Filler type

1 Nitride

Nitrides usually have advantages such as high thermal conductivity, high temperature resistance, and good electrical insulation performance. They can improve the thermal conductivity of plastics without reducing the electrical insulation performance of the material. However, their disadvantage is that they are expensive, which limits their widespread application in plastics. The nitrides used as thermal conductive fillers mainly include boron nitride (BN), silicon nitride (Si3N4), and aluminum nitride (AlN), whose thermal conductivity can reach 200-300 W/(m · K).

2 Carbides

Silicon carbide can be divided into hexagonal crystal systems（ α－ SiC and cubic crystal systems（ β－ SiC, with a thermal conductivity coefficient of 80-120 W/(m · K), is a high-performance thermal conductive filler. It also has advantages such as high temperature resistance, high modulus, and good oxidation resistance, and is used in microelectronic packaging materials. Boron carbide (B4C) is also a high-temperature resistant material with extremely high hardness and thermal conductivity, but its expensive price leads to its limited application in thermal conductive plastics.

3 Oxides

Oxide fillers mainly include aluminum oxide (Al2O3), zinc oxide (ZnO), and magnesium oxide (MgO), etc. Although their thermal conductivity is not as high as that of nitrides and carbides, generally between 30-50 W/(m · K), they are also much higher than polymer matrices, and have excellent electrical insulation performance. Especially with their wide sources, low prices, and market competitiveness, they are commonly used fillers for preparing insulating and thermal conductive plastics.

4 metal powders

Usually, metal powders have extremely high thermal conductivity, up to 100-400 W/(m · K), making them good thermal conductive fillers. However, due to the electronic thermal conductivity of metal based fillers, their poor electrical insulation performance limits their application in the electronic industry where electrical insulation requirements are strict.

5 New Carbon Materials

New carbon materials such as graphite, carbon nanotubes, and diamond also have extremely high thermal conductivity. The thermal conductivity of carbon nanotubes and diamond can reach over 1000 W/(m · K). However, due to their extremely high cost, they have not been widely used, and the addition of carbon based fillers usually causes the color of products to turn black, which is limited in the application of light colored products.

Analysis of influencing factors

The influence of filling amount of fillers

The filling amount of thermal conductive fillers is closely related to the thermal conductivity of composite materials. When the filler content is low, an effective thermal conductivity network cannot be formed, and the improvement effect on the material's thermal conductivity is not significant. As the filler content increases, a thermal conductivity network begins to form and improve inside the material, thereby significantly improving the thermal conductivity of the material.

The influence of filler shape and size

The shape of the thermal conductive filler affects the formation of the thermal conductive network, thereby affecting the thermal conductivity of the material. When there is only a single filler, increasing the length to diameter ratio of the filler can promote mutual contact between the fillers, which is conducive to forming a continuous thermal conductivity network. In addition, adding both high aspect ratio and low aspect ratio thermal conductive fillers in a certain proportion can improve the thermal conductivity of composite materials more effectively than single fillers; Adding a small amount of the same or different fillers with small particle sizes to larger particle size fillers can also effectively improve the thermal conductivity of composite materials.

Surface treatment of thermal conductive fillers

The interface compatibility between thermal conductive fillers and resin matrix is poor, which not only affects the thermal conductivity of the material, but also affects the mechanical properties of the material. The use of coupling agents can not only effectively remove interface defects between the two, but also improve the distribution of fillers, thereby enhancing the thermal conductivity and mechanical properties of the material. However, excessive coupling agents can also form a "barrier" between the thermal conductive filler and the resin matrix, hindering heat transfer and thereby reducing the thermal conductivity of the material.