DVD coating

I was just wondering why DVD companies don't put a clear scratch-

resistant coating on the bottom of DVDs. This would help keep the
DVD

from getting scratched. It would be like Scotch tape.

bob@coolgroups.com wrote:
> I was just wondering why DVD companies don't put a clear scratch-
>
> resistant coating on the bottom of DVDs. This would help keep the
> DVD
>
> from getting scratched. It would be like Scotch tape.
>

Then the coating would get scratched and you wouldn't have gained
anything. The adhesive of peel off layers could interfere with the laser
or leave residue behind. The polycarbonate plastic that disks are made
of is a fairly hard plastic anyway.

Check you audio/video retailer for polishing kits (might NOT be at
places like the supermarket or chain pharmacy). Some sell manually
operated kits that are less expensive than either the motorized or hand
cranked kits.

What you really have to worry about is the much thinner lacquer coating
on the TOP of single sided optical media. If damage (chemical from a
solvent based marking pen or mechanical from ball points or other
objects) penetrates that, the aluminum reflective layer corrodes.

Use the center hole release button in storage cases that are equipped
with them to reduce the chance of cracking.

<bob@coolgroups.com> wrote in message
news:a5fb58f6-7b93-4bfc-8140-a5c00d28638c@21g2000hsj.googlegroups.com...
>I was just wondering why DVD companies don't put a clear scratch-
> resistant coating on the bottom of DVDs. This would help keep the
> DVD
> from getting scratched. It would be like Scotch tape.


They already do. In fact it is an extremely thick coating. It is
almost as thick as the disc itself.

The data is not recorded on the bottom (lens-facing) side of the disc.
The data is record in pits or bubbles on the TOP side. That is the
side just under the label. That is the side that you write on. That
is the side which if scratched through will permanently destroy the
data on that disc.

bob@coolgroups.com wrote:
> I was just wondering why DVD companies don't put a clear scratch-
>
> resistant coating on the bottom of DVDs. This would help keep the
> DVD
>
> from getting scratched. It would be like Scotch tape.
>

I thought this document was neat. It covers a bit about the
various kinds of optical media.

http://www.memorex.com/downloads/whi...edia_Jul07.pdf

On Sun, 6 Jan 2008 01:43:15 -0600, "VanguardLH"
<VanguardLH@mail.invalid> wrote:

><bob@coolgroups.com> wrote in message
>news:a5fb58f6-7b93-4bfc-8140-a5c00d28638c@21g2000hsj.googlegroups.com...
>>I was just wondering why DVD companies don't put a clear scratch-
>> resistant coating on the bottom of DVDs. This would help keep the
>> DVD
>> from getting scratched. It would be like Scotch tape.
>
>
>They already do. In fact it is an extremely thick coating. It is
>almost as thick as the disc itself.

Not really a coating, it is the body of the disc, the
polycarbonate platter upon which it's all built.



>
>The data is not recorded on the bottom (lens-facing) side of the disc.
>The data is record in pits or bubbles on the TOP side. That is the
>side just under the label. That is the side that you write on. That
>is the side which if scratched through will permanently destroy the
>data on that disc.

You are thinking of a CD not a DVD. A CD has the metal
layer set on top of the polycarbonate disc then a coating
over the metal layer. A DVD has a bottom layer of
polycarbonate, a metal layer (or dye then the layer if a
writable disc), then an adhesive and top polycarbonte layer.

In the case of DL DVD, there's just a spacer and 2nd metal
layer (plus dye if recordable) before the adhesive and top
polycarbonate layer.

While I'm not certain of it, I believe the reason for this
difference has to do with focal length to read the smaller
pits on a DVD, that it's better to keep them closer to the
bottom for this purpose though a top layer is still added
for protection and to maintain a thickness enough for
acceptible rigidity.

On Sat, 5 Jan 2008 18:24:57 -0800 (PST), bob@coolgroups.com
wrote:

>I was just wondering why DVD companies don't put a clear scratch-
>
>resistant coating on the bottom of DVDs. This would help keep the
>DVD
>
>from getting scratched. It would be like Scotch tape.

Ok, but is scotch tape very scratch resistant?

I think some do have a scratch resistant coating, though
there's only so much a coating can do if the underlying
material is as soft as polycarbonate is, and if the layer
were too thick it might interfere with reading the disc.
Plus, cost has to be a factor, people will take all kinds of
shortcuts to save two cents.

Also consider that if a DVD is damaged, it's not a loss to
the company manufacturing the disc, it's a loss to someone
else who then has to buy another disc if it can't be
polished out. Wasn't there even talk in the past of
companies like Disney making discs that automatically
self-destruct within a few days of exposure to light? I
think DVDs are considered disposable to the extent that any
changes would only be made if it seems to save someone
(besides the buyer) some money.

bob wrote:
> I was just wondering why DVD companies don't put a clear scratch-
>
> resistant coating on the bottom of DVDs. This would help keep the
> DVD
>
> from getting scratched. It would be like Scotch tape.

http://www.tdk.com/procommon/press/a...id=30&site=pro

Brett Kline wrote:
> bob wrote:
>> I was just wondering why DVD companies don't put a clear scratch-
>>
>> resistant coating on the bottom of DVDs. This would help keep the
>> DVD
>>
>> from getting scratched. It would be like Scotch tape.
>
> http://www.tdk.com/procommon/press/a...id=30&site=pro

Also
http://www.newegg.com/Product/Produc...82E16817131113

"kony" wrote in message
news:iv71o399o27r4d2crt4dfb1ca1v5m898id@4ax.com...
> "VanguardLH" wrote:
>
>><bob@coolgroups.com> wrote ...
>>>I was just wondering why DVD companies don't put a clear scratch-
>>> resistant coating on the bottom of DVDs. This would help keep the
>>> DVD
>>> from getting scratched. It would be like Scotch tape.
>>
>>They already do. In fact it is an extremely thick coating. It is
>>almost as thick as the disc itself.
>
> Not really a coating, it is the body of the disc, the
> polycarbonate platter upon which it's all built.

That was tongue-in-cheek because the entire disc is the "coating";
i.e., there doesn't need to be a coating since the recording substrate
is on the other side (or in the middle).

> You are thinking of a CD not a DVD. A CD has the metal
> layer set on top of the polycarbonate disc then a coating
> over the metal layer. A DVD has a bottom layer of
> polycarbonate, a metal layer (or dye then the layer if a
> writable disc), then an adhesive and top polycarbonte layer.

And still that layer of polycarbonate is a hell of lot thicker than
any anti-scratch coating that would be apply. The point was that a
coating would be worthless. I also suspect that an anti-scratch
coating would be more hard than the polycarbonate for the disc so it
would be more difficult to repair later to remove light scratches.

I've had CDs and DVDs for years. Very few scratches, even for the
game CDs, but not even enough to bother trying to polish them.
However, some users are very clumsy and overly rough with them. I'd
tell them to treat them like their eyeglasses but many of those users
aren't too kind to their eyeglasses, either.

bob@coolgroups.com wrote:
>
> I was just wondering why DVD companies don't put a clear scratch-
> resistant coating on the bottom of DVDs. This would help keep the
> DVD from getting scratched. It would be like Scotch tape.

A waste of time/money.


--
http://www.bootdisk.com/

The laser would be impeded from burning and reading the optical pits by the
extra layer.

--
--DaveW
<bob@coolgroups.com> wrote in message
news:a5fb58f6-7b93-4bfc-8140-a5c00d28638c@21g2000hsj.googlegroups.com...
>I was just wondering why DVD companies don't put a clear scratch-
>
> resistant coating on the bottom of DVDs. This would help keep the
> DVD
>
> from getting scratched. It would be like Scotch tape.
>

DaveW wrote:
>
> The laser would be impeded from burning and reading the optical
> pits by the extra layer.

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