obtain a microcapsule solution; the microcapsule solution was then separated by suction filtration using a Buchner funnel, and rinsed with deionized water and ethanol alternately for 3 times, and dried at room temperature for 48h to obtain a repair agent capsule;

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

[0074] Comparing the cellulose self-repairing insulating paper in the above example with the traditional cellulose insulating paper, the insulating paper prepared by the present invention has self-repairing ability compared with the unmodified insulating paper, which significantly improves the performance, safety and reliability of the insulating paper. After the aging experiment, the test results are shown in the attached figure.

[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 the single-component repair agent microcapsule, the present invention avoids the defects that the capsule wall microcapsule wall cannot be 100% anti-penetration and slow penetration by respectively encapsulating the repair agent and the curing agent, and further improves the stability of the microcapsule 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 better than those of traditional cellulose insulating paper under the same conditions, and the overall performance and service life of the insulating paper can be effectively improved. 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, and the cured product of DGEBF can show more superior mechanical properties, and the thermal stability and chemical resistance of DGEBF are better. The present invention uses CNF as an emulsifier. CNF has excellent emulsifying ability, renewability, biodegradability, biocompatibility, mechanical properties, good water dispersibility and large specific surface area. In the traditional emulsion polymerization method, surfactants are harmful to the environment, and surfactants sometimes remain in the core material and wall material to affect the properties of microcapsules. When the melamine capsule wall is formed by in-situ polymerization of the CNF emulsion precursor, part of the CNF is also mixed in the capsule wall, but compared with the traditional surfactant, 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 greatly improve the tensile strength and elongation at break of the insulating paper. In the present invention, under the working temperature of the transformer, the DGEBF stabilized by CNF will also produce a cross-linking reaction of cellulose when reacting with polythiol (PETMP), and the cross-linking structure improves the thermal stability of the material, making it difficult to deform or degrade in a high temperature environment, and the relative crystallinity of the material is stable, and the thermal aging stability of the insulating paper is enhanced. Moreover, cross-linking can reduce the expansion and contraction of the material under humidity changes or temperature changes, and enhance the dimensional stability of the material. The cross-linked structure can also improve the material's power frequency breakdown field strength.

[0076] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol, characterized in that: include: Adding the prepared two-component microcapsule solution during the pulping and papermaking process of the insulating paper, wherein the two-component microcapsules contain a repairing agent microcapsule and a curing agent capsule; The repair agent in the repair agent microcapsule is diglycerol ether type bisphenol F epoxy resin treated with an emulsifier, and the curing agent in the curing agent microcapsule is polythiol treated with an emulsifier; the emulsifier is cellulose nanofiber.

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 it comprises the following steps: (1) Preparation of curing agent microcapsules 1.1) preparing microcapsule wall, dissolving melamine in formaldehyde solution to obtain melamine-formaldehyde prepolymer, adding deionized water to the melamine-formaldehyde prepolymer, adding triethanolamine to adjust the pH to 8.0-9.0, stirring, and preparing microcapsule wall prepolymer solution; 1.2) preparing a core material emulsion, dissolving cellulose nanofibers in deionized water, homogenizing and then ultrasonically treating to obtain a cellulose nanofiber aqueous suspension or a cellulose nanocrystal aqueous suspension, then adding polythiol to the cellulose nanofiber aqueous suspension or the cellulose nanocrystal aqueous suspension, and emulsifying at high speed to obtain a polythiol core material emulsion stabilized by cellulose nanofibers; 1.3) preparing microcapsules by emulsion polymerization, taking the prepared polythiol core material emulsion and diluting it with deionized water, adding an acid solution to the polythiol core material emulsion to adjust the pH to 3-4, then slowly dripping the microcapsule wall prepolymer solution, keeping the temperature for reaction, cooling, obtaining a curing agent microcapsule solution, and then filtering and separating, rinsing, and drying to obtain a curing agent microcapsule coated with melamine-formaldehyde resin polythiol; (2) Preparation of repair agent microcapsules 2.1) preparing microcapsule wall, same as step 1.1); 2.2) preparing an epoxy resin core material emulsion, dissolving cellulose nanofibers in deionized water, homogenizing at a power of 600-800w for 7-15min, and then ultrasonically treating for 10-30min to prepare a cellulose nanofiber aqueous suspension or a cellulose nanocrystal aqueous suspension, diluting a diglyceryl ether type bisphenol F epoxy resin, and adding the diluted diglyceryl ether type bisphenol F epoxy resin to the cellulose nanofiber aqueous suspension or the cellulose nanocrystal aqueous suspension to obtain a mixed solution, heating the mixed solution to 50-55°C to promote the dispersion of the diglyceryl ether type bisphenol F epoxy resin in water, and obtaining a diglyceryl ether type bisphenol F epoxy resin core material emulsion stabilized by cellulose nanofibers; 2.3) preparing microcapsules by emulsion polymerization, taking the prepared diglycerol ether type bisphenol F epoxy resin core material emulsion and diluting it 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 dripping the microcapsule wall prepolymer solution, keeping the temperature for reaction, cooling, obtaining a repair agent microcapsule solution, and then filtering and separating, rinsing, and drying to obtain a repair agent capsule of diglycerol ether type bisphenol F epoxy resin coated with melamine-formaldehyde resin; (3) mixing the prepared repair agent microcapsules and curing agent capsules into 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 the 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.

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: The particle sizes of the curing agent microcapsules and the repairing agent microcapsules are both 0.3-0.6 μm.

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: The material of the microcapsule wall is melamine-formaldehyde resin.

5. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 2, 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.

6. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 2, characterized in that: In the step (5), the doping concentration of the dual-component microcapsules in the treated pulp is 1-8 wt %.

7. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 2, characterized in that: In the step (2), the curing agent is diluted with benzyl glycidyl ether diluent.

8. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 2, 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.

9. The method for preparing a two-component microcapsule self-repairing insulating paper based on epoxy resin and polythiol according to claim 2, 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 diglycerol ether type bisphenol F epoxy resin core material emulsion to the microcapsule wall prepolymer solution is 2.5-4:

1.

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

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