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Coating Promises Scratch-Proof CDs, DVDs, LCDs
13.7BillionYears writes "NewScientist reports that TDK has developed a transparent polymer for LCD screens and optical media that is impervious to general neglect and abuse. Quoth the reporter, 'In one of the most convincing technology demonstrations this reporter has witnessed, I was handed a CD, a wire-wool pan scourer and some permanent marker pens, and invited to scratch or mark the discs. Hard as I tried, I could not make a single mark on the disc with the scourer. And the ink simply wiped off.' The coating is apparently responsible for Blu-Ray's new caddy-less form factor."
Often, CD rot is due to poor evacuation of oxygen between the layers of the CD during manufacture. If the O2 is already present, a new coating won't help much.
People should not fear what they do not understand; people should fear because they do not understand.
But I'm wary of anything touted as -proof. -proof smacks of marketing getting their grubby paws on it.
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Sure they gave you some steel wool to scratch the CD with, it's only a 3-4 on Moh's hardness scale, as in not very. I'll be impressed when it can withstand being tossed shiny side town on a little bit of sand on a hard surface and rubbed around vigrously. Quartz/glass/sand/silicon are a great deal more likely to encounter your CDs than steel wool is and they're a 7 or so on Moh's hardness scale.
I picked Moh's because to explain because: Mohs hardness is defined by how well a substance will resist scratching by another substance. from: http://www.calce.umd.edu/general/Facilities/Hardn
Question everything
Well since DVDs use visible light lasers (650nm) to both write and read, and you since you can see through the plastic to the recording surface, there's no reason it shouldn't work.
Actually, what you're referring to is the side and rear windshield tempered safety-glass, which breaks into small squarish pieces with any sharp impact.
The windshield is actually layers of glass and a clear plastic, which holds the glass together as it shatters.
Safety glass breaks into cubes, but normal glass spiderwebs.
As a volunteer firefighter, and not only being trained on how to remove automotive glass expediently, but also having seen "forehead dents" in windshields (luckily no full-ejection of occupants out the windshield), I can attest to how it actually breaks.
BMW is putting Polycarbonate windows in the 740 series cars. You can't break those with a sledgehammer (I know someone who tried, our instructor on jaws of life tools).
WRONG again. DVDs have the data in between two layers of plastic. So scratch the label as much as you want, it won't damage the data as long as you don't puncture the plastic.
;-)
Fun Tip: Nuke a DVD for a minute or two and the two plastic disks will slide apart. Double the frisbees double the fun.
I'm just this guy, you know?
Re: Automotive windows
The whole point of tempered automotive glass is to minimize injury to the heads of the passengers. Windshields use multiple layers of glass with a plastic film in between, to keep broken bits from flying into the vehicle's occupants. Side and rear windows are designed to break into small enough peices that lacerations are minimized, and lack stabilizing layers.
Contrast this with a plastic window. Most plastics are not very sharp when broken. The windows can be designed to bend outward easily. And they don't weigh anywhere near as much as glass, lessening the problems of momentum.
And since plastic doesn't have the inherent problem of normal glass (big, heavy, jugular-slicing chunks of razor-sharp material being flung about at incredible speeds), it doesn't need to have the same safeguards. To state otherwise is an example of FUD.
The safety problem, then, is easy to quantify:
Using your head at a velocity of 60MPH, does it hurt more to hit a 40lb glass windshield which will shatter (but maintain its mass and inertia) on impact, or to hit a 10-pound shatterproof plastic window which is flexibile enough to absorb your forward energy, and will remove itself outward from the vehicle on impact?
I don't have the solution to that problem, but I'd say that it's close.
On with the anecdotes:
Plastics (Lexan, in particular) have been used in race car windows for a Really Long Time Now. And since dead/blinded drivers can't win races, the people involved in selecting said windows have a rather vested interest in making sure that they're safe. So far, they've done just fine.
I'm guessing that if the automobile industry is keen enough on saving weight and materials that they're seriously discussing increasing voltage to reduce the weight of electrical wiring, that they'd really appreciate windows that aren't as heavy as the glass that they've been using forever.
If only Lexan didn't scratch so easily, I'm sure they'd jump all over it.
Oh, wait, I almost forgot. Lexan == polycarbonate == the stuff CDs are made of. Didn't TDK recently develop a coating to solve that problem?
Kid-proof tablet..
Compare a DVD and a CD of yours and you'll see that the DVD is made of two plastic layers with the reflective surface between them, while the CD only has one with the reflective surface at max barely protected bv a coating.
If you have an old or damaged DVD and CD, try scratching them from the label side. The CD will instantly have scratches that can be seen from both sides, but I'll bet you won't damage the reflective surface of the DVD if you scratch it with anything short of a box cutter. That's why the manufacturer logo and other preprinted text on the DVD-R label side appears a bit "fuzzy" sometimes - it is beneath 0,6mm a polycarbonate layer.
This was the only drawing I found without searching too long. It pictures a dual layer DVD, but the general construction scheme is the same.
Upper polycarbonate layer:
Outer label (optional, mostly used on movie DVDs)
Polycarbonate 0,3mm
Data U-1 and semi-reflective layer upper side (optional for dual-layer, double-side discs, only with no outer label)
Polycarbonate 0,3mm
Data U2 and full reflective layer upper side (optional for double-side discs, only with no outer label)
Inner label (optional, used on most DVD-Rs, only without label and not on double-sided discs of course)
Bonding glue
Lower polycarbonate layer:
Full reflective layer down side and data D-2
Polycarbonate 0,3mm
Semi-reflective layer down side and data D-1 (optional for dual-layer discs)
Polycarbonate 0,3mm
Thickness total ~1,2mm. All DVDs have two layers of polycarbonate with the primary reflective surface sandwiched between them (the secondary, if present, is embedded within). You can scratch the underside, diffracting the laser but you cannot peel off the reflective coating anymore like you could with CD-Rs. That gives DVDs a better durability and theoretical aging resistance, but how fast the glue between the sandwiches dissolves or affects the refletive layer is yet to be determined.
Each reflective surface has a capacity of ~4,7 GB, hence dual-layer discs have ~2x 4,7 and double-sided, dual-layer discs ~4x 4,7. (a little less due to longer pit lengths in dual layer recording) The rare "double-sided DVDs" actually have two sides of data like an old vinyl recording.
I have experience with plastic aircraft windows. Canada's National Research Council has a pneumatic bird gun that can fire 8 lb. birds up to mach 1.5.
.2 goes right through polycarbonate, and it does shatter. Unfortunately for the pilot, the edges of shattered polycarbonate are sharper than razor blades, certainly sharper than the edges of shattered glass. The canopy for the F-5 is about the worst design from this standpoint.
.22 cal go right through 15-year old bulletproof glass. So polycarb gets brittle when exposed to air, hence the sandwich approach used by aircraft manufacturers. Car windows would have to be done this way too.
A 4 lb bird at mach
As far as I know, the problem with aircraft applications is that the set of requirements is lengthy:
- nearly shatterproof at high speed.
- impervious to cold, changes in density, including fogging.
- able to withstand repeated pressurization/depressurization
- ability to resist bird strikes.
Tall order. Most modern aircraft (both civil and military) use a poly/glass/poly sandwich, with a thin wire mesh for increased stability.
Other problem is from bulletproofing -- polycarbonate loses its strength over time. I think it's offgassing. Anyway, for this reason, bulletproof glass loses its rating after some time, and has to be replaced. I've seen a
Yes, the muzzle area for the birdgun is a mess of vaporized bird. and it smells funny.