Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-09-12
2004-06-01
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S246000, C156S275500, C156S275700, C156S286000, C156S289000, C369S275200, C369S275400
Reexamination Certificate
active
06743320
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a manufacturing method and an optical information recording medium, and more specifically relates to a multilayer manufacturing method and a multilayer optical information recording medium.
2. Description of the Prior Art
In recent years, various types of optical information recording technology have been studied. According to the optical information recording, high density recording and non-contact recording/reproduction can be realized at a low cost. The method therefore has begun to be applied to various technical fields. An optical disk is used as a medium for the optical information recording. Optical disks are roughly classified into three types: read-only type; additional written type; and rewritable type. All the types of optical disks are commercialized and widely distributed. For example, the read-only type disk is distributed as a disk called as a compact disk (CD) on which music data is recorded or a laser disk (LD) on which image data is recorded. The additional written type disk is used for a document file or a still picture file. The rewritable type disk is used for a data file for a personal computer, or the like. The optical disk is formed in a structure in which an information recording layer is formed on a transparent resin substrate having a thickness of 1.2 mm and covered with an overcoat layer, or a structure in which an information recording layer is formed on one side or both sides of a transparent resin substrate having a thickness of 1.2 mm and the two substrates are bonded to each other.
In addition thereto, a digital versatile disk (DVD) having a larger capacity has been developed and commercialized to record not only audio data, but also video data such as a movie, and has begun to be popularized. In order to realize a high-density optical disk, a laser light beam having a short wavelength and an objective lens having a large numerical aperture (NA) are used. With use of the laser light beam having a short wavelength and the objective lens having a large NA, however, the tolerance of the inclination angle (tilt) of the disk to the incident direction of the laser beam will be decreased. In order to increase the tolerance of the tilt of the disk, it is effective to decrease the substrate in thickness. For example, in a DVD, the laser beam of the wavelength of 650 nm, and NA of 0.60, and the disk of the thickness of 0.6 mm are used. The resin substrate of 0.6 mm thick has poor mechanical strength and generates a tilt, and thus the DVD is formed by bonding two substrates to each other such that information recording face thereof is inside.
On the other hand, “a one side face reproduction and double layer DVD” has been also put into practical use, in which one substrate having a transparent reflective layer formed of gold, silicon, or the like on the information recording face and another substrate having a reflective layer formed of aluminum or the like on the information recording face are bonded each other such that the information recording faces thereof are bonded each other. For that DVD, the data on the information recording faces are reproduced by emitting a laser beam from the substrate side provided with the transparent reflective layer. Also, a rewritable DVD having the double layer structure as mentioned above in which a rewritable thin film recording layer is formed on the information recording face instead of a metal reflective layer, is also proposed.
Recently, the amount of the information grows larger as exemplarily seen in high definition television broadcasting, and therefore, the recording medium having high density is further required . In order to increase the recording density of the optical disk, various methods have been proposed: forming of the disk having a multilayer structure of more than three layers; increasing the NA of the objective lens; and using a blue-violet laser beam. As the method of forming the multilayer structure, a signal transferring (2P method) using a metal stamper has been widely used.
When the optical disk is formed to the multilayer structure, however, it is difficult to form an information recording face other than that having a groove or asperity pits formed by injection molding. It is proposed to decrease the recording/reproducing substrate in thickness and set the NA at 0.85, and the wavelength of the laser beam at 400 nm because the thinner the recording/reproducing substrate the larger the tolerance of the tilt of the disk, as described before. In a case where the recording/reproducing substrate is formed thinner than 0.3 mm that is the limit to form the groove or pits by the injection molding, the double layer structure cannot be easily formed. Also with use of the metal stamper, some problems will occur because a radiation cured resin film for transferring a signal recording face onto the disk cannot be easily formed uniformly, a radiation cured resin film cannot be formed uniformly and the radiation can not pass easily through the stamper. There are also some problems such that the radiation cured resin cannot be easily cured, a disk manufacturing apparatus is inevitably formed large, and signal transferring requires a long time.
SUMMARY OF THE INVENTION
The present invention intends to provide a manufacturing method of an optical information recording medium and an optical information recording medium having a multilayer structure, and more specifically, the optical information recording medium having a multi optical information recording layer and a thinner recording/reproducing substrate.
In a first aspect of the invention, provided is a method of manufacturing an optical information recording medium. The method comprises bonding a stamper having a principal plane formed with a groove or asperity pits and a second substrate having a thickness of 0.3 mm or less with radiation cured resin so as to cause the groove or the asperity pits to face to the second substrate, the stamper being transparent, the groove or asperity pits having a thin film formed thereon, curing the radiation cured resin, peeling off the stamper to form the groove or the asperity pits on the second substrate, forming a metal film or a recording film on the groove or the asperity pits on the second substrate to create a second information recording layer on the second substrate, and bonding a first substrate and the second substrate on which the second information recording layer is formed, such that the information recording layers are placed between the first and second substrates.
According to the above-mentioned manufacturing method, the optical disk having information recording layers can be formed on the substrate having a thickness of 0.3 mm or less which cannot be formed by the injection molding. Further, when the first substrate is provided with an information recording layer, the optical disk having a double layer structure can be attained.
According to the above-mentioned first manufacturing method, the stamper may be formed by injection molding. With this method, the disk can be formed at a low cost by the conventional optical disk manufacturing apparatus.
Preferably the stamper may be made of resin material, and more specifically, polycarbonate. With this method, a light and low-cost stamper can be attained. With this stamper, the radiation cured resin can be uniformly spread by spinning after overlapping the stamper and the first substrate by the radiation cured resin.
In the above-mentioned method, a metal film or a semimetal film may be formed on the information recording layer of the stamper. With this method, the stamper can be easily peeled off the first substrate.
The metal film may be formed from Al or metal mainly composed of Al. Thus, the stamper can be easily peeled off at a low cost. Further, the semimetal film of the information recording layer of the stamper may be formed from Si (silicon) or metal mainly composed of Si, and the manufacturing at lower cost can be attained.
In the above-mentioned first manufactur
Hayashi Kazuhiro
Hisada Kazuya
Ohno Eiji
Chan Sing P
Matsushita Electric - Industrial Co., Ltd.
Mayes Curtis
Wenderoth , Lind & Ponack, L.L.P.
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