Medical-grade polyvinyl chloride (PVC) or polycarbonate (PC) are mostly used in disposable medical devices. The thermal decomposition products in the processing of PVC have strong corrosiveness to steel, while PC has high hardness and viscosity, so the parts and components of plasticized parts must have high corrosion resistance, wear resistance and polishing performance. At present, most medical injection molding machines use hard chromium or stainless steel plating on the barrel screw to make a simple screw to meet the above special requirements. In addition, in order to prevent the gas generated by thermal decomposition during PVC processing, it is required to aluminize the surfaces of the movable template and the fixed template, and at the same time, aluminize the surrounding metal sheets or make metal sheets with stainless steel plates, and seal the flat seams of the metal sheets with non-toxic silica gel to prevent the gas generated during plastic processing from being emitted to the outside (the gas generated during plastic processing can be collected by special equipment, purified and discharged into the atmosphere).
Harm of DEHP, a common additive for PVC: DEHP (phthalate) is easy to atomize, and other vinyl products, including automobile interiors, shower curtains or floor materials, also release toxic gases into the atmosphere, and DEHP is also easy to dissolve into oily liquid. In addition, people have begun to pay attention to the safety of additives oozing out when children chew these soft plastic toys. Some studies show that this additive may complicate health problems, but further research is needed. According to some medical research, PVC plasticizer may cause chronic diseases, such as scleroderma, cholangiocarcinoma, angiosarcoma, brain cancer and acroosteoporosis. In 2004, a research team composed of Swedish and Danish scholars found that DEHP and BBzP commonly used in PVC have a strong correlation with children's allergies. For unplasticized polyvinyl chloride (U-PVC), there is no leakage of DEHP because there is no plasticizer, but stabilizers are usually added during processing. At present, most of them are lead salt stabilizers. Lead is a toxic substance, which will leak out during use and endanger human health. Similarly, it cannot be ignored. At present, there are non-lead salt stabilizers, but the cost is high and they are not popularized.