JPH0782641B2 - Ferromagnetic powder for magnetic recording medium and magnetic recording medium using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] In the present invention, a ferromagnetic powder is formed into a film together with a resin binder. The present invention relates to a ferromagnetic powder for giving recording / reproducing characteristics and a magnetic recording medium using the same.

[Technical background of the invention and its problems]

In conventional magnetic recording media, ferromagnetic powder is dispersed in a liquid containing a resin binder to form a paint, which is applied on a substrate such as polyester film, oriented, and dried, and then the surface is smoothed by a calendar or the like. It has been obtained through the process of In recent magnetic recording media, attempts have been made to reduce the particle size of ferromagnetic powder in order to increase the recording density.

However, when the particle size of the ferromagnetic powder becomes small, the following problems generally occur.

1) Dispersion becomes difficult.

When the particle size of the ferromagnetic particles is small, it is very difficult to disperse the ferromagnetic particles in the resin binder in the state of primary particles, and the particles in the coating material are often secondary aggregated. This means that the initial purpose of increasing the recording density is not achieved by using particles with small particle size, and the recording / reproducing output in the high frequency range expected from the particle size of the magnetic powder is actually achieved. Can not. Moreover, this aggregation increases noise during recording and reproduction and deteriorates S / N characteristics.

2) It is difficult to obtain a smooth and uniform coated surface.

Agglomerates generally deteriorate the dispersion stability of the paint and easily cause phase separation of the paint. In addition, orientation cohesion tends to occur after coating. These deteriorate the smoothness of the coated surface and deteriorate the C / N characteristics during recording and reproduction.

Further, as the particle size of the ferromagnetic powder becomes smaller, the fluidity of the coating becomes worse, making it difficult to obtain a smooth coated surface. As a solution to this problem, it is common to use a dispersant in addition to the binder resin, but the dispersant inhibits the adhesion of the resin binder molecule and the ferromagnetic particles, so that it has an adverse effect on the purpose of obtaining a homogeneous coating film. Show.

3) It is difficult to obtain a durable coating film.

As the particle size decreases, it becomes more difficult to wet the surface of all particles with resin molecules. As a result, the durability of the resulting coating film decreases. Although a dispersant is used in combination as an agent for improving the wetting, the dispersant finally inhibits the adhesion of the binder resin to the surface of the particles for the above-mentioned reason, and therefore, for the purpose of improving the durability of the coating film. Shows the opposite effect.

Another method is to extend the dispersion time in order to improve the wetting of the binder resin molecules on the particle surface. But in this case
The strength of the coating film generally decreases due to abrasion and mixing of the dispersion medium.

[Object of the Invention]

The present invention aims to solve the above-mentioned problems in a high-density magnetic recording medium, and to provide a ferromagnetic powder that exhibits excellent magnetic recording / reproducing characteristics with excellent dispersibility and that provides excellent coating film strength and durability. It is intended to be provided.

The present invention also provides a manufacturing process for easily obtaining a magnetic recording medium having excellent magnetic properties and coating durability.

The present invention also provides a process for producing a ferromagnetic powder for obtaining a magnetic recording medium having excellent magnetic recording characteristics and coating durability.

[Outline of Invention]

The ferromagnetic powder of the present invention has a glass transition point of 10 ° C. with the ferromagnetic powder.
It is a ferromagnetic powder for a magnetic recording medium, which is obtained by bringing the following resin particles into contact with each other.

As the above-mentioned ferromagnetic powder, Fe powder or Fe, NiCo, Cr 2
Alloy powder containing more than one kind, γ-Fe ₂ O ₃ powder and its Co modified powder, Cr ₂ O ₃ or general formula MxO ・ n (Fe _1-m・ Mym) ₂ O
₃ (where Mx is barium or strontium, and My is selected from the group consisting of titanium, cobalt, nickel, indium, copper, germanium, niobium and zirconium 1
Represents more than one element, m is a positive number from 0 to 0.2, and n is from 5.4 to 6. Magnetic powders such as substitutional ferrites shown in () can be used.

The resin powder that comes into contact with the ferromagnetic powder is polyester resin,
Resin powder represented by polyurethane resin, polyacrylic resin, polybutadiene resin, polyamide resin, polystyrene / butadiene copolymer resin, polyacrylonitrile / butadiene copolymer resin, polychloroprene resin, etc., having a glass transition point of 10 or less. Those below ℃ are used. These resin powders can be brought into contact with the above-mentioned ferromagnetic powder in the gas phase or in the state of being dispersed in the liquid phase. Further, resin particles having a glass transition point higher than 10 ° C., such as polyvinyl chloride resin, epoxy resin, acrylic resin, polyester resin, polyvinylidene chloride resin, polycarbonate resin, polyvinyl butyral resin, polyacrylon nitrile resin, phenol resin, phenoxy. It can be brought into contact with the ferromagnetic powder in a state of being mixed with a resin, a melamine resin, a polyvinyl alcohol resin, a polyvinylpyrrolidone resin, or the like.

The resin particles have a particle size of 5 nm to 10 μm, and particles having a particle size of 5 nm to 1 μm dispersed in a liquid give particularly good results. Generally, the smaller the particle size, the larger the surface area per unit weight and the more intimate contact with the ferromagnetic powder, which is advantageous. These particles may be spherical, atypical, or fibrous.

The contact with the ferromagnetic powder can be carried out in a gas phase or a liquid phase by applying a mechanical shearing force by a propeller, a stirring rod mixing medium, a roll mill, etc., in addition to the mixing and stirring in an air stream.

In order to make a high density magnetic recording medium using the ferromagnetic powder obtained in the present invention, it can be easily obtained by the following process.

1) In the case of using a paint using an organic solvent A homogenizer is prepared by adding an organic solvent and, if desired, a lubricant, an abrasive, a dispersant, and a binder resin to the ferromagnetic powder brought into contact with the resin powder having a glass transition point of 10 ° C. or lower. A paint is prepared by mechanical mixing with a ball mill, sand grinder, or the like. The obtained coating material is applied onto a substrate such as polyester resin, oriented, dried, and surface smoothed by calendering or buffing to obtain a magnetic recording medium.

2) The ferromagnetic powder which is brought into contact with the resin powder having a glass transition point of 10 ° C. or lower is pressed alone or while being heated by sandwiching the substrate. If desired, a lubricant, a flow control agent, and an abrasive may be added to the powder, and the surface after molding may be subjected to buffing or coating with a lubricant.

As is clear from the above process, the ferromagnetic powder of the present invention is subjected to smoothing treatment under pressure and heating, thereby obtaining a magnetic recording medium having excellent electromagnetic conversion characteristics. It was confirmed that a resin component having a glass transition point of 10 ° C. or lower is essential for this smoothing treatment.

〔The invention's effect〕

The ferromagnetic powder of the present invention and the magnetic recording medium using the same have the following effects.

1) It is possible to make a paint with excellent dispersion of ferromagnetic powder.

It is considered that when the ferromagnetic powder is brought into contact with the surface of the resin powder and a shearing force is applied, a part of the surface of the ferromagnetic powder becomes wet with the resin molecules. When this is dissolved in an organic solvent, Since the dispersibility is remarkably increased, a magnetic recording medium having a high C / W is provided.

2) Dispersion of the paint becomes extremely easy. Compared with the case where a resin powder is dissolved in an organic solvent and the ferromagnetic powder is dispersed therein, the resin powder can be dispersed easily and quickly by giving a significantly weak shearing force.

3) The paint obtained has good fluidity and gives a smooth coating surface,
It also shows stability over time.

4) Coating strength and durability are increased.

5) It can be directly molded and used.

Example of Invention

Example 1 Co-modified γ-ferrite powder (average particle size 0.3 μm, Hc750Oe, σs
75lmu / g) 100 parts by weight was used as a fluidized bed, and a urethane elastomer (glass transition temperature -10 ° C Mn = 40,000) was added to this fluidized bed.
After spray-drying the 10% MEK solution of 1), 5 parts by weight of the obtained particles (average particle size 1 μm) were sprinkled and mixed to obtain a Co-modified γ iron oxide powder which was brought into contact with a urethane elastomer.

When this magnetic powder was observed by SEM, it was confirmed that the Co-γ ferrite powder was densely attached to the surface of the urethane elastomer particles.

Example 2 Co, Ti-substituted Ba-ferrite slurry prepared by the glass crystallization method (average particle size 0.05 μm, Hc700 Oe, σs 56 lmu / g, solid content 25%) 400 parts by weight of polyurethane latex (average particle size 0.1 μm , Glass transition temperature -10 ℃, Mn = 40,000, solid content 35wt
%) 35 parts by weight, polyvinyl chloride latex (average particle size 0.
15 parts by weight (05 μm, Mw 100,000, solid content 30 wt%) were mixed and passed through a sand grinder twice. The obtained slurry was dried by a spray drying method to obtain a ferromagnetic powder which was brought into contact with polyurethane and polyvinyl chloride resin particles.

Incidentally, water was added to the slurry after passing through the sand grinder to dilute it, and after ultrasonic waves were added for 1 hour, the barium ferrite powder was allowed to settle by allowing it to stand, and the supernatant was analyzed. It was found that the resin particles did not exist at all, and the barium ferrite particles and the resin particles were completely in contact with each other. In the SEM observation of the dry powder, no resin particles present alone were found, and the contact state with the Ba-ferrite particles was good.

Example 3 Co- and Ti-substituted barium ferrite particles having an average particle size of 0.08 μm
Put 100 parts by weight into a Henschel mixer and rotate the mixer to make a polyamide resin latex with an average particle size of 0.1 μm (glass transition point 5 ° C., Mn = 100,000, amine value 20, solid content 10).
%) 30 parts by weight was added dropwise and connected to a degassing system to obtain barium ferrite powder contacted with a polyamide resin. When the contact state between the resin particles and the barium ferrite powder was examined in the same manner as in Example 2, it was favorable.

Example 4 As a metal powder, 200 parts by weight of Fe powder slurry having an average particle size of 0.3 μm (solid content 50%) was used as polyester latex (glass transition temperature 7 ° C., Mn 50,000, active hydrogen equivalent 1.000, solid content 30%) 50 parts by weight. Put the part in a kneader and contact it while applying an appropriate shearing force,
In the same manner as in Example 2, a uniform ferromagnetic powder in which the metal powder and the resin particles were in contact was obtained.

Example 5 and Comparative Example 200 parts by weight of cyclohexanone MEK 1: 1 mixed solution prepared by dissolving 100 parts by weight of Co-modified γ-iron oxide powder obtained in Example 1 in 5 parts by weight of vinyl chloride-vinyl acetate copolymer and 1 part by weight of stearic acid. In addition to the parts, it was dispersed by a sand grinder for 2 hours. The obtained paint was added with 2 parts by weight of an isocyanate type curing agent (Coronate 3041 Nippon Polyurethane, solid content: 50%) to 100 parts by weight after filtration, and applied on a polyester film at 60 ° C. When calendering was applied, a smooth coated surface with a surface roughness of 0.02 μm or less was obtained. This coating is
After curing in a 50 ° C. oven, it showed excellent still durability, and the output and C / N characteristics at a recording wavelength of 0.6 μm were excellent as shown in Table 1.

For comparison, exactly the same Resin as used in the paint of this example was used.
Co-γ powder was mixed in a solution of n composition at the same ratio and dispersed by a sand grinder, and a coating material was prepared in the same manner. The obtained coating material had poor stability and was easily solid-liquid separated. Further, the surface property of the coating film was as bad as 0.04 μm to 0.07 μm, and the recording / reproducing characteristics were at a low level as shown in Table 1.

Example 6 and Comparative Example 200 parts by weight of MEK-cyclohexanone 1: 1 mixed solvent was added to 100 parts by weight of the ferromagnetic powder obtained in Example 2 to prepare a paint and a coating film in the same manner as in Example 5. It was

The surface roughness of the obtained coating film was 0.01 to 0.02 μm, which was remarkably smooth, and the recording / reproducing characteristics were excellent as shown in Table 1. The coating film was excellent in still durability and weather resistance. Was excellent.

A barium ferrite powder of the same type was mixed in the same ratio in a solution having the same resin composition as that used for the paint of Example 6 as a comparative example, and the mixture was dispersed with a sand grinder to prepare a paint in the same manner. The paint had poor stability and solid-liquid separation was extremely fast. Further, the surface properties of the coating film prepared in the same manner as in Example were as poor as 0.04 μm, and the recording / reproducing characteristics were at a low level as shown in Table 1.

Examples 7 to 8 Barium ferrite powder particles brought into contact with the polyamide resins obtained in Examples 3 and 4 were pressed and heated to obtain sheet-shaped molded products. The magnetic recording medium obtained by sticking this on a substrate showed excellent electromagnetic conversion characteristics as in Example 6.

Reference Example A ferromagnetic powder was obtained in the same manner except that the polyurethane latex of Example 2 was replaced with a polyester latex having a glass transition point of 15 ° C. Then, a magnetic recording medium was prepared in the same manner as in Example 6.

According to this, although the stability of the coating material was secured, the surface properties of the coating film were poor, and the recording / reproducing characteristics and durability were at low levels.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunji Kurisu 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock Research Institute, Toshiba Research Institute (56) Reference JP-A-53-78099 (JP, A) Sho 59-218627 (JP, A)

Claims (4)

[Claims] 1. A ferromagnetic material for a magnetic recording medium, characterized in that the ferromagnetic powder is coated on the resin particles by bringing the ferromagnetic powder into contact with resin particles having a glass transition point of 10 ° C. or lower. Powder. 2. The ferromagnetic powder for a magnetic recording medium according to claim 1, wherein the resin particles having a glass transition point of 10 ° C. or lower are elastomers having a urethane bond. 3. A ferromagnetic powder for a magnetic recording medium according to claim 1, wherein resin particles having a glass transition point higher than 10 ° C. are used in combination. 4. A magnetic layer comprising a ferromagnetic powder for magnetic recording media, wherein the ferromagnetic powder is coated with resin particles having a glass transition point of 10 ° C. or lower and dispersed in a resin binder. And a magnetic recording medium.