Core-shell thermal conductive powder for reducing the viscosity of polyurethane potting glue and preparation method thereof

Abstract

The present invention discloses a core-shell thermal conductive powder and a preparation method for reducing the viscosity of polyurethane potting glue, and relates to the technical field of core-shell thermal conductive powder. The present application constructs an anchoring-bridging dual action mechanism through molecular-level interface engineering design. First, N-(N-butyl)-3-aminopropyltrimethoxysilane is used to graft thermal conductive powder. Its silane group condenses with the hydroxyl group on the filler surface to form Si-O covalent bonds, and the aminopropyl group provides an active site; then hexamethylene diisocyanate trimer is introduced to graft isocyanate groups. After being blocked with methyl ethyl ketone oxime, it cross-links with the polyurethane matrix during high-temperature curing to form a cross-scale covalent network. The outer layer is coated with a long-chain aliphatic compound, and the nano-scale monodispersion of the thermal conductive powder is achieved through the steric effect, thereby reducing the viscosity of the system.

Description

Technical Field

[0001] The invention relates to the technical field of core-shell thermal conductive powder, in particular to a core-shell thermal conductive powder for reducing the viscosity of polyurethane potting glue and a preparation method thereof. Background Art

[0002] In existing technologies, polyurethane potting compounds are commonly used in the electronics, new energy, and civilian energy storage sectors, serving a fundamental role in securing and strengthening structures. However, with technological advancements, the energy density and overall heat generation of electronic communications, new energy battery packs, and large civilian energy storage batteries have increased, leading to the emergence of thermally conductive polyurethane potting compounds. As their usage has gradually increased, so too has the demand for thermal conductivity. However, due to the cost and processing difficulties of widespread application, it is difficult to achieve an effective balance between the processability (including viscosity, flowability, self-leveling, gas generation and exhaust) and thermal conductivity and heat dissipation performance of polyurethane potting compounds. Using high-performance thermally conductive powders significantly increases costs, while using low-performance thermally conductive powders offers significant cost advantages but in most cases severely impairs the processability of the polyurethane potting compound, resulting in significant viscosity increases, difficulty in flowing, leveling, and the inability to remove bubbles. This has limited the development and application of cost-effective potting compounds.

[0003] To solve this problem, surface treatment of the filler powder in polyurethane potting compound is usually considered. Chemical substances such as silane coupling agents, titanates, and aluminates commonly used in the market can effectively improve the wettability of the powder and, to a certain extent, increase the powder filling amount while slightly reducing the viscosity to ensure the processability of the final potting compound. There are also some powders that are directly coated with saturated alkanes with lower molecular weight. However, saturated alkanes without any functional groups have obvious interfacial repulsion with polyurethane or the basic raw materials for synthetic polyurethane (isocyanates and polyols). Although they can effectively provide filling amount, they can cause stress defects, resulting in a decrease in overall strength after potting, or a decrease in thermal conductivity due to interfacial peeling.

[0004] Therefore, in order to further address this problem from the root, it is necessary to effectively improve the interfacial affinity and wettability of the powder and polyurethane. This not only needs to increase the filling amount of the powder in the polyurethane, but also significantly reduce the viscosity of the polyurethane after filling with the powder. It must also ensure that after the polyurethane is cured, there will be no interfacial defects between the powder and the polyurethane that cause peeling and cavities. Therefore, those skilled in the art have provided a core-shell thermal conductive powder and preparation method for significantly reducing the viscosity of polyurethane potting compound. Not only can the core-shell interface effectively bond, but it can also ensure the wettability and bonding between the shell and the polyurethane, thereby solving the problems raised in the above background technology. Summary of the Invention

[0005] The object of the present invention is to provide a core-shell thermal conductive powder for reducing the viscosity of polyurethane potting glue and a preparation method thereof, so as to solve the problems existing in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A core-shell thermally conductive powder for reducing the viscosity of polyurethane potting glue. The thermally conductive powder has a core-shell structure, wherein the thermally conductive powder core is a thermally conductive powder body with hydroxyl groups on the surface, and the thermally conductive powder shell is an organic shell.

[0008] As an optimization, the thermally conductive powder includes but is not limited to one or more of aluminum oxide, aluminum hydroxide, aluminum nitride, boron nitride, zinc oxide and diamond.

[0009] As an optimization, the thermal powder shell is constructed outside the thermal powder core. The surface of the thermal powder is first grafted with N-(N-butyl)-3-aminopropyltrimethoxysilane, and then the imino group on the N-(N-butyl)-3-aminopropyltrimethoxysilane is replaced by hexamethylene diisocyanate trimer, and the remaining isocyanate on the hexamethylene diisocyanate trimer is blocked with methyl ethyl ketone oxime, and finally, an aliphatic compound is used to wrap it on the outside.

[0010] As an optimization, the aliphatic compound includes but is not limited to one or more of paraffin (carbon number 18-30), sodium fatty acid, betaine, coconut oil, lauryl alcohol, dodecyl alcohol ester, laureth-6 citrate, laureth-7 citrate, dilauryl citrate, trilauryl citrate, dioctyl adipate, and dioctyl sebacate.

[0011] As an optimization, the thermal conductive powder shell accounts for 0.05% to 5.00% of the mass of the thermal conductive powder.

[0012] As an optimization, the thermally conductive powder core accounts for 95.00% to 99.95% of the mass fraction of the thermally conductive powder.

[0013] As an optimization, the particle size of the thermal conductive powder core is 0.1~300μm, and the thickness of the thermal conductive powder shell is 0.05~1.00μm.

[0014] A method for preparing a core-shell thermally conductive powder for reducing the viscosity of polyurethane potting adhesive, which is applied to any of the core-shell thermally conductive powders for reducing the viscosity of polyurethane potting adhesives described above, comprises the following steps:

[0015] S1. Under nitrogen protection, add the silane-modified thermally conductive powder to toluene with a mass of 12 to 15 times that of the silane-modified thermally conductive powder, stir evenly, then add N, N-dimethylethanolamine with a mass of 0.01 to 0.03 times that of the silane-modified thermally conductive powder, and then gradually add hexamethylene diisocyanate trimer with a mass of 0.08 to 0.1 times that of the silane-modified thermally conductive powder at a rate of 0.5 to 1.5 mL / s. After the addition is complete, heat to 45 to 55 ° C, stir and react for 1 to 1.5 hours, cool to 25 to 30 ° C after the reaction is completed, and then add 0.1 to 0.12 times the mass of the silane-modified thermally conductive powder to the mixture. After the addition is complete, heat to 60 to 80 ° C, react for 1.5 to 2 hours, and then cool to 25 to 30 ° C. Then, neutralize with triethylamine, filter and air-dry to obtain a closed thermally conductive powder;

[0016] S2. Add the closed thermal conductive powder to the aliphatic compound at a mass ratio of 1:50-60, and ultrasonically disperse for 20-25 minutes to obtain an oil phase. Add the oil phase to the aqueous phase at a volume ratio of 1:1 at a temperature of 25-30°C, and stir at a speed of 1700-1900 rpm for 3-5 minutes, then stir at a speed of 500-700 rpm for 4-6 hours. After standing, filter and centrifuge to obtain core-shell thermal conductive powder.

[0017] As an optimization, the silane-modified thermally conductive powder includes the following steps: adding the thermally conductive powder to anhydrous ethanol 1.3 to 1.5 times the mass of the thermally conductive powder, ultrasonically dispersing for 15 to 30 minutes, then adding N-(N-butyl)-3-aminopropyltrimethoxysilane 0.05 to 0.08 times the mass of the thermally conductive powder and deionized water 0.08 to 0.1 times the mass of the thermally conductive powder, and condensing and refluxing at a temperature of 75 to 85°C with stirring for 4 to 5 hours, then centrifuging and washing with anhydrous ethanol and deionized water 3 to 5 times, and vacuum drying to obtain the silane-modified thermally conductive powder.

[0018] As an optimization, the methyl ethyl ketone oxime solution is prepared by adding methyl ethyl ketone oxime to acetone at a mass ratio of 1:12-15 and stirring evenly.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This application uses the core-shell thermal conductive powder solution to construct an "anchoring-bridging" dual action mechanism through molecular-level interface engineering design. First, N-(N-butyl)-3-aminopropyltrimethoxysilane is used to graft the surface of the thermal conductive powder. Its trimethoxysilyl group and the hydroxyl group on the filler surface form Si-O covalent bonds through hydrolysis and condensation, growing a chemically anchored modified layer on the filler surface, while the aminopropyl group at the other end of the silane molecule provides an active site for subsequent reactions; then, hexamethylene diisocyanate trimer is introduced, and its isocyanate group reacts with the silane imino group to graft the isocyanate group to the surface of the silane modified layer. The unreacted isocyanate group is blocked by methyl ethyl ketone oxime to form a stable structure, ensuring that the potting compound does not cross-link prematurely during storage. During high-temperature curing, the unblocked isocyanate group cross-links with the polyol in the polyurethane matrix to form a filler-silane-isocyanate-polyurethane cross-scale covalent network, transforming the filler from an inert filler into an active cross-linking point;

[0021] The outer layer modification of the present application uses a long-chain aliphatic compound to physically coat the core-shell structure, and utilizes the spatial steric effect of its non-polar long carbon chain to prevent polar interactions between filler particles, so that the thermal conductive powder can be achieved in the polyurethane polyol at the nanometer level. The size of the filler agglomerates is reduced from the micrometer level to the nanometer level, greatly reducing the viscosity of the system. This multi-layer interface design combines chemical covalent bonding with physical dispersion optimization. The chemical bonding of silane-isocyanate enhances the bonding strength between the filler and the matrix, and the aliphatic outer layer ensures processing rheology and synergistic effects. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] Example 1: S1. Alumina was added to anhydrous ethanol (1.3 times the mass of the alumina), and ultrasonically dispersed for 15 minutes. N-(N-butyl)-3-aminopropyltrimethoxysilane (0.05 times the mass of the alumina) and deionized water (0.08 times the mass of the alumina) were then added. The mixture was condensed and refluxed at 75°C with stirring for 4 hours. The mixture was then centrifuged and washed three times with anhydrous ethanol and deionized water, and dried in vacuo to obtain a silane-modified thermally conductive powder.

[0024] S2. Under nitrogen protection, the silane-modified thermally conductive powder is added to toluene with a mass of 12 times that of the silane-modified thermally conductive powder, and after stirring evenly, N, N-dimethylethanolamine with a mass of 0.01 times that of the silane-modified thermally conductive powder is added, and then hexamethylene diisocyanate trimer with a mass of 0.08 times that of the silane-modified thermally conductive powder is gradually added dropwise at a rate of 0.5 mL / s. After the addition is completed, the temperature is raised to 45°C, and the reaction is stirred for 1 hour. After the reaction is completed, the temperature is cooled to 25°C, and then 0.1 times the mass of the silane-modified thermally conductive powder is added dropwise to the mixture. After the addition is completed, the temperature is raised to 60°C, and the reaction is cooled to 25°C after 1.5 hours. After neutralization with triethylamine, the mixture is filtered and air-dried to obtain a closed thermally conductive powder; the methyl ethyl ketone oxime solution is prepared by adding methyl ethyl ketone oxime to acetone at a mass ratio of 1:12 and stirring evenly;

[0025] S3. Add the closed thermal conductive powder to paraffin at a mass ratio of 1:50, and ultrasonically disperse for 20 minutes to obtain an oil phase; add the oil phase to the water phase at a volume ratio of 1:1 at a temperature of 25°C, stir at a speed of 1700 rpm for 3 minutes, and then stir at a speed of 500 rpm for 4 hours. After standing, filter and centrifuge to obtain core-shell thermal conductive powder.

[0026] Example 2: S1. Alumina was added to anhydrous ethanol (1.4 times the mass of the alumina), and ultrasonically dispersed for 22.5 minutes. N-(N-butyl)-3-aminopropyltrimethoxysilane (0.065 times the mass of the alumina) and deionized water (0.09 times the mass of the alumina) were then added. The mixture was stirred under condensation and reflux at 80°C for 4.5 hours. The mixture was then centrifuged and washed four times with anhydrous ethanol and deionized water, and dried in vacuo to obtain a silane-modified thermally conductive powder.

[0027] S2. Under nitrogen protection, the silane-modified thermally conductive powder was added to toluene with a mass of 13.5 times that of the silane-modified thermally conductive powder, and N, N-dimethylethanolamine with a mass of 0.02 times that of the silane-modified thermally conductive powder was added after stirring. Then, hexamethylene diisocyanate trimer with a mass of 0.09 times that of the silane-modified thermally conductive powder was gradually added dropwise at a rate of 1.0 mL / s. After the addition was completed, the temperature was raised to 50° C. and stirred for reaction for 1.2 hours. After the reaction was completed, the temperature was cooled to 27° C., and then 0.11 times the mass of the silane-modified thermally conductive powder was added dropwise to the mixture. After the addition was completed, the temperature was raised to 70° C., and after the reaction was completed for 1.75 hours, the temperature was cooled to 27° C., and then triethylamine was used for neutralization. The mixture was filtered and air-dried to obtain a closed thermally conductive powder. The methyl ethyl ketone oxime solution was prepared by adding methyl ethyl ketone oxime to acetone at a mass ratio of 1:13.5 and stirring evenly.

[0028] S3. Add the closed thermal conductive powder to paraffin at a mass ratio of 1:55, and ultrasonically disperse for 22 minutes to obtain an oil phase. At a temperature of 27°C, add the oil phase to the water phase at a volume ratio of 1:1, stir at a speed of 1800 rpm for 4 minutes, and then stir at a speed of 600 rpm for 5 hours. After standing, filter and centrifuge to obtain core-shell thermal conductive powder.

[0029] Example 3: S1. Alumina was added to anhydrous ethanol (1.5 times the mass of the alumina), and ultrasonically dispersed for 30 minutes. N-(N-butyl)-3-aminopropyltrimethoxysilane (0.08 times the mass of the alumina) and deionized water (0.1 times the mass of the alumina) were then added. The mixture was condensed and refluxed at 85°C with stirring for 5 hours. The mixture was then centrifuged and washed five times with anhydrous ethanol and deionized water, and dried in vacuo to obtain a silane-modified thermally conductive powder.

[0030] S2. Under nitrogen protection, the silane-modified thermally conductive powder is added to toluene with a mass of 15 times that of the silane-modified thermally conductive powder, and after stirring evenly, N, N-dimethylethanolamine with a mass of 0.03 times that of the silane-modified thermally conductive powder is added, and then hexamethylene diisocyanate trimer with a mass of 0.1 times that of the silane-modified thermally conductive powder is gradually added dropwise at a rate of 1.5 mL / s. After the addition is completed, the temperature is raised to 55°C, and the reaction is stirred for 1.5 hours. After the reaction is completed, the temperature is cooled to 30°C, and then 0.12 times the mass of the silane-modified thermally conductive powder is added dropwise to the mixture. After the addition is completed, the temperature is raised to 80°C, and the reaction is cooled to 30°C after 2 hours. After neutralization with triethylamine, the mixture is filtered and air-dried to obtain a closed thermally conductive powder; the methyl ethyl ketone oxime solution is prepared by adding methyl ethyl ketone oxime to acetone at a mass ratio of 1:15 and stirring evenly;

[0031] S3. Add the closed thermal conductive powder to paraffin at a mass ratio of 1:60, and ultrasonically disperse for 25 minutes to obtain an oil phase. At a temperature of 30°C, add the oil phase to the water phase at a volume ratio of 1:1, stir at a speed of 1900 rpm for 5 minutes, and then stir at a speed of 700 rpm for 6 hours. After standing, filter and centrifuge to obtain core-shell thermal conductive powder.

[0032] Example 4: The only difference from Example 2 is that step S1: "aluminum oxide" is changed to "zinc oxide";

[0033] Example 5: The only difference from Example 2 is that step S3: "paraffin" is changed to "sodium fatty acid";

[0034] Example 6: The only difference from Example 2 is that steps S2 and S3 are not performed;

[0035] Example 7: The only difference from Example 2 is that step S3 is not performed;

[0036] The thermally conductive powder prepared in Examples 1 to 7 above was added to the following preparation process, wherein the mass fraction of the thermally conductive powder was 55%;

[0037] Add thermally conductive powder to polyether polyol and stir under vacuum for 1 hour to prepare component A. Then add MDI as component B and mix evenly in an A:B mass ratio of 3:1. Pour the mixture into a mold and cure at room temperature for 24 hours before removing it from the mold and heating and curing at 60°C for 8 hours before conducting various tests.

[0038] Viscosity was measured according to GB / T 2794-2022; thermal conductivity was tested according to GB / T 3399-1982; the test results are shown in Table 1 below;

[0039] Table 1

[0040] ;

[0041] The data in Table 1 show that the thermally conductive powder prepared by the present invention exhibits good properties in all materials after being mixed with polyurethane.

[0042] Among them, the various indicators of Examples 4 and 5 also performed well, but the thermal conductivity of Examples 6 and 7 was poor, which was presumably caused by their poor dispersion. In addition, during the testing process, we also found that the curing speed of Examples 1 to 5 was slightly faster during the curing process. This is because in Examples 1 to 5, the powder was modified with isocyanate and then coated with aliphatic compounds, resulting in low viscosity in the early stage and fast curing speed in the later stage.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed therein. Any reference in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A core-shell thermal conductive powder for reducing the viscosity of polyurethane potting compound, characterized by: The thermal powder shell is constructed outside the thermal powder core. The thermal powder is first surface-grafted with N-(N-butyl)-3-aminopropyltrimethoxysilane, and then the imino group on the N-(N-butyl)-3-aminopropyltrimethoxysilane is substituted with hexamethylene diisocyanate trimer. The remaining isocyanate on the hexamethylene diisocyanate trimer is blocked with methyl ethyl ketone oxime, and finally, the outer shell is coated with an aliphatic compound. The aliphatic compound is one or more of paraffin wax with 18 to 30 carbon atoms, sodium fatty acid, betaine, coconut oil, lauryl alcohol, dodecyl alcohol ester, laureth-6 citrate, laureth-7 citrate, dilauryl citrate, trilauryl citrate, dioctyl adipate, and dioctyl sebacate.

2. The core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive according to claim 1, characterized in that: The thermal conductive powder is one or more of aluminum oxide, aluminum hydroxide, aluminum nitride and zinc oxide.

3. The core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive according to claim 1, characterized in that: The thermally conductive powder shell accounts for 0.05% to 5.00% of the mass of the thermally conductive powder.

4. The core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive according to claim 1, characterized in that: The thermally conductive powder core accounts for 95.00% to 99.95% of the mass fraction of the thermally conductive powder.

5. The core-shell thermal conductive powder for reducing the viscosity of polyurethane potting compound according to claim 1, characterized in that: The particle size of the thermal conductive powder core is 0.1-300 μm, and the thickness of the thermal conductive powder shell is 0.05-1.00 μm.

6. A method for preparing a core-shell thermal conductive powder for reducing the viscosity of polyurethane potting glue, characterized in that: The core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive as claimed in any one of claims 1 to 5 comprises the following steps: The thermal conductive powder is added to anhydrous ethanol in an amount of 1.3 to 1.5 times the mass of the thermal conductive powder, and ultrasonically dispersed for 15 to 30 minutes. Then, N-(N-butyl)-3-aminopropyltrimethoxysilane in an amount of 0.05 to 0.08 times the mass of the thermal conductive powder and deionized water in an amount of 0.08 to 0.1 times the mass of the thermal conductive powder are added. The mixture is stirred under condensation reflux at a temperature of 75 to 85°C for 4 to 5 hours, and then centrifuged and washed with anhydrous ethanol and deionized water for 3 to 5 times, and vacuum dried to obtain a silane-modified thermal conductive powder. S1. Under nitrogen protection, add the silane-modified thermally conductive powder to toluene with a mass of 12 to 15 times that of the silane-modified thermally conductive powder, stir evenly, then add N, N-dimethylethanolamine with a mass of 0.01 to 0.03 times that of the silane-modified thermally conductive powder, and then gradually add hexamethylene diisocyanate trimer with a mass of 0.08 to 0.1 times that of the silane-modified thermally conductive powder at a rate of 0.5 to 1.5 mL / s. After the addition is complete, heat to 45 to 55 ° C, stir and react for 1 to 1.5 hours, cool to 25 to 30 ° C after the reaction is completed, and then add 0.1 to 0.12 times the mass of the silane-modified thermally conductive powder to the mixture. After the addition is complete, heat to 60 to 80 ° C, react for 1.5 to 2 hours, and then cool to 25 to 30 ° C. Then, neutralize with triethylamine, filter and air-dry to obtain a closed thermally conductive powder; S2. Add the closed thermal conductive powder to the aliphatic compound at a mass ratio of 1:50-60, and ultrasonically disperse for 20-25 minutes to obtain an oil phase. Add the oil phase to the aqueous phase at a volume ratio of 1:1 at a temperature of 25-30°C, and stir at a speed of 1700-1900 rpm for 3-5 minutes, then stir at a speed of 500-700 rpm for 4-6 hours. After standing, filter and centrifuge to obtain core-shell thermal conductive powder.

7. The method for preparing the core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive according to claim 6, characterized in that: The methyl ethyl ketone oxime solution is prepared by adding methyl ethyl ketone oxime to acetone at a mass ratio of 1:12-15 and stirring evenly.