Silk screening laser cut acrylic

[Doug Griffith]

I've been told by numerous people that it is not possible to silk screen acrylic after it has been laser cut. This is because of crazing. I'm curious if others have done this and if it is true.

My goal is to either cut a shape out of the acrylic and then screen print right up to the edge of the cut or screen first and then laser (which I'm sure will burn the ink).

I'm going to register the laser cut parts by building a fixture on the screen printer platen using the cut out piece as a male plug.

Thanks

[Mitchell Andrus]

I can't imagine thst the acrylic cares how the edge came to be, nor what you paint onto it - unless you've overheated it. Even if you did, it's just ink, right?

[Doug Griffith]

I've also been told that it is not possible to glue acrylic if it was laser cut. Again, the crazing issue. This is form professional people in the POP/Display industry who deal with it all the time.

Supposedly the molecular structure of the edge changes (I'm told up to 1/16" in) when intensely heated while cutting. The chemicals in the adhesives and inks react and cause very small cracks (crazing).

I'm guessing they are correct but if anybody should know for sure, it's the brainy folks here at SMC.

[Joe Pelonio]

Most solvents will cause the crazing on the laser (or flame polished) edges of acrylic. Yes, it's the heat changing the molecular structure. Cut a piece of 1/4" some time, and then wipe the edge with denatured alcohol and watch it start to crack before your eyes. Screen printing is not as much of a problem these days because there are inks that are not solvent based, even water based is available. Also, even the solvent inks affect only the edges, so even with a bleed, if it doesn't run over the edges you will be fine. I have laser cut a variety of screen printed materials with transfer tape on them and it did not affect the ink, and have laser cut many acrylic parts that were later screen printed (wholesale work for a screen printer).

[Richard Rumancik]

Doug

Basically what you have been told is correct. The heat of the laser will stress the edges of the acrylic and leaves residual stresses in the edge. These stresses are just looking for an excuse to turn into a crack. Such as by bending the acrylic, cleaning it with solvent, or maybe even screenprinting it.

Here are some words from Cyro:
_______________________________________
Important Considerations When Cutting ACRYLITE Sheet


No matter how sophisticated the controller or how fast the feed rate, edge stress will always be a consideration in certain applications. Any time a sheet of acrylic or polycarbonate is heated, the possibility of heat stress exists. This problem is greatest when only part of the sheet is heated, which is the case with laser cutting. The interface on the non-heated body of the sheet and the rapidly heated, rapidly cooled edge of the laser cut sheet is susceptible to crazing. These highly stressed areas extend approximately 0.010-0.050” (depending on thickness) into the sheet. They are very susceptible to crazing from contact with incompatible solvents or from high mechanical stress, for instance, due to bending. Adjusting the feed rate, pulse rate, and power can minimize the edge stress problem. Lower power and a slow pulse rate, combined with a relatively rapid feed rate, reduces the amount of energy or heat which is absorbed by the sheet, thereby reducing both the amount of stress and the distance that the stress extends into the sheet. These conditions, however, will result in a less glossy edge finish. In some circumstances, it may be practical to scrape or machine away the stressed areas.

______________________________________

Unfortunately they don't say how to eliminate the stresses. If you search you may find some info on annealing acrylic. You have to raise the temperature and dwell, then cool according to a prescribed plan.

I tried annealing once, and found a few problems:

1) it is time consuming, and requires a good oven which is controlled by temperature controller. Your kitchen oven won't do it.

2) Racking is critical or else you will have marks on your parts.

3) I found dimensional change after annealing and it was unequal in each axis.

Now on the bright side, there are many types of acrylic, more than one manufacturer, and it comes in cast and extruded grades. You might find something that will work for your application but you will have to do a lot of research.

Normal screening inks have some pretty nasty solvents and thinners in them. If you can find something that requires a less agressive solvent that would be good. Maybe there is an eco-version that would be better.

Sometimes the crazing occurs in front of your eyes. But it can occur days or weeks later (after you have delivered the goods.) This could be a very bad situation so do your testing if you go this route. Since you need to go right to the edge there will be solvent on the affected area. If you could keep the solvent .10" inside the outline that might be acceptable but the design may not permit it.

You could try cutting through pre-screened acrylic but I don't know how good the edges would appear after cutting.

[Rodne Gold]

You anneal Cast acrylic at 80c for 1 hr per mm of thickness , you anneal extruded at 70c ...let em air cool after.

[Kerry Smith II]

Just curious but why not silk screen then laser cut?

[Doug Griffith]

I've never tried it but am assuming the ink will leave a charred edge.

Anyone tried this?

[Kerry Smith II]

We have cut silk screened acrylic pieces, no charring but we would get a hazing on the edges although with some tweaking of our settings it was barely noticeable unless you were looking for it.

Results also depend on the type of ink and acrylic.

Best thing to do is get some test pieces to practice with.

Good luck.

[Larry Bratton]

I've also been told that it is not possible to glue acrylic if it was laser cut. Again, the crazing issue. This is form professional people in the POP/Display industry who deal with it all the time.

Supposedly the molecular structure of the edge changes (I'm told up to 1/16" in) when intensely heated while cutting. The chemicals in the adhesives and inks react and cause very small cracks (crazing).

I'm guessing they are correct but if anybody should know for sure, it's the brainy folks here at SMC.
I glue lasered acrylic all the time with acrylic cements. If it crazes, it's not much. I use most of it in signs of the type where it wouldn't make much difference anyway. I have seen it do it with other solvents though, even Krylon Fusion paint will sometimes cause it. It contains tolulene which is the culpret there.

[Doug Griffith]

Just to finish this up, I tested cutting acrylic previously screened with various inks (conventional and UV) and they all worked great. I was surprised that my charring fears were unfounded.

Thanks for all the great input.

[Peter Boyford]

My experience is that the crazing only is an issue within the first 24 hours of lasing. If you let the material set for 24 hours, you can do whatever to it, as if it hadn´t been lased.

Tried this with some samples and a very strong solvent cleaner. Just out of the laser = crazing. Set for 24 hours = fine to go.

Just my experience.

Best regards
Peter