A color paste for vinyl silicone rubber and a method for preparing the same

Abstract

The application discloses a color paste for vinyl silicone rubber and a preparation method thereof. The color paste is prepared from raw materials comprising modified carbon black, hyperbranched polyester dispersant, vinyl silicone oil, platinum catalyst and hydrogen-containing silicone oil. The modified carbon black is prepared by first performing acid activation treatment on carbon black, and then performing hyperbranched polysiloxane grafting modification on the obtained product. The hyperbranched polysiloxane is prepared by hydrolytic polycondensation of methyltrimethoxysilane, vinyltrimethoxysilane and mercaptopropyltrimethoxysilane. The hyperbranched polyester dispersant is a hyperbranched polyester synthesized by taking trimethylolpropane as a core and 2,2-dimethylolpropionic acid as AB2 monomer, and introducing double bonds by capping with 10-undecenoic acid, and then introducing mercapto groups by thiol-ene click reaction with mercaptoacetic acid. The color paste provided by the application can be chemically co-crosslinked with a silicone rubber matrix, has the dual functions of coloring and reinforcing, has excellent comprehensive performance, and can be used as a color paste for vinyl silicone rubber.

Description

Technical Field

[0001] This invention relates to a color paste for vinyl silicone rubber and its preparation method, belonging to the field of color paste technology. Background Technology

[0002] Vinyl silicone rubber (VMQ) is widely used in electronics, automotive, and medical fields due to its excellent high and low temperature resistance, weather resistance, and electrical insulation properties. Color pastes are commonly used additives in silicone rubber products, primarily for coloring them. Among these, color pastes for vinyl silicone rubber using carbon black as a pigment are widely applied in coloring silicone rubber products.

[0003] However, the carbon black pigments used in existing vinyl silicone rubber color pastes are highly hydrophobic nanoparticles with a high specific surface area. These nanoparticles have poor compatibility with the silicone rubber matrix and poor dispersibility within it. This leads to a significant problem during the mixing process: the primary carbon black particles in the color paste readily re-agglomerate through van der Waals forces, forming secondary aggregates. This results in pitting, color differences, and a decline in the appearance quality of the rubber products. Furthermore, the poor dispersibility of carbon black in the silicone rubber matrix leads to weak interfacial bonding between the carbon black and the matrix. Under stress, the carbon black particles are prone to debonding at the matrix interface, easily forming a restricted-movement bonded rubber layer. This reduces the effective crosslinking density and toughness of the material. Moreover, the agglomerates formed by carbon black particles in the rubber matrix act as stress concentration sources, inducing microcrack initiation under stress, leading to a significant decrease in the tensile strength, tear strength, and elongation of the rubber products. Therefore, when carbon black in the color paste is added to silicone rubber in its unmodified form, coloring often comes at the cost of sacrificing the mechanical properties of the product, which severely restricts the service life and reliability of black silicone rubber products under harsh conditions such as dynamic sealing and high load.

[0004] To address the above situation, certain methods are needed to improve the dispersibility of carbon black in silicone rubber. Currently, the following two methods are mainly used: One method is physical blending, which involves breaking down carbon black by extending the mixing time and increasing the shear rate to improve its dispersibility. However, this method cannot fundamentally solve the problems of agglomeration and interfacial bonding, and high shear can easily lead to the breakage of silicone rubber molecular chains. One method is the surface modification of carbon black using silane coupling agents, which involves using silane coupling agents to modify the surface of carbon black in order to improve its dispersibility. However, current coupling agents can usually only provide a single type of anchoring group, with insufficient anchoring strength and density, and cannot form an effective chemical bonding network with silicone rubber. The interfacial bonding strength is not ideal, the improvement in dispersibility is limited, and it cannot provide a reinforcing effect.

[0005] Therefore, it is of great significance to develop a color paste for vinyl silicone rubber that can be chemically co-crosslinked with the silicone rubber matrix and has both coloring and reinforcing functions. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the purpose of this invention is to provide a color paste for vinyl silicone rubber and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A color paste for vinyl silicone rubber is prepared from raw materials comprising the following components: Modified carbon black: 30-40 parts by weight; Hyperbranched polyester dispersant: 8-12 parts by weight; Vinyl silicone oil: 45-55 parts by weight; Platinum catalyst: 0.01-0.05 parts by weight; Hydrogen-containing silicone oil: 0.5-1.5 parts by weight; The modified carbon black is prepared by first subjecting the carbon black to acid activation treatment, and then grafting the resulting product with hyperbranched polysiloxane; the hyperbranched polysiloxane is prepared by hydrolysis and condensation polymerization of methyltrimethoxysilane, vinyltrimethoxysilane and mercaptopropyltrimethoxysilane. The hyperbranched polyester dispersant is a hyperbranched polyester synthesized with trimethylolpropane as the core and 2,2-dimethylolpropionic acid as the AB2 monomer. It is prepared by introducing double bonds through 10-undecenoic acid end capping, and then introducing thiol groups through a thiol-alkene click reaction with mercaptoacetic acid.

[0008] One embodiment of the modified carbon black includes the following steps: 1) Disperse carbon black in 5-15% dilute nitric acid and stir at 75-85℃ for 1-3 hours. After the reaction is complete, filter, wash and dry to obtain activated carbon black. 2) Add methyltrimethoxysilane (MTMS), vinyltrimethoxysilane (VTMS), mercaptopropyltrimethoxysilane (MPTMS) and isopropanol to a reactor, stir until homogeneous, add 0.05-0.5 mol / L hydrochloric acid aqueous solution dropwise, control the pH of the reaction system to 2-5, and then react at 60-70℃ for 5-7 hours. After the reaction is completed, distill under reduced pressure to obtain hyperbranched polysiloxane. 3) Add activated carbon black and hyperbranched polysiloxane to toluene, mix evenly, heat to 100-110℃, and react for 6-8 hours under nitrogen protection. After the reaction is completed, distill under reduced pressure to obtain modified carbon black.

[0009] In a preferred embodiment, in step 1), the amount of dilute nitric acid used is 5-10 times the mass of carbon black.

[0010] In a preferred embodiment, in step 2), the molar ratio of methyltrimethoxysilane:vinyltrimethoxysilane:mercaptopropyltrimethoxysilane is 3-5:3-5:1-3; the amount of hydrochloric acid aqueous solution used is 20-60% of the total mass of the monomers (i.e., the total mass of methyltrimethoxysilane, vinyltrimethoxysilane, and mercaptopropyltrimethoxysilane).

[0011] In a preferred embodiment, in step 3), the mass ratio of activated carbon black to hyperbranched polysiloxane is 100:30-80.

[0012] In one embodiment, the preparation of the hyperbranched polyester dispersant includes the following steps: ① Trimethylolpropane (TMP) and 2,2-dimethylolpropionic acid (DMPA) are added to a reactor, mixed evenly, and a catalyst is added. Then, the mixture is melt-polymerized at 130-160℃ for 3-6 hours to obtain hyperbranched polyester. ② Cool to 90-110℃, add 10-undecenoic acid and stearic acid, keep the reaction at this temperature for 2-4 hours to seal the end and introduce terminal double bonds; ③ Dissolve the product obtained in step ② in an organic solvent, add mercaptoacetic acid and a photoinitiator, and react under ultraviolet light for 1-4 hours (the ultraviolet light wavelength used is 365nm). After the reaction is completed, distill under reduced pressure to obtain hyperbranched polyester dispersant.

[0013] In a preferred embodiment, in step ①, the molar ratio of trimethylolpropane to 2,2-dimethylolpropionic acid is 1:6-12; the catalyst is p-toluenesulfonic acid, and the amount used is 0.5-5.0% of the total mass of trimethylolpropane and 2,2-dimethylolpropionic acid.

[0014] In a preferred embodiment, in step ②, the molar ratio of 10-undecenoic acid to stearic acid is 1.5-3:1; and the total amount of 10-undecenoic acid and stearic acid is 2-5 times the molar amount of trimethylolpropane.

[0015] In a preferred embodiment, in step ③, the amount of mercaptoacetic acid used is 1.2-2.5 times the molar amount of 10-undecenoic acid; the organic solvent is tetrahydrofuran (THF); and the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone (i.e., Irgacure 651), the amount of which is 0.2-1.0% of the total mass of trimethylolpropane, 2,2-dimethylolpropionic acid, 10-undecenoic acid, and stearic acid.

[0016] In one embodiment, the platinum catalyst in the color paste is a Karstedt platinum catalyst (platinum-divinyltetramethyldisiloxane complex).

[0017] A method for preparing a color paste for vinyl silicone rubber includes the following steps: a) Mix the vinyl silicone oil and hyperbranched polyester dispersant until homogeneous; b) Add modified carbon black, stir to mix evenly, add the resulting slurry to a grinder for grinding, and collect the grinding liquid; c) Under nitrogen protection, slowly add platinum catalyst and hydrogen-containing silicone oil, stir evenly, and then degas under vacuum for 10-15 minutes to obtain color paste for vinyl silicone rubber.

[0018] Compared with the prior art, the present invention has the following significant advantages: 1) The carbon black used in the color paste of this invention is first acidically activated and then modified by grafting with hyperbranched polysiloxane. The hyperbranched polysiloxane is obtained by hydrolysis and condensation of methyltrimethoxysilane, vinyltrimethoxysilane and mercaptopropyltrimethoxysilane, and contains mercapto and alkoxy groups. The mercapto groups have a strong chemical anchoring effect with the carbon black surface, and the alkoxy groups condense with the hydroxyl groups on the carbon black surface to form Si-OC bonds. The dual anchoring mechanism ensures that the modified layer is firmly bonded, so that the carbon black will not migrate when the color paste is used in silicone rubber products. 2) The color paste provided by this invention contains vinyl and mercapto groups in the hyperbranched polysiloxane used to modify carbon black, and the hyperbranched polyester dispersant also contains mercapto groups. Both vinyl and mercapto groups can participate in the hydrosilylation reaction of silicone rubber, so that the modified carbon black and dispersant can become part of the silicone rubber network, fundamentally solving the problem of the decline in mechanical properties of silicone rubber products caused by traditional color pastes, and realizing the integration of coloring and reinforcement. 3) The carbon black used in the color paste provided by the present invention is modified by grafting hyperbranched polysiloxane, and also contains hyperbranched polyester dispersant and vinyl silicone oil, which makes the color paste compatible with the silicone rubber matrix. After being added to the silicone rubber matrix, it does not affect the original vulcanization characteristics and processing technology of the silicone rubber.

[0019] In summary, this invention uses modified carbon black as pigment, hyperbranched polyester as dispersant, and is supplemented with vinyl silicone oil, platinum catalyst and hydrogen-containing silicone oil, so that the prepared color paste can chemically co-crosslink with the silicone rubber matrix, and has both coloring and reinforcing functions. It has excellent comprehensive performance and can be used as a color paste for vinyl silicone rubber, and has great industrial application value. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail and completely below with reference to the embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Example 1

[0021] 1) Preparation of modified carbon black 1) Disperse 100 parts by weight of carbon black (M1300, Cabot) in 10% dilute nitric acid (the amount is 8 times the mass of carbon black), stir and react at 80°C for 2 hours. After the reaction is completed, filter, wash with deionized water until neutral, and dry at 100°C for 24 hours to obtain activated carbon black. 2) 0.4 mol (54.4 g) of methyltrimethoxysilane (MTMS), 0.4 mol (59.2 g) of vinyltrimethoxysilane (VTMS), 0.2 mol (39.2 g) of mercaptopropyltrimethoxysilane (MPTMS) and 600 mL of isopropanol were added to a reactor and stirred until homogeneous. Approximately 80 g of 0.1 mol / L hydrochloric acid aqueous solution (approximately 52% of the total monomer mass of 152.8 g) was added dropwise, controlling the pH of the reaction system to 3-4. The reaction was then carried out at 65 °C for 6 hours. After the reaction was completed, the mixture was distilled under reduced pressure (80 °C, -0.09 to -0.1 MPa) to obtain hyperbranched polysiloxane. The vinyl content in the hyperbranched polysiloxane was tested according to GB / T 36691-2018 "Determination of Vinyl Content in Methyl Vinyl Silicone Rubber - Near-Infrared Method". The Ellman reagent method (referring to GB / T) was used. (34820-2017) Determination of thiol content in hyperbranched polysiloxanes; The test results showed that the vinyl content was 3.1 mmol / g and the thiol content was 1.5 mmol / g. 3) Add 100 parts by weight of activated carbon black and 50 parts by weight of hyperbranched polysiloxane to 500 parts by weight of toluene. Under stirring conditions, use a probe-type ultrasonic disperser (frequency 20kHz, power 800W) to ultrasonically disperse for 30 minutes. During this period, the system temperature is controlled not to exceed 35℃ by circulating cooling water to ensure uniform mixing. The temperature is then raised to 105℃ and reacted for 7 hours under nitrogen protection. After the reaction is completed, the mixture is distilled under reduced pressure (70℃, -0.09~-0.1 MPa) to obtain modified carbon black.

[0022] (ii) Preparation of hyperbranched polyester dispersants ① Add 0.1 mol (13.4 g) of trimethylolpropane (TMP) and 0.9 mol (120.6 g) of 2,2-dimethylolpropionic acid (DMPA) to a reaction vessel and mix well. Add 5.0 g of p-toluenesulfonic acid catalyst (accounting for 3.7% of the total mass of TMP and DMPA 134 g), and then melt polycondense at 145℃ (-0.09~-0.1 MPa) for 4 hours. During the reaction, the generated water is continuously evaporated to obtain hyperbranched polyester. ② Cool to 100℃, add 0.6 mol (110.5 g) of 10-undecenoic acid and 0.3 mol (85.4 g) of stearic acid, keep the reaction at this temperature for 3 hours to seal the end and introduce terminal double bonds; ③ Dissolve the product obtained in step ② in 500 mL of tetrahydrofuran (THF), add 0.9 mol (82.9 g) of mercaptoacetic acid (1.5 times the molar amount of 0.6 mol of 10-undecenoic acid) and 2.0 g of photoinitiator 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651, accounting for 0.61% of the total mass of TMP, DMPA, 10-undecenoic acid, and stearic acid), and react under 365 nm ultraviolet light for 2 hours to allow the mercapto groups to undergo a click addition reaction with the terminal double bonds. After the reaction is completed, distill under reduced pressure (65 °C, -0.09 to -0.1 MPa) to obtain a pale yellow viscous liquid, which is the hyperbranched polyester dispersant.

[0023] (III) Preparation of color paste for vinyl silicone rubber a) Add 50 parts by weight of vinyl silicone oil (Runhe RH-Vi305B) and 10 parts by weight of hyperbranched polyester dispersant to a vacuum planetary mixer and stir at 600 rpm for 15 minutes until homogeneous; b) Add 38 parts by weight of modified carbon black, stir and disperse at 2000 rpm for 30 minutes to make it evenly mixed, transfer the resulting slurry to a three-roll mill and grind it 3 times, collect the grinding liquid, take a sample to test the fineness, and record it as the initial fineness; c) Under nitrogen protection, slowly add 0.03 parts by weight of Karstedt platinum catalyst (Heraene) and 1.0 parts by weight of hydrogen-containing silicone oil (Hubei Xin Sihai Chemical), stir until homogeneous, and then degas under vacuum for 15 minutes to obtain color paste S-1 for vinyl silicone rubber. Store the obtained color paste S-1 in a sealed container at 0-10℃ away from light. When using, remove the color paste from the refrigerated environment, allow it to warm to room temperature, and then mix it with the silicone rubber base according to the formula, followed by conventional high-temperature vulcanization molding. Example 2

[0024] The difference between this embodiment and Example 1 is that the content of each component in the color paste formulation is different. The specific formulation is as follows: 30 parts by weight of modified carbon black, 8 parts by weight of hyperbranched polyester dispersant, 55 parts by weight of vinyl silicone oil, 0.02 parts by weight of Karstedt platinum catalyst, and 0.8 parts by weight of hydrogen-containing silicone oil. The rest is the same as in Example 1, and color paste S-2 is obtained. Example 3

[0025] The difference between this embodiment and Example 1 is that the content of each component in the color paste formulation is different. The specific formulation is as follows: 40 parts by weight of modified carbon black, 12 parts by weight of hyperbranched polyester dispersant, 45 parts by weight of vinyl silicone oil, 0.05 parts by weight of Karstedt platinum catalyst, and 1.5 parts by weight of hydrogen-containing silicone oil. The rest is the same as in Example 1, and color paste S-3 is obtained.

[0026] Comparative Example 1 The difference between this comparative example and Example 1 is that commercially available unmodified carbon black (M1300, Cabot) was used instead of the modified carbon black in Example 1 in the color paste. The rest is the same as in Example 1, and the color paste S-C1 is obtained.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that: in the color paste, carbon black modified with silane coupling agent KH-550 is used instead of the modified carbon black in Example 1. Specifically, the preparation method of KH-550 modified carbon black is as follows: 100 parts by mass of carbon black are dispersed in an ethanol / water mixture (volume ratio 9:1), 6 parts by mass of KH-550 are added, the pH is adjusted to 4-5 with acetic acid, the reaction is carried out at 75°C for 5 hours, and KH-550 modified carbon black is obtained by centrifugation, washing and drying. The rest is the same as in Example 1, and the color paste S-C2 is obtained.

[0028] Comparative Example 3 The difference between this comparative example and Example 1 is that: in the color paste, hyperbranched polyester dispersant (SH-HPEE) is not added, but an equal amount of vinyl silicone oil is used instead, that is, the amount of vinyl silicone oil is adjusted from 50 parts by mass in Example 1 to 60 parts by mass. The rest is the same as in Example 1, and the color paste S-C3 is obtained.

[0029] The fineness and thermal storage stability at 60°C of the color pastes prepared in Examples 1-3 and Comparative Examples 1-3 were tested according to relevant standards. In addition, 10 parts by weight of the above color paste were added to 100 parts by weight of methyl vinyl silicone rubber raw rubber, and vulcanized rubber test pieces were prepared using the conventional HTV process (170°C × 10 min vulcanization). Tensile strength, elongation at break, tear strength, compression set, tensile strength retention after hot air aging, and color difference after heat aging were tested. Specifically: 1) Fineness of pigment paste: Refer to GB / T 1724-2019 "Determination of grinding fineness of paints, varnishes and printing inks" and use a 0-50μm scraper fineness meter to determine the fineness of the pigment paste after grinding; 2) Stability of heat storage at 60℃: After sealing the pigment sample, place it in a constant temperature oven at 60℃ for 7 days. After taking it out, test the fineness according to GB / T 1724-2019 and observe whether there is thickening, coarsening, or stratification. 3) Tensile strength: Refer to GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", use a dumbbell-shaped cutter to cut the specimen, stretch rate 500 mm / min, and test the tensile strength of vulcanized rubber. 4) Elongation at break: Refer to GB / T 528-2009, test simultaneously with tensile strength, and record the elongation at break of the vulcanizate; 5) Tear strength: Refer to GB / T 529-2008 "Determination of tear strength of vulcanized rubber or thermoplastic rubber (trouser-shaped, right-angled and crescent-shaped specimens)", use right-angled specimens, tensile rate of 500 mm / min to test the tear strength of vulcanized rubber. 6) Compression set: Refer to GB / T 7759-2015 "Determination of compression set of vulcanized rubber or thermoplastic rubber", use type A specimen (diameter 13 mm, height 6.3 mm), compress 25% under the condition of 177℃×22h, and calculate the compression set after unloading; 7) Tensile strength retention rate after hot air aging: Referring to GB / T 3512-2014 "Accelerated aging and heat resistance test of vulcanized rubber or thermoplastic rubber in hot air", the vulcanized rubber sample was aged in hot air at 200℃ for 72 hours, and the tensile strength was tested. The percentage of tensile strength after aging to tensile strength before aging was calculated. 8) Color difference after heat aging (ΔE): Using a spectrophotometer (X-Rite Ci64), under a D65 light source and a 10° observation angle, measure the L, a, and b values ​​of the vulcanized rubber sample before and after 72 hours of hot air aging at 200°C, and calculate the total color difference ΔE. The test results are shown in Table 1.

[0030] Table 1 Performance test data of color pastes from Examples 1-3 and Comparative Examples 1-3

[0031] As shown in Table 1, the color pastes of Examples 1-3 of this invention exhibit the following characteristics: After 7 days of heat storage at 60℃, the fineness of the color paste remained essentially unchanged, indicating good dispersion stability; the tensile strength was 8.5-9.0 MPa, the elongation at break was 420-450%, the tear strength was 31.0-33.5 kN / m, and the compression set was 15.5-17.5%, indicating that the addition of the color paste to the silicone rubber matrix does not affect the mechanical properties of the silicone rubber product while coloring it; the tensile strength retention rate after heat aging was 84-87%, and the color difference after heat aging was 1.0-1.5, indicating that the addition of the color paste to the silicone rubber does not migrate, and while coloring, it also gives the rubber product excellent heat aging performance and reinforces the silicone rubber; in summary, the color pastes of Examples 1-3 have excellent comprehensive performance and can be used as color pastes for vinyl silicone rubber. Furthermore, as can be seen from the table, the overall performance of the color pastes of Examples 1-3 is significantly better than that of the color pastes of Comparative Examples 1-3. This may be because: 1) Regarding dispersion: Under the same grinding conditions, the fineness of the pigment pastes in the examples was ≤10μm, indicating that the modified carbon black in the examples could be fully depolymerized and stably dispersed. In Comparative Example 1, the carbon black was not surface modified, resulting in a lack of functional groups that could interact with the dispersant. The dispersant relied solely on physical adsorption and could not effectively wet and depolymerize the carbon black agglomerates, leading to a larger fineness in the color paste of Comparative Example 1 compared to the example. In Comparative Example 2, the carbon black was modified only by KH-550. Although the KH-550 modification has some improvement, KH-550 can only provide a single amino anchoring group, which is insufficient for the coating and stabilization of carbon black, resulting in a finer pigment than in the example. In Comparative Example 3, there was no hyperbranched polyester dispersant. Due to the lack of the auxiliary dispersing effect of the hyperbranched polyester dispersant, the single hyperbranched polysiloxane modified carbon black was difficult to be fully wetted during the grinding stage, resulting in a finer color paste than in the Example. 2) Thermal storage stability: The fineness of the pigment paste in the example remains ≤10μm after heat storage, with no coarsening. This is because the hyperbranched polysiloxane forms a dual bond on the carbon black surface through strong chemical anchoring of thiol groups and alkoxy condensation (Si-OC bond), combined with the steric hindrance effect of the hyperbranched polyester dispersant, achieving stable dispersion. In Comparative Example 1, the carbon black was not surface modified, and the dispersant desorbed from the carbon black at high temperature, resulting in carbon black pigment agglomeration and reduced stability of the color paste. In Comparative Example 2, the carbon black was only modified with KH-550. The amino anchoring strength of KH-550 is insufficient, and its modified layer is prone to partial desorption at high temperature, resulting in reduced stability of the pigment. In Comparative Example 3, the lack of hyperbranched polyester dispersant meant that the steric hindrance of the modified carbon black's hyperbranched polysiloxane layer was still insufficient, resulting in inadequate stability of the color paste. 3) Mechanical properties of rubber products (tensile strength, elongation at break, tear strength, compression set): In the examples, the carbon black surface is modified with hyperbranched polysiloxane containing vinyl and mercapto groups. The vinyl and mercapto groups can participate in hydrosilylation reactions, making the coloring component (modified carbon black) part of the silicone rubber crosslinking network. This achieves chemical bonding reinforcement rather than physical inert filling, so that the color paste can be used in the silicone rubber matrix. While coloring, it does not affect the mechanical properties of the silicone rubber product. In Comparative Example 1, the unmodified carbon black relies solely on physical adsorption, resulting in weak interfacial bonding. Under stress, the interfacial debonding forms stress concentration points and void defects, leading to a significant decrease in the mechanical properties of the rubber products. Although the KH-550 modified carbon black in Comparative Example 2 improved the dispersibility of carbon black to some extent, KH-550 has no double bonds and cannot participate in crosslinking, so it still has a certain adverse effect on the mechanical properties of rubber products. In Comparative Example 3, the absence of hyperbranched polyester dispersant resulted in reduced dispersibility of modified carbon black in the rubber matrix, leading to agglomeration defects and consequently a decrease in the mechanical properties of the rubber products. 4) Heat aging resistance (tensile strength retention, color difference): In the embodiments, the carbon black surface is modified with hyperbranched polysiloxane. The rigid Si-O-Si skeleton of hyperbranched polysiloxane has high thermal stability and can inhibit the unbundling thermal degradation of the silicone rubber backbone. At the same time, the modified carbon black can form covalent bonds with the matrix. At high temperatures, the carbon black is not easy to migrate or oxidize in rubber products, which makes the rubber products have excellent heat aging resistance. In contrast, the unmodified carbon black in Comparative Example 1 lacks chemical anchoring on its surface. Under the influence of high temperature and oxygen, it is prone to generating colored degradation products. At the same time, due to the weak bonding force with the matrix, some nano-sized carbon black particles or fragments will detach from their original position and migrate to the surface, resulting in a decrease in the heat aging resistance of rubber products. In Comparative Example 2, high temperature will destroy the relatively weak hydrogen bonds or condensation bonds between the amino group of KH-550 and the carbon black surface. Once the anchor point breaks, the modified layer of KH-550 will fail, the carbon black will re-aggregate, and the interface will return to a physical adsorption state. In addition, KH-550 itself contains amino groups, which are easily oxidized and yellowed under high temperature and oxygen. Its degradation products may migrate to the surface, resulting in a decrease in the heat aging resistance of rubber products. In Comparative Example 3, no hyperbranched polyester dispersant was used, and the modified carbon black was used for dispersion alone. The lack of flexible hyperbranched polyester chain segment interpenetration made the carbon black particles prone to collision and aggregation under high temperature Brownian motion. Aggregated carbon black particles are prone to become stress concentration points during high temperature aging, which leads to a decrease in the heat aging resistance of rubber products.

[0032] Finally, it should be noted that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A color paste for vinyl silicone rubber, characterized in that, It is prepared from raw materials containing the following components: Modified carbon black: 30-40 parts by weight; Hyperbranched polyester dispersant: 8-12 parts by weight; Vinyl silicone oil: 45-55 parts by weight; Platinum catalyst: 0.01-0.05 parts by weight; Hydrogen-containing silicone oil: 0.5-1.5 parts by weight; The modified carbon black is prepared by first subjecting the carbon black to acid activation treatment, and then grafting the resulting product with hyperbranched polysiloxane; the hyperbranched polysiloxane is prepared by hydrolysis and condensation polymerization of methyltrimethoxysilane, vinyltrimethoxysilane and mercaptopropyltrimethoxysilane. The hyperbranched polyester dispersant is a hyperbranched polyester synthesized with trimethylolpropane as the core and 2,2-dimethylolpropionic acid as the AB2 monomer. It is prepared by introducing double bonds through 10-undecenoic acid end capping, and then introducing thiol groups through a thiol-alkene click reaction with mercaptoacetic acid.

2. The color paste for vinyl silicone rubber according to claim 1, characterized in that, The preparation of the modified carbon black includes the following steps: 1) Disperse carbon black in 5-15% dilute nitric acid and stir at 75-85℃ for 1-3 hours. After the reaction is complete, filter, wash and dry to obtain activated carbon black. 2) Add methyltrimethoxysilane, vinyltrimethoxysilane, mercaptopropyltrimethoxysilane and isopropanol to the reactor, stir evenly, add 0.05-0.5 mol / L hydrochloric acid aqueous solution dropwise, control the pH of the reaction system to 2-5, and then react at 60-70℃ for 5-7 hours. After the reaction is completed, distill under reduced pressure to obtain hyperbranched polysiloxane. 3) Add activated carbon black and hyperbranched polysiloxane to toluene, mix evenly, heat to 100-110℃, and react for 6-8 hours under nitrogen protection. After the reaction is completed, distill under reduced pressure to obtain modified carbon black.

3. The color paste for vinyl silicone rubber according to claim 2, characterized in that, In step 1), the amount of dilute nitric acid used is 5-10 times the mass of carbon black.

4. The color paste for vinyl silicone rubber according to claim 2, characterized in that, In step 2), the molar ratio of methyltrimethoxysilane:vinyltrimethoxysilane:mercaptopropyltrimethoxysilane is 3-5:3-5:1-3.

5. The color paste for vinyl silicone rubber according to claim 2, characterized in that, In step 3), the mass ratio of activated carbon black to hyperbranched polysiloxane is 100:30-80.

6. The color paste for vinyl silicone rubber according to claim 1, characterized in that, The preparation of the hyperbranched polyester dispersant includes the following steps: ① Trimethylolpropane and 2,2-dimethylolpropionic acid are added to a reaction vessel, mixed evenly, and a catalyst is added. Then, the mixture is melt-polymerized at 130-160℃ for 3-6 hours to obtain hyperbranched polyester. ② Cool to 90-110℃, add 10-undecenoic acid and stearic acid, keep the reaction at this temperature for 2-4 hours to seal the end and introduce terminal double bonds; ③ Dissolve the product obtained in step ② in an organic solvent, add mercaptoacetic acid and a photoinitiator, and react under ultraviolet light for 1-4 hours. After the reaction is completed, distill under reduced pressure to obtain hyperbranched polyester dispersant.

7. The color paste for vinyl silicone rubber according to claim 6, characterized in that, In step ①, the molar ratio of trimethylolpropane to 2,2-dimethylolpropionic acid is 1:6-12; the catalyst is p-toluenesulfonic acid, and the amount used is 0.5-5.0% of the total mass of trimethylolpropane and 2,2-dimethylolpropionic acid.

8. The color paste for vinyl silicone rubber according to claim 6, characterized in that, In step ②, the molar ratio of 10-undecenoic acid to stearic acid is 1.5-3:1; the total amount of 10-undecenoic acid and stearic acid used is 2-5 times the molar amount of trimethylolpropane.

9. The color paste for vinyl silicone rubber according to claim 6, characterized in that, In step ③, the amount of mercaptoacetic acid used is 1.2-2.5 times the molar amount of 10-undecenoic acid; the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, and its amount is 0.2-1.0% of the total mass of trimethylolpropane, 2,2-dimethylolpropionic acid, 10-undecenoic acid and stearic acid.

10. A method for preparing a color paste for vinyl silicone rubber according to claim 1, characterized in that, Includes the following steps: a) Mix the vinyl silicone oil and hyperbranched polyester dispersant until homogeneous; b) Add modified carbon black, stir to mix evenly, add the resulting slurry to a grinder for grinding, and collect the grinding liquid; c) Under nitrogen protection, slowly add platinum catalyst and hydrogen-containing silicone oil, stir evenly, and then degas under vacuum for 10-15 minutes to obtain color paste for vinyl silicone rubber.

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