Highly heat-conductive electrical castable and preparation method thereof

Abstract

This invention discloses a high thermal conductivity electrical casting refractory and its preparation method. The casting refractory contains, by weight: 75-90 parts inorganic filler, 7-13 parts bisphenol A type liquid epoxy resin, 2-5 parts aliphatic diglycidyl ether reactive diluent, 7-13 parts alicyclic anhydride curing agent, 0.2-1.2 parts monoalkoxy type titanate coupling agent, and 0.01-0.5 parts curing accelerator. The inorganic filler is a gradient particle size compound, comprising 80%-95% large-particle-size (500-2000 μm) quartz sand and 5%-20% small-particle-size (23-120 μm) alumina, modified by the coupling agent. The modified inorganic filler is mixed with resin, diluent, curing agent, and accelerator, and after degassing under reduced pressure, cured in stages at 80℃-160℃. This invention constructs a continuous thermal conductivity path with a thermal conductivity ≥2.0 W / (m·K) after curing. It also features high insulation, high mechanical strength, excellent heat resistance and flame retardancy. The process is simple and low-cost, and it is suitable for electrical equipment such as busbars, instrument transformers, and transformers.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin-based electrical insulation casting technology, specifically relating to a high thermal conductivity inorganic filler compound epoxy resin casting material and its preparation method. Background Technology

[0002] As power systems develop towards larger capacity, more compact designs, and longer lifespans, higher demands are placed on the thermal conductivity, insulation, flame retardancy, mechanical strength, and heat resistance of castables used in electrical equipment. Epoxy resin castables are widely used due to their excellent processability and insulation properties; however, pure epoxy resin has a low thermal conductivity, making it difficult to dissipate heat quickly during equipment operation, which can easily lead to excessive temperature rise, accelerated insulation aging, and shortened service life.

[0003] As power systems develop towards larger capacity, more compact designs, and longer lifespans, higher requirements are being placed on the thermal conductivity, insulation, flame retardancy, mechanical strength, and heat resistance of castables used in electrical equipment. Epoxy resin castables are widely used due to their excellent processability and insulation properties; however, pure epoxy resin has a low thermal conductivity, making it difficult to dissipate heat quickly during equipment operation, which can easily lead to excessive temperature rise, accelerate insulation aging, and shorten service life.

[0004] Existing technologies typically improve thermal conductivity by adding inorganic thermally conductive fillers, such as alumina, quartz sand, aluminum hydroxide, carbon fiber, and boron nitride. Chinese invention patent CN105061994B describes a high thermal conductivity epoxy resin composite casting material for LEDs, obtained by mixing 60g (75µm) of alumina modified with a silane coupling agent and 420g of carbon fiber (7μm in diameter and 4mm in length) with 100kg of epoxy resin and 14kg of curing agent. The thermal conductivity of the cured material reaches 1.35W / (m·K). Wang Yi [Wang Yi. Research on High Thermal Conductivity Epoxy Casting Adhesive [D], Harbin: Harbin University of Science and Technology, 2011] used 65wt% of a mixture of 325-mesh and 800-mesh alumina powder as filler and 7wt% of KH570 inorganic filler as coupling agent, achieving a thermal conductivity of 0.919 W / (m·K) for the cured epoxy casting adhesive. Guo Jian [Guo Jian. Research on High Thermal Conductivity and Flame Retardant Dry-Type Transformer Castable [D]. Beijing: Beijing Jiaotong University, 2020] 20μm silica and aluminum hydroxide were mixed in four weight ratios of 1:0, 1:1, 2:3, and 1:4. After surface modification with 2.5% JFCA-1 silane coupling agent at 90℃, composite materials were prepared with epoxy resin. The volume resistivity of all four materials remained above 10. 14In the Ω·m order of magnitude, the AC breakdown field strength remained around 20 kV / mm, and the thermal conductivity of the four materials were 1.6547, 1.5421, 1.5412, and 1.4505 W / (m·K), respectively. The aforementioned reports used silane coupling agent-modified alumina, silica, and aluminum hydroxide, all with thermal conductivity below 1.7 W / (m·K). While the approach using boron nitride and high aspect ratio carbon fibers achieved thermal conductivity above 4.0 W / (m·K), it suffered from problems such as filler agglomeration, a sharp increase in system viscosity, poor flowability, difficulty in one-time casting of thick-walled / large-sized components, and high cost, limiting its large-scale engineering application.

[0005] Therefore, there is an urgent need to develop a high thermal conductivity electrical castable that has high thermal conductivity, good fluidity, low cost, excellent comprehensive performance, and is suitable for industrial production. Summary of the Invention

[0006] This invention addresses the problems of insufficient thermal conductivity, poor processability, or excessive cost of existing castables by providing a high thermal conductivity electrical castable and its preparation method. By using gradient particle size compound fillers and titanate coupling agents for modification, a continuous thermal conductivity path is constructed, significantly improving the thermal conductivity while ensuring good insulation, mechanical, heat resistance, and flame retardant properties. The process is simple and easy to mass-produce.

[0007] The technical solution of the present invention is as follows: A high thermal conductivity electrical casting refractory comprises the following components by weight: 75-90 parts of inorganic filler 7-13 parts of bisphenol A type liquid epoxy resin, 2-5 parts of aliphatic diglycidyl ether reactive diluent. Alicyclic anhydride curing agent, 7-13 parts. 0.2–1.2 parts of monoalkoxy titanate coupling agent, Curing accelerator 0.01 to 0.5 parts.

[0008] The inorganic filler is a gradient particle size composite filler, comprising quartz sand and alumina, based on the total weight of the inorganic filler: Quartz sand accounts for 80% to 95% of the total content, with a particle size of 500 μm to 2000 μm, and is used to construct a thermally conductive framework. Alumina accounts for 5% to 20% and has a particle size of 23 μm to 120 μm. It is used to fill gaps and work together to form a continuous heat conduction path.

[0009] The inorganic filler is pre-modified with a titanate coupling agent to enhance the interfacial bonding force between the filler and the resin matrix, reduce the viscosity of the system, and improve the thermal conductivity and mechanical strength.

[0010] Preferably, the aliphatic diglycidyl ether reactive diluent is any one or a mixture of several of ethylene glycol diglycidyl ether, butylene glycol diglycidyl ether, and neopentyl glycol diglycidyl ether.

[0011] Preferably, the monoalkoxy titanate coupling agent is any one or a mixture of two of isopropyl tris(dioctylphosphoyloxy) titanate and isopropyl tris(dioctylpyrophosphoyloxy) titanate.

[0012] Preferably, the alicyclic anhydride curing agent is any one or a mixture of several of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride.

[0013] Preferably, the curing accelerator is any one or a mixture of two of 2,4,6-tris(dimethylaminomethyl)phenol and benzyldimethylamine.

[0014] A method for preparing a high thermal conductivity electrical castable includes the following steps: Step 1: Inorganic packing coupling modification Weigh out the quartz sand and alumina according to the formula, add them to a high-speed mixer and mix evenly. Heat the mixture to 65℃~75℃. Dilute the titanate coupling agent with ethanol at a mass ratio of 1:2~1:10, slowly add it to the filler and stir at 500rpm~1500rpm until the filler is fully wetted. Then heat the mixture to 95℃~105℃ and keep it at that temperature for 0.5~3 hours. At the same time, remove the ethanol solvent by venting or vacuuming the mixture and cool it to room temperature to obtain the coupling modified inorganic filler.

[0015] Step 2: Premixing the resin matrix Bisphenol A type liquid epoxy resin and aliphatic diglycidyl ether reactive diluent are added to the reaction vessel and stirred until homogeneous.

[0016] Step 3: Dispersing the filler Add the coupling modified inorganic filler obtained in step one to the reactor and stir continuously to form a uniform suspension system.

[0017] Step 4: Adding and degassing the curing system Alicyclic anhydride curing agent and curing accelerator are added to the system and stirred evenly at 500 rpm to 1500 rpm under 25℃ to 50℃ conditions; then degassing is carried out under reduced pressure of 200 Pa to 1000 Pa for 5 to 30 minutes, and the high thermal conductivity electrical casting material is obtained.

[0018] Furthermore, the resulting castable material is cured in stages: at 80℃ to 160℃, the curing temperature is reduced to 2 to 7 hours, and it is molded into an electrical insulation component.

[0019] The present invention also provides an electrical insulation casting product, which is obtained by curing the above-mentioned high thermal conductivity electrical casting material; the electrical insulation casting product is a power transmission bus insulation layer, a current transformer casting body, a voltage transformer casting body, a dry-type transformer winding enclosure, or an electrical insulator.

[0020] The beneficial effects of this invention are: 1. Excellent thermal conductivity: This invention enhances the interfacial bonding between the filler and the epoxy resin matrix by rationally selecting the ratio and particle size of quartz sand and alumina in the inorganic filler and modifying it with a specific titanate coupling agent, thereby effectively improving the heat transfer efficiency. Compared with traditional electrocasting materials, it significantly improves thermal conductivity and avoids the use of fillers such as spherical boron nitride, which are complex to manufacture and costly.

[0021] 2. Excellent Overall Performance: In addition to improved thermal conductivity, the cured electrical castable also possesses excellent insulation, flame retardant, mechanical, and heat resistance properties due to the synergistic effect of its components. Epoxy resin itself has good insulation and mechanical properties; the anhydride curing agent ensures full curing of the epoxy resin; the reactive diluent improves the flowability of the castable; and the curing accelerator accelerates the curing reaction. The phosphorus-containing titanate coupling agent not only improves the interfacial compatibility of the inorganic filler, but the phosphorus element in its molecular structure also plays a synergistic flame-retardant role with the inorganic filler, increasing the limiting oxygen index of the system. The electrical castable of this invention meets the performance requirements of electrical equipment in multiple aspects.

[0022] 3. Simple process and controllable cost: The preparation method has a clear operation process and adopts conventional processes such as stirring, drying, reaction vessel stirring, and degassing. It does not require complicated equipment or special production conditions, making it easy to carry out industrial production. At the same time, the raw materials selected are all common chemical materials with wide availability and relatively low cost, which helps to reduce product costs and improve market competitiveness.

[0023] 4. Wide range of applications: It is suitable for casting various electrical equipment such as busbars, instrument transformers, transformers, and insulators. It can also be used for casting other power equipment, meeting the needs of different power equipment for high-performance castables and has broad application prospects. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to embodiments and comparative examples. All raw materials used in the present invention are commercially available conventional industrial products. Ethanol is used as a solvent and is not included in the parts by weight.

[0025] Performance testing methods: Thermophysical properties: Thermal conductivity was measured according to GB / T 3139-2005 standard; Glass transition temperature (T gDifferential scanning calorimetry (DSC) was used for testing according to GB / T 19466.2-2004. Electrical and mechanical properties: Volume resistivity was determined according to GB / T 31838.2-2019; compressive strength was tested using a universal testing machine according to GB / T2567-2021. Combustion performance: Limiting oxygen index (LOI) was determined according to GB / T 2406.2-2009 using an oxygen index meter via the room temperature test method.

[0026] Comparative Example 1

[0027] By weight: 70 parts of quartz sand (500μm~2000μm), 10 parts of alumina (23μm~120μm), 7 parts of E54 epoxy resin, 3 parts of butylene glycol diglycidyl ether, 9 parts of methyltetrahydrophthalic anhydride, and 0.05 parts of 2,4,6-tris(dimethylaminomethyl)phenol.

[0028] Preparation: Quartz sand and alumina were mixed, wetted with ethanol at 65℃~75℃, and kept at 95℃~105℃ for 1 hour to remove the ethanol; after cooling, the remaining components were added, stirred at 1000rpm for 15 minutes, and degassed at 500Pa for 15 minutes; cured at 110℃ for 2 hours and then at 140℃ for 3 hours. Ethanol was added to maintain consistent solvent treatment conditions with the examples. No titanate coupling agent was used for modification.

[0029] Comparative Example 2

[0030] By weight: 70 parts of quartz sand (50μm~100μm), 10 parts of alumina (23μm~120μm), 7 parts of E54 epoxy resin, 3 parts of butylene glycol diglycidyl ether, 9 parts of methyltetrahydrophthalic anhydride, 0.05 parts of 2,4,6-tris(dimethylaminomethyl)phenol, and 0.5 parts of isopropyltris(dioctylphosphoyloxy)titanate.

[0031] Preparation: The coupling agent was diluted with ethanol and then the filler was modified. The remaining processes were the same as those in Comparative Example 1. Example 1

[0032] By weight: 70 parts of quartz sand (500μm~2000μm), 10 parts of alumina (23μm~120μm), 7 parts of E54 epoxy resin, 3 parts of butylene glycol diglycidyl ether, 9 parts of methyltetrahydrophthalic anhydride, 0.05 parts of 2,4,6-tris(dimethylaminomethyl)phenol, and 0.5 parts of isopropyltris(dioctylphosphoyloxy)titanate.

[0033] Preparation: Ethanol dilutes the coupling agent. Quartz sand and alumina are mixed, and the mixture is moistened with an ethanol solution of the coupling agent at 65℃~75℃. The mixture is then kept at 95℃~105℃ for 1 hour to remove the ethanol. After cooling, the remaining components are added, and the mixture is stirred at 1000rpm for 15 minutes and degassed at 500Pa for 15 minutes. The mixture is then cured at 110℃ for 2 hours and at 140℃ for 3 hours. Example 2

[0034] By weight: 70 parts of quartz sand (500μm~2000μm), 16 parts of alumina (23μm~120μm), 9 parts of E54 epoxy resin, 3 parts of neopentyl glycol diglycidyl ether, 11 parts of methyl nadic anhydride, 0.25 parts of benzyl dimethylamine, and 0.8 parts of isopropyl tris(dioctylphosphoyloxy)titanate.

[0035] Preparation: Ethanol dilutes the coupling agent. Quartz sand and alumina are mixed, and the mixture is moistened with an ethanol solution of the coupling agent at 65℃~75℃. The mixture is then kept at 95℃~105℃ for 3 hours to remove the ethanol. After cooling, the remaining components are added, and the mixture is stirred at 1000rpm for 15 minutes and degassed at 500Pa for 20 minutes. The mixture is then cured at 120℃ for 2 hours and at 150℃~160℃ for 3~4 hours. Example 3

[0036] By weight: 60 parts of quartz sand (500μm~2000μm), 15 parts of alumina (23μm~120μm), 13 parts of E54 epoxy resin, 2 parts of butylene glycol diglycidyl ether, 13 parts of methyl hexahydrophthalic anhydride, 0.2 parts of 2,4,6-tris(dimethylaminomethyl)phenol, and 0.5 parts of isopropyltris(dioctylphosphoyloxy)titanate.

[0037] Preparation: Ethanol dilutes the coupling agent. Quartz sand and alumina are mixed, and the mixture is moistened with an ethanol solution of the coupling agent at 65℃~75℃. The mixture is then kept at 95℃~105℃ for 3 hours to remove the ethanol. After cooling, the remaining components are added, and the mixture is stirred at 1000rpm for 15 minutes and degassed at 500Pa for 20 minutes. The mixture is then cured at 80℃ for 1 hour, 110℃ for 2 hours, and 140℃ for 3~4 hours. Example 4

[0038] By weight: 70 parts of quartz sand (500μm~2000μm), 10 parts of alumina (23μm~120μm), 7 parts of E54 epoxy resin, 2 parts of ethylene glycol diglycidyl ether, 9 parts of methyl nadic anhydride, 0.05 parts of 2,4,6-tris(dimethylaminomethyl)phenol, and 0.5 parts of isopropyltris(dioctylpyrophosphate)titanate.

[0039] Preparation: Ethanol dilutes the coupling agent. Quartz sand and alumina are mixed, and the mixture is moistened with an ethanol solution of the coupling agent at 65℃~75℃. The mixture is then kept at 95℃~105℃ for 0.5 hours to remove the ethanol. After cooling, the remaining components are added, and the mixture is stirred at 1000rpm for 15 minutes and degassed at 500Pa for 20 minutes. The mixture is then cured at 120℃ for 2 hours and at 150℃~160℃ for 3~4 hours.

[0040] Table 1. Performance measurement data of the cast blocks after curing obtained from the comparative examples and embodiments. sample Thermal conductivity (W / (m·K)) Volume resistivity (Ω·m) Compressive strength (MPa) Glass transition temperature (°C) LOI (%) Comparative Example 1 1.63 1.25×10¹³ 38.9 125 23 Comparative Example 2 1.23 5.38×10¹³ 40.2 118 25 Example 1 2.28 <![CDATA[1.73×10¹ 4 ]]> 51.5 142 27 Example 2 2.12 8.12×10¹³ 45.6 138 25 Example 3 2.06 <![CDATA[6.38×10¹ 4 ]]> 55.3 112 24 Example 4 2.20 <![CDATA[2.38×10¹ 4 ]]> 48.5 138 28 Table 1 lists the performance test data of the castable blocks obtained in Comparative Examples 1-2 and Examples 1-4 after curing. Comparative Example 1, without modification by a titanate coupling agent, had poor interfacial bonding and low thermal conductivity and mechanical properties. Comparative Example 2, due to the excessively small particle size of the quartz sand, could not form an effective thermally conductive framework, resulting in a significant decrease in thermal conductivity. A comparison of the comparative examples and the examples shows that the electrical castable material of this invention has a simple preparation process, and the resulting product has good thermal conductivity, insulation properties, mechanical properties, heat resistance, and flame retardant properties, which can meet the high-performance requirements of electrical equipment.

Claims

1. A high thermal conductivity electrical castable, characterized in that, The following components are included in parts by weight: 75-90 parts of inorganic filler, 7-13 parts of bisphenol A type liquid epoxy resin, 2-5 parts of aliphatic diglycidyl ether reactive diluent, 7-13 parts of alicyclic acid anhydride curing agent, 0.2-1.2 parts of monoalkoxy type titanate coupling agent, and 0.01-0.5 parts of curing accelerator; The inorganic filler is a gradient particle size composite filler, with the following composition by total weight of inorganic filler: quartz sand accounts for 80% to 95%, with a particle size of 500 μm to 2000 μm; alumina accounts for 5% to 20%, with a particle size of 23 μm to 120 μm. The inorganic filler is modified by the monoalkoxy titanate coupling agent.

2. The high thermal conductivity electrical castable according to claim 1, characterized in that, The aliphatic diglycidyl ether reactive diluent is any one or a mixture of several of ethylene glycol diglycidyl ether, butylene glycol diglycidyl ether, and neopentyl glycol diglycidyl ether.

3. The high thermal conductivity electrical castable according to claim 1, characterized in that, The monoalkoxy titanate coupling agent is any one or a mixture of two of isopropyl tris(dioctylphosphoyloxy) titanate and isopropyl tris(dioctylpyrophosphoyloxy) titanate.

4. The high thermal conductivity electrical castable according to claim 1, characterized in that, The alicyclic anhydride curing agent is any one or a mixture of several of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride.

5. The high thermal conductivity electrical castable according to claim 1, characterized in that, The curing accelerator is any one or a mixture of two of 2,4,6-tris(dimethylaminomethyl)phenol and benzyldimethylamine.

6. A method for preparing the high thermal conductivity electrical castable according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Weigh quartz sand and alumina according to the formula described in claim 1, add them to a high-speed mixer and mix, then heat to 65℃~75℃; weigh titanate coupling agent according to the formula, and dilute it with ethanol solvent at a mass ratio of 1:2~1:10, then slowly add it to the filler and stir at 500rpm~1500rpm until fully wetted; then heat to 95℃~105℃, keep the temperature for 0.5~3 hours, and at the same time remove the ethanol solvent by venting or vacuuming, then cool to room temperature to obtain the coupling modified inorganic filler; Step 2: Add epoxy resin and reactive diluent into the reaction vessel and stir to mix evenly; Step 3: Add the coupling modified inorganic packing obtained in Step 1 to the reactor and continue stirring to form a uniform suspension system; Step 4: Add alicyclic anhydride curing agent and curing accelerator to the system, stir evenly at 500 rpm to 1500 rpm under 25℃~50℃ conditions, and then degas under reduced pressure of 200Pa~1000Pa for 5~30 minutes to obtain high thermal conductivity electrical casting material.

7. The preparation method according to claim 6, characterized in that, The castable material is cured in stages at 80℃ to 160℃, with a total curing time of 2 to 7 hours.

8. An electrically insulating cast product, characterized in that, The electrical insulation casting product is obtained by curing the high thermal conductivity electrical casting material according to any one of claims 1 to 5; the electrical insulation casting product is a power transmission bus insulation layer, a current transformer casting body, a voltage transformer casting body, a dry-type transformer winding enclosure, or an electrical insulator.