JPS6390038A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the generation of corrosion, crack and exfoliation at the end of the recording layer of a substrate by a taper to the end of the optical recording layer so as to decrease the thickness each slightly over the entire width of a specific value or above. CONSTITUTION:A part A where the recording layer is not provided is provided near the end of the substrate 1. The width thereof is about 0.3-20mm. The recording layer 2a is formed by tapering B said part gently to eliminate steps until the tapered part connects to the part A. The width of the part B is enough with 50mum and is set at >=50mum if the film thickness of the layer 2a is about usual 100Angstrom -2mum. The corrosion, crack and exfoliation to be generated at the end of the layer 2a are thereby prevented and the annihilation of the recorded information at the end is obviated. The reliability of preservation is improved and the recording region is widened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which recording and reproduction can be performed using a light beam.

[Conventional technology]

Conventionally, optical recording media used in optical disks include rare earth-transition metal alloy thin films, reducing oxide thin films such as chalcogen compounds that utilize phase transition from amorphous to crystalline, and heat mode recording media. , thermoplastic recording media, etc. are known. For example, as a magneto-optical recording medium formed of a rare earth-transition metal alloy thin film,
MnB1. Polycrystalline thin films such as MnCuB1, GdGo
, GdFe, TbFe, DyFe.

Amorphous thin films such as GdTbFe and TbDyFe, Gd
Single crystal thin films such as IG are known.

Among these thin films, there are various issues such as film formability when manufacturing large-area thin films at temperatures near room temperature, writing efficiency for writing signals with small photothermal energy, and readout of written signals with a good S/N ratio. Recently, the amorphous thin film is considered to be excellent as an optical recording medium in consideration of read efficiency and the like. GdTbFe has a large Kerr rotation angle and a Curie point of around 150° C., so it is suitable as a magneto-optical recording medium. Furthermore, as a result of our research aimed at improving the Kerr rotation angle, we found that GdTbFeCo is a magneto-optical recording medium that has a sufficiently large Kerr rotation angle and allows readout with a good S/N ratio.

However, amorphous magnetic materials such as GdTbFe generally have poor corrosion resistance, and have the drawback that they are corroded in a magnetic atmosphere, resulting in deterioration of magnetic properties. This drawback is a common problem not only with magneto-optical recording media but also with the above-mentioned optical recording media.

In order to eliminate these drawbacks, conventional methods have been to provide a protective layer on the recording magnetic layer made of an amorphous magnetic material, or to create an air sandwich structure in which the recording magnetic layer is sealed with an inert gas or a disc-shaped laminated structure. Magneto-optical recording media have been proposed.

The causes of corrosion of magneto-optical recording media are thought to be dirt on the substrate, oil and dirt from handling after the medium is formed, humidity, oxygen, and the like. Therefore, corrosion of a magneto-optical recording medium tends to start from the end surface of the substrate and spread.

Conventionally, therefore, the portion of the optical recording layer formed on the entire surface of the substrate, which is formed at the edge of the substrate, has not been used as a recording section. However, when corrosion begins in a part of the recording layer, a local battery is formed at that location, and the corrosion around it accelerates, eventually progressing to the recording area.
Not using the portion of the recording layer formed on the end surface of the substrate as a recording section is meaningless from the standpoint of improving corrosion resistance. Therefore, a method of not forming an optical recording layer on parts of the outer and/or inner edges of the substrate that are not used as a recording part has been conventionally practiced as an effective means of substantially preventing corrosion of the recording part. .

Such an optical recording medium and an optical recording medium provided with a recording layer over the entire surface will be explained with reference to the drawings. FIG. 3 is a sectional view of the vicinity of the outer edge of an optical recording medium in which a recording layer is provided up to the edge of the substrate. FIG. 4 is a sectional view of the vicinity of the outer edge of the optical recording medium, showing a state in which no recording medium is formed near the edge of the substrate. In FIGS. 3 and 4, 1 is a substrate and 2 is an optical recording layer. The optical recording layer 2a may be a single layer, but may also have a multilayer structure in which a protective layer, a reflective layer, etc. are laminated above and below. The thickness of these optical recording layers is generally about several hundred λ to 2 μ.

The width of A in FIG. 4 is generally about 0.3 mm to 20 mm. In FIG. 4, the boundary between the area where the recording layer is formed and the area where it is not formed is clear, and a step corresponding to the thickness of the recording layer is formed there.

[Problem that the invention seeks to solve]

However, in the case of a recording medium with the structure shown in Figure 4, the boundary between the area where the recording layer is formed and the area where it is not formed, that is, the edge of the recording layer, is not durable enough to corrode or crack during long-term use. or peeling may occur. This is thought to be caused by latent strain stress at the edge of the recording layer.

The present invention has been made in view of the above-mentioned problems, and its object is to provide an optical recording medium in which corrosion, cracking, and peeling occurring at the ends of the recording layer of a substrate are prevented.

[Means for solving problems]

The above objects of the present invention are achieved by the following optical recording medium.

That is, the present invention provides an optical recording medium in which an optical recording layer is formed on a substrate at a certain distance from the edge thereof, and the optical recording layer has a width of 50p or more at the edge. This is an optical recording medium that has a slope that gradually becomes thinner over the entire length.

FIG. 1 is a schematic cross-sectional view of the vicinity of an end of an optical recording medium according to the present invention. In the figure, 1.2a is a substrate and a recording layer as in FIGS. 3 and 4. Similarly, the recording layer may have a multilayer structure. The range A is the area near the edge where no recording layer is provided, as in Figure 2, and its width is 0.3 mm to 20 mm.
It is about +++m. The range B is a feature of the present invention,
This is a portion where the recording layer is formed so that the recording layer No. 2 smoothly connects to the portion A where no recording layer is provided, without any step.

The width of B needs to be sufficient for the thickness of the recording layer,
When the thickness of the recording layer is normally used for about 100 people to 2 households, 50u+ is sufficient, and the thickness is at most 1 mm. Specifically, the degree of this inclination is preferably 50 μm to 0.5+nm for the entire inclination group.

A method for forming part B will be described below.

Conventional methods for forming a thin film recording layer include vapor deposition, sputtering, and CVD. In these methods, a mask is usually used to create the portion A in FIG. 4, which prevents a film from being formed on the portion A of the substrate. FIG. 5 is a schematic diagram showing this, where 1 is a substrate and 3 is a mask. Fifth
When a recording layer is formed with the mask 3 attached as shown, a recording layer as shown in FIG. 4 is formed.

On the other hand, FIGS. 6 and 7 are examples of a method for forming the portion B in FIG. 1, where 1 is a substrate and 3 is a mask, as in FIG. 5. In FIG. 6, a chamfered portion 4 is provided on seven masks 3, and in FIG. 7, a gap is provided between the mask and the substrate. The size of the chamfer or gap may be determined depending on the characteristics of the film forming method, since the ability to wrap around the shadow area differs depending on the film forming method.

By forming a gentle edge of the recording layer as shown in the area B in Figure 1, the potential strain stress at the edge of the recording layer is reduced, resulting in corrosion, cracking, and peeling occurring at the edge of the recording layer. This is considered to be prevented.

FIG. 8 shows an embodiment of the present invention in which the recording layer has a multilayer structure. The optical recording medium shown in FIG. 8 has an air sandwich structure in which two substrates each having a recording layer are bonded together via a member. 1 is the substrate, 2a is the recording layer, 2b is the reflective layer, and 2c is the It is a subbing layer. In the case of such a multilayer structure, the following factors are also considered to be causes of improved durability. That is, in FIG. 1, the thickness of the recording layer at the end portion in contact with A in the range B is about 0 to 100 mm. Since the film is too thin in this part, it is not a continuous film, but has a so-called island shape. This also applies to the terminal portion in contact with A in the range B in FIG. 8, and a partially enlarged view thereof is shown in FIG.

In the area surrounded by the broken line C in Figure 9, the multilayer film is stacked in this island shape, so the boundaries between each layer of the multilayer film are not clear in this area, and they are formed as mixed layers. As a result, it is thought that delamination etc. are less likely to occur.

Note that the cross-sectional views near the edges of the optical recording medium, which is a feature of the present invention, shown in Figure 1.8.9 are schematic views, and in these figures, the film thickness is linearly increased within the range B. Although shown as having a decreasing slope, the slope is not limited to this, and may be a curvilinear film thickness decreasing slope. Furthermore, as shown in Figure 2, even if a small step remains at the edge of the recording layer, the effect can be recognized as long as a part of the gradual B thickness decreasing slope is formed. .

The present invention is not limited to providing the edges of the recording layer with an inclination as described above, but also makes the edges of the undercoat layer, protective layer, antireflection layer, reflective layer, heat insulating layer, interference layer, etc. have a similar shape. By doing so, peeling of each layer can be prevented, and the reliability of the recording medium as a whole can be improved. In this embodiment, when the protective layer is formed in the same manner as the recording layer, it is also effective to form the protective layer larger than the recording layer but not to the edge of the substrate.

(Example) Hereinafter, the present invention will be explained in more detail by giving examples of the present invention.

Example 1 As shown in FIG. 1, an optical recording medium having a recording layer on which a protective layer and a protective glass plate were arranged was manufactured in the following manner. A donut-shaped 1.2 mm thick glass substrate 1 with an outer circumference of 200 mmφ and a center hole diameter of 35 mmφ.
A mask with a thickness of 1 mm covering the outer peripheral edge 5 mm and a mask covering the inner peripheral edge 10+ nm were installed. The edge portion of the mask was chamfered in the shape of a right isosceles triangle with the length of the two sides sandwiching the right angle being 0.2 mm, as shown in 4 in FIG. 6. After that, GdT was formed by sputtering.
A bFeGo magnetic thin film recording layer 2a was formed to a thickness of 1000 mm. Next, on the magnetic thin film recording layer, AI was deposited as a protective layer to a thickness of 300 mm by resistance heating using a vacuum evaporation device.
Vapor deposition was performed by 0 people. This glass plate with the recording layer and a protective glass plate were bonded together with an adhesive [trade name: Bond E Set M, publisher: Konishi ■] to produce a photothermal magnetic recording medium.

For comparison, a photothermal magnetic recording medium was produced under the same conditions except that a mask without a chamfer was used.

When the edges of the recording layer near the outer periphery of the above two recording media were observed using a transmission microscope, it was found that in the medium using a mask with a chamfer, the amount of transmitted light was approximately 0.2 mm wide at the edge of the recording layer. It was confirmed that there was a gradual change in the film thickness in the area shown in B in Figure 1. On the other hand, for comparison, in the recording layer created using a mask without a chamfer, a clear brightness ratio was observed under a microscope, and it was confirmed that a recording film with steps as shown in Figure 4 was formed. .

This photothermal magnetic recording medium was placed in a constant temperature and humidity chamber at 75°C and relative humidity of 85%, and a corrosion resistance test was conducted for 1000 hours, after which it was visually observed. As a result, no corrosion was observed in the recording layer created using a mask with a chamfer, but corrosion occurred from the edges of the recording layer at the outer and inner edges of the recording layer created using a mask without a chamfer. The maximum corrosion penetration distance from the edge was 3 mm.

Example 2 A photothermal magnetic recording medium was produced under exactly the same conditions as in Example 1 except that the protective film A1 was not provided. As a result of microscopic observation,
As in Example 1, it was confirmed that the mask with a chamfer had a gradual decrease in film thickness at the end of the recording layer, and the mask without a chamfer had a step.

This photothermal magnetic recording medium was placed in a constant temperature and humidity chamber at 60° C. and relative humidity of 90%, and a corrosion resistance test was conducted for 1000 hours, after which it was visually observed. As a result, no corrosion was observed in the recording layer created with a mask with a chamfer, but on the outer edge of the recording layer created with a mask without a chamfer,
Corrosion occurred from the edge of the recording layer at the inner edge, and the maximum corrosion penetration distance from the edge was 5 mm.

Example 3 The same mask as in Example 1 was placed on the same substrate as in Example 1, and a SiO undercoat layer of 1,000 ml was formed by sputtering.
GdTbFe1 on top of the undercoat layer.
A 1:0 magnetic thin film recording layer 2a was formed to a thickness of 1,000 layers. Furthermore, a protective layer of 1 (1 (1
A photothermal magnetic recording medium was obtained. These two photothermal magnetic recording media were pasted together with a two-component thermal epoxy polyamide adhesive with the recording layer facing inside through an annular aluminum group member, 1 mm thick, and 3 mm wide inner and outer periphery spacers. A photothermal magnetic recording medium having an air sandwich structure as shown in the cross-sectional view in FIG. 8 was obtained.

When the edge of the recording layer near the outer periphery of this photothermal magnetic recording medium was observed using a transmission microscope, it was found that the amount of transmitted light gradually changed in a portion approximately 0.2 mm wide at the edge of the recording layer. It was confirmed that the film thickness changed gently as shown in B in the figure.

This photothermal magnetic recording medium was subjected to a corrosion resistance test for 1000 hours in a constant temperature and humidity chamber at 75° C. and 85% relative humidity, and then visually observed. As a result, no corrosion was observed in the recording layer.

〔Effect of the invention〕

As described above, the optical recording medium of the present invention is less prone to deterioration such as cracks at the edges of the recording layer, so the recorded information at the edges does not disappear, resulting in high storage reliability and a wide recordable area. There is an advantage.

[Brief explanation of the drawing]

1 and 2 are partial sectional views showing characteristic parts of the optical recording medium of the present invention, FIGS. 3 and 4 are partial sectional views of a conventional optical recording medium, and FIG. is a schematic diagram showing a method for producing an optical recording medium having the structure shown in FIG. 4; FIGS. 6 and 7 are schematic diagrams showing a method for producing an optical recording medium of the present invention; FIG. 8 is a schematic sectional view of the optical recording medium of the present invention having an air sandwich structure, and FIG. 9 is a partially enlarged view of FIG. 8. 1: Substrate 2a: Recording layer 2b 2 Reflective layer 2c: Undercoat layer 3: Mask 4: Chamfering A: Portion where no recording layer is provided

Claims (2)

[Claims] (1) An optical recording medium in which an optical recording layer is formed on a portion of a substrate excluding a certain distance from the edge thereof,
An optical recording medium characterized in that the optical recording layer is sloped at its end so as to gradually become thinner over a width of 50 μm or more. (2) One or more of a subbing layer, a protective layer, an antireflection layer, a reflective layer, a heat insulating layer, an interference layer, etc., which are laminated above and below the optical recording layer, are the same as the optical recording layer. 2. The optical recording medium according to claim 1, wherein the end portion thereof is sloped so as to gradually become thinner over a width of 50 μm or more.