High-flame-retardant insulating liquid silicone rubber as well as preparation method and application thereof

Abstract

The invention relates to the technical field of silicone rubber preparation, in particular to high-flame-retardant insulating liquid silicone rubber and a preparation method and application thereof. The high-flame-retardant insulating liquid silicone rubber is prepared from the following raw materials in parts by mass: 60 to 75 parts of vinyl-terminated polydimethylsiloxane, 5 to 8 parts of methylhydrosiloxane, 20 to 24 parts of a flame retardant, 0.1 to 0.2 part of a platinum catalyst, 25 to 30 parts of modified silicon dioxide and 2 to 3 parts of a silane coupling agent, and the flame retardant is prepared by mixing decabromodiphenyl ethane and modified magnesium hydroxide. The high-flame-retardant insulating liquid silicone rubber not only has excellent flame retardance, insulativity, high-temperature-resistant stability and the like, but also has remarkable advantages in mechanical properties and environmental adaptability, and provides safer and more reliable material choices for related fields.

Description

Technical Field

[0001] The present application relates to the technical field of silicone rubber preparation, and in particular to a highly flame-retardant insulating liquid silicone rubber and a preparation method and application thereof. Background Art

[0002] Liquid silicone rubber in power systems generally refers to addition-type liquid silicone rubber, which is completed by the hydrogen siloxane addition reaction of vinyl-containing siloxane and multi-Si-H bond siloxane catalyzed by eighth group transition metal compounds such as platinum, and finally forms a silicone rubber elastomer whose main component is polydimethylsiloxane. As an important electrical insulation material, this silicone rubber elastomer has been widely used in electronic, electrical, mechanical, chemical and other industries.

[0003] Silicone rubber is a composite material composed of polysiloxane, reinforcing fillers, crosslinking agents, catalysts and other additives. Due to the high bond energy of Si-O bonds, it has good thermal stability. In addition, when burning under high-temperature flames, Si-O bonds will be transformed into continuous, insulating network-like SiO2 ash covering the surface, thereby effectively preventing further ablation of the substrate. Organic or inorganic flame retardants, such as phosphate esters and phosphazene organic flame retardants, and inorganic flame retardants such as alumina and aluminum hydroxide, are compounded into silicone rubber. The biggest problem with this type of flame retardant during application is uneven dispersion, which leads to local ablation during the ablation process, thereby affecting the overall flame retardant effect.

[0004] Therefore, there is an urgent need to develop a highly flame-retardant insulating liquid silicone rubber with good flame retardancy and good mechanical properties to meet market demand. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present application provides a highly flame-retardant insulating liquid silicone rubber and a preparation method and application thereof. The highly flame-retardant insulating liquid silicone rubber prepared in the present application has excellent flame retardancy, excellent insulation, high temperature stability and good mechanical properties, and is widely used in high-voltage cable insulation layers, power equipment seals or new energy vehicle battery pack fireproof packaging and other fields.

[0006] In the first aspect, the present application provides a highly flame-retardant insulating liquid silicone rubber, which adopts the following technical solution: A highly flame-retardant insulating liquid silicone rubber, the preparation raw materials of which include, by weight: 60-75 parts of vinyl-terminated polydimethylsiloxane, 5-8 parts of methyl hydrogensiloxane, 20-24 parts of flame retardant, 0.1-0.2 parts of platinum catalyst, 25-30 parts of modified silicon dioxide, and 2-3 parts of silane coupling agent, wherein the flame retardant is prepared by mixing decabromodiphenylethane and modified magnesium hydroxide.

[0007] By adopting the above technical solution, vinyl-terminated polydimethylsiloxane is used as the base polymer to provide highly pure siloxane segments, which contribute to the formation of excellent insulation properties. At the same time, the vinyl termination can undergo a crosslinking reaction with other components to form a stable network structure. Methylhydrosiloxane: Used as a crosslinking agent to optimize the network structure of the silicone rubber and enhance its temperature resistance stability. Meanwhile, methylhydrosiloxane can also react with other components to form stable chemical bonds. Flame retardant: Prepared by mixing decabromodiphenylethane and modified magnesium hydroxide. Decabromodiphenylethane interrupts the combustion chain reaction by releasing bromine free radicals. Modified magnesium hydroxide increases the number of surface hydroxyl groups and reaction sites by in-situ growing porous titanium dioxide nanoparticles on the surface of magnesium hydroxide, thereby improving the flame retardant performance and high-temperature stability. Platinum catalyst is used as a catalyst to promote the crosslinking reaction of the silicone rubber and ensure the smooth progress of the reaction. Modified silica: After specific treatment, the surface of the modified silica contains organosiloxane segments and urethane bonds, and these functional groups improve its compatibility with the silicone rubber matrix. Modified silica not only enhances the filling effect and mechanical properties of the silicone rubber, but also can react with other components to form a stable crosslinked structure, improving the thermal stability and high-temperature resistance performance. Silane coupling agent: Can form more stable chemical bonds in the silicone rubber system, enhance the interfacial bonding force, and further improve the comprehensive performance of the liquid silicone rubber. These components, through their respective functions and their synergistic effects, jointly improve the flame retardancy, insulation, high-temperature stability, and mechanical properties of the silicone rubber material. For example, the synergistic effect of modified magnesium hydroxide and decabromodiphenylethane improves the flame retardant performance; the synergistic effect of modified silica and silane coupling agent enhances the mechanical properties and stability of the material. This synergistic effect ensures the application performance of the silicone rubber material in fields such as high-voltage cable insulation layers, power equipment seals, or fireproof encapsulations for new energy vehicle battery packs.

[0008] Preferably, the mass ratio of decabromodiphenylethane to modified magnesium hydroxide is 3:6 - 8.

[0009] By adopting the above technical solutions, decabromodiphenylethane is a commonly used flame retardant, and its main function is to interrupt the combustion chain reaction by releasing bromine free radicals. This flame retardant decomposes at high temperatures to produce bromine free radicals, which can capture the active particles in the reaction, thus inhibiting the combustion process. However, the sole use of decabromodiphenylethane may cause the release of toxic bromide gases during the combustion of materials. Modified magnesium hydroxide is a non-toxic flame retardant, which increases the number of surface hydroxyl groups and reaction sites by in-situ growth of porous titanium dioxide nanoparticles on the surface of magnesium hydroxide. This modified magnesium hydroxide can form a heat insulation barrier and interrupt the combustion chain reaction, delay thermal decomposition, and also inhibit high-temperature oxidation. When these two flame retardants are used in combination at a specific mass fraction ratio, they can produce a synergistic effect. Decabromodiphenylethane provides the ability to quickly interrupt the combustion chain reaction, while modified magnesium hydroxide provides long-term heat insulation and inhibition of high-temperature oxidation. This combination can more comprehensively improve the flame retardancy of materials while reducing the release of toxic gases. In addition, the selection of this ratio also takes into account other performance requirements of the materials, such as insulation, high-temperature stability, and mechanical properties. By adjusting the ratio of the two flame retardants, these properties can be maintained or enhanced while meeting the flame retardancy requirements. Generally speaking, through orthogonal experiments, the optimal ratio is determined to be 3:6 - 8. When the mass fraction ratio of decabromodiphenylethane and modified magnesium hydroxide is 3:6 - 8, it can ensure high flame retardancy while reducing the release of toxic gases, and at the same time maintain or enhance other key properties of the material. This synergistic effect is the key to preparing high-performance high-flame-retardant insulating liquid silicone rubber.

[0010] Preferably, the preparation method of the modified magnesium hydroxide includes the following steps: S31. According to the mass fraction, 100 parts of magnesium hydroxide, 100 parts of isopropyl titanate, 6 parts of sodium dodecyl sulfonate, and 7 parts of ammonia water are placed in 500 parts of distilled water and mixed. Stir in a reaction kettle at 25 - 30 °C for 2 - 3 h, then raise the temperature to 60 - 65 °C, continue stirring and reacting for 4 - 6 h, and cool and filter; then calcine in a muffle furnace at 250 °C for 2 h, cool to room temperature, and obtain solid A with porous titanium dioxide nanoparticles grown in-situ on the surface of magnesium hydroxide. S32. According to the mass fraction, 100 parts of solid A are placed in a reaction kettle with nitrogen protection, add 200 parts of tetrahydrofuran and stir for 2 - 3 h, then dropwise add a tetrahydrofuran solution of 60 parts of diphenylphosphinic chloride with a concentration of 0.1 g / mL. After the addition is completed within 1 h, raise the temperature to 55 °C at a rate of 3 °C / min, continue stirring and reacting for 7 h, cool and filter, and dry to obtain modified magnesium hydroxide.

[0011] By adopting the above technical solution, the modified magnesium hydroxide grows porous titanium dioxide nanoparticles in-situ on the surface of magnesium hydroxide, increasing the number of surface hydroxyl groups of magnesium hydroxide and the number of reaction sites with diphenylphosphinic chloride, and improving the grafting rate of diphenylphosphinic chloride. This modified magnesium hydroxide can form a heat insulation barrier and interrupt the combustion chain reaction, delay thermal decomposition, and inhibit high-temperature oxidation at the same time. The modified magnesium hydroxide can maintain its structure and properties in a high-temperature environment, and is not easily decomposed or deformed, thereby improving the high-temperature stability of the silicone rubber material. The compatibility between the modified magnesium hydroxide and the silicone rubber matrix is improved, and it can better combine with the silicone rubber matrix, enhancing the filling and reinforcing effects of the silicone rubber material, thereby improving the mechanical properties of the silicone rubber. The modified magnesium hydroxide acts together with other raw materials such as decabromodiphenylethane, vinyl-terminated polydimethylsiloxane, and methylhydrosiloxane to synergistically improve the comprehensive properties of the high flame-retardant insulating liquid silicone rubber. For example, the bromine radicals released by decabromodiphenylethane can interrupt the combustion chain reaction, while the modified magnesium hydroxide provides the ability to form a heat insulation barrier and interrupt the combustion chain reaction. The two work together to improve the flame retardancy of the silicone rubber. In summary, the modified magnesium hydroxide plays a key role in the preparation of the high flame-retardant insulating liquid silicone rubber, not only improving the flame retardancy and high-temperature stability of the silicone rubber, but also improving its mechanical properties. At the same time, its synergistic effect with other raw materials further enhances the comprehensive properties of the silicone rubber, making it have broad application prospects in fields such as high-voltage cable insulation layers, power equipment seals, or fireproof encapsulations of new energy vehicle battery packs.

[0012] Preferably, the preparation method of the modified silica includes the following steps: S41. According to the mass parts, 100 parts of silica with an average particle size of 1-2 microns and 300 parts of water are stirred and mixed to obtain a silica aqueous solution; at 80 °C, the pH value of the silica aqueous solution is adjusted to 11-11.5 with a sodium hydroxide aqueous solution with a mass concentration of 30%, stirred and mixed for 1-2 h, cooled to 25 °C, filtered, and the solid is washed with pure water until neutral, and then the solid is dried at 70 °C for 12-14 h to obtain hydroxylated silica; S42. According to the mass parts, 7-octenyltrimethoxysilane and hexamethylene diisocyanate are stirred and mixed at 125 °C for 3-4 h, and then hydroxylated silica is added and stirred and mixed for 1-2 h to obtain modified silica.

[0013] By adopting the above technical solutions, the prepared modified silica contains silicone chain segments and urethane bonds through surface treatment. These functional groups can improve the compatibility between the modified silica and the silicone rubber matrix, enabling the modified silica to better combine with the silicone rubber matrix. The modified silica can enhance the filling effect of the silicone rubber material and improve the mechanical strength and stability of the material. The functional groups on the surface of the modified silica can react with other components in the silicone rubber system to form a more stable cross-linked structure, thereby improving the thermal stability and high-temperature resistance of the silicone rubber material. The modified silica and other raw materials such as vinyl-terminated polydimethylsiloxane and methylhydrosiloxane act together to synergistically improve the comprehensive performance of the high-flame-retardant insulating liquid silicone rubber, including flame retardancy, insulation, high-temperature stability, and mechanical properties. In the specific preparation method, these steps of the modified silica ensure that the modified silica can effectively improve the performance of the silicone rubber material, making it meet the application requirements in fields such as high-voltage cable insulation layers, power equipment seals, or fireproof encapsulation of new energy vehicle battery packs.

[0014] Preferably, the mass ratio of the hydroxylated silica, 7-octenyltrimethoxysilane, and hexamethylene diisocyanate is 100:(6-8):(4-5).

[0015] Preferably, the mass concentration of platinum element in the platinum catalyst is 1-2 ppm.

[0016] Preferably, the silane coupling agent is composed of vinyltris(2-methoxyethoxy)silane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 3:2.

[0017] By adopting the above technical solutions, the main function of the silane coupling agent is to enhance the interfacial bonding force between different components in the silicone rubber system and form more stable chemical bonds. Vinyltris(2-methoxyethoxy)silane and γ-glycidoxypropyltrimethoxysilane are composed in a mass ratio of 3:2. This combination may aim to utilize the different characteristics of the two silane coupling agents to achieve better effects. Vinyltris(2-methoxyethoxy)silane: This silane coupling agent may have strong reactivity and can chemically react with other components in the silicone rubber matrix to form stable chemical bonds. At the same time, its vinyl structure helps to improve the thermal stability and high-temperature resistance of the silicone rubber. γ-Glycidoxypropyltrimethoxysilane: This silane coupling agent may have good adhesion performance and can enhance the interfacial bonding force between the silicone rubber and the filler. At the same time, its glycidoxypropyl structure helps to improve the mechanical strength and toughness of the silicone rubber. The combined use of the two silane coupling agents further improves the comprehensive performance of the silicone rubber by leveraging their respective advantages. For example, vinyltris(2-methoxyethoxy)silane may play a role in improving thermal stability and high-temperature resistance, while γ-glycidoxypropyltrimethoxysilane may play a role in enhancing interfacial bonding force and improving mechanical strength. In summary, the role of the silane coupling agent in the silicone rubber system is mainly to enhance the interfacial bonding force, form stable chemical bonds, and improve the thermal stability and mechanical properties of the silicone rubber, so as to improve the comprehensive performance of the high-flame-retardant insulating liquid silicone rubber.

[0018] Second, the present application provides a preparation method of a high-flame-retardant insulating liquid silicone rubber, adopting the following technical solutions: As a general technical concept, the present application also provides the preparation method of the above high-flame-retardant insulating liquid silicone rubber, including the following steps: S81. According to the mass parts, mix vinyl-terminated polydimethylsiloxane, methylhydrogensiloxane, flame retardant, modified silica, and silane coupling agent, and then add them to a kneader for heating and kneading. The kneading temperature is 45-50 °C, and the kneading time is 2-3 h to obtain mixture A; S82. According to the mass parts, add a platinum catalyst to mixture A and knead to obtain mixture B; S83. Inject mixture B into a mold and vulcanize it at 100-120 °C for 50-60 minutes to obtain the high-flame-retardant insulating liquid silicone rubber.

[0019] Third, the present application provides an application of a high-flame-retardant insulating liquid silicone rubber, adopting the following technical solutions: As a general technical concept, the present application also provides the above high-flame-retardant insulating liquid silicone rubber for use in the insulation layer of high-voltage cables, the seals of power equipment, or the fireproof encapsulation of new energy vehicle battery packs.

[0020] In summary, the present application includes at least one of the following beneficial technical effects: 1. Excellent flame retardancy: By using decabromodiphenylethane and modified magnesium hydroxide as flame retardants, the combustion chain reaction can be effectively interrupted. At the same time, the porous structure of modified magnesium hydroxide and the increase in the number of surface hydroxyl groups improve the flame retardant performance.

[0021] 2. Excellent insulation: Vinyl-terminated polydimethylsiloxane provides high-purity siloxane chains, ensuring the excellent insulation performance of the silicone rubber.

[0022] 3. High-temperature stability: The methylhydrogensiloxane crosslinking agent optimizes the network structure and improves the temperature resistance stability of the silicone rubber. At the same time, the use of modified silica and silane coupling agent enhances the thermal stability and high-temperature resistance performance of the silicone rubber.

[0023] 4. Good mechanical properties: Modified silica improves the mechanical properties and stability of the silicone rubber by enhancing the filling effect and the bonding force of the silicone rubber.

[0024] 5. Environmental adaptability: The use of modified silica and silane coupling agent improves the stability of the silicone rubber in high-temperature environments, reduces deformation and aging phenomena, making it more suitable for application fields such as high-voltage cable insulation layers, power equipment seals, or fireproof encapsulations of new energy vehicle battery packs.

[0025] 6. Improvement in comprehensive performance: Through the synergistic effect among various raw materials, the high-flame-retardant and insulating liquid silicone rubber prepared in the present application can effectively reduce costs and improve production efficiency while maintaining excellent performance. Detailed implementation manners

[0026] The implementation manners of the present application will be described in detail below in conjunction with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0027] In the following examples and preparation examples, 1 part represents 100 g.

[0028] Preparation Example 1 The preparation method of modified magnesium hydroxide includes the following steps: S31. According to the parts by mass, 100 parts of magnesium hydroxide with an average particle size of 1 μm, 100 parts of isopropyl titanate, 6 parts of sodium dodecyl sulfonate, and 7 parts of ammonia water are placed in 500 parts of distilled water and mixed. Stir for 2.5 h at 28 °C in a reaction kettle, then raise the temperature to 63 °C, continuously stir and react for 5 h, and cool and filter; then calcine in a muffle furnace at 250 °C for 2 h, cool to room temperature to obtain solid A with porous titanium dioxide nanoparticles in-situ grown on the surface of magnesium hydroxide; S32. According to the parts by mass, 100 parts of solid A are placed in a reaction kettle with nitrogen protection, add 200 parts of tetrahydrofuran and stir for 2.5 h, then dropwise add a tetrahydrofuran solution of 60 parts of diphenylphosphinic chloride with a concentration of 0.1 g / mL. After the addition is completed within 1 h, raise the temperature to 55 °C at a rate of 3 °C / min, continuously stir and react for 7 h, cool and filter, and dry to obtain modified magnesium hydroxide.

[0029] Preparation Example 2 Preparation of Modified Silicon Dioxide The preparation method of modified silicon dioxide includes the following steps: S41. According to the parts by mass, 100 parts of silicon dioxide with an average particle size of 1.5 μm and 300 parts of water are stirred and mixed to obtain an aqueous silicon dioxide solution; adjust the pH value of the aqueous silicon dioxide solution to 11.2 with a 30% sodium hydroxide aqueous solution at 80 °C, stir and mix for 1.2 h, cool to 25 °C, filter, wash the solid with pure water until neutral, and then dry the solid at 70 °C for 13 h to obtain hydroxylated silicon dioxide; S42. According to the parts by mass, 7 parts of 7-octenyltrimethoxysilane and 4.5 parts of hexamethylene diisocyanate are stirred and mixed at 125 °C for 3.4 h, then add 100 parts of hydroxylated silicon dioxide and stir and mix for 1.5 h to obtain modified silicon dioxide.

[0030] Example 1 A highly flame-retardant and insulating liquid silicone rubber, calculated by parts by mass, the preparation raw materials include: 60 parts of vinyl-terminated polydimethylsiloxane, 5 parts of methylhydrosiloxane, 20 parts of flame retardant, 0.1 part of platinum catalyst (mass concentration of platinum element is 2 ppm), 25 parts of modified silicon dioxide, 2 parts of silane coupling agent. Among them, the flame retardant is prepared by mixing decabromodiphenylethane and modified magnesium hydroxide in a mass ratio of 3:6, and the silane coupling agent is composed of vinyltris(2-methoxyethoxy)silane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 3:2.

[0031] The preparation method of the above-mentioned highly flame-retardant and insulating liquid silicone rubber includes the following steps: S81. Mix vinyl-terminated polydimethylsiloxane, methylhydrosiloxane, flame retardant, modified silica, and silane coupling agent according to parts by mass, and then add them to a kneader for heating and kneading. The kneading temperature is 45 °C and the kneading time is 3 h to obtain mixture A; S82. Add platinum catalyst to mixture A according to parts by mass and knead to obtain mixture B; S83. Inject mixture B into a mold and vulcanize at 100 °C for 60 minutes to obtain a highly flame-retardant insulating liquid silicone rubber.

[0032] Example 2 A highly flame-retardant insulating liquid silicone rubber, calculated by parts by mass, the preparation raw materials include: 75 parts of vinyl-terminated polydimethylsiloxane, 8 parts of methylhydrosiloxane, 24 parts of flame retardant, 0.2 part of platinum catalyst (mass concentration of platinum element is 1 ppm), 30 parts of modified silica, and 3 parts of silane coupling agent. Among them, the flame retardant is prepared by mixing decabromodiphenylethane and modified magnesium hydroxide in a mass ratio of 3:8, and the silane coupling agent is composed of vinyltris(2-methoxyethoxy)silane and γ-glycidyletheroxypropyltrimethoxysilane in a mass ratio of 3:2.

[0033] The preparation method of the above-mentioned highly flame-retardant insulating liquid silicone rubber includes the following steps: S81. Mix vinyl-terminated polydimethylsiloxane, methylhydrosiloxane, flame retardant, modified silica, and silane coupling agent according to parts by mass, and then add them to a kneader for heating and kneading. The kneading temperature is 50 °C and the kneading time is 2 h to obtain mixture A; S82. Add platinum catalyst to mixture A according to parts by mass and knead to obtain mixture B; S83. Inject mixture B into a mold and vulcanize at 120 °C for 50 minutes to obtain a highly flame-retardant insulating liquid silicone rubber.

[0034] Example 3 A highly flame-retardant insulating liquid silicone rubber, calculated by parts by mass, the preparation raw materials include: 68 parts of vinyl-terminated polydimethylsiloxane, 6.3 parts of methylhydrosiloxane, 22 parts of flame retardant, 0.15 part of platinum catalyst (mass concentration of platinum element is 1.5 ppm), 27 parts of modified silica, and 2.5 parts of silane coupling agent. Among them, the flame retardant is prepared by mixing decabromodiphenylethane and modified magnesium hydroxide in a mass ratio of 3:7, and the silane coupling agent is composed of vinyltris(2-methoxyethoxy)silane and γ-glycidyletheroxypropyltrimethoxysilane in a mass ratio of 3:2.

[0035] The preparation method of the above-mentioned highly flame-retardant insulating liquid silicone rubber includes the following steps: S81. Mix vinyl-terminated polydimethylsiloxane, methylhydrogensiloxane, flame retardant, modified silica, and silane coupling agent according to parts by mass, and then add them to a kneader for heating and kneading. The kneading temperature is 48 °C, and the kneading time is 2.3 h to obtain mixture A. S82. Add platinum catalyst to mixture A according to parts by mass and knead to obtain mixture B. S83. Inject mixture B into a mold and vulcanize at 110 °C for 55 minutes to obtain a highly flame-retardant insulating liquid silicone rubber.

[0036] Comparative Example 1 Same as Example 3, except that magnesium hydroxide with an average particle size of 1 μm in equal parts by mass is used instead of modified magnesium hydroxide.

[0037] Comparative Example 2 Same as Example 3, except that silica with an average particle size of 1.5 μm in equal parts by mass is used instead of modified silica.

[0038] Comparative Example 3 Same as Example 3, except that the flame retardant is decabromodiphenylethane.

[0039] Comparative Example 4 Same as Example 3, except that the flame retardant is modified magnesium hydroxide.

[0040] Comparative Example 5 Same as Example 3, except that the silane coupling agent is vinyltris(2-methoxyethoxy)silane.

[0041] Comparative Example 6 Same as Example 3, except that the silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0042] Performance Detection Test Sample the highly flame-retardant insulating liquid silicone rubbers prepared in Examples 1 - 3 and Comparative Examples 1 - 6 respectively, and process them into test strips for the following tests. The test results are shown in Table 1. Limiting oxygen index: Test according to ASTM D2863. Tensile strength and elongation at break are tested according to standard No. GB / T528 - 2009, and the tensile rate is 50 mm / min. Volume resistivity: Test according to ASTM D257. High-temperature stability: Put the test strip into an electrothermal constant-temperature forced-air drying oven at 200 °C, and then test the tensile strength every 48 h, and calculate the tensile strength retention rate.

[0043] Table 1 Performance Test By analyzing the data in Table 1, it can be seen that: 1) The highly flame-retardant insulating liquid silicone rubber prepared in Examples 1 - 3 has excellent flame retardancy, excellent insulation, high-temperature stability, and good mechanical properties, and is widely used in fields such as the insulation layer of high-voltage cables, seals for power equipment, or fireproof encapsulation of new energy vehicle battery packs.

[0044] 2) Through the comparative analysis of the performance of the highly flame-retardant insulating liquid silicone rubber prepared by combining Example 3 and Comparative Example 1, it is shown that the modified magnesium hydroxide prepared in this application, by in-situ growing porous titanium dioxide nanoparticles on the surface of magnesium hydroxide, increases the number of surface hydroxyl groups of magnesium hydroxide and the number of reaction sites with diphenylphosphinic chloride, and improves the grafting rate of diphenylphosphinic chloride. This modified magnesium hydroxide can form a heat insulation barrier and interrupt the combustion chain reaction, delay thermal decomposition, and at the same time inhibit high-temperature oxidation. The modified magnesium hydroxide can maintain its structure and properties in a high-temperature environment, and is not prone to decomposition or deformation, thus improving the high-temperature stability of the silicone rubber material. The compatibility of the modified magnesium hydroxide with the silicone rubber matrix is improved, and it can better combine with the silicone rubber matrix, enhancing the filling and reinforcing effects of the silicone rubber material, thereby improving the mechanical properties of the silicone rubber. The modified magnesium hydroxide acts together with other raw materials such as decabromodiphenylethane, vinyl-terminated polydimethylsiloxane, and methylhydrogensiloxane to synergistically improve the comprehensive performance of the highly flame-retardant insulating liquid silicone rubber.

[0045] 3) Through the comparative analysis of the performance of the highly flame-retardant insulating liquid silicone rubber prepared by combining Example 3 and Comparative Example 2, it is shown that the modified silica prepared in this application, through surface treatment, contains organosilicon segments and urethane bonds. These functional groups can improve the compatibility of the modified silica with the silicone rubber matrix, making the modified silica better combine with the silicone rubber matrix. The modified silica can enhance the filling effect of the silicone rubber material, improving the mechanical strength and stability of the material. The functional groups on the surface of the modified silica can react with other components in the silicone rubber system to form a more stable cross-linked structure, thereby improving the thermal stability and high-temperature resistance of the silicone rubber material. The modified silica acts together with other raw materials such as vinyl-terminated polydimethylsiloxane and methylhydrogensiloxane to synergistically improve the comprehensive performance of the highly flame-retardant insulating liquid silicone rubber, including flame retardancy, insulation, high-temperature stability, and mechanical properties.

[0046] 4) Combining the performance comparison and analysis of the highly flame-retardant insulating liquid silicone rubber prepared in Example 3 and Comparative Examples 3 - 4 shows that the flame retardant is prepared by mixing decabromodiphenylethane and modified magnesium hydroxide in a mass ratio of 3:7. When these two flame retardants are used in combination at a specific mass ratio, they can produce a synergistic effect. Decabromodiphenylethane provides the ability to rapidly interrupt the combustion chain reaction, while modified magnesium hydroxide provides long-term heat insulation and inhibits high-temperature oxidation. This combination can more comprehensively improve the flame retardant performance of the material while reducing the release of toxic gases. In addition, the selection of this ratio can also enhance other performance requirements of the highly flame-retardant insulating liquid silicone rubber, such as insulation, high-temperature stability, and mechanical properties.

[0047] 5) Combining the performance comparison and analysis of the highly flame-retardant insulating liquid silicone rubber prepared in Example 3 and Comparative Examples 5 - 6 shows that the silane coupling agent is composed of vinyltris(2-methoxyethoxy)silane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 3:2. By utilizing their combined action, the comprehensive performance of the highly flame-retardant insulating liquid silicone rubber is improved by enhancing the interfacial bonding force, forming stable chemical bonds, and improving the thermal stability and mechanical properties of the silicone rubber.

[0048] The above embodiments are only used to explain the technical solutions of the present application and not to limit them. Although the above embodiments have specifically described the present application, those skilled in the art should understand that the specific implementation manners of the present application can still be modified or equivalently replaced. Any modification and equivalent replacement without departing from the spirit and scope of the present application should be covered within the protection scope of the present application.

Claims

1. A highly flame-retardant insulating liquid silicone rubber, characterized in that: The raw materials for preparation include, by weight: 60-75 parts of vinyl-terminated polydimethylsiloxane, 5-8 parts of methyl hydrogensiloxane, 20-24 parts of flame retardant, 0.1-0.2 parts of platinum catalyst, 25-30 parts of modified silicon dioxide, and 2-3 parts of silane coupling agent, wherein the flame retardant is prepared by mixing decabromodiphenylethane and modified magnesium hydroxide.

2. The highly flame-retardant insulating liquid silicone rubber according to claim 1, characterized in that: The mass ratio of decabromodiphenylethane to modified magnesium hydroxide is 3:6-8.

3. The highly flame-retardant insulating liquid silicone rubber according to claim 1, characterized in that: The preparation method of the modified magnesium hydroxide comprises the following steps: S31. According to the mass fractions, 100 parts of magnesium hydroxide, 100 parts of isopropyl titanate, 6 parts of sodium dodecyl sulfate and 7 parts of ammonia water are placed in 500 parts of distilled water and mixed, stirred at 25-30° C. for 2-3 hours in a reactor, then heated to 60-65° C., continuously stirred and reacted for 4-6 hours, cooled and filtered; then calcined at 250° C. for 2 hours in a muffle furnace, cooled to room temperature, and obtained a solid A with porous titanium dioxide nanoparticles in situ grown on the surface of magnesium hydroxide; S32. According to the mass fractions, 100 parts of solid A are placed in a reactor with nitrogen protection, 200 parts of tetrahydrofuran are added and stirred for 2-3 hours, and then 60 parts of diphenylphosphinoyl chloride tetrahydrofuran solution with a concentration of 0.1 g / mL are added dropwise. After the addition is completed within 1 hour, the temperature is raised to 55°C at a rate of 3°C / min, and the mixture is continuously stirred and reacted for 7 hours. The mixture is cooled and filtered, and dried to obtain modified magnesium hydroxide.

4. The highly flame-retardant insulating liquid silicone rubber according to claim 1, characterized in that: The preparation method of the modified silicon dioxide comprises the following steps: S41. According to the mass fractions, 100 parts of silicon dioxide having an average particle size of 1-2 microns and 300 parts of water are stirred and mixed to obtain a silicon dioxide aqueous solution; the pH value of the silicon dioxide aqueous solution is adjusted to 11-11.5 with a sodium hydroxide aqueous solution having a mass concentration of 30% at 80° C., the mixture is stirred and mixed for 1-2 hours, cooled to 25° C., filtered, the solid is washed with pure water until it is neutral, and then the solid is dried at 70° C. for 12-14 hours to obtain hydroxylated silicon dioxide; S42. According to the mass fractions, 7-octenyltrimethoxysilane and hexamethylene diisocyanate are stirred and mixed at 125° C. for 3-4 hours, and then hydroxylated silica is added and stirred and mixed for 1-2 hours to obtain modified silica.

5. The highly flame-retardant insulating liquid silicone rubber according to claim 4, characterized in that: The mass ratio of the hydroxylated silica, 7-octenyltrimethoxysilane and hexamethylene diisocyanate is 100:(6-8):(4-5).

6. The highly flame-retardant insulating liquid silicone rubber according to claim 1, characterized in that: The mass concentration of platinum element in the platinum catalyst is 1-2 ppm.

7. The highly flame-retardant insulating liquid silicone rubber according to claim 1, characterized in that: The silane coupling agent is composed of vinyl tri(2-methoxyethoxy)silane and gamma-glycidyloxypropyl trimethoxysilane in a mass ratio of 3:

2.

8. A method for preparing a highly flame-retardant insulating liquid silicone rubber as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: S81, vinyl-terminated polydimethylsiloxane, methyl hydrogensiloxane, flame retardant, modified silica and silane coupling agent are mixed according to their weight parts, and then added into a kneader for heating and kneading. The kneading temperature is 45-50° C. and the kneading time is 2-3 hours to obtain a mixture A; S82, adding a platinum catalyst to mixture A according to parts by mass, and kneading to obtain mixture B; S83, injecting mixture B into a mold and vulcanizing at 100-120° C. for 50-60 minutes to obtain highly flame-retardant insulating liquid silicone rubber.

9. An application of the highly flame-retardant insulating liquid silicone rubber according to any one of claims 1 to 7, characterized in that: Used for high-voltage cable insulation, power equipment seals or fireproof packaging of new energy vehicle battery packs.

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