JPH01276423A - Disk-shaped magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease the difference between the reproduced outputs near the outermost circumference and the innermost circumference by incorporating metal powder having the coercive force higher than 1,400oersted and a resin of a specific vinyl chloride copolymer as well as polycarbonate system polyurethane into a magnetic layer. CONSTITUTION:The ferromagnetic powder incorporated into the magnetic layer of the disk-shaped magnetic recording medium is the metal powder having the coercive force higher than 1,400oersted and a liquid dispersion contg. the vinyl chloride copolymer as a binder contg. at least an epoxy group, hydroxyl group and sulfonic acid radical group as well as polycarbonate system polyurethane resin in said powder is supplied onto a nonmagnetic base and the binder is cured by a heating treatment. A ferromagnetic metal alone or the alloy thereof (Fe, Co, Ni, Fe-Ni, Fe-Co, Fe-Ni-Co, etc.) is usable as the metal powder. The other components (O, N, C, Al, Si, S, Ti, Cr, Mn, Cu, Zm, Y, Ba, W, Te, Gd, Nd, P, etc.) may be incorporated therein within the range of <=20wt.% by the total weight of the Fe, Co and Ni.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a disk-shaped magnetic recording medium for use in, for example, still video devices and floppy disk devices.

[Prior art 1] Conventionally, the shortest recording wavelength for electronic still cameras, etc. is 1.
γ-Fa alloy powder is widely used as the ferromagnetic powder contained in the magnetic layer of a disc-shaped magnetic recording medium of 0 μm or less.

These conventional ferromagnetic powders have a low coercive force of 1400 Oe or less.

For example, among the current disk-shaped magnetic recording media, a small floppy disk (for image recording,
(for data recording, etc.), metal powder having a coercive force of about 1200 to 1350 degrees is used.

Furthermore, for example, with regard to the disk-shaped magnetic recording medium for electronic still cameras described in Japanese Patent Application Laid-Open No. 58-122623, it is proposed to use ferromagnetic powder of 1000 Oe or more; In the examples, only ferromagnetic powders (metallic powders) with coercive forces below 1300 Oe are used.

Furthermore, for example, for the disc-shaped magnetic recording medium for electronic still cameras described in Japanese Patent Application Laid-Open No. 61-230624, it is possible to use ferromagnetic powder (metal or alloy powder) of about 1,200 to 1,400 nanometers. It is described as suitable, and in the examples of the publication, 1
A ferromagnetic powder with a coercive force of 310 oersteds is used.

In addition, vinyl chloride-vinyl acetate copolymer, thermoplastic polyurethane resin, and the like are used as binders in the magnetic properties 1.

[Problem to be Solved by the Invention 1] When recording is performed on a conventional disk-shaped magnetic recording medium using a recording signal of a relatively high frequency, the playback output and S/N between the outermost and innermost tracks of the medium will change. There was a problem that there was a large difference in the ratio.

For example, when recording is performed on a disc-shaped magnetic recording medium for an electronic still camera with a diameter of 47.0 mm at 3600 revolutions per minute and a carrier signal with a frequency of 7 MHz, the innermost track (diameter 30.0 mm ) is approximately 6 decibels lower than the reproduction output of the outermost track (diameter 40.0 mm). Therefore, the image quality is different between the image recorded near the innermost circumference and the image recorded near the outermost circumference.

In the above example, the recording wavelength at the outermost circumference is 1.08μ.
However, the recording wavelength at the innermost circumference is as short as about 0.81 μm, and in conventional disc-shaped recording media, when the recording wavelength becomes shorter than about 1.0) ua, the reproduction output decreases. This is the cause of the large difference in reproduction output between the outermost circumference and the innermost circumference in conventional disc-shaped magnetic recording media.

Conventionally, in order to compensate for the difference in playback output between the outer and inner circumferences as described above, expensive and special heads and circuits have been used for recording and playback devices, and in some cases, the playback output and S/N ratio have been corrected and improved. be. However, in this case, the selection range of heads and circuits of the recording/reproducing device is limited, the device must be expensive, and there is a limit to the improvement of the correction.

On the other hand, in the case of magnetic recording media for electronic still cameras, the medium usually slides against the magnetic head at 3,600 revolutions per minute, and for example, if used for 48 hours, it will slide about 10 million times. , high abrasion resistance is required, which is incomparable to the still mode of conventional VTR tapes and floppy disks for data recording.

The present invention has been made to solve these problems, and its purpose is to provide a disk-shaped magnetic recording medium with a small difference in reproduction output between the outermost circumference and the innermost circumference of the track. be.

Still another object of the present invention is to provide a disc-shaped magnetic recording medium that has sufficient wear resistance performance required for media for electronic still cameras and the like.

[Means for Solving the Problems 1] The present invention provides a disc-shaped magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder provided on the support, in which the magnetic layer has a It must be obtained by curing a mixture containing a vinyl chloride copolymer having at least an epoxy group, a hydroxyl group, and a sulfonic acid group, and a polycarbonate polyurethane resin, in which a metal powder having a coercive force higher than that of Oersted is dispersed. This is a disc-shaped magnetic recording medium characterized by:

Since the disk-shaped magnetic recording medium of the present invention contains metal powder having a coercive force higher than 1400 Oe in its magnetic layer, the reproduction output is improved compared to conventional media, especially when the recording wavelength is short. Therefore, the reproduction output near the innermost circumference of the track is particularly improved, and the difference in reproduction output between the innermost circumference and the outermost circumference is reduced.

Furthermore, in the magnetic recording medium of the present invention, since the vinyl chloride copolymer and the polyurethane resin are used as the binder, the metal powder is uniformly and well dispersed in the magnetic layer. This results in the effect on the reproduction output due to the metal powder becoming more pronounced.

In particular, since the medium of the present invention contains the polyurethane resin, the wear resistance of the magnetic layer can be easily improved by further containing an appropriate abrasive or lubricant in the magnetic layer. As the abrasive or lubricant, non-magnetic inorganic powder having a Mohs hardness of 6 or more and fatty acid ester such as batyl monoisostearate are suitable.

The magnetic recording medium of the present invention will be explained in detail below.

The ferromagnetic powder contained in the magnetic layer of the disk-shaped magnetic recording medium of the present invention is a metal powder having a coercive force higher than 1400 Oe. Note that the coercive force is preferably 2000 Oe or less in terms of the erasure rate of the medium. Furthermore, when the medium of the present invention is used as a magnetic recording medium for electronic still cameras, its coercive force is 1700 Oe or less in combination with heads currently used in electronic still cameras. It is preferable.

The ferromagnetic powder (metal powder) is preferably a metal powder with a saturation magnetization of 120 emu/g or more in order to obtain sufficient output even at a relatively long recording wavelength. In addition, from the viewpoint of ease of making it into a paint and balance of electromagnetic conversion characteristics, its specific surface area is 40%.
Preferably, the metal powder is 65 rrf'/g.

The metal powder contained in the magnetic layer of the medium of the present invention may be a single ferromagnetic metal or an alloy (Fe, Co, Ni,
Fe-Ni %Go-Ni, Fe-Co, Fe
-Ni-Co, etc.) can be used. Also, Fe, G
Other components (0, N, C, A1. Si, 3% T
i, Cr%Mn, Cu, Zm, Y.

(Ba, W, Te, Gd, Nd, P, etc.).

Note that other ferromagnetic powders may be used in combination as long as they do not inhibit the effects caused by the metal powder described above.

The method for producing the medium of the present invention includes the above-mentioned metal powder,
A dispersion containing a vinyl chloride copolymer as a binder having at least an epoxy group, a hydroxyl group, and a sulfonic acid group and a polycarbonate polyurethane resin (magnetic paint)
is applied onto a non-magnetic support, followed by heat treatment to harden the binder. Note that both have excellent compatibility.

Therefore, the medium of the present invention has a magnetic layer containing a cured product in which the vinyl chloride copolymer and polycarbonate polyurethane resin are mixed together as a binder.

The average degree of polymerization of the vinyl chloride copolymer in the magnetic paint before heat treatment is preferably 200 to 500.

Further, the vinyl chloride component of the vinyl chloride copolymer in the magnetic paint before heat treatment is preferably 70% by weight or more, and the amount of epoxy groups in the copolymer is 0.5% by weight.
The amount of hydroxyl groups is preferably 0.1 to 5% by weight, and the amount of sulfonic acid groups is 0% by weight in terms of -503.
．． 2 to 20% by weight is preferred. In addition, the "sulfonic acid group" as used in the present invention means a sulfonic acid group or a sulfonic acid group (eg, an alkali metal salt, an ammonium salt, etc.).

The weight percent value of each component of the above-mentioned copolymer can be determined by quantifying the amount of hydrogen chloride generated by combustion for the vinyl chloride component, by titration for the amount of epoxy groups, and by determining the amount of hydroxyl groups. can be determined by infrared absorption analysis, and the amount of sulfonic acid radicals can be determined quantitatively by a combination of elemental analysis and infrared absorption analysis.

Examples of the method for producing the vinyl chloride copolymer include a method of copolymerizing a vinyl chloride monomer, a monomer having an epoxy group, a monomer having a hydroxyl group, and a monomer having a sulfonic acid group.

Examples of epoxy group-containing agents include acrylic glycidyl ether, methacryl glycidyl ether,
Various monomers can be mentioned, such as glycidyl acrylate and glycidyl methacrylate.

Examples of the monomer having a hydroxyl group include various monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxyethyl maleate. Moreover, a hydroxyl group can also be introduced by a ring-opening reaction of the introduced epoxy group.

Examples of the monomer having a sulfonic acid group include various monomers such as methyl vinyl sulfonic acid, ethyl acrylic acid-sulfonate, styrene sulfonic acid, and alkali metal salts or ammonium salts thereof.

However, the method for producing the vinyl chloride copolymer is not limited to the above example. For example, the method for producing the vinyl chloride copolymer is not limited to the above example. A method of additionally introducing it may also be used.

Further, the vinyl chloride copolymer is not limited to a random copolymer, and includes, for example, a block copolymer,
A graft copolymer or the like may also be used.

The content of the vinyl chloride copolymer in the magnetic layer of the medium of the present invention is desirably 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the metal powder.

The polycarbonate-based polyurethane resin contained in the magnetic layer of the present invention uses polycarbonate as a long-chain polyol component constituting the resin, and conventionally used TDI, MD as a polyisocyanate component.
I, IPDI, HMDI, etc. can be used.

The total amount of vinyl chloride copolymer and polycarbonate polyurethane resin in the magnetic layer of the medium of the present invention is preferably 5 to 50 parts by weight based on 100 parts by weight of metal powder.
Parts by weight, preferably 10 to 20 parts by weight.

In addition, the blending ratio of the vinyl chloride copolymer and the polycarbonate polyurethane resin is preferably in the range of 1:5 to 5:1 by weight.If the vinyl chloride copolymer is less than 115, metal powder If the amount of the polycarbonate-based polyurethane resin is less than 115%, the excellent abrasion resistance may not be fully exhibited.

The magnetic layer of the medium of the present invention may contain, as necessary, for example, as long as it does not inhibit the effects caused by the vinyl chloride copolymer and polycarbonate polyurethane resin.
Other types of polyurethane resins, polyester resins, nitrocellulose, etc. may be included as subcomponents of the binder. The content of the subcomponents is preferably 30 parts by weight or less per 100 parts by weight of vinyl chloride copolymer + polycarbonate polyurethane resin.

In addition, when producing the medium of the present invention, a curing agent such as polyisocyanate may be added for the purpose of promoting crosslinking and curing of the binder.

Suitable curing conditions for curing the copolymer vary depending on the desired physical properties of the magnetic layer and the weight percentage of the multigroup, but for example, heating at a temperature of about 40 to 80°C for lθ to about 60 hours is preferred. This can be done by

The magnetic layer of the magnetic recording medium of the present invention may contain a suitable dispersant, abrasive, or lubricant, if necessary.

In addition, in terms of the wear resistance of the magnetic layer, it is preferable that the magnetic layer of the magnetic recording medium of the present invention contains a nonmagnetic inorganic powder having a Mohs hardness of 6 or more as an abrasive.

Examples of the non-magnetic inorganic powder include chromium oxide, α-
Examples include alumina, a-Fe2o3, TiO2, and the like. The content of the non-magnetic inorganic powder is preferably 5 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder. If the content is less than 5 parts by weight, the improvement in wear resistance may not be sufficient. , more than 20 parts by weight may inhibit the effect of the present invention on reproduction output.

Note that the magnetic layer of the magnetic recording medium of the present invention preferably contains a fatty acid ester as a lubricant, since the abrasion resistance of the magnetic layer can be improved by a lubricating effect.

Examples of the fatty acid ester include saturated or unsaturated fatty acids such as capric acid, erucic acid, cetoleic acid, elaidic acid, oleic acid, myristic acid, pentadecyl acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, and glyceric acid. Methyl esters, ethyl esters, propyl esters, butyl esters, amyl esters, etc. may be used alone or in combination. In particular, in the medium of the present invention, it is preferable to use batyl monoisostearate, which is an ester of batyl alcohol and isostearic acid, alone or in combination with other fatty acid esters.

Further, as the non-magnetic support of the medium of the present invention, a suitable support may be used depending on the usage purpose and usage environment of the medium, such as polyester film, polyimide film, polyaramid film, polyacetate film, etc. The following members can be mentioned.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 First, a dispersion liquid was prepared by dispersing the following materials using a sand grinder.

"Acicular ferromagnetic powder""Binder""Dispersant" - Phosphate ester 1 part by weight "Abrasive""Lubricant" - N-Butyl stearate 3 parts by weight - Batyl monoisostearate 2 parts by weight "Solvent"・100 parts by weight of toluene ・100 parts by weight of methyl ethyl ketone ・100 parts by weight of cyclohexane Next, 7 parts of polyisocyanate (manufactured by Nippon Polyurethane Industries ■, trade name: Coronate L) as a curing agent was added to the dispersion.
The weight part was added to make magnetic paint.

Next, the magnetic paint was applied to both sides of a 33 μm thick polyester base film to a dry thickness of 3 μm, and calendered at 80°C.

Next, the resin in the magnetic paint was left to stand at a temperature of 50° C. for 24 hours to crosslink and harden.

Next, it was punched into a disk shape with a diameter of 47 mm to produce a disk-shaped magnetic recording medium of the present invention.

Example 2 "Acicular ferromagnetic powder" was an Fe-Ni alloy with a coercive force of 1550 Oe (major axis 0.25 pm, axial ratio 8, saturation magnetization 130 emu/g, specific surface area 55 m2/g).
A disc-shaped magnetic recording medium of the present invention was produced in exactly the same manner as in Example 1, except that the following was used.

Example 3 The method of the present invention was carried out in exactly the same manner as in Example 1, except that the amount of α-AI2203 powder as the "abrasive" was changed to 10 parts by weight, and the amount of Cr2O powder was changed to 10 parts by weight. A disc-shaped magnetic recording medium was fabricated.

Example 4 A disk-shaped magnetic recording medium of the present invention was produced in exactly the same manner as in Example 1, except that 3 parts by weight of isoamyl stearate was used instead of n-butyl stearate as the "lubricant".

Example 5 The present invention was prepared in the same manner as in Example 1, except that the amount of α-8 to 203 powder as the "abrasive" was changed to 2 parts by weight, and the amount of Cr2O3 powder was changed to 2 parts by weight. A disk-shaped magnetic recording medium was fabricated.

Example 6 A disc-shaped product of the present invention was prepared in the same manner as in Example 1, except that the amount of a-Aβ203 powder as the "abrasive" was changed to 15 parts by weight, and the amount of Cr203 powder was changed to 15 parts by weight. A magnetic recording medium was manufactured.

Example 7 The method of the present invention was carried out in exactly the same manner as in Example 1, except that the amount of n-butyl stearate as a "lubricant" was changed to 5 parts by weight, and batyl monoisostearate was not added. A disc-shaped magnetic recording medium was fabricated.

Example 8 Dimethyl silicone oil (manufactured by Shin-Etsu Chemical, K F
A disc-shaped magnetic recording medium of the present invention was produced in exactly the same manner as in Example 7, except that 5 parts by weight of -69) was used.

Comparative Example 1 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (UCC
Polyester polyurethane resin (manufactured by Japan Polyurethane Industries, Ltd., N
A disk-shaped magnetic recording medium was produced in exactly the same manner as in Example 1, except that 10 parts by weight of 2301) was used.

Comparative Example 2 "Acicular ferromagnetic powder" was a Fe-Ni alloy with a coercive force of 1300 Oersted (major axis (1.25 pffi, axial ratio 7, saturation magnetization 140 amu/g, specific surface area 50 m).
A disk-shaped magnetic recording medium was produced in exactly the same manner as in Example 1, except that 2/g) was used.

Comparative Example 3 Except for using an Fe-Ni alloy with a coercive force of 1300 Oe (major axis 0.25 μs, axial ratio 7, saturation magnetization 140 emu/g, specific surface area 50 m”/g) as “acicular magnetic powder”. A disk-shaped magnetic recording medium was produced in exactly the same manner as in Comparative Example 1.

Evaluation of reproduction output: Recording was performed on the disk-shaped magnetic recording media produced in Examples 1 to 8 and Comparative Examples 1 to 3 using a recording signal of a frequency of 7 M)Iz and a disk rotation speed of 3600 rpm. (diameter: 40 mm) and the 50th track (diameter: 30 mm) were measured. Furthermore, the difference in reproduction output between the first track and the 50th track was calculated. The results are shown in Table-1.

Note that each playback output is OdB higher than the first track of Comparative Example 7.
Expressed as a standard. Further, the recording wavelength in the first track is about 1.08μ, and the recording wavelength in the 50th track is about 0.81μ.

Evaluation of wear resistance: After recording was performed on the disk-shaped magnetic recording media prepared in Examples 1 to 8 and Comparative Examples 1 to 3 with a recording signal of a frequency of 7M)lz and a disk rotation speed of 3600 rpm, Temperature -5℃", "Temperature +25℃, Humidity 60%RH
J, "Temperature +40℃, Humidity 85% R)" Reproduction was performed at a rotation speed of 3600 rpm using a ferrite head under each environment of IJ, and the 25th track (diameter 35mm
) The time required for the reproduction output to deteriorate by -3 dB from the initial value was measured. The results are shown in Table-1.

As is clear from the results shown in Table 1, the magnetic recording medium of the example has a smaller difference in reproduction output between the first track and the 50th track than the magnetic recording medium of the comparative example.

Furthermore, the magnetic recording media of Examples 1 to 4 containing polycarbonate-based polyurethane resin, nonmagnetic powder, and fatty acid ester in preferred amounts have better resistance under various environments than the magnetic recording media of other Examples. Excellent abrasion resistance and regeneration output.

To describe the abrasion resistance in more detail, the effect of the polycarbonate polyurethane resin is clear from a comparison between Example 1 and Comparative Example 1, and a comparison between Comparative Example 1 and Comparative Example 2. Regarding the effect of non-magnetic inorganic powder, a comparison between Example 1 or 3 and Example 5 or 6 shows that if the amount added is too small, the wear resistance at -5°C will be poor, and if the amount added is too large, the regeneration will occur. It has been found that this has a negative effect on output. Regarding the effect of lubricants,
By comparing Example 1 or 2 and Example 7 or 8,
It has become clear that batyl monoisostearate is more suitable than n-butyl stearate, dimethyl silicone oil, and the like.

[Effects of the Invention] As explained above, the disc-shaped magnetic recording medium of the present invention has the following effects:
Since the magnetic layer contains metal powder with a coercive force of 1,400 mm or more, a resin after curing of a specific vinyl chloride copolymer, and a polycarbonate polyurethane resin, the magnetic layer has a strong magnetic field near the outermost periphery and near the innermost periphery of the track. There is little difference in playback output.

Furthermore, since the reproducing apparatus used for the magnetic recording medium of the present invention does not necessarily require an expensive and special head or circuit for correcting and improving the difference in reproduction output, there is a possibility of reducing the cost of the apparatus.

Furthermore, since the medium of the present invention contains a specific polyurethane resin, a suitable abrasive or lubricant such as a non-magnetic inorganic powder having a Mohs hardness of 6 or more or a fatty acid ester such as batyl monoisostearate is added to the magnetic layer. The abrasion resistance of the magnetic layer can be easily improved by incorporating it into the magnetic layer.

The magnetic recording medium of the present invention having the above effects is particularly useful as a magnetic recording medium for electronic still cameras.

Claims (4)

[Claims] (1) In a disc-shaped magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder provided on the support, the magnetic layer includes a metal powder having a coercive force higher than 1400 Oe. 1. A disc-shaped magnetic recording medium obtained by curing a mixture containing a dispersed vinyl chloride copolymer having at least an epoxy group, a hydroxyl group, and a sulfonic acid group, and a polycarbonate polyurethane resin. (2) The disk-shaped magnetic recording medium according to claim 1, wherein the magnetic layer contains 5 to 20% by weight of nonmagnetic inorganic powder having a Mohs hardness of 6 or more based on the metal powder. (3) The disk-shaped magnetic recording medium according to claim 1 or 2, wherein the magnetic layer contains a fatty acid ester. (4) The disk-shaped magnetic recording medium according to claim 3, wherein the fatty acid ester is a fatty acid ester containing at least batyl monoisostearate.