A high thermal conductivity, low viscosity epoxy potting adhesive and preparation method thereof

Abstract

The present invention provides a high-thermal-conductivity, low-viscosity epoxy potting compound and a preparation method thereof. The epoxy potting compound comprises the following raw materials: an epoxy resin, a hyperbranched epoxy resin, a curing agent, a curing accelerator, a modified thermally conductive filler, a toughening filler, a reinforcing filler, and a diluent. The modified thermally conductive filler is obtained by reacting the thermally conductive filler with a hydrolyzate of an inactive organosilane, wherein the hydrolyzate of the inactive organosilane is obtained by hydrolyzing the inactive organosilane in a solution of ethanol, water, and a nonionic surfactant, and the inactive organosilane contains only hydrolyzable siloxane and no other active functional groups. The surface of the thermally conductive filler is modified by the inactive organosilane to reduce the hydroxyl groups that can enhance thixotropy, thereby covering the surface of the thermally conductive filler with the organosilane. This not only enhances the compatibility of the thermally conductive filler with the potting compound system, but also prevents thixotropy, reduces the viscosity of the system, and improves fluidity.

Description

Technical Field

[0001] The invention belongs to the technical field of epoxy potting adhesives, and particularly relates to a high-thermal-conductivity, low-viscosity epoxy potting adhesive and a preparation method thereof. Background Art

[0002] New energy electric vehicles use batteries, motors and energy conversion systems to replace traditional drive devices such as fuel engines and gearboxes. Therefore, they can effectively reduce dependence on non-renewable energy such as oil, and have become the main reason for the leapfrog development of the automotive industry.

[0003] In the field of electric vehicles, the composition and design of core components are very different from those of traditional vehicles, especially thermal conductive materials. Due to the design of new energy electric vehicles, many components require strict thermal management, such as batteries, electronic controls, motors, entertainment systems, etc. Heat needs to be discharged in a timely manner to avoid component damage and the risk of fire caused by battery overheating.

[0004] Epoxy thermal potting glue is a kind of thermal conductive material, which is commonly used for thermal potting of electric vehicle motor parts. It keeps close contact with the motor heating components and radiator, and plays the role of waterproof and moisture-proof, heat-conducting, confidential, anti-corrosion, dust-proof, insulating, temperature-resistant and shock-proof. For example, the epoxy resin potting glue disclosed in patent CN111040698B

[0005] Sealing glue, preparation method and novel electric drive motor, epoxy resin potting glue disclosed in patent CN100355851C.

[0006] In order to obtain higher thermal conductivity and crack resistance, general epoxy potting glue needs to be mixed with a large amount of thermal conductive fillers and reinforcing fillers. The above-mentioned potting glue is no exception. A large amount of fillers leads to a large viscosity of the colloid. The inventor used a hyperbranched epoxy resin in the prior application CN2023111941582. This hyperbranched epoxy resin contains more amide bonds, which will cause the rubber to become thixotropic when it interacts with thermal conductive fillers or reinforcing fillers. Although the divergent structure of the hyperbranched polymer has the characteristic of not being easily entangled, when the number of generations of the hyperbranched epoxy resin is low, the internal space of the hyperbranched molecules is larger, which will still cause the colloid to become thixotropic, resulting in increased viscosity and decreased fluidity.

[0007] Therefore, it is necessary to develop a high thermal conductivity, low viscosity epoxy potting compound to address this problem. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a high thermal conductivity, low viscosity epoxy potting compound and a preparation method thereof. The surface of the thermally conductive filler is modified by an inactive organosilane to reduce the hydroxyl groups that can improve thixotropy, so that the surface of the thermally conductive filler is covered with the organosilane. This can not only enhance the compatibility of the thermally conductive filler with the potting compound system, but also avoid thixotropy, reduce the viscosity of the system, and improve the fluidity.

[0009] To achieve the above objectives, the following specific plans are adopted:

[0010] A high-thermal-conductivity, low-viscosity epoxy potting compound comprises the following raw materials: an epoxy resin, a hyperbranched epoxy resin, a curing agent, a curing accelerator, a modified thermally conductive filler, a toughening filler, a reinforcing filler, and a diluent. The modified thermally conductive filler is obtained by reacting a thermally conductive filler with a hydrolyzate of an inactive organosilane. The hydrolyzate of the inactive organosilane is obtained by hydrolyzing the inactive organosilane in a solution of ethanol, water, and a nonionic surfactant. The inactive organosilane contains only hydrolyzable siloxane and does not contain other active functional groups.

[0011] The present invention uses a hydrolyzed solution of an inactive organosilane to modify the thermally conductive filler. Unlike organosilane coupling agents, inactive organosilanes possess only hydrolyzable groups in their molecular structure. The alkylene groups are connected to non-reactive alkyl groups, rather than reactive functional groups such as amino groups, double bonds, epoxy groups, or mercapto groups. The hydrolyzate, devoid of reactive organic groups, forms covalent bonds with the hydroxyl groups on the surface of the thermally conductive filler, coating the filler surface with the organosilane. This improves the compatibility of the filler with the potting compound system, prevents thixotropy, reduces the viscosity of the system, and improves fluidity.

[0012] Furthermore, the high thermal conductivity, low viscosity epoxy potting compound comprises the following raw materials in parts by weight: 60-80 parts of epoxy resin, 5-10 parts of hyperbranched epoxy resin, 90-100 parts of curing agent, 0.5-2 parts of curing accelerator, 800-1000 parts of modified thermally conductive filler, 10-30 parts of toughening filler, 80-100 parts of reinforcing filler, and 10-15 parts of diluent, and the amount of the inactive organosilane is 1-2 wt% of the modified thermally conductive filler.

[0013] The thermal conductive filler includes large particle size filler, medium particle size filler and small particle size filler. The average particle size of the large particle size filler is 20-60 μm, the average particle size of the medium particle size filler is 1-10 μm, and the average particle size of the small particle size filler is 0.1-1 μm.

[0014] The weight ratio of the large particle size filler, the medium particle size filler and the small particle size filler is 1-3:3-5:1-3.

[0015] The thermally conductive filler is selected from one or a combination of two or more of aluminum hydroxide, aluminum oxide, silicon dioxide, boron nitride, aluminum nitride, silicon nitride, boron nitride, magnesium oxide, silicon carbide, zinc oxide, and magnesium oxide.

[0016] The non-reactive organosilane is selected from one or a combination of two or more of amyltrimethoxysilane, ethyltriethoxysilane, amyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, methyltripropoxysilane, methyltriisopropoxysilane, methyldiethoxysilane, propyltrimethoxysilane and propyltriethoxysilane.

[0017] The modified thermally conductive filler is prepared by a method comprising the following steps:

[0018] A solution is prepared with ethanol, water and a nonionic surfactant, the pH is adjusted, and an inactive organosilane is added under stirring to carry out a hydrolysis reaction. After the reaction is completed, a thermal conductive filler is added and the reaction is carried out at room temperature. After the reaction is completed, the modified thermal conductive filler is filtered, washed, dried and ground.

[0019] The hydrolysis time is 0.5-2h, the weight ratio of the organic alcohol, water and nonionic surfactant is 95-100:1-5:0.1-0.3, the nonionic surfactant is fatty alcohol polyoxyethylene ether, selected from one or a combination of two or more of fatty alcohol polyoxyethylene (3) ether, fatty alcohol polyoxyethylene (5) ether, fatty alcohol polyoxyethylene (7) ether, fatty alcohol polyoxyethylene (9) ether, fatty alcohol polyoxyethylene (10) ether, fatty alcohol polyoxyethylene (15) ether and fatty alcohol polyoxyethylene (22) ether, the pH is adjusted to 4-6, the inactive organosilane accounts for 1-2wt% of the total weight of ethanol, water and nonionic surfactant, the room temperature reaction time is 1-3h, the washing is 1-3 times with ethanol, the drying temperature is 70-100℃, the drying time is 10-24h, and the amount of the inactive organosilane is 1-2wt% of the modified thermal conductive filler.

[0020] The hyperbranched epoxy resin is prepared by a method comprising the steps of:

[0021] S1: uniformly mixing an amino acid compound containing two carboxyl groups, a monohydric alcohol, p-toluenesulfonic acid, and a first organic solvent, heating the mixture to react, extracting the mixture with a first alkali solution after the reaction, drying the organic layer, and separating the organic layer by distillation and column chromatography to obtain an amino acid ester compound for later use;

[0022] S2: adding the amino acid ester compound obtained in step S1 and the second organic solvent to a reaction kettle, mixing them uniformly, cooling them in an ice bath, and respectively adding 1,3,5-benzenetricarboxylic acid chloride solution and the second alkali solution dropwise under stirring, and reacting at a constant temperature after the addition. After the reaction is completed, adjusting the pH to neutral, separating the oil layer, washing, separating the liquids, distilling, and distilling under reduced pressure to obtain a first-generation polyamide-ester star polymer for use;

[0023] S3 determines the ester group content of the first-generation polyamide-ester star polymer, adds the polyamide-ester star polymer obtained in step S2 to a third organic solvent, mixes evenly, raises the temperature and maintains a constant temperature, drops the solution of the product obtained in step S1, and reacts at a constant temperature after the addition is completed. After the reaction is completed, distillation and reduced pressure distillation are performed to obtain a second-generation polyamide-ester star polymer; repeating the reaction of the obtained (N-1)-generation polyamide-ester star polymer with the amino acid ester compound obtained in step S1 to obtain an N-generation polyamide-ester star polymer, where N is an integer ≥3;

[0024] S4: dispersing the N-generation polyamide-ester star polymer obtained in step S3 into a third alkali solution, heating and maintaining the temperature, reacting under stirring conditions, adjusting the pH to neutral after the reaction, separating the oil layer, and drying to obtain the N-generation polyamide-carboxylic acid star polymer for later use;

[0025] S5 determines the carboxyl content of the N-generation polyamide-carboxylic acid star polymer. The N-generation polyamide-carboxylic acid star polymer, epichlorohydrin, and quaternary ammonium salt are added to a reactor and mixed evenly. The temperature is raised for reaction, then the temperature is lowered and kept constant, and the fourth alkali solution is added dropwise. After the addition is completed, the reaction is continued at a constant temperature. After the reaction is completed, the mixture is filtered and distilled, the pH is adjusted to neutral, and the mixture is filtered and vacuum dried to obtain a hyperbranched epoxy resin.

[0026] In step S1, the amino acid compound containing two carboxyl groups is selected from one or a combination of two or more of aspartic acid, glutamic acid, and 2-amino-2-methylglutaric acid; the monohydric alcohol is selected from at least one of methanol and ethanol; the molar ratio of the amino acid compound containing two carboxyl groups, the monohydric alcohol, and p-toluenesulfonic acid is 1:2.08-2.12:2.08-2.12, the first organic solvent is selected from one or a combination of two or more of benzene, toluene, and carbon tetrachloride, and the heating is raised to 120-150°C. The reaction time is 3-5 hours, the extract is a first alkali solution with a concentration of 5-8wt%, the number of extractions is 1-3 times, the first alkali solution is not particularly limited, and sodium hydroxide and potassium hydroxide solutions are commonly used in the art. The drying is performed with a desiccant, and the desiccant includes but is not limited to sodium sulfate and magnesium sulfate. The drying time is 12-36 hours. The distillation is to remove the organic solvent and / or unreacted alcohol. The eluent used in the column chromatography is a mixture of petroleum ether and isopropanol in a volume ratio of 8-10:1;

[0027] Step S2: the second organic solvent is selected from one or a combination of two or more of dichloromethane, methyl formate, and ethyl acetate. The second alkali solution is not particularly limited, and sodium hydroxide and potassium hydroxide solutions commonly used in the art can be used. The concentration of the second alkali solution is 1-3 mol / L, and the addition time is 0.5-3 h. The concentration of the 1,3,5-benzenetricarboxylic acid chloride solution is 0.1-0.3 mol / L, and the addition time is 1-3 h. The solvent used is one of hexane, carbon tetrachloride, and chloroform. or a combination of two or more; the molar ratio of the amino group of the product obtained in step S1), the alkali in the alkali solution, and the acyl chloride group of 1,3,5-benzenetricarboxylic acid chloride is 1:0.95-1.1:0.90-0.95, the reaction time is 1-3 hours, the pH is adjusted to a concentration of 10-20wt% dilute hydrochloric acid, the washing and separation are performed alternately 1-3 times with water, the distillation is performed to remove the solvent, and the reduced pressure distillation is performed to remove unreacted amino acid ester compounds.

[0028] The third organic solvent in step S3 is selected from one or a combination of benzene, toluene, dichloromethane, and carbon tetrachloride; the temperature is raised to 40-100° C., the product obtained in step S1) is added dropwise within 1-3 hours, and the reaction time is 6-12 hours; the solution concentration of the product obtained in step 1) is 10-20 wt%, and the solvent is the second organic solvent; when preparing the N-generation polyamide-ester star polymer, the molar ratio of the amino group on the amino acid ester compound obtained in step 1) to the ester group on the (N-1)-generation polyamide-ester star polymer is 1:1.08-1.2, and the ester group content is determined according to the standard GB / T 8021-2003 Determination of Saponification Value of Petroleum Products; the distillation is to remove the solvent and the generated small molecule byproducts, and the reduced pressure distillation is to remove the unreacted amino acid ester compound;

[0029] In step S4, the mass ratio of the N-generation polyamide-ester star polymer to the third alkali solution is 1:100-120. The third alkali solution is not particularly limited, and sodium hydroxide and potassium hydroxide solutions commonly used in the art can be used. The concentration of the third alkali solution is 5-7.5 g / L, the temperature is raised to 40-60° C., the reaction time is 1-2 h, the pH is adjusted to neutral with hydrochloric acid having a concentration of 10-20 wt%, and the drying is dried with a desiccant, the desiccant includes but is not limited to anhydrous sodium sulfate and anhydrous magnesium sulfate, and the carboxyl group is determined by alkali titration;

[0030] The temperature in step S5 is raised to 90-110° C., the reaction time is 2-6 hours, the temperature is lowered to 70-100° C., the concentration of the fourth alkali solution is 10-15 mol / L, there is no special limitation on the fourth alkali solution, and sodium hydroxide and potassium hydroxide solutions commonly used in the art can be used. The fourth alkali solution is added dropwise for 1-3 hours, and the constant temperature reaction time after the fourth alkali solution is added dropwise is 1-2 hours. The filtration is to remove the generated sodium chloride, and the distillation is to remove the unreacted epichlorohydrin; the epichlorohydrin The molar ratio of oxychloropropane to carboxyl groups in the N-generation polyamide-carboxylic acid star polymer is 18.0-21.6:1.2, the molar amount of the quaternary ammonium salt is 1-3% of the molar amount of the carboxyl groups in the N-generation polyamide-carboxylic acid star polymer, the amount of the alkali in the alkali solution is 1.1-1.5 mol of alkali per 1 mol of carboxyl groups in the N-generation polyamide-carboxylic acid star polymer, and the quaternary ammonium salt is selected from one or a combination of two of tetrabutylammonium bromide, tetraethylammonium chloride, tetramethylammonium bromide, and benzyltriethylammonium chloride.

[0031] The amount of the base used in the present invention refers to the hydroxide (OH) in the base.

[0032] The epoxy resin has an epoxy value of 0.3-0.55 and is selected from one or a combination of two or more of alicyclic epoxy resin, bisphenol A epoxy resin, and bisphenol F epoxy resin.

[0033] The curing agent is an acid anhydride curing agent, which is selected from one or a combination of two or more of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, dodecenyl anhydride, glutaric anhydride, and polyazelaic anhydride.

[0034] The curing accelerator is selected from one or a combination of amine curing accelerators and imidazole curing accelerators.

[0035] The amine curing accelerator is selected from one or a combination of two or more of benzyldimethylamine, triethylamine, and benzyltriethylammonium chloride.

[0036] The imidazole curing accelerator is selected from one or a combination of two or more of 2-ethyl-4-methylimidazole, 2-methylimidazole, 2-phenylimidazole, and 2-heptadecylimidazole.

[0037] The toughening agent is selected from one or a combination of two or more of polyacrylic acid derivatives, nitrile rubber, core-shell structured acrylic polymer-epoxy system, elastomer-modified epoxy resin, and polyester microspheres.

[0038] The average particle size of the reinforcing filler is 20-50 μm. The reinforcing filler is not particularly limited and includes but is not limited to one or a combination of silicon dioxide and calcium carbonate.

[0039] The diluent is selected from one or a combination of two or more of 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

[0040] The present invention also provides a method for preparing the above-mentioned high thermal conductivity, low viscosity epoxy potting adhesive, comprising the following steps:

[0041] Add epoxy resin, hyperbranched epoxy resin, and toughening filler into the mixer, heat and mix evenly, cool to room temperature, add diluent and mix evenly, add curing agent and curing accelerator and mix evenly, add modified thermal conductive filler and reinforcing filler and mix evenly, vacuum and continue stirring, and release the pressure to obtain the above-mentioned anti-cracking epoxy thermal conductive potting glue.

[0042] The temperature is raised to 90-150° C.; the vacuum degree of the vacuuming is 0.08-0.1 MPa, and the stirring time under vacuum is 60-90 min.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention modifies the surface of the thermally conductive filler by using inactive organosilane, reduces the hydroxyl groups that can improve thixotropy, and covers the surface of the thermally conductive filler with organosilane, which can not only enhance the compatibility of the thermally conductive filler with the potting glue system, but also avoid thixotropy, reduce the viscosity of the system, and improve fluidity. DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0046] The quantitative determination of ester groups is carried out in accordance with the standard GB / T 8021-2003 Determination of saponification value of petroleum products;

[0047] The quantitative test method for carboxyl groups is alkaline titration;

[0048] The epoxy value was determined by the hydrochloric acid-acetone method;

[0049] Alicyclic epoxy resin S-21, epoxy equivalent weight 140, was purchased from Nantong Synasia New Materials Co., Ltd.

[0050] Toughening filler is Arkema acrylic polymer

[0051] Silicon dioxide was purchased from Jiangsu Lianrui New Materials Co., Ltd., brand NQ1177D, d50=28 μm.

[0052] Large-particle spherical alumina A1, with an average particle size of 30 μm, was purchased from Ya'an Baitu High-tech Materials Co., Ltd., brand BAK-30;

[0053] Medium-sized spherical alumina A2, with an average particle size of 8 μm, was purchased from Ya'an Baitu High-tech Materials Co., Ltd., brand BAM-10M6;

[0054] Small-particle spherical alumina A3, with an average particle size of 0.8 μm, was purchased from Danyang Yunhui Electronics Co., Ltd., with the brand name HL-08H.

[0055] Preparation of modified thermal conductive fillers

[0056] Preparation a1

[0057] A solution was prepared with 95 parts of ethanol, 4.9 parts of water, and 0.1 part of fatty alcohol polyoxyethylene (3) ether, and the pH was adjusted to 5 with acetic acid. 2 parts of methyltriethoxysilane were added under stirring conditions to carry out hydrolysis reaction for 0.5 hours. After the reaction, 100 parts of a thermal conductive filler prepared by compounding large-particle spherical alumina A1, medium-particle spherical alumina A2, and small-particle spherical alumina A3 in a weight ratio of 3:5:2 were added. The mixture was stirred and reacted at room temperature for 3 hours. After the reaction, the mixture was filtered, washed with ethanol 3 times, dried at 80°C for 10 hours, and ground to obtain the above-mentioned modified thermal conductive filler.

[0058] Preparation a2

[0059] The rest is the same as Preparation Example a1, except that an equal amount of ethyltriethoxysilane is used instead of methyltriethoxysilane.

[0060] Preparation a3

[0061] The rest is the same as Preparation Example a1, except that the amount of methyltriethoxysilane used is 1 part.

[0062] Preparation a4

[0063] The rest is the same as Preparation Example a1, except that the weight ratio of spherical alumina A1, spherical alumina A2, and spherical alumina A3 is 1:3:1.

[0064] Comparative Preparation Example a1

[0065] The rest is the same as Preparation Example a1, except that methyltriethoxysilane is replaced by an equal mass of 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0066] Preparation of hyperbranched epoxy resin

[0067] Preparation Example b1

[0068] 1) 1 mol of aspartic acid, 2.12 mol of methanol, 2.12 mol of p-toluenesulfonic acid, and 300 mL of toluene were mixed uniformly and heated to 130° C. for reaction. After the reaction, the mixture was extracted three times with a 5 wt % sodium hydroxide solution. The organic layer was dried over anhydrous sodium sulfate for 24 h, the methanol was distilled off, and aspartic acid methyl ester was separated by column chromatography (the eluent was a mixture of petroleum ether and isopropanol in a volume ratio of 8:1), which was set aside.

[0069] 2) 1 mol of aspartic acid methyl ester obtained in step 1) and 200 mL of dichloromethane were added to a reactor and mixed uniformly. The mixture was cooled in an ice bath, and 3 L of a 0.3 mol / L 1,3,5-benzenetricarboxylic acid chloride solution (solvent: hexane) and 0.5 L of a 2 mol / L sodium hydroxide solution were added dropwise with stirring for 3 hours. The reaction was continued at a constant temperature for 1 hour. After the reaction, the pH was adjusted to neutral with 10 wt % dilute hydrochloric acid. The oil layer was separated, washed with water, and then the separation was repeated three times in alternating order. The solvent was distilled off, and the unreacted aspartic acid methyl ester was removed by distillation under reduced pressure to obtain a first-generation polyamide-ester star polymer for use.

[0070] 3) 191.7 g of the first generation polyamide-ester star polymer obtained in step 2) (the ester group -COO- content was 40.8 wt% by quantitative determination of the ester group, and the theoretical content of the ester group in the first generation polyamide-ester star polymer was 41.3 wt%) was added to 250 mL of benzene and mixed evenly. The mixture was heated to 80 ° C and kept at a constant temperature. A solution of 0.2 mol / L aspartic acid methyl ester (solvent: dichloromethane) was added dropwise. The amount of aspartic acid methyl ester solution added was such that the molar ratio of the amino group in aspartic acid methyl ester to the ester group in the polyamide-ester star polymer was 1:0.9. The mixture was added dropwise for 1 h and kept at a constant temperature. The reaction was carried out for 10 hours. After the reaction was completed, the solvent and the generated methanol were distilled off, and the unreacted aspartic acid methyl ester was distilled off under reduced pressure to obtain a second-generation polyamide-ester star polymer; the obtained second-generation polyamide-ester star polymer (the ester group -COO- content was 36.7 wt% by quantitative determination of the ester group, and the theoretical content of the ester group in the first-generation polyamide-ester star polymer was 37.4 wt%) was reacted with aspartic acid methyl ester to obtain a third-generation polyamide-ester star polymer; the amount of aspartic acid methyl ester solution added still satisfied that the molar ratio of amino groups to ester groups in the polyamide-ester star polymer was 1:0.9;

[0071] 4) The third-generation polyamide-ester star polymer obtained in step 3) was dispersed into a sodium hydroxide solution with a concentration of 6 g / L, with a mass ratio of 1:100, and the temperature was raised to 60° C. and kept constant, and the reaction was carried out under stirring for 1.5 hours. After the reaction, the pH was adjusted to neutral with 15wt% dilute hydrochloric acid, the oil layer was separated, and dried over anhydrous magnesium sulfate to obtain a third-generation polyamide-carboxylic acid star polymer for later use; the carboxyl group -COOH content in the third-generation polyamide-carboxylic acid star polymer was measured by alkali titration to be 40.4wt%, close to the theoretical value of 41.1wt%.

[0072] 5) 133.7 g of a third-generation polyamide-carboxylic acid star polymer (calculated based on a carboxyl group-COOH content of 40.4 wt% in step 4), 21.6 mol of epichlorohydrin, and 0.036 mol of tetrabutylammonium bromide were added to a reaction kettle and mixed uniformly. The temperature was raised to 100° C. and maintained at this temperature for a ring-opening reaction for 5 h. The temperature was then lowered to 90° C. and maintained at this temperature. 0.12 L of a 15 mol / L sodium hydroxide solution was added dropwise over 1.5 h, and the ring-closing reaction was continued at this temperature for 2 h. After the reaction, the sodium chloride was filtered out and the unreacted epichlorohydrin was removed by distillation. The pH was adjusted to neutral using 10 wt% dilute hydrochloric acid, the sodium chloride was filtered out, and the reaction was dried under vacuum to obtain a hyperbranched epoxy resin. The epoxy value, measured by the hydrochloric acid-acetone method, was 0.570 (theoretical value: 0.605).

[0073] Preparation Example b2

[0074] The rest of the preparation was the same as that of Preparation Example b1, except that the reaction of the second-generation polyamide-ester star polymer with methyl aspartate was not performed in step 3), i.e., the final product of step 3) was a second-generation polyamide-ester star polymer. Steps 4) and 5) were then performed on the basis of the second-generation polyamide-ester star polymer to finally produce a hyperbranched epoxy resin. The epoxy value measured by the hydrochloric acid-acetone method was 0.614 (theoretical value is 0.626).

[0075] Preparation of potting compound

[0076] Example 1

[0077] Add 80 parts of alicyclic epoxy resin S-21, 10 parts of hyperbranched epoxy resin obtained in Preparation Example b1, and 10 parts of toughening filler into the mixer. Heat to 150°C and mix evenly, then cool to room temperature, add 15 parts of 1,6-hexanediol diglycidyl ether, 100 parts of methylhexahydrophthalic anhydride, and 1 part of benzyltriethylammonium chloride and mix evenly, then add 1000 parts of the modified thermal conductive filler of Preparation Example a1 and 80 parts of the reinforcing filler silica NQ1177D and mix evenly, evacuate at a vacuum degree of 0.1 MPa, continue stirring for 60 minutes, and release the pressure to obtain the anti-cracking epoxy thermal conductive potting adhesive.

[0078] Examples 2-4

[0079] The rest is the same as Example 1, except that the modified thermally conductive filler is prepared by Preparation Examples a2-a4.

[0080] Example 5

[0081] The rest is the same as Example 1, except that the hyperbranched epoxy resin is prepared by Preparation Example b2.

[0082] Example 6

[0083] The rest is the same as Example 1, except that the amount of the modified thermal conductive filler is 800 parts.

[0084] Comparative Example 1

[0085] The rest is the same as Example 1, except that the modified thermally conductive filler is prepared by Comparative Preparation Example a1.

[0086] Comparative Example 2

[0087] The rest is the same as Example 1, except that the thermal conductive filler is not modified.

[0088] The potting compounds prepared in the above examples and comparative examples were subjected to the following performance tests:

[0089] Viscosity: Use NDJ-77 rotational viscometer, refer to standard GB / T 2794-1995 "Determination of viscosity of adhesives", rotate the 14# rotor continuously at 20 rpm at 60±0.1℃ for 2 minutes, and read the reading after the NDJ-77 rotational viscometer reading stabilizes.

[0090] Glass transition temperature test: Tested in accordance with standard GB / T 27816-2011.

[0091] Thermal conductivity test: carried out in accordance with standard GB / T 29313-2012.

[0092] Linear expansion coefficient: German NETZSCH DIL402C linear expansion coefficient instrument was used, and the heating rate was 2℃ / min.

[0093] Thermal shock test: Bolt and nut inserts were prepared according to the standard GB / T15023-1994. The thermal shock test procedure is as follows: Place a group of five bolt and nut insert specimens in a 180°C forced air oven for 1 hour, then remove them. Immediately place them in a mixture of antifreeze and dry ice (at -35 to -40°C) with a volume of at least 10L. After 10 minutes, remove the specimens, wipe off the antifreeze, and observe whether the specimens crack. This constitutes one test cycle. Repeat the above steps until two out of the five specimens exhibit cracking. Record the number of thermal shock cycles; a higher number indicates better thermal shock resistance.

[0094] Table 1

[0095]

[0096] From the viscosity test results of the examples and comparative examples in Table 1, it can be seen that the viscosity of the potting compound using the thermally conductive filler modified with the inactive organosilane is significantly lower than that of the potting compound using the unmodified thermally conductive filler.

[0097] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A high thermal conductivity, low viscosity epoxy potting compound, characterized in that: The high thermal conductivity, low viscosity epoxy potting compound comprises the following raw materials in parts by weight: 60-80 parts of epoxy resin, 5-10 parts of hyperbranched epoxy resin, 90-100 parts of curing agent, 0.5-2 parts of curing accelerator, 800-1000 parts of modified thermal conductive filler, 10-30 parts of toughening filler, 80-100 parts of reinforcing filler, and 10-15 parts of diluent. The modified thermal conductive filler is obtained by reacting the thermal conductive filler with the hydrolyzate of inactive organosilane, and the hydrolyzate of inactive organosilane is obtained by reacting the inactive organosilane in ethanol, water, The non-ionic surfactant is obtained by hydrolysis in a solution; the non-reactive organosilane is selected from one or a combination of two or more of amyltrimethoxysilane, ethyltriethoxysilane, amyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, methyltripropoxysilane, methyltriisopropoxysilane, methyldiethoxysilane, propyltrimethoxysilane, and propyltriethoxysilane; the amount of the non-reactive organosilane is 1-2wt% of the modified thermal conductive filler; The hyperbranched epoxy resin is prepared by a method comprising the steps of: S1: uniformly mixing an amino acid compound containing two carboxyl groups, a monohydric alcohol, p-toluenesulfonic acid, and a first organic solvent, heating the mixture to react, extracting the mixture with a first alkali solution after the reaction, drying the organic layer, and separating the organic layer by distillation and column chromatography to obtain an amino acid ester compound for later use; S2: adding the amino acid ester compound obtained in step S1 and the second organic solvent to a reaction kettle, mixing them uniformly, cooling them in an ice bath, and respectively adding 1,3,5-benzenetricarboxylic acid chloride solution and the second alkali solution dropwise under stirring, and reacting at a constant temperature after the addition. After the reaction is completed, adjusting the pH to neutral, separating the oil layer, washing, separating the liquids, distilling, and distilling under reduced pressure to obtain a first-generation polyamide-ester star polymer for use; S3 determines the ester group content of the first-generation polyamide-ester star polymer, adds the polyamide-ester star polymer obtained in step S2 to a third organic solvent, mixes evenly, raises the temperature and maintains a constant temperature, drops the solution of the product obtained in step S1, and reacts at a constant temperature after the addition is completed. After the reaction is completed, distillation and reduced pressure distillation are performed to obtain a second-generation polyamide-ester star polymer; repeating the reaction of the obtained (N-1)-generation polyamide-ester star polymer with the amino acid ester compound obtained in step S1 to obtain an N-generation polyamide-ester star polymer, where N is an integer ≥3; S4: dispersing the N-generation polyamide-ester star polymer obtained in step S3 into a third alkali solution, heating and maintaining the temperature, reacting under stirring conditions, adjusting the pH to neutral after the reaction, separating the oil layer, and drying to obtain the N-generation polyamide-carboxylic acid star polymer for later use; S5 determines the carboxyl content of the N-generation polyamide-carboxylic acid star polymer, adds the N-generation polyamide-carboxylic acid star polymer, epichlorohydrin, and quaternary ammonium salt into a reaction kettle, mixes evenly, raises the temperature for reaction, then lowers the temperature and maintains a constant temperature, drops the fourth alkali solution, continues the constant temperature reaction after the addition, filters and distills after the reaction, adjusts the pH to neutral, filters, and vacuum-dries to obtain a hyperbranched epoxy resin; In step S1, the amino acid compound containing two carboxyl groups is selected from one or a combination of two or more of aspartic acid, glutamic acid, and 2-amino-2-methylglutaric acid; the monohydric alcohol is selected from at least one of methanol and ethanol; and the molar ratio of the amino acid compound containing two carboxyl groups, the monohydric alcohol, and p-toluenesulfonic acid is 1:2.08-2.12:2.08-2.12; In step S2, the molar ratio of the amino group of the product obtained in step S1, the base in the alkali solution, and the acyl chloride group of 1,3,5-benzenetricarboxylic acid chloride is 1:0.95-1.1:0.90-0.95; The molar ratio of the amino groups on the amino acid ester compound obtained in step S1 added in step S3 to the ester groups on the (N-1) generation polyamide-ester star polymer is 1:1.08-1.2; In step S4, the mass ratio of the N-generation polyamide-ester star polymer to the third alkali solution is 1:100-120, and the concentration of the third alkali solution is 5-7.5 g / L; In step S5, the molar ratio of epichlorohydrin to the carboxyl groups in the N-generation polyamide-carboxylic acid star polymer is 18.0-21.6:1.2, the molar amount of the quaternary ammonium salt is 1-3% of the molar amount of the carboxyl groups in the N-generation polyamide-carboxylic acid star polymer, the amount of the alkali in the alkali solution is 1.1-1.5 mol of alkali per 1 mol of carboxyl groups in the N-generation polyamide-carboxylic acid star polymer, and the quaternary ammonium salt is selected from one or a combination of two of tetrabutylammonium bromide, tetraethylammonium chloride, tetramethylammonium bromide, and benzyltriethylammonium chloride.

2. The high thermal conductivity, low viscosity epoxy potting compound according to claim 1, characterized in that: The thermal conductive filler includes a large-particle filler, a medium-particle filler, and a small-particle filler. The average particle size of the large-particle filler is 20-60 μm, the average particle size of the medium-particle filler is 1-10 μm, and the average particle size of the small-particle filler is 0.1-1 μm. The weight ratio of the large-particle filler, the medium-particle filler, and the small-particle filler is 1-3:3-5:1-3.

3. The high thermal conductivity, low viscosity epoxy potting compound according to claim 1, characterized in that: The thermally conductive filler is selected from one or a combination of two or more of aluminum hydroxide, aluminum oxide, silicon dioxide, boron nitride, aluminum nitride, silicon nitride, boron nitride, magnesium oxide, silicon carbide, zinc oxide, and magnesium oxide.

4. The high thermal conductivity, low viscosity epoxy potting compound according to claim 1, characterized in that: The modified thermally conductive filler is prepared by a method comprising the following steps: A solution is prepared with ethanol, water and a nonionic surfactant, the pH is adjusted, and an inactive organosilane is added under stirring to carry out a hydrolysis reaction. After the reaction is completed, a thermal conductive filler is added and the reaction is carried out at room temperature. After the reaction is completed, the modified thermal conductive filler is filtered, washed, dried and ground.

5. The high thermal conductivity, low viscosity epoxy potting compound according to claim 4, characterized in that: The weight ratio of the organic alcohol, water and nonionic surfactant is 95-100:1-5:0.1-0.3, the nonionic surfactant is fatty alcohol polyoxyethylene ether, and the inactive organic silane accounts for 1-2wt% of the total weight of ethanol, water and nonionic surfactant.

6. The high thermal conductivity, low viscosity epoxy potting compound according to claim 1, characterized in that: The epoxy value of the epoxy resin is 0.3-0.55, and is selected from one or a combination of two or more of alicyclic epoxy resin, bisphenol A epoxy resin, and bisphenol F epoxy resin; the curing agent is an acid anhydride curing agent; and the curing accelerator is selected from one or a combination of two of an amine curing accelerator and an imidazole curing accelerator.

7. The high thermal conductivity, low viscosity epoxy potting compound according to claim 6, characterized in that: The curing agent is selected from one or a combination of two or more of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, dodecenyl anhydride, glutaric anhydride, and polyazelaic anhydride.

8. The method for preparing the high thermal conductivity, low viscosity epoxy potting compound according to any one of claims 1 to 7, characterized in that: The steps include: Add epoxy resin, hyperbranched epoxy resin and toughening filler to the mixer and mix evenly with the temperature. Cool to room temperature, add diluent and mix evenly. Add curing agent and curing accelerator and mix evenly. Add modified thermal conductive filler and reinforcing filler and mix evenly. Vacuum and continue stirring and release the pressure.

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