Injection Molding
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Uneven Surface Gloss of Low-Density Polyethylene Injection Molded Products
Problem Phenomenon
The glossiness of different areas of the product surface differs significantly, with local darkening or high-gloss areas appearing, affecting appearance consistency.
Uneven gloss is usually related to the melt flow direction and differences in cooling conditions, and is particularly common in large flat products.
Cause Analysis
（1）The surface finish of the mold cavity is inconsistent, with local wear or uneven polishing
（2）The melt temperature is uneven, and the temperature difference of the flow front leads to different surface replication effects
（3）The mold cooling system design is unreasonable, and the cooling rate differences between parts are large
（4）The injection speed is improper, the melt flow in the cavity is unstable, and different textures form on the surface
（5）The release agent is used too much or unevenly, affecting the surface gloss of the product
Solution
（1）Check and re-polish the mold cavity to ensure consistent surface finish, with roughness Ra≤0.4μm
（2）Optimize the barrel temperature settings to ensure uniform melt temperature, with the temperature difference controlled within ±5°C (160-220°C range)
（3）Improve the cooling water channel design to ensure uniform cooling of all parts of the cavity, with the temperature difference not exceeding 5°C
（4）Adjust the injection speed and adopt multi-stage injection to make the melt fill the mold smoothly
（5）Reduce the release agent dosage or switch to a silicone-free release agent, and ensure uniform application
Key Takeaway
Uneven gloss reflects the inconsistency of the mold surface condition and melt flow, and needs to be improved from three aspects: mold polishing, temperature uniformity, and injection process.
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