Black contamination in show surface of polypro part

[InnoDan71]

Hello,

I am hoping to get some help with a contamination problem I am trying to resolve. I am seeing a black spot on the show surface on apart that I am molding out of 20% talc filled poly pro. The spot is consistently on the same corner of 1 cavity in a two cavity mold with a fall out of 4%. I am also seeing build up of black debris in the vent closest to the affected corner.

So far I have been unable to determine if that debris is the cause or another effect of the main problem. During our investigation we have found that the colorant we are using (4% colorant to natural resin mix ratio) has had some problems with poorly mixed pigment that is visible as black streaks under a microscope.

Any suggestions on root cause would be much appreciated.

Thanks,

Dan

I have attached a picture of the blemish and then a shot or the same contamination under a microscope.

[Valentin Leung]

If it's happening always at the exact same spot, I would say it's a burn mark, if you short the part, are you trapping air around that area?

If it was coming from the material and colorant mix, it should not be affecting just one single area of your part, but all the part and both cavities.

Some of my tools show black burn mark if the tool is not clean (layer of oil). Usually, if I burn once, the vent will get clogged up and it will burn again and again, requiring my operator to clean the area.

[rickbatey]

Looks like a burn but it will take some tool work to remove it. If there are ejector pins under that area they need venting. I also think you'll need a flow helper to make the melt front meet first at one side then finish meeting at the outside edge.
Rick.

[Josue]

yes, looks like the vents are clogg, may be need a clean or remake,, and clean the mold surface very well