In the silicone industry, a wide variety of coatings are implemented to enhance the physical properties of silicone products. There are many benefits of using chemical coatings, which include, but are not limited to: increased chemical resistance, decreased coefficient of friction, and decreased permeability to moisture.
Amongst the many types of chemical coatings available for silicone products, Parylene coatings are one of the most commonly used materials for silicone products in the food and medical sectors. Parylene is the colloquial name for a series of vapour-deposited coatings that provide chemical and moisture resistance to a range of different products. Parylene-C is the most popular type of Parylene coating used in the silicone industry, due to its ease of application, low cost, and the significant barrier properties it provides. Below is the chemical structure of a Parylene-C monomer, as well as its raw dimer form, known as diparaxylene.
Currently, Parylene-C coatings are used in the silicone industry to provide a low-friction, almost impervious barrier that can resist chemical attack and high electric currents. The inert, non-toxic properties of Parylene-C make it an ideal coating for silicone materials in the medical industry. Additionally, Parylene-C coatings are FDA approved, which make it an ideal coating for silicone products in the food industry. Furthermore, the high level of coating thickness control during the vapour deposition process can allow Parylene-C coated products to be used in high-precision instruments, such as seals in medical sterilisers.
Parylene-C is a thin conformal coating, meaning that it conforms to the topography of the material it is applied to. This is very beneficial for products such as oddly-shaped silicone extrusions, that may not be compatible with other forms of coatings. The ability of Parylene-C to conform to the topography of the given product is due to its unique vapour-deposition application process. Additionally, the vapour-deposition of the Parylene-C coating is normally conducted at room temperature, with no additional catalysts or solvents needed, which allows for the coating of thermo-sensitive or delicate products.
The application process of Parylene-C, while relatively simple, is an integral factor of the effectiveness of Parylene-C coatings. Raw, solid Parylene-C dimer is vapourised into a gas at 100-150°C and is split into individual Parylene-C monomers following exposure to temperatures >500°C. Under vacuum, the monomer gas is pulled into a deposition chamber, in which the desired product is coated at room temperature as the monomer gas polymerises into a solid, uniform coating. The product is removed to storage, and a cold trap at -100°C following the deposition chamber is used to remove residual Parylene-C.
At Jehbco, we strive to provide the perfect silicone product for your needs. For further information or advice about which silicone rubber and coating best suits your application, please review the Jehbco website www.jehbco.com.au, and contact us with any questions