U.S. patent application number 09/887881 was filed with the patent office on 2001-11-29 for machine-readable optical disc with reading-inhibit agent.
This patent application is currently assigned to SpectraDisc Corporation. Invention is credited to Carlson, Eric J., Ehntholt, Daniel J., Marmo, Christopher J., Powell, John R., Rollhaus, Philip E., Valentine, James R., Winkler, Irwin C..
Application Number | 20010046204 09/887881 |
Document ID | / |
Family ID | 26701179 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046204 |
Kind Code |
A1 |
Rollhaus, Philip E. ; et
al. |
November 29, 2001 |
Machine-readable optical disc with reading-inhibit agent
Abstract
An optical disc having machine-readable, information-encoding
features is provided with a barrier layer secured to the disc. This
barrier layer is configured to prevent machine-reading of the
features. A reading-inhibit agent, included in the disc and
activated by removal of the barrier layer, is operative, once
activated, to alter the disc to inhibit reading of the disc
Alternately, the barrier layer can be eliminated, and the
reading-inhibit agent can be activated by initial reading of the
disc, as for example by exposure to optical radiation associated
with reading of the disc, or rotation of the disc.
Inventors: |
Rollhaus, Philip E.;
(Chicago, IL) ; Powell, John R.; (Arlington,
MA) ; Carlson, Eric J.; (Sudbury, MA) ;
Ehntholt, Daniel J.; (Hudson, MA) ; Winkler, Irwin
C.; (Arlington, MA) ; Marmo, Christopher J.;
(Boxboro, MA) ; Valentine, James R.; (Reading,
MA) |
Correspondence
Address: |
HARRY F. SMITH, ESQ.
OHLANDT, GREELEY, RUGGIERO & PERLE, L.L.P.
ONE LANDMARK SQUARE, 10th FLOOR
STAMFORD
CT
06901-2682
US
|
Assignee: |
SpectraDisc Corporation
|
Family ID: |
26701179 |
Appl. No.: |
09/887881 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09887881 |
Jun 22, 2001 |
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09421490 |
Oct 20, 1999 |
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09421490 |
Oct 20, 1999 |
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08902844 |
Jul 30, 1997 |
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6011772 |
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60026390 |
Sep 16, 1996 |
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Current U.S.
Class: |
369/284 ;
369/283; G9B/20.002; G9B/20.009; G9B/7.139 |
Current CPC
Class: |
G11B 20/00608 20130101;
G11B 20/10 20130101; G11B 20/00086 20130101; G11B 7/24
20130101 |
Class at
Publication: |
369/284 ;
369/283 |
International
Class: |
G11B 003/70; G11B
005/84; G11B 007/26 |
Claims
We claim:
1. In an optical disc comprising machine-readable,
information-encoding features, the improvement comprising: a
barrier layer releasably coupled to the disc, said barrier layer
configured to prevent machine-reading of the features; and a
reading-inhibit agent, included in the disc and activated by
removal of the barrier layer, said reading-inhibit agent operative,
once activated, to alter the disc to inhibit reading of the
disc.
2. The invention of claim 1 wherein the disc comprises a first
surface, wherein the features are adjacent the first surface,
wherein the inhibit agent is adjacent the features, and wherein the
barrier layer is adjacent the inhibit agent.
3. The invention of claim 1 wherein the disc comprises a
translucent layer operative to transmit a beam of light toward the
features, wherein the inhibit agent is incorporated in or adjacent
to the translucent layer, and wherein the barrier layer comprises a
sheet adjacent the translucent layer.
4. The invention of claim 1 wherein the disc comprises a reflective
film, and wherein the inhibit agent comprises a corrosion-enhancing
agent disposed in or adjacent to the reflective film.
5. The invention of claim 3 wherein the inhibit agent is operative,
once activated, to increase scattering of the beam of light.
6. The invention of claim 3 wherein the inhibit agent is operative,
once activated, to absorb the beam of light.
7. The invention of claim 1 wherein the inhibit agent is operative,
once activated, to alter a physical dimension of the disc.
8. in an optical disc comprising machine-readable,
information-encoding features, the improvement comprising: a
reading-inhibit agent, included in the disc and activated by
machine-reading the disc, said reading-inhibit agent operative,
once activated, to alter the disc to inhibit reading of the
disc.
9. The invention of claim 8 wherein the inhibit agent is activated
by optical radiation incident on the disc during machine-reading of
the disc.
10. The invention of claim 8 wherein the inhibit agent is activated
by rotation of the disc during machine-reading.
11. The invention of claim 8 further comprising a reservoir on the
disc containing the reading-inhibit agent, said reservoir
configured to release the reading-inhibit agent when the disc is
rotated during machine-reading.
12. A method for inhibiting reading of an optical disc, comprising
the following steps: (a) providing an optical disc comprising
machine-readable, information-encoding features, and a
reading-inhibit agent, said inhibit agent activated by optical
radiation and operative, once activated, to alter the disc to
inhibit reading; (b) providing a reading device operative to read
the disc, said reading device comprising a source of optical
radiation; and (c) reading the disc with the reading device and
concurrently activating the inhibit agent with optical radiation
from the source.
13. The method of claim 12 wherein the reading device provided in
step (b) additionally comprises a source of a reading beam, in
addition to the source of optical radiation.
14. A method for inhibiting reading of an optical disc, comprising
the following steps: (a) providing an optical disc comprising
machine-readable, information-encoding features, and a
reading-inhibit agent, said inhibit agent activated by optical
radiation and operative, once activated, to alter the disc to
inhibit reading; (b) providing a reading device operative to read
the disc, said reading device comprising first and second sources
of optical radiation; and (c) reading the disc with the first
source and concurrently activating the inhibit agent with the
second source.
15. A method for inhibiting reading of an optical disc, comprising
the following steps: (a) providing an optical disc comprising
machine-readable, information-encoding features, and a
reading-inhibit agent, said inhibit agent activated by optical
radiation and operative, once activated, to alter the disc to
inhibit reading; (b) providing a reading device operative to read
the disc, said reading device comprising a source of optical
radiation; and (c) reading the disc with the source while
concurrently activating the inhibit agent with optical radiation
from the source.
16. In an optical disc comprising machine-readable,
information-encoding features, the improvement comprising: a
reservoir included in the disc; a passageway interconnecting the
reservoir and a portion of the disc comprising the
information-encoding features; and a reading-inhibit agent,
included in the reservoir and activated by machine-reading the
disc, said reading-inhibit agent operative, once activated, to
alter the disc to inhibit reading of the disc.
17. The invention of claim 16 wherein the passageway comprises a
valve.
18. The invention of claim 17 wherein the valve comprises a valve
element that is soluble in the reading-inhibit agent.
19. The invention of claim 17 wherein the valve comprises a
mechanical valve.
20. The invention of claim 16 comprising a wick disposed in the
reservoir.
21. The invention of claim 16 further comprising at least one vent
in communication with the passageway.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to machine-readable optical discs of
all types, including for example digital discs such as compact
discs (CD's), digital video discs (DVD's), CDROM's, and the
like.
[0002] Conventional optical discs have reached widespread
acceptance as a low-cost, reliable storage medium for digital
information including music, video, and data. One of the
traditional advantages of optical discs is their long life.
[0003] However, in some applications, the long life of the
conventional optical disc may represent a disadvantage. For
example, if music, movies or software is to be rented for a limited
time period, the original optical disc must be returned at the end
of the rental period.
[0004] A need presently exists for an improved machine-readable
optical disc that eliminates the need for the return of an optical
disc at the end of a rental period.
SUMMARY OF THE INVENTION
[0005] According to a first aspect of this invention, an optical
disc comprising machine-readable, information-encoding features is
provided with a barrier layer releasably coupled to the disc. This
barrier layer is configured to prevent machine-reading of the disc.
A reading-inhibit agent is included in the disc, and is activated
by removal of the barrier layer. This reading-inhibit agent is
operative, after it is activated, to alter the disc to inhibit
reading of the disc. Both the barrier layer and the reading-inhibit
agent can take many forms, as discussed by way of example
below.
[0006] According to another aspect of this invention, an optical
disc comprising machine-readable, information-encoding features is
provided with a reading-inhibit agent that is activated by
machine-reading the disc. This reading-inhibit agent is operative,
after it is activated, to alter the disc to inhibit reading of the
disc. In alternate embodiments, the reading-inhibit agent may be
activated by optical radiation incident on the disc during
machine-reading of the disc, or by rotation of the disc during
machine-reading of the disc.
[0007] According to a third aspect of this invention, a method is
provided for inhibiting reading of an optical disc. According to
this method, an optical disc is provided comprising
machine-readable, information-encoding features, and a
reading-inhibit agent. The reading-inhibit agent is activated by
optical radiation, and is operative, once activated, to alter the
disc to inhibit reading. A reading device is provided to read the
disc, and this reading device comprises a source of optical
radiation. According to the method of this invention, the disc is
read with the reading device, and the inhibit agent is concurrently
activated with optical radiation from the source. The source of
optical radiation that activates the reading-inhibit agent can
either be the source of optical radiation that forms the reading
beam, or a second source, separate from the reading beam
source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGS. 1 through 3 are partial cross-sectional views of three
barrier layers suitable for use in embodiments of this
invention.
[0009] FIGS. 4, 5, 6, 7 and 8 are partial cross-sectional views of
optical discs that incorporate first, second, third, fourth, and
fifth preferred embodiments of this invention, respectively:
[0010] FIGS. 9 and 10 are plan views of optical discs that
incorporate sixth and seventh preferred embodiments of this
invention, respectively.
[0011] FIGS. 11 and 12 are partial cross-sectional views of optical
discs that incorporate eighth and ninth preferred embodiments of
this invention, respectively.
[0012] FIG. 13 is a plan view of an optical disc that incorporates
a tenth preferred embodiment of this invention.
[0013] FIGS. 14 and 15 are partial cross-sectional views of optical
discs that incorporate embodiments of the invention employing
galvanic cells.
[0014] FIG. 16 is a partial cross-sectional view of a prior art
compact disc.
[0015] FIG. 17 is a partial cross-sectional view of a disc
containing a reservoir.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0016] The present invention can be implemented in many different
ways, and the following discussion will describe selected
embodiments of the invention. These embodiments are intended as
examples only, and not as an exhaustive list of all forms that the
invention can take. Generally speaking, the embodiments discussed
below can be classified into two groups. The first group uses a
barrier layer to prevent premature activation of the
reading-inhibit agent, while the second group does not use such a
barrier layer.
[0017] In general, this invention can be used with the widest
possible variety of optical discs comprising machine-readable,
information-encoding features. FIG. 16 shows a highly schematic
cross section of an optical disc such as a prior art compact disc.
FIG. 16, like all of the other figures, is not drawn to scale;
selected features have been exaggerated in size for clarity of
illustration. The disc of FIG. 16 includes a substrate 10 which is
formed with an array of information-encoding features such as pits
12. The surface defining the information-encoding features 12 is
covered with a reflective layer 14, which may be, for example,
formed of aluminum. The reflective layer 14 is in turn covered with
a protective layer 16 which protects the reflective layer 14 from
oxidation and physical damage. A reading beam aligned with the
arrow 18 is incident on the surface of the substrate 10 opposite
the information-encoding features 12. This reading beam passes
through the substrate 10, is reflected by the reflective layer 14,
and then passes out through the substrate 10 for detection.
Features 10-18 described above are completely conventional. As used
herein, the term "information-encoding features" is intended
broadly to encompass the widest possible range of such features,
regardless of the particular encoding mechanism or reading beam
interaction mechanism that is used.
Embodiments That Utilize a Barrier Layer
[0018] The following embodiments of the invention utilize a barrier
layer to prevent activation of the reading-inhibit agent until the
barrier layer has been removed. FIGS. 1-3 show three different
types of barrier layers that can be used. In FIGS. 1-3, the
reference symbol 20 is used to depict the optical disc, which
includes information-encoding features 22 on the upper surface of
the disc, in the orientation shown in the figures. In the
embodiment of FIG. 1, a barrier layer 24 is releasably secured (as
for example with a suitable adhesive) adjacent the surface of the
optical disc 20 that carries the information-encoding features 22.
In the embodiment of FIG. 2, the barrier layer 26 is releasably
secured to the surface of the disc 20 opposite the surface that
carries the information-encoding features 22. In the embodiment of
FIG. 3, the barrier layer 28 is formed as a closed package which
completely seals the optical disc 20 from contact with ambient
oxygen and moisture. In this case, there is no need for the barrier
layer 28 to be adhesively secured to the disc 20. As used herein, a
barrier layer which is releasably coupled to an optical disc may be
coupled adhesively as shown in FIGS. 1 and 2, coupled by enveloping
the disc as shown in FIG. 3, or coupled in any other way that
reliably associates the barrier layer and the disc prior to removal
of the barrier layer.
[0019] As pointed out below, the reading-inhibit agent can take
many forms and can be applied at many different places on the
optical disc 20. Depending upon the reading-inhibit agent used and
its location, the position and physical and chemical
characteristics of the barrier layer 24, 26, 28 can be selected as
appropriate.
[0020] It is not essential in all applications that the barrier
layer cover an entire surface of the disc 20. If the
reading-inhibit agent is localized to a particular portion of the
disc, the barrier layer may cover only an area adjacent to and
aligned with that portion. Preferably, the barrier layer should
prevent machine-reading of the optical disc until it is
removed.
Reading-Inhibit Agents that Disrupt Readability of the Optical Disc
by Controlled Degradation of the Reflective Layer
[0021] A first type of reading-inhibit agent disrupts the
reflectivity of the reflective layer in optically read discs to
such an extent that the encoded data is rendered unusable. By
disrupting the readability of the disc at a known time after the
initial use of the disc, or after removal of the barrier layer, the
practical usage lifetime of the disc can be limited and
controlled.
[0022] The reflective layer 14 that is conventionally used in
optical discs is typically formed as a thin film of metallic
aluminum. This aluminum film can be corroded by exposure to an
oxidizing environment to such an extent that the film no longer has
sufficient reflectivity to support optical reading of the disc. For
example, water and oxygen from the atmosphere can form a suitable
oxidizing environment for such an aluminum film. The rate and
timing of the corrosion of the aluminum film can be controlled by
several approaches, including control of the concentration of an
oxidizing species, control of the solution pH, introduction of
dissimilar metal couples, and introduction of chemical species to
control solubility of aluminum. For example, in the case where
atmospheric oxygen is the oxidant, a porous polymer film may be
placed over the aluminum film to provide known permeability
characteristics for moisture and oxygen from the atmosphere as it
migrates to the aluminum film. In this case, corrosion can be
substantially prevented by a barrier layer such as the barrier
layer 24 of FIG. 1 or the barrier layer 28 of FIG. 3 until the
barrier layer is removed prior to initial reading of the optical
disc.
[0023] A key feature of optically read discs is the use of a
reflective layer 14 as described above to reflect light from the
interrogating light source, generally a laser operating with a
principal wavelength in the visible portion of the spectrum, to the
detector. The reflective layer 14 is most generally composed of
metallic aluminum which is deposited on to the information-encoding
features by sputtering a very thin film. This thin film is
approximately 55 nanometers in thickness in conventional compact
discs.
[0024] Conventional reflective layers are subject to corrosion
reactions involving oxidation of the metallic aluminum and
subsequent formation of aluminum compounds such as hydroxy salts
which are not reflective:
A.fwdarw.A.sup.+3+3e.sup.- (oxidation),
A.sup.+3+3OH.sup.-.fwdarw.A(OH).sub.3 (compound formation).
[0025] The oxidation of the aluminum metal is balanced by a
reduction reaction such as the following:
O.sub.2+2H.sub.2O+2e.sup.-.fwdarw.40H.sup.- (in neutral or alkaline
solutions),
2H.sup.++2e.sup.-.fwdarw.H.sub.2 (in acidic solutions).
[0026] The corrosion reaction typically involves an electrolyte
film on the surface of the aluminum to form an ionic path between
the oxidation and reduction sites on the aluminum surface. In the
example of atmospheric oxygen, a film or layer or water on the
surface is one suitable electrolyte. The rate of corrosion will be
influenced by the availability of the oxidizing species (e.g.
oxygen or hydronium, H+), the addition of soluble salts to
influence the conductivity of the electrolyte, the addition of
chlorides to alter the stability of the normally protective
aluminum oxide film, pH buffers to influence the stability of the
normally protective aluminum oxide layer or to influence the
reduction reaction, or the addition of complexing agents to
dissolve protective aluminum oxides or to keep aluminum corrosion
products in solution. Such salts and other complexing agents may be
deliberately added in a layer of material placed next to the
aluminum layer. Addition of a hygroscopic material and salts to
this layer can also aid in collecting atmospheric moisture for
subsequent release as liquid water solution at the corrosion
reaction site. The hygroscopic material or salts effectively lower
the dew point of the aluminum surface, the relative humidity at
which a liquid film forms on the metal surface.
[0027] Cupric and ferric chloride are specific examples of
oxidizers that may be incorporated into an electrolyte layer next
to the aluminum layer to accelerate corrosion of the aluminum.
These materials offer several advantages. If the metal cation is
reduced to the metallic state in the oxidation reaction, the metal
(e.g. copper or iron) deposited on the aluminum surface forms local
cathodes that can accelerate corrosion of aluminum in adjacent
areas. If the metal cation is not completely reduced to the
metallic state, the cuprous or ferrous species may react with
oxygen to restore the oxidizing power of the solution.
[0028] FIG. 4 shows one preferred embodiment of this invention
which includes a substrate 10 and a reflective layer 14 as
described above. In this case, an electrolyte layer 30 is applied
adjacent to the reflective layer 14. The electrolyte layer 30
contains substances which aid the corrosion reactions, such as
hygroscopic salts, pH buffers, complexing agents for aluminum, and
the like. The electrolyte layer 30 is in turn covered with an outer
layer 32 of a material which is permeable to environmental moisture
and oxygen. The permeable layer 32 is in turn initially covered by
a barrier layer 24 as described above. The barrier layer 24
prevents oxygen and water from reaching the permeable layer 32
during storage and transport. When a user wishes to read
information from the optical disc of FIG. 4, the user removes the
barrier layer 24. Oxygen and water vapor from the atmosphere then
diffuse through the permeable layer 32 at a controlled rate. The
water vapor can be, for example, collected by hygroscopic materials
in the electrolyte layer 30, and subsequently made available to aid
in the aluminum corrosion reactions discussed above.
[0029] Based on typical corrosion rates for aluminum, and an
assumed reflective layer thickness of 55 nanometers, the reflective
layer may be degraded adequately to prevent machine-reading of the
optical disc in, for example, 1 to 100 hours after removal of the
barrier layer 24, depending upon the availability of moisture, and
the parameters of the electrolyte layer 30 and the permeable layer
32.
[0030] Table 1 illustrates the relationship between the corrosion
rate i.sub.corr, the rate of aluminum film removal L, and the time
t.sub.(55 nm) to corrode 55 nanometers of aluminum. In Table 1, L
is estimated using Farady's law.
1TABLE I i.sub.corr L t.sub.(55 nm) (uA/cm2) (nm/hr) (Hours) 0.1
0.1 442.3 1 1.2 44.2 10 12.4 4.4 100 124.4 0.4
[0031] If desired, metallic films or pieces of a more noble metal
(for example a metal such as copper or silver, or carbon) can be
placed in electrical contact with an aluminum reflecting layer 14
and with an electrolyte layer 30 containing oxygen as described
above or other suitable oxidizing species. In this case the
galvanic couple due to the presence of the more noble element will
result in more rapid and directed corrosion of the aluminum
reflecting layer 14 than would otherwise occur in the absence of
that second, more noble element.
[0032] Additionally, if desired the reflective layer 14 can be
sputter-coated in such a manner that the reflective layer 14 itself
includes more noble elements such as copper in the reflective film
itself. The aluminum alloy film will have a higher corrosion rate
than a purer aluminum film due to the formation of localized
cathodes at the sites of the more noble elements.
[0033] FIG. 14 is a schematic view of an optical disc 80 which
includes an aluminum layer 82 and a copper layer 84, separated by
an electrolyte layer 86. The metal layers 82, 84 may be configured
for example as a conventional two-sided DVD to encode information,
and the copper layer 84 provides sufficient reflectivity for
conventional reading. The metal layers 82, 84 are connected
electrically in any convenient manner, for example by a metal foil
88 or a conductive adhesive (e.g. an epoxy filled with carbon,
silver or copper particles). The three layers 82, 84, 86 and the
foil 88 form a galvanic cell, in which the aluminum layer 82 is the
anode that corrodes relative to the more noble metal. The
electrolyte layer 86 provides ionic continuity between the layers
82, 84, while the foil 88 provides electronic contact.
[0034] FIG. 15 shows an optical disc 80' that is similar to the
disc 80 of FIG. 14. Primed reference numerals are used in FIG. 15
for elements corresponding to elements 82-88 of FIG. 14. In FIG. 15
the area of the copper layer 84' is greater than the area of the
aluminum layer 82' to increase the aluminum corrosion rate. Also,
openings 90' are provided through the copper layer 84' and the
adjacent polycarbonate layer 92' to further increase the aluminum
corrosion rate. Preferably, the openings 90' are located in an area
of the disc 80' not containing stored information, such as the
central portion of the disc 80'.
[0035] As shown in FIG. 5, it is not essential in all embodiments
that atmospheric oxygen and water be used as the oxidizing species.
For example, as shown in FIG. 5, microcapsules 34 can be provided
between the barrier layer 24 and the permeable layer 36. These
microcapsules can contain any suitable oxidizing species and
electrolyte. In this example removal of the barrier layer 24
ruptures at least some of the microcapsules 34, thereby releasing
electrolyte and oxidant into the permeable layer 36. The
electrolyte and oxidant migrate through the permeable layer 36 and
come into contact with the reflective layer 14 in order to initiate
a controlled corrosion process. This embodiment is less sensitive
to the availability of atmospheric moisture than the embodiment of
FIG. 4.
[0036] From the foregoing it should be apparent that the
reading-inhibit agent can take many forms, including electrolytes,
oxidizing species, various elements more noble than the reflective
metal, and permeable films that control the rate at which
atmospheric oxygen and water reach the reflective layer. In various
embodiments the inhibit agent can take the form of films, or it can
be contained in various ways, including by use of
microcapsules.
[0037] The following paragraphs detail test results related to the
use of hygroscopic salts, placed on an aluminum surface, to pick up
water from the atmosphere and form an electrolyte film. The
hygroscopic salts may be sufficiently corrosive by themselves, or
alternately they may be used in conjunction with other salts and
complexing agents to provide the desired aluminum removal rate. The
salts are preferably applied in the anhydrous form to the surface,
and are then protected by a barrier to exclude moisture from the
salts. Activation of the corrosion process occurs when the barrier
is removed.
[0038] The corrosion approach is based on the principle that a dry
salt will come to equilibrium with its environment. In the process
of coming to equilibrium, the salt can either dissolve, to form an
electrolyte solution, or become drier. Table 1a lists the humidity
above saturated solutions of several salts in a closed environment.
If the salt is placed in air with higher humidity than the table
value, it will pick up water. If the humidity is lower than the
table value, the solution will lose water. The salts used in this
application include magnesium chloride and quaternary ammonium
amine chlorides.
2TABLE 1a Humidity Above Saturated Solutions of Various Salts Solid
Phase t.degree. C. % Humidity H.sub.3PO.sub.4.1/2H.sub.2O 24 9
LiCl.H.sub.2O 20 15 KC.sub.2H.sub.3O.sub.2 20 20 Pb(NO.sub.3).sub.2
20 98
[0039] Lithium chloride and potassium acetate were tested as the
candidate salts. To these, either potassium hydroide (KOH) or
trisodium phosphate (TSP) were added to increase the aggressiveness
of the electrolyte. Placement of dilute solutions of either KOH or
TSP on the disc surface quickly dissolved the aluminum film. With
these aggressive salts, complexing agents, such as citrate, were
not needed to remove any passive films on the aluminum.
[0040] Further, tests were conducted by placing the salts onto the
unprotected aluminum layer of CDs. Some of the CDs were then left
exposed to room air while others were placed in desiccators with
relative humidities of 20% and 8.5%. The relative humidities in the
desiccators were controlled by solutions of sulfuric acid; the
specific gravity of the sulfuric acid solution was selected to
provide the desired relative humidity. During these experiments,
ambient relative humidities ranged from 20 to 30 percent. Four
salts were used: potassium acetate (KAc), lithium chloride (LiCl),
KOH, and TSP and were mixed as shown in Table 1b. The concentration
of salt in the solution on the disc surface depended on the amount
of water that was absorbed.
3TABLE 1b Salts Mixtures SALT TSP KOH KAc (4 grams) 1.31 g or .13 g
0.58 g or 0.06 g LiCl (4 grams) 1.31 g or 0.13 g 0.58 g or 0.06
g
[0041] When LiCl was placed on the disc's aluminum surface under
ambient conditions, droplets of water formed on the salt mass
within 30 minutes; with KAc it took 3 hours. The water droplets
formed with LiCl were clearly visible to the unaided eye; the
droplets formed with KAc could be observed with the use of a
magnifying glass. After these samples were allowed to stand
overnight, the aluminum with LiCl showed partial corrosion, while
the aluminum with KAc was intact.
[0042] The tests also showed that KOH alone was highly hygroscopic
and corroded the discs under all conditions. Within the limitations
of existing equipment, under the driest conditions KOH corroded the
aluminum surface in all tests. The water retained in the KOH was
sufficient to corrode the aluminum surface, even when a glove bag
was used to apply the KOH, and a dry desiccator was used to store
the sample.
[0043] At 20% RH, the LiCl (alone and in mixtures) continued to
form water droplets on the disc surface and to attack the aluminum.
In the 8.5% RH desiccator, visible water droplets did not form, in
agreement with the table values.
[0044] TSP did not attack the aluminum when placed on the surface
by itself, even under ambient conditions. TSP was not sufficiently
hygroscopic to form an aggressive electrolyte film. However, when
used in conjunction with LiCl at 20% RH, enough water was picked up
to form an aggressive solution, which attacked the aluminum. A
mixture of LiCl and TSP did not attack the aluminum in the 8.5% RH
desiccator (no breakthrough after four days).
[0045] These tests demonstrated that the corrosion process can be
activated by ambient moisture down to at least 20% relative
humidity, and probably down to 15% based on published values for
LiCl. Other salts or drier KOH may allow one to go to even lower
humidities.
Reading-inhibit Agents that Operate by Absorbing Optical Radiation
of the Reading Beam
[0046] The digital video disk (DVD) format uses a 650 nm laser to
read information from the disk. If this reading beam is absorbed to
a significant degree, the return signal from the disk is
attenuated. By including a light-absorbing material in the disk, it
is possible to attenuate the reading signal enough to prevent the
disk from being read. Preferably, the light-absorbing material is
strongly absorbing at the wavelength of the reading beam. Many
compounds absorb at 650 nm, and they usually appear blue or green
in color.
[0047] In order to allow the disc to be read on its first use, the
light-absorbing material is initially nonabsorbent at the
wavelength of the reading beam. Over time, for example four to 24
hours, this light-absorbing material becomes absorbing at the
wavelength of the reading beam in response to some environmental
stimulus. One approach is to use a compound for the light-absorbing
material that is initially colorless, but which oxidizes to a new
compound which is colored upon exposure to oxygen in the
atmosphere, or some other oxidant. Many compounds are known which
exhibit this behavior. Four compounds which may be particularly
appropriate are given in Table 2 (in their oxidized form).
4 TABLE 2 Compound Color Index Number Indigo Carmine 73015
Methylene Blue 52015 Thionin 52000 Gallocyanine 51030
[0048] The colorless precursor to the light-absorbing material is
incorporated in the optical disc somewhere along the path taken by
the laser light of the reading beam. For instance, the colorless
precursor can be compounded within the material (typically
polycarbonate) that makes up the substrate 10, or the colorless
precursor can be included in a coating on a surface of the
substrate 10.
[0049] Preferably, the rate at which atmospheric oxygen reaches the
colorless precursor is controlled in order to render the optical
disc unreadable at a selected time after the barrier layer is
removed. The rate at which oxygen reaches the colorless precursor
should be selected such that the optical disc can be read at least
once before sufficient color is generated to make the optical disc
unreadable. The rate at which oxygen reaches the colorless
precursor should be high enough to ensure that the optical disc
becomes unreadable within the desired time period (for example four
to 24 hours). Various methods can be used to control the rate at
which oxygen reaches the colorless precursor. If the
light-absorbing compound is contained within the body of the
substrate 10, the amount of the absorbing compound can be adjusted
as appropriate for the application; higher loadings will result in
quicker obscuration. The rate at which the absorbing compound
becomes absorbing to the reading beam can be lowered by lowering
the concentration of the absorbing compound in the substrate, or by
applying an outer coating to the substrate which acts as a
semipermeable oxygen barrier.
[0050] Alternately, the absorbing compound can be placed as shown
in FIG. 6 in a layer 38 on a surface of the substrate 10. The rate
of the oxidation reaction can be controlled in this case by
choosing a matrix such as a suitable polymer for the absorbing
compound layer having the appropriate barrier properties.
Alternately, an additional coating layer can be employed over the
absorbing layer, and this additional coating can act as a
semipermeable oxygen barrier which allows oxygen to reach the
absorbing layer at the desired rate.
[0051] As shown in FIG. 6, a barrier layer 26 is used to protect
the absorbing layer 38 from atmospheric oxygen during storage and
transport. The barrier layer can also take the form of an air-tight
package, as shown in FIG. 3.
Reading-inhibit Agents that Operate by Altering Physical Dimensions
of the Optical Disc
[0052] Certain embodiments of the invention use a reading-inhibit
agent which alters its physical dimension when activated. A
superabsorbing polymer is one such material, for example a polymer
or copolymer containing a carboxylic or alcohol moiety. For
example, a water-absorbent resin may be formed from a cross-linked
polymer or a copolymer of acrylic acid, methacrylic acid,
methylacrylate-vinylacetate, starch-ethyl acrylate,
starch-acrylonitrile, carboxymethyl cellulose, ethylene oxide,
vinyl alcohol, acrylamide, and the like.
[0053] Such materials can be used in several ways to make an
optical disc unreadable, for example as the material absorbs
ambient moisture. The absorption of such moisture creates a volume
change in the material, which can be used to cause a combination of
any of the following effects to prevent reading: delamination, a
change in the refractive index, or a change in spinning
characteristics.
[0054] For example, as shown in FIG. 7, a superabsorber layer 42
can be placed between two digital video disc substrates 40. The
entire digital video disc is then protected with an encapsulating
barrier layer 28 similar to that shown above in FIG. 3. When the
barrier layer 28 is removed, ambient moisture is allowed gradually
to reach the superabsorber layer 42. As the superabsorber layer
absorbs moisture, it will increase in volume, thereby causing the
digital video disc to delaminate and preventing further reading of
the disc.
[0055] In the example of FIG. 8, a superabsorber layer 44 is placed
on the readable surface of a digital video disk 40, and this
superabsorber layer is protected by a barrier layer 26. When the
barrier layer 26 is removed, the superabsorber layer 44 will absorb
ambient moisture and increase in volume. This volume increase
causes a significant change in the refractive index of the
material, which renders the digital video disc unreadable.
[0056] As shown in FIG. 9, a superabsorber layer 48 may be placed
either partially or completely around a spindle hole 46 of the
digital video disk 40. This superabsorber layer 48 is protected by
a barrier layer (not shown in FIG. 9) prior to use. When the
barrier layer is removed, ambient moisture will gradually cause the
superabsorber layer 48 to expand. If the superabsorber layer 48 is
placed as shown in FIG. 9, this can cause the spindle hole 46 to
assume an eccentric position, thereby rendering the optical disc
unreadable. Alternately, if the superabsorber layer 48 extends
substantially around the spindle hole 46, the superabsorber layer
48 may expand to the point where the spindle hole 46 is too small
to fit on the spindle of the reading device.
[0057] FIG. 10 shows another embodiment in which the superabsorber
layer 50 is mounted near the outer rim of the digital video disk
40. As before, the superabsorber layer 50 is initially protected by
a barrier layer (not shown in FIG. 10). Once the barrier layer is
removed, the superabsorber layer 50 absorbs atmospheric moisture,
thereby rendering the disc sufficiently out of balance to prevent
reliable reading.
[0058] In all of the examples discussed above, the rate at which
the superabsorber layer absorbs moisture can be modified by placing
a semipermeable barrier over the exposed surface of the
superabsorber layer. This barrier can regulate the diffusion of
ambient moisture to the superabsorber layer, which in this way
controls the time period during which the optical disc is readable
after the barrier layer has been removed.
Reading-inhibit Agents that Operate by Scattering the Reading
Beam
[0059] As discussed above, a laser beam is typically used as a
reading beam for optical discs. If the reading beam is scattered or
otherwise attenuated to a significant degree, the disc cannot be
accurately read. For example, as shown in FIG. 11, a digital video
disc 40 can be provided with a layer 52 that includes a material
such as a solvent that will alter the optical characteristics of
the adjacent portion of the digital video disc 40. For example, a
polycarbonate exposed to solvent is known to craze, i.e. to form a
diffuse, opaque film or layer, which scatters the reading beam.
Suitable solvents include organic liquids or vapors such as
acetone, xylene and the like. Depending upon the concentration of
the solvent and the exposure time, various rates of loss of
transparency can be obtained. Other coatings in addition to
polycarbonates can exhibit the same effective behavior by slight
dissolution in an organic solvent followed by deposition on the
surface of the disc as the solvent evaporates or is lost. The
redeposition process may also include a recrystalization of a
glassy coating layer. This redeposition results in a less
transparent and therefore less readable surface on the disc. The
layer 52 of FIG. 10 can include microencapsulated solvent beads
which will rupture on removal of the adjacent barrier layer 26.
Embodiments That Include Reading-inhibit Agents Without Barrier
Layers
[0060] As pointed out above, it is not essential in all embodiments
that a barrier layer be included. Rather, in some embodiments it is
the act of reading the disc that activates the reading-inhibit
agent. For example, optical radiation associated with disc reading,
or rotation associated with disc reading can activate the
reading-inhibit agent.
[0061] As shown in FIG. 12, one such embodiment includes an optical
disc 54 which includes a reading-inhibit agent 56 adjacent one
surface. In this case the reading-inhibit agent 56 is a photoactive
material that, when activated by suitable optical radiation, is
suitably changed in optical or physical characteristics so as to
inhibit further reading of the disc. The photoactive material can
alternately be dispersed in the bulk of the disk and can for
example change from clear to opaque at the wavelength of the
reading beam upon exposure to suitable optical radiation. As shown
in FIG. 12, the disc 54 is installed in a reading device 58. The
reading device 58 includes a first optical source such as a laser
60 that directs the reading beam 62 against the disc 54. Returning
radiation from the disc 54 is sensed by a detector 64, in the
conventional manner. In this embodiment, the reading device 58
further includes a second optical source 66. The second optical
source 66 destroys or degrades the optical transmission or
reflection required to read the disc. The second source 66 may be a
conventional source such as a high pressure arc, an incandescent
bulb, a fluorescent lamp, or a laser. As the disc 54 is read,
radiation from the second source 62 interacts with the
reading-inhibit agent 56 to inhibit further reading of that portion
of the disc 54. The second source 62 is arranged such that the
second source 62 does not illuminate any portion of the disc 54
until after that portion of the disc 54 has been read by the
reading beam 62.
[0062] In alternate embodiments the reading beam 62 itself may
initiate optical changes in the read inhibiting agent 56, thereby
dispensing with the need for the second source 62.
[0063] Alternately, when the second source 62 is used, the need for
a separate read inhibit agent 56 may be eliminated. In this case,
the second source 66 may for example be a passively q-switched
microchip laser focused on the surface of the disc. The effect of
this laser is to create scattering centers by ablating the read
surface of the disc. The scattering centers reduce the optical
transmission of the disc to the reading beam 62.
[0064] In either case, the second source 66 should be interlocked
in a way that prevents consumer tampering, and should track in a
way so as not to interfere with the initial reading of the disc.
When the second source 62 is of sufficient power to provide the
ablating action described above, access to the information on the
disc will be denied almost immediately after it is read.
[0065] FIG. 13 shows another embodiment having a reading-inhibit
agent which is activated by the act of reading the disk. In this
case an optical disc 70 includes a reservoir 72 that contains a
reading-inhibit agent, such as a suitable solvent. The reservoir 72
includes an opening 74. When the disc is first rotated in order to
be read, solvent passes out of the reservoir 72 via the opening 74,
and in this way a small quantity of solvent is released to the
disc. The solvent can degrade the optical characteristics of the
disc, as discussed above, to prevent reading of the disc a
predetermined time after the solvent has left the reservoir. As one
example, the reservoir 72 may be formed in a region bounded by two
concentric annular ridges, similar to the stacking rings
conventionally used in current optical discs.
Additional Embodiment
[0066] FIG. 17 shows a cross-sectional view that illustrates one
form of a disc 100 containing a reservoir 102 as discussed
immediately above. One or more capillary-tube-sized passages 104
are radially oriented to allow a suitable reading-inhibit agent
(such as a solvent or a corrosive agent as discussed above) to flow
from the reservoir 102 radially outwardly to the region of the disc
that stores information via information-encoding features. The
reservoir 102 and the passage 104 are closed by a silicone membrane
108 that defines an array of vents 110,112. In this example, the
vents 110, 112 are formed as pin pricks. The silicone membrane 108
is covered by a polycarbonate sheet 114 that defines vents on
116,118 aligned with the vents 110,112, respectively.
[0067] A releasable, peel-off label 120 is removably secured by a
suitable adhesive to the polycarbonate layer 114. This peel-off
label 122 includes a tab 122 to facilitate removal and a protrusion
124. The protrusion 124 passes through an opening in the
polycarbonate layer 114 and presses the silicone membrane 108 into
the passage 104 to create a mechanical valve that stops the flow of
reading-inhibit agent radially outwardly from the reservoir 102.
Optionally, the passage 104 may also include a valve element 106 of
a material that is dissolved by the reading-inhibit agent. For
example, a valve element 106 of aluminum can be used in cases where
the reading-inhibit agent is corrosive to aluminum. Preferably, the
reservoir 102 includes a wick 103 made of cotton or microfiber to
retain fluid in the reservoir 102. The passage 104 may have a
cross-sectional size of 0.02 inch.
[0068] Preferably, the peel-off label 120 is sized such that the
label must be removed in order to allow the disc 100 to be read.
Once the label 120 has been removed, the vents 110, 112 are opened,
and the protrusion 124 is removed. This allows the silicone
membrane 108 to relax upwardly, thereby opening the passage 104.
When the disc 100 is rotated during a reading operation centrifugal
force causes the reading-inhibit agent in the reservoir 102 to flow
radially outwardly via the passage 104 onto the
information-encoding portion of the disc 100.
[0069] In some embodiments the reading-inhibit agent may be
selected so as not to interfere with normal reading of the disc 100
until a selected time after the reading-inhibit agent has contacted
the information carrying portion of the disc. As an alternative,
when the optional valve element 106 is used, the valve element 106
prevents the reading-inhibit agent from reaching the information
carrying portion of the disc 100 until the valve element 106 is
dissolved by the reading-inhibit agent. In this way, the plug 106
provides a timed release of the reading-inhibit agent onto the
information carrying portion of the disc.
[0070] Tests have shown that two-pass transmission of the disc
typically must fall to about 45 percent of the original value
before a significant number of reading errors occur, and to
approximately 30 percent of the original value before the disc
becomes unplayable.
Conclusion
[0071] The optical discs described above have a short effective
life, limited either by the number of times the disc is played
(e.g. one, two or more times), or by the passage of time after the
disc is dispensed (e.g. a selected number of hours after the disc
is sold or rented, after the consumer opens a package, or after the
disc is inserted into a disc player). The effective life of the
disc may be limited in response to reading of the disc, opening of
the disc, or rotation of the disc. Various methods for limiting the
effective life of the disc have been described, including physical,
chemical, and electrochemical methods. Physical methods include the
diffusion of air or a component of air such as oxygen, resulting in
physical and/or chemical effects; the use of optical activation to
cause a physical change in the disc; or the use of physical forces
or the removal of forces associated with rotation of the disc or
removal of a label to cause a physical change in the disc. Chemical
methods include a layer of the disc interacting with a chemical
applied when the package is opened or by the vendor at the time of
sale. Electrical or electrochemical methods include the use of an
electrochemically active system to accelerate corrosion.
[0072] It should be apparent from the foregoing detailed
description that the present invention can be implemented in a wide
variety of forms. Barrier layers can take the form of sheets or
patches on a surface of the disc, or of encapsulating packaging. In
some cases barrier layers are not required. Reading-inhibit agents
can take many forms, including materials which change optical or
physical characteristics of the reflecting layer, or various other
components of the optical disc. Reading-inhibit agents can be
employed as microencapsulated materials, materials formed in layers
over selected regions of a disc, or materials incorporated into
other components of a disc. Reading-inhibit agents may extend over
the entire information-encoding surface of the optical disc, or
alternately may be limited to selected portions, for example
portions that encode indexing or other introductory
information.
[0073] It should therefore clearly be understood that the foregoing
detailed description is intended by way of illustration, not
limitation. It is only the following claims, including all
equivalents, that are intended to define the scope of this
invention.
* * * * *