JPS6286557A - Information recording medium - Google Patents

Abstract

PURPOSE:To improve a recording characteristic and to execute especially both writing and reading by fitting two substrates forming a recording layer on a pre-groove by adhesive layer facing to the recording layer and providing them so that the adhesive layer does cover the surface of the recording layer. CONSTITUTION:On two diskoid substrates 1a and 1b, pre-groove forming layers 3a and 3b to form pre-grooves 2a and 2b respectively and recording layers 4a and 4b provided on them are provided. The substrates 1a and 1b are fit facing to the recording layers 4a and 4b through bonding layers 5a and 5b formed on the junctioning surface of the outer peripheral end part and the inner peripheral end part of respective surfaces. At such a time, the recording layers 4a and 4b are not covered with the adhesives. Thus, both the writing and reading can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an information recording medium on which information can be written and/or read using a high energy density laser beam. More specifically, the present invention provides a disc-shaped substrate having a bonding surface on each of the outer peripheral edge and the inner peripheral edge of the surface, and a recording layer formed on a pre-groove formed between the re-bonding surfaces. This invention relates to an improvement in an information recording medium in which two sheets of information recording media are bonded together by an adhesive layer so that their respective recording layers face each other.

[Technical Background of the Invention] In recent years, information recording media that use high energy density beams such as laser light have been developed and put into practical use.

This information recording medium is called an optical disk, and is used for applications such as video disks, audio disks, large-capacity still image files, and large-capacity computer disk memories.

The basic structure of optical discs is plastic.

It has a disk-shaped transparent substrate made of glass or the like, and a recording layer made of metal or semimetal such as Bi, Sn, In, Te, etc. provided thereon. Note that the surface of the substrate on which the recording layer is provided is coated with an undercoat layer made of a polymeric substance or a Ci intermediate layer in order to improve the flatness of the substrate, improve the adhesion with the recording layer, and improve the sensitivity of the optical disc. Layers may also be provided.

Information is written on an optical disk by, for example, irradiating the optical disk with a laser beam, and the irradiated portion of the recording layer absorbs the light and locally rises in temperature, causing physical or chemical changes. information is recorded by changing its optical properties. Also reading information from optical discs. This is performed by irradiating the optical disc with a laser beam, etc., and information is reproduced by detecting reflected light or transmitted light according to changes in the optical characteristics of the recording layer.

Since optical discs are required to have improved information recording density and high tracking accuracy, recently it has become common practice to previously provide a spiral tracking pregroove (guide groove) on the substrate.

For example, a substrate provided with pre-grooves is obtained by forming a coated layer of a photocurable polymer material on a stamper corresponding to the pre-grooves, then placing the substrate on the coated layer and irradiating it with ultraviolet rays. The polymer is cured by
Thereafter, the substrate is peeled off from the stamper. and.

A recording layer on which information can be written and/or read by a laser is formed at the bottom of the pregroove.

Information is recorded on the recording medium having the pre-groove by irradiating the recording layer provided on the pre-groove with a laser beam, thereby improving tracking accuracy and recording density. However, since the recording layer itself on the substrate has low mechanical strength, it is easily damaged and dust is easily attached to it, which poses problems such as impeding information recording and reproduction.

To solve this problem, an information recording medium has already been proposed in which two substrates each having a recording layer with a pregroove are directly bonded with an adhesive with the recording layer inside. Publication No. 58-45633).

In optical discs with such a structure, the recording layer is not in direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate. Therefore, the recording layer is generally subject to mechanical damage or In addition, dust does not adhere to the surface and interfere with recording and reproducing information.

However, in the information recording medium disclosed in this publication, the entire surfaces of two substrates are bonded together using an adhesive. That is, the surface of the recording layer is completely covered with adhesive.

Therefore, the recording layer of the recording medium configured in this way has
It is difficult to record information using methods such as forming bits. Furthermore, the adhesive used must not deteriorate the recording layer, which limits the types of adhesives that can be used. Furthermore, since adhesives generally undergo curing shrinkage, when two substrates are entirely bonded together using an adhesive, deformations such as "warp" may occur in the optical disk over time.

[Object of the Invention] An object of the present invention is to provide an information recording medium with improved recording characteristics.

In particular, it is an object of the present invention to provide an improved information recording medium on which information can be both written and read.

[Summary of the Invention] The present invention provides a recording device that has a bonding surface at least at the outer peripheral edge, and in which information can be written and/or read by a laser on a pregroove formed inside the outer peripheral edge bonding surface. In an information recording medium in which two disk-shaped substrates each having layers formed thereon are joined by an adhesive layer so that the respective recording layers face each other, the adhesive layer substantially covers the surface of the recording layer. To provide an information recording medium characterized in that the information recording medium is attached in such a way that there is no problem.

[Effects of the Invention] The information recording medium of the present invention is of a type in which two disc-shaped substrates each having a recording layer formed on a pregroove are joined by an adhesive layer so that the respective recording layers face each other. Although it is an information recording medium.

Since the recording layer is not coated with adhesive, it functions as a recording layer that can be both written to and read from.

In addition, since the recording layer and adhesive are not in substantial contact and the surface of the recording layer is in contact with the gas phase, there are few restrictions on the adhesive used, and deformation such as "warp" can occur. It also has the advantage of being less likely to occur.

[Configuration of the Invention] The information recording medium of the present invention has an external shape as shown in FIG. 1, for example, and a cross-sectional configuration as shown in FIG. 2. However, since the information recording medium of the present invention is substantially symmetrical, only the cross-sectional configuration on the right side of the center line is illustrated to avoid complexity.

In FIG. 2, pregroove forming layers 3a and 3b in which pregrooves 2a and 2b are formed, respectively, are formed on two disc-shaped substrates 1a and lb, and a recording layer attached on the pregrooves (usually at the bottom). Layers 4a, 4b are provided. The substrates 1a and 1b each have an adhesive layer 5a, which is formed on the bonding surface of the outer peripheral edge and the inner peripheral edge of each surface.
They are joined to each other via 5b.

It is preferable that the pregroove 2a, 2b17) sides mytm on both substrates are substantially in contact with each other because mechanical strength is high, but such contact is not essential.

Note that the same material as the recording layer is often formed in layers at the tops of the sidewalls of the pregrooves 2a and 2b, and in that case, contact between the tops of the sidewalls is made through those layers. . In FIG. 2, pregrooves 2a, 2
b is shown with the top and bottom exactly facing each other, in which case adhesive may be applied between the tops of the pregroove side walls.

In addition, in FIG. 2, as mentioned above, the pregroove 2
Although a and 2b are shown so that the upper and lower sides face each other exactly, there is no particular problem even if there is a misalignment between the upper and lower pregrooves.

Further, in the configuration shown in FIG. 2, the pregroove is formed in the pregroove forming layer provided on the substrate, but the pregroove may be formed in advance when molding the substrate. As another embodiment of the information recording medium, an information recording medium in which a pregroove is formed on the substrate itself is shown in FIG. 3 as a cross-sectional view similar to FIG. 2. In FIG. Recording layers 8a and 8b are provided above (usually at the bottom) of pregrooves 7a and 7b formed on substrates 6a and 6b, respectively. Board 6
a, 6b are bonded to each other via adhesive layers 9a, 9b formed on the bonding surfaces of the outer peripheral edge and inner peripheral edge of each surface.

The information recording medium shown in FIGS. 2 and 3 shows an example of the configuration of the information recording medium according to the present invention, and the information recording medium of the present invention is not limited to the above configuration.

The information recording medium of the present invention can be manufactured, for example, by the following method.

The substrate used in the present invention can be arbitrarily selected from various materials used as substrates for conventional information recording media. Optical properties, flatness, processability of the substrate,
In terms of ease of handling, stability over time, and manufacturing cost,
Examples of substrate materials include glass such as soda lime glass; acrylic resins such as cell cast polymethyl methacrylate and injection molded polymethyl methacrylate; vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers; and polycarbonate. I can do it.

Among these, from the point of view of dimensional stability, transparency and flatness, glass such as tempered glass,
Acrylic resin and polycarbonate.

The thickness of the substrate is, for example, about 1.0 to 1.5 mm in the case of an injection molded polymethyl methacrylate substrate.

The surface on which the recording layer is provided is coated with an undercoat layer for the purpose of improving flatness, improving adhesive strength, and preventing deterioration of the recording layer, as well as for improving recording sensitivity and increasing the S/N ratio. Examples of the material for the undercoat layer that may be provided include polymethyl methacrylate and acrylic acid/methacrylic acid copolymer.

Styrene fist maleic anhydride copolymer, polyvinyl alcohol, N-methylol acrylamide, styrene/sulfonic acid copolymer, styrene/vinyltoluene copolymer,
Chlorinated polyethylene, chlorosulfonated polyethylene,
Polymeric substances such as nitrocellulose, polyvinyl chloride, polyester, polyimide, vinyl acetate/vinyl chloride copolymer, ethylene/vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate; organic substances such as silica coupling agents; and inorganic oxides (Si02
, Al120. etc.), and inorganic substances such as inorganic fluoride (MgFz).

When using a glass plate as a substrate, styrene or
Preferably, an undercoat layer made of a polymer having a wood-philic group and/or a maleic anhydride group, such as a maleic anhydride copolymer, is provided.

Furthermore, in order to increase the sensitivity and improve the S/N ratio due to the heat insulation effect, it is preferable to provide an undercoat layer made of polymethyl methacrylate or nitrocellulose.

The undercoat layer can be formed by, for example, dissolving or dispersing the above-mentioned substance in a suitable solvent, and then applying this coating solution to the substrate surface by a coating method such as spin cording, dip coating, or extrusion coating.

Pregrooves are formed on the substrate (or undercoat layer) for the purpose of forming tracking grooves or irregularities representing information such as address signals.

Examples of materials for forming a layer having pregrooves (also referred to herein as a pregroove forming layer) include:
Examples include a mixture of at least one monomer (or oligomer) of acrylic acid monoester, diester, triester, and tetraester and a photopolymerization initiator.

Examples of monoesters of acrylic acid include alkyl acrylates such as ethyl acrylate, n-butyl acrylate, hexyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate; flukoxyalkyl acrylates such as ethoxyethyl acrylate; and phenoxyethyl acrylate. Examples include phenoxyalkyl acrylate; and phenyl acrylate.

Examples of diesters of acrylic acid include alkanediol diacrylates such as 1,3-propanediol diacrylate; and flukene glycol diacrylates such as diethylene glycol diacrylate, tetraethylene glycol diacrylate, and hexamethylene diol diacrylate. .

Examples of triesters of acrylic acid include trimethylolpropane triacrylate, pentaerythritol triacrylate, and the like. Furthermore, an example of the tetraester of acrylic acid is pentaerythritol tetraacrylate. Further examples include oligomeric acrylic esters such as polyethylene glycol acrylate and epoxy acrylate.

Examples of the photopolymerization initiator include benzoin compounds such as benzoin isobutyl ether.

The layer with pregrooves is applied on the substrate, for example, by the method described below.

First, a photocurable polymer material such as the above-mentioned mixture of acrylic acid ester and polymerization initiator is applied in a layer onto a matrix (stambar) corresponding to the precisely made pregroove, and then this coating is applied. After the substrate is placed on the liquid layer, the liquid layer is cured by irradiation with ultraviolet rays through the substrate or the matrix to form a cured layer in which pregrooves are formed, and at the same time, the substrate and the cured layer are fixed. Then, by peeling the substrate from the mother mold, a substrate provided with a layer having pregrooves is obtained.

The layer thickness of the layer with pregrooves is generally from 0.05 to 1100 IL, preferably from 0.1 to 50 μm. Further, as an example of the dimensions of the pregroove, pitch: 2.5 pm.

Examples of dimensions include @: 0.8 JLm and depth: about 260 nm.

As mentioned above, the pregroove may be formed directly on the substrate, or the pregroove may be formed using a method of attaching a resin film with pregrooves formed from a photocurable polymer material to the substrate. It may be attached.

Next, a recording layer is provided on the pregroove.

Examples of materials used for the recording layer include Te, Zn, I
Metals such as n, Sn, Zr, An, Cu, Ga; Bi, A
Metalloids such as S and Sb; semiconductors such as Ge and Si; and alloys thereof or combinations thereof. In addition, sulfides, oxides of these metals or metalloids,
Compounds such as borides, silicon compounds, carbides and nitrides; and mixtures of these compounds with metals can also be used in the recording layer.

The recording layer is formed on the substrate using the above-mentioned materials by a method such as vapor deposition, sputtering, or ion blasting. Note that when the above-mentioned methods such as vapor deposition are used, the generated ephemeris is formed continuously over the entire surface having the pregroove, but the recording layer is formed on the pregroove (usually at the bottom) and is used as a recording layer. This is the layer where

The recording layer may be a single layer or a multilayer, but the layer thickness is generally 100 to 500 ml from the viewpoint of optical density required for optical information recording.
It is in the range of 500 angstroms.

Note that the surface of the substrate opposite to the side on which the recording layer is provided is used to increase scratch resistance, moisture resistance, etc.

For example, a thin film made of an inorganic substance such as silicon dioxide, tin oxide, or magnesium fluoride; or a polymeric substance such as a thermoplastic resin or a photocurable resin may be provided.

Next, the two substrates on which the recording layer has been formed are joined together with the recording layer inside using an adhesive.

The adhesive is not particularly limited, and various known adhesives can be used. Examples of such adhesives include:
Examples include epoxy adhesives, polyurethane adhesives, silicone adhesives, hot melt adhesives, and radiation-curable adhesives. Among these, it is preferable to use radiation-curable adhesives, and in particular from the viewpoint of durability, radiation-curable adhesives that are cured by irradiation with ultraviolet rays, electron beams, etc. are preferable. Examples thereof include (meth)acrylic acid, ( Mention may be made of meth)acrylic esters, (meth)acrylamides, acrylonitriles and derivatives thereof; (meth)acrylic esters of polyhydric alcohols: and mixtures thereof.

Note that a photopolymerization initiator (a polymerization initiator for generating radicals) may be added to the radiation-curable adhesive.
Examples of photopolymerization initiators used for such purposes include benzoin alkyl ethers, benzyl ketals, acetals, acetophenone derivatives, benzophenone derivatives, xanthone derivatives, thioxanthone derivatives, anthraquinone derivatives, benzaldehyde derivatives, and the like. These photopolymerization initiators can be used alone or in appropriate combinations.

Additionally, a silane coupling agent may be used in conjunction with the above adhesive to strengthen adhesion to the substrate.

To join the substrates, for example, the radiation-curable adhesive described above is applied to the bonding surfaces set in an annular shape on the inner and outer edges of the substrates using a transfer printing method, and then the two substrates are bonded together on a plate. This is done by bonding under an inert gas atmosphere such as nitrogen gas so that the grooves are facing each other.

The thickness of the adhesive layer is usually 30 to 80 m.

Next, the adhesive is polymerized and cured by irradiation with electromagnetic radiation such as ultraviolet rays, thereby completing the bonding between the substrates and obtaining the information recording medium according to the present invention.

In addition, in the case of an information recording medium that has a through hole for rotational driving in the center, the substrates are generally bonded together at the outer periphery of the substrate and also at the periphery of the through hole in the substrate, as described above. Although it is carried out on the joint surface provided, it is used as an information recording medium by the applicant of this application
As stated in the specification of patent application (2) filed in Japan,
When using an information recording medium that does not have a rotationally driven through hole in the center, the substrates can be bonded only at the bonding surface provided only at the outer periphery of the substrates.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing an information recording medium of the present invention. FIG. 2 is a sectional view taken along the line XX in FIG. 1, and is a diagram showing an example of the information recording medium of the present invention. FIG. 3 is a diagram showing another example of the information recording medium of the present invention. la, lb, 6a, 6b: substrate

Claims (1)

[Claims] 1. A recording layer that has a bonding surface at least at the outer periphery and on which information can be written and/or read by a laser on the pregroove formed inside the outer periphery bonding surface. In an information recording medium in which two disc-shaped substrates each having a recording layer formed thereon are joined by an adhesive layer such that the respective recording layers face each other, the adhesive layer substantially covers the surface of the recording layer. An information recording medium characterized in that the information recording medium is attached such that there is no. 2. The information recording medium according to claim 1, characterized in that the information recording medium has a through hole for rotational driving in the center, and the bonding surface is further provided on the periphery of the through hole of the substrate. . 3. The information recording medium according to claim 1 or 2, wherein both substrates are bonded by an adhesive layer provided on the bonding surface. 4. Claim 1, characterized in that the recording layers on both substrates are recording layers capable of both writing and reading.
The information recording medium described in item 2 or item 2. 5. The information recording medium according to claim 1 or 2, wherein the tops of the side walls of the pregrooves on both substrates are substantially in contact with each other.