Philadelphia, PA--Stockwell Elastomerics, Inc. has developed cost-saving capabilities for applying pressure-sensitive adhesive tabs and full, pressure-sensitive adhesive backings to custom-molded silicone rubber components. The components are widely used as vertically mounted gaskets for moisture and environmental sealing applications.

Traditionally, silicone rubber components that required pressure-sensitive adhesive backings were die cut from sheets of solid or sponge materials. At lower sealing pressures, however, sponge materials can lack the required moisture-sealing properties. Also, larger die cut gaskets can become expensive due to the large amount of "center" material that is discarded from the die-cutting process.

Stockwell reports that its low-durometer, custom-molded silicone rubber gaskets-with pressure-sensitive adhesives-are meeting moisture and environmental sealing requirements in numerous applications. In applications where sponge gaskets have been unable to meet moisture-sealing requirements, the company says, its silicone rubber components have been successful. This is especially true where liquid tight sealing is required of housings with low closure force.

In one case study, the company worked closely with a customer to develop triple-ribbed gaskets, custom-molded from a 20-durometer silicone rubber. It used the "shape effect" to replicate the compressibility of a sponge gasket. An RTV silicone bonding system had been under consideration as a means of adhering the gasket to the housing. However, Stockwell developed a process to apply 3M No. 9731 acrylic adhesive to the smooth underside of the molded gasket, using steel rule cutting dies to die cut the trim.

Eliminating the RTV silicone adhesive reduced the customer's assembly time. The molded rib design effectively sealed the unit and, in conjunction with the "very soft" 20-durometer silicone rubber, eliminated the customer's need to redesign the housing to increase closure force.

The company reports that production-run quantities yield molded components at a lower per-unit cost than die cutting from sheets, in addition to reducing the waste stream. Stockwell also said that molding becomes an economically viable alternative when the thickness of the gasket is .125 inch or greater, and the interior "center" mass exceeds the gasket mass by three times or more.