JPH04192111A - magnetic recording medium - Google Patents

Abstract

PURPOSE:To largely decrease the surface specific resistance and to improve output and durability by forming a conductive layer containing specified conductive oxide fine particles on a supporting body and forming a magnetic recording layer containing magnetic particles thereon. CONSTITUTION:A conductive layer containing conductive oxide fine particles of <=1.0 mum average particle size is formed on a supporting body, and a magnetic to recording layer containing a hexagonal ferrite magnetic powder is formed on this conductive layer. By this method, the surface specific resistance is largely reduced and output and durability is significantly improved. As for the hexagonal ferrite magnetic powder, a plate-type barium fierrite magnetic powder having <=0.1 mum average particle size and <=4 aspect ratio is preferable. Especially, it is preferable that the powder has 20 - 100 m<2>/g BET specific surface area, >=30 emu/g saturation magnetization, and 300 - 1000 Oe coercive force.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a coated magnetic recording medium in which a conductive layer is formed on a support, and a magnetic recording layer containing magnetic particles is formed on the conductive layer. In particular, the present invention relates to a coated magnetic recording medium in which a conductive layer contains specific conductive oxide fine particles.

(Prior Art and its Problems) Magnetic recording media are widely used in audio, video, computer, and other fields.

In recent years, as the amount of information has increased, there has been an increasing demand for higher density magnetic recording.

However, in the conventional in-plane magnetic recording method in which recording is performed by orienting acicular magnetic particles in the magnetic layer in the longitudinal direction of the plane, the demagnetizing field increases as the recording density increases, making it difficult to perform high-density recording. It was difficult to achieve.

On the other hand, the perpendicular magnetic recording method, which utilizes residual magnetization perpendicular to the magnetic layer surface, does not have the above drawbacks and is suitable for high-density recording.

Therefore, development of a perpendicular magnetic recording system using hexagonal ferrite magnetic powder such as barium ferrite magnetic powder is underway.

However, when hexagonal ferrite magnetic powder is used, although good short wavelength recording characteristics can be obtained, its surface resistivity is 101! Due to the high resistance of ~1014Ω, dust tends to adhere during the production of coating media, and it also tends to stick to guide rollers and calendar rollers, stick to the head while the media is running, and cause pinholes in the media. Alternatively, there are problems in that amplifier overflow occurs during characteristic measurements using a certifier, and that durability and weather resistance are adversely affected.

To solve these problems, the surface resistivity can be reduced by incorporating a conductive substance such as carbon black into the magnetic layer or by coating the surface of the magnetic powder with an oxide such as spinel. is proposed.

However, with the method of incorporating carbon black into the magnetic layer, if a large amount is added to obtain a sufficient effect, the electromagnetic conversion characteristics deteriorate, and the method of coating the surface of the magnetic powder with an oxide such as spinel However, these methods have disadvantages in that they adversely affect the magnetic properties of magnetic powder and reduce dispersibility.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned drawbacks, to form a conductive layer containing specific conductive oxide fine particles on a support, and to form a magnetic recording layer containing magnetic particles on the conductive layer. The object of the present invention is to provide a magnetic recording medium whose surface resistivity is significantly reduced and whose output and durability are improved by forming the layer.

(Means for Solving the Problems) The present invention is characterized in that a conductive layer containing conductive oxide fine particles having an average particle diameter of 1.0 μm or less is formed on a support, and a hexagonal ferrite magnetic layer is formed on the conductive layer. The present invention relates to a magnetic recording medium characterized in that it is provided with a magnetic layer containing powder.

As the hexagonal ferrite magnetic powder in the present invention, plate-shaped barium ferrite magnetic powder having an average particle diameter of 0.1 μm or less and a plate ratio of 4 or less is preferable.

In particular, the specific surface area by BET method is 20 to 100 po/g,
Saturation magnetization is 30 emu/g or more, coercive force is 300~
10000e is preferred.

Such hexagonal ferrite magnetic powder can be produced by conventionally known glass crystallization methods, ceramic methods, coprecipitation methods, flux methods,
It can be produced by an alkoxide method, a hydrothermal synthesis method, etc.

The conductive oxide fine particles of the present invention may be any oxide that easily conducts static electricity, and tin oxide, indium oxide, etc. are particularly preferably used.

Furthermore, although the particle shape can be either spherical or scaly, the scaly shape with a larger aspect ratio (major axis/minor axis) is preferable because conductivity can be imparted with a small amount added.

The average particle diameter is 1.0 μm or less, preferably 0.05 to 1
．． It is 0 μm. Furthermore, an amorphous material can also be used.

Examples of the support of the present invention include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, synthetic resins such as polycarbonate, polyimide, polysulfone, polyethylene naphthalate, aromatic aramid, and aromatic polyester. A film is used. The thickness of the support is generally 3 to 100 μm, preferably 5 to 8 μm.
It is 0 μm.

The conductive layer in the present invention is formed by, for example, mixing and dispersing conductive oxide fine particles and a binder with a solvent, applying the mixture onto a support, and drying the mixture.

Binders used in the conductive layer include binders normally used in magnetic recording media, such as vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, and cellulose derivatives such as nitrocellulose resins. , acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin, polyurethane resin, polyester resin, epoxy resin, phenoxy resin and the like.

The proportion of the conductive oxide fine particles and the binder in the conductive layer is preferably in the range of 80 to 90% by weight based on the total of both.

If the content of conductive oxide fine particles is less than 80% by weight, the effect of reducing the surface resistivity of the conductive layer will be small (and 9% by weight).
If the amount is more than 0% by weight, the adhesion to the support will decrease, which is not preferable.

As a solvent, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, alcohols such as methanol, ethanol, propatool, butanol, methyl acetate, ethyl acetate, butyl acetate,
Esters such as ethyl lactate and ethylene glycol senoacetate, ethers such as glycol dimethyl ether, glycol monoether, dioxane and tetrahydrofuran, and aromatic hydrocarbons such as benzene, toluene and xylene are used.

Further, it is desirable that the surface resistivity of the conductive layer is 1×10°Ω·1 or less. If it is higher than 1X10'' Ω, the effect of reducing the electrical resistance of the magnetic layer formed thereon will be small.

Next, a magnetic paint is produced by mixing and dispersing hexagonal ferrite magnetic powder, a binder, or various additives together with a solvent, and this magnetic paint is applied onto the conductive layer to form a magnetic layer. A magnetic recording medium of the present invention is manufactured.

As the binder, as mentioned above, a binder commonly used in magnetic recording media is used. The content of the binder is preferably 5 to 30 parts by weight based on 100 parts by weight of the hexagonal ferrite magnetic powder.

Further, the above-mentioned solvents are used as a solvent to be added to the magnetic paint or as a diluting solvent when applying the paint.

Furthermore, as additives, abrasives, dispersants, antistatic agents,
Known additives such as lubricants may also be used.

As the polishing agent, Al2is, Crabs, TlO2
,Sin,,CaO1caco,,ZnO1a-Fe0
Inorganic particles such as 0H1a-Fe20s can be used alone or in combination. By including inorganic particles in the magnetic layer, the abrasive action of the head can prevent clogging of the head and improve running durability. The content of the abrasive is based on 100 parts by weight of hexagonal ferrite magnetic powder.
It is usually 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight.

Dispersants include organic titanium coupling agents, silane coupling agents, oily or powdered lecithin, and carbon atoms of 12 to 2.
2 saturated or unsaturated fatty acids, alkali metal salts of the fatty acids, esters of the fatty acids or compounds in which some or all of their hydrogen atoms are replaced with fluorine atoms, amides of the fatty acids, aliphatic amines, higher alcohols, etc. It will be done. The amount of dispersant added is 100% of the hexagonal ferrite magnetic powder.
It is usually 0.1 to 10 parts by weight.

Antistatic agents include natural surfactants such as saponin, anionic surfactants such as alkylene oxide, glycerin, and grindol, higher alkylamines, quaternary ammonium salts, pyridine, and other heterocyclic compounds. Examples include cationic surfactants such as salts, phosphoniums or sulfoniums, amphoteric surfactants such as amino acids, aminosulfonsanes, and sulfuric or phosphoric acid esters of amino alcohols. The amount of antistatic agent added is usually 0.00 parts by weight per 100 parts by weight of hexagonal ferrite magnetic powder.
1-10 parts by weight.

As lubricants, saturated or unsaturated fatty acids with 12 to 22 carbon atoms, higher alcohols, monobasic acids and fatty acids with 12 to 20 carbon atoms such as butyl stearate, sorbitan oleate, and monovalent fatty acids with 3 to 22 carbon atoms are used. or esters consisting of polyhydric alcohols, mineral oils, animal and vegetable oils, olefin low polymers, fatty acid amides, silicone oils, modified silicone oils, alkylene oxide adducts of fatty acids, fine graphite powder, fine molybdenum disulfide powder, tetrafluoroethylene. Known lubricants such as fine polymer powder and lubricants for plastics may be mentioned. The amount of lubricant added is usually 0.1 parts by weight per 100 parts by weight of hexagonal ferrite magnetic powder.
-10 parts by weight.

There are no particular restrictions on the method of mixing, and ordinary mixing machines such as two-roll mills, three-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. Moreover, the order of addition of each component can also be set as appropriate.

Application methods include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, spray coating, and spin cord. It will be done.

The thickness of the magnetic layer to be applied is generally 0.000 mm after drying.
It is 5 to 15 μm, preferably 1 to 10 μm.

Drying after application may be performed with the magnetic particles oriented in a magnetic field, or may be performed in a non-oriented state. Furthermore, a magnetic recording medium can be obtained by smoothing the surface of the medium by supercalendering or the like, and drying it in an oven or the like to harden the medium.

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

Example 1 A slurry having the following composition was prepared and mixed and dispersed in a ball mill for 48 hours to prepare a coating material for a conductive layer.

Tin oxide (TL-22; Catalyst Kasei Co., Ltd.) 100 parts by weight (average particle size 0.05 μm, bulk density 0.6 g/al) Vinyl chloride-vinyl acetate copolymer (VAGH) 7 parts by weight Polyurethane resin 5 parts by weight ( OR-8200,
(manufactured by Toyobo) Coronet) L 3 parts by weight cyclohexanone 500 parts by weight toluene
500 parts by weight of the obtained conductive layer paint was applied to both sides of a 75 μm thick polyethylene terephthalate film so that the film thickness after drying was 0.5 μm, and dried.

Further curing was performed at 80° C. for 24 hours to form a conductive layer.

Next, prepare a slurry with the following composition and use it in a ball mill for 40 minutes.
A magnetic paint was prepared by mixing and dispersing for 8 hours.

Magnetic powder ioo parts by weight Vinyl chloride vinyl acetate copolymer (VAGH) 10 parts by weight Polyurethane resin 6 parts by weight (OR-820
0, manufactured by Toyobo) Coronatized 5 parts by weight alumina (
Two-tone E440) 5 parts by weight Saturated fatty acid ester 3 parts by weight (NEWLON B-26
-Q ; Takemoto Yushi) cyclohexanone
300 parts by weight toluene 300
Part by weight of the obtained magnetic coating material was applied onto the conductive layer and dried. Furthermore, the surface of the magnetic layer was smoothed using a supercalender device, so that the thickness of the magnetic layer was 2 μm.

The obtained medium was punched into a disk shape with a diameter of 3.5 inches,
A magnetic disk was prepared by curing at 80° C. for 24 hours.

Table 1 shows the results of measuring the characteristics of the obtained magnetic disk.

Example 2 In Example 1, except that tin oxide (TL-20; manufactured by Catalyst Kasei Co., Ltd., average particle diameter 0.1 μm, bulk density 0.4 g/car) was used as the conductive oxide fine particles. A magnetic disk was produced in the same manner as above.

Table 1 shows the results of measuring the characteristics of the obtained magnetic disk.

Example 3 In Example 1, indium oxide (average particle diameter 0.05 μm 1 bulk density 0.4 g/
A magnetic disk was produced in the same manner as in Example 1 except that aIr) was used.

Table 1 shows the results of measuring the characteristics of the obtained magnetic disk.

Comparative Example 1 A slurry having the following composition was prepared using the same barium ferrite magnetic powder as in Example 1, and mixed and dispersed in a pole mill for 48 hours to prepare a magnetic paint.

Magnetic powder 100 parts by weight Vinyl chloride vinyl acetate copolymer (VAGH) 10 parts by weight Polyurethane resin 6 parts by weight (UR-8200
; manufactured by Toyobo) 5 parts by weight alumina (two-tone E 440) 5 parts by weight tin oxide (
TL-22; Catalyst Kasei Co., Ltd.) 5 parts by weight (average particle size 0.05 μm, bulk density 0.6 g/co?) Saturated fatty acid ester 3 parts by weight (NEWLON B
-26-Q; Takemoto Yushi) cyclohexanone
300 parts by weight toluene
300 parts by weight of the obtained magnetic paint was applied to both sides of a 75 μm thick polyethylene terephthalate film and dried. Furthermore, the surface of the magnetic layer was smoothed using a supercalender device, so that the thickness of the magnetic layer was 2 μm.

The obtained medium was punched into a disk shape with a diameter of 3.5 inches,
A magnetic disk was prepared by curing at 80°C for 24 hours.

Table 1 shows the results of measuring the characteristics of the obtained magnetic disk.

Comparative Example 2 A magnetic disk was produced in the same manner as in Comparative Example 1, except that conductive oxide fine particles were not added.

Table 1 shows the results of measuring the characteristics of the obtained magnetic disk.

(Effects of the Invention) The magnetic recording medium of the present invention comprises forming a conductive layer containing specific conductive oxide fine particles on a support, and forming a magnetic recording layer containing magnetic particles on the conductive layer. As a result, the surface resistivity is significantly reduced, and the output and durability are significantly improved, making it suitable for use as a magnetic recording medium for high-density recording.

Claims (4)

[Claims] (1) A conductive layer containing conductive oxide fine particles with an average particle diameter of 1.0 μm or less is formed on the support, and a magnetic layer containing hexagonal ferrite magnetic powder is provided on the conductive layer. A magnetic recording medium characterized by: (2) Hexagonal ferrite magnetic powder has an average particle diameter of 0.1
2. The magnetic recording medium according to claim 1, which is a plate-shaped barium ferrite magnetic powder having a plate-like barium ferrite magnetic powder of .mu.m or less and a plate-like ratio of 4 or less. (3) The magnetic recording medium according to claims 1 and 2, wherein the conductive oxide fine particles are scale-shaped tin oxide. (4) The magnetic recording medium according to claims 1 and 2, wherein the conductive oxide fine particles are scaly indium oxide.