Unlike thermoplastic elastomers, which can melt and distort when exposed to high temperatures, liquid silicone rubber (LSR) offers superior physical properties that withstand extreme heat. Because of its durability, manufacturers in a wide range of industries use LSR for injection-molded parts and products that must withstand harsh conditions.
LSR is an inorganic, polydimethylsiloxane elastomer that is cured by a platinum-based chemical reaction. This process produces crosslinks that make up the backbone of the material. LSR is available in two different grades that have distinct physical properties. The general-purpose grade is characterized by low viscosity and good tear strength and tensile strength, while the electrical-grade version can resist corona discharge and other electrical stress without impacting conductivity.
Manufacturers choose to fabricate LSR components via injection molding and overmolding. The injection molding process requires no melt and can produce complex parts with tight tolerances. This manufacturing method is ideal for the fabrication of products that must withstand vibration, impact and shock. Injection-molded LSR can also be combined with resin substrates like copolyesters to create robust, durable molded parts. For instance, Dow recently introduced two new LSRs that are suitable for medical device components designed to address respiratory issues or provide external communication capabilities for patients.
The LSR injection molding process uses a cold-runner system to mix the liquid raw materials before injecting them into hot molds. This allows the LSR to cure within seconds, which is a significant advantage over the traditional reaction injection molding (RIM) process. With this fast curing cycle, the LSR injection process is perfect for high-volume production. It also ensures that the resulting part meets the exact specifications of the product designer, which is especially important when creating hygienic products like bottle nipples for nursing mothers.
In addition to its durability and elongation, LSR has high tear and tensile strength and flexibility. It can also withstand a wide temperature range, making it an excellent choice for automotive parts that must be placed in close proximity to engines. The material is also fire retardant, meaning that it can withstand high temperatures without melting.
Many of the same benefits offered by LSR are also found in other types of silicone, such as fluorosilicone. This type of rubber is particularly effective for applications that require resistance to chemicals and oils, as well as extreme temperatures. However, the UL 94 HB rating is not as high for fluorosilicone as it is for general-purpose LSR.
In the past, most manufacturers chose to fabricate their products using plastics because they were strong, lightweight and affordable. But these materials often cannot withstand extreme temperatures, which can warp, discolor or break them. That is why a growing number of manufacturers have switched to the more durable LSR, which can be used in a wider variety of products than other types of elastomers. The high-performance properties of this material also allow it to be pigmented, so manufacturers can customize their products to match human skin tones. In the end, it is this versatility that makes the LSR a popular choice for manufacturers of everything from nipple protectors to power cords.