Page 203 - Injection Molding Advanced Troubleshooting Guide

21.3 Cloudiness Troubleshooting 193

Figure 21.2 Jetting in a clear polycarbonate plaque resulting in a cloudy appearance

21.3.1.2„ Molding Process: Improper Material Change
An often-seen cause of cloudiness is a poor changeover. When conducting a mate-
rial change any residue from the previous material can lead to a cloudy appearance
on a transparent material.
When changing to a clear material the material changeover procedure is very im-
portant. Any leftover material anywhere in either the feed stream or the melt deliv-
ery stream can lead to cloudy parts. Always ensure adequate amounts of the clear
material have been purged to ensure an uncontaminated melt stream. Always take
the time to conduct a thorough material change.
See Chapter 10 for more information on changeover recommendations.

21.3.1.3„ Molding Process: Mold Temperature

A change in mold temperature may impact the cloudiness of a molded part. This
can be especially true when molding something like a clarified polypropylene.
Running cold molds with clarified polypropylene tends to minimize the size and
growth of crystallinity and will produce a clearer part. But if the crystallinity of
clarified polypropylene builds it is more likely to be cloudy.
For every material being molded the recommended process settings must be
known. Verify the actual process results to the specified process settings. During
process development try adjusting the mold temperature to determine impact on
cloudiness issues.