How to Produce Qualified Translucent Plastic Parts?

To produce qualified translucent plastic parts, the key is to strictly control material purity, mold precision, injection molding process and post-treatment, and minimize bubbles, internal stress, haze, weld lines and surface defects throughout the process.

1.Material Selection & Pre-treatment (Foundation)

1.1 Material Selection

• Common translucent materials: PMMA, PC, transparent PP, PETG, SAN, transparent ABS.
• Key requirements:
• High purity, low impurities, low residual monomers.
• Refractive index of additives (plasticizers, stabilizers, antioxidants) matches the base resinto avoid light scattering.
• Avoid additives that are prone to precipitation or degradation.

1.2 Drying (Critical but often overlooked)

• Hygroscopic materials (PC, PMMA, PETG) must be dehumidified and dried; moisture content ≤ 02%.
• Typical drying parameters:
• PC: 120°C, 4–8 h
• PMMA: 80–90°C, 3–4 h
• Transparent PP: 80–90°C, 2–4 h
• Equipment: Preferred dehumidifying dryer, avoid hot-air drying.

1.3 Mixing & Plasticization

• Uniform mixing, avoid agglomeration or local enrichment of additives.
• Medium-low screw speed + proper back pressureto ensure uniform melt and sufficient venting.

2.Mold Design & Machining

2.1 Runner & Gate

• Runner: round, large diameter, large taper, smooth transition, no dead corners.
• Gate: Preferred fan gate, submarine gate, pin-point gate; gate polished to Ra < 0.2 μm.
• Sufficient cold slug well to prevent cold material entering the cavity.

2.2 Cavity Surface

• Mirror polishing: Ra ≤ 0.05 μm, diamond + ultrasonic polishing.
• Mold steel: mirror steel (such as S136, STAVAX), with chrome or DLC coating.

2.3 Venting & Cooling

• Venting: 0.02–0.05 mm deep vents at parting lines and weld line areas.
• Uniform and rapid cooling to reduce internal stress and warpage.

2.4 Wall Thickness & Structure

• Uniform wall thickness(±0.1 mm); avoid sudden changes.
• Rib thickness ≤ 50–60% of main wall thickness.

3.Injection Molding Parameters (Core Control)

3.1 Temperature

• Barrel: gradient temperature to avoid overheating.
• PC: 260–300°C
• PMMA: 220–260°C
• Transparent PP: 200–240°C
• Mold temperature:
• PC: 80–100°C
• PMMA: 60–80°C
• Transparent PP: 50–90°C

3.2 Pressure

• Injection pressure: PC 80–120 MPa, PMMA 60–100 MPa.
• Holding pressure: 50–70% of injection pressure.
• Back pressure: 5–15 bar.

3.3 Speed

• Multi-stage injection: slow–fast–slow
• Start slow: prevent jetting
• Middle fast: fast filling
• End slow: smooth packing

3.4 Cooling & Cycle

• Sufficient cooling time to avoid white marks or deformation.
• Stable cycle.

4.Post-treatment

• Annealing: Heat PC/PMMA below glass transition temperature for 1–4 hours to relieve internal stress.
• Surface treatment: slight polishing, deburring to avoid scratches.

5.Common Defects & Solutions

• High haze / poor transparency: impurities, moisture, crystallization, internal stress

→ Improve drying, use pure material, anneal, raise mold temp

• Bubbles / silver streaks: moisture, poor venting, over-shear

→ Dry material, optimize venting, reduce speed

• Obvious weld lines: gate position, speed, mold temp

→ Adjust gate, raise mold temp, multi-stage speed

• Stress cracking: uneven cooling, improper ejection

→ Uniform cooling, annealing

6.Quality Inspection

• Appearance: no bubbles, silver streaks, weld lines, scratches, black spots, deformation.
• Optical: hazeand light transmittance meet requirements.
• Performance: no obvious internal stress, stable dimension, qualified strength.

7.Summary

Qualified translucent parts =

High-purity material + strict drying + precision mirror mold + stable injection parameters + proper annealing

Small-batch process validation is recommended before mass production.