U.S. patent application number 10/163855 was filed with the patent office on 2003-07-03 for limited play optical devices with interstitial reactive layer and methods of making same.
Invention is credited to LeBlanc, Arthur R. III, Thompson, Robert F..
Application Number | 20030123302 10/163855 |
Document ID | / |
Family ID | 23139712 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030123302 |
Kind Code |
A1 |
Thompson, Robert F. ; et
al. |
July 3, 2003 |
Limited play optical devices with interstitial reactive layer and
methods of making same
Abstract
Methods and apparatus are provided for making an optically
readable storage media in which the reading beam passes through a
bonding layer configured with a reactive material that transforms
from an optically transparent state to an optically opaque state
after exposure to a predefined stimulus, thereby inhibiting access
to the data encoded on the optically readable storage media. The
method includes steps of synthesizing a blocked dye combining the
blocked dye with a carrier material curing the resultant
combination deblocking the dye to produce a reduced dye in the
resultant bonding layer exposing the optically readable storage
media with the reactive material in its bonding layer to a
predetermined stimulus. In a further aspect of the present
invention methods and apparatus are provided for making an
optically readable storage media wherein the reading light passes
through the bonding layer and the data encoded information is
encoded on the L1 substrate. In yet another aspect of the present
invention methods and apparatus are provided for making an
optically readable storage media with at least two mechanisms for
limiting access to the encoded data of the optically readable
storage media.
Inventors: |
Thompson, Robert F.;
(Kennebunk, ME) ; LeBlanc, Arthur R. III;
(Kennebunk, ME) |
Correspondence
Address: |
HALE AND DORR LLP
300 PARK AVENUE
NEW YORK
NY
10022
US
|
Family ID: |
23139712 |
Appl. No.: |
10/163855 |
Filed: |
June 5, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60295903 |
Jun 5, 2001 |
|
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|
Current U.S.
Class: |
365/200 ;
G9B/20.002; G9B/23.087; G9B/7.196 |
Current CPC
Class: |
G11B 7/244 20130101;
Y10T 428/31504 20150401; G11B 7/256 20130101; G11B 20/00586
20130101; G11B 20/00608 20130101; G11B 20/00086 20130101; G11B
7/263 20130101; G11B 7/2534 20130101; G11B 7/259 20130101; G11B
20/00927 20130101; Y10T 428/21 20150115; Y10T 428/31551 20150401;
G06F 21/80 20130101; G11B 7/253 20130101; G11B 7/257 20130101; G11B
7/2578 20130101; G11B 7/246 20130101; G11B 7/2531 20130101; G11B
7/2542 20130101; G11B 7/258 20130101; G11B 7/24038 20130101; G11B
23/282 20130101; Y10T 428/31511 20150401; G11B 7/2595 20130101;
G11B 7/2533 20130101; G11B 7/252 20130101 |
Class at
Publication: |
365/200 |
International
Class: |
G11C 007/00 |
Claims
What is claimed is:
1. A method of authoring a master to produce a substrate of a
multi-substrate, optically-readable storage medium, comprising the
acts of: receiving information defining a topology having a
plurality of pits and lands; producing an inverted version of the
topology; and using the inverted version of the topology as the
topology of the master.
2. The method of claim 1 wherein the topology-defining information
is recorded in a predefined format to laser beam record a blank in
a given rotational direction, and wherein the acts of producing and
using the inverted version of the topology includes the act of
rotating a blank in a direction opposite the given rotational
direction and using the information to laser beam record the blank
to produce the master.
3. The method of claim 1 wherein the optically-readable storage
medium is a DVD, and wherein the information is for a topology of a
recorded layer corresponding to one substrate, and wherein at least
one of the other substrates of the medium is a dummy substrate.
4. The method of claim 2 wherein information corresponding to a pit
is used to record a land and information corresponding to a land is
used to record a pit.
5. The method of claim 1 wherein the act of receiving information
defining a topology includes the act of receiving a father stamper
for the substrate, and wherein the act of producing an inverted
version of the topology includes the act of producing a mother
stamper from the father stamper, and wherein the mother stamper is
used as the master.
6. A method of forming a multi-substrate, optically-readable
storage medium, wherein the medium has information defined as a
plurality of pits and lands on an upper substrate and said
information is to be read by light being transmitted through a
lower substrate, the method comprising the acts of: receiving
information defining a recording layer of a substrate of a DVD;
using the received information to produce an upper substrate by
forming an inverted version of the topology and using the inverted
version as the topology of the upper substrate; receiving a lower
substrate; forming the optically-readable storage medium by bonding
the lower substrate to the upper substrate via an adhesive.
7. The method of claim 6 wherein the adhesive includes a reactive
agent that interferes with the passage of light through at least a
portion of the adhesive in response to predetermined stimulus.
8. The method of claim 6 including the act of receiving information
defining instructions to direct a reading device to read a portion
of the upper substrate, prior to the reading device accessing a
predefined portion of the lower substrate.
9. A method of forming a multi-substrate, optically-readable
storage medium, wherein the medium has information defined as a
plurality of pits and lands on an upper substrate and said
information is to be read by light being transmitted through a
lower substrate, the method comprising the acts of: receiving
information defining a recording layer of a substrate of a DVD;
using the received information to produce an upper substrate;
receiving a lower substrate; forming the optically-readable storage
medium by bonding the lower substrate to the upper substrate via an
adhesive and so that the medium includes a reactive agent that, in
response to predetermined stimulus, interferes with the passage of
light through an optical path for the light to the upper substrate
from the lower; and wherein the medium is formed to instructions to
direct a reading device to read a portion of the upper substrate,
prior to the reading device accessing a predefined portion of the
lower substrate.
Description
[0001] Priority is herewith claimed under 35 U.S.C. .sctn.119(e)
from copending Provisional Patent Application 60/295903, filed Jun.
5, 2001. The disclosure of this Provisional Patent Application is
incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to optically readable data storage
media and, more particularly, to methods, compositions, and
articles of manufacture of optically readable data storage media
wherein the data is accessible for a finite period of time.
BACKGROUND OF THE INVENTION
[0003] Optical discs such as CDs and DVDs are sold and rented to
consumers. The content of the optical discs may be music, movies,
video clips, software or data. The purchase price of CDs and DVDs
can be high; this reflects the value of the information encoded on
the discs, such as movies or software, rather than the
manufacturing cost of these optical discs. Frequently, content
providers, such as movie studios or software companies, do not want
to sell at a low cost copies of their information that will have a
long lifetime in the marketplace. Consumers frequently want to
access content information only for a brief period and at a low
cost. Rentals of CDs and DVDs enable consumers to access content
information at a lower cost than if consumers had to purchase the
media, but the need to return the physical media is inconvenient.
It would be desirable to have limited play/expiring optical media
that the user could purchase at a low cost, would address the
concerns of the content providers about lifetime of their content
in the marketplace, and which would not have the disadvantage of
having to be returned, as is the case with videotape movie rentals
today. It would also be desirable to manufacture such optical media
at low cost and with minimum changes to existing manufacturing
processes for optical discs. Finally, in order for the content
providers to be willing to provide their content through limited
play/expiring optical media, the mechanism that limits playing of
the media should not be easily defeatable, enabling access to the
content beyond the intended period of use.
[0004] Heretofore, the requirements of low cost, limited content
lifetime, avoidance of rental returns, resistance to attempts to
defeat, and minimum changes to existing manufacturing processes
referred to above have not been fully met. What is needed is a
solution that simultaneously addresses all of these requirements.
One embodiment of the present invention is directed to meeting
these requirements, among others.
[0005] Several approaches have been proposed to make a limited play
(expiring) optical disc based on a layer that changes from a
non-interfering ("transparent") state where it does not interfere
with the reliable reading of the information on the optical disc to
an interfering ("opaque") state where the layer interferes with the
reading of the data on the optical disc (e.g., see U.S. Pat. No.
5,815,484 assigned to Smith et al. and U.S. Pat. No. 6,011,772
assigned to Rollhaus et al.). The interference may be due to the
layer becoming dark, reflective, highly birefringent, pitting,
bubbling, shattering, corroding, bending, changing refractive
properties or combinations of these, among other possibilities.
[0006] Optical discs with such a layer changing from a transparent
to an opaque state in response to a stimulus such as exposure to
oxygen in the atmosphere, or the light of the reading laser, can be
used to manufacture limited-play optical discs (such as DVDs) that
become unusable in a predetermined way (such as within a certain
period of exposure to environmental oxygen). Such discs can find a
variety of commercial applications, such as the viewing of a video
by consumers at a moment chosen by the consumer and without the
need to return the expired optical disc.
[0007] The interfering layer that renders the disc unplayable by
inhibiting the reading of the data can be applied via a variety of
techniques to the surface of an optical disc. Such an approach,
however, has a number of disadvantages. For example, it may be
defeated by finding a way to reverse the transition of the layer to
an opaque state, such as exposing the disc to a reducing chemical
substance that reverses an oxidation reaction, or by entirely
removing the layer through chemical means (such as solvents) or
mechanical means (such as polishing or grinding). Also, adding an
additional layer can complicate manufacturing of the optical discs,
for example by requiring additional capital equipment and
additional steps in the manufacturing process, and thus can
increase the costs and/or decrease the yields for the manufacturing
of optical discs.
[0008] A protective layer engineered to resist attempts to defeat
the disc can be applied on top of the interfering layer, an
approach that has been used by at least some of the present
inventors. However, this introduces still another step in the
manufacturing process, further adding to costs and possibly further
reducing manufacturing yields. Furthermore, since the protective
layer would still be at the surface of the disc, it could still be
removed by chemical means (such as solvents) or mechanical means
(such as polishing or grinding), or could be defeated by chemical
substances that could diffuse through the protective layer and
reach the reactive layer.
[0009] As explained above, when manufacturing expiring optical
discs, it is desirable to employ a cost effective manufacturing
process and to make discs that are not easily defeatable. In
addition, it is desirable for the disc to make a rapid transition
from the playable to the expired state. Among other benefits, this
would reduce the variation of the playing period among optical
media players and drives, despite the fact that there is
substantial variability in the ability of the players and drives in
the market to play discs with a given deterioration in their
physical playability characteristics (such as the reflectivity to
the light of the reading laser).
SUMMARY OF THE INVENTION
[0010] Under a first aspect of the present invention limited play
optical devices are provided with an interstitial reactive layer
and methods of making same.
[0011] Under a second aspect of the present invention a method is
provided for authoring a master to produce a substrate of a
multi-substrate, optically-readable storage medium wherein a
topology having a plurality of pits and lands is used to create an
inverted version of the topology in which said inverted version of
the topology is used as the topology of the master.
[0012] Under a third aspect of the present invention a method is
provided for forming a multi-substrate, optically-readable storage
medium, wherein the medium has information defined as a plurality
of pits and lands on an upper substrate and said information is to
be read by light being transmitted through a lower substrate
wherein an adhesive layer bonds the upper substrate and lower
substrate together.
[0013] Under a fourth aspect of the present invention a data
storage device is provided having a first substrate having defined
thereon a plurality of pits and lands covered by a reflective
material and a second substrate wherein a bonding layer containing
a reactive agent, which inhibits transmission of light in response
to a predetermined stimulus, resides between the first substrate
and the second substrate.
[0014] Under a fifth aspect of the present invention an adhesive is
provided for bonding a first substrate and a second substrate,
wherein said adhesive comprises a carrier material and a reactive
material that renders the data encoded substrate unreadable.
[0015] Under a sixth aspect of the present invention a mechanism is
provided that causes the data stored on an optically-readable data
storage medium to first become unreadable and second destroyed.
[0016] Under a seventh aspect of the present invention an
optically-readable data storage medium is provided having a first
substrate and a second substrate, wherein at least one of said
first substrate and said second substrate has information encoding
features, and a bonding layer between first substrate and second
substrate in which said bonding layer comprises a carrier material
and a reactive material where said reactive material changes from a
transparent state to an optically opaque state as a result of a
predefined stimulus.
[0017] Under a eighth aspect of the present invention a method
making an adhesive is provided for bonding a first substrate and a
second substrate wherein a blocked dye is combined with a carrier
material in which said blocked dye is subsequently unblocked
resulting in the reduced form of the unblocked dye.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic cross sectional view of select stages
in the process of creating a physical stamper used in replicating
DVD-5 substrates.
[0019] FIG. 2 is a schematic cross sectional view of a single layer
DVD-5 disc.
[0020] FIG. 3 is a schematic cross sectional view illustrating the
manufacturing and reading of a standard DVD-5.
[0021] FIG. 4 is a diagram representing single sided single layer,
single sided double layer, double layer single sided, and double
layer double sided DVD constructs.
[0022] FIG. 5 is a graphic depicting the index of refraction as a
function of substrate thickness for single layer and double layer
DVDs.
[0023] FIG. 6 is a schematic illustrating the read-out
possibilities for single-layer and dual-layer DVDs.
[0024] FIG. 7 is a schematic cross sectional view illustrating a
modified DVD-5 construct with the bonding layer in the optical path
of the reading laser.
[0025] FIG. 8 is schematic cross sectional view illustrating the
manufacturing and reading of an altered DVD-5 construct with the
bonding layer in the optical path of the reading laser in which the
mother stamper was used to mold the L1 substrate.
[0026] FIG. 9 is a schematic cross sectional view illustrating the
stamper reference plane of a standard DVD-5 construct wherein the
pits and lands are molded in the L0 substrate.
[0027] FIG. 10 is a schematic cross sectional view illustrating the
stamper reference plane of a modified DVD-5 construct wherein the
pits and lands are molded in the L1 substrate.
[0028] FIG. 11 is a graphic depicting an atomic force microscope
image of a DVD-5 father stamper.
[0029] FIG. 12 is a graphic depicting an atomic force microscope
image of a DVD-5 mother stamper.
[0030] FIG. 13 is a graphic depicting an atomic force microscope
image of the L1 layer of a modified DVD-5 that was molded from a
mother stamper.
[0031] FIG. 14 is a schematic cross sectional view illustrating the
manufacturing and reading of a modified DVD-5 in which the L1 layer
was molded from a father stamper wherein the direction of the
spiral track was reversed during mastering.
[0032] FIG. 15 is a schematic cross sectional view illustrating the
stamper reference plane of a modified DVD-5 construct wherein the
pits are above the surfaces of the lands and the lands are at the
reference plane of the L1 substrate.
[0033] FIG. 16 is a schematic cross sectional view illustrating the
stamper reference plane of a modified DVD-5 construct wherein the
pits are above the reference plane of the L1 substrate and the
lands are at the reference plane of the L1 substrate.
[0034] FIG. 17 illustrates a potential synthetic pathway for the
synthesis of triisopropylsilyloxycarbonylleucomethylene blue.
[0035] FIG. 18 illustrates the cyan reflectance density of
optically readable storage media coated with
triisopropylsilyloxycarbonylleucomethy- lene blue as a function of
time in the presence 1,4-diazabicyclo[2,2,2]oct- ane.
[0036] FIG. 19 is a graphic depicting the spectral absorption of
methelene blue.
[0037] FIG. 20 is a schematic cross sectional view illustrating a
modified DVD-9 construct, wherein the L0 layer is partially
metallized.
[0038] FIGS. 21A and 21B are graphics depicting Koch test results
for a modified DVD-5 construct wherein the pits are molded as
depressions in the L1 substrate using a father stamper in which the
direction of the spiral track is reversed during mastering.
DETAILED DESCRIPTION
[0039] Certain optical discs, such as DVDs, consist of two plastic
halves ("substrates"), which are metallized and bound together with
an interstitial bonding layer. It would be desirable to use an
interstitial layer between the two substrates to interfere with the
reading laser in order to inhibit reading of the disc. This would
result in a disc that is more difficult to defeat, as the two
halves of the optical disc would protect the interfering layer.
Using an interstitial layer as the interfering layer still allows
triggering the process of disc expiration. For example,
polycarbonate, which is typically used to manufacture DVD
substrates, allows the propagation of oxygen that could reach the
interstitial reactive layer and trigger a reaction that causes the
expiration of the disc.
[0040] Furthermore, it would be desirable to use the bonding layer
itself as the interfering layer, for example by changing the
chemical composition of the bonding layer through the incorporation
of a reactive substance. This could simplify the manufacturing of
limited-play optical discs because no additional layers would be
introduced, and attempting to defeat the limited-play mechanism by
removing this layer could destroy the optical disc itself, as the
bonding layer is critical to the integrity of the optical disc.
However, in certain types of optical discs, such as a DVD-5, the
bonding layer is not in the optical path. FIG. 2 illustrates a
cross sectional view of the layers typical of a DVD-5 construct.
Thus while the bonding layer could play part in an expiration
process for a DVD-5 that does not rely on direct interference with
the reading laser (e.g., by corroding the reflective metal layer
that is in contact with the bonding layer), it would not be
possible to make this type of disc expire by transitioning the
bonding layer to a state that prevents the reading laser from
reading the data on the disc. Since it is often desirable to make
the disc unplayable by means of a process that interferes with the
reading laser, it is desirable to have a disc similar to a DVD-5
where the interstitial bonding layer is in the optical path.
[0041] In limited use optical discs where the expiration process
relies on interference with the reading laser, the data encoding
structures (such as metallized pits on a polycarbonate substrate)
typically are preserved in an expired disc, although the reading
laser is prevented from reading the encoded information. As long as
these data structures are present, there is always the possibility
of the disc being defeated by enabling the reading laser to access
the information. It would thus be desirable to have additional
mechanisms that prevent recovery of the data, such as permanently
erasing the data by compromising the integrity of the data
structures on the optical disc.
[0042] These, and other, goals and embodiments of the invention
will be better appreciated and understood when considered in
conjunction with the following description and the accompanying
drawings. It should be understood, however, that the following
description, while indicating preferred embodiments of the
invention and numerous specific details thereof, is given by way of
illustration and not of limitation. Many changes and modifications
may be made within the scope of the invention without departing
from the spirit thereof, and the invention includes all such
modifications.
[0043] A clear conception of the advantages and features
constituting the present invention, and of the components and
operation of model systems provided with the invention, will become
more readily apparent by referring to the exemplary, and therefore
non-limiting, embodiments illustrated in the drawings accompanying
and forming a part of this specification. It should be noted that
the features illustrated in the drawings are not necessarily drawn
to scale.
[0044] We now describe the different aspects of the current
invention, and several corresponding embodiments and examples.
[0045] DVDs are the most common optical discs used for distribution
of movies. DVDs are made from two bonded plastic substrates,
typically referred to as L0 for the bottom substrate and L1 for the
top substrate, where "top" and "bottom" refer to a DVD in a playing
position where it is read from the bottom, as is the common
convention. These substrates are molded from materials such as
polycarbonate, acrylic, or polyolefine, which is injected in a
molten form to a mold and pressed against a stamper. The process of
creating the physical stampers used in replicating the DVD
substrates is referred to as Mastering. The following procedure is
used, which is illustrated in FIG. 1:
[0046] 1. Float glass blank 5 is polished and coated with a primer
10 to enhance adhesion with the photo resist layer 15.
[0047] 2. Photo resist coating 15 is applied, baked, and then
exposed to the laser for recording. The formatted data signal is
used to modulate the cutting laser of a laser beam recorder (LBR)
machine which creates pits 20 in the glass disc.
[0048] 3. The exposed glass is then developed leaving pits 20 and
lands 25 across the surface.
[0049] 4. This "Glass Master" then has a thin (110 nm) metal layer
sputter-applied to make the surface conductive for
electroplating.
[0050] 5. The glass master is then placed into an electroplating
solution where nickel is formed to the desired thickness.
(Typically 0.300 mm).
[0051] 6. This "Metal Father" (or "father stamper 30") is then
separated from the glass master 35 and cleaned. At this step, the
metal father 30 could be used for the molding process, but if the
part gets destroyed or damaged in replication, the entire process
must be repeated.
[0052] 7. Therefore, most manufacturers will grow "Metal Mothers"
(or "mother stampers 40"), which are negatives of the father 30.
Typically, four mother stampers 40 can be grown from one father 30
without quality degradation, and from each mother 40, up to 8
stampers ("sons 45") can be grown.
[0053] 8. Stampers get sent to replication facilities and mothers
40 are stored for reorders or replacement parts.
[0054] In the case of a DVD-5, which is a single layer disc
illustrated in FIG. 2, the L0 substrate 100 is covered with a thin
reflective layer 105 of aluminum by a sputtering process. This
creates a metallic coating between 60 and 100 angstroms thick (the
L0 layer). The L0 substrate 100 is then bonded 110 to a blank L1
substrate 110, as illustrated in FIG. 3. For a DVD-9, which is a
two-layer disc, the L0 layer is formed as a very thin,
semi-reflective metal layer, and is typically made of gold. A fully
reflective aluminum layer is formed on the L1 substrate (the L1
layer). The two substrates are subsequently bonded with appropriate
adhesive material, which forms a transparent bonding layer, to form
the DVD-9 disc.
[0055] As seen in the DVD family illustration in FIG. 4, a DVD disc
may contain either one or two information layers for each
substrate, resulting to different types of disc capacities, such as
DVD-5 200 (single sided, single layer, 4.7 Gbyte capacity), DVD-9
205 (single sided, dual layer, 8.5 Gbyte capacity), DVD-10 210
(double sided, single layer, 9.4 Gbyte capacity), DVD-14 (double
sided, one side single layer, one side dual layer, 13.2 Gbyte
capacity), and DVD-18 215 (double sided, dual layer, 17 Gbyte
capacity).
[0056] A dual layer disc such as a DVD-9 205 must conform to the
"DVD Specifications for Read-Only Disc, Part 1 Physical
Specifications Version 1.0", which require the following:
[0057] 1. Total Disc thickness, including bonding layer 110,
spacer(s) and label(s), shall be 1.20 mm+0.30 mm/-0.06 mm
[0058] 2. Index of refraction (RI) of the transparent substrate
shall be 1.55+/-0.10 The index of refraction of the spacer shall be
(RI of the substrate +/-0.10)
[0059] 3. Thickness of the transparent substrate is specified as a
function of its index of refraction. Typically with polycarbonate
at RI=1.56, the thickness values for the disc substrate would be
0.57 mm.about.0.63 mm (see FIGS. 5A and 5B)
[0060] There is no specification for the DVD-5 200 and DVD-10 210
spacer layer (bonding layer 110), as long as the total disc
thickness conforms to the DVD specification and the half discs
(molded substrates) conform to RI related specifications as
above.
[0061] The information in DVDs is encoded in the pits 20 and lands
25 (data areas that are not pits) that are molded into the
substrates and subsequently are metallized to form the
corresponding data layer. The pits and the lands are organized in a
spiral track, which, in the case of a DVD-5 200, is read in a
clockwise direction beginning at the inside of the disc and
proceeding towards the outside of the disc. The reference area of
the disc that is not occupied by data is used for tracking of the
reading laser. The reading laser, which has a wavelength of 630-650
nanometers in vacuum, is focused on the L0 layer 100 of a DVD-5 200
or DVD-9 205, or on the L1 layer 115 of a DVD-9 by penetrating
through the semi-reflective L0 layer 100, and it is reflected back
to a photo detector. During transitions from a pit 20 to a land 25
or vice versa, interference patterns develop, which are detected by
the photo detector and result in changes in its electrical output.
These changes in the electrical output of the photo detector allow
the player to read the information recorded on the DVD.
[0062] Dual-layer discs, such as DVD-9s 205, typically utilize one
of two methods for read-out of the disc information:
[0063] A dual-layer Parallel Track Path (PTP) disc 299 will have a
Lead-in 300 and a Lead-out 305 area on both layers, as illustrated
in FIG. 6. For each layer, the lead-in 300 area is located at the
inner radius of the disc, and lead-out 305 area is located at the
outer radius of the disc. This layout structure is comparable with
the layout of the single layer 320 disc. Reading of the data is
done, as in a DVD-5, 200 from the inner radius of the disc to the
outer radius, for both layers. With proper authoring of the content
on the disc, the PTP method can allow quick access from layer to
layer, for example in order to provide background information and
commentary in one track along with the movie in the other
track.
[0064] A dual-layer Opposite Track Path (OTP) 325 disc, also
illustrated in FIG. 6, offers the possibility of seamless
continuation of the playback from the L0 100 to the L1 115 layer.
The first information layer (L0) 100 starts with a lead-in area at
the inner radius of the disc and ends with a so-called middle area
330 at the outer radius. The second information layer starts with a
Middle Area 330 at the outer radius and ends with a lead-out 300
area at the inner radius of the disc. Reading the data 335 stored
on the disc will start at the inner radius of the first information
layer and proceed until the Middle Area 330 of this layer is
reached. Then a switch over to the Middle Area in the second
information layer is made, in order to continue reading of the data
from the outer radius up to the lead-out 305 Area in the inner
radius of the second layer (L1) 115.
Single Layer Optical Discs
[0065] One embodiment of the present invention is an optical disc
similar to a DVD-5 where, unlike a standard DVD-5, the interstitial
layer 400 typically used as the bonding layer 401 is in the optical
path 405 of the reading laser (e.g., see FIG. 7). In one embodiment
of the present invention (labeled below as "Special DVD-5 design
#1"), this disc is manufactured by inverting the reflective layer
410 of a standard DVD-5, and reading the information through the
non-information-bearing substrate 415 and the bonding layer 401. In
another embodiment of the present invention (labeled below as
"Special DVD-5 design #2"), the direction of the spiral track is
inverted during mastering, the information bearing substrate is
flipped "upside down", and the information is read through the
non-information bearing substrate 415 and the bonding layer 401. In
this type of optical disc, the bonding layer 401 is an integral
part of the optical path 405 of the reading laser. Even though the
structure of the "Special DVD-5" disc described herein differs from
a standard DVD-5, a player would play this disc as if it were a
standard DVD-5.
[0066] This embodiment of the present invention has significant
advantages in terms of allowing the manufacturing of a low-cost
"limited-play" optical disc that is resistant to attempts to defeat
it. In particular, because it does not incorporate any additional
layers compared to a standard DVD-5, it can be manufactured on
equipment designed to manufacture DVD-5 discs with minimal changes
to that equipment. Furthermore, because the bonding layer 401 is in
the optical path, 405 modifying that layer to interfere with the
reading of data in response to a predetermined stimulus results in
a disc that is very difficult to defeat, as the interfering layer
400 is protected by the two substrates 415 and 420, respectively of
the optical disc. For example, grinding the interfering layer 400
off the disc is impractical, as it would most likely destroy the
disc. Similarly, attempting to compromise the bonding/interfering
layer in other ways is likely to destroy the structural integrity
of the optical disc.
[0067] We now describe in detail the manufacturing of three
embodiments of the current invention, which we label as "Special
DVD-5" designs 1, 2 and 3.
Special DVD-5 Design #1
[0068] In one embodiment of the invention, the above process is
modified by using the mother stamper to replicate the L1 disc
substrate 420. FIG. 3 shows how the stamper or father is used to
mold a normal single layer DVD-5 substrate. FIG. 8 illustrates
manufacturing this embodiment of the current invention by using the
mother stamper 40 and creating a disc with the bonding layer 401 in
the optical path 405.
[0069] In a normally molded standard DVD-5 information is encoded
on the L0 100 side with "pits" 20 and "lands" 25 molded on the L0
substrate 100 and metallized with a reflective metal coating, 105
as illustrated in FIG. 2, FIG. 3 and FIG. 9. In one embodiment of
the current invention, the mother stamper 40 is used to mold the L1
side 420 as shown in FIG. 8. This side is subsequently metallized
and bonded with a blank L0 substrate, 415 leaving the bonding layer
401 in the optical path, 405 as shown in FIG. 10. Using the
specified layer thickness of 0.055 mm +/-0.015, the thickness of
the L0 substrate 100 is targeted at 0.55 mm.about.0.57 during
molding, to yield a focal length of the disc thickness (including
the bonding layer) consistent with standard DVD specifications,
allowing the player to be in the normal focusing range for reading
a L0 layer 100. Thus the player interprets the disc as a standard
single layer DVD-5. Field experience has shown that spacer layer
thickness can be maintained at 0.045.about.0.065 mm consistently in
production. This controlled variation in production along with the
reduced thickness of the molded disc keeps the focus and optics
within the specifications set by the DVD licensing authority and
the hardware manufacturers.
[0070] For the replication facility, most applications would remain
unchanged in the actual pressing and bonding portions of
production. The main areas of change would be in the LBR (laser
beam recording) and developing areas of mastering. Typically,
masters are cut with larger pit volumes to compensate for plastic
shrinkage and replication inefficiencies. The ratio of pit to land
areas on a disc is measured by a term called asymmetry. Because
asymmetry is a ratio of pit to land area, and because for each pit
area, typically defined by I3 to I14 pit, there is an equal and
opposite land area I3 to I14 land, typically it is easier for
manufacturers to target a positive asymmetry (larger pit area) to
account for loses in replication to the plastic substrate. For
example, the master may be cut with a positive 10.about.12% for
asymmetry, while the end result from molding may be 5.about.7%. The
specification for the disc substrate is:
-0.05.ltoreq.asymmetry.ltoreq.+0.15. In the case of DVD discs, a
positive asymmetry represents a larger pit volume compared with the
land area.
[0071] For this embodiment of the invention, it may be desirable to
change the asymmetry set point on the LBR to produce a higher
asymmetry value on the father stamper while subsequently increasing
the asymmetry on the mother stamper used for molding. Asymmetry can
be changed on the master by modifying the power of exposure,
focusing intensity and offset, developing time/endpoint detection,
or baseline (control of how fast the laser diode cuts the laser
exposure beam off between exposure). There are many other possible
ways to control asymmetry, but the basic process or set point
control would be the easiest to implement. This process of molding
from the mother stamper would also eliminate the need to grow
additional stampers and the subsequent yield loses attributed to
the family process.
[0072] In this embodiment of the invention, the pits 20 are molded
in the L1 layer 420 using a mother stamper, 40 and as a result the
surface of the pits 20 is elevated relative to the reference plane
450 of the L1 layer 420 as illustrated in FIG. 10. This reference
plane 450 is typically used for tracking by the disc player
(tracking area). By contrast, in a normal DVD-5 the pits 20 are
molded as cavities in the L0 substrate 100 as illustrated in FIG.
9. Using the common convention of describing a disc as if it is in
a play position where it is read from the bottom, and a convention
that we will follow hereinafter unless otherwise specified, in a
normal DVD-5 the pits 20 are lower than the reference plane 450,
while the lands 25 are at the reference plane 450 (see FIG. 9). In
the embodiment of the invention described above the blank L0
substrate 415 and the bonding layer 401 are below the L1 substrate
420 in the optical path 405 of the reading laser, and the surface
of the pits 20 in the L1 substrate 420 is below the reference plane
450 while the lands 25 are at the reference plane 450 (see FIG.
10). Note that this construction requires the pits 25 to be molded
in an unconventional way (they protrude from the reference plane
450 of the disc), which is achieved by molding the L1 substrate 420
from a mother stamper 40. FIG. 11 shows an Atomic Force Microscope
(AFM) image of a Father stamper 30 for a DVD-5, FIG. 12 shows an
AFM image of the corresponding Mother stamper 40, and FIG. 13 shows
an AFM image of the L1 layer of a Special DVD-5 Design #1, molded
from the Mother stamper 40.
[0073] This molding required for this embodiment of the invention
can present certain challenges. In a typical injection molding
process, the polymer material flows around the pits 20 on the
stamper, which are raised from the reference plane 450. This is
easier than to mold from the mother, where the polymer material
must flow into cavities that will form the pits 20 on the separated
part. As the material flows over the surface of the mother stamper
40, the molecular chains cool off through contact with the
relatively colder reference surface of the stamper. After the mold
is completely filled, then pressure must be applied to bend and
force the cooler polymer material into the pit 20 cavities.
Although this method is capable to reproduce discs within the
specifications of a standard DVD-5 configuration, the molding
process is more difficult. However, one skilled in the art can
address such challenges by adjusting the process characteristics of
the molding machine, e.g., by increasing mold surface temperature
and cycle time. Alternatively appropriate materials with higher
melt flow rate could be used, such as PMMA or high melt flow rate
polycarbonate. For example, General Electric's SPOQ research grade
polycarbonate has twice the melt flow rate of standard grade
polycarbonate.
[0074] As long as the index of refraction (RI) of the bonding
adhesive used is approximately equal to the RI of the L0 substrate
415, the thickness of the bonding layer 401 is uniform, and the
thickness of the L0 substrate 415 has been adjusted to compensate
for the presence of the bonding layer 401 in the optical path 405
of the reading layer, the player will not be able to distinguish
Special DVD-5 Design #1 from a standard DVD-5. Experience has shown
that playable discs can be manufactured even without these
adjustments, because most players will play discs that do not fully
conform to the DVD specification, as long as the departure from the
specification is not excessive.
EXAMPLE 1
Special DVD-5 Design #1
[0075] A father stamper 30 was mastered with slightly increased
symmetry (positive asymmetry=larger pits 20 compared to lands 25).
The asymmetry can be increased or decreased many ways. The simplest
method and the one used for this design, was to increase the
development time (endpoint detection set point) to overdevelop the
pits 20. By lengthening the development process, the pit volume
surrounding, that which was exposed, will increase in volume
causing a shift to positive asymmetry.
[0076] A mother stamper 40 was grown from the father stamper 30 as
with a normal family process. Disc substrates were molded from the
mother stamper 40, taking advantage of the larger indentation
caused by the positive asymmetry. The larger pits 20 that resulted
from molding with the mother 40 helped to compensate for the
additional shrinkage of the pit 20, which is now an extremity to
the body of the substrate, rather than a cavity as in the standard
molding process. Typically, the molten plastic flows around the
pits 20 in a normal (father 30 or son 45) stamper like a river
flows around a hill. As the level rises, the hill or the pit 20
will be covered. As the molten plastic flows across the cooler
stamper surface, a skin layer forms right on the surface that acts
as a heat insulator. This allows for the plastic to maintain its
flow rate necessary to form the pit volume without undue stress or
cooling. In the case of Special DVD-5 design #1, the plastic has to
flow into the indentations of the mother stamper 40, rather than
around the bumps of a father/son stamper 30 and 45 respectively.
This is difficult because as the plastic flows across the surface
of the mother stamper 40, it again forms a skin layer on the
surface. Then as the mold volume increases with continued injection
and packing/holding time, the molten plastic must be forced into
the indentation. Because this skin layer is solidified typically
below the glass transitional temperature of the plastic, the
material does not free flow into the indentation. Because the
pit-formiing plastic in the L1 substrate 420 of Special DVD-5
design #1 is not in the optical path of the reading laser, the
material can be filled with greater force without the concern for
birefringence and residual stress, although there is a limit to the
pressure due to warping (tilt) caused by excessive packing pressure
on the plastic. In this example, the combination of larger
indentations in the mother stamper 40 as well as increased mold
temperatures assisted in replicating the desired pits 20.
Typically, in direct water injection systems for the mold heating
and cooling, safety interlocks of 120.degree. C. max temperature
limit the temperature of the water. By using a 50/50 solution of
glycol and water, the temperature can be effectively run at a max
temperature of 130.degree. C. This added temperature assists in
keeping the skin layer in the molten state, close to its glass
transition temperature, which facilitates the replication of L1
substrates 420 for Special DVD-5 design #1. Also, the mother
stamper 40 must be filled quickly with molten plastic in order to
prevent skinning on the surface.
[0077] L1 substrates 420 were molded as above using a mother
stamper 40. FIG. 13 shows an Atomic Force Microscope (AFM) image of
an L1 layer 420 molded from a mother stamper 40. FIGS. 11 and 12
show AFM images of the father 30 and mother 40 stampers used in the
process. For these discs to be formed, it was necessary to raise
the melt temperature from 360.degree. C. to 390.degree. C. while
maintaining a mold temperature of 121.degree. C. compared to the
standard of around 100.degree. C. The clamp force was set at
maximum of 30 tons and the filling time was decreased from 0.13 to
0.09 seconds. These parameters were adjusted until the proper pit
20 formations were achieved.
[0078] The molded L1 substrates 420 were bonded using optical grade
UV curable DVD adhesives, as used in DVD-9 production, to blank L0
substrates 415, to manufacture design #1 of the Special DVD-5. L0
substrates 415 were molded at a thickness of 0.55.about.0.57 mm
(i.e., 30.about.50 micron thinner than standard DVD halves) to
compensate for the bonding layer in the optical path, thus
preserving the same focal depth for the information-carrying layer
as in a standard DVD-5.
Special DVD-5 design #2
[0079] The electronics of optical media drives, including DVD
players, are typically designed to read the information contained
in a layer on the disc by identifying the interference patterns
caused by the transitions from a "land" 25 to a "pit" 20 in that
layer. The pits 20 are often molded with a height approximately
equal to, and typically somewhat less than, one quarter of the
wavelength of the reading laser. For example, in DVDs the typical
wavelength of the reading laser is 635-650 nanometers (in vacuum),
or 410-420 nm in a material with RI=1.55 (which is typical of the
materials used to manufacture the DVD substrates), and thus the
height of the pits 20 in a standard DVD-5 should be approximately
100-105 nanometers. Consequently, a transition from a land 25 to a
pit 20 or vice versa corresponds to a change to the path of the
reading laser of approximately one half wavelength, or a phase
change of approximately 180 degrees. Two identical waves with a
phase difference of 180 degrees will interfere with each other and
cancel out, and the electronics of the optical drive are designed
to detect the resulting interference patterns. Using the standard
convention of the disc being read from below, in a standard DVD-5
the surface of the pits 20 is below the surface of the land 25, and
a transition from a land 25 to a pit 20 is a "down" transition,
while a transition from a pit 20 to a land 25 is an "up"
transition. If the height of the pits 20 is one quarter of the
wavelength of the reading laser then a transition from a land 25 to
a pit 20 in a standard DVD-5 is a "down" transition that
corresponds to a phase change of +180 degrees, and a transition
from a pit to a land 25 is an "up" transition that corresponds to a
phase change of -180 degrees. If an "up" and a "down" transition
differ by 360 degrees, as in the case described above, their
effects will be identical. One implication of this is that the pits
20 of a DVD-5 could be molded in the opposite direction, i.e., with
the pit surface approximately one quarter wavelength above the land
25 surface, and the electronics of the optical disc player are
unlikely to be influenced by whether a detected transition is in
the "up" or "down" direction, i.e. whether a pit 20 area is higher
or lower than the land 25 area.
[0080] In a standard DVD-5, the laser pick up will read through the
L0 substrate 100 focusing on the pits 20 aligned in a spiral track.
The rotation of the disc would be in the counterclockwise direction
(as seen from the side of the reading laser), and the spiral track
would be in the clockwise direction. Given that the pit 20
direction can be reversed without changing the electrical signal
seen by the player, in another embodiment of the current invention
the pits 20 are molded as depressions 500 into the L1 substrate
420, by employing a normal (father/son) DVD-5 stamper 30/45, as
illustrated in FIG. 14. The direction of the spiral track is
reversed during mastering, as the disc will be read from the side
of the bonding layer 401, rather than through the substrate as in a
standard DVD-5. The resulting disc has information encoded as a
DVD-5, although the pits 20 are formed in the L1 layer 420: the
surfaces of the pits 20 are above the surfaces of the lands 25, and
the lands 25 are at the reference plane of the L1 layer 420, as
illustrated in FIG. 15. The pit 20 width, length, height, and shape
give the corresponding HF signals needed to decode the data on the
DVD. The signals are encoded utilizing an eight-to-fourteen
modulation (EFM) signal. The pit 20 edges and slopes of the
sidewalls serve to distinguish the logical transition of 0's and
1's. This results in pit 20 length units measured as 3 units long
to 14 units long, which set the frequency limits of the EFM signal,
read from the disc. This measurement is commonly referred to as
3T-14T signal with T referring to a period of time. As long as the
pits 20 are replicated in standard fashion, the player will still
be able to distinguish the pit 20 start and end position, while
reading from the reverse side, to correctly identify its data
identity. In many circumstances this will be the preferred
embodiment of the invention, as it does not require molding from
the mother stamper 40, as is the case with Special DVD-5 design #1
above.
[0081] The actual height of the pits 20 in a standard DVD-5 is
typically somewhat less than one quarter wavelength of the reading
laser. This is intended to avoid complete cancellation of the
reflected laser during a pit-to-land transition, which facilitates
the functioning of player electronics. For example, a value of
0.88*(laser wavelength)/4 is sometimes recommended, i.e.
approximately 90 nanometers for a material with RI=1.55. Thus it
may be desirable to mold the pit 20 surfaces in this embodiment of
the current invention somewhat higher than one quarter the
wavelength of the reading laser, so that the change in the path of
the reading laser during a transition from a land 25 to a pit 20 in
the special DVD-5 design #2 will be exactly one wavelength longer
than the corresponding change in a standard DVD-5. For example, if
the reading laser wavelength is 650 nanometers (i.e., 420 nm in a
polycarbonate substrate of RI=1.55), and the pits in a standard
DVD-5 are 90 nanometers, the pits 20 in this embodiment (Special
DVD-5 design #2) can be molded at 120 nanometers, i.e., one half
wavelength (210 nm) from the position of the pit 20 surface in
design #1.
EXAMPLE 2
Special DVD-5 Design #2
[0082] A special stamper for molding L1 substrates 420 for Special
DVD-5 Design #2 was produced through a modified mastering process,
where the direction of rotation of the laser beam recorder
turntable was reversed during the cutting process, resulting in a
spiral tracking path in the opposite direction from that in a
normal DVD-5. This stamper was produced by forcing the turntable to
rotate in the reverse direction from cutting a normal DVD-5, while
the content information was fed to the laser beam recorder as a
DVD-5 image. The scanning velocity that is normally preset for DVD
formats was manually set to the velocity of 3.49 m/s typical in
DVD-5 mastering. L1 substrates 420 were then molded on standard
molding machines set up for DVD-5 fabrication.
[0083] Some of the molded L1 substrates 420 were bonded using
optical grade UV curable DVD adhesives to blank L0 substrates 415,
to manufacture design #2 of the Special DVD-5. As in Example 1, the
L0 substrates 415 were molded at a thickness of 0.55.about.0.57 mm
(i.e., 30.about.50 micron thinner than standard DVD halves) to
compensate for the bonding layer 401 in the optical path, thus
preserving the same focal depth for the information-carrying layer
as in a standard DVD-5. To bond the discs, the machines were placed
into a DVD-9 production mode and the semi-reflective metallizer for
the L0 layer was taken offline. Then the cure time was adjusted to
compensate for the decrease in cure exposure needed due to the
missing semi-reflective layer. Curing was basically set for a DVD-5
disc, and the disc was flipped to cure through the L0 layer. This
function is typically reserved for DVD-9 production.
[0084] The discs were then tested with a Koch DVD testing system
and played in four different DVD players. They performed
indistinguishably from regular DVD-5 discs, as illustrated in FIGS.
21 and 22. Also, the discs played with no errors in an additional
three DVD players and two DVD-ROM drives.
[0085] Some of the molded substrates were used to manufacture discs
with a reactive bonding layer (see Example 9).
Special DVD-5 Design #3
[0086] The electronics of optical media drives, including DVD
players, can be designed to read the information contained in a
layer on the disc by identifying pits 20 and lands 25 in that layer
based on the absolute and/or relative elevation of these pits 20
and lands 25, thus distinguishing between an "up" and a "down"
transition in the information encoding layer, but without being
influenced by the elevation of the pits 20 and lands 25 relative to
the reference plane 450 of the layer. Thus in another embodiment of
the current invention, during mastering the direction of the spiral
track is reversed and also the pits 20 and lands 25 are reversed,
so that the pits 20 become lands 25 on the resulting stamper 30,
and lands 25 become pits 555. The L1 substrate 420 is then molded
by employing 550 a normal (father) stamper 30 and is bonded to a
blank L0 substrate 415. The resulting disc has information encoded
as a DVD-5, the relative elevation of pits and lands, and the "up"
and "down" transitions in the information encoding layer, are
identical to a DVD-5. Specifically, the surface of the pits is
below the surface of the lands. However, while in a standard DVD-5
the surface of the lands is at the reference plane of the L0 layer,
in this embodiment it is the surface of the lands 560
(corresponding to pits on a standard DVD-5) that is at the
reference plane of the L1 layer, with the pits 565 (corresponding
to lands on a regular DVD-5) being above this reference plane, as
illustrated in FIG. 16.
The Reactive Bonding Layer
[0087] Another embodiment of the present invention is having a
reactive material incorporated in an interstitial layer. In one
embodiment, the interstitial layer is the bonding layer of the
disc.
[0088] In one embodiment of the invention, the stimulus triggering
the reaction is exposure to atmospheric oxygen. Upon exposure to
oxygen, a reactive material, e.g., leuco methylene blue, which is
essentially colorless, is oxidized to form an opaque or semi-opaque
layer (e.g., the deep blue dye, methylene blue). Data storage media
with the opaque/semi-opaque layer can no longer be played in media
players. By adjusting the time it takes to turn opaque, this method
can be used to provide limited-play data storage media having the
desired life for the given application.
[0089] The reactive layer, which comprises both a carrier and a
reactive material, should initially have sufficient transmission to
enable data retrieval by the data storage media device, and
subsequently form a layer which inhibits data retrieval by that
device (e.g., which absorbs a sufficient amount of light i.e.,
incident and/or reflected light) at the wavelength of the laser in
the given device). Typically a layer that allows an initial percent
reflectivity from the reflective layer of about 50% or greater can
be employed, with an initial percent reflectivity of about 65% or
greater preferred, and an initial percent reflection of about 75%
or greater more preferred. Once the media has been exposed to
oxygen, e.g., air, for a desired period of time (e.g., the desired
allowable play time of the media), the layer preferably comprises a
percent reflectivity of about 45% or less, with about 30% or less
preferred, about 20% or less more preferred, and about 15% or less
especially preferred.
[0090] Possible reactive materials include oxygen sensitive leuco
or reduced forms of Methylene Blue, Brilliant Cresyl Blue, Basic
Blue 3, Methylene Green, Taylor's Blue, Meldola's Blue, New
Methylene Blue, Thionin, Nile Blue, Celestine Blue, and Toluidine
0, as well as reaction products and combinations comprising at
least one of the foregoing material; the structures of which are
set forth below:
1 1 Methylene Blue 661 nm 2 Brilliant Cresyl Blue 622 nm 3
Toluidine Blue O 626 nm 4 Basic Blue 3 654 nm 5 Methylene Green
657,618 nm 6 Taylor`s Blue 649 nm 7 Janus Green B 660,395 nm 8
Meldola`s Blue 570 nm 9 New Methylene Blue 630,591 nm 10 Thionin
598 nm 11 Nile Blue 638 nm 12 Celestine Blue 642 nm
[0091] A method of synthesis of leucomethylene blue and the oxygen
dependent reoxidation to form the colored form of the methylene
blue dye is shown below: 13
[0092] In addition to the above reactive materials, numerous other
dyes and light blocking materials, can be synthesized to operate to
render the data storage media limited play. For example, some other
possible reactive materials can be found in U.S. Pat. No.
4,404,257, hereafter incorporated by reference, and U.S. Pat. No.
5,815,484, hereafter incorporated by reference. The reactive
materials can further comprise a mixture comprising at least one of
any of the above mentioned reactive materials.
[0093] The reactive material is preferably mixed with a carrier for
deposition on and/or impregnation into at least a portion of the
surface of the substrate. Possible carriers comprise the
thermoplastic acrylic polymers, polyester resins, epoxy resins,
polythiolenes, UV curable organic resins, polyurethanes,
thermosettable acrylic polymers, alkyds, vinyl resins and the like,
as well as combinations comprising at least one of the foregoing
carriers. Polyesters include, for example the reaction products of
aliphatic dicarboxylic acids including, e.g., fumaric or maleic
acid with glycols, such as ethyleneglycol, propyleneglycol,
neopentylglycol, and the like, as well as reaction products and
mixtures comprising at least one of the foregoing.
[0094] Some epoxy resins, which can be the used as the organic
resin, include monomeric, dimeric, oligomeric, or polymeric epoxy
material containing one or a plurality of epoxy functional groups.
For example, reaction products of bis phenol-A and epichlorohydrin,
or the epichlorohydrin with phenol-formaldehyde resins, and the
like. Other organic resins can be in the form of mixtures of
polyolefin and polythiols, such as shown by Kehr et al, U.S. Pat.
Nos. 3,697,395 and 3,697,402, hereafter incorporated by
reference.
A Non-bonding Reactive Layer
[0095] Optionally, the reactive layer can be applied to the
substrate using various coating techniques such as painting,
dipping, spraying, spin coating, screen printing, and the like. For
example, the reactive layer can be mixed with a relatively volatile
solvent, preferably an organic solvent, which is substantially
inert towards the polycarbonate, i.e., will not attack and
adversely affect the polycarbonate, but which is capable of
dissolving the carrier. Examples of some suitable organic solvents
include ethylene glycol diacetate, butoxyethanol, the lower
alkanols, and the like.
[0096] For surface coatings, the reactive layer may also optionally
contain various additives such as flatting agents, surface active
agents, thixotropic agents, and the like, and reaction products and
combinations comprising at least one of the foregoing additives.
The thickness of the reactive layer is dependent upon the
particular reactive material employed, the concentration thereof in
the reactive layer, and the desired absorption characteristics of
the layer both initially and after a desired period of time.
Development of Blocked Reactive Compounds
[0097] One embodiment of the present invention is the use of
blocked forms of the reactive compounds in the reactive layer.
These compounds will unblock within a predetermined time period
after the disc is manufactured or packaged, and typically before
the disc is used by the consumer. This is desirable when the
stimulus that triggers the reaction that causes the disc to become
unplayable (e.g., atmospheric oxygen) can trigger this reaction
during the manufacturing of the disc, and thus measures need to be
taken so that the reactive compound is not activated during the
manufacturing of the disc. For example, in the case of oxygen
triggered reactions, unless a blocked form of the reactive compound
is used, manufacturing may need to take place in an oxygen free
environment, such as a nitrogen atmosphere.
[0098] One embodiment of the present invention comprises the idea
of using a chemically blocked reactive substance for the purpose of
producing optical discs that become unplayable after being exposed
to oxygen, a specific such blocked leuco dye, a method of preparing
this leuco dye precursor, a formulation including this leuco dye
precursor which permits the deblocking and oxidation of the leuco
dye precursor at acceptable rates, methods of applying this
formulation to optical discs both on the surface of optical discs
and as bonding layers for optical discs, the use of bases to
increase the rate of methylene blue generation in blocked leuco
dye-containing layers in or on optical discs, and the use of
silyllaating agents such as hexamethyldisilazane to stabilize the
blocked leuco dye in coating fluids.
[0099] In one embodiment of the invention, to manufacture an
optical disc that becomes unplayable after being removed from its
package (a "limited-play disc"), the disc incorporates a reactive
layer with a composition containing a leuco dye which oxidizes to a
colored dye which absorbs light at the wavelength of the reading
laser of an optical disc player, preventing enough of the reading
laser light from being reflected off the disc to render the disc
unplayable. The oxidation of the leuco dye can be initiated by
exposure of the coating containing the dye to atmospheric oxygen,
which diffuses through the coating to oxidize the leuco dye
molecules. One problem with putting such a coating on the surface
of the disc is the possibility of the coating being removed by a
consumer to make the disc permanently playable. Another problem
with putting such a coating on the surface of an optical disc is
that this requires an additional step in the disc manufacturing
process, entailing higher cost, special tooling for production
equipment, and inevitably lower manufacturing yields. Finally, the
oxygen-sensitive fluid used to make such a coating is difficult to
handle because of its oxygen sensitivity.
[0100] In some methods of coating a leuco-dye-containing fluid on
the surface of an optical disc, some of which were described above,
the coating is solvent based and the solvent must evaporate to
yield a hard coat containing the leuco dye and any other components
required, typically bound in a polymer matrix. There are several
disadvantages to such a solvent coating. First, most of the solvent
based fluid is spun off of the disc during a spin coating
manufacturing process and is difficult or impossible to recover due
to solvent evaporation, which both wastes fluid (increasing the
cost of the process) and fouls the coating equipment. Second,
evaporation of the solvent takes time, which reduces the rate at
which such coated discs can be manufactured and thereby increases
the cost of the process. Third, the solvent vapors emitted by the
coated disc during the coating and drying process must be vented
from the manufacturing equipment, increasing the cost of the
installed equipment and presenting process and environmental
obstacles to disc replicators considering adopting this
manufacturing process.
[0101] All of the problems discussed in the previous two paragraphs
could be avoided if the leuco dye could be coated in a solventless,
light or radiation cured (hereafter called generically "UV-cured")
layer, and if this layer could be the same as the optical disc
bonding layer that is used to bond the two substrates which compose
certain types of optical disc, such as a DVD. The major obstacle to
creating such a system is that many leuco dyes, and in particular
leucomethylene blue (hereafter "LMB", which has been used by the
present inventors to render DVDs unplayable in a solvent-based,
surface coated system), inhibit both radical and cationic
polymerization reactions of the type used to cure UV-curable
monomers such as the acrylates that are commonly used as adhesives
for bonding DVD substrates. The oxidized dyes (including methylene
blue) also are inhibitors of such polymerization reactions. So
putting a leuco dye (which will inevitably contain some of the
oxidized, colored dye) in a UV-curable composition will either
prevent the UV-curing from taking place, or slow the UV-curing and
make the process much less economical by reducing the rate at which
discs can be manufactured. Moreover, the process of UV-curing can
result in some of the leuco dye becoming oxidized if any oxygen or
other oxidizing agent is present in the layer to be cured,
resulting in a product prematurely containing oxidized dye which
may interfere with the readability of the disc or change the rate
at which it becomes unreadable after exposure to oxygen.
[0102] Chemically blocked (sometimes called "protected") leuco dyes
(also called "leuco dye precursors") are known and have been used
for decades in applications such as "carbonless copy paper". In
particular, blocked versions of leucomethylene blue are known and
have been used in such applications, and one such compound at
least, benzoyl-leucomethylene blue (BLMB), is commercially
available. However, we have found that BLMB does not deblock easily
enough to yield an acceptable limited play DVD product. Other
blocked leucomethylene blue compounds share this problem, or
deblock too easily such that oxidizable leucomethylene blue is
generated in the coating fluid before it is desired.
[0103] We have found that
triisopropylsilyloxycarbonylleucomethylene blue (hereafter
"TIPSOCLMB"), whose structure and exemplary synthesis are
illustrated in FIG. 17 and described in Example 4, has the
following desirable properties for use in creating limited-play
DVDs:
[0104] 1. It is readily synthesized in two steps from commercially
available starting materials. By isolating and purifying the
BOC-LMB produced in the first step as shown in FIG. 17, the
TIPSOCLMB is prepared from a pure compound rather than from the
typically very impure methylene blue.
[0105] 2. It can be incorporated into an acrylate formulation
described in Example 5 in which it is stable (to conversion to
oxidized methylene blue) for at least several weeks at temperatures
below 0 C., allowing coating formulations to be prepared at one
facility and shipped to another facility for DVD manufacturing if
desired.
[0106] 3. It can be deblocked in a period of a week or less,
presumably by a hydrolysis reaction involving water or other
nucleophiles which can either be provided in the acrylate
formulation or be absorbed from the atmosphere in which the DVD is
manufactured or in the DVD packaging material.
[0107] 4. The deblocked LMB is stable (to oxidation to methylene
blue) in the absence of oxygen. The rate at which the deblocked LMB
oxidizes in the presence of oxygen can be controlled by controlling
the effective pH of the coating formulation. It is known in the art
that the rate of oxidation of LMB increases as the pH of its
environment increases. Thus the rate of oxidation can be increased
by the addition of basic substances that are soluble in the matrix
containing deblocked or blocked LMB and which do not react with the
matrix or substrate used. One such basic compound is DABCO
(1,4-diazabicyclo[2.2.2] octane), an amine. Other amines may be
added or substituted. Further, the addition of a strong protic acid
such as camphorsulfonic acid decreases the rate of LMB oxidation in
a polymer film.
[0108] 5. In the absence of water or other nucleophiles, it is a
stable solid which can be stored after synthesis for at least
several months, even in the presence of oxygen. Acrylate-based
coating fluids containing TIPSOCLMB can be handled in the presence
of oxygen until the deblocking reaction has taken place, which
reaction is slow enough that the handling of the coating fluid
during the DVD manufacturing process can be done in normal
(undried) air and is not difficult.
EXAMPLE 3
BocLMB Preparation
[0109]
2 Chemical Amount Moles Mol. Wt. Na.sub.2S.sub.2O.sub.4 60.0 g
0.345 (2.1 eq) 174.11 H.sub.2O 300 mL 10% aq. NaOH 240 mL Methylene
Blue 60.0 g 0.160 373.90 CH.sub.2Cl.sub.2 700 mL + 25 mL Boc.sub.2O
81 mL (d = 0.95 g/mL) 0.352 (2.2 eq) 218.25 DMAP 3.0 g 0.025 (0.15
eq) 122.17 Hexanes 400 mL Methanol 200 mL estimate
[0110] In a 2-liter separatory funnel was dissolved 60.0 g of
sodium hydrosulfite (sodium dithionite, Na.sub.2S.sub.2O.sub.4) in
300 mL cold distilled water. To this solution was added 60.0 g
methylene blue (dark green powder) from several different bottles,
and the separatory funnel was stoppered and shaken vigorously over
a 30-minute period, during which time the dark green solids
gradually form a tan suspension of insoluble leucomethylene blue.
To this suspension was added three 60-mL portions of 10% aqueous
sodium hydroxide solution with vigorous shaking after each
addition. Some heat is evolved, and a lighter suspension results.
After allowing the mixture to stand for a short while to cool, 700
mL methylene chloride was added and the separatory funnel was
stoppered and shaken to dissolve the solids. An amber organic layer
began to separate below an emulsion. An additional portion of 60 mL
aqueous NaOH was added, the stoppered funnel was shaken, and the
emulsion was allowed to stand for 30-60 minutes to separate into
two liquid phases. Alternatively, fresh Na.sub.2S.sub.2O.sub.4 and
reasonably pure methylene blue may be used to result in a faster
and cleaner phase separation.
[0111] To a 1-liter, 3-necked, round-bottomed flask equipped with a
magnetic stirrer and nitrogen inlet inside a fluted adapter
(Aldrich Z11,563-0) packed with 1.5 sheets of crumpled small
Kimwipe.RTM. tissues (11.times.21 cm) was added 81.0 mL
di-tert-butyldicarbonate (Boc.sub.2O) diluted with 25 mL methylene
chloride. After stirring under nitrogen for 5-10 minutes, 3.0 g of
4-(dimethylamino)pyridine (DMAP) was added followed by dropwise
addition of the leucomethylene blue solution from the separatory
funnel and through the fluted Kimwipe-containing tube. The stem of
the separatory funnel was connected to the fluted tube through a
one-holed rubber stopper so that the addition was performed under
nitrogen. Gas evolution (CO.sub.2) began immediately. After two
hours, the addition was completed to give a dusty green reaction
mixture that was stirred overnight under nitrogen at room
temperature.
[0112] On the following morning, the dusty green reaction mixture
was arranged for atmospheric distillation. About 550 mL
CH.sub.2Cl.sub.2 was distilled off and replaced with 300 mL
hexanes. A gray-blue solid separated out. Distillation was
continued until the head temperature reached about 55.degree. C.
The mixture was allowed to cool; then the solid was collected by
filtration through a sintered glass funnel. The solid was washed
with hexanes (2.times.50 mL) to remove excess Boc.sub.2O, and then
it was washed with methanol (amount unspecified, 4.times.50 mL
estimate) to remove unreacted and oxidized leucomethylene blue
until the wash liquid was only faintly blue. The resulting gray
solid was dried in air and then under vacuum at room temperature.
Yield: 47.0 g (76%). (MW of BocLMB=385.53)
[0113] Thin layer chromatography analysis on a 5.times.10 cm
Whatman K5F silica gel plate eluting with 5% acetone in methylene
chloride showed a faint blue spot at the origin, a very weak spot
at R.sub.f=0.58, and a large product spot at R.sub.f=0.63. The
initially colorless product spot became dark blue upon standing in
air, and rapidly when heated in a 120.degree. C. oven.
[0114] Repetition of this reaction at the same scale resulted in a
yield of 48.0 g (78%).
EXAMPLE 4
TipsocLMB Preparation
[0115]
3 Chemical Amount Moles Mol. Wt. BocLMB 35.61 g 0.092 385.53
CH.sub.2Cl.sub.2 200 mL 2,6-Lutidine 26.0 mL (d = 0.92 g/mL) 0.223
(2.5 eq) 107.16 TipsOTf 39.0 mL (d = 1.14 g/mL) 0.145 (1.5 eq)
306.42 Hexanes 420 mL
[0116] To a 500-mL, 3-necked, round-bottomed flask equipped with a
magnetic stirrer, addition funnel, and condenser under a nitrogen
bubbler was dissolved 35.61 g BocLMB in 200 mL methylene chloride
to give a blue solution. To this solution was added 26.0 mL
2,6-lutidine followed by dropwise addition of 39.0 mL of
triisopropylsilyl trifluoromethanesulfona- te (TipsOTf) over a 15
minute time period. The green-blue reaction mixture was then
stirred under reflux for 6 hours. TLC analysis (K5F silica, 5%
acetone/CH.sub.2Cl.sub.2) showed only a small amount of BocLMB
starting material present at R.sub.f=0.67 with a large product spot
at R.sub.f=0.74. The reaction mixture was then stirred overnight at
room temperature under nitrogen.
[0117] On the next morning, the green-blue clear reaction mixture
was again stirred under reflux for one hour. TLC analysis still
indicated that a trace of BocLMB or similar R.sub.f impurity was
present. The solution was then concentrated on a rotary evaporator
under vacuum to remove most of the methylene chloride, resulting in
a dark green-blue syrup. After addition of 200 mL hexanes, the
mixture was stirred by hand to effect the separation of a blue-gray
solid. Upon heating this mixture under reflux with continued hand
stirring, the TipsocLMB product dissolved in the hot hexanes
leaving behind a dark blue salt residue as a melt or crusty solid.
The hot hexanes solution was decanted from the residue, and the
residue was further extracted with 60 mL boiling hexanes. The
combined hot hexanes extract (green in color) was allowed to cool
slightly and was then filtered through a 1.5 cm-thick layer of
Celite to obtain a clear, pale tan filtrate. After washing the
Celite twice with 30 mL portions of hot hexanes, the combined
filtrate (.about.320 mL volume) was placed in the freezer (about
-20.degree. C.) overnight.
[0118] On the following morning, an off-white solid with a greenish
cast was observed to have crystallized. The mixture was filtered
cold, and the product was washed with cold hexanes (2.times.50 mL),
sucked dry, and dried under vacuum at room temperature to an
off-white solid. Yield: 33.3 g (75%). (MW of TipsocLMB=485.77) The
melting point from an earlier run was 121-123.degree. C.
[0119] TLC analysis (K5F silica, 3% acetone/CH.sub.2Cl.sub.2)
showed very weak spots at the origin and at R.sub.f=0.53 (probably
unreactied BocLMB) with the main spot at R.sub.f=0.61 that is
initially colorless and becomes dark blue upon standing at room
temperature for several hours, or in a 120.degree. C. oven for a
few minutes.
[0120] Examples 5 and 6 illustrate how TIPSOCLMB can be
incorporated in a coating fluid that can be UV-cured to create a
reactive layer containing TIPSOCLMB. Example 7 illustrates how the
above technique can produce an interstitial reactive layer, which
allows the Special DVD-5 designs 1, 2 and 3 to be used to
manufacture expiring optical discs. Example 8 illustrates how
TIPSOCLMB deblocks and becomes oxygen sensitive LMB in either a
surface or an interstitial layer. When exposed to oxygen, the LMB
oxidizes into methylene blue, as illustrated by the increasing cyan
density in FIG. 18; methylene blue strongly absorbs light in the
650 nm wavelength, as illustrated in FIG. 19.
EXAMPLE 5
Formulation of Coating Fluid Containing TIPSOCLMB
[0121] 80 mg TIPSOCLMB
[0122] 80 mg Irgacure 819 (Ciba Geigy; sensitizer)
[0123] 4.0 ml CD-501 acrylate (Sartomer; propoxylated[6]
trimethylolpropanetriacrylate)
[0124] 18.5 mg 1,4-diazabicyclo[2.2.2]octane ("Dabco"; Aldrich;
base)
[0125] 155 .mu.l 1,1,1,3,3,3-hexamethyldisilazane ("HMDZ";
Aldrich"; stabilizer)
[0126] The TIPSOCLMB, Irgacure 819, and Dabco are weighed into a
brown glass bottle, a stir bar is added, the CD-501 is poured in to
the proper weight, and the HMDZ is added by syringe. Dry nitrogen
is blown into the bottle for a few minutes and the bottle is capped
and the cap covered by parafilm. The contents are stirred at room
temperature for at least two hours to dissolve the solids. If not
all of the material is used, blow the bottle with nitrogen, cap and
seal with parafilm, and store in a freezer; warm the bottle before
opening to prevent water from condensing in the bottle.
EXAMPLE 6
Preparation of Disk Surface-coated with TIPSOCLMB/acrylate
Formulation
[0127] A DVD clear half disk (an unmetalized 0.6 mm thick and 120
mm diameter polycarbonate disc) or a full DVD (two layers bonded
together, back to back with a adhesive) is centered on a laboratory
spin coating turntable rotating at roughly 60 rpm's. A 4 ml
solution from example #5 is then applied uniformly in a circular
ring by a syringe at about a 34 to 40 mm diameter from the center
of the disc. The spin speed is then rapidly increased to about 200
rpm for about 15 seconds, resulting in a coating of
acrylate/TIPSOCLMB fluid about five .mu.m thick. The spinning is
slowed; excess fluid wiped off of the edge of the disk with a
tissue and base solvent, if available, and then removed to a lab
bench. At this point, the disc is subjected to about five flashes
from a Norlite 400 xenon flash lamp at its max setting. The time
between flashes is dictated by the charging of the flash lamp, but
should be sufficient as to not induce added stress from heat
generated in the cure (typically about 5 seconds). This process
will yield a clear, uncolored, fully cured acrylate film. Other
disks are also prepared with similar acrylate formulations that
contain either no Dabco or 10.times. the amount of Dabco described
in Example 5.
EXAMPLE 7
Preparation of Disk Sandwich-coated with TIPSOCLMB/acrylate
Formulation
[0128] A DVD half disk is centered data side up on the turntable as
stated above. The turntable is held stationary while the fluid is
dispensed on the data side in a manner creating drops with a
syringe roughly 3.about.5 mm round. These are evenly spaced about 3
mm apart on a diameter of 30.about.40 mm. The disc to be bonded is
then placed data side facing the solution and slightly bowed away
from the bottom disc by the edges. The disc will be lowered at an
angle until the first contact point between a fluid drop and top
disc occurs. We do not want to place the top disc immediately on
the bottom because of entrapped air and subsequent bubbles.
Therefore, to get a more uniform capillary flow, we can rotate the
disc in a clockwise rotation while keeping it slightly bent under
light pressure until each of the fluid drops begins to form a
capillary bridge ring. Once the capillary ring is completed, the
top disc can be released and the capillary action will continue. We
can wait for the capillary flow to cover the surface, or we can
spin the disc at 100 rpm's until the material at least reaches the
maximum OD diameter. At this point the turntable can be turned on
and rotated at about 500 rpm's for 5 seconds. This will level the
spacer layer (adhesive layer) and remove excess material from the
OD. The disc edge can then be wiped and the disc will then be UV
cured. It is important that prior to curing, the disc halves be
aligned as close as possible to avoid center hole misalignment an
subsequent play back problems. At this point, the disc is subjected
to about 20.about.30 flashes from a Norlite 400 xenon flash lamp at
its max setting. The time between flashes is dictated by the
charging of the flash lamp, but should be sufficient as to not
induce added stress from heat generated in the cure (Typically 5
seconds). This process will yield a clear, uncolored, fully cured
acrylate film. Other disks are prepared with similar acrylate
formulations that contain either no Dabco or 10.times. the amount
of Dabco described in Example 5.
EXAMPLE 8
Deblocking and Oxidation of TIPSOCLMB in Surface and
Sandwich-coated Disks, and the Effect of a Base Included in the
Coating Formulation
[0129] Disks prepared as described in Examples 6 and 7 were cut
into six `chips` each and the chips were stored in either dry
nitrogen, dry air, or room air (average RH about 30%) and their
cyan reflectance densities were recorded periodically with an
X-Rite 504 densitometer (the samples stored in nitrogen were only
tested at the start and end of the experiment as they were visibly
unchanged and it was desired to minimize their exposure to oxygen).
In all cases the samples stored in nitrogen showed no methylene
blue (MB) generation, as expected. Incorporating
1,4-diazabicyclo[2.2.2]octane (Dabco) into an acrylate formulation
at 1.0 equivalent with respect to the TIPSOCLMB gave very
significant acceleration of the deblocking/oxidation rate compared
to a control (FIG. 18), while a higher concentration of this
compound was actually less effective. In general the open samples
(those with the TIPSOCLMB layer coated on top of a DVD half without
any cover) generated MB only slightly faster than the sandwich
structures, indicating that deblocking and oxidation of the LMB is
not significantly limited by the transfer of either water or oxygen
through an unmetallized 0.6 mm polycarbonate layer. Rather, the
deblocking of the TIPSOCLMB is likely to be rate-limiting in these
systems. The control samples without any added base shows
noticeably faster MB generation in room air than in dry air,
suggesting that moisture in the air speeds deblocking in this
sample.
[0130] Example 9 illustrates how a reactive bonding layer was
incorporated into Special DVD-5 Design #2, thus manufacturing a
disc that was normally playable like a DVD-5 and subsequently
became unplayable.
EXAMPLE 9
Incorporating TIPSOCLMB into a Special DVD-5 Design #2 Bonding
Layer
[0131] A set of experiments was performed to test whether a
formulation containing TIPSOCLMB, Irgacure-819, Dabco,
1,1,1,3,3,3-hexamethyldisilaza- ne (as a fluid stabilizer), and
Sartomer CD-501 acrylate monomer could be used as a DVD adhesive to
produce playable DVDs. Using the formulation described in Example
5, filtered through a 1.0 .mu.m glass syringe filter, the fluid was
syringed onto either clear or metallized Special DVD-5 Design #2
halves manufactured as in Example 2. A DVD half disk is centered
data side up on the turntable as stated above. The turntable is
held stationary while the fluid is dispensed on the data side in a
manner by creating drops with a syringe roughly 3.about.5 mm round.
These are evenly spaced circularly about a diameter of 30.about.40
mm. The disc to be bonded is then placed data side facing the
solution and slightly bowed away from the bottom disc by the edges.
The disc will be lowered at an angle until the first contact point
between the fluid and top disc occurs. We do not want to place the
top disc immediately on the bottom because of entrapped air and
subsequent bubbles. Therefore, to get a more uniform capillary
flow, we can rotate the disc in a clockwise rotation while keeping
it slightly bent under light pressure until each of the fluid drops
begins to form a capillary bridge ring. Once the capillary ring is
completed, the top disc can be released and the capillary action
will continue. We can wait for the capillary flow to cover the
surface, or we can spin the disc at 100 rpm until the material
reaches the maximum OD diameter. At this point the turntable can be
turned up and rotated at about 500 rpm's for 5 seconds to thin out
the adhesive and achieve a resulting 50 .mu.m adhesive films
(determined by profilometry). This will level the spacer layer
(adhesive layer) and remove excess material from the OD. The disc
edge can then be wiped and then the disc UV cured. It is important
that prior to curing, the disc halves be aligned as close as
possible to avoid center hole misalignment an subsequent play back
problems. At this point, the disc is subjected to about 20.about.30
flashes from a Norlite 400 xenon flash lamp at its max setting. The
time between flashes is dictated by the charging of the flash lamp,
but should be sufficient as to not induce added stress from heat
generated in the cure (Typically 5 seconds). This process will
yield a clear, uncolored, fully cured acrylate film that plays on
the DVD test player.
[0132] The discs were manufactured under normal ambient conditions,
and were subsequently put in a nitrogen box for 3-4 days, to remove
the oxygen dissolved in the substrates (which would take an
estimated 12-20 hours), and to allow TIPSOCLMB to unblock into LMB
(which would take 2-3 days).
[0133] The Special DVD-5 design #2 discs were subsequently removed
from the nitrogen box and were measured for reflectivity at the 650
nm wavelength as a function of time. The discs were clear and
playable for 12-16 hours after which time they turned dark blue
within 24 hours and became unplayable with reflectivities under 2%
at 650 nm.
Multiple-layer Optical Discs
[0134] As seen in the DVD family illustration in FIG. 4, in a dual
layer optical disc designed to read multiple layers from one side,
the spacer (bonding) layer is in the optical path. In the case of
Dual Layer DVDs, the given specification for this spacer layer
thickness is 0.055+/-0.015 mm. The thickness of the substrate for a
dual layer DVD with optical path bonding is typically 0.55
mm.about.0.64 mm.
[0135] Incorporating a reactive compound inhibiting the reading
laser in the bonding layer 800 of either type of dual-layer disc
would only inhibit the player from reading the L1 layer 805, as the
bonding layer 800 is not in the optical path for reading the L0
layer 810. Furthermore, the metal 815 in the L0 layer 810 might act
as a barrier preventing a predetermined stimulus such as moisture
or oxygen to permeate to the reactive compound in the bonding layer
800 in a controllable manner.
[0136] One method around this potential problem would be as
follows. Typically, when a player or a drive begins reading a disc,
it looks for the table of contents or information area in the
lead-in area for the L0 layer 810 (see FIG. 6). When authoring the
disc, it is possible to have the L0 lead-in 820 area contain
commands to directly access the L1 layer 805. In order to be able
to read the L0 layer 810 to direct the play sequence to the L1 805,
we would have to metallize the L0 side 810. This would then
possibly interfere with the reactive adhesive material 800 causing
unstable or uncontrolled kinetics of reaction that would be
dependent on the permeability of the metal layer. One approach
around this would be to change the metallizer masking for the L0
semi-reflective layer 800, which is typically run out to 58 mm to
59 mm radius on the disc, to something closer to the lead-in or
information data area on the L0.
[0137] To facilitate activation of the reactive material 800, e.g.,
when the activating stimulus is oxygen or moisture that might be
prevented from reaching the reactive bonding layer 800 because of
the L0 metal layer 820, part of the L0 layer 810 can be masked
during metallization, so that part of the reactive layer will be
easier to expose to the stimulus and thus the corresponding part of
the L0 layer will be disabled. These discs would have a partially
metallized L0 layer 810, as illustrated in FIG. 20. For example, if
only the lead-in area or program start portion of the L0 layer 810
is metallized, the player is able to read the lead-in data, and is
able to access the information stored on L1 layer 805. As only a
small area on the L0 layer 810 would be metallized, a substantial
part of the reactive bonding layer would be in direct contact with
the L0 substrate 810, which is typically permeable by stimuli such
as oxygen or moisture. When the reactive bonding layer responds to
the appropriate stimuli and starts interfering with the reading
laser, the player is no longer able to access the corresponding
part of the L1 layer 805.
[0138] Another embodiment of the present invention is utilizing
authoring techniques, such as sequencing and branching commands to
be executed by the optical media player, to ensure that making a
certain part of a disc unplayable will interfere with playing other
parts of the disc, or the entire disc. The part of the disc made
unplayable for this purpose may be in the single layer of a
one-layer disc, or in any of the layers of a multi-layer disc. For
example, one embodiment of this invention consists of a DVD-9
authored so that making a certain part of the L1 layer unplayable
would interfere with playing other parts of the disc, or the
entirety of the disc. For example, reading the L0 layer lead-in
area would direct the player to access a part of the L1 layer that
would become unreadable when the reactive layer starts interfering
with the reading laser, which would cause the disc to be
inoperable. A DVD-9 disc can be authored so that all or part of the
L1 layer is essential in order to play any information on L0 and/or
L1. For example each chapter on the disc can be authored so that it
requires reading certain information on L1 before proceeding.
[0139] In another embodiment of this invention, activation of the
reactive material is facilitated by controlling the deposition of
the L0 layer. For example, fast deposition of a gold or silver or
silicon L0 layer through sputtering is known to result in grainy
dendritic formations that are easier to penetrate by oxygen and
moisture. Also, a thinner L0 layer can be deposited, which is
easier to penetrate by oxygen and moisture. While depositing grainy
or thin L0 layers may be unacceptable for a permanent, archival
quality disc, it is often adequate for a limited use, expiring
disc.
EXAMPLE 10
DVD-9 Discs with TIPSOCLMB Incorporated in a Reactive Bonding
Layer
[0140] A DVD-9 with parallel track path encoding can have two
distinctly different layers for play back. In the encoding or data
mastering process, the Lead-in area normally found on the L0 disc,
can have information telling the reading players to read from
either or both layers on the disc. Therefore, for this example
using a reactive bonding material, the reactive layer could prevent
play back from the L1 layer while not affecting the L0. For this
example corresponding L0 and L1 masters were manufactured, and L0
and L1 substrates were normally molded and metallized.
[0141] The DVD halves were bonded as in example 9 above using an
adhesive containing the formulation TIPSOCLMB, Irgacure-819, Dabco,
1,1,1,3,3,3-hexamethyldisilazane (as a fluid stabilizer), and
Sartomer CD-501 acrylate monomer described in Example 5. The
solution was filtered through a 1.0-.mu.m glass syringe filter. A
DVD half disk is centered data side up on the turntable as stated
above. The turntable is held stationary while the fluid is
dispensed on the data side in a manner by creating drops with a
syringe roughly 3.about.5 mm round. These are evenly spaced
circularly about a diameter of 30.about.40 mm. The disc to be
bonded is then placed data side facing the solution and slightly
bowed away from the bottom disc by the edges. The disc will be
lowered at an angle until the first contact point between the fluid
and top disc occurs. We do not want to place the top disc
immediately on the bottom because of entrapped air and subsequent
bubbles. Therefore, to get a more uniform capillary flow, we can
rotate the disc in a clockwise rotation while keeping it slightly
bent under light pressure until each of the fluid drops begins to
form a capillary bridge ring. Once the capillary ring is completed,
the top disc can be released and the capillary action will
continue. We can wait for the capillary flow to cover the surface,
or we can spin the disc at 100 rpm until the material reaches the
maximum OD diameter. At this point the turntable can be turned up
and rotated at about 500 rpm's for 5 seconds to thin out the
adhesive and achieve a resulting 50 .mu.m adhesive films
(determined by profilometry). This will level the spacer layer
(adhesive layer) and remove excess material from the OD. The disc
edge can then be wiped and then the disc UV cured. It is important
that prior to curing, the disc halves be aligned as close as
possible to avoid center hole misalignment an subsequent play back
problems. At this point, the disc is subjected to about 20.about.30
flashes from a Norlite 400 xenon flash lamp at its max setting. The
time between flashes is dictated by the charging of the flash lamp,
but should be sufficient as to not induce added stress from heat
generated in the cure (Typically 5 seconds). This process will
yield a clear, uncolored, fully cured acrylate film that plays on
the DVD test player.
[0142] The discs were manufactured under normal ambient conditions,
and were subsequently put in a nitrogen box for 7 days, to remove
the oxygen dissolved in the substrates (which would take an
estimated 12-20 hours), and to allow TIPSOCLMB to unblock into LMB
(which was estimated to take up to 5-6 days). The discs were
subsequently removed from the nitrogen box and were normally
playable on both the L0 and L1 layer for 2-3 days on a Pioneer
player. After 7 days of exposure to ambient oxygen, the discs
became unplayable on the L1 layer, although they would play
normally on the L0 layer.
EXAMPLE 11
DVD-9 Discs with Partially Metallized L0 Layer
[0143] As in example 10 above, DVD-9 master tapes were generated
with the data area being identified on layer L1 and the L0 layer
serving only to provide the lead-in and subsequent table of
contents relating to the disc type and information. During play
back, the L0 lead-in would instruct the disc to read from the L1
data side. In this case, we would not have to metalize the entire
surface of the L0 layer because there is no information to be read
outside of the lead-in area. Therefore, DVD-9 master tapes were
produced with lead-in and command information on L0 and data area
on L1. Typically, the metalizer masking covers areas from 25 mm
through 118 mm diameters on both layers. Being as the lead-in area
data covers the diameters of 25.2 mm to a maximum of 48 mm, and the
subsequent information area starts at no less than 48 mm diameter,
the metalizer masking can be reduced to cover the lead-in only.
This would allow a reflective signal to read the lead-in on the L0
layer and then switch to the L1 layer for data playback without
having to read through additional semi-reflective metal.
[0144] In this example, we manufactured donut-masking plates that
dropped into the metalizer OD mask assembly. By registering the
masking from the OD, we are able to reduce the metalized diameter
to an area allowing lead-in playback. We extended the mask just
outside of the lead-in 48 mm diameter in order to compensate for
eccentricity tolerance with the masking position. Additionally, in
order to prevent a reflective spike from the transition of clear
disc area to metalized disc area when reading the L1 layer, the
edge of the masking was slightly raised above the disc to cause a
shadowing or tapered layer uniformity. This would cause a gradual
focusing compensation rather than a large "speed bump" effect
causing its radial noise and focusing error to fall out of
specification and perhaps jump track.
[0145] The resulting DVD-9 halves were bonded as in Example 10. The
DVD-9s constructed were tested for playability in a Pioneer DVD
player and in a DVD-ROM drive, and were subsequently put in a
nitrogen box for 7 days, so that the TIPSOCLMB would unblock into
LMB. The discs were subsequently removed from the nitrogen box and
were clear and playable for 12-16 hours, and turned dark blue
within 24 hours after that, becoming unplayable. The discs were
effectively prevented from having information read from either L0
or L1.
Controlling the Timing of the Reaction
[0146] Preferably, the data quality of the disc should remain high
for the intended period of use and then decay rapidly resulting in
a rapid degradation of the ability to read data off the optical
disc. One benefit of this embodiment of the present invention is
that for a broad class of stimuli, such as those requiring
diffusion of a substance through a barrier layer, incorporating the
reactive material in an interstitial layer results in substantial
advantages regarding the timing characteristics of the
reaction.
[0147] One method of achieving the above mentioned desirable timing
characteristics is to use a reactive interstitial material between
the disc substrates, as described earlier, which reacts with a
substance that needs to diffuse through the substrates of the disc.
For example, if the reactive material is sensitive to oxygen, there
will be an extended period in which there will be no reaction while
the oxygen diffuses through the disc substrates. Once oxygen
reaches the reactive layer, the resulting reaction can be fast,
resulting in rapid expiration of the disc.
[0148] When oxygen is used as the diffusing substance, it may be
necessary to remove oxygen that dissolves in the disc during the
different stages of its manufacture. This can be done, for example,
by storing the discs in a vacuum or in an oxygen free environment
for an appropriate period of time. It has been established
theoretically and experimentally that 24 hours is an adequate
period to extricate oxygen dissolved in a 0.6 mm thick
polycarbonate disc substrate. Alternatively, if a blocked reactive
material is used as described earlier, an oxygen scavenging
material, such as iron or an organometallic compound, can be used
to extricate oxygen from the optical disc before the blocked
reactive material unblocks. This method has several manufacturing
advantages; for example, it can avoid oxygen extrication during
manufacturing of the disc by including the oxygen scavenging
material in the packaging of the disc, which allows the extrication
of the oxygen to take place after the disc is manufactured and
packaged.
[0149] Another means for controlling the timing of the expiration
of the disc is to include in or adjacent to the reactive layer a
finite, controlled quantity of an appropriate protective substance,
such as an antioxidant in the case that the reactive layer reacts
with oxygen. The protective substance would prevent the reactions
that cause the disc to expire until such time as the anti-oxidant
was consumed, at which time the disc would rapidly degrade and
become unplayable. For example, an organometallic compound that
reacts with oxygen can be packaged with the disc to protect the
disc from oxidation while in the package. Alternatively, the
organometallic compound can be incorporated into the substrate,
thus continuing to protect the metal layer for a period of time
after the package has been opened.
[0150] Depletion of a protective substance could be combined with
diffusion of the triggering substance through the substrate of the
disc, to result in longer delays before the disc expires, or to
enable finer control of the characteristics of the expiration
process, such as the steepness of reflectivity degradation.
Example of Antioxidant in Reactive Layer
[0151] Alternatively, the protective substance may be a reducing
agent which may be incorporated into the reactive bonding layer
itself. In an experiment in which the concentration of TLMB was
also varied and shown to have an effect, the play time was shown to
be more greatly affected by varying the amount of stannous
ethylhexanoate reducing agent (see Table I).
4 TABLE I Concentration Play Time (hrs) Formulation # TLMB Sn(II)
EtHexanoate short long A 1% 2% 14 22 B 1% 4% 38 55 C 0.5% 2% 18 26
D 0.5% 4% 46 58
[0152] DVD-5 discs were made using a TIPSOCLMB-containing adhesive
formulation, and deblocked in an oxygen-free atmosphere for 48
hours at 60.degree. C. At that time the discs were exposed to
ambient room air and the rate of methylene blue color development
was quantified with an X-Rite reflection densitometer. The short
Play Time was chosen to be the time at which the cyan density
increased by 0.35, which roughly corresponds to a playability
cutoff at 45% reflectance as typified by a low quality DVD player.
The long Play Time was chosen to be the time at which the cyan
density increased by 0.85, which roughly corresponds to a
playability cutoff at 10% reflectance as typified by a high quality
DVD player.
[0153] The most likely mechanism for this extended play is
reduction of the initially formed methylene blue dye back to the
leuco form until most of the reducing agent is consumed. Alternate
mechanisms, such as the stannous compound acting as a primary
oxygen scavenger to consume oxygen before the leuco dye is
affected, are also possible.
[0154] The mobility within the cured matrix is expected to have a
significant effect upon the reduction rate; indeed, the calculated
glass transition temperature (Tg) of the monomers used in this
example is -34.degree. C. In such a soft matrix, adequate molecular
mobility should exist to allow molecular contact of reducing agent
and dye molecules.
[0155] Alternate reducing agents might include other Sn(II)
compounds which would be soluble in the UV cure formulation, such
as acetylacetonate chelates, fatty alpha-aminoacid chelates and
salts; soluble iron(II) compounds, such as fatty carboxylates and
chelates such as acetylacetonates; ascorbic acid and its
derivatives such as ascorbyl palmitate; hydroquinones, such as
2,5-di-tert-amylhydroquinone; alkylhydroxylamines; hydrazines;
dithionates with a solubilizing counterion; reducing saccharides
such as glucose; alpha-hydroxyketones, such as acetol;
appropriately substituted boron and silicon hydrides. Although many
of these materials are difficultly soluble in current active
adhesive formulations, a more expeditious choice of monomers and
oligimers might allow the use of one of these alternate reducing
agents while still providing good adhesive and dye stabilization
properties.
Preventing Expired Discs from Playing in Future Generation
Players
[0156] Future generations of optical discs and players are
typically developed to offer increased performance for consumers
and other users of the technology. For example, DVDs offer
increased storage capacity compared to CDs, and the next generation
of "blue laser" DVDs will offer improved capacity compared to
today's DVDs. Subsequent generations of optical storage media, such
as the "DVR" format currently under development, will have even
greater capacity and performance.
[0157] Optical media players are typically engineered with the
ability to play previous generations of discs. For example, while
CD players employ a laser with a wavelength of 780 nanometers to
read CDs, DVD players typically employ their reading laser with a
wavelength of 650 nanometers to read CD discs. The next generation
DVDs ("blue laser DVDs") is designed to be read with a laser with a
wavelength of 450-460 nanometers; the "DVR" format will use lasers
emitting around 405 nm. Future generation players are likely to be
able to read current DVDs with their 450-460 nanometer or 405
nanometer lasers.
[0158] Dyes used to inhibit the reading laser in current optical
disc players are typically designed to interfere with the reading
laser employed by these players; such dyes, however, may not
interfere with the reading laser future players, which is likely to
have a shorter wavelength. The implication is that expired discs,
even though they may not play in the current generation of players,
they may become playable when future generation players become
available. Dyes used to inhibit the reading laser in current DVD
players are typically designed to interfere with a 650 nanometer
reading laser; such dyes, however, may not interfere with a reading
laser in the 450-460 nanometer range. For example, methylene blue,
which is one of the read inhibit dyes proposed in Smith et al,
while strongly absorbent in the 650 nanometer wavelength, it is
essentially transparent in the 450-460 nanometer range (see FIG.
19). The implication is that expired DVDs may play in blue laser
DVD players.
[0159] Another embodiment of the present invention is an optical
disc that will not play in future generation players, thus
preventing an expired disc from becoming playable when future
generation players (e.g., blue laser DVD players) become available.
This can be accomplished by incorporating in the optical path of
the disc a selectively interfering layer that will interfere with
the reading laser of future generation players, and thus will
inhibit reading of the disc in such players. Such a layer can be
designed by incorporating a dye or pigment that does not interfere
with the reading laser in a certain type of players, but does
interfere with the reading laser in other types of players (or will
change to become interfering in response to a predetermined
stimulus). For example, Acridine Yellow [135-49-9], is essentially
transparent at the 635-650 nanometer wavelength but strongly
absorbs at the 450-460 and 405 nanometer wavelengths (absorption
max in ethanol at 462 nm, molar absorptivity=37,000 M.sup.-1
cm.sup.-1). Alternatively 9,10-bis(phenylethynyl)anthracene
[10075-85-1] also does not absorb at all in the 635-650 nanometer
range, but is strongly absorbent in the 450-460 and 405 nanometer
range (absorbance max 455 nm in cyclohexane, molar absorptivity
33,000 M.sup.-1 cm.sup.-1). Other classes of dyes and pigments that
can be used for blocking blue laser light (at either 450-460 or 405
nm) include aromatic hydrocarbons, azo dyes, cyanines,
polymethines, carotinoids, hemicyanines, styryls, quinaldines,
coumarins, di- and triarylmethines, anthraquinones, nitro and
nitrosos. As mentioned above, methylene blue is essentially
transparent at the 450-460 nanometer wavelengths, but strongly
absorbs at the 635-650 nanometer range.
[0160] In one embodiment of the current invention, the selectively
interfering layer is a dedicated layer in the optical path of the
reading laser. In another embodiment, which is likely to be the
preferred embodiment because it does not introduce an additional
design element for the optical disc, the selectively interfering
layer is combined with another element of the disc, such as the
substrate or the reactive layer. For example, this could be
accomplished by mixing an appropriate dye or pigment, such as
Acridine Yellow [135-49-9] or 9,10-bis(phenylethynyl)ant- hracene
[10075-85-1], with the polycarbonate or other polymer used to mold
the substrate of the disc, or with the reactive layer in an
expiring disc, such as the bonding layer in the special DVD-5
designs described earlier.
Use of Additional Mechanisms to Prevent Recovery of Data
[0161] Another embodiment of the present invention is combining the
mechanism(s) that prevent reading of the optical disc by inhibiting
the reading laser with additional mechanism(s) for preventing
recovery of the information encoded in the data structures on the
disc. These additional mechanism(s) can be designed with less
accurate control of the timing of their activation than the
mechanism(s) that work by inhibiting the reading laser. Thus it may
be desirable to combine the mechanism that controls expiration of
the optical disc by interfering with the reading laser with
additional mechanism(s) that permanently prevent the recovery of
the data on the optical disc. For example, a disc may become
unplayable by transitioning a layer in the optical path from
transparent to opaque in a controlled time period, for example
approximately 24 hours after a predetermined stimulus, such as
removing the disc from its packaging. In addition, a secondary
mechanism could corrode the metal layer on the disc, such mechanism
acting over a longer period of time, such as 1-2 weeks, and being
triggered by the same or a different stimulus. Additional
mechanisms may also be employed, such as an additive that degrades
the polycarbonate material from which the disc is composed, which
process can be triggered by the same stimulus (such as exposure to
ambient air), or a different stimulus (such as the centrifugal
forces generated when a disc is played in a CD or DVD player).
Other triggering stimuli for these backup mechanisms can include
various constituents of air, light, physical motion, and time from
manufacturing or packaging. Many other mechanisms are possible.
[0162] One method of accomplishing this is to deposit a layer of
metallic silver separated from the information bearing aluminum
layer by a material incorporated for this purpose, or by an
existing material, such as the bonding layer or one of the
substrates of the optical disc. This silver layer can be above or
below the aluminum layer, and if it is below (and thus in the
optical path of the reading laser) it needs to be sufficiently
transparent initially so that the reading laser can read the
information on the aluminum layer.
[0163] In one embodiment of the invention, a DVD-9 disc is
manufactured with a reactive bonding layer consisting of a material
with appropriate dielectric properties, and with appropriate
selection of metals for L0 and L1. For example, L0 can be made of
silver and L1 can be made of aluminum.
[0164] When a silver layer and an aluminum layer are separated by
an appropriate dielectric material, then upon exposure to oxygen
the silver serves as a cathode, on which O.sub.2 is reduced, and
aluminum serves as an anode. Corrosion is fast only if a short
develops between the silver and the aluminum layers. The
development of the short results from the growth of a silver
dendrite through the separating material. To grow the dendrite
through the separating material it is desirable to use a material
that has some ionic conductivity. Several likely separating
materials consist of or contain polyacrylate. If the polyacrylate
is slightly hydrolyzed, or if it is, for example, a
2-hydroxyethylacrylate copolymer, there will be some ionic
conductivity. Preferred are co-polymers of poly(acrylonitrile), or
of poly(4-vinylpyridine), or of poly(1-vinylimidazole). All of
these should conduct silver, copper or thallium ions (Ag.sup.+
Cu.sup.+ or Tl.sup.+). Thallium is less preferred due to its
toxicity.
[0165] The chemical equations are as follows:
[0166] Silver is air-oxidized:
4Ag+O.sub.2.fwdarw.Ag.sub.2O (complexed with lacquer)
Ag.sub.2O+H.sub.2O+complexant.fwdarw.2Ag.sup.+
(complexed)+2OH.sup.-
[0167] Ag.sup.+ is reduced by aluminum, which is oxidized (if
Ag.sup.+ is mobile in the lacquer, which is designed to conduct
Ag.sup.+)
Ag.sup.++Al.fwdarw.A1.sup.3++3Ag.sup.0
Al.sup.3++3OH.sup.-.fwdarw.Al(OH).fwdarw.Al(O)OH+H.sub.2O
[0168] A silver dendrite starts growing from the aluminum to the
silver. When the two layers are shorted, the "switch" between a
battery's (Al) anode and (Ag) cathode is closed. Corrosion is rapid
and catastrophic. One skilled in the art will recognize that other
similar metals may be substituted for Al and Ag in this
example.
[0169] Alternatively, other ways of permanently corroding data
layers via the reactive layer can be employed. For example, certain
embodiments of this invention may have a bonding layer that
promotes the corrosion of the reflective metal layer or may involve
the diffusion of some substance from the bonding layer to the
reflective layer(s). In other embodiments, the additional
mechanisms will not be part of the bonding material. For example, a
precursor of a corrosive substance may be deposited adjacent to the
metal layer. When oxygen or some other appropriate substance
diffuses through the substrate and reaches the corrosive precursor,
a reaction could be initiated that results in producing a corrosive
substance that over a period of time permanently destroys the data
structures on the disc. Alternatively, the material in the
substrate of the disc, such as polycarbonate, could be engineered
so that it degrades over a period of time, thus making the disc
unusable. Such substances and reactions are known to the skilled in
the art.
[0170] Another composition that performs a similar function is one
in which the substrate itself is modified over time. The
modification of the substrate could cause it to change its optical
qualities, thereby degrading the signal reaching the reader. These
optical qualities could include its index of refraction or its
transparency.
[0171] Moreover, the modification of the substrate could cause the
underlying metal layer to change its optical properties, as
described above. In this way, a time-sensitive substrate and/or
lacquer could be combined with a reflective layer that becomes
non-reflective.
[0172] The transparency of a polymer film can be changed by any of
the following: reaction of the film with water; reaction of the
film with oxygen; or crystallization of the polymer, meaning
increased alignment of polymer molecules in the film.
[0173] As an example, a substrate could be chosen that is changed
by components in air such as oxygen or water. For example, oxygen
could oxidize the substrate, causing a change in its transparency
or its index of refraction. Alternatively, the substrate could be
designed to absorb water in the air, causing it to swell and change
its optical properties. Another example is that the substrate could
change its permeability to oxygen over time, thereby permitting the
oxidation of the metallic layer. In the later case, the overall
time sensitivity of the optical media could be a function of the
properties of both the substrate and/or lacquer and the reflective
layer.
[0174] The substrate or the metallic layer could also be made
sensitive to specific wavelengths of light. Exposure to these
wavelengths would cause a change in the optical qualities of the
layer, thereby degrading the signal reaching the reader. Examples
include photodepolymerization of the substrate; photogeneration of
acid; photogeneration of singlet oxygen; and unzipping of the
polymers (e.g., fissure of cross linking hydrogen bonds).
Incorporation of light-activated catalysts into the substrate or
the metallic layer can assist in this process.
[0175] Accordingly, the present invention has been described at
some degree of particularity directed to the exemplary embodiments
of the present invention. It should be appreciated, though, that
the present invention is defined by the following claims construed
in light of the prior art so that modifications or changes may be
made to the exemplary embodiments of the present invention without
departing from the inventive concepts contained herein.
* * * * *