Core-shell heat-conducting powder for reducing viscosity of polyurethane pouring sealant and preparation method of core-shell heat-conducting powder

Abstract

The invention discloses core-shell heat-conducting powder for reducing the viscosity of a polyurethane pouring sealant and a preparation method, and relates to the technical field of core-shell heat-conducting powder. According to the method, an anchoring-bridging dual-action mechanism is constructed through molecular level interface engineering design. The preparation method comprises the following steps: firstly, N-(N-butyl)-3-aminopropyltrimethoxysilane is used for grafting heat-conducting powder, silane groups of the heat-conducting powder and hydroxyl groups on the surface of filler are condensed to form Si-O covalent bonds, and aminopropyl provides active sites; then introducing hexamethylene diisocyanate tripolymer to graft an isocyanate group, sealing by methyl ethyl ketoxime, and crosslinking with a polyurethane matrix during high-temperature curing to form a cross-scale covalent network. The outer layer is coated with a long-chain aliphatic compound, nano-scale monodispersion of the heat-conducting powder is realized through a steric hindrance effect, and the viscosity of a system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of core-shell heat-conducting powder, and specifically to a core-shell heat-conducting powder for reducing the viscosity of polyurethane potting adhesive and a preparation method thereof. Background Technique

[0002] In the prior art, polyurethane potting adhesive is usually applied in the fields of electronics, new energy, and civil energy storage, playing a basic role in fixing the structure and enhancing the structural strength. However, with the development of technology, the energy density of electronic communication, new energy battery packs, and large civil energy storage batteries has increased, the overall heat generation has increased, and heat-conducting polyurethane potting adhesive has emerged as the times require. While the usage is gradually increasing, the requirements for heat-conducting performance are also gradually increasing. However, limited by the cost of popularization and application and the processing difficulty, it is difficult to achieve an efficient balance between the processability (including viscosity, fluidity, self-leveling property, gas generation and exhaust) of polyurethane potting filling and the heat-conducting and heat-dissipating performance. Filling high-performance heat-conducting powder leads to a substantial increase in cost, and filling low-performance heat-conducting powder has a high cost advantage but in most cases will seriously damage the processability of polyurethane potting adhesive, such as a significant increase in viscosity, difficulty in flowing, inability to level, and inability to remove bubbles, etc., restricting the development and application of high-cost-effective potting adhesive.

[0003] To solve this problem, surface treatment of the filler powder in polyurethane potting adhesive is usually considered. Commonly used chemical substances such as silane coupling agents, titanates, and aluminate esters in the market can effectively improve the wettability of the powder, and to a certain extent, can also increase the powder filling amount on the premise of slightly reducing the viscosity to ensure the processability of the final potting adhesive; there are also some powders directly coated with low-molecular-weight saturated alkanes, but the saturated alkanes without any functional groups have obvious interfacial repulsive forces with polyurethane or the basic raw materials (isocyanates and polyols) for synthesizing polyurethane. Although they can effectively provide the filling amount, they will cause stress defects, resulting in a decrease in the overall strength after potting, or a decrease in heat-conducting performance due to interfacial peeling.

[0004] Therefore, in order to further solve this problem from the root cause, it is necessary to effectively improve the interfacial affinity and wetting ability between the powder and polyurethane, not only to meet the requirement of increasing the filling amount of the powder in polyurethane, but also to be able to significantly reduce the viscosity of polyurethane filled with powder, and at the same time, it is necessary to ensure that there are no interfacial defects between the cured polyurethane and the powder to cause peeling and cavities. Therefore, those skilled in the art have provided a core-shell heat-conducting powder for significantly reducing the viscosity of polyurethane potting adhesive and a preparation method thereof, not only the core-shell interface can be effectively combined, but also the wettability and bonding force between the shell and polyurethane can be ensured to solve the problems raised in the above background technique. Summary of the Invention

[0005] The object of the present invention is to provide a core-shell heat-conducting powder and a preparation method thereof for reducing the viscosity of polyurethane potting adhesive, 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: A core-shell heat-conducting powder for reducing the viscosity of polyurethane potting adhesive, the heat-conducting powder having a core-shell structure, wherein the core of the heat-conducting powder is a heat-conducting powder body with hydroxyl groups on the surface, and the shell of the heat-conducting powder is an organic shell.

[0007] As an optimization, the heat-conducting powder body includes, but is not limited to, one or several of alumina, aluminum hydroxide, aluminum nitride, boron nitride, zinc oxide, and diamond.

[0008] As an optimization, the shell of the heat-conducting powder is constructed outside the core of the heat-conducting powder. First, N-(N-butyl)-3-aminopropyltrimethoxysilane is used to carry out surface graft modification on the heat-conducting powder body, and then hexamethylene diisocyanate trimer is used to replace the imino group on N-(N-butyl)-3-aminopropyltrimethoxysilane, and methyl ethyl ketoxime is used to block the remaining isocyanate group on hexamethylene diisocyanate trimer. Finally, it is externally wrapped with an aliphatic compound.

[0009] As an optimization, the aliphatic compound includes, but is not limited to, one or several of paraffin (carbon number 18-30), sodium fatty acid, betaine, coconut oil, lauryl alcohol, dodecyl alcohol ester, lauryl polyether-6 citrate, lauryl polyether-7 citrate, dilauryl citrate, trilauryl citrate, dioctyl adipate, and dioctyl sebacate.

[0010] As an optimization, the shell of the heat-conducting powder accounts for 0.05% to 5.00% of the mass of the heat-conducting powder.

[0011] As an optimization, the core of the heat-conducting powder accounts for 95.00% to 99.95% of the mass fraction of the heat-conducting powder.

[0012] As an optimization, the particle size of the core of the heat-conducting powder is 0.1 to 300 μm, and the thickness of the shell of the heat-conducting powder is 0.05 to 1.00 μm A preparation method of a core-shell heat-conducting powder for reducing the viscosity of polyurethane potting adhesive, applied to any one of the above-mentioned core-shell heat-conducting powders for reducing the viscosity of polyurethane potting adhesive, includes the following steps: S1. Under the condition of nitrogen protection, add the silane-modified thermal conductive powder into toluene which is 12 - 15 times the mass of the silane-modified thermal conductive powder. After stirring evenly, add N,N-dimethylethanolamine which is 0.01 - 0.03 times the mass of the silane-modified thermal conductive powder. Then gradually dropwise add hexamethylene diisocyanate trimer which is 0.08 - 0.1 times the mass of the silane-modified thermal conductive powder at a speed of 0.5 - 1.5 mL / s. After the dropping is completed, raise the temperature to 45 - 55 °C and stir and react for 1 - 1.5 h. After the reaction ends, cool to a temperature of 25 - 30 °C. Then dropwise add methyl ethyl ketoxime solution which is 0.1 - 0.12 times the mass of the silane-modified thermal conductive powder to the mixture. After the dropping is completed, raise the temperature to 60 - 80 °C and react for 1.5 - 2 h, then cool to 25 - 30 °C. Then neutralize with triethylamine, filter and air-dry to obtain the encapsulated thermal conductive powder; S2. According to the mass ratio of 1:50 - 60, add the encapsulated thermal conductive powder into the aliphatic compound and ultrasonically disperse for 20 - 25 min to obtain the oil phase. Under the condition of a temperature of 25 - 30 °C, add the oil phase to the water phase according to the volume ratio of 1:1. Stir for 3 - 5 min under the condition of a rotation speed of 1700 - 1900 rmp, and then stir for 4 - 6 h under the condition of a rotation speed of 500 - 700 rmp. After standing, filter, centrifuge and dry to obtain the core-shell thermal conductive powder.

[0013] As an optimization, the silane-modified thermal conductive powder includes the following steps: add the thermal conductive powder into anhydrous ethanol which is 1.3 - 1.5 times the mass of the thermal conductive powder, ultrasonically disperse for 15 - 30 min, then add N-(N-butyl)-3-aminopropyltrimethoxysilane which is 0.05 - 0.08 times the mass of the thermal conductive powder and deionized water which is 0.08 - 0.1 times the mass of the thermal conductive powder. Under the condition of a temperature of 75 - 85 °C, carry out condensation reflux and stirring for 4 - 5 h. Then carry out centrifugal separation and wash with anhydrous ethanol and deionized water for 3 - 5 times, and dry in vacuum to obtain the silane-modified thermal conductive powder.

[0014] As an optimization, the methyl ethyl ketoxime solution is prepared by adding methyl ethyl ketoxime to acetone according to the mass ratio of 1:12 - 15 and stirring evenly.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: 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; 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

[0016] 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.

[0017] 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. S2. Under nitrogen protection, add the silane-modified thermally conductive powder to toluene which is 12 times the mass of the silane-modified thermally conductive powder. After stirring evenly, add N,N-dimethylethanolamine which is 0.01 times the mass of the silane-modified thermally conductive powder. Then gradually dropwise add hexamethylene diisocyanate trimer which is 0.08 times the mass of the silane-modified thermally conductive powder at a speed of 0.5 mL / s. After the dropping is completed, raise the temperature to 45 °C and stir and react for 1 h. After the reaction is completed, cool to a temperature of 25 °C. Then dropwise add methyl ethyl ketoxime solution which is 0.1 times the mass of the silane-modified thermally conductive powder to the mixture. After the dropping is completed, raise the temperature to 60 °C and react for 1.5 h, then cool to 25 °C. Then neutralize with triethylamine, filter and air-dry to obtain the blocked thermally conductive powder; the methyl ethyl ketoxime solution is prepared by adding methyl ethyl ketoxime to acetone according to a mass ratio of 1:12 and stirring evenly. S3. According to a mass ratio of 1:50, add the blocked thermally conductive powder to paraffin wax and ultrasonically disperse for 20 min to obtain the oil phase. Under the condition that the temperature is 25 °C, add the oil phase to the water phase according to a volume ratio of 1:1. Under the condition that the rotation speed is 1700 rmp, stir for 3 min, then under the condition that the rotation speed is 500 rmp, stir for 4 h. After standing, filter, centrifuge and dry to obtain the core-shell thermally conductive powder.

[0018] Example 2: S1. Add alumina to absolute ethanol which is 1.4 times the mass of alumina and ultrasonically disperse for 22.5 min. Then add N-(N-butyl)-3-aminopropyltrimethoxysilane which is 0.065 times the mass of alumina and deionized water which is 0.09 times the mass of alumina. Under the condition that the temperature is 80 °C, carry out condensation reflux stirring for 4.5 h. Then carry out centrifugal separation and wash 4 times with absolute ethanol and deionized water, and vacuum dry to obtain the silane-modified thermally conductive powder. S2. Under nitrogen protection, add the silane-modified thermally conductive powder to toluene which is 13.5 times the mass of the silane-modified thermally conductive powder. After stirring evenly, add N,N-dimethylethanolamine which is 0.02 times the mass of the silane-modified thermally conductive powder. Then gradually dropwise add hexamethylene diisocyanate trimer which is 0.09 times the mass of the silane-modified thermally conductive powder at a speed of 1.0 mL / s. After the dropping is completed, raise the temperature to 50 °C and stir and react for 1.2 h. After the reaction is completed, cool to a temperature of 27 °C. Then dropwise add methyl ethyl ketoxime solution which is 0.11 times the mass of the silane-modified thermally conductive powder to the mixture. After the dropping is completed, raise the temperature to 70 °C and react for 1.75 h, then cool to 27 °C. Then neutralize with triethylamine, filter and air-dry to obtain the blocked thermally conductive powder; the methyl ethyl ketoxime solution is prepared by adding methyl ethyl ketoxime to acetone according to a mass ratio of 1:13.5 and stirring evenly. 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.

[0019] 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. 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; 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.

[0020] Example 4: The only difference from Example 2 is that step S1: "aluminum oxide" is changed to "zinc oxide"; Example 5: The only difference from Example 2 is that step S3: "paraffin" is changed to "sodium fatty acid"; Example 6: The only difference from Example 2 is that steps S2 and S3 are not performed; Example 7: The only difference from Example 2 is that step S3 is not performed; 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%; Thermal conductive powder is added to the polyether polyol, and the mixture is stirred under vacuum for 1 h to obtain Component A. Then, MDI is added as Component B, and the mixture is uniformly mixed according to the mass ratio of A:B of 3:1. The mixture is poured into a mold and cured at room temperature for 24 h and then taken out. After curing at 60 °C for 8 h, various tests are carried out. The viscosity is measured according to GB / T 2794-2022; the thermal conductivity is tested according to GB / T 3399—1982. The results of various tests are shown in Table 1 below. Table 1 ; As shown in the data of Table 1, all the properties of the material prepared by mixing the thermal conductive powder prepared in the present invention with polyurethane are good.

[0021] Among them, the various indicators of Examples 4 and 5 are also good, but the thermal conductivity is poor in Examples 6 and 7. It is speculated that this is due to the poor dispersion degree. And during the test, we also found that the curing speed in Examples 1-5 is faster during the curing process. This is because in Examples 1-5, the powder is modified with isocyanate and then coated with aliphatic compounds in the later stage, making its viscosity low in the early stage and the curing speed fast in the later stage.

[0022] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any regard, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be construed as limiting the claimed rights.

Claims

1. A core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive, characterized in that, The thermal conductive powder has a core-shell structure, wherein the core of the thermal conductive powder is a thermal conductive powder body with hydroxyl groups on the surface, and the shell of the thermal conductive powder is an organic shell.

2. The core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive according to claim 1, wherein The thermal conductive powder body includes one or more of, but is not limited to, alumina, aluminum hydroxide, aluminum nitride, boron nitride, zinc oxide, and diamond.

3. The core-shell thermal conductive powder for reducing the viscosity of polyurethane potting adhesive according to claim 1, wherein The shell of the thermal conductive powder is constructed outside the core of the thermal conductive powder. First, N-(N-butyl)-3-aminopropyltrimethoxysilane is used to modify the surface of the thermal conductive powder body by grafting. Then, the imino group on N-(N-butyl)-3-aminopropyltrimethoxysilane is substituted by hexamethylene diisocyanate trimer, and the remaining isocyanate groups on the hexamethylene diisocyanate trimer are blocked by methyl ethyl ketoxime. Finally, it is externally wrapped with an aliphatic compound.

4. The core-shell thermal conductive powder for reducing the viscosity of the polyurethane potting adhesive according to claim 3, characterized in that, The aliphatic compound includes one or more of, but is not limited to, paraffin wax (carbon number 18-30), sodium fatty acid, betaine, coconut oil, lauryl alcohol, dodecyl alcohol ester, lauryl polyether-6 citrate, lauryl polyether-7 citrate, dilauryl citrate, trilauryl citrate, dioctyl adipate, and dioctyl sebacate.

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

6. The core-shell thermal conductive powder for reducing the viscosity of the polyurethane potting adhesive according to claim 1, wherein The core of the thermal conductive powder accounts for 95.00% - 99.95% of the mass fraction of the thermal conductive powder.

7. The core-shell thermal conductive powder for reducing the viscosity of the polyurethane potting adhesive according to claim 1, wherein The particle size of the core of the thermal conductive powder is 0.1 - 300 μm, and the thickness of the shell of the thermal conductive powder is 0.05 - 1.00 μm.

8. A preparation method of a core-shell heat-conducting powder for reducing the viscosity of polyurethane potting adhesive, which is applied to the core-shell heat-conducting powder for reducing the viscosity of polyurethane potting adhesive described in any one of the above claims 1 to 7, characterized in that, It includes the following steps: S1. Under the protection of nitrogen, add the silane-modified thermal conductive powder body into toluene with a mass 12 - 15 times that of the silane-modified thermal conductive powder body. After stirring evenly, add N,N-dimethylethanolamine with a mass 0.01 - 0.03 times that of the silane-modified thermal conductive powder body. Then, gradually dropwise add hexamethylene diisocyanate trimer with a mass 0.08 - 0.1 times that of the silane-modified thermal conductive powder body at a speed of 0.5 - 1.5 mL / s. After the dropping is completed, raise the temperature to 45 - 55 °C and stir and react for 1 - 1.5 h. After the reaction is completed, cool to a temperature of 25 - 30 °C. Then, dropwise add a methyl ethyl ketoxime solution with a mass 0.1 - 0.12 times that of the silane-modified thermal conductive powder body. After the dropping is completed, raise the temperature to 60 - 80 °C and react for 1.5 - 2 h, then cool to 25 - 30 °C. Then, neutralize with triethylamine, filter and air-dry to obtain the blocked thermal conductive powder body. S2. According to a mass ratio of 1:50 - 60, add the blocked thermal conductive powder body into the aliphatic compound and ultrasonically disperse for 20 - 25 min to obtain an oil phase. Under the condition that the temperature is 25 - 30 °C, add the oil phase into the water phase according to a volume ratio of 1:

1. Stir at a rotation speed of 1700 - 1900 rmp for 3 - 5 min, and then stir at a rotation speed of 500 - 700 rmp for 4 - 6 h. After standing, filter, centrifuge and dry to obtain the core-shell thermal conductive powder.

9. The preparation method of the core-shell thermal conductive powder for reducing the viscosity of the polyurethane potting adhesive according to claim 8, wherein, The silane-modified thermal conductive powder comprises the following steps: adding the thermal conductive powder into absolute ethanol which is 1.3 to 1.5 times the mass of the thermal conductive powder, performing ultrasonic dispersion for 15 to 30 minutes, then adding N-(N-butyl)-3-aminopropyltrimethoxysilane which is 0.05 to 0.08 times the mass of the thermal conductive powder and deionized water which is 0.08 to 0.1 times the mass of the thermal conductive powder, carrying out condensation reflux stirring for 4 to 5 hours under the condition that the temperature is 75 to 85 °C, then performing centrifugal separation and washing with absolute ethanol and deionized water for 3 to 5 times, and drying in vacuum to obtain the silane-modified thermal conductive powder.

10. The preparation method of the core-shell thermal conductive powder for reducing the viscosity of the polyurethane potting adhesive according to claim 8, characterized in that, The methyl ethyl ketoxime solution is prepared by adding methyl ethyl ketoxime into acetone according to a mass ratio of 1:12 to 15 and stirring evenly.