JPS60157719A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To improve well the high density recording characteristics by smoothening the surface of the magnetic layer contg. magnetic powder of a specified average single particle size at a relatively high temp. so as to increase well the squareness ratio in the vertical direction as well as to improve the surface smoothness. CONSTITUTION:An aqueous alkali soln. is added to an aqueous soln. contg. an iron salt and one or more kinds of metallic salts selected among Ba salts, Sr salts and Pb salts to cause coprecipitation. The resulting precipitate is hydrothermally treated to produce magnetic powder of platelike hexagonal ferrite adjusted to 0.1-0.3mum average single particle size, and a magnetic coating material is prepd. by mixing the magnetic powder with a binder resin, an org. solvent, etc. The coating material is coated on a substrate such as a polyester film by an arbitrary coating means such as a roll coater, and it is dried to form a magnetic layer. The surface of the magnetic layer is smoothened at 80 deg.C.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a magnetic recording medium and a method for manufacturing the same, and more particularly relates to a magnetic recording medium for high-density recording using hexagonal ferrite magnetic powder as the magnetic powder and a method for manufacturing the same. .

[Background technology]

Generally, the magnetic properties of magnetic recording media are improved by orienting the acicular magnetic powder in the magnetic layer in the longitudinal direction of the horizontal magnetic layer. However, when attempting to increase the density of magnetic recording, the demagnetizing field within the magnetic recording medium increases.
There is a limit to the improvement in recording density, and there is a drawback that recording resuspension is poor in the short wavelength region.

In order to overcome these drawbacks, various attempts have been made in recent years to use perpendicular magnetic recording methods that use magnetization in a direction perpendicular to the surface of the magnetic layer. It has been carried out to utilize the magnetization component in the perpendicular direction by using a hexagonal ferrite powder having a shape of 14.

However, in conventional magnetic recording media that use this type of hexagonal ferrite magnetic powder, when applying a magnetic paint containing this type of plate-shaped hexagonal ferrite magnetic powder onto a substrate, some degree of mechanical placement is required. 111, the plate-shaped magnetic powder is oriented parallel to the surface of the magnetic layer, but the orientation is not to the same degree as that of acicular magnetic powder, and this mechanical orientation alone is not sufficient to align the plate-shaped magnetic powder in the vertical direction. Since it is not possible to obtain a high square shape, magnetic field alignment treatment is performed using opposite magnetic fields with different polarities.This magnetic field orientation treatment with opposite magnetic fields with different polarities causes the magnetic paint to be applied to the top and bottom of the cloth surface. The problem is that the magnetic paint is pulled by a force that reduces the surface smoothness of the magnetic layer.

[Purpose of the invention]

The present invention was made with the aim of solving these problems and providing a magnetic recording medium for high-density recording that has a sufficiently high squareness in the vertical direction and excellent surface smoothness.
The intended purpose was achieved by using plate-shaped hexagonal ferrite magnetic powder with a predetermined particle size, and performing mechanical orientation followed by surface smoothing treatment at a relatively high temperature.

[Summary of the invention]

In this invention, the average single particle diameter is 0.1 to 0.
Forming a magnetic layer containing 3μ plate-shaped hexagonal Ferrite I-magnetic powder 1. Next, by performing surface smoothing treatment at a temperature of 80'C or higher, the squareness in the vertical direction is made to be 0.7 or higher. At the same time, the surface roughness of the magnetic layer is 0.0 in center line average roughness.
It is characterized by having an average single particle diameter of 0.1 to 0.3 microns, and is smoothed at a relatively high temperature to reduce the square shape in the vertical direction. It has a sufficiently high density and good surface smoothness to sufficiently improve high-density recording characteristics.

In this invention, the magnetic powder contained in the magnetic +ff1a is preferably a plate-shaped hexagonal ferrite magnetic powder with an average single particle size of 0.1-0.3μ, and an average single particle size of 0.1-0.3μ. If it is smaller than .1μ, the vertical squareness cannot be sufficiently improved by surface smoothing treatment at a temperature of 80°C or higher, and if it is larger than 0.3μ, the surface smoothing treatment at a temperature of 80'C or higher will not improve the vertical squareness sufficiently. Although the squareness in the vertical direction is improved by surface smoothing treatment, the surface smoothness is poor and unsuitable for high-density recording, which is not preferable. Such plate-shaped hexagonal ferrite magnetic powders include Ba salt, Sr
one or more metal salts selected from salt, PB salt,
Co-precipitates obtained by adding alkaline water/8 solution to an aqueous solution of metal salts containing iron salts and hydrothermally treating the coprecipitates are used. ,, by adding an appropriate amount of metal ions such as Mn, etc., the average single particle diameter can be adjusted to the above 0.1~
It is preferable to use one adjusted within the range of 0.3μ.

The magnetic layer formed by applying a magnetic paint containing such a plate-shaped hexagonal ferrite magnetic powder exhibits a behavior different from that of conventional needle-shaped magnetic powder during surface smoothing treatment, and exhibits a behavior different from that of conventional needle-shaped magnetic powder at 80°C. When the surface smoothing treatment is performed at a temperature above, the magnetic layer becomes easy to flow, and the average single particle diameter is 0.1 to 0.3μ.
The hexagonal ferrite magnetic powder is well oriented so that its plate surface is parallel to the magnetic layer surface, and the squareness in the vertical direction is significantly improved and the surface smoothness is also improved. For this reason, it is preferable to carry out the surface smoothing treatment at a temperature of 80°C or higher.The higher the temperature, the higher the squareness in the vertical direction and the better the surface smoothness.However, if the temperature is higher than 120°C, the binder 8 because it may not have a negative effect on the resin.
It is preferable to carry out the reaction within the range of 0 to 120°C. Further, this surface smoothing treatment is preferably carried out at a linear pressure of 100 Kg/cm or more and a speed of 100 m/min or less. The magnetic layer subjected to such surface smoothing treatment preferably has a squareness in the vertical direction of 0.7 or more and a surface roughness of 0.05μ or less in terms of centerline average roughness. If the squareness of the disc becomes lower than 0.7 and the surface roughness is larger than 0.05μ in terms of center line average roughness, high density recording cannot be performed satisfactorily. Also, when performing such surface smoothing treatment,
After forming the magnetic layer, performing magnetic field orientation using opposing magnetic fields of different polarities, and then performing surface smoothing treatment, the squareness in the vertical direction is further improved, but even if magnetic field orientation treatment is not performed, this method When the surface smoothing process is performed, a field angle shape can be obtained in the vertical direction.

The magnetic recording medium of the present invention can be manufactured according to a conventional method. For example, a magnetic paint is prepared by mixing and dispersing the plate-shaped hexagonal ferrite magnetic powder with a binder resin, an organic solvent, etc. This may be applied onto a substrate such as a polynisdel film using any coating means such as a roll coater, dried, and then subjected to a surface smoothing treatment at a temperature of 80°C or higher.

The binder resin used here includes binder resins conventionally used for σL, such as chlorinated hydrogen-vinyl acetate copolymer, polyhinyl butyral resin, cellulose resin, polyurethane resin, polyester resin, and isocyanate compound. is widely used.

In addition, (a/8 agents include toluene, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone,
Conventionally widely used organic solvents such as tetrahydrofuran and r'il: ethyl acid may be used alone or in combination of two or more.

Note that various commonly used additives such as dispersants, lubricants, abrasives, antistatic agents, etc. may be optionally added to the magnetic paint.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 A mixed solution of 1 mole of ferric chloride, 1/10 mole of barium chloride, and 1/4.0 mole of cobalt chloride dissolved in 1ρ water was added to a 1β caustic soda aqueous solution in which 5 moles of caustic soda was dissolved. Stirred. Next, this suspension was left to stand for one day, then placed in an autoclave and heated to react at 300° C. for 2 hours.

After washing the reaction product with water, dehydrating it, and drying it,
°C for 2 hours to transform the Ba ferrite magnetic powder into i
M. The obtained Ba ferrite magnetic powder had a hexagonal plate shape, an average single particle diameter of 0.25 μ, a coercive force of 1220 oersted, a saturation magnetization of 58.6 emu 7 g, and a square shape of 0.43.

Using the thus obtained plate-shaped hexagonal Ba ferrite magnetic powder, 800 parts by weight of hexagonal Ba ferrite magnetic powder VAG
H (manufactured by U, C, C, USA, chloride 110 - vinyl-acetate-vinyl alcohol copolymer) Bandesox T-5250 (large mouth 70μ Hon Ink Manufactured by Kagaku Kogyo Co., Ltd., Urekun Elas [・Mar) Col: J Ne 1- L (manufactured by Nippon Polyurethane Industry Co., Ltd., trifunctional low molecular weight isocyane-I compound) A composition consisting of 8 n-butyl stearate, 504 methyl isobutyl ketone, 504 toluene /l was prepared in a hole mill at 48 m/l. A magnetic paint was prepared by time-mixing and dispersing. Apply this magnetic paint to a thickness of 12
The magnetic layer was coated on a polyester base film having a thickness of 3μ and dried to form a magnetic layer having a dry thickness of 3μ. Next, the formed magnetic layer was subjected to a linear pressure of 30° using a super calendar roll.
Surface smoothing treatment was performed at various processing temperatures at 0 kg/cm and a speed of 6 Qrn/min, and then cut into a predetermined width to produce a large number of magnetic tapes.

Example 2 In Example 1, the amount of barium chloride used was changed from 1/10 mol to 1/8 mol, the amount of Kohar chloride 1 to 1 was changed from 1/40 mol to 1/30 mol, and further caustic soda was added. The procedure was the same as in Example 1 except that the amount of - added was changed from 5 mol to 10 mol, and the average single particle f
A Ba ferrite magnetic powder having an M of 0.15 μ, a coercive force of 1010 oersted, a saturation magnetization of 54.1 emu, 7 g, and a square shape of 0.42 was obtained, and a large number of magnetic tapes were made.

Example 3 In Example 1, the amount of barium chloride used was changed from 710 mol to 1/8 mol, 1/20 mol of nickel chloride was used in place of cobalt chloride, and caustic soda was added.
The procedure was the same as in Example 1 except that the amount added was changed from 5 mol to 15 mol.
0 μ, coercive force 1080 oersted, saturation magnetization 53.
Ba ferrite magnetic powder weighing 8 emu and 7 g and having a square shape of 0.42 mm was obtained, and a large number of magnetic tapes were made.

Example 4 Example 1 except that the amount of barium chloride used was changed from 1/10 mol to 1712 mol, and the amount of conol chloride used was changed from 1/40 mol to 1/30 mol. Similarly to (2), the average single particle diameter is 0.
30 μ, coercive force 1200 oersted, saturation magnetization 58
．． 4emu/g, square 0.43 Ba ferrite 1~
A large number of θ magnetic tapes were obtained from the magnetic powder.

Comparative Example 1 In Example 1, the amount of barium chloride used was changed from 1/10 mol to 1/8 mol, the amount of cobalt chloride was changed from 1/40 mol to 1/Xθ mol, and the amount of caustic soda was changed from 1/40 mol to 1/Xθ mol. The procedure was the same as in Example 1, except that the addition amount was changed from 5 mol to 20 mol.
Ba ferrite magnetic powder with a diameter of 52.1 cmu/g and a square shape of 0.42 mm was obtained, and a large number of magnetic tapes were made.

Comparative Example 2 Same as Example 1 except that the amount of barium chloride used was changed from 1/10 mol to 1/8 mol and cobalt chloride was omitted. A 13a ferrite magnetic powder having a particle size of 0.32 μ, a coercive force of 1280 oersted, a saturation magnetization of 59.2 emu/g, and a square shape of 0.44 was obtained, and a large number of magnetic tapes were made.

Vertical squareness and surface roughness were measured for the magnetic tapes obtained in each Example and Comparative Example. The square shape in the vertical direction is shown as a value after demagnetizing field correction, assuming that the demagnetizing field coefficient is 4π. The surface roughness was determined by measuring the center line average roughness using a stylus type surface roughness meter manufactured by Tokyo Seiki Co., Ltd. with a cutoff of 0.08 mm.

Figure 1 shows the relationship between the square shape in the vertical direction measured in this way and the processing temperature of the surface smoothing treatment, where graph A is the magnetic tape obtained in Example 1, graph B is
is the magnetic tape obtained in Example 2, and graph C is the magnetic tape obtained in Example 3.
Graph D shows the magnetic tape obtained in Example 4, graph E shows the magnetic tape obtained in Comparative Example 1, and graph F shows the magnetic tape obtained in Comparative Example 2.

Further, FIG. 2 shows the relationship between the center line average roughness measured as described above and the processing temperature of the surface smoothing treatment, where graph A is the magnetic tape obtained in Example 1,
Graph B is the magnetic tape obtained in Example 2, graph C is the magnetic tape obtained in Example 3, graph D is the magnetic tape obtained in Example 4, and graph E is the magnetic tape obtained in Comparative Example 1. Tape, graph F shows the magnetic tape obtained in Comparative Example 2.

〔Effect of the invention〕

As is clear from the graphs in FIGS. 1 and 2, the magnetic tape obtained in Comparative Example 1 has a vertical square shape and a centerline average of The magnetic tape obtained in Comparative Example 2, which showed almost no change in roughness, had a large centerline average roughness, although the vertical squareness was improved by surface smoothing treatment at a temperature of 80°C or higher. In contrast, the Vtt tapes obtained in Examples 1 to 4 did not have good surface smoothness.
The surface smoothing treatment at temperatures above °C improves the squareness in the vertical direction and reduces the centerline average roughness. Therefore, according to the present invention, the average single particle diameter is 0.
．． Using hexagonal ferrite magnetic powder with a size of 1 to 0.3μ, the surface is smoothed at a temperature of 80°C or higher, resulting in a magnetic layer with a high vertical square shape and a smooth surface. is formed, indicating that a magnetic recording medium suitable for density recording can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the vertical square shape of the magnetic tape obtained by this invention and the surface smoothing treatment temperature, and Fig. 2 shows the relationship between the centerline average roughness and surface smoothness of the magnetic tape obtained by this invention. There is a diagram of the relationship with the heat treatment temperature - ζ. Patent applicant: Hitachi Maxell, Ltd., Cy, :,,,, 1 Agent: Haru Takaoka, 2゛゛,1:"', -+ -N -- Figure 1 0 40 60 80 1.00 .120 Surface smoothing treatment temperature (0C) Fig. 2 0 40 60 80 100 120 Surface smoothing treatment temperature (OC)

Claims (1)

[Claims] 1. Platy hexagonal ferrite magnetic powder with an average single particle diameter of 0.1 to 0.3μ is contained in the magnetic layer, and the square shape in the vertical direction is 0.7 or more. A magnetic recording medium 2 characterized in that the surface roughness of the magnetic layer is 0.05μ or less in terms of center line average roughness, and a plate having an average single grain diameter of 0.1 to 0.3μ on the substrate. A magnetic layer containing magnetic powder is formed on the hexagonal ferrite 1 of
Δl/digestion treatment is applied to make the squareness in the vertical direction 0.7 or more, and the surface roughness of the magnetic layer is 0 in terms of center line average roughness.
．． A method for producing a magnetic recording medium characterized by a magnetic recording medium having a thickness of 0.05 μm or less