Preparation method of highly degradable epoxy resin and insulating material

Abstract

The present invention provides a method for preparing a highly degradable epoxy resin and an insulating material, and relates to the technical field of epoxy resins. The molecular structure thereof is: wherein 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; Secondly, the present invention also provides a preparation method of the above-mentioned highly degradable epoxy resin, which comprises preparing 1,2,4,5-tetrahydroxyphenol, aliphatic ketone and p-toluenesulfonic acid in a molar ratio for a polyhydroxy compound with a condensed ring ketal as a molecular skeleton; then, the polyhydroxy compound, epichlorohydrin and a catalyst prepared in a molar ratio are subjected to a ring-opening reaction, a ring-closing reaction, etc. to obtain a light yellow condensed ring ketal-based epoxy resin; the highly degradable epoxy resin obtained in the present application has the characteristics of mild degradation conditions and fast degradation speed.

Description

Technical Field

[0001] The present 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] Cured epoxy resins exhibit excellent insulation, mechanical, and chemical stability, making them widely used as core insulation materials for precision electronic device packaging, advanced electrical equipment manufacturing, and high-end power equipment. However, the highly stable three-dimensional crosslinked network formed by crosslinking and curing epoxy materials makes them difficult to degrade and recycle. Consequently, retired or discarded epoxy insulation materials pose environmental pollution and resource waste. The development of degradable epoxy resin materials that efficiently decompose the three-dimensional crosslinked network is crucial 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. By breaking the CN bond in the hexahydrotriazine-based skeleton under strong acid conditions, the epoxy resin was decomposed 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 can also aggravate environmental pollution, so this method is not environmentally friendly.

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

[0005] Existing bisphenol A epoxy resin molecules contain a high content of rigid benzene rings and have poor chain segment mobility. When the resin crosslinks to form a three-dimensional network, chemical degradation agents have difficulty effectively penetrating the network. Furthermore, the high bond energy and high chain segment stability within the crosslinked network require high temperatures and strong acidic or alkaline solutions to promote the breaking of chemical bonds within the epoxy crosslinked network.

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

[0007] (1) Technical problems solved

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

[0009] (2) 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 having the molecular structure:

[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] A 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] 1,2,4,5-tetrahydroxyphenol and aliphatic ketone are placed in organic solvent A and stirred at 60-120°C to completely dissolve them. Then, p-toluenesulfonic acid is added and stirred for 4-8 hours. After the reaction is complete, the excess organic solvent A is filtered and evaporated to obtain a polyhydroxy compound with a condensed ring ketal as a molecular skeleton.

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

[0018] The polyol and epichlorohydrin are heated and mixed in a container, and after dissolving 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 the ring-opening reaction is completed when the polyol is completely converted into chlorohydrin ether;

[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-closure 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 aliphatic 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 high-degradable epoxy resin, acid anhydride curing agent and amine accelerator according to the 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 mixing 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 0.1 MPa using a vacuum pouring device at a pouring rate of 3 to 6 mL / s. After the pouring is completed, the vacuum condition is maintained for 10 to 20 minutes, the mold is transferred to an oven, and the curing program is set to pre-curing at 80°C for 6 hours and post-curing at 120°C for 6 to 12 hours. After the curing is completed, the sample in the mold is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation 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] (3) 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 to the prior art:

[0033] 1. The condensed ring ketal-based epoxy resin molecule provided in this 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 within 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 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 by 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 structures 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 micro defects in the composite material, thereby ensuring 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 band gap width and a similar molecular energy level structure. The band gap width range of both is 5.3 to 5.6 eV. The wide band gap energy level structure also gives the condensed ring ketal-based epoxy resin better intrinsic insulation ability. At the same time, by designing the fatty ketone molecular structure 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 insulation material provided by this application has a higher bulk modulus, shear modulus, and Young's modulus than bisphenol A epoxy insulation material. The ratio of the bulk modulus to the Young's modulus (reflecting toughness) of the insulation material is also higher than that of the bisphenol A epoxy insulation material. This also gives the condensed ring ketal-based epoxy insulation material a higher mechanical modulus, mechanical strength, and toughness. The excellent mechanical properties of the epoxy insulation 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

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

[0039] Figure 2 Schematic diagram of the planar skeleton and dihedral angles of the condensed ring ketal molecule in embodiment 1;

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

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

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

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

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort 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 of existing degradable epoxy resin materials when degrading with strong acid, external radiation, etc., as well as the difficulty in balancing degradability with other service performance, the main ideas of this application are:

[0046] Based on 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 multiple branches is constructed. The condensed ring ketal-based epoxy resin has the characteristics of high degradation and low viscosity.

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

[0048]

[0049] Among them, influenced 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 fused ring ketal-based epoxy resin of 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] 1,2,4,5-tetrahydroxyphenol and aliphatic ketone are placed in dichloromethane, an organic solvent A, and mechanically stirred at 60-120°C to completely dissolve them. Then, p-toluenesulfonic acid is added and stirred for 4-8 hours. After the reaction is complete, the mixture is filtered and the excess organic solvent A is evaporated to obtain a polyhydroxy compound with a 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] preparing 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: The polyol and epichlorohydrin are heated and mixed in a container. After dissolution to form a uniform mixed solution, a catalyst is added and heated and stirred at 60-150°C until the ring-opening reaction is completed (generally, the heating and stirring time is 4-12 hours). The products of the ring-opening reaction are detected by liquid chromatography. The ring-opening reaction is completed when the polyol is completely converted into chlorohydrin ether.

[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 0.06-0.1 MPa 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. Subsequently, the water vapor is condensed and enters the oil-water separator in the form of a liquid phase, and the water phase is separated from the reaction system in the separator, thereby preventing 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 and R0=CH2OH as an example is:

[0066]

[0067] After the ring-closure 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 aliphatic 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 includes:

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

[0074] Place the entire condensed ring ketal-based epoxy resin and anhydride curing agent into a reaction kettle and heat with stirring at 60-120°C. Once the two components are uniformly mixed, vacuum degassing is performed at 0.08-0.1 MPa. After degassing for 30-90 minutes, an amine accelerator is added to the reaction system and vacuum degassing is continued for 5-10 minutes. The mixture is then poured into a mold preheated to 80°C using a vacuum casting machine under a vacuum of 0.1 MPa. Maintain a pouring rate of 3-6 mL / s in the vacuum casting machine. After pouring, maintain vacuum for 10-20 minutes. The mold filled with the mixture is then transferred to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6-12 hours. After the curing process is complete, the sample is naturally cooled to room temperature before demolding to obtain a cross-linked, cured condensed ring ketal-based epoxy insulation material.

[0075] Wherein, the acid anhydride curing agent is one or more of hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride and methylnadic anhydride;

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

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

[0078] Example 1

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

[0080] 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 according to the molar ratio.

[0081] First, all of the 1,2,4,5-tetrahydroxyphenol and hydroxyacetone were placed in dichloromethane and heated with stirring at 80°C until completely dissolved. Then, all of the p-toluenesulfonic acid was added and stirring was continued at 80°C for 4-8 hours. After the reaction was complete, the mixture was filtered and the excess dichloromethane solvent was evaporated to obtain a polyhydroxy compound with a fused-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: Mix the weighed polyol and epichlorohydrin at 100°C in a 500mL four-necked flask. Once a uniform mixed solution is formed, add benzyltriethylammonium chloride and continue heating and stirring at 100°C for 4-12 hours until the ring-opening reaction is complete. Liquid chromatography is used to detect the ring-opening reaction product. The ring-opening reaction is complete when all the polyol is converted into chlorohydrin ether.

[0085] Ring-closing reaction: After the ring-opening reaction is completed, the heating temperature is lowered to 90°C, and a 50% mass fraction NaOH solution is added dropwise at a feeding rate of 1 second / drop under vacuum conditions of 0.095 MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction. 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-closure 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 to obtain an organic phase of a toluene solution containing the epoxy resin. The NaCl inorganic salt in the organic phase of the toluene solution is separated by filtration, and the obtained product is then heated to remove the toluene therein to obtain 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 molecules have a wide bandgap energy level structure, a rigid and flexible molecular chain, and a multifunctional and branched structure, which makes the resin molecules have low viscosity and efficient and mild degradation capabilities. Similarly, the insulating material after cross-linking and curing of the condensed ring 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-based epoxy resin obtained in Step 2, 1 mol of hexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol. Place the condensed-ring ketal-based epoxy resin and hexahydrophthalic anhydride curing agent into a reactor and heat and stir at 80°C. Once uniformly mixed, degas the mixture under a vacuum of 0.1 MPa. After degassing for 30 minutes, add 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system and continue vacuum degassing for 2-5 minutes to obtain a liquid mixture. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s. After pouring, maintain vacuum conditions for 10 minutes. Transfer the mold to an oven and perform a pre-cure at 80°C for 6 hours followed by a post-cure at 120°C for 6 hours. After the curing process is completed, the sample is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation 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. Then, heat and stir the bisphenol A epoxy resin and hexahydrophthalic anhydride curing agent in a reactor at 80°C. Once a homogeneous liquid is formed, degas the mixture under a vacuum of 0.1 MPa. After 30 minutes of degassing, add all the 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain the vacuum condition for 10 minutes. Transfer the mold filled with the mixture to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. 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. Then, heat and stir the bisphenol F epoxy resin and hexahydrophthalic anhydride curing agent in a reactor at 80°C. Once a homogeneous liquid phase is formed, degas under a vacuum of 0.1 MPa. After 30 minutes of degassing, add all the 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain vacuum for 10 minutes. Transfer the mold filled with the mixture to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. 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] Example 2:

[0101] Study on the Effect of the Functionality of Condensed Ring Ketal-Based Epoxy Resins on the Properties of Insulation Materials (Examples 1, 2, 3, and 4)

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

[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 a molar ratio. First, dissolve the 1,2,4,5-tetrahydroxyphenol and 1,3-dihydroxyacetone in dichloromethane and heat at 80°C with stirring until completely dissolved. Then, add the entire amount of p-toluenesulfonic acid and continue stirring at 80°C for 4-8 hours. After the reaction is complete, filter and evaporate the excess dichloromethane to obtain a polyhydroxy compound with a fused-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, 1 mol of the polyhydroxy compound obtained in step 1, 9 mol of epichlorohydrin, and 0.006 mol of benzyltriethylammonium chloride were weighed respectively. The weighed polyhydroxy compound and epichlorohydrin were heated and mixed at 100°C in a 500 mL four-necked flask. After forming a uniform mixed solution, benzyltriethylammonium chloride (catalyst) was added and heated and stirred at 100°C for 4 to 12 hours. The heating was stopped when the ring-opening reaction was completed. The product of the ring-opening reaction was detected by liquid chromatography. When the polyhydroxy compound was completely converted into chlorohydrin ether, the ring-opening reaction was completed.

[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 vacuum conditions of 0.095 MPa until the epoxy value of the resulting product (the resulting 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-closure 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 to obtain an organic phase of a toluene solution containing the epoxy resin. The NaCl inorganic salt in the organic phase of the toluene solution is separated by filtration, and the obtained product is then heated to remove the toluene therein to obtain 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. Place the condensed ring ketal epoxy resin and hexahydrophthalic anhydride curing agent in a reactor and heat with stirring at 80°C. Once a homogeneous liquid phase is formed, degas under a vacuum of 0.1 MPa. After degassing for 30 minutes, add 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain vacuum for 10 minutes. Transfer the mold filled with the mixture to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. After the curing process is completed, the sample is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation material sample.

[0113] Example 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 and heated and stirred at 80°C until completely dissolved. The catalyst, p-toluenesulfonic acid, is added to the completely dissolved mixed solution and stirred at 80°C for 4-8 hours. After the reaction is complete, the mixture is filtered and the excess dichloromethane is 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 polyol and epichlorohydrin were heated and mixed at 100°C in a 500mL four-necked flask. After a uniform mixed solution was formed, benzyltriethylammonium chloride (catalyst) was added and heated and stirred at 100°C for 4-12 hours. Heating was stopped when the ring-opening reaction was complete. The ring-opening reaction product was detected by liquid chromatography. The ring-opening reaction was complete when the polyol was completely converted into chlorohydrin ether.

[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 vacuum conditions of 0.095 MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction. 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-closure 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 to obtain an organic phase of a toluene solution containing the epoxy resin. The NaCl inorganic salt in the organic phase of the toluene solution is separated by filtration, and the obtained product is then heated to remove the toluene therein to obtain 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. Place the condensed ring ketal epoxy resin and hexahydrophthalic anhydride curing agent in a reaction kettle and heat with stirring at 80°C. Once a homogeneous liquid phase is formed, degas the mixture under a vacuum of 0.1 MPa. After degassing for 30 minutes, add 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system, and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain vacuum for 10 minutes. Transfer the mold filled with the mixture to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. After the curing process is completed, the sample is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation material sample.

[0126] Example 4:

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

[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 and heated with stirring at 80°C until completely dissolved. p-Toluenesulfonic acid was added and stirring was continued at 80°C for 4-8 hours. After the reaction was complete, the mixture was filtered and the excess dichloromethane was 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 polyol and epichlorohydrin were heated and mixed at 100°C in a 500mL four-necked flask. After a uniform mixed solution was formed, benzyltriethylammonium chloride was added to the mixed solution and heated and stirred at 100°C for 4-12 hours. Heating was stopped when the ring-opening reaction was complete. The ring-opening reaction product was detected by liquid chromatography. The ring-opening reaction was complete when the polyol was completely converted into chlorohydrin ether.

[0133] Ring-closing reaction: After the ring-opening reaction is completed, the heating temperature is lowered to 90°C, and a 50% mass fraction NaOH solution is added dropwise at a feeding rate of 1 second / drop under vacuum conditions of 0.095 MPa until the epoxy value of the obtained product reaches the target range, thereby completing the ring-closing reaction. 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-closure 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 to obtain an organic phase of a toluene solution containing the epoxy resin. The NaCl inorganic salt in the organic phase of the toluene solution is separated by filtration, and the obtained product is then heated to remove the toluene therein to obtain 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. Place the condensed ring ketal epoxy resin and hexahydrophthalic anhydride curing agent in a reactor and heat with stirring at 80°C. Once a homogeneous liquid phase is formed, degas the mixture under a vacuum of 0.1 MPa. After degassing for 30 minutes, add 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain vacuum for 10 minutes. Transfer the mold filled with the mixture to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. After the curing process is completed, the sample is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation material sample.

[0140] Example 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 condensed ring ketal molecular skeleton:

[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 resulting condensed-ring ketal-based epoxy resin, 1 mol of methylhexahydrophthalic anhydride curing agent, and 0.01 mol of 2,4,6-tris(dimethylaminomethyl)phenol. Place the resulting condensed-ring ketal-based epoxy resin and methylhexahydrophthalic anhydride curing agent into a reaction kettle and heat with stirring at 80°C. Once a uniform liquid phase is formed, degas the mixture under a vacuum of 0.1 MPa. After degassing for 30 minutes, add 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. Maintain vacuum conditions for 10 minutes after pouring. The mold, filled with the slurry, was then transferred to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. After the curing process was complete, the sample was naturally cooled to room temperature before demolding, resulting in a cross-linked, cured, condensed-ring ketal-based epoxy insulation material. This insulation material sample was then subjected to various performance tests.

[0148] Example 6:

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

[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. Then, heat and stir the condensed ring ketal epoxy resin and methyltetrahydrophthalic anhydride curing agent in a reaction kettle at 80°C. Once a homogeneous liquid phase is formed, degas the mixture under a vacuum of 0.1 MPa. After degassing for 30 minutes, add 2,4,6-tris(dimethylaminomethyl)phenol to the reaction system, and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain vacuum for 10 minutes. The mold filled with the mixture is then transferred to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. After the curing process is completed, the sample is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation material sample.

[0155] Example 7:

[0156] Study on the Effect of Different Amine Accelerators on the Performance of Condensed Ring Ketal-Based Epoxy Insulation Materials (Examples 1, 7, and 8)

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

[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. Place the condensed ring ketal epoxy resin and hexahydrophthalic anhydride curing agent in a reaction kettle and heat with stirring at 80°C. Once a homogeneous liquid phase is formed, degas under a vacuum of 0.1 MPa. After degassing for 30 minutes, add N,N-dimethylbenzylamine to the reaction system and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain vacuum for 10 minutes. Transfer the mold filled with the mixture to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. After the curing process is completed, the sample is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation material sample.

[0163] Example 8:

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

[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. Place the condensed ring ketal epoxy resin and hexahydrophthalic anhydride curing agent into a reactor and heat with stirring at 80°C. Once a homogeneous liquid phase is formed, degas under a vacuum of 0.1 MPa. After degassing for 30 minutes, add triethanolamine to the reaction system and continue degassing under vacuum for 5 minutes. Next, use a vacuum casting machine to pour the mixture under a vacuum of 0.1 MPa into a mold preheated to 80°C. Maintain a pouring rate of 5 mL / s in the vacuum casting machine. After pouring, maintain vacuum conditions for 10 minutes. Transfer the mold filled with the mixture to an oven for a pre-cure at 80°C for 6 hours and a post-cure at 120°C for 6 hours. After the curing process is completed, the sample is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation material, and a number of performance tests are performed on the insulation material sample.

[0170] Example 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 condensed ring ketal molecular skeleton:

[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: Mix the weighed polyol and epichlorohydrin at 100°C in a 500mL four-necked flask. Once a uniform mixed solution is formed, add benzyltriethylammonium chloride and continue heating and stirring at 100°C for 4-12 hours. Heating is discontinued when the ring-opening reaction is complete. Liquid chromatography is used to detect the ring-opening reaction product. The ring-opening reaction is complete when the polyol is completely converted into chlorohydrin ether.

[0177] The condensed ring ketal-based epoxy resin was synthesized according to the ring-closure 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] Example 10:

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

[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: Mix the weighed polyol and epichlorohydrin at 100°C in a 500mL four-necked flask. Once a uniform mixed solution is formed, add benzyltriethylammonium chloride and continue heating and stirring at 100°C for 4-12 hours. Heating is discontinued when the ring-opening reaction is complete. Liquid chromatography is used to detect the ring-opening reaction product. The ring-opening reaction is complete when the polyol is completely converted into chlorohydrin ether.

[0186] The condensed ring ketal-based epoxy resin was synthesized according to the ring-closure 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 result 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 within the molecule, the characteristic peaks at positions ② and ③ belong to the characteristic peaks of the epoxy hydrogen on the main chain, 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-based epoxy resin in Example 2. Due to the symmetry of the molecular structure of the tetrafunctional condensed ring ketal-based epoxy resin, the characteristic peaks in its hydrogen and carbon nuclear magnetic resonance spectra are degenerate.

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

[0192] The methods for testing the examples or comparative examples of the present application are as follows:

[0193] Epoxy resin viscosity test: Based on the national standard GB / T 22314-2008, "Standard for Determination of Viscosity of Plastic Epoxy Resins," a rotational viscometer was used for testing at a temperature of 25°C.

[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 of epoxy resin samples and blank control group are titrated. The average value of the epoxy value obtained by the test is taken as the final epoxy value of the epoxy resin.

[0195] Epoxy insulation material glass transition temperature test: According to the national standard GB / T 40396-2021 "Test method for glass transition temperature of polymer-based composite materials - Dynamic mechanical analysis (DMA)", a dynamic thermomechanical analyzer is used to test the glass transition temperature of the material. The test mode is single and double cantilever mode. The test conditions are air atmosphere, a heating rate of 5°C / min, a loading frequency of 1Hz, and the temperature is raised from room temperature to 250°C. After cooling to room temperature, the temperature is raised to 250°C again at the same rate. The program heating is terminated when the modulus change tends to be flat. The test curve is processed to obtain the glass transition temperature of the test material.

[0196] Epoxy insulation material dielectric strength test: According to the national standard GB / T 1408.1-2016, "Electrical Strength Test Method for Insulating Materials," the dielectric strength of each sample was measured under a short-term electric field at a voltage ramp rate of 2 kV / s. The measurement environment temperature was 25°C, and the test specimens were 100 mm diameter, 1 mm thick discs. The test voltage frequency was 50 Hz. Three finished products were selected for each sample, and three points were tested on each sample, resulting in nine dielectric strength data points for each sample. The test results were averaged, and the material dielectric strength data were fitted using a Weibull distribution.

[0197] Epoxy insulation material flexural strength test: Based on the national standard GB / T2567-2008, "Test Method for Properties of Cast Resin," a universal mechanical testing machine was used to measure the elastic modulus and flexural strength of the specimens. The test specimens were cast and prepared according to the technical requirements specified in GB / T2567-2008. The test temperature was 25°C and the ambient humidity was 50% RH. The test speed was 10 mm / min for flexural strength and 2 mm / min for elastic modulus. The arbitration test speed was 2 mm / min. Each specimen was tested three times, and the measurement results were averaged.

[0198] Epoxy insulation material tensile strength test: Based on the national standard GB / T2567-2008, "Test Methods for Properties of Cast Resin," a universal mechanical testing machine was used to measure the tensile strength and elongation at break of the specimens. The test specimens were cast according to the technical requirements of GB / T2567-2008. The test temperature was 25°C and the relative humidity was 50%. The test speed was 10 mm / min for tensile strength and 2 mm / min for arbitration tests. For other properties, the test speed was 2 mm / min. Each specimen was tested three times, and the measurement results were averaged.

[0199] Chemical degradation performance test of epoxy insulation materials: Epoxy material samples of the same mass and size are selected, placed in a degradation reactor, and chemically degraded 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 epoxy resin and insulating material obtained are shown in Tables 1 and 2. Figures 1 to 6 shown.

[0201] Table 1 Comparison of performance parameters of condensed ring 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 features in terms of 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 performance parameters that can be adjusted 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 example is in the range of 0.47 to 0.78. By regulating the epoxy value of the epoxy resin, the network microscopic properties such as the cross-linking density and free volume ratio 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, 0.5462, which has the best invention effect.

[0204] The condensed ring ketal-based epoxy resin obtained in this application also has a lower viscosity value. Wherein, as shown in Table 1, the viscosity range of the condensed ring ketal-based 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-based 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 epoxy resin casting and curing process, reducing the risk of insulation failure of the epoxy resin material, and ensuring 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 resin viscosity. It can be found that when the condensed ring ketal-based skeleton and epichlorohydrin and 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, by adding an excess of epichlorohydrin, the reaction can be promoted to the right and the conversion rate of the reaction can be improved. 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 the organic chlorine content in the epoxy resin can give the epoxy insulating material better electrical insulation performance. 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, by optimizing the material ratio of the polyhydroxy compound with a condensed ring ketal molecular skeleton to epichlorohydrin and the catalyst during the open loop process, and the amount of NaOH added dropwise during the closed loop process, a lower hydrolyzable chlorine content in the condensed ring ketal epoxy resin can be achieved, 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 properties 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 insulation materials in Comparative Examples 1 and 2 were 73 MPa and 78 MPa, respectively. The tensile strengths of the condensed ring ketal epoxy insulation materials in Examples 1, 2, 3, and 4 can reach more than 80 MPa. The tensile strength of the trifunctional condensed ring ketal epoxy insulation material (Example 3) can reach 88 MPa. The tensile strength of the condensed ring ketal epoxy insulation material with a longer molecular chain (Example 4) can also reach 86 MPa, which is more than 10% higher than that of the comparative example. The higher tensile strength of the epoxy material can, to a certain extent, reflect the improvement in the rigidity and toughness of the material, giving the material 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 106 MPa and 112 MPa respectively, and the bending strengths of the condensed ring ketal-based epoxy insulating materials in Examples 1, 2, 3 and 4 can reach more than 108 MPa, and when the functionality of the epoxy resin is 3 (Example 3), the bending strength of the condensed ring ketal-based epoxy insulating material can be 126 MPa, which is more than 15% higher than that of 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 110 MPa, which also reflects the compatibility of the condensed ring ketal epoxy resin with a variety of anhydride curing agents and amine accelerators. The improvement of the bending strength of the epoxy insulating material 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 values ​​of commercial bisphenol A and bisphenol F epoxy insulation materials in Examples 1 and 2 are g They are 136°C and 132°C respectively. The glass transition temperature of the condensed ring ketal-based epoxy insulating material in Examples 1, 2, 3 and 4 can reach above 142°C, and with the improvement 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 the condensed ring ketal-based epoxy insulating material can still reach above 140°C, and its thermal properties are significantly improved compared to commercial epoxy insulating materials.

[0213] In terms of dielectric strength, the dielectric strength of the commercial bisphenol A and bisphenol F epoxy insulation materials in Comparative Examples 1 and 2 are both around 35.5kV / mm. The dielectric strength of the condensed ring ketal-based epoxy insulation materials in Examples 1, 2, 3 and 4 is in the range of 37.8 to 40.9kV / mm, which is 6.5% to 15% higher than the dielectric strength of commercial epoxy insulation materials. The multifunctional condensed ring ketal-based epoxy insulation material has 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 insulation material. And after selecting other types of anhydride curing agents and amine accelerators, the dielectric strength of the condensed ring ketal-based epoxy insulation material can still be 37kV / 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 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 degrading a piece of commercial epoxy insulating material with a mass of 1.5g, it takes at least 30h to completely degrade. In comparison, 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 these conditions 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 achieving efficient degradation of thermosetting epoxy materials. In addition, when other anhydride curing agents and amine accelerators are selected, the chemical degradation rate of condensed ring ketal-based epoxy insulation materials in a 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 insulation material provided in this application, due to the structurally adjustable characteristics, give the epoxy insulation 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 this 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 document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising 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 they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. 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 various embodiments of the present invention.

Claims

1. A highly degradable epoxy resin having the molecular structure: in, R1, R2, R3, and R4 are any of the following four combinations: Combination 1: R1 = CH2, R2 = CH2, R3 = CH3, R4 = CH3; Combination 2: R1=CH2, R2=CH2, R3=CH2OC3H5O, R4=CH2OC3H5O; Combination 3: R1=CH2, R2=CH2, R3=CH2OC3H5O, R4=CH3; Combination 4: R1=C3H6, R2=C3H6, R3=CH3, R4=CH3.

2. The method for preparing the highly degradable epoxy resin according to claim 1, wherein: The method comprises: Prepare 1,2,4,5-tetrahydroxyphenol, aliphatic ketone and p-toluenesulfonic acid in a molar ratio of 1:2:0.1; 1,2,4,5-tetrahydroxyphenol and fatty ketone are placed in organic solvent A, stirred at 60-120°C to completely dissolve, and then p-toluenesulfonic acid is added and stirred for 4-8 hours. After the reaction is complete, the mixture is filtered and the excess organic solvent A is evaporated to obtain a polyhydroxy compound with a condensed ring ketal as a molecular skeleton. preparing a polyol, epichlorohydrin, and a catalyst in a molar ratio of 0.5-1.5:3-20:0.001-0.1; The polyol and epichlorohydrin are heated and mixed in a container, and after dissolving 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 the ring-opening reaction is completed when the polyol is completely converted into chlorohydrin ether; 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-closure 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, 1,3-dihydroxyacetone, and 5-hydroxy-2-pentanone.

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 insulation material using the highly degradable epoxy resin according to any one of claims 1 to 6, characterized in that: The method comprises: Prepare high-degradable epoxy resin, acid 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 mixing 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 0.1 MPa using a vacuum pouring device at a pouring rate of 3 to 6 mL / s. After the pouring is completed, the vacuum condition is maintained for 10 to 20 minutes, the mold is transferred to an oven, and the curing program is set to pre-curing at 80°C for 6 hours and post-curing at 120°C for 6 to 12 hours. After the curing is completed, the sample in the mold is naturally cooled to room temperature and then demolded to obtain a cross-linked and cured condensed ring ketal-based epoxy insulation 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 accelerators.

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