Anti-scorching high-hardness extrusion molding silicone rubber

Abstract

This invention discloses a scorch-resistant, high-hardness extruded silicone rubber, comprising the following raw materials in parts by weight: 92-98 parts of methyl vinyl silicone rubber A and 2-8 parts of methyl vinyl silicone rubber B, totaling 100 parts; further comprising: 6-10 parts of a structure control agent, 0.05-0.5 parts of an internal release agent, 50-70 parts of reinforcing silica, 0.1-0.5 parts of an anti-blooming agent, 3-5 parts of a silicone heat resistant agent, and 1-3 parts of a hardening additive composition; the hardening additive composition is made from the following components: 100 parts of hydroxyl silicone oil, 20-40 parts of 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide, 80-120 parts of multifunctional acrylate, and 20-30 parts of hydrophobic fumed silica. This invention utilizes multifunctional acrylate to enhance the hardness of the silicone resin, and 4-hydroxyl TEMPO acts as a free radical scavenger to extend the scorch time; it exhibits good extrudability and extended shelf life.

Description

Technical Field

[0001] This invention belongs to the field of silicone rubber production technology, specifically relating to a scorch-resistant, high-hardness extruded silicone rubber. Background Technology

[0002] Methyl vinyl silicone rubber is a copolymer of dimethylsiloxane and a small amount of vinylsiloxane, with a vinyl content typically ranging from 0.1% to 0.3 mol%. The introduction of a small amount of unsaturated vinyl groups significantly improves its vulcanization process and finished product properties, particularly its resistance to heat aging and high-temperature compression set. General-purpose methyl vinyl silicone rubber has high temperature resistance and excellent flexibility, oil resistance, and water resistance.

[0003] bis-(2,4-dichlorobenzoyl peroxide), CAS No.: 1115-91-9, is the most commonly used peroxide vulcanizing agent for silicone rubber extrusion molding. It has the characteristics of high reactivity and fast vulcanization speed. However, its decomposition temperature (45℃) is relatively low, which makes the rubber compound very prone to scorching (or self-vulcanization) during processing and storage.

[0004] Furthermore, there are generally two approaches to preparing high-hardness bis(2,4)v2 vulcanizate silicone rubber: One is to increase the average vinyl content of the formulation. This method is effective in improving the hardness of medium- and low-hardness compounds, but its ability to further improve the hardness of high-hardness silicone rubber (e.g., at 70°C and above) is limited. This is because bis(2,4)v2 vulcanizate is a highly active general-purpose vulcanizate, and when the vinyl content is too high, the effect on hardness improvement has a marginal effect. The second approach is to significantly increase the proportion of powdered filler (usually silica). However, excessive silica can lead to problems such as high Mooney viscosity of the silicone rubber, difficulty in extrusion, and deterioration of mechanical properties.

[0005] Patent document CN108219476A discloses a heat-resistant silicone rubber compound, comprising the following components by weight: 80-120 parts methyl vinyl raw rubber, 40-60 parts fumed silica, 812 parts methoxy silicone oil, 15 parts nano titanium dioxide, 15 parts nano cerium dioxide, 0.5-2.5 parts phenyl silicone oil, and 0.1-0.9 parts zinc stearate. The nano cerium dioxide is obtained by modification using the following steps: Step 1: Mix 1-5 parts nano cerium dioxide, 2-8 parts diisopropyl hydrogen peroxide, and 1-2 parts silicon by weight, and react at 150°C for 2-4 hours. In this document, cerium dioxide and titanium dioxide cannot react directly with silicon dioxide; diisopropyl hydrogen peroxide is added as an initiator to form silicon-coated nano cerium dioxide and silicon-coated nano titanium dioxide, which significantly enhance the heat resistance of the silicone rubber compound. However, this document does not mention improvements in hardness or resistance to scorching.

[0006] Patent document CN121343364A discloses a high-hardness, easily cut silicone rubber material, its preparation method, and its application, comprising the following components in parts by weight: 100 parts methyl vinyl silicone rubber, 25-40 parts fumed silica, 1.5-3 parts hydroxyl silicone oil, 0.8-1.2 parts crosslinking agent, 0.05-0.1 parts platinum catalyst, and 1-2 parts heat-resistant stabilizer. This document achieves synergistic optimization of the Shore hardness and elongation at break of the silicone rubber material through the screening and synergistic compounding of specific components, ensuring that the material exhibits no cracking after aging at 180℃ for 3000 hours. However, this document increases hardness by increasing the content of fumed silica and vinyl groups, without using hardening additives or addressing scorch resistance.

[0007] Patent document CN112063172A discloses a high-hardness, gas-pressure-resistant silicone rubber and its preparation method, comprising the following raw materials in parts by weight: 4-8 parts of hydroxyl-terminated polydimethylsiloxane, 100-115 parts of methyl vinyl silicone rubber, 60-70 parts of modified fumed silica, 1-3 parts of vinyl hydroxyl silicone oil, 0.4-0.8 parts of silane coupling agent, 0.06-0.18 parts of release agent, and 0-1.5 parts of hardening agent. Although this document also uses silicone rubbers with different vinyl contents, it mainly relies on the physical filling and hardening of inorganic / organic rigid particles (ceramic powder, quartz powder, PMMA powder, etc.), and the hardening mechanism is completely different.

[0008] Patent document CN110606986A discloses a silicone rubber crosslinking agent containing a dynamic covalent bond (C-ON bond) of "nitrile radical (TEMPO derivative)-styrene," with Si-H bonds at both ends. The preparation method involves reacting nitrile radical piperidinol and styrene under the action of an initiator to obtain alkoxyamine diol; then, adding the alkoxyamine diol (containing C-ON bonds) to a catalyst, an acid-binding agent, and a reaction medium, followed by the dropwise addition of chlorosilane to obtain the final crosslinking agent. This method achieves the reproducible processability (thermoplasticity) of silicone rubber itself, independent of other plastic matrices. However, the TEMPO derivative in this document is covalently linked to the crosslinking agent molecule, becoming part of the crosslinking network; while this invention uses 4-hydroxy TEMPO as a small-molecule free radical scavenger, not participating in the final crosslinking network, existing in a physically dispersed form in the rubber compound, inhibiting the decomposition of the vulcanizing agent at room temperature, and achieving anti-scorching. Summary of the Invention

[0009] This invention provides a scorch-resistant, high-hardness extruded silicone rubber, aiming to solve the problems in the existing technology, such as the high scorch risk (short shelf life) of the bis(2,4) vulcanization system, the bottleneck in hardness improvement (≥70A is difficult to achieve), poor processability due to high filler content, and the systematic design of hardening additives.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention discloses a scorch-resistant, high-hardness extruded silicone rubber comprising the following raw materials in parts by weight: 92-98 parts of methyl vinyl silicone rubber A and 2-8 parts of methyl vinyl silicone rubber B, the total of which is 100 parts; further comprising: 6-10 parts of a structure control agent, 0.05-0.5 parts of an internal release agent, 50-70 parts of reinforcing silica, 0.1-0.5 parts of an anti-blooming agent, 3-5 parts of a silicone heat resistant agent, and 1-3 parts of a hardening additive composition; The methyl vinyl silicone rubber A is a vinyl-terminated methyl vinyl silicone rubber raw rubber with an average molecular weight of 600,000 to 700,000; wherein the molar content of vinyl is 0.05% to 0.25%, and it is composed of 1 to 3 silicone rubbers with different vinyl contents within this content range, such as the methyl vinyl silicone rubber raw rubber of Hesheng Silicon Industry 110 series, and the methyl phenyl vinyl silicone rubber IOTA 3120 and IOTA 120 of Anhui Aiyota; it is used for addition reaction to grow the main chain; The methyl vinyl silicone rubber B is a methyl-terminated methyl vinyl silicone rubber raw rubber with an average molecular weight of 500,000 to 600,000; wherein the molar content of vinyl is 1% to 10%, and it is made by mixing 1 to 3 silicone rubbers with different vinyl contents within this content range; for example, the methyl vinyl silicone rubber raw rubber of the 112-4 to 112-9 series from Hesheng Silicon Industry. The structure control agent is hydroxyl silicone oil or methoxy silicone oil (also known as methoxy-terminated polydimethylsiloxane, with a viscosity of 5-20 mm at 25°C). 2 At least one of the following: / s), vinyl hydroxyl silicone oil, dimethyl dimethoxysilane, dimethyl diethoxysilane, hexamethyldisilazane, and vinylsilazane; The internal release agent is at least one of zinc stearate, calcium stearate, magnesium stearate, barium stearate, stearic acid, and octadecyl alcohol. The reinforcing silica is precipitated silica and / or fumed silica, preferably fumed silica; the specific surface area is 150–300 g / m². 2 Preferred concentration: 190–220 g / m 2 ; The anti-blooming agent is nano-active magnesium oxide, used to suppress surface blooming problems after di-tetrasulfidation; for example, the active magnesium oxide from Shanghai Huijingya Nanomaterials Co., Ltd. The heat-resistant silica gel agent is nano-cerium dioxide (CeO2) or cerium trioxide (Ce2O3); The hardening additive composition is made from the following components in parts by weight: 100 parts hydroxyl silicone oil, 20-40 parts 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide (4-hydroxyTEMPO), 80-120 parts polyfunctional acrylate, and 20-30 parts hydrophobic fumed silica; wherein the hydroxyl silicone oil has a viscosity of 25-50 mm at 25°C.2 / s, such as Dow Corning PMX-0930; used to dissolve 4-hydroxy TEMPO as a dispersant to ensure uniform distribution of 4-hydroxy TEMPO in the rubber compound; the 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide (4-hydroxy TEMPO, CAS: 2226-96-2, polymerization inhibitor 701) is an orange-red flake compound at room temperature and requires pre-dispersion; as a free radical scavenger, it exists in free or physically dispersed form, does not participate in the formation of crosslinking networks, does not affect vulcanization, can block free radical reactions, releases activity at high temperatures, and inhibits early crosslinking at room temperature. The compound is designed to resist scorching, preventing the rubber compound from burning and extending its shelf life and processing safety time. The multifunctional acrylate is at least one of trimethylolpropane trimethacrylate (TMPTMA), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), and dipentaerythritol hexaacrylate (DPHA). During vulcanization, it forms additional crosslinking points, increasing the crosslinking density and compensating for the slight crosslinking delay that may be caused by the presence of 4-hydroxy TEMPO, ensuring that the hardness meets the requirements. The hydrophobic fumed silica has a specific surface area of ​​180–220 g / m². 2 For example, Wacker HDK H20; as a thickener and anti-settling agent, it is used to prevent the aggregation of additives, improve flowability, and ensure the stability of the composition during storage and transportation.

[0011] The preparation method of the hardening agent composition includes the following steps: (1) adding hydroxy silicone oil to a reaction vessel, heating to 100-120°C, and dehydrating under a vacuum of -0.065--0.09 MPa for 30-60 min; (2) cooling to 70-80°C, slowly adding 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide under stirring, and stirring until completely dissolved; (3) continuing to cool to 50-60°C, slowly adding the multifunctional acrylate, and stirring for 30-80 min after the addition is complete; (4) adding the hydrophobic fumed silica in batches, dispersing at high speed until a uniform paste is formed, cooling to room temperature, and discharging to obtain the hardening agent composition.

[0012] The method for preparing the scorch-resistant, high-hardness extruded silicone rubber of the present invention includes the following steps: S1, add the methyl vinyl silicone rubber A, methyl vinyl silicone rubber B, structure control agent and internal release agent to a kneader at 60-75°C and stir evenly; S2, the reinforcing silica is added to the kneader in batches and stirred evenly to form a dough, forming a rubber compound, and the material temperature is controlled not to exceed 120℃; then the rubber compound is left to stand for 4 to 8 hours; S3, the rubber compound is mixed at a constant temperature of 150-170℃ under a vacuum of not less than -0.075MPa for 1-3 hours; S4. Cool the rubber compound to 100-120°C, add the composition of anti-blowing agent, silicone heat resistant agent and hardening agent, stir evenly and discharge; cut the rubber and cool for 4-8 hours, then extrude, filter and vacuum package to obtain scorch-resistant high-hardness extrusion molding silicone rubber.

[0013] Compared with the prior art, the present invention has the following advantages: This invention is the first to propose the combination of multifunctional acrylates and 4-hydroxy TEMPO for use in peroxide-cured (especially di-2,4-dichloro) silicone rubber systems. Through the synergistic effect of chemical crosslinking hardening and anti-scorching, the unity of "storable, easy to process, and high hardness" is achieved: (1) Hardening function: Under the initiation of free radicals generated by the decomposition of di-2,4-dichlorophenoxy ... (2) Anti-scorching function: 4-hydroxy TEMPO is a stable nitrogen oxide free radical with high antioxidant activity. At room temperature, it can effectively capture the primary free radicals generated by the decomposition of bis(2,4) vulcanizing agent, which can quickly terminate the reaction and inhibit the early cross-linking reaction, thereby prolonging the scorching time and storage period of the rubber compound. When the vulcanization temperature increases (>150℃), the activity of 4-hydroxy TEMPO decreases or thermal decomposition occurs, releasing free radicals and allowing the vulcanization reaction to proceed normally.

[0014] This invention also incorporates nano-active cerium dioxide as a heat-resistant agent. CeO2 can capture free radicals at high temperatures, inhibiting the degradation of the silicone rubber backbone. It forms a dual free radical capture mechanism with 4-hydroxy TEMPO: 4-hydroxy TEMPO dominates anti-scorching at room temperature or processing temperatures, while CeO2 dominates heat aging resistance at high temperatures or aging environments. This synergistic heat resistance + anti-scorching mechanism has not been reported in existing literature.

[0015] Compared with existing technologies, this application overcomes the technical bias of "hardening inevitably leads to scorching" in the bis(2,4) vulcanization system, and avoids the processability degradation caused by physical filler hardening through chemical cross-linking hardening. The raw materials of this invention are readily available, the process is simple, the equipment is universal, the cost is controllable, it is suitable for mass production, and it is applicable to extruded products (sealing strips, pipes, miscellaneous parts, etc.). Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 The preparation method of the hardening additive composition includes the following steps: (1) 100 parts of hydroxyl silicone oil (Dow Corning PMX-0930) are added to the reaction vessel, heated to 110°C, and dehydrated under a vacuum of -0.08MPa for 30 min; (2) the temperature is lowered to 80°C, and 30 parts of 4-hydroxy TEMPO (chemically pure, Leyan Chemical Reagent) are slowly added under stirring, and stirred for about 28 min until completely dissolved; (3) the temperature is further lowered to 55°C, and 100 parts of multifunctional acrylate (trimethylolpropane triacrylate) are slowly added dropwise under nitrogen protection, with the dropwise addition time controlled at 20-30 min, and the temperature is maintained and stirred for 30 min after the dropwise addition is completed; (4) 30 parts of hydrophobic fumed silica (Wacker HDK) are added in 2-3 portions. H2O (treated with HMDS) is dispersed at high speed (800-1000 rpm) until a uniform, fine, and flowable paste is formed. After cooling to room temperature, the hardening additive composition is obtained by discharging.

[0018] Example 2 The preparation method of the hardening agent composition includes the following steps: (1) 100 parts of hydroxyl silicone oil (Dow Corning PMX-0930) are added to the reaction vessel, heated to 110°C, and dehydrated under a vacuum of -0.08MPa for 30 min; (2) the temperature is lowered to 80°C, and 20 parts of 4-hydroxy TEMPO (chemically pure, Leyan Chemical Reagent) are slowly added under stirring, and stirred for about 28 min until completely dissolved; (3) the temperature is further lowered to 55°C, and 80 parts of polyfunctional acrylate (trimethylolpropane triacrylate) are slowly added dropwise under nitrogen protection, with the dropwise time controlled at 20-30 min, and the temperature is kept warm and stirred for 30 min after the dropwise addition is completed; (4) 30 parts of hydrophobic fumed silica (Wacker HDK H20, treated with HMDS) are added in 2-3 portions, dispersed at high speed (speed 800-1000 rpm) until a uniform, fine, and flowable paste is formed, cooled to room temperature, and the hardening agent composition is obtained by discharge.

[0019] Examples 3-5 and Comparative Examples 1-4 Table 1 shows the components and mass parts of the scorch-resistant, high-hardness extruded silicone rubbers of Examples 3-5 and Comparative Examples 1-4. The preparation method includes the following steps: S1, methyl vinyl silicone rubber A (Hesheng Silicon Industry 110-2), methyl vinyl silicone rubber B (Hesheng Silicon Industry 112-9), and structure control agent (Baichuan's hydroxyl silicone oil, viscosity 30 mm). 2 Add the following ingredients (9.5% active hydroxyl content) and internal release agent (zinc stearate) to a kneader at 70°C and mix thoroughly. S2 will be used to reinforce the silica (Evonik A200 fumed silica, specific surface area 205 mm²). 2 / g) is added to the kneader in several batches and stirred evenly to form a dough, forming a rubber compound. The material temperature is controlled not to exceed 120℃; then the rubber compound is allowed to stand for 5 hours. S3, the rubber compound is mixed at a constant temperature of 160°C and a vacuum degree of not less than -0.075MPa for 2 hours; S4. Cool the rubber compound to 110°C, add anti-blowing agent (active magnesium oxide from Shanghai Huijingya Nanomaterials Co., Ltd.), silicone heat resistant agent (nano cerium dioxide CeO2), and hardening agent composition (prepared in Example 1), stir evenly and discharge; cut the rubber and cool for 6 hours, then extrude, filter and vacuum package to obtain scorch-resistant high-hardness extrusion molding silicone rubber.

[0020] Table 1. Components and parts by mass of Examples 3-8 and Comparative Examples 1-4 Compared with Example 1, Comparative Example 1 did not add a hardening composition, but was otherwise the same as Example 1.

[0021] Compared with Example 1, the hardening additive composition of Comparative Example 2 did not contain 4-hydroxy TEMPO. Its preparation method included the following steps: (1) 100 parts of hydroxy silicone oil (Dow Corning PMX-0930) were added to a reaction vessel, heated to 110°C, and dehydrated under a vacuum of -0.08 MPa for 30 min; (2) the temperature was lowered to 55°C, and 100 parts of polyfunctional acrylate (trimethylolpropane triacrylate) were slowly added dropwise under nitrogen protection. The dropwise addition time was controlled at 20-30 min, and the mixture was kept warm and stirred for 30 min after the dropwise addition was completed; (3) 30 parts of hydrophobic fumed silica (Wacker HDK H20, treated with HMDS) were added in 2-3 portions and dispersed at high speed (800-1000 rpm) until a uniform, fine, and flowable paste was formed. The mixture was then cooled to room temperature and discharged. The remaining components and preparation method of Comparative Example 2 were the same as those of Example 1.

[0022] Compared with Example 1, the hardening composition of Comparative Example 3 did not contain acrylate. Its preparation method included the following steps: (1) 100 parts of hydroxyl silicone oil (Dow Corning PMX-0930) were added to a reaction vessel, heated to 110°C, and dehydrated under a vacuum of -0.08 MPa for 30 min; (2) the temperature was lowered to 80°C, and 30 parts of 4-hydroxy TEMPO (chemically pure, Leyan Chemical Reagent) were slowly added under stirring, and stirred for about 28 min until completely dissolved; (3) 30 parts of hydrophobic fumed silica (Wacker HDKH20, treated with HMDS) were added in 2 to 3 portions, dispersed at high speed (800 to 1000 rpm) until a uniform, fine, and flowable paste was formed, cooled to room temperature, and discharged. The remaining components and preparation method of Comparative Example 3 were the same as those of Example 1.

[0023] Compared with Example 1, Comparative Example 4 did not add a hardening composition, but used physical (ceramic powder / quartz powder mass ratio 1:1) filling for hardening, referring to CN112063172A; all other aspects were the same as Example 1.

[0024] Examples 6-8 Table 1 shows the components and mass parts of the scorch-resistant, high-hardness extruded silicone rubbers of Examples 6-8. The preparation method includes the following steps: S1, mix methyl vinyl silicone rubber A (Hesheng Silicon Industry 110-2 and 110-3 in a 1:1 ratio), methyl vinyl silicone rubber B (Hesheng Silicon Industry 112-8), and structure control agent (methoxy silicone oil, Zhonghe Silicon-based JZH-203B, viscosity 14 mm). 2 Add the active methoxyl content (7.9%) and internal release agent (stearic acid) to a kneader at 70°C and stir evenly; S2, add the reinforcing silica (fumed silica, Zhonglan Chenguang Chemical Research Institute) to the kneader in batches and stir evenly to form a ball, forming a rubber compound, and control the material temperature to not exceed 120℃; then let the rubber compound stand for 5 hours. S3, the rubber compound is mixed at a constant temperature of 170℃ under a vacuum of not less than -0.075MPa for 2.5 hours; S4. Cool the rubber compound to 105°C, add anti-blowing agent (active magnesium oxide from Shanghai Huijingya Nanomaterials Co., Ltd.), silicone heat resistant agent (cerium trioxide Ce2O3), and hardening agent composition (prepared in Example 2), stir evenly and discharge; cut the rubber and cool for 6 hours, then extrude, filter and vacuum package to obtain scorch-resistant high-hardness extrusion molding silicone rubber.

[0025] Test Experiment Example The properties of the scorch-resistant, high-hardness extrusion silicone rubbers prepared in Examples 3-8 and Comparative Examples 1-4 were tested, and the results are listed in Table 2.

[0026] Add 1.8% of the bis(2,4)dichlorobenzene (DCBP) vulcanizing agent (Perkadox PD-50S-PS) to the rubber compound on a two-roll mill. After thorough mixing, extrude the mixture through a 6mm roller gap and cut it into 10cm x 10cm samples for testing. Seal the samples in PE bags and store them in a 35℃ oven. After certain periods (0 days, 15 days, and 30 days), measure the Mooney viscosity (Mv). Observe the change in Mv to determine the improvement in the rubber compound's shelf life at room temperature. When the rubber compound shows signs of scorching, the Mooney viscosity (Mv) will gradually increase, the mixing process will become rough, and eventually, significant self-vulcanization will occur, making mixing impossible. If the Mooney viscosity (Mv) remains essentially unchanged or changes very little, it indicates that scorching has not occurred, and the rubber compound will have a longer shelf life.

[0027] The rubber compound was mixed with a 1.5% DCBP (Perkadox PD-50S-PS) vulcanizing agent on a two-roll mill. The mixture was then molded on a flat vulcanizing machine at 120°C for 10 minutes to prepare 2mm test pieces and 6.3mm thick hardness blocks. The mechanical properties (according to GB / T 28610-2020) and Shore A hardness (according to ISO 868:2003) were then tested.

[0028] Mooney scorch time was tested according to GB / T 1233-2008 using a large rotor at a test temperature of 120℃. The Mooney viscosity was recorded from the start of the test. The time required for the Mooney viscosity to rise by 5 Mooney values ​​after reaching its lowest point was the scorch time t5, expressed in minutes. A longer scorch time indicates better processing safety of the rubber compound and a lower likelihood of premature vulcanization during processing.

[0029] Hot air aging performance was tested according to GB / T 3512-2014. The vulcanized samples were placed in an aging test chamber at 200℃ for 72 hours continuously. After aging, they were removed and conditioned at standard laboratory temperature for 16 hours before testing their Shore A hardness. The change in hardness before and after aging, ΔH, was calculated. The changes in tensile strength and elongation at break were recorded simultaneously. Hardness change (ΔH) = Hardness after aging - Hardness before aging. The smaller the hardness change, the better the material's heat aging resistance. For silicone rubber with high hardness, the hardness usually increases after aging. If the hardness increases too quickly (e.g., exceeding +10 degrees), it indicates that the material becomes brittle and has poor aging resistance.

[0030] Table 2 Performance test results of Examples 3-8 and Comparative Examples 1-4 As can be seen from Table 1, the present invention uses multifunctional acrylates to form additional chemical crosslinking points during the vulcanization process to increase the crosslinking density, thereby increasing the hardness of the silicone resin (hardness ≥70A, or even ≥80A); and uses 4-hydroxy TEMPO as a free radical scavenger to inhibit early crosslinking at room temperature, extending the scorch time (Mooney scorch time increased by more than 50%); it has good extrusion molding properties (good flowability, smooth surface) and extended storage period (≥6 months at room temperature).

[0031] Comparative Example 1, without the addition of the hardening composition, showed a short scorch time and short shelf life for the rubber compound. The target hardness (≥70A) could not be achieved by simply adjusting the vinyl content and the amount of silica, indicating that the hardening composition made a significant contribution to both hardness and scorch resistance.

[0032] The hardening composition of Comparative Example 2 did not contain TEMPO. Although its hardness was still close to that of Example 1 (due to the presence of acrylate), the scorch time was significantly shortened and the shelf life was reduced, indicating that TEMPO is a key component for scorch resistance and can also significantly improve processing safety.

[0033] The hardening composition of Comparative Example 3 did not contain any acrylate, and its hardness was close to that of Comparative Example 1, indicating that acrylate is the key component for hardening.

[0034] Comparative Example 4 uses physical filler hardening. Although the hardness is similar to that of the Example, the elongation at break is significantly reduced, the extruded surface is rough, and the storage period is shortened. This shows that the chemical crosslinking hardening of the present invention is superior to physical filler hardening in maintaining processability and mechanical properties.

Claims

1. An anti-scorching type high hardness extrusion molding silicone rubber, characterized by, The raw materials include the following parts by weight: 92-98 parts of methyl vinyl silicone rubber A and 2-8 parts of methyl vinyl silicone rubber B, with a total of 100 parts; and also include: 6-10 parts of structure control agent, 0.05-0.5 parts of internal release agent, 50-70 parts of reinforcing silica, 0.1-0.5 parts of anti-blooming agent, 3-5 parts of silicone heat resistant agent, and 1-3 parts of hardening additive composition; The hardening additive composition is made from the following components in parts by weight: 100 parts hydroxy silicone oil, 20-40 parts 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide, 80-120 parts polyfunctional acrylate, and 20-30 parts hydrophobic fumed silica.

2. The scorch-resistant high hardness extrusion molding silicone rubber according to claim 1, characterized by, The methyl vinyl silicone rubber A is a vinyl-terminated methyl vinyl silicone rubber raw rubber with an average molecular weight of 600,000 to 700,000; wherein the molar content of vinyl is 0.05% to 0.25%, and it is made by mixing 1 to 3 silicone rubbers with different vinyl contents within this content range.

3. The scorch-resistant, high-hardness extruded silicone rubber according to claim 1, characterized in that, The methyl vinyl silicone rubber B is a methyl-terminated methyl vinyl silicone rubber raw rubber with an average molecular weight of 500,000 to 600,000; wherein the molar content of vinyl is 1% to 10%, and it is made by mixing 1 to 3 silicone rubbers with different vinyl contents within this content range.

4. The scorch-resistant, high-hardness extruded silicone rubber according to claim 1, characterized in that, The structure control agent is at least one of hydroxyl silicone oil, methoxy silicone oil, vinyl hydroxyl silicone oil, dimethyl dimethoxysilane, dimethyl diethoxysilane, hexamethyldisilazane, and vinylsilazane.

5. The scorch-resistant, high-hardness extruded silicone rubber according to claim 1, characterized in that, The internal release agent is at least one of zinc stearate, calcium stearate, magnesium stearate, barium stearate, stearic acid, and octadecanol; the reinforcing white carbon is precipitated white carbon or / and fumed white carbon, and the specific surface area is 150-300 g / m 2 .

6. The scorch-resistant, high-hardness extruded silicone rubber according to claim 1, characterized in that, The anti-blowing agent is nano-active magnesium oxide; the silicone heat-resistant agent is nano-cerium dioxide (CeO2) or cerium trioxide (Ce2O3).

7. The scorch-resistant, high-hardness extruded silicone rubber according to claim 1, characterized in that, The hydroxyl silicone oil has a viscosity of 25 to 50 mm 2 / s; and the multifunctional acrylate is at least one of trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate.

8. The scorch-resistant, high-hardness extruded silicone rubber according to claim 1, characterized in that, The specific surface area of the hydrophobic fumed white carbon black is 180 to 220 g / m 2 .

9. The scorch-resistant, high-hardness extruded silicone rubber according to claim 1, characterized in that, The preparation method of the hardening agent composition includes the following steps: (1) adding hydroxy silicone oil to a reaction vessel, heating to 100-120°C, and dehydrating under a vacuum of -0.065--0.09 MPa for 30-60 min; (2) cooling to 70-80°C, slowly adding 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide under stirring, and stirring until completely dissolved; (3) continuing to cool to 50-60°C, slowly adding the multifunctional acrylate, and stirring for 30-80 min after the addition is complete; (4) adding the hydrophobic fumed silica in batches, dispersing at high speed until a uniform paste is formed, cooling to room temperature, and discharging to obtain the hardening agent composition.

10. The method for preparing scorch-resistant, high-hardness extruded silicone rubber according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1, add the methyl vinyl silicone rubber A, methyl vinyl silicone rubber B, structure control agent and internal release agent to a kneader at 60-75°C and stir evenly; S2, the reinforcing silica is added to the kneader in batches and stirred evenly to form a dough, forming a rubber compound, and the material temperature is controlled not to exceed 120℃; then the rubber compound is left to stand for 4 to 8 hours; S3, the rubber compound is mixed at a constant temperature of 150-170℃ under a vacuum of not less than -0.075MPa for 1-3 hours; S4. Cool the rubber compound to 100-120°C, add the composition of anti-blowing agent, silicone heat resistant agent and hardening agent, stir evenly and discharge; cut the rubber and cool for 4-8 hours, then extrude, filter and vacuum package to obtain scorch-resistant high-hardness extrusion molding silicone rubber.

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