With the development of industry, people have put forward more stringent performance requirements for rubber in the packaging and heat dissipation of electronic devices, heat conduction of electrical insulation materials and thermal control side of aerospace and other special occasions. Therefore, it is urgent to develop a kind of rubber material with excellent comprehensive performance of heat conduction and insulation.

Thermal insulating rubber is mainly silicone rubber (SR), and the thermal conductivity of the unfilled SR is generally only 0.165W/(m·K). Thermal insulating rubber prepared by filling thermal insulating inorganic filler in SR has the unique advantages of high polymer materials such as excellent electrical insulation, good aging resistance and so on.It has the advantages of room temperature curing, no by-products, good dimensional stability, simple process and so on. It is widely used in the fields of aviation, aerospace, electronics and electricity. It has the effect of enhancing the heat dissipation of components, as well as the function of insulation and shock absorption.Due to the poor thermal conductivity of SR itself, its application is limited to a certain extent. At present, filler metals, carbon series and inorganic thermal conductivity particles are often used to improve the thermal conductivity [3].Due to the high thermal conductivity of metal and carbon particles, the thermal conductivity of the system is significantly improved when a small amount of metal and carbon particles are filled, but the insulation performance is obviously decreased.When inorganic thermal conductivity particles such as boron nitride, silicon oxide and silicon carbide are filled, the thermal conductivity performance of the system is improved, and the insulation performance will not be greatly affected. The filling amount of inorganic thermal conductivity particles is usually between 30% and 150%, and too high filling amount will seriously reduce the mechanical properties of silicone rubber.Although the research history of conductive SR is not long, it has been widely used in industry, and with the development of modern science and technology and industrial production, its application field is more and more wide, and its performance requirements are also higher and higher.


1.Nitride/silicone rubber system

Nitride has high thermal conductivity and good insulation, so it is the first choice of filler for thermal conductive insulating rubber. The dosage of filler, particle size and distribution, surface treatment and other factors all have an effect on the performance of SR.PSZ and SiOC coatings can improve the interfacial force between AlN and Sr, reduce the interfacial thermal resistance and improve the thermal conductivity. The effect of SiOC coating is better than that of PSZ coating, which is attributed to the decrease of surface toughness and thickness after high temperature treatment.In addition, PSZ and Sioc coatings also improved the Td and tensile strength of AlN/ Sr.AlN is easy to absorb tidal solution, and the rubber material with high thermal conductivity and heat resistance can be used to manufacture thermal radiation sheet by filling SR with AlN powder after Al2O3 gas phase coating.


2 alumina/silicon rubber system

The amount of Al2O3, particle size, surface modification, structure and processing conditions of Sr all affect the thermal conductivity of the composite Sr.The thermal conductivity of Al2O3/ Sr is related to the filling amount and particle size of Al2O3, and there is a critical particle diameter. When the particle size of Al2O3 is greater than a certain value d, the thermal conductivity of Al2O3 composites with small particle size is smaller than that filled with large particle size under the same powder content. When the particle size of Al2O3 composites is less than a certain amount d, the results are opposite.Nanometer and micrometer Al2O3 with different particle sizes were used to fill SR. When the filling amount was small, compared with small particle size Al2O3, the SR filled with large particle size Al2O3 had better thermal conductivity, but its mechanical properties were reduced.When the filling amount reaches a certain degree, the difference of thermal conductivity between the two decreases significantly.The Sr thermal conductivity of nano-sized Al2O3 is significantly higher than that of micro-sized Al2O3, and the mechanical properties are still stable when the filling amount is large.The mixed filling of Sr with different particle sizes in a certain proportion has better thermal conductivity than that of single particle filling, and at the same time, the mechanical properties and process properties are also significantly improved [13].Spherical Al2O3 with different particle diameters was used to enhance Sr, and Al2O3 with large particle diameters obtained higher thermal conductivity, which was attributed to lower interfacial thermal resistance. The thermal conductivity model considering interfacial factors could better predict the thermal conductivity of Sr system with high content of ions.


3.Other thermal conductivity particles and hybrid particles/silicone rubber system

Other thermal conductivity particles, such as ZnO, MgO, SiO2, SiC, etc., have high thermal conductivity, and the thermal insulation properties can be improved by filling them into SR alone or mixed, and they also have good mechanical properties.The mechanical and thermal properties of the room temperature sulfurization SR filled with ZnO showed that the tensile strength of SR increased significantly with the increase of filler amount, and the elongation at break decreased. The 100% constant elongation stress, hardness and tear strength all increased with the increase of filler amount, and the thermal conductivity increased gradually. When the dosage of 70% (wt) was used,The thermal conductivity reaches 2.1142 W/ (m·K), and increases gradually with the increase of temperature.With the increase of ZnO, the number of thermal conduction channels also increases. Compared with single particle size, filling with particles with mixed particle size is easier to increase the filling density, form a dense accumulation, improve the thermal conductivity, and the thermal resistance has a positive temperature coefficient.