JPH0481265B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to magnetic recording media such as magnetic cards and magnetic tapes. BACKGROUND OF THE INVENTION In recent years, automatic devices have become extremely popular for the purpose of saving administrative labor, and the spread of magnetic recording media used in these devices has also been remarkable. For example, cash cards are widely used in banks, and magnetic tickets such as various magnetic commuter passes and expressway passes are widely used in transportation facilities. These magnetic recording media perform digital recording as seen in cash cards or analog recording as used in recording tapes, but in order to improve the recording and reproducing characteristics of the signal information recorded on these media, When manufacturing a magnetic recording medium by applying and drying a magnetic paint, a magnetic alignment treatment is often performed. This magnetic orientation treatment involves applying a magnetic field to the magnetic paint immediately after it is applied onto the substrate, but before it is dried and solidified, to align the axis of easy magnetization of the magnetic powder in the magnetic paint in a desired direction. This is aimed at improving recording and reproducing characteristics in the orientation direction. The degree of orientation of this magnetic powder is expressed as a value called squareness ratio, and an ideally oriented state is defined as 1. For example, as a method for improving this squareness ratio, it is desirable to disperse magnetic powder as highly as possible when producing a paint. However, once dispersed particles tend to agglomerate due to interactions between particles, resulting in a decrease in squareness ratio, and a method of applying a strong magnetic field in the magnetic field heightening treatment process after coating is also used. However, this resulted in significant aggregation of the magnetic powder particles during the passage of the magnetic field, often resulting in a decrease in the squareness ratio. OBJECTS OF THE INVENTION It is an object of the present invention to solve the problems of the prior art as described above and to provide a magnetic recording medium with an improved squareness ratio. Structure of the Invention According to the present invention, a magnetic coating film in a magnetic recording medium is formed of a magnetic coating material containing acicular, granular, or plate-shaped magnetic powder as a product and a solid substance of silicon dioxide as an additive. The solid matter is in the form of fine particles with a volume of one particle being 1×10 ^-12 cm ³ or less, and the amount of the solid matter added is equal to or less than 100% of the magnetic powder.
It ranges from 0.1 to 20 parts by weight. Embodiments Next, the present invention will be described in more detail with reference to embodiments of the present invention based on the accompanying drawings. FIG. 1 is a schematic cross-sectional view of a magnetic recording medium as an embodiment of the present invention. This magnetic recording medium is
A magnetic recording layer 2 made of a magnetic coating film is provided on the surface of the substrate 1 . The magnetic coating film constituting the magnetic recording layer 2 includes acicular, granular, or plate-shaped magnetic powder particles 2A and inorganic or organic solid particles 2B. These inorganic or organic solid particles 2B are not so large as to obstruct the movement of the magnetic powder particles 2A during the magnetic orientation treatment when forming the magnetic coating film, and are not so large as to inhibit the mutual magnetic interaction between the magnetic powder particles 2A. The amount necessary to prevent the magnetic powder particles 2A from agglomerating is added to the magnetic paint. Further, the particle shape of this inorganic or organic solid may be the same as or different from the magnetic powder particles. In the present invention, the following inorganic or organic solid materials used to prevent agglomeration of magnetic powder particles may be used alone or in combination. (1) Particulate silicic acid and silicates such as anhydrous silicic acid, hydrous silicic acid, aluminum silicate, kaolin, sericite, bentonite, organic bentonite, diatomaceous earth, silica powder, zircon, and talc, (2)
Silicon carbide, (3) alumina, (4) goethite, (5) carbon black, (6) fine lead powder, (7) barium carbonate, (8) cadmium sulfide, (9) graphite, (10) carbon fiber, (11) Aluminum oxide, (12) Titanium dioxide, (13) Zinc oxide, (14) Diiron trioxide, (15) Ferric hydroxide, (16) Ferric oxide, (17) Cuprous oxide , cupric, (18) calcium carbonate, (19) calcium hydroxide, (20) magnesium carbonate, (21) barium sulfate, (22) chrome yellow, (23) cadmium color pigment, (24) iron ferrocyanide Ammonium, (25) Phthalocyanine color pigment, (26)
First yellow, (27) polyethylene powder,
(28) Polystyrene powder, (29) Polyacrylamide, (30) Nylon powder, (31) Polytrifluorochloroethylene, (32) Magnesium oxide, (33)
Fine metal powders such as silver and aluminum Next, magnetic recording media were created using magnetic paints containing various types of these inorganic or organic solids, and the effects of the particle size and amount of the inorganic or organic solids added were investigated. I will explain the results I tried. Specific Example 1 In FIG. 1, the base 1 has a thickness of 100 to 300 μm.
Using polyethylene terephthalate (PET), etc., apply a magnetic paint having the composition A below using a known method such as a knife coater or gravure coater to the surface of the material so that the coating thickness after drying is 5 to 10 μm. After performing orientation treatment (magnetic field density 1000 Oe), it was dried to obtain a magnetic recording layer 2. Composition A Magnetic powder (Fe ₃ O ₄ ) 30 parts Vinyl chloride/vinyl acetate copolymer resin 20 parts Cyclohexanone 180 parts Silicon dioxide 3 parts On the other hand, for comparison, the weight part X of the magnetic powder in the above composition A was 60, 20, 12, and the weight part Y of silicon dioxide as an added solid substance was 0, 40, and 48, magnetic coatings with the same pigment/resin ratio were prepared, and magnetic recording layers were obtained in the same manner as composition A. The magnetic properties of each magnetic recording layer were as shown in the table below.

[Table] In this way, the magnetic recording layer with composition A has composition B ~
The squareness ratio was better than that of any of the magnetic recording layers of D. Specific Example 2 A magnetic recording medium having the same configuration as Example 1 was
It was produced by changing the paint composition. The paint shown in composition E below was used and applied by a known method. The magnetic orientation treatment was performed using a magnetic field (magnetic field strength: 4000 Oe) that would orient the film in a direction perpendicular to the coating surface, to obtain a magnetic recording layer. Composition E Magnetic powder Platy barium ferrite (particle size 0.1μ, thickness 0.02μ) 30 parts Vinyl chloride/vinyl acetate copolymer resin 10 parts Methyl ethyl ketone 25 parts Cyclohexanone 30 parts Silicon dioxide 5 parts On the other hand, for comparison, the above composition E The weight part of the magnetic powder is 35, and the silicon dioxide as an added solid is 0.
A magnetic recording layer was prepared in the same manner as above. The magnetic properties of each magnetic recording layer were as shown in the table below.

[Table] As described above, the magnetic recording layer with composition E had a higher squareness ratio in the vertical direction than composition F. When the coating films prepared as in compositions A and E of Examples 1 and 2 were used as various magnetic recording media by known methods, the squareness ratio was improved;
It was possible to increase the reproducing power while the recording current was low. Therefore, the S/N ratio was improved and a more reliable magnetic recording medium was obtained. From the above results, in order to obtain a magnetic recording medium with an improved squareness ratio, it is necessary to add inorganic or organic solids in a proportion suitable for each magnetic material, and the yield value of the magnetic paint must be It is necessary that the In other words, this appropriate addition amount is an amount that is not so large as to inhibit the movement of the magnetic powder during magnetic orientation treatment, and is an amount necessary to prevent magnetic interaction between the magnetic powder particles. This is the amount that can prevent particle agglomeration. Next, various experiments were conducted to investigate in more detail the relationship between the amount of inorganic or organic solids added and the resulting squareness ratio, and as a result, the relationship shown in FIG. 2 was obtained. From the graph in Figure 2, it can be seen that in order to improve the squareness ratio,
It is found that it is effective to add the inorganic or organic solid in an amount within the range of 0.1 parts by weight to 20 parts by weight. This curve varied depending on the conditions, but in all cases it was effective within the range of 0.1 to 20 parts. Further, when the volume of one inorganic or organic solid particle was used as a parameter, and the relationship between the amount added and the relative residual magnetic flux density was investigated, a relationship as shown in FIG. 3 was obtained. It is clear from FIG. 3 that the residual magnetic flux density decreases as the amount of solids added increases, and if it is less than 90% of that without the addition of solids, it is not favorable in terms of magnetic properties. Here, the second
As is clear from the relationship in the figure, in order to improve the squareness ratio, it is necessary to add 0.1 parts by weight or more of solid matter, so the volume of one solid particle is 1×
It can be seen that it is necessary to keep it below 10 ^-12 cm ³ . Effects of the Invention As explained above, the magnetic coating film of the magnetic recording medium of the present invention can be subjected to magnetic orientation treatment very easily and the squareness ratio can be improved, so that recording in the in-plane longitudinal direction and In either case of recording in the perpendicular direction, a highly reliable magnetic recording medium with an improved S/N ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 of the accompanying drawings is a schematic cross-sectional view of a magnetic recording medium as an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the amount of inorganic or organic solid added and the squareness ratio.
FIG. 3 is a diagram showing the relationship between the amount of solids added and the relative residual magnetic flux density using the volume of one inorganic or organic solid particle as a parameter. 1...Substrate, 2...Magnetic recording layer, 2A...Magnetic powder particles, 2B...Inorganic or organic solid particles.

Claims (1)

[Claims] 1. It has a magnetic coating film formed of a magnetic paint containing acicular, granular, or plate-shaped magnetic powder as a main component and a solid substance of silicon dioxide as an additive, and the solid substance has a volume of one particle. A magnetic material having a particle size of 1×10 ^-12 cm ³ or less, and the amount of the solid added is in the range of 0.1 to 20 parts by weight based on 100 parts by weight of the magnetic powder. recoding media.