A low-friction liquid silicone rubber composite and a method of making the same

Abstract

The application discloses a kind of low-friction liquid silicone rubber composite and preparation method thereof, the present application simultaneously introduces spherical inorganic microbead and lamellar filler in silicone rubber matrix, corresponding base glue preparation method includes: first, part of vinyl silicone oil is kneaded with filler treating agent, white carbon black, spherical inorganic microbead, lamellar filler and heat-resistant agent, remaining vinyl silicone oil is added to cool to obtain base glue;Base glue is then opened on the open mill with hydrogen-containing silicone oil, catalyst, inhibitor, and lamellar filler is preliminarily oriented along the shear direction;Finally, it is molded into shape by flat vulcanizing machine, and lamellar filler is formed parallel to the regular orientation of friction surface by using unidirectional pressure field.The low-friction liquid silicone rubber composite prepared by the present application has small friction coefficient, and the process is simple, suitable for sealing parts, automobile parts and medical devices and other fields.

Description

Technical Field

[0001] This invention relates to the field of organosilicon materials, specifically to a low-friction liquid silicone rubber composite material and its preparation method. Background Technology

[0002] Liquid silicone rubber (LSR) is widely used in electronics, automotive manufacturing, medical devices, and precision sealing due to its excellent heat resistance, weather resistance, electrical insulation, and physiological inertness. As applications evolve towards higher dynamics and higher loads (such as high-speed printer rollers, automotive sealing strips, and keyboard keys), higher demands are placed on the surface friction properties of liquid silicone rubber: the material needs a low coefficient of friction to reduce power loss and temperature rise. In high-precision equipment such as semiconductor manufacturing, precision instruments, and industrial robots, silicone rubber is often used to manufacture key components such as seals, conveyor rollers, and guides. Its high coefficient of friction can lead to increased equipment operating resistance, higher energy consumption, accelerated wear, decreased positioning accuracy, and even vibration and noise. Low-friction silicone rubber is also crucial in high-end medical devices, new energy vehicles, and flexible electronics.

[0003] From the perspective of technical approaches to reducing the coefficient of friction, the main methods include bulk lubrication modification, surface coating / film application, and surface microstructure design. While surface coatings can achieve extremely low coefficients of friction, for highly elastic, low-surface-energy substrates such as silicone rubber, the coating is prone to peeling due to deformation or interfacial stress, and its thickness is limited. After wear, performance deteriorates sharply, and the process is complex and costly. Surface microstructure design only alters the surface morphology without filler dispersion issues, but silicone rubber is prone to large deformation under pressure, and its texture is easily flattened or filled. Furthermore, it requires precision equipment and is difficult to achieve at low cost on large-area curved surfaces, resulting in insufficient long-term effectiveness. In contrast, bulk lubrication modification has significant advantages: the newly exposed surface after wear retains lubrication capability, and the lubrication effect lasts throughout the material's lifespan; there is no coating peeling problem; it can be achieved through conventional mixing and injection molding processes without secondary processing; and its performance can be flexibly controlled by the type, particle size, and compounding ratio of fillers. Therefore, bulk lubrication modification is the most suitable low-friction solution for liquid silicone rubber.

[0004] However, compared to solid plastics, silicone rubber is an elastomer. Its high elasticity and low surface energy system mean that conventional lubricant addition methods cannot be directly transferred into the silicone rubber matrix. Existing technologies for low-friction modification of the silicone rubber matrix mainly include: (a) Conventional lubricating oil / grease addition: relies on the migration and seepage of lubricant to form a lubricating layer, but the lubricant is prone to migration and loss or oil-glue phase separation during friction, resulting in poor long-term stability.

[0005] (II) Solid lubricant filler blends: such as polytetrafluoroethylene (PTFE) micro powder, molybdenum disulfide (MoS2), graphite, etc. This approach faces challenges such as difficult filler dispersion, weak interfacial bonding, and easy agglomeration. Among these, although PTFE micro powder does not significantly affect platinum vulcanization, the high elasticity of silicone rubber limits the formation of its shear transfer film, resulting in a limited reduction in the coefficient of friction. Nano-MoS2 is considered an ideal anti-friction filler due to its unique layered crystal structure, but its large specific surface area and high surface polarity make it prone to agglomeration in hydrophobic silicone rubber. Furthermore, it lacks chemical bonding with the matrix, making it easily pulled out during friction and exacerbating abrasive wear. More importantly, MoS2 readily undergoes complexation reactions with platinum catalysts, inhibiting vulcanization activity and leading to incomplete vulcanization or a decline in mechanical properties.

[0006] (III) Introduction of Spherical Fillers: In recent years, some researchers have attempted to introduce spherical organosilicon resins or hollow glass microspheres to transform sliding friction into rolling friction by utilizing their spherical morphology. For example, Chinese patent application CN117903602A discloses a solid silicone rubber with a low coefficient of friction, which reduces the coefficient of friction through the synergistic effect of hollow microspheres and polyethylene glycol. However, ordinary spherical inorganic fillers exist only in a physical blending manner with the silicone rubber matrix, lacking chemical anchoring. After vulcanization, they cannot be firmly fixed and are easily squeezed out or rolled out during friction, posing a risk of insufficient long-term wear resistance.

[0007] (iv) Introduction of lamellar fillers: Chinese patent application CN121592195A discloses an alkylated MoS2 nanosheet and a rubber composite containing it. The dispersion of MoS2 in natural rubber is improved by alkyl thiol modification, and the layered structure of MoS2 is used to release a lubricating film during friction to reduce the coefficient of friction. However, lamellar fillers (such as mica, molybdenum disulfide, boron nitride, graphite, etc.) are disordered in orientation during conventional processing and cannot fully utilize their layered slip characteristics or rigid load-bearing capacity.

[0008] In addition, Chinese patent application CN119192856A discloses a high wear-resistant rubber material, which uses fluorosilicone rubber, PTFE powder, and fluorinated graphene to form a lubricating layer by utilizing the low friction properties of PTFE. However, it also does not involve the synergistic orientation structure of spherical fillers and sheet fillers.

[0009] In summary, the technical challenge to be solved in this field is how to simultaneously address the problems of disordered rolling and easy settling failure of spherical inorganic microspheres, as well as disordered orientation and easy agglomeration of sheet fillers, in order to obtain silicone rubber composite materials with low friction coefficient, high wear resistance, and simple processing. Summary of the Invention

[0010] This invention introduces spherical inorganic microspheres and sheet fillers simultaneously into a silicone rubber matrix. The high shear force of the open mill further homogenizes the fillers and induces initial orientation of the sheet fillers along the shear direction. Then, the unidirectional pressure field during molding and vulcanization forces the sheet fillers parallel to the friction surface, forming highly consistent planar orientation tracks. The spherical inorganic microspheres are distributed between adjacent sheets, forming a "sheet parallel track—spherical ball" composite lubrication structure: the sheet tracks provide a continuous, smooth, rigid rolling surface for the balls, transforming the random rolling of the spherical inorganic microspheres into directional, low-resistance rolling along the track direction. Simultaneously, the layered slippage of the sheet fillers themselves (e.g., molybdenum disulfide, graphite) or rigid support (e.g., mica, boron nitride) further synergistically reduces friction, achieving a stepwise reduction in the coefficient of friction.

[0011] The basic concept of the technical solution adopted in this invention is as follows: A method for preparing a low-friction liquid silicone rubber composite material, comprising the following steps: (1) Take a portion of the double-ended vinyl-terminated vinyl silicone oil, other additives and filler treatment agent and knead them together. Then add fumed silica, spherical inorganic microspheres and sheet filler in batches. First, knead at room temperature, then heat up and knead under vacuum. Stop heating and add the remaining double-ended vinyl-terminated vinyl silicone oil for kneading and cooling to obtain the base adhesive. The portion of the double-ended vinyl-terminated vinyl silicone oil accounts for 70% to 95% of its total mass. The other additives are silazane and / or water. (2) The base glue, methyl-terminated side-group hydrogen-containing silicone oil, single-terminated methyl end-group hydrogen-containing silicone oil, platinum catalyst, and inhibitor are mixed on a two-roll mill to make the sheet filler initially oriented along the shear direction. (3) The mixture after open milling is molded and vulcanized by a flat vulcanizing machine. The unidirectional pressure field during the molding process causes the sheet filler to be arranged parallel to the friction surface.

[0012] As one implementation method, in step (1), a heat-resistant agent is added before kneading at room temperature.

[0013] In one embodiment, the vinyl content of the double-ended vinyl silicone oil is 0.1-20 wt%, preferably 0.2-10 wt%; and the viscosity at 25°C is 100-100000 mPa·s.

[0014] Optionally, the filler treatment agent is one or more of mercaptosilane coupling agents, vinylsilazane, and hexamethyldisilazane; preferably, the mercaptosilane coupling agent is selected from one or more of γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropylmethyldimethoxysilane.

[0015] In one embodiment, the silica is fumed silica, and the preferred specific surface area is 200-300 m² / g. 2 / g.

[0016] Optionally, the spherical inorganic microspheres are one or more of spherical silicone resin, polymethylsilsesquioxane, and spherical boron nitride.

[0017] Preferably, the particle size of the spherical inorganic microspheres is 1–15 μm.

[0018] In one embodiment, the sheet filler is one or a mixture of mica, molybdenum disulfide, boron nitride, and graphite; preferably, the particle size of the sheet filler is 2 to 30 μm.

[0019] Optionally, the heat-resistant agent is one or more of rare earth oxides, ferrites, and cerium dioxide.

[0020] In one embodiment, the hydrogen atom content of the methyl-terminated side-group hydrogen-containing silicone oil is 0.1~1.5wt%, preferably 0.3~1wt%.

[0021] Optionally, the hydrogen atom content of the single-terminal methyl-terminated hydrogen-containing silicone oil is 0.01~0.2wt%, preferably 0.03~0.1wt%.

[0022] Optionally, the inhibitor is one or a mixture of more of 1-ethynyl-1-cyclohexanol, 2-methyl-3-butynyl-2-ol, 3-methyl-1-ethynyl-3-ol, or 3,5-dimethyl-1-hexynyl-3-ol.

[0023] In one embodiment, the mass ratio of the sheet-like filler to the spherical inorganic microspheres is (0.05~5):1.

[0024] As one implementation method, in step (1), the vacuum kneading after heating is: heating to 185°C, evacuating to ≤-0.09MPa, and kneading under vacuum.

[0025] In one embodiment, the raw materials used, by weight, include: 50-100 parts of double-vinyl-terminated vinyl silicone oil, 3-15 parts of filler treatment agent, 1-5 parts of other additives, 15-45 parts of silica, 2-15 parts of spherical inorganic microspheres, 0.1-20 parts of sheet filler, 0.1-5 parts of heat resistant agent, 3-10 parts of methyl-terminated side-group hydrogen-containing silicone oil, 1-5 parts of single-methyl-terminated end-group hydrogen-containing silicone oil, 0.1-1 parts of platinum catalyst, and 0.01-0.1 parts of inhibitor.

[0026] The present invention also provides a low-friction liquid silicone rubber composite material, which is obtained by the preparation method of the low-friction liquid silicone rubber composite material as described in any of the above contents, comprising a silicone rubber matrix, spherical inorganic microspheres and sheet fillers, wherein the sheet fillers are oriented in a direction parallel to the friction surface.

[0027] Compared with the prior art, the present invention has the following advantages: 1. This invention simultaneously adds two types of fillers during the kneading stage and uses silane coupling agents and silazanes for covalent bonding modification, effectively improving filler dispersibility and interfacial compatibility without inhibiting the activity of the platinum vulcanization system. It overcomes the problems of easy settling and failure of spherical inorganic microspheres in silicone rubber, easy agglomeration of sheet fillers, and weak interfacial bonding.

[0028] 2. This invention uses open mill shearing pre-orientation and molding pressure to orient the sheet filler into regular tracks parallel to the friction surface, guiding the spherical inorganic microspheres to roll in a specific direction. By utilizing the ball effect of the spherical microspheres (transforming sliding friction into rolling friction) and the layered sliding or rigid support of the sheet filler, a "spherical ball-nano-layered lubrication" synergistic system is constructed to achieve a stepwise reduction in the coefficient of friction.

[0029] 3. This invention enhances the smoothness of polymer chains and helps reduce the coefficient of friction by introducing an appropriate amount of hydrogen-containing silicone oil with single-terminal methyl groups.

[0030] 4. By adding heat-resistant agents and combining them with other components, this invention enables the composite material to maintain stable low-friction properties under high-temperature and frequent-motion conditions, thus broadening its application in fields such as automotive sealing strips and high-power electronic devices.

[0031] 5. Through the above-mentioned synergistic modification, the friction coefficient of the silicone rubber composite material is significantly reduced, which helps to extend the service life of the material under dynamic friction conditions. Moreover, the process is simple and applicable to various occasions such as seals, guide rails, medical devices, and automotive parts. Attached Figure Description

[0032] Figure 1 SEM image of the cross section of the low-friction liquid silicone rubber composite material prepared in Example 1.

[0033] The image is labeled as follows: 1-Spherical inorganic microspheres; 2-Layered filler; f-Pressure direction. Detailed Implementation

[0034] To make the objectives, features, and advantages of the technical solutions proposed in this invention more apparent and understandable, the embodiments of the technical solutions proposed in this invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the proposed technical solutions, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] In the specific implementation, the particle size of the spherical inorganic microspheres is preferably 1–15 μm. Specifically, in the implementation of this invention, the particle size of the spherical inorganic microspheres can be 1 μm, 5 μm, 8 μm, or 15 μm.

[0036] In the specific implementation of this invention, the amount of spherical inorganic microspheres added is 2 to 15 parts, specifically 2 parts, 8 parts, 10 parts or 15 parts.

[0037] As an example, the vinyl-terminated silicone oil has a viscosity of 100–100,000 mPa·s at 25°C, specifically 1,000 mPa·s, 10,000 mPa·s, 20,000 mPa·s, 50,000 mPa·s, or 100,000 mPa·s; and a vinyl content (the vinyl content in the silicone oil determined by iodometric titration) of 0.1–20 wt%, preferably 0.2–10 wt%, specifically 0.2 wt%, 0.5 wt%, 1 wt%, 5 wt%, or 10 wt%.

[0038] In a preferred embodiment of the present invention, the mass ratio of the sheet-like filler to the spherical inorganic microspheres is (0.05~5):1, specifically 0.05:1, 0.1:1, 0.2:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, and 5:1. The inventors have found that when the mass ratio of the sheet-like filler to the spherical microspheres is below 0.05:1, the sheet-like tracks cannot form a continuous network, and the balls are prone to derailment; when it is above 5:1, the number of balls is too small, and the rolling effect is weakened. A significant synergistic friction-reducing effect can be observed within the range of 0.05~5:1.

[0039] As an example, the catalyst is a platinum catalyst. In specific implementations, the catalyst may be 0.1 to 1 part, specifically, for example, 0.1 part, 0.2 part, 0.3 part, or 0.4 part.

[0040] As an example, the silica is fumed silica with a surface area of ​​200~300 m². 2 / g (BET method), specifically 200m 2 / g、250m 2 / g or 300m 2 / g.

[0041] In the low-friction liquid silicone rubber provided by the present invention, as an example, the methyl-terminated side group hydrogen-containing silicone oil has a hydrogen atom content of 0.1wt% to 1.5wt% (the hydrogen atom content in the silicone oil is determined by iodometric titration), preferably 0.3wt% to 1wt%, specifically 0.3wt%, 0.5wt%, 0.8wt%, or 1wt%.

[0042] In specific implementation, the methyl-terminated side-group hydrogen-containing silicone oil used as a crosslinking agent can be 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts.

[0043] In the low-friction liquid silicone rubber provided by the present invention, the hydrogen-containing silicone oil with a single methyl terminal as an example has a hydrogen atom content of 0.01wt% to 0.2wt% (the hydrogen atom content in the silicone oil is determined by iodometric titration), preferably 0.03wt% to 0.1wt%, and specifically 0.03wt%, 0.04wt%, 0.06wt%, 0.08wt%, or 0.1wt%.

[0044] In specific implementation, the single-terminal methyl end-hydrogen-containing silicone oil used as an auxiliary crosslinking agent can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts.

[0045] In the low-friction liquid silicone rubber provided by the present invention, the inhibitor is one or a mixture of more of the following: 1-ethynyl-1-cyclohexanol, 2-methyl-3-butynyl-2-ol, 3-methyl-1-ethynyl-3-ol, and 3,5-dimethyl-1-hexynyl-3-ol.

[0046] In some specific cases, the inhibitor may be 0.01 parts, 0.03 parts, 0.04 parts, or 0.05 parts.

[0047] In the low-friction liquid silicone rubber provided by the present invention, the filler treatment agent is one or more of mercaptosilane coupling agent, vinylsilazane, and hexamethyldisilazane; specifically, the mercaptosilane coupling agent is selected from one or more of γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropylmethyldimethoxysilane.

[0048] In the low-friction liquid silicone rubber provided by this invention, the heat-resistant agent is one or more of rare earth oxides, ferrites, and cerium dioxide. In some specific examples, the heat-resistant agent may be 1 part, 2 parts, 3 parts, or 5 parts.

[0049] Example 1 A method for preparing a low-friction liquid silicone rubber composite material includes the following steps: (1) Add 90 parts of double-vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, vinyl content 0.3 wt%), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; then add 45 parts of silica (specific surface area 300 m² / g) 2 5 parts of spherical silicone resin (particle size 5μm), 10 parts of lamellar mica (particle size 15μm), and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was combined, and kneaded at room temperature for 1 hour; then the temperature of the kneader was raised to 185℃, and a vacuum was drawn to <-0.1MPa. The vacuum was maintained, and the mixture was kneaded under vacuum for 3 hours; the heating was turned off, and 10 parts of vinyl-terminated silicone oil were added, the mixture was combined, and the mixture was kneaded for another hour; the mixture was cooled to room temperature to obtain the base resin; (2) Take 100 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor, and fully refining them on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, refining for 20min) to make the sheet filler initially oriented along the shear direction. (3) The mixture after open milling is molded and vulcanized by a flat vulcanizing machine at 150℃×400s and 1.5MPa. The unidirectional pressure field during the molding process causes the sheet filler to be arranged parallel to the friction surface.

[0050] Example 2 A method for preparing a low-friction liquid silicone rubber composite material includes the following steps: (1) Add 90 parts of vinyl-terminated silicone oil (viscosity 20000 mPa·s, vinyl content 0.3 wt%), 9 parts of silazane, 1 part of γ-mercaptopropyltrimethoxysilane (KH-590), and 3 parts of water to a kneader and knead for 10 minutes at room temperature; then add 45 parts of silica (specific surface area 300 m² / g) 2 5 parts of spherical silicone resin (particle size 5μm), 10 parts of molybdenum disulfide (particle size 3μm), and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was combined, and kneaded at room temperature for 1 hour; then the kneader temperature was raised to 185℃, and a vacuum was drawn to <-0.1MPa. The vacuum was maintained, and the mixture was kneaded under vacuum for 3 hours; the heating was turned off, and 10 parts of double-ended vinyl-terminated silicone oil were added, the mixture was combined, and the mixture was kneaded for another hour; the mixture was cooled to room temperature to obtain the base resin; (2) Take 100 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor and fully refining them on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, refining for 20min) to make the sheet filler initially oriented along the shear direction. (3) The mixture after open milling is molded and vulcanized by a flat vulcanizing machine at 150℃×400s and 1.5MPa. The unidirectional pressure field during the molding process causes the sheet filler to be arranged parallel to the friction surface.

[0051] Example 3 A method for preparing a low-friction liquid silicone rubber composite material includes the following steps: (1) Add 90 parts of double-vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, 20 wt% vinyl content), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; then add 45 parts of silica (specific surface area 300 m² / g). 2 5 parts of spherical silicone resin (particle size 5μm), 10 parts of boron nitride (particle size 20μm), and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was sealed, and kneaded at room temperature for 1 hour; then the kneader temperature was raised to 185℃, vacuum was drawn to <-0.1MPa, and the mixture was kneaded under vacuum for 3 hours; the heating was turned off, and 10 parts of double-ended vinyl-terminated silicone oil were added, the mixture was sealed, and kneading continued for 1 hour; the mixture was cooled to room temperature to obtain the base resin; (2) Take 100 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor and fully refining them on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, refining for 20min) to make the sheet filler initially oriented along the shear direction. (3) The mixture after open milling is molded and vulcanized by a flat vulcanizing machine at 150℃×400s and 1.5MPa. The unidirectional pressure field during the molding process causes the sheet filler to be arranged parallel to the friction surface.

[0052] Example 4 A method for preparing a low-friction liquid silicone rubber composite material includes the following steps: (1) Add 90 parts of vinyl-terminated silicone oil (viscosity 20000 mPa·s, vinyl content 0.1 wt%), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; then add 45 parts of silica (specific surface area 300 m² / g) 214.285 parts of spherical silicone resin (particle size 5μm), 0.715 parts of lamellar mica (particle size 15μm), and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was combined, and kneaded at room temperature for 1 hour; then the temperature of the kneader was raised to 185℃, and a vacuum was drawn to <-0.1MPa. The vacuum was maintained, and the mixture was kneaded under vacuum for 3 hours; the heating was turned off, and 10 parts of vinyl-terminated silicone oil were added, the mixture was combined, and the mixture was kneaded for another hour; the mixture was cooled to room temperature to obtain the base resin; (2) Take 100 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor, and fully refining them on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, refining for 20min) to make the sheet filler initially oriented along the shear direction. (3) The mixture after open milling is molded and vulcanized by a flat vulcanizing machine at 150℃×400s and 1.5MPa. The unidirectional pressure field during the molding process causes the sheet filler to be arranged parallel to the friction surface.

[0053] Example 5 A method for preparing a low-friction liquid silicone rubber composite material includes the following steps: (1) Add 90 parts of vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, 10 wt% vinyl content), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; then add 45 parts of silica (specific surface area 300 m² / g). 2 2.5 parts of spherical silicone resin (particle size 5μm), 12.5 parts of lamellar mica (particle size 15μm), and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was sealed, and kneaded at room temperature for 1 hour; then the temperature of the kneader was raised to 185℃, and a vacuum was drawn to <-0.1MPa. The vacuum was maintained, and the mixture was kneaded under vacuum for 3 hours; the heating was turned off, and 10 parts of vinyl-terminated silicone oil were added, the mixture was sealed, and kneading continued for 1 hour; the mixture was cooled to room temperature to obtain the base resin; (2) Take 100 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor, and fully refining them on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, refining for 20min) to make the sheet filler initially oriented along the shear direction. (3) The mixture after open milling is molded and vulcanized by a flat vulcanizing machine at 150℃×400s and 1.5MPa. The unidirectional pressure field during the molding process causes the sheet filler to be arranged parallel to the friction surface.

[0054] Example 6 A method for preparing a low-friction liquid silicone rubber composite material includes the following steps: Add 90 parts of double-vinyl-terminated vinyl silicone oil, 10 parts of silazane, and 3 parts of water to a kneader and knead at room temperature for 10 minutes. Add 45 parts of silica, 5 parts of spherical silicone resin with a particle size of 5 μm, and 10 parts of lamellar mica with a particle size of 15 μm to the kneader in batches, combine the kneaders, and knead at room temperature for 1 hour. Raise the temperature of the kneader to 185°C, evacuate to <-0.1 MPa, maintain the vacuum, and knead under vacuum for 3 hours. Turn off the heating, add another 10 parts of double-vinyl-terminated vinyl silicone oil, combine the kneaders, and continue kneading for 1 hour. Cool to room temperature to obtain the base resin. 100 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil, 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil, 0.3 parts of catalyst, and 0.05 parts of inhibitor were thoroughly mixed on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, mixing for 20min) until uniform. The mixture was then molded on a flat vulcanizing machine at 150℃×400s and 1.5MPa.

[0055] Comparative Example 1 A method for preparing liquid silicone rubber includes the following steps: Add 90 parts of double-vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, 0.3 wt% vinyl content), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; add 45 parts of silica (specific surface area 300 m² / g). 2 / g), 2 parts of heat resistant agent were added in batches to the kneader, the mixture was put into the kneader, and kneaded at room temperature for 1 hour; the temperature of the kneader was raised to 185℃, the vacuum was drawn to <-0.1MPa, and the vacuum was maintained for 3 hours; the heating was turned off, and 10 parts of double-ended vinyl silicone oil were added, the mixture was put into the kneader, and kneading was continued for 1 hour; the mixture was cooled to room temperature to obtain the base rubber; 90.65 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8 wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05 wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor were thoroughly mixed on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, mixing for 20min) until homogeneous. The mixture was then molded on a flat vulcanizing machine at 150℃×400s and 1.5MPa.

[0056] Comparative Example 2 A method for preparing liquid silicone rubber includes the following steps: Add 90 parts of double-vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, 0.3 wt% vinyl content), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; add 45 parts of silica (specific surface area 300 m² / g). 2 5 parts of spherical silicone resin with a particle size of 5μm and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was combined, and kneaded at room temperature for 1 hour; the temperature of the kneader was raised to 185℃, the vacuum was drawn to <-0.1MPa, and the vacuum was maintained for 3 hours; the heating was turned off, and 10 parts of vinyl-terminated silicone oil were added, the mixture was combined, and kneading was continued for 1 hour; the mixture was cooled to room temperature to obtain the base resin; 93.8 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8 wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05 wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor were thoroughly mixed on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, mixing for 20min) until homogeneous, and then molded on a flat vulcanizing machine at 150℃×400s and 1.5MPa.

[0057] Comparative Example 3 A method for preparing liquid silicone rubber includes the following steps: Add 90 parts of double-vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, 0.3 wt% vinyl content), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; add 45 parts of silica (specific surface area 300 m² / g). 2 5 parts of spherical silicone resin with a particle size of 5 μm, 10 parts of lamellar mica with a particle size of 15 μm, and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was combined, and kneaded at room temperature for 1 hour; the temperature of the kneader was raised to 185℃, and a vacuum was drawn to <-0.1MPa. The vacuum was maintained, and the mixture was kneaded under vacuum for 3 hours; the heating was turned off, and 10 parts of vinyl silicone oil with double-ended vinyl groups were added, the mixture was combined, and the mixture was kneaded for another hour; the mixture was cooled to room temperature to obtain the base resin; 100 parts of base adhesive, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8 wt%), 3 parts of single-methyl-terminated end-group hydrogen-containing silicone oil (hydrogen atom content of 0.05 wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor were mixed evenly in a planetary mixer and then poured and cured at high temperature (without orientation pressure). After pouring and molding, the mixture was cured at 150°C for 400 seconds, ensuring that the temperature and time were consistent with those in Example 1.

[0058] Comparative Example 4 A method for preparing liquid silicone rubber includes the following steps: Add 90 parts of double-vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, 0.3 wt% vinyl content), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; add 45 parts of silica (specific surface area 300 m² / g). 2 / g), 2 parts of heat resistant agent were added in batches to the kneader, the mixture was put into the kneader, and kneaded at room temperature for 1 hour; the temperature of the kneader was raised to 185℃, the vacuum was drawn to <-0.1MPa, and the vacuum was maintained for 3 hours; the heating was turned off, and 10 parts of double-ended vinyl silicone oil were added, the mixture was put into the kneader, and kneading was continued for 1 hour; the mixture was cooled to room temperature to obtain the base rubber; 90.65 parts of base rubber, 3.12 parts of spherical silicone resin (particle size 5μm), 6.23 parts of lamellar mica (particle size 15μm), 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content 0.8wt%), 3 parts of single-methyl-terminated end-group hydrogen-containing silicone oil (hydrogen atom content 0.05wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor were thoroughly mixed on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, mixing for 20min) until homogeneous. The mixture was then molded on a flat vulcanizing machine at 150℃×400s and 1.5MPa.

[0059] Comparative Example 5 A method for preparing liquid silicone rubber includes the following steps: Add 90 parts of double-vinyl-terminated vinyl silicone oil (viscosity 20000 mPa·s, 0.3 wt% vinyl content), 10 parts of silazane, and 3 parts of water to a kneader and knead for 10 minutes at room temperature; add 45 parts of silica (specific surface area 300 m² / g). 2 10 parts of lamellar mica with a particle size of 15μm and 2 parts of heat resistant agent were added in batches to a kneader, the mixture was stirred and kneaded at room temperature for 1 hour; the temperature of the kneader was raised to 185℃, the vacuum was drawn to <-0.1MPa, and the vacuum was maintained for 3 hours; the heating was turned off, and 10 parts of vinyl silicone oil were added, the mixture was stirred and kneaded for another hour; the mixture was cooled to room temperature to obtain the base rubber; 97.6 parts of base rubber, 5 parts of methyl-terminated side-group hydrogen-containing silicone oil (hydrogen atom content of 0.8 wt%), 3 parts of single-terminated methyl-terminated hydrogen-containing silicone oil (hydrogen atom content of 0.05 wt%), 0.3 parts of platinum catalyst, and 0.05 parts of inhibitor were thoroughly and uniformly mixed on a two-roll mill (roll temperature 25±5℃, roll gap 1mm, mixing for 20min), and then molded on a flat vulcanizing machine at 150℃×400s and 1.5MPa.

[0060] Example of effect Test samples: Examples 1-6 and Comparative Examples 1-5 of this invention.

[0061] Tensile strength / elongation: Tested according to GB / T 528-2008 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber"; Hardness: Tested according to GB / T531-2009 "Shore A Hardness Test Method for Vulcanized Rubber".

[0062] Friction coefficient test: The friction coefficient was tested in accordance with GB / T 3960-2016 (test method for sliding friction and wear of plastics), with frosted glass as the grinding material, load of 20N, and sliding speed of 0.05m / s.

[0063] Each sample was tested 5 times, and the average value was taken.

[0064] The results of the friction coefficient and mechanical properties after one vulcanization are shown in Table 1.

[0065] Table 1

[0066] The molded and vulcanized samples were placed in a 200℃ forced-air oven for a second vulcanization for 24 hours, and then naturally cooled before performance testing. The results of the friction coefficient, mechanical properties, etc. after the second vulcanization (200℃×24h) are shown in Table 2.

[0067] Table 2

[0068] A comparison of Examples 1-3 with Comparative Examples 1 and 2 shows that: The synergistic use of spherical inorganic microspheres and layered fillers significantly reduces the coefficient of friction of silicone rubber. The mechanism lies in the fact that the spherical inorganic microspheres act as "balls" at the microscale, transforming sliding friction into rolling friction; while the layered fillers form a continuous low-shear transfer lubricating film at the friction interface. The two complement each other at the macroscopic rolling drag reduction and microscopic interface lubrication scales, respectively, thus achieving a significant friction reduction effect.

[0069] A comparison between Comparative Example 1 and Comparative Example 2 shows: Adding spherical inorganic microspheres alone can significantly reduce the coefficient of friction of silicone rubber. This is attributed to the fact that the microspheres convert sliding friction into rolling friction, while reducing the actual contact area and furrowing resistance, and achieving stable rolling under the guidance of the "track" formed by the sheet filler, thereby effectively reducing the coefficient of friction.

[0070] A comparison of Examples 1-3 and Comparative Example 2 shows that: The addition of lamellar fillers can also significantly reduce the coefficient of friction of silicone rubber, mainly due to its low shear characteristics of interlayer slip and the effect of forming a transfer film on the friction surface.

[0071] Comparison between Example 1 and Comparative Example 3: Oriented silicone rubber exhibits a lower coefficient of friction. This is because the sheet filler transforms from a "partial, unstable shear orientation" to a "highly consistent, stable, locked planar orientation," thus truly achieving a synergistic friction-reducing effect of "track-guided balls." Specifically, through open-mill shear pre-orientation and molding pressure orientation, the sheet filler can form regular tracks parallel to the friction surface, guiding the spherical silicone resin to roll in a specific direction. This, combined with the sliding or supporting effect of the sheets, results in a stepwise reduction in the coefficient of friction.

[0072] A comparison between Example 1 and Comparative Example 4 shows that: Silicone rubber prepared by simultaneously adding spherical silicone resin and lamellar filler during the kneading stage exhibits a lower coefficient of friction and superior overall performance. This is because this feeding method effectively avoids the problems of random rolling and easy settling failure of spherical silicone resin, as well as the problems of easy agglomeration and poor compatibility with the silicone rubber matrix of lamellar filler. Furthermore, the covalent bonding modification of both materials using silane coupling agents and silazane further improves the dispersion of the filler in the silicone rubber, thereby enhancing both its frictional and mechanical properties.

[0073] Comparing Example 1 with Example 6, we found that: Example 6, without the addition of a heat-resistant agent, already solved the technical problems of low friction coefficient and high wear resistance silicone rubber after its primary vulcanization. However, in silicone rubber systems requiring secondary vulcanization, the crosslinking network suffers severe thermal degradation after secondary vulcanization, leading to deterioration of mechanical properties and an increase in the friction coefficient. This is because the addition of a heat-resistant agent provides stable crosslinking network support for the frictional environment, allowing spherical silicone resin and lamellar fillers to maintain good friction reduction effects even at high temperatures. This further illustrates the crucial role of heat-resistant agents in material stability under high-temperature conditions. Therefore, the addition of heat-resistant agents can significantly improve the thermal stability of the rubber compound and its ability to maintain the friction coefficient under high-temperature conditions.

[0074] The comparison between Comparative Example 5 and Example 1 further verifies the synergistic mechanism of the present invention. Although Comparative Example 5 added the same amount of lamellar mica and underwent orientation treatment, its friction coefficient after the first vulcanization was as high as 0.45, and after the second vulcanization it rose to 0.55, because no spherical inorganic microspheres were added. Compared with Comparative Example 2, it can be seen that whether lamellar filler or spherical microspheres are used alone, there is a significant bottleneck in the friction reduction effect (approximately 0.42~0.45). However, after introducing two fillers simultaneously and constructing an orientation structure, the friction coefficient in Example 1 dropped sharply to 0.25, significantly lower than the expected value of the simple sum of the two single filler systems (0.35~0.40). This indicates that the guiding and confining effect of the lamellar track on the spherical balls is the decisive factor in breaking through the friction reduction bottleneck of single filler and achieving a stepwise reduction in the friction coefficient.

[0075] In summary, the liquid silicone rubber prepared by this invention has a low coefficient of friction, which can meet the low friction performance requirements under complex working conditions. It can be widely used in fields such as electronics, automobile manufacturing, medical devices and precision seals. Moreover, the preparation process is simple and has broad prospects for industrial application.

Claims

1. A method for preparing a low-friction liquid silicone rubber composite material, characterized in that, Includes the following steps: (1) Take a portion of the double-ended vinyl-terminated vinyl silicone oil, other additives and filler treatment agent and knead them together. Then add fumed silica, spherical inorganic microspheres and sheet filler in batches. First, knead at room temperature, then heat up and knead under vacuum. Stop heating and add the remaining double-ended vinyl-terminated vinyl silicone oil for kneading and cooling to obtain the base adhesive. The portion of the double-ended vinyl-terminated vinyl silicone oil accounts for 70% to 95% of its total mass. The other additives are silazane and / or water. (2) The base glue, methyl-terminated side-group hydrogen-containing silicone oil, single-terminated methyl end-group hydrogen-containing silicone oil, platinum catalyst, and inhibitor are mixed on a two-roll mill to make the sheet filler initially oriented along the shear direction. (3) The mixture after open milling is molded and vulcanized by a flat vulcanizing machine. The unidirectional pressure field during the molding process causes the sheet filler to be arranged parallel to the friction surface.

2. The method for preparing the low-friction liquid silicone rubber composite material according to claim 1, characterized in that, Step (1) Before kneading at room temperature, add a heat resistant agent.

3. The method for preparing the low-friction liquid silicone rubber composite material according to claim 1, characterized in that, The vinyl content of the double-ended vinyl silicone oil is 0.1–20 wt%, preferably 0.2–10 wt%; the viscosity at 25°C is 100–100,000 mPa·s. Optionally, the filler treatment agent is one or more of mercaptosilane coupling agents, vinylsilazane, and hexamethyldisilazane; preferably, the mercaptosilane coupling agent is selected from one or more of γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropylmethyldimethoxysilane.

4. The method for preparing the low-friction liquid silicone rubber composite material according to claim 1, characterized in that, The silica is fumed silica, and its specific surface area is preferably 200-300 m² / g. 2 / g; Optionally, the spherical inorganic microspheres are one or more of spherical silicone resin, polymethylsilsesquioxane, and spherical boron nitride; Preferably, the particle size of the spherical inorganic microspheres is 1–15 μm.

5. The method for preparing the low-friction liquid silicone rubber composite material according to claim 1, characterized in that, The sheet filler is one or a mixture of mica, molybdenum disulfide, boron nitride, and graphite; preferably, the particle size of the sheet filler is 2-30 μm. Optionally, the heat-resistant agent is one or more of rare earth oxides, ferrites, and cerium dioxide.

6. The method for preparing the low-friction liquid silicone rubber composite material according to claim 1, characterized in that, The hydrogen atom content of the methyl-terminated side-group hydrogen-containing silicone oil is 0.1~1.5wt%, preferably 0.3~1wt%; Optionally, the hydrogen atom content of the single-terminated methyl-terminated hydrogen-containing silicone oil is 0.01~0.2wt%, preferably 0.03~0.1wt%; Optionally, the inhibitor is one or a mixture of more of 1-ethynyl-1-cyclohexanol, 2-methyl-3-butynyl-2-ol, 3-methyl-1-ethynyl-3-ol, or 3,5-dimethyl-1-hexynyl-3-ol.

7. The method for preparing the low-friction liquid silicone rubber composite material according to claim 1, characterized in that, The mass ratio of the sheet filler to the spherical inorganic microspheres is (0.05~5):

1.

8. The method for preparing the low-friction liquid silicone rubber composite material according to claim 1, characterized in that, In step (1), the vacuum kneading after heating is as follows: heat to 185°C, evacuate to ≤-0.09MPa, and knead under vacuum.

9. The method for preparing the low-friction liquid silicone rubber composite material according to any one of claims 1-8, characterized in that, The raw materials used, by weight, include: 50-100 parts of double-vinyl-terminated vinyl silicone oil, 3-15 parts of filler treatment agent, 1-5 parts of other additives, 15-45 parts of silica, 2-15 parts of spherical inorganic microspheres, 0.1-20 parts of lamellar filler, 0.1-5 parts of heat resistant agent, 3-10 parts of methyl-terminated side-group hydrogen-containing silicone oil, 1-5 parts of single-methyl-terminated end-group hydrogen-containing silicone oil, 0.1-1 parts of platinum catalyst, and 0.01-0.1 parts of inhibitor.

10. A low-friction liquid silicone rubber composite material, characterized in that, The low-friction liquid silicone rubber composite material is obtained by the preparation method according to any one of claims 1-9, comprising a silicone rubber matrix, spherical inorganic microspheres and sheet fillers, wherein the sheet fillers are oriented in a direction parallel to the friction surface.

Images