JPS6151622A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with excellent magnetic characteristics by decreasing stepwise each scattering energy of a multi-stage sand mill scattering magnetic powder toward the progressing direction of a magnetic paint to scatter uniformly the magnetic powder into the magnetic paint. CONSTITUTION:The magnetic paint mixed to some degree in a tank 2 flows into a tank 4 of the sand mill 1A, the magnetic paint is scattered with being rotated in a medium 7 such as beads by the rotation of a disc 5, the paint is separated from the medium 7 by a screen 9 and carried to the next mills one after another. The grain diameter of the media 7 or the quantity in the sand mill of each stage is decreased to reduce stepwide the scattering energy of each stage thereby scattering uniformly the magnetic powder into the magnetic paint. Thus, a magnetic recording medium with excellent magnetic characteristics is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a magnetic recording medium. In particular, it relates to a method of manufacturing a coated magnetic recording medium.

Conventionally, coated magnetic recording media have been manufactured as follows. That is, a magnetic recording medium has been manufactured by mixing magnetic powder with a binder, a solvent, etc. to prepare a flexible paint, and coating this magnetic paint on a non-magnetic substrate. In order to obtain excellent magnetic recording media, it is necessary that the magnetic powder in the magnetic paint is uniformly dispersed. In the conventional manufacturing method, magnetic powder and binder are mixed and dispersed using a sand mill. Ta.

In conventional manufacturing methods, in order to uniformly disperse the magnetic powder, a plurality of sand mills are connected in multiple stages to disperse the magnetic powder.

However, in conventional manufacturing methods using such multi-stage sand mills, the dispersion energy (the energy required to disperse aggregated magnetic powder into primary particles, hereinafter the same) of each sand mill is equal, so the magnetic powder is It was difficult to disperse efficiently and uniformly. That is, if the dispersion energy of the sand mill was too large, the particles of the magnetic powder would be crushed, making it impossible to obtain a magnetic recording medium with good magnetic properties. Also, if the dispersion energy of the sand mill is too small,
The aggregated magnetic powder did not form into primary particles well, and it was difficult to uniformly disperse it in the magnetic paint.

The present invention has been made in view of the above-mentioned circumstances, and therefore provides a method for manufacturing a magnetic recording medium that can uniformly disperse magnetic powder in a magnetic paint and obtain a magnetic recording medium with excellent magnetic properties. The purpose is to provide

In the manufacturing method of the present invention, a magnetic powder is mixed with a binder, a solvent, etc. using a multi-stage sand mill to create a magnetic paint, and this magnetic paint is applied onto a non-magnetic substrate. The present invention is characterized in that the dispersion energy is reduced in stages according to the direction in which the magnetic paint moves.

In other words, as the magnetic powder in the magnetic paint is dispersed,
By gradually reducing the dispersion energy of each sand mill, the magnetic powder can be uniformly dispersed without being crushed. Dispersion energy here refers to the energy required to disperse agglomerated magnetic powder into primary particles as described above. 0 dispersion energy is, in the case of a sand mill,
It depends on the bead diameter, bead amount, and disk rotation speed. Therefore, in the manufacturing method of the present invention, the dispersion energy can be gradually reduced by decreasing the bead diameter stepwise according to the direction in which the magnetic paint moves. Alternatively, the amount of beads in each sand mill may be reduced stepwise. Furthermore, the rotational speed of the disc of each sand mill may be slowed down.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a sand mill used in the manufacturing method of the present invention, and shows IA, IB, and Ic.

ID indicates a sand mill In the present invention, a plurality of sand mills IA, IB, IC, and ID are connected in multiple stages and used. In the embodiment shown in FIG. 1, four sand mills IA,
Although IB, IC, and ID are connected, the number is not limited to this number.

Now, the magnetic paint that has been stirred to some extent in the tank 2 flows into the vessel 4 of the sand mill IA by the pump 3. A disk 5 is provided in the center of the vessel 4 via a shaft 6. The disk 5 is rotated by rotation of the shaft 6. Further, a large number of media 7 are placed in the vessel 4. As the media 7, for example, glass beads, ceramic beads, steel beads, etc. are used.

When the disk 5 rotates, the magnetic paint rotates together with the media 7, and the magnetic paint is dispersed.

The magnetic paint dispersed in the sand mill IA is discharged from the discharge port 8 and guided to the sand mill IB. Thereafter, similar dispersion is performed using sand mills IB, 1c, and 10, and the dispersion is completed. Note that 9 is a screen that separates the magnetic paint and the media 7.

Now, in the manufacturing method of the present invention, sand mill IA,
The distributed energies of IB, IC, and ID are set to be different. That is, the dispersion energy of the sand mills IA, IB, Ic, and 10 decreases in stages according to the direction in which the magnetic paint moves. In the embodiment shown in FIG. 1, the diameter of the media 7 is sand mill IA.
.

IB, IC, and ID are gradually becoming smaller. Specifically, in the illustrated example, 1, glass beads with a diameter of 2.5 to 3.0 ml11 are used in the sand mill IA, glass beads with a diameter of 2.0 to 2.5 am are used in the sand mill IB, Sand mill IC diameter 1.5-2.0
10111 glass beads with a diameter of 1.0 to 1.5 ml were used in a sand mill ID.

In addition, the amount of media 7 may be reduced in stages using sand mills IA to ID. For example, if a vessel with a capacity of 20 is used, from sand mill IA to ID,
60%, 50%, 40%, 30 to sand mill volume
% of glass peas may be added.Furthermore, disk 5
For example, the rotation speed of the disk 5 may be decreased in steps from sand mills IA to ID to 1300 rpm, 1250 rpm, 120 rpm.
The speed may be 0 rpm or 1150 rpm, however, the diameter of the media, the amount of media, and the number of rotations of the disk are not limited to the values shown above. The diameter of the media, the amount of media, and the number of revolutions of the disc can be varied depending on the type of magnetic paint.

In the manufacturing method of the present invention, as explained above, the dispersion energy of each sand mill is set to decrease in stages according to the direction in which the magnetic paint moves, so that the magnetic powder in the magnetic paint is not crushed. This method is particularly effective for metal magnetic powders where the magnetic powder has a strong cohesive force.

Hereinafter, the manufacturing method of the present invention will be explained in more detail with reference to Examples 1 to 3.

Example 1 Approximately 100 parts by weight of Fe-Ni alloy metal magnetic powder (major axis 0.2 mm, axial ratio 8), vinyl chloride-vinyl acetate-vinyl alcohol copolymer (for example, trade name VAGH, union carbide) A magnetic paint was prepared by mixing about 30 parts of Poly Nippon Polyurethane Co., Ltd.) and Poly Nippon Polyurethane Co., Ltd., about 1 part by weight of lecithin, about 5 parts by weight of alpha alumina, and about 274 parts by weight of methyl ethyl ketone and toluene. This magnetic coating material was placed in a sand mill shown in FIG. 1 and dispersed. Glass peas were used as methias. The diameter of the glass beads ranges from 2.5 mm to 3.0 mm in order from sand mill IA to ID.
mm, 2.0-2.5 mm, 1, 5-2. Omm
, 1. It was O~1.5mm. The amount of glass peas is
Sand mill IA~ID all, sand mill capacity a 20
It was 60% with respect to fL. In addition, the rotational speed of the disc was 1300 rpm for all sand mills IA to ID.

After adding 5 parts by weight of a trifunctional polyisocyanate crosslinking agent (for example, brand name Coronatore, manufactured by Nippon Polyurethane Industries Co., Ltd.) to this completely dispersed magnetic paint and stirring thoroughly, it was applied onto a 9 JLm thick polyester film and subjected to orientation treatment. ,
After drying and calendering, heat at 50°C.
It was left in an oven for 24 hours to carry out a curing reaction. After the curing reaction was completed, the tape was cut into a predetermined width to obtain a magnetic tape.

Next, the magnetostatic properties of this magnetic tape were measured.

The measurement results are shown in Table 1. In addition, Br is the residual magnetic flux density, and Bm is the feed magnetic flux density.

Example 2 A magnetic paint having the same composition as in Example 1 was dispersed using a sand mill shown in FIG. Glass beads were used as the media. The diameter of the glass beads is 2.0 for all sand mill IA~ID? , 5■. The amount of glass beads was 60%, 50%, 40%, and 30% of the 20 sand mill volumes in order from sand mill IA to ID. Further, the rotational speed of the disks was 130 rpm in all of the sand mills IA to ID1.

Using this completely dispersed magnetic paint, a magnetic tape was prepared in the same manner as in Example 1, and the magnetostatic properties were added to 3111. The measurement results are shown in Table 1.

Example 3 A magnetic paint having the same composition as in Example 1 was dispersed using a sand mill shown in FIG. Glass beads were used as the media. The diameter of the glass beads in all sand mills 1A to ID was 2.0 to 2.5 . The amount of glass beads was 60% of the sand mill volume of 20 sand mills in all sand mills IA to ID. The rotational speed of the disc is 1300 rpm and 1250 rpm in order from sand mill IA to LD.
m, 1200 rpm, and 1150 rpm.

A magnetic tape was prepared in the same manner as in Example 1 using this completely dispersed magnetic paint, and its magnetostatic properties were measured. The measurement results are shown in Table 1.

For comparison, a magnetic paint having the same composition as in Example 1 was dispersed using a sand mill as shown in FIG. Glass beads were similarly used as the media.

The diameter of the glass beads is sand mill IA~ID all 2
．． It was 0 to 2.5 mm. The amount of glass beads was 60% of the sand mill volume Wt 201 in all sand mills IA to LD. Further, the rotational speed of the disks was 1300 rpm in all sand mills IA to ID.

Using this completely dispersed magnetic paint, a magnetic tape was prepared in the same manner as in Example 1, and its magnetostatic properties were measured. The measurement results are shown in Table 1.

As is clear from Table 1, according to the manufacturing method of the present invention, it is possible to obtain a magnetic recording medium having excellent magnetic properties.

Table 1

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a sand mill used in the manufacturing method of the present invention. 1--Sand mill, 2--Tank, 3--Pump, 4--Vessel, 5--M-disc, 6--Shaft, 7--Media, 8--M-Discharge port, 9 -m-screen.

Claims (1)

[Claims] In a method for producing a magnetic recording medium, the magnetic powder is mixed with a binder, a solvent, etc. using a multistage sand mill to create a magnetic coating material, and the magnetic coating material is applied onto a non-magnetic substrate. A method for manufacturing a magnetic recording medium, characterized in that energy is reduced stepwise according to the direction in which the magnetic paint moves.