JP2941514B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a magneto-optical recording medium having a magnetic recording layer on one side of a light-transmitting substrate on which sound and image information are written.

[0002]

2. Description of the Related Art At present, a disk-shaped magneto-optical recording medium, which is widely used as a recordable / reproducible / erasable recording medium for music and images, has recorded information on one principal surface of a substrate. Is generally provided with a magnetic recording layer composed of a perpendicular magnetic film on which is written. Normally, when recording information is written to this type of magneto-optical recording medium, the magnetic recording layer is heated by a laser beam, and a magnetic field is applied in a state where the coercive force is reduced at this location to form recording bits.

Here, the recording power of the laser beam at which the second harmonic of the reproduced waveform is minimized when the recording bit is reproduced is defined as the recording sensitivity. Must be provided with a recording sensitivity compatible with That is, since the rotation speed and laser output of the magneto-optical recording medium vary depending on the type of the drive device, it is necessary to minimize reading errors during reproduction 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, and the reflectance of the reflective layer.
In order to obtain a magneto-optical recording medium having a predetermined recording sensitivity by adjusting the thickness, characteristics, and the like of each of these layers, characteristics other than the recording sensitivity may be changed. Providing a magneto-optical recording medium having a corresponding optimum recording sensitivity was very troublesome, and there was a problem that characteristics other than the recording sensitivity could be deteriorated.

Further, since the erasing and reproducing sensitivities change following the recording sensitivities, the erasing and reproducing sensitivities increase as the recording sensitivities are increased. A magnetic recording medium has been desired.

[0006]

Therefore, the present invention solves the above-mentioned 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 the characteristics of only the recording sensitivity by a simple method with respect to a 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 of a light-transmitting substrate and a light-scattering protective layer of 1 to 20 μm on the other main surface. Is 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 beam is incident during recording / reproducing. It can be changed according to the thickness, and it is possible to provide an optimum magneto-optical recording medium suitable for the laser output at the time of writing the recording 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,
A magneto-optical recording medium in which the recording sensitivity is changed by a simple method of changing the thickness of the protective layer by adding a film forming step similar to the above-described film formation of the protective layer can be provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described in detail. FIG.
Is an example of a cross section of a disk-shaped magneto-optical recording medium D having a diameter of 3.5 inches in which recording information can be recorded / reproduced / erased,
A first dielectric layer 2 (up to 1100 mm thick) made of a dielectric material such as yttrium sialon and a perpendicular magnetization film such as a Gd-Dy-Fe system are formed on one main surface side of a substrate 1 made of a light-transmitting polycarbonate resin. Magnetic recording layer 3 (up to 250 mm thick), first
The second dielectric layer 4 (up to 300 と) having the same configuration as the dielectric layer 2
) And a reflective layer 5 (up to 400 Å thick) made of a material having high reflectivity such as Al, and these layers are formed by an appropriate method such as a magnetron sputtering method. On the other hand, a protective layer 6 is formed on the other main surface side of the substrate 1 by spin coating, and has an appropriate thickness so that the substrate 1 is not damaged. The reflection layer 5
On top of this, a protective coat layer such as an acrylic UV-curable resin may be applied by a spin coat method to protect this. Further, the 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 constructed as described above
The first and second dielectric layers 2 provided for the purpose of writing recording information to the magnetic recording layer 3 or increasing the Kerr rotation angle when a laser beam is incident from the protective layer 6 side during recording / reproducing of information. , 4 and the reflective layer 5 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 ultraviolet-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%, and a sample was applied to a thickness of 1 to 20 μm. In addition, a sample made of only an acrylic ultraviolet curable resin containing no light scattering agent was prepared in the same manner as a conventional protective layer.

[0013]

[Table 1]

Here, the reason why the thickness of the protective layer 6 is set to 1 to 20 μm is that, as is apparent from Table 1, when the film thickness is thinner than 1 μm or thicker than 20 μm, coating unevenness by the spin coating method is reduced. This is because a so-called coating defect occurs, or a portion where the protective layer 6 is not applied, that is, a so-called coating defect occurs, which may adversely affect readout performance during reproduction and laser beam tracking characteristics.

The acrylic UV-curable resin used as the protective layer is merely an example. For example, various UV-curable resins such as epoxy, polyester, acrylate, urethane acrylic, polyether, and silicon can be used. It is also possible to use various resins such as resins and thermosetting types, anaerobic setting types, and moisture setting types. Further, the material to be contained in the resin is not limited to the above-mentioned inorganic fine particle agent, and any material effective as a light scattering agent is sufficient. For example, a material containing a predetermined amount of a dye such as an aniline dye or a phenylenediamine dye. May be. Further, it is clear that even if both the inorganic fine particle agent and the pigment 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 the 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 were prepared by changing the film thickness as described above. To C4 (acrylic ultraviolet curable resin only), the recording power of the laser beam that minimizes the second harmonic during reproduction as an index of recording sensitivity (hereinafter, referred to as
2nd-Dip recording power), a C / N value as an index of read performance, a recording power margin, and a recording magnetic field margin will be described. Here, the recording power margin and the recording magnetic field margin are the maximum C
4 shows the recording power and the width of the recording magnetic field in a range 2 dB lower than the / N value.

FIG. 2 is a graph showing the relationship between the film thickness of the protective layer 6 and the 2nd-Dip recording power. It can be seen from FIG.
The d-Dip recording power also tends to increase, and
When the thickness was set to 20 μm, the sample in which titanium oxide was diffused in the resin (samples A1 to A4; indicated by 中 in the figure) showed an increase of about 2.5 mW, and the sample in which tin oxide was diffused in the resin (sample B1 to B4; indicated by △ in the figure) showed an increase of 1.5 mW or more. On the other hand, those of the resin alone (samples C1 to C4; indicated by x in the figure) have 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 if these numerical values are further increased, the recording sensitivity tends to decrease.

[0018]

[Table 2]

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

When the thickness of the protective layer 6 was changed to 1 to 20 μm, a resin in which titanium oxide was diffused (sample A1)
A to A4) show a C / N value of 49.4 to 49.6 dB, a recording power margin of 4.0 to 4.3 mW, and a recording magnetic field margin of almost 460 Oe, which is a constant change of tin oxide in the resin (samples B1 to B4). B4) is 49.5 to 49.7 dB in C / N value, 4.0 to 4.2 mW in recording power margin, and almost 46 in recording magnetic field margin.
0 Oe was a constant change. On the other hand, in the case of the resin alone (samples C1 to C4), the C / N value was 49.6 to 49.8 dB, the recording power margin was 4.1 to 4.2 mW, and the recording magnetic field margin was approximately 450.
~ 470 Oe change.

The change of each characteristic value due to the change of the film thickness is as follows.
When the light scattering agent is diffused in the resin, the dispersion tends to be slightly smaller than that in the case of the resin alone, but the change can be regarded as substantially constant. Thus, various 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, when changing the recording sensitivity once, the same protective layer formation was performed once. Since it can be performed by a simple method only by repeating the film process, it is extremely effective for product design of a magneto-optical recording medium suitable for various drive devices.

The magneto-optical recording medium is not limited to the one described above, and may be any medium having a magnetic recording layer on a substrate, and various types of magneto-optical recording media can be used. It can be changed as appropriate within the range not to be performed.

[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 (the information reading surface side) is set to 1 to 20 μm, and the Since only the recording sensitivity of the magnetic recording medium can be changed, the optimum magneto-optics suitable for various drive devices having the same characteristics such as the C / N value, the recording magnetic field, and the recording power but differing only in the recording sensitivity. A recording medium can be provided.

Further, even after the formation of each layer once formed on the substrate is completed, it is possible to change only the recording sensitivity by a simple method of adding the same steps as the formation of the protective layer. .

[Brief description of the drawings]

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

FIG. 2 is a graph showing the relationship between the 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 ... Reflective layer 6 ... Protective layer D ... Magneto-optical recording medium

Claims (1)

(57) [Claims] 1. A magneto-optical recording medium comprising a magnetic recording layer on one main surface of a light-transmitting substrate and a light-scattering protective layer of 1 to 20 μm on another main surface.