Medical-grade polycarbonate is widely manufactured into infusion connectors, transparent instrument shells and minimally invasive medical accessories, which are required to satisfy USP Class VI and ISO10993 biocompatibility standards and withstand EO and gamma sterilization. Unlike conventional general plastic molding, medical PC production requires strict full-chain supervision covering raw material management, cleanroom production, mold maintenance and parameter control. Improper operation will trigger hydrolysis speckles, harmful substance precipitation and post-sterilization cracking, leading to batch scrapping. Formulated based on mature production experience of China’s injection molding industry, this specification standardizes each working link to secure long-term stable qualified output.
1. Raw Material Acceptance and Preprocessing StandardsAll incoming medical PC pellets must attach original COA certification, biocompatibility test reports and sterilization performance documents. Non-medical recycled plastic and mixed heterogeneous raw materials are forbidden to blend into qualified stocks. Raw material warehouse keeps constant temperature from 20℃ to 25℃ and humidity below 55%; leftover pellets after package opening need immediate vacuum sealing to block moisture invasion. PC is highly hygroscopic, and moisture content over 0.02% causes hydrolysis and silver marks during high-temperature melting. Raw materials are dried in closed dehumidifying hoppers at 120℃ for 4 to 6 hours with dryer dew point below -40℃, and material stacking height inside hoppers is limited under 25mm. Dried pellets cannot expose in non-clean environment over 30 minutes; overtime materials must go through full re-drying, while high-precision transparent products demand extra moisture testing to control water content under 0.015%. During barrel purging for grade switching, only brand-new medical PC is permitted for machine cleaning. Runner scraps are generally banned from recycling; only non-liquid-contact parts can adopt recycled scraps within maximum 5% proportion.
2. Cleanroom Environment and Equipment Sanitation Control
Ordinary medical consumable production workshops comply with ISO8 (100,000-grade) cleanroom criteria, while implant and body-fluid-contacting component workshops upgrade to ISO7 (10,000-grade). Indoor temperature maintains 18~26℃ and relative humidity ranges 45%~60%, supported by HEPA filter and vertical laminar flow system with daily microbial and particle inspection recorded completely. Operators receive 30-second air shower before entry and wear full-body dust-free suits, nitrile gloves and lint-free masks without any metal ornaments. Full-electric servo molding machines are preferred to separate hydraulic oil from molten plastic for anti-pollution purpose. Feed hoppers and screw joints adopt fully enclosed design; operators disassemble and wipe feeding positions with dust-free cloth per shift. Silicon-containing releasing agents and oily anti-rust grease are prohibited, and only medical dry-type lubricant is available for mold moving part maintenance.
3. Mold Design and Daily Maintenance SpecificationsMedical PC molds select S136H pre-hardened stainless steel for cavity with SPI-A1 mirror polishing to avoid rust precipitation hidden risk of ordinary mold steel. Mold cavity reserves shrinkage tolerance from 0.5% to 0.7% matching PC actual shrink rate; main runner taper is designed between 3° and 5°, and thin-wall components adopt hot runner layout to cut weld line and sprue waste. Conformal surrounding cooling channels keep mold temperature fluctuation within ±1℃ and balance cooling efficiency to reduce residual stress. New molds implement ultrasonic cleaning and plasma impurity removal before formal mass production; full mold deep cleaning is arranged every 5000 production shots, and key dimensional data is periodically verified via CMM inspection. Idle finished molds are stored in dry dustproof warehouse after medical-grade anti-rust treatment.
4. Graded Injection Molding Parameter Standards
Barrel temperature adopts segmented gradient setting: rear feeding zone 270~280℃, middle compression zone 285~295℃, front nozzle section 285~295℃, and overall melt temperature strictly limited below 305℃ to prevent thermal degradation and yellowing. Mold temperature is adjusted according to wall thickness: conventional 2~4mm products keep 85~95℃, ultra-thin transparent parts raise to 95~110℃ to improve melt fluidity and lower internal stress. Multi-stage speed and pressure setting is adopted: low initial injection speed avoids jetting, medium speed fills cavity and terminal slowdown stabilizes packing. Injection pressure is 80~110MPa with three-step descending packing pressure, backpressure controls 0.4~0.7MPa and screw speed remains 40~60rpm for low-shear molding. Cooling duration is customized by wall thickness to guarantee full cooling and prevent internal vacuum bubbles and ejection deformation.
5. Post-treatment and Finished Product Quality ControlComponents needing subsequent sterilization receive constant-temperature annealing at 55~65℃ for stress elimination to avoid cracking after sterilization. Semi-finished goods are sorted inside clean area to pick out defective pieces with scratch, bubble and silver streak defects, and qualified items are packed with sealed sterile PE bags to isolate external contamination. Every production batch reserves test samples for biocompatibility and precipitation detection; all information including raw material batch number, molding parameters and inspection records is archived to realize full-process traceability satisfying medical industry compliance demands.
