Gloss is defined as the amount of light that is reflected off a surface. The rating used for gloss
based on how much light is reflected at different angles and the degree of light that is scattered
Parts with high gloss reflect the majority of light with very low scatter. Low gloss is low reflection
at differing angles with large scatter. The correct amount of gloss is determined by the requirements
of the end-use application. The following solutions will provide ways to control gloss and assume
untextured part surface. The lists causes and solutions for gloss.
Cause:
1. Cold melt temperatures provide low gloss on untextured surfaces
2. Low packing pressure is another cause of low gloss, since the plastic material is not fully packed onto the cavity surface and does not replicate the surface
3. Injection speeds that are too slow will reduce the gloss on the surface since these also may cause the melt not to replicate the mold surface
4. Cold mold temperatures will give low gloss surfaces since this causes the melt front to cool too soon and not replicate the cavity
5. The type of mold surface, such as a dull surface, gives a low gloss
6. Insufficient venting in the mold can cause gases to be trapped, creating the dieseling effect. This causes the surface of the part to show low gloss
7. Part sticking in the cavity or on a core upon ejection results in drag marks on the part, resulting in a low gloss surface finish
Solutions:
1. If higher gloss is needed, processing at higher temperatures is needed. In some cases, too hot a melt temperature can also cause low gloss. In this case, additives that are mixed in with the base
resin, such as plasticizers or some flame retardants, can bloom on the surface. Reducing the melt temperature may help in this situation
2. Increasing pack pressure will allow the melt to pick up all the details of the mold cavit
3. Increasing injection speed will raise the melt temperature and pack out the part
4. Higher mold temperatures will keep the melt warmer for a longer time, enough to fill the cavity
5. Polishing and cleaning the cavity will increase the gloss
6. Following recommendations for venting a specific material can prevent this
7. The cavity or core should be checked for machine marks that may be found on the surface that are not in the direction of part ejection
The effects on gloss are different for textured surfaces. Textured parts are made up, on a
microscopic scale, of a group of peaks and valleys. As a result, light scattering is different from that
in untextured parts where light is reflected at a very low scatter, giving high gloss. However,
textured surfaces cause more light scatter, producing low gloss. So in this case, the texture provides
low gloss. If a part is not fully packed out, or if the mold and melt temperatures are too cold, the
eaks and valleys of the texture will not fill completely, creating a microscopic short shot. This will
result in high gloss on the textured part. High mold and melt temperatures, high packing pressures,
and high injection speeds are needed to achieve low gloss since they will all help to fill all the peaks
and valleys completely and give the textured part low-gloss surface
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Tuofang company is specialized in designing and manufacturing Plastic Injection.
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