JP2847812B2 - Magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium that records and reproduces an information signal using a magneto-optical effect.

[Summary of the Invention]

The present invention forms a pattern of guide grooves and signal bits by transfer to a photocurable resin layer formed on a substrate,
In a magneto-optical recording medium manufactured by the so-called 2P method, by adopting a structure in which a high magnetic permeability layer, a photocurable resin layer, a magneto-optical recording layer, and a transparent protective plate are sequentially laminated on a substrate, the transparent protective plate side To improve the perpendicular magnetic field efficiency that enables the application of a magnetic field from the surface, alleviate the stress between the high magnetic permeability layer and the magneto-optical recording layer, form a precise pattern on the magneto-optical recording layer, and support magnetic field modulation recording. It is also possible to provide a double-sided magneto-optical recording medium.

[Conventional technology]

In recent years, as a rewritable high-density recording method, a magneto-optical recording method, in which magnetic domains are written on a magnetic thin film using thermal energy of a semiconductor laser beam or the like to record information, and the information is read using a magneto-optical effect, has attracted attention. ing.

The magneto-optical recording medium used in this magneto-optical recording system is
Usually, a magneto-optical recording layer including a dielectric film, a recording magnetic layer, a metal reflection film, and the like is formed on a transparent substrate having a thickness sufficient to achieve practically sufficient rigidity. It is configured to be covered with a protective film made of
It is necessary to form guide grooves and signal pits for ID on the transparent substrate.
A method of forming the transparent substrate simultaneously with the molding of the transparent substrate by injection molding using a stamper in which these inversion patterns are formed in advance, and applying an ultraviolet curable resin on the transparent substrate, bringing the stamper into close contact with this resin layer, from the substrate side There is a method of transferring a pattern by performing ultraviolet irradiation (so-called 2P method). In recent years, mass production and economy have been emphasized, and the injection molding method has become the mainstream. However, the 2P method has high transfer fidelity, dimensional stability, heat resistance, low birefringence, etc. There are many advantages such as obtaining a disk substrate which is excellent in point, providing a magneto-optical recording medium having excellent recording characteristics due to the low thermal conductivity of the ultraviolet curable resin layer, and simplifying the manufacturing apparatus. .

The recording method of the above-described magneto-optical recording medium includes a light modulation method in which a weak DC external magnetic field is always applied and a laser beam is irradiated in accordance with the presence or absence of a signal, and a signal beam in which a constant intensity laser beam is always irradiated. There is a magnetic field modulation method for inverting an external magnetic field according to the above. Research on the optical modulation method has been conducted from an early stage because the device configuration is relatively simple. But,
Overwriting is not possible when re-recording is performed on an already recorded portion, and there is a drawback that the writing speed is reduced by the amount that an erasing operation for aligning the magnetization direction in a certain direction is required. . On the other hand, in the magnetic field modulation system, although the device configuration is slightly complicated, overwriting is possible and high-speed recording comparable to a computer hard disk is possible, and practical expectations are high.

By the way, in the magnetic field modulation method, the magnetic field is reversed at a high speed, so that a magnetic field applying means must be arranged as close as possible to the recording magnetic layer in order to obtain a required magnetic field strength. Therefore, the magnetic field applying means is generally arranged not on the thick transparent substrate side but on the thin protective film side. On the other hand, since the laser beam passes through several material layers constituting the magneto-optical recording medium and reaches the recording magnetic layer, it is necessary to pass through the material layer having excellent optical characteristics as much as possible. The optical pickup is arranged on the substrate side.

However, in such a device configuration, the magnetic field applying means and the optical pickup are arranged to face each other with the magneto-optical recording medium interposed therebetween, which inevitably increases the size of the magneto-optical recording system and complicates the device configuration. Further, since polycarbonate, which is most widely used as a substrate material, has birefringence, there is still a problem with laser light irradiation from the transparent substrate side. Further, when an attempt is made to construct a double-sided magneto-optical recording medium capable of performing double-sided recording / reproducing with a structure for recording / reproducing a signal from the transparent substrate side, the distance from the recording magnetic layer is no matter how the magnetic field applying means is arranged. For example, there are many difficulties in realizing a double-sided magneto-optical recording medium by a magnetic field modulation method, such as an increase in size.

Under such circumstances, the applicant of the present application firstly formed a photocurable resin layer having a pattern of guide grooves and ID signal pits on a substrate by a 2P method, and further reflected a magneto-optical recording layer, There has been proposed a magneto-optical recording medium including an adhesive layer that absorbs the above-mentioned pattern and flattens the surface of the substrate, and a transparent protective plate adhered by the adhesive layer. Since a cover glass or the like having excellent optical properties is used as the transparent protective plate, laser light can be emitted from the transparent protective plate side. Moreover, since this transparent protective plate is a thin material layer having a thickness of 50 to 200 μm, the distance between the magnetic field applying means disposed on the transparent protective plate side and the recording magnetic layer does not greatly increase, and the magnetic field can be applied. It does not affect anything. Therefore, laser light irradiation and a magnetic field can be applied from the transparent protective plate side, and a double-sided magneto-optical recording medium capable of performing magnetic field modulation recording by providing recording portions on both sides of the substrate can be provided.

[Problems to be solved by the invention]

However, in order to achieve truly excellent practical characteristics in the magnetic field modulation method, the key is how to efficiently use the applied magnetic field. If the applied magnetic field can be used efficiently, for example, heat generation of the magnetic field applying means can be suppressed, and the mechanical strength can be increased by increasing the thickness of the transparent protective plate.

To use the applied magnetic field efficiently, see, for example,
As disclosed in JP-A-105838 and JP-A-57-105839, it is conceivable to employ a high magnetic permeability layer. However, when actually trying to apply to the medium of the above configuration,
Several problems arise.

One of them is the effect of heating in the manufacturing process.
The recording magnetic layer of the magneto-optical recording medium is usually formed by sputtering or the like, and the heat generated at this time decreases the magnetic permeability of the high-permeability magnetic thin film, or the gap between the adjacent recording magnetic layer and Stress may be generated due to the difference in the coefficient of thermal expansion.

Another problem is that the pattern of the guide groove and the pit for the ID signal is blurred by repeating the lamination of the functional thin film. In the medium configuration disclosed in Japanese Patent Application Laid-Open No. 57-105839, these patterns are previously formed on the substrate by means of transfer using a stamper, etching, 2P method, or the like. However, the recording magnetic layer has a high permeability magnetic thin film
Further, in some cases, since the recording magnetic layer is formed via the nonmagnetic intermediate layer, the pattern in the recording magnetic layer is considered to be unclear. In particular, these high-permeability magnetic thin films and non-magnetic intermediate layers require a certain thickness in order to exhibit a predetermined effect. Therefore, depending on the situation of step coverage, these patterns are accurately reflected on the recording magnetic layer. It becomes difficult.

Therefore, the present invention is capable of efficiently using an applied magnetic field, reliably forming a guide groove and a pit pattern for an ID signal in a magneto-optical recording layer, and further irradiating a laser beam from a transparent protective plate side with a magnetic field. It is an object of the present invention to provide a magneto-optical recording medium to which application is possible.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, as long as the magnetic field is applied from the transparent protective plate side, the above-described high magnetic permeability layer is of course a substrate rather than a recording magnetic layer. In order to alleviate the stress caused by heating in the manufacturing process and to form a precise pattern, it is preferable that the formation position is between the substrate and the photocurable resin layer. Was found.

The magneto-optical recording medium according to the present invention is proposed based on the above findings, and has a thickness t of 1 μm on a substrate.
It is assumed that a high magnetic permeability layer in the range of <t ≦ 10 μm, a photocurable resin layer having guide grooves and / or signal pits formed thereon, a magneto-optical recording layer, and a transparent protective plate are laminated in this order. It is a feature.

[Operation] The magneto-optical recording medium of the present invention is based on the premise that laser light irradiation and magnetic field application are both performed from the transparent protective plate side.

The first layer formed in contact with the substrate is a high magnetic permeability layer. Due to the presence of the high magnetic permeability layer, the magnetic flux generated from the magnetic field applying means such as a magnetic coil causes the upper transparent protective plate, magneto-optical recording layer, and photo-curable resin layer to be substantially perpendicular to the medium surface. After passing through the high-permeability layer, it travels in the in-plane direction by a distance corresponding to the magnetic field strength, passes through the upper layer again, and returns to the magnetic field applying means, thereby drawing a closed magnetic loop. This means a significant improvement in vertical magnetic field efficiency. That is, if the strength of the magnetic field in the magneto-optical recording layer is sufficient, it is possible to use a magnetic field applying means having a relatively low magnetic field.
On the other hand, if the intensity of the magnetic field generated by the magnetic field applying means is sufficient, it is possible to increase the thickness of the transparent protective plate,
This is effective in increasing the mechanical strength and reliability of the magneto-optical recording medium.

Further, a transparent protective plate is disposed on the uppermost layer of the magneto-optical recording medium of the present invention. If a cover glass or the like is used as this transparent protective plate, the birefringence that causes a reproduction error is eliminated, and even if a magnetic field applying means is arranged on the laser light irradiation side, the distance from the magneto-optical recording layer is greatly increased. It does not increase.

Further, since laser light irradiation is performed from the transparent protective plate side, it is possible to configure a double-sided magneto-optical recording medium by providing a magneto-optical recording layer on both sides of the substrate. Conventional double-sided magneto-optical recording media are manufactured by opposing two single-sided magneto-optical recording media so that the magneto-optical recording layer is on the inside and the substrate is on the outside. In addition, since the distance between the magnetic field applying means and the magneto-optical recording layer necessarily increases, it has been difficult to apply the magnetic field modulation method. On the other hand, in the present invention, since the magnetic field applying means can be approached from the transparent protective plate side as described above, it is possible to provide a double-sided magneto-optical recording medium compatible with the magnetic field modulation system.

On the other hand, in the present invention, the photocurable resin layer is formed on the high magnetic permeability layer. However, since this formation is performed without passing through the heating step, the magnetic permeability of the high magnetic permeability layer is not reduced. . Further, since this photocurable resin layer has a low thermal conductivity, even when a magneto-optical recording layer is formed thereon, it has an effect of reducing stress due to heat and preventing cracks and the like. . In addition, even when the high magnetic susceptibility layer has a slight unevenness in film thickness, an effect of being covered by the fluidity of the resin itself when forming the photocurable resin layer can be expected. Further, since the magneto-optical recording layer is formed directly on the photo-curable resin layer, the pattern of the photo-curable resin layer is accurately reflected on the magneto-optical recording layer, and a reproduction error occurs due to unclear pattern. There is no danger.

〔Example〕

Hereinafter, specific examples in which the present invention is applied to a magneto-optical disk will be described with reference to the drawings.

As shown in FIG. 1, the magneto-optical disk of this embodiment
A photocurable resin layer (3) having a pattern of a high magnetic permeability layer (2), a guide groove (3a) and an ID signal pit (not shown) formed on one surface of a substrate (1); A thin magneto-optical recording layer (4) formed according to the pattern of the curable resin layer (3), and an adhesive layer (5) formed flat by absorbing the pattern of the magneto-optical recording layer (4) And a transparent protective plate (6) for covering the uppermost surface of the medium via the above.

The substrate (1) is a disk having a thickness of about several mm, here 1.2 mm, and is made of a material such as acrylic resin, polycarbonate resin, polyolefin resin, polymethyl methacrylate resin, epoxy resin, glass, Rigid materials such as metals and ceramics are used. In particular, when glass is used, a magneto-optical disk with less dust adherence can be obtained because the glass is less likely to be damaged or bent by the action of an external force and is less likely to be charged. Since the magneto-optical disk of the present invention does not receive laser light irradiation from the substrate side, the substrate (1) does not necessarily need to be made of a transparent material. It is also effective to use a material having a high light reflectance such as Al.

The high magnetic permeability layer (2) is made of a transition metal such as Fe, Co, or Ni, or a soft magnetic material having a high magnetic permeability such as an alloy thereof, such as permalloy or sendust, by means such as sputtering, vacuum deposition, and plating. It is formed by being applied to a thickness of about 1 to 10 μm. The initial permeability of this layer is chosen to be about 500 or more. If it is lower than the above range, the film thickness must be increased in order to obtain a predetermined external magnetic field focusing effect, which increases the thickness of the medium or blurs the pattern of the magneto-optical recording layer. There is a possibility that. The high magnetic permeability layer (2) desirably has a high magnetic flux density of about 5000 gauss or more in combination with the above-mentioned initial magnetic permeability.

The photo-curable resin layer (3) is formed of a resin that is polymerized and cured by light irradiation.
It is formed to a thickness of the order of magnitude. The photocurable resin used in the 2P method has excellent adhesiveness with the high magnetic permeability layer (2), excellent transferability to a stamper and excellent releasability, low polymerization shrinkage, unreacted monomer after polymerization, A material in which no volatile low-molecular compound remains is selected. For example, a conventionally known ultraviolet curable resin composition in which a sensitizer or the like is mixed with various acrylic resins can be applied. In the general 2P method, a metal stamper in which a guide groove or an inverted pattern of ID signal pits is formed in advance and a substrate are arranged at a predetermined interval so as to face each other, and a photocurable resin is injected therebetween, and then the substrate is formed. The curing reaction is performed by irradiating ultraviolet rays from the side. Therefore, the substrate must of course be transparent. However, in the present invention, even if the substrate (1) is transparent, since the opaque high magnetic permeability layer (2) is laminated thereon, the stamper is made of a transparent material, and light is irradiated from the stamper side. It is necessary to devise to do. The transparent stamper can be formed by etching on a glass substrate, injection molding of a polymer material, 2P method, patterning of a resist material, and the like.

Since the step of forming the photocurable resin (3) does not involve heating, there is no possibility that the magnetic permeability of the previously formed high magnetic permeability layer (2) is reduced.

The magneto-optical recording layer (4) formed next is a layer in which a perpendicular magnetic thin film for retaining information is appropriately combined with a functional thin film such as a dielectric film or a metal reflection film.

First, as the material of the perpendicular magnetic thin film that holds information signals and directly participates in recording / reproduction, the perpendicular anisotropy energy is large, it is easy to become the perpendicular magnetization film required for high-density recording, and the Kerr rotation angle is relatively high. A material having characteristics such as being large, having a low Curie point (150 to 200 ° C.), and realizing recording / erasing power with a commercially available semiconductor laser (20 to 40 mW) is selected. Rare earth elements (RE) such as Gd, Tb, Dy and F
A RE-TM amorphous alloy film in combination with a transition element (TM) such as e or Co is a typical example. In particular, a TbFeCo film containing Gb as a rare earth element, a GdTbFe film, etc. have a large perpendicular magnetic anisotropy. ,
It is a highly practical perpendicular magnetic thin film.

The dielectric film is provided for the purpose of improving corrosion resistance and increasing the Kerr rotation angle (Kerr effect enhancement) due to multiple reflection, and is made of a material such as oxide, nitride, oxynitride or the like by vacuum thin film formation. To obtain a film. This dielectric film is generally formed so as to sandwich a perpendicular magnetic thin film.

The metal reflection film is provided to increase the rotation angle by synergizing the Faraday effect with the Kerr effect by also reflecting the laser light transmitted through the RE-TM film, and is usually provided with Al, Au, Pt. , Cu and the like. In this magneto-optical disk, since recording and reproduction are performed from the transparent protective plate (6) side, it is natural that this metal reflection film is arranged on the side closest to the substrate (1) in the magneto-optical recording layer (4). is necessary.

These functional thin films constituting the magneto-optical recording layer (4) are formed by a vacuum thin film forming technique such as sputtering. Therefore, some heat is generated during film formation,
Since the adjacent photocurable resin layer (3) having low thermal conductivity reduces this, there is almost no influence on the high magnetic permeability layer (2). The total thickness of the magneto-optical recording layer (4) is several hundreds to
It is about several thousand square meters. With this thickness, the guide groove (3a) and the step of the pit formed at a depth of 1/4 (around 2000 mm) of the wavelength of the ordinary near-infrared semiconductor laser light are not absorbed, and the magneto-optical recording layer is not absorbed. These patterns are accurately reflected on the surface of (4).

The uppermost surface of the magneto-optical disk is covered by attaching a transparent protective plate (6) having a thickness of about 50 to 300 μm via an adhesive layer (5).

As the material of the adhesive layer (5), the resin used for forming the photocurable resin layer (3) described above can be used as it is. The thickness of the adhesive layer (5) is selected so as to be able to absorb the surface steps of the magneto-optical recording layer (4) and to ensure sufficient adhesiveness. In order to dispose it in the vicinity of ()), it is desirable that it is as thin as possible.

The transparent protective plate (6) is also the same as the photocurable resin layer (4).
For the same reason as described above, it is desirable to reduce the thickness as much as possible. However, in the present invention, since the perpendicular magnetic field efficiency is enhanced by the presence of the high magnetic permeability layer (2), the transparent protective plate (6)
Has a relatively large tolerance for thickness, and those having a thickness of 50 to 300 μm can be used. The greater the thickness, the higher the resistance against external impacts and the like. The transparent protective plate (6) is required to have excellent optical characteristics such as transparency, and the most suitable material therefor is a cover glass. However, since the thickness is extremely thin as compared with the substrate (1), even if a material having a slight birefringence is used, the influence is small.

In the magneto-optical disk having the above configuration, an optical pickup for irradiating laser light and a magnetic field applying means such as a magnetic coil are both disposed on the transparent protective plate (6) side.
At this time, since the thickness of the transparent protective plate (6) is thin, the magnetic field applying means can be brought closer to the magneto-optical recording layer (4), and can be adapted to the magnetic field modulation method. Also,
Since the laser light is irradiated from the transparent protective plate (6) side,
There is no adverse effect due to birefringence as in the case where irradiation is performed from the conventional polycarbonate substrate side, and the reliability of reproduction is improved. When the aperture of the objective lens of the optical pickup and the working distance (the distance between the lens frame and the disk surface) are considered to be constant, laser light irradiation is performed from the side of the thin transparent protective plate (6) to perform magneto-optics. Focusing on the recording layer (4) means that the focal length is shortened, and as a result, the numerical aperture of the objective lens is increased. Therefore, high recording density can be achieved.

Further, such a configuration of the magneto-optical disk also provides some advantages to the device configuration of a magneto-optical recording system using the same.

First, a coil for applying a magnetic field is wound around an optical pickup provided with, for example, a focus servo mechanism, a trunking servo mechanism, and the like, so that the optical pickup and the magnetic field applying means can be compactly integrated. However, in the present invention, since the high magnetic permeability layer (2) provided on the magneto-optical disk effectively converges the magnetic flux generated from the magnetic field applying means, it is necessary to increase the number of turns of the coil or increase the coil diameter. It is not necessary to devise a strong magnetic field,
This makes it possible to reduce the size of the pickup and reduce the amount of heat generated.

Further, even when designing a drive system of the disk, restrictions on loading and chucking of the disk are reduced, and the degree of freedom can be increased.

By the way, the above description has been made on the assumption of a single-sided disk, but the present invention can be applied to a double-sided disk.

FIG. 2 shows an example in which the present invention is applied to a double-sided disk. A high magnetic permeability layer (12), a photo-curable resin layer (13), and a magneto-optical recording layer are formed on both sides of one substrate (11). Layer (14),
An adhesive layer (15) and a transparent protective plate (16) are sequentially laminated. In this double-sided disk, since the substrate (11) is common, it is possible to reduce the thickness of the medium to about half as compared with the conventional double-sided disk bonded.

Further, as in the case of the single-sided disk, it is possible to arrange the optical pickup and the magnetic field applying means on the same surface side to perform recording / reproduction on each magneto-optical recording layer (14) by the magnetic field modulation method. . The fact that the magnetic field modulation method can be applied to a double-sided disk is one of the greatest advantages of the present invention. According to such a configuration, both sides can be simultaneously accessed.

The form of the magneto-optical recording medium to which the present invention is applied is not limited to the above-described disk, but may be a card, a tape, a drum, or the like.

〔The invention's effect〕

As is clear from the above description, in the magneto-optical recording medium of the present invention, the high magnetic permeability layer is first formed in contact with the substrate, and then the photo-curable resin layer, the magneto-optical recording layer, and the transparent protective plate are sequentially laminated. The structure is made. Therefore, when a magnetic field is applied from the transparent protective plate side, the vertical magnetic field efficiency can be increased. In addition, a highly reliable magneto-optical recording medium is provided because the photo-curing resin layer can reduce stress between the high magnetic permeability layer and the magneto-optical recording layer and form a precise pattern on the magneto-optical recording layer. Is done. Further, a double-sided magneto-optical recording medium based on a magnetic field modulation method, which has been considered difficult to use in the past, opens the way to practical use.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an essential part showing an example in which the present invention is applied to a single-sided magneto-optical disk, and FIG. 2 is a schematic sectional view of an essential part showing an example in which the present invention is applied to a double-sided magneto-optical disk. 1,11 ... substrate 2,12 ... high magnetic permeability layer 3,13 ... photocurable resin layer 4,14 ... magneto-optical recording layer 5,15 ... adhesive layer 6,16 ... transparent protective plate

Claims (1)

(57) [Claims] 1. A high-permeability layer having a thickness t in a range of 1 μm <t ≦ 10 μm, a photocurable resin layer having a guide groove and / or a signal bit formed thereon, a magneto-optical recording layer,
A magneto-optical recording medium in which transparent protective plates are laminated in this order.