JPH07153074A - Manufacture for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium showing high RF output properties and high chroma output properties by mixing and dispersing magnetic powders together with necessary components while processing the same in an ultrasonic treatment, thereby preparing a magnetic paint, applying/drying the paint and forming a magnetic layer. CONSTITUTION:In producing a magnetic paint, magnetic powders are processed by an ultrasonic treatment while the powders are mixed and dispersed together with a coupler resin, an organic solvent and other necessary components. Therefore, an aggregate of the magnetic powders is crushed in the ultrasonic treatment, whereby thixotropy of the magnetic paint is decreased to enhance a fluidity. A dispersibility of the magnetic powders is sufficiently improved. By mixing/dispersing magnetic powders together with the coupler resin, organic solvent and other necessary components while performing the ultrasonic treatment, molecules of the coupler resin are turned easy to move and the magnetic powders are favorably dispersed. Accordingly, a magnetic recording medium with superior electromagnetic converting properties is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium having a magnetic layer having good dispersibility of magnetic powder and excellent electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art A magnetic recording medium is usually prepared by mixing and dispersing magnetic powder with a binder resin, an organic solvent and other necessary components to prepare a magnetic paint, and coating the magnetic paint on a non-magnetic support. It is produced by drying, and it is required that the magnetic powder has good dispersibility, excellent electromagnetic conversion characteristics, and excellent durability. For this reason, conventionally, it has been performed to improve the dispersibility of the magnetic powder by using a binder resin having excellent dispersibility of the magnetic powder or by using a dispersant.

[0003]

However, in recent years,
With the increasing density of magnetic recording, fine particle metal magnetic powder with excellent magnetic properties has come to be used, and with this, it is difficult to disperse fine particle metal magnetic powder with strong cohesive force by the conventional method. It has become to. Further, the viscosity of the magnetic coating material prepared by using these fine metal magnetic powders is higher than that of the conventional magnetic coating material, and since the coating material has a large thixotropy, it is difficult to improve the dispersibility.

[0004]

SUMMARY OF THE INVENTION The present invention has been made as a result of various investigations in view of the above-mentioned current situation. Magnetic powder is mixed with a binder resin, an organic solvent and other necessary components while subjecting to ultrasonic treatment. Disperse to prepare a magnetic paint, apply this magnetic paint on a non-magnetic support, and dry it to form a magnetic layer, thereby sufficiently improving the dispersibility of magnetic powder and improving electromagnetic conversion characteristics. It was made.

In the present invention, the magnetic coating material is prepared by ultrasonically treating the magnetic powder when mixing and dispersing the magnetic powder together with the binder resin, the organic solvent and other necessary components. For this reason, the agglomerates of the magnetic powder are crushed by this ultrasonic treatment, the thixotropy of the magnetic paint is reduced, the fluidity is improved, and the dispersibility of the magnetic powder is sufficiently improved.

Therefore, according to the production method of the present invention in which the magnetic powder is mixed and dispersed with the binder resin, the organic solvent and other necessary components while subjecting to ultrasonic treatment, the molecules of the binder resin become easy to move, The magnetic powder is well dispersed, and a magnetic recording medium having excellent electromagnetic conversion characteristics can be obtained.

As described above, the ultrasonic treatment involves
When mixing and dispersing with the binder resin, the organic solvent and other necessary components, it is preferable to carry out at the same time, and particularly to carry out at the final stage of the mixing and dispersing step.

If the ultrasonic treatment is carried out when the viscosity of the magnetic coating material in the mixed dispersion is 20 poise or less, the effect is sufficiently exhibited, the fluidity of the magnetic coating material is further improved, and the magnetic powder is Since the dispersibility of is further improved, it is preferable to apply it when the viscosity of the magnetic coating material in the mixed dispersion is 20 poise or less.

Further, such ultrasonic treatment is performed with a frequency of 18 to 50 KHz, a high frequency power of 0.2 to 8 KW, and an amplitude of 10
〜3000μm, time 0.5 ~ 60 seconds is preferable. If the frequency and high frequency power are too small or the time is too short, the desired effect cannot be obtained and the frequency and high frequency power are too large. However, if the time is too long, dispersion may proceed and re-aggregation may occur.

Here, as the magnetic powder, for example, γ
-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, Co-containing γ-Fe
_{In addition to 2} O ₃ powder, Co-containing Fe ₃ O ₄ powder, CrO ₂ powder, various conventionally known magnetic powders such as Fe powder, Co powder, and metal powder such as Fe—Ni powder are widely applied, but in particular, agglomeration Easy to do Long axis diameter 0.3μm or less, coercive force 10
Suitable for needle-shaped fine particle magnetic metal powders having a major axis diameter of 0.3 μm or less and a coercive force of 1000 oersteds or higher because the effect is sufficiently exhibited and the dispersibility is improved in the needle-shaped fine particle magnetic metal powder of 00 oersted or more Applied to.

The binder resin used is a vinyl chloride-vinyl acetate copolymer, a fibrin resin, a butyral resin, a polyurethane resin, a polyester resin, an epoxy resin, a polyether resin. Any binder resin that has been widely used in magnetic recording media such as resins and isocyanate compounds can be used.

Further, as the organic solvent, a ketone solvent such as cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone, an ester solvent such as ethyl acetate and butyl acetate, an aromatic hydrocarbon solvent such as benzene, toluene and xylene, and dimethyl sulfoxide. Solvents suitable for dissolving the binder resin to be used, such as sulfoxide-based solvents such as, ether solvents such as tetrahydrofuran and dioxane, are used alone or in combination of two or more without particular limitation. .

In the magnetic coating composition, various commonly used additives such as lubricants, abrasives, antistatic agents, dispersants and the like may be optionally added.

As the disperser used for mixing and dispersing the magnetic powder with the binder resin, the solvent and other necessary components, any disperser generally used for preparing magnetic paints can be used. -Lumille, sand grinder mill, disperser, etc. are used.

[0015]

EXAMPLES Next, examples of the present invention will be described. Example 1 α-Fe magnetic powder (major axis diameter 0.175 μm, coercive force 1675 E 82 parts by weight Rusted) vinyl chloride-vinyl acetate-vinyl alcohol copolymer 9 〃 polyurethane resin 4.5 〃 alumina 8.2 〃 cyclohexanone 105 〃 toluene 105 〃 Put the above composition in the sand grinder mill and
Mixed and dispersed for time.

Next, 1.64 parts by weight of myristic acid, n-butyl stearate, 1.23 〃 coroneto L (manufactured by Nippon Polyurethane Industry Co., Ltd .; trifunctional low content 4.5 〃 isocyanate compound) cyclohexanone 12〃 toluene 12〃 When the above composition was added in an appropriate order and mixed and dispersed for 0.75 hours, ultrasonic treatment was performed with an ultrasonic treatment device at a frequency of 20 KHz, a high frequency power of 600 W and an amplitude of 30 μm for 3 seconds to prepare a magnetic paint.

Next, the magnetic coating material obtained was applied to a thickness of 14 μm.
Coated on the polyester film of No.2, oriented, then dried and calendered to a thickness of 2.5 μm.
The magnetic layer of was formed. Then, it was cut into a width of 8 mm to prepare a magnetic tape.

Example 2 A magnetic coating material was prepared in the same manner as in Example 1 except that the ultrasonic treatment time by the ultrasonic treatment apparatus was changed from 3 seconds to 9 seconds, and a magnetic tape was prepared. Created.

Comparative Example 1 A magnetic coating material was prepared and a magnetic tape was prepared in the same manner as in Example 1 except that the ultrasonic treatment by the ultrasonic treatment apparatus was omitted.

In each of the examples and comparative examples, the fluidity of the prepared magnetic paint was examined by the following method, and the RF output and the chroma output of the obtained magnetic tape were measured by the following methods.

<Fluidity of Magnetic Paint> The fluidity of the paint is measured by a double cylinder type rotational viscometer, a shear stress curve is drawn, and the curve is represented by the Casson paint flow formula τ ^0.5 = k ₀ + k ₁ ν
^It was approximated to ^0.5 and linearized. The slope of the straight line is k ₁
Values and intercepts show k ₀ values, and the fluidity of the magnetic paint was evaluated by the coefficient.

<RF output> A 100% white signal was recorded on the obtained magnetic tape at a standard recording current, and the reproduction output was shown as a relative value with respect to the reference tape.

<Chroma Output> A 100% chroma signal was recorded on the obtained magnetic tape at a standard recording current, and its reproduction output was shown as a relative value with respect to the reference tape. Table 1 below shows the results.

[0024]

[0025]

As is apparent from Table 1 above, the magnetic paints prepared by the manufacturing method of the present invention (Examples 1 and 2)
Has better fluidity than the magnetic paint prepared in Comparative Example 1, and the magnetic tapes obtained in the present invention (Examples 1 and 2) are the magnetic tapes obtained in Comparative Example 1. In comparison with the above, the RF output and the chroma output are both high, which means that according to the manufacturing method of the present invention, a magnetic recording medium having good dispersibility of magnetic powder and excellent electromagnetic conversion characteristics can be obtained. .

Claims (2)

[Claims] 1. A magnetic coating material is prepared by mixing and dispersing magnetic powder with a binder resin, an organic solvent and other necessary components while subjecting to ultrasonic treatment, and coating the magnetic coating material on a non-magnetic support, A method for manufacturing a magnetic recording medium, which comprises drying to form a magnetic layer 2. The method for producing a magnetic recording medium according to claim 1, wherein the magnetic powder is a needle-shaped fine metal magnetic powder having a major axis diameter of 0.3 μm or less and a coercive force of 1000 oersteds or more.