Global Silicone Network reported on January 16: The reaction mechanism of platinum vulcanized silicone is a hydrosilylation reaction, that is, Si-Vi vinyl-containing polymers (such as vinyl silicone rubber, vinyl silicone oil, vinyl silicone resin, etc.) and Si-H hydrogen-containing polymers (such as hydrogen-containing silicone oil, hydrogen-containing silicone resin) undergo cross-linking reaction under the catalysis of platinum catalyst to form a network-structured silicone elastomer.
Compared with other polymer materials, platinum vulcanized silicone rubber has the following advantages: no by-products during the vulcanization process, small shrinkage, deep curing, no corrosion to the contacting materials, safe and environmentally friendly production process, short molding cycle, high degree of automation, good strength of finished products, transparent, odorless, easy to reach food grade and medical grade, etc. Therefore, it is increasingly widely used in medical, baby, electronic power, wearable devices, silicone leather, new energy vehicle silicone foam and other fields.
In addition-type silicone, platinum catalyst must be added to make the hydrosilylation reaction proceed. However, the activity of platinum catalyst is very high. After mixing with vinyl polymer and hydrogen-containing polymer, the operation time is very short. Cross-linking will occur quickly within a few seconds or minutes, resulting in poor fluidity of silicone rubber or even dead rubber, which cannot be used. Therefore, it is generally necessary to add inhibitors (retarders) to the formula to adjust the curing speed.
The working principle of the inhibitor is to form a coordination bond with the platinum catalyst at room temperature to prevent the coordination between Si-H and Si-Vi; after heating to a certain temperature, the coordination bond weakens or decomposes, restoring the activity of the platinum catalyst, and Si-H and Si-Vi can react quickly. The more inhibitors are added, the better the inhibitory effect and the longer the room temperature operation time, but correspondingly, the high temperature vulcanization speed will also slow down.
The most commonly used inhibitor in the silicone industry is ethynyl cyclohexanol, with molecular formula: C8H12O, molecular weight: 124.18, melting point 30℃-33℃, slightly yellow transparent liquid at high temperatures, and white crystals at low temperatures. Ethynyl cyclohexanol has the advantages of good inhibitory effect, small addition amount, strong applicability, and moderate cost. It is widely used in addition-type platinum vulcanized silicone rubber and food, baby, medical, consumer goods and other industries.
However, ethynyl cyclohexanol also has some disadvantages:
1. It is easy to freeze in autumn and winter, which is inconvenient to use;
2. There is still a small amount of odor;
3. The storage time of the prepared rubber at room temperature is not ideal;
4. Platinum extruded silicone rubber products that are vulcanized by hot air are prone to bubbles.
