Injection Molding
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Uneven color/color difference appearing in random copolymer polypropylene injection molded products
Problem Phenomenon
Areas of varying color depth appear on the product surface, or there is color difference from the standard color sample.
Color difference may appear between different parts of the product, different cavities or different batches, affecting product appearance consistency.
Cause Analysis
(1) Color masterbatch is unevenly dispersed, with insufficient mixing time or unstable mixing ratio
(2) Barrel temperature fluctuates greatly; color masterbatch has different coloring effects at different temperatures
(3) Improper screw speed and back pressure settings; plasticizing and mixing are insufficient
(4) The barrel or screw is worn; stagnation zones produce discoloration or uneven coloring
(5) Mold surface conditions vary; gloss differences in different areas cause visual color difference
Solution
(1) Ensure color masterbatch is fully mixed with the raw material, with mixing time of 5-10min, using weighing equipment for precise metering
(2) Stabilize barrel temperature, with temperature difference of each section controlled within ±3°C (190-260°C range)
(3) Appropriately increase back pressure to 5-10MPa and optimize screw speed to ensure uniform plasticizing and mixing
(4) Check screw and barrel wear, and replace the screw head or check ring if necessary
(5) Regularly clean mold cavities to ensure consistent surface condition of all cavities
Key Takeaway
Color difference is caused by uneven colorant dispersion or process parameter fluctuations and needs to be ensured from three aspects: mixing, plasticizing and temperature control.
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