Low-viscosity high-transparency liquid silicone rubber and preparation method thereof

Abstract

The invention relates to the technical field of silicone rubber, and particularly discloses low-viscosity high-transparency liquid silicone rubber and a preparation method thereof. Comprising vinyl silicone oil, vinyl silicone oil with the viscosity of 3000-10000 mPa.s, fumed silica, precipitated white carbon black, silazane, deionized water, vinyl silicone resin, hydrogen-containing silicone oil, an inhibitor and a platinum catalyst. The exposed number of hydroxyl groups on the surface of the white carbon black and the viscosity are reduced by utilizing the relatively good coating property of the low-viscosity vinyl silicone oil and the white carbon black, and part of gas-phase white carbon black is replaced by precipitated white carbon black with a low specific surface area and is dispersed by a closed device in advance; part of hexamethyldisilazane and water are added for surface hydroxyl treatment, heating and vacuum treatment are conducted, the dispersion degree of hexamethyldisilazane in a kneading machine is increased, and the viscosity can be reduced. A negative pressure type vacuum feeding device is used for continuous feeding in the base rubber cold mixing process, white carbon black dispersion reinforcement is facilitated, it is guaranteed that the shear force of the base rubber is uniform, and the method is suitable for the injection molding technology.

Description

Technical Field

[0001] The invention belongs to the technical field of silicone rubber, and in particular relates to a low-viscosity, highly transparent liquid silicone rubber and a preparation method thereof. Background Art

[0002] Addition liquid silicone rubber (LSR) is a fluid rubber compound based on vinyl-containing polyorganosiloxane polymers. Liquid silicone rubber has low viscosity, high fluidity, and has the advantages of simple processing, energy saving and emission reduction, and low production cost. It can be continuously processed by injection molding and compression molding. Because of its good mechanical properties and electrical insulation properties, it has excellent extreme temperature tolerance and aging resistance. The prepared product is used as an environmental barrier potting glue, which is applied to aerospace, power cables and other aspects, and has broad market prospects. At the same time, the high transparency can also be used in optical applications, such as potting optical glasses. With the development of science and technology, the subsequent estimated demand will grow steadily. Liquid silicone rubber is an excellent material for making injection molding accessories due to its high strength, aging resistance, no discoloration, high insulation and other advantages. Therefore, a low-viscosity, high-strength, high-transmittance liquid silicone rubber is developed, which can be used in many optical instruments and equipment to meet market needs.

[0003] A Chinese patent with publication number 117801537A discloses a low-viscosity, highly transparent silicone rubber that uses relatively low-viscosity silicone oil to adjust the fluidity of the silicone, thereby improving the optical and mechanical properties. However, there are also the following problems: the selected silica A380 has a large specific surface area, and the lack of a continuous feeding device will lead to an uneven dispersion process of silica, and the rubber has obvious rubber block particles, which are easy to cluster during the experiment, causing a sharp increase in viscosity; the current mainstream processing method is injection molding, and excessive viscosity is not conducive to processing, resulting in reduced production efficiency and cumbersome operation; and the hardness range of the product is not universal, and lacks the applicability of relatively low hardness products.

[0004] A Chinese patent with publication number 116715965A discloses a high-transparency addition-type liquid vulcanized silicone rubber that increases its optical transmittance by adding modified transparent powder, with an average transmittance of about 90%. However, there are also the following problems: the modified transparent powder used requires multiple steps to prepare, the process is cumbersome, and reagents are required when preparing the transparent powder, which will make the subsequent silicone rubber products unable to meet the testing and use standards for food and medical treatment; another problem is that the viscosity of the methyl vinyl silicone rubber raw rubber is too high, and the modified transparent powder is unevenly dispersed during the subsequent base rubber kneading process. Summary of the invention

[0005] In view of the problems in the prior art, the present invention solves the effect of uneven dispersion of white carbon black on the viscosity of silicone rubber-based adhesive. The mixed white carbon black that has been dispersed and treated in a closed container in advance is continuously fed in the cold refining stage using a negative pressure vacuum feeding device to ensure that the white carbon black is evenly dispersed. At the same time, more contact area can be treated with hexamethyldisilazane to reduce the viscosity. At the same time, the use of vinyl silicone resin effectively reduces the effect of increased viscosity of white carbon black after use, and solves the problem of subsequent injection molding process. In order to achieve the above technical objectives, the technical solution of the present invention is: A low-viscosity, highly transparent liquid silicone rubber and a preparation method thereof, wherein the mass ratio of the silicone rubber comprises: 50-100 parts of vinyl silicone oil with a viscosity of 3000-10000mPa·s, 5-25 parts of fumed silica, 5-25 parts of precipitated silica, 1-10 parts of hexamethyldisilazane, 1-5 parts of water, 1-10 parts of triphenylmethoxysilane, 20-70 parts of vinyl silicone resin, 1-5 parts of hydrogenated silicone oil, 0.1-0.5 parts of inhibitor, 1-10 parts of hydroxy silicone oil, 1-10 parts of dimethylvinylethoxysilane, and 0.00001-0.0001 parts of platinum catalyst.

[0006] Furthermore, the low-viscosity vinyl silicone oil has a viscosity of 3000-10000 mPa·s, a vinyl content of 0.13-0.33%, and a volatile matter of ≤1%.

[0007] In some embodiments, it is a mixture of one or more of 3000 mPa.s, 5000 mPa.s, 8000 mPa.s, and 10000 mPa.s.

[0008] The particle size of the fumed silica is 5-10 μm, and the specific surface area of ​​the fumed silica is 200-325 m 2 / g; the particle size of the precipitated white carbon black is 7-12 μm, and the specific surface area of ​​the precipitated white carbon black is 150-200m 2 / g.

[0009] Furthermore, the fumed silica and precipitated silica are first mixed as a mixed silica, and the mixing step is to add a certain proportion of hexamethyldisilazane and water to the fumed silica and the precipitated silica in a closed environment, and disperse for 5-30 minutes under the conditions of a temperature of 50-150°C, a vacuum degree of 0.02-0.08Mpa, and a stirring speed of 2000-3000rpm, and the water is added in the form of steam.

[0010] The superiority of mixed silica of precipitated silica and vapor phase silica lies in: after being dispersed in a closed device in advance, adding part of hexamethyldisilazane and water to treat the surface hydroxyl groups and heating and vacuum treatment can treat the number of hydroxyl groups on the surface of silica and reduce the bound water of silica itself, which can reduce the dispersion time of silica in the cold refining of rubber and increase its dispersion degree in the kneader, ultimately reducing the viscosity and ensuring excellent reinforcement effect.

[0011] Furthermore, the hydrogen content of the hydrogen-containing silicone oil is selected from 0.1-2%, and it is a mixture of one or more of terminal hydrogen-based silicone oil, pendant hydrogen-based silicone oil and terminal-side hydrogen-based silicone oil.

[0012] Furthermore, the hydroxyl content of the hydroxy silicone oil is 4.5-9.0%.

[0013] Furthermore, the inhibitor is 1-ethynylcyclohexanol.

[0014] Furthermore, the vinyl silicone resin is hydroxy vinyl polysiloxane. In some embodiments, the vinyl polysiloxane is a mixture of one or more of 1.5%, 2.2%, 3.2%, 4.5%, and 5.5%.

[0015] Furthermore, the base rubber of the low-viscosity silicone rubber is processed by the following method: S1. Add a portion of vinyl silicone oil into a vertical closed kneader; S2, after adding the vinyl silicone resin, start the internal mixing and kneading of the cold mixing stage; S3. Use a negative pressure vacuum feeding device to continuously feed mixed silica in the cold refining stage, and the mixed silica feed flow rate is 300-500g / h; S4, adding dimethylvinylethoxysilane, hexamethyldisilazane, water, hydroxy silicone oil, and triphenylmethoxysilane, and continuing cold refining; S5, after the cold refining is completed, the temperature is raised for mixing and kneading, and the remaining vinyl silicone oil is added for dilution, and the above mixed rubber material is fully mixed; S6, after the rubber material is fully heated and mixed and kneaded uniformly, vacuum kneading is performed to obtain the rubber material; S7. Take out the rubber material, cool it to room temperature, grind it, vacuum degas, and filter it to obtain the rubber material.

[0016] The temperature of the cold refining stage is 30-70°C, and the cold refining lasts 40-100 minutes.

[0017] The temperature of the heating, mixing and kneading is 100-180° C., and the time of the heating, mixing and kneading is 60-270 minutes.

[0018] The vacuum kneading temperature is 130-180° C., the vacuum degree is set to -0.1-0.05 MPa, and the kneading is performed for 60-180 min.

[0019] The amount of the vinyl silicone oil added in step S1 is 60-70%; the amount of the vinyl silicone oil added in step S6 is 30-40%, so that the total is 100%.

[0020] The application of the technical solution of the present invention has the following beneficial effects: on the basis of the existing high-transmittance liquid silicone rubber product process, firstly, in a closed container, white carbon black is mixed by using hexamethyldisilazane and water treatment for a certain period of time, and a negative pressure vacuum feeding device is used to continuously feed the material in the cold refining stage, and the feed flow rate is maintained at 500g / h during the whole process to ensure that the white carbon black has sufficient time to disperse in the cold refining stage. Secondly, by adjusting the order and number of additions of hydroxy vinyl silicone resin, and optimizing and improving methods such as reducing the refractive index of triphenylmethoxysilane, a high-transmittance liquid silicone rubber with high mechanical properties and no need to add a transparent agent is prepared, which effectively improves the light transmittance and service life of the high-transmittance liquid silicone rubber. Its strong high strength and aging resistance enable it to be used for a long time in harsh environments. Due to the advanced nature of the technical solution, it can be widely used in optical instruments and equipment, high-strength seals, shockproof parts and other application fields. This technical solution effectively reduces the viscosity of silicone rubber by adding low-viscosity vinyl silicone oil and the continuous feeding technology of pre-mixed white carbon black, solves the problems of subsequent injection molding process, improves production efficiency and reduces production costs. Secondly, this technical solution improves the light transmittance and mechanical properties of silicone rubber by adding vinyl silicone resin and phenylsilazane, making it more suitable for optical instruments and high-intensity application scenarios. Finally, the implementation of this technical solution can not only improve the performance of silicone rubber, but also reduce its production cost, which has high economic value and social benefits. DETAILED DESCRIPTION

[0021] The present application is further described in detail below with reference to the embodiments.

[0022] The vinyl silicone oil with a viscosity of 3000-10000mPa.s, and the vinyl silicone oil with a viscosity of 3000mPa.s, 5000mPa.s, 8000mPa.s, 10000mPa.s, 20000mPa.s, and 100000mPa.s used in the embodiments of the present application are self-made products of Xingrui Company, and the vinyl silicone oil with a viscosity of 60000mPa.s is selected from Bluestar Star.

[0023] The precipitated silica filler was purchased from Evonik of Germany, and the fumed silica filler was purchased from Wacker Chemicals.

[0024] Vinylsilazane and hexamethyldisilazane were purchased from Shanghai Anaiji.

[0025] Hydroxy silicone oil is a homemade product.

[0026] Dimethylvinylethoxysilane is a homemade product.

[0027] Triphenylmethoxysilane was selected from Hubei Qiniu Chemical.

[0028] The vinyl silicone resin was selected from Guangzhou Delta Chemical.

[0029] Hydrogenated silicone oil is a homemade product.

[0030] Example of preparation of silicone rubber.

[0031] Preparation Example 1 Liquid silicone rubber includes the following raw materials in parts by weight: 2500g of vinyl silicone oil with a viscosity of 5000mPa.s, 700g of fumed silica filler, 300g of precipitated silica filler, 210g of hexamethyldisilazane, 120g of water, 50g of triphenylmethoxysilane, 50g of hydroxy silicone oil, 300g of vinyl silicone resin (hydroxyvinyl polysiloxane, wherein the vinyl content is 1.5%), and 35g of dimethylvinylethoxysilane. The silica filler is fumed silica A, and the specific surface area of ​​silica A is 325m 2 / g, average particle size is 7μm; precipitated white carbon black B, the specific surface area of ​​white carbon black B is 185m 2 / g, and an average particle size of 12μm. The particle size of the fumed silica is 5-6μm, and the specific surface area of ​​the fumed silica is 300-325m 2 / g; the particle size of the precipitated white carbon black is 10-12 μm, and the specific surface area of ​​the precipitated white carbon black is 150-180m 2 / g.

[0032] The preparation method of the base glue comprises the following specific steps: S1, add 1750g vinyl silicone oil into a vertical closed kneader; S2, adding vinyl silicone resin and kneading at 50°C for 10 minutes; S3. Use a negative pressure vacuum feeding device to continuously feed mixed silica during the cold refining stage, and the mixed silica feed rate is 500 g / h; Mixed silica: Mix the fumed silica and precipitated silica in a sealed container in advance, and add 110g hexamethyldisilazane and 40g water. The water is added in the form of water vapor. Then the temperature is raised to 120°C. The vacuum degree is controlled at 0.02MPa and the dispersion is carried out at a stirring speed of 2000rpm for 20min. The obtained product is heated and degassed, and placed in a negative pressure vacuum feeding device to wait for feeding.

[0033] S4, adding dimethylvinylethoxysilane, hexamethyldisilazane, water, hydroxy silicone oil and triphenylmethoxysilane and continuing cold refining for 30 minutes; S5, after the cold refining is completed, the temperature is raised to 150°C and mixed and kneaded for 60 minutes to fully mix the above mixed rubber materials; S6, after the rubber material is fully heated to 180°C and kneaded evenly, the remaining vinyl silicone oil is added for dilution, and finally vacuum kneading for 3 hours to obtain the rubber material; S7. Take out the rubber material, cool it to room temperature, grind it, vacuum degas, and filter it to obtain the rubber material.

[0034] Preparation Example 2: The difference between Preparation Example 2 and Preparation Example 1 is that the fumed silica and the precipitated silica are mixed in advance in a mass ratio of 8:2 (i.e., the amount of fumed silica is 800 g and the amount of precipitated silica is 200 g), and the other parameters remain unchanged to obtain liquid silicone rubber base 2.

[0035] Preparation Example 3: The difference between Preparation Example 3 and Preparation Example 1 is that the fumed silica and the precipitated silica are mixed in advance in a mass ratio of 9:1 (i.e., the amount of fumed silica is 900 g and the amount of precipitated silica is 100 g), and the other parameters remain unchanged to obtain liquid silicone rubber base 3.

[0036] Preparation Example 4: The difference between Preparation Example 4 and Preparation Example 1 is that the fumed silica and the precipitated silica are mixed in advance in a mass ratio of 7:3 (i.e., the amount of fumed silica is 700 g and the amount of precipitated silica is 300 g), and the mixing time is 10 minutes to obtain liquid silicone rubber base 4.

[0037] Preparation Example 5: The difference between Preparation Example 5 and Preparation Example 1 is that the fumed silica and the precipitated silica are mixed in advance in a mass ratio of 7:3 (i.e., the amount of fumed silica is 700 g and the amount of precipitated silica is 300 g), and no vacuum heating treatment is performed to obtain liquid silicone rubber base 5.

[0038] The present invention is further explained below with reference to the examples, but the examples do not limit the present invention in any form.

[0039] Example 1 This experiment provides a low-viscosity, highly transparent silicone rubber, comprising the following raw materials in parts by weight: 170 g silicone rubber base, 5.26 g hydrogen-containing silicone oil, 2 g vinyl-terminated silicone oil with a viscosity of 100,000 mPa·s, 0.53 g platinum catalyst, and 0.106 g inhibitor. The silicone rubber base is prepared from Preparation Example 1, and the hydrogen-containing silicone oil and the vinyl-terminated silicone oil with a viscosity of 100,000 mPa·s are homemade products.

[0040] The vulcanization method of silicone rubber includes the following specific steps: Add silicone rubber base, inhibitor, hydrogen-containing silicone oil, and terminal vinyl silicone oil with a viscosity of 100000mPa·s and stir evenly at room temperature. Then add platinum catalyst and continue stirring until uniform. Pour the rubber mixture into a vulcanization mold and use a flat vulcanizer to compression mold at 140°C for 10-20 minutes. Then continue heating at 200°C for 4 hours. Demold the sample for testing.

[0041] Example 2 The difference between Example 2 and Example 1 is that hexamethyldisilazane and water are not used in the stage of preparing the mixed silica, and the amount of hexamethyldisilazane and water used is added together with the hexamethyldisilazane and water used in the base rubber preparation process (i.e., step S4).

[0042] Example 3 The difference between Example 3 and Example 1 is that the silicone rubber base raw material is that of Preparation Example 2.

[0043] Example 4 The difference between Example 4 and Example 1 is that the silicone rubber base raw material is that of Preparation Example 3.

[0044] Example 5 The difference between Example 5 and Example 1 is that the viscosity of the vinyl silicone oil of the silicone rubber base raw material is 100000 mPa.s, and other parameters remain unchanged.

[0045] Comparative Example 1 The difference between the preparation of Comparative Example 1 and Example 1 is that the white carbon black in the silicone rubber base raw material is all gas phase white carbon black.

[0046] Comparative Example 2 The difference between the preparation of Comparative Example 2 and Example 1 is that the white carbon black is not mixed in advance (the fumed white carbon black and the precipitated white carbon black are not mixed), and the other parameters remain unchanged.

[0047] Comparative Example 3 The difference between Preparation Comparative Example 3 and Example 1 is that the silicone rubber base raw material is Preparation Example 4.

[0048] Comparative Example 4 The difference between Preparation Comparative Example 4 and Example 1 is that the silicone rubber base raw material is Preparation Example 5.

[0049] Comparative Example 5 The difference between the preparation of comparative example 5 and example 1 is that a negative pressure vacuum feeding device is used to continuously feed the mixed silica in the cold refining stage, and the feed flow rate of the mixed silica is 600 g / h.

[0050] Detection Methods 1. Light transmittance A low-viscosity, highly transparent liquid silicone rubber prepared in the present application was vulcanized at high temperature to form a sample with a thickness of 2 mm and a weight of 50 g. The light transmittance at 450 nm was detected by a UV-visible light split-tube photometer. The measurement was performed at least three times, and the average value was taken as the standard.

[0051] 2. Viscosity Refer to GBT 2794-2013 "Determination of viscosity of adhesives - Single cylinder rotational viscometer method", use a 7# rotor, keep the torque between 30 and 70%, and the speed between 1 and 10 ram. Measure at least three times and take the average value.

[0052] 3. Hardness With reference to the standard of GBT 531.1-2008 "Test method for indentation hardness of vulcanized rubber or thermoplastic rubber Part 1: Shore hardness method (Shore hardness)", the hardness of a low-viscosity, high-transparent silicone rubber prepared in the present application was tested.

[0053] 4. Tensile strength, elongation and tear strength With reference to the standard GB / T528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", the tensile strength, elongation and tear strength of a low-viscosity, high-transparent liquid silicone rubber prepared in this application were tested.

[0054] Table 1: Performance test data table Example Light transmittance (%) Refractive index Viscosity (mP·s) Hardness (ShA) Tensile strength (MPa) Elongation (%) Tear strength (KN / m) Example 1 92.8 1.41 <![CDATA[7.5×10 4 ]]> 28 9.4 756 26 Example 2 92.5 1.40 <![CDATA[9×10 4 ]]> 29 8.1 721 35 Example 3 92.7 1.40 <![CDATA[1.5×10 5 ]]> 30 9.8 476 41 Example 4 92.9 1.39 <![CDATA[2×10 5 ]]> 35 10.2 422 41.9 Example 5 92.5 1.39 <![CDATA[5.53×10 5 ]]> 37 9 498 42 Comparative Example 1 92.8 1.38 <![CDATA[3×10 5 ]]> 33 8.4 435 38.4 Comparative Example 2 89.8 1.37 <![CDATA[3.2×10 5 ]]> 37 6.6 652 25.7 Comparative Example 3 88.5 1.38 <![CDATA[4.2×10 5 ]]> 31 8 684 23.5 Comparative Example 4 90.1 1.37 <![CDATA[2.6×10 5 ]]> 29 8.3 643 22.8 Comparative Example 5 90.7 1.39 <![CDATA[1.2×10 5 ]]> 29 9.1 703 25 From the performance test results, it can be seen that the low-viscosity, highly transparent liquid silicone rubber prepared in this application can meet the requirements of the injection molding process in terms of viscosity, has a wide range of applications, and has an overall light transmittance of more than 92%. Its mechanical properties are maintained at a high level.

[0055] By comparing Example 1 with Example 2, at the same hardness, the viscosity of Example 1 is less than that of Example 2. This is because the mixed silica treated with hexamethyldisilazane and water can reduce the surface hydroxyl groups, resulting in better dispersion in the base rubber and less viscosity swelling.

[0056] By comparing Example 1 with Examples 3 and 4, it can be seen that as the proportion of fumed silica in the mixed silica increases, the mechanical strength gradually increases. This is because fumed silica has a small particle size, a large specific surface area, a good dispersion effect, and a better reinforcement effect on the base rubber.

[0057] By comparing Example 1 with Example 5, the high-viscosity 100000 mPa.s vinyl-terminated silicone oil will increase the viscosity. This is because the high-viscosity silicone oil itself has a large molecular weight and a longer molecular chain, which will be entangled with each other, and the mutual coating effect with silica is not strong, resulting in poor clustering and dispersion of silica itself.

[0058] By comparing Comparative Example 1 with Example 1, the presence of only fumed silica will cause a sharp increase in the viscosity of the silicone rubber base. This is because the fumed silica itself has a small particle size, a high degree of dispersion, and a strong bonding force with the silicone oil.

[0059] By comparing Example 2 with Example 1, the fumed silica and the precipitated silica are not mixed and pretreated in advance, the transmittance drops to 89.8%, and the mechanical properties drop significantly. This is because the untreated silica is hydrophilic and easily clusters with each other, resulting in uneven dispersion.

[0060] By comparing Comparative Example 3 with Example 1, the time for mixing silica was reduced, the transmittance dropped to 88.5%, and the mechanical properties decreased significantly. This was because the hydrolysis time of hexamethyldisilazane was relatively long, the surface treatment of silica was insufficient in a short time, and the structuring was aggravated, resulting in an increase in viscosity.

[0061] By comparing Comparative Example 4 with Example 1, when the heating vacuum environment is not turned on when mixing white carbon black, the transmittance drops to 90.1%, and the mechanical properties decrease significantly. The reason for this is that the hydrolysis reaction of hexamethyldisilazane is an endothermic reaction that releases ammonia. Not turning on heating and vacuum may inhibit the hydrolysis of silazane.

[0062] By comparing Example 5 with Example 1, the transmittance and mechanical properties are slightly reduced. The reason is that white carbon black needs to be fed continuously and evenly during the dispersion process. Too fast feeding will cause hard rubber lumps to appear in the rubber compound, which makes it difficult for the kneader to disperse.

[0063] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed. However, as long as it is within the scope of the claims of the present application, it shall be protected by the patent law.

Claims

1. A low-viscosity, highly transparent liquid silicone rubber, characterized in that: The invention comprises the following raw materials in parts by weight: 50-100 parts of vinyl silicone oil with a viscosity of 3000-10000 mPa·s, 5-25 parts of fumed silica, 5-25 parts of precipitated silica, 1-10 parts of hexamethyldisilazane, 1-5 parts of water, 1-10 parts of triphenylmethoxysilane, 20-70 parts of vinyl silicone resin, 1-5 parts of hydrogenated silicone oil, 0.1-0.5 parts of inhibitor, 1-10 parts of hydroxy silicone oil, 1-10 parts of dimethylvinylethoxysilane and 0.00001-0.0001 parts of platinum catalyst.

2. The low-viscosity, highly transparent liquid silicone rubber according to claim 1, characterized in that: The vinyl silicone oil is vinyl polysiloxane, the vinyl polysiloxane is 3000-10000 mPa·s, the vinyl content is 0.13-0.33%, and the volatile matter is ≤1%.

3. The low-viscosity, highly transparent liquid silicone rubber according to claim 1, characterized in that: The vinyl silicone resin is hydroxy vinyl polysiloxane.

4. The low-viscosity, highly transparent liquid silicone rubber according to claim 1, characterized in that: The hydrogen-containing silicone oil is hydrogen-containing polysiloxane.

5. The low-viscosity, highly transparent liquid silicone rubber according to claim 4, characterized in that: The particle size of the fumed silica is 5-10 μm, and the specific surface area of ​​the fumed silica is 200-325 m 2 / g; the particle size of the precipitated white carbon black is 7-12 μm, and the specific surface area of ​​the precipitated white carbon black is 150-200m 2 / g.

6. The low-viscosity, highly transparent liquid silicone rubber according to claim 5, characterized in that: The fumed silica and precipitated silica are first mixed to form a mixed silica. The mixing step is to add a certain proportion of hexamethyldisilazane and water to the fumed silica and the precipitated silica in a closed environment, and disperse for 5-30 minutes under the conditions of a temperature of 50-150° C., a vacuum degree of 0.02-0.08 MPa, and a stirring speed of 2000-3000 rpm.

7. A method for preparing a low-viscosity, highly transparent liquid silicone rubber as claimed in any one of claims 1 to 6, characterized in that: The method comprises the following specific steps: uniformly mixing the kneaded base rubber, vinyl silicone oil, hydrogen-containing silicone oil and inhibitor, adding a platinum catalyst, removing bubbles and heating for reaction, cooling, rolling, sheeting and filtering to obtain a low-viscosity and highly transparent silicone material.

8. The method for preparing a low-viscosity, highly transparent liquid silicone rubber according to claim 7, characterized in that: The preparation method of the kneaded rubber base comprises the following steps: S1. Add a portion of vinyl silicone oil into a vertical closed kneader; S2, after adding the vinyl silicone resin, start the internal mixing and kneading of the cold mixing stage; S3. Use a negative pressure vacuum feeding device to continuously feed mixed silica in the cold refining stage, and the mixed silica feed flow rate is 300-500g / h; S4, adding dimethylvinylethoxysilane, hexamethyldisilazane, water, hydroxy silicone oil and triphenylmethoxysilane to continue cold refining; S5, after the cold refining is completed, the temperature is raised and the mixing and kneading is performed to fully mix the above mixed rubber materials; S6, after the rubber material is fully heated and mixed and kneaded uniformly, the remaining vinyl silicone oil is added for dilution, and finally vacuum kneading is performed to obtain the rubber material; S7. Take out the rubber material, cool it to room temperature, grind it, vacuum degas, and filter it to obtain the rubber material.

9. The method for preparing a low-viscosity, highly transparent liquid silicone rubber according to claim 8, characterized in that: The temperature of the cold refining stage is 30-70°C, and the cold refining is 40-100 minutes; The temperature of the heating, mixing and kneading is 100-180°C, and the time of the heating, mixing and kneading is 60-270min; The vacuum kneading temperature is 130-180° C., the vacuum degree is set to -0.1-0.05 MPa, and the kneading is performed for 60-180 min.

10. The method for preparing a low-viscosity, highly transparent liquid silicone rubber according to claim 8, characterized in that: The amount of the vinyl silicone oil added in step S1 is 60-70%; the amount of the vinyl silicone oil added in step S6 is 30-40%, so that the total is 100%.