1. Field of the Invention
The present invention relates to an optical disk and a method for producing the same. In particular, the present invention relates to an optical disk in which a substrate on an incident side of laser light is thinner, and a method for producing the same.
2. Description of the Related Art
In recent years, various studies have been conducted on the recording of optical information in the field of information recording. Recording of optical information can be conducted at higher density, and optical information can be recorded/reproduced in a non-contact manner; therefore, as a method for realizing the recording/reproducing of optical information at a low cost, applications for use in a wide range are being realized. Examples of current optical disks include those having a structure in which an information layer is provided on a transparent resin substrate with a thickness of 1.2 mm and protected by an overcoat or those having a structure in which an information layer is provided on one side or both sides of a transparent resin substrate with a thickness of 0.6 mm, and two substrates are attached to each other.
Recently, in order to increase the recording density of an optical disk, a method for increasing a numerical aperture (NA) of an objective lens, a method for shortening a wavelength of the laser to be used, and the like have been considered. As the thickness of a recording/reproducing side substrate (i.e., substrate on an incident side of laser light) becomes smaller, the influence of aberration on a laser spot can be decreased, and an allowable value of a tilt of a disk can be increased. Because of this, it is proposed that the thickness of a recording/reproducing side substrate, a NA, and a laser wavelength are prescribed to be about 0.1 mm, about 0.85, and about 400 nm, respectively.
In a current DVD (digital versatile disk), mainly, a method is used in which two transparent resin substrates (thickness: 0.6 mm), on which film formation and the like are conducted, are attached, with radiation curable resin. Even when the thickness of a recording/reproducing side substrate becomes about 0.1 mm for the purpose of achieving high density, it is desirable to attach substrates to each other by the same method using the same facility as those currently used.
However, with an optical disk in which two substrates are attached to each other, it is necessary to enhance durability. Furthermore, when the centers of two substrates are shifted from each other, deflections occur when the optical disk is rotated. Therefore, it is required to align the centers of two substrates with each other with high precision. There also is a demand for a method for easily producing such optical disks.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical disk that is recordable at high density by attaching two substrates to each other, and a method for producing the same.
In order to achieve the above-mentioned object, an optical disk of the present invention includes a first substrate having a signal area on a principal plane and a central hole A and a second substrate that is transparent and attached to the first substrate, wherein the second substrate is thinner than the first substrate and has a central hole B whose diameter is larger than that of the central hole A, and the first substrate and the second substrate are attached to each other with an adhesive member disposed therebetween so as to extend at least from an inner peripheral edge of the second substrate to an outer peripheral edge thereof.
According to the above-mentioned configuration, an easy-to-handle optical disk is obtained that is capable of conducting high-density recording. Because of this, when a disk is handled, cracking or peeling of a contact portion can be prevented. The term xe2x80x9cradiationxe2x80x9d used herein includes a particle wave such as an electron beam and ultraviolet-rays and an electromagnetic wave.
In the above-mentioned optical disk, the adhesive member may be radiation curable resin. According to this configuration, an optical disk can be produced easily.
In the above-mentioned optical disk, a thickness of the second substrate may be in a range of 0.03 mm to 0.3 mm. According to this configuration, in particular, an optical disk that is recordable at high density can be obtained.
In the above-mentioned optical disk, the central hole B may be larger than a clamp area of the optical disk. According to this configuration, an optical disk can be fixed stably. Furthermore, when an optical disk is clamped, the second substrate can be prevented from peeling.
In the above-mentioned optical disk, the adhesive member may be disposed on an outer peripheral side of a clamp area or disposed so as to cover the entire clamp area. According to this configuration, since a thickness of the clamp area can be rendered uniform, a tilt is prevented from occurring during recording/reproduction.
In the above-mentioned optical disk, a thickness of a clamp area of the first substrate may be in a range of 1.1 mm to 1.3 mm.
In the above-mentioned optical disk, the first substrate includes, on the principal plane, at least one selected from the group consisting of a convex portion formed in a circular shape so as to surround the central hole A and having an outer diameter equal to or smaller than a diameter of the central hole B, and a concave portion formed in a circular shape so as to surround the central hole A and having a diameter equal to or smaller than the diameter of the central hole B.
In the above-mentioned optical disk, a height of the convex portion may be larger than a sum of a thickness of the second substrate and a thickness of the adhesive member.
In the above-mentioned optical disk, an average thickness of the adhesive member may be in a range of 0.5 xcexcm to 30 xcexcm.
In the above-mentioned optical disk, the optical disk is adapted for reproduction of information by application of a laser having a wavelength of 450 nm or less. According to this configuration, in particular, information can be recorded at high density.
Furthermore, a first method for producing an optical disk of the present invention including a first substrate having a central hole A and a second substrate that is transparent and has a central hole B whose diameter is larger than that of the central hole A includes the processes of: (a) bringing the first substrate having a signal area on a principal plane and the second substrate that is thinner than the first substrate into contact with each other with radiation curable resin interposed therebetween so that the principal plane faces inside; and (b) irradiating the radiation curable resin with radiation to cure the radiation curable resin, thereby attaching the first substrate to the second substrate, wherein, in the process (a), the radiation curable resin is disposed so as to extend at least from an inner peripheral edge of the second substrate to an outer peripheral edge thereof.
According to the first production method, an easy-to-handle optical disk that is recordable at high-density can be produced easily.
In the first production method, a thickness of the second substrate may be in a range of 0.03 mm to 0.3 mm.
In the first production method, the process (a) may include interposing the radiation curable resin between the first and second substrates, and rotating the first and second substrates to draw the radiation curable resin. According to this configuration, the thickness of resin easily can be rendered uniform.
In the first production method, the process (a) may include pouring the radiation curable resin onto the first substrate, rotating the first substrate to coat the first substrate with the radiation curable resin, and bringing the first substrate and the second substrate into contact with each other with the radiation curable resin interposed therebetween.
In the first production method, in the process (a), the first substrate and the second substrate are brought into contact with each other in a vacuum atmosphere. According to this configuration, air bubbles can be prevented from entering between the first substrate and the second substrate. The term xe2x80x9cvacuum atmospherexe2x80x9d as used here refers to an atmosphere with a reduced pressure (e.g., an atmosphere of 1000 Pa or less).
In the first production method, the first substrate may include, on the principal plane, at least one selected from the group consisting of a convex portion formed in a circular shape so as to surround the central hole A and having an outer diameter equal to or smaller than a diameter of the central hole B, and a concave portion formed in a circular shape so as to surround the central hole A and having a diameter equal to or smaller than that of the central hole B.
In the first production method, a height of the convex portion may be larger than a sum of a thickness of the second substrate and a thickness of the radiation curable resin.
Furthermore, a second method for producing an optical disk of the present invention includes the processes of: (A) bringing a first substrate having a signal area on a principal plane and a central hole A and a second substrate that is transparent and thinner than the first substrate into contact with each other with radiation curable resin interposed therebetween so that the principal plane faces inside; (B) irradiating the radiation curable resin with radiation to cure the radiation curable resin, thereby attaching the first substrate to the second substrate; and (C) removing a part of the second substrate to form a central hole B whose diameter is larger than that of the central hole A in the second substrate, wherein, in the process (A), the radiation curable resin is disposed so as to extend at least from an outer periphery of a position where the central hole B is formed to an outer peripheral edge of the second substrate.
According to the second production method, an easy-to-handle optical disk that is recordable at high density can be produced.
In the second production method, a thickness of the second substrate may be in a range of 0.03 mm to 0.3 mm.
In the second production method, the process (A) may include interposing the radiation curable resin between the first and second substrates, and rotating the first and second substrates to draw the radiation curable resin.
In the second production method, the process (A) may include pouring the radiation curable resin onto the first substrate, rotating the first substrate to coat the first substrate with the radiation curable resin, and bringing the first substrate and the second substrate into contact with each other with the radiation curable resin interposed therebetween.
In the second production method, in the process (A), the first substrate and the second substrate are brought into contact with each other in a vacuum atmosphere.
Furthermore, a third method for producing an optical disk of the present invention includes the processes of: (i) opposing a first substrate in which a central hole A with a diameter dA is formed to a second substrate in which a central hole B with a diameter dB is formed with radiation curable resin interposed therebetween so that a center of the first substrate is aligned with a center of the second substrate; and (ii) irradiating the radiation curable resin with radiation to cure the radiation curable resin, wherein dA less than dB, and a thickness of the second substrate is in a range of 0.03 mm to 0.3 mm.
According to the above-mentioned configuration, an optical disk that is recordable at high density can be produced with good precision.
In the third production method, in the process (i), the center of the first substrate is aligned with the center of the second substrate by using a pin that fits in the first and second central holes A and B. According to this configuration, it is easy to align the center of the first substrate with the center of the second substrate. As a result, an optical disk can be obtained in which deflections are unlikely to occur even when the optical disk is rotated at a high speed during recording/reproduction.
In the third production method, the process (i) may include the processes of: (i-1) fixing the second substrate on a table in which the pin is disposed so that the pin is inserted into the central hole B; (i-2) pouring the radiation curable resin onto the second substrate; (i-3) moving the first substrate so that the pin is inserted into the central hole A, thereby opposing the first substrate to the second substrate with the radiation curable resin interposed therebetween; and (i-4) rotating the first and second substrates to draw the radiation curable resin. According to this configuration, the thickness of the radiation curable resin can be rendered uniform. Therefore, an optical disk with good productivity and reliability can be produced.
In the third production method, the pin may include a first pin that fits in the central hole A and a second pin that fits in the central hole B, in the process (i-1), the second substrate may be fixed with the second pin, and in the process (i-3), the first substrate may be fixed with the first pin.
The third production method may include, after the process (i-1) and before the process (i-2), lowering an upper surface of the second pin below an upper surface of the second substrate.
In the third production method, the second pin may have a cylindrical shape, and the first pin may be inserted into the second pin.
Furthermore, a fourth method for producing an optical disk of the present invention is a method for producing an optical disk including a first substrate in which a central hole A with a diameter dA is formed and a second substrate in which a central hole B with a diameter dB is formed, including the processes of: (I) coating at least one substrate selected from the group consisting of the first substrate and the second substrate with radiation curable resin; (II) opposing the first substrate to the second substrate with the radiation curable resin interposed therebetween in a vacuum atmosphere so that a center of the first substrate is aligned with a center of the second substrate; and (III) irradiating the radiation curable resin with radiation to cure the radiation curable resin, wherein dA less than dB, and a thickness of the second substrate is in a range of 0.03 mm to 0.3 mm.
According to the fourth production method, an optical disk that is recordable at high density can be produced. Furthermore, the first substrate and the second substrate are opposed to each other in vacuum, so that air bubbles can be prevented from entering therebetween.
In the fourth production method, in the process (II), the center of the first substrate is aligned with the center of the second substrate by using a pin that fits in the first and second central holes A and B. According to this configuration, it is easy to align the center of the first substrate with the center of the second substrate.
In the fourth production method, the process (II) may include the processes of: (II-1) fixing the second substrate on a table in which the pin is disposed so that the pin is inserted into the central hole B; and (II-2) in a vacuum atmosphere, moving the first substrate so that the pin is inserted into the central hole A, thereby opposing the first substrate to the second substrate with the radiation curable resin interposed therebetween. According to this configuration, by fixing a second thin substrate on a table, the surface of the second substrate can be rendered flat; as a result, the thickness of the radiation curable resin can be rendered uniform. Furthermore, according to this configuration, air bubbles can be prevented from entering between the first substrate and the second substrate.
In the fourth production method, the pin may include a first pin that fits in the central hole A and a second pin that fits in the central hole B, in the process (II-1), the second substrate may be fixed with the second pin, and in the process (II-2), the first substrate may be fixed with the first pin.
The fourth production method further may include, after the process (II-1) and before the process (II-2), lowering an upper surface of the second pin below an upper surface of the second substrate.
In the fourth production method, the second pin may have a cylindrical shape, and the first pin may be inserted into the second pin.
Furthermore, a production apparatus of the present invention is an apparatus for producing an optical disk including a first substrate in which a central hole A is formed and a second substrate in which a central hole B is formed, including: a coating member for coating at least one substrate selected from the group consisting of the first substrate and the second substrate with radiation curable resin; a disposing member for disposing the first substrate and the second substrate so that a center of the first substrate is aligned with a center of the second substrate; and an irradiating member for irradiating the radiation curable resin with radiation.
According to the above-mentioned apparatus for producing an optical disk, the third and fourth production methods of the present invention can be conducted easily.
In the above-mentioned production apparatus, the disposing member may include a pin that fits in the first and second central holes A and B.
In the above-mentioned production apparatus, the pin may include a first pin that fits in the central hole A and a second pin that fits in the central hole B.
In the above-mentioned production apparatus, the second pin may have a cylindrical shape, and the first pin may be inserted into the second pin.
In the above-mentioned production apparatus, the disposing member may include a table for fixing the at least one substrate.
In the above-mentioned production apparatus, the disposing member further may include a container surrounding the table and an exhaust member for exhausting the container.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.