1 Topic by BMMal

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Topic: Colorant Dispersion

I have about 20 pounds of Polylac PA 757 ABS from chimeicorp

It is a natural ABS base resin with a black colorant loading already mixed in. My filastruder ran great with the natural ABS provided. When I switched to the polylac I started getting brittle sections every 6 to 10 feet. These sections appear to be due to poorly dispersed colorant. I know that the dispersion will improve under the proper shearing conditions. I tried increasing the temperature to 200C thinking that a longer melt zone may allow for better dispersion but it did not make a difference. A proper mixing screw is obviously not feasible. Is there anything I can do differently without any major changes?

Thanks!

2 Reply by elmoret

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Re: Colorant Dispersion

That's interesting. Does the colorant appear poorly dispersed in the raw material?

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3 Reply by BMMal

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Re: Colorant Dispersion

No, the raw material has been tumbled around a lot.

4 Reply by elmoret

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Re: Colorant Dispersion

Interesting.

I know that not all colorants and masterbatches are created equal. In fact, a masterbatch is typically not just colorant, but mixing agents and more. Typically in my experience, colorants don't cause brittleness with the materbatches I've tried (mostly what OS Printing sells) but if the additive to the PA757 is less robust, I can see it causing problems. Without a doubt, home extruders are not as good at mixing as industrial extruders.

Was the raw material sealed against moisture? Perhaps it has absorbed humidity, which can also result in the brittleness you described?

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5 Reply by BMMal

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Re: Colorant Dispersion

The particular stuff I have was dried in a commercial dryer about 18 months ago. It's been stored in a sealed zip loc since then. The ambient air is usually pretty dry as well. Most of the filament did not show any bubbles indicating moisture and as far as I know ABS does not undergo hydrolysis. The brittle sections were about a foot in length. The filament outside of the brittle areas appears to be normal ABS. There were a few spots in the filament where the two materials were not mixing at all (the natural resin had kind of encapsulated a piece of the master batch) which leads me to think the colorant carrier is a different polymer.

As far as I can tell the master batch resin appears to be something other than ABS. It is very brittle. It may be a very low molecular weight ABS and/or it may be so brittle due to the high colorant concentration. I understand what you mean in that master batches can have a lot of different additives. I'll see if I can figure out what the differences are between its thermal characteristics and those of the ABS. It will be a visual observation but may lead to some insight.

6 Reply by elmoret

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Re: Colorant Dispersion

Yeah, sounds like moisture is no problem then. Just a thought. If the masterbatch is pelletized (not powder or dried liquid), the Filastruder isn't physically big enough to do great mixing of pellets much larger than 1mm - so you're seeing a varying concentration of masterbatch in the extrusion, and the high concentration areas are more brittle. Some masterbatches mix more easily than others. There is probably an additive you can use, but this is quickly getting outside of the area of my expertise - I've only used a few varieties of masterbatch, and no premixed stuff. You said the resin is PA757 - do you have a ID number for the masterbatch?

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7 Reply by BMMal

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Re: Colorant Dispersion

Yea, the pellets are all about 2.5mm. So that makes sense. I don't have an ID number for the master batch. I was given the material as leftovers from a molding/material testing sample. I didn't pay anything for it so I'm not worried about that.

Do you think using another heating band just behind the coupling, thereby extending the melt zone and opportunity for mixing would work?

8 Reply by BMMal

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Re: Colorant Dispersion

I just ordered a nozzle/mesh filter. I need one anyway but maybe it will help with this problem.

9 Reply by BMMal

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Re: Colorant Dispersion

I think it would be helpful to integrate a static mixer. Check out psi-polymersystems. If the screen filter doesn't eliminate the problem I might try to get a static mixer that will fit inside the pipe. I'll add another nipple and heater band around it.

10 Reply by DePartedPrinter

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Re: Colorant Dispersion

BMMal wrote:

The particular stuff I have was dried in a commercial dryer about 18 months ago. It's been stored in a sealed zip loc since then. The ambient air is usually pretty dry as well. Most of the filament did not show any bubbles indicating moisture and as far as I know ABS does not undergo hydrolysis. The brittle sections were about a foot in length. The filament outside of the brittle areas appears to be normal ABS. There were a few spots in the filament where the two materials were not mixing at all (the natural resin had kind of encapsulated a piece of the master batch) which leads me to think the colorant carrier is a different polymer.

As far as I can tell the master batch resin appears to be something other than ABS. It is very brittle. It may be a very low molecular weight ABS and/or it may be so brittle due to the high colorant concentration. I understand what you mean in that master batches can have a lot of different additives. I'll see if I can figure out what the differences are between its thermal characteristics and those of the ABS. It will be a visual observation but may lead to some insight.


I had similar issues to what you are describing when I used Polylac ABS with an HDPE colorant

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11 Reply by Dakota

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Re: Colorant Dispersion

I'd be curious as to what a second heating band and a longer melt zone would do.  If you do it, please post your results.

BMMal wrote:

Yea, the pellets are all about 2.5mm. So that makes sense. I don't have an ID number for the master batch. I was given the material as leftovers from a molding/material testing sample. I didn't pay anything for it so I'm not worried about that.

Do you think using another heating band just behind the coupling, thereby extending the melt zone and opportunity for mixing would work?

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