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Painting Defects : Cracks
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As with pin holes, these fine cracks on the painted
surface are caused by solvent attack, and this phenomenon is often
seen in acrylic painting. These cracks generally occur near gates
and at edges in particular.
We
recommend our special painting grades for use in painted products.
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Example: Acrylic paint
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Cause :
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 Solvent in the
paint attacks sections of the substrate material where levels
of residual strain are high, thus causing chemical stress.
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| Countermeasures: |
- Selection of a less aggressive solvent
- Modification of the paint and solvent mixture ratios
- Annealing (at between 60deg.C and 70deg.C for 20 to 60 minutes)
- Raising of the cylinder temperature and die temperature.
- Lowering of the injection and dwell pressures, and raising of
the injection speed
* Generally speaking, the addition of retarder is not a good means
of treating chemical cracks. |
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