All properties of silicones can be customized to enable unique capabilities. Silicone Solutions product line is comprised of all custom developed silicone products. These have been developed to meet previously unmet customer needs. Some are LSR's and HCR's. Many are adhesives, sealants, coatings and gels. The unique aspects of the non-LSR's can be implemented into LSR and HCR products formulations. For a full listing of the product line, check-out http://www.siliconesolutions.com/. Silicone Solutions offers consulting and custom silicone products to industry, government and academia.
Additional capabilities include enabling: extremely high elongation, lubricity, unprimed adhesion to unusual substrates, unique rheologies, customized cure schedules, very high temperature resistance and thermal stability, very low modulus, non-bleeding gels and smart silicones.
Silicone combined with barium can be used as an x-ray marker. This application will verify the location of a medical device in the body.
A. Oil Bleeding Grades of Silicones
Source: Wacker Chemie AG, http://www.wacker.com
Self-lubricating liquid silicone rubbers from the ELASTOSIL® LR series are treated with special silicone fluids (methylphenylsilicone fluids). These fluids can be dispersed homogeneously in the rubber where, after vulcanization, they produce a self-lubricating effect that is useful for installation and assembly applications.
Physically, the incompatibility of the silicone fluid in the rubber stems from the differences in chemical potential between the liquid and solid phases in the system. This potential gradient induces passive migration of the silicone fluid. The bleeding or diffusion behavior of the oil-bleeding grades depends on the following parameters:
– Particle cross-section or size
Fluctuations in the bleeding behavior of silicone rubber articles can lead to considerable difficulties. Especially when single-wire seals or cable bushing mats are fabricated in automatic processes. For this reason, certain inter-related factors must be taken into account when self-lubricating liquid silicone rubbers are being processed:
The distance between particles depends on the crosslinking density in the silicone rubber. And this, in turn, can be controlled via different processing parameters:
– by the vulcanization conditions: injection pressure, mold temperature and heating time.
– by the hardness of the rubber: filler and crosslinker content.
– by the color: the pigment incorporated.
However, the crosslinking density is easily kept constant by using a special rubber blend and an appropriate window in a state-of-the-art process.
Aside from the oil content of the rubber blend, the pressure depends on the article’s design and the storage conditions. Small molded articles, especially, are frequently tightly packed in plastic bags and stored for protracted periods of time. Such conditions can readily cause bleeding.
Not only temperature and pressure, but the storage duration as well affect the oil content at the surface of silicone rubber articles. It is therefore imperative that storage conditions be optimized.
The storage temperature has a considerable influence on the speed of the diffusion process. Diffusion occurs much faster at high temperatures than at low ones. Therefore, seasonal temperature fluctuations can affect bleeding behavior. Especially if the finished silicone rubber articles are not stored under controlled conditions: whereas in winter it might seem that a silicone rubber article bleeds hardly at all, a similar article in summer could be
extensively wetted with silicone fluid.