A: Addition silicone rubber is the most actively developed product series among silicone materials in recent years. Compared with other silicone rubbers, it has the following advantages: no by-products are produced during the vulcanization process, the shrinkage rate is small, and it can be deeply cured. The material is non-corrosive, the production process is safe and environmentally friendly, the molding cycle is short, the degree of automation is high, the finished product has good strength, is transparent, odorless, and can easily reach food grade, medical grade, etc. Therefore, addition silicone rubber is increasingly used in medical, food, electronic appliances, packaging, smart wearable devices and other fields.
Addition silicone rubber is made by hydrogen-containing polymers (such as vinyl raw rubber, vinyl silicone oil, vinyl silicone resin, etc.) and hydrogen-containing polymers (such as hydrogen-containing silicone oil, hydrogen-containing silicone Resin) is cross-linked to form a silicone elastomer with a network structure; during this process, a catalyst must be added to allow the hydrosilylation reaction to proceed. The most widely used catalyst with the highest catalytic efficiency and the highest cost performance is platinum catalyst (commonly known as platinum water).
Traditional platinum catalysts can be divided into the following categories:
1. Solvent-based Speier catalyst: a solution of chloroplatinic acid in isopropyl alcohol, ethanol, etc.; this catalyst is simple and quick to make and easy to use; but the disadvantages are low catalytic efficiency, yellow color, and easy oxidation. Therefore it is only used in a few special products and industries.
2 Karstedt PT5000-TMDVDS600 (Karstedt's) catalyst: a complex of chloroplatinic acid and vinyl double-heading; this catalyst has high reactivity, light color, good storage stability, and good compatibility with silicone products . Therefore it is the most widely used in industry.
3. Delayed platinum Ashby’s catalyst PT5000-VMC1000: a complex of chloroplatinic acid and vinyl ring; this catalyst has high reactivity, good yellowing resistance, and excellent storage stability. It is mostly used in products and industries with high appearance requirements.
4. The first domestic microencapsulated platinum platinum catalyst PT5000D/PT2500D (Microencapsulation)
Microencapsulated platinum catalyst background technology and application fields:
In the field of silicone, the main curing and cross-linking methods of silicone rubber include peroxide cross-linking, UV curing, addition cross-linking, and condensation cross-linking. Among them, peroxide cross-linking is mainly suitable for high-temperature adhesive systems; UV curing requires special equipment and cures quickly, but the equipment is expensive and may have certain negative effects on health; condensation cross-linking releases small molecules during the curing process. The complete curing time is too long and is not suitable for high-precision application scenarios: the addition cross-linking method has low curing requirements because it does not produce by-products. It can be cured and cross-linked at room temperature and is widely used. However, the curing process is difficult to control. The problem. In order to control the curing process, traditional addition silicone rubber usually separates the cross-linking agent and catalyst during application, and then mixes them together for cross-linking. This is not only inconvenient to use, but also complicated to operate. The existing addition-type silicone rubber controls the curing process by adding one or more inhibitors in addition to the cross-linking agent and catalyst. Among them, inhibitors are non-metals and their compounds with unshared electron pairs, unsaturated compounds and heavy metal ion compounds. This type of substance can significantly inhibit the activity of the platinum catalyst, and as the amount of inhibitor added increases, this addition type silicone rubber product can be stably stored for 3 to 7 months in an environment below 10°C, but its curing cross-linking is common. It is required to heat to 100~200℃ and the heating time is 10~60 minutes. In addition, capsule-type platinum catalysts made of acrylic acid and polyperoxide have also been reported. For example, polyvinyl chloride is used as the wall material of the capsule and a platinum catalyst is coated in the middle to prepare a microcapsule platinum catalyst. The advantage of this preparation method is that the intermediate platinum catalyst is not easy to leak out, which facilitates the processing of the product. However, the catalyst needs to be heated to above 100°C to play a catalytic role. Another example is the direct use of polycaprolactone as the wall material of capsules to prepare microencapsulated catalysts. Although the curing temperature point is relatively low, polycaprolactone itself is easily degraded under natural conditions, so it is used to prepare addition-type catalysts. There is a risk of easy leakage during storage of silicone rubber. Therefore, how to provide a catalyst that is stable at room temperature and has a low softening point to prepare an addition-type silicone rubber that is easy to store and transport and can be assimilated at low temperatures has become An objective need.
Platinum catalyst
