High insulation resistance cable silicone rubber and preparation method thereof

Abstract

The present invention relates to a high insulation resistance type cable silicone rubber and a preparation method thereof, wherein the insulation resistance type cable silicone rubber comprises the following components calculated by weight: a first methyl vinyl silicone rubber component, 50 to 100 weight parts; a second methyl vinyl silicone rubber component, 20 to 50 weight parts; white carbon black, 20 to 60 weight parts; silicone oil, 5 to 15 weight parts; a vulcanizing agent component, 0.5 to 5 weight parts; and a high temperature resistant agent, 0.5 to 5 weight parts. The insulation resistance type silicone rubber of the present invention has achieved excellent test results in various aspects of mechanics and electricity, and is particularly suitable for the application of high insulation and high resistance insulation type cables in applications with certain mechanical strength.

Description

Technical Field

[0001] The invention relates to the field of polymer compositions, and in particular to a high insulation resistance type cable silicone rubber and a preparation method thereof. Background Art

[0002] In the field of chemical applications, silicone rubber is an organic silicon compound with a silicon-oxygen bond as the main chain, and the side groups are usually composed of methyl, vinyl, phenyl, trifluorosilicon and other substituents. Its main chain is composed of alternating silicon atoms and oxygen atoms, which determines that silicone rubber has good high and low temperature resistance. It can usually be used for a long time in harsh working conditions within a range of more than 200°C. It also has excellent electrical insulation properties, and the mechanical properties can be adjusted according to the application scenario. Because silicone rubber has the above excellent comprehensive properties, it is widely used in various fields such as aviation, aerospace, construction, electronics, electrical appliances, and automobiles.

[0003] However, the high insulation and high mechanical and electrical isolation properties of silicone rubber have been widely studied and paid attention to. For example, CN107033599B discloses a flame-retardant single-component moisture-curing silicone rubber, which uses alkoxysilane as a cross-linking agent. It is a highly plastic strip material before contacting moisture in the air. It can tightly wrap around the electrical exposed parts with irregular structures within a period of time after just contacting the air. After a certain period of curing and shaping, it has certain mechanical strength, good electrical properties, and good bonding effect with the wrapped substrate. However, the mechanical support performance of this type of product is insufficient, and the resistance and dielectric properties have not been fully developed and studied.

[0004] Therefore, there is still a need for further development and research of related technologies. Summary of the invention

[0005] The present invention focuses on providing a high-performance high-insulation resistance silicone rubber with improved mechanical and electrical insulation properties and a preparation method thereof. The silicone rubber product prepared by the raw materials and process of the components of the present invention has good comprehensive mechanical and electrical properties, especially resistance properties, dielectric properties and mechanical support properties. The various characteristics and effects of the present invention will be described in detail in the following technical solutions and specific embodiments.

[0006] In a first aspect of the present invention, an insulating resistance type cable silicone rubber is provided, wherein the insulating resistance type cable silicone rubber comprises the following raw materials calculated by weight: a first methyl vinyl silicone rubber component, 50 to 100 parts by weight; a second methyl vinyl silicone rubber component, 20 to 50 parts by weight; white carbon black, 20 to 60 parts by weight; silicone oil, 5 to 15 parts by weight; a vulcanizing agent component, 0.5 to 5 parts by weight; and a high temperature resistant agent, 0.5 to 5 parts by weight.

[0007] The "high insulation" in the "high insulation resistance cable" of the present invention can be defined as a rubber composition or a component having a volume resistivity greater than 4.5×10 15 Ω·cm, preferably, it can be greater than 5×10 15 Ω·cm, most preferably, the volume resistivity is greater than 5.5×10 15 Ω·cm; and alternatively, the relative dielectric constant is greater than 3.0, preferably greater than 3.2, most preferably greater than 3.5.

[0008] In an optional solution, in the raw material components, the white carbon black includes a first white carbon black and a second white carbon black, and the specific surface area of ​​the first white carbon black is 300m 2 / g-350m 2 / g, the specific surface area of ​​the second white carbon black is 100m 2 / g-150m 2 / g; the silicone oil includes a first silicone oil and a second silicone oil, the first silicone oil includes an epoxy-terminated silicone oil, and the second silicone oil includes methyl vinyl silicone oil; the vulcanizing agent component includes a first vulcanizing agent and a second vulcanizing agent, the first vulcanizing agent is preferably di-tert-butyl peroxide, and the second vulcanizing agent is preferably diisopropylbenzene peroxide; and the high temperature resistant agent is selected from nano titanium oxide and / or nano aluminum oxide.

[0009] In a further optional scheme, the first white carbon black is 30 to 60 parts by weight; the second white carbon black is 5 to 30 parts by weight; the first silicone oil is 5 to 10 parts by weight; the second silicone oil is 1 to 5 parts by weight; the first vulcanizing agent is 0.5 to 2 parts by weight; the second vulcanizing agent is 0.1 to 2 parts by weight; the nano titanium oxide and nano aluminum oxide are each 0.5 to 2 parts by weight, and preferably, the nano titanium oxide and nano aluminum oxide are each subjected to hydrophilic surface modification.

[0010] Preferably, the raw material of the insulating resistance type cable silicone rubber further includes an acid absorber component, and the acid absorber component is preferably calcium hydroxide, and the content of the acid absorber is 0.1 to 1 part by weight.

[0011] Further preferably, the raw material of the insulating resistance type cable silicone rubber also includes a dielectric strength agent, and the dielectric strength agent is glass fiber powder, and the weight of the glass fiber powder is 0.5 to 3 parts by weight.

[0012] In an optional technical solution, the raw material of the insulating resistance type cable silicone rubber also includes an auxiliary cross-linking agent (the silicone oil component can mainly play a cross-linking role), and the auxiliary cross-linking agent is preferably γ-glycidyloxypropyltrimethoxysilane, and the content of γ-glycidyloxypropyltrimethoxysilane is 0.1 to 2 parts by weight.

[0013] A second aspect of the present invention provides a method for preparing insulating resistance type cable silicone rubber, wherein the insulating resistance type cable silicone rubber is prepared from any one of the raw materials of the above-mentioned rubber products through a first step of mixing and a second step of re-milling.

[0014] More specifically, according to the technical solution of the present invention, in the first step, the first and second methyl vinyl silicone rubber components, the white carbon black component, the second silicone oil, the dielectric strength agent, the acid absorber, and the high temperature resistant agent are added to an internal mixer under an inert atmosphere for mixing at room temperature until the mixture is uniform. The internal mixer is kept at a temperature of 130°C to 140°C during the mixing process, and the system is vacuumed for refining for 0.5 to 3 hours; after an interval of 30 minutes, a secondary mixing is performed for 1 to 3 hours, followed by cooling, discharging, and filtering to obtain a rubber mix; in the second step, the rubber mix obtained in the first step is allowed to stand overnight, and then the rubber mix is ​​re-mixed, the first silicone oil component, the optional auxiliary cross-linking agent, and the first vulcanizing agent and the second vulcanizing agent are added, and the re-mixing continues for 30 to 60 minutes until the mixture is fully uniform, and the temperature is raised to 150°C to 160°C for preliminary vulcanization for 15 minutes; then the temperature is raised to 180°C to 190°C for vulcanization for 1 to 2 hours, thereby obtaining an insulating resistance type cable silicone rubber.

[0015] In a third aspect, the present invention also relates to an insulating resistance type cable silicone rubber, wherein the resistance type cable silicone rubber is prepared by any one of the above methods.

[0016] The rubber composition in the technical solution of the present invention may be formed only by the above components without containing other components. However, it can be understood by those skilled in the art that the rubber composition in the technical solution of the present invention may include the raw material components and may also include other auxiliary raw material components. However, preferably, the rubber product of the present invention no longer contains major or minor components other than those described in the technical solution.

[0017] It should be noted that the product and process of the present invention may include the above steps and other related steps. In an optional or preferred scheme, the scheme of the present invention may only include the above steps or components, no longer include other steps and components, or do not significantly include other main steps or main components. In addition, the steps should be performed in a sequential order in the optional scheme, and the components and steps of the present invention can be implemented independently or arbitrarily superimposed and combined with each other.

[0018] In the following, the technical solutions and advantages of the present invention will be explained and described in more detail in conjunction with specific implementation methods. It should be understood that the contents presented in the specification and specific implementation methods are only for the purpose of more clearly illustrating the technical solutions and advantages of the present invention, and do not limit the protection scope of the present invention. Those skilled in the art can obtain the changed technical solutions based on the disclosure of the specification for various reasonable transformations. As long as they do not deviate from the spirit of the present invention, the various changed technical solutions should be understood to be included in the protection scope of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described in more detail hereinafter to facilitate understanding of the invention.

[0020] Before describing the specific implementation scheme, it should be noted that those skilled in the art can select appropriate raw materials according to the enlightenment and teaching of the present disclosure, and use relevant testing equipment to perform relevant tests and obtain corresponding results. For raw materials without specific manufacturers or pathways, those skilled in the art can select raw materials that meet corresponding requirements as reaction starting materials according to the disclosure and requirements of this specification. The reaction raw materials of the process part compounds are derived from the initial products synthesized in the preamble step of the present invention, which can also be understood according to the present disclosure.

[0021] Table 1 lists the main raw materials used in the present invention and the corresponding acquisition channels or raw material origins. It should be noted that the raw materials not described in the present invention are raw material varieties that can be obtained by those skilled in the art based on common technical knowledge and existing market products.

[0022] Table 1: Description of the main raw materials used in the present invention

[0023]

[0024]

[0025] Preparation Example 1:

[0026] In the embodiment of the present invention, nano-aluminum oxide and nano-titanium oxide can be modified by using a hydrophilic surface modifier, for example, using a Tween series emulsifier.

[0027] In a typical modification process, nano-alumina and nano-titanium oxide powders (which can be purchased commercially or made by existing technologies) are heated to 120°C-130°C respectively, and 5%-10% of polyoxyethylene sorbitan laurate (Tween 20) by weight of the total powder is added through an atomization process. The reaction is maintained for about 10 minutes to promote sufficient mixing and surface coating to achieve hydrophilic surface-modified nano-oxide powders.

[0028] Example 1 (E1 to E4)

[0029] This embodiment describes in detail the composition ratio and preparation process of the insulating resistance type silicone rubber. The rubber composition ratio of each main embodiment is as follows (unless otherwise specified, the data in the following table are in parts by weight):

[0030] Table 2: Composition ratio of insulation resistance type silicone rubber

[0031]

[0032]

[0033] The specific preparation process is described as follows.

[0034] Step 1): Under an inert atmosphere (a typical embodiment is nitrogen), add the methyl vinyl silicone rubber component (first and second components), white carbon black component (first and second components), second silicone oil component, dielectric strength agent, acid absorber, and high temperature resistant agent (first and second components) in each embodiment to an internal mixer for mixing at room temperature until the mixture is uniform. Each of the white carbon black, dielectric strength agent, acid absorber, and high temperature resistant agent is divided into 3 parts by weight during the mixing process and added in 3 times during the mixing and refining process. The internal mixer is kept at a temperature of 130°C to 140°C during the internal mixing process, and the system is vacuumed for 1 hour. After an interval of 30 minutes, perform secondary mixing for 1.5 hours, cool to 60°C, discharge, and filter to obtain a mixed rubber;

[0035] Step 2): The rubber mix obtained in step 1) is allowed to stand overnight, and then the rubber mix is ​​re-mixed, and the first silicone oil component, the auxiliary cross-linking agent (if any), the first vulcanizing agent, and the second vulcanizing agent component are added, and the re-mixing is continued for 30 minutes until the mixture is fully and uniformly mixed, and the temperature is raised to 160°C for preliminary vulcanization for 15 minutes; then the temperature is raised to 190°C for vulcanization for 1.5 hours. Insulating resistance type silicone rubber is obtained.

[0036] The obtained product can be used to obtain various insulating resistance silicone rubber components through molds or extrusion processes at relatively high temperatures according to the needs of insulation, impedance and mechanical support.

[0037] Test Example 1

[0038] In this test example, the performance tests were performed on the various implementation schemes obtained in Example 1, and the tests were in compliance with the corresponding industry or national standards. The test results are shown in Table 3 below.

[0039] Table 3: Insulation resistance type silicone rubber performance test obtained in Example 1

[0040]

[0041]

[0042] From the test results of the embodiments of the present invention, the insulating resistance type silicone rubber of each embodiment has achieved relatively good test results in terms of mechanics and electricity, and is particularly suitable for the application of high insulation and high resistance insulated cables in applications with certain mechanical strength. Without limitation, the inventor does not want the interpretation or description of the above experimental results to be bound by any physical or chemical theory, but attempts to make corresponding interpretations of the rubber composition and formulation of the present invention, and at least part of these interpretations and descriptions will be further explained and verified in the comparative experimental examples.

[0043] The raw rubber component of the present invention uses a two-component basic silicone rubber with "high vinyl content" and "low vinyl content". In the experimental example of the present invention, "high vinyl content" refers to a basic silicone rubber component with a vinyl content controlled within "0.21-0.25% (mol)", and the methyl vinyl silicone rubber has a tendency to have stronger subsequent cross-linking performance. The low vinyl content methyl vinyl silicone rubber refers to a basic silicone rubber component with a vinyl content of 0.05-0.09% (mol). The combination of the two makes a part of the rubber component with a high tendency to cross-link provide relatively higher cross-linking and support, while the other part of the low vinyl content methyl vinyl silicone rubber provides a very small vinyl content on the side chain, and the cross-linking density after vulcanization is relatively small, providing better resilience. Compared with the basic silicone rubber component of the related art, when the vinyl content in the high vinyl content basic silicone rubber component exceeds 0.3% (mol) or even exceeds 0.5% (mol), since the basic silicone rubber component accounts for a large proportion of the composition, the sensitivity of the vinyl content is relatively high, resulting in excessive hardness of the rubber insulation product, and relatively deteriorated rebound and elongation properties. When the high vinyl content of the basic silicone rubber component is less than 0.20 mol%, the support performance provided at this time is significantly reduced, including tensile strength and the appropriate hardness required for support. In addition, the mass ratio of the first methyl vinyl silicone rubber to the second methyl vinyl silicone rubber is preferably 1:1. In an optional embodiment, the mass ratio of the first methyl vinyl silicone rubber to the second methyl vinyl silicone rubber can be 1:1 to 3:1. When it exceeds 3:1, the cross-linking efficiency decreases, resulting in insufficient rigidity and relative degradation of the rubber product.

[0044] In addition, unlike related technical reports, the use of fine particle size white carbon black (for example, greater than 300, or even greater than 350 μm) 2 / g) is conducive to filling the rubber tissue inside, thereby enhancing the density and mechanical strength of the rubber composition. However, the inventors found that the use of fine-grained white carbon black alone is not conducive to the hardness required by the rubber material when it acts as an insulating support, and also affects the volume resistivity and tensile strength. Therefore, in the embodiment of the present invention, the inventors use coarse-grained white carbon black (100-150m 2 / g) and fine white carbon black (300-350m 2 / g) of filler, and both filling and mechanical properties are met. Fine white carbon black (300-350m 2 / g) and coarse particle size white carbon black (100-150m 2 In particular, when the surface roughness requirement of silicone rubber insulation materials is not high, such as non-surface insulation wrapping materials or internal insulation support materials, fine white carbon black (300-350m 2 / g) and coarse particle size white carbon black (100-150m 2 The mass ratio of coarse particles to fine particles of silica can be expanded to (5:1) to (1:3). At the same time, the inventors also found that the combination of coarse particles and fine particles of silica is conducive to maintaining and increasing the volume resistivity and dielectric constant while maintaining the supporting strength.

[0045] In addition, in the high temperature resistant insulating composition of the present invention, a two-component high temperature resistant component is introduced. In the typical high temperature resistant component, nano titanium oxide and nano aluminum oxide are used. Preferably, the average particle size of nano titanium oxide and nano aluminum oxide is less than 80 nanometers, between 50-80 nanometers. After the introduction of the two-component high temperature resistant component, the insulating resistance type silicone rubber can work effectively in an environment of 250°C or even up to 280°C for a long time. When introducing this component, the inventor surprisingly found that after the hydrophilic surface modification of nano titanium oxide and nano aluminum oxide, and then adding it to the rubber component, the volume resistivity and dielectric constant are effectively improved. This may be due to the additional isolation effect between a small part of the hydrophilic phase and the rubber phase. At the same time, the small amount of hydrophilic component does not have a significant negative effect on the mechanical properties of the rubber. The mass of the hydrophilic high temperature resistant component accounts for 2% or less of the total mass of the methyl vinyl silicone rubber component and white carbon black, preferably 1.5% or less, 1% or less. In the hydrophilic surface modification, typically a polyoxyethylene sorbitan ester surface modifier (Tween series) can be used to modify the surface of the nanopowder.

[0046] In addition, the present invention adopts a cross-linking system of two composite silicone oils. In the auxiliary cross-linking step, methyl vinyl silicone oil is added. This component has good lubricity, miscibility with organic resins, and impact resistance, and forms a mixed rubber system in the pre-cross-linking stage. In the main cross-linking step, the use of terminal epoxy silicone oil helps to improve the cross-linking uniformity and the degree of cross-linking. In an optional embodiment, an auxiliary cross-linking agent component, such as γ-glycidyloxypropyltrimethoxysilane, can also be added to help further improve the tensile strength of the insulating resistance rubber composition.

[0047] Comparative Example (C)

[0048] In the comparative example series of experiments, the same preparation process as in the examples was used, except that the types or proportions of the components in the examples were adjusted. The components of the rubber composition of the comparative example series are shown in the following table.

[0049] Table 4: Comparative Example Insulation High Resistance Insulation Rubber Composition

[0050]

[0051]

[0052] The comparative experiment also performed the same test standard as the embodiment, and the results are shown in the following table:

[0053] Table 5: Performance test of comparative insulation high resistance type insulation rubber composition

[0054]

[0055] The inventors do not wish to be bound by any theory regarding the fluctuations and differences in performance between the comparative examples and the examples of the present invention. When the composition uses a raw rubber component with a low vinyl content (such as C1, with a vinyl content of 0.01-0.03% (mol) and a molecular weight of 500,000-600,000), the hardness of the synthetic rubber component becomes significantly softer (compared with E1), probably due to insufficient pre-crosslinking and secondary crosslinking. Surprisingly, when a raw rubber component with a low vinyl content is used, the volume resistivity is deteriorated to less than 5×10 15 Ω·cm, which may be due to the insufficient support of the raw rubber matrix, so that the filling isolation and dielectric properties of white carbon black cannot be fully exerted. Therefore, the composition of the specific raw rubber component and white carbon black of the present invention jointly ensures high insulation and high dielectric properties.

[0056] On the other hand, when a raw rubber component with a higher vinyl content is used (such as C2, 0.3-0.5% (mol), molecular weight 850,000-950,000), the rubber hardness increases, but the rebound rate deteriorates significantly. This may be because the raw rubber with a high vinyl content leads to excessive crosslinking and insufficient rebound, and the further increase in hardness has little effect on the application of high-insulation rubber (compared with E2); as the rubber product becomes softer, the rebound also decreases.

[0057] In comparative example 3, the inventors only used fine-particle silica, without combining fine and coarse-particle silica. Comparative example (E3) found that the use of fine-particle silica alone was not conducive to further improving the support and volume resistivity, and unexpectedly had a certain impact on the tensile strength. On the one hand, coarse-particle silica increased the proportion and volume of the insulating part in the rubber system during the filling process. On the other hand, the combination of coarse and fine silica can also better blend with the two raw rubber components with different crosslinking ratios.

[0058] Finally, in Comparative Example 4 (C4), the inventors tried to use intrinsic commercially purchased nano oxides as high temperature resistant agents without surface modification with hydrophilic Tween reagents. The experimental test results show that the nano oxides without hydrophilic modification do not affect the improvement of high temperature resistance, and the composite rubber can still maintain an effective working state at a temperature above 250°C for a long time. However, unexpectedly, the volume resistivity and dielectric constant of the unmodified nano oxides are deteriorated compared to the hydrophilic modified nano heat-resistant components. The inventors believe that the nano oxide itself is not only a heat-resistant component, but also a dielectric and isolation phase, and a small part of the hydrophilic phase produces an additional isolation effect with the rubber.

[0059] According to the implementation scheme and technical contents recorded in the specification of the present invention, the present invention can at least provide the following technical solutions: Although the present disclosure includes specific embodiments, it is obvious to those skilled in the art that various formal and detailed replacements or changes can be made to these embodiments without departing from the gist and scope of the invention of the present claims and their equivalent technical solutions. The embodiments described herein should be considered to be illustrative only and not for the purpose of limitation. The description of the features and aspects in each embodiment is considered to be applicable to similar features and aspects in other embodiments. Therefore, the scope of the present disclosure should not be limited by the specific description, but by the technical solutions of the claims, and all changes within the scope of the claims and their equivalents are interpreted as being included in the technical solutions of the present disclosure.

Claims

1. An insulation resistance type cable silicone rubber, characterized in that: The insulating resistance type cable silicone rubber comprises the following raw materials calculated by weight: The first methyl vinyl silicone rubber component, 50 to 100 parts by weight; The second methyl vinyl silicone rubber component, 20 to 50 parts by weight; White carbon black, 20 to 60 parts by weight; Silicone oil, 5 to 15 parts by weight; Vulcanizing agent component, 0.5 to 5 parts by weight; High temperature resistant agent, 0.5 to 5 parts by weight; as well as In the raw material components, the white carbon black includes a first white carbon black and a second white carbon black, and the specific surface area of ​​the first white carbon black is 300m 2 / g-350m 2 / g, the specific surface area of ​​the second white carbon black is 100m 2 / g-150m 2 / g; The silicone oil comprises a first silicone oil and a second silicone oil, wherein the first silicone oil comprises an epoxy-terminated silicone oil, and the second silicone oil comprises methyl vinyl silicone oil; The vulcanizing agent component comprises a first vulcanizing agent and a second vulcanizing agent, wherein the first vulcanizing agent is di-tert-butyl peroxide, and the second vulcanizing agent is diisopropylbenzene peroxide; and The high temperature resistant agent is selected from nano titanium oxide and nano aluminum oxide; and The first white carbon black is 30 to 60 parts by weight; The second white carbon black is 5 to 30 parts by weight; The first silicone oil is 5 to 10 parts by weight; The second silicone oil is 1 to 5 parts by weight; The first vulcanizing agent is 0.5 to 2 parts by weight; The second vulcanizing agent is 0.1 to 2 parts by weight; The nano titanium oxide and the nano aluminum oxide are each in an amount of 0.5 to 2 parts by weight, and the nano titanium oxide and the nano aluminum oxide are each subjected to hydrophilic surface modification.

2. The insulation resistance type cable silicone rubber according to claim 1, characterized in that: The raw material of the insulating resistance type cable silicone rubber also includes an acid absorber component, the acid absorber component is calcium hydroxide, and the content of the acid absorber is 0.1 to 1 part by weight.

3. The insulation resistance type cable silicone rubber according to claim 1, characterized in that: The raw materials of the insulating resistance type cable silicone rubber also include a dielectric strength agent, and the dielectric strength agent is glass fiber powder, and the weight of the glass fiber powder is 0.5 to 3 parts by weight.

4. The insulation resistance type cable silicone rubber according to claim 1, characterized in that: The raw material of the insulating resistance type cable silicone rubber also includes an auxiliary cross-linking agent, the auxiliary cross-linking agent is γ-glycidyl ether oxypropyl trimethoxy silane, and the content of the γ-glycidyl ether oxypropyl trimethoxy silane is 0.1 to 2 parts by weight.

5. A method for preparing insulating resistance type cable silicone rubber, characterized in that: The insulating resistance type cable silicone rubber is made from the raw materials used in the insulating resistance type cable silicone rubber according to any one of claims 1 to 4 through a first step of mixing and a second step of re-milling.

6. The method according to claim 5, characterized in that The mixing step of the first step and the re-milling step of the second step specifically include: The first step is to add the first methyl vinyl silicone rubber component and the second methyl vinyl silicone rubber component, the white carbon black component, the second silicone oil, the dielectric strength agent, the acid absorber, and the high temperature resistant agent into an internal mixer under an inert atmosphere for mixing at room temperature until the mixture is uniform. During the internal mixing process, the temperature of the internal mixer is maintained at 130° C. to 140° C., and the system is vacuumed for refining for 0.5 to 3 hours; after an interval of 30 minutes, a second mixing is performed for 1 to 3 hours, followed by cooling, discharging, and filtering to obtain a mixed rubber; In the second step, the rubber mixture obtained in the first step is allowed to stand overnight, and then the rubber mixture is re-refined, and the first silicone oil component, the auxiliary cross-linking agent, the first vulcanizing agent, and the second vulcanizing agent are added. The re-refining is continued for 30 to 60 minutes until the mixture is fully and uniformly mixed, and the temperature is raised to 150°C to 160°C for preliminary vulcanization for 15 minutes; then the temperature is raised to 180°C to 190°C for vulcanization for 1 to 2 hours, thereby obtaining an insulating resistance type cable silicone rubber.

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