A high-strength, low-pressure variable silicone rubber foam material and its preparation method

Abstract

This invention relates to the field of silicone rubber technology and discloses a high-strength, low-pressure variable silicone rubber foam material and its preparation method. The invention involves mixing, thinning, sheeting, and foaming ethylene propylene diene monomer (EPDM) rubber, reinforcing agents, modified phenolic resin, methyl vinyl silicone rubber, and foaming agents to obtain a high-strength, low-pressure variable silicone rubber foam material. The modified phenolic resin exhibits a large number of thiol groups that undergo addition reactions with the alkenyl groups of EPDM and methyl vinyl silicone rubber, improving the interfacial properties and compatibility between the two. This results in higher tensile strength and lower compression set in the foam material, exhibiting excellent compression resistance. The modified phenolic resin has a high carbon content, strong ablation resistance, and contains a large number of phosphate ester flame-retardant groups. During combustion, it produces phosphoric acid, promoting the dehydration and charring of the phenolic resin and rubber groups, thus providing excellent cohesive flame retardancy and improving the limiting oxygen index and flame retardant properties of the foam material.

Description

Technical Field

[0001] This invention relates to the field of silicone rubber technology, specifically to a high-strength, low-pressure variable silicone rubber foam material and its preparation method. Background Technology

[0002] Rubber is a common polymer material, mainly including silicone rubber, EPDM rubber, nitrile rubber, and fluororubber. Among them, silicone rubber has good flexibility and excellent flame retardancy, but its mechanical strength is relatively low. EPDM rubber, on the other hand, has high mechanical strength and good weather resistance, but its flame retardancy and other properties are not good. Mixing silicone rubber, EPDM rubber, compatibilizers, and other materials to produce blended rubbers and foamed materials can combine excellent flexibility, mechanical strength, and flame retardancy, and is widely used in medical devices, petrochemicals, and the automotive industry.

[0003] Phenolic resins possess excellent mechanical strength, high-temperature resistance, and flame retardancy, making them important in materials such as silicone rubber and EPDM rubber. The journal article "Preparation and Ablation Properties of Silicone Rubber / Phenolic Resin Thermal Insulation Composites" in Volume 17, Issue 3 of the *Journal of Materials and Metallurgy* reports that adding phenolic resin to silicone rubber can improve the material's mechanical properties, ablation resistance, and flame retardancy. However, this article does not address the issues of poor compatibility and unsatisfactory mechanical properties between EPDM rubber and silicone rubber. Summary of the Invention

[0004] The technical problem solved by this invention is to address the low strength, compressive strength, and flame retardancy of EPDM-silicone rubber foam materials.

[0005] The technical solution of this invention is: a method for preparing a high-strength, low-pressure variable silicone rubber foam material. (1) Add cysteine, potassium hydroxide, and 4-aldehyde phenyl diphenyl phosphate to ethanol. After the reaction is cooled, hydrochloric acid is added dropwise to adjust the pH to 4-5. After filtration, the product is washed with ethanol and dried to obtain a mercapto flame retardant. The reaction formula is: .

[0006] (2) Add toluene, phenolic resin, mercapto flame retardant and p-toluenesulfonic acid to the reaction vessel, stir and react, then distill under reduced pressure, wash the product with petroleum ether, and dry to obtain modified phenolic resin.

[0007] (3) Add EPDM rubber, reinforcing agent, modified phenolic resin and additives to a two-roll mill for mixing, add methyl vinyl silicone rubber, continue mixing, add vulcanizing agent and foaming agent, mix, thin pass, and sheet, and finally foam in a flat vulcanizing machine to obtain high-strength low-pressure modified silicone rubber foam material.

[0008] Preferably, the ratio of cysteine, potassium hydroxide and 4-aldehyde phenyl diphenyl phosphate in (1) is 1 mol: 1 mol: (0.92-1) mol.

[0009] Preferably, the reaction temperature in (1) is 50-70℃ and the reaction time is 5-8h.

[0010] Preferably, the reaction temperature in (2) is 110-115℃ and the reaction time is 10-18h.

[0011] Preferably, in (2), the ratio of phenolic resin, mercapto flame retardant and p-toluenesulfonic acid is 100g: (40-120)g: (0.7-2.5)g.

[0012] Preferably, the ratio of methyl vinyl silicone rubber, EPDM rubber, reinforcing agent, modified phenolic resin, additives, vulcanizing agent and foaming agent in (3) is (55-70)g:(30-45)g:(25-50)g:(5-20)g:(7.5-9)g:(1.2-2.1)g:(4-7)g.

[0013] Preferably, the additives in (3) include zinc oxide, stearic acid, and paraffin oil.

[0014] Preferably, the reinforcing agent in (3) is carbon black.

[0015] Preferably, the foaming agent in (3) is azodicarbonamide.

[0016] Preferably, the sulfiding agent in (3) is dicumyl peroxide or bis-tert-butylperoxide.

[0017] Preferably, in (3), the pressure of the flat vulcanizing machine is 10-15MPa, the temperature is 155-165℃, and the time is 8-12min.

[0018] The beneficial technical effects of this invention are as follows: This invention involves esterifying the carboxyl group of a mercapto flame retardant with the hydroxyl group of a phenolic resin to obtain a modified phenolic resin, which is then blended and foamed with methyl vinyl silicone rubber, EPDM rubber, fillers, foaming agents, etc., to obtain a high-strength, low-pressure modified silicone rubber foam material.

[0019] In the high-temperature molding process, the modified phenolic resin undergoes an addition reaction with the alkenyl groups of EPDM rubber and methyl vinyl silicone rubber, thereby forming a chemical bond between EPDM rubber and silicone rubber through the phenolic resin. This improves the interfacial properties and compatibility between the two, resulting in higher tensile strength of the foamed material, while maintaining low compression set and excellent compression resistance. Furthermore, the phenolic resin has a certain reinforcing effect on the composite rubber, further improving the tensile strength of the foamed material.

[0020] The modified phenolic resin of this invention has a high carbon content, strong ablation resistance, and contains a large number of phosphate ester flame retardant groups. When burned, it produces phosphoric acid substances, which promote the dehydration and char formation of phenolic resin and rubber groups, thus playing a good cohesive flame retardant role and improving the limiting oxygen index and flame retardant performance of foamed materials. Detailed Implementation

[0021] The specific embodiments of the present invention will now be described in detail. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0022] The methyl vinyl silicone rubber, model MVQ, was purchased from Dongguan Shuang'ao Plastics Co., Ltd. The ethylene propylene diene monomer (EPDM) rubber, model IP 3720P, was purchased from Dongguan Nabaichuan Plastics Co., Ltd. The phenolic resin is a primary phenolic resin with an effective content of 99%, purchased from Dongguan Xiangteng Plastics Co., Ltd.

[0023] 4-Aldehyde-phenyl diphenyl phosphate was prepared according to the method described in patent document CN113583047B, "A porphyrin phosphate compound, its preparation method and its application as a flame retardant." The structural formula is as follows: .

[0024] Example 1, (1) Add 0.3 mol cysteine, 0.3 mol potassium hydroxide and 0.3 mol 4-aldehyde phenyl diphenyl phosphate to 2L ethanol, heat to 70°C, stir and reflux for 5h, cool, add 10% hydrochloric acid to adjust pH to 5, filter, wash the product with ethanol, dry, and obtain mercapto flame retardant.

[0025] (2) Add 300 mL toluene, 100 g phenolic resin, 40 g mercapto flame retardant and 0.7 g p-toluenesulfonic acid to the reaction vessel, heat to 110 °C, stir and reflux for 12 h, distill under reduced pressure after stirring, wash the product with petroleum ether, dry and obtain modified phenolic resin.

[0026] (3) Add 300g of EPDM rubber, 250g of carbon black, 50g of modified phenolic resin, 28g of zinc oxide, 22g of stearic acid and 34g of paraffin oil to a two-roll mill for mixing. Add 700g of methyl vinyl silicone rubber and continue mixing. Add 14g of dicumyl peroxide and 64g of azodicarbonamide, mix, pass through a thin sheet, and cut into sheets. Finally, in a flat vulcanizing machine, at 10MPa and 160℃, mold and foam for 10min to obtain a high-strength low-pressure modified silicone rubber foam material.

[0027] Example 2, (1) Add 0.3 mol cysteine, 0.3 mol potassium hydroxide and 0.276 mol 4-aldehyde phenyl diphenyl phosphate to 1.8 L ethanol, heat to 50 °C, stir and reflux for 8 h, cool, add 15% hydrochloric acid to adjust pH to 4, filter, wash the product with ethanol, dry, and obtain mercapto flame retardant.

[0028] (2) Add 300 mL toluene, 100 g phenolic resin, 65 g mercapto flame retardant and 1.2 g p-toluenesulfonic acid to the reaction vessel, heat to 110 °C, stir and reflux for 18 h, distill under reduced pressure after stirring, wash the product with petroleum ether, dry and obtain modified phenolic resin.

[0029] (3) Add 350g of EPDM rubber, 300g of carbon black, 100g of modified phenolic resin, 25g of zinc oxide, 22g of stearic acid and 38g of paraffin oil to a two-roll mill for mixing. Add 650g of methyl vinyl silicone rubber and continue mixing. Add 12g of dicumyl peroxide and 40g of azodicarbonamide, mix, pass through a thin sheet, and cut into sheets. Finally, in a flat vulcanizing machine, at 10MPa and 165℃, mold and foam for 8min to obtain a high-strength low-pressure modified silicone rubber foam material.

[0030] Example 3, (1) Add 400 mL toluene, 100 g phenolic resin, 90 g mercapto flame retardant (prepared according to the method of Example 1) and 0.18 g p-toluenesulfonic acid to the reaction vessel, heat to 115 °C, stir and reflux for 10 h, stir and then distill under reduced pressure, wash the product with petroleum ether, and dry to obtain modified phenolic resin.

[0031] (2) Add 400g of EPDM rubber, 500g of carbon black, 150g of modified phenolic resin, 24g of zinc oxide, 10g of stearic acid and 41g of paraffin oil to a two-roll mill for mixing. Add 600g of methyl vinyl silicone rubber and continue mixing. Add 12g of dicumyl peroxide and 70g of azodicarbonamide, mix, pass through a thin sheet, and sheet the mixture. Finally, in a flat vulcanizing machine, at 15MPa and 155℃, mold and foam for 12min to obtain a high-strength low-pressure modified silicone rubber foam material.

[0032] Example 4, (1) Add 400 mL toluene, 100 g phenolic resin, 120 g mercapto flame retardant (prepared according to the method of Example 1) and 2.5 g p-toluenesulfonic acid to the reaction vessel, heat to 110 °C, stir and reflux for 18 h, stir and then distill under reduced pressure, wash the product with petroleum ether, and dry to obtain modified phenolic resin.

[0033] (2) Add 450g of EPDM rubber, 500g of carbon black, 200g of modified phenolic resin, 30g of zinc oxide, 14g of stearic acid and 46g of paraffin oil to a two-roll mill for mixing. Add 550g of methyl vinyl silicone rubber and continue mixing. Add 21g of bis-tert-butylperoxyisopropylbenzene and 53g of azodicarbonamide. Mix, pass through a thin sheet, and cut into sheets. Finally, in a flat vulcanizing machine, at 10MPa and 160℃, mold and foam for 12min to obtain silicone rubber foam material.

[0034] Comparative Example 1, (1) 300g of EPDM rubber, 250g of carbon black, 28g of zinc oxide, 22g of stearic acid and 34g of paraffin oil were added to a two-roll mill for mixing. 700g of methyl vinyl silicone rubber was added and mixing continued. 14g of dicumyl peroxide and 64g of azodicarbonamide were added, and the mixture was mixed, thinned, and sheeted. Finally, it was molded and foamed for 10min at 10MPa and 160℃ in a flat vulcanizing machine to obtain silicone rubber foam material.

[0035] Comparative Example 2, (1) 300g of EPDM rubber, 250g of carbon black, 50g of phenolic resin, 28g of zinc oxide, 22g of stearic acid and 34g of paraffin oil were added to a two-roll mill for mixing. 700g of methyl vinyl silicone rubber was added and mixing continued. 14g of dicumyl peroxide and 64g of azodicarbonamide were added, and the mixture was mixed, thinned, and sheeted. Finally, it was molded and foamed for 10min at 10MPa and 160℃ in a flat vulcanizing machine to obtain a high-strength low-pressure silicone rubber foam material.

[0036] Comparative Example 3, (1) 300g of EPDM rubber, 250g of carbon black, 50g of mercapto flame retardant, 28g of zinc oxide, 22g of stearic acid and 34g of paraffin oil were added to a two-roll mill for mixing. 700g of methyl vinyl silicone rubber was added and mixing continued. 14g of dicumyl peroxide and 64g of azodicarbonamide were added, and the mixture was mixed, thinned, and sheeted. Finally, it was molded and foamed for 10min at 10MPa and 160℃ in a flat vulcanizing machine to obtain silicone rubber foam material.

[0037] Comparative Example 4, (1) 100g of phenolic resin and 40g of mercapto flame retardant were added to the reaction vessel and stirred to obtain a flame retardant-phenolic resin blend.

[0038] (2) Add 300g of EPDM rubber, 250g of carbon black, 50g of flame retardant-phenolic resin blend, 28g of zinc oxide, 22g of stearic acid, and 34g of paraffin oil to a two-roll mill for mixing. Add 700g of methyl vinyl silicone rubber and continue mixing. Add 14g of dicumyl peroxide and 64g of azodicarbonamide, mix, pass through a thin sheet, and sheet the material. Finally, in a flat vulcanizing machine, at 10MPa and 160℃, mold and foam for 10min to obtain silicone rubber foam material.

[0039] The flame retardant properties of the silicone rubber foam were tested according to GB / T 10707-2008 standard. The tensile strength was tested according to GB / T 528-2009 standard. The compression set was tested according to GB / T 7759.1-2015 method at a test temperature of 25℃.

[0040] Table 1 Properties of Silicone Rubber Foaming Materials

[0041] In Comparative Example 1, the poor compatibility between EPDM rubber and silicone rubber resulted in low tensile strength, large compression set, and poor compression resistance of the foamed material. It also exhibited a low limiting oxygen index and poor flame retardant properties. Examples 1-4 incorporated modified phenolic resin, which contains a large number of thiol groups. During high-temperature molding, these thiol groups undergo addition reactions with the alkenyl groups of EPDM rubber and methyl vinyl silicone rubber, forming chemical bonds between the EPDM rubber and silicone rubber through the phenolic resin. This improves the interfacial properties and compatibility between the two materials, resulting in higher tensile strength and lower compression set in the foamed material, exhibiting excellent compression resistance. The addition of phenolic resin also provides reinforcement to the composite rubber, further enhancing tensile strength. The modified phenolic resin has a high carbon content, strong ablation resistance, and contains a large number of phosphate ester flame-retardant groups. During combustion, it produces phosphoric acid, promoting dehydration and char formation of the phenolic resin and rubber groups, thus providing excellent cohesive flame retardant properties and significantly improving the limiting oxygen index and flame retardant performance of the foamed material.

[0042] Compared with Example 1, Comparative Example 2 only added phenolic resin, which made it difficult for EPDM rubber and silicone rubber to form chemical bonds. The two had poor compatibility, poor mechanical properties, and a low limiting oxygen index.

[0043] Comparative Example 3 only added a mercapto flame retardant, which contains only one mercapto group. It cannot simultaneously undergo an addition reaction with the alkenyl groups of EPDM rubber and silicone rubber. EPDM rubber and silicone rubber did not form chemical bonds, and their compatibility was lower than that of Example 1. This resulted in the tensile strength of the foamed material being lower than that of Example 1, but higher than that of Comparative Example 1. This may be because both EPDM rubber and silicone rubber were grafted with mercapto flame retardant structures, which improved structural similarity and compatibility. Furthermore, no phenolic resin was added, resulting in poor ablation resistance and flame retardant properties of the foamed material, and a limiting oxygen index lower than that of Example 1.

[0044] Comparative Example 4 involved the physical blending of phenolic resin and mercapto flame retardant. The tensile strength of the foamed material was significantly lower than that of Example 1, and the permanent compression deformation was larger.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments without departing from the scope of the present invention and based on the technical essence of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a high-strength, low-pressure variable silicone rubber foam material, characterized in that, The preparation method includes: S1. Add toluene, phenolic resin, mercapto flame retardant, and p-toluenesulfonic acid to the reaction vessel, stir and react, then distill under reduced pressure, wash the product, and dry to obtain modified phenolic resin. The structural formula of the mercapto flame retardant is: ; S2. Add EPDM rubber, reinforcing agent, modified phenolic resin, and additives to a two-roll mill for mixing. Add methyl vinyl silicone rubber and continue mixing. Add vulcanizing agent and foaming agent, mix, pass through a thin sheet, and finally foam in a flat vulcanizing machine to obtain high-strength, low-pressure modified silicone rubber foam material.

2. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 1, characterized in that, The reaction temperature in S1 is 110-115℃, and the reaction time is 10-18h.

3. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 1, characterized in that, The ratio of phenolic resin, mercapto flame retardant, and p-toluenesulfonic acid in S1 is 100g:(40-120)g:(0.7-2.5)g.

4. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 1, characterized in that, The preparation method of the mercapto flame retardant is as follows: add cysteine, potassium hydroxide and 4-aldehyde phenyl diphenyl phosphate in a ratio of 1 mol: 1 mol: (0.92-1) mol to ethanol, heat to 50-70℃, react for 5-8 h, cool and add hydrochloric acid dropwise to adjust the pH to 4-5, filter, wash the product and dry to obtain the mercapto flame retardant.

5. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 1, characterized in that, The ratio of the methyl vinyl silicone rubber, EPDM rubber, reinforcing agent, modified phenolic resin, additives, vulcanizing agent, and foaming agent is (55-70)g:(30-45)g:(25-50)g:(5-20)g:(7.5-9)g:(1.2-2.1)g:(4-7)g.

6. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 5, characterized in that, The additives in S2 include zinc oxide, stearic acid, and paraffin oil.

7. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 5, characterized in that, The reinforcing agent in S2 is carbon black; the foaming agent is azodicarbonamide.

8. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 5, characterized in that, The vulcanizing agent in S2 is dicumyl peroxide or bis-tert-butylperoxide.

9. The method for preparing high-strength, low-pressure variable silicone rubber foam material according to claim 1, characterized in that, The pressure of the flat vulcanizing machine in S2 is 10-15 MPa, the temperature is 155-165℃, and the time is 8-12 min.

10. A high-strength, low-pressure variable silicone rubber foam material obtained by the preparation method according to any one of claims 1-9.

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