Causes and Process Adjustment Solutions for White Haze Defects in Transparent Plastic Parts

White haze is one of the most common and difficult-to-eliminate internal defects in transparent injection parts. It appears as tiny scattered cloud-like turbidity inside the product, reducing light transmittance and causing unqualified appearance. Different from surface flaws, internal white haze cannot be removed by polishing. It is mainly caused by moisture vapor entrapment, residual air, material thermal degradation and internal stress, which requires targeted process and mold optimization.

1. Raw Material Moisture Induced White Haze

Most transparent plastics such as PC, PMMA and PET have strong hygroscopicity. Un-dried or secondary moisture-absorbed raw materials produce water vapor under high barrel temperature. During filling, water vapor is sealed inside the melt and forms fine cloud-like haze after cooling. Insufficient drying temperature, short drying time and long-term material exposure in air are the main causes. The solution is to strictly implement drying standards, adopt hot-air sealed hoppers, and avoid moisture re-absorption before injection.

2. Cavity Entrapped Gas and Poor Venting

Incomplete cavity exhaust during high-speed filling causes tiny air bubbles to be wrapped in the melt. Dense micro-bubbles form visual white haze after solidification, especially at melt convergence positions and flow terminals. Blocked vents, insufficient vent depth and unreasonable vent distribution will aggravate haze defects. Technically, segmented low-speed injection can reduce air entrapment. Mold optimization includes cleaning carbon deposits, increasing venting at trapped-gas positions and matching vent depth with transparent material characteristics.

3. Material Thermal Degradation Caused Haze

Transparent materials are sensitive to temperature. Excessive barrel temperature, long material residence time and high shear back pressure cause molecular chain degradation and produce tiny volatile precipitates. These precipitates form uniform faint white haze inside transparent parts. The optimization method is to properly reduce barrel and nozzle temperature, lower screw back pressure, shorten molding cycle and avoid material degradation caused by overheating and retention.

4. Internal Stress Type White Haze

Uneven cooling and excessive holding pressure produce residual internal stress inside plastic parts. Stress concentration causes inconsistent optical refraction, forming local white haze. Thick-wall uneven transition, excessive holding time and low mold temperature will aggravate stress haze. Process adjustment includes reducing holding pressure, shortening holding time and raising proper mold temperature to balance cooling speed. Annealing treatment can effectively release residual stress and eliminate stress haze.

5. Impurity and Carbon Deposit Pollution

Mold oil stains, excessive release agent, barrel carbon falling off and mixed recycled materials will form tiny impurity particles inside transparent parts, showing diffuse white foggy texture. Production management must strictly control raw material purity, prohibit excessive recycled materials, regularly clean screw carbon deposits, and minimize release agent use during transparent part production.

6. Comprehensive Process Stabilization Strategy

Mold temperature fluctuation, air suction during feeding and unreasonable parameter matching will continuously induce haze defects. In actual debugging, follow the sequence of drying check → temperature and speed optimization → venting improvement. Avoid multiple parameter changes at one time to quickly locate root causes. Through standardized raw material management, precise injection parameters and optimized mold exhaust structure, transparent parts can achieve high light transmittance and stable appearance quality.