Silicon dioxide for high-transparency silicon rubber and preparation method thereof

Abstract

The invention relates to the technical field of preparation of silicon dioxide, in particular to silicon dioxide for high-transparency silicon rubber and a preparation method of the silicon dioxide. The preparation method comprises the following steps: mixing a high-transparency sodium silicate solution and a sulfuric acid solution for reaction by adopting a distributed acidification technology, and then carrying out homogenization reaction; filtering and washing the homogenized material in sequence, and then mixing a silane coupling agent and alcohol to prepare slurry; and drying and crushing the slurry to obtain the silicon dioxide for the high-transparency silicon rubber. The silicon dioxide has the characteristics of high pore volume, low surface hydroxyl content and uniform particle size distribution, and has high transparency in silicon rubber.

Description

Technical Field

[0001] The invention relates to the technical field of silicon dioxide preparation, and in particular to highly transparent silicon dioxide for silicone rubber and a preparation method thereof. Background Art

[0002] Silicone rubber is an important material for high-end manufacturing industries such as electronics, medical equipment, automobile manufacturing, and rail transit. With the continuous improvement of my country's industrial development level, the demand for highly reinforced and highly transparent silicone rubber products is growing rapidly. Highly transparent silicone rubber has good optical and mechanical properties and is widely used in silicone rubber products that require high transparency, such as highly transparent silicone tubes, highly transparent LED silicone sleeves, swimming goggles, Bluetooth headsets, eye nose pads, highly transparent infant pacifiers, and highly transparent silicone water cups. As the most widely used high-transparency silicone rubber reinforcing agent, fumed silica can not only give the material excellent mechanical properties, but also achieve the optical performance requirements of high transparency. However, it is expensive and the production process is prone to produce polluting gases. Using precipitated silica instead of fumed silica is a development hotspot in this field.

[0003] As a reinforcing filler, silica has a great influence on the transparency of silicone rubber products. It requires a narrow particle size distribution, few impurities, few surface hydroxyls, low hygroscopicity, and a large specific surface area. Compared with untreated white carbon black, surface-modified silica has better compatibility with organosiloxane, so the resulting silicone rubber products have high transparency. However, due to its large surface area, conventional synthetic silica always tends to aggregate secondary, and due to its high surface hydroxyl content, it easily absorbs moisture in the air, resulting in strong hydrogen bonding between hydroxyls. After being stored for a period of time, the transparency of the rubber will be greatly reduced, making its application in transparent silicone rubber far less than that of fumed silica. For the above reasons, its application in high-transparency silicone rubber is limited.

[0004] Therefore, how to develop and produce highly transparent silica for silicone rubber with high purity, narrow particle size distribution, low surface hydroxyl content and the ability to replace fumed silica has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a highly transparent silicon dioxide for silicone rubber with high production purity, narrow particle size distribution and low surface hydroxyl content and capable of replacing fumed silicon dioxide and a preparation method thereof.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing silicon dioxide for highly transparent silicone rubber, comprising the following steps:

[0007] S1: Mixing concentrated sulfuric acid, water and an inorganic salt dispersant to obtain a sulfuric acid solution for reaction;

[0008] S2: adding a highly transparent sodium silicate solution to water until the pH is 10.5-11.5, then adjusting the pH to 9.5-10.0 with a sulfuric acid solution for reaction, and adding an organic ether surfactant; then maintaining the pH, adding the highly transparent sodium silicate solution and the sulfuric acid solution for reaction at the same time to react;

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

[0010] S4: filtering and washing the homogenized material in sequence, and then mixing the silane coupling agent and alcohol to prepare a slurry;

[0011] S5: After the slurry is dried and crushed, highly transparent silicon dioxide for silicone rubber is obtained.

[0012] Another technical solution adopted by the present invention is: the highly transparent silicon dioxide for silicone rubber is prepared by the above-mentioned preparation method of the highly transparent silicon dioxide for silicone rubber.

[0013] The beneficial effects of the present invention are as follows: the preparation method of the present invention removes impurities and purifies the raw materials, uses an organic ether surfactant during the reaction process, and adds an inorganic salt dispersant to the reaction acid to effectively disperse and surface-modify the newly generated silica particles, effectively preventing the agglomeration of the particles and greatly reducing the content of hydroxyl groups on the surface, greatly reducing the generation of gel. At the same time, the step-by-step acidification technology is adopted to make the particle distribution more uniform; and the addition of a silane coupling agent and an alcohol modifier in the pulping process effectively reduces the content of hydroxyl groups on the surface of silica, reducing the collapse of particle holes during the drying process. Through the above technical means, the present 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Shown is a particle size distribution diagram of silicon dioxide obtained in Example 1 of the present invention;

[0015] Figure 2 Shown is a particle size distribution diagram of silicon dioxide prepared in Example 2 of the present invention;

[0016] Figure 3 Shown is a particle size distribution diagram of silicon dioxide obtained in Example 3 of the present invention;

[0017] Figure 4Shown is a particle size distribution diagram of silicon dioxide prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0018] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes and the accompanying drawings.

[0019] A method for preparing highly transparent silicon dioxide for silicone rubber comprises the following steps:

[0020] S1: Mixing concentrated sulfuric acid, water and an inorganic salt dispersant to obtain a sulfuric acid solution for reaction;

[0021] S2: adding a highly transparent sodium silicate solution to water until the pH is 10.5-11.5, then adjusting the pH to 9.5-10.0 with a sulfuric acid solution for reaction, and adding an organic ether surfactant; then maintaining the pH, adding the highly transparent sodium silicate solution and the sulfuric acid solution for reaction at the same time to react;

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

[0023] S4: filtering and washing the homogenized material in sequence, and then mixing the silane coupling agent and alcohol to prepare a slurry;

[0024] S5: After the slurry is dried and crushed, highly transparent silicon dioxide for silicone rubber is obtained.

[0025] From the above description, it can be seen that the beneficial effects of the present invention are as follows: the present invention first adopts a highly transparent sodium silicate solution, starts to prepare a certain number of crystal nuclei during the reaction process, and adopts an organic ether surfactant to effectively disperse and modify the newly generated SiO2 particles, so that the uniformity of the size of the newly generated particles is effectively improved, effectively preventing the agglomeration of the particles and greatly reducing the content of the surface hydroxyl groups. Inorganic salt dispersants are added to the acid used for the reaction, which greatly reduces the generation of gel. At the same time, the step-by-step acidification technology is adopted to make the particle distribution more uniform; finally, alcohol and silane coupling agents of specific components and proportions are added in the pulping process to further reduce the surface hydroxyl content of SiO2 particles and reduce the agglomeration of particles during the drying process. Through the above technical means, the product indicators of the present invention are compared with the existing silicon dioxide products for silicone rubber, and the surface hydroxyl content, ignition loss, particle size distribution width, etc. are effectively reduced, which greatly improves the transparency and anti-fogging effect of the product in silicone rubber.

[0026] During the reaction, 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: adding hydrogen peroxide and sodium sulfide to liquid sodium silicate to react, letting the reaction stand and then filtering after the reaction is completed, mixing the filtered residue with water to obtain a highly transparent sodium silicate solution.

[0028] From the above description, it can be seen that divalent and trivalent iron ions exist in the highly transparent sodium silicate solution in the form of soluble complexes. The addition of hydrogen peroxide can oxidize the divalent iron ions into trivalent iron ions to generate more active yellow ferric hydroxide. Then, the addition of sodium sulfide solution quickly forms insoluble iron sulfide, which is then heated to form ferrous sulfide precipitation, thereby achieving the purpose of purification and impurity removal.

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

[0030] Furthermore, the preparation method of liquid sodium silicate is specifically as follows: low-iron solid water glass and water are added to a static pressure autoclave in sequence, 0.7 MPa steam is introduced for dissolution, the pressure is maintained for 2 to 2.5 hours, and then the mixture is placed in a storage tank and allowed to stand for more than 24 hours, filtered with a plate and frame filter press, and sodium silicate is obtained after filtration; and then sodium silicate and water are used to prepare liquid sodium silicate.

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

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

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

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

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

[0036] Furthermore, the standing time is 8 to 10 hours.

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

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

[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 high-transparency sodium silicate solution has a transparency greater than 200 mm.

[0042] Furthermore, the concentration of the sulfuric acid solution for the reaction is 17.3-30 wt %.

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

[0044] Furthermore, S2 is specifically as follows: stirring water at 80-95°C and adding a highly transparent sodium silicate solution until the pH is 10.5-11.5, then adjusting the pH to 9.5-10.0 with a reaction sulfuric acid solution, and adding an organic ether surfactant; then maintaining the pH, adding a highly transparent sodium silicate solution and a reaction sulfuric acid solution at the same time 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 water at 80 to 95° C. is stirred and the highly transparent sodium silicate solution is added, the volume ratio of water to the highly transparent sodium silicate solution is 25 to 30:1.5 to 3.0.

[0047] Furthermore, the organic ether surfactant includes any one of lauryl dodecanol polyether, cetyl alcohol polyoxyethylene ether and isomeric alcohol ether.

[0048] Furthermore, the mass of the organic ether surfactant is 0.02 to 0.05 wt % of the mass of the silicon dioxide for high-transparency silicone rubber.

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

[0050] Furthermore, the mass of the silane coupling agent is 0.1 to 0.5% of the mass of the silicon dioxide for high-transparency silicone rubber.

[0051] Furthermore, the mass of the alcohol is 1 to 2% of the mass of the silica for highly transparent silicone rubber.

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

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

[0054] Further, the alcohol includes isopropyl alcohol or n-octanol.

[0055] From the above description, it can be seen that adding alcohol and silane coupling agent with 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 the present invention will not cause the color of silicone rubber to turn yellow, and are beneficial to improving the transparency of silicone rubber. Adding alcohol can prevent the silane coupling agent from hydrolyzing too quickly, resulting in poor effect of modified silicon dioxide.

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

[0058] Furthermore, the particle size of the silicon dioxide for the highly transparent silicone rubber is D5 to 4.5 to 10 μm.

[0059] Another technical solution adopted by the present invention is: the highly transparent silicon dioxide for silicone rubber is prepared by the above-mentioned preparation method of the highly transparent silicon dioxide for silicone rubber.

[0060] Embodiment 1 of the present invention is: a method for preparing silicon dioxide for highly transparent silicone rubber, the steps are as follows:

[0061] Step 1: Preparation of reaction materials:

[0062] Solid water glass with an iron content of ≤120ppm and water with an electrical conductivity of ≤100μs / cm are added to a static autoclave in a mass ratio of 1:1.5-2.5, 0.7MPa steam is introduced for dissolution, the pressure is maintained for 2h, and then placed in a storage tank for 26h, filtered with a plate and frame filter press to obtain sodium silicate; then the sodium silicate and water are mixed into 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 20-30r / min, 20m 3 Add 3.6kg hydrogen peroxide and 5.4kg sodium sulfide to liquid sodium silicate, react at 82℃ for 12min, let stand for 8.5h, filter through bag filter and mix with 9m 3 The pure water was mixed evenly to obtain a highly transparent sodium silicate solution A1 (transparency>200mm) with a sodium silicate concentration of 20.6wt%;

[0064] Under stirring conditions, 2m 3 Slowly add concentrated sulfuric acid with a transparency of ≥200 mm to 13.5 m 3 Pure water, then add 0.8 kg of sodium chloride and mix well, then filter through a precision ceramic filter to obtain a 20 wt% sulfuric acid solution B1 for reaction;

[0065] Step 2: 26m 3 Water was added to the reactor and heated to 85°C with saturated steam. Then 1.8 m 3 The pH of the highly transparent sodium silicate solution A1 was measured at 10.9, and the pH was adjusted to 9.8 with the reaction sulfuric acid solution B1. 2.5 kg of lauryl alcohol dodecanol polyether was added, and the highly transparent sodium silicate solution A1 was prepared at a flow rate of 13 m 3 / h and the flow rate of sulfuric acid solution B1 for reaction is 4.53m 3 / h is added into the reactor at the same time, the process controls the pH value in the range of 9.5-10, the temperature control index is in the range of 85±1℃, and the reaction time is 85min;

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

[0067] Step 4: The homogenized material is pumped into a plate and frame filter press, and then washed with water until the outlet water conductivity is 312 μs / cm, and then washed with pure water until the outlet water conductivity is 86 μs / cm;

[0068] Step 5: The fully washed filter cake is conveyed to a slurry tank by a belt conveyor, and 0.2% of the weight of the product converted to A151 silane coupling agent and 1.5% of isopropanol are added, and the block filter cake is made into a slurry with a viscosity of 570 cps by high-speed stirring;

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

[0070] Step 7: The primary product C1 is subjected to air flow milling to reduce the particle size D50 to 6.13 μm, thereby obtaining a highly transparent silicon dioxide product D1 for silicone rubber.

[0071] Embodiment 2 of the present invention: A method for preparing silicon dioxide for highly transparent silicone rubber, comprising the following steps:

[0072] Step 1: Preparation of reaction materials:

[0073] Solid water glass with an iron content of ≤120ppm and water with an electrical conductivity of ≤100μs / cm are added to a static autoclave in a mass ratio of 1:1.5-2.5, 0.7MPa steam is introduced for dissolution, the pressure is maintained for 2.2 hours, and then placed in a storage tank for 24 hours, filtered with a plate and frame filter press to obtain sodium silicate; then the sodium silicate and water are mixed into 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 20-30r / min, 20m 3 Add 3.6kg hydrogen peroxide and 5.4kg sodium sulfide to liquid sodium silicate, react at 82℃ for 12min, let stand for 8.5h, filter through bag filter and mix with 12m 3 The pure water was mixed evenly to obtain a highly transparent sodium silicate solution A2 (transparency>200mm) with a sodium silicate concentration of 18.9wt%;

[0075] Under stirring conditions, 2m 3 Slowly add 15.5m concentrated sulfuric acid with a transparency of ≥200mm 3 Pure water, then add 0.8 kg of sodium chloride and mix well, then filter through a precision ceramic filter to obtain a sulfuric acid solution B2 with a concentration of 18.0 wt% for reaction;

[0076] Step 2: 26m 3 Water was added to the reactor and heated to 88°C with saturated steam. Then, 2.0 m 3 The pH of the highly transparent sodium silicate solution A2 was measured at 10.8, and the pH was adjusted to 9.7 with the reaction sulfuric acid solution B2. 2.5 kg of cetyl alcohol polyoxyethylene ether was added, and the highly transparent sodium silicate solution A2 was prepared at a flow rate of 13 m 3 / h and the flow rate of sulfuric acid solution B2 for reaction is 4.53m 3 / h is added into the reactor at the same time, the process controls the pH in the range of 9.5-10, the temperature control index is in the range of 88±1℃, and the reaction time is 88min;

[0077] Step 3: After the reaction is completed, stop adding the highly transparent sodium silicate solution A2 and adjust the flow rate of the sulfuric acid solution B2 for the reaction to 2.92 m 3 / h, acidify until the pH of the material is 9.0, stop adding acid, and homogenize for 10 minutes. Then adjust the flow rate of sulfuric acid solution B2 for reaction to 4.53m 3 / h, acidify until the pH value 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 with water until the outlet water conductivity is 306 μs / cm, and then wash with pure water until the outlet water conductivity is 82 μs / cm;

[0079] Step 5: The fully washed filter cake is conveyed to a slurry tank by a belt conveyor, and 0.2% of the weight of the product converted to A171 silane coupling agent and 1.5% of isopropanol are added, and the block filter cake is made into a slurry with a viscosity of 562 cps by high-speed stirring;

[0080] Step 6: Drying the slurry by spray drying to obtain the primary product C2;

[0081] Step 7: The primary product C2 is subjected to air flow milling to reduce the particle size D50 to 5.18 μm, thereby obtaining a highly transparent silicon dioxide product D2 for silicone rubber.

[0082] Embodiment 3 of the present invention: A method for preparing silicon dioxide for highly transparent silicone rubber, comprising the following steps:

[0083] Step 1: Preparation of reaction materials:

[0084] Solid water glass with an iron content of ≤120ppm and water with an electrical conductivity of ≤100μs / cm are added to a static autoclave in a mass ratio of 1:1.5-2.5, 0.7MPa steam is introduced for dissolution, the pressure is maintained for 2h, and then placed in a storage tank for 26h, filtered with a plate and frame filter press to obtain sodium silicate; then the sodium silicate and water are mixed into 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 20-30r / min, 20m 3 Add 3.6kg hydrogen peroxide and 5.4kg sodium sulfide to liquid sodium silicate, react at 85℃ for 12min, let stand for 8.5h, filter through bag filter and mix with 15m 3 The pure water was mixed evenly to obtain a highly transparent sodium silicate solution A3 (transparency>200mm) with a sodium silicate concentration of 17.8wt%;

[0086] Under stirring conditions, 2m 3 Slowly add 16.5m3 of concentrated sulfuric acid with a transparency of ≥200mm 3 Pure water, then add 0.8 kg of sodium chloride and mix well, then filter through a precision ceramic filter to obtain a 17.3 wt% sulfuric acid solution B3 for reaction;

[0087] Step 2: 26m 3 Water was added to the reactor and heated to 90°C with saturated steam. Then, 2.3 m 3The pH of the highly transparent sodium silicate solution A3 was measured at 10.8, and the pH was adjusted to 9.6 with the reaction sulfuric acid solution B3. 2.5 kg of lauryl alcohol dodecanol polyether was added, and the highly transparent sodium silicate solution A3 was prepared at a flow rate of 13 m 3 / h and the flow rate of sulfuric acid solution B3 for reaction is 4.55m 3 / h is added into the reactor at the same time, the process controls the pH value in the range of 9.5-10, the temperature control index is in the range of 90±1℃, and the reaction is carried out for 90min;

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

[0089] Step 4: The homogenized material is pumped into a plate and frame filter press, and then washed with water until the outlet water conductivity is 296 μs / cm, and then washed with pure water until the outlet water conductivity is 81 μs / cm;

[0090] Step 5: The fully washed filter cake is conveyed to a slurry tank by a belt conveyor, and 0.2% of the weight of the product converted to A189 silane coupling agent and 1.5% of n-octanol are added, and the block filter cake is made into a slurry with a viscosity of 563 cps by high-speed stirring;

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

[0092] Step 7: The primary product C3 is subjected to air flow milling to reduce the particle size D50 to 6.39 μm, thereby obtaining a highly transparent silicon dioxide product D3 for silicone rubber.

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

[0094] Step 1: Preparation of reaction materials:

[0095] Solid water glass with an iron content of ≤120ppm and water with an electrical conductivity of ≤100μs / cm are added to a static autoclave in a mass ratio of 1:1.5-2.5, 0.7MPa steam is introduced for dissolution, the pressure is maintained for 2.5 hours, and then placed in a storage tank for 24 hours, filtered with a plate and frame filter press to obtain sodium silicate; then the sodium silicate and water are mixed into 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 3The pure water is mixed evenly and filtered through a bag filter to obtain sodium silicate; then sodium silicate and water are mixed to form a liquid highly transparent sodium silicate solution A (transparency>200mm) with a concentration of 18.2wt%;

[0097] Under stirring conditions, 2m 3 Slowly add 16m3 of concentrated sulfuric acid with a transparency of ≥200mm 3 After being uniformly mixed in pure water, the mixture is filtered through a precision ceramic filter element to obtain a sulfuric acid solution B with a concentration of 18.1 wt% for reaction;

[0098] Step 2: 26m 3 Water was added to the reactor and heated to 88°C with saturated steam. Then, 2.3 m 3 The pH of the highly transparent sodium silicate solution A was measured at 10.9, and the pH was adjusted to 9.8 with the reaction sulfuric acid solution B. The flow rate of the highly transparent sodium silicate solution A was 13m 3 / h and the flow rate of sulfuric acid solution B for reaction is 4.55m 3 / h is added into the reactor at the same time, the process controls the pH in the range of 9.5-10, the temperature control index is in the range of 90±1℃, and the reaction time is 88min;

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

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

[0101] Step 5: The fully washed filter cake is conveyed to a slurry 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: Dry the slurry by spray drying, control the heating loss within the range of 5-7%, and grind the particle size D50 to 5.02 μm by air flow to obtain the silicon dioxide product for silicone rubber.

[0103] Table 1 is a comparison of the main quality indicators of the silicon dioxide prepared in Examples 1 to 3 and Comparative Example 1.

[0104] Table 1

[0105]

[0106] Note: Hygroscopicity and light transmittance are measured with silicone rubber primary film. The specific test method is as follows:

[0107] 1) Preparation of silicone rubber sheet: Weigh 1kg methyl vinyl rubber, 3g zinc stearate, 21g hydroxy silicone oil respectively, put into a 5L internal mixer, add 450g silica into the kneader in 3-4 times for mixing, after adding silica, heat to 150℃ and heat for 50min, after hot refining, cold refining for 30min to 120℃, vacuumize for 1.5-2h and discharge, wait for the rubber to cool to room temperature.

[0108] 2) Take 50g of rubber and add 0.25g of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, chemical name 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, mix well on an open mixing mill and put into a mold, then push the mold into a flat-plate vulcanizer with a set temperature of 165-175°C and vulcanize for 4-6 minutes for primary vulcanization molding.

[0109] 3) After cooling the once vulcanized sheet to room temperature, weigh it and measure the transmittance. Then leave it open for a week and test the transmittance and weight gain of the film again. Calculate the moisture absorption rate based on the weight gain:

[0110]

[0111] Where: 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, the present invention removes impurities and purifies the raw materials, uses an organic ether surfactant and adds an inorganic salt dispersant to the reaction acid during the reaction process to effectively disperse and surface modify the newly generated silica particles, effectively preventing the particles from agglomerating and greatly reducing the content of hydroxyl groups on the surface. Adding a silane coupling agent and an alcohol modifier in the pulping process effectively reduces the content of hydroxyl groups on the surface of silica and reduces the collapse of particle holes during the drying process. Compared with existing silica products for silicone rubber, the product indicators of the present invention have high pore volume, low surface hydroxyl content, and uniform particle size distribution. The water absorption rate of the product in silicone rubber is significantly reduced, ensuring the high transparency of the product in silicone rubber.

[0114] Figures 1 to 4 The particle size distribution diagram of the silicon dioxide obtained in Examples 1 to 3 and Comparative Example 1 is shown in FIG. Figures 1 to 4 It can be seen that the particle size of the silicon dioxide prepared by the present invention is close to a normal distribution.

[0115] Embodiment 4 of the present invention: A method for preparing silicon dioxide for highly transparent silicone rubber, comprising the following steps:

[0116] Step 1: Preparation of reaction materials:

[0117] Solid water glass with an iron content of ≤120ppm and water with an electrical conductivity of ≤100μs / cm are added to a static autoclave in a mass ratio of 1:1.5-2.5, 0.7MPa steam is introduced for dissolution, the pressure is maintained for 2h, and then placed in a storage tank for 26h, filtered with a plate and frame filter press to obtain sodium silicate; then the sodium silicate and water are mixed into 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 20-30r / min, 20m 3 Add 3.6kg hydrogen peroxide and 5.4kg sodium sulfide to liquid sodium silicate, react at 80℃ for 20min, let stand for 8h, filter through bag filter and mix with 15m 3 The pure water was mixed evenly to obtain a highly transparent sodium silicate solution A4 (transparency>200mm) with a sodium silicate concentration of 17.8wt%;

[0119] Under stirring conditions, 2m 3 Slowly add 16.5m3 of concentrated sulfuric acid with a transparency of ≥200mm 3 Pure water, then add 0.8 kg of sodium chloride and mix well, then filter through a precision ceramic filter to obtain a 17.3 wt% sulfuric acid solution B4 for reaction;

[0120] Step 2: 25m 3 Water was added to the reactor, heated to 90°C with saturated steam, and 1.5 m 3 The pH of the highly transparent sodium silicate solution A4 was measured at 10.5, and the pH was adjusted to 9.5 with the reaction sulfuric acid solution B4. 2.5 kg of isomeric alcohol ether was added, and the highly transparent sodium silicate solution A4 was prepared at a flow rate of 13 m 3 / h and the reaction sulfuric acid solution B4 flow rate 6.5m 3 / h is added into the reactor at the same time, the process controls the pH value in the range of 9.5-10, the temperature control index is in the range of 95±1℃, and the reaction time is 95min;

[0121] Step 3: After the reaction is completed, stop adding the highly transparent sodium silicate solution A4 and adjust the flow rate of the sulfuric acid solution B4 for the reaction to 3.9 m 3 / h, acidify until the pH of the material is 8.8, stop adding acid, and homogenize for 12 minutes. Then adjust the flow rate of sulfuric acid solution B4 for reaction to 6.5m 3 / h, acidify until the pH value 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 with water until the outlet water conductivity is 300 μs / cm, and then wash with pure water until the outlet water conductivity is 83 μs / cm;

[0123] Step 5: The fully washed filter cake is conveyed to a slurry tank by a belt conveyor, and 0.1% of the weight of the product converted to A189 silane coupling agent and 1.0% of n-octanol are added, and the block filter cake is made into a slurry with a viscosity of 570 cps by high-speed stirring;

[0124] Step 6: Drying the slurry by spray drying to obtain the primary product C4;

[0125] Step 7: The primary product C4 is subjected to air flow milling to reduce the particle size D50 to 4.5 μm, thereby obtaining a highly transparent silicon dioxide product D4 for silicone rubber.

[0126] Embodiment 5 of the present invention: A method for preparing silicon dioxide for highly transparent silicone rubber, comprising the following steps:

[0127] Step 1: Preparation of reaction materials:

[0128] Solid water glass with an iron content of ≤120ppm and water with an electrical conductivity of ≤100μs / cm are added to a static autoclave in a mass ratio of 1:1.5-2.5, 0.7MPa steam is introduced for dissolution, the pressure is maintained for 2h, and then placed in a storage tank for 26h, filtered with a plate and frame filter press to obtain sodium silicate; then the sodium silicate and water are mixed into 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 20-30r / min, 20m 3 Add 3.6kg hydrogen peroxide and 5.4kg sodium sulfide to liquid sodium silicate, react at 80℃ for 20min, let stand for 8h, filter through bag filter and mix with 15m 3 The pure water was mixed evenly to obtain a highly transparent sodium silicate solution A5 (transparency>200mm) with a sodium silicate concentration of 17.8wt%;

[0130] Under stirring conditions, 2m 3 Slowly add 16.5m3 of concentrated sulfuric acid with a transparency of ≥200mm 3 Pure water, then add 0.8 kg of sodium chloride and mix well, then filter through a precision ceramic filter to obtain a 17.3 wt% sulfuric acid solution B5 for reaction;

[0131] Step 2: 30m 3 Water was added to the reactor, heated to 95°C with saturated steam, and 3.0 m 3 The pH of the highly transparent sodium silicate solution A5 was measured at 11.5, and the pH was adjusted to 10.0 with the reaction sulfuric acid solution B5. 2.5 kg of isomeric alcohol ether was added, and the highly transparent sodium silicate solution A5 was prepared at a flow rate of 13 m 3 / h and the flow rate of sulfuric acid solution B5 for reaction is 3.71m 3 / h is added into the reactor at the same time, the process controls the pH value in the range of 9.5-10, the temperature control index is in the range of 95±1℃, and the reaction time is 95min;

[0132] Step 3: After the reaction is completed, stop adding the highly transparent sodium silicate solution A5 and adjust the flow rate of the sulfuric acid solution B5 for the reaction to 2.6 m 3 / h, acidify until the pH of the material is 8.8, stop adding acid, and homogenize for 15 minutes. Then adjust the flow rate of sulfuric acid solution B5 for reaction to 6.5m 3 / h, acidify until the pH value 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 with water until the outlet water conductivity is 294 μs / cm, and then wash with pure water until the outlet water conductivity is 82 μs / cm;

[0134] Step 5: The fully washed filter cake is conveyed to a slurry tank by a belt conveyor, and 0.5% of the weight of the product converted to A189 silane coupling agent and 2.0% of n-octanol are added, and the block filter cake is made into a slurry with a viscosity of 562 cps by high-speed stirring;

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

[0136] Step 7: The primary product C5 is crushed by air flow to reduce the particle size D50 to 10 μm to obtain a highly transparent silicon dioxide product D5 for silicone rubber.

[0137] Example 6 of the present invention is: highly transparent silicon dioxide for silicone rubber prepared by the preparation method of Example 5.

[0138] In summary, the highly transparent silicon dioxide for silicone rubber and the preparation method thereof provided by the present invention have the following advantages:

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

[0140] 2. The step-by-step acidification technology is used to make the particle distribution more uniform;

[0141] 3. Adding alcohol and silane coupling agent with specific composition and proportion in the pulping process further reduces the hydroxyl content on the surface of SiO2 particles and reduces particle agglomeration during the drying process.

[0142] 4. The surface hydroxyl content, ignition loss, particle size distribution width, etc. of the silicon dioxide 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. By adding hydrogen peroxide and sodium sulfide, the purpose of purification and impurity removal can be achieved, and the uniformity of particle size can be further improved.

[0144] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing highly transparent silicon dioxide for silicone rubber, characterized in that: The following steps are involved: S1: Mixing concentrated sulfuric acid, water and an inorganic salt dispersant to obtain a sulfuric acid solution for reaction; S2: adding a highly transparent sodium silicate solution to water until the pH is 10.5-11.5, then adjusting the pH to 9.5-10.0 with a sulfuric acid solution for reaction, and adding an organic ether surfactant; then maintaining the pH, adding the highly transparent sodium silicate solution and the sulfuric acid solution for reaction at the same time to react; S3: stop adding the highly transparent sodium silicate solution, adjust the flow rate of the reaction sulfuric acid solution to 60-70% of the flow rate of the reaction sulfuric acid solution during the S2 reaction, acidify until the pH value of the material is 8.8-9.2, stop adding acid, and homogenize for 10-15 minutes; then adjust the flow rate of the reaction sulfuric acid solution to the flow rate of the reaction sulfuric acid solution during the S2 reaction, acidify until the pH value of the material is 2.8-3.3, stop adding acid, and homogenize for 30-40 minutes; S4: filtering and washing the homogenized material in sequence, and then mixing the silane coupling agent and alcohol to prepare a slurry; S5: After the slurry is dried and crushed, highly transparent silicon dioxide for silicone rubber is obtained.

2. The method for preparing highly transparent silicon dioxide for silicone rubber according to claim 1, characterized in that: The specific preparation method of the highly transparent sodium silicate solution is: adding hydrogen peroxide and sodium sulfide to liquid sodium silicate to react, letting the reaction stand and then filtering after the reaction is completed, and mixing the filtered residue with water to obtain the highly transparent sodium silicate solution.

3. The method for preparing highly transparent silicon dioxide for silicone rubber according to claim 2, characterized in that: The conditions for the reaction of the liquid sodium silicate with hydrogen peroxide and sodium sulfide are: reacting at 80-90° C. for 10-20 minutes.

4. The method for preparing highly transparent silicon dioxide for silicone rubber according to claim 1, characterized in that: The mass ratio of the concentrated sulfuric acid, water and inorganic salt dispersant is 1:4-6:0.001-0.

003.

5. The method for preparing highly transparent silicon dioxide for silicone rubber according to claim 1, characterized in that: The inorganic salt dispersant includes at least one of sodium sulfate and sodium chloride.

6. The method for preparing highly transparent silicon dioxide for silicone rubber according to claim 1, characterized in that: The organic ether surfactant includes any one of lauryl dodecanol polyether, cetyl alcohol polyoxyethylene ether and isomeric alcohol ether.

7. The method for preparing highly transparent silicon dioxide for 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 the silicon dioxide for high-transparency silicone rubber.

8. The method for preparing highly transparent silicon dioxide for silicone rubber according to claim 1, characterized in that: The mass of the silane coupling agent is 0.1-0.5% of the mass of the silicon dioxide for high-transparency silicone rubber.

9. The method for preparing highly transparent silicon dioxide for silicone rubber according to claim 1, characterized in that: The mass of the alcohol is 1 to 2% of the mass of the silicon dioxide for high-transparent silicone rubber.

10. Highly transparent silicon dioxide for silicone rubber prepared by the method for preparing highly transparent silicon dioxide for silicone rubber according to any one of claims 1 to 9.

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