Paint for acrylic or polycarbonate window frit

I'm trying to see if there is a better choice than the krylon or rustoleum rattle can paint to paint the bonding surface of the acrylic window when installing with vhb tape and silicone. There are lots of folks posting about their window instals on various forums and everyone seems to just use a rattle can to paint the acrylic but it seems to me when you are spending $100 for VHB tape, which stands for Very High Bond, the weak link may be the rattle can paint to the acrylic even assuming proper prep of the acrylic. But in my searching online for alternatives I have not come up with one. Decades ago I used to manufacture snowboards and we bonded some pretty difficult materials with very dissimilar properties very successfully. The most tenacious bond line in the entire product being that to the uhmwpe base, a low surface energy material but properly prepped. We used a 2 part epoxy screen printing ink to do the graphics on the pe and then the glass laminates to that with epoxy. I thought that may be a good choice for the window frit but alas, not uv resistant (although it does work just fine on skis and snowboards) So I'm open to suggestions or maybe the plastics paint in a rattle can is fine. I don't know.

 

Whats a "windows frit" ?

 

Its where you paint the back side of the window where you will be bonding it to the cabinside. You see this on every automobile windshield extending even further in in the form of little dots. In that case it is screen printed to the glass and it's purpose as I understand it is so that when they install the window, which is done with an adhesive caulk, you won't see any missed spots or air bubbles that may be there from the outside, but also, in their case they use a polyurethane caulk which needs protection from UV. This is the same reasoning as to why folks use a painted frit on acrylic or polycarbonate boat windows except more commonly we would use a 100% silicone caulk which doesn't really need the protection from UV. Don't ask me why the stupid name, its just what I see it refered to online.
There are quite a few articles and videos online of this method of installing windows. The Coastal Passage magazine being one. It just seems strange to me that we would be using this very expensive 3M VHB tape but then ultimately are relying on the bond of some cheap paint in a rattle can from the hardware store for the frit.

 

Frit technically is a treated portion of glass that's porous or semi-porous. In automotive applications it can be simply paint, though a special formulation, with high UV resistance and peel strength. On Acrylics and polycarbonates like in boats, the paint is usually the etch type of paint that is relatively new, which actively "tooth" the surface for better adhesion. I did some side by sides a few years ago and the plastic etch was significantly better than other paints. Steve I think your concerns aren't as necessary as you might think, assuming surface area is overly sufficient for the loads involved. In the automotive industry, these bonds are incorporated into roll over protection predictions, so pretty darn good.

 

I used the rattle can/ VHB method, installed 7 windows on this project, been over 3 years in the harsh tropical sun with no problems or leaks so far.

 

Looks nice KapnD. Do you remember which rattle can paint you used and which caulk? Even which VHB tape for that matter? Yeah Par, I know I'm a little anal about this but the way that 3m hypes their tape as a replacement for rivets and screws etc it just strikes me that it would be nice to have a paint of equal bond strength since that is what one side is bonding to. Maybe the rattle can paint is good enough and it appears from reports of successful instals that it likely is. Like you say as long as you have enough faying surface its not that much stress but I cant help wondering if the super high bond (and price) of VHB tape is not wasted in this application and a lesser tape would suffice to simply hold the window until the silicone sets up, as its more than capable of holding the window without the tape. When you talk of etching paints are you talking rattle can paints such as Krylon Fusion and Rustoleums paint for plastics or are you talking something else? If so what. I have to install a couple of windows on my own boat when the weather gets a bit better and I'm up for trying something different.

 

Yep, the "Fusion" and similar rattle can stock on the plastics.

 

I tested a bit before installing, the VHB tape was the weak link, but that doesn’t say it’s no good, it just sort of stretches under extreme pressure. If I remember correctly, I used a 4000 black sealant, no problems there either.
I sprayed Fusion on both the polycarbonate and the structure, which was fiberglassed plywood with Awlgrip paint.
The glass separated from the plywood on that side.
Edit—when forced under test conditions