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Multi-Material SLA with different colors

Posted by der_Bam 
Multi-Material SLA with different colors
March 22, 2016 07:07AM
I have done some research and could not find any relating threads.

I am printing with near UV and diacrylate polymers. My tests with pigments and dyes have not been fruitful so far as my material has a very high water content (~90%) and color just diffuses over time. Even if my parts are beautifully stained right after the printing, the defined color distributes throughout the object over time.

So I am looking for some kind of water soluble dye/pigment that stays in place after polymerization, maybe even by covalent bonding. Any ideas are highly appreciated.
Re: Multi-Material SLA with different colors
March 22, 2016 01:09PM
I'm not sure from your description exactly what you are looking for. Are you saying that your resin has 90% water content? That seems weird because water is generally inmiscible with acrylate 3D printing resins.

Or are you saying that in your application, you are staining your object by immersing it in dye after it is printed rather than adding dye to the liquid resin?
Re: Multi-Material SLA with different colors
March 22, 2016 02:05PM
I do actually mean the resin has 90% water content. It is based on PEG. The reason for that is that it is being used for bioprinting. However, toxicity of the dye is not a problem.

Edited 1 time(s). Last edit at 03/22/2016 02:12PM by der_Bam.
Re: Multi-Material SLA with different colors
March 22, 2016 02:46PM
And then in your failure cases for dyes and pigments, what are you seeing?

Dyes are dissolved into solution with the material, so even if they migrate over time, any movement should not be visible. The drawback of dyes is that even the most durable dyes (e.g. metal complex dyes) will fade over time with exposure to UV. However, unless your printed objects are outdoors in the sun for long periods of time, or perhaps exposed to repeated UV sterilization, objects indoors would not be exposed to enough UV for this to happen.

Pigments, on the other hand, are suspensions. If the cured material isn't completely solid but is actually a gel, it is possible for pigment to settle over time according to Stokes' Law. But given the viscosity of the typical gel, this would occur very slowly if you use a fine pigment in the 1 micron particle size range, and would tend to settle towards the pull of gravity.

I notice also that you said the problem was "color distributes throughout the object over time". Does this mean that you are somehow producing a multi-color print with two differently colored resins and you're seeing that the colors diffuse into each other, like perhaps via osmosis?
Re: Multi-Material SLA with different colors
March 22, 2016 03:04PM
I am using two differently colored resins. One is clear and the other forms a structure within the first material. And yes, osmosis is the very problem. The pore size of the cured resin is quite big and neither pigment nor dye stayed in place so far. After a couple of hours or sometimes a few days, the color is evenly distributed, no difference between the two resins can be made out. The perfect solution would be some kind of dye that takes part in the polymerization process and is thereby permanently bound. My chemical knowledge is too limited to figure this out myself and my research did not get me close to a solution either so far.
Re: Multi-Material SLA with different colors
March 22, 2016 03:20PM
Hmm... the problem with a dye that reacts with the polymerization process is that since acrylates polymerize in a free-radical chain reaction, dyes that are very reactive to free radicals would likely lose their color once they react, which is generally the opposite of what is desirable for a dye.

I think pigments might be more promising; you maybe able add an additive that would increase the thixotropy of the resulting gel and slow down the migration.

The next thing I might try would be to add cabosil (fumed silica) to the resin, starting with about 1%, and see if that slows the rate of pigment migration.

Is your printer very sensitive to the viscosity of the resin you print with? If it's not very viscosity sensitive, you can keep upping the amount of cabosil to see if it improves stability, and can go to quite high concentrations.
Re: Multi-Material SLA with different colors
March 23, 2016 06:37AM
Unfortunately the printing is rather viscosity sensitive.

I tested acrylic paint yesterday and that seems to do the job.

I will try to raise the thixotropy if the object becomes uniformly colored over time.

Thank you very much for your help, new ideas for the next tests.
Re: Multi-Material SLA with different colors
April 21, 2017 04:14AM
Sorry to reply too late

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