metallic color

[MRFARRAN]

hello,
we are always having flow marks on the surface of product when we mold metallic color products. we have tried everything to eliminate it but could't.
material is PP ( pre colored)
any ideas?

thanks

[rickbatey]

I see that the color is poorly distributed in the melt. Raise the melt temperature on the barrel. That is probably a last ge shot size on the press so the injection unit is pumping large amounts of resin through it. Lastly I see tiger striping or slip stick which raising the melt temperature will help and if not completely you can raise mold water temperature to help with that issue as well.
Rick

[MRFARRAN]

we are using pre colored polypropylene for metallic color so there is no chance for color to be poorly distributed. I tried to raise the mold temperature but no difference.
we have this problem only with metallic color. we don't have any problem with other colors even though they are not precolored.

[rickbatey]

The carrier resin of the colorant is NOT melting with the base polymer as evidenced by the pictures. You need to raise heats slightly and watch recovery pressure as I’m sure you are too cold on the barrel settings. Also you are pumping lots of resin through the screw which further exacerbated the poor melting and dispersion.
Rick

[chrisprocess]

Is it exact same failure shot to shot? To where those flow lines and zebra strips line up more-or-less identically?
If so, I would think maybe not color dispersion. Then again it is pre colored...

It does look rather flow specific... Jetting maybe?
Slower fill speed comes to mind
Possibly a combination of shear causing colorant separation in those fast fill areas?

[MRFARRAN]

It was required to raise temperature too much to find out a difference the wave marks became less but the color more became more dark. I think material has been little bit burned
now barrel temperature is 280 C, I don't know if I can get it more up to eliminate the wave marks completely

[Joel JS]

It was required to raise temperature too much to find out a difference the wave marks became less but the color more became more dark. I think material has been little bit burned
now barrel temperature is 280 C, I don't know if I can get it more up to eliminate the wave marks completely

If it makes you feel better, I had this same problem, to a lesser extent, and ended up telling the customer that this is inherent with metallic color, which I believe is true. One idea is to come back down a bit on barrel temps so you are not degrading the material and try a dispersion disc.

Joel