Injection Molding
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Uneven Color/Color Difference Appearing on Low-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.
Color difference may appear between different parts of the product, different 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 rotation speed and back pressure are set improperly, and the plasticization and mixing are insufficient
（4）The barrel or screw is worn, and the material retention areas produce discoloration or uneven coloring
（5）The mold surface conditions are inconsistent, and the gloss differences in different areas cause visual color difference
Solution
（1）Ensure the color masterbatch is fully mixed with the raw material, 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 (160-220°C range)
（3）Appropriately increase the back pressure to 5-10MPa and optimize the screw rotation speed to ensure uniform plasticization and mixing
（4）Check the wear of the screw and barrel, and replace the screw head or check ring when necessary
（5）Regularly clean the mold cavity to ensure consistent surface conditions of all cavities
Key Takeaway
Color difference is caused by uneven dispersion of the colorant or fluctuations in process parameters, and consistency needs to be ensured from three aspects: mixing, plasticization, and temperature control.
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