JPH0589538A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the magneto-optical recording medium having the recording sensitivity suitable for various driving devices and to provide such magneto- optical recording medium which can change the characteristic of only the recording sensitivity of the once produced magneto-optical recording medium by a simple method. CONSTITUTION:The degree of scattering of a laser beam is changed according to the film thickness of a protective layer 6 by the magneto-optical recording medium D constituted by providing a magnetic recording layer 3 on one main surface side of a light transparent substrate 1 and the light scattering protective layer 6 of 1 to 20mum on the other main surface side. The magneto-optical recording medium D which is changed in the recording sensitivity is obtd. by the simple method consisting of merely changing the film thickness of the protective layer 6 by adding the film forming stage similar to the film forming stage for the protective layer 6 even after the end of once forming the recording layer 3, etc., on the one main surface side of the substrate 1 and the protective layer 6 on the other main surface side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a magneto-optical recording medium having a magnetic recording layer on which one side of a light-transmissive substrate is written, such as voice and image information.

[0002]

2. Description of the Related Art At present, a disc-shaped magneto-optical recording medium, which is widely used as a recordable / reproducible / erasable recording medium for music or images, has a recording information on one main surface of a substrate. It is common to have a magnetic recording layer composed of a perpendicularly magnetized film in which is written. Usually, when recording information on a magneto-optical recording medium of this type, the magnetic recording layer is heated by laser light, and a magnetic field is applied with the coercive force at this portion reduced to form a recording bit.

Here, the recording power of the laser light that minimizes the second harmonic of the reproduced waveform when the above-mentioned recorded bits are reproduced is defined as the recording sensitivity, and each drive device in which a magneto-optical recording medium is mounted is defined. Shall have a recording sensitivity that conforms to. That is, the number of rotations and the laser output of the magneto-optical recording medium differ depending on the type of the drive device, and therefore the read error during reproduction must be minimized by using a magneto-optical recording medium suitable for the drive device.

However, the above-mentioned recording sensitivity greatly changes depending on characteristics such as the Curie point of the magnetic recording layer, the thickness of the reflective layer laminated on the magnetic recording layer, the reflectance of the reflective layer, and the like.
If the magneto-optical recording medium having a predetermined recording sensitivity is to be adjusted by adjusting the film thickness and the characteristics of each of these layers, the characteristics other than the recording sensitivity may be changed. It was very troublesome to provide a magneto-optical recording medium having a corresponding optimum recording sensitivity, and various characteristics other than the recording sensitivity were deteriorated, which was a problem.

Since the erasing and reproducing sensitivities change following the recording sensitivities, increasing the recording sensitivities also increases the erasing and reproducing sensitivities. Therefore, it is possible to change the recording sensitivities by a simpler method than before. A magnetic recording medium has been longed for.

[0006]

[Purpose] Therefore, the present invention solves the above conventional problems,
It is possible to provide a magneto-optical recording medium having a recording sensitivity suitable for various drive devices, and to provide a magneto-optical recording medium capable of changing only the characteristic of the recording sensitivity by a simple method with respect to the once manufactured magneto-optical recording medium. The purpose is to do.

[0007]

The above object is achieved by providing a magnetic recording layer on one main surface side of a light-transmissive substrate and a light-scattering protective layer of 1 to 20 μm on the other main surface side. To be done.

[0008]

According to the magneto-optical recording medium having the above-described structure, the light scattering protective layer is provided on the substrate surface side on which the laser light is incident during recording / reproduction. It is possible to provide an optimum magneto-optical recording medium which can be changed according to the thickness and which is adapted to the laser output at the time of writing recorded information and the rotation speed of the drive device.

Further, even after the recording layer and the like are once formed on one main surface side of the substrate and the protective layer is formed on the other main surface side,
It is possible to provide a magneto-optical recording medium in which the recording sensitivity is changed by a simple method in which the film thickness of the protective layer is changed by adding a film forming step similar to the film forming of the protective layer.

[0010]

Embodiments of the present invention will be described in detail. Figure 1
Is an example of a cross section of a disk-shaped magneto-optical recording medium D having a diameter of 3.5 inches, which enables recording / reproducing / erasing of recorded information.
A first dielectric layer 2 (up to 1100 Å thickness) made of a dielectric material such as yttrium sialon, a perpendicular magnetization film such as a Gd-Dy-Fe system is formed on one main surface side of the substrate 1 made of a light-transmitting polycarbonate resin. Magnetic recording layer 3 (up to 250 Å thickness), first
The second dielectric layer 4 (up to 300 Å) having the same structure as the dielectric layer 2
Thickness) and a reflective layer 5 (up to 400 Å thickness) made of a material having a high reflectance such as Al are sequentially laminated, and each of these layers is formed by an appropriate method such as magnetron sputtering. On the other hand, a protective layer 6 is formed on the other main surface side of the substrate 1 by a spin coating method, and has a proper film thickness so that the substrate 1 is not scratched or the like. The reflective layer 5
In order to protect this, a protective coating layer such as an acrylic UV-curable resin may be applied on top by spin coating. Further, the above-mentioned laminated structure is not limited to this, and for example, a structure without the second dielectric layer 4 is also possible.

The magneto-optical recording medium D configured as described above.
Laser light is incident from the protective layer 6 side at the time of recording / reproducing information, the first and second dielectric layers 2 provided for the purpose of writing recorded information in the magnetic recording layer 3 and increasing the Kerr rotation angle. , 4 and the reflective layer 5 can effectively reflect the laser light to read the recorded information.

Next, an experimental example in which the protective layer 6 is compared with a conventional protective layer will be described in detail. The protective layer 6 was made of an acrylic UV-curable resin in which a light scattering agent of tin oxide or titanium oxide having a diameter of about 0.15 μm was diffused by about 20 wt% each, and a sample having a thickness of 1 to 20 μm was applied. In addition, as a conventional protective layer, a sample made of only an acrylic ultraviolet curable resin containing no light scattering agent was prepared by the same method.

[0013]

[Table 1]

Here, the thickness of the protective layer 6 is set to 1 to 20 μm, as is apparent from Table 1, when the film thickness is thinner than 1 μm or thicker than 20 μm, coating unevenness due to the spin coating method is caused. This is because a so-called coating defect may occur, which may occur or a portion where the protective layer 6 is not applied, which may adversely affect read performance during reproduction and tracking characteristics of laser light.

The acrylic UV curable resin used as the protective layer is only an example, and various UV curable resins such as epoxy, polyester, acrylic ester, urethane acryl, polyether, silicone and the like are used. It is also possible to use various resins such as resins and thermosetting types, anaerobic curing types, and moisture curing types. Further, the material to be contained in the resin is not limited to the above-mentioned inorganic fine particle agent, as long as it is effective as a light scattering agent, for example, a material containing a predetermined amount of a dye such as an aniline dye and a phenylenediamine dye. But it's okay. Furthermore, it is clear that even if both the inorganic fine particle agent and the dye are mixed with various resins, the function as a light scattering agent can be achieved, and a resin containing both of them may be used as a protective layer.

Next, samples A1 to A4 (acrylic UV curable resin + titanium oxide), samples B1 to B4 (acrylic UV curable resin + tin oxide), and sample C1 manufactured by changing the film thickness as described above. .About.C4 (only acrylic ultraviolet curable resin), the recording power of the laser beam (hereinafter,
2nd-Dip recording power), C / N value which is an index of read performance, recording power margin, and recording magnetic field margin will be described. Here, the recording power margin and the recording magnetic field margin are the maximum C
The recording power and the recording magnetic field width in the range of 2 dB lower than the / N value are shown.

FIG. 2 is a diagram showing the relationship between the film thickness of the protective layer 6 and the 2nd-Dip recording power. From this figure, it can be seen that when the light scattering agent is diffused in resin, the film thickness increases to 2n as the film thickness increases.
The d-Dip recording power also tends to increase, and the film thickness is 1
-20 μm, titanium oxide diffused into the resin (Samples A1 to A4; indicated by ○ in the figure) showed an increase of about 2.5 mW, and tin oxide diffused into the resin (sample B1 to B4; indicated by Δ in the figure) showed an increase of 1.5 mW or more. On the other hand, the resin only (Samples C1 to C4; indicated by x in the figure) has almost no light scattering property, so that the 2nd-Dip recording power did not change at all even if the film thickness was increased. The content and particle size of the light scattering agent are set to appropriate numerical values, and the recording sensitivity tends to decrease as the numerical values increase.

[0018]

[Table 2]

Next, Table 1 shows how the characteristics other than the recording sensitivity of each of the samples, that is, the C / N value, the recording power margin, and the recording magnetic field margin change.
The rotation speed of the disk of the drive device is constant at 2400 rpm, the measurement position is about 24.1 mm from the center of the magneto-optical recording medium,
The recording frequency was about 3.9 MHz and the recording pulse width was 60 nsec.

Titanium oxide diffused into the resin when the thickness of the protective layer 6 was changed to 1 to 20 μm (Sample A1)
.About.A4), the C / N value is 49.4 to 49.6 dB, the recording power margin is 4.0 to 4.3 mW, and the recording magnetic field margin is almost constant at 460 Oe, and tin oxide is diffused in the resin (Sample B1 to Sample B1). B4) is a C / N value of 49.5 to 49.7 dB, a recording power margin of 4.0 to 4.2 mW, and a recording magnetic field margin of approximately 46.
0 Oe It was a constant change. On the other hand, the resin only (Samples C1 to C4) has a C / N value of 49.6 to 49.8 dB, a recording power margin of 4.1 to 4.2 mW, and a recording magnetic field margin of approximately 450.
It was a change of ~ 470 Oe.

The change in each of the above characteristic values due to the change in film thickness is
The dispersion of the light-scattering agent in the resin tends to be slightly smaller than that of the resin alone, but the change can be regarded as almost constant. As described above, the characteristics other than the recording sensitivity hardly change even if the thickness of the protective layer is changed,
From these results, it is possible to change the recording sensitivity only by changing the film thickness of the protective layer. For example, after forming each layer on the substrate once, the same protective layer formation that was performed once when changing the recording sensitivity was performed. Since it can be performed by a simple method of repeating the film process, it is extremely effective for product design of a magneto-optical recording medium suitable for various drive devices.

Incidentally, the magneto-optical recording medium is not limited to the above-mentioned one, but any magneto-optical recording medium may be used as long as it has a magnetic recording layer on the substrate, and various magneto-optical recording media can be used, which deviates from the gist. It can be appropriately modified and implemented within the range not to do.

[0023]

As described above in detail, according to the magneto-optical recording medium of the present invention, the thickness of the protective layer formed on the light incident side (information reading surface side) is set to 1 to 20 μm. Since only the recording sensitivity of the magnetic recording medium can be changed, the optimum magneto-optical characteristics suitable for various drive devices having the same characteristics such as C / N value, recording magnetic field, and recording power but different recording sensitivity. A recording medium can be provided.

Further, even after the film formation of each layer formed on the substrate is completed, only the recording sensitivity can be changed by a simple method in which the same steps as those for forming the protective layer are added. ..

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium according to the present invention.

FIG. 2 is a graph showing a relationship between a film thickness of a protective layer and 2nd-Dip power.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... 1st dielectric layer 3 ... Magnetic recording layer 4 ... 2nd dielectric layer 5 ... Reflection layer 6 ... Protective layer D ... Magneto-optical recording medium

Claims (1)

[Claims] 1. A magneto-optical recording medium comprising a light-transmissive substrate having a magnetic recording layer on one main surface side and a light-scattering protective layer having a thickness of 1 to 20 μm on the other main surface side.