High flame retardant fast ceramic silicone rubber and preparation method thereof

Abstract

The application discloses high-flame-retardant rapid ceramicized silicone rubber and a preparation method thereof. The silicone rubber comprises the following components in parts by weight: 100 parts of raw silicone rubber, 35-45 parts of reinforcing filler, 80-120 parts of flame-retardant ceramic filler, 10-20 parts of fluxing agent, 2.0 parts of crosslinking agent and 5 parts of heat-resistant agent, wherein the heat-resistant agent is a silicone resin. The silicone rubber is prepared by the following steps: weighing the raw silicone rubber, white carbon black, the flame-retardant ceramic filler, the fluxing agent and the heat-resistant agent according to the proportions, adding them into a torque rheometer, adding the white carbon black for multiple times, mixing them into a group, heating the equipment to 180 DEG C and keeping for 1 hour to obtain a mixed rubber, placing the obtained mixed rubber at room temperature for at least 24 hours, opening the mixed rubber in an open mill at room temperature and adding the corresponding proportion of the crosslinking agent, and obtaining the product after rolling, thinning and sheeting. The obtained product has the characteristics of low temperature, rapidness and compact ceramicization, the ceramic has good high-temperature electrical insulation performance, and meets the requirements of fire-resistant cable insulation and other similar applications.

Description

Technical Field

[0001] This invention relates to a high flame-retardant, rapidly ceramizing silicone rubber, suitable for the manufacture of fire-resistant cables, used as an insulation layer, sheath layer, or fire-resistant filling and insulating layer for fire-resistant cables. It can also be used in other electrical, electronic, and automotive components with fire-resistant and fire-resistant requirements, belonging to the field of cable material design and preparation technology. This invention also relates to a method for preparing the aforementioned silicone rubber. Background Technology

[0002] Fire-resistant cables are cables with specified fire-resistant properties (such as line integrity, smoke density, smoke toxicity, and corrosion resistance). Due to their superior fire-resistant properties compared to conventional cables, fire-resistant cables can continue operating for a certain period during a fire, providing more time for people to escape and for firefighters to conduct rescue operations. With economic and social development, national and public awareness of fire safety is constantly increasing, especially with higher safety requirements for major public facilities and projects, leading to a growing demand for fire-resistant cables. However, traditional fire-resistant cables, such as mica tape fire-resistant cables, mineral-insulated fire-resistant cables, and flexible mineral-insulated fire-resistant cables, have their own shortcomings in fire resistance, production processes, installation, and cost, hindering their promotion and application. Therefore, developing new types of fire-resistant cables is increasingly becoming a social need and a research hotspot in the cable and cable material industry. The industry's development approach is to endow existing insulation and sheathing materials with ceramic-like functions to achieve the fire-resistant function of the cable. Research on ceramic polymer composite materials mainly focuses on two directions: ceramicized silicone rubber and ceramicized polyolefins. While ceramicized polyolefin materials offer the advantage of ease of use, the complete high-temperature decomposition of polyolefins means that the material basis for ceramicization relies entirely on additives, leading to a large amount of filler and a decline in material performance. Furthermore, the expansion of volatile gases generated during the high-temperature decomposition of the polyolefin matrix is ​​detrimental to the formation of a dense and complete ceramic layer. Silicone rubber, on the other hand, produces a large amount of SiO2 upon decomposition, providing a material basis for ceramicization and facilitating the formation of a complete and dense ceramic layer. Therefore, research on ceramicized silicone rubber is one of the directions in ceramicized polymer research.

[0003] Flame retardants for silicone rubber generally use inorganic hydroxides as flame retardants, the most common being aluminum hydroxide and magnesium hydroxide. Besides inorganic hydroxides, other flame retardant systems can also be used for silicone rubber, such as chloroplatinic acid, halogenated flame retardant systems, and phosphorus-nitrogen flame retardant systems. While these systems have high flame retardant efficiency, the residues after high temperatures or combustion are lower than those of inorganic hydroxides, resulting in a lack of the material basis for vitrification in the rubber compound. This leads to more volatile substances at high temperatures and more severe expansion, all of which are detrimental to vitrification.

[0004] Ceramic-forming fillers come in various types, including those with both ceramic-forming and other functions, and those that function solely as ceramic-forming fillers. Fillers with both ceramic-forming and other functions, such as the aforementioned inorganic hydroxides, have the advantage of imparting a certain degree of flame retardancy to the material while forming ceramics. Fillers that function solely as ceramic-forming fillers are of many varieties:

[0005] (1) Mineral fillers: These fillers generally contain more impurities, or produce more volatiles at high temperatures, or both. For example, mica powder, attapulgite, bentonite, calcined clay, etc., have high total contents of Na2O, K2O, and Fe2O3, which introduce more metal and alkali metal ions that cause a serious decrease in high-temperature insulation performance at high temperatures, and have extremely serious damage to the high-temperature insulation performance of ceramics; some mineral fillers may generally contain fewer impurities, but because they are mineral fillers, the stability and consistency of their chemical composition cannot be guaranteed, which also makes it impossible to guarantee the high-temperature insulation performance of the material.

[0006] (2) Metal oxides such as magnesium oxide, aluminum oxide and silicon dioxide, although these fillers do not produce volatiles due to high temperature, cannot give the material good flame retardant properties.

[0007] (3) Glass and ceramic powders, these materials also do not produce volatiles due to high temperature, nor can they give the materials good flame retardancy. Moreover, they may have high cost, high density, low cost performance and even contain more alkali metal elements.

[0008] The commonly used fluxing systems for ceramicized silicone rubber are low-melting-point glass powder, borate, phosphate, etc. These systems have slightly insufficient fluxing effect, and some contain more alkali metal components, which are detrimental to the high-temperature electrical insulation performance of the ceramicized material.

[0009] Due to the above factors, the existing ceramicized silicone rubber has some or all of the following properties, such as flame retardancy, ceramicization speed, strength, density and high-temperature insulation, which are not ideal. The market urgently needs to develop products with better overall performance. Summary of the Invention

[0010] The purpose of this invention is to provide a highly flame-retardant silicone rubber capable of low-temperature, rapid, and dense ceramization. The ceramized form of this silicone rubber exhibits high electrical insulation properties at high temperatures, meeting the flame-retardant and fire-resistant requirements of relevant applications. This invention achieves high flame retardancy and low-temperature, rapid, and dense ceramization of the ceramized silicone rubber while ensuring the high-temperature electrical insulation properties of the ceramized form. This invention also provides a method for preparing the aforementioned silicone rubber.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] High flame retardant rapid ceramicization silicone rubber comprises the following components by weight: 100 parts of raw silicone rubber, 35-45 parts of reinforcing filler silica, 80-120 parts of flame retardant ceramic filler, 10-20 parts of flux, 2.0 parts of crosslinking agent, and 5 parts of heat resistant agent.

[0013] The flame-retardant ceramic filler is calcium borate. The flux is composed of surface-treated anhydrous zinc borate, surface-treated nano zinc oxide, and surface-treated nano magnesium oxide, with the ratio of anhydrous zinc borate: nano zinc oxide: nano magnesium oxide = 7:4:9. The crosslinking agent is 2,5-dimethyl-2,5-bis-(tert-butylperoxy)hexane (bis(2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane). The heat resistant agent is silicone resin.

[0014] Silicone rubber possesses excellent properties such as high temperature resistance, low temperature resistance, weather resistance, ozone resistance, arc resistance, electrical insulation, high air permeability, and physiological inertness. Silicone rubber is generally composed of raw silicone rubber, reinforcing fillers, other functional fillers or additive fillers, structure control agents, vulcanizing agents, heat resistant agents, and pigments.

[0015] The raw rubber used in compound silicone rubber mainly includes dimethyl silicone raw rubber, methyl vinyl silicone raw rubber, methyl phenyl vinyl silicone raw rubber, and methyl trifluoropropyl silicone raw rubber. Dimethyl silicone raw rubber was the earliest silicone raw rubber used, but due to its many shortcomings, it is now rarely used. Although methyl phenyl vinyl silicone raw rubber and methyl trifluoropropyl silicone raw rubber have some excellent properties, they are also expensive and are not essential for the application of this invention, so they are not considered for selection. Methyl vinyl silicone raw rubber contains a small amount of vinyl groups, but this small amount of vinyl groups greatly improves its vulcanization activity, broadens the selection range of crosslinking agents, effectively improves extrusion molding efficiency, simplifies the vulcanization process of thick products, and improves the aging resistance, mechanical strength, and permanent deformation properties of the vulcanized rubber.

[0016] The properties of silicone rubber are significantly affected by the molecular weight of the raw silicone rubber. The degree of polymerization of raw silicone rubber is typically 5000-10000, with an average molar mass of 400,000-800,000 g / mol. Both excessively high and low molecular weights will negatively impact the compounding and processing performance, as well as the physical and mechanical properties of the vulcanizate. Higher molecular weights result in better mechanical and physical properties of the vulcanizate, but reduce processability and flowability, and slow down the incorporation of fillers into the raw rubber. Conversely, excessively low molecular weights lead to poor mechanical properties, even causing stickiness or hindering molding. The vinyl group content in the raw silicone rubber directly affects the performance of the vulcanizate. Low vinyl group content results in a low crosslinking density, generally leading to poor performance. High vinyl group content accelerates vulcanization, limiting production time, while excessive crosslinking density can cause the vulcanizate to become brittle, affecting its use and aging performance.

[0017] Taking into account mechanical and physical properties, processability, and the absence of additives such as structure control agents, the raw silicone rubber is methyl vinyl silicone rubber with a molecular weight range of 550,000 g / mol and a molar percentage content of methyl vinyl siloxane repeating units of 0.3%.

[0018] Pure silicone rubber has very low mechanical strength and requires the addition of reinforcing fillers. Reinforcing fillers include high-reinforcing, reinforcing, and semi-reinforcing fillers. The most commonly used reinforcing filler for silicone rubber is high-fineness silica, including fumed silica and precipitated silica. Two points regarding the reinforcing mechanism of silica on raw silicone rubber are currently widely accepted: first, the crystallization effect caused by adsorption strengthens the intermolecular attraction within the adsorption layer; second, the silicon-oxygen bonds or terminal hydroxyl groups in the raw silicone rubber molecules form physical or chemical bonds with the silanol groups on the surface of silica, improving the physical and mechanical properties of the vulcanized rubber. Generally, as the particle size of silica decreases, the specific surface area increases, and the reinforcing effect of silica improves, but its dispersion in raw silicone rubber deteriorates. Fumed silica (FHM) boasts advantages such as high purity, low silanol content, high reinforcing rate, hot air vulcanization capability, high transparency of vulcanized rubber, good electrical properties, excellent sealing performance, heat resistance, and dynamic fatigue resistance. However, it is costly, its reinforced compounds are prone to structuring, and the elasticity of its vulcanized rubber is inferior to that of precipitated silica. Precipitated silica-reinforced compounds exhibit better resilience, compression set, swelling resistance, and processability, and are less prone to structuring. However, due to the excessive silanol content on the surface of precipitated silica, the vulcanized rubber has lower strength, poor dielectric and heat resistance, high water absorption, and is prone to bubbling during extrusion molding. It also cannot be hot air vulcanized.

[0019] Due to its large specific surface area and abundant silanol groups, high-reinforcing silica particles are prone to agglomeration and structuring in the compound, posing numerous challenges to crosslinking, storage, processing, and application. To address this, a structure control agent can be added to the material system, or surface-treated silica can be used to transform its hydrophilic surface into a hydrophobic one. This simultaneously improves the dispersibility of silica in the raw silica rubber and reduces or prevents structuring in the compound.

[0020] As described above, the reinforcing filler is surface-treated fumed silica with a surface treatment rate of approximately 60% and a specific surface area of ​​approximately 300 m². 2 / g.

[0021] Calcium borate is a novel borate-based flame retardant. Its flame retardant mechanism is similar to that of zinc borate, namely, the covering and charring effect of the glassy phase formed by high-temperature decomposition, and the cooling and dilution effect of losing crystal water. As a new flame retardant, there are far fewer research reports on its flame retardant properties and influencing factors compared to other borates such as zinc borate. From the perspective of reducing volatile matter in materials, the flame-retardant ceramic filler described in this invention is surface-treated anhydrous calcium borate with a particle size of approximately 1.5 μm.

[0022] Fluxes are commonly used components in glass melting, mainly consisting of alkali metal carbonates, silicates, borates, and boric acids, and some metal oxides also have a fluxing effect. In this invention, a combination of surface-treated anhydrous zinc borate, surface-treated nano-magnesium oxide, and surface-treated nano-zinc oxide was discovered and selected. Therefore, the flux described in this invention is a mixture of surface-modified anhydrous zinc borate, surface-modified nano-magnesium oxide, and surface-modified nano-zinc oxide, in the ratio of anhydrous zinc borate: nano-zinc oxide: nano-magnesium oxide.

[0023] = 7:4:9. The particle size of anhydrous zinc borate is approximately 2.6 μm, while the particle size of nano zinc oxide and nano magnesium oxide is less than 90 nm.

[0024] Silicone rubber typically undergoes side-chain organic group oxidation, main-chain Si-O-Si bond cleavage, and cross-linking reactions at high temperatures. The rate of these reactions is related to the raw rubber structure, thermal aging temperature and time, oxygen concentration, and whether heat-resistant additives are added. Heat-resistant additives that improve the thermal oxidation stability of silicone rubber include metal oxides, silazanes, and silicone resins. Metal oxides include iron oxide, iron hydroxide, ferrooctanoate, organosilicon ferrocene, ferrosilicon silanolate, titanium dioxide, manganese oxide, cesium dioxide, cesium carbonate, barium zirconate, etc.; silazanes include hexamethyldisilazane, hexamethylcyclotrisilazane, etc.; and silicone resins. To reduce the introduction of metal elements and the generation of volatiles, thus facilitating the high-temperature insulation of ceramics and ceramicized products, the heat-resistant agent described in this invention is silicone resin.

[0025] The vulcanization of compounded silicone rubber is mainly achieved through crosslinking of organic groups in the rubber by initiating the reaction of organic peroxides. There are six commonly used organic peroxide vulcanizing agents, which can be divided into high-activity (general-purpose) and low-activity (vinyl-specific) types based on their activity. High-activity vulcanizing agents have low vulcanization temperatures and short times, but are prone to scorching and producing acidic decomposition products, which have a degrading effect on silicone rubber. They are also unsuitable for rubber systems containing carbon black, and their dosage has a significant impact on the performance of the vulcanized rubber. Low-activity vulcanizing rubbers have high vulcanization temperatures and long times, but are less prone to scorching, and their decomposition products have a smaller impact on the performance of the rubber compound. They can be used in rubber systems containing carbon black, and their dosage also has a smaller impact on the performance of the rubber compound. The crosslinking agent described in this invention is a commonly used and environmentally friendly bis(2,5-dioxanone).

[0026] The selection and proportioning of each component in the material are based on considerations of the overall product performance. In this invention, silicone rubber is used as the single base material, with 100 parts of it used to adjust the addition amount of other components. If the amount of reinforcing material silica added is too small, it will not have a sufficient reinforcing effect, resulting in low strength and elongation of the material; if the amount added is too large, the strength and elongation of the material will not only fail to improve significantly, but may even begin to decrease, while also causing the material density to be too large, requiring the addition of more flame-retardant ceramic fillers and fluxes to achieve flame-retardant and ceramic effects, but the tensile properties of the material will decrease significantly due to excessive fillers. The amount of flame-retardant ceramic filler added should be determined based on the requirements of flame retardancy and ceramic formation of the material, and is determined according to the amount of reinforcing material silica added. If the amount added is too small, both flame-retardant and ceramic performance will decrease significantly, while if the amount added is too large, it will cause a mismatch with the ratio of reinforcing material and flux, which will neither be conducive to ceramic formation nor to improving the tensile properties of the material. The primary function of flux in materials is to lower the vitrification temperature and accelerate the vitrification process. Therefore, its addition amount depends on the quantity of reinforcing fillers and flame-retardant vitrifying fillers. Insufficient fluxing will result in ineffective fluxing, slow vitrification, and low vitrification strength. Excessive fluxing may lead to insufficient refractoriness of the vitrified material, causing it to melt at high temperatures and lose its function as a high-temperature insulating layer. Crosslinking agents should be added in as little as possible while meeting crosslinking requirements. Too little will affect the crosslinking speed and performance, while too much will lead to excessively rapid crosslinking, increased costs, and reduced performance. Heat-resistant agents are added to improve the material's thermal aging performance. They should be added in as little as possible while meeting the required thermal aging performance, both to reduce costs and minimize adverse effects on the material's overall performance and vitrification properties.

[0027] The preparation method of the above-mentioned high flame retardant rapid ceramicization silicone rubber includes the following steps:

[0028] After weighing the silicone rubber, silica, flame-retardant ceramic filler, flux, and heat resistant agent according to the specified proportions, add them to the torque rheometer (the silica needs to be added in multiple batches). After mixing into a ball, heat the equipment to 180°C and maintain it for 1 hour to obtain the compound.

[0029] The obtained compound was left at room temperature for at least 24 hours, then rolled in a two-roll mill at room temperature with the addition of a crosslinking agent in the appropriate proportion. After rolling, thinning, and sheeting, the compound with added crosslinking agent was obtained.

[0030] This invention uses silicone rubber as a base material, anhydrous calcium borate as a flame-retardant ceramic filler, without adding structure control agents, and uses silicone resin as a heat-resistant agent. This increases the proportion of high-temperature residues and reduces the proportion of high-temperature volatile substances, mitigating the adverse effects of volatile substance expansion and release on the ceramicization process. This provides a material basis and favorable conditions for the formation of a dense ceramic compound. Because the silica, calcium borate, and silicone resin produced by the decomposition of silicone rubber contain far less alkali metal than those found in mineral ceramic fillers, the high-temperature insulation performance of the ceramic compound is improved. While reducing the amount of high-temperature volatile substances produced and the amount of alkali metal elements introduced, the combination of silicone rubber (including silica) and calcium borate also achieves a high flame-retardant effect, which is unattainable by commonly used flame retardants and systems. With a sufficient material basis for ceramic formation and better ceramic formation conditions, a flux composed of zinc borate, magnesium oxide, and zinc oxide was added to reduce the ceramic formation temperature and increase the ceramic formation speed. This enabled the material to ceramicize earlier and faster at lower temperatures, resulting in a material with high flame retardancy, rapid ceramicization at lower temperatures, high electrical insulation, and denser ceramics, meeting the requirements for fire-resistant cable insulation materials.

[0031] Of particular note is that this invention achieves a high flame-retardant effect on silicone rubber when using anhydrous calcium borate as a flame retardant alone, although the flame-retardant mechanism is still unclear. Similar to zinc borate, calcium borate's flame-retardant properties are not particularly pronounced when used alone. However, in this invention, when it is added in large quantities as the main flame retardant to silicone rubber, it produces a flame-retardant effect similar to or better than commonly used inorganic flame retardants. This may be due to a synergistic flame-retardant effect resulting from the reaction between calcium borate and silica, the covering and isolating effect of the glassy phase, or the chemical inhibition of the combustion chain reaction. Further in-depth research is warranted.

[0032] Through the above-described technical solution using silicone rubber as the base material, calcium borate as the flame-retardant ceramic filler, and a compound flux, this invention achieves high flame retardancy, low-temperature, rapid, and dense ceramicization of silicone rubber, and significantly improves the high-temperature insulation performance of the ceramicized material. Specifically, silicone rubber, as the base material, produces fewer volatile substances during high-temperature decomposition, with nearly 60% silicon and oxygen residues, providing a material basis for the ceramicization of the material. Polyolefin materials, on the other hand, do not produce residues that would provide a material basis for ceramicization. Using anhydrous calcium borate as the flame retardant avoids the shortcomings of inorganic flame retardants such as aluminum hydroxide, magnesium hydroxide, and zinc borate containing crystallization water, as well as phosphorus and nitrogen-based intumescent flame retardants, which produce a large amount of volatile substances at high temperatures. This minimizes the adverse effects of volatile substance expansion on the ceramicization of the material, while achieving flame retardant performance similar to or higher than commonly used flame retardants. Furthermore, it overcomes the shortcomings of existing research and reports that commonly use mineral ceramic fillers and other ceramicizing powders introduce alkali metals, significantly improving the high-temperature insulation performance of the product. In compound fluxes, zinc borate decomposes earlier to produce boron oxide, which has a lower melting point. The liquid phase formed by boron oxide wets the entire material, creating a cohesive whole that helps maintain the material's shape. Furthermore, under the wetting effect of the boron oxide liquid phase, the flux nano-magnesium oxide and nano-zinc oxide can promote the reaction between silica and calcium borate more quickly and earlier, accelerating the vitrification speed and degree of the material. The reduction of volatiles during the vitrification process of silicone rubber reduces defects such as pores caused by volatiles, thus improving the high-temperature insulation performance of the vitrified material. It is particularly noteworthy that, similar to zinc borate, calcium borate's flame-retardant properties are not particularly significant when used alone. However, in this invention, it is added in large quantities as the main flame retardant to silicone rubber, producing a flame-retardant effect similar to or better than commonly used inorganic flame retardants. This may be due to the synergistic flame-retardant effect produced by the reactions between silica, calcium borate, zinc borate, magnesium oxide, and zinc oxide; the covering and isolating effect of the glass phase; or the chemical inhibition of the combustion chain reaction. Further research is warranted.

[0033] The preparation steps of the silicone rubber test sample of the present invention are as follows: the compound is vulcanized in a flat vulcanizing machine at 16MPa and 180℃ for 10min to obtain a sheet of the required thickness for testing and to prepare the sample required for testing.

[0034] The tensile strength and elongation at break tests shall be conducted in accordance with GB / T 528. The specimen shall be a type 1 dumbbell plate with a thickness of (2.0±0.2) mm and a test speed of (500±50) mm / min.

[0035] The vitrification performance was tested according to standard T / SHPTA 036-2023, which involved preparing three pre-vitrified square samples, approximately 50 mm on each side and 3 mm thick. The initial weights were weighed and recorded. The muffle furnace was heated to 950°C and preheated for 30 minutes after reaching the temperature. The test samples were fixed with asbestos mesh, then embedded in quartz sand for further fixation, and placed in the preheated muffle furnace for calcination for 120 minutes. The samples were then removed and cooled in a desiccator for 60 minutes, or cooled to room temperature. The weights after vitrification were weighed and recorded. The appearance, vitrification rate, and drop test integrity of the vitrified material were then evaluated and calculated.

[0036] The vertical burning test of the material was conducted in accordance with UL94, and the sample thickness was approximately 0.75 mm.

[0037] The product obtained by this invention has the characteristics of low temperature, rapid and dense ceramization. The ceramized material has good high temperature electrical insulation properties, which meets the requirements of fire-resistant cable insulation and other similar applications. Detailed Implementation

[0038] Example 1

[0039] (1) Weigh 100 parts of raw silicone rubber, 35 parts of fumed silica, 120 parts of calcium borate, 7.0 parts of anhydrous zinc borate, 4.0 parts of nano zinc oxide, 9.0 parts of nano magnesium oxide, 2.0 parts of bis(2,5)5 and 5 parts of silicone resin in the correct proportions.

[0040] (2) Weigh the raw silicone rubber, silica, calcium borate, anhydrous zinc borate, nano zinc oxide, nano magnesium oxide and silicone resin according to the proportion and add them to the torque rheometer (the silica needs to be added in multiple batches). After mixing into a ball, heat the equipment to 180°C and keep it for 1 hour to obtain the compound rubber.

[0041] (3) The obtained compound was left at room temperature for at least 24 hours, and then rolled in a room temperature open mill with the appropriate proportion of 25% bisphenol A added. After rolling, thinning, and sheeting, the compound with added crosslinking agent was obtained. Then it was vulcanized in a flat vulcanizing machine at 16 MPa and 180°C for 10 minutes to obtain a sheet of the required thickness for testing and to prepare the sample required for testing.

[0042] Example 2

[0043] (1) Weigh 100 parts of raw silicone rubber, 40 parts of fumed silica, 100 parts of calcium borate, 5.25 parts of anhydrous zinc borate, 3.0 parts of nano zinc oxide, 6.75 parts of nano magnesium oxide, 2.0 parts of bis(2,5)5 and 5.0 parts of silicone resin in the correct proportions.

[0044] (2) The preparation process and technology are the same as in Example 1.

[0045] Example 3

[0046] (1) Weigh 100 parts of raw silicone rubber, 45 parts of fumed silica, 80 parts of calcium borate, 3.5 parts of anhydrous zinc borate, 2.0 parts of nano zinc oxide, 4.5 parts of nano magnesium oxide, 2.0 parts of bis(2,5)5, ​​and 5.0 parts of silicone resin in the specified proportions.

[0047] (2) The sample preparation process and technology are the same as those in Example 1.

[0048] Comparative Example 1

[0049] (1) Weigh 100 parts of raw silicone rubber, 35 parts of fumed silica, 120 parts of aluminum hydroxide, 7.0 parts of anhydrous zinc borate, 4.0 parts of nano zinc oxide, 9.0 parts of nano magnesium oxide, 2.0 parts of bis(2,5)5 and 5 parts of silicone resin in the correct proportions.

[0050] The composition differs from Example 1 in that all the ceramic flame-retardant fillers are replaced with aluminum hydroxide in equal amounts;

[0051] (2) The sample preparation process and technology are the same as those in Example 1.

[0052] Comparative Example 2

[0053] (1) Weigh 100 parts of raw silicone rubber, 35 parts of fumed silica, 120 parts of magnesium hydroxide, 7.0 parts of anhydrous zinc borate, 4.0 parts of nano zinc oxide, 9.0 parts of nano magnesium oxide, 2.0 parts of bis(2,5)5 and 5 parts of silicone resin in the correct proportions.

[0054] The composition differs from Example 1 in that all the ceramic flame-retardant fillers are replaced with magnesium hydroxide in equal amounts;

[0055] (2) The sample preparation process and technology are the same as those in Example 1.

[0056] Comparative Example 3

[0057] (1) Weigh 100 parts of raw silicone rubber, 35 parts of fumed silica, 120 parts of anhydrous zinc borate, 7.0 parts of anhydrous zinc borate, 4.0 parts of nano zinc oxide, 9.0 parts of nano magnesium oxide, 2.0 parts of bis(2,5)5 and 5 parts of silicone resin in the correct proportions.

[0058] The composition differs from that of Example 1 in that all the ceramic flame-retardant fillers are replaced with anhydrous zinc borate in equal amounts;

[0059] (2) The sample preparation process and technology are the same as those in Example 1.

[0060] Comparative Example 4

[0061] (1) Weigh 100 parts of raw silicone rubber, 35 parts of fumed silica, 120 parts of calcium borate, 20 parts of anhydrous zinc borate, 2.0 parts of bis(2,5)5 and 5 parts of silicone resin in the correct proportions.

[0062] The composition differs from that of Example 1 in that the flux is removed and replaced with an equal amount of anhydrous zinc borate.

[0063] (2) The sample preparation process and technology are the same as those in Example 1.

[0064] The performance of the products obtained in Examples 1-3 and Comparative Examples 1-4 is shown in Table 1.

[0065] Table 1 Performance of Examples and Comparative Examples

[0066]

[0067] The above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A high flame-retardant, rapidly ceramizing silicone rubber, characterized in that... It is composed of the following components by weight: 100 parts of raw silicone rubber, 35-45 parts of reinforcing filler, 80-120 parts of flame-retardant ceramic filler, 10-20 parts of flux, 2.0 parts of crosslinking agent, and 5 parts of heat resistant agent, wherein the heat resistant agent is silicone resin; The reinforcing filler is surface-treated fumed silica with a surface treatment rate of 60% and a specific surface area of ​​300 m². 2 / g; The flame-retardant ceramic filler is surface-modified anhydrous calcium borate; The anhydrous calcium borate has a particle size of 1.5 μm; The flux is a mixture of surface-modified anhydrous zinc borate, surface-modified nano magnesium oxide, and surface-modified nano zinc oxide; The mass ratio of anhydrous zinc borate, nano zinc oxide, and nano magnesium oxide is 7:4:

9.

2. The high flame-retardant, rapid ceramization silicone rubber according to claim 1, characterized in that: The raw silicone rubber is methyl vinyl silicone rubber with a molecular weight of 550,000 g / mol and a molar percentage content of methyl vinyl siloxane repeating units of 0.3%.

3. The high flame-retardant, rapid ceramicization silicone rubber according to claim 1, characterized in that: The anhydrous zinc borate has a particle size of 2.6 μm, and the nano zinc oxide and nano magnesium oxide both have a particle size of 90 nm.

4. The method for preparing the high flame-retardant, rapidly ceramized silicone rubber according to any one of claims 1-3, characterized in that... Including the following steps: After weighing the raw silicone rubber, silica, flame-retardant ceramic filler, flux, and heat resistant agent according to the proportion, add them to the torque rheometer. The silica is added in multiple batches. After mixing into a ball, heat the equipment to 180°C and keep it for 1 hour to obtain the compound rubber. The obtained compound was left at room temperature for at least 24 hours, then rolled in a two-roll mill at room temperature with the addition of a crosslinking agent in the appropriate proportion, and obtained after rolling, thinning, and sheeting.

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