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

Abstract

The invention discloses a preparation method and a composition of low-hardness and high-strength methyl vinyl silicone rubber, and belongs to the technical field of organic silicon materials. The composition comprises a compound raw rubber system (vinyl-terminated and methyl-terminated methyl vinyl silicone rubber), fumed silica, a structured control agent, a hydrogen-containing silicone oil anti-yellowing agent, a zinc stearate release agent, deionized water and a peroxide vulcanizing agent. The preparation method comprises the following steps: mixing the raw rubber and the auxiliary agent, adding the white carbon black in batches for mixing, and carrying out vacuum heat treatment, plastication and vulcanization molding. Through the cooperation of the double-end-capped raw rubber molecule design and the deionized water activation process, the problem of mutual exclusion of low hardness and high strength is solved, the Shore A hardness is smaller than or equal to 20, the tensile strength is larger than or equal to 8 MPa, the tearing strength is larger than or equal to 22.7 kN / m, the high-temperature strength retention rate is larger than 85%, and the dispersion index is smaller than or equal to 15%. And the sealing device is suitable for severe scenes such as high-end medical equipment and new energy power battery sealing.

Description

Technical Field

[0001] The present invention relates to the technical field of organic silicon materials, and specifically to a preparation method of low-hardness and high-strength methyl vinyl silicone rubber and a composition thereof, which is suitable for application fields such as high-end medical devices, new energy power battery seals, and aerospace dynamic seals. Background Art

[0002] To achieve the technical goal of a Shore A hardness of ≤25, traditional low-hardness silicone rubber generally relies on the addition of plasticizers or reduced filler content. This leads to bottlenecks such as insufficient tensile strength (<6 MPa), degraded thermal stability, and reduced long-term reliability. Hu Guangfa et al. (Synthetic Rubber Industry, 2002, Vol. 25, pp. 248-250) employed a single base rubber compound with highly filled silica. Their solution achieved a measured Shore A hardness as high as 38 (see Table 1, Comparative Example 1), far below the ultra-low hardness requirement of ≤20A, and exhibited a tensile strength of only 6.1 MPa. This solution highlights a long-standing industry dilemma: the conflict between molecular chain flexibility and crosslink density. While plasticizers or low crosslinking can reduce hardness, they weaken mechanical strength. While high filler reinforcement improves rigidity, it can also cause filler agglomeration and stress concentration.

[0003] Existing technologies have always been unable to synergistically achieve the stringent indicators of Shore A hardness ≤ 20, tensile strength ≥ 8MPa, and tear strength ≥ 22.7 kN / m without plasticizers. The root cause is the failure to reconstruct the cross-linked network topology at the molecular level and solve the defects of the high-filling dispersion process. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing silicone rubber and its composition with low hardness, high tensile strength and tear strength while ensuring processability and thermal stability, so as to solve the collaborative problem of silicone rubber having a tensile strength of ≥8MPa when the Shore A hardness is ≤20.

[0005] In order to achieve the purpose of the invention, the technical solution adopted by the present invention is:

[0006] A methyl vinyl silicone rubber composition comprising, in parts by mass:

[0007] 100 parts of compound raw rubber system, consisting 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 a structure control agent;

[0010] 0.1 to 0.5 parts of hydrogenated silicone oil anti-yellowing agent;

[0011] 0.1 part of zinc stearate release agent;

[0012] 0.5 to 2 parts deionized water;

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

[0014] in,

[0015] The molecular weight of the vinyl terminated rubber is 60×10 4 g / mol to 64×10 4 g / mol, vinyl content 0.03mol% to 0.24mol%; methyl terminated rubber molecular weight 51×10 4 g / mol to 60×10 4 g / mol, vinyl content 1.0 mol% to 3.0 mol%;

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

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

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

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

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

[0021] (c) adding an anti-yellowing agent, raising the temperature to 150 to 180° C., and heat treating at a vacuum degree of −0.06 to −0.08 MPa for 1 to 2 hours;

[0022] (d) The cooled rubber compound is plasticized on a mixing mill until the surface is smooth and free of visible particles, and then a vulcanizing agent is added to form the compound.

[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 condition in step (d) is 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 prepared silicone rubber has the following performance indicators: Shore A hardness ≤ 20, tensile strength ≥ 8 MPa, tear strength ≥ 22.7 kN / m; strength retention rate after heat aging at 200°C for 72 h ≥ 85%; and silica dispersion index (DI) ≤ 15%.

[0027] The present invention adopts the collaborative design of different end-capping types in the double-end-capped raw rubber compound system, uses vinyl end-capping to provide reactive sites to ensure cross-linking density, and methyl end-capping to reduce steric hindrance and enhance molecular chain flexibility, matching the vinyl end-capped low vinyl content raw rubber (molecular weight 60×10 4 g / mol to 64×10 4 g / mol, vinyl content 0.03 mol% to 0.24 mol%) and methyl terminated high vinyl content rubber (51×10 4 g / mol to 60×10 4 g / mol, vinyl content 1.0 mol% to 3.0 mol%), a specific blend ratio precisely matching molecular weight and vinyl distribution, along with a hydrolyzable structuring control agent and a step-by-step water pretreatment process, solve the conflict between low hardness and high strength, achieving the following breakthroughs: Shore A hardness consistently below 20, tensile strength exceeding 8 MPa, tear strength ≥ 22.7 kN / m, strength retention greater than 85% after 72 hours of heat aging at 200°C, silica dispersion index (DI) ≤ 15%, achieving excellent results, and no roll sticking or oil seepage. This invention surpasses the limits of material performance with its "ultra-soft, high-strength" properties, providing a new generation of sealing and flexible load-bearing solutions for healthcare, new energy, high-end equipment, and other fields, representing a significant technological advancement. DETAILED DESCRIPTION

[0028] Example 1

[0029] 70 parts of vinyl terminated rubber (Dow Corning® E60, molecular weight 62×10 4 g / mol, vinyl content 0.15 mol%), 30 parts of methyl-terminated rubber (WACKER® PR40, molecular weight 55×10 4g / mol, 2.2 mol% vinyl), 8 parts of dimethyldimethoxysilane, 0.1 parts of zinc stearate, and 1.0 parts of deionized water were put into a kneader (SHR-10L, 45 r / min) and mixed for 4 minutes; 25 parts of fumed silica (Evonik AEROSIL® 200, specific surface area 200 m² / g) were added in 4 batches, and each batch was mixed for 12 minutes; after adding 0.3 parts of hydrogenated silicone oil (hydrogen content 1.0%), the temperature was raised to 165℃ and treated under a vacuum of -0.07 MPa for 1.5 hours; after cooling, the rubber compound was masticated on an open mill (XK-160) until the surface was smooth and no visible particles were visible, and 1.5 parts of 2,5-di(tert-butylperoxy)hexane were added for vulcanization (170℃×10 min).

[0030] Example 2

[0031] 60 parts of vinyl terminated rubber (Dow Corning® E60, molecular weight 62×10 4 g / mol, vinyl content 0.15 mol%), 40 parts of methyl-terminated rubber (WACKER® PR40, molecular weight 55×10 4 g / mol, 2.2 mol% vinyl), 10 parts of hexamethyldisilazane, 0.1 parts of zinc stearate, and 1.5 parts of deionized water were put into a kneader (SHR-10L, 45 r / min) and mixed for 4 minutes; 28 parts of fumed silica (Evonik AEROSIL® 200, specific surface area 200 m² / g) were added in four batches, and each batch was mixed for 12 minutes; after adding 0.4 parts of hydrogenated silicone oil (hydrogen content 1.0%), the temperature was raised to 165°C and treated under a vacuum of -0.07 MPa for 1.5 hours; after cooling, the rubber compound was masticated on an open mill (XK-160) until the surface was smooth and no visible particles were visible, and 1.6 parts of 2,5-di(tert-butylperoxy)hexane were added for vulcanization (170°C × 10 min).

[0032] Example 3

[0033] 80 parts of vinyl terminated rubber (Dow Corning® E60, molecular weight 62×10 4 g / mol, vinyl content 0.15 mol%), 20 parts of methyl-terminated rubber (WACKER® PR40, molecular weight 55×10 4g / mol, 2.2 mol% vinyl), 3 parts of dimethyldimethoxysilane, 3 parts of hexamethyldisilazane, 0.1 parts of zinc stearate, and 0.8 parts of deionized water were put into a kneader (SHR-10L, 45 r / min) and mixed for 4 minutes; 22 parts of fumed silica (Evonik AEROSIL® 200, specific surface area 200 m² / g) were added in three batches, and each batch was mixed for 12 minutes. After adding 0.3 parts of hydrogenated silicone oil (hydrogen content 1.0%), the temperature was raised to 165℃ and treated under a vacuum of -0.07 MPa for 1.5 hours. After cooling, the rubber compound was masticated on an open mill until the surface was smooth and no visible particles were visible. 1.6 parts of 2,5-di(tert-butylperoxy)hexane was added and vulcanized (170℃×10 min).

[0034] Comparative Example 1

[0035] According to the document "Formulation Design for Improving the Tear Strength of Low-Hardness Silicone Rubber" by Hu Guangfa et al. (Synthetic Rubber Industry, 2002, Vol. 25, P. 248-250), the following solution was implemented:

[0036] Formula: Methyl vinyl silicone rubber (molecular weight 60×10 4 g / mol, vinyl content 0.15 mol%) 100 parts, fumed silica (specific surface area 200 m² / g) 25 parts, hydroxy silicone oil 4 parts, diphenylsilane diol 0.6 parts, 2,5-bis(tert-butylperoxy)-2,5-hexane 0.6 parts.

[0037] Preparation process: After kneading the raw rubber and the structure control agent for 3 minutes, add the white carbon black at one time and mix for 30 minutes; after cooling, add the vulcanizing agent and pass it through 5 times, and vulcanize at 160℃ for 15 minutes to form.

[0038] Table 1 Performance comparison between examples and comparative examples

[0039] Components / Performance unit Example 1 Example 2 Example 3 Comparative Example 1 Vinyl terminated rubber share 70 60 80 100 Methyl terminated rubber share 30 40 20 0 Silica 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] Test 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 % 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] The data show that the compounded raw rubber system shortens T90 by 37.5% and increases the maximum torque by 40.3%.

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

[0046] Unmodified silica:

[0047] 3420 cm -1 There is a broad peak (OH stretching vibration).

[0048] Modified silica of the present invention:

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

[0050] 1080 cm -1 The Si-O-Si characteristic peak (1060-1100 cm -1 standard interval).

[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 Filler dispersion index

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

Claims

1. A low hardness and high strength methyl vinyl silicone rubber composition, characterized in that: Contains the following components by mass: 100 parts of compound raw rubber system, consisting 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 a structure control agent; 0.1 to 0.5 parts of hydrogenated silicone oil anti-yellowing agent; 0.1 part of zinc stearate release agent; 0.5 to 2 parts deionized water; 1 to 2 parts of peroxide curing agent; in, The molecular weight of the vinyl terminated rubber is 60×10 4 g / mol to 64×10 4 g / mol, vinyl content 0.03 mol% to 0.24 mol%; The molecular weight of the methyl terminated rubber is 51×10 4 g / mol to 60×10 4 g / mol, vinyl content 1.0 mol% to 3.0 mol%; The mass ratio of the vinyl terminated rubber to the methyl terminated 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 composition has a Shore A hardness of ≤20, a tensile strength of ≥8 MPa, a tear strength of ≥22.7 kN / m, a strength retention rate of ≥85% after heat aging at 200°C for 72 h, and a silica dispersion index (DI) of ≤15%.

2. A method for preparing a low-hardness, high-strength methyl vinyl silicone rubber using the composition as claimed in claim 1, characterized in that: The following steps are included in sequence: (a) Place the raw rubber, structure control agent, release agent, and deionized water into a kneader and mix for 3 to 5 minutes; (b) Add fumed silica in 3 to 4 equal batches, mixing each batch for 10 to 15 minutes until the surface of the rubber compound is smooth; (c) adding an anti-yellowing agent, heating to 150°C to 180°C, and heat treating at a vacuum of -0.06 MPa to -0.08 MPa for 1 to 2 h; (d) The cooled rubber compound is plasticized in an open mill until the surface is smooth and free of particles, and then a vulcanizing agent is added to form the compound.

3. The preparation method according to claim 2, wherein: The kneader speed in step (a) is 45 r / min; 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; The vulcanization condition in step (d) is 170° C.×10 min.