The transparency of key compounds is directly related to the transparency of white carbon black, so white carbon black with better transparency can be selected.
In terms of formula and process, the transparency of the mixed rubber is not good, indicating that the surface hydroxyl treatment of the white carbon black is insufficient, which affects the transparency of the mixed rubber. That is to say, the hydroxyl silicone oil we added is not sufficient to treat the hydroxyl groups on the surface of white carbon black, indicating the presence of some pseudo hydroxyl groups in the hydroxyl silicone oil, and some substances that did not participate in the reaction are extracted during vacuum or heat treatment. At the same time, it also indicates that the binding between white carbon black molecules and raw rubber molecules is incomplete or the binding time is not enough, and adjustments can be made from the process. Raw rubber and white carbon black are first mixed at room temperature, and the hydroxyl groups on the surface of white carbon black are treated with a combination of hydroxyl silicone oil and alkoxysilane in the formula. Then, they are cured at 30-40 ℃ for about 8 hours, and then vacuumed to improve the transparency of the mixed rubber. At the same time, in addition to physical properties, key adhesive should also control key force and fatigue life. We can use instruments to test and control its indicators within a certain range.
How to improve the structure of existing mixed rubber?
Structured mixed rubber is a mixture of hydrophilic silica and raw rubber that gradually hardens, decreases plasticity, and loses the process performance of tempering molding during storage. The main reason for the formation of structural rubber compounds is that the silicon hydroxyl group on the surface of silica interacts with the silicon oxygen bond in the raw rubber molecule or the terminal hydroxyl group in the raw rubber molecule to produce hydrogen bonds, or even chemical bonding, which changes the linear polysiloxane into the solid structure of the pseudo crosslinked semi elastomer, reduces the solubility of rubber compounds, and increases the gel content.
Generally speaking, the plasticity of compounds can be restored through backmixing, and the length of backmixing time depends on the severity of the compound's structure. In order to reduce the hydrogen bonding and structural degree of the compound, structural control agents such as hydroxysilicone oil or alkoxysilane can be added, and an appropriate amount of dimethyl silicone oil can be added to regulate the flow performance of the compound. Adding too much hydroxysilicone oil to the rubber material can lead to a sticky feel and slow vulcanization speed. Therefore, it is necessary to find a suitable balance point to control each type of rubber material within a suitable range of plasticity values. Low or high plasticity can have an impact on the later processing of products. If the plasticity is low, the rollers may stick during the processing, and there may be mucous membranes during the product production process. If the plasticity value is too high, it will lead to poor structural and flowability of the rubber material, and the product may lack glue or flow marks.
It can also be improved from the production process of mixed rubber. We are currently using a one-step method for mixed rubber production, which results in incomplete bonding between white carbon black and raw rubber. Although there are no obvious abnormalities on the surface, small white spots can sometimes be observed in the rubber material, which can be produced through the process of mixing (at room temperature) - vulcanization - internal mixing, thereby improving the bonding degree between white carbon black and raw rubber and improving the structure of the mixed rubber.
Regarding silicone rubber, please refer to the details:
https://www.htvsilicone.com/product-general-purpose-fumed-type-silicone-rubber-for-molding-.html 
