JPH06187630A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease the production cost and to enlarge the area where recording can be done by forming a layer containing such a coloring matter which changes the optical property by irradiation with light between a nonmagnetic supporting body and a magnetic layer. CONSTITUTION:A magnetic layer containing a magnetic material is formed on a nonmagnetic supporting body. A layer containing a coloring matter (coloring matter contg. layer) which changes its optical property by irradiation with light is formed between the supporting body and the magnetic layer. This layer is formed by dissolving or dispersing a coloring matter and mixing the obtd. coloring matter liquid with a resin or dispersant, it necessary, to prepare a coating liquid, and then applying the liquid directly on the nonmagnetic supporting body or other layer interposed before the magnetic layer is formed. Any coloring matter may be used as far as it changes its optical property with irradiation with light (changes in light transmittance, reflectance, etc.,) and effectively absorbs the irradiation light. For example, cyanine-based or azo-based coloring matter are used. As for the magnetic layer, Fe, Ni, Co, Fe-Co alloy, etc., are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a floppy disk, and more particularly to a magnetic recording medium suitable for use in positioning a recording / reproducing head using an optical detecting means.

[0002]

2. Description of the Related Art A large number of floppy disk devices are used for recording information in computers and word processors. In a normal floppy disk device, since the head used for recording and reproducing information is positioned by open loop control using a step motor, there is a problem that the positioning accuracy is poor and the track density cannot be increased. .

In recent years, it has been proposed to measure the position of the head by providing a servo groove on the surface of the magnetic recording medium and reading the position of the groove by an optical sensor provided integrally with the head. According to this method, since the head is positioned by closed loop control,
The positioning accuracy is improved and a track density that is an order of magnitude higher than that of conventional media can be realized.

[0004]

The magnetic recording medium used for such an optical servo system has been proposed so far, which is of a type in which a groove is previously formed on the surface. As a method of forming a groove, a method of pressing a die having a convex groove portion onto a medium to transfer the shape of the die to the medium (stamping process) and irradiating a laser beam to decompose and remove a part of the magnetic layer A method (laser processing) is known.

However, in all of these methods, the processing apparatus is expensive, dust is generated during processing, a cleaning step is required, and the manufacturing cost is high. Further, the magnetic recording medium having a groove on the surface has a problem that the recording capacity is lowered because the groove portion is not suitable for magnetic recording. Further, there is a problem that the difference in optical properties due to the presence or absence of the groove is small, the detection sensitivity is low, and it is easily affected by noise.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned state of the art, and its gist is magnetic recording comprising a magnetic layer containing a magnetic substance provided on a non-magnetic support. The magnetic recording medium is characterized in that the medium has a layer containing a dye (dye-containing layer) whose optical property is changed by light irradiation, between the non-magnetic support and the magnetic layer.

Since the optical properties of the magnetic recording medium of the present invention are changed by light irradiation, if the light irradiation is performed in correspondence with the signal to be recorded, an optically detectable signal can be easily recorded on the medium. It is possible to record, and it is possible to record and reproduce optical signals. As a light irradiation method used for writing an optical signal, an optical system may be used to modulate and irradiate a laser beam focused on a certain spot diameter according to a signal to be recorded, or to correspond to a signal to be recorded. Then, a method of irradiating light rays (for example, strobe light, ultraviolet rays, etc.) through a mask having a light shielding portion and a light transmitting portion can be adopted.

Examples of the change in the above optical properties include an increase in light transmittance, a decrease in light transmittance, an increase in reflectance, and a decrease in reflectance. For example, when a dye whose light transmittance is increased by light irradiation is used, an optical signal can be obtained from a portion having a high light transmittance in a medium surface having a low light transmittance. Further, when a dye having a reduced light transmittance is used, an optical signal can be obtained from a portion having a low light transmittance in a medium surface having a high light transmittance.

The dye to be used is not particularly limited as long as it has a change in optical property upon irradiation with light and can effectively absorb the irradiation light, and may be selected and determined appropriately. Specifically, various known dyes such as cyanine type, phthalocyanine type, naphthalocyanine type, azo type, anthraquinone type, naphthoquinone type, pyrylium type, azurenium type, squarylium type, indophenol type, indoaniline type, triarylmethane type Is used.

In order to form the dye-containing layer, a dye solution in which the above dye is dissolved or dispersed is mixed with a resin, a dispersant, etc., if necessary, to prepare a coating solution, and a magnetic layer is formed on a non-magnetic support. Previously, there is a method of coating directly or through another layer. As a coating method, various commonly applied methods such as air doctor coating, blade coating, reverse roll coating and gravure coating are adopted. It is also possible to use a method such as vapor deposition or transfer. The dye-containing layer may contain additives such as an antistatic agent and an anti-degradation agent as long as the effects of the present invention are not impaired. The amount of dye depends on the type of dye used,
Although it depends on the thickness of the easily adhesive layer, the performance of the optical signal detector, and the like, it is usually contained in an amount such that the light transmittance, the light reflectance, and the like change to a measurable degree by light irradiation. A preferred method for forming the dye-containing layer is a method in which the dyes are simultaneously mixed and applied at the time of the surface modification treatment for improving the adhesiveness of the non-magnetic support. One method is that a non-magnetic support such as polyester film has poor adhesiveness, so treatment with a surface modifier such as an alkali, amine aqueous solution, trichloroacetic acid, or phenols is performed to improve the adhesiveness with the magnetic layer. In this case, the dye is mixed with the surface modifier and applied. Another preferable method is a method in which a dye is contained in the intermediate layer when the intermediate layer containing a conductive material is provided between the magnetic layer and the non-magnetic support in order to improve the charging property of the magnetic layer. is there. Examples of the conductive material include conductive metal powders and metal compounds, and are not particularly limited. For example, metal powders such as Ag and Pt and metal compound powders such as tin oxide, zinc oxide and potassium titanate are used. To be done. The average particle size of these powders is preferably 0.005 to 0.6 μm. A magnetic recording medium provided with a conductive intermediate layer containing this dye has a low electric resistance on the surface of the magnetic layer and can reduce the amount of carbon black in the magnetic layer, so it is excellent in light transmission, and thus writing and reproducing optical servo signals. Suitable for The thickness of the dye-containing layer is usually 0.005 to 5 μm as a dry film thickness.

Other than the dye in the magnetic recording medium of the present invention
Known elements can be used as the elements.
Examples of the magnetic material used for the magnetic layer in the present invention include
For example, Fe, Ni, Co, Fe-Co alloy, Fe-Ni alloy
Gold, Fe-Co-Ni alloy, Fe-Ni-Zn alloy, F
Fe such as e-Co-Ni-Cr alloy and Co-Ni alloy,
Ferromagnetic metals such as Ni and Co or containing these as main components
Magnetic alloy powder, γ-Fe₂O₃, Fe ₃O_Four, Co included
Yes γ-Fe₂O₃, Co-containing Fe₃O_FourIron oxide magnetism
Powder, CrO₂, Barium ferrite, strontium
Various ferromagnetic powders such as metal oxide magnetic powders such as ellite
Is mentioned.

The amount of the magnetic substance used is 50 to 90% by weight, particularly 55 to 90% by weight as the amount of the ferromagnetic powder in the magnetic layer.
It is preferably set to 85% by weight. As the binder resin used in the magnetic layer, one having excellent adhesion to the support and abrasion resistance is appropriately used. For example, polyurethane resins, polyester resins, cellulose acetate butyrate, cellulose diacetate, cellulose derivatives such as nitrocellulose, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylic copolymers. Vinyl chloride resin such as polymer,
Examples thereof include various synthetic rubbers such as styrene-butadiene copolymer, epoxy resins, phenoxy resins, and the like, and these can be used alone or in combination of two or more kinds.

The content of the binder resin in the magnetic layer is 2
It is preferably used in an amount of ˜50% by weight, especially 5 to 35% by weight. By further containing a low molecular weight polyisocyanate compound having a plurality of isocyanate groups in the magnetic paint, a three-dimensional network structure can be formed in the magnetic layer and its mechanical strength can be improved. Examples of such a low molecular weight polyisocyanate compound include a trimethylolpropane adduct of tolylene diisocyanate. Such a low molecular weight polyisocyanate compound is preferably used in a proportion of 5 to 100% by weight with respect to the binder resin.

Further, various additives such as a lubricant, an abrasive, an antistatic agent, and a dispersant can be used in the magnetic coating material for forming the magnetic layer, if necessary. Here, as the lubricant, various kinds of lubricants such as aliphatic type, fluorine type, silicone type and hydrocarbon type can be used. Examples of the aliphatic lubricant include fatty acids, fatty acid metal salts,
Examples thereof include fatty acid esters, fatty acid amides, and fatty alcohols. Examples of the fatty acid include oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid,
Examples include behenic acid. Examples of the fatty acid metal salt include magnesium salts of these fatty acids, aluminum salts,
Examples thereof include sodium salt and calcium salt. Examples of the fatty acid ester include butyl ester of the above fatty acid,
Examples of the fatty acid amide such as octyl ester or glyceride include amides of the above acids, linoleic acid amide, caproic acid amide, and the like. Examples of the aliphatic alcohol include lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol and the like. Examples of the fluorine-based lubricant include perfluoroalkyl polyether and perfluoroalkyl carboxylic acid.
Examples of the silicone lubricant include silicone oil and modified silicone oil. Further, solid lubricants such as molybdenum disulfide and tungsten disulfide, and phosphoric acid esters can also be used. As a hydrocarbon lubricant,
Examples thereof include paraffin, squalane, wax and the like. The amount of lubricant used is usually 0.1 in the magnetic layer.
-20% by weight, preferably 1-10% by weight. When two magnetic layers are laminated, the content of the lubricant may be different between the upper layer and the lower layer.

Examples of the abrasive include alumina, fused alumina, corundum, silicon carbide, chromium oxide, silicon nitride and the like, and among these, those having relatively high hardness are preferably used. The number average particle diameter is preferably 2 μm or less. The content of the abrasive in the magnetic layer is preferably in the range of 1 to 20% by weight. As the antistatic agent, natural surfactants such as carbon black, graphite and saponin, nonionic surfactants such as alkylene oxide and glycerin, higher alkylamines, quaternary ammonium salts, pyridinium salts and other heterocyclic salts Anionic surfactants containing acidic groups such as carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, phosphoric acid groups, sulfuric acid ester groups, phosphoric acid ester groups, etc., amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols Amphoteric surfactants such as the like are used. These surfactants may be used alone or in combination. The amount of the antistatic agent used is usually in the range of 1 to 15% by weight in the magnetic layer. These are used as antistatic agents, but sometimes their purpose is to improve dispersibility and lubricity.

Examples of the dispersant include fatty acids having 12 to 18 carbon atoms such as capric acid, lauric acid, myristic acid, oleic acid and linoleic acid, metal soaps containing alkali metal or alkaline earth metal salts of this fatty acid, lecithin and the like. Is used. The amount of the dispersant used is usually in the range of 0 to 20% by weight in the magnetic layer. As a solvent to be used for kneading, dispersing, and coating a magnetic coating material containing the above components, for example, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, and methyl acetate. , Esters such as ethyl acetate and butyl acetate, ethers such as diethyl ether and tetrahydrofuran, aromatic hydrocarbons such as benzene, toluene and xylene, and aliphatic hydrocarbons such as hexane.

The kneading and dispersing methods, the order of addition of each component, and the like may be the usual methods applied to the kneading and dispersing of magnetic paints. The magnetic recording medium of the present invention can be obtained by coating and drying the magnetic coating material thus prepared on the dye-containing layer provided on the non-magnetic support, either directly or through another layer.

As the non-magnetic support, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene and polyethylene, cellulose derivatives such as cellulose acetate, various plastics such as polycarbonate, polyamide and polyimide can be used. .

As a method for applying the magnetic paint, various methods which are usually applied, such as air doctor coating, blade coating, reverse roll coating and gravure coating, are adopted. When a plurality of magnetic coating materials are applied, the lower layer coating solution and the upper layer coating solution may be applied simultaneously in a wet state, or each layer may be applied sequentially.

The thickness of the magnetic layer is usually 0.
It is 1 to 10 μm, preferably 0.3 to 2 μm. Further, a top coat layer for imparting lubricity or a back coat layer for preventing electrification can be provided. If necessary, alignment treatment, random treatment, smoothing treatment, or the like may be performed.

Since the magnetic recording medium of the present invention has a dye-containing layer suitable for optical signal writing, writing can be performed with a smaller amount of light than conventional signal writing, and an inexpensive writing device can be used. . Also, since there is no removal of the material associated with writing, no dust is generated,
A cleaning process after writing is unnecessary. Furthermore, the optical signal writing does not affect the magnetic recording material, and the entire magnetic layer can be used for magnetic recording. In addition, the change in the optical property of the dye due to the light irradiation is large, and the signal can be detected with high sensitivity.

[0022]

EXAMPLES Specific embodiments of the present invention will now be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. Example 1 A Ni-containing indoaniline dye solution represented by Structural Formula (I) was applied on a polyethylene terephthalate film having a thickness of 75 μm to form a dye layer having a dry thickness of about 0.2 μm. Next, a magnetic paint obtained by mixing 74 parts by weight of barium ferrite powder, 10 parts by weight of polyurethane resin, 2 parts by weight of phosphoric acid ester, 7 parts by weight of aluminum oxide, 1 part by weight of carbon black, and 5 parts by weight of butyl stearate in tetrahydrofuran was dried to a thickness of about A magnetic recording medium was manufactured by applying it to a thickness of 0.5 μm.

[0023]

[Chemical 1]

The Ni-containing indoaniline dye represented by the structural formula (I) has an absorbance peak near 780 nm,
And it decomposes by heating at 200 to 400 ° C., and the peak is reduced to a negligible level. The absorbance curve of the magnetic recording medium manufactured as described above is shown by the solid line in FIG. In FIG. 1, the curve indicated by the dotted line is the absorbance curve of the magnetic recording medium containing no dye. The magnetic recording medium containing the dye has an absorption peak near 780 nm which is the wavelength of the semiconductor laser used for recording detection. When the dye is locally decomposed and decolorized by local light irradiation, the absorbance of that portion becomes almost equal to that of the magnetic recording medium containing no dye. This difference is extremely large, and as shown in FIG. 1, the transmittance at 780 nm is 2% when the dye is contained.
On the other hand, in the case where no dye is contained, the change greatly changes to 17%, and thus the recorded signal can be easily read using a semiconductor laser.

An example of writing an optical signal by light irradiation is shown in FIGS. In an actual system, the recording signal pitch is about 5 μm to 10 μm,
In this figure, the pitch is enlarged to facilitate understanding. For each track (indicated by i in FIG. 2),
An optical recording portion ai having a short recording wavelength λa and an optical recording portion bi having a long recording wavelength λb (where λb = 2λa) are provided, and the optical recording b has the same phase on each track and the optical recording a has each track Have different phases by λa / 4.

In FIG. 2, the light transmission in the shaded area is measured by a photodetector provided integrally with the magnetic head.
An AC signal is output from the detector due to the rotation of the disk, but because optical recording of two types of wavelengths is provided,
The output signal contains signals of two types of frequencies. The phase of the high frequency component generated by the optical recording a changes as the detector moves across the track, whereas the phase of the low frequency component generated by the optical recording b is constant. Therefore, each frequency component is separated by a bandpass filter, the head position is obtained by measuring the phase difference between the two frequency components, and by controlling the head position so that this phase difference becomes a predetermined value, Accurate tracking can be performed.

Since the magnetic recording medium of the present invention has the dye-containing layer suitable for optical writing between the non-magnetic support and the magnetic layer, the entire magnetic layer can be used for magnetic recording. However, the problem that the recording capacity is reduced does not occur.

[0028]

The magnetic recording medium of the present invention is characterized in that the manufacturing cost is low and the magnetic recording area is wide.
It is suitable for a magnetic recording medium used in an optical head positioning system.

[Brief description of drawings]

FIG. 1 is a diagram showing an absorbance curve of a magnetic recording medium manufactured in Example 1.

FIG. 2 is a detailed schematic diagram showing an example of writing an optical signal to a magnetic recording medium by light irradiation.

FIG. 3 is a schematic diagram showing an example of an optical signal writing pattern on a magnetic recording medium by light irradiation.

[Explanation of symbols]

 λa Short recording wavelength λb Long recording wavelength ai, bi Optical recording section

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing a magnetic material provided on a non-magnetic support, wherein a dye whose optical properties are changed by light irradiation is provided between the non-magnetic support and the magnetic layer. A magnetic recording medium having a layer containing.