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Molding Defects: Color Streaks
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The phenomenon of color streaking is characterized
by localized changes in the color of a molded component or by streaking. |
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Examples of variation from the original color
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Causes :
Countermeasures:
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- This type of problem is principally caused by poor thermal
stability of the coloring agent. Furthermore, it occurs more
easily in locations such as welds, ribs, and the like which
are likely to induce shear flow.
- Switch to a coloring agent with good thermal stability.
- In terms of molding conditions, it is desirable for the plastic
and die temperature to be high, and for the speed of flow to
be low (i.e., hot-slow molding).
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Example of a streaking pattern in a molded product |
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Cause :
Countermeasures:
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- Poor distribution of coloring agent. (The quality of coloring-agent
distribution can be evaluated by using a compressing molding
machine to manufacture thin sheeting.)
- Cleaning effect of plastic deposited within the molding machine
(or cylinder).
- Improve the quality of distribution during compounding.
- Fully clean the inside of the cylinders. (We recommend our
own UMG Clean ™ for this purpose.)
- Check the screw head, back-flow prevention rings, and other
similar items for defects.
- Change the molding machine.
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