Material selection for medical-grade injection molds must adhere to the "Three Nos" principle: non-adsorbing, non-reactive, and easy to clean.
1. Highly corrosion-resistant base materials
Martensitic stainless steel (e.g., 316L, 420SS) is the preferred choice. Containing elements such as chromium and nickel, these steels offer corrosion resistance 5–8 times greater than standard mold steels, enabling them to withstand prolonged exposure to disinfectants like medical-grade alcohol and sodium hypochlorite. For instance, a mold used to produce IV set connectors made from 316L stainless steel showed no rust or corrosion pits on its surface after undergoing a 1,000-hour salt spray test.
Surface hardening treatments: Vacuum quenching (achieving a hardness of 52–56 HRC) and nitriding (surface hardness ≥1000 HV) are employed to enhance scratch resistance, preventing dirt and contaminants from accumulating in microscopic scratches. After nitriding, the surface roughness of a medical syringe mold was reduced from Ra 0.8 μm to Ra 0.2 μm, making it difficult for stains to adhere during cleaning.
2. Careful selection of non-metallic materials
Fluoroelastomers for sealing rings: While ordinary rubber tends to age and leach small molecules, fluoroelastomers (such as Viton) are chemically resistant and do not release organic compounds. When used for sealing mold parting lines, they ensure that particulate contamination within a Class 10,000 cleanroom remains below 0.1 mg/m³.
Food-grade lubricants for guide rails: Traditional lubricants may contain impurities such as sulfur or phosphorus; therefore, medical molds require white oil (mineral oil) or silicone-based grease that has passed ISO 10993 biocompatibility testing to prevent lubricant contamination of the finished products.