Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in

High stiffness plastic or composite for glass replacement 2

Status
Not open for further replies.
FlixFlix

FlixFlix

Electrical
Feb 2, 2010
12
0
0
US
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!
 
Replies continue below

Recommended for you

Sort by date Sort by votes
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.

 
Upvote 0 Downvote
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.
 
Upvote 0 Downvote
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?
 
Upvote 0 Downvote
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

Consultant to the plastics industry
 
Upvote 0 Downvote
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?
 
Upvote 0 Downvote
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
Footwell%20Animation%20Tiny.gif
 
Upvote 0 Downvote
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!
 
Upvote 0 Downvote
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

Consultant to the plastics industry
 
Upvote 0 Downvote
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.
 
Upvote 0 Downvote
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

Consultant to the plastics industry
 
Upvote 0 Downvote
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.



 
Upvote 0 Downvote
@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?
 
Upvote 0 Downvote
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.


Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
Upvote 0 Downvote
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.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

Thanh_fromVietnam
  • Locked
  • Question
Best plastic material/ grade for Plastic Pallet 1
Replies
2
Views
17
dgallup
dgallup
Snowshovel1
  • Locked
  • Question
Best plastic material /grade for snow shovels
Replies
4
Views
32
IRstuff
IRstuff
Kami.K
  • Locked
  • Question
Bonding glass to plastic 1
Replies
5
Views
31
TugboatEng
TugboatEng
Azeen
  • Locked
  • Question
Mixing virgin and recycled Polypropylene Granules in single use plastic straw extrusion machine
Replies
5
Views
17
Linda0510
Linda0510
clyde Verse
  • Locked
  • Question
Any way to produce a 100% same plastic lampshell without injection mold?
Replies
5
Views
25
Pud
Pud
Back
Top