JPH0449546A - Magneto-optical recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coated magneto-optical recording medium using rare earth iron garnet fine particles.

(Prior Art and its Problems) Conventionally, as a magnetic material used in a magneto-optical recording medium, one made of an amorphous alloy of a rare earth metal and a transition metal is known.

However, such amorphous alloy magnetic bodies have the drawback of being susceptible to oxidative corrosion and deteriorating magneto-optical properties. In addition, in magneto-optical recording using amorphous alloys, reproduction is performed using the magneto-optic effect (Kerr effect) caused by reflection on the magnetic film surface, but since amorphous alloys generally have a small Kerr rotation angle, There was a problem with low sensitivity.

In contrast, Japanese Patent Publication No. 56-15125, Japanese Patent Application Publication No. 6
No. 1-89605 proposes magneto-optical recording media using polycrystalline oxide thin films of garnet and hexagonal ferrite, respectively. A magnetic material using this oxide is
It has excellent corrosion resistance and reproduces using the magneto-optical effect (Faraday effect) caused by light transmitted through the magnetic film.
It has the advantage of high sensitivity. However, since it is polycrystalline, it has the disadvantage that medium noise increases due to light scattering at crystal grain boundaries, disturbances in the shape of written bits due to birefringence, domain wall movement, and the like.

On the other hand, JP-A-62-119758 discloses a coated magneto-optical recording medium using yttrium iron garnet particles. In such a coating type medium, there is no adverse effect of grain boundaries as in the polycrystalline oxide thin film, but the garnet particles described in this publication have a particle size of 1.
The particles are as large as 5 μm, and when such particles are used, light scattering occurs, making them unsuitable for high-density recording using submicron wavelength light.

In addition, in coated media, it is difficult to uniformly disperse the particles in the magnetic film, which causes the problem of light scattering.

(Object of the invention) The present invention solves the above-mentioned drawbacks and provides a coated magneto-optical recording medium in which rare earth iron garnet fine particles are extremely well dispersed, the magneto-optic effect is large, and the light scattering of the medium is extremely small. It is something.

(Means for Solving the Problems) The present invention provides rare earth iron garnet particles having an average particle size of 30 to 1000 particles on a substrate, and a vinyl copolymer consisting of each of the following structural units, (a) Vinyl chloride unit, (b) Vinyl monomer unit whose side chain is a hydroxyl group-containing monovalent organic group, (c) Monovalent organic group whose side chain is a 13O, M group or -303M group ( (d) a vinyl monomer unit having an epoxy group in its side chain; Regarding.

As the rare earth iron garnet fine particles in the present invention, those represented by the general formula RIIBibFecMaOe are used.

R in the above general formula is Y, La, Ce, Pr, Nd
, Pm.

Sm, [iu, Gd + Tb, Dy + Ilo,
Er, Tm+ Indicates one or more rare earth elements selected from the group consisting of Yb and Lu.

In addition, M is an element that can be replaced with iron, such as AI, GaCr
, Mn, Sc, In, Ru, Rh, Co, Fe(U
), Cu, Ni, Zn, Li, 5iGe, Zr, T
i, Hf, Sn, Pb, Mo, V and Nb
Indicates one or more elements selected from the group consisting of. Among the M elements, the trivalent elements 8 I, Ga, Cr, Mn,
Sc, In, Ru, Rh and Co are used alone, divalent elements Co, Fe, Cu, Ni and Zn, or monovalent elements Li are tetravalent elements Si, Ge, Zr, Ti,
It is preferable to substitute Hf, Sn, Pb, and Mo, or a combination of pentavalent elements (■) and Nb as an element equivalent to trivalent.

The proportion of each element in the above general formula is a +
b + c 10d = 7.5~8. Ola+b
= 2.0-3°5, c + d = 4.5-6.
Ola=0.5~3.01b=0~2.5, c=
3.0 to 5.01d=o to 2.0, and e is the number of oxygen atoms satisfying the valences of other elements.

In particular, a portion of the rare earth elements of garnet is preferably 0.
By substituting Bi of 25 to 2.5, the Faraday rotation angle can be increased. Further, by replacing a part of iron with preferably 0.3 to 2.00M, the Curie temperature can be lowered and the saturation magnetization can be reduced.

Further, a part of R in the rare earth iron garnet fine particles may be further substituted with a divalent element such as Pb, Ca, Mg, etc. In that case, charge compensation may be performed with a tetravalent or pentavalent element of M. good.

The average particle diameter of the rare earth iron garnet fine particles in the present invention is 30 to 1000 particles, preferably 100 to 600 particles. When the average particle size is smaller than 30 particles, it becomes superparamagnetic due to thermal disturbance. Moreover, if the number of people exceeds 1000, light scattering will occur and noise will be generated, which is not preferable.

In addition, it is preferable that the particle shape is optically symmetrical,
A spherical shape is preferable, but a polyhedral shape or a plate shape may also be used.

The method for producing the rare earth iron garnet fine particles is not particularly limited as long as particles having the above-mentioned characteristics can be obtained, and production methods such as a hydrothermal synthesis method, a coprecipitation method, a melting method, an alkoxide method, a gas phase method, etc. can be used. It will be done.

Below, a method for producing rare earth iron garnet fine particle powder by coprecipitation method will be described.

The alkali hydroxide concentration after mixing a solution containing ions of each element selected in proportions constituting the rare earth iron garnet represented by the above general formula and an alkali hydroxide is 0.1 to 8 mol/i! Rare earth iron garnet fine particles are obtained by mixing to form a precipitate and firing the precipitate at 600 to 900°C.

The solution containing ions of each element is obtained by dissolving compounds of each element, such as nitrates, sulfates, chlorides, etc., in a solvent.

The solvent may be any solvent as long as it can dissolve the compounds of the above-mentioned elements, and water, alcohols, ethers, and mixed solvents thereof are usually used.

It is desirable that the solution containing each of the elemental ions is prepared so that the total ion concentration contained in the slurry after precipitation is 0.01 to 2.0 mol/1.

Total ion concentration is 0.01 mol/! If it is less than 2.0 mol/l, the amount of garnet produced will be small, and if it is more than 2.0 mol/l, the particles will become large or a foreign phase will be produced, which is not preferable.

In addition, the proportion of each element ion is determined by the proportion of each element constituting the rare earth iron garnet represented by the above general formula,
R and old may be used in excess of about 10 mol% of their required amounts.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide, aqueous ammonia, etc. are used.

The amount of alkali hydroxide used is such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 0.1 to 8 mol/1. If the amount of alkali hydroxide is too small, particles may become large or unreacted substances may remain. Further, it is not economical to increase the amount of alkali hydroxide excessively.

Examples of methods for mixing the solution containing ions of each element and the alkali hydroxide include a method of adding a solution containing ions of each element to an aqueous solution of alkali hydroxide, and a method of continuously mixing the two. Further, the precipitation may be formed at once or in multiple stages.

Next, the obtained precipitate is washed with water to remove free alkali, and then filtered, dried, and fired to obtain rare earth iron garnet fine particles. The firing temperature varies depending on the composition of the rare earth iron garnet, but is between 600 and 900°C.
It is °C. If the temperature is too low, crystallization will not be sufficient, and if the temperature is too high, particles will become large or sintering will occur, which is not preferable. Appropriate firing time is about 10 minutes to 30 hours. The firing atmosphere is not particularly limited, but an air atmosphere is generally convenient.

In the present invention, it is preferable that a surfactant is adhered to the rare earth iron garnet fine particles.

Examples of the surfactant include polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, sulfosuccinate salt,
polyoxyethylene alkyl ether phosphate ester,
Examples include polyoxyethylene alkylamine, polyoxyethylene alkylamide, quaternary ammonium salts, and the like.

The amount of surfactant added is preferably 1 to 20% by weight based on the rare earth iron garnet fine particles.

The deposition of the surfactant is carried out by adding rare earth iron garnet fine particles and the surfactant to an organic solvent and performing a dispersion treatment.

The vinyl copolymer in the present invention includes the above-mentioned (a) to
It is composed of each unit of (d).

The unit (a) is a vinyl chloride unit which is the main constitutional unit of the vinyl copolymer. The proportion of (a) units is preferably 50 to 95% by weight. If the amount of the (a) unit is too small, the physical strength of the magnetic layer will decrease, and if it is too large, the solubility of the vinyl copolymer will decrease, which is not preferable.

The unit (b) is a vinyl monomer unit whose side chain is a hydroxyl group-containing monovalent organic group.

(b) Monomers corresponding to the unit include hydroxypropyl acrylate, hydroxyethyl methacrylate,
Examples include 2-hydroxypropyl methacrylate and N-methylolacrylamide.

The proportion of the unit (b) is preferably 1 to 15% by weight. (b)
If there are too few units of fireflies, the dispersibility of the magnetic powder will be reduced, and if there are too many, the durability of the magnetic layer will be reduced, which is not preferable.

(c) The unit is a monovalent organic group whose side chain has a -SO3M group or a -3O,M group (M in the formula is a hydrogen atom or a metal atom)
It is a vinyl monomer unit.

(c) Monomers corresponding to the unit include vinylsulfonic acid, arylsulfonic acid, alkylarylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-medylpropanesulfonic acid, allyldodecylsulfosuccinate, etc. Examples include alkali metal salts of.

The proportion of the unit (c) is preferably 0.5 to 10% by weight.

Outside this range, the dispersibility of the magnetic powder decreases, which is not preferable.

The unit (d) is a vinyl monomer unit having an epoxy group in its side chain.

(d) Monomers corresponding to the unit include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methacryl glycidyl ether; glycidyl esters of unsaturated acids such as glycidyl acrylate, glycidyl methacrylate, and glycidyl ethyl maleate; Examples include epoxide olefins such as butadiene monooxide and vinylcyclohexene monooxide.

The proportion of the unit (d) is preferably 0.1 to 20% by weight.

Outside this range, the dispersibility of the magnetic powder decreases, which is not preferable.

The average degree of polymerization of the vinyl copolymer composed of the units (a) to (d) described above is preferably 100 to 1000. If the average degree of polymerization is too low, the physical strength of the magnetic layer decreases, and if it is too high, the solution viscosity increases, resulting in poor workability, which is not preferred.

The vinyl copolymer of the present invention can be produced by a general suspension polymerization method, emulsion polymerization method, solution polymerization method, bulk polymerization method, or the like.

The vinyl copolymer in the present invention includes the above-mentioned (a) to
In addition to the structural unit (d), various structural units may be contained in order to improve the solubility and flexibility of the copolymer. Examples include vinyl esters such as vinyl acetate and vinyl propionate, vinyl ethers such as ethyl vinyl ether and isobutyl vinyl ether, and unsaturated acid esters such as ethyl acrylate, propyl methacrylate, diethyl maleate, and dibutyl fumarate.

In the present invention, the content of the vinyl copolymer in the magnetic layer is based on 100 parts by weight of rare earth iron garnet fine particles.
10 to 40 parts by weight is preferred.

In the present invention, in addition to vinyl-based copolymers, binders that are commonly used in magnetic recording media, such as vinyl chloride-vinylidene chloride copolymers, cellulose derivatives such as nitrocellulose resin, acrylic resins, Polyvinyl acecool resin, polyvinyl butyral resin, epoxy resin, polyurethane resin, phenoxy resin, etc. may be used in combination.

The magneto-optical recording medium of the present invention can be obtained by adding the rare earth iron garnet fine particles and a binder to an organic solvent and dispersing the mixture to prepare a magnetic paint, applying this onto a substrate, and then drying it. can get.

Examples of organic solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohols such as methanol, ethanol, propatool, and butanol, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol heptanoacetate. Ethers such as glycol dimethyl ether, glycol monoether, dioxane, and tetrahydrofuran, and aromatic hydrocarbons such as benzene, toluene, and xylene are used.

There are no particular restrictions on the dispersion method, and ordinary kneading machines such as two-roll mills, Miki roll mills, ball mills, pebble mills, thoron mills, sand grinders, high-speed impeller dispersing machines, high-speed stone mills, dispersers, and kneaders can be used.
1. A high-speed mixer, homogenizer, ultrasonic disperser, etc. are used.

Application methods include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, reverse roll coating, transfer roll coating 1, gravure coating, kiss coating, cast coating, spray coating, and spin coating. Can be mentioned.

The thickness of the applied magnetic layer is 0.05 to 0.05 after drying.
2.0 pm, particularly preferably in the range of 0.2 to 1.0 pm in terms of stability of recording bits.

The substrate is not particularly limited, and may be a single crystal substrate, a polycrystalline substrate, an amorphous substrate such as glass, another inorganic material substrate such as a composite substrate, or acrylic resin, polycarbonate resin,
An organic material substrate such as polyester resin, polyamide resin, polyimide resin, etc. can be used.

Further, it is preferable to provide a light reflective layer between the substrate and the magnetic layer or on the magnetic layer.

As the light reflecting layer, Cu, Cr, AI, Ag,
Au, TiN, etc. are used. This light-reflecting layer is formed on the substrate or on the magnetic layer by a coating method, plating method, vapor deposition method, or the like.

(Example) The present invention will be explained in more detail by showing Examples and Comparative Examples below.

Note that the measurement of light scattering for 633 nm light was performed using the apparatus shown in FIG. That is, light with a wavelength of 633 nm emitted from a HeNe laser light source is irradiated perpendicularly to the film surface of the medium, and a beam spot that passes through the medium and is projected onto a projection plate is monitored through an infrared camera. Then, the degree of light scattering was evaluated by comparing the obtained light intensity profile with the background (in the case of only a substrate to which no medium was applied).

Example 1 1.93 mol of sodium hydroxide (NaOH) was added to 8 mol of water.
0d, and separately bismuth nitrate [formerly (NO3)3.
511□010.020mol, dysprosium nitrate [
Dy(N03)3'5H20] 0.040 mol, iron nitrate [Fe(N03)3.91z010.091 mol and aluminum nitrate [AI(NO3)+.9HzO] 0
．． 010 mol was dissolved in 5N=nitric acid solution 220rd. Next, while stirring the sodium hydroxide solution, a nitric acid solution was gradually added dropwise to neutralize the solution to form a precipitate.

The obtained precipitate was washed with water, filtered, dried, and heated at 700'C.
and fired to obtain garnet fine particles.

The obtained garnet fine particles had an average particle size of 380 mm, and as a result of X-ray powder diffraction spectrum and composition analysis, Dyz, oBi, , Fea, 5AI0.50
+2, and had a single garnet phase.

4.5 g of these garnet fine particles and 0.45 g of a polyoxyethylene alkyl ether type surfactant (Hycol 02; manufactured by Nikko Chemicals ■) were placed in a mixed organic solvent (4.5 g of toluene, 4.5 g of methyl ethyl ketone, and 4.5 g of cyclohexanone). In addition, a dispersion treatment was performed for 75 minutes using a paint conditioner dispersion machine.

Next, vinyl chloride-vinyl acetate copolymer (MPR-DSA2: manufactured by Kuchigae Kagaku) was added to this dispersion as a binder.
0.9 g and a mixed organic solvent (4.5 g of toluene, 4.5 g of methyl ethyl ketone and 4.5 g of cyclohexanone) were added and dispersed for 300 minutes using a paint conditioner disperser to prepare a magnetic paint.

The obtained magnetic paint was applied onto a glass substrate using a spin coater to obtain a magneto-optical recording medium.

The film thickness of the obtained medium was 0.5 μm, and the Faraday rotation coefficient for 633 nm light was 2000 deg/c.
It was m.

In addition, the results of investigating light scattering for light of the above wavelengths were
As shown in the figure. The scattering profile of the transmitted light shown in FIG. 2 almost matched that of the case of only the glass substrate, and it was found that light scattering was extremely small.

Example 2 A magneto-optical recording medium was obtained in the same manner as in Example 1, except that the binder was changed to MRIIO (manufactured by Nippon Zeon ■).

When the obtained medium was examined for light scattering with respect to light of 633 nm, it was found that the scattering profile of transmitted light almost matched that of the case of only a glass substrate, indicating that light scattering was extremely small.

Comparative Example 1 In Example 1, the binder was VAGH (manufactured by UCC).
A magneto-optical recording medium was produced in the same manner as in Example 1 (!) except that the material was changed to

FIG. 3 shows the results of examining the light scattering of 633rzn light for the obtained medium. The scattering profile of the transmitted light in FIG. 3 has a broad base and a wide half-width of the peak, indicating that light scattering is occurring.

(Effects of the Invention) The magneto-optical recording medium of the present invention has rare earth iron garnet fine particles dispersed very well, so it has a large magneto-optic effect, has very little light scattering in the medium, and is suitable for high-density magneto-optical recording. ing. In addition, it can be manufactured by a coating method and has good productivity.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a light scattering measuring device for 633 nm light of a magneto-optical recording medium, and FIGS. 2 and 3 are diagrams of magneto-optical recording media obtained in Example 1 and Comparative Example 1. It is a figure which shows the measurement result of the light scattering profile of. 1...l(e-N e laser (λ=633
nm) 2... Projection plate 3... Infrared camera 4... Monitor 5... Magnetic film 6... Substrate

Claims (1)

[Scope of Claims] On a substrate, rare earth iron garnet fine particles having an average particle diameter of 30 to 1000 Å, and a vinyl copolymer consisting of each of the following structural units: (a) a vinyl chloride unit; (b) the side A vinyl monomer unit whose chain is a monovalent organic group containing a hydroxyl group, (c) a monovalent organic group whose side chain is a -SO_3M group or a -SO_3M group (M in the formula is a hydrogen atom or a metal atom) A magneto-optical recording medium provided with a magnetic layer containing a vinyl monomer unit; (d) a vinyl monomer unit having an epoxy group in its side chain.