UV stable translucent inflammable polymer

[mark0310]

Glass seems to be the only suitable material for the bulb part of a lightbulb, because of all the demands on thermal,optical, inflamability and mechanical requirements....however I have a design need for a secondary off-white opaque covering adjacent to the glass bulb on a low-energy lightbulb.....effectively a second skin to the glass bulb but with a small (circa 5mm)air gap between them. This immediately removes the thermal demand but the optical (UV stability) and inflammable requirements remain.
I have looked at blow-moulding using PC or a PC alloy but am concerned about Yellowing of the cover.
I am looking for advice on the most suitable polymer to use.
Many Thanks
Mark

 

[mark0310]

Sorry just noted I wrote Opaque, I meant translucent...which leads to the question.."What degree of light transmission"...effectively as for an Opal lightbulb....the light source has a clear glass bulb.

Second issue is the exposure, the UV stability has to be OK for the source light over 4000 hours as well as daylight exposure.

 

[IRstuff]

Whatever they use for automobile head and tail light shrouds, probably.

TTFN

FAQ731-376

 

[mark0310]

Thanks,I believe they tend towards PC-ABS, would this be OK in a translucent opal and given the adjacency to the light source it's a big ask on the UV stability?

 

[IRstuff]

Depends on the level and range of the UV, probably. But my headlights and taillights are exposed to external ambient 10 hrs a day, 260 days a year, for 5 yrs with no obvious degradation.

There are other materials that are inherently translucent-like, like Kynar, which is used for the color coating on aluminum roofs and in vinyl siding.

TTFN

FAQ731-376

 

[mark0310]

I'll check out the polymers used for the head and tail lights for flammability, if they're PC based alloy then should be reasonable. Similarly I'll check up on Kynar.

Domestic use is usually heavier than the automotive, ie. taking the 4000 hrs target then for an average 30mph that gives 120K miles, perhaps the average life of a vehicle?

thanks

Mark

 

[mark0310]

Just read this off Wikipedia;
""Plastic" (polycarbonate) lenses can become cloudy and discoloured. This is due to oxidation of the painted-on lens hardcoat by ultraviolet light from the sun and the headlamp bulbs. If it is minor, it can be polished out using a reputable brand of a car polish that is intended for restoring the shine to chalked paint. In more advanced stages, the deterioration extends through the actual plastic material, rendering the headlamp useless and necessitating complete replacement. Sanding or aggressively polishing the lenses, or plastic headlight restoration, can buy some time, but doing so removes the protective coating from the lens, which when so stripped will deteriorate faster and more severely."

Because my cover needs to be fairly thin (circa 1mm) and is very close to the light source then the polymer of choice must be as UV stable as possible.

 

[Demon3]

ASA could work, it's milky and is just like ABS only UV stable (10-20 years outdoors) and of course more expensive than ABS.

Check

http://www.lurans.com

there is one FR grade.

Chris

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[btrueblood]

Because my cover needs to be fairly thin (circa 1mm) and is very close to the light source then the polymer of choice must be as UV stable as possible. "

Unless the bulb "glass" is actually quartz, or pure fused silica, it is unlikely to pass any significant amount of UV radiation.

It will, however, pass quite a bit of IR radiation, and I'm not sure a 5mm airspace would be sufficient to keep the temperature of a polymer cover below an arbitrary limit in all possible surroundings...

 

[mark0310]

Chris, thanks, I'll check out the ASA....I think it is a styrene alloy? so not surprised there's just the one FR....also need to see how it is for light transmission, hopefully not Milky opaque!

Trueblood..interesting comment re: UV and IR..the lightbulb type I'm working with is the low-energy type, basically a compact fluorescent, so the heat side is low, circa 50C.

 

[Demon3]

It's for sure possible to formulate something to meet your needs but that's a bit beyond the scope of this thread.

If the ASA is too milky at that thickness then you could dilute it with either SAN or PETG to make it more transparent. That'll let you adjust the opacity.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Demon3]

By the way, I developed a brand new polymer called ThermoShift. It changes transparency reversibly when you heat and cool it. I always wanted someone to make a light shade out of it but didn't have contacts to the right people. Does it sound interesting?

Your posting reminded me of it as you're going for a translucent effect.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Opalescent, UV stable and FR all together.

I think your stuck with a heavily UV stabilised FR PC.

You need to check if the opalescent pigment, UV stabiliser and FR additives interact to reduce effectiveness. I know the opalescent pigments used for light diffusers are difficult formulations.

The difficulties are translucent at a repeatable level of transmission and diffusion along with transparent flame retardants. FR additives in general tend to be unstable

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[mark0310]

Pat, as you note, my expectation is that the opalescent pigment along with the base polymer (PC) both needs UV stability and with FR additive may be time limited. At least PC is nominally FR. Where these then affect translucency and it's repeatability I have no idea. Many thanks for your comment.

Chris, interesting sounding polymer, Thermoshift, reminds me of a glaze used in the ceramics industry for indicating when a mug (cup) has hot fluid in it. If it goes transparent when cool and gradually less so when hot there must be many applications out there wanting to speak to you!

 

[Pud]

FR to UL Vo at 1mm is not going to happen if you want transparent.

iirc, 10% GF PC is Vo at thin sections. With a good UV package might work.

(We make PC covers for CF festoon lights - never had a problem reported yet regarding yellowing, but the PC is around 15mm from the tubes.)

http://www.tynevalleyplastics.co.uk

 

[mark0310]

Hello Pud; I need opalescent, as for the usual practice with conventional light-bulbs, so it's translucent but not transparent. It's a good point that with a low % GF the 1mm section with PC may have sufficient light transmission. Thanks for your advice.

 

[Demon3]

Funny as I used to work on ceramic glazes in my first ever job at Cookson!

ThermoShift is getting a lot of interest alright, just keen to get someone to try it in a lighting application as I think it'd look cool. You can choose whatever transparency temperature you want from -20C to +80C.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

If you simply want to diffuse the light GF might just do it. If you want something like the old Perspex 040 opal that used to be the lighting industry std spec where the tubes or bulbs should be hidden by the diffuser that will be more problematic. to emulate a frosted light bulb, probably GF will do it. Good call Harry.

I really do keep looking for an application for thermoshift as I find it fascinating.

Bayer certainly make a transparent FR PC, but it does not get down to V0 at 1mm. To get that level, transparency is (or was last time I looked) lost.

What is the real maximum temperature and what is the real risk of fire.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[mark0310]

Pat,
The cover has to comply with “Luminaires – BS-EN 60588 – 1 , to amendment A11” this is because the cover would be within 30mm of a potential heat source. i.e the electrics of the Compact Fluorescent. So the risk is not the normal running temperature (a contact thermo-couple gave 65C peak on the glass of the CF, with 5mm air gap I'd expect circa 50C for the cover)but the risk, however small, of the ignition source from the FC electrics causing the cover to catch fire. I shall check up on the above standard to see if it specifies a performance standard to comply with, such as V0, V1, V2 from UL94, but all that I've been told to date is that the polymer must be inherently inflammable.
Concerning the translucency a very frosted look wouldn't be acceptable, it has to be a homogeneous dispersion resulting in a look just as for Opal lightbulbs (I note these are clear glass that have been painted on the inside).
Thanks again for your input.
Mark

 

[Demon3]

Nearly forgot, there is a new type of phosphorous based polymer that could work either alone or as a transparent blend with polycarbonate.

http://www.frxpolymers.com/

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry