JPH06251420A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain an optical disk having extremely high reliability so that even the optical disk housed in a cartridge having a metal shutter does not cause arc discharge. CONSTITUTION:An optical recording layer and a first protective layer 3 to cover the optical recording layer 2 are successively formed on at least one principal plane of the substrate 1. Further, the second protective layer 4 having smaller surface resistance than the first protective layer 3 is formed on the other principal plane of the sustrate 1. Thereby, even when a charged body touches the cartridge to cause arc discharge, charges transmit the second protective layer 4 formed on the opposite surface of the substrate to the optical recording layer 2 since the second protective layer 4 has smaller surface resistance than the first protective layer 3 which covers the optical recording layer 2. Thus, transmission of charges in the optical recording layer 2 is prevented as possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc such as a CD-ROM, a write-once optical disc, and a rewritable optical disc.

[0002]

2. Description of the Related Art In recent years, optical discs including magneto-optical discs have been put to practical use as high-density recording media, and glass or plastic is used as the substrate material for the optical discs. The glass substrate has various required characteristics,
Although it is excellent in reliability, it requires high processing cost and makes the optical disc expensive. On the other hand, a plastic substrate is often used because it is possible to easily make a large number of replicas by reducing the manufacturing cost by first preparing a master mold.

However, plastic materials generally have low surface hardness and are easily scratched, and since the resin itself is a dielectric substance, it is electrically charged and dust is likely to adhere thereto. As a result, due to these factors, the laser beam is scattered and a fatal problem of causing a reading error occurs.

Therefore, in order to overcome the above-mentioned problems,
It has been proposed to form an inorganic coating layer such as SiO ₂ having sufficient surface hardness and light transmittance on the side of the reading surface opposite to the side of the substrate on which the optical recording layer is formed (Japanese Patent Laid-Open No. 63-155450). No. A protective layer such as an ultraviolet curable resin is generally formed on the optical recording layer in order to protect this layer from corrosion and the like.

By the way, an optical disk cartridge (hereinafter, also referred to as a cartridge) for accommodating an optical disk as described above is provided with a shutter so that an opening window formed in a shell can be opened and closed by a disk drive device into which the cartridge is inserted. This is opened and closed to read the information written on the optical disc in the opening window,
Writing information to optical discs. here,
Shutters are roughly classified into metal ones and resin ones. Metal shutters are more resistant to cracking than resin shutters and are preferable in strength. In addition, warpage and dimensional changes due to moisture absorption etc. It is commonly used because it is scarce.

[0006]

However, when a charged body such as a human body comes into contact with the cartridge, particularly when the shutter is made of a conductive material such as metal, this acts as a ground and the optical disk of high electrical conductivity is used. Arc discharge may occur in the optical recording layer, and as a result, the optical recording layer may be destroyed and read / write becomes impossible.

[0007]

SUMMARY OF THE INVENTION Therefore, in order to solve the above-mentioned problems, the present invention has an extremely reliable optical disk in which arc discharge does not occur even if the optical disk is housed in a cartridge having a metal shutter. The purpose is to provide.

[0008]

In order to achieve the above object, the optical disc of the present invention has at least an optical recording layer and a first protective layer covering the optical recording layer, which are sequentially formed on one main surface of a substrate. Further, a second protective layer having a surface resistance value smaller than that of the first protective layer is formed on the other main surface side of the substrate.

[0009]

According to the optical disc having the above structure, even if the charged body comes into contact with the cartridge and arc discharge occurs, the second protective layer has a smaller surface resistance value than the first protective layer covering the optical recording layer. Since the second protective layer formed on the main surface of the substrate, which is not the side on which the optical recording layer is formed, serves as a path for passing charges, charges are prevented from passing through the optical recording layer as much as possible.

[0010]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a typical layer structure in an example of a magneto-optical disk according to the present invention. An optical recording layer 2 having a thickness of about 0.2 to 0.3 μm, that is, a first dielectric layer is formed on one main surface of a substrate 1. , A magneto-optical recording layer, a second dielectric layer, and a reflective layer are sequentially laminated to form an optical recording layer 2 having a thickness of 20 to 50.
The first protective layer 3 having a thickness of about μm is formed. Further, the second protective layer 4 having a thickness of 3 to 10 μm is formed on the other main surface which is the reading surface. The optical recording layer may have a well-known configuration other than the above configuration.

Here, the substrate 1 is not limited to polycarbonate, epoxy, polyolefin, acrylic, polyester, and other various resins, but various transparent members such as glass can be used in addition to the resin.

The first and second dielectric layers of the optical recording layer 2 act as a protective layer for blocking the influence of the substrate and the environment on the magneto-optical recording layer, and have an enhancement effect for improving the C / N ratio. Has an action of inducing, Si, Al, Ti nitride, Si carbide, Cd, Zn sulfide, Mg fluoride,
These can be used alone or in combination depending on the oxides of Al, Ce, Zr, Si, Cd, Bi and the like. Also,
The magneto-optical recording layer is an amorphous perpendicular magnetization film, for example, Gd
DyFe, GdTbFe, TbFeCo, DyFeCo, NdGdDyFe, GdTbDyFe,
Well-known magnetic materials such as GdTbFeCo, TbDyFeCo, GdDyFeCo, and NdDyFeCo can be used. The reflective layer is made of Ti, C
It is also formed of a corrosion resistant metal such as r, Ta, Al, Zr, Au, Ag, SUS, or an alloy thereof, or the same material as that used for the first dielectric layer. Furthermore, a layer formed by combining a metal layer and a compound layer, a metal layer and a dielectric layer, and the like can be used according to the purpose. Each layer of the optical recording layer 2 is a known thin film forming means, for example,
It can be formed by various known layer configurations by the sputtering method.

The first protective layer 3 and the second protective layer 4 are, for example, an ultraviolet curable resin (UV resin) such as an epoxy resin, an unsaturated polyester resin, a polymethacryl resin, an acrylic resin, a urethane resin, or an acrylic urethane resin. , Urea-based, melamine-based, sialyl-starate-based thermosetting resins, thermosetting UV resins, anaerobic curable resins, moisture curable resins, etc. are used, and these resins are applied by spin coating or the like. Is formed by. Among these resins, the ultraviolet curable resin is preferable in production because it is cured in a short time. When a filler or the like is mixed in these resins, the filler material is In2O3, SnO2, ITO,
SnO2-Sb, Sb2O3, IrO3, MoO2, NbO2, PtO2, RuO2, WO
2 such as oxides, carbides such as MoC, NbC, TaC, TiC and WC, nitrides such as NbN, Ta2N, TiN, VN and ZrN, SiO2, etc.
Al2O3, CeO3, ZrO2, CdO, Bi2O3, Si3N4, TiN, SiC
Various inorganic substances and organic substances such as CdC, ZnS, etc. can be used. These fillers have the effect of increasing the surface hardness of the optical disc and preventing the adsorption of dust.

Next, specific examples will be described. First, the following samples 1 to 6 were prepared. Sample 1; an optical recording layer 2 and a first protective layer 3 (surface resistance value: 5.0 × 10 ¹⁵ Ω / □) of a urethane acrylic UV curable resin were formed on one main surface of a substrate 1 made of a polycarbonate resin. , A conductive filler (Sb-SiO ₂ 8.
2% of acrylic UV curable resin mixed with 5 wt.%)
A protective layer 4 (surface resistance value: 5.0 × 10 ¹³ Ω / □) was formed. Sample 2; Optical recording layer 2 on one main surface of substrate 1 made of polycarbonate resin, and conductive filler (Sb-SiO ₂ 8.5 wt.%)
The first urethane-acrylic UV-curing resin mixed with
Form a protective layer 3 (surface resistance value: 5.0 × 10 ¹³ Ω / □),
On the other main surface of the substrate 1, a conductive filler (Sb-SiO ₂ 15 wt.
%) Was mixed to form a second protective layer 4 (surface resistance value: 5.0 × 10 ¹¹ Ω / □) of a urethane acrylic ultraviolet curing resin. Sample 3; optical recording layer 2 on one main surface of substrate 1 made of polycarbonate resin, and conductive filler (Sb-SiO ₂ 15 wt.%)
The first urethane-acrylic UV-curing resin mixed with
Form a protective layer 3 (surface resistance value: 5.0 × 10 ¹¹ Ω / □),
On the other main surface of the substrate 1, a conductive filler (Sb-SiO ₂ 30 wt.
%) Was mixed to form a second protective layer 4 (surface resistance value: 5.0 × 10 ⁹ Ω / □) of a urethane acrylic ultraviolet curing resin. Sample 4; in Sample 1, the first protective layer 3 and the second protective layer 4
And replaced. Sample 5; in Sample 2, the first protective layer 3 and the second protective layer 4
And replaced. Sample 6; in Sample 3, the first protective layer 3 and the second protective layer 4
And replaced.

Next, a large number of optical disks of each of Samples 1 to 6 can be stored in a conventional cartridge (a 3.5-inch optical disk can be housed between one shell on one side and the other shell on the other side formed of polycarbonate resin. And
An opening window provided for performing reading and writing operations of information is formed on both shells, and the opening window is housed in a body whose main body is opened and closed by a shutter having a thickness of about 0.3 mm formed of SUS304). As shown in FIG. 2, the cartridge C is placed upright on the grounded conductor plate 5, and the probe 6 (330 Ω, 150 pF, 15 kV) of the electrostatic tester is applied to the outer periphery of the cartridge C to perform the electrostatic withstand voltage test. I went. The results are shown in Table 1.

[0016]

[Table 1]

According to this, when an arc discharge occurs, the two places, the entrance and the exit of the discharge, are destroyed and pinholes are generated in the optical recording layer 2 of the optical disk.
After confirming the electrostatic withstand voltage for each of 5 of 6,
In Samples 3 to 4 in which the surface resistance value of the second protective layer 4 is larger than that of the first protective layer 3, it was confirmed that many pinholes of about 80 to 500 μm were generated in all the samples. In Samples 1 to 3 in which the surface resistance value of the first protective layer 3 is larger than that of the second protective layer 4, in all of the samples, the difference in surface resistance value between the first protective layer 3 and the second protective layer 4 is at least 10 ² In the above cases, it was not possible to confirm the occurrence of pinholes. The thickness of the first protective layer suitable for protecting the optical recording layer 2 was 20 μm or more.

In the above-mentioned embodiment, the magneto-optical disk has been described as an example of the optical disk, but the present invention is not limited to this, and a read-only optical disk mainly having a reflective layer as the optical recording layer 2 can be applied. . Also,
The difference in surface resistance between the first protective layer 3 and the second protective layer 4 is 10
It is sufficient that the surface resistance value of the first protective layer 3 is at least ^two orders of magnitude higher than that of the second protective layer 4, and the material is not limited to a resin material and may be an inorganic material such as ITO.

[0019]

According to the optical disk of the present invention, the second protective layer having a surface resistance value larger than that of the first protective layer is formed on the surface of the substrate on which the optical recording layer is not formed. When a charged body such as a human body comes into contact, arc discharge is prevented from occurring in the optical recording layer of the optical disc, and the optical recording layer is destroyed even if the shutter is made of a conductive material such as metal. It is possible to solve the problem that reading and writing becomes impossible due to such problems, and it is possible to provide an optical disc with excellent reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of an optical disc according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating an electrostatic breakdown voltage test.

[Explanation of symbols]

1 ... Substrate 2 ... Optical recording layer 3 ... First protective layer 4 ... Second protective layer D ... Optical disc

Claims (1)

[Claims] 1. At least an optical recording layer and a first protective layer covering the optical recording layer are sequentially formed on one main surface side of the substrate, and smaller than the first protective layer on the other main surface side of the substrate. An optical disc formed by forming a second protective layer having a surface resistance value.