JPS6226658A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To improve recording and reproducing characteristics by providing a protective film on both or one side of a magnetic film for magnetic recording having the axis of easy magnetization in the direction perpendicular to the film plane. CONSTITUTION:A mold plate 2 inscribed with rugged information patterns 1 is formed to a pan-shape into which liquid can be poured. A liquid photosetting resin 3 is poured into such mold plate. A releasable transparent plate 4 as a top cap is put on the photosetting resin 3 and thereafter an energy beam such a UV rays is irradiated from at least either direction of the plate 2 or the cap 4 to cure the resin 3, by which the substrate having the information patterns is obtd. The 1st transparent dielectric film 6 consisting of, for example, SiO2, ZnS, etc. is formed on the substrate 5 for a photomagnetic disk obtd. in such a manner and further an amorphous rate earth transition metallic layer 7 as a photomagnetic recording layer is formed on the layer 6; finally a dielectric layer prepd. by a sputtering or vapor deposition method as a layer 8 to protect the magnetic layer 7 from the outside is deposited thereon. The recording and reproducing characteristics of the photomagnetic recording are thereby improved.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the formation of media grooves in a magneto-optical recording disk, and in particular, the present invention relates to a structure in which the entire disk has good heat resistance and uses light as a heating source. Suitable for optical beam recording, and during playback, the magneto-optic playback signal is not optically disturbed.
The present invention relates to a magneto-optical recording medium that is sufficient to enable good reproduction.

[Background of the invention]

Magneto-optical recording disks or tape media are especially erasable media among optical recording, and are new media that can be rewritten any number of times like magnetic recording. Moreover, compared to conventional magnetic recording, it has two to three orders of magnitude higher recording density and has the remarkable advantages of easy medium exchange. In order to produce this magneto-optical medium at a low cost and meet the demands of society: First of all, the track guide groove of the optical head and the pit for the header signal (pit hole for information)
It is important to realize a so-called information pattern direct transfer method, in which information patterns are directly formed on the surface of a plastic substrate with a film thickness of about 0.5 to 3 m, and to use a substrate with information pits produced by this method. The second requirement is to construct a recording medium using a substrate that does not disturb the slight polarization angle rotation (Kerr rotation) of linearly polarized light reflected from a magnetic medium, which is the reproduction principle of magneto-optical recording. This can be mentioned. For this purpose, the birefringence of the substrate itself must be extremely small, and the retardation (phase delay of light) must be kept within a practical range (within about 10 nm). Furthermore, the third requirement is that the recording medium be constructed using a substrate that does not undergo thermal deformation even after being heated by a light beam of several tens of gallons or more (the normal value is 5 to 10 mW at the film surface during recording). , to make the medium sufficiently durable for long-term use.

Conventionally, an injection molding method (injection method) is known as a method for directly forming an information pattern on the surface of a resin substrate. For example, optical discs dedicated to digital audio playback, such as compact discs, are made of polycarbonate substrates (hereinafter referred to as PC boards), and optical discs for image playback are made of acrylic resin substrates (hereinafter referred to as PMMA boards). It is manufactured using a molding method and is supplied at low cost. Media configurations using these substrates are also being considered for magneto-optical disks. For example, as an example using a PC board, there is an example described in the 8th 2nd Japanese Society of Applied Magnetics Academic Lecture Abstracts, p. 223 (1984). Also,
An example using a PMMA substrate is the Journal of the Japanese Society of Applied Magnetics, Vol. 8, No. 5.

There is a report on page 355 (January 198). However, in magneto-optical disks using the above two methods, the following points have not been considered from a practical standpoint. First, in a magneto-optical disk using a PC board, the retardation due to the birefringence of the board is 30 to 150 nm.
This is extremely large, and a normal magneto-optical signal reproducing system has a fatal problem in that the reproduced signal is disturbed and the signal level drops by 10 to 20 decibels or more, making reproduction impossible. Furthermore, even if an optical system that cancels out the magnitude of retardation is incorporated into the magneto-optical signal reproducing section, the PC
Since the birefringence of the substrate varies every 5 to 10 μm in length, it is extremely difficult to create an optical head element that can follow this variation at high speed, and it is impossible to satisfy practical requirements. In any case, if a PC board is used, magneto-optical recording cannot be reproduced satisfactorily. Next, P.M.
In the case of the MA substrate, the birefringence is small, the retardation is as small as 4 to 100 nm, and there is no problem in reproducing magneto-optical signals. However, its heat resistance is significantly inferior to that of a PC board. For example, on a PC board, it is 100 to 1.
Even when heated at 40° C., no phenomena such as warping or deformation were observed, and the material was extremely thermally stable. However, PMMA substrates already undergo thermal deformation such as warping at about 60°C.

Unlike read-only optical discs, magneto-optical recording can be erased and rewritten, so heating for erasing and re-recording of about 5 to 10 mW is constantly performed, making it more heat resistant than read-only discs. The requirements for this are extremely strict.

In magneto-optical recording using a PMMA substrate, even a single light beam irradiation (5 mW or more) causes minute thermal deformation over a length of about 1 to 3 μm.As a result, the amount of reflected light decreases and the magneto-optical signal quantity is reduced. Therefore, when a PMMA substrate is used as a magneto-optical substrate, it has a fatal drawback that it cannot be used as a practical disk that requires rewriting of several tens of gal or more. As mentioned above, until now,
As a magneto-optical recording medium, there has not existed a substrate and a medium configuration that satisfies all of the first to third requirements described above.

[Purpose of the invention]

An object of the present invention is to provide a magneto-optical recording substrate that satisfies the first to third requirements and a recording medium using the same. That is, the substrate uses a formation method that allows the information pattern to be easily formed directly on the substrate surface,
Moreover, it is an object of the present invention to provide a substrate having a small retardation due to birefringence of 10 nm or less and a small thermal deformation, and further to provide a magneto-optical recording medium using this substrate.

[Summary of the invention]

In the present invention, the substrate material is dropped while in a liquid state onto a template in which an information pattern is engraved. Thereafter, it is photocured by irradiation with light such as ultraviolet rays to form a plate with a thickness of about 0.5 to 31 m, which is then released from the mold and used as a substrate. This method has the following advantages:

First of all, since it contacts the template in a liquid state, no internal distortion occurs due to contact pressure. In addition, since the light for curing is evenly irradiated, internal distortion occurs during the curing process, as a result,
A substrate suitable for a magneto-optical medium, which does not produce a photoelastic effect due to internal strain and therefore has extremely small birefringence or turbulence, can be obtained.

Second, if a material with good photo-curing sensitivity is used, the curing process can be completed in about one minute, making it possible to efficiently obtain a board with an information button and achieving mass productivity equivalent to or better than the casting method. be able to. Furthermore, thirdly, it becomes possible to select a photocurable resin, which has better heat resistance than a PMMA substrate, as the substrate material, thereby overcoming the drawback in terms of heat resistance.

Now, a substrate is manufactured by the above method, and then a high refractive index dielectric layer is used as a multi-reflection film layer to enhance the Kerr effect, a rare earth/transition metal magnetic layer is used as a storage layer, and a dielectric layer is used as a protective layer. If a disk is manufactured by sequentially forming the body layers, etc., it becomes possible for the first time to obtain a good magneto-optical recording medium that is excellent in mass productivity, has good reproduction efficiency, and has excellent weather resistance.

An example of a photocurable resin suitable for the present invention is a liquid acrylic and/or methacrylic photocurable resin. The photocurable resin has one or more acrylic or methacrylic groups in the molecule, and rapidly undergoes a crosslinking reaction with a radical polymerization initiator when irradiated with light.
There are no particular limitations as long as they result in an optically transparent cured product, but for example, the following are useful.

Monosensual Motsuma n-hexyl acrylate.

n-hexyl methacrylate, 2-ethylhexyl acrylate, '2-ethylhexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, decyl acrylate, decyl methacrylate, lauryl acrylate.

Lauryl methacrylate, tridecyl acrylate, tridecyl methacrylate, dicyclopentenyl acrylate, dicyclopentenyl methacrylate, dicyclopentenyloxyethyl acrylate, dicyclopentenyloxyethyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, tetrahydrofurfuryl acrylate, Tetrahydrofurfuryl methacrylate, isobornyl acrylate, isobornyl methacrylate, polyfunctional monomaneopentyl glycol diacrylate.

Neopentyl glycol dimethacrylate, 1.6 hexanediol diacrylate, 1.6 hexanediol dimethacrylate, trimethylolethane triacrylate, trimethylolethane trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, acrylate of epoxy compounds and diacrylate of bisphenol A diglycidyl ether, dimethacrylate of hydrogenated bisphenol A diglycidyl ether, dimethacrylate of hydrogenated bisphenol A diglycidyl ether, diacrylate of bisphenol F diglycidyl ether, Dimethacrylate of bisphenol F diglycidyl ether, diacrylate of hydrogenated bisphenol F diglycidyl ether, dimethacrylate of hydrogenated bisphenol F diglycidyl ether, acrylate and methacrylate of ester compounds, hydroxyhybalic acid neopentyl glycol diacrylate, hydroxyhybalin Neopentyl glycol dimethacrylate, diethylene glycol diacrylate phthalate, diethylene glycol dimethacrylate phthalate ether compound acrylates and methacrylates, dipentaerythritol hexaacrylate, dipentaerythritol hexamethacrylate, tripropylene glycol diacrylate, tripropylene glycol dimethacrylate , acrylate and methacrylate of urethane compounds; reaction product of 1 mol of isophorone diisocyanate and 2 mol of 2-hydroxyethyl acrylate; reaction product of 1 mol of isophorone diisocyanate and 2 mol of 2-hydroxyethyl methacrylate; Anatomethyl) cyclohexane 1
reaction product of 2 moles of 2-hydroxyethyl acrylate, 1.3-bis(isocyanatomethyl)cyclohexane 1
A reaction product of 2 moles of 2-hydroxyethyl methacrylate, 2 moles of tolylene diisocyanate is reacted with 1 mole of poly-1,2-butadiene having hydroxyl groups at both ends, and 2 moles of acrylic acid is added to the excess isocyanate group. 2 moles of tolylene diisocyanate are reacted with 1 mole of poly-1,2-butadiene having a molecular weight of about 1,000 to 2000 and has hydroxyl groups at both ends, and 2 moles of methacrylate is added to the excess isocyanate group. It is made by reacting with an acid and has a molecular weight of about 1000 to 2000.

The liquid acrylic group and/or methacrylic photocurable resin used in the present invention contains O, -5 to 10% by weight of a photopolymerization initiator that generates radicals when irradiated with light to the mixture of monofunctional and polyfunctional monomers. Add and make. When the amount of photopolymerization initiator added is less than 0.5% by weight, photocuring becomes insufficient, and when it is more than 10% by weight, the mechanical strength of the cured resin product tends to decrease, which is not preferable.

Examples of the photopolymerization initiator used in the photocurable resin of the present invention include benzyls, benzoin, benzoins such as benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether, benzophenone,
Benzophenones such as 4-methoxybenzophenone,
Acetophenone, acetophenones such as 2,2-jethoxyacetophenone, 2-chlorothioxanthone, 2
-thioxanthone such as methylthioxanthone, 2-
Anthraquinones such as ethyl anthraquinone and 2-methyl anthraquinone, benzyl dimethyl ketal, 1-
Hydroxycyclohexyl phenyl ketone, etc.
These may be used alone or in combination of two or more.

[Embodiments of the invention]

The present invention will be explained in detail below using examples.

First, a method of constructing an information patterned substrate suitable for a magneto-optical storage medium according to the present invention is performed as follows.

As shown in FIG. 1, a template 2 on which a concavo-convex information pattern 1 is carved is shaped like a pot into which liquid can be injected, and a liquid photocurable resin 3 is injected into the template. This photocurable resin is mainly composed of a compound having an acrylic group or a methacrylic group.

An ultraviolet curable organic resin with a photopolymerization initiator and other appropriate ingredients is used.

Here, 40% by weight of dipentaerythol derivative hexaacrylate (trade name DPCA30 manufactured by Nippon Kayaku Co., Ltd.)
, 30% by weight of the reaction product of 1 mol of isophorone diisocyanate and 2 mol of 2-hydroxyethyl methacrylate
, 28% by weight of isobornyl methacrylate, and 2% by weight of benzoin isopropyl ether as a photopolymerization initiator. The top of this photocurable resin 3 is covered with a releasable transparent plate 4 as an upper lid.

Then, as shown in the figure, an energy beam 1 of ultraviolet light or the like is applied from at least one of the directions of the template or the upper lid.
1 (at least one of the template and the upper lid is made of a transparent material) and the resin is cured to obtain a substrate with an information pattern. Needless to say, the substrate and the plate are separated by releasing the mold from the template.

) - Now, the magneto-optical disc substrate 5 obtained in this way
As shown in Fig. 2, SiO2, Si○, A Q N, Si3 N 4 are deposited on the film by sputtering or vapor deposition.
.

A transparent first dielectric film 6 made of ZnS or the like is formed.

The thickness of this layer is typically between 50 and 200 nm.

Further, on top of this layer, a rare earth/transition metal amorphous layer 7 (for example, T b Fe
, T b F e Co , G d T b F
e, HoGdFe film, etc.) is formed by a vapor deposition method, a sputtering method, or the like. It goes without saying that the material for this magnetic layer is generally not limited to the above materials as long as it is a perpendicularly magnetized film having a magneto-optic effect. The thickness of this magnetic layer may be in the range of 5 to 200 nm. Finally, as a layer for protecting the magnetic layer 7 from the outside, S io z +Si manufactured by sputtering or vapor deposition is used.
○ A dielectric layer, including AIIIN, etc., is deposited.

Of course, in addition to these materials, it goes without saying that an organic protective film formed by a spin code method, an inorganic material protective film, etc. may be used.

Now, the disc glue tarp formed as described above.
The size of the john is shown in FIG. 3 as a function of the disk inner radius. As shown in the figure, in the case of polycarbonate substrate (31), the internal strain differs significantly in the radial direction.
At a radius of 251m, it is -60nm, while at a radius of 125nwn, it is +60nm.
has reached. On the other hand, PMMA resin with low birefringence (32) or the ultraviolet curable resin substrate of the present invention (3
In 3), the retardation has a maximum value of only 10 nm or 4 nm near the outside of the disk, respectively, and there is no risk of disturbing the reproduced signal as a magneto-optical recording substrate. However, as shown in FIG. 4, the warpage of the substrate due to thermal deformation is extremely large (approximately 0.2 m or more) in the PMMA substrate (42), and the device is not suitable for practical use. Therefore, it can be said that there is no other substrate other than the photocurable substrate of the present invention that has excellent mass productivity, low retardation, and good heat resistance. Now, FIG. 5 shows the signal-to-noise ratio C/N of disks manufactured using each substrate as a function of the film surface recording power Pw. In the disk 51 using a polycarbonate substrate, the signal level is significantly degraded due to the birefringence of the substrate, and the C/N is only about 25 dB, making it impossible to put it into practical use. On the other hand, in the case of disk (52) using a PMMA substrate, when Pw is 5 mW or more, reflectance changes occur due to thermal deformation of the film surface, and as a result, the signal level decreases to P
It decreases with w. On the other hand, in the disk (53) using an ultraviolet curable resin substrate, the signal level increases to 52 dB due to small birefringence. Moreover, even when the recording power Pw was increased, no reduction in signal level due to thermal deformation or the like was observed.

As another embodiment of the present invention, as shown in FIG. 6, a magnetic film 7 is directly deposited on a photocurable resin substrate 5, and further,
Some are provided with a protective film 8. As another example, as shown in FIG. 7, the magnetic layer 7 is made of a thin layer of about 5 to 10 nm that allows light to pass through, and a reflective layer 9 of AQ, Pt, Au, etc. is provided behind it. Examples include attempts to increase the magneto-optical signal by the Faraday effect or the overlap effect with the Kerr effect. In this case as well, with the medium configuration of the present invention, very good signal reproduction of 50 dB or more is possible with small board distortion.

Although the embodiments of the present invention have been described above, it goes without saying that the substrate can be cured by irradiation with electron beams, X-rays, etc. in addition to irradiation with light.

〔Effect of the invention〕

According to the present invention, by using a substrate that is highly mass-producible, has extremely small optical deviations such as birefringence, and has good heat resistance, good results can be obtained in the recording and reproducing characteristics of magneto-optical recording. It is possible to construct a magneto-optical medium.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a method for manufacturing a photocurable magneto-optical disk substrate, Fig. 2 is a cross-sectional configuration diagram of a magneto-optical disk medium (Example 1), and Fig. 3 is a disk radius of each substrate adhesive tarpion. Figure 4 is a diagram showing the holding temperature dependence of the amount of thermal deformation warpage of each substrate, and Figure 5 is a film recording of the signal-to-noise ratio of a magneto-optical disk constructed using each substrate. Figure 6 shows the power dependence and is a cross-sectional diagram of the magneto-optical medium (
Embodiment 2), FIG. 7 is a cross-sectional configuration diagram of a magneto-optical medium (Embodiment 3). ■... Information pattern groove, 2... Template with information pattern, 3... Photo-curable resin, 4... Transparent release plate, 5...
Light curing. mold resin substrate, 6... transparent dielectric layer, 7... magneto-optical magnetic layer, 8... protective layer, 9... reflective layer. Agent Masaru Ogawa Patent Attorney Ogawa Masaru Otoko/Izuzo Gaikō O1）

Claims (1)

[Claims] 1. A structure in which a protective layer is provided on both sides or either side of a magnetic film for magneto-optical recording having an axis of easy magnetization in a direction perpendicular to the film surface, and at least one of the protective layers. is a layer made of a transparent conductive film, a transparent metal thin film, a reflective film that reflects light, or a multilayer film made of a combination of these, and these are combined with integrally formed grooves and information patterns made of photocurable resin. A magneto-optical recording medium characterized by being formed on a template.