Transparent liquid silicone rubber with controllable electrical property and preparation method thereof

Abstract

The invention provides transparent liquid silicone rubber with controllable electrical properties and a preparation method thereof, and the liquid silicone rubber comprises the following components in parts by mass: 10-40 parts of polydimethylsiloxane grafted with sulfonate groups, 60-90 parts of vinyl silicone oil, 10-40 parts of white carbon black and 5-15 parts of hexamethyldisilazane. The preparation method comprises the following steps: mixing the vinyl silicone oil, the polydimethylsiloxane grafted with the sulfonate group, the white carbon black and the hexamethyldisilazane, heating and kneading; and adding vinyl silicone oil, and uniformly stirring to obtain the liquid silicone rubber. The obtained liquid silicone rubber is controllable in surface resistance and can be applied to the field of antistatic materials or humidity monitoring.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of silicone rubber, and particularly relates to transparent and electrically controllable liquid silicone rubber and a preparation method thereof. BACKGROUND

[0002] The excellent flexibility and high and low temperature resistance of silicone make the silicone related material technology develop rapidly. However, the following shortcomings still exist: (1) stable structure, poor electrical conductivity, easy to form static electricity, and cause equipment failure or related accidents; (2) poor compatibility with other materials, the addition of large amount of conductive materials will cause the mechanical properties of vulcanized rubber to deteriorate, and the material is opaque, the increase of electrical conductivity seriously affects the processing performance and appearance of the material.

[0003] The traditional silicone rubber is prepared by using polydimethylsiloxane (PDMS), and the molecular structure of PDMS is symmetrical and stable. The PDMS has good insulation and poor electrical conductivity, and is easy to accumulate static electricity. Therefore, it is often necessary to add conductive fillers or antistatic agents. The conductive fillers such as carbon black and metal affect the transparency of silicone rubber after being added, such as the addition of carbon nanotubes and conductive nickel powder in CN115197577A; the use of modified acetylene carbon black and carbon fiber in CN114479473A. The antistatic agent is often a carbon-based material, which has poor compatibility with silicone rubber and is easy to precipitate, affecting the service life of the material, such as the use of non-ionic antistatic agent (coconut oil diethanolamide) in CN115197577A. The above patents do not describe the optical properties of the prepared materials, and there are few technologies of silicone rubber with both transparency and good electrical properties. SUMMARY

[0004] In view of the above problems, the present application provides a transparent and electrically controllable liquid silicone rubber and a preparation method thereof. In the preparation process of the liquid silicone rubber, polydimethylsiloxane grafted with sulfonate groups is added. The sulfonate has a polysiloxane backbone structure and good compatibility with the base silicone oil. The prepared liquid glue is stable, and has high light transmittance. The sulfonate part has the characteristics of inorganic salt, can effectively capture trace amount of water in the air, can reduce the surface resistance of the liquid silicone rubber, and has antistatic effect. At the same time, the change of the surface resistance can reflect the size of the humidity, and can be applied to humidity monitoring.

[0005] The present application provides a transparent and electrically controllable liquid silicone rubber, which contains polydimethylsiloxane grafted with sulfonate groups 10-40 parts by mass, and vinyl silicone oil 60-90 parts by mass. The structure of the polydimethylsiloxane grafted with sulfonate groups is as follows:

[0006] The relative molecular weight of the polydimethylsiloxane grafted with sulfonate groups is 50-100 thousand, m:n=0.3~0.9, and M is at least one of lithium, sodium or potassium.

[0007] Further, the grafting sulfonate group-containing polydimethylsiloxane is prepared by the following steps:

[0008] Further, the grafting sulfonate group-containing polydimethylsiloxane is prepared by the following steps: (a) stirring excess tetramethyltetra-vinylcyclotetrasiloxane, mercaptoethanesulfonic acid and a photoinitiator in tetrahydrofuran / water as a mixed solvent, and then performing a photoinitiation reaction at room temperature, and then vacuum removing the solvent from the obtained mixed solution to obtain a mixed ring body in a milky white liquid form; (b) adding a catalyst to the mixed ring body, heating and reacting, then adding a terminating agent to terminate the reaction, and then performing post-treatment to obtain the grafting sulfonate group-containing polydimethylsiloxane; (c) adding an alkali-containing tetrahydrofuran / water mixed solution to the grafting sulfonate group-containing polydimethylsiloxane, stirring and reacting, and then performing post-treatment after the reaction to obtain the grafting sulfonate group-containing polydimethylsiloxane.

[0009] Further, the photoinitiator is at least one of benzoin dimethyl ether, benzophenone or methyl benzoylformate, and is preferably benzoin dimethyl ether.

[0010] Further, in the step (a), the photoinitiation reaction condition is ultraviolet light irradiation at a wavelength of 365 nm for 5-10 min; and the vacuum removal of the solvent is performed at 90°C and -0.09 MPa. In the step (b), the catalyst is potassium hydroxide; the heating and reaction condition is warming and reacting at 70-110°C for 4-8 h; the terminating agent is phosphoric acid; and the post-treatment mode includes: after the reaction liquid is cooled to room temperature, methanol is added for washing and impurity removal to obtain a milky white liquid, and then methanol is vacuum removed at 90°C and -0.09 MPa. In the step (c), the alkali is one or more of lithium hydroxide, sodium hydroxide or potassium hydroxide; the reaction time is 18-25 h, and the reaction temperature is 25-70°C; and the post-treatment includes adding methanol to the reaction liquid for washing and impurity removal, and then further vacuum removing the methanol at 90°C and -0.09 MPa.

[0011] Further, the mass ratio of the tetramethyltetra-vinylcyclotetrasiloxane to the mercaptoethanesulfonic acid is (0.9-6.4):1.

[0012] Further, the specific surface area of the white carbon black is 230-500 m 2g, particle size D50 is 5-25 μm, D95 is 15-100 μm; the vinyl silicone oil is one or more of end vinyl silicone oil, side vinyl silicone oil or end side vinyl silicone oil, the viscosity is 7-130,000, the vinyl mass fraction is 0.05-0.2%.

[0013] The application also provides a preparation method of the transparent and electrically controllable liquid silicone rubber, comprising the following steps: The vinyl silicone oil, the grafted sulfonate group-containing polydimethylsiloxane, the white carbon black and the hexamethyldisilazane are mixed and kneaded by heating; then the vinyl silicone oil is added and stirred uniformly to obtain the liquid silicone rubber.

[0014] Further, the kneading by heating is carried out at 170-190 DEG C for 4-6 h.

[0015] The liquid silicone rubber obtained by the application can be used in the fields of antistatic materials or humidity monitoring.

[0016] The application has the following beneficial effects: (1) The liquid silicone rubber of the application is not filled with colored conductive fillers, which can guarantee good optical performance of the silicone, and the particle size of the fumed silica and the ultrasonic dispersion effect are strictly required, thereby reducing the negative influence of the white carbon black on the optical performance, and the light transmittance of the vulcanized test piece with a thickness of 2 mm is more than 70%.

[0017] (2) The grafted polydimethylsiloxane with sulfonate groups can capture trace moisture in the air, ionize metal ions, and form electron hopping sites with water molecules or sulfonic acid ions, thereby reducing the surface resistance of the liquid silicone rubber; by adjusting the proportion of the sulfonic acid groups or the compounding ratio of the grafted polydimethylsiloxane with the vinyl silicone oil, the surface resistance of the liquid silicone rubber can be controlled, and the liquid silicone rubber can be applied to antistatic materials and humidity monitoring. In addition, the grafted polydimethylsiloxane with sulfonate groups has flexible siloxane segments, compared with conventional antistatic agents, when the grafted polydimethylsiloxane with sulfonate groups is applied to the silicone rubber system, the transparency of the silicone rubber can be maintained, and the mechanical properties of the silicone rubber can be significantly improved. DETAILED DESCRIPTION

[0018] The embodiments of the application will be described in detail below with reference to the examples, which are only used to illustrate the application and should not be regarded as limiting the scope of the application.

[0019] For convenience of description, 100000 cs end vinyl silicone oil (vinyl mass fraction 0.07%) is referred to as "silicone oil", grafted polydimethylsiloxane is referred to as "grafted PDMS", and fumed silica is referred to as "white carbon black".

[0020] Example 1 S1, preparation of grafted polydimethylsiloxane with sulfonate groups: S1-1, 45 parts of tetramethyltetraethenylcyclotetrasiloxane, 50 parts of mercaptoethanesulfonic acid and 2 parts of benzoin dimethyl ether were stirred uniformly with 100 parts of tetrahydrofuran / water (mass ratio 1:1) as a mixed solvent, and then irradiated with ultraviolet light of wavelength 365 nm for 7 min at room temperature. Subsequently, the mixed solution was treated at 90°C under a vacuum of -0.09 MPa for 3 h to obtain a mixed ring body in the form of a milky white liquid.

[0021] S1-2, 30 ppm of potassium hydroxide was added to the above mixed ring body, and then the temperature was raised to 110°C for 5 h. Subsequently, 15 ppm of phosphoric acid was added to terminate the reaction. After cooling to room temperature, methanol was added for washing to remove impurities, to obtain a milky white liquid. The methanol was removed by vacuum at 90°C and -0.09 MPa to obtain a polydimethylsiloxane grafted with sulfonic acid groups.

[0022] S1-3, 50 parts of a tetrahydrofuran / water mixed solution (mass ratio, tetrahydrofuran: water: lithium hydroxide = 1:1:0.7) containing lithium hydroxide was added to 100 parts of the polydimethylsiloxane grafted with sulfonic acid groups, and then stirred at 45°C for 24 h. Subsequently, methanol was added for washing to remove impurities. Further, the methanol was removed by vacuum at 90°C and -0.09 MPa to obtain a polydimethylsiloxane grafted with lithium sulfonate groups, with a molecular weight of 63,000 (wherein m:n = 0.3).

[0023] S2, liquid silicone rubber: 10 parts of silicone oil, 40 parts of lithium sulfonate grafted PDMS (wherein m:n = 0.3), 30 parts of white carbon black (specific surface area: 425 m 2 / g, D50: 5 μm, D95: 18 μm), 10 parts of hexamethyldisilazane and 3 parts of water were put into a kneader and kneaded for 2 h. Further, the temperature was raised to 180°C for 5 h, and then the low molecular weight components were removed by vacuum for 3 h.

[0024] After the silicone oil was added to the kneader in three portions, the liquid silicone rubber was obtained by stirring for 1 h and then vacuuming for 0.5 h.

[0025] Example 2 In Example 2, the polydimethylsiloxane grafted with sulfonic acid groups was treated with a tetrahydrofuran / water mixed solution (mass ratio, tetrahydrofuran: water: sodium hydroxide = 1:1:0.9) containing sodium hydroxide to obtain a polydimethylsiloxane grafted with sodium sulfonate groups, with a molecular weight of 64,000 (wherein m:n = 0.3). The rest was the same as in Example 1.

[0026] Example 3 S1-3, instead of using potassium hydroxide in tetrahydrofuran / water mixed solution (mass ratio, tetrahydrofuran: water: potassium hydroxide = 1:1:1) to treat the obtained grafted sulfonic acid group polydimethylsiloxane, to obtain grafted potassium sulfonate group polydimethylsiloxane, the molecular weight of which is 69,000, and the rest is the same as example 1.

[0027] Example 4 30 parts of silicone oil, 20 parts of lithium sulfonate grafted PDMS (m:n=0.3) obtained in example 1, 30 parts of white carbon black (specific surface area: 425 m 2 / g, D50: 5 μm, D95: 18 μm), 10 parts of hexamethyldisilazane, and 3 parts of water were put into a kneader and kneaded for 2 h, and then further heated to 180°C and kneaded for 5 h, and then vacuumed for 3 h to remove low molecular weight substances.

[0028] 50 parts of silicone oil were added to the kneader in three times, and after completion, stirring was carried out for 1 h, and then vacuumed for 0.5 h to obtain the liquid silicone rubber.

[0029] Example 5 40 parts of silicone oil, 10 parts of lithium sulfonate grafted PDMS (m:n=0.3) obtained in example 1, 30 parts of white carbon black (specific surface area: 425 m 2 / g, D50: 5 μm, D95: 18 μm), 10 parts of hexamethyldisilazane, and 3 parts of water were put into a kneader and kneaded for 2 h, and then further heated to 180°C and kneaded for 5 h, and then vacuumed for 3 h to remove low molecular weight substances.

[0030] 50 parts of silicone oil were added to the kneader in three times, and after completion, stirring was carried out for 1 h, and then vacuumed for 0.5 h to obtain the liquid silicone rubber.

[0031] Example 6 S1, preparation of grafted sulfonate group polydimethylsiloxane: S1-1, instead of using the same S1 in example 1, the amount of tetramethyltetra-vinylcyclotetrasiloxane added was 60 parts, and the amount of mercaptoethanesulfonic acid added was 40 parts, and the rest was the same as S1 in example 1, to obtain grafted lithium sulfonate group polydimethylsiloxane, the molecular weight of which was 650,000 (m:n=0.6).

[0032] S2, preparation of liquid silicone rubber: 10 parts of silicone oil, 40 parts of lithium sulfonate grafted PDMS (m:n=0.6), 30 parts of white carbon black (specific surface area: 425 m 2 / g, D50: 5 μm, D95: 18 μm), 10 parts of hexamethyldisilazane, and 3 parts of water were put into a kneader and kneaded for 2 h, and then further heated to 180°C and kneaded for 5 h, and then vacuumed for 3 h to remove low molecular weight substances.

[0033] The liquid silicone rubber was obtained by adding 50 parts of silicone oil into the kneader in three times, stirring for 1 h after completion, and vacuumizing for 0.5 h.

[0034] Example 7 S1, Preparation of polydimethylsiloxane grafted with sulfonate groups: Different from S1 of Example 1, in S1-1, the addition amount of tetramethyltetavinylcyclotetrasiloxane was 95 parts, the addition amount of mercaptoethanesulfonic acid was 15 parts, and the rest was the same as S1 of Example 1, to obtain polydimethylsiloxane grafted with lithium sulfonate groups, the molecular weight of which was 62,000 (wherein m:n = 0.9).

[0035] S2, Preparation of liquid silicone rubber: 10 parts of silicone oil, 40 parts of lithium sulfonate grafted PDMS (wherein m:n = 0.9), 30 parts of white carbon black (specific surface area: 425 m 2 / g, D50: 5 μm, D95: 18 μm), 10 parts of hexamethyldisilazane, and 3 parts of water were put into a kneader and kneaded for 2 h, and then further heated to 180°C and kneaded for 5 h, and then vacuumized for 3 h to remove low molecular weight substances.

[0036] The liquid silicone rubber was obtained by adding 50 parts of silicone oil into the kneader in three times, stirring for 1 h after completion, and vacuumizing for 0.5 h.

[0037] Comparative Example 1 Different from Example 1, the parameters of white carbon black were adjusted to specific surface area 228 m 2 / g, D50: 28 μm, D95: 107 μm, and the rest was the same as Example 1.

[0038] Comparative Example 2 50 parts of silicone oil, 30 parts of white carbon black (specific surface area: 425 m 2 / g, D50: 5 μm, D95: 18 μm), 10 parts of hexamethyldisilazane, and 3 parts of water were put into a kneader and kneaded for 2 h, and then further heated to 180°C and kneaded for 5 h, and then vacuumized for 3 h to remove low molecular weight substances.

[0039] The liquid silicone rubber was obtained by adding 50 parts of silicone oil into the kneader in three times, stirring for 1 h after completion, and vacuumizing for 0.5 h.

[0040] Comparative Example 3 50 parts of silicone oil, 20 parts of white carbon black (specific surface area: 425 m 2 / g, D50: 5 μm, D95: 18 μm), 10 parts of commercially available conductive carbon black (specific surface area 750 m 2 / g), 10 parts of hexamethyldisilazane, and 3 parts of water were put into a kneader and kneaded for 2 h, and then further heated to 180°C and kneaded for 5 h, and then vacuumized for 3 h to remove low molecular weight substances.

[0041] The 50 parts of silicone oil were added into the kneader in three times, and after completion, the stirring was carried out for 1 h, and then the vacuum was carried out for 0.5 h to obtain the liquid silicone rubber.

[0042] The liquid silicone rubbers obtained in the above examples and comparative examples were subjected to performance test, and the test standards were as follows: 1. Mechanical property test The breaking strength and elongation at break were tested according to GB / T 528-2009.

[0043] The tear strength was tested according to GB / T 529-2008, and the right-angle cutter was used.

[0044] 2. Light transmittance test The light transmittance-haze was tested according to GB / T 2410-2008, and the sample thickness was 2 mm.

[0045] 3. Surface resistance test The surface resistance was tested according to GB / T 1692-2008.

[0046] 4. Humidity monitoring test The liquid silicone rubber sheets with a thickness of 0.1 mm were prepared from the liquid silicone rubbers obtained in Example 1 and Comparative Example 2, and were placed in an environment with a relative humidity of 11% to 95% to test the surface resistivity and observe the response to humidity.

[0047] The test results are shown in Table 1 (wherein the resistance test conditions were temperature: 25°C, and relative humidity: 67%).

[0048] Table 1

[0049] As can be seen from the above table, different metal ions (lithium, sodium, potassium) were used in Examples 1 to 3, and lithium ion, as the ion with the smallest metal radius, has the strongest hydration ability and the best effect on reducing the surface resistance.

[0050] Examples 1, 4 and 5 compared the influence of the addition amount of grafted PDMS in the liquid silicone rubber on the performance of the liquid silicone rubber, and it can be seen that with the decrease of the amount of grafted PDMS, the mechanical properties and optical properties showed an upward trend, indicating that the sulfonate grafted PDMS would have a certain influence on the mechanical properties of the silicone rubber, which was related to the occurrence of microphase separation in the liquid silicone rubber; however, it was found that the increase of the surface resistance was significantly higher than the decrease of the amount of grafted PDMS, which was due to the fact that the above-mentioned microphase separation could form a charge transmission channel, which was beneficial to reducing the surface resistance.

[0051] Examples 1, 6, 7 compare the influence of varying grafting degree in grafted PDMS on liquid silicone rubber. As can be seen from Examples 1 and 6, under the condition of the same amount of grafted PDMS used, the optical properties and mechanical properties increase with the decrease of grafting degree, and the surface resistance increases accordingly. When the grafting degree is reduced to a certain range, as in Examples 6 and 7, the above-mentioned performance changes are not obvious. Overall, the liquid silicone obtained in Examples 1-7 has good mechanical properties and excellent optical transparency, and can be applied in the field of antistatic materials. Comparative Example 1 uses white carbon black with low specific surface area and poor dispersibility, which seriously affects the optical transparency of the liquid silicone rubber. Comparative Example 2 does not add grafted PDMS, and the surface resistance is too high, which shows that the grafted PDMS in the present application can effectively reduce the surface resistance of the liquid silicone rubber.

[0052] It is found from Example 7 and Comparative Example 3 that after adding commercially available antistatic agent conductive carbon black, the mechanical strength, elongation at break and tear strength decrease significantly, because untreated conductive carbon black is more likely to cause defects due to agglomeration in the liquid silicone rubber, affecting the mechanical properties. At the same time, the surface resistance is also higher than that of Example 7, mainly due to the agglomeration of carbon black, the reduction of internal conductive path. Although the present application can further increase the amount of conductive carbon black used to reduce the surface resistance, the mechanical strength of the silicone rubber will inevitably decrease in a stepwise manner. In addition, the use of conductive carbon black will completely abandon the excellent light transmittance performance of the liquid silicone rubber itself.

[0053] The present application further films the liquid silicone rubber, and the liquid silicone rubber obtained in Examples 1 and Comparative Example 2 is respectively cast and vulcanized to obtain a 0.1 mm thick liquid rubber film, and the surface resistance of the film is tested in a humidity changing space, and the test results are shown in Table 2 (test temperature: 25℃).

[0054] Table 2

[0055] As can be seen, the surface resistance of the liquid silicone rubber of Comparative Example 2 without grafted PDMS is stable at about 10 14 Ω, which is an excellent insulator. The liquid silicone rubber film of Example 1 has an effective surface resistance response to humidity change, and the resistance change range is 10 2 -10 12 Ω, which can be applied in the field of humidity response.

Claims

1. A transparent, electrically controllable liquid silicone rubber, characterized in that 10-40 parts by mass of the polydimethylsiloxane containing grafted sulfonate groups, 60-90 parts by mass of a vinyl silicone oil, 10-40 parts by mass of white carbon black, and 5-15 parts by mass of hexamethyldisilazane. The polydimethylsiloxane containing grafted sulfonate groups has the following structural formula: The polydimethylsiloxane containing grafted sulfonate groups has a relative molecular weight of 50-100 thousand, m:n=0.3-0.9, and M is at least one of lithium, sodium, or potassium.

2. A transparent, electrically controllable liquid silicone rubber according to claim 1, characterized in that 10-40 parts by mass of the polydimethylsiloxane containing grafted sulfonate groups, 60-90 parts by mass of a vinyl silicone oil, 10-40 parts by mass of white carbon black, and 5-15 parts by mass of hexamethyldisilazane.

3. A transparent, electrically controllable liquid silicone rubber according to claim 1, characterized in that The polydimethylsiloxane containing grafted sulfonate groups is prepared by the following method: (a) Excess tetramethyltetra-vinylcyclotetrasiloxane, mercaptoethanesulfonic acid, and a photoinitiator are stirred uniformly in tetrahydrofuran / water as a mixed solvent, and then a photoinitiation reaction is performed at room temperature. The obtained mixed solution is vacuumed to remove the solvent, and a milky white liquid mixed ring body is obtained. (b) A catalyst is added to the mixed ring body, and then a heating reaction is performed. Subsequently, a terminating agent is added to terminate the reaction, and post-processing is performed to obtain the polydimethylsiloxane containing grafted sulfonic acid groups. (c) An alkali-containing tetrahydrofuran / water mixed solution is added to the polydimethylsiloxane containing grafted sulfonic acid groups, and then stirring and reaction are performed. After the reaction is completed, post-processing is performed to obtain the polydimethylsiloxane containing grafted sulfonate groups.

4. A transparent, electrically controllable liquid silicone rubber according to claim 3, characterized in that The photoinitiator is at least one of benzpinacol, benzpinacol, or methyl benzoylformate, and is preferably benzpinacol.

5. A transparent, electrically controllable liquid silicone rubber according to claim 3, wherein In step (a), the photoinitiation reaction is performed by irradiating with ultraviolet light of a wavelength of 365 nm for 5-10 min. The vacuum removal of the solvent is performed at 90°C and -0.09 MPa. In step (b), the catalyst is potassium hydroxide. The heating reaction is performed at 70-110°C for 4-8 h. The terminating agent is phosphoric acid. The post-processing includes washing with methanol to remove impurities after the reaction solution is cooled to room temperature, and then a milky white liquid is obtained. The methanol is vacuumed at 90°C and -0.09 MPa. In step (c), the alkali is one or more of lithium hydroxide, sodium hydroxide, or potassium hydroxide. The reaction time is 18-25 h, and the reaction temperature is 25-70°C. The post-processing includes washing with methanol to remove impurities, and then the methanol is vacuumed at 90°C and -0.09 MPa.

6. A transparent, electrically controllable liquid silicone rubber according to claim 3, wherein The mass ratio of the tetramethyltetra-vinylcyclotetrasiloxane to the mercaptoethanesulfonic acid is (0.9-6.4):

1.

7. A transparent, electrically controllable liquid silicone rubber according to claim 1, characterized in that The white carbon black has a specific surface area of 230-500 m 2 / g, a particle size D50 of 5-25 μm, and a D95 of 15-100 μm. The vinyl silicone oil is one or more of a terminal vinyl silicone oil, a side vinyl silicone oil, or a terminal and side vinyl silicone oil, has a viscosity of 70-130 thousand, and has a vinyl mass fraction of 0.05-0.2%.

8. A process for the preparation of a transparent, electrically controllable liquid silicone rubber, characterized in that The method includes the following steps: The vinyl silicone oil, the polydimethylsiloxane containing grafted sulfonate groups, the white carbon black, and the hexamethyldisilazane are mixed and kneaded at an elevated temperature. Then, the vinyl silicone oil is added and stirred uniformly to obtain a liquid silicone rubber.

9. A process for the preparation of a transparent, electrically controllable liquid silicone rubber according to claim 8, characterized in that The kneading at an elevated temperature is performed at 170-190°C for 4-6 h.

10. Use of the liquid silicone rubber according to any one of claims 1 to 7 or of the liquid silicone rubber obtained by the production process according to any one of claims 8 to 9, characterized in that, The liquid silicone rubber is used for antistatic materials or humidity monitoring.

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