Preparation method of flame-retardant silicone rubber foam and product thereof

Abstract

The application discloses a preparation method of a silicon rubber flame-retardant foam, which comprises the following steps: S1, mixing raw silicon rubber, white carbon black and a structure control agent to obtain a mixed rubber; and S2, mixing the mixed rubber, a flame retardant, a flame-retardant ceramic precursor masterbatch and a foaming agent, adding a vulcanizing agent after uniform mixing, and foaming and molding to obtain the silicon rubber flame-retardant foam. According to the preparation method, the core-shell double-metal hydroxide prepared by a specific process is used as the flame retardant and is used in cooperation with the flame-retardant ceramic precursor masterbatch prepared by a specific process, the prepared silicon rubber flame-retardant foam can reach the highest flame-retardant grade UL94 V-0, the oxygen index is not less than 32%, and the silicon rubber flame-retardant foam has high foaming ratio, low density, excellent mechanical properties and thermal insulation performance.

Description

Technical Field

[0001] This invention relates to the technical field of polymer materials, and in particular to a method for preparing silicone rubber flame-retardant foam and its product. Background Technology

[0002] The molecular backbone of silicone rubber is composed of alternating silicon and oxygen atoms (Si-O-Si), with two organic groups typically attached to each silicon atom. Silicone rubber combines the properties of both organic and inorganic polymers, exhibiting excellent resistance to high and low temperatures, aging resistance, electrical insulation, chemical stability, and physiological inertness. Therefore, it has wide applications in high-end manufacturing fields such as electronics, new energy, and medical health. Silicone rubber foam, on the other hand, is a porous elastic material made from silicone rubber through a foaming process, combining the elasticity of rubber with the lightweight properties of foam.

[0003] Although silicone rubber foam has a higher limiting oxygen index (approximately 17-28%) than many carbon-chain polymers, and exhibits a low heat release rate and no melting dripping during combustion, its inherent flammability severely limits its application in high-temperature environments. Therefore, flame-retardant modification of silicone rubber foam to impart flame-retardant or self-extinguishing properties has become a key technology for expanding its application range.

[0004] Flame retardant modification of silicone rubber foam is typically achieved by adding flame retardants. However, to achieve an effective UL-94 V-0 flame retardant rating, extremely high addition amounts are usually required (typically 40-60 parts or even over 100 parts). Such a large amount of inorganic filler severely disrupts the molecular chain movement and cross-linked network structure of the silicone rubber foam, leading to hardening and brittleness of the compound, a sharp decrease in tensile strength, elongation at break, and tear strength, reduced processing fluidity, and a significant deterioration in the foaming ratio and density of the foamed products.

[0005] For example, Chinese patent document CN 111057378 A discloses a foamed silicone rubber foam, its preparation method, and its application. This silicone rubber foam comprises: 55-70 parts vinyl silicone oil, 4-15 parts hydrogen-containing foaming agent, 8-15 parts fumed silica, 0.01-2 parts platinum catalyst, 0.001-1 parts reaction inhibitor, and 40-65 parts flame retardant powder. The flame retardant powder used in this technical solution is a mixture of one or two of aluminum hydroxide, magnesium hydroxide, decabromodiphenyl ether, and antimony oxide. According to Example 1, when the amount of flame retardant powder is 50 parts by mass, a V-0 flame retardant level can be achieved, but the foaming ratio is only 1.25 times; while in Example 3, when the amount of flame retardant powder is 44 parts by mass, the foaming ratio is 3.5 times, but only a V-1 flame retardant level can be achieved.

[0006] Therefore, there is an urgent need for a new type of flame retardant to match the foaming process of silicone rubber foam in order to overcome the shortcomings of existing technologies. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention discloses a method for preparing flame-retardant silicone rubber foam. A core-shell bimetallic hydroxide prepared using a specific process is used as a flame retardant, which, in conjunction with a flame-retardant ceramic masterbatch prepared using a specific process, synergistically retards the foam. The resulting flame-retardant silicone rubber foam achieves the highest flame retardant rating of UL94 V-0, with an oxygen index of not less than 32%, and also possesses high foaming ratio, low density, and excellent mechanical and thermal insulation properties.

[0008] The specific technical solution is as follows:

[0009] A method for preparing silicone rubber flame-retardant foam includes the following steps:

[0010] S1. Mix raw silicone rubber, silica and structure control agent to obtain compound;

[0011] S2. Mix the aforementioned compound rubber, flame retardant, flame retardant ceramic masterbatch and foaming agent, add vulcanizing agent after uniform mixing, and obtain silicone rubber flame retardant foam through foaming molding.

[0012] The flame retardant is prepared using the following steps:

[0013] (1) Mix monodisperse silica, intercalating agent and water to obtain solution A; mix soluble divalent metal salt and soluble trivalent metal salt with water to obtain solution B;

[0014] (2) Mix solution B with solution A, and keep the pH of the system alkaline during the mixing process. After the reaction, the core-shell bimetallic hydroxide is obtained through post-treatment.

[0015] (3) The core-shell bimetallic hydroxide is placed in an alkylsilane coupling agent solution and hydrophobically modified to obtain the flame retardant;

[0016] The flame-retardant ceramic masterbatch is prepared using the following steps:

[0017] (a) An aminosilane coupling agent, an organic solvent and deionized water are mixed and hydrolyzed to obtain a branched aminopolysiloxane ligand;

[0018] (b) The platinum catalyst is mixed with the branched aminopolysiloxane ligand to obtain a flame-retardant ceramic-forming agent;

[0019] (c) The flame-retardant ceramic-forming agent is mixed with silicone rubber to prepare the flame-retardant ceramic-forming masterbatch.

[0020] In the preparation method disclosed in this invention, a core-shell bimetallic hydroxide prepared by a specific process is used as a flame retardant, which, in conjunction with a flame-retardant ceramic masterbatch prepared by a specific process, synergistically retards the flame. The resulting silicone rubber flame-retardant foams all achieve the highest flame retardant rating of UL94V-0. Experiments revealed that if only the flame retardant or the flame-retardant ceramic masterbatch is used for flame retardancy, the prepared silicone rubber foam either does not self-extinguish or has a self-extinguishing time exceeding 100 seconds. Unexpectedly, the experiments also found that as the amount of flame retardant increases, while improving flame retardant performance, it does not lead to a deterioration in mechanical properties; on the contrary, it improves them simultaneously.

[0021] In step (S1):

[0022] Preferably, the raw silicone rubber is selected from methyl vinyl silicone rubber, and more preferably vinyl-terminated methyl vinyl silicone rubber.

[0023] Preferably, the molecular weight of the raw silicone rubber is 30-100W and the vinyl content is 0.03-5.0mol%; more preferably, the molecular weight is 50-60W and the vinyl content is 0.03-3.0mol%.

[0024] By adjusting the composition of the raw silicone rubber, the mechanical properties of the prepared flame-retardant silicone rubber foam, including tensile strength, elongation at break, and tear strength, can be controlled to meet different application requirements.

[0025] Preferably, the silica is selected from fumed silica, including hydrophilic fumed silica and hydrophobic fumed silica; more preferably, it is hydrophobic fumed silica.

[0026] Experiments have shown that, in the system of this invention, compared with hydrophilic fumed silica, the silicone rubber flame-retardant foam prepared with hydrophobic fumed silica has a higher foaming ratio and higher mechanical properties at the same foaming ratio.

[0027] Further preferably, the hydrophobic fumed silica is selected from hexamethyldisilazane-modified hydrophobic fumed silica; more preferably, it has a hydrophobic modification degree of more than 30%, such as 40%, 50%, 60%, 70%, etc.

[0028] Preferably, the primary particle size of the silica is 5-20 nm, and the specific surface area is 50-500 m². 2 / g; further preferably, the primary particle size is 5~10nm, and the specific surface area is 100~400m². 2 / g; more preferably, the primary particle size is 7nm and the specific surface area is 200m². 2 / g.

[0029] Preferably, the structure control agent is selected from one or more of hydroxyl silicone oil, diphenylsilanediol, diphenyldihydroxysilane, hydroxyl-terminated methylphenyl silicone oil, methoxy silicone oil, ethoxy silicone oil, dimethyldiethoxy silicone oil, methylphenyldiethoxysilane, methylphenyldimethoxysilane, tetramethylethylenedioxydimethylsilane, hexamethyldisilazane, hexamethylcyclotrisilazane, octamethylcyclotetrasilazane, fluorinated silazane, vinyl hydroxyl silicone oil, and borosilicate; more preferably, hydroxyl silicone oil.

[0030] Preferably, based on 100 parts by weight of raw silicone rubber, the amount of silica is 1 to 50 parts by weight, and the amount of structure control agent is 0.1 to 10 parts by weight.

[0031] Further optimization involves using 20-40 parts by weight of silica and 2-8 parts by weight of structure control agent.

[0032] More preferably, the amount of silica used is 30 parts by mass and the amount of structure control agent used is 5 parts by mass.

[0033] In step (S2):

[0034] Preferably, the foaming agent is selected from common types in the art, such as one or more of azodicarbonamide (AC foaming agent), 4,4'-oxobisbenzenesulfonyl hydrazine (OBSH foaming agent), sodium bicarbonate, N,N'-dinitrospentamethylenetetramine (H foaming agent), azobisisobutyronitrile, and expanded microsphere foaming agents.

[0035] Preferably, the vulcanizing agent is selected from common types in the art, such as one or more of 2,4-dichlorobenzoyl peroxide (bis(2,4-dichlorobenzoyl)peroxide (BPO), dicumyl peroxide (DCP), di-tert-butyl peroxide (BIPB), and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (bis(2,5-dichlorobenzoyl)peroxide (B ...

[0036] The preparation method disclosed in this invention can be adapted to different foaming molding processes, such as compression molding, extrusion molding, or calendering molding.

[0037] Preferably, based on 100 parts by weight of raw silicone rubber, the amount of flame retardant is 8-50 parts by weight, the amount of flame retardant ceramic masterbatch is 3-8 parts by weight, the amount of foaming agent is 0.1-50 parts by weight, and the amount of vulcanizing agent is 0.5-3 parts by weight.

[0038] Further preferred, the amount of flame retardant is 8-20 parts by weight, and the amount of flame retardant ceramic masterbatch is 3-5 parts by weight; more preferably, the amount of flame retardant is 15 parts by weight, and the amount of flame retardant ceramic masterbatch is 5 parts by weight.

[0039] In step (1):

[0040] Preferably, the intercalating agent is selected from polysilsesquioxanes; specifically, one or more of random polysilsesquioxanes, ladder-type polysilsesquioxanes, cage-type polysilsesquioxanes, and partially cage-type polysilsesquioxanes; more preferably, the intercalating agent is selected from ladder-type polysilsesquioxanes, such as ladder-type phenylsulfonic acid polysilsesquioxanes.

[0041] In the preparation process of core-shell bimetallic hydroxides, inorganic anions, such as sodium chloride, are often added as intercalating agents. Experiments have shown that in the system of this invention, if the core-shell bimetallic hydroxide obtained using this conventional preparation method is used as a flame retardant after hydrophobic modification, the flame retardant performance will significantly decrease. The reason for this may be that the core-shell bimetallic hydroxide prepared with this conventional intercalating agent is deactivated during the silicone rubber processing, leading to a decrease in the flame retardant rating.

[0042] Preferably, the mass ratio of monodisperse silica, intercalating agent and water is 1:(0.1~10):(10~50); more preferably 1:0.5:20.

[0043] Preferably, the divalent metal in the soluble divalent metal salt is selected from one or more of divalent zinc, divalent magnesium, divalent calcium, divalent copper, divalent cobalt, divalent nickel, divalent iron, divalent manganese, divalent vanadium, divalent cadmium, divalent strontium, and divalent barium;

[0044] Preferably, the trivalent metal in the soluble trivalent metal salt is selected from one or more of trivalent aluminum, trivalent iron, trivalent chromium, trivalent manganese, trivalent gallium, trivalent indium, trivalent vanadium, trivalent cobalt, trivalent gadolinium, trivalent titanium, and trivalent nickel;

[0045] Experiments have shown that the specific surface area of ​​the prepared flame retardant can be controlled by changing the types of divalent and trivalent metals, thereby affecting the performance of the final prepared silicone rubber flame retardant foam.

[0046] Further preferably, the divalent metal is selected from divalent cobalt, and the trivalent metal is selected from trivalent iron.

[0047] Preferably, the mass ratio of soluble trivalent metal salt, soluble divalent metal salt and water is 1:(1~5):(10~50); more preferably, the mass ratio is 1:4:(10~20).

[0048] In step (2):

[0049] Preferably, the mass ratio of solution B to solution A is 1:(0.5~2);

[0050] Preferably, the pH of the system is maintained at 10-13 during the mixing process;

[0051] Preferably, the post-processing includes filtration, washing, and drying;

[0052] In step (3):

[0053] Preferably, the concentration of the alkylsilane coupling agent solution is 10-20% (v / v).

[0054] Preferably, the alkylsilane coupling is selected from γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, octyltriethoxysilane, dodecyltriethoxysilane, hexadecyltriethoxysilane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, hexamethyldisilazane, vinyltriethoxysilane, dimethyldimethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, propyltrimethoxysilane, preferably methyltriethoxysilane, vinyltriethoxysilane, and hexamethyldisilazane;

[0055] Preferably, the solvent is selected from one or more of ethanol, methanol, isopropanol, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, toluene, xylene, n-hexane, cyclohexane, petroleum ether, dichloromethane, acetone, and butanone.

[0056] Preferably, the hydrophobic modification time is 12-24 hours; stirring is maintained during the hydrophobic modification process.

[0057] Preferably, the hydrophobically modified crude product also needs to be dried.

[0058] In step (a):

[0059] Preferably, the aminosilane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane.

[0060] Preferably, the organic solvent is selected from one or more of ethanol, methanol, isopropanol, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, toluene, xylene, n-hexane, cyclohexane, petroleum ether, dichloromethane, acetone, and butanone.

[0061] Preferably, the mass ratio of aminosilane coupling agent, organic solvent and deionized water is 1:(1~30):(0.01~1); more preferably, the mass ratio of the three is 1:(1~5):(0.1~1); even more preferably, it is 1:2:0.2.

[0062] Preferably, the hydrolysis is carried out at a temperature of 50~70℃ for 2~5 hours.

[0063] The branched aminopolysiloxane ligand obtained after hydrolysis has the chemical structure shown in formula (Ⅰ):

[0064] (I);

[0065] In the formula, R1 is a C1-C10 branched alkyl, straight-chain alkyl, or phenylalkyl containing an amino group, and R2 is a methoxy or ethoxy group.

[0066] In step (b):

[0067] Preferably, the mass ratio of platinum catalyst to branched aminopolysiloxane ligand is 1:(1~100); more preferably, it is 1:10.

[0068] In step (c):

[0069] The silicone rubber is selected from methyl vinyl silicone rubber. The specific type may be the same as or different from the raw silicone rubber in step S1.

[0070] Preferably, the flame retardant ceramic agent accounts for 50-70% of the total mass of the flame retardant ceramic masterbatch, which is 100% of the total mass.

[0071] Experiments have shown that if the branched aminopolysiloxane coordinating agent is not added, i.e., the platinum catalyst and silicone rubber are directly used to prepare the masterbatch instead of the flame-retardant ceramic masterbatch prepared by the specific process in this invention; or if the aminosilane coupling agent is not hydrolyzed, i.e., the aminosilane coupling agent and platinum catalyst are directly mixed to prepare the flame-retardant ceramic masterbatch instead of the flame-retardant ceramic masterbatch prepared by the specific process in this invention, the flame-retardant properties of the prepared silicone rubber flame-retardant foam will be significantly reduced.

[0072] More preferably, the aminosilane coupling agent is selected from N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane and / or N-β-(aminoethyl)-γ-aminopropyltriethoxysilane.

[0073] In the preparation method of silicone rubber flame retardant foam disclosed in this invention, other additives may be added as needed, including heat resistant agents such as cerium oxide; anti-yellowing agents such as benzotriazoles; colorants such as carbon black and iron oxide red; and release agents such as natural wax and synthetic wax.

[0074] The present invention also discloses silicone rubber flame-retardant foam prepared according to the above method, all of which achieve the UL94 V-0 flame retardant rating and have a limiting oxygen index of not less than 32%.

[0075] Preferably, the density of the silicone rubber flame-retardant foam is in the range of 0.1–0.8 g / cm³. 3 More preferably, it is 0.3–0.5 g / cm³. 3The bubbles can be open, closed, or semi-open.

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] This invention discloses a method for preparing flame-retardant silicone rubber foam, which involves synergistic flame retardancy using a core-shell bimetallic hydroxide flame retardant prepared by a specific process and a flame-retardant ceramic masterbatch prepared by a specific process. The flame retardant prepared by this specific process has a large specific surface area and excellent dispersibility in silicone rubber, resulting in relatively transparent silicone rubber products. The catalyst is also relatively stable, and after synergistic flame retardancy with the flame-retardant ceramic masterbatch, the prepared synergistic flame retardant can achieve a UL94 V-0 flame retardancy rating with a limiting oxygen index of not less than 32%. At the same time, as the amount of the flame retardant increases, the flame retardant performance is improved while the mechanical properties of the flame-retardant silicone rubber foam are also improved simultaneously without affecting its foaming ratio.

[0078] The silicone rubber flame-retardant foam prepared by this invention not only achieves excellent flame-retardant properties, but also overcomes the shortcomings of traditional hot-cured silicone rubber, such as difficulty in foaming and high density. Furthermore, it maintains excellent tensile strength, elongation at break, and tear resistance, making the hot-cured silicone rubber foam material more promising for application in high-temperature environments with greater mechanical loads. Attached Figure Description

[0079] Figure 1 TEM images of the flame retardant prepared in Example 1 at different magnifications;

[0080] Figure 2 The image shows a SEM image of the flame retardant prepared in Example 1. Detailed Implementation

[0081] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially. The features and performance of the present invention will be further described in detail below with reference to the embodiments.

[0082] Example 1

[0083] Step 1: In a reactor, 450 parts by weight of anhydrous ethanol and 100 parts by weight of a 36 wt% ammonia solution were added and mixed thoroughly. The temperature was maintained at 50°C for 5 minutes. Then, 30 parts by weight of tetraethyl orthosilicate were added. The mixture was stirred at 500 rpm for 1 hour at 50°C. Subsequently, stirring was continued for 4 hours in an air atmosphere at 25°C to volatilize the ammonia. The resulting silica was collected by centrifugation and washed three times with ethanol. Finally, it was dried at 70°C for 12 hours to obtain monodisperse silica with an average particle size of 250 nm.

[0084] Step 2: Add 100 parts by mass of monodisperse silica and 2000 parts by mass of deionized water to the reactor and place it at room temperature. Disperse the mixture by ultrasonic treatment for 30 minutes. Then add 50 parts by mass of ladder-type phenylsulfonic acid-based polysilsesquioxane (preparation method according to reference in application publication number CN 120349515 A), followed by ultrasonic dispersion for another 10 minutes to form solution A. Dissolve 120 parts by mass of ferric chloride hexahydrate and 480 parts by mass of cobalt chloride hexahydrate in 2000 parts by mass of deionized water to form solution B. Subsequently, add solution B dropwise to solution A and stir at 500 r / min. Throughout the addition process, maintain the pH at 11.0 using sodium hydroxide solution. After the addition is complete, continue stirring for 1 hour. Collect the resulting precipitate by centrifugation and wash three times with deionized water. Dry the precipitate at 80°C for 12 hours. Finally, the dried hydrophilic core-shell bimetallic hydroxide was added to an ethanol solution containing 10% (v / v) methyltriethoxysilane, stirred continuously for 12 hours, and dried at 80°C to obtain a hydrophobic core-shell bimetallic hydroxide as a flame retardant.

[0085] Tests showed that the specific surface area of ​​this flame retardant is 253 m². 2 / g.

[0086] Figure 1 These are TEM images of the flame retardant prepared in this embodiment at different magnifications. Figure 2 The image shows an SEM image of the flame retardant prepared in this embodiment. It is observed that the flame retardant prepared in this embodiment has a core-shell structure, with a semi-solid silica core having a diameter of 230 nm and a thin layer of bimetallic hydroxide on the outside having a sheet particle size of 150 nm.

[0087] Step 3: Add 200 parts by weight of N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, 40 parts by weight of deionized water, and 400 parts by weight of anhydrous ethanol to the reactor. Then, heat the reactor to 60°C and react for 4 hours. Finally, evaporate to remove the solvent, obtaining a colorless oily product: a branched aminopolysiloxane ligand.

[0088] Step 4: Add 10 parts by weight of commercially available platinum catalyst to 100 parts by weight of branched amino polysiloxane ligand, stir for 12 hours to obtain flame retardant ceramic agent.

[0089] Step 5: Prepare a ceramic masterbatch containing 50% flame retardant ceramic agent by mixing 50 parts by mass of flame retardant ceramic agent with 50 parts by mass of methyl vinyl silicone rubber (molecular weight of 500,000 and vinyl content of 0.22 mol%) in an internal mixer.

[0090] Step 6: Add 100 parts by weight of methyl vinyl silicone rubber raw material (molecular weight 500,000, vinyl content 0.22 mol%) to a mixer, and add 30 parts by weight of hexamethyldisilazane modified hydrophobic fumed silica (particle size 7 nm, specific surface area 200 m²). 2 / g, hexamethyldisilazane hydrophobic modification degree 60%), add 5 parts by weight of hydroxyl silicone oil (viscosity 30cst, hydroxyl value 9%), mix at 80℃ for 30 minutes and discharge, place the compound in an oven at 150℃ for 4 hours, and then store at room temperature.

[0091] Step 7: Place the rubber compound prepared in Step 6 into a two-roll mill for back-mixing. After the rubber compound softens and is rolled, add 15 parts by weight of flame retardant, 5 parts by weight of flame retardant ceramic masterbatch and 5 parts by weight of OBSH foaming agent. After mixing evenly, add 1.2 parts by weight of bis(2,5) vulcanizing agent.

[0092] Step 8: Use compression molding at 160℃ for 10 minutes to obtain silicone rubber flame retardant foam.

[0093] Example 2

[0094] The preparation process is basically the same as in Example 1, except that:

[0095] In step 7, the foaming agent is replaced with an equal mass of microsphere foaming agent;

[0096] In step 8, extrusion foaming molding is used at a temperature of 130°C, the rear baking temperature is 200°C, and the speed is 3m / min.

[0097] Example 3

[0098] The preparation process is basically the same as in Example 1, except for step 2:

[0099] Replace ferric chloride hexahydrate with an equal part by mass of aluminum chloride hexahydrate, and replace cobalt chloride hexahydrate with an equal part by mass of magnesium chloride hexahydrate.

[0100] The flame retardant prepared in this embodiment has a specific surface area of ​​167 m², as tested. 2 / g.

[0101] Example 4

[0102] The preparation process is basically the same as in Example 1, except for step 7:

[0103] Replace the amount of flame retardant with 8 parts by weight.

[0104] Example 5

[0105] The preparation process is basically the same as in Example 1, except for step 7:

[0106] Replace the amount of flame retardant with 20 parts by weight.

[0107] Example 6

[0108] The preparation process is basically the same as in Example 1, except for step 6:

[0109] Replace the silica with an equal part by mass of hydrophilic fumed silica (particle size 7 nm, specific surface area 200 m²). 2 / g).

[0110] Example 7

[0111] The preparation process is basically the same as in Example 1, except for step 6:

[0112] Replace the silica with an equal mass of hydrophobic fumed silica (7 nm particle size, 200 m² / g) with a hydrophobic modification degree of 30% by hexamethyldisilazane.

[0113] Example 8

[0114] The preparation process is basically the same as in Example 1, except for step 3:

[0115] Replace N-β-(aminoethyl)-γ-aminopropyltriethoxysilane with an equal part by mass of γ-aminopropyltriethoxysilane.

[0116] Example 9

[0117] The preparation process is basically the same as in Example 1, except for step 6:

[0118] Replace 100 parts by weight of methyl vinyl silicone rubber raw material with a mixture of 95 parts by weight of methyl vinyl silicone rubber raw material (molecular weight of 500,000, vinyl content of 0.03 mol%) and 5 parts by weight of methyl vinyl silicone rubber raw material (molecular weight of 450,000, vinyl content of 3.0 mol%).

[0119] Comparative Example 1

[0120] The preparation process is basically the same as in Example 1, except that:

[0121] Flame-retardant ceramic masterbatch was not prepared, i.e. steps 3 to 5 were not performed;

[0122] In step 7, no flame-retardant ceramic masterbatch was added; the amount of flame retardant was replaced with 20 parts by weight.

[0123] Comparative Example 2

[0124] The preparation process is basically the same as in Example 1, except that:

[0125] Flame retardant was not prepared, i.e. steps 1-2 were not performed;

[0126] In step 7, no flame retardant was added; the amount of flame retardant ceramic masterbatch was replaced with 20 parts by weight.

[0127] Comparative Example 3

[0128] Steps 1-2: exactly the same as in Example 1;

[0129] Step 3: Prepare a platinum-containing masterbatch by mixing 4.5 parts by mass of platinum catalyst and 95.5 parts by mass of methyl vinyl silicone rubber (molecular weight of 500,000, vinyl content of 0.22 mol%) in an internal mixer;

[0130] Step 4: Add 100 parts by weight of methyl vinyl silicone rubber raw material (molecular weight 500,000, vinyl content 0.22 mol%) to a mixer, and add 30 parts by weight of hexamethyldisilazane modified hydrophobic fumed silica (particle size 7 nm, specific surface area 200 m²). 2 / g, hexamethyldisilazane hydrophobic modification degree 60%), add 5 parts by weight of hydroxyl silicone oil (viscosity 30cst, hydroxyl value 9%), mix at 80℃ for 30 minutes and discharge, place the compound in an oven at 150℃ for 4 hours, and then store at room temperature.

[0131] Step 5: Place the rubber compound prepared in Step 4 into a two-roll mill for back-mixing. After the rubber compound has softened and been rolled, add 15 parts by weight of flame retardant, 5 parts by weight of platinum-containing masterbatch and 5 parts by weight of OBSH foaming agent. After mixing evenly, add 1.2 parts by weight of bis(2,5) vulcanizing agent.

[0132] Step 6: Use compression molding at 160℃ for 10 minutes.

[0133] Comparative Example 4

[0134] Steps 1-2: exactly the same as in Example 1;

[0135] Step 3: Add 10 parts by weight of commercially available platinum catalyst to 100 parts by weight of N-β-(aminoethyl)-γ-aminopropyltriethoxysilane and stir for 12 hours to obtain flame retardant ceramic agent;

[0136] Step 4: Mix 50 parts by weight of the flame retardant ceramic-forming agent prepared in Step 3 with 50 parts by weight of methyl vinyl silicone rubber (molecular weight of 500,000, vinyl content of 0.22 mol%) in an internal mixer to prepare a ceramic-forming masterbatch containing 50% flame retardant ceramic-forming agent.

[0137] Step 5: Add 100 parts by weight of methyl vinyl silicone rubber raw material (molecular weight 500,000, vinyl content 0.22 mol%) to a mixer, and add 30 parts by weight of hexamethyldisilazane modified hydrophobic fumed silica (particle size 7 nm, specific surface area 200 m²). 2 / g, hexamethyldisilazane hydrophobic modification degree 60%), add 5 parts by weight of hydroxyl silicone oil (viscosity 30cst, hydroxyl value 9%), mix at 80℃ for 30 minutes and discharge, place the compound in an oven at 150℃ for 4 hours, and then store at room temperature.

[0138] Step 6: Place the rubber compound prepared in Step 5 into a two-roll mill for back-mixing. After the rubber compound softens and is rolled, add 15 parts by weight of flame retardant, 5 parts by weight of flame retardant ceramic masterbatch and 5 parts by weight of OBSH foaming agent. After mixing evenly, add 1.2 parts by weight of bis(2,5) vulcanizing agent.

[0139] Step 7: Use compression molding at 160℃ for 10 minutes.

[0140] Comparative Example 5

[0141] The preparation process is basically the same as that of Comparative Example 4, except for step 6:

[0142] Replace the amount of flame-retardant ceramic masterbatch with 8 parts by weight.

[0143] Comparative Example 6

[0144] The preparation process is basically the same as in Example 1, except for step 2:

[0145] Replace the ladder-type phenylsulfonic acid-based polysilsesquioxane with an equal part by mass of sodium chloride.

[0146] The flame retardant prepared in this comparative example has a specific surface area of ​​75 m². 2 / g.

[0147] Comparative Example 7

[0148] Step 1: Add 100 parts by weight of methyl vinyl silicone rubber raw material (molecular weight 500,000, vinyl content 0.22 mol%) to a mixer, and add 30 parts by weight of hexamethyldisilazane modified hydrophobic fumed silica (particle size 7 nm, specific surface area 200 m²). 2 / g, hexamethyldisilazane hydrophobic modification degree 60%), add 5 parts by weight of hydroxyl silicone oil (viscosity 30cst, hydroxyl value 9%), mix at 80℃ for 30 minutes and discharge, place the compound in an oven at 150℃ for 4 hours, and then store at room temperature.

[0149] Step 2: Place the rubber compound prepared in Step 1 into a two-roll mill for back-mixing. After the rubber compound has softened and rolled, add 20 parts by weight of aluminum hydroxide and 5 parts by weight of OBSH foaming agent. After mixing evenly, add 1.2 parts by weight of bis(2,5)-pentachlor vulcanizing agent.

[0150] Step 3: Use compression molding at 160℃ for 10 minutes.

[0151] Comparative Example 8

[0152] Step 1: Add 100 parts by weight of methyl vinyl silicone rubber raw material (molecular weight 500,000, vinyl content 0.22 mol%) to a mixer, and add 30 parts by weight of hexamethyldisilazane modified hydrophobic fumed silica (particle size 7 nm, specific surface area 200 m²). 2 / g, hexamethyldisilazane hydrophobic modification degree 60%), add 5 parts by weight of hydroxyl silicone oil (viscosity 30cst, hydroxyl value 9%), mix at 80℃ for 30 minutes and discharge, place the compound in an oven at 150℃ for 4 hours, and then store at room temperature.

[0153] Step 2: Place the rubber compound prepared in Step 1 into a two-roll mill for back-mixing. After the rubber compound softens and is rolled, add 20 parts by weight of magnesium aluminum hydrotalcite and 5 parts by weight of OBSH foaming agent. After mixing evenly, add 1.2 parts by weight of bis(2,5) vulcanizing agent.

[0154] Step 3: Use compression molding at 160℃ for 10 minutes.

[0155] Performance testing:

[0156] Expansion ratio: The test standard refers to GB / T 6343-2009;

[0157] Density: The test standard refers to GB / T 6343;

[0158] Tensile strength and elongation at break: Test standards refer to GB / T 528-2009;

[0159] Tear strength: The test standard is based on GB / T 529-2008;

[0160] Rubber compound modulus: tested using a rotational rheometer;

[0161] Compression set: Test standard refers to GB / T 7759;

[0162] Flame retardant performance: including vertical burning test parameters GB / T 2408-2021, limiting oxygen index test according to GB / T2406; thermal conductivity test standard according to GB / T 10297.

[0163] The test data for each embodiment and comparative example are listed in Table 1 below:

[0164] Table 1

[0165]

[0166] As can be seen from the data in Table 1, the hydrophobic core-shell bimetallic hydroxide flame retardant in this invention synergistically retards the ceramic masterbatch, enabling the prepared silicone rubber flame retardant foam to achieve a UL94 V-0 flame retardant rating, and also exhibiting high foaming ratio, low density, high mechanical strength, and thermal insulation properties.

[0167] Examples 1 and 2 show that the preparation method of the silicone rubber flame-retardant foam of the present invention can be applied to molding and extrusion processes and has excellent processing performance.

[0168] Comparing Examples 1 and 3 shows that the specific surface area of ​​the flame retardant can be controlled by changing the type of outer metal. The catalyst prepared with trivalent iron and divalent cobalt in Example 1 has a higher specific surface area and a more significant improvement in the tensile properties of silicone rubber.

[0169] Comparative examples 1 and 4-5 show that even with a flame retardant addition amount as low as 8 parts by weight, the prepared silicone rubber flame-retardant foam can achieve the highest flame retardant rating of UL-94 V-0. It was also unexpectedly found that the mechanical properties of the prepared silicone rubber flame-retardant foam increased with increasing flame retardant dosage; however, due to cost considerations, the preferred catalyst dosage is 8-20 parts by weight.

[0170] Comparing Examples 1 and 6-7, it is shown that, compared to the hydrophilic silica of Example 6, the preparation system disclosed in this invention preferably uses hydrophobic fumed silica. This not only reduces the modulus of the compound but also helps to obtain silicone rubber foam with a higher foaming ratio. To achieve the same foaming ratio, silicone rubber foam prepared using hydrophobic fumed silica exhibits superior mechanical properties. Furthermore, among hydrophobic fumed silica, the silicone rubber foam prepared using hexamethyldisilazane, which has a higher degree of hydrophobic modification, in Example 1 exhibits superior overall performance. In addition, the density of the flame-retardant silicone rubber foam prepared by this invention is basically the same as that of liquid silicone rubber foam, but it has higher tensile strength and elongation at break. Therefore, the heat-cured flame-retardant silicone rubber foam of this invention has higher application value in low-density and high-mechanical-load scenarios.

[0171] Comparative examples 1 and 8 show that, under the same mass fraction, the flame-retardant ceramic masterbatch prepared using N-β-(aminoethyl)-γ-aminopropyltriethoxysilane with a higher nitrogen content results in a silicone rubber flame-retardant foam with superior performance.

[0172] Example 9 provides a tear-resistant formulation through optimization of the raw rubber composition. The silicone rubber flame-retardant foam obtained by this invention still retains high tear strength at low density.

[0173] Comparative Examples 1 and 2 show that in the system of the present invention, flame retardants and flame-retardant ceramic masterbatches cannot exert a good flame retardant effect on silicone rubber on their own and must be used in combination. This is also the key factor of synergistic flame retardancy in the present invention.

[0174] Comparing Example 1 and Comparative Examples 3-5, Comparative Example 3 demonstrates the crucial role of branched amino polysiloxane ligands in flame-retardant ceramic-forming agents, as the amino group can protect the high reactivity of platinum at high temperatures. Comparative Example 4 shows that, when used as a platinum ligand, branched amino polysiloxane ligands exhibit a higher flame-retardant rating compared to amino silane coupling agents. Comparative Example 5 shows that increasing the amount of flame-retardant ceramic-forming masterbatch prepared with amino silane coupling agents can improve the flame-retardant rating of silicone rubber flame-retardant foam, but it compromises mechanical properties. Therefore, the use of branched amino polysiloxane ligands to prepare the flame-retardant ceramic-forming masterbatch in this invention is crucial for achieving silicone rubber flame-retardant foam with excellent flame-retardant, foaming, and mechanical properties.

[0175] Comparative Examples 1 and 6 demonstrate the crucial role of the ladder-type phenylsulfonic acid-based polysilsesquioxane intercalating agent in the flame retardant of this invention. While commonly used inorganic anions can successfully prepare core-shell structured bimetallic hydroxides using intercalating agents, they are not suitable for use as flame retardants in the silicone rubber foam applications of this invention. The reason for this may be that the ladder-type phenylsulfonic acid-based polysilsesquioxane improves the thermal stability of the bimetallic hydroxide nanoparticles, maintaining the thermal decomposition temperature above 200°C, thus ensuring stability and preventing decomposition during the thermal vulcanization of silicone rubber. Commonly used anions form unstable bimetallic hydroxides, which deactivate during silicone rubber processing, resulting in a decrease in flame retardant rating.

[0176] Comparative Examples 7 and 8 used commercially available unmodified magnesium aluminum hydrotalcite and aluminum hydroxide as single flame retardants. The addition of 20 parts by weight was insufficient to make the silicone rubber foam reach the UL-94 V-0 flame retardant rating.

[0177] In summary, the core-shell bimetallic hydroxide prepared by a specific process proposed in this invention, together with the flame-retardant ceramic masterbatch prepared by a specific process, exhibits a superior synergistic flame-retardant effect on silicone rubber. Furthermore, the silicone rubber possesses excellent processing performance, mechanical properties, and thermal insulation properties.

[0178] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. The specific examples used above to illustrate the present invention are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Those skilled in the art to which this invention pertains can make several simple deductions, modifications, substitutions, or combinations based on the concept of the present invention. These deductions, modifications, substitutions, or combinations also fall within the scope of the claims of the present invention.

Claims

1. A method for preparing silicone rubber flame-retardant foam, characterized in that, Includes the following steps: S1. Mix raw silicone rubber, silica and structure control agent to obtain compound; S2. Mix the aforementioned compound rubber, flame retardant, flame retardant ceramic masterbatch and foaming agent, add vulcanizing agent after uniform mixing, and obtain silicone rubber flame retardant foam through foaming molding. The flame retardant is prepared using the following steps: (1) Mix monodisperse silica, intercalating agent and water to obtain solution A; mix soluble divalent metal salt and soluble trivalent metal salt with water to obtain solution B; (2) Mix solution B with solution A, and keep the pH of the system alkaline during the mixing process. After the reaction, the core-shell bimetallic hydroxide is obtained through post-treatment. (3) The core-shell bimetallic hydroxide is placed in an alkylsilane coupling agent solution and hydrophobically modified to obtain the flame retardant; The flame-retardant ceramic masterbatch is prepared using the following steps: (a) An aminosilane coupling agent, an organic solvent and deionized water are mixed and hydrolyzed to obtain a branched aminopolysiloxane ligand; (b) The platinum catalyst is mixed with the branched aminopolysiloxane ligand to obtain a flame-retardant ceramic-forming agent; (c) The flame-retardant ceramic-forming agent is mixed with silicone rubber to prepare the flame-retardant ceramic-forming masterbatch.

2. The method for preparing silicone rubber flame-retardant foam according to claim 1, characterized in that, In step (S1): The raw silicone rubber is selected from methyl vinyl silicone rubber, with a molecular weight of 30~100W and a vinyl content of 0.03~5.0 mol%; The silica is selected from fumed silica, with a primary particle size of 5-20 nm and a specific surface area of ​​50-500 m². 2 / g; The structure control agent is selected from one or more of the following: hydroxyl silicone oil, diphenylsilanediol, diphenyldihydroxysilane, hydroxyl-terminated methylphenyl silicone oil, methoxy silicone oil, ethoxy silicone oil, dimethyldiethoxy silicone oil, methylphenyldiethoxysilane, methylphenyldimethoxysilane, tetramethylethylenedioxydimethylsilane, hexamethyldisilazane, hexamethylcyclotrisilazane, octamethylcyclotetrasilazane, fluorinated silazane, vinyl hydroxyl silicone oil, and borosilicate. Based on 100 parts by weight of raw silicone rubber, the amount of silica is 1 to 50 parts by weight, and the amount of structure control agent is 0.1 to 10 parts by weight.

3. The method for preparing silicone rubber flame-retardant foam according to claim 1, characterized in that, In step (S2): The foaming agent is selected from one or more of azodicarbonamide, 4,4'-oxobis(benzenesulfonylhydrazine), sodium bicarbonate, N,N'-dinitrospentamethylenetetramine, azobisisobutyronitrile, and expanded microsphere foaming agents. The vulcanizing agent is selected from one or more of 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; The foaming process is selected from compression molding, extrusion molding, or calendering molding. Based on 100 parts by weight of raw silicone rubber, the amount of flame retardant is 8-50 parts by weight, the amount of flame retardant ceramic masterbatch is 3-8 parts by weight, the amount of foaming agent is 0.1-50 parts by weight, and the amount of vulcanizing agent is 0.5-3 parts by weight.

4. The method for preparing silicone rubber flame-retardant foam according to claim 1, characterized in that, In step (1): The intercalating agent is selected from polysilsesquioxane; The mass ratio of monodisperse silica, intercalating agent and water is 1:(0.1~10):(10~50); The divalent metal in the soluble divalent metal salt is selected from one or more of the following: zinc, magnesium, calcium, copper, cobalt, nickel, iron, manganese, vanadium, cadmium, strontium, and barium. The trivalent metal in the soluble trivalent metal salt is selected from one or more of trivalent aluminum, trivalent iron, trivalent chromium, trivalent manganese, trivalent gallium, trivalent indium, trivalent vanadium, trivalent cobalt, trivalent gadolinium, trivalent titanium, and trivalent nickel; The mass ratio of soluble trivalent metal salts, soluble divalent metal salts and water is 1:(1~5):(10~50).

5. The method for preparing silicone rubber flame-retardant foam according to claim 1, characterized in that, In step (2): The mass ratio of solution B to solution A is 1:(0.5~2); Maintain the pH of the system at 10-13 during the mixing process; The post-processing includes filtration, washing, and drying; In step (3): The volume concentration of the alkylsilane coupling agent solution is 10-20%; The alkylsilane coupling is selected from γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, octyltriethoxysilane, dodecyltriethoxysilane, hexadecyltriethoxysilane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, hexamethyldisilazane, vinyltriethoxysilane, dimethyldimethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, propyltrimethoxysilane, preferably methyltriethoxysilane, vinyltriethoxysilane, and hexamethyldisilazane; The solvent is selected from one or more of the following: ethanol, methanol, isopropanol, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, toluene, xylene, n-hexane, cyclohexane, petroleum ether, dichloromethane, acetone, and butanone; The hydrophobic modification time is 12~24h; The crude product after hydrophobic modification still needs to be dried.

6. The method for preparing silicone rubber flame-retardant foam according to claim 1, characterized in that, In step (a): The aminosilane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane. The organic solvent is selected from one or more of the following: ethanol, methanol, isopropanol, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, toluene, xylene, n-hexane, cyclohexane, petroleum ether, dichloromethane, acetone, and butanone. The mass ratio of aminosilane coupling agent, organic solvent and deionized water is 1:(1~30):(0.01~1); The hydrolysis is carried out at a temperature of 50~70℃ for 2~5 hours.

7. The method for preparing silicone rubber flame-retardant foam according to claim 1, characterized in that, In step (b): The mass ratio of platinum catalyst to branched aminopolysiloxane ligand is 1:(1~100). In step (c): Based on the total mass of flame-retardant ceramic masterbatch as 100%, the mass ratio of flame-retardant ceramic agent is 50-70%.

8. The method for preparing silicone rubber flame-retardant foam according to any one of claims 1 to 7, characterized in that: In step (1), the divalent metal is selected from divalent cobalt, and the trivalent metal is selected from trivalent iron; In step (a), the aminosilane coupling agent is selected from N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane and / or N-β-(aminoethyl)-γ-aminopropyltriethoxysilane.

9. The method for preparing silicone rubber flame-retardant foam according to claim 8, characterized in that, Based on 100 parts by weight of raw silicone rubber, the amount of flame retardant is 8 to 20 parts by weight, and the amount of flame retardant ceramic masterbatch is 3 to 5 parts by weight.

10. A silicone rubber flame-retardant foam prepared according to any one of claims 1 to 9, characterized in that, It meets the UL94 V-0 flame retardant rating and has a limiting oxygen index of not less than 32%.

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