JP2000268406A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a near-field optical recording medium having a lubricating layer which hardly causes head crash or hardly decreases optical characteristics. SOLUTION: This optical recording medium has at least an optical recording layer on a substrate 11 and further a layer comprising a perfluoropolyether deriv. as a lubricating layer 16 having >=0.3 nm and <2.0 nm film thickness on the surface. By this method, the obtd. near-field optical recording medium is suitable for near-field optical recording and which hardly causes head crush or hardly decreases optical characteristics by laser beams or the like.

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 magneto-optical recording medium for recording, reproducing and erasing information by causing an optical change in a recording layer by a laser beam, or a phase change. It relates to a 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.

[0004] On the other hand, so-called near-field optical recording, in which an optical head is brought close to a recording film for recording and reproduction, that is, near-field optical recording, has attracted attention (Applied Physics Letter (Appl. Phys. Lett.), vo
l. 68, p. 141 (1996)).

In this recording method, Solid Imager is used.
The recording limit (ビ ー ム λ / 2NA: NA is the numerical aperture of the objective lens) shorter than the recording limit determined by the laser wavelength (λ) of the conventional light source is achieved by reducing the size of the laser beam spot by using a SION LENS (hereinafter abbreviated as SIL) head. Reproduction with marks is possible, and recording and reproduction with an ultra-high recording density can be realized.

[0006] Near-field optical recording can achieve an extremely high recording density as described above, but it is necessary to bring the optical head closer to the recording medium (up to 100 nm). For this reason, it has been proposed to use a floating slider head.

Similarly, in a hard disk using a slider head, a lubricating layer is often provided on the surface of the medium in order to ensure the floating property of the slider head.

[0008]

In the near-field optical recording, an ultra-high recording density is possible as described above, but it is necessary to bring the optical head closer to the medium. In this case, there is a problem that a floating slider head collides with a medium, that is, a so-called head crash easily occurs.

In addition, unlike near-field optical recording, near-field optical recording involves recording, reproduction,
In order to perform erasing, a surface lubricating layer showing stable optical characteristics and other physical properties is required even if the temperature of the recording medium is increased by the laser.

An object of the present invention is to provide a near-field optical recording medium having a lubricating layer in which head crash hardly occurs and optical characteristics and the like are not impaired.

[0011]

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, the present invention relates to an optical recording medium having at least an optical recording layer and a lubricating underlayer formed on a substrate,
A layer made of a perfluoropolyether derivative is formed as a lubricating layer on the surface of the lubricating underlayer by a thickness of 0.3 nm or more and 2.0 n
m, which is less than m.

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 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, an ester group (-
It is preferable that a functional group such as COOR) or a piperonyl group (3,4-methylenedioxybenzyl) is introduced.

Examples of the ester group include an optionally substituted alkyl group having 1 to 10 carbon atoms. The functional group may be introduced at either end or one end of the molecule, but it is particularly preferable that the functional group is present at both ends because the adsorptivity to the lubricating underlayer is higher.

The weight average molecular weight of the perfluoropolyether derivative is from 1,000 to 10,000, especially from 2,000
It is preferably from 10,000 to 10,000. Weight average molecular weight of 10
If it is less than 00, the fluidity is too high, and the distribution on the medium surface tends to be non-uniform. If the weight average molecular weight exceeds 10,000, the fluidity is too low, and it is difficult to obtain sufficient lubricating properties. In addition, low molecular weight compounds have higher long-term stability because the weight loss due to thermal decomposition occurs at a lower temperature than high molecular weight compounds.

As a material for forming such a lubricating layer, for example, "Fomblin A," manufactured by Ausimont, Inc.
M-2001 "and" Fomblin Z DEAL ",
Examples of the product include “Demnum SP” and “Demnum SY-3” manufactured by Daikin. "Fomblin AM-2001" has a piperonyl group at both ends,
As the main chain,

[0018]

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A compound having the formula: "Fomblin Z
DEAL "has ester groups at both ends and has a main chain of

[0020]

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Is a compound having

"Demnum SP" and "Demnum SY-3" have an ester group at one end and have a main chain

[0023]

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Is a compound having The thickness of the lubricating layer of the present invention is preferably from 0.3 nm to less than 2.0 nm, and more preferably from 0.5 nm to 1.8 nm.
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 lubrication properties, but the ratio of free lubricant molecules not adsorbed to the lubricating underlayer increases, so that when the medium comes into contact with the SIL head, it adheres to the SIL head side, Migrating lubricant molecules become visible. The lubricant molecules attached to the SIL head are decomposed by heat generated from a laser beam or the like. However, the structure may be partially changed and colored residue may be generated due to the structure, and the residue may adhere to the lens. In this case, the transmittance decreases, and the characteristics of the optical system deteriorate.

The lubricating underlayer of the present invention can be exemplified by diamond-like carbon or SiO ₂ . The diamond-like carbon layer and the SiO ₂ layer can be formed by a sputtering method, an ion beam sputtering method, a plasma CVD method, or the like.

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 or Ag is used, and is formed by a sputtering method, a vacuum evaporation method, or the like. The recording layer 13 is formed on the reflective layer 12.
With TbFeCo, DyFeCo, GdTbFeCo, N
A magneto-optical recording film material such as dDyFeCo is used and is formed by a sputtering method or a vacuum evaporation method. AlN dielectric layer 14 on the recording layer _{13, SiN, Ta 2 O 5} , ZnS-
It is formed by a sputtering method or a vacuum evaporation method using a material such as SiO ₂ . The lubricating underlayer 1 is formed on the dielectric layer 14.
In step 5, a diamond-like carbon layer or a SiO ₂ layer is formed by a sputtering method or the like. Further, a lubricating layer 16 is formed on the lubricating base layer 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 A near-field magneto-optical recording medium having a structure as shown in FIG. 1 was manufactured. That is, a reflecting layer 12 made of Al _0.97 Cr _0.03 and having a thickness of 50 nm made of Al _0.97 Cr _0.03 by a DC sputtering method on a disc-shaped substrate 11 made of polycarbonate having a diameter of 130 mm and provided with a guide groove having a track pitch of 0.45 μm. A magneto-optical recording layer 13 made of Tb ₂₀ (Fe ₉₀ Co ₁₀ ) ₈₀ and having a thickness of 20 nm, on which Si is formed by reactive RF sputtering.
A dielectric layer 14 made of N and having a thickness of 30 nm, and a lubricating underlayer 15 made of diamond-like carbon and having a thickness of 20 nm were further formed thereon by a reactive RF sputtering method.

Thereafter, this medium was used as a perfluoropolyether-based solvent (trade name "Galden S", manufactured by Ausimont).
V-70 "), immersed in a solution of perfluoropolyether having a weight average molecular weight of 2400 and having a piperonyl group at both molecular ends (trade name" Fomblin AM2001 ", manufactured by Audimont Co.) The lubricating layer 16 was formed by pulling up the magnetic recording medium.

At this time, by changing the solution concentration, the thickness of the lubricating layer is reduced to 0.2, 0.5, 1.0, 1.5 n
m and 2.0 nm. The lubricating layer has a thickness of E
Measured by SCA.

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 a lubricating layer film thickness of 0.5, 1.0, 1.5, and 2.0 nm was contacted within three times in all cases. The ratio of the medium having 0 times of contact was as good as 40% or more. In the case of a magneto-optical recording medium having a lubricating layer thickness of 0.2 nm, the number of contacts was about 5 times on average.

Next, the lubricating layer thickness is 1.0, 1.5, 2.0
The magneto-optical recording medium of nm was set in a recording / reproducing evaluator of an optical system of a SIL head having a laser wavelength of 680 nm and an effective NA of 1.2, and the recording / reproducing characteristics were evaluated.
The medium is rotated at a linear velocity of 7.0 m / s, and a magnetic field modulated to a magnitude of ± 150 Oe at a frequency of 7.0 MHz while irradiating a laser whose output is adjusted to 6.0 mW in front of the objective lens. Was recorded from the coil of the SIL head, and then reproduced 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 recording was 43 dB for all the media of 0 nm, but when the same recording and reproduction were repeated 10 times on the same track, no change in the CNR was observed for the media having the lubricant layer thickness of 1.0 nm and 1.5 nm. The medium having a lubrication layer of 2.0 nm had a CNR of 35 dB. When the cause was confirmed, the lubricant adhering to the lens surface of the SIL head was discolored black.

Example 2 A lubricating underlayer was laminated in the same manner as in Example 1, and then the medium was dissolved in a perfluoropolyether-based solvent (trade name "Galden SV-70", manufactured by Audimont). After immersion in a solution of perfluoropolyether having a weight average molecular weight of 2,000 and having ester groups at both molecular ends (trade name “Fomblin ZDEAL” manufactured by Ausimont), the medium is pulled up to form a lubricating layer. Thus, a magneto-optical recording medium was manufactured.

At this time, the thickness of the lubricating layer was changed to 1.5 and 2.0 nm by changing the solution concentration.

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 40%.
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 43 dB in all cases, when the same recording / reproduction was repeated 10 times on the same track, no change was observed in the CNR of the medium having a lubricating layer thickness of 1.5 nm. The 2.0 nm medium has a CNR of 3
It dropped to 8 dB. After confirming the cause, SI
This was because the lubricant attached to the lens surface of the L head was discolored black.

Comparative Example 1 A lubricating underlayer was laminated in the same manner as in Example 1, and thereafter a magneto-optical recording medium was manufactured without forming a lubricating layer.

The magneto-optical recording medium obtained as described above was evaluated for glide characteristics in the same manner as in Example 1. At the start of the seek, the head was in intense contact with the medium and generated abnormal noise, so that the entire surface could not be evaluated.

COMPARATIVE EXAMPLE 2 A dielectric layer was laminated in the same manner as in Example 1 without forming a lubricating underlayer. Thereafter, a medium was used as a perfluoropolyether solvent (trade name "Galden SV", manufactured by Ausimont Co.)
-70 "), a perfluoropolyether having a piperonyl group at both molecular ends having a weight average molecular weight of 2400 (trade name" Fomblin A, manufactured by Audimont Corporation ")
M2001 ”), the medium was pulled up to form a 2.0 nm-thick lubricating layer, and a magneto-optical recording medium was manufactured.

The magneto-optical recording medium obtained as described above was evaluated for glide characteristics in the same manner as in Example 1. Abnormal noise was generated during the seek, and a thin scratch was generated on the entire surface of the disc after the seek.

[0046]

According to the present invention, a near-field optical recording medium having a lubricating layer which is unlikely to cause head crash suitable for near-field optical recording and whose optical characteristics are not impaired even by a laser beam or the like can be obtained.

[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 (3)

[Claims] In an optical recording medium having at least an optical recording layer and a lubricating underlayer formed on a substrate, a layer made of a perfluoropolyether derivative is formed on the surface of the lubricating underlayer as a lubricating layer having a thickness of 0.3 nm or more. An optical recording medium formed with a thickness of less than 0.0 nm. 2. The optical recording medium according to claim 1, wherein the lubricating underlayer is a diamond-like carbon layer or a SiO ₂ layer. 3. The optical recording medium according to claim 1, wherein the weight average molecular weight of the perfluoropolyether derivative is 1,000 or more and 10,000 or less.