Flame-retardant silicone rubber and method for producing the same

Abstract

The application specifically relates to a fire-retardant silicone rubber and a preparation method thereof, wherein the fire-retardant silicone rubber comprises the following raw materials in parts by weight: 90-100 parts of a silicone rubber base glue, 20-30 parts of a porcelain-forming filler, 15-25 parts of a reinforcing filler, 5-15 parts of a fluxing agent, 5-10 parts of a fire retardant, 2-8 parts of a synergist, and 0.5-4 parts of a vulcanizing agent. The silicone rubber is prepared by compounding the silicone rubber base glue with the porcelain-forming filler, the reinforcing filler, the fluxing agent, the fire retardant and the synergist, and the like, and the raw materials synergistically act to make the prepared silicone rubber have good mechanical properties and processing performance, good fire-retardant effect, and a sintered ceramic structure, and the preparation method has stable process and is convenient to operate and beneficial to industrialized production.

Description

Technical Field

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

[0002] Ceramicizable silicone rubber is a new type of fireproof material that maintains the elasticity of silicone rubber at room temperature and can form a self-supporting ceramic protective layer under high-temperature flame or electric arc ablation. Its ceramic formation mechanism is as follows: at high temperature, the ceramic filler, such as silicate minerals such as mica and wollastonite, undergoes a eutectic reaction with the flux to form a liquid phase, which solidifies into a ceramic body after cooling, thereby playing the role of fireproofing and heat insulation, and isolating flames and high-temperature airflow. It can be applied in the fields of fire-resistant wires and cables, fireproof sealing materials, and fireproof partitions in buildings.

[0003] To meet stringent fire resistance requirements, existing ceramic-forming silicone rubbers typically require the addition of halogenated flame retardants or large amounts of inorganic flame retardants. However, existing inorganic flame retardants are dispersed in the silicone rubber matrix as inorganic powders through physical-mechanical blending. This physical blending method has the following technical drawbacks: First, poor compatibility, deteriorating mechanical and processing properties. The large polarity difference between inorganic powders and organic polysiloxane alkyl groups results in weak interfacial bonding, making them prone to agglomeration and uneven dispersion in the matrix. To achieve the required flame retardancy rating, excessive addition is often necessary, which reduces the tensile strength, elongation at break, and processing properties of the silicone rubber. Furthermore, physically blended inorganic powders, such as zinc borate, exist as independent particles in the matrix, making it difficult for boron to fully react with the decomposition products of the flame retardant at the molecular level, leading to low efficiency in the phosphorus-boron synergistic flame retardancy and ceramic-forming effect. Second, low molecular weight inorganic powders are prone to migration, precipitation, and hydrolysis loss under long-term use and high-temperature environments, causing the flame retardant performance to gradually decline over time. The precipitates may also contaminate contact parts. Therefore, developing silicone rubber with good flame retardancy and mechanical processing properties is of great significance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a flame-retardant silicone rubber. This flame-retardant silicone rubber has good mechanical properties and flame-retardant effect, and is sintered to form a ceramic structure. The preparation method of this flame-retardant silicone rubber is stable, easy to control, and conducive to industrial production.

[0005] The objective of this invention is achieved through the following technical solution: a flame-retardant silicone rubber, comprising the following raw materials in parts by weight: 90-100 parts of silicone rubber base, 20-30 parts of ceramic filler, 15-25 parts of reinforcing filler, 5-15 parts of flux, 5-10 parts of flame retardant, 2-8 parts of synergist, and 0.5-4 parts of vulcanizing agent.

[0006] Furthermore, the silicone rubber base is boron-containing polysiloxane silicone rubber, and the preparation method of the boron-containing polysiloxane silicone rubber includes the following steps: A1. Mix octamethylcyclotetrasiloxane and a portion of tetramethyltetravinylcyclotetrasiloxane to obtain a monomer mixture; add an initiator and a accelerator, and react at 85-95℃ to obtain mixture one; A2. Add a pre-prepared borosilicate solution dropwise to mixture one to carry out the reaction. The borosilicate solution includes trimethoxycycloborosilicate and the remaining tetramethyltetravinylcyclotetrasiloxane. After the addition is complete, heat to 105-125℃ to obtain mixture two. Add a capping agent to mixture two and continue the reaction to obtain mixture three. A3. The mixture is kept at 145-155℃ and then vacuum de-lowered under nitrogen purging; the reaction mixture is then vacuum treated at 100-105℃ and cooled to obtain boron-containing polysiloxane silicone rubber.

[0007] Furthermore, in step A1, the molar ratio of octamethylcyclotetrasiloxane to the added tetramethyltetravinylcyclotetrasiloxane is 12-20:0.5-3; the octamethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane are each pre-dehydrated, or dehydrated after mixing, so that the residual water content of the mixed monomer mixture is reduced to below 100 ppm.

[0008] Furthermore, in step A1, the initiator is tetramethylammonium hydroxide silanoate, and the amount of the initiator added is 0.05-0.2 wt% of the total mass of the monomer mixture; the accelerator is N,N-dimethylformamide, and the amount of the accelerator added is 0.5-2 wt% of the total mass of the monomer mixture.

[0009] Furthermore, in step A2, the capping agent is deionized water, and the amount of capping agent added is 0.05-0.5 wt% of the total mass of the mixture formed after the addition in step A2.

[0010] Further, in step A3, the mixture is kept at 145-155℃ for 30-60 min; then, under nitrogen purging, it is subjected to de-lowering treatment at 145-155℃ and a vacuum degree of -0.08 to -0.095 MPa for 60-120 min; then, the reaction mixture is subjected to vacuum treatment at 100-105℃ for 90-150 min, and after cooling, boron-containing polysiloxane silicone rubber is obtained.

[0011] Furthermore, in step A3, the molar ratio of trimethoxycycloboroxane and the remaining tetramethyltetravinylcyclotetrasiloxane to the octamethylcyclotetrasiloxane added in step A1 is 0.5-4:0.5-3:12-20; the concentration of trimethoxycycloboroxane in the borosilicate solution is 0.5-5 mol / L.

[0012] This invention employs a staged anionic ring-opening polymerization process. First, octamethylcyclotetrasiloxane and a portion of tetramethyltetravinylcyclotetrasiloxane are prepolymerized to form a prepolymer backbone. Then, trimethoxycycloboroxane and the remaining tetramethyltetravinylcyclotetrasiloxane are introduced dropwise from a solution, embedding boron-containing segments into the polysiloxane backbone via chemical bonds. Deionized water is used as a capping agent to obtain boron-containing polysiloxane silicone rubber. In this boron-containing polysiloxane silicone rubber, the boron element is chemically bonded to the polysiloxane backbone, imparting excellent flame retardancy and ceramic-forming properties to the base rubber. This boron-containing polysiloxane silicone rubber can be used as a silicone rubber base rubber in combination with ceramic fillers, reinforcing fillers, fluxes, flame retardants, and synergists to produce silicone rubber with excellent flame retardant properties, mechanical properties, and processing properties.

[0013] Furthermore, the ceramic filler is at least one of mica powder, wollastonite, kaolin, and calcium carbonate.

[0014] Furthermore, the reinforcing filler is fumed silica.

[0015] Furthermore, the vulcanizing agent is at least one selected from 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, bis(2,4-dichlorobenzoyl)peroxide, di-tert-butylperoxide, and dicumyl peroxide.

[0016] Furthermore, the flux is at least one of low-melting-point glass powder and boron oxide.

[0017] Furthermore, the flame retardant is at least one of modified aluminum hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. The flame-retardant silicone rubber of the present invention uses boron element chemically bonded to the polymer backbone, and in combination with the aforementioned flame retardant added in small amounts, helps to solve the problems of migration and precipitation of small molecules caused by the addition of large amounts of inorganic flame retardants, which severely degrade the mechanical and processing properties of silicone rubber. This allows the flame-retardant silicone rubber to maintain excellent mechanical and processing properties, and exhibits excellent long-term stability.

[0018] Furthermore, the flame retardant comprises the following raw materials in parts by weight: 3-6 parts of modified aluminum hydroxide and 2-4 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0019] Furthermore, the synergist is a trisilyl alcohol phenyl cage-like polysilsesquioxane. This trisilyl alcohol phenyl cage-like polysilsesquioxane contains active silanol groups and phenyl groups, which can chemically bond into the polysiloxane crosslinking network, increasing the crosslinking density. It has good compatibility with boron-containing polysiloxane silicone rubber, which helps improve mechanical properties and dimensional stability. It also works synergistically with low-melting-point glass powder, ceramic fillers, and flame retardants to improve flame retardant effects, as well as the density and strength of the ceramic layer.

[0020] Another object of the present invention is to provide a method for preparing flame-retardant silicone rubber, comprising the following steps: (1) Put the silicone rubber base into a kneader and stir; then add the reinforcing filler, ceramic filler, flux, and flame retardant into the kneader, mix evenly and heat treat to obtain the basic compound; (2) Place the basic compound rubber in a two-roll mill, add synergist and vulcanizing agent, mix evenly and then sheet to obtain the rubber material to be vulcanized; (3) Add the rubber material to be vulcanized into the mold and vulcanize it once to obtain a vulcanized product; (4) The product is vulcanized twice and cooled to room temperature to obtain flame-retardant silicone rubber.

[0021] Further, in step (1), silicone rubber base is added to the kneader and plasticized at 60-80℃ for 5-15 minutes; reinforcing filler is added in 2-4 batches, and kneaded for 5-10 minutes after each addition; then ceramic filler and flux are added and kneaded at 60-80℃ for 30-60 minutes; then flame retardant is added and kneaded for another 10-20 minutes; the mixture is heat-treated at 100-120℃ and vacuum of -0.08 to -0.095 MPa for 60-120 minutes, cooled and discharged to obtain the basic compound.

[0022] Furthermore, in step (2), the base compound is placed in a two-roll mill, and synergists and vulcanizing agents are added at room temperature. After being mixed evenly, the compound is sheeted out to obtain the rubber material to be vulcanized.

[0023] Furthermore, in step (3), the rubber compound to be vulcanized is added to the preheated mold and vulcanized for 5-15 minutes at a temperature of 170-180℃ and a pressure of 8-15MPa to obtain a vulcanized product.

[0024] Furthermore, in step (3), the first-cured product is subjected to a second curing at 180-210°C for 2-5 hours; then cooled to room temperature to obtain flame-retardant silicone rubber.

[0025] The beneficial effects of this invention are as follows: This invention prepares silicone rubber by compounding silicone rubber base with ceramic fillers, reinforcing fillers, fluxing agents, flame retardants and synergists. The synergistic effect of each raw material gives the prepared silicone rubber good mechanical properties and processing properties, good flame retardant effect, and can be sintered to form a ceramic structure. Its preparation method is stable, easy to control, and conducive to industrial production. Detailed Implementation

[0026] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0027] In some embodiments of the present invention, a flame-retardant silicone rubber comprises the following raw materials in parts by weight: 90-100 parts of silicone rubber base, 20-30 parts of ceramic filler, 15-25 parts of reinforcing filler, 5-15 parts of flux, 5-10 parts of flame retardant, 2-8 parts of synergist, and 0.5-4 parts of vulcanizing agent.

[0028] Furthermore, the silicone rubber base is boron-containing polysiloxane silicone rubber, and the preparation method of the boron-containing polysiloxane silicone rubber includes the following steps: A1. Mix octamethylcyclotetrasiloxane and a portion of tetramethyltetravinylcyclotetrasiloxane to obtain a monomer mixture; add an initiator and a accelerator, and heat to 85-95℃ for 30-60 min to obtain mixture one; A2. Add a pre-prepared borosilicate solution, including trimethoxycycloborosilicate and the remaining tetramethyltetravinylcyclotetrasiloxane, dropwise to mixture one over 30-90 minutes. After the addition is complete, heat to 105-125°C to obtain mixture two. Add a capping agent to mixture two and continue the reaction for 1.5-2.5 hours to obtain mixture three. A3. The mixture is kept at 145-155℃ for 30-60 minutes, and then vacuum de-lowered under nitrogen purging; the reaction mixture is then vacuum treated at 100-105℃, and after cooling, boron-containing polysiloxane silicone rubber is obtained.

[0029] Furthermore, in step A1, the molar ratio of octamethylcyclotetrasiloxane to the added tetramethyltetravinylcyclotetrasiloxane is 12-20:0.5-3; octamethylcyclotetrasiloxane and a portion of tetramethyltetravinylcyclotetrasiloxane are pre-dehydrated to reduce the residual water content to below 100 ppm.

[0030] Furthermore, in step A1, the initiator is tetramethylammonium hydroxide silanoate, and the amount of the initiator added is 0.05-0.2 wt% of the total mass of the monomer mixture; the accelerator is N,N-dimethylformamide, and the amount of the accelerator added is 0.5-2 wt% of the total mass of the monomer mixture.

[0031] Furthermore, in step A2, the capping agent is deionized water, and the amount of capping agent added is 0.05-0.5 wt% of the total mass of the mixture formed after the addition in step A2.

[0032] Further, in step A3, the mixture is kept at 145-155℃ for 30-60 min to deactivate the initiator; then, under nitrogen purging, it is subjected to de-lowering treatment at 145-155℃ and a vacuum degree of -0.08 to -0.095 MPa for 60-120 min; then, the reaction mixture is subjected to vacuum treatment at 100-105℃ for 90-150 min, and after cooling, boron-containing polysiloxane silicone rubber is obtained.

[0033] Furthermore, in step A3, the molar ratio of trimethoxycycloboroxane and the remaining tetramethyltetravinylcyclotetrasiloxane to the octamethylcyclotetrasiloxane added in step A1 is 0.5-4:0.5-3:12-20; the concentration of trimethoxycycloboroxane in the borosilicate solution is 0.5-5 mol / L; and the solvent of the borosilicate solution is at least one of tetrahydrofuran and toluene.

[0034] Furthermore, the ceramic filler is at least one of mica powder, wollastonite, kaolin, and calcium carbonate.

[0035] Furthermore, the reinforcing filler is fumed silica with a specific surface area of ​​100-200 m². 2 / g.

[0036] Furthermore, the vulcanizing agent is at least one selected from 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, bis(2,4-dichlorobenzoyl)peroxide, di-tert-butylperoxide, and dicumyl peroxide.

[0037] Furthermore, the flux is at least one of low-melting-point glass powder and boron oxide, wherein the melting temperature of the low-melting-point glass powder is 500-700°C.

[0038] Furthermore, the flame retardant is at least one of modified aluminum hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0039] Furthermore, based on the total amount of flame retardant, the flame retardant comprises the following raw materials in parts by weight: 3-6 parts of modified aluminum hydroxide and 2-4 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. The modified aluminum hydroxide is modified using a silane coupling agent. The preparation method of the modified aluminum hydroxide includes the following steps: adding the silane coupling agent to an aqueous ethanol solution and mixing thoroughly, then adding aluminum hydroxide to react, and drying to obtain the modified aluminum hydroxide. The amount of silane coupling agent added is 0.5-3 wt% of the mass of the aluminum hydroxide.

[0040] Another object of the present invention is to provide a method for preparing flame-retardant silicone rubber, comprising the following steps: (1) Put the silicone rubber base into a kneader and stir; then add the reinforcing filler, ceramic filler, flux, and flame retardant into the kneader, mix evenly and heat treat to obtain the basic compound; (2) Place the basic compound rubber in a two-roll mill, add synergist and vulcanizing agent, mix evenly and then sheet to obtain the rubber material to be vulcanized; (3) Add the rubber material to be vulcanized into the mold and vulcanize it once to obtain a vulcanized product; (4) The product is vulcanized twice and cooled to room temperature to obtain flame-retardant silicone rubber.

[0041] Further, in step (1), silicone rubber base is added to the kneader and plasticized at 60-80℃ for 5-15 minutes; reinforcing filler is added in 2-4 batches, and kneaded for 5-10 minutes after each addition; then ceramic filler and flux are added and kneaded at 60-80℃ for 30-60 minutes; then flame retardant is added and kneaded for another 10-20 minutes; the mixture is heat-treated at 100-120℃ and vacuum of -0.08 to -0.095 MPa for 60-120 minutes, cooled and discharged to obtain the basic compound.

[0042] Furthermore, in step (2), the basic compound is placed in a two-roll mill, and the synergist and vulcanizing agent are added sequentially at room temperature. After being mixed evenly, the compound is sheeted out to obtain the rubber material to be vulcanized.

[0043] Furthermore, in step (3), the rubber compound to be vulcanized is added to the preheated mold and vulcanized for 5-15 minutes at a temperature of 170-180℃ and a pressure of 8-15MPa to obtain a vulcanized product.

[0044] Furthermore, in step (3), the first-cured product is subjected to a second curing at 180-210°C for 2-5 hours; then cooled to room temperature to obtain flame-retardant silicone rubber.

[0045] Example 1

[0046] This embodiment provides a flame-retardant silicone rubber, comprising the following raw materials in parts by weight: 95 parts silicone rubber base, 25 parts ceramic filler, 20 parts reinforcing filler, 10 parts flux, 8 parts flame retardant, 5 parts synergist, and 2 parts vulcanizing agent.

[0047] Furthermore, the silicone rubber base is boron-containing polysiloxane silicone rubber, and the preparation method of the boron-containing polysiloxane silicone rubber includes the following steps: A1. Add 296g of octamethylcyclotetrasiloxane and 25.8g of tetramethyltetravinylcyclotetrasiloxane to the reaction vessel. Dry and dehydrate for 40min under a nitrogen atmosphere at 90℃ and a vacuum of -0.09MPa to obtain a monomer mixture. Add 0.24g of initiator tetramethylammonium hydroxide silanolate and 4.8g of accelerator N,N-dimethylformamide. React at 90℃ for 45min to obtain mixture one. A2. 17.4 g of trimethoxycycloboroxane and 17.2 g of tetramethyltetravinylcyclotetrasiloxane were dissolved in 30 mL of anhydrous tetrahydrofuran to prepare a borosilicate solution. The borosilicate solution was added dropwise to mixture one under stirring for 60 min. After the addition was complete, the temperature was raised to 115 °C to obtain mixture two. 0.36 g of deionized water was added to mixture two, and the reaction was continued for 2 h to obtain mixture three. A3. The mixture was kept at 150℃ for 40 min to deactivate the initiator; then, under nitrogen purging, it was subjected to deactivation treatment at 150℃ and vacuum degree of -0.09MPa for 80 min; the reaction mixture was then subjected to vacuum treatment at 105℃, cooled and discharged to obtain boron-containing polysiloxane silicone rubber.

[0048] Furthermore, the ceramic filler is composed of mica powder and wollastonite in a mass ratio of 2:1. The reinforcing filler is fumed silica. The vulcanizing agent is 2,5-dimethyl-2,5-di-tert-butylperoxyhexane. The flux is Anmi Micro-Nano low-melting-point glass powder D255. The synergist is trisilyl alcohol phenyl cage-like polysilsesquioxane.

[0049] Furthermore, the flame retardant comprises the following raw materials in parts by weight: 5 parts modified aluminum hydroxide and 3 parts 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0050] Furthermore, the modified aluminum hydroxide is modified using a silane coupling agent. The preparation method of the modified aluminum hydroxide includes the following steps: 1.5g of silane coupling agent KH-570 is added to a mixed solution composed of 15g of anhydrous ethanol and 1.5g of deionized water, and stirred at 40°C for 20min; then 100g of aluminum hydroxide powder is added, and stirring is continued for 40min; the resulting material is dried in an oven at 105°C for 2h, and ground through a 200-mesh sieve to obtain silane coupling agent modified aluminum hydroxide.

[0051] Furthermore, the synergist is trisilyl alcohol phenyl cage-like polysilsesquioxane.

[0052] In this embodiment, the preparation method of the above-mentioned flame-retardant silicone rubber includes the following steps: (1) Put the silicone rubber base into a kneader and plasticize it at 70°C for 10 min; add the reinforcing filler in 3 batches, and mix for 8 min after each addition; then add the pre-mixed ceramic filler and flux, and mix at 70°C for 40 min; then add the flame retardant and continue mixing for 15 min; heat treat the mixture at 110°C and -0.09MPa for 90 min, cool and discharge to obtain the base compound; (2) Place the base compound on a two-roll mill, add the synergist and vulcanizing agent in sequence at room temperature, pass through the mill 6 times, mix evenly, and then sheet to obtain the rubber compound to be vulcanized. (3) Place the rubber material to be vulcanized into a preheated mold and vulcanize it in a vulcanizing machine at a temperature of 175℃ and a pressure of 10MPa for 10 minutes to obtain a vulcanized product. (4) Place the vulcanized product in an oven and vulcanize it again at 200°C for 2.5 hours. Then let it cool naturally to room temperature to obtain flame-retardant silicone rubber.

[0053] Example 2

[0054] This embodiment provides a flame-retardant silicone rubber, comprising the following raw materials in parts by weight: 95 parts silicone rubber base, 25 parts ceramic filler, 20 parts reinforcing filler, 10 parts flux, 6 parts flame retardant, 5 parts synergist, and 2 parts vulcanizing agent.

[0055] Furthermore, the silicone rubber base is boron-containing polysiloxane silicone rubber, and the preparation method of the boron-containing polysiloxane silicone rubber includes the following steps: A1. Add 296g of octamethylcyclotetrasiloxane and 25.8g of tetramethyltetravinylcyclotetrasiloxane to the reaction vessel. Dry and dehydrate for 40min under a nitrogen atmosphere at 90℃ and a vacuum of -0.09MPa to obtain a monomer mixture. Add 0.24g of initiator tetramethylammonium hydroxide silanolate and 4.8g of accelerator N,N-dimethylformamide. React at 90℃ for 45min to obtain mixture one. A2. A borosilicate solution was prepared by dissolving 26.1 g of trimethoxycycloboroxane and 17.2 g (0.05 mol) of tetramethyltetravinylcyclotetrasiloxane in 30 mL of anhydrous tetrahydrofuran. The borosilicate solution was then added dropwise to mixture one under stirring for 60 min. After the addition was complete, the temperature was raised to 115 °C to obtain mixture two. 0.36 g of deionized water was added to mixture two, and the reaction was continued for 2 h to obtain mixture three. A3. The mixture was kept at 150℃ for 40 min to deactivate the initiator; then, under nitrogen purging, it was subjected to deactivation treatment at 150℃ and vacuum degree of -0.09MPa for 80 min; the reaction mixture was then subjected to vacuum treatment at 105℃, cooled and discharged to obtain boron-containing polysiloxane silicone rubber.

[0056] Furthermore, the ceramic filler is composed of mica powder and kaolin in a mass ratio of 2:1. The reinforcing filler is fumed silica produced by fumed silica production. The vulcanizing agent is 2,5-dimethyl-2,5-di-tert-butylperoxyhexane. The flux is low-melting-point glass powder with a melting temperature of 500-700℃.

[0057] Furthermore, the flame retardant comprises the following raw materials in parts by weight: 4 parts modified aluminum hydroxide and 2 parts 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0058] In this embodiment, the preparation method of the above-mentioned flame-retardant silicone rubber includes the following steps: (1) Put the silicone rubber base into a kneader and plasticize it at 70°C for 10 min; add the reinforcing filler in 3 batches, and mix for 8 min after each addition; then add the pre-mixed ceramic filler and flux, and mix at 70°C for 40 min; then add the flame retardant and continue mixing for 15 min; heat treat the mixture at 110°C and -0.09MPa for 90 min, cool and discharge to obtain the base compound; (2) Place the base compound on a two-roll mill, add the synergist and vulcanizing agent in sequence at room temperature, pass through the mill 6 times, mix evenly, and then sheet to obtain the rubber compound to be vulcanized. (3) Place the rubber material to be vulcanized into a preheated mold and vulcanize it in a vulcanizing machine at a temperature of 175℃ and a pressure of 10MPa for 15 minutes to obtain a vulcanized product. (4) Place the vulcanized product in an oven and vulcanize it again at 200°C for 3 hours. Then let it cool naturally to room temperature to obtain flame-retardant silicone rubber.

[0059] The rest of the content of this embodiment is the same as that of Embodiment 1, and will not be repeated here.

[0060] Example 3

[0061] This embodiment provides a flame-retardant silicone rubber, comprising the following raw materials in parts by weight: 95 parts silicone rubber base, 20 parts ceramic filler, 20 parts reinforcing filler, 8 parts flux, 10 parts flame retardant, 5 parts synergist, and 2 parts vulcanizing agent.

[0062] Furthermore, the flame retardant comprises the following raw materials in parts by weight: 6 parts modified aluminum hydroxide and 4 parts 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0063] In this embodiment, the preparation method of the above-mentioned flame-retardant silicone rubber includes the following steps: (1) Put the silicone rubber base into a kneader and plasticize it at 75°C for 8 minutes; add the reinforcing filler in 3 batches, and mix for 8 minutes after each addition; then add the pre-mixed ceramic filler and flux, and mix at 70°C for 40 minutes; then add the flame retardant and continue mixing for 15 minutes; heat treat the mixture at 105°C and -0.09MPa for 100 minutes, cool and discharge to obtain the base compound; (2) Place the base compound on a two-roll mill, add the synergist and vulcanizing agent in sequence at room temperature, pass through the mill 6 times, mix evenly, and then sheet to obtain the rubber compound to be vulcanized. (3) Place the rubber material to be vulcanized into a preheated mold and vulcanize it for 8 minutes in a vulcanizing machine at a temperature of 180℃ and a pressure of 10MPa to obtain a vulcanized product. (4) Place the vulcanized product in an oven and vulcanize it again at 200°C for 3 hours. Then let it cool naturally to room temperature to obtain flame-retardant silicone rubber.

[0064] The rest of the content of this embodiment is the same as that of Embodiment 1, and will not be repeated here.

[0065] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example provides a flame-retardant silicone rubber, comprising the following raw materials in parts by weight: 95 parts silicone rubber base, 25 parts ceramic filler, 20 parts reinforcing filler, 10 parts flux, 8 parts flame retardant, 5 parts synergist, and 2 parts vulcanizing agent.

[0066] Furthermore, the preparation method of the silicone rubber-based adhesive includes the following steps: A1. Add 296g of octamethylcyclotetrasiloxane and 25.8g of tetramethyltetravinylcyclotetrasiloxane to the reaction vessel. Dry and dehydrate for 40min under a nitrogen atmosphere at 90℃ and a vacuum of -0.09MPa to obtain a monomer mixture. Add 0.24g of initiator tetramethylammonium hydroxide silanolate and 4.8g of accelerator N,N-dimethylformamide. React at 90℃ for 45min to obtain mixture one. A2. Dissolve 17.2 g of tetramethyltetravinylcyclotetrasiloxane in 30 mL of anhydrous tetrahydrofuran to prepare a siloxane solution; add the siloxane solution dropwise to mixture one under stirring for 60 min; after the addition is complete, heat to 115 °C to obtain mixture two; add 0.36 g of deionized water to mixture two and continue the reaction for 2 h to obtain mixture three; A3. The mixture was kept at 150℃ for 40 min to deactivate the initiator; then, under nitrogen purging, it was subjected to deactivation treatment at 150℃ and vacuum degree of -0.09MPa for 80 min; the reaction mixture was then subjected to vacuum treatment at 105℃, cooled and discharged to obtain polysiloxane silicone rubber.

[0067] The rest of the contents of this comparative example are the same as those of Example 1, and will not be repeated here.

[0068] Comparative Example 2 The difference between this comparative example and Example 1 is that the flame-retardant silicone rubber provided in this comparative example does not contain synergists, and uses an equal amount of silicone rubber base rubber instead.

[0069] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example provides a flame-retardant silicone rubber comprising the following raw materials in parts by weight: 95 parts silicone rubber base, 25 parts ceramic filler, 20 parts reinforcing filler, 10 parts flux, 8 parts flame retardant, 5 parts synergist, 2 parts vulcanizing agent, and 5 parts zinc borate. The silicone rubber base is the silicone rubber base prepared in Comparative Example 1.

[0070] The rest of the contents of this comparative example are the same as those of Example 1, and will not be repeated here.

[0071] The flame-retardant silicone rubbers prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. The sample thickness was 2 mm. The test results are shown in Table 1 below: The hardness was tested according to GB / T531.1-2008. Tensile strength and elongation at break were tested according to GB / T528-2009, using dumbbell-shaped Type I specimens with a thickness of 2 mm and a tensile rate of 200 mm / min. The UL94 vertical flammability rating was tested according to ANSI / UL 94-2018, with a standard silicone rubber test strip size of 130×13×3 mm. The limiting oxygen index (LOI) was tested according to GB / T 2406.2-2009. The char residue at 800℃ was tested using thermogravimetric analysis (TGA) with a 10 mg sample in air, heated from 25℃ to 800℃ at a rate of 10℃ / min. Compression set was tested according to GB / T7759-2015. The test method for the flexural strength of ceramic bodies is as follows: The vulcanized rubber sheet is placed in a muffle furnace, heated to 800℃ at a rate of 5℃ / min and held for 2 hours. After natural cooling, the ceramicized sample is removed, and a test strip processed into 50×5×3mm is taken. A three-point bending test is performed according to GB / T 6569-2006, with a span of 30mm and a loading rate of 0.5mm / min. The test strips in Examples 1-3 have smooth surfaces and excellent surface quality.

[0072] Compared to Example 1, Comparative Example 1 used a boron-free polysiloxane silicone rubber instead of a boron-containing polysiloxane silicone rubber. As shown in Table 1, Example 1 exhibited superior tensile strength compared to Comparative Example 1, with improved limiting oxygen index and UL94 rating. The char residue at 800°C and the flexural strength of the ceramic body were also significantly enhanced, indicating that the use of boron-containing polysiloxane silicone rubber helps improve flame retardancy and ceramic-forming properties.

[0073] Compared to Example 1, Comparative Example 2 did not contain the trisilyl phenyl cage-like polysilsesquioxane synergist. As shown in Table 1, the tensile strength, elongation at break, and compression set of Example 1 were superior to those of Comparative Example 2. The limiting oxygen index and flexural strength of the ceramic body were significantly improved compared to Comparative Example 2. This indicates that the addition of trisilyl phenyl POSS not only improves crosslinking uniformity, enhances mechanical properties and dimensional stability, but also contributes to improving flame retardancy and ceramic layer quality.

[0074] Compared to Example 1, Comparative Example 3 used the polysiloxane silicone rubber without endogenous boron prepared in Comparative Example 1 as the base rubber, and added an additional 5 parts of zinc borate. Table 1 shows that the limiting oxygen index of Comparative Example 3 was higher than that of Comparative Example 1, indicating that the addition of zinc borate improved the flame retardant properties to some extent. However, the tensile strength of Example 1 was better than that of Comparative Example 3, and the limiting oxygen index and flexural strength of the ceramic body were significantly improved compared to Comparative Example 3, indicating that endogenous boron, embedded in the polysiloxane backbone by chemical bonds, is more conducive to improving mechanical properties and ceramic layer quality than physically blended zinc borate.

[0075] In summary, this invention prepares silicone rubber by compounding silicone rubber base with ceramic fillers, reinforcing fillers, fluxing agents, flame retardants, and synergists. The synergistic effect of these raw materials gives the prepared silicone rubber excellent mechanical and processing properties. It does not require the addition of high amounts of exogenous flame retardants, has good flame retardant effect, can be sintered to form a ceramic structure, has excellent ceramic properties, and the sintered ceramic layer has high flexural strength. The preparation method is stable, has high production efficiency, and is conducive to industrial production.

[0076] The specific embodiments described above are further illustrations of the technical solution and beneficial effects of the present invention, and are not intended to limit the implementation methods. For those skilled in the art, any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A flame-retardant silicone rubber, characterized in that: The raw materials include the following parts by weight: 90-100 parts of silicone rubber base, 20-30 parts of ceramic filler, 15-25 parts of reinforcing filler, 5-15 parts of flux, 5-10 parts of flame retardant, 2-8 parts of synergist, and 0.5-4 parts of vulcanizing agent.

2. The flame-retardant silicone rubber according to claim 1, characterized in that: The silicone rubber base is boron-containing polysiloxane silicone rubber, and the preparation method of the boron-containing polysiloxane silicone rubber includes the following steps: A1. Mix octamethylcyclotetrasiloxane and a portion of tetramethyltetravinylcyclotetrasiloxane to obtain a monomer mixture; add an initiator and a accelerator, and react at 85-95℃ to obtain mixture one; A2. Add a pre-prepared borosilicate solution dropwise to mixture one to carry out the reaction. The borosilicate solution includes trimethoxycycloborosilicate and the remaining tetramethyltetravinylcyclotetrasiloxane. After the addition is complete, heat to 105-125℃ to obtain mixture two. Add a capping agent to mixture two and continue the reaction to obtain mixture three. A3. The mixture is kept at 145-155℃ and then vacuum de-lowered under nitrogen purging; the reaction mixture is then vacuum treated at 100-105℃ and cooled to obtain boron-containing polysiloxane silicone rubber.

3. The flame-retardant silicone rubber according to claim 1, characterized in that: The ceramic filler is at least one of mica powder, wollastonite, kaolin, and calcium carbonate.

4. The flame-retardant silicone rubber according to claim 1, characterized in that: The reinforcing filler is fumed silica.

5. The flame-retardant silicone rubber according to claim 1, characterized in that: The vulcanizing agent is at least one selected from 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, bis(2,4-dichlorobenzoyl)peroxide, di-tert-butylperoxide, and dicumyl peroxide.

6. The flame-retardant silicone rubber according to claim 1, characterized in that: The flux is at least one of low-melting-point glass powder and boron oxide.

7. The flame-retardant silicone rubber according to claim 1, characterized in that: The flame retardant is at least one of modified aluminum hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

8. The flame-retardant silicone rubber according to claim 1, characterized in that: The flame retardant comprises the following raw materials in parts by weight: 3-6 parts of modified aluminum hydroxide and 2-4 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

9. The flame-retardant silicone rubber according to claim 1, characterized in that: The synergist is trisilyl phenyl cage-like polysilsesquioxane.

10. A method for preparing flame-retardant silicone rubber according to any one of claims 1-9, characterized in that: Includes the following steps: (1) Put the silicone rubber base into a kneader and stir; then add the reinforcing filler, ceramic filler, flux, and flame retardant into the kneader, mix evenly and heat treat to obtain the basic compound; (2) Place the basic compound rubber in a two-roll mill, add synergist and vulcanizing agent, mix evenly and then sheet to obtain the rubber material to be vulcanized; (3) Add the rubber material to be vulcanized into the mold and vulcanize it once to obtain a vulcanized product; (4) The product is vulcanized twice and cooled to room temperature to obtain flame-retardant silicone rubber.

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