Low-volatility low-yellowing heat-conducting silicone rubber and preparation method thereof

Abstract

The invention discloses low-volatility low-yellowing heat-conducting silicone rubber and a preparation method thereof, and belongs to the technical field of silicone rubber, the low-volatility low-yellowing heat-conducting silicone rubber comprises the following raw materials by weight: 100 parts of base rubber, 8-15 parts of a plasticizer, 3-8 parts of a cross-linking agent, 2-6 parts of a coupling agent, 1-5 parts of a catalyst, 30-50 parts of a flame retardant filler, 80-120 parts of a heat-conducting filler, and 5-10 parts of a thixotropic agent; the base adhesive is one of trimethoxy-terminated polydimethylsiloxane and dimethoxy-terminated polydimethylsiloxane, so that the effect that the cured adhesive still has good strength under the condition that the dosage of the cross-linking agent is reduced is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of silicone rubber, and in particular to a low-volatile, low-yellowing thermally conductive silicone rubber and a preparation method thereof. Background Art

[0002] The commonly used single-component condensation-type thermally conductive silicone rubber currently uses terminal hydroxyl polysiloxane as the base polymer, methyltrimethoxysilane as the crosslinking agent, and is further combined with flame retardant fillers, thermally conductive fillers, catalysts (bis(ethyl acetoacetate) titanate diisopropyl ester), and coupling agents. It gradually undergoes a crosslinking reaction from the outside to the inside when in contact with moisture in the air and solidifies into a solid. The existing power supply for consumer electronics (such as mobile phone chargers) has a high degree of process automation. The thermally conductive silicone rubber is dotted onto the PCB, and then ultrasonically sealed and subjected to load aging. During this process, the thermally conductive silicone rubber has not been fully cured. During load aging, the crosslinking agent, catalyst, coupling agent, etc. in the thermally conductive silicone rubber will volatilize due to the increase in temperature, filling the interior of the power supply shell and escaping through the tiny gaps in the power supply shell. As the power of consumer electronics becomes increasingly powerful and airtight, these volatilized gases can easily cause cracks in the places with greater stress on the power shell (such as the pins), and the glue is prone to yellowing under heat conditions. The crosslinking agent methyltrimethoxysilane is the main factor affecting the shell cracking, and the catalyst diisopropyl di(ethyl acetoacetate) titanate is the main factor affecting the yellowing. Reducing the amount of methyltrimethoxysilane alone can effectively reduce the cracking of the power shell, but it also has a greater impact on the extrusion and strength of the thermally conductive silicone rubber. Summary of the invention

[0003] In order to solve the problems in the prior art, the present invention provides a low-volatile, low-yellowing thermally conductive silicone rubber and a preparation method thereof, which can achieve good strength of the cured colloid while reducing the amount of cross-linking agent used.

[0004] The first object of the present invention is to provide a low volatility and low yellowing thermal conductive silicone rubber, which adopts the following technical scheme: A low-volatile, low-yellowing thermally conductive silicone rubber comprises the following raw materials in parts by weight: 100 parts of base rubber, 8-15 parts of plasticizer, 3-8 parts of cross-linking agent, 2-6 parts of coupling agent, 1-5 parts of catalyst, 30-50 parts of flame retardant filler, 80-120 parts of thermally conductive filler, and 5-10 parts of thixotropic agent; the base rubber is one of trimethoxy-terminated polydimethylsiloxane and dimethoxy-terminated polydimethylsiloxane.

[0005] Preferably, the crosslinking agent is one of cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 1,2-bis(trimethoxysilyl)ethane, and 1,2-bis(triethoxysilyl)ethane.

[0006] Preferably, the viscosity of the trimethoxy-terminated polydimethylsiloxane and dimethoxy-terminated polydimethylsiloxane is 500-2000 mPa·s at 23°C.

[0007] Preferably, the plasticizer is dimethyl silicone oil having a viscosity of 50-350 mPa·s at 23°C.

[0008] Preferably, the coupling agent is one of γ-glycidyloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane and γ-methacryloxypropyltriethoxysilane.

[0009] Preferably, the catalyst is butyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diisooctylmaleate, dimethyltin diceneodecanoate, hydroxydimethyltin, or tert-butyl titanate.

[0010] Preferably, the flame retardant filler is one of aluminum hydroxide, magnesium hydroxide and melamine cyanurate.

[0011] Preferably, the thermally conductive filler is one of aluminum oxide, zinc oxide, magnesium oxide and aluminum nitride.

[0012] Preferably, the thixotropic agent is fumed silica with a specific surface area of ​​100-300m 2 / g.

[0013] The second aspect of the present invention is to provide a method for preparing the low-volatile, low-yellowing thermally conductive silicone rubber described above, comprising the following preparation steps: S1. Stir the base rubber, plasticizer, flame retardant filler, thermal conductive filler and thixotropic agent at room temperature and pressure for 25-35 minutes, then heat to 115-125°C, and stir under vacuum for 80-100 minutes; S2, reducing the temperature of the material obtained in step S1 to below 35°C; S3. Add a catalyst, a cross-linking agent and a coupling agent to step S2, and stir for 50-70 minutes under negative pressure to obtain a low-volatile, low-yellowing thermally conductive silicone rubber.

[0014] In summary, the present invention has the following beneficial effects: 1. When the base rubber in the present application is trimethoxy-terminated polydimethylsiloxane or dimethoxy-terminated polydimethylsiloxane, it has more reactive groups than terminal hydroxyl polydimethylsiloxane. Therefore, the silicone rubber of the present application can still have good strength of the cured colloid while reducing the amount of cross-linking agent, and will not affect the extrusion performance of the silicone rubber; and after curing, the silicone rubber of the present application has good bonding force with the power shell, thereby greatly improving the anti-drop effect of the power shell.

[0015] 2. In the present application, when the cross-linking agent is selected from one of cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 1,2-bis(trimethoxysilyl)ethane, and 1,2-bis(triethoxysilyl)ethane with a higher boiling point, the volatilization amount of silicone rubber during heat curing can be reduced, thereby effectively reducing the probability of cracking of the power supply shell and reducing the scrap rate of the power supply shell.

[0016] 3. When one of butyl tin acetate, dibutyl tin dilaurate, dioctyl tin dilaurate, dibutyl tin diisooctyl maleate, dimethyl tin dineodecanoate, hydroxydimethyl tin, and tert-butyl titanate is selected as a catalyst in this application, its combination with the base rubber and the cross-linking agent makes the silicone rubber have a good anti-yellowing effect when it is heated and aged before curing, and the above-mentioned catalyst, the base rubber and the cross-linking agent in this application can form a curing system with good storage stability.

[0017] 4. Compared with the single-component condensation silicone rubber used in the existing power supply production process, the silicone rubber obtained in the present application is highly compatible with the power supply shell and does not need to be left in the air in the power supply production process (the existing single-component condensation silicone rubber dispensing needs to be left in the air for more than 2 hours before ultrasonic sealing box load aging can be performed). After dispensing, ultrasonic sealing box load aging can be performed directly, and continuous production can be carried out, which can greatly improve production efficiency. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the embodiments.

[0019] The raw materials used in the examples of this application are all commercially available.

[0020] A low-volatile, low-yellowing thermally conductive silicone rubber comprises the following raw materials in parts by weight: 100 parts of base rubber, 8-15 parts of plasticizer, 3-8 parts of cross-linking agent, 2-6 parts of coupling agent, 1-5 parts of catalyst, 30-50 parts of flame retardant filler, 80-120 parts of thermally conductive filler, and 5-10 parts of thixotropic agent; the base rubber is one of trimethoxy-terminated polydimethylsiloxane and dimethoxy-terminated polydimethylsiloxane.

[0021] In the present application, the cross-linking agent is one of cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 1,2-bis(trimethoxysilyl)ethane, and 1,2-bis(triethoxysilyl)ethane. The effects that can be achieved by cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 1,2-bis(trimethoxysilyl)ethane, and 1,2-bis(triethoxysilyl)ethane are basically the same. Therefore, cyclohexyltrimethoxysilane is used as an example in the following embodiments of the present application.

[0022] In the present application, the viscosity of the trimethoxy-terminated polydimethylsiloxane and the dimethoxy-terminated polydimethylsiloxane is 500-2000 mPa·s at 23°C.

[0023] In the present application, the plasticizer is dimethyl silicone oil having a viscosity of 50-350 mPa·s at 23°C.

[0024] In the present application, the coupling agent is one of γ-glycidyloxypropyl trimethoxysilane, γ-aminopropyl triethoxysilane, γ-methacryloxypropyl trimethoxysilane, and γ-methacryloxypropyl triethoxysilane, and the effects that can be achieved by γ-glycidyloxypropyl trimethoxysilane, γ-aminopropyl triethoxysilane, γ-methacryloxypropyl trimethoxysilane, and γ-methacryloxypropyl triethoxysilane are basically the same. Therefore, γ-glycidyloxypropyl trimethoxysilane is used as an example in the following embodiments of the present application.

[0025] In the present application, the catalyst is butyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diisooctylmaleate, dimethyltin diceneodecanoate, hydroxydimethyltin, and tert-butyl titanate, and the effects that can be achieved by butyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diisooctylmaleate, dimethyltin diceneodecanoate, hydroxydimethyltin, and tert-butyl titanate are basically the same, so butyltin diacetate is used as an example in the embodiments of the present application.

[0026] In the present application, the flame retardant filler is one of aluminum hydroxide, magnesium hydroxide, and melamine cyanurate, and aluminum hydroxide, magnesium hydroxide, and melamine cyanurate have basically the same effect on the flame retardant properties of silicone rubber, so aluminum hydroxide is used as an example in the embodiments of the present application.

[0027] In the present application, the thermally conductive filler is one of aluminum oxide, zinc oxide, magnesium oxide, and aluminum nitride. Aluminum oxide, zinc oxide, magnesium oxide, and aluminum nitride have basically the same effects on the thermal conductivity of silicone rubber, so aluminum oxide is used as an example in the embodiments of the present application.

[0028] In the present application, the thixotropic agent is fumed silica with a specific surface area of ​​100-300m 2 / g.

[0029] Example 1 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber comprises the following preparation steps: S1. Put 100 kg of trimethoxy-terminated polydimethylsiloxane, 8 kg of dimethyl silicone oil, 30 kg of aluminum hydroxide, 80 kg of aluminum oxide and 5 kg of fumed silica into a bonding machine, stir for 25 min at a stirring rate of 50 r / min at room temperature and pressure, then heat to 115°C and stir in a vacuum for 80 min; wherein the viscosity of trimethoxy-terminated polydimethylsiloxane at 23°C is 500 mPa·s, and the viscosity of dimethyl silicone oil at 23°C is 50 mPa·s; S2, transferring the material obtained in step S1 to a planetary machine, and passing cooling water to reduce the material temperature to below 35°C; S3. Add 1 kg of butyltin diacetate, 3 kg of cyclohexyltrimethoxysilane and 2 kg of γ-glycidyloxypropyltrimethoxysilane to step S2, and stir for 50 min at a negative pressure rate of 45 r / min and a dispersion rate of 300 r / min to obtain a low-volatile, low-yellowing thermally conductive silicone rubber.

[0030] Example 2 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber comprises the following preparation steps: S1. Put 100 kg of dimethoxy-terminated polydimethylsiloxane, 12 kg of dimethyl silicone oil, 40 kg of aluminum hydroxide, 100 kg of aluminum oxide and 8 kg of fumed silica into a bonding machine, stir for 30 min at a stirring rate of 50 r / min at normal temperature and pressure, then heat to 120°C, and stir in a vacuum for 90 min; wherein the viscosity of dimethoxy-terminated polydimethylsiloxane at 23°C is 500 mPa·s, and the viscosity of dimethyl silicone oil at 23°C is 50 mPa·s; S2, transferring the material obtained in step S1 to a planetary machine, and passing cooling water to reduce the material temperature to below 35°C; S3. Add 3 kg of butyltin diacetate, 5 kg of cyclohexyltrimethoxysilane and 4 kg of γ-glycidyloxypropyltrimethoxysilane to step S2, and stir for 60 min at a stirring rate of 45 r / min and a dispersion rate of 300 r / min under negative pressure to obtain a low-volatile, low-yellowing thermally conductive silicone rubber.

[0031] Example 3 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber comprises the following preparation steps: S1. Put 100 kg of trimethoxy-terminated polydimethylsiloxane, 15 kg of dimethyl silicone oil, 50 kg of aluminum hydroxide, 120 kg of aluminum oxide and 10 kg of fumed silica into a bonding machine, stir for 35 min at a stirring rate of 50 r / min at normal temperature and pressure, then heat to 125°C, and stir in a vacuum for 100 min; wherein the viscosity of trimethoxy-terminated polydimethylsiloxane at 23°C is 500 mPa·s, and the viscosity of dimethyl silicone oil at 23°C is 50 mPa·s; S2, transferring the material obtained in step S1 to a planetary machine, and passing cooling water to reduce the material temperature to below 35°C; S3. Add 5 kg of butyltin diacetate, 8 kg of cyclohexyltrimethoxysilane and 6 kg of γ-glycidyloxypropyltrimethoxysilane to step S2, stir at a negative pressure rate of 45 r / min and a dispersion rate of 300 r / min for 70 min to obtain a low-volatile, low-yellowing thermally conductive silicone rubber.

[0032] Example 4 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber, which is different from Example 2 in that the viscosity of dimethoxy-terminated polydimethylsiloxane at 23° C. is 1200 mPa·s, and the rest is the same as Example 2.

[0033] Example 5 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber, which is different from Example 2 in that the viscosity of dimethoxy-terminated polydimethylsiloxane at 23° C. is 2000 mPa·s, and the rest is the same as Example 2.

[0034] Example 6 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber, which is different from Example 4 in that the viscosity of dimethyl silicone oil at 23° C. is 200 mPa·s, and the rest is the same as Example 4.

[0035] Example 7 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber, which is different from Example 4 in that the viscosity of dimethyl silicone oil at 23° C. is 350 mPa·s, and the rest is the same as Example 4.

[0036] Comparison example A method for preparing thermally conductive silicone rubber, which is the same as the preparation method in Example 2 of the present application, and the amount of raw materials used is: 100 kg of terminal hydroxyl polydimethylsiloxane (viscosity at 23°C is 1500 mPa·s), 5 kg of dimethyl silicone oil, 10 kg of cross-linking agent methyltrimethoxysilane, 5 kg of catalyst diisopropyl di(ethyl acetoacetate), 60 kg of aluminum hydroxide, 80 kg of aluminum oxide, and 10 kg of calcium carbonate.

[0037] Comparative Example 1 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber, which is different from Example 2 in that an equal amount of methyltrimethoxysilane is used instead of cyclohexyltrimethoxysilane, and the rest is the same as Example 2.

[0038] Comparative Example 2 A method for preparing low-volatile, low-yellowing thermally conductive silicone rubber, which differs from Example 2 in that an equal amount of terminal hydroxyl polydimethylsiloxane is used instead of dimethoxy-terminated polydimethylsiloxane, and an equal amount of bis(ethyl acetoacetate) diisopropyl titanate is used instead of butyltin diacetate, and the rest are the same as Example 2.

[0039] Performance Testing The silicone rubber obtained from the above embodiments, control examples and comparative examples was tested for surface drying time, hardness, tensile strength, elongation, shear strength, thermal conductivity, volume resistivity, dielectric strength, high temperature yellowing performance and compatibility with power supply. The power supply compatibility test was conducted by temperature shock test and damp heat test. The conditions of the temperature shock test were: -40°C (30min) ~ 80°C (30min), 96h, and the conditions of the damp heat test were: placed at 85°C and 85% relative humidity for 96h. The test results are shown in Table 1.

[0040] Table 1 Silicone rubber test results From the table above we can see that: Compared with the control example, the thermally conductive silicone rubber obtained in Examples 1-7 still has good tensile strength and shear strength when the cross-linking agent is reduced. Moreover, after the silicone rubber obtained in Examples 1-3 of the present application is used in a power supply shell, the power supply shell will not crack after the temperature shock test and the damp heat test, while the silicone rubber obtained in the control example will crack when used in the power supply shell. Therefore, the combined use of the base rubber, the cross-linking agent, and the catalyst in the present application can improve the strength and yellowing resistance of the silicone rubber when the cross-linking agent content is reduced. Moreover, due to the combined use of the components in the present application, the volatilization amount of the silicone rubber can be reduced, thereby effectively preventing the power supply shell from cracking after the temperature shock test and the damp heat test.

[0041] Compared with Example 2, when the base rubber is dimethoxy-terminated polydimethylsiloxane and the cross-linking agent is methyltrimethoxysilane, the tensile strength and shear strength of the silicone rubber obtained in Comparative Example 1 are greatly reduced compared with those in Example 2. It can be seen that the combination of dimethoxy-terminated polydimethylsiloxane and cyclohexyltrimethoxysilane in the present application can effectively improve the strength of the silicone rubber.

[0042] Compared with Example 2, when the base rubber is terminal hydroxyl polydimethylsiloxane and the catalyst is diisopropyl bis(ethyl acetoacetate) titanate, the hardness, tensile strength and shear strength of the silicone rubber obtained in Comparative Example 2 are lower than those in Example 2, and the yellowing resistance of the silicone rubber is also reduced. This can further illustrate that the combined use of the components in the present application can effectively improve the strength, yellowing resistance and low volatility of the silicone rubber, while also improving the compatibility of the silicone rubber with the power supply shell.

[0043] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low volatility and low yellowing thermally conductive silicone rubber, characterized in that: The invention comprises the following raw materials in parts by weight: 100 parts of base glue, 8-15 parts of plasticizer, 3-8 parts of cross-linking agent, 2-6 parts of coupling agent, 1-5 parts of catalyst, 30-50 parts of flame retardant filler, 80-120 parts of thermal conductive filler and 5-10 parts of thixotropic agent; the base glue is one of trimethoxy-terminated polydimethylsiloxane and dimethoxy-terminated polydimethylsiloxane.

2. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The crosslinking agent is one of cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 1,2-bis(trimethoxysilyl)ethane and 1,2-bis(triethoxysilyl)ethane.

3. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The viscosity of the trimethoxy-terminated polydimethylsiloxane and the dimethoxy-terminated polydimethylsiloxane is 500-2000 mPa·s at 23°C.

4. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The plasticizer is dimethyl silicone oil with a viscosity of 50-350 mPa·s at 23°C.

5. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The coupling agent is one of γ-glycidyloxypropyl trimethoxysilane, γ-aminopropyl triethoxysilane, γ-methacryloxypropyl trimethoxysilane and γ-methacryloxypropyl triethoxysilane.

6. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The catalyst is butyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diisooctylmaleate, dimethyltin dineodecanoate, hydroxydimethyltin, and tert-butyl titanate.

7. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The flame retardant filler is one of aluminum hydroxide, magnesium hydroxide and melamine cyanurate.

8. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The thermal conductive filler is one of aluminum oxide, zinc oxide, magnesium oxide and aluminum nitride.

9. The low-volatile, low-yellowing thermally conductive silicone rubber according to claim 1, characterized in that: The thixotropic agent is fumed silica with a specific surface area of ​​100-300m 2 / g.

10. A method for preparing the low-volatile, low-yellowing thermally conductive silicone rubber according to any one of claims 1 to 9, characterized in that: The method comprises the following preparation steps: S1. Stir the base rubber, plasticizer, flame retardant filler, thermal conductive filler and thixotropic agent at room temperature and pressure for 25-35 minutes, then heat to 115-125°C, and stir under vacuum for 80-100 minutes; S2, reducing the temperature of the material obtained in step S1 to below 35°C; S3. Add a catalyst, a cross-linking agent and a coupling agent to step S2, and stir for 50-70 minutes under negative pressure to obtain a low-volatile, low-yellowing thermally conductive silicone rubber.

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