Why can't I use film for heat and uv control?

[thinwater]

Originally Posted by Ric Sheridan

...I read somewhere here that the only sealer to use on sailboat windows is the Dow Corning Commercial grade window caulking.

AKA DOW 795.

[joelhemington]

Originally Posted by RKsailsolo

The tropical sun is degrading my plexi cabin windows and hatches. Will an exerior application of solar/uv control film stop this or at least retard it to some degree?

As the 3M distributor for Schotchshield window films in the central Pacific for many years. I can you tell that films won't work on plastics due to the outgassing of the plastic. We lost a lot of potential customers with plexiglass skylights because of this. Tempered glass windows will profit greatly with even a medium performance film due to UV and temperature control factors.

[qwert]

Originally Posted by Cliffhanger

As for the original question about the UV film, I wouldn't use it. Depending on the adhesive it might actually do more damage than it prevents.

I'll second that,I had some acrylic stored for three or four years on a shelf down the back of the shed - no UV, no stress. There were three sheets held together by a length of duct tape around the bunch. When I removed the tape there was severe crazing where it had been.

The acrylic was fit only for the dustbin. Destroyed by the adhesive.

[Ric Sheridan]

Funny I live in Hawaii on the Beach and I have a piece of Polycarbonate that has been sitting in the sun and weather protecting some ladders from the rain and sun for twenty years and it is as good as new. Plexi is soft and if you put rubbing alcohol on it it will crack all the way through, even having a big chunk fall off of the otherside in one case. I would go with polycarbonate it flexes better than plexiglas and scratches less... All in my opinion. I have been working with plastics for thirty years but not on Boats. Go put some isopropyl alcohol on your windows to check after you replace them.

[RKsailsolo]

Originally Posted by RKsailsolo

The tropical sun is degrading my plexi cabin windows and hatches. Will an exerior application of solar/uv control film stop this or at least retard it to some degree?

Let me first thank everyone for their responses, very insightful. Then to clarify my original question intent which I now see is hidden in the vague wording, the situation is not sun damage to the window material itself but rather the bedding or bonding system design to attach the window to the cabin house. The original window is fine but the window's thermal expansion fatigued the factory bonding system letting portions of it to release from the cabin house. Therefore, I theorize that shading from the outside to dampen the daily thermal cycling will result in less forces applied to the rebedded Window.

Possible ext. shading solutions include window films, phifertex, awnings when docked and snap on canvas covering. If films can knock down damaging UV and higher cycle temps, it seems the simpler and more robust solution.

[RKsailsolo]

Originally Posted by qwert

I'll second that,I had some acrylic stored for three or four years on a shelf down the back of the shed - no UV, no stress. There were three sheets held together by a length of duct tape around the bunch. When I removed the tape there was severe crazing where it had been.

The acrylic was fit only for the dustbin. Destroyed by the adhesive.

Excellent points both. Solvents of any kind may craze the substrate. Could static cling film work? Or find a film that's been tested to not damage underlying plastic substrate.

[RKsailsolo]

Originally Posted by joelhemington

As the 3M distributor for Schotchshield window films in the central Pacific for many years. I can you tell that films won't work on plastics due to the outgassing of the plastic. We lost a lot of potential customers with plexiglass skylights because of this. Tempered glass windows will profit greatly with even a medium performance film due to UV and temperature control factors.

Thank you Joel for the specific feedback...I am an ex 3Mr and was curious about the storehouse of adhesive and precision coatings experience that 3M can apply to this application.

[RKsailsolo]

Originally Posted by thinwater

AKA DOW 795.

I will rebed the window myself using Dow 795 and 3M VHB 4991. This system is the one Don't Casey wrote about in Sail magazine. Once its completed I want to shade it in some fashion, along with the rest of the cabin house windows.

[RKsailsolo]

Originally Posted by Cliffhanger

Crazing of clear plastics is due to internal stresses in the material. Those stresses are relieved over time, causing surface cracks (crazing). This process can be accelerated by some chemicals. Acrylic and polycarbonate are amorphous and so prone to chemical attack. The casting process creates less internal stress than extrusion and so cast acrylic is less prone to crazing.

Perhaps the most important thing to extend the life of clear plastics is to make sure you keep them clean (pollution can contain a variety of chemicals) but only clean them with soapy water or a cleaner specifically designed for clear plastics. Never, ever use an organic solvent to clean any clear plastic.

UV will make polycarbonate go yellow over time but UV stabilisers minimise this.

So, in my opinion, cast acrylic is a better option than polycarbonate for boat windows and hatches as it has better scratch, UV and chemical resistance. It also has slightly better clarity and is cheaper. Polycarbonate has superior impact strength though which might be an important consideration.

As for the original question about the UV film, I wouldn't use it. Depending on the adhesive it might actually do more damage than it prevents.

Awesome technical discussion from cliffhanger... Very useful.

[RKsailsolo]

Wfteer, steady, sounds like you both have perf application experience. What about the possible crazing from the perf adhesive?

[barnakiel]

It is done. I have seen film applied inside. Hence a waterproof thing will be available for exteriors.


b.

[Chotu]

Originally Posted by RKsailsolo

I will rebed the window myself using Dow 795 and 3M VHB 4991. This system is the one Don't Casey wrote about in Sail magazine. Once its completed I want to shade it in some fashion, along with the rest of the cabin house windows.

This won’t be a permanent fix in hot, tropical climates depending on your window size. Mine has failed yet again, so I’m just going with mechanical fastening.

Also, yes... you can put UV films on plexiglass and polycarbonate, but they must be specific, special new films that are designed for the plastic substrates. That they will lift from the out gassing is 5-10 year old information. They have developed new films specifically for this application

[Sailing Ohm]

Ours were pretty bad but we went a different route. We got the inside window films (usually for homes) and stuck them no issue. Ours are mirrored on the outside which I think helps at docks. They’re great. We hardly notice the crazing anymore and they keep the direct sun out of the cabin quite well.
I know one day I’ll have to replace them but that day it’s not soon.

Doesn’t answer your question directly but it was a nice cheap solution that we found and enjoy so thought I’d share.

[Sailing Ohm]

Guess I really didn’t answer your question at all...
So in follow up your clarification... what bedding compound are you currently using? And what type of material are your window frames? If they are aluminum you have more options but ensure they are not painted black. If they are screw into the cabin wall types like mine then butyl tape might be your best friend.

If you need an adhesive and sealant, lately I’ve been using 3M 4000 for other jobs as it has high UV resistance and unlike a lot of other bedding compounds, it can actually be used with some plastics (which can be an issue with bedding ports).
So far no complaints and best part is it’s actually removable!

I think a lot of factories originally used construction grade silicon around hatches and ports that have addition fasteners.

[RKsailsolo]

Originally Posted by Chotu

This won’t be a permanent fix in hot, tropical climates depending on your window size. Mine has failed yet again, so I’m just going with mechanical fastening.

Also, yes... you can put UV films on plexiglass and polycarbonate, but they must be specific, special new films that are designed for the plastic substrates. That they will lift from the out gassing is 5-10 year old information. They have developed new films specifically for this application

Interesting, your note on old adhesive technology. I'll research that, thanks.


Good luck on fasteners as a perimeter secured plastic window expanded can micro fracture and crack.

I'd rather bet on successful adhesion of the two bonding systems that are both engineered to perform well within plastic substrate thermal cycling.