Injection Molding
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Uneven color/color difference of homopolymer polypropylene injection products
Problem Phenomenon
Areas of varying color depth appear on the product surface, or color difference from the standard color sample exists.
Color difference may appear between different product parts, different cavities, or different batches, affecting product appearance consistency.
Cause Analysis
(1) Uneven dispersion of color masterbatch particles; insufficient mixing time or unstable mixing ratio
(2) Large barrel temperature fluctuation; color masterbatch particles have different coloring effects at different temperatures
(3) Improper screw rotation speed and back pressure settings, insufficient plasticizing and mixing
(4) Barrel or screw wear; stagnation zones produce discoloration or uneven coloring
(5) Inconsistent mold surface conditions; gloss differences in different areas cause visual color difference
Solution
(1) Ensure color masterbatch particles are fully mixed with raw material, mixing time 5-10min, use weighing equipment for precise metering
(2) Stabilize barrel temperature, control temperature difference of each zone within ±3°C (200-280°C range)
(3) Appropriately increase back pressure to 5-10MPa, optimize screw rotation speed to ensure uniform plasticizing and mixing
(4) Check screw and barrel wear; replace screw tip or non-return ring when necessary
(5) Regularly clean mold cavities, ensure consistent surface condition of each cavity
Key Takeaway
Color difference is caused by uneven colorant dispersion or process parameter fluctuation; consistency needs to be ensured from mixing, plasticizing, and temperature control.
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