Color Part IV

In the previous parts we talked about the basics’, definitions and matching of the colors. In the next installment the common or hopefully not so common problems of color.

Black specs, or what people perceive of as black specs.  In one of the early tips we talked of this problem of dispersion. If in fact we have black specs in the finished parts there are a few things that we need to determine first.
1- How big are the black specs, and what is the volume of them.
2- If we dig the black spec out of the part and smear it on a white piece of paper do we see the color or just the black spec?
3- If we see color than we have a dispersion problem of the pigment system
4- If we see just the spec than we need to further look at the raw material and see if we find specs.
5- This is done with a sample of material randomly selected and a specified weight. For example using 500 grams or 1 pound of material, as the sample size and inspecting this sample for black specs and classifying them by size. Data has now been generated.
6- When than inspecting an equal weighted sample of parts, does the volume of black specs equal that found in the raw material sample. Is it less or more? Is the size bigger or smaller?
7- If the black specs are less than in raw material than the problem may be in the raw materials.
8- If the black specs are greater than raw material than we are producing them, in the process.
9- If they are bigger than what we find in raw material than we are producing them, if smaller than maybe they are from the raw material.
10- Do the black specs start at the beginning of the run and than disappear or do they get worst as we run.
 

As shown, if steps are followed the solution to the black specs can be solved. There is an assumption that the machine was properly cleaned, and all systems were a go from the beginning. Though this is a big assumption what type of system is being used. If for example a hot runner is involved, than the manifold has to be of suspicion.
 

Thanks for the time.

Steven L Silvey
Sr. Technical Service
General Polymers Division
ADC