Injection Molding
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Uneven gloss on the surface of polypropylene injection molded products
Fenómeno del problema
The gloss of different areas of the product surface differs significantly, with local darkening or high-gloss areas, 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.
Análisis de la causa
（1）The mold cavity surface finish is inconsistent, with local wear or uneven polishing
（2）The melt temperature is uneven, and the temperature difference of the flow front causes different surface replication effects
（3）The mold cooling system design is unreasonable, and the cooling rate of each part differs greatly
（4）The injection speed is improper, the melt flows unsteadily in the cavity, and different textures form on the surface
（5）Too much release agent is used or it is uneven, affecting the surface gloss of the product
Solución
（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 (200-280°C range)
（3）Improve the cooling water circuit design to ensure uniform cooling of each part of the cavity, with the temperature difference not exceeding 5°C
（4）Adjust the injection speed, using multi-stage injection to make the melt fill the mold smoothly
（5）Reduce the amount of release agent or switch to a silicone-free release agent to ensure uniform coating
Conclusión clave
Uneven gloss reflects inconsistencies in 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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