plastic used as a protective window on an LCD for outdoor use

[fpiergen]

I am looking for any suggestions on what type of Plastic I will need for an outdoor application on a moving vehicle. In short it will be used to protect an LCD Display. Therefore, it needs to be
1. As clear as possible (for viewing LCD Display in the day)
2. Resist scratching
3. Have UV and IR blocking
4. obviously resistant to sun damage

Thanks for any help.

 

[patprimmer]

Umm

Why does it have to block UV and IR.

If impact resistance is not really critical, and by UV blocking, you actually mean UV resistant, Acrylic would be your best choice.

If it requires very high impact resistance polycarbonate may be required, but with PC you sacrifice a few other properties. Some of these can be improved with surface treatments and stabilisers, but it's tendency to stress crack in the presence of some very common everyday chemicals is a real problem.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[fpiergen]

UV to protect against damage to LCD and IR to block out some of the suns heat.

It does require impact resistance so I think I will need a PC. You say PC is sensitive to some common materials. Will it be sensitive to the materials used in a car wash?

Thanks for your help

 

[btrueblood]

Yes, polycarbonate will craze (stress crack) when exposed to some (most?) detergents, especially those with high alkalinity and/or quaternary ammonium compounds.

 

[Pud]

PC is used for car headlight assemblies, but I think they are coated after moulding to prevent scratching, etc. which must protect them chemically too.

How about a transparent nylon? Pricey though - hope it's a small part - here you go - data sheet here:

http://www.emsgrivory.com/mytools/datenblaetter/datenblaetter/grilamid_tr/TR_90_UV_E.pdf

Cheers

Harry

 

[patprimmer]

You can get UV absorbers added to acrylic. They are normally used as UV stabilisers but the do block transmission.

IR absorbers normally also take out a significant portion of the visable light.

Light absorbers may stop the LCD getting hot, but they will cause the cover to get hot, thereby heating the air between them and the LCD. It gives some reduction in heat at the LCD, but not nearly so much as window tinting sales brouchers would have you believe. There is no free lunch. The energy has to go somewhere.

PC is normally OK in normal detergents and alkalis only really effect it at higher temperatures (like starting at about 60 deg C and really ramping up at about 80 deg C)

The things that really get into it are solvents (from paints and adhesives) fuels and lubricants (from the aromatic hydrocarbons in there as additives or impurities) and chlorinated hydrocarbons. Also propellants in aerosols, perfumes, sun tan oil, dissinfectants etc can be a problem.

Pud is right, PC headlights have a protective coating. It tends to last 10 or so years, at least in the normal environment in Oz.

PC is occasionally used in tail lights when engineers or toolmakers stuff up and acrylic won't bend enough to allow assembly. These normaly are normally UV stabilised but not coated and do not normally solvent stress crack unless someone uses bug remover or solvent on them, but they do scratch so badly that at only 2 or 3 years old they look VERY second hand.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[IRstuff]

It gets trickier. ANY enclosure around an LCD panel WILL suck in moisture. During the day, or during use, the interior heats up, pressure builds and releases through the seams. At night, or when the box cools down, pressure drops and sucks in moist air. Do that a few cycles, and you'll get condensation on the inside of the PC.

Additionally, LCDs don't like it very cold, so you'll probably need heaters when the temperature drops. You might need to have a simmer heater just to keep the moisture out of the box.

TTFN

FAQ731-376

 

[fpiergen]

thank you all for your input. It is much appreciated!

 

[Demon3]

To avoid heating you need an IR reflective coating not an adsorbing one. The most common is tin oxide, that's what they use on the glass for oven doors, it reflects the heat back in (90%), thus helping the cooking and preventing the outside getting dangerously hot.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[fpiergen]

Demon3

Do you know if this can be used on plastic?

 

[BrunoPuntzJones]

fpiergen,

Demon3 is refering to fluorinated tin oxide-- just tin oxide won't do much. You certainly can get FTO to coat most materials (I've done it myself).

 

[Demon3]

Thank BrunoPuntzJones, my colleagues always just called it tin oxide so you've taught me something there. Thanks for the clarification.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell