JPH06187632A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce the production cost and to enlarge the area where recording can be done by incorporating a coloring matter which changes its optical property by irradiation with light into a nonmagnetic supporting body. CONSTITUTION:A magnetic layer containing a magnetic material is formed on a nonmagnetic supporting body. This nonmagnetic supporting body contains a coloring matter which changes its optical property by irradiation with light. To incorporate the coloring matter into the nonmagnetic supporting body, usually, the coloring matter is kneaded with the raw material resin when a resin film such as polyester to be used as the nonmagnetic supporting body is produced. Or the coloring matter is added to the raw material resin when the raw resin is produced. 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,
Positioning accuracy is improved and a track density that is an order of magnitude higher than that of conventional devices can be realized.

[0004]

The magnetic recording medium used in such an apparatus needs to have grooves formed on its surface in advance. 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. In the medium, there is a magnetic recording medium characterized in that the non-magnetic support contains a dye whose optical property is changed by light irradiation.

In the magnetic recording medium of the present invention, since the optical properties of the non-magnetic support are changed by light irradiation, if the light irradiation is performed corresponding to the signal to be recorded, an optically detectable signal is It can be easily recorded on the medium and optical signals can be written. As a light irradiation method used for writing an optical signal, an optical system may be used, for example, to modulate and irradiate a laser beam focused on a certain spot diameter in accordance with a signal to be recorded, or to generate a signal to be recorded. Correspondingly, 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 changes in the optical properties of the non-magnetic support include an increase in light transmittance, a decrease in light transmittance, an increase in reflectance, a decrease in reflectance, and the like. 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.

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. .

To contain a dye in the non-magnetic support,
Usually, a conventionally known blending method such as kneading a dye with a raw material resin at the time of producing a resin film such as polyester used as a non-magnetic support or adding it at the time of producing a raw material resin can be applied. The dye content varies depending on the type of dye used, the thickness of the dye-containing layer, the performance of the optical signal detector, etc. The amount is usually 0.001 to 30% by weight in the non-magnetic support.

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.

In the magnetic recording medium of the present invention, the amount of the magnetic substance used is such that the content of the ferromagnetic powder in the magnetic layer is 50 to 90% by weight, particularly 55 to 85% by weight. Is preferred. As the binder resin used in the magnetic layer, one having excellent adhesion to the non-magnetic 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. Examples thereof include vinyl chloride resins such as polymers, various synthetic rubbers such as styrene-butadiene copolymers, epoxy resins, phenoxy resins, etc. These may be used alone or in combination of two or more.

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 a 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.

As the dispersant, fatty acids having 12 to 18 carbon atoms such as capric acid, lauric acid, myristic acid, oleic acid and linoleic acid, metal soaps composed of alkali metal or alkaline earth metal salts of these fatty acids, lecithin, etc. 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 are 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 the magnetic coating material thus prepared on a dye-containing non-magnetic support and drying.

As a method of coating the magnetic coating material on such a dye-containing support, air doctor coating,
Blade coating, reverse roll coating,
Various methods usually applied such as 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 contains a dye suitable for optical signal writing in the non-magnetic support, writing can be performed with a smaller amount of light as compared with conventional signal writing, and an inexpensive writing device is available. Can be used. Further, since the material is not removed during writing, dust is not generated and 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 74 parts by weight of barium ferrite powder, 10 parts by weight of polyurethane resin, 2 parts by weight of phosphoric acid ester, on a 75 μm polyethylene terephthalate film containing 5% by weight of a Ni-containing indoaniline dye represented by the following structural formula (I): A mixture of 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 applied to a dry thickness of about 0.5 μm to manufacture a magnetic recording medium.

[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.

In the magnetic recording medium of the present invention, since an optical signal can be written on the non-magnetic support, the entire surface of the magnetic layer can be used for magnetic recording, and the problem of reduction in recording capacity 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 in which a magnetic layer containing a magnetic material is provided on a non-magnetic support, wherein the non-magnetic support contains a dye whose optical property is changed by light irradiation. Magnetic recording medium.