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Lasering off paint from Plexiglass

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Laser
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2023-03-10

I have a project where I have to burn off black paint from a plexiglass. (a transparent scale for a tank with liquid) I got a sheet of transparent, fully clear, not matte, plexiglass (acrylic glass) I spray painted it with black paint (have two choices, from a spray can, of can use an airbrush and paint it with water based acrylic paint, same results) Then I remove just the paint with my 60W MOPA Fiber laser (15% power 100ns 50kHz, 0.005mm) leave the black as some marking, a scale, numbers, etc. The result looks nice, the black paint is removed fully where needed, the plexiglass is unharmed.

 

BUT the plexiglass turned into a matte surface where the paint was burned off, but I need it to be clear transparent as it was before the painting. First I thought I applied too much power that matted the plexiglass, but the results were worse with less power. Then I had a closer look at the plexiglass and saw it was some residue of the paint the laser left, it could be scraped off with a blade. Then I tried with more power, at some point the residue was gone but also the plexiglass melted, even bubbles appeared in it.

 

Does anybody have experience with a similar thing? The task is similar to lasering off just the paint from a powder painted tumbler and leaving the metal intact. But the plexiglass is not that forgiving as stainless steel, Should I keep on trying, is there some fine setting to completely burns off just the paint, or is it impossible, and should I make peace with not using my laser (do it with screen printing, whatever)


Thank you for any clues.

C

    • Abel

      2023-03-13
      This is also probably the wrong tool to use with acrylic. It’s more likely that you could engrave with the co2 and fill it with some color, more easily.

There is also dual color acrylic… which might be another angle if you only have a fiber machine.

For the fiber, I would think you would have to try and figure out pulses per mm to see if you can dial it into the perfect speed, power, frequency and q-pulse to do what you want… Probably a pretty fine adjustment from acceptable to not.

The paint thickness needs to be considered… as it will heat differently and require changes in one or more of machines parameters to be modified to compensate for variations in thickness.

The issue will probably resolve to heat, enough to vaporize the paint but keep the acrylic surface below softening point. Acrylic starts to soften at 210F (99C), below the boiling point of water, you could probably see that effect. If the paint must exceed that to vaporize, then it might be a near impossible battle.

I have an MP-60 also. I have a spread sheet to detemine pules per mm and I’ve been working with similar issues regarding power applied and pulses, at least applying it to coating removal…

Maybe it can assist and guide you in your adjustments…

This is in the jpt manual, but shows the q-pulse output waveforms. It should help you decide on the heating duration you wish to apply. Note the peak kW applied with a pulse.
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