Using Silicone on Second surface Printed vinyl applied to acrylic

[LenXIII]

Hello All,

I have some questions regarding installing small acrylic signs (less than 1 square foot) on to texture walls such as stucko and concrete. My clients have been installing signs for years on to these surfaces with a particular silicone (non shrinking) and usually vhb or similar for initial tack.

My main question is...is it safe to put silicone on the backside of the acrylic (where the vinyl is applied?) They have done this for years without incident but lately on a particular job we have been having huge problems with the silicone causing the vinyl to pull back from the acrylic. This has happened with both using intermediate permanent calendared vinyl and cast vinyl with perm adhesive. The vinyl is digitally printed clear backed with white vinyl. I have redone the job once entire already and after switching to a cast vinyl we are still having issues and I just don't know what to do. I tried looking through all of the 3m datasheets I could find but nothing says anything about using silicone (or not to use it) and I couldn't find anything about "cure times" on the adhesive other than a strength rating after 24 hours.

I usually stick with the printing end of things so I am not very knowledge on the intricacies of the do's and don'ts for installing graphics. ANY input or opinions would be greatly appreciated.

 

[Dan360]

It sounds like the problem isn't the bond between silicone and vinyl, but the bond between the vinyl and the acrylic. The silicone is well adhered to the vinyl so the stress of the weight of the acrylic is causing the vinyl to peel away.

 

[LenXIII]

It sounds like the problem isn't the bond between silicone and vinyl, but the bond between the vinyl and the acrylic. The silicone is well adhered to the vinyl so the stress of the weight of the acrylic is causing the vinyl to peel away.

I agree that the issue is the adhesive between the graphic and the acrylic - but I guess my question is would that be because silicone was used in the first place or the adhesive on the vinyl have an issue? I am wondering if using silicone is a common practice and considered acceptable for this application? The signs weigh less than a pound each, maybe less than half a pound. I assume when the silicone is curing it is overpowering the bond between the acrylic and vinyl. So I guess that still brings me back to are we installing these signs improperly by using silicone (although even the taped areas have pulled vinyl) or is it more likely the vinyl is defective or acrylic is contaminated somehow.

The job size was over 500 acrylics, so it is a huge deal for us.

 

[Dan360]

I think you're fine with the silicone, I would look at a more aggressive adhesive vinyl or possibly priming the acrylic before laying it down. What vinyl are you using?

 

[signbrad]

We had the same issue a couple years ago. HospitaI room signs with a printed clear, second surface, and a backer. I can't remember how it was resolved and I can't ask the installers at the moment. We are all gone for the day.
Some of the installers speculated that the silicone was attacking the vinyl. I have read somewhere that silicone does attack PVC, so that would make sense.

On a related note, years ago, when I cut some letters out of Plexiglas Mirrorplex, I recall instructions to use only a specific rubber-based glue for mounting glue pads. The warning was that other glues would attack the mirror backing. The rubber-based glue was a 3M product formulated to not attack the backing on the Mirrorplex.

Brad in Kansas City

 

[CanuckSigns]

We make a lot of interior acrylic signs, we always try to paint the reverse side instead of using vinyl for this very reason. I have stuck some small acrylic room signs up with just VHB tape and have had issues where after a few months you can see exactly where the tape strips are on the back because the vinyl has completely pulled away from the acrylic in these spots.

My understanding is that acrylic shrinks and expands more than the tape will allow for, so the path of least resistance is for the vinyl to separate from the acrylic.

What you could try that has worked for us is cut a piece of HIPS slightly smaller than the acrylic, cover 1 side completely with a mounting adhesive such as 468mp then stick that to the back side of the sign and put your foam tape and silicone on that to attach to the wall. This spreads out the stress and the vinyl shouldn't pull off this way.

 

[LenXIII]

Hey guys, thanks for the replies. I must have had notifications off as I didn't catch these replies sooner. The vinyl I am using is 3m180MC-114 in CLEAR. Backed up with a 3m 7725 white cast vinyl. The acrylics are only 6.5" so I don't think weight is the issue, which was also suggested as a potential issue by 3m.

I like the idea of backing the sign with something using a mounting adhesive, but that would literally double the labor and not allow me to make a competitively priced sign. Obviously I care more about quality than anything, but I also need to find a way to keep the signs affordable. Using two cast films already makes it difficult.

A vendor of mine told me she switched to using a particular type of FOAM tape, I assume it must be outdoor rated, because they had issues like this as well. I have never run in to this in the past, and have never had anyone tell me they have had this problem - but now that I'm asking around it seems to be super common. This is very frustrating that I wasn't aware of this being an issue so that I could do my best to account for it.

EDIT: Also - we did in fact use that blue (and gold on some occasions) labeled GE silicone because it says non shrinking on it. This is the silicone we have had the best success with in the past, but again this problem is new to me.