Abstract: In a flexible magnetic disc adapted for mounting on a drive spindle of a recording and/or reproducing apparatus and having a hub structure secured to a flexible magnetic sheet member at the center of the latter and defining a bore for receiving the drive spindle; the hub structure includes a substantially circular metal plate with a central aperture substantially registering with the bore and which, at its edge, defines a pair of positioning surfaces projecting into the bore at locations spaced apart about its axis, and a metal spring also projecting into the bore at a side of the latter remote from the positioning surfaces and located by positioning seats also defined at the edge of the aperture in the circular metal plate for engaging the metal spring with the drive spindle in the bore and securely seating the drive spindle against the metal positioning surfaces.

Abstract: Stretched surface recording disk (SD) 10 comprises an annular support 12 having raised annular ridges 42 and 28 at its inside and outside diameters 22 and 30 with a base portion 24 in between the two ridges, and an annular recording medium film 14 held in radial tension and stretched across the base portion by adhering the film to attachment surfaces 48 and 36 near the inside and outside diameters respectively. The SD is annealed twice duringmanufacture to relieve stress in the stretched film 14. This annealing results in SD essentially free from track anisotropy and stress distribution anisotropy in the plane of the disk. As a result, data tracks are more stable than in previous SD, track density can be greater, and the SD is generally more reliable.

Abstract: An interchangeable optically readable storage disk has a substrate with a recording surface, and a cover thereon which may comprise a second substrate with a further recording layer. The disk includes a protecting arrangement at the circumference of the substrate, which includes a balancing arrangement. The balancing may be effected by apertures in the protecting arrangement, or balancing masses affixed thereto.

Abstract: A laser recording material comprising a base, a polysiloxane coating film provided on at least one side of the base, said coating film being produced from a monomer represented by the formula:R.sub.x Si(OR').sub.4-xwherein all the symbols are defined in the specification. The material has reduced surface defects and improved focus-servocontrol, is free from formation of a precipitate, appearance of white turbidity or deformation, and does not undergo reduction of sensitivity or reflectance.

Abstract: In an information recording medium having an air-sandwich structure comprising two disc-shaped substrates opposed to each other at a given space by interposing therebetween a ring-shaped inner spacer and a ring-shaped outer spacer and a recording layer for writing and/or reading information with laser beam which is provided on the inner surface of at least one substrate, the improvement in which at least one spacer is an adhesive-retainable spacer comprising a ring portion of protecting circumferences of the substrates and a protruding ring portion of arranging the two substrates apart, the latter ring portion protruding from a side of the protective ring portion and comprising a front portion for defining the space between the substrates and a stem portion being thinner than the front portion for retaining an adhesive, whereby an excessive adhesive or a volatile material of the adhesive is discharged through a space between the substrate and the stem portion of the protruding ring portion.

Abstract: An information record disc for use in a magnetic recording and reproducing apparatus to provide a plurality of still pictures in a plurality of spiral tracks on a magnetic disc thereof, includes an annular magnetic plate having an aperture therein; and a cylindrical central core made of plastic and formed with the magnetic plate by an outsert molding process in which the central core includes an upper section extending above the magnetic plate, a lower section extending below the magnetic plate and a connecting section connecting the upper and lower sections through the aperture, the upper and lower sections being offset from the aperture, so that an integral structure is provided with the central core and the magnetic plate, and with the magnetic plate thereby having an outwardly extending radial flange which extends radially outward from the central core and to which the magnetic disc is secured and an inwardly extending radial section which extends inwardly of the central core and which is attracted by a m

Abstract: An optical floppy disk system is described in which the optical disk is enclosed in a flexible housing which is optically transparent. Both the optical disk and its protective housing can be made at very low cost from inexpensive materials. The disk is enclosed within the protective housing and the housing and disk rotate as a unit during operation. The protective housing does not adversely affect the optics of the system.

Abstract: A recording medium having an air-sandwich structure comprising two disc-shaped substrates opposed to each other at a given distance by interposing therebetween a ring-shaped inner spacer and a ring-shaped outer spacer and a recording layer for writing and/or reading information with laser beam which is provided on the inner surface of at least one substrate,characterized in that the distance between said two substrates satisfies the following expression (I): ##EQU1## wherein h is the distance in mm between two substrates, E.sub.1 and E.sub.2 are each a Young's modulus (in kg/mm.sup.2) of each substrate, l is the distance (in mm) between the inner spacer and the outer spacer, and t.sub.1 and t.sub.2 are each the thickness (in mm) of each substrate.

Abstract: The invention relates to information carriers for optically readable information. The information carrier is built up from an actual carrier and a metal layer provided thereon. The actual carrier is manufactured from a polycarbonate resin consisting of a mixture of an aromatic polycarbonate, an epoxy compound and usual additives. The presence of an epoxy compound in the polycarbonate resin results in a better bonding between the metal layer and the polycarbonate resin. In order to be able to manufacture the actual carrier by means of injection molding, it is to be preferred to use a polycarbonate having a weight-averaged molecular weight from 10,000 to 20,000.

Abstract: A magnetic disk assembly is comprised of a magnetic disk and a hub member centrally positioned on that disk and having a non-circular opening for receiving a circular drive shaft which serves to rotatably drive the magnetic disk. The hub member includes at least two reference surfaces which converge toward each other and which form two respective walls of the opening, and one or more resilient members having a surface which forms a third wall of the opening. The three walls are positioned and dimensioned such that when a circular drive shaft is received, the reference surfaces and the surface of the resilient member all tangentially contact the drive shaft to be rotated thereby when the drive shaft rotates.

Abstract: An optical disc comprises a resin disc substrate, a recording medium layer formed on the disc substrate, a high purity of transparent layer, and a transparent protective resin layer. The transparency of the transparent layer is larger than that of the transparent protective resin layer. A laser beam is focused on the recording medium layer through the transparent protective layer and the transparent layer. The transparent layer is a transparent adhesive layer or an air layer. The focused laser beam is not affected by foreign matter in the vicinity of the recording medium layer due to the high transparency of the transparent layer on the recording medium layer.

Abstract: An optical recording medium comprising a transparent substrate of a synthetic resin and an information recording layer provided thereon, on which medium information can be optically written, read and erased by means of a laser light, wherein said transparent substrate consists essentially of a cast-cured product of an epoxy resin composition comprising an alicyclic epoxy resin, or a mixture of a major amount of an alicyclic epoxy resin and a minor amount of an aromatic epoxy resin, an organic polybasic acid anhydride, a curing-accelerator and an anti-discoloring agent.

Abstract: A material for optical disks which comprises a polymer containing at least 20 wt. % of a structural unit represented by the formula ##STR1## wherein X is fluorine or alkyl having 1 to 6 carbon atoms, and R.sup.1 is fluoroalkyl having 2 to 10 carbon atoms.

Abstract: A radiation-sensitive record disc is disclosed having a first disc and a second disc coaxially positioned adjacent the first disc to reinforce the first disc. A first spacer is positioned between the first and second discs for fixedly connecting the discs together and to form an air space between the discs. A recording layer is formed on one surface of the first or second discs within the air space. A second spacer is radially displaced from the first spacer, and positioned between the first and second discs. This second spacer enables the discs to move relative to each other in a radial direction in response to expansion or contraction of at least one of the discs due to changes in temperature, humidity, atmospheric pressure, etc.

Abstract: A protected optical disk for recording information is fabricated by a method whereby at least one cover is rigidly fixed by a welding to an optical disk having at least one layer of recording material which can be both written and read optically. At least two joints are thus formed by welding, each joint being constituted by at least two weld zones each located respectively within a concentric ring.

Abstract: An unconstrained removable protective cover for optical disks. With this apparatus a transparent protective cover can be mounted to an optical information recording disk wherein the different thermal expansion coefficients of the disk and the protective cover will not result in read write errors due to warping of the protective cover. An inner spacer ring is fixedly bonded to the inner diameter of the disk substrate and the protective cover. However, on the outer perimeter of the disk, a U-shaped spacer ring is fitted thereon and fixedly mounted to the outer perimeter of the transparent protective cover. This allows the transparent protective cover to expand and contract relative to the disk substrate by lateral movement of the spacer ring relative to the disk, without warping of the protective covering. A plurality of methods of mounting the outer spacer ring to the protective covering are disclosed.

Abstract: An optical disk with a recording layer formed on the inner surface of a protective plate has data which is read out upon irradiation of a laser beam. A substrate supports the protective plate such that the recording layer opposes the substrate and a space is formed therebetween. The spacer is sandwiched between the protective plate and the substrate so as to couple them. The spacer is an elastically deformable member. Therefore, when the protective plate expands or contracts relative to the substrate, due to deformation of the spacer, excessive force does not affect the recording medium. Warp, wave or damage to the disk due to expansion/contraction of the protective plate or substrate can be prevented, thereby allowing stable data processing.

Abstract: A device is disclosed for clamping disk assemblies in a manner to impart constant tension to a support web and cover sheet, while assuring easy and quick loading and unloading of the assembly. The optical disk assembly includes a web assembly including a flexible disk-shaped support web and preferably an opposed cover sheet. An annular retaining ring engages the web assembly around its periphery. The support web carries a record layer with an information storage region. The optical disk assembly is mounted on a reference structure. The web assembly is drawn over an annular locating surface integral with the reference structure to subject the web assembly to circumferentially-symmetric tension. The tension may be constant or, in some embodiments of the invention, may be changeable from a low "storage" tension to a higher "operating" tension. Clamping elements are movable radially over the optical disk assembly from a retracted position.

Abstract: A protected optical disc adapted for optical recording and playback of information (particularly digital recording) with a rigid element carrying the recording surface, and a flexible element permeable to optical radiation, one of these two elements having the shape of a dish. At least one of the elements is provided with a central hole for receiving a driving shaft, with the joined annular portion or portions of the two elements concentric with the central hole.

Abstract: An optical disk assembly includes a web assembly having a flexible disk-shaped support web carrying a record layer. The support web has an information storage region. A pair of annular retaining ring members engage opposite sides of an annular peripheral region of the web assembly to clamp the support therebetween are formed from malleable stock material which is deformed during assembly of the optical disk assembly to provide a locking interfit therebetween with the peripheral region of the web assembly interleaved between the ring members. The peripheral region of the support is wrapped about an annular reference surface of one ring member and is pushed into an annular recess with undercut area in that ring member. The other ring member is deformed into the recess undercut.

Abstract: An optical disc assembly includes a flexible disc-shaped support carrying a record layer. The support has an information storage region. A pair of annular retaining ring members engage opposite sides of an annular peripheral region of the support as the ring members close together to clamp the support therebetween. The peripheral region of the support is wrapped about an annular reference surface of one ring member and is pushed into an annular recess in that ring member. Cooperative surfaces on the ring members provide a locking interfit therebetween with the peripheral region of the support interleaved between the ring members.

Abstract: A method for protecting the recording surfaces of optical data storage and recording tape provides the tape edges with protuberances formed by plastic coatings, embossments or thickness gradients of the recording material.

Abstract: A flexible hub for a disk is described. The disk includes a relatively large center hole into which a flexible planar member is mounted or clamped. The size of the flexible member is slightly larger than the hole, thereby requiring that the flexible member be slightly bowed or flexed in order for it to fit within the hole. The flexible member is preferably attached to the disk at three respective equi-angularly spaced locations around the periphery of the hole. In the center of the flexible member is a collar adapted to receive a protruding spindle neck from a spindle mechanism upon which the disk is mounted. The end of the spindle neck and the inside wall of the collar are tapered at the same angle. Insertion of the spindle neck into the collar thereby forces alignment or centering of the center of the collar with the longitudinal axis of the spindle neck.

Abstract: An optical disc structure including two resilient disc members which are bonded together adjacent their outer peripheries and which include an air channel allowing communication between the chamber formed between the discs and the atmosphere. An information layer is formed on the inner surface of at least one of the members. When the members are spun, a pressure differential is caused tending to push the two members apart, thereby assuring that one member will not contact the information layer formed on the other member and that the two members will not be close enough together to cause optical interference.

Abstract: An optical disk unit, of the kind having a record element and a flexible cover sheet that are attached around an outer periphery in a manner providing an outer spacing and a generally enclosed inter-space therebetween, has an improved construction which significantly reduces the likelihood of contact between the record element and cover sheet. Central spacing means provide a central sheet-to-element spacing that is significantly larger than said outer spacing and vent means, into and out of the inter-space cause a reduction in the spacing between the record portion of the element and the cover sheet during write/read operation. The air flow through the vent means also reduces the formation of visible debris in the enclosed record element/cover sheet inter-space.

Abstract: An optical disk assembly includes a flexible disk-shaped support carrying a record layer. The support has an information storage region. An annular retaining ring engages the annular peripheral region of the support. The support, and preferably a cover sheet, are captured between the outer annular reference ring member and an inner annular reference ring member which has been conically deformed to spring toward the outer ring member.

Abstract: A polymer coated information storage device, such as a disc, is disclosed. A coating composition for preparing such polymeric coating comprises certain esters of beta-acryloxypropionic acid with certain diacrylates. The coating composition also comprises under certain circumstances, a photoinitiator.

Abstract: An information recording medium which includes a light-transmitting substrate, a recording layer formed on the substrate, the recording layer having the characteristic of changing an optical characteristic upon heating thereof, together with a protective layer having light-absorbing properties disposed over the recording layer and arranged to absorb light passing through the recording layer upon recording, in combination with a planar layer superimposed on the protective layer and capable of suppressing mechanical deformation of the recording layer.

Abstract: An improved conductive molding composition for the preparation of high density capacitance electronic discs is disclosed. The disclosed compositions are improved by the utilization of a solid plasticizer, cumylphenyl isophthalate, represented by the formula ##STR1## The use of this plasticizer permits the formulation of a conductive molding composition wherein all ingredients are solids.

Abstract: An improved conductive molding composition for the preparation of high density capacitance electronic discs is disclosed. The disclosed compositions are improved by the replacement of most or all of the conventionally used stabilizer ingredient with a tin mercapto ester or alkyl mercaptide represented by the formulae ##STR1## wherein R is a straight-chain alkyl radical having 4 to 8 carbon atoms; R.sub.1 is selected from --S-CH.sub.2 -COOR.sub.3 and --S-R.sub.3 ;R.sub.2 is R or R.sub.1 ; andR.sub.3 is a straight-chain alkyl radical having from 8 to 18 carbon atoms.

Abstract: A protected optical disc intended for the recording of information is protected against the harmful consequences of humidity by the presence of a hydrophylous material situated at a particular distance from the recording surface, which thus retains a high sensitivity during the write or read operations. The invention may be applied especially to discs intended for digital recording.

Abstract: A conductive molding composition for the compression molding of high density information discs (video discs). The composition includes a polyvinylchloride-based resin containing sufficient carbon black particles to obtain a desired conductivity (bulk resistivity of about 500 ohm-cm at 900 mHz or less,) from about 1 to 5 weight percent of a stabilizer, from about 0.5 to 3 weight percent of a lubricant, from about 1 to 5 weight percent of a plasticizer and from about 0.1 to 1 weight percent of an organo-silicone compound having polar groups.

Abstract: A disk clamping device having a turntable fixedly secured at a predetermined height to a spindle. A clamper is adapted to depress the disk against the turntable. A movable ring is slidable in parallel with said spindle and a member having a conical outer wall is slidable in parallel with the spindle while being in contact therewith. A magnet is positioned by a yoke or plate to form a magnetic circuit with the magnetic flux clamping the disk. The center of the disk coincides with the center of rotation of the spindle when the disk together with the movable ring and the conical member is moved downwardly while in contact with the conical member and maintained horizontal by said movable ring. The disk is clamped at a predetermined height when it is brought into contact with the turntable.

Abstract: An optically readable storage disc comprises a transparent substrate 1 on which a recording layer 2 is deposited which can be modified locally by means of a radiation beam, which recording layer is covered by a cover disc 3 which is secured to the substrate in a gas-tight manner at some distance from the part of the recording layer which is intended for recording, so that a sealed space 4 is enclosed between the substrate 1 and the cover disc 3. The cover disc 3 will be deformed to the greatest extent under the influence of differences between the gas pressure in the sealed space 4 and the barometric pressure because its resistance to deformation is substantially smaller, so that deformation of the substrate 1 is substantially precluded.

Abstract: Optical disc write/read apparatus and systems of the type having a flexible record disc and turntable which interface in a manner forming a generally enclosed space between record portions of the disc and opposing turntable portions is provided with inner and outer ventilation means which effect a continuous, controlled air flow through said space during write/read operations.

Abstract: A radiation-sensitive record disc having a first substrate and a second substrate, coaxially positioned and spaced from the first substrate. The second substrate has an inner vent hole perpendicular to its surface which provides fluid communication between the space and the outer surface to the substrate. A pressure equilibrium housing is coaxially provided on the outer surface of the second substrate in communication with the vent hold. This housing has a recess on its inner surface adjacent the outer surface of the second substrate so as to form a cavity. An expansible membrane is provided in the cavity for receiving, through the vent hole, the internal pressure which exists in the air space. This cavity also contains an outer vent hole, on its outer surface, to provide equilibrium between the pressure within the air space and the surrounding air so as to absorb the change of intended pressure within the air space.

Abstract: A cover assembly for use with a disk-shaped optical recording medium, having two substantially identical halves, each having an inner surface adapted to provide upon assembly with the medium an air gap adjacent an optical recordable coating on the medium. Each cover half is transparent and has substantially no birefringent characteristics on the region overlying the air gap, thus allowing light to pass unimpeded therethrough. The cover assembly is adapted to be coupled to the central hub of the optical recording medium and to have a raised annulus adjacent thereto to support the assembly and minimize contact with the transparent portion.

Abstract: This disclosure relates to an optical disk unit with two states in which the web assembly is in different circumferentially-symmetric tensions. One tension is sufficiently great to provide the desired degree of planarity when used with write/read apparatus. The other tension is significantly reduced, keeping the web assembly materials well below their elastic limits to reduce tension and prolong product life. The optical disk unit includes a flexible disk-shaped web assembly including a support web and preferably an opposed cover sheet. An annular retaining ring engages the web assembly around its periphery. The support web carries a record layer with an information storage region. The annular retaining ring includes selectively operable means for changing the state of the disk unit to adjust the web assembly tension between the two tensions. In one embodiment, the state-changing means includes a bi-stable spring having a stable condition for each of the two web assembly tensions.

Abstract: Laminated optical recording medium that provides desired optical properties in combination with pregrooved channels that define data tracks on which data may be written. Annular or spiral grooves are selectively placed on a base disc substrate. A recording layer is deposited on a transparent disc substrate. The two disc substrates are then bonded together so that the recording layer on the transparent disc substrate confronts the grooves on the base disc substrate. The covered grooves thus form chambers exposed to the recording layer. Prior to bonding the two disc substrates together, the chambers may be filled with an inert gas. A rigid support disc, such as is made from aluminum, may optionally be bonded to the underside of the grooved base disc substrate.

Abstract: Provided is an erasable recording medium and a method for recording and erasing same. The erasable recording medium comprises a thermally stable substrate and a polymeric layer deposited on the substrate comprised of a dimer acid polyamide. Such a recording medium has an excellent dimensional and mechanical stability on storage, readily and easily records information, and has an ability to be easily and completely erased when erasure is desired.

Abstract: An optical disc assembly for use with optical disc apparatus includes a flexible disc-shaped support. An annular retaining ring engages the support around its periphery. The support carries a record layer with an information storage region. Cooperating optical disc write/read apparatus has an annular, rotatable locating surface against which the support abuts. Annular spring means integral with the locating surface engage the retaining ring, applying a force to center the ring with respect to the axis of rotation of the locating surface, and to bring the support into a predetermined abutting force against the locating surface. This provides firm contact between the disc assembly support and the locating surface. The retaining ring holds the support in a first, predetermined circumferentially-symmetric storage tension. The abutting force of the support against the locating surface, induced by the spring means, may increase the tension in the support to a second, operating tension.

Abstract: In the recording and/or reproducing device according to the present invention, a disc unit (i.e., recording member) is utilized which comprises upper and lower spaced centrally apertured recording portions. Each recording portion is provided with an annular recording layer on its inner surface and an aperture at its center for rotatably mounting on a turntable. Upon rotating the turntable with the disc unit, the recording and reproducing device records information signals on, and reads information signals from, the recording layer on each recording portion by using a light beam. The light beam is positioned to strike only the recording layer on the lower recording portion. When the disc unit is turned on its other side, the previously positioned upper unit is then positioned as the lower unit to receive the light beam. The turntable comprises a perpendicularly orientated centering member which engages the aperture of a recording portion. The centering member centers the disc unit on the turntable.

Abstract: This disclosure relates to means for receiving disk assemblies in a manner to impart constant tension to the support and cover sheet, while assuring easy and quick loading and unloading of the disk assemblies.An optical disk assembly includes a web assembly including a flexible disk-shaped support and an opposed cover sheet. An annular retaining ring engages the web assembly around its periphery. The support carries a record layer with an information storage region. Cooperating optical disk write/read apparatus has an annular, rotatable locating surface against which the web assembly abuts. Detent means releasably secure the disk assembly retaining ring in an active position, with firm contact between the web assembly and the rotatable locating surface. The detent means is releasable when subjected to a predetermined force from the retaining ring, whereby the retaining ring is movable into and out of its active position by mere application of sufficient force thereto.

Abstract: An optical disc assembly includes a flexible disc-shaped support. An annular retaining ring engages the support around its periphery. The support carries a record layer with an information storage region of the record layer located between the retaining ring and a central hub. In use on cooperating optical disc write/read apparatus having disc assembly receiving structure, the central hub positions an annular area of the support, which area is radially inward of the storage region, against a locating surface of the receiving structure with a predetermined abutting force, whereby firm contact is assured between the support and the location surface radially inwardly of the storage region of the record layer. The disc assembly includes a flexible, transparent cover sheet which is coextensive with the support.

Abstract: A disk cartridge having a housing in which a substantially rigid disk is completely enclosed, the disk having a nub which is accessible through an opening in the housing for engagement by a rotatable drive spindle. The housing has an opening for receiving a read/write head to apply or pick off data from the magnetically permeable surface of the disk. The head receiving opening is normally closed by a door which is opened by a cam when the cartridge is inserted in a drive unit. When not in use, the disk hub is held against the interior of the hub opening to seal the cartridge against contamination. When the cartridge is inserted in a drive unit, the drive spindle is guided into a self-centering socket in the hub and lifts the hub clear of the opening for free rotation of the disk.

Abstract: An optical disc assembly includes a record layer carrying, flexible disc-shaped support with an information storage region. An annular retaining ring comprising an inner and an outer member clamps an outer peripheral portion of the support as the ring members close together. The outer peripheral portion of the support is wrapped about a radially outward facing surface of the inner ring member and a second, larger radius peripheral support portion is pushed into an annular recess in the inner ring member. Means on the retaining ring cause the portion of the support which is pushed into the recess to form a scalloped configuration within the recess. This inhibits buckling of the support. Such buckling would set up stresses in the support which would tend to be transmitted radially along the support to the information storage region.

Abstract: An optical disc assembly includes a flexible disc-shaped support. An annular retaining ring engages the support around its periphery. The support carries a record layer with an information storage region of the record layer located between the retaining ring and a central hub. In use on cooperating optical disc write/read apparatus having disc assembly receiving structure, the cental hub positions an annular area of the support, which area is radially inward of the storage region, against a locating surface of the receiving structure with a predetermined abutting force, whereby firm contact is assured between the support and the location surface radially inwardly of the storage region of the record layer. The disc assembly includes a flexible, transparent cover sheet which is coextensive with the support.

Abstract: An optical disc-unit including (i) a flexible, disc-shaped support bearing a record layer, (ii) a flexible disc-shaped cover sheet which is transparent to write/read light and (iii) annular retaining means which engage the support and sheet, in spaced relation, substantially continuously around peripheral regions. In preferred embodiments the retaining means symmetrically tension the sheet and support into substantially flat dispositions. Cooperative optical disc write/read apparatus and optical disc-unit fabrication methods are also disclosed.

Abstract: A flexible magnetic disk cassette having a disk enclosed in a cover formed of an upper half and a lower half, the lower half having a driving hole through which a center positioning pin of a driving means may extend into a center aperture of a center core disk rigidly and non removably secured at the center of the disk, the center core disk being further provided with driving and positioning means for receiving a driving pin of the driving means, said driving and positioning means structured so that engagement with the driving pin will cause the disk to move to bring the center aperture of the attached center core disk into proper centering engagement with the positioning pin.

Abstract: A symmetrical video disc structure and method for making the structure are described. The video disc structure is symmetrical about a plane passing through a core member and equidistant and parallel to a first information bearing surface and a second information bearing surface carried by the core. First and second reflective layers are formed over the first and second information bearing surfaces, respectively. The combination of two reflective layers, so oriented, operates as a vapor barrier for preventing the absorptions of water into the core member of the symmetrical video disc structure situated between the two vapor barriers. First and second protective layers are formed over the first and second reflective layers, respectively. The thickness of the first and the second protective layers is maintained the same over the entire area of the video disc structure.