CA2265744C - Machine-readable optical disc with reading-inhibit agent - Google Patents

Abstract

An optical disc (20) having machine-readable, information-encoding features (22) is provided with a barrier layer secured to the disc. This barrier layer (24) is configured to prevent machine-reading of the features. A reading-inhibit agent (14, 34), 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 after some period of time. 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.

Description

101520W0 98/1 1539CA 02265744 l999-03- 10PCT/US97/16277Machine-Readable Optical Disc with Reading-Inhibit AgentBackground of the InventionThis invention relates to machine-readable optical discs of all types,including for example digital discs such as compact discs (CD's), digital videodiscs (DVD's), CDROM's, and the like.Conventional optical discs have reached widespread acceptance as alow-cost, reliable storage medium for digital information including music,video, and data. One of the traditional advantages of optical discs is theirlong life.However, in some applications, the long life of the conventional opticaldisc may represent a disadvantage. For example, if music, movies orsoftware is to be made available for a limited time period, as in the rentalperiod for entertainment, the original optical disc must be returned at the endof the rental period.A need presently exists for an improved machine—readable optical discthat eliminates the need for the return of an optical disc at the end of a rentalpenod.Summary of the InventionAccording to a first aspect of this invention, an optical disc comprisingmachine—readable, information-encoding features is provided with a barrierlayer releasably coupled to the disc. This barrier layer is configured toprevent machine-reading of the disc. A reading-inhibit agent is included inthe disc, and is activated by removal of the barrier layer. This reading-inhibitagent is operative, after it is activated, to alter the disc to inhibit reading of1015202530CA 02265744 l999-03- 10W0 98/1 1539 PCT/U S97/ 16277the disc. Both the barrier layer and the reading—inhibit agent can take manyforms, as discussed by way of example below.According to another aspect of this invention, an optical disccomprising machine—readable, information-encoding features is provided witha reading-inhibit agent that is activated by machine-reading the disc. Thisreading-inhibit agent is operative, after it is activated, to alter the disc toinhibit reading of the disc. In alternate embodiments, the reading—inhibitagent may be activated by optical radiation incident on the disc duringmachine-reading of the disc, or by rotation of the disc during machine-readingof the disc.According to a third aspect of this invention, a method is provided forinhibiting reading of an optical disc. According to this method, an optical discis provided comprising machine—readable, information-encoding features, anda reading-inhibit agent. The reading—inhibit agent is activated by opticalradiation, and is operative, once activated, to alter the disc to inhibit reading.A reading device is provided to read the disc, and this reading devicecomprises a source of optical radiation. According to the method of thisinvention, the disc is read with the reading device, and the inhibit agent isconcurrently activated with optical radiation from the source. The source ofoptical radiation that activates the reading-inhibit agent can either be thesource of optical radiation that forms the reading beam, or a second source,separate from the reading beam source.Brief Description of the DrawingsFIGS. 1 through 3 are partial cross-sectional views of three barrierlayers suitable for use in embodiments of this invention.FIGS. 4, 5, 6, 7 and 8 are partial cross-sectional views of optical discsthat incorporate first, second, third, fourth, and fifth preferred embodiments ofthis invention, respectively.FIGS. 9 and 10 are plan views of optical discs that incorporate sixthand seventh preferred embodiments of this invention, respectively.1015202530W0 98/11539CA 02265744 l999-03- 10PCTIUS97/16277FIGS. 11 and 12 are partial cross—sectional views of optical discs thatincorporate eighth and ninth preferred embodiments of this invention,respectively.FIG. 13 is a plan view of an optical disc that incorporates a tenthpreferred embodiment of this invention.FIGS. 14 and 15 are partial cross—sectional views of optical discs that .incorporate embodiments of the invention employing galvanic cells.FIG. 16 is a partial cross—sectional view of a prior art compact disc.FIG. 17 is a partial cross—sectional view of a disc containing areservoir.Detailed Description of thePresently Preferred EmbodimentsThe 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 anexhaustive list of all forms that the invention can take. Generally speaking,the embodiments discussed below can be classified into two groups. Thefirst 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.In general, this invention can be used with the widest possible varietyof optical discs comprising machine—readable, information-encoding features.FIG. 16 shows a highly schematic cross section of an optical disc such as aprior art compact disc. FIG. 16, like all of the other figures, is not drawn toscale; selected features have been exaggerated in size for clarity ofillustration. The disc of FIG. 16 includes a substrate 10 which is formed withan array of information-encoding features such as pits 12. The surfacedefining the information-encoding features 12 is covered with a reflectivelayer 14, which may be, for example, formed of aluminum. The reflectivelayer 14 is in turn covered with a protective layer 16 which protects thereflective layer 14 from oxidation and physical damage. A reading beam1015202530W0 98/ 1 1539CA 02265744 l999-03- 10PCT/U S97/ 16277aligned with the arrow 18 is incident on the surface of the substrate 10opposite the information—encoding features 12. This reading beam passesthrough the substrate 10, is reflected by the reflective layer 14, and thenpasses out through the substrate 10 for detection. Features 10-18 describedabove are completely conventional. As used herein, the term "information—encoding features" is intended broadly to encompass the widest possiblerange of such features, regardless of the particular encoding mechanism orreading beam interaction mechanism that is used.Embodiments That Utilize a Barrier LayerThe following embodiments of the invention utilize a barrier layer toprevent activation of the reading-inhibit agent until the barrier layer has beenremoved. FIGS. 1-3 show three different types of barrier layers that can beused. In FIGS. 1-3, the reference symbol 20 is used to depict the opticaldisc, which includes information—encoding features 22 on the upper surface ofthe 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 suitableadhesive) adjacent the surface of the optical disc 20 that carries theinformation—encoding features 22. In the embodiment of FIG. 2, the barrierlayer 26 is releasably secured to the surface of the disc 20 opposite thesurface that carries the information—encoding features 22. In the embodimentof FIG. 3, the barrier layer 28 is formed as a closed package whichcompletely 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 beadhesively secured to the disc 20. As used herein, a barrier layer which isreleasably coupled to an optical disc may be coupled adhesively as shown inFIGS. 1 and 2, coupled by enveloping the disc as shown in FIG. 3, or coupledin any other way that reliably associates the barrier layer and the disc prior toremoval of the barrier layer.As pointed out below, the reading-inhibit agent can take many formsand can be applied at many different places on the optical disc 20.1015202530W0 98/] 1539CA 02265744 l999-03- 10PCT/US97/162775Depending upon the reading-inhibit agent used and its location, the positionand physical and chemical characteristics of the barrier layer 24, 26, 28 canbe selected as appropriate.It is not essential in all applications-that the barrier layer cover anentire surface of the disc 20. If the reading—inhibit agent is localized to aparticular portion of the disc, the barrier layer may cover only an area ,adjacent to and aligned with that portion. Preferably, the barrier layer shouldprevent machine-reading of the optical disc until it is removed.Reading-Inhibit Agents That DisruptReadability Of The Optical Disc By ControlledDegradation Of The Reflective LayerA first type of reading—inhibit agent disrupts the reflectivity of thereflective layer in optically read discs to such an extent that the encoded datais rendered unusable. By disrupting the readability of the disc at a knowntime after the initial use of the disc, or after removal of the barrier layer, thepractical usage lifetime of the disc can be limited and controlled.The reflective layer 14 that is conventionally used in optical discs istypically formed as a thin film of metallic aluminum. This aluminum film canbe corroded by exposure to an oxidizing environment to such an extent thatthe film no longer has sufficient reflectivity to support optical reading of thedisc. For example, water and oxygen from the atmosphere can form asuitable oxidizing environment for such an aluminum film. The rate andtiming of the corrosion of the aluminum film can be controlled by severalapproaches, including control of the concentration of an oxidizing species,control of the solution pH, introduction of dissimilar metal couples, andintroduction of chemical species to control solubility of aluminum. Forexample, in the case where atmospheric oxygen is the oxidant, a porouspolymer film may be placed over the aluminum film to provide knownpermeability characteristics for moisture and oxygen from the atmosphere asit migrates to the aluminum film. In this case, corrosion can be substantiallyprevented by a barrier layer such as the barrier layer 24 of FIG. 1 or the1015202530W0 98/1 1539CA 02265744 l999-03- 10PCT/US97/1 6277barrier layer 28 of FIG. 3 until the barrier layer is removed prior to initialreading of the optical disc.A key feature of optically read discs is the use of a reflective layer 14as described above to reflect light from the interrogating light source,generally a laser operating with a principal wavelength in the visible portionof the spectrum, to the detector. The reflective layer 14 is most generallycomposed of metallic aluminum which is deposited on to the information-encoding features by sputtering a very thin film. This thin film isapproximately 55 nanometers in thickness in conventional compact discs.Conventional reflective layers are subject to corrosion reactionsinvolving oxidation of the metallic aluminum and subsequent formation ofaluminum compounds such as hydroxy salts which are not reflective:Al ——~ Al” + 3e‘ (oxidation),Al” + 30H’ ——~ A|(OH)3 (compound formation).The oxidation of the aluminum metal is balanced by a reduction reaction suchas the following:02 + 2H2O + 2e" ——~ 40H" (in neutral or alkaline solutions),2H‘ + 2e" —-— H2 (in acidic solutions).The corrosion reaction typically involves an electrolyte film on the surface ofthe aluminum to form an ionic path between the oxidation and reduction siteson the aluminum surface. In the example of atmospheric oxygen, a film orlayer of water on the surface is one suitable electrolyte. The rate of corrosionwill be influenced by the availability of the oxidizing species (e.g. oxygen or‘hydronium, H+), the addition of soluble salts to influence the conductivity ofthe electrolyte, the addition of chlorides to alter the stability of the normallyprotective aluminum oxide film, pH buffers to influence the stability of thenormally protective aluminum oxide layer or to influence the reductionreaction, or the addition of complexing agents to dissolve protectivealuminum oxides or to keep aluminum corrosion products in solution. Suchsalts and other complexing agents may be deliberately added in a layer ofmaterial placed next to the aluminum layer. Addition of a hygroscopic1015202530W0 98/1 1539CA 02265744 l999-03- 10PCT/US97/16277material and salts to this layer can also aid in collecting atmospheric moisturefor subsequent release as liquid water solution at the corrosion reaction site.The hygroscopic material or salts effectively lower the dew point of thealuminum surface, the relative humidity at which a liquid film forms on themetal surface.Cupric and ferric chloride are specific examples of oxidizers that may _be incorporated into an electrolyte layer next to the aluminum layer toaccelerate corrosion of the aluminum. These materials offer severaladvantages. If the oxidizing metal cation is reduced to the metallic state inthe oxidation reaction, the product metal (e.g. copper or iron) deposited onthe aluminum surface forms local cathodes that can accelerate corrosion ofaluminum in adjacent areas. If the oxidizing metal cation is not completelyreduced to the metallic state, the cuprous or ferrous species may react withoxygen to restore the oxidizing power of the solution.FIG. 4 shows one preferred embodiment of this invention whichincludes a substrate 10 and a reflective layer 14 as described above. in thiscase, an electrolyte layer 30 is applied adjacent to the reflective layer 14.The electrolyte layer 30 contains substances which aid the corrosionreactions, such as hygroscopic salts, pH buffers, complexing agents foraluminum, and the like. The electrolyte layer 30 is in turn covered with anouter layer 32 of a material which is permeable to environmental moistureand oxygen. The permeable layer 32 is in turn initially covered by a barrierlayer 24 as described above. The barrier layer 24 prevents oxygen and waterfrom reaching the permeable layer 32 during storage and transport. When auser wishes to read information from the optical disc of FIG. 4, the userremoves the barrier layer 24. Oxygen and water vapor from the atmospherethen diffuse through the permeable layer 32 at a controlled rate. The watervapor can be, for example, collected by hygroscopic materials in theelectrolyte layer 30, and subsequently made available to aid in the aluminumcorrosion reactions discussed above.101520W0 98/1 1539CA 02265744 l999-03- 10PCT/U S97/ 16277Based on typical corrosion rates for aluminum, and an assumedreflective layer thickness of 55 nanometers, the reflective layer may bedegraded adequately to prevent machine-reading of the optical disc in, forexample, 1 to 100 hours after removal of the barrier layer 24, depending uponthe availability of moisture, and the parameters of the electrolyte layer 30 andthe permeable layer 32.Table 1 illustrates the relationship between the corrosion rate i.;.,,,, therate of aluminum film removal L, and the time t(55,,,,,) to corrode 55 nanometersof aluminum. In Table 1, L is estimated using Farady's law.TABLE 1icon L t(55 nrn)(uA/cm2) (nm/hr) (Hours)0.1 0.1 442.31 1.2 44.210 12.4 4.4100 124.4 0.4If desired, metallic films or pieces of a more noble metal (for example ametal such as copper or silver, or carbon) can be placed in electrical contactwith an aluminum reflecting layer 14 and with an electrolyte layer 30containing oxygen as described above or other suitable oxidizing species. Inthis case the galvanic couple due to the presence of the more noble elementwill result in more rapid and directed corrosion of the aluminum reflectinglayer 14 than would otherwise occur in the absence of that second, morenoble element.Additionally, if desired the reflective layer 14 can be sputter-coated insuch a manner that the reflective layer 14 itself includes more noble elementssuch as copper in the reflective film itself. The aluminum alloy film will have a1015202530W0 98/1 1539CA 02265744 l999-03- 10PC T/U S97/ 16277higher corrosion rate than a purer aluminum film due to the formation oflocalized cathodes at the sites of the more noble elements.Figure 14 is a schematic view of an optical disc 80 which includes analuminum layer 82 and a copper layer 84, separated by an electrolyte layer86. The metal layers 82, 84 may be configured for example as aconventional two-sided DVD to encode information, and the copper layer 84provides sufficient reflectivity for conventional reading. The metal layers 82,84 are connected electrically in any convenient manner, for example by ametal foil 88 or a conductive adhesive (e.g. an epoxy filled with carbon, silveror copper particles). The three layers 82, 84, 86 and the foil 88 form agalvanic cell, in which the aluminum layer 82 is the anode that corrodesrelative to the more noble metal. The electrolyte layer 86 provides ioniccontinuity between the layers 82, 84, while the foil 88 provides electroniccontact.Figure 15 shows an optical disc 80' that is similar to the disc 80 ofFigure 14. Primed reference numerals are used in Figure 15 for elementscorresponding to elements 82-88 of Figure 14. in Figure 15 the area of thecopper layer 84' is greater than the area of the aluminum layer 82' to increasethe aluminum corrosion rate. Also, openings 90' are provided through thecopper layer 84' and the adjacent polycarbonate layer 92' to further increasethe aluminum corrosion rate. Preferably, the openings 90' are located in anarea of the disc 80' not containing stored information, such as the centralportion of the disc 80'.As shown in Figure 5, it is not essential in all embodiments thatatmospheric oxygen and water be used as the oxidizing species. Forexample, as shown in Figure 5, microcapsules 34 can be provided betweenthe barrier layer 24 and the permeable layer 36. These microcapsules cancontain any suitable oxidizing species and electrolyte. In this exampleremoval of the barrier layer 24 ruptures at least some of the microcapsules34, thereby releasing electrolyte and oxidant into the permeable layer 36.The electrolyte and oxidant migrate through the permeable layer 36 and10152025CA 02265744 l999-03- 10W0 98/11539 PCT/US97/1627710come into Contact with the reflective layer 14 in order to initiate a controlledcorrosion process. This embodiment is less sensitive to the availability ofatmospheric moisture than the embodiment of Figure 4.From the foregoing it should be apparent that the reading-inhibit agentcan take many forms, including electrolytes, oxidizing species, variouselements more noble than the reflective metal, and permeable films thatcontrol the rate at which atmospheric oxygen and water reach the reflectivelayer. In various embodiments the inhibit agent can take the form of films, orit can be contained in various ways, including by use of microcapsules.The following paragraphs detail test results related to the use ofhygroscopic salts, placed on an aluminum surface, to pick up water from theatmosphere and form an electrolyte film. The hygroscopic salts may besufficiently corrosive by themselves, or alternately they may be used inconjunction with other salts and complexing agents to provide the desiredaluminum removal rate. The salts are preferably applied in the anhydrousform to the surface, and are then protected by a barrier to exclude moisturefrom the salts. Activation of the corrosion process occurs when the barrier isremoved.The corrosion approach is based on the principle that a dry salt willcome to equilibrium with its environment. In the process of coming toequilibrium, the salt can either dissolve, to form an electrolyte solution, orbecome drier. Table la lists the humidity above saturated solutions ofseveral salts in a closed environment. if the salt is placed in air with higherhumidity than the table value, it will pick up water. If the humidity is lowerthan the table value, the solution will lose water. The salts used in thisapplication include magnesium chloride and quaternary ammonium aminechlorides.101520W0 98/1 1539CA 02265744 l999-03- 10PCTIUS97/1627711Table 1a. Humidity Above Saturated Solutions of Various SaltsSolid Phase t°C % HumidityH3PO4-1/2H2O 24 9LiC|. H20 20 15KC2H3O2 1&0 20Pb(NO3);_ 20 98Lithium chloride and potassium acetate were tested as the candidatesalts. 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 surfacequickly dissolved the aluminum film. With these aggressive salts, complexingagents, such as citrate, were not needed to remove any passive films on thealuminum.Further, tests were conducted by placing the salts onto theunprotected aluminum layer of CDs. Some of the CD5 were then left exposedto room air while others were placed in desiccators with relative humidities of20% and 8.5%. The relative humidities in the desiccators were controlled bysolutions of sulfuric acid; the specific gravity of the sulfuric acid solution wasselected to provide the desired relative humidity. During these experiments,ambient relative humidities ranged from 20 to 30 percent. Four salts wereused: potassium acetate (KAC), lithium chloride (LiCl), KOH, and TSP andwere mixed as shown in Table 1b. The concentration of salt in the solutionon the disc surface depended on the amount of water that was absorbed.Table 1b. Salts MixturesSALT TSP KOHKAc (4 grams) 1.31 gor.13g 0.58 gor 0.069QLiCl (4 grams) 1.31 g or 0.13 g 0.58 g or 0.06 g10152025W0 98/1 1539CA 02265744 l999-03- 10PCT/US97ll62771 2When LiCl was placed on the disc’s aluminum surface under ambientconditions, droplets of water formed on the salt mass within 30 minutes; withKAc it took 3 hours. The water droplets formed with LiCl were clearly visibleto the unaided eye; the droplets formed with KAc could be observed with theuse of a magnifying glass. After these samples were allowed to standovernight, the aluminum with LiCl showed partial corrosion, while thealuminum with KAc was intact.The tests also showed that KOH alone was highly hygroscopic andcorroded the discs under all conditions. Within the limitations of existingequipment, under the driest conditions KOH corroded the aluminum surfacein all tests. The water retained in the KOH was sufficient to corrode thealuminum surface, even when a glove bag was used to apply the KOH, and adry desiccator was used to store the sample.At 20% RH, the LiCl (alone and in mixtures) continued to form waterdroplets on the disc surface and to attack the aluminum. in the 8.5% RHdesiccator, visible water droplets did not form, in agreement with the tablevalues.TSP did not attack the aluminum when placed on the surface by itself,even under ambient conditions. TSP was not sufficiently hygroscopic to forman aggressive electrolyte film. However, when used in conjunction with LiClat 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 thealuminum in the 8.5% RH desiccator (no breakthrough after four days).These tests demonstrated that the corrosion process can be activatedby ambient moisture down to at least 20% relative humidity, and probablydown to 15% based on published values for LiCl. Other salts or drier KOHmay allow one to go to even lower humidities.1015202530W0 98/1 1539CA 02265744 l999-03- 10PCT/U S97/ 162771 3Reading-Inhibit Agents That Operate ByAbsorbing Optical Radiation Of The Reading BeamThe digital video disk (DVD) format uses a 650 nm laser to readinformation from the disk. If this reading beam is absorbed to a significantdegree, the return signal from the disk is attenuated. By including a light-absorbing material in the disk, it is possible to attenuate the reading signalenough to prevent the disk from being read. Preferably, the light-absorbingmaterial is strongly absorbing at the wavelength of the reading beam. Manycompounds absorb at 650 nm, and they usually appear blue or green in color.In order to allow the disc to be read on its first use, the light-absorbingmaterial is initially nonabsorbent at the wavelength of the reading beam.Over time, for example four to 24 hours, this light-absorbing materialbecomes absorbing at the wavelength of the reading beam in response tosome environmental stimulus. One approach is to use a compound for thelight-absorbing material that is initially colorless, but which oxidizes to a newcompound which is colored upon exposure to oxygen in the atmosphere, orsome 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).TABLE 2Compound Color Index NumberIndigo Carmine 73015Methylene Blue 52015Thionin 52000Gallocyanine 51030The colorless precursor to the light-absorbing material is incorporatedin the optical disc somewhere along the path taken by the laser light of thereading beam. For instance, the colorless precursor can be compoundedwithin the material (typically polycarbonate) that makes up the substrate 10,or the colorless precursor can be included in a coating on a surface of thesubstrate 10.10152025W0 98/1 1539CA 02265744 l999-03- 10PCT/US97/162771 4Preferably, the rate at which atmospheric oxygen reaches the colorlessprecursor is controlled in order to render the optical disc unreadable at aselected time after the barrier layer is removed. The rate at which oxygenreaches the colorless precursor should be selected such that the optical disccan be read at least once before sufficient color is generated to make theoptical disc unreadable. The rate at which oxygen reaches the colorlessprecursor should be high enough to ensure that the optical disc becomesunreadable within the desired time period (for example four to 24 hours).Various methods can be used to control the rate at which oxygen reaches thecolorless precursor. If the light—absorbing compound is contained within thebody of the substrate 10, the amount of the absorbing compound can beadjusted as appropriate for the application; higher loadings will result inquicker obscuration. The rate at which the absorbing compound becomesabsorbing to the reading beam can be lowered by lowering the concentrationof the absorbing compound in the substrate, or by applying an outer coatingto the substrate which acts as a semipermeable oxygen barrier.Alternately, the absorbing compound can be placed as shown inFigure 6 in a layer 38 on a surface of the substrate 10. The rate of theoxidation reaction can be controlled in this case by choosing a matrix such asa suitable polymer for the absorbing compound layer having the appropriatebarrier properties. Alternately, an additional coating layer can be employedover the absorbing layer, and this additional coating can act as asemipermeable oxygen barrier which allows oxygen to reach the absorbing"layer at the desired rate.As shown in Figure 6, a barrier layer 26 is used to protect theabsorbing layer 38 from atmospheric oxygen during storage and transport.The barrier layer can also take the form of an air-tight package, as shown inFigure 3.1015202530W0 98/1 1539CA 02265744 l999-03- 10PCT/U S97/ 162771 5Reading-Inhibit Agents That Operate By AlteringPhysical Dimensions Of The Optical DiscCertain embodiments of the invention use a reading-inhibit agentwhich alters its physical dimension when activated. A superabsorbingpolymer is one such material, for example a polymer or copolymer containinga carboxylic or alcohol moiety. For example, a water—absorbent resin may beformed 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.Such materials can be used in several ways to make an optical discunreadable, for example as the material absorbs ambient moisture. Theabsorption of such moisture creates a volume change in the material, whichcan be used to cause a combination of any of the following effects to preventreading: delamination, a change in the refractive index, or a change inspinning characteristics.For example, as shown in Figure 7, a superabsorber layer 42 can beplaced between two digital video disc substrates 40. The entire digital videodisc is then protected with an encapsulating barrier layer 28 similar to thatshown above in Figure 3. When the barrier layer 28 is removed, ambientmoisture is allowed gradually to reach the superabsorber layer 42. As thesuperabsorber layer absorbs moisture, it will increase in volume, therebycausing the digital video disc to delaminate and preventing further reading ofthe disc.In the example of Figure 8, a superabsorber layer 44 is placed on thereadable surface of a digital video disk 40, and this superabsorber layer isprotected by a barrier layer 26. When the barrier layer 26 is removed, thesuperabsorber layer 44 will absorb ambient moisture and increase in volume.This volume increase causes a significant change in the refractive index ofthe material, which renders the digital video disc unreadable.1015202530W0 98/ 1 1539CA 02265744 l999-03- 10PCT/US97/ 162771 6As shown in Figure 9, a superabsorber layer 48 may be placed eitherpartially 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 inFigure 9) prior to use. When the barrier layer is removed, ambient moisturewill gradually cause the superabsorber layer 48 to expand. If thesuperabsorber layer 48 is placed as shown in Figure 9, this can cause thespindle hole 46 to assume an eccentric position, thereby rendering the opticaldisc unreadable. Alternately, if the superabsorber layer 48 extendssubstantially around the spindle hole 46, the superabsorber layer 48 mayexpand to the point where the spindle hole 46 is too small to fit on the spindleof the reading device.Figure 10 shows another embodiment in which the superabsorberlayer 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 shownin Figure 10). Once the barrier layer is removed, the superabsorber layer 50absorbs atmospheric moisture, thereby rendering the disc sufficiently out ofbalance to prevent reliable reading.In all of the examples discussed above, the rate at which the super-absorber layer absorbs moisture can be modified by placing a semipermeablebarrier over the exposed surface of the superabsorber layer. This barrier canregulate the diffusion of ambient moisture to the superabsorber layer, whichin this way controls the time period during which the optical disc is readableafter the barrier layer has been removed.Reading-Inhibit Agents That OperateBy Scattering The Reading BeamAs discussed above, a laser beam is typically used as a reading beamfor optical discs. If the reading beam is scattered or otherwise attenuated toa significant degree, the disc cannot be accurately read. For example, asshown in Figure 11, a digital video disc 40 can be provided with a layer 52that includes a material such as a solvent that will alter the optical1015202530W0 98/1 1539CA 02265744 l999-03- 10PCT/U S97/ 162771 7characteristics of the adjacent portion of the digital video disc 40. Forexample, a polycarbonate exposed to solvent is known to craze, i.e. to form adiffuse, opaque film or layer, which scatters the reading beam. Suitablesolvents include organic liquids or vapors such as acetone, xylene and thelike. Depending upon the concentration of the solvent and the exposure time,various rates of loss of transparency can be obtained. Other coatings inaddition to polycarbonates can exhibit the same effective behavior by slightdissolution in an organic solvent followed by deposition on the surface of thedisc as the solvent evaporates or is lost. The redeposition process may alsoinclude a recrystalization of a glassy coating layer. This redeposition resultsin a less transparent and therefore less readable surface on the disc. Thelayer 52 of Figure 10 can include microencapsulated solvent beads which willrupture on removal of the adjacent barrier layer 26.Embodiments That Include Reading-Inhibit Agents Without Barrier LayersAs pointed out above, it is not essential in all embodiments that abarrier layer be included. Rather, in some embodiments it is the act ofreading the disc that activates the reading-inhibit agent. For example, opticalradiation associated with disc reading, or rotation associated with discreading can activate the reading-inhibit agent.As shown in Figure 12, one such embodiment includes an optical disc54 which includes a reading-inhibit agent 56 adjacent one surface. In thiscase the reading-inhibit agent 56 is a photoactive material that, whenactivated by suitable optical radiation, is suitably changed in optical orphysical characteristics so as to inhibit further reading of the disc. Thephotoactive material can alternately be dispersed in the bulk of the disk andcan for example change from clear to opaque at the wavelength of thereading beam upon exposure to suitable optical radiation. As shown inFigure 12, the disc 54 is installed in a reading device 58. The reading device58 includes a first optical source such as a laser 60 that directs the reading1015202530W0 98/1 1539CA 02265744 l999-03- 10PCT/US97/1627718beam 62 against the disc 54. Returning radiation from the disc 54 is sensedby a detector 64, in the conventional manner. In this embodiment, thereading device 58 further includes a second optical source 66. The secondoptical source 66 destroys or degrades the optical transmission or reflectionrequired to read the disc. The second source 66 may be a conventionalsource such as a high pressure arc, an incandescent bulb, a fluorescentlamp, or a laser. As the disc 54 is read, radiation from the second source 62interacts with the reading—inhibit agent 56 to inhibit further reading of thatportion of the disc 54. The second source 62 is arranged such that thesecond source 62 does not illuminate any portion of the disc 54 until after thatportion of the disc 54 has been read by the reading beam 62.in alternate embodiments the reading beam 62 itself may initiateoptical changes in the read inhibiting agent 56, thereby dispensing with theneed for the second source 62. 'Alternately, when the second source 62 is used, the need for aseparate read inhibit agent 56 may be eliminated. In this case, the secondsource 66 may for example be a passively q-switched microchip laserfocused on the surface of the disc. The effect of this laser is to createscattering centers by ablating the read surface of the disc. The scatteringcenters reduce the optical transmission of the disc to the reading beam 62.In either case, the second source 66 should be interlocked in a waythat prevents consumer tampering, and should track in a way so as not tointerfere 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 theinformation on the disc will be denied almost immediately after it is read.Figure 13 shows another embodiment having a reading—inhibit agentwhich is activated by the act of reading the disk. In this case an optical disc70 includes a reservoir 72 that contains a reading—inhibit agent, such as asuitable solvent. The reservoir 72 includes an opening 74. When the disc isfirst rotated in order to be read, solvent passes out of the reservoir 72 via theopening 74, and in this way a small quantity of solvent is released to the disc.10152025CA 02265744 l999-03- 10W0 98/11539 PCTIUS97/1627719The solvent can degrade the optical characteristics of the disc, as discussedabove, to prevent reading of the disc a predetermined time after the solventhas left the reservoir. As one example, the reservoir 72 may be formed in aregion bounded by two concentric annular ridges, similar to the stacking ringsconventionally used in current optical discs.Additional EmbodimentFigure 17 shows a cross-sectional view that illustrates one form of adisc 100 containing a reservoir 102 as discussed immediately above. One ormore capillary—tube—sized passages 104 are radially oriented to allow asuitable reading—inhibit agent (such as a solvent or a corrosive agent asdiscussed above) to flow from the reservoir 102 radially outwardly to theregion of the disc that stores information via information—encoding features.The reservoir 102 and the passage 104 are closed by a silicone membrane108 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 apolycarbonate sheet 114 that defines vents on 116, 118 aligned with thevents 110, 112, respectively.A releasable, peel—off label 120 is removably secured by a suitableadhesive to the polycarbonate layer 114. This peel—off label 122 includes atab 122 to facilitate removal and a protrusion 124. The protrusion 124passes through an opening in the polycarbonate layer 114 and presses thesilicone membrane 108 into the passage 104 to create a mechanical valvethat stops the flow of reading—inhibit agent radially outwardly from thereservoir 102. Optionally, the passage 104 may also include a valve element106 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 includesa 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.1015202530CA 02265744 l999-03- 10wo 93/11539 PCT/US97/1627720Preferably, the peel—off label 120 is sized such that the label must beremoved in order to allow the disc 100 to be read. Once the label 120 hasbeen removed, the vents 110, 112 are opened, and the protrusion 124 isremoved. This allows the silicone membrane 108 to relax upwardly, therebyopening the passage 104. When the disc 100 is rotated during a readingoperation centrifugal force causes the reading—inhibit agent in the reservoir102 to flow radially outwardly via the passage 104 onto the information-encoding portion of the disc 100.In some embodiments the reading—inhibit agent may be selected so asnot to interfere with normal reading of the disc 100 until a selected time afterthe reading—inhibit agent has contacted the information carrying portion of thedisc. As an alternative, when the optional valve element 106 is used, thevalve element 106 prevents the reading—inhibit agent from reaching theinformation carrying portion of the disc 100 until the valve element 106 isdissolved by the reading—inhibit agent. In this way, the plug 106 provides atimed release of the reading—inhibit agent onto the information carryingportion of the disc.Tests have shown that two—pass transmission of the disc typically mustfall to about 45 percent of the original value before a significant number ofreading errors occur, and to approximately 30 percent of the original valuebefore the disc becomes unplayable.ConclusionThe optical discs described above have a short effective life, limitedeither 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 numberof 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 discmay be limited in response to reading of the disc, opening of the disc, orrotation of the disc. Various methods for limiting the effective life of the dischave been described, including physical, chemical, and electrochemical10152025CA 02265744 l999-03- 10w() 93/1 1539 PCT/US97/1627721methods. Physical methods include the diffusion of air or a component of airsuch as oxygen, resulting in physical and/or chemical effects; the use ofoptical activation to cause a physical change in the disc; or the use ofphysical forces or the removal of forces associated with rotation of the disc orremoval of a label to cause a physical change in the disc. Chemical methodsinclude a layer of the disc interacting with a chemical applied when thepackage is opened or by the vendor at the time of sale. Electrical orelectrochemical methods include the use of an electrochemically activesystem to accelerate corrosion.It should be apparent from the foregoing detailed description that thepresent invention can be implemented in a wide variety of forms. Barrierlayers can take the form of sheets or patches on a surface of the disc, or ofencapsulating packaging. In some cases barrier layers are not required.Reading—inhibit agents can take many forms, including materials whichchange optical or physical characteristics of the reflecting layer, or variousother components of the optical disc. Reading—inhibit agents can beemployed as microencapsulated materials, materials formed in layers overselected regions of a disc, or materials incorporated into other components ofa disc. Reading—inhibit agents may extend over the entire information-encoding surface of the optical disc, or alternately may be limited to selectedportions, for example portions that encode indexing or other introductoryinformation.it should therefore clearly be understood that the foregoing detaileddescription is intended by way of illustration, not limitation. It is only thefollowing claims, including all equivalents, that are intended to define thescope of this invention.

Claims (22)

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 initially allow reading of the disc, and then to alter the disc to inhibit reading of the disc, thereby providing a short effective life for the disc;
said barrier layer preventing premature activation of the reading-inhibit agent.

2. The invention of Claim 1 or 22 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 or 22 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 or 22 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 or 22 wherein the inhibit agent is operative, once activated, to alter a physical dimension of the disc.

8. 1n 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 and to provide a short effective life for 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-needing.

11. The invention of Claim 8 farther 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 and to provide a short effective life for the disc;
(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 and to provide a short effective life for the disc;
(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 and to provide a short effective life for the disc;
(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 automatically activated by machine-reading the disc, said reading-inhibit agent operative, once activated, to alter the disc to inhibit reading of the disc and to provide a short effective life for 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.

22. A method for inhibiting reading of an optical disc, said method comprising the following steps:
(a) providing an optical disc comprising:
machine-readable, information-encoding features;
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 initially allow reading of the disc, and then to alter the disc to inhibit reading of the disc; then (b) removing the barrier layer to allow machine reading of the features and to activate the reading inhibit agent; then (c) reading the disc after removal of the barrier layer but before the disc is altered by the reading-inhibit agent to inhibit reading of the disc; and then (d) said reading-inhibit agent then altering the disc to provide a short effective life for the disc.