Medical-Long Term Implantable Silicone designed to stay in the body normally as part of an implantable device. This grade is generally too expensive for Menstrual cups and food grade applications.
Medical-Healthcare Grade, Class VI Silicone, tested for Biocompatibility. Medical Class VI is the material choice for Casco Bay Molding’s Menstrual Cups, Baby Bottle Nipples, food skin contact, Scuba Athletic Mouthpieces.
Both Medical-Healthcare Grade, Class VI Silicone and Medical-Long Term Implantable Silicones are considered safe for food contact. Both grades are almost always LSR (liquid silicone rubbers) that are normally processed via injection molding.
There are four major types Silicone commercially available:
LSR- Liquid Silicone Rubber: LSR is designed for injection molding and is almost always Medical Grade Silicone delivered to processors in two sealed drums or 40 lbs. buckets. One drum/bucket has catalyst, the other has the cross linker. LSR advantages are that it is pumped directly from the drum/bucket into the molding machine with little to no possibly of modifying the material with the exception of silicone colorant. Most medical parts are LSR.
HCR- High Consistency Rubber: Premixed, playdough-like that starts with a “base stock” of silicone then a catalyst and fillers/additives are added to silicone base stock on a two roll mill. Once this step is complete, the HCR is brought to the compression molding press (to make parts) or extruder (to make tubes).
HCR has the advantage of being able to mix in different additives or fillers to change the Silicone’s physical characteristics. This can also be a disadvantage if the additive filler amounts and ingredients are not shared with the end user. It is also tempting to use extra filler (filler is much cheaper the silicone base) to make more parts with the same amount of silicone base material. Frequently evidence of filler can be seen in wrist bands, children’s toys and even menstrual cups that turn white when stretched. HCR can be a Platinum, Peroxide or Tin cure system, see below for more info on cure systems.
FSR- Fluorosilicone Rubber: flame resistant, brake fluid resistant silicone used mostly in the auto industry.
RTV- Room Temperature Vulcanize Silicone: RTV solidifies or vulcanizes at room temperature. It is used in prototype parts Silicone caulks fall into this category.