Polycarbonate (PC) Injection Molding Process

1. Material Processing

Polycarbonate (PC) is highly hygroscopic and absorbs moisture easily. Proper drying before processing is critical to avoid defects such as bubbles, silver streaks, or discoloration during injection molding.

• Drying Conditions:

• Pure PC: 120 °C for 4–6 hours

• Modified PC: 110 °C for at least 4 hours

• Maximum drying time: Do not exceed 10 hours

• Dryness test: Use the air extrusion method to confirm proper drying

• Recycled Material Usage:

• Standard: Up to 20%

• Maximum: Can reach 100% depending on product quality requirements

• ⚠️ Do not mix recycled materials containing different masterbatches—this compromises product integrity

2. Injection Molding Machine Selection

Modern PC molding—especially for flame-retardant or alloyed PC materials—requires specialized machines due to the high viscosity and thermal sensitivity of PC.

• Requirements:

• A corrosion-resistant plasticizing system

• High mixing capability

• Dedicated PC screws are preferred for consistent melt and material protection

• Conventional screws are unsuitable for flame-retardant or glass-filled PC

3. Mold and Gate Design

Proper mold and gate design helps prevent shear-related defects and promotes better material flow.

• Mold Temperature:

• Standard PC: 80–100 °C

• Glass-filled PC: 100–130 °C

• Gate Types & Sizes:

• Pinpoint gates for small parts

• Gate depth: ~70% of the part's thickest section

• Larger gates reduce shear-induced flow marks and improve fill

• Runner & Venting:

• Runner: Short and round to minimize pressure drop

• Vent depth: 0.03–0.06 mm

• Ejection slope: 30′ to 1°

4. Processing Parameters

• Melt Temperature:

• Standard PC: 270–320 °C

• Modified/low molecular weight PC: 230–270 °C

• Injection Speed:

• Typically medium to fast

• For precision electrical parts, use gradual acceleration from slow to fast

• Injection Pressure (Packing):

• Standard: ~10 bar

• Adjust as needed based on part geometry and visual quality (e.g., flow lines or color mixing)

5. Dwell Time & Cleaning

PC is sensitive to thermal degradation. Extended residence time at high temperatures will cause discoloration, bubble formation, or gas emissions.

• Cleaning Guidelines:

• If downtime is expected, purge the barrel with general-purpose PS (polystyrene)

• ⚠️ Do not use LDPE, POM, ABS, or PA as purging agents—they can chemically react with PC

• Prevent PC from sitting idle at high temperatures to avoid yellowing and CO₂ release

6. Special Notes & Recommendations

• Recycled PC with decreased molecular weight or poor blending often results in dark brown bubbles or visible degradation in molded parts.

• For high-quality optical or structural parts, standard injection units may not provide sufficient precision or consistency.

• A specialized injection barrel designed for high-density PC is recommended for best results.

Work with a Professional Polycarbonate Molding Supplier

High-performance polycarbonate injection molding requires technical expertise, precision tooling, and specialized equipment. Whether you're producing clear lenses, structural components, or flame-retardant housings, choosing the right partner is key.

Looking for reliable PC injection molding services?
SWY MOULD specialize in high-quality polycarbonate mold design and molding production. Contact us (shine@swymould.com or +86 15757668880) to discuss your project today!