China Medical Plastic Bottle Injection Mold Design: Molding Requirements for Cleanroom

Medical plastic bottles are used for liquid medicine and reagent storage. The products contact medium directly, with strict standards for cleanliness, extractable substance and dimensional stability. Mold design cannot follow the scheme of ordinary packaging parts. Cleanliness control should be integrated in material selection, structure layout, venting, demolding and maintenance, to control particles, oil stain and debris pollution and meet medical industry specifications.

1. Mold Material and Surface Treatment for Cleanliness

Cavity and inserts adopt corrosion-resistant, low-precipitation stainless mold steel such as S136 and 420SS. Impurity and inclusion content in steel are strictly controlled to reduce pitting and particle peeling during long-term production. High-grade mirror polishing is applied on molding surface to eliminate tiny pits and gaps that trap residual plastic and carbon deposit. Drop-proof and low-precipitation PVD coating can be used for wear resistance. Ordinary nitriding is not recommended for its loose surface layer. Fasteners, locating pins and springs use stainless steel of matching grade to avoid rust debris.

2. Runner System Design with No Material Stagnation and Easy Cleaning

Stagnant melt in runner will decompose at high temperature and produce black spots, volatile matter and debris. Valve hot runner is the preferred option, with smooth internal flow channel and rounded transition at corners to eliminate dead zones. Each hot runner zone realizes independent temperature control to prevent local overheating and material decomposition. Gates are set on non-liquid-contact area of products, with clean cut to reduce wire drawing and falling debris. Cold runner design keeps short flow path and smooth section for fast disassembly and cleaning.

3. Venting System for Volatile Matter and Particle Control

Small molecular volatile matters released from melting plastic will form scale on cavity surface and fall off as foreign particles if gas cannot be discharged smoothly. Vents are set at melt convergence and flow end. Vent depth matches plastic material to exhaust gas without flash. Dedicated vent inserts can be detached separately for carbon deposit cleaning without full mold disassembly. Vacuum exhaust is equipped for advanced molds to reduce residual gas inside cavity.

4. Anti-Pollution Design for Ejection and Core-Pulling Mechanism

Common lithium-based grease is forbidden in cleanroom, for oil vapor and dripping will cause over-limit extractable substance. The structure of lifters, sliders and ejector pins is simplified to reduce friction pairs. Self-lubricating wear-resistant parts are used to cut lubrication demand. Only medical-grade dry lubricant can be used when lubrication is necessary. Ejector pins are arranged away from the inner surface of bottles, and ejection movement keeps stable to reduce plastic micro powder from friction.

5. Cooling Circuit and Anti-Leakage Sealing Design

Seals of cooling circuit must be reliable to prevent cooling water leakage into cavity and parting surface. Sealing ring material meets low-extraction requirement. Independent cooling loops stabilize mold temperature and reduce internal stress and molecular migration risk. Water baffle structure is set at water interface to avoid condensate dripping on cavity and molded parts.

6. Dust-Proof Design for Parting Surface and Whole Mold

Sealing area of parting surface keeps flat to reduce hidden dirt gaps. Dust-proof groove is arranged outside the parting surface to block suspended particles in cleanroom air. Outer non-forming surface of molds is designed smoothly with less grooves to avoid dust accumulation. Dust cover made of non-shedding fiber material is equipped for mold standby and storage.

7. Mold Trial and Maintenance Specification for Cleanroom

Molds are fully cleaned before trial molding. Lint-free cloth and dry clean air are used to blow cavity and runner to remove dust and oil before installation. Regular cleaning cycle is set in mass production for vents, parting surface and ejection parts. Mold disassembly and repair must be operated in clean environment. Cleaning log is built to record cleaning time, position and foreign body inspection. Purge hot runner and cavity before material change or long shutdown to remove stagnant melt.