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Product details
LIQUID SILICONE RUBBER (LSR) LSR is designed for injection molding and is almost always medical grade. This is delivered to us in either two sealed drums or 40 lb buckets. One drum/bucket has a catalyst, the other has the crosslinker. The advantage of LSR is that it’s pumped directly from the drum/bucket into the molding machine with little to no possibility of modifying the material. The exception to this is if you add a colorant. For this reason, most medical parts are LSR. HIGH CONSISTENCY RUBBER (HCR) HCR is premixed and has a playdough-like texture. High Consistency Rubber starts with a “base stock” of silicone. Then, a catalyst and fillers/additives are added on a two-roll mill. After this, HCR is brought to the compression molding press to make parts or extruder to make tubes. HCR can be a platinum, peroxide, or tin cure system, see below for more info on cure systems HCR has the advantage of being able to mix in different additives or fillers to change its physical characteristics. This can also be a disadvantage if the additive and filler amounts and ingredients are not shared with the end-user. It is also tempting for manufacturers to use extra filler — filler is much cheaper than food safe silicone rubber — to make more parts with the same amount of silicone base material. HIGH TEMP SILICONE CURING There are different ways to “cure” silicone rubber. Curing is a chemical process during which the material transitions from a liquid or gel to a solid. It typically occurs when the material is exposed to oxygen, though there are different ways to accelerate the process. There are several different catalysts that a manufacturer can add. Liquid silicone rubber and HCR cure quickly when exposed to high heat (350F +/- 60F). At room temperature, it may take days for LSR or weeks for HCR to cure. That isn’t ideal for most manufacturers or product lines. With that in mind, most use a curing system. The following are the three most common you’ll encounter. PLATINUM SILICONE LSR is almost always platinum-catalyzed. However, properly molded platinum menstrual cups do not need to be post cured. Platinum cured LSR is generally medical grade silicone and what we use at Casco Bay Molding. PEROXIDE A good deal of HCR silicone is peroxide cured and used for extrusion, transfer, or compression molding. Peroxide cured HCR needs to be post-baked in order to remove the volatiles. This can be a time-consuming and expensive step. If a company tries to cut costs by shortcutting the necessary post-bake step, volatiles can remain in the material. Peroxide cure systems are generally much less expensive than platinum systems but require a time-consuming post-bake. Casco Bay Molding does not do extrusion or compression molding. Our expertise lies in medical grade silicone production and design, for which injection molding is most suitable. TIN CONDENSATION CURE SYSTEMS The third type of curing system, tin condensation is not recommended for healthcare or medical applications. This is because the tin (Sn) remains in the compound after curing.
