JP2001319374A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium which adopts a surface optical recording system, hardly causes head crash and does not impair the optical characteristics of an optical head. SOLUTION: At least an optical recording layer and a lubricative underlayer are formed on a substrate with a spiral guide groove or concentric guide grooves which take part in recording and reproduction, a layer comprising a perfluoro-polyether derivative and having 0.3 to <2.0 nm thickness is formed as a lubricative layer on the lubricative underlayer and the aggregated state of the perfluoro-polyether derivative obtained by analyzing the distribution of fragment ion peaks using TOF-SIMS is adjusted to <=10 μm.

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, and more particularly, to a surface optical recording type magneto-optical recording medium in which information is recorded, reproduced and erased by a laser beam using a floating optical head. The present invention relates to a change recording medium.

[0002]

2. Description of the Related Art An optical recording medium is a portable recording medium capable of large-capacity and high-density recording, and is demanded as a rewritable medium for recording a moving image or the like as a large-capacity storage file of a computer with the recent increase in multimedia. It is increasing rapidly.

[0003] Conventional rewritable optical recording media generally form a multilayer film including a recording layer on a disc-shaped substrate such as plastic, and irradiate a laser from the plastic substrate side to record.
Playing and erasing were performed.

On the other hand, a so-called surface optical recording system, in which an optical head is brought close to a recording film for recording / reproducing, has attracted attention as a means for increasing the density.

In the surface optical recording method, it is necessary to bring the optical head close to the recording medium on the recording surface side, and it has been proposed to use a floating type slider head.

Similarly, in a hard disk using a slider head, a lubricating layer is often provided on the surface of the medium for the purpose of securing the floating property of the slider head and protecting the medium.

[0007]

In the surface optical recording system, it is necessary to bring the optical head close to the medium as described above. In this case, a floating slider head collides with the medium.
There is a problem that a head crash easily occurs.

In the surface optical recording system, unlike a hard disk, an optical head is installed on a floating slider head and used for recording and irradiation with a laser beam.
In order to perform reproduction and erasure, if a large amount of liquid lubricant adheres to the surface of the optical head, the characteristics of the optical system deteriorate, and there is a problem that stable recording, reproduction and erasure characteristics cannot be obtained. I have. SUMMARY OF THE INVENTION An object of the present invention is to provide a surface optical recording medium in which head crash hardly occurs and the optical characteristics of the optical head are not impaired.

[0009]

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

That is, according to the present invention, an optical recording layer and a lubricating underlayer are formed on a substrate having at least a spiral or concentric guide groove involved in recording and reproduction. By forming a layer made of a fluoropolyether derivative with a film thickness of 0.3 nm or more and less than 2.0 nm, the dispersibility of the lubricant can be measured using a secondary ion mass spectrometer (TOF-SIMS). The present invention relates to an optical recording medium characterized in that the aggregation state of a lubricant obtained by analyzing an ion peak is 10 μm or less.

The optical recording layer of the optical recording medium of the present invention is made of TbFe
Co, DyFeCo, GdTbFeCo, NdDyFe
Magneto-optical recording film of Co or GeSbTe, AgI
It is composed of a film such as a phase change recording film such as nSbTe, which can be recorded by changing the polarization plane, the reflectance, the phase of light, and the like.

The substrate surface of the optical recording medium of the present invention has at least a spiral or concentrically arranged guide groove structure related to recording and reproduction.

By having the groove structure in the present invention, the lubricating layer formed on the surface of the lubricating underlayer is uniformly dispersed on the disk surface, excess lubricant accumulates in the lower part of the groove, and the upper part of the groove is lubricated. With the minimum required lubricant layer.

Therefore, even if recording and reproduction are repeated by the floating slider head provided with the optical head, no optical abnormality occurs due to adhesion of the lubricant to the optical head, and stable recording, reproduction and erasing characteristics can be obtained.

In general, when an optical head is levitated by using a floating slider head, if the amount of a lubricant such as a perfluoropolyether derivative applied to the surface of an optical recording medium is too large, the surface of the floating slider head may be reduced. The floating slider head is contaminated, and the floating slider head is contaminated, and a phenomenon of sticking of the floating slider head to the recording medium called stiction occurs, which hinders the stable floating of the floating slider head. On the other hand, when a lubricant such as a perfluoropolyether derivative that does not cause stiction is applied to the recording medium, the lubricant is uniformly applied to the surface of the recording medium due to the difference in surface energy between the lubricant and the surface of the recording medium. The lubricant does not spread, and the lubricant is aggregated, and the lubricant is separated into a portion where the lubricant does not exist on the medium surface and a portion where the lubricant is aggregated.

Such a state of aggregation of the lubricant can be actually measured by measuring the distribution of fragment ion peaks of the lubricant using a secondary ion mass spectrometer (TOF-SIMS).
According to the present invention, the agglomerated state is that the lubricant has a diameter of 10 μm or less, that is, the diameter of the lubricant which is agglomerated into an island is 10 μm or less (when the agglomerated state of the lubricant is 10 μm or less There is). In addition, the diameter of the lubricant refers to a region where the lubricant is agglomerated in an island shape in the lubricant distribution measurement result on the surface of the optical recording medium obtained by the fragment ion peak distribution analysis using TOF-SIMS. It means the diameter of the circumscribed circle.

If the agglomerated state of the lubricant exceeds 10 μm, the adhesion of the lubricant to the surface of the optical head due to the repetition of recording and reproduction by the floating optical head causes the surface of the optical head to be stained, resulting in defective recording and reproduction.

The track pitch of the guide groove in the present invention is not particularly limited, but is preferably 1.6 μm or less because it is involved in data recording and reproduction.

The groove depth in the present invention is preferably 20 nm or more and 150 nm or less after the formation of the lubricating underlayer.

When the groove depth is less than 20 nm, tracking of the groove by the optical head becomes difficult, and the lubricant is not sufficiently accumulated at the lower portion of the groove, and the lubricant is excessively present at the upper portion of the groove. Exceeds 10 μm,
Repetition of recording and reproduction by the floating optical head causes adhesion of a lubricant to the surface of the optical head, resulting in defective recording and reproduction.

When the groove depth exceeds 150 nm, the aggregation state of the lubricant is 10 μm or less, but the lubricant layer on the groove is not sufficiently covered, and the floating optical head comes into contact with the surface of the optical recording medium. The impact when doing so tends to increase.

The lubricating layer of the optical recording medium of the present invention is composed of a perfluoropolyether derivative. The main chain structure of the perfluoropolyether may be a linear structure or a side chain structure, but a linear structure is particularly desirable from the viewpoint of lubricating properties. As the derivative structure, those having a functional group such as an ester group, a hydroxyl group, an isocyanate group, a carbonyl group, or a piperonyl group introduced at both ends or one end of the main chain are preferable.

Examples of a material for forming such a lubricating layer include “Fomblin ZDEAL” and “Fomblin ZDOL-2000” (trade names, manufactured by Ausimont).
And "Fomblin AM2001", manufactured by Daikin,
The product names “Demnum SP” and “Demnum SY-3” can be exemplified.

The thickness of the lubricating layer of the present invention is at least 0.3 nm and less than 2.0 nm, more preferably at least 0.5 nm.
It is 1.8 nm or less. If it is less than 0.3 nm, the film thickness is too thin, and sufficient lubricating properties cannot be obtained, and the lubricating underlayer is easily damaged by the slider head. When the thickness is 2.0 nm or more, there is no problem in lubricating properties, but the ratio of free lubricant molecules not adsorbed to the lubricating underlayer increases, the aggregation state exceeds 10 μm in diameter, and recording and reproduction by a floating optical head are performed. By the repetition of the above, the adhesion of the lubricant to the surface of the optical head occurs, the surface of the optical head becomes dirty, and recording / reproduction failure occurs.

The lubricating underlayer of the present invention can be exemplified by diamond-like carbon, SiO ₂ or UV-curable resin. Diamond-like carbon layer and Si
The O ₂ layer can be formed by a sputtering method, an ion beam sputtering method, a plasma CVD method, or the like. The ultraviolet curable resin is applied by a spin coating method or the like and then cured by irradiation with ultraviolet light to form a film.

FIG. 1 is a partial sectional view of one embodiment of the optical recording medium of the present invention. On a substrate 11, a reflective layer 12, a recording layer 13 composed of a magneto-optical recording film, a dielectric layer 14, a lubricating underlayer 1
5. The lubrication layer 16 is laminated.

The substrate 11 is not particularly limited as long as it satisfies the characteristics of a medium substrate such as mechanical characteristics, and may be glass, polycarbonate, amorphous polyolefin, or the like.
Engineering plastics and the like can be used. A reflective layer 12 is formed on this substrate 11 by Al, Al alloy, A
A metal material such as u, Ag, an Au alloy, or an Ag alloy is used, and is formed by a sputtering method, a vacuum evaporation method, or the like. On the reflective layer 12, a recording layer 13 is formed of TbFeCo, DyFeC.
o, using a magneto-optical recording film material such as GdTbFeCo, NdDyFeCo, etc., and formed by a sputtering method or a vacuum evaporation method. On this recording layer 13, a dielectric layer 14 is formed of AlN, S
Using materials such as iN, Ta ₂ O ₅ , ZnS—SiO ₂ ,
It is formed by a sputtering method or a vacuum evaporation method. A lubricating underlayer 15 is formed on the dielectric layer 14, and a lubricating layer 16 is formed on the lubricating underlayer 15 by a dip pulling method or the like.

[0028]

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 and Comparative Example 1 A near-field magneto-optical recording medium having a structure as shown in FIG. 1 was manufactured. That is, a polycarbonate diameter 130 with a spiral guide groove having a track pitch of 0.45 μm and a depth of 85 nm.
mm on a disk-shaped substrate 11 with a DC sputtering method.
A reflective layer 12 made of _0.97 Cr _0.03 and having a thickness of 50 nm, a magneto-optical recording layer 13 made of Tb ₂₀ (Fe ₉₀ Co ₁₀ ) _{80 having a} thickness of 20 nm formed by DC sputtering and a reactive layer R formed thereon.
A 30 nm-thick dielectric layer 14 of SiN was formed by F sputtering, and a 20 nm-thick lubricating underlayer 15 of diamond-like carbon was formed thereon by reactive RF sputtering.

The depth of the groove after formation of the lubricating underlayer was 94 nm as measured by an atomic force microscope (AFM).

Thereafter, this medium was used as a perfluoropolyether solvent (trade name: Galden S, manufactured by Ausimont Co., Ltd.).
V-70 "), a perfluoropolyether having a weight-average molecular weight of 2400 and having hydroxyl groups at both molecular ends (trade name" Fomblin ZD ", manufactured by Audimont Co., Ltd.)
OL-2000 "), the medium was pulled up to form a lubricating layer 16, thereby producing a magneto-optical recording medium.

At this time, the thickness of the lubricating layer is changed to 0.5, 1.0, 1.
It was changed to 5 nm. As a comparative example, the thickness of the lubricating layer was set to 0.
A magneto-optical recording medium having a thickness of 2, 2.5 nm was prepared. The thickness of the lubricating layer is determined by an X-ray photoelectron spectrometer (ESC).
Measured according to A).

Each of the medium surfaces is formed by TOF-SIMS.
Using the -CF ₂ CH ₂ OH fragment ions (81a
mu) was subjected to surface analysis, and the aggregation state of the lubricant was measured to be 0.3 μm.

The magneto-optical recording medium obtained as described above was set on a glide tester, and the linear velocity was 7.5 m / s.
Glide head with a piezo element (made by Glidelight: 70% slider, 0.01
2 "x 6.0 gr) was sought in a radius of 30 to 60 mm and evaluated for glide characteristics. The flying height of this glide head was 0.05 µm at a linear velocity of 7.5 m / s.
m. The voltage induced in the piezo element when the glide head was sought was observed with an oscilloscope, and when the voltage value exceeded 800 mV, it was determined that the head was in contact with the medium, and the number of times was recorded.

As a result of measuring ten sheets each, the magneto-optical recording medium having the lubricating layer thickness of 0.5, 1.0, 1.5 of the example and the lubricating layer thickness of 2.5 nm of the comparative example was as follows. The number of times of contact was 2 or less, and the ratio of the medium with 0 times of contact was 6
It was as good as 0% or more. The lubricating layer thickness of the comparative example is 0.2
On the magneto-optical recording medium of nm, the number of contacts was about 5 times on average.

Next, the lubricating layer thickness is 1.0, 1.5, 2.5
The magneto-optical recording medium of nm was set in a recording / reproduction evaluator of an optical system of a near-field recording head having a laser wavelength of 680 nm and an effective NA of 1.2, and the recording / reproduction characteristics were evaluated. The medium was rotated at a linear velocity of 7.0 m / s, and irradiated with a laser whose output was adjusted to 6.0 mW in front of the objective lens.
Recording was performed on the medium by applying a magnetic field modulated to the magnitude of Oe from the coil of the SIL head, and then reproduction was performed while irradiating a laser whose output was adjusted to 1.0 mW before the objective lens.

The CNR is 1.0, 1.5, 2.
The medium was 48 dB for all 5 nm media, but when the same recording and reproduction were repeated 10 times on the same track, the CNR of the media having the lubricating layer thickness of 1.0 nm and 1.5 nm of the example was not changed. However, the medium having a lubricating layer of 2.5 nm in the comparative example had a CNR reduced to 35 dB. When the cause was confirmed, it was because dirt stained black had adhered to the lens surface of the SIL head.

Example 2 and Comparative Example 2 A magneto-optical recording medium was produced in the same manner as in Example 1, except that a polycarbonate substrate having a spiral pitch of 0.35 μm and a depth of 120 nm was used. .

At this time, the groove depth after the formation of the lubricating underlayer was 142 nm.

At this time, the thickness of the lubricating layer was changed to 1.0 and 1.5 nm by changing the solution concentration when applying the lubricating layer. Further, as a comparative example, a magneto-optical recording medium having a lubricating layer thickness of 2.5 nm was prepared.

The aggregation state of the lubricant is determined by TOF-SIM.
S had a diameter of 0.25 μm.

The magneto-optical recording medium obtained as described above was evaluated for glide characteristics in the same manner as in Example 1.

As a result of measuring 10 sheets at a time, the number of times of contact was 3 times or less, and the ratio of the medium having 0 times of contact was 50%.
And was good.

Next, this medium was evaluated for recording and reproduction characteristics in the same manner as in Example 1.

Although the CNR was 44 dB in all cases, when the same recording / reproduction was repeated 10 times on the same track, the medium having the lubricating layer film thickness of 1.0 nm and 1.5 nm of the example showed no change in CNR. However, the medium having a lubricating layer of 2.5 nm in the comparative example had a CNR reduced to 30 dB.
When the cause was confirmed, it was because dirt had adhered to the lens surface of the optical head.

Example 3 A magneto-optical recording medium was manufactured in the same manner as in Example 1, except that a polycarbonate substrate provided with a spiral guide groove having a track pitch of 0.45 μm and a depth of 150 nm was used.

At this time, when the groove depth after the formation of the lubricating underlayer was measured, it was 164 nm.

At this time, the thickness of the lubricating layer was changed to 0.5, 1.0, and 1.5 nm by changing the solution concentration.

The aggregation state of the lubricant of the magneto-optical recording medium thus prepared was determined by TOF-SIMS to have a diameter of 0.2 μm.
Met.

The magneto-optical recording medium obtained as described above was evaluated for glide characteristics in the same manner as in Example 1.

As a result of measuring 10 sheets at a time, the number of times of contact was slightly increased as compared with Examples 1 and 2;
Within the number of times, the ratio of the medium having 0 contact times was 15%.

Comparative Example 3 A magneto-optical recording medium was manufactured in the same manner as in Example 1 except that a polycarbonate substrate having no guide groove was used.

At this time, the thickness of the lubricating layer is adjusted to 0.5, 1.0, 1.5, 2.5 n by changing the solution concentration.
m.

When the dispersion state of the lubricant in the medium having no guide groove is similarly measured by TOF-SIMS, the dispersion state changes depending on the lubricant film thickness.
m, 18 μm for 1.0 nm film thickness, 25 μ for 1.5 nm film thickness
m and 37 μm at 2.5 nm.

With respect to the magneto-optical recording medium obtained as described above, after the optical head was floated for a time equivalent to 10 times of recording and reproduction, the surface condition of the optical head was observed. The lens surface was dirty.

[0056]

According to the present invention, it is possible to obtain an optical recording medium of a surface optical recording system in which head crash hardly occurs and the optical characteristics of the optical head are not impaired even by irradiation with a laser beam or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a partial cross section of an example of an optical recording medium of the present invention.

[Explanation of symbols]

 11: substrate 12: reflective layer 13: optical recording layer 14: dielectric layer 15: lubricating underlayer 16: lubricating layer

Claims (4)

[Claims] An optical recording layer and a lubricating underlayer are formed on a substrate having at least a spiral or concentric guide groove involved in recording and reproduction, and a perfluoropolyether is formed on the surface of the lubricating underlayer as a lubricating layer. Forming a layer made of a derivative with a thickness of 0.3 nm or more and less than 2.0 nm,
-An optical recording medium, wherein the aggregation state of the perfluoropolyether derivative obtained by distribution analysis of fragment ion peaks using SIMS is 10 µm or less in diameter. 2. A spiral or concentric guide groove involved in recording and reproduction has a depth of 20 n after the formation of the lubricating underlayer.
2. The structure according to claim 1, wherein the thickness is not less than m and not more than 150 nm.
An optical recording medium according to claim 1. 3. The optical recording medium according to claim 1, wherein the lubricating underlayer is a diamond-like carbon layer or a SiO ₂ layer. 4. The optical recording medium according to claim 1, wherein the lubricating underlayer is a layer made of an ultraviolet curable resin composition.