Flame-retardant thermal insulation silicone rubber and method for producing the same

Abstract

The application relates to the technical field of silicone rubber, and discloses a flame-retardant heat-insulating silicone rubber and a preparation method thereof. A flame-retardant auxiliary agent and hollow glass microbeads are reacted, and then methyl vinyl silicone rubber, hydroxyl silicone oil, a reinforcing agent, a flame retardant, and a vulcanizing agent are added into an open mill for mixing and vulcanization to obtain the flame-retardant heat-insulating silicone rubber. The flame-retardant auxiliary agent contains a siloxane structural unit and is grafted on the surface of the hollow glass microbeads, the compatibility between the flame-retardant auxiliary agent and the methyl vinyl silicone rubber is improved, the hollow glass microbeads are more uniformly dispersed in the silicone rubber matrix, a uniform heat-insulating network is formed, the thermal conductivity is reduced, and the heat-insulating performance is improved. The flame-retardant auxiliary agent contains a nitrogen-rich triazine group, and nitrogen gas and other non-combustible gases are generated during combustion, the oxygen concentration of the combustion atmosphere can be diluted, and the limiting oxygen index, the flame-retardant performance, and the high-temperature resistance of the silicone rubber are improved.

Description

Technical Field

[0001] This invention relates to the field of silicone rubber technology, specifically to a flame-retardant and heat-insulating silicone rubber and its preparation method. Background Technology

[0002] Silicone rubber is widely used in household appliances, medical devices, the automotive industry, and building construction due to its high elasticity, good mechanical properties, excellent electrical insulation, and high temperature resistance. However, silicone rubber is flammable and releases smoke when burned, posing a significant safety hazard. Flame retardants, such as zinc borate, aluminum hydroxide, and magnesium hydroxide, are typically added to address this issue. Chinese patent CN103819897B discloses a nitrogen-based flame retardant, its preparation method, and a flame-retardant silicone rubber composite. Using melamine, cyanuric acid, pentaerythritol, sodium hypophosphite, and zinc borate as raw materials, a nitrogen-based flame retardant was prepared, improving the flame retardant properties of silicone rubber. However, the addition of nitrogen-based flame retardants and zinc borate can negatively impact the high-temperature resistance of silicone rubber.

[0003] Hollow glass microspheres are a type of lightweight, micron-sized material with low thermal conductivity and good mechanical properties. They are mainly used in polymer materials such as silicone rubber, nylon, polyethylene, and polystyrene. However, hollow glass microspheres have poor compatibility with silicone rubber, and surface modification is usually required to effectively improve the thermal insulation and mechanical properties of the material. Summary of the Invention

[0004] (i) This invention solves the problem of poor heat insulation and flame retardant properties of silicone rubber.

[0005] (II) Technical solution of the present invention: A method for preparing flame-retardant and heat-insulating silicone rubber, comprising:

[0006] (1) The preparation method of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine is as follows: 2,4-dichloro-6-phenyl-1,3,5-triazine, 4-vinylphenylboronic acid, and tetra(triphenylphosphine)palladium are added to toluene in a molar ratio of 1:(2-2.2):(0.05-0.06). A potassium carbonate aqueous solution is added dropwise. The mixture is heated to 90-100℃ under a nitrogen atmosphere and reacted for 12-18 h. After concentration under reduced pressure and drying, the crude product is separated by silica gel column chromatography and eluted with ethyl acetate in petroleum ether solution to obtain 2,4-bis(styryl)-6-phenyl-1,3,5-triazine. The preparation reaction formula is as follows:

[0007]

[0008] (2) Add a solution of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine and chloroplatinic acid in isopropanol to toluene. Under a nitrogen atmosphere, add 1,1,3,3-tetramethyldisiloxane dropwise, stir the reaction, then add KH570, continue the reaction, concentrate under reduced pressure, wash with acetone, and dry to obtain the flame retardant additive. The preparation reaction formula is as follows:

[0009]

[0010] (3) Add flame retardant additive to toluene, stir, add ethanol and aqueous solution containing hollow glass microspheres, stir to react, concentrate under reduced pressure and dry to obtain flame retardant grafted hollow glass microspheres, then add methyl vinyl silicone rubber, hydroxyl silicone oil, reinforcing agent, flame retardant and vulcanizing agent into open mill for mixing and sheeting; finally vulcanize in flat vulcanizing machine and cool to obtain flame retardant heat insulation silicone rubber.

[0011] Furthermore, in (2), the molar ratio of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine, 1,1,3,3-tetramethyldisiloxane, and KH570 is 1:(1.04-1.1):(0.05-0.08).

[0012] Furthermore, the first reaction in (2) is carried out at 90-100℃ for 2-3 hours.

[0013] Furthermore, the second reaction in (2) is carried out at 90-100℃ for 20-40 min.

[0014] Furthermore, in (3), the mass ratio of flame retardant additive, hollow glass microspheres, methyl vinyl silicone rubber, hydroxyl silicone oil, reinforcing agent, flame retardant and vulcanizing agent is (20-40):(10-25):100:(2.5-4):(30-40):(2.5-4):(1.3-2).

[0015] Furthermore, in (3), the reinforcing agent is silica, the flame retardant is zinc borate, and the vulcanizing agent is bis(2,5).

[0016] Furthermore, the reaction in (3) is stirred at 75-90℃ for 2-4 hours.

[0017] Furthermore, in (3), the vulcanization temperature in the flat vulcanizing machine is 160-170℃, the pressure is 10-12MPa, and the time is 4-7min.

[0018] (III) Technical effects of the present invention: 2,4-bis(styryl)-6-phenyl-1,3,5-triazine and 1,1,3,3-tetramethyldisiloxane are subjected to hydrosilylation polymerization. Then, the terminal silane-hydrogen bonds react with the alkenyl group of KH570 to obtain a flame retardant additive. The trimethoxysilane at the end of the flame retardant additive is used to perform a hydrolysis-condensation reaction on the hydroxyl groups on the surface of hollow glass microspheres to obtain flame retardant additive-grafted hollow glass microspheres. Finally, the microspheres are mixed and vulcanized with methyl vinyl silicone rubber, hydroxyl silicone oil, and zinc borate, etc., to obtain flame retardant and heat-insulating silicone rubber.

[0019] The flame retardant additive of the present invention contains siloxane structural units grafted onto the surface of hollow glass microspheres, which improves its compatibility with methyl vinyl silicone rubber, making the hollow glass microspheres more uniformly dispersed in the silicone rubber matrix, forming a uniform heat insulation network, which is beneficial to reducing thermal conductivity and improving heat insulation performance.

[0020] The flame retardant additive of the present invention contains nitrogen-rich triazine groups, which produce non-combustible gases such as nitrogen during combustion. This can dilute the oxygen concentration in the combustion atmosphere, promote the formation of an expanded char layer in silicone rubber, and improve the limiting oxygen index and flame retardant properties of silicone rubber. Furthermore, the flame retardant additive contains a phenyltriazine fused ring structure that is resistant to thermal decomposition. When added to silicone rubber, it helps to improve its initial thermal decomposition temperature and high-temperature resistance. Detailed Implementation

[0021] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments.

[0022] A method for preparing flame-retardant and heat-insulating silicone rubber, comprising:

[0023] (1) The preparation method of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine is as follows: 2,4-dichloro-6-phenyl-1,3,5-triazine, 4-vinylphenylboronic acid and tetra(triphenylphosphine)palladium are added to toluene in a molar ratio of 1:(2-2.2):(0.05-0.06), potassium carbonate aqueous solution is added dropwise, and the mixture is heated to 90-100℃ under a nitrogen atmosphere and reacted for 12-18h. After concentration under reduced pressure, the mixture is dried, and the crude product is separated by silica gel column chromatography and eluted with ethyl acetate in petroleum ether solution to obtain 2,4-bis(styryl)-6-phenyl-1,3,5-triazine.

[0024] (2) Add 2,4-bis(styryl)-6-phenyl-1,3,5-triazine and isopropanol solution of chloroplatinic acid to toluene. Under a nitrogen atmosphere, add 1,1,3,3-tetramethyldisiloxane dropwise, stir and react. Then add KH570 and continue the reaction. After concentration under reduced pressure, wash with acetone and dry to obtain flame retardant additive.

[0025] (3) Add flame retardant additive to toluene, stir, add ethanol and aqueous solution containing hollow glass microspheres, stir to react, concentrate under reduced pressure and dry to obtain flame retardant grafted hollow glass microspheres, then add methyl vinyl silicone rubber, hydroxyl silicone oil, reinforcing agent, flame retardant and vulcanizing agent into open mill for mixing and sheeting; finally vulcanize in flat vulcanizing machine and cool to obtain flame retardant heat insulation silicone rubber.

[0026] Furthermore, in (2), the molar ratio of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine, 1,1,3,3-tetramethyldisiloxane, and KH570 is 1:(1.04-1.1):(0.05-0.08).

[0027] Furthermore, the first reaction in (2) is carried out at 90-100℃ for 2-3 hours.

[0028] Furthermore, the second reaction in (2) is carried out at 90-100℃ for 20-40 min.

[0029] Furthermore, in (3), the mass ratio of flame retardant additive, hollow glass microspheres, methyl vinyl silicone rubber, hydroxyl silicone oil, reinforcing agent, flame retardant and vulcanizing agent is (20-40):(10-25):100:(2.5-4):(30-40):(2.5-4):(1.3-2).

[0030] Furthermore, in (3), the reinforcing agent is silica, the flame retardant is zinc borate, and the vulcanizing agent is bis(2,5).

[0031] Furthermore, the reaction in (3) is stirred at 75-90℃ for 2-4 hours.

[0032] Furthermore, in (3), the vulcanization temperature in the flat vulcanizing machine is 160-170℃, the pressure is 10-12MPa, and the time is 4-7min.

[0033] The methyl vinyl silicone rubber in the following raw materials is of type MVQ and was purchased from Dongguan Shuang'ao Plastics Co., Ltd. The hydroxyl silicone oil has a hydroxyl content of 4.5% and was purchased from Zhongshan Dixin Chemical Co., Ltd. The hollow glass microspheres, with a specification of 140µm, were purchased from Guangdong Dexini Building Materials Co., Ltd.

[0034] Example 1

[0035] (1) Add 80 mmol of 2,4-dichloro-6-phenyl-1,3,5-triazine (CAS Registry No. 1700-02-3), 160 mmol of 4-vinylphenylboronic acid (CAS Registry No. 2156-04-9), and 4.8 mmol of tetra(triphenylphosphine)palladium to 1 L of toluene, and add dropwise 250 mL of aqueous solution containing 160 mmol of potassium carbonate. Heat to 100 °C under a nitrogen atmosphere, stir and reflux for 12 h, concentrate under reduced pressure and dry. Separate the crude product by silica gel column chromatography and elute with ethyl acetate in petroleum ether solution to obtain 2,4-bis(styryl)-6-phenyl-1,3,5-triazine.

[0036] (2) Add 200 mmol of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine and 1.2 mL of isopropanol solution containing 9.7 mg of chloroplatinic acid to 100 mL of toluene. Under a nitrogen atmosphere, add 210 mmol of 1,1,3,3-tetramethyldisiloxane (CAS Registry No. 3277-26-7) dropwise, heat to 90 °C, stir for 3 h, then add 12 mmol of KH570, continue the reaction for 40 min, concentrate under reduced pressure, wash the product with acetone, and dry to obtain the flame retardant additive.

[0037] (3) Add 200g of flame retardant to 3L of toluene, stir, add 3L of ethanol and an aqueous solution containing 300mL of 100g of hollow glass microspheres, bring to room temperature to 80℃, stir and react for 4h, concentrate under reduced pressure and dry to remove solvent, and obtain flame retardant grafted hollow glass microspheres. Then, add 1kg of methyl vinyl silicone rubber, 33g of hydroxyl silicone oil, 350g of silica, 40g of flame retardant zinc borate and 16g of vulcanizing agent bis2,5 into an open mill for mixing and sheeting. Finally, vulcanize in a flat vulcanizing machine at a vulcanizing temperature of 160℃, a pressure of 12MPa and a time of 6min, cool to obtain flame retardant and heat-insulating silicone rubber.

[0038] Example 2

[0039] (1) Add 80 mmol of 2,4-dichloro-6-phenyl-1,3,5-triazine, 176 mmol of 4-vinylphenylboronic acid, and 4 mmol of tetra(triphenylphosphine)palladium to 1.2 L of toluene, and add 250 mL of an aqueous solution containing 192 mmol of potassium carbonate dropwise. Heat to 90 °C under a nitrogen atmosphere, stir and react for 18 h, concentrate under reduced pressure and dry. Separate the crude product by silica gel column chromatography and elute with ethyl acetate in petroleum ether solution to obtain 2,4-bis(styryl)-6-phenyl-1,3,5-triazine.

[0040] (2) Add 200 mmol of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine and 1 mL of isopropanol solution containing 8 mg of chloroplatinic acid to 150 mL of toluene. Under a nitrogen atmosphere, add 220 mmol of 1,1,3,3-tetramethyldisiloxane dropwise, heat to 100 °C, stir and reflux for 2 h, then add 16 mmol of KH570 and continue the reaction for 40 min. After concentration under reduced pressure, wash the product with acetone and dry to obtain the flame retardant additive.

[0041] (3) Add 300g of flame retardant to 4L of toluene, stir, add 4.5L of ethanol and an aqueous solution containing 500mL of 170g of hollow glass microspheres, bring to room temperature to 75℃, stir and react for 4h, concentrate under reduced pressure and dry to remove solvent, and obtain flame retardant grafted hollow glass microspheres. Then, add 1kg of methyl vinyl silicone rubber, 25g of hydroxyl silicone oil, 400g of silica, 33g of flame retardant zinc borate and 13g of vulcanizing agent bis2,5 into an open mill for mixing and sheeting. Finally, vulcanize in a flat vulcanizing machine at a vulcanizing temperature of 170℃, a pressure of 10MPa and a time of 4min, cool to obtain flame retardant and heat-insulating silicone rubber.

[0042] Example 3

[0043] (1) Add 200 mmol of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine (prepared from Example 1) and 1.5 mL of isopropanol solution containing 11 mg of chloroplatinic acid to 100 mL of toluene. Under a nitrogen atmosphere, add 208 mmol of 1,1,3,3-tetramethyldisiloxane dropwise, heat to 90 °C, stir for 3 h, then add 10 mmol of KH570, continue the reaction for 20 min, concentrate under reduced pressure, wash the product with acetone, and dry to obtain the flame retardant additive.

[0044] (2) Add 400g of flame retardant to 4L of toluene, stir, and then add 5.5L of ethanol and an aqueous solution containing 600mL of 250g of hollow glass microspheres. Stir the reaction at room temperature to 90℃ for 2h, concentrate under reduced pressure, and dry to remove the solvent to obtain flame retardant grafted hollow glass microspheres. Then, add 1kg of methyl vinyl silicone rubber, 40g of hydroxyl silicone oil, 300g of silica, 25g of flame retardant zinc borate, and 20g of vulcanizing agent bis(2,5) into a two-roll mill for mixing and sheeting. Finally, vulcanize in a flat vulcanizing machine at a vulcanizing temperature of 160℃, a pressure of 10MPa, and a time of 7min. Cool to obtain flame retardant and heat-insulating silicone rubber.

[0045] Comparative Example 1

[0046] (1) 100g of hollow glass microspheres, 1kg of methyl vinyl silicone rubber, 33g of hydroxyl silicone oil, 350g of silica, 40g of flame retardant zinc borate, and 16g of vulcanizing agent bis2,5 were added to an open mill for mixing and sheeting. Finally, the mixture was vulcanized in a flat vulcanizing machine at a temperature of 160℃, a pressure of 12MPa, and a time of 6min. After cooling, flame-retardant and heat-insulating silicone rubber was obtained.

[0047] Comparative Example 2

[0048] (1) Add 200 mmol of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine (prepared from Example 1) and 1.2 mL of isopropanol solution containing 9.7 mg of chloroplatinic acid to 100 mL of toluene. Under a nitrogen atmosphere, add 210 mmol of 1,1,3,3-tetramethyldisiloxane dropwise, heat to 90 °C, stir and react for 3 h. After concentration under reduced pressure, wash the product with acetone and dry to obtain the flame retardant additive.

[0049] (2) Add 200g of flame retardant to 3L of toluene, stir, add 3L of ethanol and an aqueous solution containing 300mL of 100g of hollow glass microspheres, bring to room temperature to 80℃, stir for 4h, concentrate under reduced pressure and dry to remove solvent, and obtain flame retardant grafted hollow glass microspheres. Then, add 1kg of methyl vinyl silicone rubber, 33g of hydroxyl silicone oil, 350g of silica, 40g of flame retardant zinc borate and 16g of vulcanizing agent bis2,5 into an open mill for mixing and sheeting. Finally, vulcanize in a flat vulcanizing machine at a vulcanizing temperature of 160℃, a pressure of 12MPa and a time of 6min, cool to obtain flame retardant and heat-insulating silicone rubber.

[0050] Comparative Example 3

[0051] (1) Add 200 mmol of 1,4-divinylbenzene and 1.2 mL of isopropanol solution containing 9.7 mg of chloroplatinic acid to 100 mL of toluene. Under a nitrogen atmosphere, add 210 mmol of 1,1,3,3-tetramethyldisiloxane dropwise, heat to 90 °C, stir for 3 h, then add 12 mmol of KH570 and continue the reaction for 40 min. After concentration under reduced pressure, wash the product with acetone and dry to obtain the flame retardant additive.

[0052] (2) Add 200g of flame retardant to 3L of toluene, stir, add 3L of ethanol and an aqueous solution containing 300mL of 100g of hollow glass microspheres, bring to room temperature to 80℃, stir and react for 4h, concentrate under reduced pressure and dry to remove solvent, and obtain flame retardant grafted hollow glass microspheres. Then, add 1kg of methyl vinyl silicone rubber, 33g of hydroxyl silicone oil, 350g of silica, 40g of flame retardant zinc borate and 16g of vulcanizing agent bis2,5 into a two-roll mill for mixing and sheeting. Finally, vulcanize in a flat vulcanizing machine at a vulcanizing temperature of 160℃, a pressure of 12MPa and a time of 6min, cool to obtain flame retardant and heat-insulating silicone rubber.

[0053] The thermal conductivity of silicone rubber was tested according to GB / T 11205-2009 standard. The oxygen index was tested according to GB / T 10707-2008 standard.

[0054] Weigh 10 mg of silicone rubber and place it in a thermogravimetric analyzer. Test the sample in a nitrogen atmosphere at a temperature range of 25-800℃.

[0055] Table 1 Performance Tests of Silicone Rubber

[0056]

[0057] The silicone rubber in Comparative Example 1 exhibits high thermal conductivity, low limiting oxygen index, and low initial thermal decomposition temperature, resulting in poor thermal insulation, flame retardancy, and high-temperature resistance. In the embodiments, flame retardant additives grafted onto hollow glass microspheres are added to the silicone rubber. These additives contain siloxane structural units grafted onto the surface of the hollow glass microspheres, improving their compatibility with methyl vinyl silicone rubber. This allows the hollow glass microspheres to be more uniformly dispersed within the silicone rubber matrix, forming a uniform thermal insulation network, which helps reduce thermal conductivity and improve thermal insulation performance. Furthermore, the flame retardant additives contain nitrogen-rich triazine groups, which produce non-combustible gases such as nitrogen during combustion. This dilutes the oxygen concentration in the combustion atmosphere, promotes the formation of an expanded char layer in the silicone rubber, and improves the limiting oxygen index and flame retardant properties of the silicone rubber. Additionally, the flame retardant additives contain a heat-resistant phenyltriazine fused ring structure. Adding it to silicone rubber helps to improve its initial thermal decomposition temperature and high-temperature resistance.

[0058] Comparative Example 2's flame retardant additive lacked the KH570 structure, making it unable to react with the surface of hollow glass microspheres and thus unable to perform surface chemical grafting. The absence of a polymer containing siloxane structural units on the hollow glass microsphere surface resulted in poor compatibility between the hollow glass microsphere surface and the methyl vinyl silicone rubber. Consequently, the hollow glass microspheres were difficult to disperse uniformly in the silicone rubber matrix, failing to form a uniform thermal insulation network, leading to high thermal conductivity and poor thermal insulation performance. Comparative Example 3 involved a hydrosilylation reaction of 1,4-divinylbenzene, 1,1,3,3-tetramethyldisiloxane, and KH570, followed by surface grafting onto hollow glass microspheres, resulting in flame retardant-grafted hollow glass microspheres. However, this flame retardant additive lacked the phenyltriazine structure, making it difficult to effectively improve the flame retardancy and high-temperature resistance of the silicone rubber, resulting in a low limiting oxygen index and thermal decomposition temperature.

[0059] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing flame-retardant and heat-insulating silicone rubber, characterized in that, The preparation method includes: (1) Add 2,4-bis(styryl)-6-phenyl-1,3,5-triazine and chloroplatinic acid isopropanol solution to toluene, add 1,1,3,3-tetramethyldisiloxane dropwise under nitrogen atmosphere, stir the reaction, then add KH570, continue the reaction, concentrate under reduced pressure, wash and dry to obtain flame retardant additive; (2) Add flame retardant additive to toluene, stir, add ethanol and aqueous solution containing hollow glass microspheres, stir to react, concentrate under reduced pressure and dry to obtain flame retardant grafted hollow glass microspheres, then add methyl vinyl silicone rubber, hydroxyl silicone oil, reinforcing agent, flame retardant and vulcanizing agent into open mill for mixing and sheeting; finally vulcanize in flat vulcanizing machine and cool to obtain flame retardant heat insulation silicone rubber; The molar ratio of 2,4-bis(styryl)-6-phenyl-1,3,5-triazine, 1,1,3,3-tetramethyldisiloxane, and KH570 in (1) is 1:(1.04-1.1):(0.05-0.08). In (1), the first reaction is carried out at 90-100℃ for 2-3 hours, and the second reaction is carried out at 90-100℃ for 20-40 minutes; The mass ratio of flame retardant, hollow glass microspheres, methyl vinyl silicone rubber, hydroxyl silicone oil, reinforcing agent, flame retardant and vulcanizing agent in (2) is (20-40):(10-25):100:(2.5-4):(30-40):(2.5-4):(1.3-2). The reaction in (2) is stirred at 75-90℃ for 2-4 hours.

2. The method for preparing flame-retardant and heat-insulating silicone rubber according to claim 1, characterized in that, The reinforcing agent is silica, the flame retardant is zinc borate, and the vulcanizing agent is bis(2,5)sulfurization agent.

3. The method for preparing flame-retardant and heat-insulating silicone rubber according to claim 1, characterized in that, The vulcanization temperature in the flat vulcanizing machine in (2) is 160-170℃, the pressure is 10-12MPa, and the time is 4-7min.

4. The method for preparing flame-retardant and heat-insulating silicone rubber according to claim 1, characterized in that, The preparation method of the 2,4-bis(styryl)-6-phenyl-1,3,5-triazine is as follows: 2,4-dichloro-6-phenyl-1,3,5-triazine, 4-vinylphenylboronic acid, and tetra(triphenylphosphine)palladium are added to toluene in a molar ratio of 1:(2-2.2):(0.05-0.06), and potassium carbonate aqueous solution is added dropwise. The mixture is heated to 90-100℃ under a nitrogen atmosphere and reacted for 12-18 h. After concentration under reduced pressure, the mixture is dried, and the crude product is separated by silica gel column chromatography to obtain 2,4-bis(styryl)-6-phenyl-1,3,5-triazine.

5. A flame-retardant and heat-insulating silicone rubber obtained by the preparation method according to any one of claims 1-4.

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