Silicone rubber is gaining popularity in a variety of industries because it’s able to handle harsh and demanding conditions exceptionally well. While there are several ways to produce custom, high-quality silicone rubber keypads and components, the most efficient way is by using Liquid Injection Molding. Liquid Injection Molding is a process that uses a binary liquid silicone rubber that is supplied in a closed loop system. The closed loop system helps it avoid contamination from dirt and debris that can cause problems in the production process and produce inferior parts.
Origin and Composition
Silicone rubber evolves from the inorganic origins of ordinary beach sand. The unique chemistry resulting from the silicon-oxygen (Si-O) polymer backbone is responsible for the rugged temperature stability of silicone rubber, as well as its extreme resistance to oxidation and ozone degradation. This silicon-oxygen linkage is the same as to the chemical bond found in highly stable materials such as sand and glass, and is responsible for its outstanding high temperature performance, as well as its general resistance to deterioration under high and low temperatures and harsh environments.
Many organic polymers contain unsaturated double bonds in their primary backbone, which are particularly susceptible to oxidation and ozone deterioration. The absence of any unsaturation in the silicone backbone makes it highly durable and perform exceptionally without fail for the life of the component.
Properties and Crosslinks
A number of curing agents can be added to the raw material to ensure proper curing. The most common agents for silicone rubber compounds are organic peroxides which, when heated, decompose to form free radicals that react with the pendant organic groups on the silicone polymer. The result is a crosslink between the polymer chains, the number and distribution of which influences the final physical property profile of the cured rubber.
Silicone rubber’s low relative viscosity and fast cure rate make it an excellent material for liquid silicone injection molding. Injection molding cure cycles are faster than other methods, tending to be between 0.5 and 3 minutes, depending on part size, and mold shrinkage tends to be lower than other molding methods due to high injection pressures. Balanced gates and venting are designed into the mold to avoid air entrapment and ensure complete fill in multi-cavity molds.
At Si-Tech, we use only Dow and GE materials because of their UL listing, six sigma quality rating for consistency, and traceability of material batch runs along with Liquid Injection Molding capabilities. Contact us today for more information about custom silicone rubber keypads or components at 757-887-8488 or at CS@Sitech-corp.com.
