Preparation method of high-degradation epoxy resin and insulating material

Abstract

The invention provides high-degradation epoxy resin and a preparation method of an insulating material, and relates to the technical field of epoxy resin, the molecular structural formula of the high-degradation epoxy resin is # imgabs0 #, R1 is Cn1H2n1, n1 is equal to 1-6, R2 is Cn2H2n2, n2 is equal to 1-6, R3 is Cn3H2n3 + 1 or Cn3H2n3OC3H5O, n3 is equal to 0-6, R4 is Cn4H2n4 + 1 or Cn4H2n4OC3H5O, and n4 is equal to 0-6; secondly, the invention also provides a preparation method of the high-degradation epoxy resin, and the method comprises the following steps: preparing 1, 2, 4, 5-tetrahydroxyphenol, aliphatic ketone and p-toluenesulfonic acid according to a molar ratio, and preparing a polyhydroxy compound with condensed ring ketal as a molecular skeleton; then a polyhydroxy compound, epichlorohydrin and a catalyst which are prepared according to the molar ratio are subjected to a ring-opening reaction, a ring-closing reaction and the like, and faint yellow condensed ring ketal epoxy resin is obtained; the high-degradation epoxy resin disclosed by the invention has the characteristics of mild degradation conditions and high degradation speed.

Description

Technical Field

[0001] The invention relates to the technical field of epoxy resins, and in particular to a high-degradation, low-viscosity condensed ring ketal-based epoxy resin and an insulating material. Background Art

[0002] Epoxy resin cured products have excellent insulation, mechanical and chemical stability, and have been widely used as core insulating materials for precision electronic device packaging, advanced electrical equipment manufacturing, and high-end power equipment. However, the highly stable three-dimensional cross-linked network formed after the epoxy material is cross-linked and cured makes it difficult to degrade and recycle. Therefore, retired or discarded epoxy insulation materials have problems of environmental pollution and waste of resources. The development of degradable epoxy resin materials and the efficient deconstruction of the epoxy three-dimensional cross-linked network have become the key to overcoming this challenge.

[0003] In existing research, Zhang Daohong et al. from South-Central University for Nationalities (Nature Sustainability 2020, 3, 29-34) constructed a hexahydrotriazine-based six-membered cyclic skeleton in epoxy resin, and used the rupture of the CN bond in the hexahydrotriazine-based skeleton under strong acid conditions to decompose the epoxy resin into small molecular compounds such as formaldehyde and amines, thereby achieving chemical degradation of the epoxy resin material. However, the limitation of this method is that the degradation conditions of epoxy resin are relatively harsh, and only strongly acidic conditions can achieve the chemical degradation of the above-mentioned epoxy materials. However, strongly acidic solutions will also aggravate environmental pollution, so this method is not environmentally friendly.

[0004] Some researchers have also introduced polybenzene ring conjugated structures that can respond to ultraviolet radiation and various electromagnetic waves into the epoxy cross-linked network (Mater. Horiz 2022, 9, 1495-1502). The response characteristics of the conjugated structure to external radiation are used to trigger free radical reactions, causing the chemical bonds in the epoxy resin molecules to break, ultimately achieving the purpose of degrading the epoxy resin material. However, the degradation reaction of epoxy materials caused by this external radiation is often uncontrollable, and the degradation efficiency is low, making it difficult to achieve efficient and gentle degradation of epoxy materials.

[0005] The existing bisphenol A epoxy resin molecules have a high content of rigid benzene rings and poor chain segment mobility. When the resin is cross-linked to form a three-dimensional network, it is difficult for chemical degradation agents to effectively penetrate into the network. At the same time, the bond energy of the chemical bonds in the cross-linked network is large and the stability of the chain segments is high. High temperature conditions and strong acid and alkaline solutions are required to promote the breaking of chemical bonds in the epoxy cross-linked network.

[0006] Therefore, it is urgent to provide an epoxy resin with mild degradation conditions. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In view of the deficiencies of the prior art, the present invention provides a method for preparing a highly degradable epoxy resin and an insulating material to solve the technical problems of environmental pollution when the epoxy resin is degraded by strong acid, external radiation, etc. in the prior art.

[0009] (II) Technical solution

[0010] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0011] The first aspect of the present invention provides a highly degradable epoxy resin, the molecular structure of which is:

[0012]

[0013] Where R1 is C n1 H 2n1 , n1=1~6, R2 is C n2 H 2n2 , n2=1~6, R3 is C n3 H 2n3+1 or C n3 H 2n3 OC3H5O, n3=0~6, R4 is C n4 H 2n4+1 or C n4 H 2n4 OC3H5O, n4=0~6.

[0014] The second aspect of the present invention further provides a method for preparing the above-mentioned highly degradable epoxy resin, the method comprising:

[0015] Prepare 1,2,4,5-tetrahydroxyphenol, aliphatic ketone and p-toluenesulfonic acid in a molar ratio of 1:2:0.1;

[0016] Put 1,2,4,5-tetrahydroxyphenol and fatty ketone into organic solvent A dichloromethane, stir to completely dissolve them under heating conditions of 60-120°C, then add p-toluenesulfonic acid and stir for 4-8 hours; after the reaction is complete, filter and evaporate the excess organic solvent A to obtain a polyhydroxy compound with condensed ring ketal as a molecular skeleton;

[0017] Prepare a polyol, epichlorohydrin and a catalyst in a molar ratio of (0.5-1.5):(3-20):(0.001-0.1);

[0018] The polyhydroxy compound and epichlorohydrin are heated and mixed in a container, and after being dissolved to form a uniform mixed solution, a catalyst is added, and the mixture is heated and stirred at 60 to 150° C. until the ring-opening reaction is completed; wherein the product of the ring-opening reaction is detected by liquid chromatography, and when the polyhydroxy compound is completely converted into chlorohydrin ether, the ring-opening reaction is completed;

[0019] After the ring-opening reaction is completed, the heating temperature is adjusted to 60-120° C., and a 50% mass fraction NaOH solution is added dropwise at a feeding rate of 1-5 seconds / drop under a vacuum condition of 0.06-0.1 MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction;

[0020] After the ring-closing reaction is completed, the vacuum condition is removed, and an organic solvent B is added to the reaction system to dissolve the resin organic phase to obtain an organic solution organic phase in which the epoxy resin is dissolved. The NaCl inorganic salt in the organic phase of the obtained organic solution is separated by suction filtration, and then the obtained product is heated (100° C. to 150° C.) to remove the organic solvent B in the reaction system to obtain a highly degradable epoxy resin.

[0021] Furthermore, the organic solvent A is any one of dichloromethane, ethyl acetate, benzene, ether, toluene, methanol and ethanol.

[0022] Furthermore, the catalyst is any one of benzyltriethylammonium chloride, tetrabutylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, tributylamine, polyethylene glycol dialkyl ether, and cyclic crown ether.

[0023] Furthermore, the fatty ketone is one or more of hydroxyacetone, 1-hydroxy-2-butanone, 4-hydroxy-2-butanone, 5-hydroxy-2-pentanone, 5-hydroxy-3-pentanone, 1,3-dihydroxyacetone, 1,4-dihydroxybutanone, and 1,5-dihydroxypentanone.

[0024] Furthermore, the organic solvent B is one or more of methyl isobutyl ketone, acetone, butanone, methyl ethyl ketone, cyclohexanone, 1,4-dioxane, benzene and toluene.

[0025] A third aspect of the present invention further provides a method for preparing an epoxy insulating material using the above-mentioned highly degradable epoxy resin, the method comprising:

[0026] Prepare highly degradable epoxy resin, anhydride curing agent and amine accelerator in a molar ratio of 1: (0.8-1.2): (0.005-0.02);

[0027] Put the high-degradable epoxy resin and the acid anhydride curing agent into a reaction kettle, heat and stir at 60-120° C., and after being mixed uniformly, vacuum degassing for 30-90 minutes at 0.08-0.1 MPa, add an amine accelerator, and continue vacuum degassing for 5-10 minutes to obtain a mixed liquid;

[0028] The mixed liquid is poured into a mold preheated to 80°C under a vacuum condition of 0.1Mpa using a vacuum pouring device, with a pouring rate of 3-6mL / s; after pouring, the vacuum condition is maintained for 10-20min, the mold is transferred to an oven, and the curing program is set to pre-curing 80°C / 6h+post-curing 120°C / 6-12h. After curing, the sample in the mold is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material.

[0029] Furthermore, the acid anhydride curing agent is one or more of hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride and methylnadic anhydride.

[0030] Furthermore, the amine accelerator is one or more of aliphatic amine, alicyclic amine, aromatic amine, and heterocyclic amine accelerators.

[0031] (III) Beneficial effects

[0032] The present invention provides a method for preparing a highly degradable epoxy resin and an insulating material, which has the following beneficial effects compared with the prior art:

[0033] 1. The condensed ring ketal-based epoxy resin molecule provided in the present application uses a benzene ring-condensed two-membered cyclic ketal as the main molecular skeleton of the resin. The dynamic covalent bonds of the ketal in the molecule can give the three-dimensional cross-linked network the ability to quickly respond to changes in external temperature and pH, so that the epoxy material can achieve the ring opening and chemical bond breaking of the condensed ring skeleton only in a weakly acidic solution, thereby achieving the purpose of efficiently degrading epoxy insulating materials under mild degradation conditions.

[0034] 2. The condensed ring ketal skeleton in the epoxy resin molecule provided in the present application almost presents a planar structure, and the dihedral angle on the plane of the condensed ring skeleton is close to 0°, such as Figure 2 As shown. The multi-branched structure on both sides of the condensed ring skeleton can effectively regulate the free volume ratio within the molecule, making it have a higher free volume ratio within the molecule than bisphenol A epoxy resin. In addition, the resin molecular chain is shorter than bisphenol A resin, and the ratio of rigid groups within the molecule is also lower. Therefore, the condensed ring ketal-based epoxy resin shows a lower process viscosity, which can improve the wetting effect between the resin matrix and the inorganic reinforcing filler, thereby reducing the microscopic defects in the composite material, so as to ensure the stability of the high service performance of the condensed ring ketal-based epoxy insulation material.

[0035] 3. Compared with bisphenol A epoxy resin, the condensed ring ketal-based epoxy resin provided in this application has a roughly equal bandgap width and a similar molecular energy level structure. The bandgap width range of both is 5.3 to 5.6 eV. The wide bandgap energy level structure also gives the condensed ring ketal-based epoxy resin a good intrinsic insulation ability. At the same time, by designing the molecular structure of the fatty ketone during the construction of the condensed ring ketal skeleton, it is also possible to adjust the functionality and number of branches of the condensed ring ketal-based epoxy resin, thereby regulating the crosslinking density, free volume and network rigidity and flexibility of the epoxy insulating material after crosslinking and curing. This also greatly broadens the adjustable performance range of the epoxy insulating material, thereby realizing on-demand regulation of the service performance of the material in multiple application scenarios such as high insulation.

[0036] 4. The condensed ring ketal-based epoxy insulating material provided by the present application has a higher bulk modulus, shear modulus and Young's modulus than the bisphenol A epoxy insulating material, and the ratio of the bulk modulus to the Young's modulus (reflecting toughness) of the insulating material is also higher than that of the bisphenol A epoxy insulating material, which also makes the condensed ring ketal-based epoxy insulating material have a higher mechanical modulus, mechanical strength and toughness. The excellent mechanical properties of the epoxy insulating material can greatly reduce the risk of cracking of the material, thereby greatly improving the safety, stability and operational reliability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 is the mass change curve of the degradation process of the epoxy insulation material samples in Examples 1, 2, 3 and 4 and Comparative Examples 1 and 2;

[0039] Figure 2 is a schematic diagram of the planar skeleton and dihedral angles of the condensed ring ketal molecule in Implementation 1;

[0040] Figure 3 is the NMR of the condensed ring ketal epoxy resin molecule in Example 1 1 H result schematic diagram;

[0041] Figure 4 is the NMR of the condensed ring ketal epoxy resin molecule in Example 1 13 C. Schematic diagram of the results;

[0042] Figure 5 is the NMR of the condensed ring ketal epoxy resin molecule in Example 2 1H result schematic diagram;

[0043] Figure 6 is the NMR of the condensed ring ketal epoxy resin molecule in Example 2 13 C Schematic diagram of the results. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] In order to overcome the problems of low degradation efficiency and serious environmental pollution when existing degradable epoxy resin materials are degraded by strong acid, external radiation, etc., as well as the problem that it is difficult to coordinate the degradability with other service performance. The main ideas of this application are:

[0046] According to the multi-dimensional performance requirements of epoxy materials in high-insulation operating scenarios in high-end power equipment, the topological structure of the epoxy cross-linking network is designed, and then a condensed ring ketal-based epoxy resin with a planar condensed ring molecular skeleton and a large number of branches is constructed. The condensed ring ketal-based epoxy resin has the characteristics of high degradation and low viscosity.

[0047] The molecular structure of the condensed ring ketal epoxy resin is:

[0048]

[0049] Among them, affected by the structure of the fatty ketone reaction reagent, R1 is C n1 H 2n1 , n1=1~6, R2 is C n2 H 2n2 , n2=1~6, R3 is C n3 H 2n3+1 or C n3 H 2n3 OC3H5O, n3=0~6, R4 is C n4 H 2n4+1 or C n4 H 2n4 OC3H5O, n4=0~6.

[0050] In order to obtain the condensed ring ketal-based epoxy resin with the above structure, the present application also provides a corresponding preparation method, which comprises:

[0051] Prepare 1,2,4,5-tetrahydroxyphenol, aliphatic ketone and p-toluenesulfonic acid in a molar ratio of 1:2:0.1;

[0052] Put 1,2,4,5-tetrahydroxyphenol and fatty ketone into organic solvent A dichloromethane, stir mechanically to completely dissolve them under heating conditions of 60-120°C, then add p-toluenesulfonic acid and stir for 4-8 hours; after the reaction is complete, filter and evaporate the excess organic solvent A to obtain a polyhydroxy compound with condensed ring ketal as a molecular skeleton;

[0053] The reaction equation is:

[0054]

[0055] Where R = C n5 H 2n5 OH, n5=1~6; R0=C n0 H 2n0+1 or C n0 H 2n0 OH, n0=1~6.

[0056] Prepare a polyol, epichlorohydrin and a catalyst in a molar ratio of (0.5-1.5):(3-20):(0.001-0.1);

[0057] Ring-opening reaction: heat and mix the polyhydroxy compound and epichlorohydrin in a container, and after dissolving to form a uniform mixed solution, add a catalyst, and heat and stir at 60-150°C until the ring-opening reaction is completed (generally, the heating and stirring time is 4-12 hours); wherein, the product of the ring-opening reaction is detected by liquid chromatography, and when the polyhydroxy compound is completely converted into chlorohydrin ether, it indicates that the ring-opening reaction is completed;

[0058] Among them, the ring-opening reaction equation taking R=CH2OH and R0=CH3 as an example is:

[0059]

[0060] The ring-opening reaction equation taking R=CH2OH, R0=CH2OH as an example is:

[0061]

[0062] Ring-closing reaction: After the ring-opening reaction is completed, the heating temperature is adjusted to 60-120°C, and a 50% mass fraction NaOH solution is added dropwise at a feeding rate of 1-5 seconds / drop under a vacuum condition of 0.06-0.1MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction; wherein, under the heating temperature of 60-120°C, the water in the reaction system is heated and distilled, and leaves the reaction flask in the form of steam, and then the water vapor is condensed and enters the oil-water separator in the form of liquid phase, and the water phase is separated from the reaction system in the separator, thereby avoiding the water phase from participating in side reactions such as hydrolysis caused by the ring-closing reaction.

[0063] Among them, the closed-loop reaction equation taking R=CH2OH and R0=CH3 as an example is:

[0064]

[0065] The closed-loop reaction equation taking R=CH2OH, R0=CH2OH as an example is:

[0066]

[0067] After the ring-closing reaction is completed, the vacuum condition is removed, and an organic solvent B is added to the reaction system to dissolve the resin organic phase to obtain an organic solution organic phase in which the epoxy resin is dissolved. The NaCl inorganic salt in the organic phase of the obtained organic solution is separated by suction filtration, and then the obtained product is heated (100° C. to 150° C.) to remove the organic solvent B in the reaction system to obtain a highly degradable epoxy resin (light yellow).

[0068] Furthermore, the organic solvent A is any one of dichloromethane, ethyl acetate, benzene, ether, toluene, methanol and ethanol.

[0069] Furthermore, the catalyst is any one of benzyltriethylammonium chloride, tetrabutylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, tributylamine, polyethylene glycol dialkyl ether, and cyclic crown ether.

[0070] Furthermore, the fatty ketone is one or more of hydroxyacetone, 1-hydroxy-2-butanone, 4-hydroxy-2-butanone, 5-hydroxy-2-pentanone, 5-hydroxy-3-pentanone, 1,3-dihydroxyacetone, 1,4-dihydroxybutanone, and 1,5-dihydroxypentanone.

[0071] Furthermore, the organic solvent B is one or more of methyl isobutyl ketone, acetone, butanone, methyl ethyl ketone, cyclohexanone, 1,4-dioxane, benzene and toluene.

[0072] At the same time, in order to obtain a condensed ring ketal-based epoxy insulating material, the present application also provides a corresponding preparation method, which comprises:

[0073] The above-obtained condensed ring ketal epoxy resin, anhydride curing agent and amine accelerator are prepared in a molar ratio of 1: (0.8-1.2): (0.005-0.02).

[0074] Put all the condensed ring ketal epoxy resin and anhydride curing agent into the reactor and heat and stir at 60-120℃. After the two components are mixed evenly, vacuum degassing is carried out at 0.08-0.1Mpa. After degassing for 30-90min, add amine accelerator to the reaction system and continue vacuum degassing for 5-10min. Then, the mixed liquid is poured into the mold preheated to 80℃ under the vacuum condition of 0.1Mpa by vacuum casting equipment. Keep the pouring rate of the liquid in the vacuum casting machine at 3-6mL / s. After the pouring of the liquid is completed, continue to maintain the vacuum condition for 10-20min. Then transfer the mold filled with liquid to the oven and adopt pre-curing 80℃ / 6h+post-curing 120℃ / 6-12h. After the program curing is completed, the sample is demoulded after natural cooling to room temperature to obtain a cross-linked and cured condensed ring ketal epoxy insulation material.

[0075] Wherein, the acid anhydride curing agent is one or more of hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyl hexahydrophthalic anhydride, methyl tetrahydrophthalic anhydride and methyl nadic anhydride;

[0076] The amine accelerator is one or more of aliphatic amine, alicyclic amine, aromatic amine and heterocyclic amine accelerator.

[0077] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific embodiments of the specification.

[0078] Example 1

[0079] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0080] According to the molar ratio, 1.0 mol of 1,2,4,5-tetrahydroxyphenol, 2.0 mol of hydroxyacetone and 0.1 mol of p-toluenesulfonic acid were weighed respectively.

[0081] First, all 1,2,4,5-tetrahydroxyphenol and hydroxyacetone are put into dichloromethane, heated and stirred at 80°C to completely dissolve, and then all p-toluenesulfonic acid is added, and stirring is continued at 80°C for 4 to 8 hours. After the reaction is complete, filter and evaporate the excess dichloromethane solvent to obtain a polyhydroxy compound with a condensed ring ketal group.

[0082] Step 2: Ring-opening and ring-closing reaction of polyols with epichlorohydrin:

[0083] According to the molar ratio, 1 mol of the polyhydroxy compound, 9 mol of epichlorohydrin and 0.006 mol of benzyltriethylammonium chloride were weighed respectively.

[0084] Ring-opening reaction: The weighed polyhydroxy compound and epichlorohydrin are heated and mixed in a 500mL four-necked flask at 100°C. After a uniform mixed solution is formed, benzyltriethylammonium chloride is added, and heating and stirring are continued at 100°C for 4 to 12 hours until the ring-opening reaction is completed and heating is stopped. The product of the ring-opening reaction is detected by liquid chromatography. When all the polyhydroxy compounds are converted into chlorohydrin ethers, the ring-opening reaction is completed.

[0085] Ring-closing reaction: After the ring-opening reaction is completed, the heating temperature is reduced to 90°C, and a 50% mass fraction NaOH solution is added dropwise at a feeding rate of 1 second / drop under a vacuum condition of 0.095MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction; wherein, the water added to the reaction system during the reaction and the water generated during the ring-closing process are heated and distilled, and the water phase is separated from the reaction system through an oil-water separator to prevent the water phase from participating in the ring-closing reaction and inducing side reactions such as hydrolysis.

[0086] After the ring-closing reaction is completed, the vacuum condition is removed, and toluene is added to the reaction system to dissolve the epoxy resin obtained by the cyclization reaction, and an organic phase of a toluene solution containing the epoxy resin is obtained. The NaCl inorganic salt in the organic phase of the toluene solution is separated by suction filtration, and then the obtained product is heated to remove the toluene therein, thereby obtaining a light yellow condensed ring ketal-based epoxy resin.

[0087] In this embodiment, the molecular structure of the obtained condensed ring ketal epoxy resin is:

[0088]

[0089] In this embodiment, R1=CH2, R2=CH2, R3=CH3, R4=CH3;

[0090] like Figure 2 The resin molecule has a wide bandgap energy level structure, a rigid and flexible molecular chain, and a multi-functional and branched structure, which makes the resin molecule have low viscosity and efficient and mild degradation ability. Similarly, the insulating material after cross-linking and curing of the condensed ketal epoxy resin also has high dielectric constant, high T g And high mechanical strength and other excellent service performance.

[0091] Step 3: Preparation of condensed ring ketal-based epoxy insulation material:

[0092] Weigh 1 mol of the condensed ring ketal epoxy resin obtained in step 2, 1 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the condensed ring ketal epoxy resin and the hexahydrophthalic anhydride curing agent into the reactor and keep heating and stirring at 80°C. After mixing evenly, degassing is carried out under a vacuum degree of 0.1MPa. After degassing for 30 minutes, 2,4,6-tris(dimethylaminomethyl)phenol is added to the reaction system, and vacuum degassing is continued for 2 to 5 minutes to obtain a mixed liquid. Then, a vacuum casting equipment is used to pour the above mixed liquid into a mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the vacuum casting machine at 5mL / s. After the pouring is completed, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold to the oven and adopt pre-curing 80°C / 6h + post-curing 120°C / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material, and a number of performance tests are performed on the insulating material sample.

[0093] Preparation of commercial epoxy insulation materials:

[0094] Comparative Example 1:

[0095] Preparation of bisphenol A epoxy insulation material:

[0096] Weigh 1 mol of bisphenol A epoxy resin, 1 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the bisphenol A epoxy resin and the hexahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniformly mixed liquid, degas it under a vacuum degree of 0.1MPa. After degassing for 30 minutes, add all the prepared 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system, and continue to vacuum degas for 5 minutes. Then use a vacuum casting equipment to pour the above mixed liquid into a mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the liquid in the vacuum casting equipment at 5mL / s. After the liquid is poured, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold filled with liquid to the oven, and take pre-curing 80°C / 6h + post-curing 120°C / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and demolded to obtain bisphenol A epoxy insulation material, and the performance of the epoxy insulation material is tested.

[0097] Comparative Example 2:

[0098] Preparation of bisphenol F epoxy insulation material:

[0099] Weigh 1 mol of bisphenol F epoxy resin, 1 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the bisphenol F epoxy resin and the hexahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniform liquid phase, degas the mixture under a vacuum degree of 0.1MPa. After degassing for 30 minutes, add all the prepared 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system, and continue to degas under vacuum for 5 minutes. Then, use a vacuum casting device to pour the mixed liquid into a mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the liquid in the vacuum casting equipment at 5mL / s. After the liquid is poured, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold filled with liquid to the oven, and take pre-curing 80°C / 6h + post-curing 120°C / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and demolded to obtain bisphenol F epoxy insulation material, and the performance of the epoxy insulation material is tested.

[0100] Embodiment 2:

[0101] Study on the influence of the functionality of condensed ring ketal epoxy resin on the performance of insulating materials (Examples 1, 2, 3, 4)

[0102] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0103] Weigh 1.0 mol of 1,2,4,5-tetrahydroxyphenol, 2.0 mol of 1,3-dihydroxyacetone and 0.1 mol of p-toluenesulfonic acid in the molar ratio. First, put 1,2,4,5-tetrahydroxyphenol and 1,3-dihydroxyacetone into dichloromethane, and heat and stir at 80°C to completely dissolve them. Then add all the p-toluenesulfonic acid and continue stirring at 80°C for 4 to 8 hours. After the reaction is complete, filter and evaporate the excess dichloromethane to obtain a polyhydroxy compound with a condensed ring ketal molecular skeleton.

[0104] Step 2: Ring-opening and ring-closing reaction of the obtained polyhydroxy compound with epichlorohydrin:

[0105] According to the molar ratio of substances, 1 mol of the polyhydroxy compound obtained in step 1, 9 mol of epichlorohydrin and 0.006 mol of benzyltriethylammonium chloride are weighed respectively. The weighed polyhydroxy compound and epichlorohydrin are heated and mixed at 100°C in a 500mL four-necked flask. After a uniform mixed solution is formed, benzyltriethylammonium chloride (catalyst) is added, and heated and stirred at 100°C for 4 to 12 hours, and heating is stopped when the ring-opening reaction ends. The product of the ring-opening reaction is detected by liquid chromatography, and when all the polyhydroxy compounds are converted into chlorohydrin ethers, the ring-opening reaction ends.

[0106] Ring-closing reaction: After the ring-opening reaction is completed, the heating temperature is adjusted to 90°C, and a 50% mass fraction of NaOH solution is added dropwise at a feeding rate of 1 second / drop under a vacuum condition of 0.095MPa until the epoxy value of the obtained product (obtained epoxy resin) reaches the target range, thereby completing the ring-closing reaction; wherein, the water added to the reaction system during the reaction and the water generated during the ring-closing process are heated and distilled, and the water phase is separated from the reaction system through an oil-water separator to prevent the water phase from participating in the ring-closing reaction and inducing side reactions such as hydrolysis.

[0107] After the ring-closing reaction is completed, the vacuum condition is removed, and toluene is added to the reaction system to dissolve the epoxy resin obtained by the cyclization reaction, and an organic phase of a toluene solution containing the epoxy resin is obtained. The NaCl inorganic salt in the organic phase of the toluene solution is separated by suction filtration, and then the obtained product is heated to remove the toluene therein, thereby obtaining a light yellow condensed ring ketal-based epoxy resin.

[0108] In this embodiment, the molecular structure of the obtained condensed ring ketal epoxy resin is:

[0109]

[0110] In this embodiment, R1 = CH2, R2 = CH2, R3 = CH2OC3H5O, R4 = CH2OC3H5O;

[0111] Step 3: Preparation of condensed ring ketal epoxy insulation material:

[0112] Weigh 1 mol of condensed ring ketal epoxy resin, 2 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the condensed ring ketal epoxy resin and the hexahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniform liquid phase, degas the mixture under a vacuum degree of 0.1MPa. After degassing for 30 minutes, add 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system and continue to degas in vacuum for 5 minutes. Then, use a vacuum casting equipment to pour the above mixed liquid into a mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the liquid in the vacuum casting machine at 5mL / s. After the liquid is poured, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold filled with liquid to the oven and take pre-curing 80°C / 6h + post-curing 120°C / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material, and a number of performance tests are performed on the insulating material sample.

[0113] Embodiment 3:

[0114] 1.0 mol of 1,2,4,5-tetrahydroxyphenol, 1.0 mol of 1,3-dihydroxyacetone, 1.0 mol of hydroxyacetone, and 0.1 mol of p-toluenesulfonic acid were weighed in a substance molar ratio.

[0115] First, 1,2,4,5-tetrahydroxyphenol, 1,3-dihydroxyacetone and hydroxyacetone are placed in dichloromethane, heated and stirred at 80°C to completely dissolve them, and the catalyst p-toluenesulfonic acid is added to the completely dissolved mixed solution, and stirring is continued at 80°C for 4 to 8 hours. After the reaction is complete, the excess dichloromethane is filtered and evaporated to obtain a polyhydroxy compound with a condensed ring ketal molecular skeleton.

[0116] Step 2: Ring-opening and ring-closing reaction of polyols with epichlorohydrin:

[0117] 1 mol of a polyhydroxy compound having a condensed ring ketal molecular skeleton, 9 mol of epichlorohydrin and 0.006 mol of benzyltriethylammonium chloride were weighed respectively.

[0118] The polyhydroxy compound and epichlorohydrin are heated and mixed at 100°C in a 500mL four-necked flask. After a uniform mixed solution is formed, benzyltriethylammonium chloride (catalyst) is added and heated and stirred at 100°C for 4 to 12 hours, and the heating is stopped when the ring-opening reaction is completed. The product of the ring-opening reaction is detected by liquid chromatography, and when the polyhydroxy compound is completely converted into chlorohydrin ether, the ring-opening reaction is completed.

[0119] Ring-closing reaction: After the ring-opening reaction is completed, the heating temperature is adjusted to 90°C, and a 50% mass fraction of NaOH solution is added dropwise at a feeding rate of 1 second / drop under a vacuum condition of 0.095MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction; wherein, the water added to the reaction system during the reaction and the water generated during the ring-closing process are heated and distilled, and the water phase is separated from the reaction system through an oil-water separator to prevent the water phase from participating in the ring-closing reaction and inducing side reactions such as hydrolysis.

[0120] After the ring-closing reaction is completed, the vacuum condition is removed, and toluene is added to the reaction system to dissolve the epoxy resin obtained by the cyclization reaction, and an organic phase of a toluene solution containing the epoxy resin is obtained. The NaCl inorganic salt in the organic phase of the toluene solution is separated by suction filtration, and then the obtained product is heated to remove the toluene therein, thereby obtaining a light yellow condensed ring ketal-based epoxy resin.

[0121] In this embodiment, the molecular structure of the obtained condensed ring ketal epoxy resin is:

[0122]

[0123] In this embodiment, R1 = CH2, R2 = CH2, R3 = CH2OC3H5O, R4 = CH3;

[0124] Step 3: Preparation of condensed ring ketal-based epoxy insulation material:

[0125] Weigh 1 mol of condensed ring ketal epoxy resin, 1.5 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the obtained condensed ring ketal epoxy resin and hexahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniform liquid phase, degassing is carried out under a vacuum degree of 0.1MPa. After degassing for 30 minutes, 2,4,6-tris(dimethylaminomethyl)phenol is added to the reaction system, and vacuum degassing is continued for 5 minutes. Then, a vacuum casting equipment is used to pour the above-mentioned mixed liquid into a mold preheated to 80°C under a vacuum condition of 0.1MPa. The pouring rate of the liquid in the vacuum casting machine is maintained at 5mL / s. After the liquid is poured, the vacuum condition is maintained for 10 minutes. Then the mold filled with liquid is transferred to the oven, and pre-curing 80°C / 6h + post-curing 120°C / 6h is adopted. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material, and a number of performance tests are performed on the insulating material sample.

[0126] Embodiment 4:

[0127] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0128] 1.0 mol of 1,2,4,5-tetrahydroxyphenol, 2.0 mol of 5-hydroxy-2-pentanone and 0.1 mol of p-toluenesulfonic acid were weighed respectively according to the molar ratio.

[0129] First, 1,2,4,5-tetrahydroxyphenol and 5-hydroxy-2-pentanone were placed in dichloromethane, heated and stirred at 80°C to completely dissolve them, and p-toluenesulfonic acid was added, and stirring was continued at 80°C for 4 to 8 hours. After the reaction was complete, the excess dichloromethane was filtered and evaporated to obtain a polyhydroxy compound with a condensed ring ketal molecular skeleton.

[0130] Step 2: Ring-opening and ring-closing reaction of polyols with epichlorohydrin:

[0131] According to the molar ratio, 1 mol of the polyhydroxy compound obtained in step 1, 9 mol of epichlorohydrin and 0.006 mol of benzyltriethylammonium chloride were weighed respectively.

[0132] The polyhydroxy compound and epichlorohydrin are heated and mixed at 100°C in a 500mL four-necked flask. After a uniform mixed solution is formed, benzyltriethylammonium chloride is added to the mixed solution and heated and stirred at 100°C for 4 to 12 hours, and the heating is stopped when the ring-opening reaction is completed. The product of the ring-opening reaction is detected by liquid chromatography, and when the polyhydroxy compound is completely converted into chlorohydrin ether, the ring-opening reaction is completed.

[0133] Ring-closing reaction: After the ring-opening reaction is completed, the heating temperature is reduced to 90°C, and a 50% mass fraction NaOH solution is added dropwise at a feeding rate of 1 second / drop under a vacuum condition of 0.095MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction; wherein, the water added to the reaction system during the reaction and the water generated during the ring-closing process are heated and distilled, and the water phase is separated from the reaction system through an oil-water separator to prevent the water phase from participating in the ring-closing reaction and inducing side reactions such as hydrolysis.

[0134] After the ring-closing reaction is completed, the vacuum condition is removed, and toluene is added to the reaction system to dissolve the epoxy resin obtained by the cyclization reaction, and an organic phase of a toluene solution containing the epoxy resin is obtained. The NaCl inorganic salt in the organic phase of the toluene solution is separated by suction filtration, and then the obtained product is heated to remove the toluene therein, thereby obtaining a light yellow condensed ring ketal-based epoxy resin.

[0135] In this embodiment, the molecular structure of the obtained condensed ring ketal epoxy resin is:

[0136]

[0137] In this embodiment, R1=C3H6, R2=C3H6, R3=CH3, R4=CH3;

[0138] Step 3: Preparation of condensed ring ketal-based epoxy insulation material:

[0139] Weigh 1 mol of condensed ring ketal epoxy resin, 1 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the condensed ring ketal epoxy resin and the hexahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniformly mixed liquid phase, degassing is carried out under a vacuum degree of 0.1MPa. After degassing for 30 minutes, 2,4,6-tris(dimethylaminomethyl)phenol is added to the reaction system, and vacuum degassing is continued for 5 minutes. Then, a vacuum casting equipment is used to pour the above-mentioned mixed liquid into a mold preheated to 80°C under a vacuum condition of 0.1MPa. The pouring rate of the liquid in the vacuum casting machine is maintained at 5mL / s. After the liquid is poured, the vacuum condition is maintained for 10 minutes. Then the mold filled with liquid is transferred to the oven, and pre-curing at 80°C / 6h + post-curing at 120°C / 6h is adopted. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material, and a number of performance tests are performed on the insulating material sample.

[0140] Embodiment 5:

[0141] Compatibility study of different anhydride curing agents with condensed ring ketal-based epoxy resins (Examples 1, 5, and 6)

[0142] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0143] The condensed ring ketal molecular skeleton was constructed according to the method in Example 1.

[0144] Step 2: Ring-opening and ring-closing reaction of condensed ring ketal polyol with epichlorohydrin:

[0145] The condensed ring ketal-based epoxy resin was synthesized according to the ring-opening and cyclization reaction steps in Example 1.

[0146] Step 3: Preparation of condensed ring ketal-based epoxy insulation material:

[0147] Weigh 1 mol of the obtained condensed ring ketal epoxy resin, 1 mol of methyl hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the obtained condensed ring ketal epoxy resin and methyl hexahydrophthalic anhydride curing agent into a reactor and heat and stir at 80°C. After forming a uniformly mixed liquid phase, degassing is carried out under a vacuum degree of 0.1MPa. After degassing for 30 minutes, 2,4,6-tris(dimethylaminomethyl)phenol is added to the reaction system, and vacuum degassing is continued for 5 minutes. Then, a vacuum casting equipment is used to pour the above-mentioned mixed liquid into a mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the liquid in the vacuum casting machine at 5mL / s. After the liquid casting is completed, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold filled with liquid material into the oven and adopt pre-curing at 80℃ / 6h + post-curing at 120℃ / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation material sample.

[0148] Embodiment 6:

[0149] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0150] The condensed ring ketal molecular skeleton was constructed according to the method in Example 1.

[0151] Step 2: Ring-opening and ring-closing reaction of condensed ring ketal polyol with epichlorohydrin:

[0152] The condensed ring ketal-based epoxy resin was synthesized according to the ring-opening and cyclization reaction steps in Example 1.

[0153] Step 3: Preparation of condensed ring ketal epoxy insulation material:

[0154] Weigh 1 mol of condensed ring ketal epoxy resin, 1 mol of methyltetrahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol respectively. Then put the condensed ring ketal epoxy resin and methyltetrahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniform liquid phase, degassing is carried out under a vacuum degree of 0.1MPa. After degassing for 30 minutes, 2,4,6-tris(dimethylaminomethyl)phenol is added to the reaction system, and vacuum degassing is continued for 5 minutes. Then, the vacuum casting equipment is used to pour the above mixed liquid into the mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the liquid in the vacuum casting machine at 5mL / s. After the liquid is poured, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold filled with liquid to the oven, and adopt pre-curing 80°C / 6h + post-curing 120°C / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material, and a number of performance tests are performed on the insulating material sample.

[0155] Embodiment 7:

[0156] Study on the influence of different amine accelerators on the performance of condensed ring ketal-based epoxy insulation materials (Examples 1, 7, 8)

[0157] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0158] The condensed ring ketal molecular skeleton was constructed according to the method in Example 1.

[0159] Step 2: Ring-opening and ring-closing reaction of condensed ring ketal polyol with epichlorohydrin:

[0160] The condensed ring ketal-based epoxy resin was synthesized according to the ring-opening and cyclization reaction steps in Example 1.

[0161] Step 3: Preparation of condensed ring ketal epoxy insulation material:

[0162] Weigh 1 mol of condensed ring ketal epoxy resin, 1 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of N, N-dimethylbenzylamine respectively. Then put the condensed ring ketal epoxy resin and hexahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniform liquid phase, degas under a vacuum degree of 0.1MPa. After degassing for 30 minutes, add N, N-dimethylbenzylamine to the reaction system and continue vacuum degassing for 5 minutes. Then use vacuum casting equipment to pour the above mixed liquid into the mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the liquid in the vacuum casting machine at 5mL / s. After the liquid is poured, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold filled with liquid to the oven and take pre-curing 80°C / 6h + post-curing 120°C / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material, and a number of performance tests are performed on the insulating material sample.

[0163] Embodiment 8:

[0164] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0165] The condensed ring ketal molecular skeleton was constructed according to the method in Example 1.

[0166] Step 2: Ring-opening and ring-closing reaction of condensed ring ketal polyol with epichlorohydrin:

[0167] The condensed ring ketal-based epoxy resin was synthesized according to the ring-opening and cyclization reaction steps in Example 1.

[0168] Step 3: Preparation of condensed ring ketal epoxy insulation material:

[0169] Weigh 1 mol of condensed ring ketal epoxy resin, 1 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of triethanolamine respectively. Then put the condensed ring ketal epoxy resin and the hexahydrophthalic anhydride curing agent into the reactor and heat and stir at 80°C. After forming a uniformly mixed liquid phase, degas it under a vacuum degree of 0.1MPa. After degassing for 30 minutes, add triethanolamine to the reaction system and continue vacuum degassing for 5 minutes. Then use vacuum casting equipment to pour the above mixed liquid into the mold preheated to 80°C under a vacuum condition of 0.1MPa. Keep the pouring rate of the liquid in the vacuum casting machine at 5mL / s. After the liquid is poured, continue to maintain the vacuum condition for 10 minutes. Then transfer the mold filled with liquid to the oven and take pre-curing 80°C / 6h + post-curing 120°C / 6h. After the curing process is completed, the sample is naturally cooled to room temperature and then demoulded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material, and a number of performance tests are performed on the insulating material sample.

[0170] Embodiment 9:

[0171] The effects of different material ratios on the performance parameters of condensed ring ketal-based epoxy resins during the ring-opening reaction were investigated (Examples 1, 9 and 10).

[0172] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0173] The condensed ring ketal molecular skeleton was constructed according to the method in Example 1.

[0174] Step 2: Ring-opening and ring-closing reaction of condensed ring ketal polyol with epichlorohydrin:

[0175] According to the molar ratio, 1 mol of the polyhydroxy compound, 6 mol of epichlorohydrin and 0.006 mol of benzyltriethylammonium chloride were weighed respectively.

[0176] Ring-opening reaction: The weighed polyhydroxy compound and epichlorohydrin are heated and mixed in a 500mL four-necked flask at 100°C. After a uniform mixed solution is formed, benzyltriethylammonium chloride is added, and heating and stirring are continued at 100°C for 4 to 12 hours, and heating is stopped when the ring-opening reaction is completed. The product of the ring-opening reaction is detected by liquid chromatography, and when all the polyhydroxy compounds are converted into chlorohydrin ethers, the ring-opening reaction is completed.

[0177] The condensed ring ketal-based epoxy resin was synthesized according to the ring-closing reaction steps in Example 1.

[0178] Step 3: Preparation of condensed ring ketal-based epoxy insulation material:

[0179] The material sample was prepared according to the preparation steps of the condensed ring ketal-based epoxy insulation material sample in Example 1.

[0180] Embodiment 10:

[0181] Step 1: Construction of the molecular skeleton of condensed ring ketal:

[0182] The condensed ring ketal molecular skeleton was constructed according to the method in Example 1.

[0183] Step 2: Ring-opening and ring-closing reaction of condensed ring ketal polyol with epichlorohydrin:

[0184] According to the molar ratio, 1 mol of the polyhydroxy compound, 12 mol of epichlorohydrin and 0.006 mol of benzyltriethylammonium chloride were weighed respectively.

[0185] Ring-opening reaction: The weighed polyhydroxy compound and epichlorohydrin are heated and mixed in a 500mL four-necked flask at 100°C. After a uniform mixed solution is formed, benzyltriethylammonium chloride is added, and heating and stirring are continued at 100°C for 4 to 12 hours, and heating is stopped when the ring-opening reaction is completed. The product of the ring-opening reaction is detected by liquid chromatography, and when all the polyhydroxy compounds are converted into chlorohydrin ethers, the ring-opening reaction is completed.

[0186] The condensed ring ketal-based epoxy resin was synthesized according to the ring-closing reaction steps in Example 1.

[0187] Step 3: Preparation of condensed ring ketal-based epoxy insulation material:

[0188] The material sample was prepared according to the preparation steps of the condensed ring ketal-based epoxy insulation material sample in Example 1.

[0189] Test results analysis

[0190] like Figure 3 From the nuclear magnetic resonance characterization of the molecular structure of the condensed ring ketal-based epoxy resin obtained in Example 1, it can be seen that the characteristic peak at position ① corresponds to the characteristic peak of hydrogen on the branched methyl group in the molecule, the characteristic peaks at positions ② and ③ belong to the characteristic peaks of hydrogen of the epoxy group on the main chain, and the characteristic peak at position ④ corresponds to the hydrogen in the ortho-methylene group of the ketal, and the characteristic peak at position ⑤ belongs to the characteristic peak of hydrogen on the benzene ring. Figure 4 The nuclear magnetic resonance carbon spectrum of the condensed ring ketal-based epoxy resin further verified the rationality of the molecular structure of the obtained epoxy resin. Figure 5 and Figure 6 They are respectively the hydrogen and carbon nuclear magnetic resonance spectra of the tetrafunctional condensed ring ketal epoxy resin in Example 2. Due to the symmetry of the molecular structure of the tetrafunctional condensed ring ketal epoxy resin, the characteristic peaks in its hydrogen and carbon spectra are degenerate.

[0191] The above-mentioned nuclear magnetic resonance spectrum also verifies the accuracy and rationality of the molecular structure of the synthesized condensed ring ketal-based epoxy resin.

[0192] The method of testing the examples or comparative examples of the present application is as follows:

[0193] Epoxy resin viscosity test: According to the national standard GB / T 22314-2008 "Plastic Epoxy Resin Viscosity Determination Method Standard", a rotational viscometer is used for testing. The test temperature is 25°C to test the viscosity of epoxy resin.

[0194] Determination of epoxy value of epoxy resin: According to the test standard of national standard GB-T1677-2008 "Determination of epoxy value of plasticizer - hydrochloric acid - acetone method", the epoxy value of epoxy resin is tested by hydrochloric acid - acetone method. Three groups are taken for titration for each group of epoxy resin samples and blank control group. The average value of the epoxy value obtained by the test is taken as the final epoxy value of the epoxy resin.

[0195] Glass transition temperature test of epoxy insulation material: According to the national standard GB / T 40396-2021 "Test method for glass transition temperature of polymer-based composite materials - Dynamic mechanical analysis (DMA)", the glass transition temperature of the material is tested by a dynamic thermomechanical analyzer. The test mode is single and double cantilever mode. The test conditions are air atmosphere, the heating rate is 5℃ / min, the loading frequency is 1Hz, the temperature is increased from room temperature to 250℃, and then it is cooled to room temperature and then heated to 250℃ again at the same rate. The program heating is terminated after the modulus change tends to be flat, and the glass transition temperature of the test material is obtained by processing the test curve.

[0196] Dielectric strength test of epoxy insulation materials: According to the test standard of GB / T 1408.1-2016 "Electrical Strength Test Method of Insulating Materials", the dielectric strength of the samples under the action of short-term electric field is measured at a voltage increase rate of 2kV / s. The measurement environment temperature is 25℃, the test sample is a disc with a diameter of 100mm and a thickness of 1mm, the test voltage frequency is 50Hz, 3 finished products are taken for each sample, 3 points are tested for each sample, and 9 dielectric strength data can be obtained for each sample. The test results are averaged, and the Weibull distribution is used to fit the dielectric strength of the material.

[0197] Epoxy insulation material bending strength test: According to the test standard of GB / T2567-2008 "Resin casting performance test method", a universal mechanical testing machine is used to measure the elastic modulus and bending strength of the sample. The test sample is cast according to the technical conditions specified in GB / T2567-2008. The test temperature is 25°C and the ambient humidity is 50% RH. When measuring the bending strength, the test speed is 10mm / min, when measuring the elastic modulus, the test speed is 2mm / min, and the arbitration test speed is 2mm / min. Each sample is tested 3 times and the measurement results are averaged.

[0198] Epoxy insulation material tensile strength test: According to the test standard of GB / T2567-2008 "Resin casting performance test method", a universal mechanical testing machine is used to measure the tensile strength and tensile elongation of the sample. The test sample is cast according to the technical conditions specified in GB / T2567-2008. The test temperature is 25°C and the relative humidity is 50%. When measuring the tensile strength, the test speed is 10mm / min, the arbitration test speed is 2mm / min, and when measuring other properties, the test speed is 2mm / min. Each sample is tested 3 times and the average value of the measurement results is taken.

[0199] Chemical degradation performance test of epoxy insulation materials: select epoxy material samples of the same mass and size, place them in a degradation reactor, and chemically degrade them in a degradation solution at 100°C. The degradation rate of the material is calculated based on the degradation time required for the complete degradation of the epoxy material samples. Five groups of sample strips are taken from each group of samples, and the degradation rate is the average value of the five groups of sample strips.

[0200] The performance characterization results of the obtained epoxy resin and insulating material are shown in Tables 1 to 2 and Figures 1 to 6 shown.

[0201] Table 1 Comparison of performance parameters of condensed cyclic ketal and commercial epoxy resin materials

[0202]

[0203] As can be seen from Table 1, by selecting different aliphatic ketone molecules, the condensed ring ketal-based epoxy resins synthesized in Examples 1, 2, 3 and 4 have adjustable functionality, number of branches and molecular chain length. The adjustability of the resin molecular structure also gives the condensed ring ketal-based epoxy insulating materials adjustable performance parameters on demand for different application scenarios, which is specifically reflected in the viscosity, breakdown strength, glass transition temperature and mechanical strength of the epoxy resin. Among them, the epoxy value of the condensed ring ketal-based epoxy resin synthesized in the embodiment is in the range of 0.47 to 0.78. By regulating the epoxy value of the epoxy resin, the cross-linking density, free volume ratio and other network microscopic properties of the three-dimensional network after the material is cross-linked and cured can be effectively adjusted, thereby realizing the on-demand switching of the electrical, mechanical and thermal properties of the epoxy insulating material. The experimental results of Examples 1, 9, and 10 reflect that during the ring-opening reaction of the ring-opening condensed-ring ketal-based epoxy resin, the material ratio of the condensed-ring ketal polyhydroxy compound, epichlorohydrin, and the catalyst affects the epoxy value of the synthesized epoxy resin. When the ratio of the three is 1:6:0.006, the epoxy value of the obtained epoxy resin is the highest at 0.5462, which has the best invention effect.

[0204] The condensed ring ketal epoxy resin obtained in this application also has a lower viscosity value. Among them, as shown in Table 1, the viscosity range of the condensed ring ketal epoxy resin is only 3500-5500mpa·s, which is basically equivalent to the viscosity value of commercial bisphenol F resin, and is much lower than the commercial bisphenol A epoxy resin (its viscosity is 8000-11000mpa·s). The lower viscosity value of the condensed ring ketal epoxy resin can greatly improve the wetting effect between the epoxy resin matrix and the inorganic reinforcing filler, thereby reducing the number of micro-defects formed during the pouring and curing of the epoxy resin, and reducing the risk of insulation failure of the epoxy resin material, so as to ensure the safe and stable operation of power equipment. It is worth mentioning that Examples 1, 9, and 10 reflect the effect of the material ratio in the open-loop process on the viscosity of the resin. It can be found that when the condensed ring ketal skeleton and epichlorohydrin and the catalyst are 1:6:0.006, the resulting epoxy value has a lower viscosity value. This is also related to the fact that the synthesized epoxy resin has a higher epoxy value and a relatively more concentrated molecular weight distribution.

[0205] The present invention optimizes the synthesis process of condensed ring ketal epoxy resin. On the one hand, excessive epichlorohydrin is added to promote the reaction to the right and improve the conversion rate of the reaction. On the other hand, by heating and separating the water produced during the reaction, the hydrolysis side reaction of epichlorohydrin can be well suppressed, so that the epoxy resin has a lower hydrolyzable chlorine content after the two-step synthesis reaction. The reduction of organic chlorine content in epoxy resin can give epoxy insulating materials better electrical insulation properties. Therefore, the condensed ring ketal epoxy resin prepared by Examples 1, 2, 3 and 4 has better comprehensive service performance than commercial resins. At the same time, the material ratio of polyhydroxy compounds with condensed ring ketal molecular skeletons, epichlorohydrin and catalysts in the open-loop process is optimized, and the amount of material added by NaOH in the closed-loop process can achieve a lower hydrolyzable chlorine content in the condensed ring ketal epoxy resin, thereby optimizing the performance parameters of the insulating material.

[0206] Table 2 Performance comparison of condensed ketal epoxy insulation materials and commercial epoxy and insulation materials

[0207]

[0208]

[0209] As shown in Table 2, through the characterization of the performance of the epoxy insulation materials obtained in each embodiment and comparative example, it can be seen that compared with commercial bisphenol A and bisphenol F type epoxy insulation materials, the condensed ring ketal-based epoxy insulation material obtained in the present application has significantly improved performance in various aspects such as tensile strength, flexural strength, dielectric strength, glass transition temperature and degradation rate.

[0210] In terms of tensile strength, the tensile strengths of bisphenol A and bisphenol F epoxy insulating materials in Comparative Examples 1 and 2 are 73MPa and 78MPa respectively, the tensile strengths of condensed ring ketal epoxy insulating materials in Examples 1, 2, 3 and 4 can reach more than 80MPa, the tensile strength of trifunctional condensed ring ketal epoxy insulating materials (Example 3) can reach 88MPa, and the tensile strength of condensed ring ketal epoxy insulating materials with longer molecular chains (Example 4) can also reach 86MPa, which is more than 10% higher than that of the comparative example. The higher tensile strength of epoxy materials can reflect the improvement of material rigidity and toughness to a certain extent, giving the materials better mechanical properties.

[0211] In terms of bending strength, the bending strengths of bisphenol A and bisphenol F epoxy insulating materials in Comparative Examples 1 and 2 are 106MPa and 112MPa respectively, and the bending strengths of condensed ring ketal epoxy insulating materials in Examples 1, 2, 3 and 4 can reach more than 108MPa, and when the functionality of the epoxy resin is 3 (Example 3), the bending strength of the condensed ring ketal epoxy insulating material can be 126MPa, which is more than 15% higher than the insulating material cross-linked and cured by commercial epoxy resin. When different anhydride curing agents and accelerators are selected, the bending strength of the epoxy insulating material is also above 110MPa, which also reflects the compatibility of condensed ring ketal epoxy resin with a variety of anhydride curing agents and amine accelerators. The improvement of the bending strength of epoxy insulating materials can better meet the performance requirements of high mechanical strength of epoxy materials for power equipment.

[0212] In terms of glass transition temperature, the T of commercial bisphenol A and bisphenol F epoxy insulation materials in Examples 1 and 2 is g They are 136°C and 132°C respectively. The glass transition temperature of the condensed ring ketal-based epoxy insulating materials in Examples 1, 2, 3 and 4 can reach above 142°C, and with the increase of the functionality of the epoxy resin, the glass transition temperature of the epoxy insulating material can be increased to 165°C. Compared with commercial epoxy insulating materials, the maximum increase in its glass transition temperature can reach 25%. The substantial increase in the glass transition temperature of epoxy insulating materials has greatly expanded the range of service scenarios of the materials. By selecting different curing agents and accelerators, the glass transition temperature of condensed ring ketal-based epoxy insulating materials can still reach above 140°C, and the thermal properties are significantly improved compared to commercial epoxy insulating materials.

[0213] In terms of dielectric strength, the dielectric strength of commercial bisphenol A and bisphenol F epoxy insulating materials in Comparative Examples 1 and 2 are both around 35.5 kV / mm. The dielectric strength of the condensed ring ketal-based epoxy insulating materials in Examples 1, 2, 3 and 4 is in the range of 37.8 to 40.9 kV / mm, which is 6.5% to 15% higher than the dielectric strength of commercial epoxy insulating materials. The multifunctional condensed ring ketal-based epoxy insulating materials have a smaller free volume ratio, which reduces the mean free path of electrons in the epoxy material, significantly improving the electrical resistance of the epoxy insulating material. And after selecting other types of anhydride curing agents and amine accelerators, the dielectric strength of the condensed ring ketal-based epoxy insulating materials can still be 37 kV / mm, which also shows that the epoxy material has excellent insulation properties and can meet the service performance of the material in high insulation scenarios.

[0214] In terms of chemical degradation rate, firstly, through the screening of chemical degradation agents, it can be found that when a mixed solution of hydrochloric acid: acetone = 2:8 is selected as a chemical degradation agent, the condensed ring ketal-based epoxy insulation material has a higher degradation rate, such as Figure 1 As shown. It can be obtained that the degradation rate of the commercial bisphenol A and bisphenol F epoxy insulating materials selected in Comparative Examples 1 and 2 in a mixed solution of hydrochloric acid: acetone = 2:8 is relatively slow, and the fastest degradation rate is only 0.05g / h. When a piece of commercial epoxy insulating material with a mass of 1.5g is degraded, it takes at least 30h to completely degrade. In contrast, the degradation rate of the condensed ring ketal-based epoxy insulating material in Examples 1, 2, 3 and 4 in the above solution can reach up to 0.62g / h, and the degradation rate of the multifunctional condensed ring ketal epoxy insulating material can also be maintained at above 0.3g / h. The time required for the epoxy sample with a mass of 1.5g to completely degrade under this condition is only 3 to 5h. Therefore, compared with the chemical degradation rate of commercial epoxy insulating materials, the condensed ring ketal-based epoxy resin greatly improves the chemical degradation performance of the epoxy insulating material after cross-linking and curing, thereby enabling the efficient degradation of thermosetting epoxy materials. In addition, when other anhydride curing agents and amine accelerators are selected, the chemical degradation rate of the condensed ring ketal-based epoxy insulation material in the mixed degradation agent of hydrochloric acid: acetone = 2:8 can still be maintained above 0.4g / h, which is significantly improved compared with commercial epoxy insulation materials.

[0215] That is, the highly degradable epoxy resin and condensed ring ketal-based epoxy insulating material provided in the present application, due to the adjustable structural characteristics, give the epoxy insulating material obtained after cross-linking and curing the ability to be adjusted on demand in different application scenarios. Secondly, while giving the epoxy material degradation functionality, it also meets the high requirements of multiple operating environments for material insulation, mechanical, heat resistance and process performance, thereby enabling the epoxy resin proposed in the present application to be effectively used in multiple environments of electrical, mechanical and thermal coupling (such as high insulation scenarios of high-end power equipment).

[0216] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0217] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly degradable epoxy resin, whose molecular structure is: in, R1 is C n1 H 2n1 , n1=1~6, R2 is C n2 H 2n2 , n2=1~6, R3 is C n3 H 2n3+1 or C n3 H 2n3 OC3H5O, n3=0~6, R4 is C n4 H 2n4+1 or C n4 H 2n4 OC3H5O, n4=0~6.

2. The method for preparing the highly degradable epoxy resin according to claim 1, characterized in that: The method comprises: Prepare 1,2,4,5-tetrahydroxyphenol, aliphatic ketone and p-toluenesulfonic acid in a molar ratio of 1:2:0.1; Put 1,2,4,5-tetrahydroxyphenol and fatty ketone into organic solvent A dichloromethane, stir to completely dissolve them under heating conditions of 60-120°C, then add p-toluenesulfonic acid, stir for 4-8 hours, filter and evaporate excess organic solvent A after the reaction is complete, and obtain a polyhydroxy compound with condensed ring ketal as a molecular skeleton; Prepare a polyol, epichlorohydrin and a catalyst in a molar ratio of 0.5-1.5:3-20:0.001-0.1; The polyhydroxy compound and epichlorohydrin are heated and mixed in a container, and after being dissolved to form a uniform mixed solution, a catalyst is added, and the mixture is heated and stirred at 60 to 150° C. until the ring-opening reaction is completed; wherein the product of the ring-opening reaction is detected by liquid chromatography, and when the polyhydroxy compound is completely converted into chlorohydrin ether, the ring-opening reaction is completed; After the ring-opening reaction is completed, the heating temperature is adjusted to 60-120° C., and a 50% mass fraction NaOH solution is added dropwise at a feeding rate of 1-5 seconds / drop under a vacuum condition of 0.06-0.1 MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction; After the ring-closing reaction is completed, the vacuum condition is removed, and an organic solvent B is added to the reaction system to dissolve the resin organic phase to obtain an organic solution organic phase in which the epoxy resin is dissolved. The NaCl inorganic salt in the organic phase of the obtained organic solution is separated by suction filtration, and then the obtained product is heated to remove the organic solvent B in the reaction system to obtain a highly degradable epoxy resin.

3. The preparation method according to claim 2, characterized in that: The organic solvent A is any one of dichloromethane, ethyl acetate, benzene, ether, toluene, methanol and ethanol.

4. The preparation method according to claim 2, characterized in that: The catalyst is any one of benzyltriethylammonium chloride, tetrabutylammonium bromide, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, tributylamine, polyethylene glycol dialkyl ether, and cyclic crown ether.

5. The preparation method according to claim 2, characterized in that: The fatty ketone is one or more of hydroxyacetone, 1-hydroxy-2-butanone, 4-hydroxy-2-butanone, 5-hydroxy-2-pentanone, 5-hydroxy-3-pentanone, 1,3-dihydroxyacetone, 1,4-dihydroxybutanone and 1,5-dihydroxypentanone.

6. The preparation method according to claim 2, characterized in that: The organic solvent B is one or more of methyl isobutyl ketone, acetone, methyl ethyl ketone, cyclohexanone, 1,4-dioxane, benzene and toluene.

7. A method for preparing epoxy insulating material using the highly degradable epoxy resin according to any one of claims 1 to 6, characterized in that: The method comprises: Prepare highly degradable epoxy resin, anhydride curing agent and amine accelerator according to the molar ratio of 1:0.8-1.2:0.005-0.02; Put the high-degradable epoxy resin and the acid anhydride curing agent into a reaction kettle, heat and stir at 60-120° C., and after being mixed uniformly, vacuum degassing for 30-90 minutes at 0.08-0.1 MPa, add an amine accelerator, and continue vacuum degassing for 5-10 minutes to obtain a mixed liquid; The mixed liquid is poured into a mold preheated to 80°C under a vacuum condition of 0.1Mpa using a vacuum pouring device, with a pouring rate of 3-6mL / s; after pouring, the vacuum condition is maintained for 10-20min, the mold is transferred to an oven, and the curing program is set to pre-curing 80°C / 6h+post-curing 120°C / 6-12h. After curing, the sample in the mold is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured polycyclic ketal-based epoxy insulating material.

8. The preparation method according to claim 7, characterized in that: The acid anhydride curing agent is one or more of hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride and methylnadic anhydride.

9. The preparation method according to claim 7, characterized in that: The amine accelerator is one or more of aliphatic amine, alicyclic amine, aromatic amine and heterocyclic amine accelerator.

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