JPH06180882A - Magneto-optical disk - Google Patents

Abstract

(57) [Summary] [Structure] In a magneto-optical disk in which a recording magnetic layer 5 and an overcoat layer 6 are laminated on a transparent substrate 4, the overcoat layer 6 is made of an ultraviolet curable resin and has a silicone oil. Let [Effect] Sliding performance is added to the overcoat layer as well as protection performance. Both of these performances in low temperature and high temperature environment,
The magneto-optical disk is maintained even after storage in a high temperature and high humidity environment, exhibits good performance even in a severe environment, and is suitable for a sliding recording system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk suitable for use in a sliding recording system.

[0002]

2. Description of the Related Art In a magneto-optical recording system, a magnetic thin film is partially heated above a Curie point or a temperature compensation point to eliminate the coercive force of this portion and magnetize in the direction of a recording magnetic field applied from the outside. The basic principle is to reverse the direction of the above, and it is being put to practical use in an optical file system, an external storage device of a computer, or a recording device of audio and video information.

As a magneto-optical disk used in this magneto-optical recording system, a recording magnetic layer having a large magneto-optical effect and having an easy axis of magnetization in the direction perpendicular to the film surface on one main surface of a transparent substrate made of polycarbonate or the like. Layer (for example, a rare earth-transition metal alloy amorphous thin film), a reflective layer, and a dielectric layer are laminated to form a recording portion, and in order to prevent corrosion of the recording portion, an ultraviolet curable resin is formed on the recording portion. It is known that an overcoat layer made of, for example, is formed so as to cover the overcoat layer.

By the way, the magneto-optical recording method is roughly classified into an optical modulation method and a magnetic field modulation method. Among them, the magnetic field modulation method is noted because it can be overwritten. For example, the diameter is about 64 mm. The adoption as a recording method for small magneto-optical discs is under consideration.

The above-mentioned magnetic field modulation method writes information in a magnetic thin film by reversing the applied magnetic field at a high speed, and the magnetic field is usually applied by a magnetic head having magnetic field generating means.

In this case, a magnetic head applying a high-speed reversal magnetic field can generate only a very small magnetic field due to various restrictions, and the magnetic head must be as close to the recording magnetic layer as possible.

Therefore, in such a magnetic field modulation method, adoption of a sliding recording method in which a magnetic head is brought into direct contact with the disk surface of a magnetic disk and recording is performed while sliding is being considered. If this sliding recording method is adopted, a sufficient magnetic force can be applied to the recording magnetic layer even with the magnetic head that applies the high-speed reversal magnetic field. Moreover,
The method in which the head floats above the disk surface requires a complicated servo mechanism to keep the distance between the disk surface and the head constant, but the sliding recording method does not require such a servo mechanism. is there. Therefore, it is also advantageous in simplifying and downsizing the device.

[0008]

By the way, in the sliding recording system, the magnetic head is arranged on the side of the overcoat layer of the magneto-optical disk and directly slides on the surface of the overcoat layer. Therefore, it is an important requirement for the magneto-optical disk used in the sliding recording system that the overcoat layer can withstand the sliding of the head.

However, in view of the conventional magneto-optical disk from this point of view, the ultraviolet curable resin layer formed as the overcoat layer in the conventional magneto-optical disk has a large frictional force with respect to the head. For this reason, it is unsuitable for use in the sliding recording system as it is, and it is necessary to further provide a sliding film on the overcoat layer or add sliding performance to the overcoat layer.

In this case, if a sliding film is further provided on the overcoat layer, the number of manufacturing steps is increased and the cost is increased. Therefore, it is more preferable to provide the overcoat layer with sliding performance as well as protection performance. I can say. For example, if an ultraviolet-curing resin that has sliding performance as well as protection performance, or one in which a lubricant is added to the ultraviolet-curing resin is used as the overcoat layer material, an overcoat layer that has sliding performance in almost the same process as the current process. Can be obtained.

However, the ultraviolet curable resin having excellent protection performance has insufficient sliding performance, and if the sliding performance is to be provided, the protection performance is insufficient, and the ultraviolet curing resin has both the protection performance and the sliding performance at the same time. Is rare. Further, even a resin having both properties has a drawback that it deteriorates when left in a high temperature and high humidity environment, and it is difficult to obtain an overcoat layer for sliding recording only with an ultraviolet curable resin.

On the other hand, the lubricant to be added to the UV-curable resin layer has not only excellent lubricity but also good compatibility with the resin, and can slide in an environment of −25 to 70 ° C. Moreover, it is necessary that the sliding performance and the protection performance are maintained even after storage under the environment of -40 to 80 ° C, and there are more severe requirements than the lubricant used in magnetic media (video tape, floppy disk, etc.). Desired. Therefore, organic lubricants such as fatty acid esters, which are usually used as lubricants in magnetic media, do not meet the above requirements and are insufficient, and the selection range of lubricants is limited.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and has both protection performance and sliding performance, and both performances are high temperature, low temperature environment, high temperature and high humidity. An object of the present invention is to provide a magneto-optical disk that can be maintained even after being stored in an environment.

Further, in another invention, when fine dust or the like adheres to the disk surface, even if the dust adhered to the disk surface is wiped off with a cloth containing alcohol or the like, it is internally added to the protective film. It is an object of the present invention to provide a magneto-optical disk capable of maintaining good sliding characteristics with almost no wiping off of the existing lubricant.

[0015]

In order to achieve the above object, the magneto-optical disk of the present invention is a magneto-optical disk comprising a transparent substrate on which a recording magnetic layer and an overcoat layer are laminated. It is characterized in that the layer is made of an ultraviolet curable resin and contains silicone oil.

Further, as the silicone oil in the above overcoat layer, a polyether-modified polysiloxane represented by Chemical formula 4, a phenyl-modified polysiloxane represented by Chemical formula 5,
It is characterized in that at least one of the long-chain alkyl-modified polysiloxanes represented by Chemical formula 6 is internally added.

[0017]

[Chemical 4]

[0018]

[Chemical 5]

[0019]

[Chemical 6]

Next, a magneto-optical disk according to another invention,
In a magneto-optical disk having a recording magnetic layer and a protective film laminated on a transparent substrate, a top coat layer is formed on the protective film, and the protective film is made of an ultraviolet curable resin internally added with silicone oil, The top coat layer is formed by applying a silicone oil-based lubricant.

[0021]

When the overcoat layer is made of an ultraviolet curable resin and the silicone oil is retained in the overcoat layer, the sliding performance is added by the silicone oil, and the sliding performance is provided together with the protection performance. It will be maintained even after storage under high temperature and low temperature environment, and high temperature and high humidity environment.

Further, in particular, when a polyether-modified polysiloxane having a predetermined molecular structure, a phenyl-modified polysiloxane, and a long-chain alkyl-modified polysiloxane are internally added,
These polyether modified polysiloxane, phenyl modified polysiloxane, long chain alkyl modified polysiloxane are
It is stably held in the resin and on the surface, and the sliding performance becomes more stable.

When fine dust adheres to the disk surface, it is usually necessary to wipe the dust off with a cloth containing alcohol or the like. At this time, the lubricant internally added to the ultraviolet curable resin may be almost completely wiped off, and good sliding characteristics may be lost.

In the magneto-optical disk according to another invention, a top coat layer is formed by applying a silicone oil-based lubricant on a protective film formed of an ultraviolet curable resin internally added with a silicone oil-based lubricant. As described above, when fine dust or the like adheres to the disk surface (upper surface of the top coat layer) as described above,
Even if the dust adhering to the disk surface is wiped off with a cloth containing alcohol, etc., the lubricant internally added to the UV-curable resin that forms the protective film is hardly wiped off, and good sliding is achieved. The dynamic characteristics will be maintained. Therefore, the high quality period of the magneto-optical disk can be maintained for a long time, and the life of the magneto-optical disk can be extended.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings.

In the magneto-optical disk of the present invention, as shown in FIG. 1, an optical head 2 and a magnetic head 3 are arranged to face each other with the magneto-optical disk 1 sandwiched therebetween, and the magnetic head 3 is opposed to the magneto-optical disk 1. It is used in a sliding recording method in which a signal is recorded while sliding.

More specifically, as shown in FIG. 4, the magneto-optical disk 1 is installed in a cartridge 21 which can be freely loaded and ejected in a recording / reproducing apparatus, and opened in the cartridge 21 when recording a signal. A magnetic head for magnetic field modulation recording from a window 22 (window on the disk surface side on which the recording magnetic layer and its protective film are formed) via a supporting member 23 composed of a leaf spring, a gimbal spring, etc. on the disk surface. 3 is arranged, and the magnetic field for recording is generated by the magnetic head 3
Is applied more.

Further, the cartridge 21 also has a window on the surface opposite to the magnetic head 3 with the magneto-optical disk 1 interposed therebetween, and the optical head 2 is arranged so as to face the window. At the time of recording, the optical head 2 irradiates the recording surface of the magneto-optical disc 1 placed in the magnetic field applied by the recording magnetic head 3 with laser light to heat the portion a of the recording surface. As the magneto-optical disk 1 rotates, the irradiation point a
Rapidly cools, and a recording pit having a magnetization direction (perpendicular magnetic recording) corresponding to the direction of the applied magnetic field is formed in the recording magnetic layer. Further, the optical head 2 is also used for reading the binary data recorded by the above method by the Kerr effect, by irradiating the optical head with the irradiation power lower than that during recording.

The optical head 2 never contacts the disk surface, but the magnetic head 3 simplifies the device,
For the purpose of downsizing and power consumption reduction, a method of contacting and sliding on the disk surface may be used at least during recording.

In the magneto-optical disk 1 according to the first embodiment of the present invention, the recording magnetic layer 5 is laminated on one main surface of the substrate 4, and the surface of the recording magnetic layer 5 is covered with the overcoat layer 6. The overcoat layer 6 is slid by the magnetic head 3.

The substrate 4 is a disk-shaped transparent substrate having a thickness of about 4 mm, and as the material thereof, a plastic material such as an acrylic resin, a polycarbonate resin, a polyolefin resin, an epoxy resin or the like, or glass or the like is used. It

The recording magnetic layer 5 is an amorphous magnetic thin film having a direction of easy magnetization in a direction perpendicular to the film surface, and it has excellent magneto-optical characteristics and has a large coercive force at room temperature. Also, it is desirable to have a Curie point near 200 ° C. As a recording material satisfying such a condition, a rare earth-transition metal alloy amorphous thin film or the like can be mentioned.
A bFeCo-based amorphous thin film is suitable. An additional element such as Cr may be added to the recording magnetic layer 5 for the purpose of improving the corrosion resistance.

The overcoat layer 6 is the recording magnetic layer 5.
It is provided to protect the equipment from external shock and to isolate it from atmospheric water and oxygen.

Here, in the magneto-optical disk according to the first embodiment, since recording is performed while the magnetic head 3 slides on the disk surface, the overcoat layer 6 is made of an ultraviolet curable resin and the overcoat layer 6 is made of an ultraviolet curable resin. Coat layer 6
Silicone oil will be retained in order to suppress wear due to sliding and ensure the running performance of the magnetic head.

That is, since the silicone oil functions as a lubricant, and the ultraviolet curable resin contains the silicone oil, the sliding performance is added and the frictional force against the magnetic head is reduced.

The above silicone oil is chemically inert and has a low pour point (melting point) (melting point: <-40.
℃), high thermal decomposition temperature (thermal decomposition temperature:> 200 ° C),
A variety of lubricants with different viscosities and extremely low viscosity-temperature dependency are used as lubricants. In particular, among the silicone oils having the above characteristics, the polyether-modified polysiloxane represented by Chemical formula 4, the phenyl-modified polysiloxane represented by Chemical formula 5, and the chemical formula 6
The long-chain alkyl-modified polysiloxane represented by is also suitable for internal addition to the resin because it has excellent compatibility with the resin, and the manufacturing process can be simplified due to the ease of internal addition operation.

In the polyether-modified polysiloxane represented by the above chemical formula 4, the ether chain of R ¹ is preferably composed of ethylene oxide and / or propylene oxide, and modification of propylene oxide only is particularly preferred.

In the phenyl-modified polysiloxane represented by Chemical formula 5, the phenyl content x is 10 mol.
It is desirable that% <x <25 mol%. When the phenyl content is 10 mol% or less, the compatibility with the resin is insufficient, and when it is 25 mol% or more, the lubricity is insufficient. The alkyl group of R ⁵ is introduced for ensuring compatibility with the resin particularly when the phenyl content is in the range of 10 mol% <x <20 mol%.

Further, the length of the hydrocarbon group introduced into R ⁸ of the long-chain alkyl-modified polysiloxane represented by Chemical formula 6 is preferably C _{5 to} C _100, but the lubricity and the compatibility with the resin are In order to improve, the length of the hydrocarbon group is preferably C ₆ or more. Further, it may be a copolymer with a phenyl-modified siloxane in which R ⁶ and R ⁷ are phenyl groups.

The ultraviolet curable resin containing such a silicone oil may be any of those usually used as a material for an overcoat layer of a magneto-optical disk, and is excellent in waterproofness. Acrylic UV curable resin is suitable. In addition, the thickness of the overcoat layer is 10 μ from the viewpoint of securing strength and device configuration.
It is about m.

The basic structure of the magneto-optical disk according to the first embodiment has been described above. As a modified example thereof, FIG.
As shown in, the recording magnetic layer 5 as well as the dielectric layers 7 and 8,
A reflective layer 9 and the like are provided, and for example, a recording section 10 including four layers of a first dielectric layer 7, a recording magnetic layer 5, a second dielectric layer 8, and a reflective layer 9 is provided on a substrate 4, and the recording section 10 is provided. Alternatively, the overcoat layer 6 may be covered on the layer 10.

As the dielectric layers 7 and 8, oxides and nitrides can be used. However, since oxygen in the dielectric may adversely affect the recording magnetic layer 5, nitride is more preferable. Preferably, silicon nitride, aluminum nitride, or the like is suitable as the substance that does not transmit oxygen and moisture and can sufficiently transmit the used laser beam.

The reflective layer 9 is the second dielectric layer 8 described above.
It is preferable to use a high-reflectance film that reflects 70% or more of the laser light at the boundary with the film, and a non-magnetic metal vapor-deposited film is preferable. The reflective layer 9 is preferably a good thermal conductor, and aluminum is suitable in consideration of availability and film formation.

Next, two experimental examples of the magneto-optical disk according to the first embodiment will be shown below.

Experimental Example 1 A magneto-optical disk (Example disk 1) was prepared by forming a recording magnetic layer on a substrate and forming an overcoat layer containing silicone oil on the recording magnetic layer. Then, the frictional force of the manufactured magneto-optical disk was measured.

The overcoat layer contains 2% by weight of propylene oxide-modified dimethylpolysiloxane as shown in Chemical formula 7 in polyester / polyfunctional acrylate.
It was formed by adding it, dispersing it well, applying it to a substrate by a spin coating method, and then curing it with a high pressure mercury lamp.

[0047]

[Chemical 7]

The frictional force of the overcoat layer was measured by a spin stand under normal temperature environment and high temperature environment (temperature 70 ° C.).
The measurement was carried out under conditions of a low temperature environment (temperature -15 ° C) and after storage in a high temperature and high humidity environment (80 ° C, 95% RH, 100 hr).

As shown in FIG. 3, the spin stand used for the measurement includes a disk table 11, a plastic head 12, a load converter 13, a bridge box 14 having a temperature compensation function, a strain amplifier 15, an A / D converter 16, It is composed of a personal computer 17. In this spin stand, when the disc table 11 on which the disc is placed is rotated, the load is applied to the load converter 13 by the frictional force generated between the disc and the plastic head 12. This load is converted into an electric signal and is converted to bridge box 14, strain amplifier 15, A /
Personal computer 17 through D converter 16
Entered in.

In Experimental Example 1, using such a spin stand, the measurement conditions were a head pressure of 2 g and a linear velocity of 1.4 m /
Set to seconds, and under the conditions of room temperature environment, high temperature environment (temperature 70 ° C), low temperature environment (temperature -15 ° C), and storage under high temperature and high humidity environment (80 ° C, 95% RH, 100h) as described above. The frictional force was measured below.

For comparison, a magneto-optical disk (comparative example disk 1) in which an organic lubricant diglycerin tetralaurate was added to the overcoat layer instead of silicone oil, and a magneto-optical disk in which isocetyl stearate was added were used. The frictional force was similarly measured for the disk (comparative disk 2) and the magneto-optical disk in which the lubricant was not added to the overcoat layer (comparative example disk 3).

Table 1 also shows the frictional force of each magneto-optical disk.

[0053]

[Table 1]

As can be seen from Table 1, the disc 1 of the example in which propylene oxide-modified dimethylpolysiloxane was added as a lubricant to the overcoat layer was compared to the disc 3 of the comparative example in which the lubricant was not added, under normal temperature environment. ,
The frictional force is low in any of the high temperature environment, the low temperature environment, and the high temperature and high humidity environment after storage.

On the other hand, in Comparative Example Disk 1 to which diglycerin tetralaurate was added as a lubricant, the frictional force after storage under normal temperature and high temperature environments and under high temperature and high humidity environment was
Although the value is relatively low, the frictional force is extremely high in a low temperature environment.

Further, in the comparative disk 2 to which isocetyl stearate was added, the frictional force at room temperature has a relatively low value, but after storage in a high temperature environment and a high temperature and high humidity environment, the frictional force is reduced. The force was extremely high, and the frictional force was too large to measure in a low temperature environment.

Therefore, in order to obtain good slidability from the low temperature to the high temperature environment and to obtain good slidability even after storage in the high temperature and high humidity environment, Conventionally used organic lubricants such as diglycerin tetralaurate and isocetyl stearate have insufficient sliding performance after storage under high temperature or low temperature environment, high temperature and high humidity environment, and silicone oil is suitable. I found out.

Experimental Example 2 Next, the sliding performance was examined for other silicone oils. As the silicone oil, polyether modified polysiloxane, phenyl modified polysiloxane, and styrene modified polysiloxane were used. As the polyether-modified polysiloxane, the propylene oxide-modified dimethylpolysiloxane used in Example Disc 1 was used.

Magneto-optical disks (Sample Disk 1 to Sample Disk 4) were prepared in the same manner as in Experimental Example 1 except that the silicone oil shown in Table 2 was used. It was measured.
The results are shown in Table 2.

[0060]

[Table 2]

As can be seen from Table 2, sample disks 1 to 4 in which polyether-modified polysiloxane, phenyl-modified polysiloxane or styrene-modified polysiloxane was added as a lubricant to the overcoat layer were comparative disk 3 (rubbing). The frictional force is lower than the force of 15 to 20 mN). Particularly, the sample disk 1 using propylene oxide-modified dimethylpolysiloxane as the polyether-modified polysiloxane, the phenyl content of the phenyl-modified polysiloxane is 20 mol.
% Sample disk 2 and phenyl-long chain alkyl co-modified sample disk 3 have a lower coefficient of friction than the other sample disks.

Therefore, it was found that all the silicone oils have good sliding performance, but when the molecular structure of the silicone oil is regulated, more excellent sliding performance is exhibited. That is, when a polyether-modified polysiloxane is used, the modified part is composed of propylene oxide, and when a phenyl-modified polysiloxane is used, the phenyl group content x is 10 mol%.
It is preferable to select <x <25 mol%.

Next, a magneto-optical disk according to the second embodiment will be described with reference to FIGS. The same reference numerals are given to those corresponding to those in FIGS. 1 and 2.

The magneto-optical disk 1 according to the second embodiment.
Has substantially the same structure as the magneto-optical disk 1 according to the first embodiment, but is formed by further forming a top coat layer 31 on the overcoat layer 6 formed as the uppermost layer in the first embodiment. There is. Therefore, the overcoat layer 6 will be described below as a protective film.

Also in the magneto-optical disk 1 according to the second embodiment, as shown in FIG. 2, the recording magnetic layer 5 and the dielectric layers 7 and 8, the reflection layer 9 and the like are provided, and for example, the substrate 4 is used.
A recording portion 10 including four layers of a first dielectric layer 7, a recording magnetic layer 5, a second dielectric layer 8 and a reflective layer 9 is provided on the recording portion 10, and a protective film 6 and a top coat layer are provided on the recording portion 10. Alternatively, 31 may be sequentially stacked.

In the second embodiment, the protective film 6 is formed of an ultraviolet curable resin internally added with a silicone oil type lubricant, and the top coat layer 31 is formed.
Is formed by applying a silicone oil-based lubricant.

In this example, the protective film 6 has a sliding resistance by selecting a polyester acrylate as the UV curable resin and adding silicone oil manufactured by Shin-Etsu Chemical Co., Ltd. to the UV curable resin. It has an improved structure.

Here, as the silicone oil-based lubricant for forming the top coat layer 31, a polysiloxane oil (for example, polydimethylsiloxane shown in Chemical formula 8) can be used. In this case, the degree of polymerization is
It is about 70-80.

[0069]

[Chemical 8]

On the other hand, when polydimethylsiloxane shown in Chemical formula 8 above is used as the silicone oil-based lubricant added to the ultraviolet curable resin constituting the protective film 6, it does not dissolve in the ultraviolet curable resin. It is possible to use an oil obtained by substituting a part of the substituted polydimethylsiloxane polymer shown in 1) with a polyalcohol group, a phenyl group or a polyether group. Then, by adding at most 10% by weight of this oil to the ultraviolet curable resin, the protective film 6
Can be formed.

[0071]

[Chemical 9]

The coating thickness of the lubricant (top coat layer 31) coated on the protective film 6 is measured by measuring the coating thickness of the sample previously coated on the silicon wafer by using ellipsometry and calibrated. It can be determined by measuring the amount of Si by X-ray based on this calibration curve. When the coating thickness of the top coat layer 31 is measured by this measuring method and the thickness of the lubricant (top coat layer 31) coated on the protective film 6 is 100 nm or more, the surface of the protective film 6 becomes sticky, However, there is a problem that minute dust easily adheres. Therefore, in order to maintain the lubricating effect for a long time, it is not possible to blindly apply a large amount of lubricant. Therefore, in this example, when forming the top coat layer, the coating thickness of the lubricant was set to about 70 nm.

Two experimental examples of the magneto-optical disk according to the second embodiment will be shown below.

Experimental Example 3 First, one experimental example was a comparative example disk in which the protective film 6 was formed of an ultraviolet curable resin without addition of a lubricant, and polydimethylsiloxane shown in Chemical formula 8 was applied on the protective film 6 to a thickness of 70 nm. The protective disk 6 is formed from a UV-curable resin containing 2% by weight of the substituted polydimethylsiloxane copolymer shown in Chemical formula 9, and the polydimethylsiloxane shown in Chemical formula 8 is applied on the protective film 6 to a thickness of 70 nm. Prepared and measured the frictional force of both.

The frictional force was measured using the spin stand shown in FIG. Since this spin stand has already been described in Experimental Example 1, its description is omitted here. However, in this measurement, the plastic head 12 is made of Unitika polyarylate A.
For X1500, a spherical surface having a radius of curvature of 5 mm at the tip was used.

In Experimental Example 3, first, the frictional force in the normal state (initial frictional force) was measured without wiping the disc surface with a cloth impregnated with alcohol, and then the disc surface was alcoholized. An experimental method was adopted in which the cloth was soaked with a cloth, the cloth was soaked for 1 hour, and then the frictional force was measured again.

As a result of the experiment, in both cases, the initial friction force is shown in FIG.
As shown in FIG. 7A and FIG. 8A, it was in the range of 4 ± 0.5 mN, but when the disc surface was wiped off with a cloth soaked with alcohol, as shown in FIG.
Friction force is 8mN when the number of passes is about 100
Is slightly exceeded, and the number of passes exceeds 2500,
The frictional force suddenly increased, and when it reached 10,000 times, the frictional force jumped up to 20 mN or more, and as a result, a sliding noise was generated, which made it unusable for practical use. Some discs had sliding scratches on the disc surface.

On the other hand, in the embodiment disk, as shown in FIG. 8B, the frictional force slightly exceeded 8 mN at the stage when the number of passes was about 100, and then this state continued for a long time,
Even when the number of passes reaches 10,000, the frictional force is 9
It is about mN. Then, the frictional force gradually increased from around 100,000 times, and the sliding noise was generated around 400,000 times.

Experimental Example 4 Another experimental example is a comparative example disk in which the protective film 6 is formed only by the UV-curable resin containing 2% by weight of the substituted polydimethylsiloxane copolymer shown in Chemical formula 9 and Chemical formula 9. The protective film 6 is formed from an ultraviolet curable resin containing 2% by weight of a substituted polydimethylsiloxane copolymer,
70 nm of polydimethylsiloxane shown in FIG.
The coated example disk was prepared and the frictional force between them was measured. Also in this measurement of the friction force, the spin force shown in FIG. 3 was used, and the friction force was measured in the same manner as in Experimental Example 3 above. In Experimental Example 4, the disc surface was wiped from the beginning with a cloth soaked with alcohol and
An experimental method was adopted in which the frictional force was measured again after being left for a time.

As a result of the experiment, FIG.
As shown in FIG. 5, the frictional force at the stage when the number of passes is about 2,000,000 is 5 ± 0.27 mN, while the friction of the example disk is at the stage when the number of passes is about 2 million. The force was 4.2 ± 0.21 mN. From this, the example disc is 20% more than the comparative example disc.
It can be seen that the sliding characteristics are improved.

As described above, in the magneto-optical disk 1 according to the second embodiment, the protective film 6 formed of the ultraviolet curable resin internally added with the silicone oil type lubricant is
Since the silicone oil-based lubricant is applied to form the top coat layer 31, when fine dust or the like adheres to the disk surface (the top surface of the top coat layer 31) as described above, Even if the dust adhering to the disk surface is wiped off with a cloth containing alcohol or the like, the lubricant internally added to the ultraviolet curable resin forming the protective film 6 is hardly wiped off, and is excellent. Sliding characteristics will be maintained. Therefore, the high quality period of the magneto-optical disk 1 can be maintained for a long time, and the life of the magneto-optical disk 1 can be extended.

[0082]

As is apparent from the above description, in the magneto-optical disk of the present invention, the overcoat layer is made of an ultraviolet curable resin, and the overcoat layer contains silicone oil. The layer has a sliding property as well as a protective property, and both properties are maintained even after storage in high temperature and low temperature environments and in high temperature and high humidity environments. In particular, by internally adding silicone oil having a predetermined molecular structure, the sliding performance becomes more stable.
Therefore, according to the present invention, it is possible to obtain a practical magneto-optical disk exhibiting a good sliding performance even under a harsh environment and for a sliding recording system.

Further, the magneto-optical disk of the present invention can be manufactured by substantially the same manufacturing process as the current one, unlike the case where a sliding layer is further provided on the overcoat layer, and the manufacturing process can be simplified and the cost can be reduced. It is advantageous.

According to another aspect of the present invention, in a magneto-optical disk having a recording magnetic layer and a protective film laminated on a transparent substrate, a top coat layer is formed on the protective film. Since the protective film is formed of the ultraviolet curable resin internally added with the silicone oil type lubricant, and the top coat layer is formed by applying the silicone oil type lubricant, it is possible to form a fine film on the disc surface. If dust adheres to the disk surface, even if it is wiped off with a cloth containing alcohol, the lubricant internally added to the protective film is hardly wiped off. It is possible to maintain various sliding characteristics, and it is possible to extend the life of the magneto-optical disk.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a first embodiment of a magneto-optical disk of the present invention, together with the schematic structure of a sliding type magneto-optical recording system.

FIG. 2 is a sectional view showing a configuration of a modified example of the magneto-optical disk according to the first embodiment.

FIG. 3 is a schematic diagram showing a configuration of a measuring device for measuring a frictional force of a magneto-optical disk with respect to a head.

FIG. 4 is a perspective view showing a structure of a cartridge having a magneto-optical disk built therein, together with a schematic structure of a sliding type magneto-optical recording system.

FIG. 5 is a sectional view showing the configuration of a second embodiment of the magneto-optical disk of the present invention.

FIG. 6 is a sectional view showing a configuration of a modified example of the magneto-optical disk according to the second embodiment.

FIG. 7 is a characteristic diagram showing the results of measurement of the initial frictional force of a comparative example disc, which is a sample of Experimental Example 3, and the frictional force after the disc surface was wiped with a cloth soaked with alcohol and left for 1 hour. .

FIG. 8 is a characteristic diagram showing the results of measurement of the initial frictional force of an example disc, which is a sample of Experimental Example 3, and the frictional force after the disc surface was wiped off with a cloth impregnated with alcohol and left for 1 hour. .

9 is a characteristic diagram showing measurement results of frictional force after wiping each disk surface of a comparative example disk and an example disk which are samples of Experimental Example 4 with a cloth impregnated with alcohol and leaving it for 1 hour. , FIG. A shows a comparative example disk,
FIG. 9B shows an embodiment disk.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magneto-optical disc 2 ... Optical head 3 ... Magnetic head 4 ... Substrate 5 ... Recording magnetic layer 6 ... Overcoat layer (protective film) 7 ... 1st dielectric Body layer 8 ... Second dielectric layer 9 ... Reflecting layer 31 ... Top coat layer

Claims (3)

[Claims] 1. A magneto-optical disk having a recording magnetic layer and an overcoat layer laminated on a transparent substrate, wherein the overcoat layer is made of an ultraviolet curable resin and contains silicone oil. Magneto-optical disk. 2. A polyether-modified polysiloxane represented by Chemical formula 1, a phenyl-modified polysiloxane represented by Chemical formula 2, and 3 as silicone oil in the overcoat layer.
The magneto-optical disk according to claim 1, wherein at least one of the long-chain alkyl-modified polysiloxanes represented by the formula (1) is internally added. [Chemical 1] [Chemical 2] [Chemical 3] 3. A magneto-optical disk comprising a recording magnetic layer and a protective film laminated on a transparent substrate, wherein a top coat layer is formed on the protective film, and the protective film contains a silicone oil type lubricant. A magneto-optical disk comprising an ultraviolet curable resin added thereto, wherein the top coat layer is formed by applying a silicone oil lubricant.