Abstract: A process of manufacturing the optical discs by injection molding includes compulsive forced cooling of the molded discs, carried out after sputtering to shorten the cooling time in the mold, in consideration of keeping the replication errors in the pits on the molded discs. The process also includes metallizing the surface of the molded discs by sputtering (to make laser beams reflect). UV resin coating for protecting the metallized surface of the discs, and inspecting the pits for replication of information signals quality.

Abstract: A process for producing high-density thin type optical disk substrates having good replicability and birefringence sufficient for practical use. In filling the resin into the cavity, the stress on the resin is reduced by controlling the relation of the cavity width and the injection compression force to reduce birefringence. Further, the mirror surface of the mold is maintained at a certain temperature to facilitate the resin flow and a good replicability and reduction of birefringence is achieved by terminating the resin filling and starting the compression process at the time at which the pressure of the resin filling is at a minimum.

Abstract: An improved injection mold for molding an information recording disc is provided.

Abstract: A mold for molding digital data discs has interchangeable stampers. An outer peripheral stamper retainer and a mirror block with a convex portion allow interchange without dismounting the mold. The outer stamper peripheral retainer has a plurality of arcuate slots connected or disconnected to a plurality of rods provided with a stationary half-mold and to a corresponding plurality of holder bushings and a mirror block with a convex portion whose diameter fits an inner diameter of the outer stamper peripheral retainer. The outer stamper peripheral retainer and the mirror block correspond in size with a disc to be molded.

Abstract: A mold for molding disk substrata is capable of changing a set position of a stamper plate on a mold cavity. A pair of mirror plates are respectively for forming the surface of a disc cavity or for back stay of stamper plate. The set position of mounting the stamper plate is capable of being performed due to changing selectively the set position of the mirror plate. An inner stamper holder and stamper plate are held on the mirror plate by vacuum force to admit setting operations to ease.

Abstract: An improved method for forming a disc substrate having a bottomed centering hole for rotating and driving the disc. The method includes injecting synthetic resin into a mold cavity formed by a first and second metal molds to form the substrate, and punching at least part of the centering hole by a movable member protruded into the mold cavity to form a through-hole. A stamper containing digital information is held in place inside the mold cavity by its inner circumference by means of a vacuum or a magnet.

Abstract: A die assembly for molding a disc such as a compact disc, a video disc or the like by employing an injection molding process. The die assembly comprises a stationary die half including as essential components a stationary platen, a base die half, and an insert die half received on the stationary platen, and a movable die half. The insert die half includes a first insert for fixing the insert die half on the stationary platen, and a first mirror surface board removably received in a cavity of the first insert. The insert die half can be easily installed and removed into/from an installation space defined by a pair of retaining members and a die receiving member and when installed, it can be certainly and easily fixed by a pair of retaining members.

Abstract: An inventive method for producing an optical tape comprises the steps of sequentially depositing a label layer and a reflection layer on a substrate. The label layer and the reflection layer has a same reflexibility in a predetermined wavelength range of a laser beam, thereby providing a label image to a user as well as capability of information recording.

Abstract: In an injection mold having a cavity formed between opposing faces of a fixed mold and a movable mold for defining a shape of a product, and cooling channels formed in the fixed mold and the movable mold, respectively, for cooling resins injected into the cavity, cooling channels of the movable mold are formed at positions at least opposite to those where cooling channels of the fixed mold are not formed, thereby obtaining an injection mold capable of securing uniformity of optical properties of the obtained molded article, such as birefringence and causing no deterioration of mechanical properties of the molded article such as a deflection even when a cooling time is shortened in order to increase cycle of the injection molding.

Abstract: An optical information recording substrate and method of producing the substrate, the substrate having a legible matter formed in a groove area thereof or a pit array area thereof, wherein the legible matter includes a plurality of grooves or pit arrays being partially different in the breadth or depth thereof. The grooves or arrays may be partially dislocated in the radial direction of the optical information recording substrate from a predetermined track. The visually legible matter may include a plurality of laser generated pit arrays wherein remaining portions of the legible matter have a plurality of continuous grooves formed therein. The legible matter may also include a plurality of continuous grooves wherein remaining portions of the legible matter includes a plurality of laser generated pit arrays formed therein.

Abstract: A method and apparatus for creating an optical disk mother or stamper wherein the number of processing steps is greatly reduced from the prior art methods. In particular, the present invention involves directly forming a mother or stamper by direct laser ablation of a conductive metal substrate. More specifically, a stream of coded digital information (for example, representing the content of an encyclopedia in the case of CD ROM or a classical music collection in the case of CD audio) is converted into a corresponding plurality of pits and lands in the conductive metal substrate by electronically switching the beam of a first laser on and off via an electro or acusto-optic modulator (EOM/AOM) in response to the digital information. As a result, selective portions of the conductive substrate are either ablated (in the case where the laser is on) thereby directly creating the pits, or the substrate is left unaltered (in the case where the laser is off) thereby creating lands.

Abstract: To injection-mold a base board for an optical disc or the like, an injection molding die includes a stamper plate attaching/detaching device installed therein. The stamper attaching/detaching device includes as essential components a stamper plate attaching/detaching bush adapted to be fitted into a tapered bush fitting hole formed in a die half on the movable side together with a stamper plate to be firmly placed on a die cavity, an actuating rod having a pinion gear formed at the fore end part thereof to mesh with a rack formed at the lower end part of the stamper plate attaching/detaching bush, and a lock nut for immovably hold the actuating rod during a series of molding operations. The stamper plate is removably fitted around the outer periphery of a flange portion of the stamper plate attaching/detaching bush.

Abstract: A method for making an optically readable medium containing a relief information track comprising the sequential steps of(a) laminating a dry photohardenable film to a surface of a transparent dimensionally stable substrate;(b) embossing the exposed surface of the photohardenable film with the relief information track by applying thereto under pressure a stamper die containing a reverse relief image of the information track;(c) passing actinic radiation through the transparent substrate and the photohardenable film to effect hardening of the photohardenable film while it is contact with the stamper die; and(d) separating the stamper die from the embossed photohardened film;The embossed film of the medium is made reflective by applying a reflective layer to either the photohardenable film prior to embossing or to the photohardened film subsequent to embossing.

Abstract: A disk substrate molding die is provided in which the quantity of eccentricity of a stamper can be reduced to a small value. The molding die includes a member having mounted thereon a thin plate (19) carrying thereon a recorded transfer signal and an adjusting device consisting of a plurality of pairs of adjusting blocks, each formed of movable blocks (9a) and (9b) and blocks (10a) and (10b) having adjacent surfaces inclined in the moving direction of the movable blocks and common to one another.

Abstract: A sprueless disc mold including: a gate insert; a hot plunger adapted to come into sliding contact with the gate insert and heated and held; drive means for moving the hot plunger to open/close the gate; and a cooling air passage. The hot plunger includes a shoulder portion formed at its leading end portion. The gate insert includes: a leading end face forming a portion of a cavity face together with the shoulder portion of the hot plunger; an annular recess for forming the disc into a shape having one face raised to the crest of a stack rib; and an inner circumference extending from the inner circumferential edge of the circumferential recess toward the gate.

Abstract: An improved method of removing a stuck sprue from the ejector assembly of an injection molding machine and a tool for use in the method in which the tool has a body with a hollow lower portion having a bottom edge with peripherally spaced indentations, In the method, the tool is first heated to above the melting point of the molding material and the lower end is inserted into the stuck sprue. The tool is cooled to below the melting point of the molding material and then rocked back and forth to free the sprue from the ejector mechanism.

Abstract: A metal mold device for molding a disc substrate formed by molding a synthetic resin material and having a raised portion on the inner surface of the disc substrate, includes a fixed metal mold and a movable metal mold for defining together a mold cavity for molding the disc substrate. A mold releasing resistance in the form of suitably sized projections or recesses, is provided at a portion of the fixed metal mold or the movable metal mold mating with the outer rim of the disc substrate being molded or at the outer peripheral surface of the raised portion to permit an as-molded disc substrate to be released easily and reliably from a stamper bearing a pattern of pits and lands or pre-grooves and to prevent molding distortions from being produced in the disc substrate being molded.

Abstract: In order to facilitate the formation of a plastic member with an aperture in a central portion thereof, a ring gating valve arrangement is provided with a multi-piston servo arrangement which enables a specially configured pin to be stepwisely reciprocated back and forth within a molding device. The pin is formed with a land at one end which is dimensioned and shaped to produce the required aperture. The pin further features a channel structure which includes an annular recess adapted to permit plastic to flow into the center of the mold cavity area when the pin is thrust to a predetermined location. After the cavity is filled with hot plastic, the pin is retracted to a position wherein the annular recess is located within a removable gate bushing and the shaped land is pulled up until it is appropriately located in the mold cavity area. As the injected plastic cools and solidifies, the shaped land acts as the aperture molding pin and forms a clean aperture in the molded part.

Abstract: In the optical disk manufacturing method a clamping plate is placed in the cavity of a disk body and the disk body is heated and compressed to connect the clamping plate to the disk body. Prior to connecting the clamping plate, a groove is established around the perimeter of the clamping plate. A disk body with or without a groove has its target surface compressed by a heat press while a region outside the target surface perimeter is pressed by an upper pressure surface to connect the clamping plate without creating a protrusion from the upper surface of the disk.

Abstract: A method produces a molding die for an information recording medium, having a mold surface with a prescribed unevenness pattern comprising a projection; the projection having different etching velocities along its projected thickness; and defining a pair of convergent opposite inclining side slopes. Each slope of the pair forms an acute inclining angle with respect to extension of the mold surface. A pattern-forming layer is formed comprising a common metal element throughout its thickness and an additional element differing in composition from the common metal element in the thickness direction of the pattern-forming layer. The common metal element and the additional elements have different etching velocities in the thickness direction of the pattern-forming layer. The pattern-forming layer is selectively etched with a common etchant to form the projection.

Abstract: A method for molding a substrate sheet for an optical recording medium by transferring a preformat pattern from a molding roll to a resin sheet molded by melting and extruding a resin. The molding roll has a roll base, a stamper detachably fixed on the peripheral surface of the roll base, and a resin layer interposed between the roll base and the stamper.

Abstract: A new compact disk ("CD") is formed providing a bright, metallic presentation of indicia such as trademarks, promotion and advertising copy and other alphanumeric information around the circumference of the disk with recorded digital data in the disk's central portion. Such a CD may be a 120 mm CD including a central portion recorded in the 80 mm format of a single CD, with the desired indicia formed by a bright metal indicia-bearing substrate in the 20 mm, radially-extending, circumferential portion of the CD that surrounds the recorded digital data.Such CD's are manufactured by recording the digital data in the central 80 mm of a 120 mm master, leaving the remaining unrecorded circumferential portion of the master with a smooth surface and applying the desired indicia onto the unrecorded outer peripheral portion of a disk used to form production stampers.

Abstract: Faster injection molding cycles in an optical disk mold which forms the centerhole by tearing out the sprue can be obtained by increasing the "hot strength" of the sprue by addition of a plurality of rigidifying ribs onto only the B side of the sprue. This plurality of molded-in ribs is formed within a mating plurality of female cavities cut into the axially displaceable ejector sleeve, within which is guided an axially displaceable ejector pin, all within the displaceable half of the moldset. These ribs are circumferentially spaced and extending between the B side displaceable half surface of the sprue flange (substantially located within the plane of the molded disk) and extending substantially downstream to the juncture with the ejector pin surface of the mold.

Abstract: In a process for producing optical disks comprising the steps of subjecting the photoresist layer on a substrate formed of silicon, quartz, glass or a metal to light exposure, developing and etching treatments to obtain a stamper and then duplicating an information pattern for an optical disk from the stamper obtained above to a transparent substrate by using a UV curable resin to prepare a replicated substrate of an optical disk, a large number of stampers can be prepared in a short time by conducting the light exposure either by contacting the mask side surface of a substrate provided with a photomask having an information pattern for an optical disk to the photoresist side surface of said substrate having the photoresist layer or by noncontact projection, and a rapid replication of large quantities of replicated substrates becomes possible by using a large number of stampers thus prepared.

Abstract: An injection mould for manufacturing disc-shaped plastic articles with a central hole comprises a first mould part and a second mould part displaceable relative to the first mould part by a first displacing mechanism. The two mould parts are displaceable between a closed first position, in which they together partially bound a mould cavity corresponding to the shape of an article for manufacture, and an open second position in which a formed article can be removed. A third mould part is provided which, in the closed position of the first and second mould parts, extends through the mould cavity and has a shape in the region of the mould cavity which corresponds to the shape of the central hole. The third mould part is axially displaceable by a guide sleeve forming part of the first mould part between a first position, in which it partially forms a bounding of the mould cavity, and a second retracted position.

Abstract: An apparatus for manufacturing an object having a relief structure on a surface thereof by pressing a first element provided with a negative of the relief structure against a second element to form the relief structure in the surface of the second element. The apparatus includes the first element and two pressure members having pressure surfaces facing each other and opposing both of the elements, the pressure members being moveable relative to each other in a direction transverse to the pressure surfaces.

Abstract: A method for making an optical image element having a high aspect ratio relief hologram comprising the sequential steps of(a) applying a dry photohardenable film to a surface of a transparent dimensionally stable substrate;(b) embossing the exposed surface of the photohardenable film with the holographic image by applying thereto under pressure a stamper containing a reverse relief image of the hologram having an aspect ratio of at least 3:1;(c) passing actinic radiation through the transparent substrate and the photohardenable film to effect hardening of the photohardenable film while it is in contact with the stamper; and(d) separating the stamper die from the embossed photohardened film.

Abstract: A method of manufacturing an object having a surface structure, the method employing pressure members (3, 5) which are movable relative to one another and which have facing pressure surfaces (23, 25). A first element (51) and a second element (53) having a relief on one surface are pressed against one another to provide the second element with a microstructure by cold deformation. During pressing use is made of a pressure body (27, 29) which is interposed between one of the pressure members and one of the elements and which is made of a material having a characteristic parameter equal to the quotient of the Poisson's ratio and the modulus of elasticity of the material, which parameter differs less from the corresponding parameter of the material of the relevant element than from the corresponding parameter of the material of the relevant pressure member.

Abstract: There is provided a cast molding die for an information recording medium, having a mold surface with a prescribed unevenness pattern including a projection; wherein the projection has at least one pair of opposite side slopes each of which forms an acute angle with respect to the extension of the mold surface. By using the cast molding die having the above-mentioned projection with a three-dimensional shape, a defect such as lack in the resultant information recording medium is prevented.

Abstract: The optical disc of the present invention has a transparent substrate provided on the surface opposite to the surface of a metallic reflective film in contact with a recording layer, and reading of predetermined information is performed by permitting a laser beam to be incident from the transparent substrate side. That is, light is reflected on the surface on the opposite side to the surface of the metallic reflective film in contact with the recording layer, and by employment of such a mechanism, it becomes possible to enhance the reflectance in the metallic reflective film, and also the difference in surface reflectance between the concavity and the convexity is effectively corrected at the uneven pit portion with memorized information.

Abstract: A method for preparing an optical memory medium having forming an uneven guide groove on a plastic resin existing directly or through another layer on a heat-resistant sheet, and laminating an optical recording layer on the surface of the resin layer having said uneven guide groove.

Abstract: An optical disk having a pair of axially oppositely directed faces and an annular outer periphery is made by first forming a mold cavity corresponding to the shape of the disk between a pair of axially spaced parts and a demolding ring sandwiched between the parts. The cavity is then filled with a hardenable resin such that the parts form the respective faces and an inner periphery of the ring forms the outer periphery of the disk and the resin is at least partially hardened in the cavity. The parts are then axially oppositely separated from each other and from the disk to leave the disk in the ring with both of its faces exposed and the ring is then transversely displaced with the disk engaged in it out from between the mold parts. The disk is then cooled and shrunk such that its outer periphery separates from the inner periphery of the ring and the disk separates from the ring.

Abstract: In an optical-disk manufacturing device in which a disklike plate is coated with an ultraviolet-set resin on one side thereof, pressed against a stamper, and irradiated by ultraviolet rays to transfer a pattern provided in the stamper to the ultraviolet-set resin, the optical-disk manufacturing device has a disklike-plate supplying section which can store a plurality of disklike plates; a resin supplying part for supplying the resin to the disklike plate; a transfer section for transferring the pattern of the stamper to the resin; a disklike-plate removing section for removing the disklike plate after transferring; and a transport device to transport the disklike plate from each proceding part to each following part.

Abstract: A bushing for the axial retention and radial centering of a matrix in an injection mold for producing information carriers such as CD's is formed on the underside of its retention shoulder with channels for carrying away the air which tends to be compressed along the outer edge of the shoulder, thereby eliminating streaks or so called schlieren in the information-carrier disk which is produced.

Abstract: A novel optodynamic method and apparatus for the manufacture of an optical record medium of the type having a multiplicity of pits or like optically detectable marks representative of digitized information to be reproduced wherein a stamper is provided which is of quartz glass or like material that transmits ultraviolet radiation and which has a stamping surface shaped as a negative of the optically detectable marks to be created, the stamping surface is pressed against a blank sheet of polycarbonate or like plastic that absorbs ultraviolet radiation the surfaces of blank sheet is irradiated with ultraviolet light through the stamper whereby the surface of the blank sheet gels, or softens, to permit the optically detectable marks to be impressed thereon. The stamping may be dome in a partial vacuum in order to assure closer contact between the stamper and the blank sheet.

Abstract: A roll stamper for continuously preparing a substrate used for optical recording mediums, having a convexity and concavity preformat pattern, is prepared by a process comprising the steps of forming a low-melting metal layer on a roll substrate, and forming an auxiliary layer comprising a material different from that of a stamper, on the back of the stamper having on its surface a pattern corresponding with a convexity and concavity preformat pattern. The stamper is overlaid on the roll substrate in such a manner that the low-melting metal layer comes into contact with the auxiliary layer, and thereafter the low-melting metal layer is melted so that the stamper is fixed to the roll substrate.

Abstract: Disclosed herein is an apparatus for manufacturing an optical substrate which has a transfer layer corresponding to an optical pattern by supplying a liquid radiation-setting resin between a stamper carrying the optical pattern and the substrate and by setting the radiation-setting resin. The apparatus includes a turnable, a center boss, gas pressure control mean, and a defoaming means including an outer circumferential means to defoam the radiation-setting resin. The turnable, the center boss and the gas pressure control means are united into a carriage base which is movable on the casing of the apparatus.

Abstract: A mold for forming an optical disk base provided with a movable specular plate, a stationary specular plate, and an annular stamper having inner and outer peripheral edges. The reverse surface of the stamper is in contact with one of the specular plates, and the stamper is supported at its inner end portion by an inner stamper retainer and at its outer end portion by an outer stamper retainer. A cavity is formed between the stamper and the other one of the specular plates when the mold is closed.

Abstract: On a cemented carbide alloy disk or a cermet disk having been coated with either an iridium (Ir) alloy film or a ruthenium (Ru) alloy film is formed guide grooves by photography or ECR ion etching. The disk thus obtained is used as an optical or magnetic disk stamper. Next, a glass or aluminium disk is placed between a pair of stampers obtained as above and molded under pressure while heating thereby to make guide grooves of an optical or magnetic disk.

Abstract: A method for producing an optical disk base to store, record, and retrieve sounds, images, and information. An improved method for producing an optical disk base includes the steps of injecting a photo-curable resin into a cavity, curing the photo-curable resin by irradiation with light, and demolding, where the photo-curable resin is injected from an injection nozzle having an outside diameter which is substantially equal to the diameter of the center hole of the optical disk base and also having a horn-shaped opening at the forward end. The injection nozzle is arranged at the center of the optical disk base. The forward end of the nozzle is closed after injection and the photo-curable resin is irradiated with light, with the injection nozzle projected into the cavity. A liquid resin is injected in the form of uniform flow without entrapped bubbles, so that the anamolous molecular orientation is avoided and the contamination with insufficiently cured or uncured resin is also avoided.

Abstract: A reproducible molding die including a base structure having an unevenness pattern, and a cleaning layer disposed on the surface of the base structure having the unevenness pattern, wherein the cleaning layer is removable while substantially retaining the unevenness pattern of the base structure. By using above-mentioned molding die, a possible molding residue left in a molding step can easily be removed together with the cleaning layer.

Abstract: A radiation-sensitive carrier body directly utilized as a stamper has a glass substrate, a first highly adhesive layer securely adhered to the substrate, a radiation-sensitive layer which discharges a gas component upon being irradiated with a laser beam and which locally forms a protuberance due to the absorbed energy, a second highly adhesive layer securely adhered to the specific material of the radiation-sensitive layer and which deforms in accordance with deformation of the layer, and a metal layer which has a high releasability to allow easy separation from a optical disk substrate material such as an acrylic material when the carrier body is used as a stamper substrate for manufacturing optical disks. A protuberance formed on the carrier body such as a continuous spiral protuberance allows formation of a corresponding spiral groove in the acrylic material, serving as a pre-track into which desired information will be digitally written by a user.

Abstract: Method and apparatus for injection compression molding of thermoplastic parts. A preferred apparatus (100) includes a platen assembly 106, a toggle clamp assembly 102, a screw injection assembly 101, a hydraulic system suitable for providing power to the toggle clamp assembly 102 and the screw injection assembly 101, and a control system 88 for operatively controlling the various hydraulic devices associated with the molding apparatus. The platen assembly 106 provides for a plurality of variable-volume mold cavities 7. In one embodiment, enlarged mold cavities 7 receive plasticized resin from the screw injection assembly 101, and compression of the injected resin is provided by the toggle clamp assembly 102. In another embodiment, the platen assembly 106 includes a floating die assembly wherein pressure created by injected resin causes die inserts 5 and support pillars 15 to slide relative to a molding plate 74. Compression in this embodiment is also preferably provided by the main toggle clamp assembly 102.

Abstract: A process for the preparation of a substrate for an optical disk having spiral or concentric guide grooves formed on the surface thereof, which comprises the steps of casting a radiation- and heat-curable liquid resin mixture between a duplicating mold and a transport substrate, curing the liquid resin mixture by irradiating it with radiation from the side of the transparent substrate, peeling the molded body from the duplicating mold and heat-polymerizing the obtained molded body by heating, wherein a mixture comprising a liquid resin having a terminal acrylic group and/or a terminal methacrylic group and an organic peroxide is used as the radiation- and heat-curable liquid resin mixture.

Abstract: An electrostatic capacitance type information signal recording disc comprises a laminated plate made up of a first sheet which is made from an inexpensive conductive or non-conductive material and is used as a core material and a second sheet which is made from a conductive material and is bound on at least one surface of the first sheet, and variations in geometrical configuration formed on the second sheet in accordance with information signals which are to be recorded. A method of manufacturing the disc comprises the steps of binding the second sheet on at least one surface of the first sheet so as to obtain a laminated sheet, cutting the laminated sheet into a plurality of laminated plates having a predetermined size, and compression molding the variations in geometrical configuration, in accordance with information signals which are to be recorded, on a recording part of the second sheet of each of the laminated plates supplied in succession.

Abstract: The molding apparatus for molding compact discs defines an openable mold cavity and the information bearing disc which forms the impression on the compact disc in held in place by vacuum in the mold cavity in order to allow ready and easy removal and replacement of the insert when necessary.

Abstract: A sprue part is cut and removed from the injection mold part during the manufacture of information storage disks by an injection molding process. The highly sensitive molding of an information storage disk is protected from damage by the sprue and the deposition of dust particles during stripping by this process. The sprue is punched into a part serving as the die of the injection molding tool and subsequently removed, in particular by suction, through an orifice leading from inside the part, together with the dust particles generated in the punching process. Preferably, the sprue is punched out and removed with the injection molding tool closed. The injection molding tool must be opened only after the sprue and the dust have already been removed, thus ensuring that the molded product has an especially good quality.

Abstract: In a method for forming articles by injection molding, in which a melted plastic material is injected into a cavity formed between a movable die and a stationary die, the method including the steps of injecting the melted plastic material into the cavity under the condition of substantially no pressure, and pressing the movable die against the stationary die during or after injection so as to press-mold the article.

Abstract: Two matrices, each bearing modulation to form a microgroove disc record, are fixed to half-moulds by means of sleeves, having first and second fixing flanges which extend into the gap between the matrices. One of the flanges is an annular blade whose inner radial surface defines the edge of a moulded disc and whose thickness is slightly less than that of the moulded disc. Formed integrally with, or attached to, the blade is a group of radially outwardly extending lugs which are attached to the body of its associated sleeve. The other flange comprises a second group of lugs mounted to the body of its associated sleeve radially outward of the blade such that the second group of lugs may lie in the spaces between the first mentioned group of lugs. The thickness of the lugs of the second group determines the thickness of the disc and the thickness of the lugs of the first and second groups differs, to determine a gap for escape of air along the first flange.

Abstract: The invention provides a process for manufacturing optical disks by pressing and disks obtained by such a process, for improving the inherent flatness of the optical disk of the thick type, obtained by a process of pressing between a recorded master and another master, recorded or not depending on whether it is a question of a single or double side disk, this latter being formed from a stack of at least two thin sheets of thermoformable material subjected to a pressure-temperature cycle after which bonding together of the sheets and duplication of the information from the masters for information recording are obtained.