JP2507597B2 - Magneto-optical recording medium - Google Patents

Description

The present invention relates to a magneto-optical recording medium having excellent durability and environmental resistance, and particularly to a magneto-optical recording medium suitable for overwriting.

[Prior Art] In recent years, commercialization and development of optical discs as one of large-capacity memories have been active. Among them, research on practical use of a magneto-optical disk as a rewritable optical recording medium is being vigorously conducted.

Conventionally, as a rewritable magneto-optical recording method, a method of using a plurality of optical heads such as a separate recording and erasing head has been studied, but the mechanism becomes complicated and overwriting in the original sense is performed. There is a demand for the development of a magneto-optical disk capable of performing such operations. As the overwriting method, it is considered preferable to use the magnetic field modulation method in the magneto-optical recording medium from the viewpoints of performance, simplicity of mechanism, and the like. This method records information,
Since erasing is performed by heating the recording film and changing the direction of the external magnetic field, the magnetic field can be modulated while continuously irradiating a constant laser beam. Is adjusted upward or downward with respect to the disk, overwriting becomes possible. However, in order to change the direction of the external magnetic field by the recording information signal (usually 1 to 5 MHz), it is necessary to bring the magnetic field generating means such as a magnet close to the disk, and the magnetic disk head is used as the magnetic field generating means. If used, leave a gap of 5μ with the surface of the recording medium.
m or less. In this case, the magnetic head may come into contact with the disk when the disk starts rotating, when the disk is stopped, or when the medium is deformed, and the disk is seriously damaged.

Another major problem in this case is the restriction on the thickness of the protective film. As described above, the distance between the magnetic head and the recording curtain is desired to be as short as possible, and is usually required to be 20 μm or less. Therefore, the protective film is also required to have a sufficient protective action with a thickness of 10 μm or less.

As the protective film on the magnetic field generating means side of the overwritable magneto-optical recording medium such as a magnetic head, 1) the performance as a protective film that provides sufficient durability with a thin film of 10 μm or less;
2) The durability against the above-mentioned head crash is required, but up to now, no material having satisfactory performance has been found.

[Object of the Invention] The present invention has been made in view of the above circumstances, and an object thereof is to provide a protective film having a film thickness of 10 μm or less, which can be used for magnetic field modulation overwrite, and has sufficient durability even under high temperature and high humidity conditions. The purpose is to provide a magneto-optical recording medium. That is, it is an object of the present invention to provide a balance-time recording medium in which deterioration of the optical recording film is prevented by the protective layer and which is excellent in durability against head crash that occurs when the magneto-optical disk starts or stops rotating.

[Structure, Action and Effect of the Invention] That is, the present invention provides (1) a functional group having reactivity with an isocyanate group on at least the surface of the magneto-optical recording medium facing the magnetic field generating means, and A compound containing no fluorine atom in the molecule, (2) an isocyanate compound containing at least two or more isocyanate groups in the molecule, and (3) fluorine in the molecule having a functional group reactive with the isocyanate group. Derived from a compound having a molecular weight of 1000 or less containing atoms, does not contain a fluorine atom bonded to a carbon atom of the main chain skeleton, a protective layer made of a resin composition containing a fluorine-containing polyurethane-based resin as a main component is provided. It is a characteristic magneto-optical recording medium.

 The details of the present invention will be described below.

The resin composition containing a fluorine-containing polyurethane resin containing no fluorine atom bonded to a carbon atom of the main chain skeleton derived from the compound in the present invention as a main component, as compared with a conventional polyurethane-based resin which has been conventionally used, It has excellent durability and lubricity, and is crosslinked and cured by an isocyanate compound, which has the effect of showing head crush resistance.

Further, the feature of the present invention is that the functional group exhibiting lubricity is incorporated in the molecule as described above, so that there is no fear that the lubricant will be liberated during the use for a long period of time to cause stains, so that stable use is always possible. In point.

Each compound used for producing the resin composition of the present invention is as follows. As a compound having a functional group reactive with an isocyanate group and containing no fluorine atom in the molecule, there is a prepolymer used in the synthesis of ordinary polyurethane, for example, polyacryl polyol, vinyl acetic acid chloride. Examples thereof include partially saponified vinyl copolymers and polyether polyols.

As an isocyanate compound containing at least two or more isocyanate groups in the molecule, a low molecular weight compound having a molecular weight of less than 1000, hexamethylene diisocyanate used in the production of ordinary polyurethane resins,
m-phenylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate and the like and dimers or trimers of these isocyanate compounds, and also a polyisocyanate compound obtained by reacting the above-mentioned isocyanate compound with a polyol. You can Examples of high molecular weight compounds having a molecular weight of 1000 or more include urethane prepolymers having an isocyanate group at the end obtained by reacting a polyether polyol and diisocyanate.

In the present invention, the above-mentioned low molecular weight and high molecular weight isocyanate compounds can be used alone, respectively, but it is also possible to use a mixture of a plurality of types of compounds with each other. There are advantages such as easy adjustment.

Further, as the compound having a molecular weight of 1000 or less containing a fluorine atom in a molecule having a functional group reactive with an isocyanate group, there are fluorine-containing alcohols, fluorine-containing amines, etc., for example, 2,2,2-trifluoro Ethanol, 2-
Examples thereof include perfluorobutyl ethanol, 2,2,3,3,3-pentafluoropropanol, 2- (perfluorooctyl) ethanol and the like.

The amount of isocyanate added is basically equimolar to the functional group that is reactive with the isocyanate group, but it can be changed within the range that does not impair the performance of the protective film depending on the conditions of use.

In the present invention, from the viewpoint of preventing deterioration of the recording film, the resin composition preferably contains an element having a greater ionization tendency than the transition metal element forming the recording film. The element is not particularly limited, but an element selected from the group consisting of aluminum, zinc, magnesium or rare earth elements is preferable. Furthermore, as the rare earth element, terbium (Tb), dysprosium (Dy), gadolinium (Gd), neodymium (Nd), praseodymium (Pr) and the like are preferable. In the present invention, when iron is used for the recording layer, magnesium, aluminum, zinc, neodymium, etc. may be mentioned. Although there are few data that can be compared regarding the ionization tendency, for example, one having a standard unipolar potential difference less base than iron may be selected. It can be said that the larger the difference in potential difference, the greater the effect of addition. However, the above-mentioned additional element group of the present invention was selected by considering not only the difference in the potential difference value but also the stability of the additional element. These metals can be used alone or in the form of a mixture or an alloy, and if any of them can be obtained in the form of fine powder, they are mixed with a resin raw material to prepare a stable dispersion and used for the purpose of the present invention. It is possible to

It is preferable that these powders are as fine particles as possible from the viewpoint of uniformity of effect. Further, in consideration of implementation in a medium used in the magnetic field modulation overwrite system, when the single particles used in the composition of the present invention are agglomerates such as spheres, the particle size is preferably 10 μm or less. From this point of view, it can be said that the foil-shaped fine particles are more preferable than the lump-shaped fine particles such as spheres.

These resins and powder can be mixed for use by using a mixing means such as a ball mill, a V-type blender, or a calendar.

There is no particular restriction on the mixing ratio of the resin and the powder. It can be appropriately determined in consideration of coatability and other conditions within a range in which a stable coating can be efficiently formed.
For example, the addition amount of these metals varies depending on the metal element and resin material used, but it is preferable to add 5 or more parts per 100 parts by weight of the resin from the viewpoint of the effect. Also, there is no restriction on the upper limit of addition, but it is determined in consideration of the overall performance as a protective film. Usually, it is preferably four times or less the resin weight.

The present invention provides a protective layer comprising the above resin composition on at least the surface of the magneto-optical recording medium facing the magnetic field generating means. In order to form this protective layer, a film forming method that is usually used in forming an organic protective film for an optical disc, such as a spin coating method or a dipping method, can be used.

It is also possible to preliminarily form the resin composition of the present invention into a sheet or film and laminate it on the surface of the recording film by a method such as heat fusion.

In the case of the above-mentioned overwrite method, the coating film thickness has a problem with an excessively thick coating film, and conversely, when the film thickness is extremely small, there is a concern about the effect, so it is necessary to determine it carefully. . Usually, it is preferably 10 μm or less.

Further, in order to stabilize the dispersed state of the powder, it is possible to use techniques and materials usually applied in the industry such as addition of a dispersion stabilizer within a range that does not adversely affect the effects of the present invention. It is a useful tool for improving sex.

Also, in order to improve the contact state against head crash and have durability, carbon black, graphite,
Lubricants such as mica, talc, kaolin, calcium carbonate, aluminum oxide, silicon oxide, molybdenum sulfide, silicon carbide and silicon nitride may be mixed in the resin composition of the present invention. Those having these internal cleavage properties, such as graphite, mica, molybdenum sulfide, etc., have cleavage properties along a specific direction or plane, so when an external force is applied,
An appropriate displacement occurs on the cleavage plane, which has an effect of improving lubricity.

Further, in the configuration of the magneto-optical recording medium to which the present invention can be applied, there is no limitation on the configuration from the substrate to the recording film or the dielectric film thereon, and a known configuration such as a dielectric film on the substrate, a recording film, The present invention can be applied to all media such as a structure in which dielectric films are laminated and a structure in which a metal thin film such as Ti is provided between the dielectric film and the recording film. For the individual elements, the transparent substrate is glass, polycarbonate resin,
A transparent substrate such as acrylic resin is used as a dielectric film for ZnS,
As a magneto-optical recording film, a film made of SiO ₂ , AlN, Si ₃ N ₄ , Al ₂ O ₃ , In ₂ O ₃ or the like is used as a TbFe-based alloy such as TbFeCo or TbFeGd, or an NdFe-based alloy such as NdFeCo, Furthermore NdDyFe
A typical example is a film made of an alloy of a rare earth element such as a Co alloy and a transition metal element. The present invention is effective for a recording layer whose main component is an alloy of the above-mentioned rare earth element and transition metal element which is easily deteriorated.

The dielectric film, the magneto-optical recording film, the metal thin film, and the base film in some cases are formed by a physical film forming method (PVD method) such as a sputtering method.

By the way, when the protective layer made of the resin composition of the present invention is provided on the surface of the recording film opposite to the substrate, it may be directly formed on the recording film, but oxidation or deterioration of the recording film in the air may be prevented. From the aspect of preventing, it is more desirable to directly form a thin film such as a dielectric film on the recording film by a physical film forming method in a vacuum, just as the recording film is formed .

[Effect of the present invention] According to the present invention, in the magneto-optical recording medium, at least the surface facing the magnetic field generating means is a composition containing as a main component a specific polyurethane resin containing a fluorine atom in the molecule. By covering, the magnetic head for modulation of the magnetic field generating means can be arranged close to the surface, so that it is possible to obtain a magneto-optical recording medium with a high degree of environmental resistance that allows easy overwriting.

 An example will be described below.

FIG. 1 is an explanatory view of a laminated structure of Examples and Comparative Examples,
An inorganic protective film 4 is provided on the dielectric film 2 and the magneto-optical recording film 3 which are provided on the transparent plastic substrate 1 and also protect the film from moisture.
Is provided, and the resin composition protective layer 5 is provided thereon.

Examples 1 to 5 and Comparative Examples 1 to 3 Using an RF magnetron sputtering device, a TbFeCo alloy target, an In ₂ O ₃ target and a Ti target were used, and In ₂ O ₃ (650Å) was formed on a transparent plastic substrate 1 made of polycarbonate. Dielectric film 2 made of TbFeCo (50
The magneto-optical recording film 3 made of 0Å) and the inorganic protective film 4 also serving as a reflection film made of Ti (550Å) were sequentially formed to prepare a predetermined number of magneto-optical disks.

Next, the magneto-optical discs obtained as described above were coated with the respective coating liquids in the table, and dried by heating (curing) under the conditions of 80 ° C. and 30 minutes to obtain the samples of Examples and Comparative Examples in the table. .

The compositions of the coating liquids A to H in the table are as follows.
The unit of the numerical value of the composition is part by weight.

Coating liquid A: Dialnal LR1503 (trade name) 10 Xylene 10 Coronate-L (trade name) 3.1 Dibutyltin dilaurylate 0.1 × 10 ^-3 2- (perfluorobutyl) ethanol 1.3 Coating liquid B: Dialnal LR1503 10 Xylene 10 Coronate -L 2.6 Dibutyltin dilaurylate 0.1 × 10 ^-3 2- (Perfluorooctyl) ethanol 1.3 Coating liquid C: Coating liquid A 20.5 Al powder (Al powder particle size <7 μm) 5 Coating liquid D: Coating liquid A 20.5 α-Al ₂ O ₃ (particle size <0.5 μm) 0.2 Coating liquid E: Coating liquid C 25.5 α-Al ₂ O ₃ (particle size <0.5 μm) 0.2 Coating liquid F: Dianal LR1503 10 Xylene 10 Coronate-L 2 Dibutyltin dilaurylate 0.1 × 10 ⁻³ Coating liquid G: Coating liquid F 22 Al powder (Al powder particle size <7 μm) 5 Coating liquid H: Coating liquid G 27 α-Al ₂ O ₃ (particle size <0.5 μm) 0.2 Of the above, A compound having a functional group reactive with an isocyanate group and containing no fluorine atom in the molecule Commercial DIANAL LR1503 used as an example of, as well as the manufacturer name or the like of commercial Coronate L was used as an example of the isocyanate compound having at least two isocyanate groups in the molecule are as follows.

DIANAL LF1503: Mitsubishi Rayon Co., Ltd. solid content 50%, OH value 32 mgKOH / g Coronate-L: Nippon Polyurethane Co., Ltd. solid content 75%, NCO content 13.4 wt% And each sample obtained, crash resistance The coefficient of kinetic friction was measured as an evaluation. The results are shown in the table.

Regarding durability, each sample was subjected to an accelerated deterioration test under the following two conditions, and evaluated by visual change before and after the test.

Condition 1: Dipped in a 1N NaCl aqueous solution for 24 hours and observed the appearance before and after Condition 2: A part of the sample was immersed in a 3 wt% NaCl aqueous solution at 80 ° C for 24 hours, and before and after the main immersion part and not dipped Observation of changes in the appearance of the boundary surface (gas-liquid interface) of the part The symbols of the evaluation results in the table are based on the following evaluation criteria.

◎: No abnormality in appearance ○: Slight (<5) increase in pinholes △: 10% or less change in appearance (reflection, etc.) or 20 or less increase in pinholes ×: Increase in pinhole (> 20) or appearance From the results in the table, it was confirmed that the present invention is excellent in slipperiness and durability.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a laminated structure of Examples and Comparative Examples. 1: transparent plastic substrate, 2: dielectric film, 3: magneto-optical recording film, 4: inorganic protective film, 5: resin composition protective film

Claims (3)

(57) [Claims] 1. A magneto-optical recording medium having (1) a functional group having reactivity with an isocyanate group and having no fluorine atom in the molecule, at least on the surface facing the magnetic field generating means. A compound, (2) an isocyanate compound having at least two or more isocyanate groups in the molecule, and (3) a compound having a fluorine atom in a molecule having a functional group reactive with the isocyanate group and having a molecular weight of 1,000 or less. A magneto-optical recording medium, which is provided with a protective layer made of a resin composition containing a fluorine-containing polyurethane resin as a main component, which does not contain a fluorine atom bonded to a carbon atom of a main chain skeleton. 2. The magneto-optical recording medium according to claim 1, wherein the resin composition contains a metal element having a greater ionization tendency than a transition metal element forming the recording film. 3. The magneto-optical recording medium according to claim 2, wherein the resin composition contains powder of at least one metal or alloy selected from the group consisting of aluminum, zinc, magnesium or rare earth elements.