I encounter this strange occurrence in the moulding shop. I use virgin PS ( VO garde) mix with dry colour pigment. under the same moulding condition the colour vary from light to yellow and back to normal and again..... I have check all possible including change of moulding m/c. But the problum remine . Dear members can you give me some advice on this issue. Thanks for your help.
Regards
I presume you are not getting any color changes with the virgin PS? If so, it looks like your color pigment is not compatible with your PS grade and you ought to ask your supplier for a more suitable color pigment ...
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How are the PS and the dry pigment mixed? If you are mixing PS and dry pigment powder, the mix could be segregating by size and density, and go through the colour variation with each hopper fill.
Ernie
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Hi Rolf and Ernie. Thanks for your response. Initially , I also suspected the cause was due to the colour pigment . The mixed material in the hopper was taken from the same lot which was tumbled for two to three hours prior to production
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One group I work with has their colors custom compounded into concentrates by the pigment manufacturer then there is no phase separation to worry about as resin and color concentrate are the same size pellet.
Is the colorant a powder or a masterbatch concentrate? What is your mix or letdown ratio?
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