A flame retardant silicone rubber resistant to long-term heat aging and preparation method thereof

Abstract

The present invention belongs to the technical field of flame retardant silicone rubber, and specifically relates to a flame retardant silicone rubber resistant to long-term heat aging and a preparation method thereof. The flame retardant silicone rubber provided by the present invention comprises the following raw materials, by weight: 40-60 parts of methyl vinyl silicone rubber with a vinyl content of 0.04-0.06%, 40-60 parts of methyl vinyl silicone rubber with a vinyl content of 0.2-0.24%, 50-60 parts of fumed silica, 5-12 parts of hydroxy silicone oil, 3-10 parts of hydrogen-containing silicone oil, 30-45 parts of modified expandable graphite, 1-5 parts of vulcanizing agent, and 0.01-0.05 parts of platinum complex. The present invention adopts modified expandable graphite as a flame retardant, and at the same time cooperates with methyl vinyl silicone rubber with a specific vinyl content, fumed silica, hydroxy silicone oil, hydrogen-containing silicone oil, vulcanizing agent and platinum complex, and the flame retardant silicone rubber prepared has excellent mechanical strength and high temperature resistance while having excellent flame retardant properties.

Description

Technical Field

[0001] The invention belongs to the technical field of flame-retardant silicone rubber, and in particular relates to a flame-retardant silicone rubber resistant to long-term heat aging and a preparation method thereof. Background Art

[0002] As a polymer material that is resistant to high temperatures, chemical reagents, and has excellent electrical insulation properties, silicone rubber is widely used in high-voltage power transmission and transformation and other fields. Silicone rubber will burn when exposed to fire, and will further degrade in a burning environment. Therefore, it is necessary to develop a silicone rubber with good flame retardant properties. At present, in order to improve the flame retardant properties of silicone rubber, the main method is to add flame retardants to silicone rubber. The flame retardants are classified by type, including physical expansion flame retardants and chemical expansion flame retardants. Chemical expansion flame retardants mainly use carbon sources to be dehydrated and carbonized by heat to form a porous carbon layer, which isolates air and heat transfer, thereby achieving a flame retardant effect. However, the flame retardant efficiency of chemical expansion flame retardants is low. Therefore, the research on physical expansion flame retardants has become a hot topic.

[0003] Expandable graphite has a wide range of sources and can be used as a physical expansion flame retardant in the flame retardancy of silicone rubber. Expandable graphite will expand dozens or even hundreds of times when heated in a high temperature environment, forming a protective layer with a "worm-like" structure. While absorbing heat, it can also block the transfer of heat, thereby achieving a flame retardant effect. However, expandable graphite is prone to excessive expansion in a high-temperature combustion environment, resulting in a loose carbon layer, which affects the flame retardant effect. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that when expandable graphite is used as a silicone rubber flame retardant, the expandable graphite is prone to excessive expansion in a high-temperature combustion environment, resulting in a loose carbon layer and affecting the flame retardant effect, and thus provide a flame retardant silicone rubber resistant to long-term heat aging and a preparation method thereof.

[0005] In order to solve the above problems, the scheme of the present invention is as follows:

[0006] A flame retardant silicone rubber, comprising the following raw materials in parts by weight:

[0007] 40-60 parts of methyl vinyl silicone rubber with a vinyl content of 0.04-0.06%, 40-60 parts of methyl vinyl silicone rubber with a vinyl content of 0.2-0.24%, 50-60 parts of fumed silica, 5-12 parts of hydroxy silicone oil, 3-10 parts of hydrogen-containing silicone oil, 30-45 parts of modified expandable graphite, 1-5 parts of vulcanizing agent, and 0.01-0.05 parts of platinum complex.

[0008] In the present invention, the vinyl content of the methyl vinyl silicone rubber with a vinyl content of 0.04-0.06% and the methyl vinyl silicone rubber with a vinyl content of 0.2-0.24% refers to the molar content. The molecular weight of the methyl vinyl silicone rubber with a vinyl content of 0.04-0.06% and the methyl vinyl silicone rubber with a vinyl content of 0.2-0.24% used in the present invention is selected to be 550,000-750,000.

[0009] Preferably, the method for preparing the modified expandable graphite comprises the following steps:

[0010] 1) expandable graphite, concentrated sulfuric acid and phosphoric acid are mixed, potassium permanganate is then added for oxidation reaction, the temperature is lowered, ice water, hydrogen peroxide and dilute hydrochloric acid are added in sequence, mixed and stirred, filtered, the filter cake is washed with water, and dried to obtain expandable graphite after oxidation treatment;

[0011] 2) mixing the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and an organic solvent, adding concentrated sulfuric acid to react, then extracting the reaction solution with water, drying the organic phase, and concentrating to obtain hydroxyl-modified expandable graphite;

[0012] 3) mixing the hydroxyl-modified expandable graphite and an organic solvent, adding phosphorus tribromide to react, and after the reaction is completed, washing the reaction solution with a saturated sodium bicarbonate solution, concentrating, and drying to obtain bromine-modified expandable graphite;

[0013] 4) Mixing the bromine-modified expandable graphite and an organic solvent, adding tributylphosphine, and reacting under a nitrogen atmosphere. After the reaction is completed, concentrating the reaction solution, washing the concentrated product with ethanol and water in sequence, and drying to obtain modified expandable graphite.

[0014] The synthesis diagram of modified expandable graphite is shown below:

[0015]

[0016] It stands for expandable graphite, which has carboxyl active groups on its surface after oxidation.

[0017] Preferably, in step 1), the mass ratio of expandable graphite, concentrated sulfuric acid and phosphoric acid is 1:(80-90):(7-10), and the amount of potassium permanganate added is 3-6 times the mass of expandable graphite;

[0018] The mass ratio of ice water, hydrogen peroxide and dilute hydrochloric acid is 5:(0.8-3):(0.8-3), and the mass ratio of concentrated sulfuric acid and ice water is 1:(1-1.5).

[0019] Preferably, in step 1), the oxidation reaction temperature is 55-70° C., the oxidation reaction time is 10-20 h, and the mixing and stirring time is 2-7 h;

[0020] In step 1), the expansion ratio of expandable graphite is 100-200 times, the mass fraction of concentrated sulfuric acid is 98-99%, the mass fraction of phosphoric acid is 85-88%, the mass content of hydrogen peroxide is 15-25%, and the mass content of dilute hydrochloric acid is 8-15%.

[0021] Preferably, the mass fraction of concentrated sulfuric acid in step 2) is 98-99%, and the amount of concentrated sulfuric acid added is 2-6% of the mass of the expandable graphite after oxidation treatment;

[0022] In step 2), the mass ratio of the expandable graphite, 1,4-bis(2-hydroxyethyl)benzene and the organic solvent after oxidation treatment is 1:(1-3):(15-23);

[0023] In step 3), the mass ratio of the hydroxyl-modified expandable graphite to the organic solvent is 1:(8-15), and the amount of phosphorus tribromide added is 25-35% of the mass of the hydroxyl-modified expandable graphite;

[0024] In step 4), the mass ratio of the bromine-modified expandable graphite to the organic solvent is 1:(80-120), and the amount of tributylphosphine added is 30-40% of the mass of the bromine-modified expandable graphite.

[0025] Preferably, in step 2), the reaction temperature is 55-65° C. and the reaction time is 1-3 h;

[0026] In step 3), the reaction temperature is 55-65°C and the reaction time is 5-15h;

[0027] In step 4), the reaction temperature is 95-105° C. and the reaction time is 5-15 h.

[0028] Preferably, the molecular weight of the hydroxy silicone oil is 350-420 g / mol, and the hydroxy content is 6.5-7.5 wt %;

[0029] The hydrogen content of the hydrogen-containing silicone oil is 0.1-0.4%, and the viscosity is 100-200 mPa·s;

[0030] The vulcanizing agent is selected from bis(2,4-dichlorobenzoyl) peroxide, the platinum complex is selected from diethyl phthalate platinum complex, and the organic solvent is selected from toluene.

[0031] The present invention also provides a method for preparing the flame retardant silicone rubber, comprising the following steps:

[0032] Methyl vinyl silicone rubber with a vinyl content of 0.04-0.06%, methyl vinyl silicone rubber with a vinyl content of 0.2-0.24%, fumed silica, hydroxy silicone oil, hydrogen-containing silicone oil and modified expandable graphite are mixed and then vacuum mixed. After the mixing is completed, a vulcanizing agent and a platinum complex are added for mixing and vulcanization to obtain the flame retardant rubber.

[0033] Preferably, the mixing temperature is 90-98°C, and the mixing time is 1-5h; the vacuum mixing temperature is 105-110°C, and the vacuum mixing time is 0.5-3h; the vulcanization temperature is 170-190°C, and the vulcanization time is 2-5h.

[0034] The present invention also provides a flame retardant silicone rubber resistant to long-term heat aging, which is the flame retardant silicone rubber described above or is prepared by the preparation method described above.

[0035] The technical solution of the present invention has the following advantages:

[0036] The flame retardant silicone rubber provided by the present invention is added with a certain amount of modified expandable graphite. The expandable graphite is first subjected to oxidation treatment to form carboxyl groups on the surface of the expandable graphite. The expandable graphite is then reacted with 1,4-bis(2-hydroxyethyl)benzene to obtain hydroxyl-modified expandable graphite. The expandable graphite is then mixed with phosphorus tribromide for bromination reaction. The modified expandable graphite is finally reacted with tributyl phosphine. The present invention grafts tributyl phosphine with positive charge on the surface of the expandable graphite through 1,4-bis(2-hydroxyethyl)benzene as a linking unit. Since the expandable graphite surface subjected to oxidation treatment has negative charge, the tributyl phosphine with the 1,4-bis(2-hydroxyethyl)benzene linking unit can be tightly attached to the surface of the expandable graphite through mutual attraction between positive and negative charges. In a high-temperature combustion environment, the 1,4-bis(2-hydroxyethyl)benzene and tributyl phosphine on the surface of the expandable graphite can inhibit the excessive expansion of the expandable graphite, increase its compactness, thereby improving the flame retardant performance of the flame retardant silicone rubber, and can also effectively improve the mechanical strength of the silicone rubber.

[0037] The present invention adopts modified expandable graphite as a flame retardant, and simultaneously combines methyl vinyl silicone rubber with a specific vinyl content, fumed silica, hydroxy silicone oil, hydrogen-containing silicone oil, a vulcanizer and a platinum complex. The prepared flame-retardant silicone rubber has excellent flame retardant properties as well as excellent mechanical strength and high temperature resistance. After aging at 300°C for 100 hours, the tensile strength retention rate can still reach more than 90%. DETAILED DESCRIPTION

[0038] The following examples are provided for further understanding of the present invention, but are not intended to limit the best mode of implementation and do not limit the scope of protection of the present invention.

[0039] The experimental steps or conditions not specified in the following embodiments of the present invention can be implemented according to the conventional experimental steps and conditions used in the existing literature in the field. The reagents or instruments used without specifying the manufacturer are all conventional reagents or instruments that can be purchased commercially.

[0040] Example 1

[0041] This embodiment provides a method for preparing a flame retardant silicone rubber, comprising the following steps:

[0042] 50kg of methyl vinyl silicone rubber with a vinyl content of 0.05% (molecular weight of 650,000), 50kg of methyl vinyl silicone rubber with a vinyl content of 0.2% (molecular weight of 600,000), 55kg of fumed silica, 7kg of hydroxy silicone oil (molecular weight of 400g / mol, hydroxyl content of 7.2wt%), 4kg of hydrogen-containing silicone oil (hydrogen content of 0.2%, viscosity of 150mPa·s), and 35kg of modified expandable graphite are mixed in a kneader at a mixing temperature of 95°C for 2.5h, then vacuum mixed at 110°C for 1h, and after the mixing is completed, 3kg of bis(2,4-dichlorobenzoyl) peroxide and 0.02kg of diethyl phthalate platinum complex are added to the open mill and mixed for 20min, and then vulcanized at 185°C for 2.5h to obtain the flame retardant rubber.

[0043] The preparation method of the modified expandable graphite comprises the following steps:

[0044] 1) expandable graphite (expansion ratio of 100 times), concentrated sulfuric acid (mass fraction of 98%) and phosphoric acid (mass fraction of 85%) are mixed (the mass ratio of expandable graphite, concentrated sulfuric acid and phosphoric acid is 1:80:8), and then potassium permanganate is slowly added (the amount of potassium permanganate added is 4 times the mass of expandable graphite), oxidation reaction is carried out at 60° C. for 10 hours, the temperature is cooled to room temperature, ice water, hydrogen peroxide (the mass content of hydrogen peroxide is 20%) and dilute hydrochloric acid (the mass content of dilute hydrochloric acid is 10%) are added in sequence, the mass ratio of ice water, hydrogen peroxide and dilute hydrochloric acid is 5:1:1, and the mass ratio of concentrated sulfuric acid and ice water is 1:1.2, mixed and stirred for 5 hours, filtered, the filter cake is washed with water, and dried to obtain expandable graphite after oxidation treatment;

[0045] 2) After the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene are mixed (the mass ratio of the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene is 1:2:20), concentrated sulfuric acid is added (the mass fraction of concentrated sulfuric acid is 98%, and the added amount is 5% of the mass of the expandable graphite after oxidation treatment), and the reaction is carried out at 60° C. for 1.5 hours, and then the reaction solution is extracted with water, the organic phase is dried, and the toluene is concentrated to obtain hydroxyl-modified expandable graphite;

[0046] 3) mixing the hydroxyl-modified expandable graphite and toluene (the mass ratio of the hydroxyl-modified expandable graphite to toluene is 1:100), slowly adding phosphorus tribromide (the amount of phosphorus tribromide added is 30% of the mass of the hydroxyl-modified expandable graphite), reacting at 60° C. for 10 hours, and after the reaction is completed, washing the reaction solution with a saturated sodium bicarbonate solution, concentrating under reduced pressure to remove toluene, and drying to obtain bromine-modified expandable graphite;

[0047] 4) Mixing the bromine-modified expandable graphite and toluene (the mass ratio of the bromine-modified expandable graphite to toluene is 1:100), slowly adding tributyl phosphine (the amount of tributyl phosphine added is 35% of the mass of the bromine-modified expandable graphite), reacting at 100° C. for 8 hours under a nitrogen atmosphere, and after the reaction is completed, concentrating the reaction solution under reduced pressure to remove toluene, and washing the concentrated product with ethanol and water in turn, and drying to obtain modified expandable graphite.

[0048] Example 2

[0049] This embodiment provides a method for preparing a flame retardant silicone rubber, comprising the following steps:

[0050] 50kg of methyl vinyl silicone rubber (molecular weight of 650,000) with a vinyl content of 0.05%, 50kg of methyl vinyl silicone rubber (molecular weight of 600,000) with a vinyl content of 0.2%, 58kg of fumed silica, 8kg of hydroxy silicone oil (molecular weight of 400g / mol, hydroxyl content of 7.2wt%), 5kg of hydrogen-containing silicone oil (hydrogen content of 0.2%, viscosity of 150mPa·s), and 37kg of modified expandable graphite are mixed in a kneader at a mixing temperature of 95°C for 2.5h, then vacuum mixed at 110°C for 2h, and after the mixing is completed, 3kg of bis(2,4-dichlorobenzoyl) peroxide and 0.03kg of diethyl phthalate platinum complex are added to the open mill and mixed for 20min, and then vulcanized at 185°C for 2.5h to obtain the flame retardant rubber.

[0051] The preparation method of the modified expandable graphite comprises the following steps:

[0052] 1) expandable graphite (expansion ratio of 100 times), concentrated sulfuric acid (mass fraction of 98%) and phosphoric acid (mass fraction of 85%) are mixed (the mass ratio of expandable graphite, concentrated sulfuric acid and phosphoric acid is 1:80:8), and then potassium permanganate is slowly added (the amount of potassium permanganate added is 5 times the mass of expandable graphite), oxidation reaction is carried out at 60° C. for 15 hours, cooling to room temperature, and ice water, hydrogen peroxide (the mass content of hydrogen peroxide is 20%) and dilute hydrochloric acid (the mass content of dilute hydrochloric acid is 10%) are added in sequence, the mass ratio of ice water, hydrogen peroxide and dilute hydrochloric acid is 5:1:1, and the mass ratio of concentrated sulfuric acid and ice water is 1:1.5, mixed and stirred for 5 hours, filtered, the filter cake is washed with water, and dried to obtain expandable graphite after oxidation treatment;

[0053] 2) After the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene are mixed (the mass ratio of the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene is 1:2:20), concentrated sulfuric acid is added (the mass fraction of concentrated sulfuric acid is 98%, and the added amount is 5% of the mass of the expandable graphite after oxidation treatment), and the reaction is carried out at 60° C. for 1.5 hours, and then the reaction solution is extracted with water, the organic phase is dried, and the toluene is concentrated to obtain hydroxyl-modified expandable graphite;

[0054] 3) mixing the hydroxyl-modified expandable graphite and toluene (the mass ratio of the hydroxyl-modified expandable graphite to toluene is 1:100), slowly adding phosphorus tribromide (the amount of phosphorus tribromide added is 30% of the mass of the hydroxyl-modified expandable graphite), reacting at 60° C. for 12 h. After the reaction is completed, washing the reaction solution with a saturated sodium bicarbonate solution, concentrating under reduced pressure to remove toluene, and drying to obtain bromine-modified expandable graphite;

[0055] 4) Mixing the bromine-modified expandable graphite and toluene (the mass ratio of the bromine-modified expandable graphite to toluene is 1:100), slowly adding tributyl phosphine (the amount of tributyl phosphine added is 35% of the mass of the bromine-modified expandable graphite), reacting at 100° C. for 10 hours under a nitrogen atmosphere, and after the reaction is completed, concentrating the reaction solution under reduced pressure to remove toluene, and washing the concentrated product with ethanol and water in turn, and drying to obtain modified expandable graphite.

[0056] Example 3

[0057] This embodiment provides a method for preparing a flame retardant silicone rubber, comprising the following steps:

[0058] 50kg of methyl vinyl silicone rubber with a vinyl content of 0.05% (molecular weight of 650,000), 50kg of methyl vinyl silicone rubber with a vinyl content of 0.2% (molecular weight of 600,000), 58kg of fumed silica, 10kg of hydroxy silicone oil (molecular weight of 400g / mol, hydroxyl content of 7.2wt%), 4kg of hydrogen-containing silicone oil (hydrogen content of 0.2%, viscosity of 150mPa·s), and 40kg of modified expandable graphite are mixed in a kneader at a mixing temperature of 95°C for 2.5h, then vacuum mixed at 110°C for 2h, and after the mixing is completed, 3kg of bis(2,4-dichlorobenzoyl) peroxide and 0.04kg of diethyl phthalate platinum complex are added to the open mill and mixed for 20min, and then vulcanized at 185°C for 2.5h to obtain the flame retardant rubber.

[0059] The preparation method of the modified expandable graphite comprises the following steps:

[0060] 1) expandable graphite (expansion ratio of 100 times), concentrated sulfuric acid (mass fraction of 98%) and phosphoric acid (mass fraction of 85%) are mixed (the mass ratio of expandable graphite, concentrated sulfuric acid and phosphoric acid is 1:80:10), and then potassium permanganate is slowly added (the amount of potassium permanganate added is 5 times the mass of expandable graphite), oxidation reaction is carried out at 60° C. for 15 hours, the temperature is cooled to room temperature, ice water, hydrogen peroxide (the mass content of hydrogen peroxide is 20%) and dilute hydrochloric acid (the mass content of dilute hydrochloric acid is 10%) are added in sequence, the mass ratio of ice water, hydrogen peroxide and dilute hydrochloric acid is 5:1:1, and the mass ratio of concentrated sulfuric acid and ice water is 1:1.5, mixed and stirred for 5 hours, filtered, the filter cake is washed with water, and dried to obtain expandable graphite after oxidation treatment;

[0061] 2) After the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene are mixed (the mass ratio of the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene is 1:2:20), concentrated sulfuric acid is added (the mass fraction of concentrated sulfuric acid is 98%, and the added amount is 5% of the mass of the expandable graphite after oxidation treatment), and the mixture is reacted at 60° C. for 2 hours, and then the reaction solution is extracted with water, the organic phase is dried, and the toluene is concentrated to obtain hydroxyl-modified expandable graphite;

[0062] 3) mixing the hydroxyl-modified expandable graphite and toluene (the mass ratio of the hydroxyl-modified expandable graphite to toluene is 1:100), slowly adding phosphorus tribromide (the amount of phosphorus tribromide added is 30% of the mass of the hydroxyl-modified expandable graphite), reacting at 60° C. for 12 h. After the reaction is completed, washing the reaction solution with a saturated sodium bicarbonate solution, concentrating under reduced pressure to remove toluene, and drying to obtain bromine-modified expandable graphite;

[0063] 4) Mixing the bromine-modified expandable graphite and toluene (the mass ratio of the bromine-modified expandable graphite to toluene is 1:100), slowly adding tributyl phosphine (the amount of tributyl phosphine added is 35% of the mass of the bromine-modified expandable graphite), reacting at 100° C. for 10 hours under a nitrogen atmosphere, and after the reaction is completed, concentrating the reaction solution under reduced pressure to remove toluene, and washing the concentrated product with ethanol and water in turn, and drying to obtain modified expandable graphite.

[0064] Example 4

[0065] This embodiment provides a method for preparing a flame retardant silicone rubber, comprising the following steps:

[0066] 50kg of methyl vinyl silicone rubber with a vinyl content of 0.05% (molecular weight of 650,000), 50kg of methyl vinyl silicone rubber with a vinyl content of 0.2% (molecular weight of 600,000), 58kg of fumed silica, 10kg of hydroxy silicone oil (molecular weight of 400g / mol, hydroxyl content of 7.2wt%), 6kg of hydrogen-containing silicone oil (hydrogen content of 0.2%, viscosity of 150mPa·s), and 42kg of modified expandable graphite are mixed in a kneader at a mixing temperature of 100°C and a mixing time of 2.5h, and then vacuum mixed at 110°C for 2h. After the mixing, 4kg of bis(2,4-dichlorobenzoyl) peroxide and 0.05kg of platinum complex of diethyl phthalate are added to the open mill and mixed for 20min, and then vulcanized at 185°C for 3h to obtain the flame retardant rubber.

[0067] The preparation method of the modified expandable graphite comprises the following steps:

[0068] 1) expandable graphite (expansion ratio of 100 times), concentrated sulfuric acid (mass fraction of 98%) and phosphoric acid (mass fraction of 85%) are mixed (the mass ratio of expandable graphite, concentrated sulfuric acid and phosphoric acid is 1:80:10), and then potassium permanganate is slowly added (the amount of potassium permanganate added is 5 times the mass of expandable graphite), oxidation reaction is carried out at 60° C. for 15 hours, the temperature is cooled to room temperature, ice water, hydrogen peroxide (the mass content of hydrogen peroxide is 20%) and dilute hydrochloric acid (the mass content of dilute hydrochloric acid is 10%) are added in sequence, the mass ratio of ice water, hydrogen peroxide and dilute hydrochloric acid is 5:1:1, and the mass ratio of concentrated sulfuric acid and ice water is 1:1.5, mixed and stirred for 5 hours, filtered, the filter cake is washed with water, and dried to obtain expandable graphite after oxidation treatment;

[0069] 2) After the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene are mixed (the mass ratio of the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene is 1:2.5:20), concentrated sulfuric acid is added (the mass fraction of concentrated sulfuric acid is 98%, and the added amount is 5% of the mass of the expandable graphite after oxidation treatment), and the reaction is carried out at 60° C. for 2 hours, and then the reaction solution is extracted with water, the organic phase is dried, and the toluene is concentrated to obtain hydroxyl-modified expandable graphite;

[0070] 3) mixing the hydroxyl-modified expandable graphite and toluene (the mass ratio of the hydroxyl-modified expandable graphite to toluene is 1:100), slowly adding phosphorus tribromide (the amount of phosphorus tribromide added is 35% of the mass of the hydroxyl-modified expandable graphite), reacting at 60° C. for 12 h. After the reaction is completed, washing the reaction solution with a saturated sodium bicarbonate solution, concentrating under reduced pressure to remove toluene, and drying to obtain bromine-modified expandable graphite;

[0071] 4) Mixing the bromine-modified expandable graphite and toluene (the mass ratio of the bromine-modified expandable graphite to toluene is 1:100), slowly adding tributyl phosphine (the amount of tributyl phosphine added is 40% of the mass of the bromine-modified expandable graphite), reacting at 100° C. for 10 hours under a nitrogen atmosphere, and after the reaction is completed, concentrating the reaction solution under reduced pressure to remove toluene, and washing the concentrated product with ethanol and water in turn, and drying to obtain modified expandable graphite.

[0072] Comparative Example 1

[0073] This comparative example provides a method for preparing a flame retardant silicone rubber, which differs from Example 1 in that the modified expandable graphite is replaced with expandable graphite of equal mass (expansion ratio is 100 times).

[0074] Comparative Example 2

[0075] This comparative example provides a method for preparing a flame retardant silicone rubber, which is different from Example 1 in that the method for preparing the modified expandable graphite comprises the following steps:

[0076] 1) expandable graphite (expansion ratio of 100 times), concentrated sulfuric acid (mass fraction of 98%) and phosphoric acid (mass fraction of 85%) are mixed (the mass ratio of expandable graphite, concentrated sulfuric acid and phosphoric acid is 1:80:8), and then potassium permanganate is slowly added (the amount of potassium permanganate added is 4 times the mass of expandable graphite), oxidation reaction is carried out at 60° C. for 10 hours, the temperature is cooled to room temperature, ice water, hydrogen peroxide (the mass content of hydrogen peroxide is 20%) and dilute hydrochloric acid (the mass content of dilute hydrochloric acid is 10%) are added in sequence, the mass ratio of ice water, hydrogen peroxide and dilute hydrochloric acid is 5:1:1, and the mass ratio of concentrated sulfuric acid and ice water is 1:1.2, mixed and stirred for 5 hours, filtered, the filter cake is washed with water, and dried to obtain expandable graphite after oxidation treatment;

[0077] 2) After the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene are mixed (the mass ratio of the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and toluene is 1:2:20), concentrated sulfuric acid is added (the mass fraction of concentrated sulfuric acid is 98%, and the added amount is 5% of the mass of the expandable graphite after oxidation treatment), and the reaction is carried out at 60° C. for 1.5 hours, and then the reaction solution is extracted with water, the organic phase is dried, and the toluene and 1,4-bis(2-hydroxyethyl)benzene are removed by concentration to obtain hydroxyl-modified expandable graphite, i.e., modified expandable graphite.

[0078] Comparative Example 3

[0079] This comparative example provides a method for preparing a flame retardant silicone rubber, which is different from Example 1 in that the method for preparing the modified expandable graphite comprises the following steps:

[0080] 1) After expanding graphite (expansion ratio of 100 times), 1,4-bis(2-hydroxyethyl)benzene and toluene are mixed (the mass ratio of expanding graphite, 1,4-bis(2-hydroxyethyl)benzene and toluene is 1:2:20), stirring at 60° C. for 1.5 hours, concentrating to remove toluene, and obtaining a mixture of 1,4-bis(2-hydroxyethyl)benzene and expanding graphite;

[0081] 2) mixing the mixture of 1,4-bis(2-hydroxyethyl)benzene and expandable graphite prepared in step 1) with toluene (the mass ratio of the mixture of 1,4-bis(2-hydroxyethyl)benzene and expandable graphite prepared in step 1) to toluene is 1:100), slowly adding phosphorus tribromide (the amount of phosphorus tribromide added is 30% of the mixture of 1,4-bis(2-hydroxyethyl)benzene and expandable graphite prepared in step 1)), reacting at 60° C. for 10 hours, and after the reaction is completed, washing the reaction solution with a saturated sodium bicarbonate solution, concentrating under reduced pressure to remove toluene, and drying to obtain a mixed product;

[0082] 3) The mixed product prepared in step 2) is mixed with toluene (the mass ratio of the mixed product prepared in step 2) to toluene is 1:100), tributyl phosphine is slowly added (the amount of tributyl phosphine added is 35% of the mass of the mixed product prepared in step 2)), and the mixture is reacted at 100° C. for 8 hours under a nitrogen atmosphere. After the reaction is completed, the reaction solution is concentrated under reduced pressure to remove toluene to obtain modified expandable graphite.

[0083] Test Example 1

[0084] The mechanical strength and flame retardant properties of the flame retardant silicone rubber prepared in the above embodiments and comparative examples were tested respectively, wherein the tensile strength of the silicone rubber was tested according to the GB / T 528-2009 standard, the tear strength was tested according to the GB / T 529-2008 standard, the Shore hardness was tested according to the ASTM D2240 standard, the limiting oxygen index (LOI) was tested according to the GB / T 2406-1993 standard, and the vertical burning (UL-94) was tested according to the ASTM D635 standard.

[0085] The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088]

[0089] Obviously, for ordinary technicians in the field, other modifications can be made based on the above embodiments, and the obvious modifications brought about by these modifications are still within the protection scope of the present invention.

Claims

1. A flame retardant silicone rubber, characterized in that: The following raw materials are included in parts by weight: 40-60 parts of methyl vinyl silicone rubber with a vinyl content of 0.04-0.06%, 40-60 parts of methyl vinyl silicone rubber with a vinyl content of 0.2-0.24%, 50-60 parts of fumed silica, 5-12 parts of hydroxy silicone oil, 3-10 parts of hydrogen-containing silicone oil, 30-45 parts of modified expandable graphite, 1-5 parts of vulcanizing agent, and 0.01-0.05 parts of platinum complex; The preparation method of the modified expandable graphite comprises the following steps: 1) Mix expandable graphite, concentrated sulfuric acid and phosphoric acid, then add potassium permanganate for oxidation reaction, cool down, add ice water, hydrogen peroxide and dilute hydrochloric acid in sequence, mix and stir, filter, wash the filter cake with water, and dry to obtain expandable graphite after oxidation treatment; 2) After the expandable graphite after oxidation treatment, 1,4-bis(2-hydroxyethyl)benzene and an organic solvent are mixed, concentrated sulfuric acid is added to react, and then the reaction solution is extracted with water, and the organic phase is dried and concentrated to obtain hydroxyl-modified expandable graphite; 3) mixing the hydroxyl-modified expandable graphite and an organic solvent, adding phosphorus tribromide to react, and after the reaction is completed, washing the reaction solution with a saturated sodium bicarbonate solution, concentrating, and drying to obtain bromine-modified expandable graphite; 4) mixing the bromine-modified expandable graphite and an organic solvent, adding tributylphosphine, and reacting under a nitrogen atmosphere. After the reaction is completed, concentrating the reaction solution, washing the concentrated product with ethanol and water in turn, and drying to obtain modified expandable graphite; In step 2), the mass ratio of the expandable graphite, 1,4-bis(2-hydroxyethyl)benzene and the organic solvent after oxidation treatment is 1:(1-3):(15-23); In step 3), the mass ratio of the hydroxyl-modified expandable graphite to the organic solvent is 1:(8-15), and the amount of phosphorus tribromide added is 25-35% of the mass of the hydroxyl-modified expandable graphite; In step 4), the mass ratio of the bromine-modified expandable graphite to the organic solvent is 1:(80-120), and the amount of tributylphosphine added is 30-40% of the mass of the bromine-modified expandable graphite.

2. The flame retardant silicone rubber according to claim 1, characterized in that: In step 1), the mass ratio of expandable graphite, concentrated sulfuric acid and phosphoric acid is 1: (80-90): (7-10), and the amount of potassium permanganate added is 3-6 times the mass of expandable graphite; The mass ratio of ice water, hydrogen peroxide and dilute hydrochloric acid is 5:(0.8-3):(0.8-3), and the mass ratio of concentrated sulfuric acid and ice water is 1:(1-1.5).

3. The flame retardant silicone rubber according to claim 1, characterized in that: In step 1), the oxidation reaction temperature is 55-70°C, the oxidation reaction time is 10-20h, and the mixing and stirring time is 2-7h; In step 1), the expansion ratio of expandable graphite is 100-200 times, the mass fraction of concentrated sulfuric acid is 98-99%, the mass fraction of phosphoric acid is 85-88%, the mass content of hydrogen peroxide is 15-25%, and the mass content of dilute hydrochloric acid is 8-15%.

4. The flame retardant silicone rubber according to claim 1, characterized in that: In step 2), the mass fraction of concentrated sulfuric acid is 98-99%, and the amount of concentrated sulfuric acid added is 2-6% of the mass of the expandable graphite after oxidation treatment.

5. The flame retardant silicone rubber according to claim 1, characterized in that: In step 2), the reaction temperature is 55-65°C and the reaction time is 1-3h; In step 3), the reaction temperature is 55-65°C and the reaction time is 5-15h; In step 4), the reaction temperature is 95-105°C and the reaction time is 5-15h.

6. The flame retardant silicone rubber according to claim 1, characterized in that: The molecular weight of the hydroxy silicone oil is 350-420 g / mol, and the hydroxyl content is 6.5-7.5 wt %; The hydrogen content of the hydrogen-containing silicone oil is 0.1-0.4% and the viscosity is 100-200 mPa •s; The vulcanizing agent is selected from bis(2,4-dichlorobenzoyl) peroxide, the platinum complex is selected from diethyl phthalate platinum complex, and the organic solvent is selected from toluene.

7. The method for preparing the flame retardant silicone rubber according to any one of claims 1 to 6, characterized in that: The steps include: Methyl vinyl silicone rubber with a vinyl content of 0.04-0.06%, methyl vinyl silicone rubber with a vinyl content of 0.2-0.24%, fumed silica, hydroxy silicone oil, hydrogen-containing silicone oil and modified expandable graphite are mixed, and then vacuum mixed. After the mixing is completed, a vulcanizing agent and a platinum complex are added, mixed, and vulcanized to obtain the flame retardant silicone rubber.

8. The preparation method according to claim 7, characterized in that: The mixing temperature is 90-98° C., and the mixing time is 1-5 hours; the vacuum mixing temperature is 105-110° C., and the vacuum mixing time is 0.5-3 hours; the vulcanization temperature is 170-190° C., and the vulcanization time is 2-5 hours.

9. A flame retardant silicone rubber resistant to long-term heat aging, characterized in that: The flame retardant silicone rubber is the flame retardant silicone rubber according to any one of claims 1 to 6 or is prepared by the preparation method according to claim 7 or 8.

Images