Preparation method of low-hardness high-strength methyl vinyl silicone rubber and composition thereof

Abstract

The application discloses a preparation method of low-hardness high-strength methyl vinyl silicone rubber and a composition thereof, and belongs to the technical field of organic silicon materials. The composition comprises a compounded raw rubber system (vinyl-terminated and methyl-terminated methyl vinyl silicone rubber), fumed white carbon black, a structure control agent, hydrogen-containing silicone oil anti-yellowing agent, zinc stearate release agent, deionized water and peroxide vulcanizing agent. The preparation method comprises the following steps: after the raw rubber and the additives are mixed, the white carbon black is added in batches for mixing, vacuum heat treatment, plasticizing and vulcanization forming. Through the synergistic effect of the double-terminated raw rubber molecular design and the deionized water activation process, the mutual exclusion problem of low hardness and high strength is solved, the Shore A hardness is less than or equal to 20, the tensile strength is greater than or equal to 8 MPa, the tear strength is greater than or equal to 22.7 kN / m, the high-temperature strength retention rate is greater than 85%, and the dispersion index is less than or equal to 15%. The application is suitable for harsh scenes such as high-end medical devices and new energy power battery sealing.

Description

Technical Field

[0001] This invention relates to the field of organosilicon materials technology, specifically to a method for preparing low-hardness, high-strength methyl vinyl silicone rubber and its composition, which is applicable to high-end medical devices, new energy power battery sealing, aerospace dynamic sealing and other application fields. Background Technology

[0002] To achieve the technical target of Shore A hardness ≤25, traditional low-hardness silicone rubber generally relies on the addition of plasticizers or the reduction of filler content, leading to bottlenecks such as insufficient tensile strength (<6 MPa), deterioration of thermal stability, and decline in long-term reliability. Hu Guangfa et al. (Synthetic Rubber Industry, 2002, Vol.25, P.248-250) used a compound of single raw rubber and highly filled silica. Their scheme achieved a Shore A hardness as high as 38 (see Table 1, Comparative Example 1 data), far from meeting the ultra-low hardness requirement of ≤20A, and the tensile strength was only 6.1 MPa. This scheme highlights a long-standing industry dilemma—the antagonism between molecular chain flexibility and crosslinking density: while plasticizers or low crosslinking designs can reduce hardness, they weaken mechanical strength; while high filler reinforcement improves rigidity, it causes filler agglomeration and stress concentration.

[0003] Existing technologies have consistently failed to achieve the stringent requirements of Shore A hardness ≤20, tensile strength ≥8MPa, and tear strength ≥22.7 kN / m without plasticizers. The root cause lies in the failure to reconstruct the cross-linked network topology at the molecular level and to resolve the defects in the high-filler dispersion process. Summary of the Invention

[0004] The purpose of this invention is to provide a method and composition for preparing silicone rubber with low hardness, high tensile strength and tear strength, while ensuring processability and thermal stability, thereby solving the problem of synergistic development of silicone rubber with tensile strength ≥8MPa when Shore A hardness ≤20.

[0005] To achieve the purpose of this invention, the technical solution adopted is as follows:

[0006] A methyl vinyl silicone rubber composition, comprising, by weight:

[0007] 100 parts of a compound raw rubber system are composed of vinyl-terminated methyl vinyl silicone rubber and methyl-terminated methyl vinyl silicone rubber;

[0008] 20 to 30 parts of fumed silica;

[0009] 4 to 10 parts of structure control agent;

[0010] Hydrogen-containing silicone oil anti-yellowing agent: 0.1 to 0.5 parts;

[0011] 0.1 parts zinc stearate release agent;

[0012] 0.5 to 2 parts deionized water;

[0013] 1 to 2 parts of peroxide vulcanizing agent;

[0014] in,

[0015] The vinyl-terminated raw rubber has a molecular weight of 60×10⁻⁶. 4 g / mol up to 64×10 4 g / mol, vinyl content 0.03mol% to 0.24mol%; methyl-terminated raw rubber molecular weight 51×10 4 g / mol up to 60×10 4 g / mol, vinyl content 1.0 mol% to 3.0 mol%;

[0016] The specific surface area of ​​fumed silica ranges from 150 to 380 m² / g; the structure control agent is selected from dimethyldimethoxysilane, hexamethyldisilazane, or a combination thereof.

[0017] The mass ratio of the above-mentioned vinyl-terminated raw rubber to methyl-terminated raw rubber is 60-80:40-20.

[0018] The preparation method includes the following steps in sequence:

[0019] (a) Add raw rubber, structure control agent, release agent and deionized water into a kneader and mix for 3 to 5 minutes;

[0020] (b) Add the fumed silica in 3 to 4 equal batches, and mix each batch for 10 to 15 minutes until the surface of the compound is smooth.

[0021] (c) After adding the anti-yellowing agent, heat the temperature to 150 to 180°C and heat-treat under a vacuum of -0.06 to -0.08 MPa for 1 to 2 hours;

[0022] (d) Cool the rubber compound and plasticize it on a two-roll mill until the surface of the rubber compound is smooth and there are no visible particles. Add vulcanizing agent and mold.

[0023] Preferably, the kneader speed in step (a) is 45 r / min;

[0024] Preferably, in step (c), the heat treatment temperature is 165°C, the vacuum degree is -0.07 MPa, and the treatment time is 1.5 h;

[0025] Preferably, the vulcanization conditions in step (d) are 170°C × 10 min.

[0026] The composition is particularly suitable for use in the preparation of medical devices, new energy battery seals or aerospace seals. The performance indicators of the prepared silicone rubber are as follows: Shore A hardness ≤20, tensile strength ≥8 MPa, tear strength ≥22.7kN / m; strength retention rate after heat aging at 200℃ for 72 h ≥85%; silica dispersion index (DI) ≤15%.

[0027] This invention utilizes a synergistic design of differentiated end-capping types in a dual-end capped raw rubber compound system. Vinyl end-capping provides reactive sites to ensure crosslinking density, while methyl end-capping reduces steric hindrance and enhances molecular chain flexibility. This is achieved by matching vinyl-end capped raw rubber with low vinyl content (molecular weight 60 × 10⁻⁶). 4 g / mol up to 64×10 4 g / mol, vinyl content 0.03 mol% to 0.24 mol%) and methyl-terminated high vinyl content raw rubber (51×10 g / mol, vinyl content 0.03 mol% to 0.24 mol%) 4 g / mol up to 60×10 4 By combining a specific blend ratio to precisely match molecular weight and vinyl distribution, along with an innovative combination of hydrolytically oriented structural control agents and a stepwise water pretreatment process, the contradiction between low hardness and high strength has been resolved, achieving the following breakthroughs: Shore A hardness consistently below 20, tensile strength above 8 MPa; tear strength ≥22.7 kN / m; strength retention rate greater than 85% after 72 hours of heat aging at 200℃; silica dispersion index DI ≤15% reaching excellent grade; and no sticking or oil seepage on rollers. This invention breaks through the limits of material performance with its "ultra-soft and high-strength" characteristics, providing a new generation of sealing and flexible load-bearing solutions for fields such as medical health, new energy, and high-end equipment, representing a significant technological leap. Detailed Implementation

[0028] Example 1

[0029] 70 parts of vinyl-terminated raw rubber (Dow Corning® E60, molecular weight 62×10⁻⁶) were used to... 4 g / mol, vinyl content 0.15mol%), 30 parts methyl-terminated raw rubber (Wacker® PR40, molecular weight 55×10 g / mol, vinyl content 0.15mol%), 4Add g / mol of vinyl 2.2 mol%, 8 parts of dimethyldimethoxysilane, 0.1 parts of zinc stearate, and 1.0 parts of deionized water to a kneader (SHR-10L, 45 r / min) and mix for 4 min. Add 25 parts of fumed silica (Evonik AEROSIL® 200, specific surface area 200 m² / g) in 4 batches and mix for 12 min per batch. Add 0.3 parts of hydrogen-containing silicone oil (hydrogen content 1.0%), heat to 165℃ and treat under -0.07 MPa vacuum for 1.5 h. After cooling, plasticize the compound on a two-roll mill (XK-160) until the surface of the compound is smooth and there are no visible particles. Add 1.5 parts of 2,5-di(tert-butylperoxy)hexane for vulcanization (170℃ × 10 min).

[0030] Example 2

[0031] 60 parts of vinyl-terminated raw rubber (Dow Corning® E60, molecular weight 62×10⁻⁶) were used. 4 g / mol, vinyl content 0.15mol%), 40 parts of methyl-terminated raw rubber (Wacker® PR40, molecular weight 55×10 g / mol, vinyl content 0.15mol%), 4 Add g / mol (vinyl 2.2 mol%), 10 parts hexamethyldisilazane, 0.1 parts zinc stearate, and 1.5 parts deionized water to a kneader (SHR-10L, 45 r / min) and mix for 4 min; add 28 parts fumed silica (Evonik AEROSIL® 200, specific surface area 200 m² / g) in 4 batches, and mix each batch for 12 min; add 0.4 parts hydrogen-containing silicone oil (hydrogen content 1.0%), heat to 165℃ and treat under -0.07 MPa vacuum for 1.5 h; after cooling, plasticize on a two-roll mill (XK-160) until the rubber compound has a smooth surface and no visible particles, and add 1.6 parts 2,5-di(tert-butylperoxy)hexane for vulcanization (170℃ × 10 min).

[0032] Example 3

[0033] 80 parts of vinyl-terminated raw rubber (Dow Corning® E60, molecular weight 62×10⁻⁶) were used. 4 g / mol, vinyl content 0.15mol%), 20 parts methyl-terminated raw rubber (Wacker® PR40, molecular weight 55×10 g / mol, vinyl content 0.15mol%), 4Add g / mol of vinyl 2.2 mol%, 3 parts of dimethyldimethoxysilane, 3 parts of hexamethyldisilazane, 0.1 parts of zinc stearate, and 0.8 parts of deionized water to a kneader (SHR-10L, 45 r / min) and mix for 4 min; add 22 parts of fumed silica (Evonik AEROSIL® 200, specific surface area 200 m² / g) in 3 batches, and mix each batch for 12 min; add 0.3 parts of hydrogen-containing silicone oil (hydrogen content 1.0%), heat to 165℃ and treat under -0.07 MPa vacuum for 1.5 h; after cooling, plasticize on an open mill until the rubber compound has a smooth surface and no visible particles, and add 1.6 parts of 2,5-di(tert-butylperoxy)hexane for vulcanization (170℃×10 min).

[0034] Comparative Example 1

[0035] The following scheme was implemented based on the literature described by Hu Guangfa et al., "Formulation Design for Improving Tear Strength of Low-Hardness Silicone Rubber" (Synthetic Rubber Industry, 2002, Vol. 25, pp. 248-250):

[0036] Formula: Methyl vinyl silicone rubber raw material (molecular weight 60×10⁻⁶) 4 100 parts of fumed silica (g / mol, vinyl content 0.15 mol%), 25 parts of fumed silica (specific surface area 200 m² / g), 4 parts of hydroxyl silicone oil, 0.6 parts of diphenylsilanediol, and 0.6 parts of 2,5-bis(tert-butylperoxide)-2,5-hexane.

[0037] Preparation process: After kneading the raw rubber and the structuring control agent for 3 min, add the fumed silica at once and mix for 30 min; after cooling, add the vulcanizing agent and pass through it 5 times, then vulcanize at 160℃ for 15 min to form the product.

[0038] Table 1. Performance Comparison of Examples and Comparative Examples

[0039] Components / Performance unit Example 1 Example 2 Example 3 Comparative Example 1 Vinyl end capped raw rubber share 70 60 80 100 Methyl-terminated raw rubber share 30 40 20 0 precipitate share 25 28 22 25 Deionized water share 1.0 1.5 0.8 0 Shore A hardness - 18 19 20 38 Tensile strength MPa 8.9 8.5 8.2 6.1 Tear strength kN / m 24.3 23.1 22.7 18.5 Dispersion Index (DI) % 12.8 13.1 13.8 34.2 Roller sticking phenomenon - none none none serious

[0040] Table 2 Performance comparison between Example 1 and Comparative Example 1

[0041] Testing items Example 1 Comparative Example 1 Test Standards Shore A hardness - 18 38 GB / T 531.1-2008 Tensile strength MPa 8.9 6.1 GB / T 528-2009 Tear strength kN / m 24.3 18.5 GB / T 529-2008 Dispersion Index (DI) % 12.8 34.2 GB / T 11210-2014 (200±2)℃×(72±0.5)h strength retention rate % 87.5 62.3 ASTM D573-2018

[0042] Table 3. Vulcanization kinetics test (according to ASTM D5289):

[0043] sample T90 (min) Maximum torque (dN·m) Minimum torque (dN·m) Example 1 2.1 8.7 0.9 Comparative Example 1 3.4 6.2 1.5

[0044] Data shows that the compound raw rubber system shortens the T90 by 37.5% and increases the maximum torque by 40.3%.

[0045] Detected using a Fourier transform infrared spectrometer (Nicolet iS50, KBr pellet method):

[0046] Unmodified silica:

[0047] 3420 cm -1 A broad peak (OH stretching vibration).

[0048] Modified silica of this invention:

[0049] 3420 cm -1 Peak shifted to 3350 cm -1 Furthermore, the half-peak width narrowed by 18% (hydrogen bonding weakened);

[0050] 1080 cm -1 Characteristic Si-O-Si peaks appear at (1060-1100 cm⁻¹) -1 (Standard range).

[0051] sample Average particle size (μm) Standard deviation (μm) Dispersion Index (DI)% Example 1 1.25 0.16 12.8 Example 2 1.28 0.17 13.1 Example 3 1.3 0.18 13.8 Comparative Example 1 2.37 0.81 34.2

[0052] Table 4. Packing Dispersibility Indicators

[0053] According to the national standard GB / T 11210-2014, the dispersion index of silica in Example 1 was 12.8%, which was significantly better than that of Comparative Example 1 (34.2%), confirming that step-by-step filling and deionized water pretreatment significantly improved the dispersion uniformity (DI≤15% is excellent grade).

Claims

1. A low-hardness, high-strength methyl vinyl silicone rubber composition, characterized in that, It consists of the following components in parts by weight: 100 parts of a compound raw rubber system are composed of vinyl-terminated methyl vinyl silicone rubber and methyl-terminated methyl vinyl silicone rubber; 20 to 30 parts of fumed silica; 4 to 10 parts of structure control agent; Hydrogen-containing silicone oil anti-yellowing agent: 0.1 to 0.5 parts; 0.1 parts zinc stearate release agent; 0.5 to 2 parts deionized water; 1 to 2 parts of peroxide vulcanizing agent; in, The vinyl-terminated methyl vinyl silicone rubber has a molecular weight of 62 × 10⁻⁶. 4 g / mol, vinyl content 0.15 mol% The methyl-terminated methyl vinyl silicone rubber has a molecular weight of 55 × 10⁻⁶. 4 g / mol, vinyl content 2.2 mol% The mass ratio of the vinyl-terminated methyl vinyl silicone rubber to the methyl-terminated methyl vinyl silicone rubber is 60-80:40-20; The specific surface area of ​​the fumed silica is 150 m² / g to 380 m² / g. The structuring control agent is selected from dimethyldimethoxysilane, hexamethyldisilazane, or a combination thereof; The silicone rubber prepared from the above composition has a Shore A hardness ≤20, tensile strength ≥8 MPa, tear strength ≥22.7 kN / m; strength retention rate ≥85% after heat aging at 200℃ for 72 h; and silica dispersion index DI ≤15%.

2. A method for preparing low-hardness, high-strength methyl vinyl silicone rubber using the composition as described in claim 1, characterized in that, The steps are as follows: (a) Add raw rubber, structure control agent, release agent and deionized water into a kneader and mix for 3 to 5 minutes; (b) Add the fumed silica in 3 to 4 equal batches, and mix each batch for 10 to 15 minutes until the surface of the compound is smooth. (c) After adding the anti-yellowing agent, heat the temperature to 150°C to 180°C and heat-treat under a vacuum of -0.06 MPa to -0.08 MPa for 1 to 2 hours; (d) Cool the rubber compound and plasticize it on a two-roll mill until the surface is smooth and free of particles, then add vulcanizing agent to form it.

3. The preparation method according to claim 2, characterized in that: In step (a), the kneader speed is 45 r / min; In step (c), the heat treatment temperature is 165℃, the vacuum degree is -0.07 MPa, and the treatment time is 1.5 h. The vulcanization conditions in step (d) are 170℃ × 10 min.