Foamable composite silicone rubber particle and preparation method thereof

Abstract

The invention discloses foamable composite silicone rubber particles and a preparation method thereof, and relates to the technical field of composite silicone rubber. The foamable composite silicone rubber particles are prepared from the following raw materials in parts by mass: 100 parts of silicone rubber-based rubber, 10-30 parts of a foaming agent, 20-80 parts of inorganic filler, 0.5-5 parts of a silane coupling agent, 0.2-2 parts of a platinum catalyst, 1-10 parts of an auxiliary agent and 0.5-5 parts of a stabilizer. By introducing the stabilizer with a specific structure, the dispersity of the inorganic filler in the silicone rubber matrix is remarkably enhanced. The stabilizer inhibits filler agglomeration through hydrogen-bond interaction, reinforces chemical bonding of the filler and a matrix through silanol condensation reaction, and improves interfacial compatibility, so that the material uniformity is improved. According to the invention, through molecular design, dispersibility is optimized, interface combination is realized, foaming / vulcanization dynamic balance is realized technologically, and finally, comprehensive performance improvement of light weight, high flame retardance and obdurability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite silicone rubber, and in particular to foamable composite silicone rubber particles and a preparation method thereof. Background Art

[0002] In modern industrial production and daily life, silicone rubber is widely used in electronics, electrical appliances, healthcare, construction, automotive, and other fields due to its excellent high and low temperature resistance, excellent weather resistance, good electrical insulation, and physiological inertness. However, with the continuous advancement of technology and people's increasing demand for material performance, the performance of traditional silicone rubber materials is gradually unable to meet the needs of some special applications.

[0003] For example, in the electronics and electrical field, the continuous miniaturization and integration of equipment have placed higher demands on the heat dissipation performance and space utilization of materials. In the construction field, to achieve better thermal insulation, materials with lower thermal conductivity and lighter weight are required. In the automotive industry, to reduce vehicle weight and improve fuel efficiency, low-density, high-strength materials have become a research hotspot. Traditional silicone rubber materials have relatively high density and are difficult to reduce through conventional foaming methods, so their application in these areas is limited.

[0004] While some foamed silicone rubber materials are currently available on the market, these materials often suffer from issues such as a mismatch between the decomposition temperature of the foaming agent and the vulcanization temperature of the silicone rubber matrix, poor dispersion of the foaming agent within the matrix, and decreased mechanical properties after foaming. Furthermore, existing foamed silicone rubber materials still require further improvement in terms of heat resistance, aging resistance, and chemical corrosion resistance.

[0005] To address these issues, the development of a foamable composite silicone rubber particle and its preparation method is of great practical significance. This new material not only overcomes the shortcomings of traditional silicone rubber materials, but also meets the demand for high-performance foam materials in various industries and expands the application range of silicone rubber materials. Summary of the Invention

[0006] The purpose of the present invention is to provide a foamable composite silicone rubber particle and a preparation method thereof to address the problems of uneven dispersion of the foaming agent, mismatch between the decomposition temperature and the vulcanization temperature, and decreased mechanical properties of existing foamed silicone rubber materials, so as to achieve uniform foaming of the material and improve its performance.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a foamable composite silicone rubber particle, composed of the following raw materials in parts by weight: 100 parts of silicone rubber base, 10-30 parts of foaming agent, 20-80 parts of inorganic filler, 0.5-5 parts of silane coupling agent, 0.2-2 parts of platinum catalyst, 1-10 parts of auxiliary agent, and 0.5-5 parts of stabilizer; The stabilizer has a structure shown in Formula 1: Formula 1;

[0008] The R1 is selected from the group consisting of: methyl, ethyl, tert-butyl, and methoxy.

[0009] Furthermore, the silicone rubber base is α,ω-dihydroxypolydimethylsiloxane.

[0010] Furthermore, the foaming agent is azodicarbonamide and / or sodium bicarbonate.

[0011] Furthermore, the inorganic filler is magnesium hydroxide and / or talc.

[0012] Furthermore, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0013] Furthermore, the platinum catalyst is platinum-divinyltetramethyldisiloxane.

[0014] Furthermore, the auxiliary agent is 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0015] Furthermore, the stabilizer is any one of the compounds shown in the following structures: ;

[0016] .

[0017] A method for preparing foamable composite silicone rubber particles comprises the following steps: S1. The silicone rubber base, inorganic filler, silane coupling agent and stabilizer are added to an internal mixer and mixed at 80-120 ° C for 10-30 minutes to obtain a uniform base; S2. The base material is transferred to an open mill, a foaming agent and additives are added, and mixed at 40-60 ℃ for 5-15 minutes to obtain a mixture; S3. The platinum catalyst is added to the mixture and mixed at room temperature for 3-10 minutes to obtain a foamable composite silicone rubber mixture; S4. The foamable composite silicone rubber mixture is granulated by a twin-screw extruder at an extrusion temperature of 70-100 ℃ to obtain a granular material; S5. The granular material is placed in a mold at 160-200°C and pressurized for vulcanization for 5-20 minutes. After foaming and molding, the mold is cooled to obtain a foamable composite silicone rubber particle.

[0018] Furthermore, the mixing is carried out under an inert gas atmosphere, and the inert gas is nitrogen or argon.

[0019] Furthermore, the vulcanizing agent in the vulcanization is sulfur.

[0020] Furthermore, the pressure of the pressurized vulcanization is 5-15 MPa, and the cooling method is water cooling or air cooling to room temperature.

[0021] The hydroxyl groups in the stabilizer molecules described in the present invention can form strong hydrogen bonds with inorganic fillers, reducing the tendency of fillers to agglomerate. The polar properties of hydroxyl groups enhance the compatibility between hydrophobic silicone rubber base glue and hydrophilic inorganic fillers. The silane group hydrolyzes into silanol (-SiOH) at the mixing temperature, undergoes a condensation reaction with the filler surface, forming a strong covalent bond, and bridges the inorganic filler and the silicone rubber matrix through chemical bonds, significantly improving the interfacial bonding force. The rigid heteroaromatic ring in the molecule prevents the filler particles from agglomerating close to each other through steric hindrance, thereby improving dispersion stability. The conjugated large π bond can absorb or disperse free radicals during the vulcanization / foaming process to prevent chain degradation. The high thermal stability of the conjugated system can delay the oxidative aging of the material during the foaming / vulcanization process.

[0022] The foaming agent described in the present invention cooperates with the temperature of the vulcanization system, and the pressurized vulcanization temperature (160-200°C) covers the decomposition range of the two types of foaming agents. Sodium bicarbonate decomposes to form bubble nuclei at the initial stage of temperature rise, and azodicarbonamide mainly decomposes in the high temperature section to achieve gradient foaming, avoiding instantaneous excess gas causing bubble rupture. The auxiliary agent decomposes to produce active free radicals, which cooperate with the platinum catalyst to control the vulcanization rate and ensure that the foaming and vulcanization reactions proceed simultaneously. One end of the silane coupling agent is bonded to the inorganic filler, and the amino group at the other end interacts with the silicone rubber base, further enhancing the filler-matrix interface bonding strength and reducing the loss of mechanical properties caused by stress concentration.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. Improved material dispersibility and compatibility: By introducing a stabilizer with a specific structure, the dispersion of inorganic fillers in the silicone rubber matrix is ​​significantly enhanced. The stabilizer inhibits filler agglomeration through hydrogen bonding and strengthens the chemical bond between the filler and the matrix through silanol condensation reactions, improving interfacial compatibility and thus enhancing material uniformity.

[0024] 2. Synergistic Optimization of the Foaming-Vulcanization Process: A composite blowing agent and a platinum catalyst / additive system work together to achieve gradient foaming and vulcanization rate matching: the blowing agent forms the initial bubble nuclei in the low-temperature section, while the main blowing agent decomposes in the high-temperature section, while the vulcanization reaction proceeds simultaneously. This design prevents gas escape or cell rupture caused by premature or delayed decomposition of the blowing agent, thereby improving the stability of the foam structure.

[0025] 3. Enhanced overall performance: While maintaining low density, the material's flame retardancy and mechanical properties are simultaneously enhanced. The stabilizer's steric effect and free radical capture capabilities delay material aging, fully utilizing the flame retardant properties of the inorganic filler. Strengthening the filler-matrix interface reduces stress concentration, enabling the material to maintain high mechanical strength while remaining lightweight. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The stabilizer 1 of the present invention 1 HNMR spectrum. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Synthesis example 1 Synthesis of stabilizer 1: ;

[0029] The first step: Under nitrogen protection, 20g of raw material 1, 36.29g of raw material 2, 14.55g of sodium tert-butoxide, 2.08g of tris(dibenzylideneacetone)dipalladium, 0.76g of tri-tert-butylphosphine and 250g of toluene were added to the reaction system in sequence, stirred evenly, heated to 110°C, and refluxed for 11h; after the reaction was completed, the temperature was slightly lowered, filtered using diatomaceous earth, the filtrate was cooled to room temperature, washed three times with water, the organic phase was retained, and the aqueous phase was then extracted with ethyl acetate; after the organic phases were combined, they were dried over anhydrous magnesium sulfate, filtered, spin-dried, and chromatographed on a silica gel column (with a mixture of petroleum ether and ethyl acetate as an eluent) to obtain 35.38g of intermediate 1.

[0030] Step 2: Under nitrogen, 35.38 g of intermediate 1, 16.43 g of raw material 3, 11.69 g of anhydrous potassium carbonate, and 2.11 g of tetrakis(triphenylphosphine)palladium were added to the reaction system in sequence. The mixture was dissolved in a mixed solution of 400 g of toluene, ethanol, and water (volume ratio 2:1:1). The mixture was heated to 95°C and refluxed for 10 hours. The heat was turned off, the mixture was cooled to room temperature, and the mixture was allowed to stand for separation. The aqueous phase was extracted twice with ethyl acetate, and the organic phases were combined, washed three times with water, and then spin-dried to dryness. Finally, the product was purified by silica gel column chromatography using petroleum ether and ethyl acetate as eluents to obtain 32.21 g of stabilizer 1.

[0031] Product structure identification: MS [MS+H] of intermediate 1 + :582; MS of stabilizer 1 [MS+H] + :665; Stabilizer 1 1 HNMR Chloroform-d: δ8.09(m,1H),8.02(m,1H),7.87-7.73(m,3H),7.73-7.64(m,1H) ),7.50-7.39(m,2H),7.36(dd,1H),7.24-7.14(m,1H),7.08(m,1H),6.75(m,1H ),4.34(d,1H),4.23(t,1H),4.11(t,1H),4.07-3.80(m,6H),3.80-3.62(m,2H) ,2.49(d,3H),1.35-1.24(m,9H),1.18(d,3H),0.93-0.83(m,9H),0.07(d,6H).

[0032] Synthesis Example 2-Synthesis Example 4 In Synthesis Examples 2-4, stabilizers 2-4 were synthesized in sequence, referring to the synthesis method of Synthesis Example 1, replacing raw material 3, and the rest remained the same as Synthesis Example 1. Specific structures of raw material 3, stabilizers 2-4, MS [MS+H] + See Table 1 for data.

[0033] Table 1. Structure of raw material 3, structure of stabilizer 2-stabilizer 4, MS [MS+H] involved in synthesis examples 2-4 + data.

[0034]

[0035] Example 1

[0036] A foamable composite silicone rubber particle comprises the following raw materials in parts by weight: 100 parts of a silicone rubber base (α,ω-dihydroxypolydimethylsiloxane), 20 parts of a foaming agent (azodicarbonamide and sodium bicarbonate mixed in a mass ratio of 1:1), 50 parts of an inorganic filler (talc), 2 parts of a silane coupling agent (γ-aminopropyltriethoxysilane), 1 part of a platinum catalyst (platinum-divinyltetramethyldisiloxane), 5 parts of an auxiliary agent (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane), and 3 parts of a stabilizer (stabilizer 1 prepared in Synthesis Example 1).

[0037] Preparation method: S1. Under nitrogen, 100 parts of α,ω-dihydroxypolydimethylsiloxane, 50 parts of talc, 2 parts of γ-aminopropyltriethoxysilane and 3 parts of stabilizer 1 were added to an internal mixer and mixed at 100 ° C for 20 minutes to obtain a uniform base; S2. The base material was transferred to an open mill, 20 parts of azodicarbonamide and 5 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane were added, and mixed at 50 ° C for 10 minutes to obtain a mixture; S3. One part of platinum - divinyltetramethyldisiloxane was added to the mixture and mixed at room temperature for 5 minutes to obtain a foamable composite silicone rubber mixture; S4. The mixture was granulated by a twin-screw extruder at an extrusion temperature of 90 ° C to obtain a granular material; S5. The granular material is placed in a mold at 180°C, sulfur is added as a vulcanizing agent, and pressure-vulcanization is performed at a pressure of 10 MPa for 10 minutes. After foaming and molding, the material is cooled to room temperature by water cooling to obtain a foamable composite silicone rubber particle.

[0038] Example 2-Example 4 A foamable composite silicone rubber particle was prepared by referring to the preparation method of Example 1, except that the stabilizer was replaced with stabilizer 2 to stabilizer 4 prepared in Synthesis Examples 2 to 4, and the rest remained the same as Example 1.

[0039] Comparative Example 1 The preparation of foamable composite silicone rubber particles was carried out by referring to the preparation method of Example 1, except that the stabilizer was not added, and the rest of the preparation was the same as that of Example 1.

[0040] Comparative Example 2 The preparation of foamable composite silicone rubber particles was carried out by referring to the preparation method of Example 1, except that the mass fraction of the platinum catalyst was replaced with 5 parts, and the rest remained the same as in Example 1.

[0041] Comparative Example 3 The preparation of foamable composite silicone rubber particles was carried out by referring to the preparation method of Example 1, except that the mass fraction of the inorganic filler was changed to 10 parts, and the rest remained the same as in Example 1.

[0042] Performance testing: 1. The density of the foamable composite silicone rubber particles in the examples and comparative examples was tested according to the method of GB / T 6343-2009. The data are shown in Table 2.

[0043] 2. The flame retardancy rating of the foamable composite silicone rubber particles of the embodiment and the comparative example was tested according to the UL-94 method, and the data are shown in Table 2.

[0044] 3. The tensile strength of the foamable composite silicone rubber particles of the embodiment and the comparative example was tested according to the method of GB / T 528-2009. The data are shown in Table 2.

[0045] Table 2. Performance test data of a foamable composite silicone rubber particle of the embodiment and the comparative example.

[0046] Density g / cm³ Flame retardant grade Tensile strength MPa Example 1 0.55 V-0 2.8 Example 2 0.52 V-0 3.0 Example 3 0.50 V-0 3.2 Example 4 0.53 V-0 2.9 Comparative Example 1 0.65 V-1 1.5 Comparative Example 2 0.60 V-0 2.0 Comparative Example 3 0.70 HB 1.0 The embodiment of adding stabilizer is superior to the comparative example 1 that is not added in density, flame retardancy, tensile strength. It shows that stabilizer optimizes the lightweight, flame retardancy and mechanical properties of the material simultaneously by enhancing filler dispersion and interfacial bonding force. The flame retardancy and mechanical strength of comparative example 3 (filler dosage reduction) are significantly reduced, and the density increases, indicating that inorganic filler is crucial to maintaining the flame retardancy and structural strength of the material, and low filler amount can cause the foam structure to deteriorate. Although comparative example 2 maintains flame retardancy, density increases and tensile strength decreases, reflecting that excessive catalyst may destroy the foaming-vulcanization balance, resulting in uneven foaming and material embrittlement. The performance difference of four stabilizers (embodiments 1-4) is smaller, indicating that the effect of its core functional group is stable, and the fine-tuning of the R1 group does not significantly change the material macroscopic properties. The synergistic effect of stabilizer and inorganic filler is the key to improving performance; process parameters (catalyst dosage, filler ratio) need to be strictly controlled, otherwise the foaming structure will be deteriorated.

[0047] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A foamable composite silicone rubber particle, characterized in that: The invention is composed of the following raw materials in parts by mass: 100 parts of silicone rubber base, 10-30 parts of foaming agent, 20-80 parts of inorganic filler, 0.5-5 parts of silane coupling agent, 0.2-2 parts of platinum catalyst, 1-10 parts of auxiliary agent, and 0.5-5 parts of stabilizer; The stabilizer has a structure shown in Formula 1: Formula 1; The R1 is selected from the group consisting of: methyl, ethyl, tert-butyl, and methoxy.

2. The foamable composite silicone rubber particles according to claim 1, characterized in that: The silicone rubber base is α,ω-dihydroxy polydimethylsiloxane.

3. The foamable composite silicone rubber particles according to claim 1, characterized in that: The foaming agent is azodicarbonamide and / or sodium bicarbonate.

4. The foamable composite silicone rubber particles according to claim 1, characterized in that: The inorganic filler is magnesium hydroxide and / or talc.

5. The foamable composite silicone rubber particles according to claim 1, characterized in that: The silane coupling agent is γ-aminopropyltriethoxysilane.

6. The foamable composite silicone rubber particles according to claim 1, characterized in that: The platinum catalyst is platinum-divinyltetramethyldisiloxane; The auxiliary agent is 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

7. The foamable composite silicone rubber particles according to claim 1, characterized in that: The stabilizer is any one of the compounds shown in the following structures: ； 。 8. A method for preparing the foamable composite silicone rubber particles according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. The silicone rubber base, inorganic filler, silane coupling agent and stabilizer are added to an internal mixer and mixed at 80-120 ° C for 10-30 minutes to obtain a uniform base; S2. The base material is transferred to an open mill, a foaming agent and additives are added, and mixed at 40-60 ℃ for 5-15 minutes to obtain a mixture; S3. The platinum catalyst is added to the mixture and mixed at room temperature for 3-10 minutes to obtain a foamable composite silicone rubber mixture; S4. The foamable composite silicone rubber mixture is granulated by a twin-screw extruder at an extrusion temperature of 70-100 ℃ to obtain a granular material; S5. The granular material is placed in a mold at 160-200°C and pressurized for vulcanization for 5-20 minutes. After foaming and molding, the mold is cooled to obtain a foamable composite silicone rubber particle.

9. The method for preparing foamable composite silicone rubber particles according to claim 8, characterized in that: The mixing is carried out under an inert gas atmosphere, and the inert gas is nitrogen or argon; The vulcanizing agent in the vulcanization is sulfur.

10. The method for preparing foamable composite silicone rubber particles according to claim 8, characterized in that: The pressure of the pressurized vulcanization is 5-15 MPa, and the cooling method is water cooling or air cooling to room temperature.

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