High stiffness plastic or composite for glass replacement 2

[FlixFlix]

Hi,

I'm looking for a suitable material, composite or layered sheet for replacing an LCD overlay, currently made of glass, with the ultimate goal of significant weight reduction.

Normally, a hard coated PMMA sheet would do the job in most applications and the weight would be cut in half. However, in this particular product, I need extra stiffness to prevent (or minimize) external factors bending the sheet and reaching the LCD, possibly damaging it.

Glass is about 10-20 times stiffer than any plastic I know of and I'm not expecting to even come close to that. Worst scenario is ending up with the aforementioned PMMA; however, I'd like to know that at least I'm using "the best" there is. Cost is not an issue.

Any suggestions? Thank you!

 

[btrueblood]

So you need the stiffest possible, optically clear plastic?

The optical clarity part will preclude fillers.

SAN, Acrylic, and styrene have the highest modulus of optically clear plastics, though there is a castable polyester listed with higher modulus in one of my references (dunno how clear this will be though). Clear nylon and polycarbonate are tougher than any of these, at slightly lower stiffness.

 

[FlixFlix]

A tiny bit of tint (not cloudy) shouldn't be a problem; after all, we're looking at a sheet just over 1 mm (3/64") thick.

As for toughness, put it like this: the LCD and probably the entire device would be destroyed beyond recognition before any plastic would even think about breaking. So really, stiffness is the #1 characteristic I'm looking for.

 

[Demon3]

SAN (3.7 GPa) has the highest followed by polystyrene (3.3 GPa) They are both really cheap. Pick SAN if you need chemical resistance, it's better than PS for that.

You can search polymers by modulus at

http://www.matweb.com

(free)

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[FlixFlix]

I did a quick search on matweb and it looks like 3-4 GPa is pretty much the most to expect.

I was thinking however that maybe I could find some kind of sheets reinforced with fibers of a matching refractive index, with minor effect on clarity. Am I out of luck?

 

[Demon3]

Refractive index matching does work, in fact I developed a new type of thermoplastic that has switchable transparency based on matching.

However, it's not so easy, you need to match the refractive index of the filler and polymer to within 0.003

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[FlixFlix]

That composite of yours is obviously not what I need here but it's very interesting, nevertheless! Is anybody making it yet?

On the other hand, are you saying that what I'm looking for is not realistic, as it would definitely need to stay transparent over a relatively wide range of temperatures?

 

[Demon3]

Hello,

Thanks for the interest! I get calls all the time about it and I'm in the process of commercialising it. You can read all about ThermoShift here:

http://www.phantomplastics.com/ThermoShift_Smart_Plastic.php

That includes info on mechanical properties and so on.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Demon3]

I have an idea how to make you a super high modulus transparent plastic. I'll do some checking to see whether the numbers pan out.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Demon3]

I checked and it should work. Modulus of 6-9GPa should be possible.

All the best,

Chris

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[MacGyverS2000]

Have you investigated Gorilla Glass? I know you said you want plastic, but if you haven't researched all available options in glass, you may be shortchanging yourself. That stuff is tough, and quite a few PDA and smart phone manufacturers are using it (Motorola being one off the top of my head).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[btrueblood]

Chris,

After you get it patented and start making your second billion, please do spill the beans here - making a high modulus transparent plastic doesn't sound easy!

 

[Demon3]

Hi btrueblood!

Still hunting for the first million although I do have some prospects. I am almost positive that I can make that plastic with very high modulus and transparent. You're right, it's not that easy unless you know a trick or two. Who wants it? What do you see as applications? Who will develop it with me? I'm a one man show.

Chris

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[btrueblood]

Hmmm. "Who wants it" is the big one, and I dunno.

What would the cost of the new plastic be (about equal to PC?), and do you expect you could make the material as tough as polycarbonate? It might make good eyewear lens material.

 

[Demon3]

Cost would be close to PC. However, impact would be poor in the base form although it is possible to improve that and retain transparency. Modulus and strength would be very good though. Chemical resistance would be good.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[btrueblood]

Chris,

Some niche ideas, maybe they'll spark some thoughts for you.

Chemical and process flow meters - the rotameter type - many for higher pressures currently use glass. A plastic window, with some reduction in fragility would be helpful.

Dive cases and/or lenses for underwater photography.

 

[FlixFlix]

@btrueblood: I think you are referring mostly to "strength" throughout your posts; at least that's how it appears to me. In that case, plain PC is the material of choice and you can't go wrong with it. If I'd lock you in a polycarbonate cage and give you a sledgehammer, you'll still be there a couple of days later. Exhausted and frustrated.
A higher modulus doesn't necessarily mean a tougher material, in fact, the opposite is true in most cases. Take glass, for example: its modulus is much higher than, say, acrylic (60-90 GPa vs 3-4 GPa) yet it can't bear a load nearly as high as the acrylic would.

@MacGyverS2000: I looked up the Gorilla Glass brand and it seems to be a good material. The "only" bad thing about it is that it's... glass. They list its density at 2.44 grams (typical for glass), whereas PMMA weighs in at roughly 1.2 - less than half. Here's how that translates into my application: with glass, a 23cm x 18cm x 1.2mm slab adds up to about 125g, whereas the same slab in acrylic would be just 60g. Considering that the whole device is 450g, those 60 grams mean quite a difference.

@Chris: When I posted on the board, I was hoping to find some references to an existing products that others might know about. However, if nothing is currently produced, I'll go with PMMA, at least for the time being.
If you're actually wondering what the potential market is for a clear, rigid composite and who would ever need it... then I guess you spend too much time in the lab, LOL
As for who will develop it with you - I really don't have a clue since I'm not connected to the "world of plastics". Would you be able to have at least some sample quantities made?

 

[patprimmer]

As far as transparent thermoplastics go, PMMA has about the highest modulus you will find.

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

http://eng-tips.com/market.cfm

for site rules

 

[Demon3]

If you go here and click the file thermoplastics performance versus cost you will see a plot of modulus and cost for all common thermoplastics. You will find SAN is stiffer and cheaper than PMMA. The prices there are from 2003. I am just finished a new version with the latest pricing.

http://www.phantomplastics.com/Downloads.php

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[btrueblood]

Flix,

No, I am talking modulus as in "E" or Young's modulus. Having a "lens" (or even an optical flat) with high stiffness is only important (that I can see)(pun hugely intended) where you must have a clear view of what's on the other side with no distortion. Or, as in your case, where what must be visible is susceptible to contact stresses. But, no matter, Chris will never point you wrong.