A continuing trend within the molding business is silicone molding, which is being used in the medical, electronics, packaging and automotive industries. The injection molding of silicone has many applications due to the hardness range of the material, from 5 to 90 durometer. All of these industries have witnessed large growth trends in silicone molding—including the multi-material/two-shot molding and overmolding market segments.

 Silicone appears to be the material of choice for more and more applications, due to the following properties and benefits:

1) Inert, odorless, tasteless, stainless; ideal for medical and food applications

2) Hypo-allergenic

3) Thermal resistance; special compounds available

4) High resistance to weathering and oxidation

5) Excellent electrical qualities

6) Flexibility and durability

7) Colorfast and light stable with FL color pastes

8) Can be compounded for special properties

One needs to realize that the technology is 180 degrees opposite of what the experienced injection molder has developed throughout his or her years in the thermoplastics business. Silicone rubbers are synthetic polymers with an alternating Si-O backbone. The molecules will cross link with the addition of a catalyst, such as platinum catalyst silicones. The two parts are mixed in a predetermined ratio, forming a compound ready to be cured.

The silicone molding process is different from that of thermoplastics in a few different ways. To mold a part, thermoplastic resin is heated in the barrel and injected into a cold mold. Typically, silicone molding of a part requires the liquid rubber to be kept cool (5 to 25oC or 60 to 77oF) and then it is injected into a heated mold (170 to 210oC or 340 to 410oF).
Silicone is a material that is driving innovation not only for medical parts, but also for electronic, automotive and soft-touch applications.

  With further development of self-adhering, chemically bonded silicone, the opportunities for multi-material applications will continue to grow. To gain the knowledge of how your application will perform, it is always recommended that a prototype mold be built to determine the amount of exact shrink and gate sizes that will be right for a specific application. A typical approach is to develop a standard prototype mold frame with quick-change locks to accept a variety of cavity configurations that will fit into the nozzle pitch area. Silicone molding will be a learning process if you are going from thermoplastics to silicone, but with some knowledge and education there can be tremendous opportunities.

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