Many manufacturers of thermally conductive silicone sheets will inevitably encounter problems of one kind or another in the process of producing thermally conductive silicone sheets. One of the most troublesome problems for thermally conductive silicone sheet manufacturers is: foaming of thermally conductive silicone sheets during the production process. Once the thermal conductive silicone sheet is foamed, it will be regarded as a defective product and thrown away, without recycling or any other value, which will directly increase the defect rate for the thermal conductive silicone sheet manufacturer and cause cost pressure. Today, the editor of GLPOLY will discuss with you the reasons and solutions for the foaming of thermal silica sheets!
There are many reasons for the foaming in the production process of thermally conductive silica gel sheets. In summary, there are mainly the following 6 points:
(1) Too low vulcanization temperature or too high vulcanization temperature is one of the main reasons for the foaming of thermally conductive silicone sheets. The vulcanization temperature is an important parameter in the molding of silicone rubber. Usually, the silicone products are set at 160~200 degrees Celsius, but sometimes the mold is not opened for a long time due to the long operation time outside the mold or other reasons. As a result, the temperature of the silicone molding mold is low and the vulcanization temperature of the silicone is low, which will cause bubbles in the product after the heat-conducting silicone sheet is formed. In this regard, we only need to increase the molding temperature, or open the empty mold into the machine to heat up for a period of time to solve the problem. If the vulcanization temperature is too high, the molding temperature will also cause air bubbles in the heat-conducting silicone sheet. why? My personal understanding is that when the molding temperature is too high, the silicone material on the surface has already begun to form during the mold clamping and pressurizing process. At this time, the air has been trapped inside and it is difficult to discharge, so it will cause air bubbles in the formation of the heat-conducting silicone sheet. For this reason, it is only necessary to reduce the molding temperature appropriately.
(2) Insufficient exhaust. After the silicone raw material is placed in the forming mold, a lot of air will be brought in at the moment of mold closing, and it is impossible for the air to integrate with the silicone raw material. If the air is not discharged, it will cause Bubbles are formed on the surface of the silicone keypad after molding.
(3) The structure of the mold is unreasonable. The unreasonable design of the silicone molding mold will also cause bubbles in the silicone molding. For example, the arrangement of the products in the mold, the partition method, the mold parting method, and the design of the mold size will cause bad bubbles. , but the cost of opening a set of molds is very high, and it is not easy to modify. If there are bubbles in the silicone mold due to the structure of the mold, it is usually solved from the points mentioned above.
(4) The vulcanization time is too short. Like the vulcanization temperature, the vulcanization time is also one of the important parameters for the molding of the thermally conductive silicone sheet. The length of the vulcanization time determines whether the thermally conductive silicone sheet can be completely vulcanized. If the vulcanization time is too short, it will not only cause the thermally conductive silicone sheet to become soft after molding, but also easily cause bubbles on the surface of the thermally conductive silicone sheet. Such defects can appropriately prolong the vulcanization time of silica gel.
(5) The production process is also very important: the anti-aging agent RD is prone to bubbles in the mixing operation of the mill. This is mainly due to the high melting point of the anti-aging agent RD and the low operating temperature of the mill. Special attention should be paid to the dispersion of zinc oxide during mixing. The uniformity of its dispersion will also cause foaming of the heat-conducting silica gel sheet, so the rubber mixing process is also a very important link.
(6) Whether the moisture content of the raw materials used in the formula and the operation of the compounded rubber and the drying of the product after being extruded through water and cooled are sufficient, which is mainly caused by the volatilization of water during vulcanization.
The heat-conducting silicone sheet is foamed and then pasted on the heat source to dissipate heat. Not only will the effective contact area of the heat-conducting silicone sheet be affected, but air will also enter the bubbles, thereby increasing the thermal resistance. The size of the effective contact area and the size of the thermal resistance are the two most important performance parameters for judging the thermal conductivity of a thermally conductive silicone sheet except for the thermal conductivity. Good product.

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