JP2001344815A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform recording / reproducing signal by keeping a distance between a head flying above an optical recording medium and a surface of the medium constant in a recording / reproducing area, and to reduce a head crash. To provide an optical recording medium with high performance. SOLUTION: A disk-shaped substrate has a recording layer and a dielectric layer in a single-plate structure having lands and grooves on both sides thereof, and a hub is provided on only one side, and recording and reproduction are performed using a floating head. In the near-field optical recording medium, when the medium is held by the hub with the hub mounting surface facing downward, the radial distance L from the innermost circumference to the outermost circumference of the recording / reproducing area is L / 3. The radial center of curvature in the region
On the side opposite to the side with the hub.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical recording medium.

[0002]

2. Description of the Related Art Magneto-optical recording media are portable recording media capable of large-capacity, high-density recording, and have been used as rewritable media for recording large-capacity files and moving images of computers accompanying the recent increase in multimedia. Demand is increasing rapidly.

A magneto-optical recording medium is generally formed by forming a multilayer film including a recording layer on a transparent disk-shaped substrate such as plastic.
Recording and erasing are performed by irradiating a laser while applying a magnetic field, and reproduction is performed by reflected light of the laser. Conventionally, the recording method is
So-called optical modulation recording, in which recording is performed by applying a fixed magnetic field in the opposite direction after erasing by applying a fixed magnetic field, has been the main focus.In recent years, a magnetic field modulation method that modulates a magnetic field according to a recording pattern while irradiating a laser, Attention has been paid to a method capable of performing recording (direct overwrite) in one rotation and accurately recording even at a high recording density.

[0004] A laser for recording / reproducing has hitherto been applied to a recording film through a substrate. Recently, so-called near-field optical recording, in which an optical head is brought close to a recording film to perform recording and reproduction, has attracted attention as a means for increasing the density (Appl.
Phys. Lett. 68, p. 141 (199
6)). In this recording method, Solid Immersi
By using an onLens (hereinafter abbreviated as SIL) head and reducing the laser beam spot size, the conventional recording limit (〜λ / 2NA: NA is the numerical aperture of the objective lens) determined by the laser wavelength (λ) of the light source is obtained. Reproduction with a short mark is possible, and recording and reproduction with an ultra-high recording density can be realized.

[0005] In this near-field optical recording, it is necessary to bring the optical head close to the optical recording medium (up to 100 nm).
Instead of irradiating the recording film with the laser beam through the substrate as in the conventional magneto-optical recording medium, a method of directly irradiating the recording film with the laser beam without passing through the substrate is used.

That is, in a conventional optical recording medium having a recording film structure of a substrate / first protective layer / recording layer / second protective layer / reflective layer, a near-field light is generally used. In the recording, recording / reproducing is performed by irradiating a laser beam from the film surface side as a film structure of the reverse structure of the substrate / reflective layer / first protective layer / recording layer / second protective layer (surface reading type recording).

At this time, a floating slider head is often used to bring the recording film and the SIL head closer to each other. As for recording, near-field magneto-optical recording is a magnetic field modulation recording in which recording is performed by irradiating a laser beam to raise the recording layer above the Curie temperature and modulating the magnetic field with a thin-film coil formed on the slider head. It is said to be suitable.

In this near-field optical recording / reproducing method, the distance between the floating optical head and the optical recording medium is very short, and even if the distance between the head and the surface of the optical recording medium fluctuates slightly, the recording / reproducing is performed. It is also conceivable that the signal strength varies and hinders recording / reproducing, or the head and the optical recording medium are damaged due to the contact between the head and the recording medium.

The near-field optical recording medium has a land, a groove, and a header having format information for tracking a laser beam. For this reason,
As a substrate of the near-field optical recording medium, it is general to obtain a thermoplastic resin by injection molding using a stamper on which lands, grooves, and headers are formed. Also,
In order to hold the optical recording medium on the spindle when the optical recording medium is installed in the drive, a hub is provided at substantially the center of one side of the optical recording medium.

In order to keep the distance between the head flying above the optical recording medium and the surface of the optical recording medium constant, it is important to strictly control so-called mechanical characteristics such as deflection and warpage of the optical recording medium. However, a substrate made of a thermoplastic resin has a lower mechanical strength than a substrate made of metal or glass, and thus is easily bent, and the optical recording medium is easily distorted due to the attachment of the hub, especially inside the vicinity of the hub. In conventional near-field optical recording media using a substrate formed by injection molding a thermoplastic resin, it is difficult to keep the distance between the head and the surface of the optical recording medium constant over the entire recording / reproducing area, and a uniform recording / reproducing signal is generated. It was difficult to get.

[0011]

The problem to be solved by the present invention is to maintain uniform distance between the head floating above the recording medium and the surface of the optical recording medium over the entire recording and reproducing area, thereby achieving uniform recording and reproducing. An object of the present invention is to provide a highly reliable optical recording medium which can obtain a signal and does not easily crash with the head.

[0012]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned current situation, and as a result, completed the present invention.

That is, the present invention provides a disk-shaped single-plate substrate formed by injection-molding a thermoplastic resin, on both front and back surfaces of which at least substantially concentric or substantially spiral lands and grooves are provided, and at least a recording layer is formed thereon. , A near-field optical recording medium having a dielectric layer, provided with a hub only on one side, and capable of recording and reproducing by laser light using a floating optical head, with the hub attached side down and the hub When the optical recording medium is held, the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area is L / 3 from the innermost circumference.
The optical recording medium is characterized in that the center of curvature in the radial direction in the region up to is located on the surface opposite to the surface to which the hub is attached.

Hereinafter, the present invention will be described in detail.

FIG. 1 is a sectional view showing an example of the optical recording medium of the present invention. A reflection layer 12 is provided on both sides of a substrate 11 having a land, a groove, and a header formed on both sides.
The recording layer 13 and the dielectric layer 14 are laminated in this order.
Furthermore, a hub 1 is provided on the surface to be installed on the drive spindle.
5 is attached to the center of the substrate.

The substrate 11 is obtained by arranging stampers on which lands, grooves, and headers are formed on both sides of a mold, and injecting a thermoplastic resin into the mold. As the substrate material, it is preferable to use a substrate obtained by injection molding polycarbonate, amorphous polyolefin, polymethyl methacrylate, polyphenylene sulfide, polyarylate, polyether ketone, polyether ether ketone and derivatives thereof.
By using these substrate materials, the center of curvature of the optical recording medium, the height of the optical recording medium, and the radius of curvature of the optical recording medium according to the present invention can be controlled by injection molding conditions.

The diameter of the substrate used for the optical recording medium is 90 to 90.
It is preferably 140 mm. Further, the thickness of the substrate used for the optical recording medium is preferably 1 to 2.5 mm. With the substrate diameter and the thickness in this range, the center of curvature of the recording medium, the height of the recording medium, and the radius of curvature of the recording medium according to the present invention can be controlled by injection molding conditions.

The reflective layer 12 is not particularly limited as long as it is a metal having a high reflectance. For example, Al, Ag, Au, C
A single metal such as u or an alloy containing these as main components can be used.

The recording layer 13 is not particularly limited as long as it can be used as an optical recording layer. For example, TbFeCo, DyFeCo, GdTbFeC
o, a magneto-optical recording film such as NdDyFeCo, GeSbT
e, a phase change recording film such as AgInSbTe can be used, and the recording layer may be a single layer or a laminated film in which films having different functions and compositions are laminated.

The dielectric layer 14 is made of SiN, AlN, SiA
It is composed of a transparent dielectric such as 1ON or Ta ₂ O ₅ . Further, a solid lubricating layer such as diamond-like carbon (DLC) in which hydrogen or nitrogen is added to carbon may be laminated on the dielectric layer, and a liquid lubricating layer may be further applied thereon. As the liquid lubricating layer, any material having lubricity such as silicone oil or fluoropolyether-based fluorine oil can be used, but perfluoropolyether and perfluoropolyether derivatives are particularly desirable.

Examples of perfluoropolyether derivatives include alcohol-modified perfluoropolyether, ester-modified perfluoropolyether, isocyanate-modified perfluoropolyether, carboxyl group-modified perfluoropolyether, and piperonyl-modified perfluoropolyether. .

The thickness of the lubricating layer in the present invention is
0.3-4.0 nm is preferred. When the thickness is less than 0.3 nm, the protective performance of the lubricating layer is insufficient, and the thin film is easily damaged. When the thickness exceeds 4.0 nm, the slider head may stick to the disk and cause a crash.

The hub 15 attached to the optical recording medium is not particularly limited as long as it can be fixed to a spindle in a drive such as a metal hub or a metal insert hub. In addition, the method of bonding the optical recording medium and the hub can be performed by a method such as an adhesive or ultrasonic welding, and is not particularly limited as long as a sufficient bonding strength is obtained.

In the optical recording medium of the present invention, when the optical recording medium is held by the hub with the surface on which the hub is attached facing down, the radial distance (L) from the innermost circumference to the outermost circumference of the optical recording / reproducing area is determined. The center of curvature in the radial direction in the region from the innermost circumference to L / 3 is located on the surface opposite to the surface to which the hub is attached.

FIG. 2 schematically shows an example of the cross-sectional shape of the optical recording medium of the present invention, but the present invention is not limited to only this figure.

When a hub is attached to an optical recording medium using an adhesive, local stress is generated in the vicinity of the bonded portion due to volume shrinkage of the adhesive and, in ultrasonic welding, due to vibration energy. This stress causes distortion inside the optical recording medium, and as a result, irregularities easily occur on the surface of the optical recording medium, and these irregularities affect the flying characteristics of the head.
In other words, the head flies so as to keep the distance from the surface of the optical recording medium constant, but the head lowers in a concave portion on the surface of the optical recording medium and rises in a convex portion, and as a result, the flying height of the head decreases. Will fluctuate. When this fluctuation becomes large, the intensity of the optical recording / reproducing signal varies, and furthermore, the head and the optical recording medium come into contact, causing a crash.

As described above, by making the center of curvature of the optical recording medium opposite to the mounting surface of the hub, the force of the optical recording medium retaining its shape is superior to the stress generated when the hub is bonded. As a result, the flatness of the optical recording medium surface is not affected. It is more preferable that the center of curvature is located on the surface opposite to the surface provided with the hub over the entire recording / reproducing area so that the optical recording medium can maintain its shape stably.

As a method of controlling the direction of the center of curvature of the surface of the optical recording medium, the temperature of the fixed side and the movable side of the mold used during injection molding is made different so that the substrate can be taken out from the mold. The pressure of the blown air can be controlled by making a difference between the fixed side and the movable side, and by injection molding conditions such as operating conditions of a protruding pin when the substrate is released from the mold.

Further, for a substrate formed by using a molding die having a floating punch and an ejection pin for projecting the injection-molded substrate, a hub is attached to the medium surface side where the floating punch and the ejection pin exist. Is preferred. The floating punch and the protruding pin operate when the injection-molded substrate is removed from the mold. However, since the substrate temperature at this stage is still high, the deflection of the central portion of the substrate tends to increase when the substrate is operated.

The optical recording medium of the present invention floats on the optical recording medium by maintaining each of the following constitutions (1) to (3) individually or plurally while maintaining the above constitution. This is preferable because the distance between the head and the surface of the optical recording medium can be kept more constant over the entire optical recording / reproducing area, so that a uniform recording / reproducing signal can be obtained and the head is less likely to crash.

The specific configuration is as follows.

(1) When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, of the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area, L In the area up to / 3, when the innermost circumference of the recording / reproducing area is set as the base point, the area outside the base point is lower by 5 μm to 100 μm than the base point.

When the optical recording medium has a deflection in the radial direction, when the optical recording medium rotates during recording and reproduction, the direction changes in a direction in which the deflection is corrected by the centrifugal force. At this time, if the outer side of the recording / reproducing area is lower than the innermost side, stress is applied in the direction in which the optical recording medium surface contracts in the direction opposite to the hub mounting surface and in the direction in which the hub mounting surface expands. The stress on the inner portion of the surface of the optical recording medium caused by the adhesion acts in a direction in which it is alleviated, and the flatness is improved, so that the flying characteristics of the head are improved.

Conversely, if the outer side of the optical recording / reproducing area is higher than the innermost side, stress is applied in the direction in which the surface of the optical recording medium expands on the side opposite to the hub mounting surface and in the direction in which the hub mounting surface contracts. Therefore, the stress on the inner portion of the surface of the optical recording medium caused by the adhesion of the hub acts in a direction in which the stress becomes larger, so that the unevenness on the surface increases, and the flying characteristics of the head deteriorate.

As for the range to be reduced, if it is less than 5 μm, the stress due to the adhesion of the hub is not reduced, and if it exceeds 100 μm, the correction amount of the deflection when the optical recording medium rotates is exceeded, and Levitation becomes unstable.

In order to effectively relieve the stress caused by the adhesion of the hub, even in a region from the position exceeding L / 3 from the innermost periphery to the outermost periphery, 5 μm to 100 μm from the base point.
It is further preferable that the height be lower by 5 μm to 100 μm than the reference point over the entire optical recording / reproducing area.

As a method for lowering the height from the base point of the surface of the optical recording medium, a difference is made between the temperatures of the fixed side and the movable side of the mold used during injection molding, and the substrate is taken out of the mold. In this case, it is possible to control the pressure of the air to be blown by making a difference between the fixed side and the movable side, and to control the injection molding conditions such as the operating condition of the protruding pin when the substrate is released from the mold.

(2) When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area is L In the region up to / 3, the radius of curvature in the radial direction of the surface of the optical recording medium having the same width as the slider width of the head is set to 10 m or more.

The stress caused by the adhesion of the hub causes distortion near the inner region of the surface of the optical recording medium. As a result, the unevenness affects the flying characteristics of the head. However,
Regarding the irregularities on the surface of the optical recording medium that occur in a large range with respect to the size of the slider of the head, since the head easily follows the irregularities, the influence on the fluctuation of the flying height is small, and the small range with respect to the slider size. The unevenness of the surface of the optical recording medium caused by the above has little effect on the flying height.

Therefore, if the radius of curvature of the surface of the optical recording medium in the radial direction equivalent to the width of the slider of the head is as large as 10 m or more, even if the flying height of the head fluctuates, the recording / reproducing signal intensity varies. Is within a negligible range. More preferably, the radius of curvature is 10 m or more over the entire recording / reproducing area.

As a method of increasing the radius of curvature, the temperature of the fixed side and the movable side of the mold used during injection molding are set to be different from each other, and the pressure of the air blown when the substrate is taken out from the mold is fixed. It can be controlled by making a difference between the movable side and the movable side, and also by injection molding conditions such as operating conditions of a protruding pin when the substrate is released from the mold.

As a method of measuring the radius of curvature of the surface of the optical recording medium, for example, a stylus-type displacement is applied to the upper surface of the optical recording medium while the optical recording medium is held by the hub with the surface to which the hub is attached facing downward. The height of the lower surface is measured using an optical displacement meter, and the radius of curvature according to the slider width or length of the head is calculated from the displacement data. It is required by doing.

(3) When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, the radius of curvature in the circumferential direction of the surface of the optical recording medium having the same length as the slider length of the head is 10 m or more. Similarly to the radius of curvature in the radial direction, if the radius of curvature in the circumferential direction is as large as 10 m or more, even if the flying height of the head fluctuates, it is slight, and the variation in the recording / reproducing signal intensity is within a negligible range.

In the above description, the case where the optical recording medium of the present invention is held with the hub surface facing down has been described. When the non-recording / reproducing area at the center of the optical recording medium is held with the hub surface facing upward, the radius of curvature Rr in the radial direction having the same width as the slider width of the head on the upper surface of the recording medium is: 1m ≦ Rr ≦ 10m, and preferably, the radius of curvature Rt in the circumferential direction of the same length as the slider length of the head is 1m ≦ Rr on the upper surface of the medium.
t ≦ 10 m. More preferably, in the radial direction of the recording medium, the center of curvature of the arc formed by the three points of the innermost circumference, the outermost circumference, and the intermediate point of the recording / reproducing area exists below the arc.

[0045]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to only these Examples.

Example 1 A polycarbonate-made diameter having a spiral land / groove portion and a header portion with a track pitch of 0.43 μm on both front and back surfaces and an optical recording / reproducing area (L) having a radius of 20 to 60 mm. 130mm and thickness 2mm
120kg / cm ² by injection molding
It was manufactured at a clamping pressure of. As a mold used for molding, a mold having a structure including a pair of a movable side and a fixed side is used,
The temperature of the movable mold mirror surface was adjusted to 112 ° C., and the temperature of the fixed mold mirror surface was adjusted to 110 ° C.

Using this substrate, a film was formed on both surfaces of the substrate by a sputtering method in the following manner.

First, a 50 nm-thick Al-3 wt% Cr alloy film was formed as a reflective layer on a substrate by DC sputtering. A first protective layer made of SiN having a thickness of 5 nm was formed thereon by a reactive RF sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ . Tb on this
_{A 20} nm thick magneto-optical recording layer made of ₂₀ (Fe ₉₀ Co ₁₀ ) _{80 is} formed of a Tb target and a Fe ₉₀ Co ₁₀ target DC.
It was formed by a simultaneous sputtering method.

Further, a second protective layer made of SiN having a thickness of 50 nm was formed thereon by a reactive RF sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ . On top of this, the refractive index at 633 nm is 1.85 and the film thickness is 10
A DLC layer having a thickness of nm was formed by a reactive RF sputtering method using a C target in a mixed atmosphere of Ar and CH ₄ .

Then, on the other side, the reflection layer, the first protective layer, the magneto-optical recording layer, the second protective layer, and the
C layer was formed. After forming the DLC layer, piperonyl-modified perfluoropolyether (trade name "Fomblin: AM2001", manufactured by Audimont Co.) using a perfluoropolyether solvent (trade name "Galden SV-70", manufactured by Audimont) By pulling up the optical recording medium from a 0.01 wt% solution of
Was applied. The thickness of the lubricating layer is determined by X-ray photoelectron spectroscopy (XP
Calculated by observing the C1S peak intensity using S).

Further, a metal insert hub was attached to the center of the substrate surface formed by the mirror surface on the movable side of the mold with an ultraviolet-curing adhesive to manufacture a magneto-optical recording medium capable of recording and reproducing on both sides.

Example 2 When a substrate is obtained by injection molding, the pressure of air blown when the substrate is taken out of the mold is set different between the fixed side and the movable side, and the pressure on the fixed side is increased by 0.5 kg / cm ^2. A magneto-optical recording medium capable of double-sided recording / reproduction was manufactured in the same manner as in Example 1 except that the measurement was performed, and the radius of curvature was measured.

Comparative Example 1 The same procedure as in Example 1 was carried out except that when the substrate was obtained by injection molding, the temperature of the movable mold mirror surface and that of the fixed mold mirror surface were different, and the fixed mirror surface temperature was raised by 2 ° C. A magneto-optical recording medium capable of double-sided recording and reproduction was manufactured by the method, and the radius of curvature was measured.

Comparative Example 2 When a substrate was obtained by injection molding, the pressure of air blown when the substrate was taken out of the mold was made different between the fixed side and the movable side, and the pressure on the movable side was increased by 0.5 kg / cm ^2. A magneto-optical recording medium capable of double-sided recording / reproduction was manufactured in the same manner as in Example 1 except that the measurement was performed, and the radius of curvature was measured.

The following evaluations were performed on the near-field magneto-optical recording media manufactured by the methods of Examples 1 and 2 and Comparative Examples 1 and 2.

The hub is held so that the surface on which the optical recording medium is attached faces downward, and the height displacement data of the upward surface and the downward surface is transferred to an RVA tester (THOT TECHNOLOGY).
Manufactured by the company). The measurement range is from the radius 19 of the optical recording medium.
The distance is set to 61 mm, and the measurement is performed at four locations in the circumferential direction of the optical recording medium. Based on the height displacement data, the radius is 20 to 33 mm and the radius is 20 to 60 m when the height of the radius is 20 mm as a base point.
m height displacement (maximum) was calculated.

The radius of curvature between 2 mm corresponding to the slider width of the flying head was obtained by sequentially calculating the radius of curvature within the range of 20 to 60 mm. At the same time, radius 20 ~ 33m
m and the center of curvature having a radius of 20 to 60 mm were determined.

Further, the radius of curvature of the optical recording medium in the circumferential direction was measured using the same measuring instrument. The measurement range is 1 mm at intervals of 1 mm between a radius of 20 to 60 mm of the optical recording medium, and one round is performed for each radius position. From the height displacement data, about 3 mm corresponding to the slider length of the flying head for each radius position is obtained. The radius of curvature between them was obtained by sequentially calculating over one round.

Subsequently, the flying characteristics of the optical recording medium were evaluated. First, the optical recording medium was set on the spindle of a glide tester (manufactured by Hitachi Electronics Engineering), followed by a 70% slider with a piezo element and an optical recording medium of a glide head (manufactured by Glidelight) with a 6.0 g load. The optical recording medium is rotated at a linear velocity of 7 m / sec so that the flying height from
A range of 60 mm was sought once on both front and back sides simultaneously. At this time, the voltage induced in the piezo element was monitored, and the number of signals whose voltage value exceeded 500 mV was counted as the number of hits.

Subsequently, the SNR was measured. The optical recording medium is rotated at 2,400 revolutions per minute, and a floating optical head having a slider with a laser wavelength of 680 nm and an effective numerical aperture of 1.2 on the thin film surface is floated to a height of 100 nm on the optical recording medium by dynamic loading. Then, while irradiating a pulsed laser to warm the recording layer above the Curie temperature, recording was performed while modulating the coil magnetic field on the head at 10 MHz, and the SNR when recording at 10 MHz was measured at the radial position 20 on both the front and back surfaces of the recording medium. , 30,40,5
Measurements were made at a total of 10 points of 0 and 60 mm, and the variation was determined from the difference between the maximum value and the minimum value for each of the front and back surfaces. The value of the SNR was obtained by adjusting the reproduction power of each medium and measuring the SNR under the condition that the SNR was maximized. Table 1 summarizes the results of each evaluation.

[0061]

[Table 1]

In the first and second embodiments, the height in the radial direction with respect to a radius of 20 mm is low in both the radial direction L / 3 region and the entire recording / reproducing region, and the displacement amount is approximately 10 to 10.
It was 80 μm. The centers of curvature in the radial direction were all opposite to the hub mounting surface, and the radius of curvature was 10 m or more. The radius of curvature in the circumferential direction also became a value of 10 m or more. The number of hits at this time is 0 to 1 on both sides, indicating good flying characteristics. Also, the variation in SNR is 1 dB.
Less and good.

In Comparative Examples 1 and 2, the substrate was injection-molded so that the bending direction of the optical recording medium was opposite to that of the embodiment. / 3 area and the entire recording / reproducing area were high, and the displacement amount was about 10 to 70 μm. The centers of curvature in the radial direction were all on the hub mounting surface side, and the radius of curvature was less than 10 m. Further, the radius of curvature in the circumferential direction also became a value of less than 10 m. The flying characteristics at this time were such that a ring-shaped hit occurred near the inner peripheral side of the optical recording medium, indicating unstable floating characteristics. Also, the SNR variation is 3 to
This is as large as 4 dB, suggesting that the influence of the fluctuation of the flying height of the head is great.

Example 3 A circular substrate made of polycarbonate having a diameter of 130 mm and a thickness of 2 mm and having a spiral land / groove portion having a track pitch of 0.43 μm and a header portion on both front and rear surfaces was manufactured by an injection molding method. The mold used for molding is a mold composed of a pair of a movable part and a fixed part. The plasticized resin is injected from the fixed part side, and the floating punch and protrusion pins operate from the movable part side to take out the substrate. After the injection was completed and the movable part mold was opened 5 seconds after the mold was opened, the floating punch and the protruding pin were operated to prepare a substrate. In addition, the mold temperature of both the fixed part and the movable part was 110 ° C.

Using this substrate, a film was formed on both surfaces of the substrate by a sputtering method in the following manner.

First, an Al-3 wt% Cr alloy film having a thickness of 50 nm was formed as a reflective layer on a substrate by DC sputtering. A first protective layer made of SiN having a thickness of 5 nm was formed thereon by a reactive RF sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ . Tb on this
_{A 20} nm thick magneto-optical recording layer made of ₂₀ (Fe ₉₀ Co ₁₀ ) _{80 is} formed of a Tb target and a Fe ₉₀ Co ₁₀ target DC.
It was formed by a simultaneous sputtering method.

Further, a second protective layer made of SiN having a thickness of 50 nm was formed thereon by a reactive RF sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ . On top of this, the refractive index at 633 nm is 1.85 and the film thickness is 10
A DLC layer having a thickness of nm was formed by a reactive RF sputtering method using a C target in a mixed atmosphere of Ar and CH ₄ .

Next, on the other side, the reflection layer, the first protective layer, the magneto-optical recording layer, the second protective layer and the DL
C layer was formed.

After the formation of the DLC layer, piperonyl-modified perfluoropolyether (trade name “Fomblin: trade name: Audimont Co., Ltd., using a perfluoropolyether solvent (trade name: Galden SV-70)”) was used. A lubricating layer was applied to a thickness of 1.5 nm by pulling up the recording medium from a 0.01 wt% solution of AM2001 "). The thickness of the lubricating layer was calculated by using X-ray photoelectron spectroscopy (XPS) and observing the C1S peak intensity.

Further, at the time of injection molding, a metal insert hub was attached to the surface of the substrate where the floating punches and the protruding pins were present with an ultraviolet-curable adhesive, thereby producing a magneto-optical recording medium capable of double-sided recording and reproduction.

The non-recording / reproducing area at the center of the optical recording medium is held so that the hub surface of the optical recording medium thus manufactured faces upward, and the radius of curvature of the upward facing surface is measured by a probe-type surface roughness measuring device Surfcoder (Kosaka). Laboratories). The measurement range is a radius of the recording medium of 17 to 61 mm, and the measurement is performed at four locations in the circumferential direction of the recording medium. From the height displacement data, a radius of curvature between 2 mm corresponding to the slider width of the flying head is sequentially determined within a radius of 18 to 60 mm. Obtained by calculation.
Also, based on this data, the radial positions 18, 39, 60 mm
It was determined whether the center of curvature of the three-point arc exists above or below the arc. Further, the radius of curvature of the recording medium in the circumferential direction is determined by an RVA tester (THOTTECHNOL).
OGY). The measurement range is radius 1 of the recording medium
One round is performed for each radial position in the range of 7 to 60 mm at intervals of 1 mm, and from the height displacement data, the radius of curvature of about 3 mm corresponding to the slider length of the flying head for each radial position is reduced to one round. Obtained by calculating over time. Table 2 shows the results.

Example 4 When a substrate was obtained by injection molding, the time between the completion of injection of the polycarbonate resin into the mold and the operation of the ejection pin in the mold was shortened by 2 seconds. A magneto-optical recording medium capable of double-sided recording and reproduction was manufactured in the same manner, and the radius of curvature was measured. Table 2 shows the results.

Example 5 When a substrate was obtained by injection molding, the temperature of the movable part side mold and that of the fixed part side mold were set different from each other, except that the movable part side mold temperature was raised by 3 ° C. A magneto-optical recording medium capable of double-sided recording and reproduction was produced in the same manner, and the radius of curvature was measured. Table 2 shows the results.

Comparative Example 3 When a substrate was obtained by injection molding, the time from the completion of injection of the polycarbonate resin into the mold to the activation of the ejection pin in the mold was shortened by 5 seconds. Example 3 except that a metal insert hub was attached to the surface opposite to the surface where the floating punch and the protruding pin were present at the time of injection molding with an ultraviolet curable adhesive.
A magneto-optical recording medium capable of double-sided recording and reproduction was manufactured in the same manner as described above, and the radius of curvature was measured. Table 2 shows the results.

Comparative Example 4 When a substrate was obtained by injection molding, the time from the completion of injection of the polycarbonate resin into the mold to the actuation of the ejection pin in the mold was set to 30 seconds after the mold was opened, and the movable part was In addition to lowering the temperature of the side mold and the fixed part side mold uniformly by 12 ° C, the metal insert hub was attached to the surface opposite to the surface where the floating punch and the protruding pin existed during injection molding with an ultraviolet curing adhesive. In the same manner as in Example 3, a magneto-optical recording medium capable of double-sided recording and reproduction was manufactured, and the radius of curvature was measured. Table 2 shows the results.

The following evaluations were performed on the near-field magneto-optical recording media manufactured in Examples 3 to 5 and Comparative Examples 3 and 4.
First, the flying characteristics of this recording medium were evaluated. First, the recording medium was set on a spindle of a glide tester (manufactured by Hitachi Electronics Engineering Co., Ltd.). Subsequently, a 70% slider with a piezo element and a flying height of 6.0 g load from a recording medium of a glide head (manufactured by Glide Light Co.) were 5
The recording medium was rotated at a linear velocity of 7 m / sec so as to be constant at 0 nm, and the recording medium was sought once in a range of a radius of 18 to 60 mm simultaneously on both the front and back surfaces. At this time, the voltage induced in the piezo element was monitored, and the number of signals whose voltage value exceeded 500 mV was counted as the number of hits. Then SNR
Was measured. The recording medium is rotated at 2400 revolutions per minute, and a floating optical head having a slider with a laser wavelength of 680 nm and an effective numerical aperture of 1.2 on the thin film surface is levitated to a height of 100 nm on the recording medium by dynamic loading. While the recording layer is heated above the Curie temperature by irradiating the
Hz while recording at 10 MHz.
The measurement was performed at a total of 10 points of 0, 30, 40, 50, and 60 mm, and the variation was obtained from the difference between the maximum value and the minimum value for each of the front and back surfaces. The value of the SNR was obtained by adjusting the reproduction power of each medium and measuring the SNR under the condition that the SNR was maximized. Table 1 summarizes the results of each evaluation.

[0077]

[Table 2]

In the third embodiment, the radius of curvature satisfies the range of 1 to 10 m in both the radial and circumferential directions, and the center of curvature exists below the arc. The number of hits at this time is 0 on both sides
Good levitation characteristics are shown for each piece. In addition, the variation in SNR was as good as 1 dB or less.

In the fourth embodiment, the radius of curvature in the circumferential direction is reduced because the time until the push-out pin is actuated during the molding of the substrate is reduced, but the radius of curvature in the radial direction satisfies the range of 1 to 10 m. The center of curvature is below the arc.

Further, in Example 5, the radius of curvature in the radial direction was small because the temperature of the mold during forming the substrate was different, but the radius of curvature in the circumferential direction satisfied the range of 1 to 10 m. The center of curvature is below the arc. In Examples 4 and 5, the number of hits was as good as 0 to 2, and the SNR was also as good as 1 dB or less in variation.

On the other hand, in Comparative Example 3, since the time until the push-out pin operation during the molding of the substrate was further shortened and the substrate was taken out of the mold before the substrate was sufficiently cooled, the radius of curvature in both the radial and circumferential directions was increased. Was partially less than 1 m, and the center of curvature was above the arc. The flying characteristics at this time are such that a ring-shaped hit occurs near the inner circumference of the recording medium,
It showed unstable levitation. Also, the SNR tends to be small on the inner circumference side and larger on the outer circumference side, and the variation is about 4%.
It has increased to dB.

In Comparative Example 4, since the time until the push-out pin was activated during the molding of the substrate was increased and the mold temperature was also decreased,
When the substrate is taken out of the mold, the substrate is sufficiently cooled. Therefore, the radius of curvature in both the radial direction and the circumferential direction exceeded 10 m, and the center of curvature was above the circular arc. The flying characteristics at this time were such that a ring-shaped hit occurred near the inner peripheral side of the recording medium, indicating unstable floating characteristics. Further, the SNR tends to be small on the inner circumference side and larger on the outer circumference side, and has a large variation of about 4 dB.

[0083]

According to the present invention, a uniform recording / reproducing signal can be obtained by keeping the distance of the head floating above the optical recording medium from the surface of the optical recording medium constant throughout the optical recording / reproducing area. And a highly reliable optical recording medium that is unlikely to crash.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a laminated structure of an optical recording medium of the present invention.

FIG. 2 is a diagram schematically illustrating an example of a cross-sectional structure of the optical recording medium of the present invention.

[Explanation of symbols]

 11: Substrate 12: Reflective layer 13: Recording layer 14: Dielectric layer 15: Hub

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/105 521 G11B 11/105 521A 536 536C 541 541B 546 546D

Claims (10)

[Claims] 1. A disc-shaped single-plate substrate obtained by injection-molding a thermoplastic resin is provided with at least lands and grooves substantially concentrically or substantially spirally on both front and back surfaces thereof, and at least a recording layer and a dielectric layer thereon. A near-field optical recording medium that has a hub on one side only and can be recorded and reproduced by laser light using a floating optical head, and the optical recording medium is mounted on the hub with the surface with the hub facing down. When held, of the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area, in the area from the innermost circumference to L / 3, the center of curvature in the radial direction is opposite to the surface to which the hub is attached. An optical recording medium characterized in that: 2. When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, of the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area, the distance from the innermost circumference to L
In the area up to / 3, when the innermost circumference of the recording / reproducing area is set as a base point, the area outside the innermost circumference is 5 μm from the base point.
2. The optical recording medium according to claim 1, wherein the distance is lower by m to 100 [mu] m. 3. When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, of the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area, the distance from the innermost circumference to L
In the region up to / 3, the radius of curvature in the radial direction of the surface of the optical recording medium having the same width as the slider width of the head is 10 m.
The optical recording medium according to claim 1, wherein: 4. When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area is L
4. A region from a position exceeding / 3 to an outermost periphery, wherein a center of curvature in a radial direction in a recording / reproducing region is located on a surface opposite to a surface to which a hub is attached. The optical recording medium according to the above. 5. When the optical recording medium is held by the hub with the surface on which the hub is attached facing down, the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area is L
5. In a region from a position exceeding / 3 to an outermost periphery, when an innermost periphery of the recording / reproducing region is set as a base point, an outer region is 5 to 100 [mu] m lower than the base point. The optical recording medium according to any one of the above items. 6. When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, the radial distance (L) from the innermost circumference to the outermost circumference of the recording / reproducing area is L
6. The optical recording medium according to claim 1, wherein a radius of curvature of a surface of the optical recording medium having a width equal to the slider width of the head in a radial direction is 10 m or more in a region from the position exceeding / 3 to the outermost periphery. The optical recording medium according to item 1. 7. When the optical recording medium is held by the hub with the surface on which the hub is attached facing downward, the radius of curvature in the circumferential direction of the surface of the optical recording medium having the same length as the slider length of the head is one.
The optical recording medium according to any one of claims 1 to 6, wherein the distance is 0 m or more. 8. The disk-shaped substrate according to claim 1, wherein the disk-shaped substrate is injection-molded using a molding die having a floating punch and a projection pin for projecting the molded substrate. The optical recording medium according to claim 1. 9. The optical recording medium according to claim 8, wherein a hub is provided on the substrate surface side where the floating punch and the protruding pin exist. 10. The substrate according to claim 1, wherein the substrate is made of polycarbonate, amorphous polyolefin, polymethyl methacrylate, polyphenylene sulfide, polyarylate, polyether ketone, polyether ether ketone and derivatives thereof.
The optical recording medium according to item 1.