Preparation And Application Performance Of Thermally Conductive Silicone Composites

Thermal conductive composite materials, having excellent insulating propertiesand good thermal conductive properties, have been widely used as the electronicdevices with high heat dispersion requirements, because they could greatly protectand extend the life of these devices. But the thermally conductive silicone gaskets willbe occur oil bleeding phenomenon in the application process, which will not onlyaffect the operability of the gaskets, but also affect the appearance of products, andmay contaminated equipment.In this paper, A, B two-component liquid silicone rubber as the matrix, thenAl(OH)3and Al2O3as the fillers, thus the thermally conductive silicone gaskets wereprepared. Following, their properties were characterized and tested, and the oilbleeding phenomenon in their application process was analyzed at the same time.The results showed that, with the increasing volume addition of fillers, thehardness of the thermally conductive gaskets increased in an S-shaped type: thehardness increased slowly when the volume addition of fillers was0.43~0.54, thenincreased sharply when the volume addition was0.54~0.65; the hardness increasedslowly again when the volume addition of fillers exceeded0.65.With the increasing volume addition of fillers, the compressive stress of thethermal gaskets increased significantly: the compressive stress increased slowly whenthe volume addition of fillers was0.43~0.54; Afterwards, the compressive stressincreased sharply when the volume addition of fillers was above0.54.For the bulk Al(OH)3fillers, when adding the same volume of fillers to thegaskets, the thermal conductivity of the fillers with larger diameter was higher thanthose with smaller diameter ones, however the compression stress was slightly lowerthan the fillers with smaller diameter, they tended to possess good thermalconductivity and excellent usability performance. For the spherical Al2O3fillers, noobvious thermal conductivity difference existed when the volume addition of fillerswas0.43~0.55, but the fillers with larger diameter have better thermal conductivitythan smaller ones when the volume addition was more than55%. To produce products with higher thermal conductivity, we need maximize the amount of fillers. But whenthe amount of fillers was too much, the hardness of the products will be too high, andsome production problems will arise. So after meeting the requirements of the thermalconductivity, the combination property needs to be considered. The thermalconductivity of globular fillers was greater than the bulk fillers when added the sameamount of Al2O3fillers with similar particle size.The result of permeability of oil showed that the functional group ratio had agreat effect on the oil bleeding of silicone thermally conductive gaskets. The amountof oil bleeding increased with the ratio of vinyl and silicon hydrogen groups (r)increased. And when r=3.25, incomplete crosslinking phenomenon occurred, theamount of oil bleeding reached to the top. With the amount of fillers increasing, thefree resin decreased, however, with the crosslinking density increasing, the amount ofoil bleeding decreased. When silicone oil with different molecular weight was added,the amount of oil bleeding reduced with the silicone molecular weight increased.