A low viscosity, high transparency liquid silicone rubber and a method for producing the same

Abstract

The application relates to the technical field of silicone rubber, and particularly discloses a high-transparency liquid silicone rubber with low viscosity and a preparation method thereof. The high-transparency liquid silicone rubber with low viscosity comprises the following components: vinyl silicone oil, vinyl silicone oil with a viscosity of 3000-10000 mPa.s, fumed white carbon black, precipitated white carbon black, silazane, deionized water, vinyl silicone resin, hydrogen-containing silicone oil, inhibitor and platinum gold catalyst. The low-viscosity vinyl silicone oil and the white carbon black have good coating property, the number of exposed hydroxyl groups on the surface of the white carbon black is reduced, and the viscosity is reduced; the precipitated white carbon black with a low specific surface area is used to replace part of the fumed white carbon black, the precipitated white carbon black is dispersed in advance through a closed device, part of the hexamethyldisilazane and water are added to treat the surface hydroxyl groups, and the surface hydroxyl groups are treated through heating and vacuum treatment, the dispersion degree of the high-transparency liquid silicone rubber in a kneader is increased, and the viscosity is reduced. In the cold rolling process of the base glue, a negative pressure type vacuum feeding device is used for continuous feeding, the white carbon black is dispersed and reinforced, the shearing force of the base glue is uniform, and the high-transparency liquid silicone rubber with low viscosity is suitable for an injection molding process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicone rubber, and particularly relates to a low-viscosity high-transparency liquid silicone rubber and a preparation method thereof. BACKGROUND

[0002] Addition type liquid silicone rubber (LSR) is a flowable compound with a vinyl-containing polyorganosiloxane as a base polymer. The liquid silicone rubber has low viscosity and high flowability, and has the advantages of simple processing, energy saving and emission reduction, and low production cost, and can be used for continuous processing by injection molding and compression molding. The prepared product has good mechanical properties and electrical insulation properties, excellent extreme temperature resistance and aging resistance. The product as an environmental barrier potting adhesive is applied to aerospace, power cables and other aspects, and has a broad market prospect. Meanwhile, the high-transparency property can also be used for optical applications, such as potting type optical glasses. With the development of science and technology, the subsequent estimated demand will steadily increase. The liquid silicone rubber is an excellent material for manufacturing injection molding accessories due to its high strength, aging resistance, colorlessness and high insulation. Therefore, the development of a liquid silicone rubber with low viscosity, high strength and high light transmittance can be applied to many optical instruments and equipment, and meet the market demand.

[0003] A low-viscosity high-transparency silicone rubber disclosed in Chinese Patent No. 117801537A uses a low-viscosity silicone oil to adjust the flowability of the silicone rubber, and further improves the optical and mechanical properties. However, the following problems exist: the selected white carbon black A380 has a large specific surface area, and the use of a continuous feeding device can cause uneven dispersion of the white carbon black, obvious particles in the compound, and easy clustering in the experimental process, which can cause a sharp increase in viscosity; the current mainstream processing method is injection molding processing, and the high viscosity is not conducive to processing, which can cause a decrease in production efficiency and complicated operation; and the hardness range of the product is not universal, and the applicability of low-hardness products is lacking.

[0004] A high-transparency addition type liquid vulcanized silicone rubber disclosed in Chinese Patent No. 116715965A increases the optical transmittance by adding modified transparent powder, and the average transmittance is about 90%. However, the following problems exist: the modified transparent powder needs to be prepared in multiple steps, the process is complicated, and reagents are needed during the preparation of the transparent powder, which can cause the subsequent silicone rubber product to fail to meet the detection and use standards of food and medical treatment; another problem is that the viscosity of the methyl vinyl silicone rubber raw rubber is too large, and the modified transparent powder is not uniformly dispersed in the subsequent base rubber kneading process. SUMMARY

[0005] In view of the problems in the prior art, the present application solves the influence of uneven dispersion of white carbon black on the viscosity of silicone rubber-based glue, the mixed white carbon black dispersed and treated in advance in a sealed container is continuously fed in the cold rolling stage using a negative pressure type vacuum feeding device, which ensures uniform dispersion of the white carbon black and at the same time, more contact area can be treated by hexamethyldisilazane to reduce the viscosity, and the use of vinyl silicone resin effectively reduces the influence of the increased viscosity after the use of white carbon black, and solves the problem of subsequent injection molding process.

[0006] A low-viscosity high-transparency liquid silicone rubber and a preparation method thereof, the mass ratio of the silicone rubber comprises:

[0007] 50-100 parts of a vinyl silicone oil with a viscosity of 3000-10000 mPa·s, 5-25 parts of fumed white carbon black, 5-25 parts of precipitated white carbon black, 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 hydrogen-containing silicone oil, 0.1-0.5 parts of inhibitor, 1-10 parts of hydroxy silicone oil, 1-10 parts of dimethyl vinyl ethoxy silane, and 0.00001-0.0001 parts of platinum catalyst.

[0008] Further, 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 content of ≤1%.

[0009] In some embodiments, the mixture is one or more of 3000 mPa.s, 5000 mPa.s, 8000 mPa.s, and 10000 mPa.s.

[0010] The fumed white carbon black has a particle size of 5-10 μm and a specific surface area of 200-325 m 2 / g; and the precipitated white carbon black has a particle size of 7-12 μm and a specific surface area of 150-200 m 2 / g.

[0011] Further, the fumed white carbon black and the precipitated white carbon black are first mixed as a mixed white carbon black, the mixing step is to add a certain proportion of hexamethyldisilazane and water to the fumed white carbon black and the precipitated white carbon black in a sealed environment, and the dispersion is carried out at a temperature of 50-150℃, a vacuum degree of 0.02-0.08 Mpa, and a stirring speed of 2000-3000 rpm for 5-30 minutes, and the water is added in the form of steam.

[0012] The mixed white carbon black of precipitated white carbon black and fumed white carbon black has the following excellent properties: the number of surface hydroxyl groups of the white carbon black can be treated, and the combined water of the white carbon black itself can be reduced by adding part of hexamethyldisilazane and water to treat the surface hydroxyl groups and heating and vacuum treatment in advance after the white carbon black is dispersed by a closed device, the dispersion time of the white carbon black in the cold rolling of the rubber compound can be reduced, the dispersion degree of the white carbon black in the kneader can be increased, the viscosity can be finally reduced, and excellent reinforcing effect can be ensured.

[0013] Further, the hydrogen content of the hydrogen-containing silicone oil is selected from 0.1-2%, and is one or a mixture of more than one of end-hydrogen silicone oil, side-hydrogen silicone oil and end-side hydrogen silicone oil.

[0014] Further, the hydroxyl content of the hydroxyl silicone oil is 4.5-9.0%.

[0015] Further, the inhibitor is 1-ethynylcyclohexanol.

[0016] Further, the vinyl silicone resin is a hydroxyl vinyl polysiloxane, and in some embodiments, the vinyl polysiloxane is a mixture of one or more of 1.5%, 2.2%, 3.2%, 4.5%, 5.5%.

[0017] Further, the base rubber of the low-viscosity silicone rubber is treated by the following method:

[0018] S1, a part of the vinyl silicone oil is added to a vertical closed kneader;

[0019] S2, after the vinyl silicone resin is added, the mixing of the cold rolling stage is started;

[0020] S3, the mixed white carbon black is continuously fed in the cold rolling stage using a negative pressure vacuum feeding device, and the feeding flow of the mixed white carbon black is 300-500 g / h;

[0021] S4, dimethyl vinyl ethoxy silane, hexamethyldisilazane, water, hydroxyl silicone oil and triphenylmethoxysilane are added, and the cold rolling is continued;

[0022] S5, after the cold rolling is completed, the temperature mixing kneading is carried out, the remaining vinyl silicone oil is added for dilution, and the above mixed rubber compound is fully mixed and uniform;

[0023] S6, after the rubber compound is fully temperature-mixed and kneaded uniformly, vacuum kneading is carried out to obtain the rubber compound;

[0024] S7, the rubber compound is taken out and cooled to room temperature, and then ground, vacuum defoaming and filtered to obtain the rubber compound.

[0025] The temperature of the cold rolling stage is 30-70℃, and the cold rolling time is 40-100 min.

[0026] The temperature of the warming kneading is 100-180℃, and the time of the warming kneading is 60-270min.

[0027] The temperature of the vacuum kneading is 130-180℃, the vacuum degree is set to -0.1~0.05Mpa, and the kneading time is 60-180min.

[0028] The amount of the vinyl silicone oil added in the step S1 is 60-70%, and the amount of the vinyl silicone oil added in the step S6 is 30-40%, so that the total is 100%.

[0029] The beneficial effects of the technical solution of the application are: based on the existing high-transparency liquid silicone rubber product process, first, the fumed silica is pre-treated in a closed container by using hexamethyldisilazane and water for a certain period of time, and a negative pressure type vacuum feeding device is used for continuous feeding in the cold rolling stage, the feeding flow rate is kept at 500g / h during the whole process, and the fumed silica has sufficient time for dispersion in the cold rolling stage. Second, by adjusting the adding sequence and number of times of the hydroxy vinyl silicone resin and reducing the refractive index of triphenylmethoxysilane, a high-transparency liquid silicone rubber without adding a transparent agent and with high mechanical properties is prepared, which effectively improves the light transmittance and service life of the high-transparency liquid silicone rubber. Its strong high strength and aging resistance make it can be used for a long time in harsh environments. Due to the advancement of the technical solution, it can be widely applied in the fields of optical instruments and equipment, high-strength sealing components, shockproof components, etc. The technical solution effectively reduces the viscosity of the silicone rubber by adding low-viscosity vinyl silicone oil and continuously feeding the pre-mixed fumed silica, solves the problem of subsequent injection molding process, improves the production efficiency, and reduces the production cost. Secondly, by adding vinyl silicone resin and phenylsilazane, the light transmittance and mechanical properties of the silicone rubber are improved, making it more suitable for optical instruments and equipment and high-strength application scenarios. Finally, the implementation of the technical solution not only improves the performance of the silicone rubber, but also reduces its production cost, which has high economic value and social benefits. DETAILED DESCRIPTION

[0030] The application will be further described in detail below in combination with examples.

[0031] The vinyl silicone oil with a viscosity of 3000-10000mPa.s used in the examples of the application, the vinyl silicone oil with a viscosity of 3000mPa.s, 5000mPa.s, 8000mPa.s, 10000mPa.s, 20000mPa.s, and 100000mPa.s are self-made products of Xingrui Company, and the vinyl silicone oil with a viscosity of 60000mPa.s is selected from Bluestar Starfire.

[0032] The precipitated silica filler is selected from WACKER, Germany, and the fumed silica filler is selected from WACKER, Germany.

[0033] The vinyl silazane and hexamethyl disilazane are selected from Shanghai An Nai Ji.

[0034] The hydroxyl silicone oil is a self-made product.

[0035] The dimethyl vinyl ethoxy silane is a self-made product.

[0036] The triphenyl methoxy silane is selected from Hubei Qi Niu Chemical.

[0037] The vinyl silicone resin is selected from Guangzhou Delta Chemical.

[0038] The hydrogen-containing silicone oil is a self-made product.

[0039] Preparation example of silicone rubber.

[0040] Preparation example 1

[0041] The liquid silicone rubber comprises the following raw materials 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 hexamethyl disilazane, 120g of water, 50g of triphenyl methoxy silane, 50g of hydroxyl silicone oil, 300g of vinyl silicone resin (hydroxyl vinyl polysiloxane, wherein the vinyl content is 1.5%), and 35g of dimethyl vinyl ethoxy silane. The fumed silica filler is fumed silica A, the specific surface area of the fumed silica A is 325m 2 / g, and the average particle size is 7μm; the precipitated silica filler is precipitated silica B, the specific surface area of the precipitated silica B is 185m 2 / g, and the average particle size is 12μm. The particle size of the fumed silica is 5-6μm, the specific surface area of the fumed silica is 300-325m 2 / g; the particle size of the precipitated silica is 10-12μm, and the specific surface area of the precipitated silica is 150-180m 2 / g.

[0042] The preparation method of the base rubber comprises the following specific steps:

[0043] S1, 1750g of vinyl silicone oil is added to a vertical closed kneader;

[0044] S2, after adding the vinyl silicone resin, cold rolling and kneading at 50℃ for 10min;

[0045] S3, a negative pressure vacuum feeding device is used to continuously feed the mixed silica filler in the cold rolling stage, and the feeding flow of the mixed silica filler is 500g / h;

[0046] Mixed white carbon black: fumed white carbon black and precipitated white carbon black are mixed uniformly in a sealed container in advance, 110 g of hexamethyldisilazane and 40 g of water are added, the water is added in the form of water vapor, and the temperature is raised to 120°C. The dispersion is carried out at a stirring speed of 2000 rpm for 20 min under a vacuum degree of 0.02 MPa. The obtained product is heated to remove low molecular weight substances, and is placed in a negative pressure type vacuum feeding device to wait for feeding.

[0047] S4, dimethyl vinyl ethoxy silane, hexamethyldisilazane, water, hydroxy silicone oil, and triphenylmethoxysilane are added and cold rolling is continued for 30 min;

[0048] S5, after cold rolling, the temperature is raised to 150°C and mixing and kneading are carried out for 60 min. The above-mentioned mixed rubber is mixed uniformly;

[0049] S6, after the rubber is uniformly mixed and kneaded at a temperature of 180°C, the remaining vinyl silicone oil is added for dilution, and finally vacuum kneading is carried out for 3 h to obtain the rubber;

[0050] S7, the rubber is taken out and cooled to room temperature, and then ground, vacuum defoaming, and filtration are carried out to obtain the rubber.

[0051] Preparation Example 2:

[0052] Preparation Example 2 is different from Preparation Example 1 in that fumed white carbon black and precipitated white carbon black are mixed uniformly in advance according to a mass ratio of 8:2 (i.e. the amount of fumed white carbon black is 800 g and the amount of precipitated white carbon black is 200 g), and the remaining parameters are unchanged, to obtain liquid silicone rubber base glue 2.

[0053] Preparation Example 3:

[0054] Preparation Example 3 is different from Preparation Example 1 in that fumed white carbon black and precipitated white carbon black are mixed uniformly in advance according to a mass ratio of 9:1 (i.e. the amount of fumed white carbon black is 900 g and the amount of precipitated white carbon black is 100 g), and the remaining parameters are unchanged, to obtain liquid silicone rubber base glue 3.

[0055] Preparation Example 4:

[0056] Preparation Example 4 is different from Preparation Example 1 in that fumed white carbon black and precipitated white carbon black are mixed uniformly in advance according to a mass ratio of 7:3 (i.e. the amount of fumed white carbon black is 700 g and the amount of precipitated white carbon black is 300 g), and the mixing time is 10 min, to obtain liquid silicone rubber base glue 4.

[0057] Preparation Example 5:

[0058] Preparation Example 5 is different from Preparation Example 1 in that the fumed white carbon black and the precipitated white carbon black are mixed uniformly in advance in a mass ratio of 7:3 (i.e. the amount of fumed white carbon black is 700 g and the amount of precipitated white carbon black is 300 g), and no vacuum heating treatment is performed, to obtain a liquid silicone rubber base glue 5.

[0059] The application is further explained in conjunction with the following examples, but the examples do not limit the application in any form.

[0060] Example 1

[0061] The experiment provides a low-viscosity high-transparency silicone rubber, which includes the following raw materials by weight: silicone rubber base glue 170 g, hydrogen-containing silicone oil 5.26 g, end-vinyl silicone oil with a viscosity of 100000 mPa·s 2 g, platinum gold catalyst 0.53 g, inhibitor 0.106 g. The silicone rubber base glue is prepared from Preparation Example 1, and the hydrogen-containing silicone oil and the end-vinyl silicone oil with a viscosity of 100000 mPa·s are self-made products.

[0062] The vulcanization method of the silicone rubber includes the following specific steps:

[0063] After the silicone rubber base glue, the inhibitor, the hydrogen-containing silicone oil, and the end-vinyl silicone oil with a viscosity of 100000 mPa·s are added, they are uniformly stirred at room temperature, then the platinum gold catalyst is added and continuously stirred until uniform, the glue mixture is poured into a vulcanization mold, and a flat plate vulcanization machine is used to press and mold at 140℃ for 10-20 min, then heated at 200℃ for 4 h, and the sample is demolded for testing.

[0064] Example 2

[0065] Example 2 is different from Example 1 in that the hexamethyldisilazane and water are not used in the preparation of the mixed white carbon black stage, and the amount of the hexamethyldisilazane and water used is added together with the hexamethyldisilazane and water used in the base glue preparation process (i.e. S4 step).

[0066] Example 3

[0067] Example 3 is different from Example 1 in that the silicone rubber base glue raw material is Preparation Example 2.

[0068] Example 4

[0069] Example 4 is different from Example 1 in that the silicone rubber base glue raw material is Preparation Example 3.

[0070] Example 5

[0071] Example 5 is different from Example 1 in that the viscosity of the vinyl silicone oil in the silicone rubber base glue raw material is 100000 mPa·s, and the other parameters remain unchanged.

[0072] Comparative Example 1

[0073] The difference between the preparation of Comparative Example 1 and Example 1 is that the white carbon black in the silicone rubber-based glue raw material is all fumed white carbon black.

[0074] Comparative Example 2

[0075] The difference between the preparation of Comparative Example 2 and Example 1 is that the white carbon black is not subjected to the pre-mixing treatment (the fumed white carbon black and the precipitated white carbon black are not subjected to the mixing treatment), and the other parameters are unchanged.

[0076] Comparative Example 3

[0077] The difference between the preparation of Comparative Example 3 and Example 1 is that the silicone rubber-based glue raw material is Preparation Example 4.

[0078] Comparative Example 4

[0079] The difference between the preparation of Comparative Example 4 and Example 1 is that the silicone rubber-based glue raw material is Preparation Example 5.

[0080] Comparative Example 5

[0081] The difference between the preparation of Comparative Example 5 and Example 1 is that the mixed type white carbon black is continuously fed in the cold rolling stage using a negative pressure type vacuum feeding device, and the feeding flow of the mixed type white carbon black is 600 g / h.

[0082] Detection method

[0083] I. Light transmittance

[0084] After a low-viscosity high-transparency liquid silicone rubber prepared in the application is high-temperature vulcanized, a sample with a thickness of 2 mm and a weight of 50 g is prepared, and the light transmittance at 450 nm is detected by a UV-visible light spectrophotometer, and the average value of at least three measurements is taken as the standard.

[0085] II. Viscosity

[0086] Referring to GBT 2794-2013 “Determination of viscosity of adhesives Single cylinder rotational viscometer method”, a 7# rotor is used, the torque is kept between 30-70%, the rotation speed is 1-10 ram, at least three measurements are taken, and the average value is taken.

[0087] III. Hardness

[0088] Referring to the standard of GBT 531.1-2008 “Vulcanized rubber or thermoplastic rubber indentation hardness test method Part 1: Shore hardness meter method (Shore hardness)”, the hardness of a low-viscosity high-transparency silicone rubber prepared in the application is detected.

[0089] IV. Tensile strength, elongation and tear strength

[0090] The tensile strength, elongation and tear strength of the low-viscosity high-transparency liquid silicone rubber prepared in the application were detected according to the standard of GB / T528-2009 “Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber”.

[0091] Table 1: Performance test data table

[0092] Example Transmittance (%) Refractive index Viscosity (mP-s) Hardness (ShA) Tensile strength (MPa) Elongation (%) Tear strength (KN / m) Example 1 92.8 1.41 7.5 x 10 4 ]]> 28 9.4 756 26 Example 2 92.5 1.40 9 x 10 4 ]] 29 8.1 721 35 Example 3 92.7 1.40 1.5 x 10 5 ]] 30 9.8 476 41 Example 4 92.9 1.39 2 x 10 5 ]] 35 10.2 422 41.9 Example 5 92.5 1.39 5.53 x 10 5 ]]> 37 9 498 42 Comparative Example 1 92.8 1.38 3 x 10 5 ]]> 33 8.4 435 38.4 Comparative Example 2 89.8 1.37 3.2 x 10 5 ]]> 37 6.6 652 25.7 Comparative Example 3 88.5 1.38 4.2 x 10 5 ]] 31 8 684 23.5 Comparative Example 4 90.1 1.37 2.6 x 10 5 ]] 29 8.3 643 22.8 Comparative Example 5 90.7 1.39 1.2 x 10 5 ]]> 29 9.1 703 25

[0093] It can be known from the performance test results that the low-viscosity high-transparency liquid silicone rubber prepared in the application can meet the requirements of the injection molding process in viscosity, has a wide range of applications, and the overall light transmittance is above 92%. The mechanical properties thereof are maintained at a high level.

[0094] By comparing Example 1 with Example 2, the viscosity of Example 1 is less than that of Example 2 at the same hardness, because the use of hexamethyldisilazane and water treated mixed white carbon black can reduce the surface hydroxyl group, so that the dispersion effect of the base rubber is better and the viscosity increase is less.

[0095] By comparing Example 1 with Examples 3 and 4, the mechanical strength gradually increases with the increase of the proportion of fumed white carbon black in the mixed white carbon black, because the fumed white carbon black has small particle size, large specific surface area and good dispersion effect, and has excellent reinforcing effect on the base rubber.

[0096] By comparing Example 1 with Example 5, the high-viscosity 100000 mPa.s vinyl-terminated silicone oil increases the viscosity, because the high-viscosity silicone oil has large molecular weight and long molecular chain, and the mutual wrapping between them is not strong, so the mutual coating effect with white carbon black is not strong, resulting in poor clustering and dispersion effect of the white carbon black itself.

[0097] By comparing Comparative Example 1 with Example 1, the presence of only fumed white carbon black causes a sharp increase in the viscosity of the silicone rubber base rubber, because the fumed white carbon black has small particle size and high dispersion degree, and has strong bonding force with the silicone oil.

[0098] By comparing Comparative Example 2 with Example 1, the fumed white carbon black and the precipitated white carbon black are not pretreated by mixing, the light transmittance decreases to 89.8%, and the mechanical properties decrease more, because the untreated white carbon black has hydrophilicity and is easy to cluster with each other, resulting in uneven dispersion.

[0099] By comparing Comparative Example 3 with Example 1, the time of the mixed white carbon black is reduced, the light transmittance decreases to 88.5%, and the mechanical properties decrease more, because the hydrolysis time of hexamethyldisilazane is long, the surface treatment of the white carbon black is not sufficient in a short time, and the structure is intensified to cause the viscosity to rise.

[0100] By comparing Example 1 with Comparative Example 4, the light transmittance is reduced to 90.1% and the mechanical properties are reduced more when the mixed white carbon black is not put in the heating and vacuum environment. The reason is that the hydrolysis reaction of hexamethyldisilazane is an endothermic reaction, which releases ammonia gas, and the lack of heating and vacuum may inhibit the hydrolysis of silazane.

[0101] By comparing Example 1 with Comparative Example 5, the light transmittance and mechanical properties are slightly reduced. The reason is that the white carbon black needs to be continuously and uniformly fed during the dispersion process, and too fast feeding leads to the presence of hard rubber blocks in the rubber compound, which is difficult to disperse in the kneader.

[0102] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are 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; The fumed silica and precipitated silica are first mixed to form a mixed silica. The mixing step is performed in a closed environment by adding a certain proportion of hexamethyldisilazane and water to the fumed silica and precipitated silica at a temperature of 50-150° C. and a vacuum degree of 0.02-0.08 MPa. 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 during the cold refining stage, with the mixed silica feed rate being 300-500 g / 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 and the mixing and kneading are 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 and cool it to room temperature, grind it, remove bubbles in vacuum, and filter it to obtain the kneaded base rubber.

2. The low-viscosity, highly transparent liquid silicone rubber according to claim 1, characterized in that: The vinyl silicone oil is vinyl polysiloxane, the viscosity of 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 silica is 7-12 μm, and the specific surface area of ​​the precipitated silica is 150-200 m 2 / g.

6. The low-viscosity, highly transparent liquid silicone rubber according to claim 1, characterized in that: During the preparation of mixed silica, the dispersion is carried out for 5-30 minutes at a stirring speed of 2000-3000 rpm.

7. The low-viscosity, highly transparent liquid silicone rubber according to claim 1, 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 minutes.

8. The low-viscosity, highly transparent liquid silicone rubber according to claim 1, characterized in that: The amount of vinyl silicone oil added in step S1 is 60-70%; the amount of vinyl silicone oil added in step S6 is 30-40%, so that the total is 100%.

9. A method for preparing a low-viscosity, highly transparent liquid silicone rubber according to any one of claims 1 to 8, characterized in that: The method comprises the following specific steps: uniformly mixing a kneaded base rubber, vinyl-terminated silicone oil with a viscosity of 100,000 mPa·s, hydrogen-containing silicone oil, and an inhibitor; adding a platinum catalyst; performing degassing, heating, and reaction; cooling, rolling, sheeting, and filtering to obtain a low-viscosity and highly transparent silicone material.