Pressure marks (white blur) are defects that leave a white blur-like pattern on the surface of mainly black resin products.
Strictly speaking, they can occur on any colour of resin, but they are more noticeable on black-coloured resins, making them more prone to appearance defects.
We investigated which products are most prone to pressure marks. We found that they are more likely to occur on concave or trough-folded shape.
Careful observation of the grain surface where the white blur was occurring showed that the grain surface was damaged. The scratches on the grain surface reflected light and appeared white.
No defected surface Pressure marks (white blur) surface
which can be seen white blur by scratched grain surface.
There are three possible countermeasures against such defects.
(No.1) Add a scratch-resistant masterbatch to the moulding material.
(No.2) Add deep grain on the opposite side (core side) of the surface where white blur occurs to restrict movement due to shrinkage.
(No.3) Raise the gloss value of the grain shape to make it less noticeable.
This time, the most effective countermeasure was (No.3) to increase the gloss value of the grain surface.
Using a blasting machine, surface treatment was carried out on the mould grain surface .
By increasing the gloss value, the overall light reflection is increased, which makes the white blurring less noticeable. In this case, this measure was most effective because the resin had a high shrinkage rate, such as PP. Also, depending on the size and output of the blasting sand, there is a possibility that the grain shape may be destroyed, so prior verification is required.
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