Lexan does NOT filter out UV

[skiguy411]

Originally posted by jaycat
skiguy, i wonder if you are asking "hypothetically" or not. i had this problem... i pulled the backing material off and blahblahblah forgot which side was which.

then i had a very close look, and you can actually see the coating on the XL10 Lexan. to make sure, i even took my fingernail and scratched a tiny section of the corner, the light green plastic coating scratched off.

so i just pointed this surface to the light, so far it seems to be working fine.

Ha, yeah I did forget.

Thanks for the tip! I'll give it a try....

[TaskMaster]

Originally posted by ace3000_1

As stated before search UV400. If polycarbonate was so great in its native state, then why is there UV400 in optical glasses?

Trev

This is because as I've said a bunch of times now, unprotected polycarbonate is degraded by UV light (the same reson the UV light is not transmitted). In an optical application such as lenses any yellowing, pitting, hazing, etc is extremely bad. Additionally lens molding requires a uniform, stress free medium as the product and thus many special grades of polycarbonate and acrylic exist just for lens molding. These grades have high dimensional stability, low shrinkage and other desirable properties like UV resistance so the plastic itself is not degraded by UV such as the UV400 you mention.

It has nothing to do with the fact that in its natural state, polycarbonate does not trasmit UV (or very small amounts).

How do you answer the graph and statement that ALL Lexan grades are in effect opaque to wavelengths below 385nm? To me, that statement sums it up nicely for all grades of polycarbonate.

Either way though I wasn't trying to debate this to death so I'll stop. People can look at the linked evidence and decide for themselves. I see neither of us will be saying "Ah, I see" any time soon.

[ace3000_1]

Originally posted by TaskMaster


Nope, all grades of polycarb have the same polymer chain which is responsible for the UV blocking charateristics. Call it a blocker, call it a filter (I am using the terms interchangeably),

Do you have a chemical block diagram of polycarb with the chians varying in different grades?

When making a differnt grade of somthing in thermal plastics, arent these chains modified to give them their acosiated designated properties, strengths ect.

You can have polycarb as just polycarb as a base and you can have Lexan XL. Lexan XL isnt just your normal polycarb anymore, its Lexan XL. Its a moddified divergence of the original. Polycarb is its base family only, it will not hold the same properties as lexan, (though similar) this goes for any grade in anything, wheather its steel right upto to paints. Aircraft aluminium is a good example.

What happends if you mix more carbon into polycarbonate resin? Its a hell of alot stronger, you instantly there and then change the structure of the molicules. It becomes a different grade with different properties.

Polycarb on its own will not block 100% UV, thats why its coated, mixed ect, just like glass in an aplication that needs 100% UV filtering ect. Lexan XL is designed for outdoor use and is UV stablised so it doesnt break down from the sun. Lexan XL (used as a filter) also is not a 100% UV filter on its own, its not designed to be a filter thats why, there are other grades for this, and on the cheap are coated to tailor a spec. Fair enough it does block UV, but take a look at its transmisibility, its a joke.

I know what your getting at and realy its pointless, unless you can find me a UV filter being sold commercially made out of Lexan XL in the optical world as a UV filter, my case stands. Sure it blocks UV, i didnt say it didnt, so does glass, but dont go telling me its a uv filter when its clearly not. Just because it blocks some UV doesnt make it a filter at all. At 80deg c will it block the same amount of UV then at being 0deg c? Thats one spec you dont have that is normally supplied with optical filters.

100% of 20000lm = 20000lm
80% of 20000lm = 16000lm

You get a 4000lm loss using Lexal XL as a UV filter, with a thickness of 3mm, per peice. Im sure Sony would be more then happy to use that in their projectors dont you?

Thats why we have specified filters.............

As ive said before, in todays world there is no need for us to use a UV filter. The UV stop in a bulb blocks a very sufficent amount of UV for our usage, and at no extra cost, fooling around, light loss ect.

Uv filters should only be used as a last resort. Choose your light source wisley.

Trev

[ace3000_1]

I see neither of us will be saying "Ah, I see" any time soon.

Thats right because your on a different frame of mind then what im going on about and we both have valid points. We both are right to different degrees, but i dont think you are getting my point.

BTW, UV400 comes in 2 flavours, there is the coating and the mix form. The mix form actually mixes into the polycarb and is the most effective. It protects the polycarb both from fading and also ups the UV filtering of the polycarb to 100%. Its typically used in saftey glasses.

Trev

[TaskMaster]

We agree losing 20% of your light is a joke. I've seen figures on the GE Polymerland website listing 88% transmissibility for some Lexan grades, but I still wouldn't want to lose 12%.