Silica for high transparent silicone rubber and method for preparing the same

Abstract

This invention relates to the field of silica preparation technology, specifically to a high-transparency silica for silicone rubber and its preparation method. The preparation method includes the following steps: mixing a high-transparency sodium silicate solution and a reaction sulfuric acid solution using a distributed acidification technique, followed by a homogenization reaction; the homogenized material is then filtered and washed sequentially, and then mixed with a silane coupling agent and an alcohol to form a slurry; the slurry is dried and pulverized to obtain the high-transparency silica for silicone rubber. This silica has the characteristics of high pore volume, low surface hydroxyl content, and uniform particle size distribution, exhibiting high transparency in silicone rubber.

Description

Technical Field

[0001] This invention relates to the field of silica preparation technology, specifically to a high-transparency silica for silicone rubber and its preparation method. Background Technology

[0002] Silicone rubber is a crucial material in high-end manufacturing industries such as electronics, medical devices, automobiles, and rail transportation. With the continuous improvement of my country's industrial development level, the demand for high-reinforcement and high-transparency silicone rubber products is rapidly increasing. High-transparency silicone rubber possesses excellent optical and mechanical properties and is widely used in silicone rubber products requiring high transparency, such as high-transparency silicone tubes, high-transparency LED silicone sleeves, diving goggles, Bluetooth headsets, nose pads for glasses, high-transparency baby bottle nipples, and high-transparency silicone water cups. Fumed silica, currently the most widely used reinforcing agent for high-transparency silicone rubber, not only imparts excellent mechanical properties to the material but also meets the requirements for high-transparency optical properties. However, it is expensive, and its production process easily generates polluting gases. Therefore, using precipitated silica to replace fumed silica is a hot development trend in this field.

[0003] Silica, as a reinforcing filler, significantly impacts the transparency of silicone rubber products. It requires a narrow particle size distribution, low impurities, few surface hydroxyl groups, low hygroscopicity, and a large specific surface area. Compared to untreated silica, surface-modified silica exhibits better compatibility with organosiloxanes, resulting in silicone rubber products with higher transparency. However, conventionally synthesized silica, due to its large surface area, tends to undergo secondary aggregation. Furthermore, its high surface hydroxyl content makes it highly susceptible to moisture absorption from the air, leading to strong hydrogen bonding between hydroxyl groups. This results in a significant decrease in the transparency of the compound after a period of storage, making its application in transparent silicone rubber far less advantageous than fumed silica. These factors limit its application in highly transparent silicone rubber.

[0004] Therefore, how to develop and produce high-purity, narrow-particle-size, low-hydroxyl-content silica that can replace fumed silica for silicone rubber has become an urgent technical problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-purity, narrow-particle-size, low-hydroxyl-content silica for producing high-transparency silicone rubber and a method for preparing the same.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing silica for high-transparency silicone rubber, comprising the following steps:

[0007] S1: A sulfuric acid solution for the reaction is obtained by mixing concentrated sulfuric acid, water, and an inorganic salt dispersant;

[0008] S2: Add highly transparent sodium silicate solution to water until the pH is 10.5-11.5, then adjust the pH to 9.5-10.0 with sulfuric acid solution for reaction, and add an organic ether surfactant; then maintain the pH and add highly transparent sodium silicate solution and sulfuric acid solution for reaction to carry out the reaction.

[0009] S3: Stop adding the highly transparent sodium silicate solution, adjust the flow rate of the sulfuric acid solution used in the reaction to 60-70% of the flow rate of the sulfuric acid solution used in the reaction during S2, acidify until the pH of the material is 8.8-9.2, stop adding acid, and homogenize for 10-15 minutes; then adjust the flow rate of the sulfuric acid solution used in the reaction to the flow rate of the sulfuric acid solution used in the reaction during S2, acidify until the pH of the material is 2.8-3.3, stop adding acid, and homogenize for 30-40 minutes;

[0010] S4: The homogenized material is filtered and washed in sequence, and then mixed with silane coupling agent and alcohol to make a slurry;

[0011] S5: After the slurry is dried and pulverized, high-transparency silicone rubber silica is obtained.

[0012] Another technical solution adopted in this invention is: high-transparency silicone rubber silica prepared by the above-mentioned method for preparing high-transparency silicone rubber silica.

[0013] The beneficial effects of this invention are as follows: The preparation method of this invention purifies the raw materials by removing impurities, and during the reaction process, it uses organic ether surfactants and adds inorganic salt dispersants to the reaction acid to effectively disperse and modify the surface of the newly generated silica particles, effectively preventing particle aggregation and greatly reducing the content of surface hydroxyl groups, thus significantly reducing gel formation. Simultaneously, a stepwise acidification technique is employed to make the particle distribution more uniform; and the addition of silane coupling agents and alcohol modifiers in the pulping process effectively reduces the hydroxyl content on the silica surface, minimizing particle pore collapse during the drying process. Through these technical means, this invention can obtain silica with high pore volume, low surface hydroxyl content, and uniform particle size distribution, ensuring the high transparency of the product in silicone rubber. Attached Figure Description

[0014] Figure 1 The figure shown is a particle size distribution diagram of the silica obtained in Example 1 of the present invention;

[0015] Figure 2 The figure shown is a particle size distribution diagram of the silica obtained in Example 2 of the present invention;

[0016] Figure 3 The figure shown is a particle size distribution diagram of the silica obtained in Example 3 of the present invention;

[0017] Figure 4The figure shown is a particle size distribution diagram of the silica prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0018] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0019] A method for preparing silica for high-transparency silicone rubber includes the following steps:

[0020] S1: A sulfuric acid solution for the reaction is obtained by mixing concentrated sulfuric acid, water, and an inorganic salt dispersant;

[0021] S2: Add highly transparent sodium silicate solution to water until the pH is 10.5-11.5, then adjust the pH to 9.5-10.0 with sulfuric acid solution for reaction, and add an organic ether surfactant; then maintain the pH and add highly transparent sodium silicate solution and sulfuric acid solution for reaction to carry out the reaction.

[0022] S3: Stop adding the highly transparent sodium silicate solution, adjust the flow rate of the sulfuric acid solution used in the reaction to 60-70% of the flow rate of the sulfuric acid solution used in the reaction during S2, acidify until the pH of the material is 8.8-9.2, stop adding acid, and homogenize for 10-15 minutes; then adjust the flow rate of the sulfuric acid solution used in the reaction to the flow rate of the sulfuric acid solution used in the reaction during S2, acidify until the pH of the material is 2.8-3.3, stop adding acid, and homogenize for 30-40 minutes;

[0023] S4: The homogenized material is filtered and washed in sequence, and then mixed with silane coupling agent and alcohol to make a slurry;

[0024] S5: After the slurry is dried and pulverized, high-transparency silicone rubber silica is obtained.

[0025] As described above, the beneficial effects of this invention are as follows: Firstly, a highly transparent sodium silicate solution is used to prepare a certain number of crystal nuclei during the reaction process. Organic ether surfactants are used to effectively disperse and modify the newly generated SiO2 particles, effectively improving the uniformity of particle size, preventing particle aggregation, and significantly reducing the content of surface hydroxyl groups. An inorganic salt dispersant is added to the acid used in the reaction, greatly reducing gel formation. Simultaneously, a stepwise acidification technique is employed to make the particle distribution more uniform. Finally, specific components and proportions of alcohol and silane coupling agents are added in the pulping process to further reduce the surface hydroxyl content of SiO2 particles and reduce particle aggregation during the drying process. Through these technical means, compared with existing silica products for silicone rubber, the product indicators of this invention are effectively reduced in terms of surface hydroxyl content, loss on ignition, and particle size distribution width, greatly improving the transparency and anti-fogging effect of the product in silicone rubber.

[0026] The size of SiO2 particles was controlled by adjusting the flow rate of the sulfuric acid solution used in the reaction.

[0027] Furthermore, the specific preparation method of the highly transparent sodium silicate solution is as follows: add hydrogen peroxide and sodium sulfide to liquid sodium silicate to react, let it stand after the reaction is completed, and then filter it. Mix the filtered residue with water to obtain the highly transparent sodium silicate solution.

[0028] As described above, highly transparent sodium silicate solution contains ferrous and ferric ions in the form of soluble complexes. Adding hydrogen peroxide can oxidize the ferrous ions to ferric ions, generating more reactive yellow ferric hydroxide. Adding sodium sulfide solution then quickly forms insoluble ferric sulfide, which is then heated to form ferrous sulfide precipitate, thereby achieving the purpose of purification and impurity removal.

[0029] Furthermore, the modulus of the liquid sodium silicate is 3.35–3.45, and the concentration is 25–35 wt%.

[0030] Furthermore, the specific preparation method of liquid sodium silicate is as follows: low-iron solid water glass and water are added to a static pressure vessel one after another, 0.7MPa steam is introduced for dissolution, pressure is maintained for 2 to 2.5 hours, and then placed in a storage tank for standing for more than 24 hours. The mixture is then filtered using a plate and frame filter press to obtain sodium silicate. Sodium silicate is then prepared by mixing sodium silicate and water to form liquid sodium silicate.

[0031] Liquid sodium silicate can also be any type available on the market that has low impurity content and high purity.

[0032] Furthermore, the iron content of solid water glass is ≤120ppm; the electrical conductivity of water is ≤100μs / cm.

[0033] Furthermore, the mass of hydrogen peroxide is 0.04 to 0.06% of the mass of liquid sodium silicate.

[0034] Furthermore, the mass of sodium sulfide is 0.07 to 0.09% of the mass of liquid sodium silicate.

[0035] Furthermore, the reaction conditions for liquid sodium silicate with hydrogen peroxide and sodium sulfide are: reaction at 80-90℃ for 10-20 min.

[0036] Furthermore, the settling time is 8–10 hours.

[0037] Furthermore, the sodium silicate concentration in the highly transparent sodium silicate solution is 15–25 wt%.

[0038] Furthermore, the mass ratio of concentrated sulfuric acid, water, and inorganic salt dispersant is 1:4 to 6:0.001 to 0.003.

[0039] Furthermore, the inorganic salt dispersant includes at least one of sodium sulfate and sodium chloride.

[0040] Furthermore, the transparency of concentrated sulfuric acid is ≥200mm.

[0041] Furthermore, the highly transparent sodium silicate solution has a transparency greater than 200 mm.

[0042] Furthermore, the concentration of the sulfuric acid solution used in the reaction is 17.3–30 wt%.

[0043] As can be seen from the above description, within a certain range, the lower the sulfuric acid concentration, the smaller the generated particles. However, if the concentration is too low, it may lead to an increase in the surface hydroxyl content. Therefore, the concentration of the sulfuric acid solution used in the reaction is controlled to be 17.3–30 wt%.

[0044] Further, S2 specifically involves: stirring water at 80–95°C and adding a highly transparent sodium silicate solution until the pH reaches 10.5–11.5; then adjusting the pH to 9.5–10.0 with a reaction sulfuric acid solution; adding an organic ether surfactant; then maintaining the pH, simultaneously adding the highly transparent sodium silicate solution and the reaction sulfuric acid solution at a flow rate of 2.0–3.5:1; and reacting at 85–95°C for 85–95 minutes.

[0045] Furthermore, the stirring speed in S2 is 60-80 r / h.

[0046] Furthermore, when stirring water at 80–95°C and adding a highly transparent sodium silicate solution, the volume ratio of water to highly transparent sodium silicate solution is 25–30:1.5–3.0.

[0047] Furthermore, organic ether surfactants include any one of lauryl dodecyl polyether, cetyl polyoxyethylene ether, and isomeric alcohol ethers.

[0048] Furthermore, the organic ether surfactant is 0.02 to 0.05 wt% of the silica used in high-transparency silicone rubber.

[0049] Furthermore, the washing process in S4 specifically involves washing with water until the effluent conductivity is ≤350μs / cm, and then washing with pure water until the effluent conductivity is ≤100μs / cm.

[0050] Furthermore, the mass of the silane coupling agent is 0.1 to 0.5% of the mass of the silica used in high-transparency silicone rubber.

[0051] Furthermore, the mass of the alcohol is 1 to 2% of the mass of the silica used in high-transparency silicone rubber.

[0052] As can be seen from the above description, the more silane coupling agent and alcohol added, the better the product modification effect and the lower the surface hydroxyl content. When used in silicone rubber products, it can reduce hygroscopicity and improve transparency.

[0053] Furthermore, the silane coupling agent includes any one of A151, A171, and A189.

[0054] Furthermore, alcohols include isopropanol or n-octanol.

[0055] As can be seen from the above description, adding alcohol and silane coupling agents of specific components and proportions in the pulping process can further reduce the hydroxyl content on the surface of SiO2 particles and reduce particle agglomeration during the drying process.

[0056] The alcohol and silane coupling agent selected in this invention do not cause the silicone rubber to yellow, and are beneficial to improving the transparency of the silicone rubber. Adding alcohol can prevent the silane coupling agent from hydrolyzing too quickly, which would lead to a decrease in the modification effect of silica.

[0057] Furthermore, the viscosity of the slurry in S4 is ≤600cps.

[0058] Furthermore, the particle size of silica used in high-transparency silicone rubber is D5 to 4.5 to 10 μm.

[0059] Another technical solution adopted in this invention is: high-transparency silicone rubber silica prepared by the above-mentioned method for preparing high-transparency silicone rubber silica.

[0060] Example 1 of the present invention is a method for preparing silica for high-transparency silicone rubber, comprising the following steps:

[0061] Step 1: Preparation of reactants:

[0062] Solid water glass with an iron content ≤120ppm and water with an electrical conductivity ≤100μs / cm were added to a static pressure vessel in a mass ratio of 1:1.5~2.5. Steam at 0.7MPa was introduced to dissolve the solid water glass, and the pressure was maintained for 2 hours. The solid water glass was then placed in a storage tank and allowed to stand for 26 hours. The solution was then filtered using a plate and frame filter press to obtain sodium silicate. Sodium silicate was then mixed with water to prepare a liquid sodium silicate with a modulus of 3.36 and a concentration of 28wt%.

[0063] Raw material purification: Under the condition of stirring speed of 20-30 r / min, 20m 3 3.6 kg of hydrogen peroxide and 5.4 kg of sodium sulfide were added to liquid sodium silicate. The mixture was reacted at 82°C for 12 minutes, then allowed to stand for 8.5 hours. After filtration through a bag filter, it was then reacted with 9 mL of... 3 Pure water was mixed evenly to obtain a highly transparent sodium silicate solution A1 with a sodium silicate concentration of 20.6 wt% (transparency > 200 mm);

[0064] Under stirring conditions, 2m 3 Slowly add concentrated sulfuric acid with a transparency ≥200mm to 13.5m. 3 In pure water, 0.8 kg of sodium chloride is added and mixed evenly. The mixture is then filtered through a precision ceramic filter to obtain a 20 wt% sulfuric acid solution B1 for the reaction.

[0065] Step 2: 26m 3 Water was added to the reactor and heated to 85°C with saturated steam. Then, 1.8 mg of water was added while stirring at 65 rpm. 3 A highly transparent sodium silicate solution A1 was sampled and measured to have a pH of 10.9. The pH was then adjusted to 9.8 using sulfuric acid solution B1 (used for reactions). 2.5 kg of lauryl dodecyl polyether was added, and the solution was prepared at a flow rate of 13 m³ / h. 3 The flow rate of sulfuric acid solution B1 used in the reaction was 4.53 m / h. 3 The mixture is added to the reactor at the same time, and the process pH is controlled within the range of 9.5 to 10, the temperature is controlled within the range of 85±1℃, and the reaction time is 85 min.

[0066] Step 3: After the reaction is complete, stop adding the highly transparent sodium silicate solution A1, and adjust the flow rate of the sulfuric acid solution B1 used for the reaction to 2.9 m. 3 Acidify the material until the pH reaches 9.1, then stop adding acid and homogenize for 10 minutes. Then adjust the reaction flow rate to 4.53 m using sulfuric acid solution B1. 3 / h, acidify until the pH of the material is 3.1, stop adding acid, and homogenize for 30min;

[0067] Step 4: Pump the homogenized material into a plate and frame filter press, then wash it with water until the conductivity of the effluent is 312 μs / cm, and then wash it with pure water until the conductivity of the effluent is 86 μs / cm.

[0068] Step 5: After thorough washing, the filter cake is conveyed to the pulping tank by a belt conveyor. At the same time, 0.2% of A151 silane coupling agent and 1.5% isopropanol (based on the product weight) are added. The block filter cake is then stirred at high speed to make a slurry with a viscosity of 570 cps.

[0069] Step 6: Dry the slurry using spray drying to obtain primary product C1;

[0070] Step 7: The primary product C1 is pulverized by airflow to reduce the particle size D50 to 6.13μm to obtain high-transparency silicone rubber silica product D1.

[0071] Example 2 of the present invention: A method for preparing silica for high-transparency silicone rubber, comprising the following steps:

[0072] Step 1: Preparation of reactants:

[0073] Solid water glass with an iron content ≤120ppm and water with an electrical conductivity ≤100μs / cm were added to a static pressure vessel in a mass ratio of 1:1.5~2.5. Steam at 0.7MPa was introduced to dissolve the solid water glass, and the pressure was maintained for 2.2h. The solid water glass was then placed in a storage tank and allowed to stand for 24h. The solution was then filtered using a plate and frame filter press to obtain sodium silicate. Sodium silicate was then mixed with water to prepare a liquid sodium silicate with a modulus of 3.36 and a concentration of 28wt%.

[0074] Raw material purification: Under the condition of stirring speed of 20-30 r / min, 20m 3 3.6 kg of hydrogen peroxide and 5.4 kg of sodium sulfide were added to liquid sodium silicate. The mixture was reacted at 82°C for 12 minutes, then allowed to stand for 8.5 hours. After filtration through a bag filter, it was reacted with 12 mL of water. 3 Pure water was mixed evenly to obtain a highly transparent sodium silicate solution A2 with a sodium silicate concentration of 18.9 wt% (transparency > 200 mm);

[0075] Under stirring conditions, 2m 3 Slowly add concentrated sulfuric acid with a transparency ≥200mm to 15.5m. 3 In pure water, 0.8 kg of sodium chloride was added and mixed evenly. The mixture was then filtered through a precision ceramic filter to obtain a 18.0 wt% sulfuric acid solution B2 for the reaction.

[0076] Step 2: 26m 3 Water was added to the reactor and heated to 88°C with saturated steam. Then, 2.0 mg of [amount missing] was added while stirring at 65 rpm. 3 A highly transparent sodium silicate solution A2 was sampled and measured to have a pH of 10.8. The pH was adjusted to 9.7 using sulfuric acid solution B2 (used for reactions). 2.5 kg of cetyl alcohol polyoxyethylene ether was added, and the solution was prepared at a flow rate of 13 m³ / h. 3 The flow rate of sulfuric acid solution B2 used in the reaction was 4.53 m / h. 3 The mixture is added to the reactor at the same time, and the pH is controlled within the range of 9.5 to 10. The temperature is controlled within the range of 88±1℃, and the reaction time is 88 min.

[0077] Step 3: After the reaction is complete, stop adding the highly transparent sodium silicate solution A2, and adjust the flow rate of the sulfuric acid solution B2 used for the reaction to 2.92 m. 3 Acidify the material until the pH reaches 9.0, then stop adding acid and homogenize for 10 minutes. Then adjust the reaction flow rate to 4.53 m using sulfuric acid solution B2. 3 / h, acidify until the pH of the material is 3.3, stop adding acid, and homogenize for 30 minutes;

[0078] Step 4: Pump the homogenized material into a plate and frame filter press, then wash it with water until the conductivity of the effluent is 306 μs / cm, and then wash it with pure water until the conductivity of the effluent is 82 μs / cm.

[0079] Step 5: The thoroughly washed filter cake is conveyed to the pulping tank by a belt conveyor. At the same time, 0.2% of A171 silane coupling agent and 1.5% isopropanol (based on the product weight) are added. The block filter cake is then stirred at high speed to make a slurry with a viscosity of 562 cps.

[0080] Step 6: The slurry is dried using a spray drying method to obtain the primary product C2;

[0081] Step 7: The primary product C2 is pulverized by airflow to reduce the particle size D50 to 5.18μm to obtain the high-transparency silicone rubber silica product D2.

[0082] Example 3 of the present invention: A method for preparing silica for high-transparency silicone rubber, comprising the following steps:

[0083] Step 1: Preparation of reactants:

[0084] Solid water glass with an iron content ≤120ppm and water with an electrical conductivity ≤100μs / cm were added to a static pressure vessel in a mass ratio of 1:1.5~2.5. Steam at 0.7MPa was introduced to dissolve the solid water glass, and the pressure was maintained for 2 hours. The solid water glass was then placed in a storage tank and allowed to stand for 26 hours. The solution was then filtered using a plate and frame filter press to obtain sodium silicate. Sodium silicate was then mixed with water to prepare a liquid sodium silicate with a modulus of 3.36 and a concentration of 28wt%.

[0085] Raw material purification: Under the condition of stirring speed of 20-30 r / min, 20m 3 3.6 kg of hydrogen peroxide and 5.4 kg of sodium sulfide were added to liquid sodium silicate. The mixture was reacted at 85°C for 12 minutes, then allowed to stand for 8.5 hours. After filtration through a bag filter, it was then reacted with 15 ml of... 3 Pure water was mixed evenly to obtain a highly transparent sodium silicate solution A3 with a sodium silicate concentration of 17.8 wt% (transparency > 200 mm);

[0086] Under stirring conditions, 2m 3 Slowly add concentrated sulfuric acid with a transparency ≥200mm to 16.5m. 3 In pure water, 0.8 kg of sodium chloride was added and mixed evenly. The mixture was then filtered through a precision ceramic filter to obtain a 17.3 wt% sulfuric acid solution B3 for the reaction.

[0087] Step 2: 26m 3 Water was added to the reactor and heated to 90°C with saturated steam. Then, 2.3 mg of [acid] was added while stirring at 65 rpm. 3A highly transparent sodium silicate solution A3 was sampled and measured to have a pH of 10.8. The pH was then adjusted to 9.6 using sulfuric acid solution B3 (used for reactions). 2.5 kg of lauryl dodecyl polyether was added, and the solution was prepared at a flow rate of 13 m³ / h. 3 The flow rate of sulfuric acid solution B3 used in the reaction was 4.55 m / h. 3 The mixture is added to the reactor at a time, and the pH is controlled within the range of 9.5 to 10. The temperature is controlled within the range of 90 ± 1℃, and the reaction time is 90 min.

[0088] Step 3: After the reaction is complete, stop adding the highly transparent sodium silicate solution A3, and adjust the flow rate of the sulfuric acid solution B3 used for the reaction to 2.9 m. 3 Acidify the material until the pH reaches 9.2, then stop adding acid and homogenize for 10 minutes. Then adjust the reaction flow rate to 4.55 m using sulfuric acid solution B3. 3 / h, acidify until the pH of the material is 3.2, stop adding acid, and homogenize for 30 minutes;

[0089] Step 4: Pump the homogenized material into a plate and frame filter press, then wash it with water until the conductivity of the effluent is 296 μs / cm, and then wash it with pure water until the conductivity of the effluent is 81 μs / cm.

[0090] Step 5: The thoroughly washed filter cake is conveyed to the pulping tank by a belt conveyor. At the same time, 0.2% of A189 silane coupling agent and 1.5% n-octanol (based on the product weight) are added. The block filter cake is then stirred at high speed to make a slurry with a viscosity of 563 cps.

[0091] Step 6: The slurry is dried by spray drying to obtain the primary product C3.

[0092] Step 7: The primary product C3 is pulverized by airflow to reduce the particle size D50 to 6.39 μm, yielding high-transparency silica product D3 for silicone rubber.

[0093] Comparative Example 1 of the present invention: A method for preparing silica for silicone rubber, comprising the following steps:

[0094] Step 1: Preparation of reactants:

[0095] Solid water glass with an iron content ≤120ppm and water with an electrical conductivity ≤100μs / cm were added to a static pressure vessel in a mass ratio of 1:1.5~2.5. Steam at 0.7MPa was introduced to dissolve the solid water glass, and the pressure was maintained for 2.5h. The solid water glass was then placed in a storage tank and allowed to stand for 24h. The solid water glass was then filtered using a plate and frame filter press to obtain sodium silicate. Sodium silicate was then mixed with water to prepare a liquid sodium silicate with a modulus of 3.36 and a concentration of 28wt%.

[0096] Under stirring conditions, 20m 3 Liquid sodium silicate and 15m 3Sodium silicate is obtained by uniformly mixing pure water and filtering it through a bag filter; then, sodium silicate and water are used to prepare a highly transparent sodium silicate solution A with a concentration of 18.2 wt% (transparency > 200 mm);

[0097] Under stirring conditions, 2m 3 Slowly add concentrated sulfuric acid with a transparency ≥200mm to 16m 3 After being thoroughly mixed in pure water, the mixture is then filtered through a precision ceramic filter to obtain a 18.1 wt% sulfuric acid solution B for the reaction.

[0098] Step 2: 26m 3 Water was added to the reactor and heated to 88°C with saturated steam. Then, 2.3 mg of [amount missing] was added while stirring at 65 rpm. 3 A highly transparent sodium silicate solution A was sampled and measured to have a pH of 10.9. The pH was then adjusted to 9.8 using sulfuric acid solution B, which is used for the reaction. The flow rate of the highly transparent sodium silicate solution A was 13 m³ / s. 3 / h and the flow rate of sulfuric acid solution B for the reaction is 4.55m 3 The mixture is added to the reactor at a time, and the pH is controlled within the range of 9.5 to 10. The temperature is controlled within the range of 90±1℃, and the reaction time is 88 min.

[0099] Step 3: After the reaction is complete, stop adding the highly transparent sodium silicate solution A, close the valve for the highly transparent sodium silicate solution A, and adjust the flow rate of the sulfuric acid solution B used for the reaction to 3.18 m. 3 / h, acidify until the pH of the material is 4.09, stop adding acid, and homogenize for 35min;

[0100] Step 4: Pump the homogenized material into a plate and frame filter press, and then wash it with purified process water until the conductivity of the effluent is 315 μs / cm.

[0101] Step 5: The thoroughly washed filter cake is conveyed to the pulping tank by a belt conveyor, and the block filter cake is made into a slurry with a viscosity of 558 cps by high-speed stirring;

[0102] Step 6: The slurry is dried by spray drying, and the weight loss due to heating is controlled within the range of 5-7%. After air jet pulverization, the particle size D50 is reduced to 5.02μm to obtain the silica product for silicone rubber.

[0103] Table 1 shows a comparison of the main quality indicators of the silica prepared in Examples 1-3 and Comparative Example 1.

[0104] Table 1

[0105]

[0106] Note: Hygroscopicity and light transmittance were measured using a silicone rubber sheet. The specific test method is as follows:

[0107] 1) Silicone rubber sheet preparation: Weigh 1kg of methyl vinyl raw rubber, 3g of zinc stearate, and 21g of hydroxyl silicone oil, and put them into a 5L internal mixer. Add 450g of silica in 3-4 batches to a kneader for mixing. After adding the silica, heat to 150℃ and heat for 50 minutes. After the heat mixing is completed, cool for 30 minutes to 120℃, then vacuum for 1.5-2 hours and discharge the material. Let the rubber compound cool to room temperature.

[0108] 2) Take 50g of rubber compound and add 0.25g of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane. Mix it evenly on a two-roll mill and put it into a mold. Then push the mold into a flat vulcanizing machine with a set temperature of 165-175℃ and vulcanize for 4-6 minutes for one vulcanization molding.

[0109] 3) After cooling the vulcanized film to room temperature, weigh it and measure its light transmittance. Then, leave it exposed for one week and test the light transmittance and film weight gain again. Calculate the moisture absorption rate based on the weight gain.

[0110]

[0111] In the formula: W1 is the initial mass of the film, in g; W2 is the mass of the film after one week, in g.

[0112] 4) Transmittance measurement: measured using a WGW photoelectric haze meter.

[0113] As shown in Table 1, this invention purifies raw materials by removing impurities. During the reaction process, organic ether surfactants and inorganic salt dispersants are added to the reaction acid to effectively disperse and modify the newly generated silica particles, effectively preventing particle aggregation and significantly reducing the content of surface hydroxyl groups. The addition of silane coupling agents and alcohol modifiers in the pulping process effectively reduces the surface hydroxyl content of silica and minimizes particle pore collapse during drying. Compared with existing silica products for silicone rubber, the product of this invention has higher pore volume, lower surface hydroxyl content, more uniform particle size distribution, and significantly reduced water absorption in silicone rubber, ensuring high transparency.

[0114] Figures 1-4 The particle size distribution diagrams are for the silica prepared in Examples 1-3 and Comparative Example 1. Figures 1-4 It can be seen that the particle size of the silica prepared by this invention is close to a normal distribution.

[0115] Example 4 of the present invention: A method for preparing silica for high-transparency silicone rubber, comprising the following steps:

[0116] Step 1: Preparation of reactants:

[0117] Solid water glass with an iron content ≤120ppm and water with an electrical conductivity ≤100μs / cm were added to a static pressure vessel in a mass ratio of 1:1.5~2.5. Steam at 0.7MPa was introduced to dissolve the solid water glass, and the pressure was maintained for 2 hours. The solid water glass was then placed in a storage tank and allowed to stand for 26 hours. The solution was then filtered using a plate and frame filter press to obtain sodium silicate. Sodium silicate was then mixed with water to prepare a liquid sodium silicate with a modulus of 3.35 and a concentration of 25wt%.

[0118] Raw material purification: Under the condition of stirring speed of 20-30 r / min, 20m 3 3.6 kg of hydrogen peroxide and 5.4 kg of sodium sulfide were added to liquid sodium silicate. The mixture was reacted at 80°C for 20 minutes, then allowed to stand for 8 hours. After filtration through a bag filter, it was then reacted with 15 ml of... 3 Pure water was mixed evenly to obtain a highly transparent sodium silicate solution A4 with a sodium silicate concentration of 17.8 wt% (transparency > 200 mm);

[0119] Under stirring conditions, 2m 3 Slowly add concentrated sulfuric acid with a transparency ≥200mm to 16.5m. 3 In pure water, 0.8 kg of sodium chloride was added and mixed evenly. The mixture was then filtered through a precision ceramic filter to obtain a 17.3 wt% sulfuric acid solution B4 for the reaction.

[0120] Step 2: Place 25m 3 Water was added to the reactor and heated to 90°C with saturated steam. Then, 1.5 mg of water was added while stirring at 60 rpm. 3 A highly transparent sodium silicate solution A4 was sampled and its pH was measured to be 10.5. The pH was then adjusted to 9.5 using sulfuric acid solution B4 for reaction. 2.5 kg of isomeric alcohol ether was added, and the solution was prepared at a flow rate of 13 m³ / h. 3 The reaction was carried out at a flow rate of 6.5 m / h for sulfuric acid solution B4. 3 The mixture is added to the reactor at a rate of / h, and the process pH is controlled within the range of 9.5 to 10, the temperature is controlled within the range of 95±1℃, and the reaction time is 95 min.

[0121] Step 3: After the reaction is complete, stop adding the highly transparent sodium silicate solution A4, and adjust the flow rate of the sulfuric acid solution B4 used for the reaction to 3.9 m. 3 Acidify the material until the pH reaches 8.8, then stop adding acid and homogenize for 12 minutes. Then adjust the reaction flow rate to 6.5 m using sulfuric acid solution B4. 3 / h, acidify until the pH of the material is 2.8, stop adding acid, and homogenize for 35 minutes;

[0122] Step 4: Pump the homogenized material into a plate and frame filter press, then wash it with water until the conductivity of the effluent is 300 μs / cm, and then wash it with pure water until the conductivity of the effluent is 83 μs / cm.

[0123] Step 5: The thoroughly washed filter cake is conveyed to the pulping tank by a belt conveyor. At the same time, 0.1% of A189 silane coupling agent and 1.0% n-octanol (based on the product weight) are added. The block filter cake is then stirred at high speed to make a slurry with a viscosity of 570 cps.

[0124] Step 6: The slurry is dried using a spray drying method to obtain the primary product C4;

[0125] Step 7: The primary product C4 is pulverized by airflow to reduce the particle size D50 to 4.5μm to obtain high-transparency silicone rubber silica product D4.

[0126] Example 5 of the present invention: A method for preparing silica for high-transparency silicone rubber, comprising the following steps:

[0127] Step 1: Preparation of reactants:

[0128] Solid water glass with an iron content ≤120ppm and water with an electrical conductivity ≤100μs / cm were added to a static pressure vessel in a mass ratio of 1:1.5~2.5. Steam at 0.7MPa was introduced to dissolve the solid water glass, and the pressure was maintained for 2 hours. The solid water glass was then placed in a storage tank and allowed to stand for 26 hours. The solution was then filtered using a plate and frame filter press to obtain sodium silicate. Sodium silicate was then mixed with water to prepare a liquid sodium silicate with a modulus of 3.45 and a concentration of 35wt%.

[0129] Raw material purification: Under the condition of stirring speed of 20-30 r / min, 20m 3 3.6 kg of hydrogen peroxide and 5.4 kg of sodium sulfide were added to liquid sodium silicate. The mixture was reacted at 80°C for 20 minutes, then allowed to stand for 8 hours. After filtration through a bag filter, it was then reacted with 15 ml of... 3 Pure water was mixed evenly to obtain a highly transparent sodium silicate solution A5 with a sodium silicate concentration of 17.8 wt% (transparency > 200 mm);

[0130] Under stirring conditions, 2m 3 Slowly add concentrated sulfuric acid with a transparency ≥200mm to 16.5m. 3 In pure water, 0.8 kg of sodium chloride was added and mixed evenly. The mixture was then filtered through a precision ceramic filter to obtain a 17.3 wt% sulfuric acid solution B5 for the reaction.

[0131] Step 2: Place 30m 3 Water was added to the reactor and heated to 95°C with saturated steam. Then, 3.0 mg of [amount missing] was added while stirring at 80 rpm. 3 A highly transparent sodium silicate solution A5 was sampled and measured to have a pH of 11.5. The pH was then adjusted to 10.0 using sulfuric acid solution B5 (used for reactions). 2.5 kg of isomeric alcohol ether was added, and the solution was prepared at a flow rate of 13 m³ / h. 3The flow rate of sulfuric acid solution B5 used in the reaction was 3.71 m / h. 3 The mixture is added to the reactor at a rate of / h, and the process pH is controlled within the range of 9.5 to 10, the temperature is controlled within the range of 95±1℃, and the reaction time is 95 min.

[0132] Step 3: After the reaction is complete, stop adding the highly transparent sodium silicate solution A5, and adjust the flow rate of the sulfuric acid solution B5 used for the reaction to 2.6 m. 3 Acidify the material until the pH reaches 8.8, then stop adding acid and homogenize for 15 minutes. Then adjust the reaction flow rate to 6.5 m using sulfuric acid solution B5. 3 / h, acidify until the pH of the material is 2.8, stop adding acid, and homogenize for 40 minutes;

[0133] Step 4: Pump the homogenized material into a plate and frame filter press, then wash it with water until the conductivity of the effluent is 294 μs / cm, and then wash it with pure water until the conductivity of the effluent is 82 μs / cm.

[0134] Step 5: The thoroughly washed filter cake is conveyed to the pulping tank by a belt conveyor. At the same time, 0.5% of A189 silane coupling agent and 2.0% n-octanol (based on the product weight) are added. The block filter cake is then stirred at high speed to make a slurry with a viscosity of 562 cps.

[0135] Step 6: Dry the slurry using spray drying to obtain primary product C5;

[0136] Step 7: The primary product C5 is pulverized by airflow to reduce the particle size D50 to 10μm, yielding high-transparency silica product D5 for silicone rubber.

[0137] Example 6 of the present invention is: a high-transparency silicone rubber silica prepared by the preparation method of Example 5.

[0138] In summary, the high-transparency silica for silicone rubber and its preparation method provided by this invention have the following advantages:

[0139] 1. By purifying the raw materials, organic ether surfactants and inorganic salt dispersants are added to the reaction acid during the reaction process to effectively disperse and modify the newly generated silica particles.

[0140] 2. The stepwise acidification technology results in a more uniform particle distribution;

[0141] 3. In the pulping process, specific components and proportions of alcohol and silane coupling agents are added to further reduce the hydroxyl content on the surface of SiO2 particles and reduce particle agglomeration during the drying process.

[0142] 4. The surface hydroxyl content, loss on ignition, and particle size distribution width of the silica product for silicone rubber of the present invention are effectively reduced, and the transparency and anti-fogging effect in silicone rubber are greatly improved.

[0143] 5. The addition of hydrogen peroxide and sodium sulfide achieves the purpose of purification and impurity removal, further improving particle size uniformity.

[0144] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing silica for high-transparency silicone rubber, characterized in that, Includes the following steps: S1: A sulfuric acid solution for the reaction is obtained by mixing concentrated sulfuric acid, water, and an inorganic salt dispersant; S2: Add highly transparent sodium silicate solution to water until the pH is 10.5~11.5, then adjust the pH to 9.5~10.0 with sulfuric acid solution for reaction, and add organic ether surfactant; then maintain the pH, and add highly transparent sodium silicate solution and sulfuric acid solution for reaction to carry out the reaction. The specific preparation method of the highly transparent sodium silicate solution is as follows: hydrogen peroxide and sodium sulfide are added to liquid sodium silicate to react. After the reaction is completed, the mixture is allowed to stand and then filtered. The filtered residue is mixed with water to obtain the highly transparent sodium silicate solution. S3: Stop adding the highly transparent sodium silicate solution, adjust the flow rate of the sulfuric acid solution used in the reaction to 60-70% of the flow rate of the sulfuric acid solution used in the reaction during S2, acidify until the pH of the material is 8.8-9.2, stop adding acid, and homogenize for 10-15 minutes; then adjust the flow rate of the sulfuric acid solution used in the reaction to the flow rate of the sulfuric acid solution used in the reaction during S2, acidify until the pH of the material is 2.8-3.3, stop adding acid, and homogenize for 30-40 minutes; S4: The homogenized material is filtered and washed in sequence, and then mixed with silane coupling agent and alcohol to make a slurry; S5: After the slurry is dried and pulverized, high-transparency silicone rubber silica is obtained.

2. The method for preparing silica for high-transparency silicone rubber according to claim 1, characterized in that, The reaction conditions for the liquid sodium silicate with hydrogen peroxide and sodium sulfide are: reaction at 80~90℃ for 10~20 min.

3. The method for preparing silica for high-transparency silicone rubber according to claim 1, characterized in that, The mass ratio of concentrated sulfuric acid, water, and inorganic salt dispersant is 1:4~6:0.001~0.

003.

4. The method for preparing silica for high-transparency silicone rubber according to claim 1, characterized in that, The inorganic salt dispersant includes at least one of sodium sulfate and sodium chloride.

5. The method for preparing silica for high-transparency silicone rubber according to claim 1, characterized in that, The organic ether surfactants include any one of lauryl dodecyl polyether, cetyl polyoxyethylene ether, and isomeric alcohol ethers.

6. The method for preparing silica for high-transparency silicone rubber according to claim 1, characterized in that, The mass of the organic ether surfactant is 0.02~0.05 wt% of the mass of silica used in high-transparency silicone rubber.

7. The method for preparing silica for high-transparency silicone rubber according to claim 1, characterized in that, The mass of the silane coupling agent is 0.1 to 0.5% of the mass of silica used in high-transparency silicone rubber.

8. The method for preparing silica for high-transparency silicone rubber according to claim 1, characterized in that, The mass of the alcohol is 1 to 2% of the mass of the silica used for high-transparency silicone rubber.

9. Highly transparent silica for silicone rubber prepared by the method for preparing highly transparent silica for silicone rubber according to any one of claims 1-8.

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