High-temperature-resistant silicone rubber and preparation method thereof

Abstract

The invention relates to the field of rubber production, and particularly discloses high-temperature-resistant silicone rubber and a preparation method thereof.The preparation method comprises the following steps that alkynyl-terminated polyimide resin and multi-walled carbon nanotubes are mixed to prepare a composite micro-framework precursor; mixing the composite micro-skeleton precursor with a first part of silicone rubber compound, and then adding a silane coupling agent A to prepare a material B; mixing cerium oxide, calcium oxide, a peroxide radical initiator and a silane coupling agent B with a second part of the methyl vinyl silicone rubber compound to prepare a material C; mixing the material B and the material C to obtain micro-framework precursor mixed glue; and vulcanizing the micro-framework precursor mixed rubber. The invention further discloses the high-temperature-resistant silicone rubber prepared by adopting the preparation method. The thermal stability of the silicone rubber is further improved, the prepared silicone rubber composite material still has good mechanical strength and elasticity at 350 DEG C for a long time, and a product prepared from the composite material has a certain use value in a high-temperature environment.

Description

Technical Field

[0001] The present application relates to the field of rubber production, and more specifically, to a high temperature resistant silicone rubber and a preparation method thereof. Background Art

[0002] With the advancement of science and technology and industrial development, especially in high-end fields such as aerospace, automobile manufacturing, electronic appliances, and nuclear energy industry, higher and higher requirements are placed on the high temperature resistance of materials. Silicone rubber is widely used in many fields due to its excellent weather resistance, chemical corrosion resistance, good insulation and elasticity. However, traditional silicone rubber is prone to thermal oxidation aging in high temperature environments, resulting in main chain breakage and rearrangement degradation, thereby reducing the mechanical properties and elasticity of the material and failing to meet the use requirements in extreme environments. Therefore, research and development of high temperature resistant silicone rubber composite materials have important practical significance and application value.

[0003] Traditional high-temperature resistant silicone rubber is mostly based on methyl vinyl silicone rubber. The high-temperature resistance of silicone rubber is enhanced by adding high-temperature resistant additives such as iron oxide and cerium oxide. Although this method can effectively inhibit the cyclization degradation of the silicone rubber main chain and the oxidation of the side chain by adsorbing free radicals, this type of silicone rubber can only be used for a short period of time in an environment of 250℃-300℃. Its high-temperature aging resistance is still poor. It is of great significance to optimize it to further improve its high-temperature aging resistance to meet the requirements of high-temperature conditions. Summary of the invention

[0004] In order to further improve the thermal stability of silicone rubber, thereby improving the high temperature aging resistance, the present application provides a high temperature resistant silicone rubber and a preparation method thereof.

[0005] In a first aspect, the present application provides a method for preparing high temperature resistant silicone rubber, using the following technical solution: A method for preparing high temperature resistant silicone rubber comprises the following steps: S1, mixing an alkynyl-terminated polyimide resin with multi-walled carbon nanotubes to prepare a composite microskeleton precursor; S2, mixing the composite micro-skeleton precursor prepared in step S1 with the first part of the silicone rubber compound, and then adding silane coupling agent A to mix to obtain material B; S3, mixing cerium oxide, calcium oxide, peroxide free radical initiator and silane coupling agent B with the second part of silicone rubber compound to obtain material C; S4, mixing material B and material C to obtain a micro-skeleton precursor mixed glue; S5. The micro-skeleton precursor mixed rubber is vulcanized to obtain the carbon nanotube / polyimide composite modified high temperature resistant silicone rubber.

[0006] By adopting the above technical scheme, the present application first mixes the alkynyl-terminated polyimide resin with carbon nanotubes. Since the carbon nanotubes have an extremely high oil absorption value, and they have an extremely high aspect ratio and a unique nanostructure, their surface provides an orderly guide for the arrangement of the polyimide resin molecular chains, so that when the two are mixed, the polyimide molecular chains are arranged along the long axis direction of the carbon nanotubes to form an ordered microscopic skeleton structure. As the silicone rubber is cross-linked in a peroxide free radical environment, the peroxide free radicals will open the alkynyl bonds on the polyimide resin, and then connect them to the nearby methyl vinyl silicone rubber segments to form a skeleton structure in which the flexible rubber segments are fixed with a rigid resin. This structure can effectively limit the migration and rearrangement of the silicone rubber molecular chains at high temperatures, thereby alleviating the thermal degradation process of the material, improving the thermal stability of the rubber main chain segment, and improving the high temperature aging resistance of the silicone rubber. Finally, the polyimide resin molecular chains are oriented on the surface of carbon nanotubes, and the formed microscopic skeleton structure forms a three-dimensional network structure in the silicone rubber matrix, which physically restricts the free movement and migration of the silicone rubber molecular chains and reduces the thermal migration of the silicone rubber. In addition, the chemical bonds formed by the reaction of the acetylenic groups on the polyimide resin with the methyl vinyl silicone rubber free radicals tightly connect the polyimide resin and the silicone rubber molecular chains together, which not only improves the physical and mechanical properties of the composite material, but also improves the thermal stability of the silicone rubber at high temperatures.

[0007] Liquid polyimide resin is arranged along the carbon nanotubes, and then forms a macromolecular skeleton with silicone rubber through the action of peroxide free radical initiator, so that the rigid materials are firmly combined together by chemical bonding, forming an overall skeleton in the rubber matrix to achieve the purpose of constructing a skeleton-reinforced silicone rubber composite material. The obtained composite material also maintains a certain elasticity at high temperature.

[0008] In the present application, the composite micro-skeleton precursor prepared above is mixed with methyl vinyl silicone rubber compound, and then a silane coupling agent is added, and then cerium oxide, calcium oxide and the silane coupling agent are added. Cerium oxide acts as a free radical adsorbent, and adsorbs free radicals generated in the system in a subsequent high temperature environment. Calcium oxide acts as a water absorbent, and adsorbs water generated by the combination of free hydroxyl groups and free hydrogen during the vulcanization process to prevent the presence of water from affecting the cross-linking process of peroxide free radicals. One end of the added silane coupling agent reacts with the surface hydroxyl groups of inorganic materials such as carbon nanotubes and oxidized fillers, and the other end is combined with polyimide resin and silicone rubber organic materials, thereby forming a strong chemical bond between the inorganic and organic phases. Cerium oxide and calcium oxide themselves have high thermal stability. Combined with the effect of the silane coupling agent, the composite micro-skeleton structure formed by the above filler and the carbon nanotube and polyimide resin is combined by chemical bonding to form an overall skeleton in the rubber matrix to enhance the high temperature resistance of the silicone rubber. The silicone rubber finally obtained has excellent thermal stability and excellent mechanical properties and elasticity in a high temperature environment.

[0009] Optionally, the alkynyl-terminated polyimide resin is specifically a phenylethynyl-terminated polyimide resin, and the weight average molecular weight of the phenylethynyl-terminated polyimide resin is 2000-3000.

[0010] By adopting the above technical solution, when phenylethynyl-terminated polyimide resin is selected, since the polyimide resin chain segment has excellent thermal stability, it will not break or migrate in an environment of 350 degrees Celsius. Afterwards, with the help of the action of peroxide free radicals, the rigid polyimide chain segment with good heat resistance and stability is cross-linked on the silicone rubber main chain segment that is prone to aging and breaking. The silicone rubber main chain is firmly fixed by the polyimide rigid link under high temperature vibration to improve the high temperature resistance of silicone rubber. In addition, the polyimide resin with a lower molecular weight is selected, which has good fluidity and processing performance. After combining with carbon nanotubes, it can be better mixed and evenly dispersed with the silicone rubber substrate in the form of a one-dimensional filler dispersion, so that the generated skeleton is evenly distributed in the rubber matrix, which is beneficial to improve its heat resistance and stability.

[0011] Optionally, in step S1, the alkynyl-terminated polyimide resin and multi-walled carbon nanotubes are ultrasonically oscillated at a frequency of 100 kHz for 50-70 min in a water bath at 0-10° C. to prepare a composite microskeleton precursor.

[0012] By adopting the above technical solution and the mixing method of low-temperature ultrasonic oscillation, the polyimide resin is evenly coated on the surface of the carbon nanotubes, which further alleviates the agglomeration of the carbon nanotubes. In addition, ultrasound at low temperature will not destroy the microstructure of the carbon nanotubes, thereby preventing the properties of the carbon nanotubes and the polyimide resin from changing, thereby further improving the thermal aging performance of the silicone rubber.

[0013] Optionally, in step S2, the composite microskeleton precursor obtained in step S1 is first mixed and stirred with polyimide chopped fibers to obtain material A, and then material A is mixed with the first part of silicone rubber compound and silane coupling agent A is added to mix to obtain material B.

[0014] By adopting the above technical scheme, the addition of polyimide chopped fibers in this application, on the one hand, the molecular structure of polyimide chopped fibers is basically the same as that of liquid polyimide resin, and the two can be cured together under high temperature environment without relying on other coupling agents. And when dispersed in the silicone rubber matrix together with carbon nanotubes, the liquid resin end will be dispersed into the rubber matrix along with the carbon nanotubes, and it is easy to form a skeleton structure similar to a dendrite, and at the same time, a corresponding heat conduction path is also constructed, so that the composite material has a longer service life at high temperature, and along with the cross-linking process, the skeleton and the rubber matrix are firmly combined together. On the other hand, polyimide chopped fibers themselves are easier to disperse in the system. Therefore, while the chopped fibers are gradually dispersed in the system, the liquid polyimide resin with similar polarity will be dispersed along with the dispersion of the chopped fibers, forming a "sea-island" effect of silicone rubber-polyimide resin and chopped fibers, which helps to build an overall skeleton network. In this way, the cooperation between the two substances with the same structure, polyimide resin and polyimide chopped fibers, is more beneficial to the construction of the skeleton structure, and the thermal stability of the silicone rubber finally obtained is better.

[0015] Optionally, in step S1, the alkynyl-terminated polyimide resin and the multi-walled carbon nanotubes are mixed in a mass ratio of (7-8):1; In step S2, the composite micro-skeleton precursor and the polyimide chopped fibers are mixed in a mass ratio of (1.5-3):1; The added mass ratio of material A to the first part of silicone rubber compound and silane coupling agent A is 1:(0.5-1):(0.05-0.1); In step S3, the mass ratio of cerium oxide, calcium oxide, peroxide free radical initiator, silane coupling agent B and the second part of silicone rubber compound is (0.8-1.2): (0.8-1.2): (0.8-1.2): (0.8-1.2): (0.8-1.2): 10; In step S4, the added mass ratio of material B to material C is 1:(3.5-4.5).

[0016] By adopting the above technical solution, the comprehensive performance of the silicone rubber prepared by adopting the above ratio is better.

[0017] Optionally, the silicone rubber compound is selected from one or both of methyl vinyl silicone rubber and low phenyl silicone rubber.

[0018] By adopting the above technical solution, the composite silicone rubber finally obtained by selecting the above silicone rubber matrix has better high temperature resistance.

[0019] Optionally, the silane coupling agent A is KH560, and the silane coupling agent B is A151.

[0020] By adopting the above technical scheme, the KH560 silane coupling agent selected in step S2 can not only improve the dispersibility of the composite microskeleton precursor in the silicone rubber matrix and reduce the agglomeration of carbon nanotubes, but also because it contains epoxy and methoxy functional groups, wherein the epoxy group can form a stable chemical bond with the organic side chain in the silicone rubber and the amino, hydroxyl and other functional groups in the polyimide resin, and the methoxy group undergoes a condensation reaction with the hydroxyl group on the surface of the carbon nanotube after hydrolysis, thereby achieving a coupling effect between the entire composite material, and the A151 silane coupling agent selected in step S3 contains vinyl and ethoxy groups, the vinyl group copolymerizes with the acetylenic group capped with the polyimide resin, and the ethoxy group condenses with the oxygen-containing functional groups on the carbon nanotubes and the polyimide chopped fibers, thereby achieving chemical bonding between the carbon nanotubes, the polyimide resin and the polyimide fibers, and further enhancing the thermal stability of the silicone rubber.

[0021] Optionally, the vulcanization treatment in step S5 includes primary vulcanization and secondary vulcanization performed sequentially, the primary vulcanization temperature is 160° C., the vulcanization is performed for 20 minutes under a pressure of 14 MPa, and the secondary vulcanization temperature is 300° C., and the secondary vulcanization time is 1 hour.

[0022] By adopting the above technical solution, under the above high temperature vulcanization conditions, it is ensured that the polyimide resin, polyimide chopped fibers and the silicone rubber matrix are fully cross-linked to form a stable chemical network structure, thereby maintaining high stability and strength at high temperatures, thereby improving the overall thermal stability of the composite rubber material.

[0023] Optionally, the polyimide chopped fibers are added after being modified, and the modification treatment comprises the following steps: soaking the polyimide chopped fibers in a 1 mol / L NaOH solution at room temperature for 50-70 minutes, and then washing and drying.

[0024] By adopting the above technical scheme, the polyimide chopped fibers themselves are used as polar materials and have good wettability in water-based liquids. The polyimide chopped fibers are treated in a strong alkaline sodium hydroxide solution. Under the action of the strong alkaline liquid, the nitrogen heterocycle on the surface of the polyimide is hydrolyzed to form an imino group and a carboxyl group. The H on the imino group is replaced by the sodium element in an alkaline environment. The modified fibers are then added to the carbon nanotube-polyimide resin-silicone rubber composite material system of the present application. As the peroxidation cross-linking of the polyimide resin and silicone rubber composite material proceeds, the hydrogen element on the imino group and the sodium element on the carboxyl group on the modified fibers are replaced, and connected to other active free radicals such as silicone rubber or polyimide resin to form a stable chemical bond structure, so that the polyimide chopped fibers are firmly bonded to the silica composite matrix, thereby further significantly improving the thermal stability of the silicone rubber.

[0025] In a second aspect, the present application provides a high temperature resistant silicone rubber, which adopts the following technical solution: A high temperature resistant silicone rubber prepared by the preparation method.

[0026] By adopting the above technical solution, the high temperature resistant silicone rubber prepared by the method provided by the present application has excellent thermal stability and high temperature thermal aging performance, and still has good mechanical properties and elasticity under high temperature aging conditions of 350°C.

[0027] In summary, this application has the following beneficial effects: 1. The present application first mixes an alkynyl-terminated polyimide resin with carbon nanotubes. Due to the adsorption effect of the carbon nanotubes, the carbon nanotubes have an extremely high aspect ratio and a unique nanostructure, and the surface provides an orderly guide for the arrangement of the polyimide resin molecular chains. When the two are mixed, the polyimide molecular chains are arranged along the long axis direction of the carbon nanotubes to form a one-dimensional two-phase composite structure. Then, with the subsequent addition of a peroxide free radical initiator, the peroxide free radicals form bonds with the alkynyl groups on the polyimide resin, and then react with the free radicals formed on the methyl vinyl silicone rubber to form a microscopic skeleton structure. The formed micro-skeleton structure can effectively limit the migration and rearrangement of the silicone rubber molecular chains at high temperatures, thereby alleviating the thermal degradation process of the material, improving the thermal stability of the rubber main chain segment, and improving the high temperature aging resistance of the silicone rubber. 2. When the phenylethynyl-terminated polyimide resin is selected in the present application, since the polyimide resin chain segment has excellent thermal stability, it will not break or migrate in an environment of 350 degrees Celsius. Later, with the help of the action of peroxide free radicals, the rigid polyimide chain segment with good heat resistance and stability is cross-linked on the silicone rubber main chain segment that is prone to aging and breaking. The silicone rubber main chain is firmly fixed by the polyimide rigid segment under high temperature vibration to improve the high temperature resistance of the silicone rubber. In addition, the polyimide resin with a lower molecular weight is selected, which has good fluidity and processing properties. After combining with carbon nanotubes, it can be better mixed and evenly dispersed with the silicone rubber substrate in the form of a one-dimensional filler dispersion, so that the generated micro-skeleton is evenly distributed in the rubber matrix, which is beneficial to improve its heat resistance and stability; 3. In the present application, liquid polyimide is distributed along the direction of carbon nanotubes and the acetylene groups on the polyimide resin react with peroxide free radicals at high temperature to form bonds, and then react with the free radicals formed on the methyl vinyl silicone rubber to form bonds, thereby constructing a complete microscopic skeleton, so as to achieve the purpose of reducing the mobility of silicone rubber chain segments and inhibiting the rearrangement and degradation of the main chain. On this basis, treated polyimide chopped fibers are introduced to make the various rigid materials firmly combined together by chemical bonding, forming an overall skeleton in the rubber matrix to achieve the purpose of constructing a skeleton-reinforced silicone rubber composite material, so that the material can maintain a certain elasticity after aging in an environment of 350°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1This is a scanning electron microscope image of a section of carbon nanotubes after the carbon nanotube / polyimide composite modified high temperature resistant silicone rubber is torn apart in Example 1 of the present application; Figure 2 This is a scanning electron microscope image of a partial cross section of polyimide chopped fibers after the high temperature resistant silicone rubber modified with carbon nanotubes / polyimide prepared in Example 1 of the present application was torn apart; Figure 3 This is a scanning electron microscope image of the high temperature resistant rubber obtained in Example 1 of the present application after destruction. DETAILED DESCRIPTION

[0029] The present application is further described in detail below in conjunction with the examples. It is particularly noted that if no specific conditions are specified in the following examples, the experiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0030] In order to improve the thermal stability of silicone rubber, the present application introduces phenylethynyl-terminated polyimide resin, arranges it along the long axis of carbon nanotubes by low-temperature ultrasonic blending to form an ordered microstructure, and then cooperates with the subsequent addition of peroxide free radical initiator. The peroxide free radical and the acetylene group on the polyimide resin open bond reaction is as follows: Then it reacts with the free radicals formed on the methyl vinyl silicone rubber to form a microscopic skeleton structure as shown in Formula 2: Through the above reaction, the alkynyl-terminated polyimide resin molecular chain reacts chemically with methyl vinyl silicone rubber to form a polymer macromolecular chain. The formed skeleton structure effectively limits the migration and rearrangement of the silicone rubber molecular chain at high temperature, thereby alleviating the thermal degradation process of the material, improving the thermal stability of the rubber main chain segment, and improving the high temperature aging resistance of the silicone rubber.

[0031] In addition, in the present application, by adding polyimide chopped fibers treated with alkali solution, the polyimide chopped fibers undergo the process shown in Formula 3 in an alkaline environment. Adding them makes the polyimide chopped fibers and the composite matrix material of carbon nanotubes-polyimide resin-silicone rubber more firmly bonded together, further improving the thermal stability of the silicone rubber.

[0032]

[0033] The invention is described below in conjunction with specific embodiments.

[0034] The methyl vinyl silicone rubber compound in the following embodiments is a silicone premix of model GA-6051F produced by Shenzhen Zhengan Organic Silicone Materials Co., Ltd., specifically a methyl vinyl silicone rubber compound; The alkynyl-terminated polyimide resin in the following embodiments is a phenylacetylene-terminated polyimide resin prepared using 4-phenylacetylene phthalic anhydride as a capping agent, which can be commercially available or homemade. The phenylacetylene-terminated polyimide resin in the following embodiments is prepared by the following method: 35kg of 1,3-bis(4-aminophenoxy)benzene (1,3,4-APB) and 72kg of p-phenylenediamine, two diamine monomers, were dissolved in 250kg of N-methylpyrrolidone, and then a mixture of 80kg of 3,3′,4,4′-diphenyl ether tetraacid dianhydride (ODPA) and 150kg of N-methylpyrrolidone was added after stirring, and the temperature was raised to 75°C, and stirred for reaction for 2h, and then 100kg of toluene was added, and the temperature was raised to 180°C for reaction for 6h, and then 20kg of 4-phenylacetylene phthalic anhydride was added as a capping agent, and the temperature was continued to rise to 200°C for reaction for 1h, and then the heating was stopped and cooled to obtain a liquid phenylacetylene-terminated polyimide resin with a weight average molecular weight of 2800.

[0035] In the following embodiments, the phenyl silicone rubber is selected from the liquid phenyl silicone rubber of Wuhan Lanabai Pharmaceutical Chemical Co., Ltd., with a phenyl content of 3-5%, which is a low phenyl silicone rubber with a product number of P20231020.

[0036] Example 1 A method for preparing high temperature resistant silicone rubber comprises the following steps: S1. Taking 100g of multi-walled carbon nanotubes as a benchmark, the multi-walled carbon nanotube powder was placed in an oven and dried at 60°C for 4h to fully dry the multi-walled carbon nanotubes, and then a polyimide resin capped with phenylacetylene having a weight average molecular weight of 2800 and the multi-walled carbon nanotubes were added in a mass ratio of 7.5:1, and then ultrasonically oscillated at a frequency of 100kHz for 60min in a 5°C water bath to obtain a composite microskeleton precursor, and then stored at a low temperature of 5°C for use; S2, mixing the composite micro-skeleton precursor prepared in step S1 with polyimide short fibers having a length of 1 mm in a mass ratio of 2:1, and stirring at room temperature to obtain material A; Material A and the first part of methyl vinyl silicone rubber compound are mixed on an open rubber mixer, and silane coupling agent KH560 is added until they are completely mixed to obtain material B, wherein the added mass ratio of material A to the first part of methyl vinyl silicone rubber compound and silane coupling agent A is 1.1:1.1:0.1; S3, mixing cerium oxide, calcium oxide, dicumyl peroxide and silane coupling agent A151 with the second part of methyl vinyl silicone rubber compound in a mass ratio of 1:1:1:1:11 to obtain material C; S4, mixing material B and material C in a mass ratio of 1:4.2 on an open rubber mixer at 50° C. for 1 h to obtain a microskeleton precursor mixed rubber; S5. The microskeleton precursor mixed rubber is re-mixed in an open rubber mixer at a roller temperature of 40°C for 10 minutes and unrolled to prepare a semi-finished film according to the calendering direction of the film, and then subjected to primary vulcanization and secondary vulcanization in sequence. The primary vulcanization temperature is 160°C, and the vulcanization is carried out at a pressure of 14 MPa for 20 minutes. The secondary vulcanization temperature is 300°C, and the secondary vulcanization time is 1 hour to obtain a carbon nanotube / polyimide composite modified high temperature resistant silicone rubber.

[0037] Example 2 A method for preparing high temperature resistant silicone rubber comprises the following steps: S1. Taking 100g of multi-walled carbon nanotubes as a benchmark, the multi-walled carbon nanotube powder was placed in an oven and dried at 60°C for 4h to fully dry the multi-walled carbon nanotubes, and then a polyimide resin capped with phenylacetylene having a weight average molecular weight of 2800 and the multi-walled carbon nanotubes were added in a mass ratio of 7:1, and then ultrasonically oscillated at a frequency of 100kHz for 50-70min in a water bath at 0-10°C to obtain a composite microskeleton precursor, and then stored at a low temperature of 0-10°C for use; S2, mixing the composite micro-skeleton precursor prepared in step S1 with polyimide short-cut fibers having a length of 1 mm in a mass ratio of 1.5:1, and stirring at room temperature to obtain material A; Material A and the first part of methyl vinyl silicone rubber compound are mixed on an open rubber mixer, and silane coupling agent KH560 is added until they are completely mixed to obtain material B, wherein the mass ratio of material A to the first part of methyl vinyl silicone rubber compound and silane coupling agent A is 1:0.8:0.08; S3, mixing cerium oxide, calcium oxide, dicumyl peroxide and silane coupling agent A151 with the second part of methyl vinyl silicone rubber compound in a mass ratio of 0.8:0.8:0.8:0.8:10 to obtain material C; S4, mixing material B and material C in a mass ratio of 1:3.5 on an open rubber mixer at 50° C. for 1 h to obtain a microskeleton precursor mixed rubber; S5. The microskeleton precursor mixed rubber is re-mixed in an open rubber mixer at a roller temperature of 40°C for 10 minutes and unrolled to prepare a semi-finished film according to the calendering direction of the film, and then subjected to primary vulcanization and secondary vulcanization in sequence. The primary vulcanization temperature is 160°C, and the vulcanization is carried out at a pressure of 14 MPa for 20 minutes. The secondary vulcanization temperature is 300°C, and the secondary vulcanization time is 1 hour to obtain a carbon nanotube / polyimide composite modified high temperature resistant silicone rubber.

[0038] Example 3 A method for preparing high temperature resistant silicone rubber comprises the following steps: S1. Taking 100g of multi-walled carbon nanotubes as a benchmark, the multi-walled carbon nanotube powder was placed in an oven and dried at 60°C for 4h to fully dry the multi-walled carbon nanotubes, and then a polyimide resin capped with phenylacetylene having a weight average molecular weight of 2800 and the multi-walled carbon nanotubes were added in a mass ratio of 8:1, and then ultrasonically oscillated at a frequency of 100kHz for 50-70min in a 0-10°C water bath to obtain a composite microskeleton precursor, and then stored at a low temperature of 0-10°C for standby use; S2, mixing the composite micro-skeleton precursor prepared in step S1 with polyimide short-cut fibers having a length of 1 mm in a mass ratio of 3:1, and stirring at room temperature to obtain material A; Material A and the first part of methyl vinyl silicone rubber compound are mixed on an open rubber mixer, and silane coupling agent KH560 is added until they are completely mixed to obtain material B, wherein the mass ratio of material A to the first part of methyl vinyl silicone rubber compound and silane coupling agent A is 1:1.3:0.12; S3, mixing cerium oxide, calcium oxide, dicumyl peroxide and silane coupling agent A151 with the second part of methyl vinyl silicone rubber compound in a mass ratio of 1:1.2:1.2:1.2:10 to obtain material C; S4, mixing material B and material C in a mass ratio of 1:4.5 on an open rubber mixer at 50° C. for 1 h to obtain a microskeleton precursor mixed rubber; S5. The microskeleton precursor mixed rubber is re-refined at a roller temperature of 40°C for 10 minutes in an open rubber mixer and unrolled to prepare a semi-finished film according to the calendering direction of the film. The film is then subjected to primary vulcanization and secondary vulcanization in sequence. The primary vulcanization temperature is 160°C and the vulcanization is carried out at a pressure of 14 MPa for 20 minutes. The secondary vulcanization temperature is 300°C and the secondary vulcanization time is 1 hour to obtain a carbon nanotube / polyimide composite modified high temperature resistant silicone rubber.

[0039] Example 4 A method for preparing high temperature resistant silicone rubber is carried out according to the method in Example 1, except that no polyimide chopped fibers are added in step S2, the composite micro-skeleton precursor prepared in step S1 is directly mixed with the first part of methyl vinyl silicone rubber compound on an open rubber mixer, and a silane coupling agent KH560 is added until completely mixed to obtain material B, wherein the mass ratio of the composite micro-skeleton precursor to the first part of methyl vinyl silicone rubber compound and the silane coupling agent A is 0.8:1:0.1.

[0040] Example 5 A method for preparing high temperature resistant silicone rubber is carried out according to the method in Example 1, except that in step S4, the mass ratio of cerium oxide to the second part of silicone rubber compound is 0.6:10.

[0041] Example 6 A method for preparing high temperature resistant silicone rubber is carried out according to the method in Example 1, except that the polyimide chopped fibers in step S2 are added after being modified. The specific operation is: the polyimide chopped fibers are immersed in a 1 mol / L NaOH solution at room temperature for 60 minutes, and then washed and dried, and the NaOH solution does not cover the polyimide chopped fibers.

[0042] Example 7 A method for preparing high temperature resistant silicone rubber is carried out according to the method in Example 1, except that the polyimide chopped fibers in step S2 are added after being modified. The specific operation is: the polyimide chopped fibers are immersed in a 1 mol / L NaOH solution at room temperature for 50 minutes, and then washed and dried, and the NaOH solution does not cover the polyimide chopped fibers.

[0043] Example 8 A method for preparing high temperature resistant silicone rubber is carried out according to the method in Example 1, except that the polyimide chopped fibers in step S2 are added after being modified. The specific operation is: the polyimide chopped fibers are immersed in a 1 mol / L NaOH solution at room temperature for 70 minutes, and then washed and dried, and the NaOH solution does not cover the polyimide chopped fibers.

[0044] Example 9 A method for preparing high temperature resistant silicone rubber is carried out according to the method in Example 1, except that the first part of the methyl vinyl silicone rubber mix is ​​replaced by the first part of the phenyl silicone rubber mix in an equal amount, and the second part of the methyl vinyl silicone rubber mix is ​​replaced by the second part of the phenyl silicone rubber mix in an equal amount.

[0045] Example 10 A method for preparing a high temperature resistant silicone rubber is carried out according to the method in Example 1, except that the first part of the methyl vinyl silicone rubber mix is ​​replaced by the first part of the phenyl silicone rubber mix, and the second part of the methyl vinyl silicone rubber mix is ​​replaced by the second part of the phenyl silicone rubber mix. Meanwhile, no polyimide chopped fibers are added to S2. Comparative Example 1 A method for preparing silicone rubber is carried out according to the method in Example 1, except that step S1 is not carried out, and in step S2, the composite micro-skeleton precursor is replaced by an equal amount of carbon nanotubes.

[0046] Comparative Example 2 A method for preparing silicone rubber is carried out according to the method in Example 1, except that step S1 is not performed, and in step S2, an equal amount of a composite micro-skeleton precursor is replaced by a phenylacetylene-terminated polyimide resin.

[0047] Comparative Example 3 A method for preparing silicone rubber is carried out according to the method in Example 1, except that step S1 is not performed, and in step S2, an equal amount of material A is replaced by polyimide chopped fibers, and the polyimide chopped fibers are directly mixed with the first part of methyl vinyl silicone rubber compound.

[0048] Comparative Example 4 A method for preparing silicone rubber is carried out according to the method in Example 1, except that step S1 is not performed, and in step S2, an equal amount of material A is replaced by carbon nanotubes, and the carbon nanotubes are directly mixed with the first part of the methyl vinyl silicone rubber compound.

[0049] Comparative Example 5 A method for preparing silicone rubber is carried out according to the method in Example 1, except that the polyimide resin terminated with phenylacetylene in step S1 is directly replaced by an equal amount of polyimide resin (liquid polyimide PI resin from Dongguan Shengbang Polymer Materials Co., Ltd. is selected).

[0050] Performance Testing The silicone rubber prepared in the examples and comparative examples of the present application was tested for tensile strength at break (MPa) after aging at 300°C for 1 hour and elongation at break (%) after aging at 300°C for 1 hour in accordance with GB / T 528-2009. The test results are shown in Table 1 below: Table 1: Referring to the test results in Table 1 above, the high temperature resistant silicone rubber prepared in the present application still has good mechanical strength and elasticity after high temperature aging, and has excellent high temperature aging resistance. Combined with the test results of Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, only carbon nanotube-polyimide fiber composite modified silicone rubber is selected, and its thermal stability is significantly reduced. Combined with the test results of Comparative Example 2, when phenylacetylene-terminated polyimide resin and polyimide fiber are used in Comparative Example 2, its elasticity after thermal aging is significantly reduced. Combined with the test results of Comparative Examples 3 and 4, when only polyimide chopped fibers or carbon nanotubes are used for modification, its thermal stability is significantly reduced. Combined with the test results of Comparative Example 5, when ordinary polyimide resin is used for composite modification, its thermal stability is poor.

[0051] Combined with the test results of Example 1 and Example 4, it can be seen that when the polyimide chopped fibers are not added to the composite modified material, although the elongation at break is high after high-temperature aging, its strength is significantly reduced, and its high-temperature aging resistance is reduced. Combined with the test results of Example 5, the amount of cerium oxide added is small, and the heat aging resistance of the prepared silicone rubber is reduced. Moreover, when cerium oxide is not added to the raw material or the ratio of cerium oxide to the first part of methyl vinyl silicone rubber is 0.5:10, the amount of cerium oxide added is too small, and the prepared silicone rubber is brittle and cannot be tested; Combined with the test results of Examples 6-8, it can be seen that the polyimide resin is added after treatment. Compared with Example 1, it can be seen that the tensile strength is higher and the elongation at break changes less after high-temperature aging treatment. Its addition after treatment further enhances its heat aging performance. Referring to the test results of Examples 1 and 9-10, it can be seen that when the rubber base in Example 9 uses phenyl silicone rubber, its elongation at break performance is better than that of the methyl vinyl silicone rubber compound in Example 1. For silicone rubber, the flexibility is better maintained after high-temperature aging treatment, and its flexibility is higher and the high-temperature resistance is better. Referring to the test results of Example 10, without adding polyimide chopped fibers, the rubber has excellent elongation at break after aging, but the tensile strength is significantly reduced. .

[0052] Also refer to Figure 1 and Figure 2 Scanning image of the cross section of the broken silicone rubber. Figure 1 The carbon nanotubes are wrapped by polyimide resin to form a micro-skeleton. Figure 2 The polyimide short fibers form a three-dimensional network structure in the micro-skeleton, which helps to improve the construction and support of the micro-skeleton structure, so that the polyimide resin is distributed along the radial direction of the carbon nanotubes. When the polyimide fibers form chemical crosslinks with the silicone rubber through peroxide free radicals, the polyimide fibers further play a limiting role, reduce the mobility of the silicone rubber, and improve the heat aging resistance of the silicone rubber. Figure 3 , is an electron microscope image of the cross section of the high temperature resistant rubber obtained in Example 1 of the present application after destruction. It can be seen that the surface of the polyimide chopped fibers is connected to carbon nanotubes to form a chopped fiber-carbon nanotube-liquid polyimide resin micro-skeleton structure.

[0053] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing high temperature resistant silicone rubber, characterized in that: The following steps are involved: S1, mixing an alkynyl-terminated polyimide resin with multi-walled carbon nanotubes to prepare a composite microskeleton precursor; S2, mixing the composite micro-skeleton precursor prepared in step S1 with the first part of the silicone rubber compound, and then adding silane coupling agent A to mix to obtain material B; S3, mixing cerium oxide, calcium oxide, peroxide free radical initiator and silane coupling agent B with the second part of silicone rubber compound to obtain material C; S4, mixing material B and material C to obtain a micro-skeleton precursor mixed glue; S5. The micro-skeleton precursor mixed rubber is vulcanized to obtain the carbon nanotube / polyimide composite modified high temperature resistant silicone rubber.

2. The method for preparing a high temperature resistant silicone rubber according to claim 1, characterized in that: The alkynyl-terminated polyimide resin is specifically a phenylethynyl-terminated polyimide resin, and the weight average molecular weight of the phenylethynyl-terminated polyimide resin is 2000-3000.

3. The method for preparing a high temperature resistant silicone rubber according to claim 1, characterized in that: In step S1, the alkynyl-terminated polyimide resin and multi-walled carbon nanotubes are ultrasonically oscillated at a frequency of 100 kHz for 50-70 minutes in a water bath at 0-10° C. to prepare a composite microskeleton precursor.

4. The method for preparing a high temperature resistant silicone rubber according to claim 1, characterized in that: In step S2, the composite micro-skeleton precursor prepared in step S1 is first mixed with polyimide chopped fibers to obtain material A, and then material A is mixed with the first part of silicone rubber compound and silane coupling agent A is added to obtain material B.

5. The method for preparing a high temperature resistant silicone rubber according to claim 4, characterized in that: In step S1, the alkynyl-terminated polyimide resin and the multi-walled carbon nanotubes are mixed in a mass ratio of (7-8):1; In step S2, the composite micro-skeleton precursor and the polyimide chopped fibers are mixed in a mass ratio of (1.5-3):1; The mass ratio of material A to the first part of silicone rubber compound and silane coupling agent A is 1: (0.5-1): (0.05-0.1); In step S3, the mass ratio of cerium oxide, calcium oxide, peroxide free radical initiator, silane coupling agent B and the second part of silicone rubber compound is (0.8-1.2): (0.8-1.2): (0.8-1.2): (0.8-1.2): 10; In step S4, the added mass ratio of material B to material C is 1:(3.5-4.5).

6. The method for preparing a high temperature resistant silicone rubber according to claim 1, characterized in that: The silicone rubber compound is selected from one or both of methyl vinyl silicone rubber and low phenyl silicone rubber.

7. The method for preparing a high temperature resistant silicone rubber according to claim 1, characterized in that: Silane coupling agent A is KH560, and silane coupling agent B is A151.

8. The method for preparing a high temperature resistant silicone rubber according to claim 1, characterized in that: The vulcanization treatment in step S5 includes primary vulcanization and secondary vulcanization performed sequentially, the primary vulcanization temperature is 160° C., the vulcanization is performed for 20 minutes under a pressure of 14 MPa, and the secondary vulcanization temperature is 300° C., and the secondary vulcanization time is 1 hour.

9. The method for preparing a high temperature resistant silicone rubber according to claim 1, characterized in that: The polyimide chopped fibers are added after being modified, and the modification process comprises the following steps: soaking the polyimide chopped fibers in a 1 mol / L NaOH solution at room temperature for 50-70 minutes, and then washing and drying.

10. High temperature resistant silicone rubber obtained by the preparation method according to any one of claims 1 to 8.

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