In recent years, the thermal conductivity of rubber products has received extensive attention. Thermally conductive rubber products are widely used in the fields of aerospace, aviation, electronics, and electrical appliances to play a role in heat conduction, insulation and shock absorption. The improvement of thermal conductivity is extremely important for thermally conductive rubber products. The rubber composite material prepared by the thermally conductive filler can effectively transfer heat, which is of great significance to the densification and miniaturization of electronic products, as well as the improvement of their reliability and the extension of their service life.
At present, the rubber materials used in tires need to have the characteristics of low heat generation and high thermal conductivity. On the one hand, in the tire vulcanization process, the heat transfer performance of the rubber is improved, the vulcanization rate is increased, and the energy consumption is reduced; The heat generated during driving reduces the temperature of the carcass and reduces tire performance degradation caused by excessive temperature. The thermal conductivity of thermally conductive rubber is mainly determined by the rubber matrix and thermally conductive filler. The thermal conductivity of either the particles or the fibrous thermal conductive filler is much better than that of the rubber matrix.
The most commonly used thermally conductive fillers are the following materials:
1. Cubic Beta phase nano silicon carbide (SiC)
Nano-scale silicon carbide powder forms contact heat conduction chains, and is easier to branch with polymers, forming Si-O-Si chain heat conduction skeleton as the main heat conduction path, which greatly improves the thermal conductivity of the composite material without reducing the composite material The mechanical properties.
The thermal conductivity of the silicon carbide epoxy composite material increases with the increase in the amount of silicon carbide, and nano-silicon carbide can give the composite material good thermal conductivity when the amount is low. The flexural strength and impact strength of silicon carbide epoxy composite materials increase first and then decrease with the increase of the amount of silicon carbide. The surface modification of silicon carbide can effectively improve the thermal conductivity and mechanical properties of the composite material.
Silicon carbide has stable chemical properties, its thermal conductivity is better than other semiconductor fillers, and its thermal conductivity is even greater than that of metal at room temperature. Researchers from Beijing University of Chemical Technology conducted research on the thermal conductivity of alumina and silicon carbide reinforced silicone rubber. The results show that the thermal conductivity of silicone rubber increases as the amount of silicon carbide increases; when the amount of silicon carbide is the same, the thermal conductivity of the small particle size silicon carbide reinforced silicone rubber is greater than that of the large particle size silicon carbide reinforced silicone rubber; The thermal conductivity of silicon rubber reinforced with silicon carbide is better than that of alumina reinforced silicon rubber. When the mass ratio of alumina/silicon carbide is 8/2 and the total amount is 600 parts, the thermal conductivity of silicon rubber is the best.
Aluminum nitride is an atomic crystal and belongs to diamond nitride. It can exist stably at a high temperature of 2200 ℃. It has good thermal conductivity and low thermal expansion coefficient, making it a good thermal shock material. The thermal conductivity of aluminum nitride is 320 W·(m·K)-1, which is close to the thermal conductivity of boron oxide and silicon carbide, and is more than 5 times larger than that of alumina. Researchers from Qingdao University of Science and Technology have studied the thermal conductivity of aluminum nitride reinforced EPDM rubber composites. The results show that: as the amount of aluminum nitride increases, the thermal conductivity of the composite material increases; the thermal conductivity of the composite material without aluminum nitride is 0.26 W·(m·K)-1, when the amount of aluminum nitride increases to At 80 parts, the thermal conductivity of the composite material reaches 0.442 W·(m·K)-1, an increase of 70%.
Alumina is a kind of multifunctional inorganic filler, which has large thermal conductivity, dielectric constant and good wear resistance. It is widely used in rubber composite materials.
Researchers from Beijing University of Chemical Technology tested the thermal conductivity of nano-alumina/carbon nanotube/natural rubber composites. The results show that the combined use of nano-alumina and carbon nanotubes has a synergistic effect on improving the thermal conductivity of the composite material; when the amount of carbon nanotubes is constant, the thermal conductivity of the composite material increases linearly with the increase of the amount of nano-alumina; when 100 When using nano-alumina as the thermally conductive filler, the thermal conductivity of the composite material increases by 120%. When 5 parts of carbon nanotubes are used as the thermally conductive filler, the thermal conductivity of the composite material increases by 23%. When 100 parts of alumina and 5 parts are used When carbon nanotubes are used as a thermally conductive filler, the thermal conductivity of the composite material increases by 155%. The experiment also draws the following two conclusions: First, when the amount of carbon nanotubes is constant, as the amount of nano-alumina increases, the filler network structure formed by conductive filler particles in the rubber gradually increases, and the loss factor of the composite material gradually increases. When 100 parts of nano-alumina and 3 parts of carbon nanotubes are used together, the dynamic compression heat generation of the composite material is only 12 ℃, and the dynamic mechanical properties are excellent; second, when the amount of carbon nanotubes is fixed, as the amount of nano-alumina increases, The hardness and tear strength of composite materials increase, while the tensile strength and elongation at break decrease.
Carbon nanotubes have excellent physical properties, thermal conductivity and electrical conductivity, and are ideal reinforcing fillers. Their reinforcing rubber composite materials have received widespread attention. Carbon nanotubes are formed by curling layers of graphite sheets. They are a new type of graphite material with a cylindrical structure with a diameter of tens of nanometers (10-30nm, 30-60nm, 60-100nm). The thermal conductivity of carbon nanotubes is 3000 W·(m·K)-1, which is 5 times the thermal conductivity of copper. Carbon nanotubes can significantly improve the thermal conductivity, electrical conductivity and physical properties of rubber, and their reinforcement and thermal conductivity are better than traditional fillers such as carbon black, carbon fiber and glass fiber. Researchers from Qingdao University of Science and Technology conducted research on the thermal conductivity of carbon nanotubes/EPDM composite materials. The results show that: carbon nanotubes can improve the thermal conductivity and physical properties of composite materials; as the amount of carbon nanotubes increases, the thermal conductivity of composite materials increases, and the tensile strength and elongation at break first increase and then decrease , The tensile stress and tearing strength are increased; when the amount of carbon nanotubes is small, large-diameter carbon nanotubes are easier to form heat-conducting chains than small-diameter carbon nanotubes, and they are better combined with the rubber matrix.