Need Help acrylic cracking after applying vinyl.

[bigben]

I have some small sign that is designed to hold paper for offices names. final size is 6inX8in and made with 1/8 thick clear acrylic.

They are cnc cut to shape, folded with a heat bar then the edges are flame polished. I need to put vinyl on the back for color. First batch was avery 750 vinyl applied with dish soap and water (I know rapidtac and alcohol is a no-no). Everything went great. For the second batch I had to print the color on a clear vinyl and laminate a white vinyl on the back because the color wasn't available in cut vinyl. I've used the same technique for the install and everything was great. The next day, I come back at the office and all the acrylic are cracked (only the ones with printed vinyl). It has the same reaction as if I've used alcohol. I thought maybe there was a contamination in my spay bottle so I've went to the store and bought a brand new spray bottle. Did some test and have the same result (crack). I've attached a picture.

I've called my acrylic distributor and showed them my picture and they suspect it's the vinyl. But both are calendred and the ink does not touch the acrylic.

Does anyone know what is the problem and how to resolve it?

Thanks.

 

[eahicks]

Solvent adhesive likely. Try a water based adhesive vinyl. Which clear did you print on?

 

[bigben]

Solvent adhesive likely. Try a water based adhesive vinyl. Which clear did you print on?

Maybe you got it. If I remember right we use oracal 3165 clear witch is solvent adhesive for the printed version. The avery 750 is an acrylic adhesive (not sure if it's solvent base or not).

So now I need to find a clear material that is not a solvent adhesive.

 

[Christian @ Visual Graphx]

Is your acrylic cast or extruded?

 

[letterman7]

I'm going with a combination of the print (if it's solvent or eco solvent, it's still alcohol based) and solvent adhesive. Fumes will crack plastic just as easily as liquid in the right conditions.

 

[James Burke]

I see that it appears to be cracking at the bend. I would hazard a guess that it has to do with a reaction between the ink or adhesive, AND the residual stress that is still in the acrylic from bending. Typically, slow cooling prevents this...it's very similar to the tempering process used in metal.

Not sure if you have this resource, but I thought I'd throw it out there anyway:

https://www.plexiglas.com/export/si...loads/sheet-docs/plexiglas-forming-manual.pdf

 

[Andy D]

Is it possible that they were cracked before you applied the vinyl and couldn't see the cracks without color behind the acrylic?
The only thing I have ever heard of cracking acrylic is acetone.

 

[Johnny Best]

its the flame polishing, I always use a buffing wheel with solid compound to polish edges and have never had cracks.

 

[bigben]

Is your acrylic cast or extruded?

Extruded

I'm going with a combination of the print (if it's solvent or eco solvent, it's still alcohol based) and solvent adhesive. Fumes will crack plastic just as easily as liquid in the right conditions.

It's ecosolvent printed with a solvent adhesive vinyl.

I see that it appears to be cracking at the bend. I would hazard a guess that it has to do with a reaction between the ink or adhesive, AND the residual stress that is still in the acrylic from bending. Typically, slow cooling prevents this...it's very similar to the tempering process used in metal.

Not sure if you have this resource, but I thought I'd throw it out there anyway:

https://www.plexiglas.com/export/si...loads/sheet-docs/plexiglas-forming-manual.pdf

Crack is all around. Not just at the bend. We apply the vinyl around 24h after bend and flame polish the acrylic.

Is it possible that they were cracked before you applied the vinyl and couldn't see the cracks without color behind the acrylic?
The only thing I have ever heard of cracking acrylic is acetone.

That was our first idea. But we did some test on few with Avery 750 colored vinyl (3 different colors) and there was no problem. Our supplier give us a 15mil clear polyester film. We stick it to the acrylic without any problem. We are trying to add the printed part right now. So maybe with the polyester layer between the acrylic and printed part, it will work.

its the flame polishing, I always use a buffing wheel with solid compound to polish edges and have never had cracks.

I did not know this one. If you apply alcohol after the polishing, does it crack?

 

[Christian @ Visual Graphx]

Alcohol will crack extruded, and it's less likely with cast.

How much of a bend does your acrylic have? Have you tried cast if it's less than 45 degrees?

 

[bigben]

Alcohol will crack extruded, and it's less likely with cast.

How much of a bend does your acrylic have? Have you tried cast if it's less than 45 degrees?

The bend is a full on itself. It's for creating a ''pocket'' to insert a paper.

 

[MikePro]

any solvents on cnc cut & flame polished acrylic will crack plexi
there's a thread somewhere here discussing it, youtube vids explaining it as well, but apparently the flame polishing creates tiny pores of stressed acrylic and the solvent glides up into, expands, and cracks.

 

[bigben]

any solvents on cnc cut & flame polished acrylic will crack plexi
there's a thread somewhere here discussing it, youtube vids explaining it as well, but apparently the flame polishing creates tiny pores of stressed acrylic and the solvent glides up into, expands, and cracks.

I knew that one, but I never thought the solvent in the vinyl adhesive or printer ink would be enough to cause this.

 

[Johnny Best]

If you cut the extruded with a blade that makes minor chips and then flame polish like Mike Pro mentioned it will crack all over with any chemical like Windex which has ammonia. When you flame polish your just melting the edge, polishing the edge smooths out and cracks or chips. Or you got some crap acrylic, I always use cast but have use extruded in the past with no problem. People like the flame polish because it is faster but on thick pieces it does not work as well as polishing with wheel and compound.

 

[Joe House]

How long after printing did you apply the white vinyl? If you trap the solvents from the ink by laminating too soon, you can force the solvents to out gas through the clear and adhesive.

 

[TammieH]

Flame polished + Wet Ap = cracked acrylic