Page 333 - Injection Molding Advanced Troubleshooting Guide

328 33 Gloss Variation

33.3.4.1„ Material: Type
Generally speaking, there are materials that will provide a glossier surface than
others. In fact, in automotive molding there has been a trend for many components
to be molded with as low a gloss level as possible. An example might be a low-gloss
versus a high-gloss ABS, each of which is formulated to provide a specific appear-
ance. Make sure that the appropriate material selection accounts for the desired
gloss levels.
Often times rubber-modified materials such as ABS, TPO, or ASA will be duller in
visual appearance than something like polycarbonate or acrylic, which both tend
to be much glossier. Note that some suppliers will offer certain materials in a high-
or low-gloss level for specific applications, so be aware of the particular version of
the material being molded, and a quick online check will verify if the material is
high or low gloss.
Also beware that trying to mold a low-gloss material in a mold with a highly pol-
ished surface may result in a variety of surface defects and inconsistency of
appearance. Initial material selection needs to account for the desired gloss level
much the same as any other desired characteristic.

33.3.4.2„ Material: Additives

Many of the additives used in plastics will impact the ability of the material to be
molded with a high-gloss surface finish. Fillers such as talc or other minerals often
lead to a duller surface finish and high levels of glass will certainly impact the
gloss of the part surface. As mentioned in Section 33.3.4.1, rubber modifiers can
lead to a part with a less glossy surface finish.
As mentioned in Section 33.3.2.1, use of wood-filled materials can have a major
impact on the gloss level of the molded part and also on the polish of the mold. Be
watchful for what additives are being used in the material and expect a change
when molding material with additives versus unmodified material. Flame-retar-
dant and toughened materials can be prone to outgassing that leads to buildup on
the mold surface. Glass-filled materials may lead to erosion of texture leading to
gloss variation over time.
Verify that the correct material and additive package are being used.

Case Study: Material Impact on Gloss
In this case parts were being molded with a black TPO. During the molding
run the machine operator noticed that the gloss of the parts seemed to be
changing. Examination of parts showed that in fact there was a significant
gloss and appearance difference between parts from the beginning of the run
and later in the run. Investigation showed that a gaylord of incorrect material
was moved to the machine and never verified. When the first gaylord