Injection Molding
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Color Unevenness/Color Difference of High-Density Polyethylene Injection-Molded Products
Problem Phenomenon
Areas of different color shades appear on the product surface, or there is a color difference from the standard color sample.
The color difference may appear between different parts of the product, different mold cavities, or different batches, affecting product appearance consistency.
Cause Analysis
(1) The color masterbatch is unevenly dispersed, the mixing time is insufficient, or the mixing ratio is unstable
(2) The barrel temperature fluctuates greatly, and the coloring effect of the color masterbatch is different at different temperatures
(3) The screw speed and back pressure are set improperly, and plasticization and mixing are insufficient
(4) The barrel or screw is worn, and discoloration or uneven coloring occurs in the stagnant material area
(5) The mold surface conditions are inconsistent, and gloss differences in different areas cause visual color differences
Solution
(1) Ensure that the color masterbatch and the raw material are fully mixed, with a mixing time of 5-10min, and use weighing equipment for accurate metering
(2) Stabilize the barrel temperature, with the temperature difference of each section controlled within ±3°C (range 180-260°C)
(3) Appropriately increase the back pressure to 5-10MPa and optimize the screw speed to ensure uniform plasticization and mixing
(4) Check the wear of the screw and barrel, and replace the screw tip or non-return ring if necessary
(5) Regularly clean the mold cavities to ensure consistent surface conditions of each cavity
Key Takeaway
Color difference is caused by uneven colorant dispersion or process parameter fluctuations, and consistency needs to be ensured from three aspects: mixing, plasticization, and temperature control.
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