JPH05258366A - Production of magneto-optical recording medium - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for manufacturing a magneto-optical recording medium having high reproduction signal characteristics and recording sensitivity. When manufacturing a magneto-optical recording medium in which at least a magnetic layer is provided on a transparent substrate, after providing at least the magnetic layer on the transparent substrate, heat treatment is performed at a temperature of 60 to 100 ° C. for 150 hours or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducible magneto-optical recording medium having high reproduction signal characteristics and high recording sensitivity.

[0002]

2. Description of the Related Art As a recording medium having a recording layer (magnetic layer) on which information can be repeatedly recorded and reproduced, that is, information can be rewritten, a fine area of the magnetic layer is heated by light to a Curie point. A magneto-optical recording medium that records information by applying an external magnetic field and reversing the magnetization direction in a state where the coercive force of the area is extremely reduced has been put into practical use.

In such a magneto-optical recording medium, information is recorded as a repetition of a reversal area and a non-reversal area of the magnetization direction corresponding to 0 and 1. The recorded information uses, for example, the Kerr effect in which the deflection surface rotates in different directions depending on the direction of magnetization when the laser light is reflected on the surface of the recording layer, and the change in this rotation angle (Kerr rotation angle θκ) Is played by reading.

The Kerr rotation angle θκ of the magnetic layer has a great influence on the reproduction characteristic of recorded information. For example, the C / N ratio (reproduction signal characteristic) which is an index of readability of information is:
It increases as the Kerr rotation angle θκ increases. By improving the C / N ratio, accurate information reproduction can be performed and the reproduction speed can be increased even if the accuracy of the optical system of the information reproduction apparatus is lowered.

The magneto-optical recording medium as described above usually has a layer structure in which a first dielectric layer, a magnetic layer as a recording layer and a second dielectric layer are sequentially formed on a substrate (special feature). Kaihei 1-
263963, JP-A-62-209750 and JP-A-62
-217444 publication). The first dielectric layer has a role of protecting the magnetic layer, and prevents permeation of oxygen, water, etc. to the magnetic layer which is easily oxidized. Further, the first dielectric layer functions as an enhancement layer that enhances the Kerr effect, and utilizes multiple reflections to increase the apparent Kerr rotation angle and improve the reproduction signal characteristics. The second dielectric layer is provided to protect the magnetic layer.

More recently, research has been conducted on a magneto-optical recording medium having a reflective layer adjacent to the magnetic layer or outside the second dielectric layer in order to obtain a larger reproduction signal characteristic. (Japanese Patent Publication No. 62-27458,
JP-A-60-63747). This is in addition to the car effect
It is intended to utilize the Faraday effect due to reflection of light transmitted through the magnetic layer.

Currently, in ISO, C of a magneto-optical recording medium is used.
The / N ratio is specified to be 45 dB or higher. If the above structure is adopted and a TbFeCo-based material is used for the magnetic layer, C
The / N ratio of 47 to 48 dB is now obtained, which satisfies the ISO standard sufficiently.

Further, in order to improve weather resistance and recording sensitivity, a relatively large amount of fourth and fifth nonmagnetic elements are added to the TbFeCo-based material of the magnetic layer, and various other layers are also added. Attempts have been made to use these materials.

[0009]

However, in such an attempt, the C / N ratio generally tends to decrease,
It becomes difficult to satisfy the ISO standard of C / N ratio ≧ 45 dB.

Therefore, it is an object of the present invention to provide a method of manufacturing a magneto-optical recording medium which has a high C / N ratio satisfying the ISO standard and which can improve the recording sensitivity.

[0011]

The present invention provides a method for manufacturing a magneto-optical recording medium in which at least a magnetic layer is provided on a transparent substrate, and at least a magnetic layer is provided on the transparent substrate, and then the temperature is 60-100. The present invention provides a method characterized by heat treatment at 150 ° C. for 150 hours or more.

The magneto-optical recording medium according to the present invention comprises a substrate /
It has at least the layer structure of the magnetic layer. Optionally, there can be a first dielectric layer between the substrate and the magnetic layer, and a reflective layer and a second dielectric layer outside the magnetic layer (opposite the substrate). Either the reflective layer or the second dielectric layer may be on the magnetic layer side.

Specific examples of the material of the substrate include inorganic materials such as glass, resin materials such as polycarbonate, polymethylmethacrylate, and epoxy resin. The thickness of the substrate is not particularly limited and can be changed as needed.

The magnetic layer is a recording layer, and usually an alloy of a rare earth metal and a transition metal can be used. For example, TbFeCo
Examples thereof include amorphous alloys such as those based on GdFeCo, GdFeCo, DyFeCo, and PrFeCo. Specifically, for example, the following _{formula: [Tb X (Fe 1-} Y Co Y) 1-X] 100-Z M Z
(In the formula, M is Cr, Ti, Zr, Pt, Pd, Rh, N
b, V and In, X, Y and Z are rational numbers satisfying 0.17 ≦ X ≦ 0.26, 0 ≦ Y ≦ 0.20 and 0 ≦ Z ≦ 6, respectively, and the following formula: Tb _a Fe
_b Co _c Mn _d Pr _e (where 16 ≦ a ≦ 25, 6
0 ≦ b ≦ 78, 5 ≦ c ≦ 15, 0.05 ≦ d ≦ 2.0,
0.1 ≦ e ≦ 10 and a + b + c + d + e = 100). The layer thickness is preferably
200-600 Angstroms. The magnetic layer may be formed by any known thin film forming method, and for example, a sputtering method, a vacuum deposition method, an ion plating method, a vapor phase growth method or the like can be used. Among them, the sputtering method is particularly preferable, and the DC sputtering method, the high frequency sputtering method and the like are preferably used.

The reflective layer is usually made of Al, Au, Ag,
Metals such as Cu are used alone or with other metals. Other metals include Cr, Ge, Ir, Mo, N
b, Pd, Pt, Rh, Ru, Si, Sn, Ta, T
h, Ti, V, W, Zn, Zr, etc. may be mentioned. Most preferred is a reflective layer containing Al and Cr. The layer thickness of the reflective layer is preferably 100 to 600 angstrom. The reflective layer can be formed by the above-described known thin film forming method. Among them, the sputtering method is particularly preferable, and the DC sputtering method, the high frequency sputtering method and the like are preferably used.
When two or more kinds of metals are used, for example, in the above-mentioned sputtering method, Al, Au, A is used as a target.
A composite target in which chips of other metals are arranged in a mosaic pattern on a metal target of g, Cu or the like is used.

The first and second dielectric layers each have Z
Sulfides such as nS, SiO, SiO ₂ , In ₂ O ₃ , Sn
Oxides such as O _2, AlN, nitrides such as silicon nitride, silicon carbide or the like can be used. Preferably silicon nitride,
For example, SiN, Si ₂ N ₃ , Si ₃ N _{4 and the} like can be mentioned. The layer thickness of each dielectric layer is preferably 400 to 1500 angstroms. Such a dielectric layer may be formed by any known thin film forming method, like the magnetic layer described above. Among them, the sputtering method is particularly preferable, and the DC sputtering method, the high frequency sputtering method, the reactive high frequency sputtering method and the like are preferably used.

The present invention is characterized in that the magneto-optical recording medium obtained by successively providing the above layers is heat-treated. The heat treatment is performed at a temperature of 60 to 100 ° C., preferably 70 to 90 ° C. for 150 hours or longer, preferably 150 to
It is carried out for 1000 hours, more preferably 150 to 500 hours. If the temperature is too high, the substrate may suffer thermal strain, and if it is too low, the effect of the present invention cannot be exhibited. 15
If it is less than 0 hours, the effect of the invention cannot be obtained. There is no particular upper limit of time, but 1000 hours or less is practically sufficient. The humidity is usually 10 to 90%, preferably 20 to 60%, because it may cause deterioration of the mechanical characteristics of the magneto-optical recording medium due to warpage. The heat treatment can be performed in the air or in an inert gas atmosphere.

Before the heat treatment, the surface of the magnetic layer side may be optionally coated with an ultraviolet curable resin and then cured. A urethane resin or the like can be used as the ultraviolet curable resin. The UV-curable resin can be applied usually by spin coating. For example, the application pressure is 1 kg / cm ² , the application time is 3 seconds, and the rotation speed is 2500 rpm.
It can be performed under the conditions of. The thickness of the coating film of the ultraviolet curable resin is preferably 1 to 40 μm. The UV curable resin after coating can be cured by a conventional method. For example, UV irradiation is performed for 10 to 60 seconds.

[0019]

The magneto-optical recording medium manufactured by the method of the present invention achieves a high C / N ratio by achieving the reduction of noise or the improvement of carriers, which is presumed to be due to the strain reduction of the magnetic layer due to the annealing effect by the heat treatment. Thought to be a thing.
Therefore, even if various non-magnetic elements or the like are added to the magnetic layer for the purpose of improving weather resistance and recording sensitivity, or the materials of the dielectric layer and the reflective layer are variously changed, the ISO standard C / N ratio Can be fully achieved.

[0020]

The present invention will be described in more detail by the following examples. Examples 1-3 and Comparative Examples 1-3 Polycarbonate (hereinafter sometimes referred to as PC) substrate, SiN _x (first dielectric layer, x = 0.6), sequentially,
Magnetic layers (Tb ₂₀ Fe ₇₂ Co ₈ ), Al ₉₇ Cr ₃ (reflection layer), and SiN _x (second dielectric layer, x = 1.3) were formed. The formation of each layer was performed in the same batch under the following conditions using a planar type magnetron sputtering apparatus (substrate rotation / revolution type, manufactured by ULVAC). However, when forming the reflective layer, a composite target in which Cr chips were arranged in a mosaic pattern on an Al target was used. Initial vacuum degree When forming the first dielectric layer, the second dielectric layer and the reflective layer: 2 ×
10 ^-6 Torr or less, when the magnetic layer formation: 5 × 10 ^-7 Torr or less, the sputtering gas species and the gas pressure first dielectric layer and at a second dielectric layer formed (Si target reactive sputtering): Ar + N ₂ ( Volume ratio Ar / N ₂
= 8/1), 6 × 10 ⁻³ Torr, when forming a magnetic layer (using Tb ₂₀ Fe ₇₂ Co ₈ target):
Ar, 4 × 10 ⁻³ Torr, reflective layer formed: Ar, 1 × 10 ⁻³ Torr, substrate / first dielectric layer / magnetic layer / reflection layer / second
A magneto-optical recording medium having a layer structure of a dielectric layer was produced.
The thickness of each layer is 600 Å for the first dielectric layer, 400 Å for the magnetic layer, and 350 for the reflective layer.
Angstroms, and the second dielectric layer was 1000 Angstroms.

Next, on the second dielectric layer of the above-mentioned magneto-optical recording medium, a urethane resin (SD-
301, manufactured by Dainippon Ink and Co., Ltd. (condition: coating pressure 1 kg / cm ² , coating time 3 seconds, rotation speed 2500 r)
pm) to a thickness of 10 μm and then cured by irradiating with ultraviolet rays for 20 seconds. Then, heat treatment was performed in the atmosphere under the conditions shown in Table 1. The reproduction signal characteristics (C / N ratio) of the obtained magneto-optical recording medium were measured at a measurement position of a radius of 24 mm, the disk rotation speed was 2400 rpm, and the recording frequency was 3.
87 MHz, resolution bandwidth 30 KHz, externally applied magnetic field ± 300 o
e, recording laser power 2.6-10 mW, reproduction laser power
The measurement was performed at 1.5 mW and erase laser power of 10 mW. In addition,
The recording laser power at C / N = 45 dB was evaluated as the recording sensitivity. The results are shown in Table 1.

[0022]

[Table 1] Examples 4 to 6 and Comparative Examples 4 to 6 The layer structure on the PC substrate was set as follows: first dielectric layer / magnetic layer /
Second dielectric layer / reflection layer (layer thickness: 800/300/400/500
Each layer was formed under the same conditions as (same material) as in Example 1 except that (unit: angstrom).

On the reflective layer of this magneto-optical recording medium, the same UV curable resin as in Example 1 was applied by spin coating to a thickness of 10 μm under the same conditions as in Example 1 and then cured. Then, heat treatment was performed in the atmosphere under the conditions shown in Table 2.
The reproduction signal characteristics (C / N ratio) and recording sensitivity of the obtained magneto-optical recording medium were measured under the same conditions as in Example 1. The results are shown in Table 2.

[0024]

[Table 2] The compositions of the magnetic layers of Examples 7 to 9 and Comparative Examples 7 to 9 were Tb _19.5 Fe _69.0 Co _7.9 Mn _0.1 Pr.
Each layer was formed under the same conditions as in Example 1 except that the layer thickness was _3.5 and the layer thickness was 700 Å, and the composition of the reflective layer was Al _97.3 Cr _2.7 . The magnetic layer was formed by using Mn and Pr on the base material target of TbFeCo.
Sputtering was performed under the same conditions as in Example 1 using a composite target in which the chips of No. 1 were arranged in a mosaic pattern.

Layer structure: first dielectric layer / magnetic layer / reflection layer /
Second Dielectric Layer (Layer Thickness: 700/400/350/1000 (Unit: Angstrom)) On the second dielectric layer of this magneto-optical recording medium, the same ultraviolet curable resin as in Example 1 was used, Under the same conditions, spin coating was applied to a thickness of 10 μm, followed by curing. Then, heat treatment was performed in the atmosphere under the conditions shown in Table 3. The reproduction signal characteristics (C / N ratio) and recording sensitivity of the obtained magneto-optical recording medium were measured under the same conditions as in Example 1. The results are shown in Table 3.
Shown in.

[0026]

[Table 3] The compositions of Examples 10 to 12 and Comparative Examples 10 to 12 the first dielectric layer and SiC _x (x = 1.0), under the same conditions a layer thickness except for using 700 Å in the same manner as in Example 4 Each layer was formed. The first dielectric layer was formed by a sputtering method using a SiC target. The sputtering conditions at this time were as follows. Initial vacuum degree: same as in Example 4, gas pressure: 10 × 10 ⁻³ To
rr, gas type: Ar.

Layer structure: first dielectric layer / magnetic layer / second dielectric layer / reflection layer (layer thickness: 700/300/400/500 (unit: angstrom)) On the reflection layer of this magneto-optical recording medium The same UV curable resin as in Example 1 was applied by spin coating to a thickness of 10 μm under the same conditions as in Example 1, and then cured. Then
The heat treatment was performed in the atmosphere under the conditions shown in Table 4. The reproduction signal characteristics (C / N ratio) and recording sensitivity of the obtained magneto-optical recording medium were measured under the same conditions as in Example 1. The results are shown in Table 4.

[0028]

[Table 4]

[0029]

According to the present invention, it is possible to provide a magneto-optical recording medium having high reproduction signal characteristics and high recording sensitivity. Therefore, the magneto-optical recording medium manufactured by the method of the present invention is highly practical and industrially useful.

Claims (1)

[Claims] 1. A method for manufacturing a magneto-optical recording medium in which at least a magnetic layer is provided on a transparent substrate, wherein a temperature of 60 is provided after providing at least the magnetic layer on the transparent substrate.
A method characterized by heat-treating at -100 ° C for 150 hours or more.