JPH0836740A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a high-density magnetic recording medium which excels in an electromagnetic conversion characteristic by incorporating a specific quantity of ferromagnetic metal powder having a specific major axis length in a magnetic layer. CONSTITUTION:In the magnetic recording medium in which a conductive layer and a magnetic layer are formed on a flexible non-magnetic supporting body such as polyethylene terephthalate, 80 to 90wt.% of a ferromagnetic metal powder which has a major axis length of 0.01 to 0.1mum is contained in the magnetic layer. The thickness of the magnetic layer is 0.1 to 0.3mum. Fe-based, Ni-based and Co-based ferromagnetic metal or ferromagnetic alloy is used as the ferromagnetic powder. In the composition of a magnetic powder, when a major axis length exceeds 0.01mum, the filling factor of a magnetic powder is lowered, accordingly, a good S/N ratio cannot be obtained, and it does not show a sufficient magnetic characteristic in such a case that the major axis length is less than 0.01mum. Therefore, since carbon black is not contained in the magnetic layer, the dispersibility and the filling factor of the magnetic powder are enhanced to improve an electromagnetic conversion characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high density magnetic recording medium excellent in electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art Magnetic tapes and floppy disks (F
The magnetic recording medium such as D) is called a coating type magnetic recording medium because it is manufactured by coating a magnetic coating on a support made of synthetic resin or the like. Such a magnetic recording medium is widely used as a general-purpose recording medium because it can be repeatedly used and it is easy to computerize signals and systemize it with peripheral devices. 2. Description of the Related Art In recent years, a recording medium having a large recording capacity and a high recording density has been demanded because of the remarkable increase in the capacity of computer software and data and the miniaturization of devices and media.

Conventionally, the magnetic recording medium has been improved in recording density by making the magnetic powder constituting the magnetic recording medium ferromagnetic, reducing the particle size, improving the dispersibility in the magnetic layer, and improving the filling rate. Along with this, it is desired to reduce the thickness of the magnetic layer in order to improve resolution and overwrite characteristics. Furthermore, in order to prevent dropouts and errors caused by dust adhesion due to electrification that occurs when the magnetic recording medium is running, a conductive material such as carbon black is added to the magnetic layer to reduce the specific resistance of the magnetic layer surface. The method is widely used.

[0004]

Since the conventional magnetic recording medium has good dispersibility, metal oxide magnetic powder or metal magnetic powder having excellent magnetic characteristics has been used as the magnetic powder.
However, these magnetic powders have a long major axis length, so that the filling rate in the magnetic layer was not sufficient. Further, as described above, it is desired to make the magnetic layer thinner, but a thickness of 0.8 to 5 μm is required for the magnetic layer for reasons such as running durability and ensuring stability when applying a magnetic paint. Therefore, there is a limit to the improvement of recording density by thinning the magnetic layer.

Further, since the conductive material such as carbon black added to the magnetic layer is bulky and does not have good dispersibility, it hinders the dispersion and filling of the magnetic powder in the magnetic layer, resulting in a poor S / N ratio. The electromagnetic conversion characteristics may be deteriorated, and the running durability may be deteriorated due to the deterioration of the mechanical strength of the magnetic layer.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a high density magnetic recording medium excellent in electromagnetic conversion characteristics. That is, the gist of the present invention is a magnetic recording medium in which a conductive layer and a magnetic layer are formed on a flexible non-magnetic support, and the magnetic layer has a major axis length of 0.01 to 0.1 μm. The ferromagnetic layer contains 80 to 90% by weight of a ferromagnetic metal powder, and the magnetic layer has a thickness of 0.
A magnetic recording medium having a thickness of 1 to 0.3 μm;
Exist in.

Hereinafter, the present invention will be described in detail. In the magnetic recording medium of the present invention, the magnetic layer can be formed on both sides or one side of the flexible non-magnetic substrate. When the magnetic layer is formed on only one side, a back coat layer may be provided on the opposite side. Examples of the flexible non-magnetic support used for the magnetic recording medium of the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene and polyethylene, cellulose derivatives such as cellulose acetate, polycarbonate, polyamide, polyimide and the like. Various plastics can be used.

Of these, polyesters such as polyethylene terephthalate and polyethylene naphthalate are preferable because of their excellent mechanical properties, heat resistance, electrical properties, chemical resistance and the like. However, since these polyester films are highly crystallographically oriented, they have poor adhesion to the magnetic layer. Therefore, in order to improve the adhesion between the support and the magnetic layer or the conductive layer, the support is treated with a surface modifier such as an aqueous alkali solution, an aqueous amine solution, trichloroacetic acid, or a phenol before magnetic recording. You may use for manufacture of a medium.

The composition of the magnetic powder used in the present invention is not particularly limited as long as it is a ferromagnetic metal powder having a major axis length of 0.01 to 0.1 μm, and any magnetic metal powder can be used. If the major axis length exceeds 0.1 μm, the filling factor of the magnetic layer decreases, so that a good S / N ratio cannot be obtained, and if it is less than 0.01 μm, sufficient magnetic properties cannot be exhibited, which is not preferable.
Specific examples of the ferromagnetic metal powder include Fe,
Ni, Co, Fe-Co, Fe-Ni, Fe-Co-N
i, Fe-Ni-Zn, Fe-Co-Ni-Cr, Co
Fe-based, Co-based, or Ni-based ferromagnetic metal or ferromagnetic alloy powder such as -Ni may be used.

The content of the magnetic powder in the magnetic layer is 8
It is preferably 0 to 90% by weight, particularly preferably 85 to 90% by weight. If it is less than 80% by weight, a high coercive force cannot be obtained because the filling rate of the magnetic powder in the magnetic layer is low, and if it exceeds 90% by weight, the dispersibility in the magnetic paint is lowered and the mechanical properties of the magnetic layer are decreased. It is not preferable because the strength may decrease. Further, in the present invention, by substantially not containing carbon black in the magnetic layer, the dispersibility and filling rate of the magnetic powder in the magnetic layer are improved, and the electromagnetic conversion characteristics such as the S / N ratio are improved. Can be good.

The magnetic layer is usually formed by coating a support with a magnetic coating in which magnetic powder is dispersed in a binder. Along with the magnetic powder, if necessary, a dispersant, a lubricant, an abrasive, etc. may be dispersed in the binder. As the binder, 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. Examples thereof include vinyl chloride resins such as polymers, various synthetic rubbers such as styrene-butadiene copolymers, epoxy resins, phenoxy resins, and the like. These may be used alone or as a mixture of two or more kinds at any ratio. May be.

The amount of the binder used depends on the content in the magnetic layer.
Generally, it is preferably 2 to 15% by weight, particularly preferably 5 to 13% by weight. When the magnetic coating material further contains a low molecular weight polyisocyanate compound having a plurality of isocyanate groups, 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 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.

Further, a lubricant, an abrasive, a dispersant, etc. may be added to the magnetic paint, if necessary. 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 such as oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid and behenic acid, salts of these with metals such as magnesium, aluminum, sodium and calcium, and butyl ester of the above fatty acids. Examples thereof include fatty acid esters such as octyl ester and glyceride, amides of the above fatty acids, linoleic acid amide, and caproic acid amide.

Aliphatic alcohols such as lauryl alcohol, stearyl alcohol, myristyl alcohol, palmityl alcohol and oleyl alcohol, fluorine-based lubricants such as perfluoroalkyl polyethers and perfluoroalkylcarboxylic acids, silicone oils and modified silicone oils. Silicone lubricants such as silicone oil, and hydrocarbon lubricants such as paraffin, squalane, and wax. Furthermore, solid lubricants such as molybdenum disulfide and tungsten disulfide, and phosphoric acid esters can also be used.

The amount of the lubricant used is such that the content in the magnetic layer is usually 0.1 to 10% by weight, preferably 1 to 5% by weight. When a plurality of magnetic layers are laminated, the content of the lubricant in each magnetic layer may be changed. As the abrasive, those having high hardness such as alumina, fused alumina, corundum, silicon carbide, chromium oxide and silicon nitride are preferable. The average particle size of the abrasive is preferably 0.5 μm or less. The content of the abrasive in the magnetic layer is preferably in the range of 1 to 5% by weight.

Examples of the dispersant include fatty acids having 10 to 18 carbon atoms such as capric acid, lauric acid, myristic acid, oleic acid, and linoleic acid, and metal soaps containing these alkali metal salts or alkaline earth metal salts, lecithin, and the like. Is used. The amount of the dispersant used is usually 0 to 5% by weight in the magnetic layer. Kneading, dispersion, coating, etc. of the magnetic coating material include, for example, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, methyl acetate, ethyl acetate, Examples of conventionally known solvents include esters such as butyl acetate, ethers such as diethyl ether and tetrahydrofuran, aromatic hydrocarbons such as benzene, toluene and xylene, and aliphatic hydrocarbons such as hexane.

Regarding the method of kneading and dispersing, the order of addition of each component, etc., a conventional method suitable for kneading and dispersing the magnetic coating material is usually used. As a coating method, various commonly applied methods such as air doctor coating, blade coating, reverse roll coating and gravure coating are adopted. When a plurality of 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 dry thickness of the magnetic layer is 0.1.
Is about 0.3 μm. If it is thicker than 0.3 μm, the resolution may be lowered, which is not suitable as a high-density magnetic recording medium, and if it is thinner than 0.1 μm, durability and output tend to be lowered, which is not preferable. The magnetic recording medium of the present invention has a conductive layer for improving the charging property of the magnetic layer. The conductive layer is in the form of a coating film or a vapor deposition film containing a conductive material and a binder, and is usually provided between the magnetic layer and the flexible nonmagnetic support, but it is provided on the magnetic layer. Is also good. Examples of the conductive material used for the conductive layer include conductive metals and metal compounds. For example, a metal powder of silver, platinum or the like, a vapor deposition film, a powder of a metal compound such as tin oxide, zinc oxide or potassium titanate can be used. The average particle size of these powders is 0.
005 to 0.6 μm is preferable. As the binder, the same binder as that used for the magnetic layer can be used. The thickness of the conductive layer is usually 0.005 to 5 μm as a dry film thickness.

Further, in the present invention, a top coat layer or the like may be provided for imparting lubricity.

[0020]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Example 1 As a conductive layer, a mixture having the following composition was applied to both sides of a support (thickness 75 μm) made of a polyester film so that the thickness after drying would be 0.5 μm.
Next, a mixture having the following composition was kneaded and dispersed in a ball mill to prepare a magnetic layer, and the thickness after drying was 0.2.
It was coated on the conductive layer to have a thickness of 5 μm. Then, after being subjected to calendering, a floppy disk was manufactured by punching into a disk shape having a diameter of 3.5 ". The results of performance evaluation are shown in Table-1.

[0021]

[Table 1] Conductive layer composition Carbon black 100 parts by weight ("# 3250", particle size 0.03 µm, manufactured by Mitsubishi Kasei) Polyurethane resin 100 parts by weight ("N2304", manufactured by Nippon Polyurethane Co.) Methyl ethyl ketone (MEK) 400 Parts by weight Cyclohexanone (CHN) 400 parts by weight

[0022]

[Table 2] Magnetic layer composition Ferromagnetic Fe-Co alloy powder (long axis length 0.08 µm) 100 parts by weight Polyurethane resin 8 parts by weight ("UR8200", Toyobo Co., Ltd.) Vinyl chloride resin 6 parts by weight ("MR110", Zeon Co., Ltd.) Polyisocyanate 4 parts by weight (“Coronate L”, Nippon Polyurethane Company) Alumina (particle size 0.1 to 0.2 μm) 3 parts by weight Butyl stearate 4 parts by weight MEK 250 parts by weight CHN 250 parts by weight (The content of the ferromagnetic metal powder in the magnetic layer was 80% by weight.)

Example 2 140 parts by weight of ferromagnetic metal powder (content in magnetic layer: 85
%), MEK and CHN were used in an amount of 330 parts by weight, and a floppy disk was manufactured in the same manner as in Example 1. The performance evaluation results are shown in Table-1. Example 3 220 parts by weight of ferromagnetic metal powder (content in the magnetic layer was 85
%), MEK, and CHN were each used in an amount of 450 parts by weight, and a floppy disk was manufactured in the same manner as in Example 1. The performance evaluation results are shown in Table-1.

Example 4 A floppy disk was manufactured in the same manner as in Example 2 except that the composition of the conductive layer was changed to the following composition and the thickness of the conductive layer after drying was 1 μm. The performance evaluation results are shown in Table-1.

[0025]

[Table 3] Conductive layer composition Tin oxide 100 parts by weight Polyurethane resin 54 parts by weight ("N2304", manufactured by Nippon Polyurethane Company) MEK 115 parts by weight CHN 115 parts by weight

Example 5 Example 2 was repeated except that a conductive polymer polyaniline (1% by weight solution of N-methylpyrrolidone) was applied as the conductive layer so that the thickness after drying was 0.1 μm. A floppy disk was manufactured in the same manner as in. The performance evaluation results are shown in Table-1.

Comparative Example 1 A floppy disk was prepared in the same manner as in Example 1 except that 75 parts by weight of ferromagnetic metal powder (content of 75% by weight in the magnetic layer) and 220 parts by weight of MEK and CHN were used. Was manufactured. The performance evaluation results are shown in Table-1. Comparative Example 2 300 parts by weight of ferromagnetic metal powder (content in magnetic layer: 92
%), MEK, and CHN were each used in an amount of 650 parts by weight, and a floppy disk was manufactured in the same manner as in Example 1. The performance evaluation results are shown in Table-1.

Comparative Example 3 A floppy disk was manufactured in the same manner as in Example 2 except that the magnetic layer was directly formed on the support without forming the conductive layer. The performance evaluation results are shown in Table-1. Comparative Example 4 A floppy disk was manufactured in the same manner as in Example 2 except that the conductive layer was not formed and 2 parts by weight of carbon black was added to the magnetic layer. Table 1 shows the performance evaluation results.
It was shown to.

Comparative Example 5 A floppy disk was manufactured in the same manner as in Example 1 except that a ferromagnetic metal powder having a major axis length of 0.2 μm was used. The performance evaluation results are shown in Table-1. Comparative Example 6 Except that the thickness of the magnetic layer after drying was 0.8 μm.
A floppy disk was manufactured in the same manner as in Example 1.
The performance evaluation results are shown in Table-1.

Comparative Example 7 A floppy disk was manufactured in the same manner as in Example 2 except that the thickness of the magnetic layer after drying was 0.05 μm. The performance evaluation results are shown in Table-1. The methods for measuring the performance of the floppy disks manufactured in the examples and comparative examples are as follows.

Output and resolution were 1F using a MIG head (gap 0.4 μm) for a floppy disk.
/312.5 KHz, 2F / 625 KHz, and was obtained by recording and reproducing digital signals. In addition, Example 1 was used as a standard sample, and the relative evaluation value was shown. S / N
The ratio is 625KH in the same way as the output and resolution measurement.
The digital signal of z was recorded, and the ratio between the signal during reproduction and the noise after erasure was measured and obtained.

The surface property (Ra) was measured using a Talystep manufactured by Taylor Hobson, which is a contact type surface roughness meter. The surface resistivity was measured by mounting a sample between electrodes having a width of 1 inch and applying a voltage of 10V. The running durability was evaluated by running with a 2 MB 3.5 "floppy disk drive and the number of passes of the head.

[0033]

[Table 4]

[0034]

INDUSTRIAL APPLICABILITY According to the present invention, a magnetic recording medium excellent in electromagnetic conversion characteristics, surface properties, surface specific resistance and running properties can be obtained, and is industrially very useful.

Claims (3)

[Claims] 1. A magnetic recording medium in which a conductive layer and a magnetic layer are formed on a flexible non-magnetic support, and a ferromagnetic metal having a major axis length of 0.01 to 0.1 μm in the magnetic layer. The powder contains 80 to 90% by weight, and the thickness of the magnetic layer is 0.1 to
A magnetic recording medium having a thickness of 0.3 μm. 2. The magnetic recording medium according to claim 1, wherein the magnetic layer contains substantially no carbon black. 3. The magnetic recording medium according to claim 1, wherein a conductive layer is formed between the flexible non-magnetic support and the magnetic layer.