Silicone rubber production involves several key ingredients and components. The formulation can vary depending on the type of silicone rubber being produced (e.g., Liquid Silicone Rubber (LSR), High Consistency Rubber (HCR), Room Temperature Vulcanizing (RTV) silicone, etc.), and the specific properties desired in the final product. However, the primary ingredients used in silicone rubber production generally include:
1. Siloxane Polymer (Base Polymer)
- Description: The main ingredient in silicone rubber is a polydimethylsiloxane (PDMS) polymer, which consists of a siloxane backbone (Si-O-Si) with organic side groups (usually methyl groups).
- Function: The siloxane polymer provides the basic rubbery, elastic properties of silicone. The molecular weight of this polymer affects the viscosity, flexibility, and mechanical properties of the silicone rubber.
2. Cross-Linking Agents (Curing Agents)
- Addition Curing Agents: Platinum catalysts are used in addition-cure systems (also called platinum-cure systems) where vinyl-terminated PDMS reacts with a cross-linker, typically a silicone hydride compound, to form a cross-linked network.
- Peroxide Curing Agents: In peroxide-cured silicone rubbers, organic peroxide compounds (e.g., benzoyl peroxide or dicumyl peroxide) decompose at high temperatures to generate free radicals, initiating cross-linking between polymer chains.
- Condensation Curing Agents: Condensation cure systems use moisture and release by-products (like alcohol or acetic acid). Typical curing agents for this type are alkoxysilanes or acetoxysilanes.
- Function: Cross-linking agents bond the PDMS polymer chains together to form a three-dimensional network, giving silicone rubber its solid, elastic structure.
3. Fillers
- Reinforcing Fillers: Fumed silica is a common reinforcing filler in silicone rubber. It increases the strength, stiffness, and tear resistance of the rubber without significantly reducing elasticity.
- Non-Reinforcing Fillers: Calcium carbonate, aluminum oxide, or quartz can be used as non-reinforcing fillers to reduce cost, modify specific properties, or increase heat resistance.
- Function: Fillers modify the mechanical, thermal, and processing properties of the silicone rubber. Reinforcing fillers are essential for providing strength and durability.
4. Plasticizers
- Examples: Silicone oils (low-molecular-weight PDMS) are commonly used as plasticizers in silicone rubber formulations.
- Function: Plasticizers improve flexibility, elongation, and flow properties. They reduce the stiffness of the rubber and make it easier to process, especially in LSR applications where flow is crucial.
5. Pigments and Colorants
- Examples: Various pigments (e.g., titanium dioxide for white, carbon black for black) or other colorants are added depending on the color requirements.
- Function: Pigments give the silicone rubber its color. They are essential for creating visually distinct products or meeting aesthetic requirements.
6. Heat Stabilizers
- Examples: Iron oxide, cerium oxide, and certain types of silicone oils.
- Function: Heat stabilizers improve the thermal stability of silicone rubber, allowing it to withstand higher temperatures without degrading. They are particularly important in applications where silicone rubber will be exposed to high heat for extended periods.
7. Flame Retardants (Optional)
- Examples: Flame retardants like platinum complexes, or additives such as aluminium trihydrate (ATH) and magnesium hydroxide.
- Function: Flame retardants are added to silicone rubber used in applications where fire resistance is required. They inhibit the spread of flames and reduce smoke generation.
8. UV Stabilizers and Anti-Oxidants (Optional)
- Examples: UV absorbers like benzophenone derivatives or hindered amine light stabilizers (HALS).
- Function: UV stabilizers protect silicone rubber from degradation due to ultraviolet light exposure, extending its outdoor durability and lifespan.
9. Release Agents (for Processing)
- Examples: These can include additives that prevent the silicone rubber from sticking to molds, such as stearates or silicones with low surface energy.
- Function: Release agents improve mold release and prevent the silicone from adhering to processing equipment, which is especially useful in injection molding.
