Preparation method of flame-retardant self-foaming silicone rubber and flame-retardant self-foaming silicone rubber

Abstract

The invention relates to the technical field of silicone rubber, in particular to a preparation method of flame-retardant self-foaming silicone rubber and the flame-retardant self-foaming silicone rubber. The preparation method of the flame-retardant self-foaming silicone rubber comprises the following steps: mixing modified montmorillonite, vinyl silicone oil and hydroxyl silicone oil to obtain a component A, mixing hydrogen-containing silicone oil, a catalyst and an inhibitor to obtain a component B, mixing the component A and the component B, and carrying out foaming curing molding, the modified montmorillonite is anionic phosphorus flame retardant intercalation modified montmorillonite. According to the invention, the anionic phosphorus flame-retardant group is grafted on the montmorillonite, so that the material has excellent flame-retardant property, and the layered montmorillonite can be attached to the bubble wall to ensure that bubbles are not easy to gather, thereby effectively controlling the size of the bubbles, further enhancing the flame-retardant effect of the material, and giving consideration to flame-retardant property, heat-conducting property and mechanical property.

Description

Technical Field

[0001] This invention relates to the field of silicone rubber technology, specifically to a method for preparing flame-retardant self-foaming silicone rubber and the flame-retardant self-foaming silicone rubber itself. Background Technology

[0002] Foamed silicone rubber is a material in which a bubble structure is introduced into a silicone rubber matrix. By controlling the number and distribution of bubbles, a porous polymer elastic material with lightweight, soft, elastic, and heat-insulating properties is formed. The main research object of this invention is addition-cure liquid silicone rubber, whose vulcanization and foaming mechanism is as follows: the vinyl groups (Si-CH=H2) in ethylene silicone oil undergo a crosslinking reaction with the silicon-hydrogen bonds (Si-H) of hydrogen-containing silicone oil to construct a polymer network. The hydroxyl groups (Si-OH, R-OH) in hydroxyl silicone oil undergo a dehydrogenation condensation reaction with the silicon-hydrogen bonds (Si-H) of hydrogen-containing silicone oil to produce hydrogen gas (H2), forming bubbles that drive the expansion of the colloid. The reaction mechanism is shown below. A common preparation method for addition-cure liquid silicone rubber is to mix component A (vinyl silicone oil, hydroxyl silicone oil, fillers, etc.) and component B (hydrogen-containing silicone oil, catalyst, inhibitor) in a certain proportion, and then allow it to stand at room temperature for foaming and curing. The reaction equation is as follows: .

[0003] Silicone rubber ranks among the top elastomers for its excellent thermal stability, and its ultra-low density foam materials are widely used in thermal insulation. However, like other carbon-chain rubbers, silicone rubber is also flammable under certain conditions. Given the numerous applications of silicone rubber, higher demands are being placed on its flame retardancy. Therefore, research on flame-retardant silicone rubber is increasingly in-depth, mainly focusing on process improvement and formulation optimization. The main approaches to improving the flame retardant properties of silicone rubber include: firstly, adding functional flame-retardant chemicals or filler-type flame retardants through physical blending; and secondly, modifying the silicone rubber macromolecular chain to introduce flame-retardant functional groups to achieve a long-lasting flame-retardant effect.

[0004] Chinese patent application CN109867963A, published on June 11, 2019, discloses a high-temperature resistant flame-retardant silicone rubber and its preparation method. The high-temperature resistant flame-retardant silicone rubber comprises the following components: 100 parts vinyl-terminated silicone rubber raw material, 40-60 parts silica, 30-70 parts filler (including nano-montmorillonite), 10-30 parts flame retardant (phosphorus-nitrogen type flame retardant and high-nitrogen content flame retardant), 3-7 parts structure control agent (including hydroxyl silicone oil), 2-5 parts heat resistant agent, 0.5-2 parts coupling agent, and 0.1-1 parts release agent. The prepared silicone rubber possesses excellent high-temperature resistance and flame retardant properties, as well as excellent mechanical properties and excellent aging resistance. However, this direct-addition flame-retardant method requires a large amount of flame retardant to achieve the flame-retardant effect and inevitably has a significant impact on the matrix itself.

[0005] Currently, organic modification of montmorillonite is usually required when preparing polymer / montmorillonite nanocomposites. Chinese Patent CN105733315B, authorized on August 7, 2018, discloses a method for preparing sodium carboxymethyl cellulose intercalated modified montmorillonite. This method involves first adding an inorganic salt to a montmorillonite suspension to undergo an ion exchange reaction to obtain primary modified montmorillonite, and then adding the anionic modifier sodium carboxymethyl cellulose to the primary modified montmorillonite suspension to obtain secondary modified montmorillonite. By using the aforementioned inorganic salt and anionic cellulose, sodium carboxymethyl cellulose enters the interlayer space of montmorillonite, effectively opening the interlayer spacing and improving the compatibility of montmorillonite with organic matter. This enhances the thermal stability and flame retardant properties of the polymer-based composite material. The organically modified montmorillonite contains transition metal ions in its structure, which can act as a catalyst in the flame retardant process, further improving the flame retardant effect.

[0006] Chinese patent application CN119708628A, published on March 28, 2025, discloses a diisobutyl aluminum hypophosphite intercalated montmorillonite flame retardant, its preparation method, and its uses. The diisobutyl aluminum hypophosphite is intercalated into montmorillonite to prevent the precipitation of diisobutyl aluminum hypophosphite, and then forms a composite material with polyimide. It has good flame retardancy and low smoke emission without the need to add other additives, with an LOI of up to 47% and a flammability rating of UL94-V-0.

[0007] However, the flame retardant properties, thermal conductivity, and mechanical properties of the composite material formed by adding modified montmorillonite to self-foaming silicone rubber cannot be synergistically improved. Summary of the Invention

[0008] The first objective of this invention is to provide a method for preparing flame-retardant self-foaming silicone rubber, thereby solving the problem that existing self-foaming silicone rubbers cannot simultaneously achieve flame retardancy, thermal conductivity, and mechanical properties.

[0009] The second objective of this invention is to provide a flame-retardant self-foaming silicone rubber that solves the problem that existing self-foaming silicone rubbers cannot simultaneously achieve flame retardancy, thermal conductivity, and mechanical properties.

[0010] To solve the above-mentioned technical problems, the technical solution of the method for preparing flame-retardant self-foaming silicone rubber of the present invention is as follows: A method for preparing flame-retardant self-foaming silicone rubber includes the following steps: mixing modified montmorillonite, vinyl silicone oil and hydroxyl silicone oil to obtain component A; mixing hydrogen-containing silicone oil, catalyst and inhibitor to obtain component B; and then mixing component A and component B and foaming and curing them; wherein the modified montmorillonite is anionic phosphorus flame retardant intercalated modified montmorillonite.

[0011] This invention improves upon existing technology by providing a method for preparing flame-retardant self-foaming silicone rubber. By "anchoring" anionic phosphorus-based flame retardants between montmorillonite layers, it not only leverages the highly efficient flame-retardant properties of the phosphorus-based flame retardant but also utilizes the unique layered structure of montmorillonite to achieve "phosphorus-silicon synergistic flame retardancy." This allows the modified montmorillonite to maintain good flame-retardant effects even at low addition levels without significantly impacting the material matrix. Structurally, the layered montmorillonite adheres to the bubble walls, preventing bubble aggregation and effectively controlling pore size, ensuring uniformity. The uniform pore structure formed during foaming blocks oxygen diffusion and heat transfer, effectively enhancing the material's flame-retardant effect. The flame-retardant self-foaming silicone rubber of this invention possesses excellent flame-retardant properties and safety.

[0012] The flame-retardant self-foaming silicone rubber of this invention achieves material lightweighting through a foaming structure while maintaining excellent compression resilience and cushioning performance. Simultaneously, the lightweight cell structure provides good shock absorption, and the ceramic filler reinforcement ensures that tensile strength and abrasion resistance do not significantly decrease due to foaming, optimizing the overall performance of the material. The silicone rubber matrix is ​​UV- and ozone-resistant, and the ceramic filler delays high-temperature aging; together, they enable the material to have long-term reliable use. It balances flame retardancy, thermal conductivity, and mechanical properties.

[0013] The method for preparing flame-retardant self-foaming silicone rubber of the present invention has significant process advantages: no additional foaming agent is required, and preheating of the base rubber is unnecessary. This effectively simplifies the process, greatly improves production efficiency, and ensures the environmental friendliness, safety, and simplicity of the production process, perfectly meeting the needs of industrial-scale production and application.

[0014] Preferably, the preparation method of the modified montmorillonite includes the following steps: performing an interlayer ion exchange reaction of montmorillonite and aluminum salt in a solvent to obtain aluminum ion modified montmorillonite; then reacting the aluminum ion modified montmorillonite and anionic phosphorus flame retardant in a solvent to obtain anionic phosphorus flame retardant intercalated modified montmorillonite.

[0015] Modified montmorillonite is first subjected to ion exchange via aluminum salts, Al 3+ The Al source forms strong coordination / electrostatic interactions with montmorillonite layers, which enhances the structural stability of the material at high temperatures after intercalation, inhibits interlayer slip and decomposition, facilitates the formation of the insulation layer, and improves flame retardant efficiency (especially when forming alumina / alumina hydroxide protective layers). During combustion, the Al source more readily forms dense aluminum oxide / aluminum oxygen-containing inorganic phases, synergistically promoting the formation of a more continuous and dense insulating ceramic / carbonized layer with the silicon-aluminum matrix framework of montmorillonite, reducing the heat release rate (HRR) and flue gas emission. 3+ Aluminum can promote the cross-linking of silicone rubber segments or interact with flame retardant additives during the curing / foaming process of self-foaming silicone rubber, thereby improving the strength of the cell walls and the structural retention at high temperatures. Compared with the risk of pollution from transition metals (Cu, Zn, Bi) or heavy metals, aluminum is safer and easier to formulate and post-process in industrial applications.

[0016] Preferably, the anionic phosphorus flame retardant is selected from one or more of aluminum hypophosphite, diammonium hydrogen phosphate, bisphenol A bis(diphenyl phosphate), and m-phenylene tetraphenyl bisphosphate; the aluminum salt is aluminum chloride.

[0017] Preferably, 0.5-1 mol of aluminum salt is added for every 10-15 g of montmorillonite; the mass ratio of aluminum ion modified montmorillonite to anionic phosphorus flame retardant is (5-6):(3-4).

[0018] Preferably, the reaction temperature for the montmorillonite interlayer ion exchange reaction, the aluminum ion modified montmorillonite reaction, and the anionic phosphorus flame retardant reaction is 60~80℃, and the reaction time is 4~6h; the pH during the montmorillonite interlayer ion exchange reaction is 1~3.

[0019] Preferably, the mass ratio of vinyl silicone oil, hydroxyl silicone oil and hydrogen-containing silicone oil is (100~110):(4~5):(15~17); 1~6 parts by weight of modified montmorillonite are added for every 100~110 parts by weight of vinyl silicone oil.

[0020] Preferably, the vinyl silicone oil comprises a high-viscosity vinyl silicone oil and a low-viscosity vinyl silicone oil in a mass ratio of (50~90):(10~50); the viscosities of the high-viscosity vinyl silicone oil and the low-viscosity vinyl silicone oil are 1000~2000 Pa·s and 200~500 Pa·s, respectively; the hydrogen-containing silicone oil comprises a high-hydrogen-content silicone oil and a low-hydrogen-content silicone oil in a mass ratio of (2~3):(14~15); the hydrogen contents of the high-hydrogen-content silicone oil and the low-hydrogen-content silicone oil are 3~4% and 1~1.6%, respectively.

[0021] Preferably, component A comprises silica aerogel powder, a reinforcing agent, and ceramic powder; the reinforcing agent is fumed silica; for every 100-110 parts by weight of vinyl silicone oil, 2-4 parts by weight of silica aerogel powder, 1.5-2 parts by weight of reinforcing agent, and 1-6 parts by weight of ceramic powder are added. The combination of ceramic-based filler and flame retardant synergist (modified montmorillonite) forms a dual physical-chemical barrier, significantly delaying flame spread and suppressing smoke release.

[0022] Preferably, for every 100-110 parts by weight of vinyl silicone oil, 0.2-0.3 parts by weight of catalyst and 0.05-0.06 parts by weight of inhibitor are added; the catalyst is a last-stage catalyst and the inhibitor is acetylenecyclohexanol.

[0023] The technical solution of the flame-retardant self-foaming silicone rubber of the present invention is as follows: A method for preparing flame-retardant self-foaming silicone rubber is described above.

[0024] The flame-retardant self-foaming silicone rubber provided by this invention is obtained through the above preparation method. Utilizing the unique layered structure of montmorillonite, it achieves "phosphorus-silicon synergistic flame retardancy," enabling the modified montmorillonite to maintain good flame retardant effect even with a small addition amount. The layered montmorillonite effectively controls the size and uniformity of the pores by adhering to the bubble wall, further enhancing the flame retardant effect of the material. The over-foaming structure achieves material lightweighting while maintaining excellent compression resilience and cushioning performance. Attached Figure Description

[0025] Figure 1 This is a reaction flow diagram of the modified montmorillonite in Example 1 of the present invention; Figure 2 SEM morphology of flame-retardant self-foaming silicone rubber; Figure 3 Infrared spectrum of flame-retardant self-foaming silicone rubber; Figure 4 The flame-retardant effect of flame-retardant self-foaming silicone rubber is shown in the diagram. Figure 5 This is a cross-sectional view and cell diameter distribution diagram of the flame-retardant self-foaming silicone rubber of Embodiment 3 of the present invention; Figure 6 This is a cross-sectional view and cell diameter distribution diagram of the flame-retardant self-foaming silicone rubber in Comparative Example 3. Detailed Implementation

[0026] The technical concept of the flame-retardant self-foaming silicone rubber provided by this invention is as follows: Existing technologies improve the compatibility and flame retardant properties of montmorillonite with polymers by intercalating sodium carboxymethyl cellulose; and improve the flame retardant properties of polyimide composites by intercalating aluminum diisobutyl phosphate with montmorillonite.

[0027] Montmorillonite, as a natural bio-based material, is also a multifunctional material with diverse and tunable properties. Its excellent performance stems from its nanolayered structure and exchangeable interlayer cations. Different modification treatments of montmorillonite can greatly expand its application range. This invention grafts anionic phosphorus-based flame-retardant groups onto montmorillonite, giving it excellent flame-retardant properties. The layered montmorillonite can adhere to the bubble wall, preventing bubble aggregation and effectively controlling the pore size, thus balancing flame retardancy, thermal conductivity, and mechanical properties.

[0028] The method for preparing flame-retardant self-foaming silicone rubber provided by the present invention includes the following steps: 1) Preparation of modified montmorillonite: Montmorillonite and aluminum salt are subjected to interlayer ion exchange reaction in a solvent to obtain aluminum ion modified montmorillonite; then aluminum ion modified montmorillonite and anionic phosphorus flame retardant are reacted in a solvent to obtain anionic phosphorus flame retardant intercalated modified montmorillonite.

[0029] This invention obtains Al by first performing ion exchange with aluminum salt. 3+ -MMT, then reacted with anionic phosphorus flame retardants to obtain anionic phosphorus flame retardant intercalated modified montmorillonite, Al 3+ As a bridge, one end connects to negatively charged montmorillonite silicate sheets, while the other end connects to negatively charged phosphorus-based flame retardant anions through electrostatic attraction or coordination. The aluminum source enhances thermal stability and insulation, forms a protective char / ceramic layer during combustion to improve the quality of the carbonized layer, and promotes the cross-linking of silicone rubber segments, thereby significantly improving the flame retardant properties of self-foaming silicone rubber.

[0030] Compared to Mg 2+ / Ca 2+ Divalent metal ions: Divalent cations have weak shielding ability for interlayer charges, and the protective phases they form (such as magnesium oxide / calcium oxide) are generally less dense and have poorer adhesion than aluminum-based phases in terms of flame retardant synergy and ceramization; compared to Fe... 3+ / Bi 3+ Trivalent metal ions: Fe 3+ It can provide oxidation catalysis / complexation, but it generates easily destructible oxide structures; Bi 3+ Al has poor film-forming properties and may be disadvantageous in terms of cost, toxicity, and resource availability. 3+ It generally offers a better balance in terms of thermal stability, film density, and environmental compatibility; compared to Zn 2+ / Cu 2+ Transition metal ions: These metals can catalyze carbonization or provide flame-retardant activity, but they easily affect the pigment / colorability of silicone rubber and may introduce toxicity or promote undesirable oxidative degradation; Al 3+More inert and stable; compared to sulfates (ZnSO4, CuSO4): sulfate ions may release SOx at high temperatures, increasing the risk of corrosion / fume toxicity; Cl - The source (AlCl3) itself requires attention to chlorine treatment, but Al... 3+ The positive effects of Cl are usually greater. - Potential disadvantages (preparation can be controlled to reduce residual chlorine).

[0031] Therefore, for foamed flame-retardant silicone rubber, AlCl3 intercalated montmorillonite is generally more advantageous than divalent metal salts and most transition metal salts in improving thermal stability, forming a dense protective layer, environmental compatibility, and improving the high-temperature retention of the foam structure.

[0032] In step 1), montmorillonite suspension and aluminum salt solution are subjected to interlayer ion exchange to obtain aluminum ion modified montmorillonite; then, the aluminum ion modified montmorillonite suspension is reacted with an anionic phosphorus flame retardant solution to obtain anionic phosphorus flame retardant intercalated modified montmorillonite. The volume of the aluminum salt solution is 500~600mL.

[0033] In step 1), 0.5-1 mol of aluminum salt is added for every 10-15 g of montmorillonite; the mass ratio of aluminum ion modified montmorillonite to anionic phosphorus flame retardant is (5-6):(3-4).

[0034] In step 1), the anionic phosphorus flame retardant is selected from one or more of aluminum hypophosphite, diammonium hydrogen phosphate, bisphenol A bis(diphenyl phosphate) (BDP), and m-phenylene tetraphenyl bisphosphate (RDP); the aluminum salt is aluminum chloride.

[0035] In step 1), the solvents for the montmorillonite suspension, aluminum salt solution, aluminum ion-modified montmorillonite suspension, and anionic phosphorus flame retardant solution are all water. 1500-2000 ml of solvent is added for every 10 g of montmorillonite. 100-110 ml of solvent is added for every (5-6) g of aluminum ion-modified montmorillonite and (3-4) g of anionic phosphorus flame retardant, respectively.

[0036] In step 1), the reaction temperature for the montmorillonite interlayer ion exchange reaction, the aluminum ion modified montmorillonite reaction, and the anionic phosphorus flame retardant reaction is 60~80℃, and the reaction time is 4~6h; the pH during the montmorillonite interlayer ion exchange reaction is 1~3.

[0037] In step 1), the interlayer ion exchange reaction of montmorillonite and the intercalation modification of montmorillonite with anionic phosphorus flame retardant were both carried out under stirring conditions.

[0038] In step 1), after the interlayer ion exchange reaction of montmorillonite is completed and the anionic phosphorus flame retardant-modified montmorillonite is obtained, it is centrifuged, filtered, and washed.

[0039] In step 1), the montmorillonite is natural or modified sodium-based montmorillonite, calcium-based montmorillonite, lithium-based montmorillonite, or magnesium-based montmorillonite. The montmorillonite used in the following examples is calcium-based montmorillonite.

[0040] 2) Modified montmorillonite, aerogel, silica, ceramic powder, vinyl silicone oil and hydroxyl silicone oil are mixed to obtain component A. Hydrogen-containing silicone oil, catalyst and inhibitor are mixed to obtain component B. Then component A and component B are mixed and foamed and cured to form a mold.

[0041] In step 2), the mass ratio of vinyl silicone oil, hydroxyl silicone oil and hydrogen-containing silicone oil is (100~110):(4~5):(15~17); for every 100~110 parts by weight of vinyl silicone oil, 1~6 parts by weight of modified montmorillonite, 2~4 parts by weight of silica aerogel powder, 1.5~2 parts by weight of fumed silica and 1~6 parts by weight of ceramic powder are added.

[0042] In step 2), the vinyl silicone oil includes high-viscosity vinyl silicone oil and low-viscosity vinyl silicone oil in a mass ratio of (50~90):(10~50); the viscosities of the high-viscosity vinyl silicone oil and the low-viscosity vinyl silicone oil are 1000~2000 Pa·s and 200~500 Pa·s, respectively; the hydrogen-containing silicone oil includes high-hydrogen-content silicone oil and low-hydrogen-content silicone oil in a mass ratio of (2~3):(14~15); the hydrogen content of the high-hydrogen-content silicone oil and the low-hydrogen-content silicone oil is 3~4% and 1~1.6%, respectively; the hydroxyl silicone oil has a hydroxyl value of 8~9% and a viscosity of 20~50 cSt.

[0043] In step 2), for every 100-110 parts by weight of vinyl silicone oil, 0.2-0.3 parts by weight of catalyst and 0.05-0.06 parts by weight of inhibitor are added; the catalyst is a last catalyst and the inhibitor is acetylenecyclohexanol.

[0044] In step 2), modified montmorillonite, silica aerogel powder, fumed silica, and ceramic powder are first mixed to obtain a prefiller. The prefiller is then mixed with vinyl silicone oil (100-500 rpm, 1-5 min), and then mixed with hydroxyl silicone oil (100-500 rpm, 1-5 min) to obtain component A. Hydrogen-containing silicone oil, catalyst, and inhibitor are mixed to obtain component B. The mixing speed is 50-100 rpm and the time is 1-5 min.

[0045] The embodiments of the present invention will be further described below with reference to specific examples. Unless otherwise specified, the chemical reagents involved in the following examples are all commercially available conventional products. All quantities are parts by weight.

[0046] I. Preparation method of flame-retardant self-foaming silicone rubber of the present invention and specific embodiments of flame-retardant self-foaming silicone rubber. Example 1 The preparation method of the flame-retardant self-foaming silicone rubber in this embodiment is as follows: (1) Preparation of modified montmorillonite: 10g of montmorillonite (MMT) was dispersed in 1500ml of deionized water, and excess AlCl3 (500mL, 1M) solution was added. The pH was controlled at 3, and the mixture was stirred at 60℃ for 6 hours to ensure that the Na+ between the montmorillonite layers was properly mixed. + / Ca 2+ By Al 3+ After thorough exchange and stirring, Al was obtained by centrifugation, filtration, and washing. 3+ -MMT. Add 3g of anionic phosphorus-based flame retardant (aluminum hypophosphite, containing anionic H2PO2). - ) and 5g Al 3+ MMT was placed in 100 mL of deionized water to form a solution and a suspension, respectively. Then, aluminum hypophosphite solution was slowly added to Al. 3+ -MMT suspension; metal cations (Al) 3+ As a bridge, one end connects to negatively charged montmorillonite silicate sheets, and the other end connects to negatively charged phosphorus-based flame retardant anions through electrostatic attraction or coordination. The mixture is stirred at 60°C for 6 hours, centrifuged, filtered, washed with deionized water, and dried under vacuum to obtain the final product, modified montmorillonite powder, grafted with phosphorus-based flame retardant groups. The reaction flow chart is shown below. Figure 1 As shown.

[0047] (2) Preparation of flame-retardant self-foaming silicone rubber: 4 parts of ceramic powder (CFP-1 ceramic composite powder provided by Shenzhen Haiyang Powder Technology Co., Ltd., whose components include aluminum hydroxide, flame retardant, wollastonite, zirconium oxide, porcelain stone, low-melting-point glass powder, etc.), 4 parts of modified montmorillonite powder obtained in Example 1, 2 parts of silica aerogel powder, and 1.5 parts of fumed silica were mixed by hand to obtain a uniformly mixed prefiller; 90 parts of high-viscosity vinyl silicone oil (viscosity 1500 Pa·s, vinyl content 0.1%) were weighed. Mix 5-1.0% of a low-viscosity vinyl silicone oil (viscosity 200 Pa·s, vinyl content 0.15-1.0%) with 10 parts of a low-viscosity vinyl silicone oil (viscosity 200 Pa·s, vinyl content 0.15-1.0%), and mix them evenly at 100 rpm for 1 min. Then, thoroughly stir the mixed vinyl silicone oil with the prefiller at 100 rpm for 3 min. Finally, add 4 parts of hydroxyl silicone oil (hydroxyl value 8-9%, viscosity 20 cSt), and stir at 100 rpm for 1 min to obtain a uniformly mixed basic colloid, which is component A.

[0048] Weigh 2 parts of high-hydrogen-content silicone oil (hydrogen content 3.5~4%) and 15 parts of low-hydrogen-content silicone oil (hydrogen content 1~1.6%), mix them evenly at 50 rpm for 1 min; then add 0.2 parts of Rastar catalyst and 0.05 parts of acetylenecyclohexanol inhibitor, mix at 50 rpm for 1 min, and stir evenly to obtain component B.

[0049] Mix the well-mixed components A and B thoroughly, stir quickly until homogeneous, place in a mold, and let stand for 1 minute to allow the material to foam and solidify, thus obtaining flame-retardant self-foaming silicone rubber.

[0050] The flame-retardant self-foaming silicone rubber obtained in this embodiment is the flame-retardant self-foaming silicone rubber provided by the present invention.

[0051] Examples 2-8 The preparation methods and the flame-retardant self-foaming silicone rubbers of Examples 2-8 are basically the same as those of Example 1, except that the amounts of each component added in the preparation methods are different. The amounts of each component added in Examples 1-8 are shown in Table 1.

[0052] II. Comparative Example The preparation methods and the flame-retardant self-foaming silicone rubbers of Comparative Examples 1 to 4 are basically the same as those of Example 1, except that the amount of each component added in the preparation method is different.

[0053] The preparation method and the flame-retardant self-foaming silicone rubber of Comparative Example 5 are basically the same as those of Example 1, except that the modified montmorillonite used is different. The modified montmorillonite is prepared as follows: 10g MMT is added to 500mL of 1M NaCl solution, stirred at 80℃ for 6h, and centrifuged and washed until no chloride ions are found, yielding Na... + -MMT; Add 3g of anionic phosphorus flame retardant (aluminum hypophosphite, of which anionic H2PO2) - ) and 5g Na + MMT was placed in 100 mL of deionized water to form a solution and a suspension, respectively. Then, aluminum hypophosphite solution was slowly added to Al. 3+ In an MMT suspension, the mixture was stirred at 60°C for 6 hours, centrifuged, filtered, washed with deionized water, and dried under vacuum to obtain modified montmorillonite powder, the final product of montmorillonite grafted with phosphorus-based flame-retardant groups. Chloride ions were detected using AgNO3.

[0054] The amounts of each component added in Comparative Examples 1 to 5 are shown in Table 1.

[0055] Table 1. Amounts of each component added in the examples and comparative examples.

[0056] III. Experimental Examples The microstructure of flame-retardant self-foaming silicone rubber was observed using SEM. The SEM images are shown below. Figure 2 As shown, the left side displays SEM images of the flame-retardant self-foaming silicone rubber of Example 3 at different magnifications, and the right side displays SEM images of the flame-retardant self-foaming silicone rubber of Comparative Example 3 at different magnifications. Figure 2 It can be seen that there is a significant difference between the bubble walls with and without montmorillonite (Example 3). After adding modified montmorillonite, agglomeration of the montmorillonite on the bubble walls occurred, mainly related to its layered structure and surface charge characteristics. However, this also confirms the hypothesis that montmorillonite is embedded in the bubble walls, as this embedding prevents bubble aggregation, effectively controlling the size of the bubbles and ensuring their uniformity.

[0057] Infrared spectra of modified and unmodified montmorillonite are shown below. Figure 3 As shown, the infrared absorption peaks of phosphorus are concentrated in a specific wavenumber range, and their specific positions are influenced by the type of chemical bond (e.g., P=O, pH), the coordination environment (phosphate, phosphite), and the crystal field effect. Taking the phosphate group as an example, its typical wavenumber for asymmetric stretching vibration is 900-1200 cm⁻¹. -1 Comparison of infrared spectral test results of montmorillonite and modified grafted montmorillonite (Figure 1) Figure 3 ), and it was found that the grafted montmorillonite soil was at 1191cm -1 The modified montmorillonite exhibits a distinct characteristic absorption peak at this location, while unmodified montmorillonite shows no characteristic absorption peak at the same location. This indicates that phosphorus-based flame-retardant groups have been successfully grafted onto the montmorillonite material.

[0058] The flame retardant effect of flame-retardant self-foaming silicone rubber is as follows: Figure 4 As shown, the top and bottom figures are flame-retardant effect diagrams of the flame-retardant self-foaming silicone rubber of Example 3 and Comparative Example 3, respectively. The times shown are the time it takes for the flame to continue burning until it is extinguished after the fire source is removed. From Figure 4 It can be seen that the flame-retardant self-foaming silicone rubber of Example 3 extinguishes the flame 3.8 seconds after the fire source is removed, demonstrating excellent flame-retardant effect, while the flame-retardant self-foaming silicone rubber of Comparative Example 3 extinguishes the flame 15.4 seconds after the fire source is removed.

[0059] The cross-sectional area and cell diameter distribution of the flame-retardant self-foaming silicone rubber in Example 3 and Comparative Example 3 are shown in the following figures. Figure 5 and Figure 6The diagram shows a cross-sectional view on the left and a cell diameter distribution on the right. By comparing the cross-sectional views and cell size distribution statistics of different foamed silicone rubbers, it can be seen that adding modified montmorillonite powder does indeed help improve the size and uniformity of the cells (Example 3). In the foamed silicone rubber material without added montmorillonite powder (Comparative Example 3), the lack of montmorillonite adhering to the bubble walls easily leads to bubble aggregation, resulting in larger cells; however, with the addition of montmorillonite powder, it disperses on the bubble walls, making it less prone to bubble aggregation, thereby effectively improving the cell size and uniformity.

[0060] The density, compressive strength, thermal conductivity, and flame retardancy rating of the flame-retardant self-foamed silicone rubbers used in the examples and comparative examples were tested. The test results are shown in Table 2. The 25%, 50%, and 75% compressive strengths refer to the pressure per unit area when the material is compressed to 25%, 50%, and 75% of its original thickness, respectively. The flame retardancy rating was determined through a vertical burning test (UL94 standard).

[0061] Table 2 Performance Test Results

[0062] The flame-retardant self-foaming silicone rubber provided by this invention has a low density (0.039~0.056 g / cm³). 3 It has high compressive strength, with a 25% compressive strength of over 0.0577 MPa, a 50% compressive strength of over 0.1254 MPa, and a 75% compressive strength of over 0.3081 MPa. At the same time, it has low thermal conductivity, below 0.1275 W / m·k, and its flame retardant rating can reach V-0.

[0063] Compared to Example 1, when the high / low vinyl silicone oil was 70 and 30 parts respectively, and the high / low hydrogen-containing silicone oil was 4 and 10 parts respectively (Comparative Example 1), the compressive strength at 25%, 50%, and 75% all decreased, while the thermal conductivity increased to 0.0913 W / m·k; when the high / low vinyl silicone oil was 70 and 30 parts respectively, and the high / low hydrogen-containing silicone oil was 6 and 5 parts respectively (Comparative Example 1), the compressive strength at 25%, 50%, and 75% all decreased, while the thermal conductivity increased by 0.1384 W / m·k, and the flame retardant rating was only V-1.

[0064] Compared to Example 3, without the addition of modified montmorillonite (Comparative Example 3), the compressive strengths at 25%, 50%, and 75% decreased from 0.0624 MPa, 0.1681 MPa, and 0.3520 MPa to 0.0563 MPa, 0.1363 MPa, and 0.3289 MPa, respectively, while the thermal conductivity increased from 0.0832 W / m·K to 0.1520 W / m·K, and the flame retardant rating was only V-1. With sodium ion modified montmorillonite (Comparative Example 5), the compressive strength decreased significantly, the thermal conductivity increased, and the flame retardant rating remained at V-1, demonstrating the synergistic effect of aluminum ion modified montmorillonite on the mechanical properties, thermal conductivity, and flame retardant properties of silicone rubber. Without the addition of ceramic powder (Comparative Example 4), the compressive strengths at 25%, 50%, and 75% decreased to 0.0576 MPa, 0.1374 MPa, and 0.3304 MPa, respectively, while the thermal conductivity increased to 0.1497 MPa. W / m·k, flame retardant rating is only V-1.

[0065] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a flame-retardant self-foaming silicone rubber, characterized in that, The method comprises the following steps: The modified montmorillonite, vinyl silicone oil and hydroxyl silicone oil are mixed to obtain component A, hydrogen-containing silicone oil, a catalyst and an inhibitor are mixed to obtain component B, and then the component A and the component B are mixed and foamed and cured to form a shape; The modified montmorillonite is an anion phosphorus flame retardant intercalated modified montmorillonite.

2. The process for preparing a flame-retardant self-foaming silicone rubber according to claim 1, characterized in that, The preparation method of the modified montmorillonite comprises the following steps: interlayer ion exchange reaction of montmorillonite and aluminum salt in a solvent to obtain aluminum ion modified montmorillonite; and reaction of the aluminum ion modified montmorillonite and an anion phosphorus flame retardant in a solvent to obtain an anion phosphorus flame retardant intercalated modified montmorillonite.

3. The process for producing a flame-retardant self-foaming silicone rubber according to claim 2, characterized in that, The anion phosphorus flame retardant is selected from one or more than two of aluminum hypophosphite, diammonium hydrogen phosphate, bisphenol A bis(diphenyl phosphate) and m-phenylene tetraphenyl bisphosphate; and the aluminum salt is aluminum chloride.

4. The process for producing a flame-retardant self-foaming silicone rubber according to claim 2, characterized in that, 0.5-1 mol of the aluminum salt is added to 10-15 g of the montmorillonite; and the mass ratio of the aluminum ion modified montmorillonite to the anion phosphorus flame retardant is (5-6):(3-4).

5. The process for preparing a flame-retardant self-foaming silicone rubber according to claim 2, characterized in that, The reaction temperature of the interlayer ion exchange reaction of the montmorillonite, the aluminum ion modified montmorillonite and the anion phosphorus flame retardant is 60-80 DEG C, and the reaction time is 4-6 h; and the pH of the interlayer ion exchange reaction of the montmorillonite is 1-3.

6. The method for preparing flame-retardant self-foaming silicone rubber as described in claim 1, characterized in that, The mass ratio of the vinyl silicone oil, the hydroxyl silicone oil and the hydrogen-containing silicone oil is (100-110):(4-5):(15-17); and 1-6 parts by weight of the modified montmorillonite is added to 100-110 parts by weight of the vinyl silicone oil.

7. The method for preparing flame-retardant self-foaming silicone rubber as described in claim 1, characterized in that, The vinyl silicone oil comprises high-viscosity vinyl silicone oil and low-viscosity vinyl silicone oil in a mass ratio of (50-90):(10-50); the high-viscosity vinyl silicone oil and the low-viscosity vinyl silicone oil have viscosities of 1000-2000 pa·s and 200-500 pa·s, respectively; and the hydrogen-containing silicone oil comprises high-hydrogen-content silicone oil and low-hydrogen-content silicone oil in a mass ratio of (2-3):(14-15); the high-hydrogen-content silicone oil and the low-hydrogen-content silicone oil have hydrogen contents of 3-4% and 1-1.6%, respectively.

8. The method for preparing flame-retardant self-foaming silicone rubber as described in claim 1, characterized in that, The component A comprises silica aerogel powder, a reinforcing agent and ceramic powder; the reinforcing agent is white carbon black; and 2-4 parts by weight of the silica aerogel powder, 1.5-2 parts by weight of the reinforcing agent and 1-6 parts by weight of the ceramic powder are added to 100-110 parts by weight of the vinyl silicone oil.

9. The method for preparing flame-retardant self-foaming silicone rubber as described in claim 1, characterized in that, 0.2-0.3 parts by weight of the catalyst and 0.05-0.06 parts by weight of the inhibitor are added to 100-110 parts by weight of the vinyl silicone oil; the catalyst is a Laust catalyst; and the inhibitor is ethynylcyclohexanol.

10. A preparation method of the flame-retardant self-foaming silicone rubber according to any one of claims 1-9.

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