Often seen in urethane painting, this phenomenon
is characterized by the appearance of small holes on the painted
surface, and it is also known as "cratering."
We recommend our special
painting grades for use in painted products.
Example: Urethane paint
Cause 1 :
Inclusion of air
Pinholes can be caused when air bubbles trapped in
the paint film expand during drying and break through the surface.
Furthermore, this phenomenon is not dependent on the substrate,
and it occurs often in high-temperature, high-humidity environments;
with thick application of paint; when there is insufficient setting
time; and when the speed of thinner evaporation during drying is
high.
Countermeasures:
- Modification of the painting environment
- Lengthening of the setting time
- Reduction of the paint's viscosity
- Slowing of the thinner evaporation speed
Cause 2 :
Residual strain
When the plastic substrate contains residual
stress, the material is attacked by the paint's solvent and fine
cracking occurs. The solvent penetrates into these cracks, and when
this then evaporates during the drying process, the resulting vapor
bursts through the surface of the painted film.
Countermeasures:
- Selection of a less aggressive solvent
- Modification of the paint and solvent mixture ratios
- Annealing of the unpainted component (at between 60deg.C and 70deg.C
for 20 to 60 minutes)
- Raising of the cylinder temperature and die temperature
- Lowering of the injection pressure and raising of the injection
speed
UMG ABS, Ltd accepts no responsibility
for the quality or safety of any customer products which use our
materials or which have made use of any type of data provided by
this company. Customers are requested to independently determine
the suitability of our materials for their products. We also request
that sufficient attention also be paid to laws, regulations, and
industrial rights.
Inclusion of air