METHOD OF MANUFACTURING RECORDING DISCS

Abstract: A method of manufacture suitable for producing data recording discs such as video recording discs is disclosed whereby each disc is formed as an extremely thin sandwich structure comprising a base disc having recorded data formed on a surface thereof, a layer of data recording medium, e.g. having high reflectivity, formed over the base disc data recording surface, and a protective layer formed over the recording medium material. The base disc and protective layer are formed of synthetic resin which is hardened by means such as application of ultra-violet radiation, and an integrally bonded structure is formed which is free from warping due to atmospheric water vapor absorption even if the disc is made extremely thin.

Description: TITLE OF THE INVENTION Method of Manufacturing Recording Discs BACKGROUND OY THE INVENTION The present invention relates to a method of manufacturing data recording discs, and in particular to a method of manufacturing an optical playback type of recording disc. In the prior art, data recording discs have been manufactured by methods such as injection molding or the 2P photo-polymer method. With such methods, a base disc is first formed, having necessary data recorded on one side thereof, i.e. as a patterned portion of the surface of that side. A material suitable for forming a data recording medium, (i.e. having properties suitable for reflecting a light beam used to read data from the disc) is then coated on the face of the base disc containing the recorded data. However such a recording disc has a two-layer construction, i.e. a base disc and a layer of recording medium material formed thereon, and as a result, absorption of water vapor from the atmosphere can result in warping of the recording medium layer. This is a serious disadvantage of this prior art methods of manufacture. As a measure for preventing such warping it has been proposed to bond a disc which is identical to the base disc, onto the layer of recording medium material, to thereby cancel the tendency to warp as a result of absorption of moisture. However, such bonding of an additional base disk will result in increased complexity of the manufacturing process for producing the data recording discs and difficulties with regard to quality control. Furthermore if such bonding means are employed, the thickness of each data recording disc is appreciably increased, so that the cost of material required to form each disc is increased. Furthermore, the weight of each disc is increased, and hence a greater amount of power must be applied to the drive equipment of the playback apparatus used with such discs. SUMMARY OF THE INVENTION It is an objective of the present invention to provide a method of manufacturing data recording discs which overcomes the problems of prior art methods, as set out above. To this end, a method of manufacturing data recording discs according to the present invention basically comprises: depositing a specific amount of a synthetic resin, of a type adapted to be rapidly converted from the liquid to a hard solid state by the application of specific processing thereto, upon a face of a master disc having data recorded as a surface pattern upon that face, then sandwiching the synthetic resin between the master disc and a flat surface of a plate and performing hardening processing upon both sides of the synthetic resin layer thus formed, by processing means acting through the master disc and the flat plate, to thereby form the synthetic resin into a base disc; separating the base disc from the the master disc and forming a layer of a material for use as a recording medium upon a copy face of the base disc, the copy face having formed thereon a copy of the data on the data recording face of the master disc, the recording medium material layer being preferably formed by a thin film deposition process; forming a second layer of synthetic resin, having similar hardening properties to the first layer of synthetic resin, over the recording medium material layer and then placing a second flat plate upon the hardening type of synthetic resin, performing hardening processing of the second layer of synthetic resin on both sides thereof by processing means acting through the first flat plate and the second flat plate, to thereby form the second layer of synthetic resin into a protective layer; separating the structure formed by the above steps, consisting of the layer of recording medium material sandwiched between the base disk and the protective layer, from the first and second flat plates; and shaping this sandwich-configuration structure into a predetermined shape to thereby form a data recording disc. BRIEF DESCRIPTION OF THE DRAWINGS Fig. l(a) to l(e) are diagrams for assistance in describing steps in a method of manufacture of data recording discs according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. l(a) to l(e) show steps of an example of a method of manufacturing data recording discs according to the present invention. In a first step, illustrated in Fig. l(a), a specific amount of an ultra-violet radiation hardening type of synthetic resin, in liquid form, is dropped onto the data recording face of a master disc 1, forming a layer of the resin thereon. An example of a suitable resin is 2.2 BIS [ 4-(acryloxy diethoxy)phenyl)propane, made by Osaka Yukikagaku Kogyo Co. Ltd., or Shinnakamura Kagaku Kogyo Co. Ltd. The master disc 1 is transparent to ultra-violet radiation, and has specific data recorded on the data recording face thereof, i.e. as a surface pattern formed on that face. A flat plate 3,- formed of a material transparent to ultraviolet radiation and having the the opposing faces thereof shaped accurately flat and mutually parallel, is then placed, by being moved slowly downward, onto the synthetic resin that was dropped onto master disc 1. The flat plate 3 is preferably formed of a material such as quartz glass or acryl, etc. Care must be taken to place the flat plate 3 onto the synthetic resin in a gradual manner, so as to avoid the inclusion of air bubbles within the resin. Next, pressure is applied to the top face of the flat plate 3, by mechanical means acting through a pressure plate, for several seconds. This action serves to increase the accuracy of forming a base disc during this step. A layer of synthetic resin 2 is thereby formed, sandwiched between the flat plate 3 and the master disc 1. Ultra-violet radiation is then directed from below onto the master disc 1, from an ultra-violet radiation source 4, and is also directed from above onto the flat plate 3 from an ultra-violet radiation source 5, to thereby irradiate the layer of synthetic resin 2 uniformly on both sides thereof. The intensities of radiation applied to the upper and lower faces of the layer of synthetic resin 2 in this way are preferably made substantially identical, for example a radiation intensity of 2 approximately 1 Kw/cm2 as measured at the center of an irradiated face, applied for approximately 5 seconds. The synthetic resin layer 2 is thereby hardened by the ultra-violet radiation, to form a base disc 6. The thickness of the base disc 6 thus formed is determined by a spacer 7. It should be noted that it is an important feature of the method of the present invention that the ultraviolet radiation is directed through both the master disc 1 and the flat plate 3, onto both sides of the resin layer 2. If the ultra-violet radiation were to be directed only onto one side, then the warping phenomenon described above, resulting from the effects of absorption of atmospheric moisture, would occur with the base disc 6. However with the method of the present invention as described, this warping of base disc 6 is effectively prevented. Next, in the step shown in Fig. 6(b), the base disc 6 is separated from the master disc 1, and a masking cover 8 is attached to the base disc 6 with the flat plate 3 remaining attached thereto. The masking cover 8 is shaped such as to mask certain parts of the base disc 6. Generally speaking, these will be a peripheral portion and a central portion of base disc 6. A layer of recording medium material 9 is then formed on the face of the base disc 6 which has the recording data copied thereon, but only on these portions of that face which are not masked by the masking cover 8. In the case of manufacturing an optical type of data recording disc, the recording medium material should be suitable for producing a reflective surface. The layer of recording medium material 9 is preferably formed by a thin-film deposition process, such as vacuum evaporative deposition, sputtering deposition, ion plating using PVD, etc. The source of recording medium material utilized in this deposition process is denoted by reference numeral 10 in Fig. l(b). Next, as shown in Fig. l(c), the base disc 6 with the layer of recording medium material 9 formed by the above thin-film deposition process thereon and having the flat plate 3 still attached thereto, is removed from the masking cover 8, and similar processing to that shown in Fig. l(a) is repeated. That is to say, a specific quantity of ultra-violet radiation hardening type of synthetic resin, in liquid form, is dropped onto the surface of the layer of recording medium material 9, then a flat plate 3' which is precisely machined flat and is transparent to ultra-violet radiation, is placed upon the latter synthetic resin, and force applied to plate 3' to thereby form the layer of synthetic resin 2' shown in Fig. l(c). Ultraviolet radiation is then directed from below, by an ultra-violet radiation source 4', through the flat plate 3', and is directed from above from an ultraviolet radiation source 5' through the flat plate 3, onto opposite sides of the synthetic resin layer 2'. In this way, the synthetic resin 2' is hardened to thereby form a protective layer 11. The thickness of the protective layer 11 is determined by a spacer 12. Since portions of protective layer 11 and base disc 6 are in direct contact (as a result of the masking of portions of base disc 6 by masking cover 8 as described above prior to formation of layer 9) and are both formed of synthetic resin, the protective layer 11 and base disc 6 become mutually bonded with an extremely high value of attachment strength. A structure has at this stage been formed, consisting of the layer of recording medium material 9 sandwiched between the protective layer 11 and the base disc 6. The flat plates 3 and 3' are now separated from this sandwich structure, which is then machined by a doughnut cutter" type of cutting tool 13 as shown in Fig. l(d3, to remove central and peripheral portions of the structure and thereby establish the shape of the disc. The completed data recording disc 14 is thereby formed, as illustrated in Fig. l(e). Assuming that the diameter of the layer of synthetic resin 2 formed in the first step of the process describe above is approximately 200 mmand the thickness thereof is approximately 100 m, then the amount of synthetic resin required at this stage of the process, to form each recording disc, is approximately 3 milliliter. The amount of synthetic resin required to form the protective layer 11 will of course be substantially less than this, so that it can be understood that the method of the present invention enables data recording discs to be produced by utilizing extremely small amounts of material, so that manufacturing costs can be held at a low level. A data recording disc manufactured by the process described above can have a thickness of approximately 50 to 200 rim. However as described above, in spite of this extreme thinness, negligible deformation of such a disc will occur as a result of absorption of atmospheric moisture, so that the warping phenomenon described above will not occur. Thus, in-addition to the above process being an extremely efficient method of manufacturing data recording discs, the process makes it unnecessary to perform bonding of an additional base disc onto the recording medium layer, as proposed in the prior art in order to overcome this problem of warping, as described hereinabove. Thus, the problems associated with such a prior art method are avoided. Although with the embodiment described above, a synthetic resin material which is hardened by ultraviolet radiation is employed, it would be equally possible to utilize a synthetic resin material which is hardened by the application of heat. It can therefore be understood from the above description that with the method of manufacture of the present invention, data recording discs can be manufactured which can be extremely thin, yet are free from warping, and that the manufacturing process is highly efficient, enabling reductions in manufacturing costs to be attained. Although the present invention has been described in the above with reference to a specific embodiment, it should be noted that various changes and modifications to the embodiment may be envisaged, which fall within the scope claimed for the invention as set out in the appended claims. The above specification should therefore be interpreted in a descriptive and not in a limiting sense.

Claims: WHAT IS CLAIMED IS 1. A method of manufacturing a data recording discs, comprising the steps of: depositing a specific amount of a hardening type of synthetic resin, in liquid form, upon a data recording face of a master disc, said master disc being transparent to a specific form of radiation energy; sandwiching said synthetic resin between said master disc and a flat plate, said flat plate being transparent to said radiation energy, and applying force acting on said flat plate, to form a thin layer of said resin; performing hardening processing of said layer of synthetic resin on both sides thereof by exposing said sides to radiation energy passed through said master disc and said flat plate to thereby form said synthetic resin layer into a base disc; separating said base disc from said said master disc; ; forming a thin layer of a recording medium material upon a copy face of said base disc which has been copied from said data recording face of said master disc; depositing a specific amount of said hardening type of synthetic resin, in liquid form, upon said recording medium material layer; placing a second flat plate upon said synthetic resin, said second flat plate being transparent to said radiation energy, and applying force to said second flat plate to form said synthetic resin into a flat layer; ; performing hardening processing of said synthetic resin layer from both sides thereof by exposing said sides to said radiation energy through said first flat plate and said second flat plate, to t#hereby form said synthetic resin into a protective layer and so form a structure comprising said layer of recording medium material sandwiched between said protective layer and said base disc; separating said sandwich-configuration structure from said first and second flat plates, and; machining said sandwich-configuration structure into a predetermined disc shape. 2. A method of manufacturing data recording discs according to claim 1, and further comprising a step of masking specific regions of said recording face of said base disc immediately prior to said step of forming said layer of recording medium material thereon. 3. A method of manufacturing data recording discs according to claim 1, in which said synthetic resin employed to form said base disc and said protective layer is hardened by the action of utra-violet radiation, and in which said master disc and said first and second flat plates are transparent to ultra-violet radiation, with said step of hardening said synthetic resin to form said base disc comprising the directing of ultra-violet radiation through said master disc and said first flat plate, and said step of hardening said synthetic resin to form said protective layer comprising the directing of ultra-violet radiation through said first flat plate and said second flat plate.

Inventors: KOMATSUBARA, SHIGEMARU
Applicants: VICTOR COMPANY OF JAPAN, LIMITED
Application year: 1986
Main classification: G11B7
IPC codes: B29D11, G11B7