JPH1021538A - Kneading method for magnetic powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a kneading method for a magnetic powder by which a finely pulverized magnetic powder can be uniformly dispersed without depending on the size and kind of a kneading machine. SOLUTION: When a magnetic coating material containing a magnetic powder having <=1.0μm average major axial length is to be kneaded, an extruder or co-kneader is used. The coating material is kneaded under such conditions that the driving force Y(Watt/g/min) to drive the machine per unit weight of the magnetic coating material and the average axial length X(μm) of the powder included in the magnetic coating material satisfy -7.3logX<=Y<=-21.9logX. Where, Y=a/b and (a) is the powder (Watt) of the extruder or co-kneader and (b) is the supply amt. (g/min) of the magnetic coating material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for kneading magnetic powder used for a coating type magnetic recording medium or the like.

[0002]

2. Description of the Related Art In recent years, high-density recording has always been required for magnetic recording media. Accordingly, the recording wavelength on magnetic tapes has been shortened, and the particle size of magnetic powder, which is responsible for magnetic recording, has been reduced. It is miniaturized.

On the other hand, in the production process of a coating type magnetic recording medium, there is a step of applying the above-mentioned magnetic powder on a carrier such as a base film, and a magnetic coating material in which the magnetic powder is uniformly dispersed in a binder such as a binder. Must be made. However, as the magnetic powder becomes finer, the specific surface area increases and the cohesiveness between the particles increases, and since the number of particles in a unit volume increases, the viscosity of the magnetic paint increases, making uniform dispersion difficult. Becomes That is, a magnetic recording medium having good magnetic properties cannot be obtained.

Accordingly, various methods have been studied for a kneading step of kneading magnetic powder into a medium such as a binder.
Conventionally, ball mills, kneaders, and sand mills have been used, but these cannot be used with magnetic powders, and co-kneaders and extruders are currently mainly studied.

[0005]

However, as the magnetic powder becomes finer, sufficient dispersion cannot be obtained even with a co-kneader or extruder, and the squareness ratio (Rs) of the magnetic recording medium is reduced and the suddenness is reduced. Increase in frequency variation (SFD),
Problems such as a decrease in output have emerged.

The present invention has been proposed in order to solve the above-mentioned problems, and it has been proposed to uniformly disperse magnetic powder even for finely divided magnetic powder regardless of the size and type of the kneading machine. It is an object of the present invention to provide a method for kneading magnetic powder to be dispersed.

[0007]

As a result, the present inventors have studied the requirements necessary to obtain a sufficient dispersion of magnetic powder using a co-kneader or extruder. By optimizing the power per unit weight of the magnetic paint, which has not been studied, according to the average major axis length of the magnetic powder, it has been found that the magnetic powder can be uniformly dispersed.

[0008] The method of kneading magnetic powder according to the present invention has been proposed based on such knowledge, and when kneading a magnetic coating material containing magnetic powder having an average major axis length of 1.0 µm or less, it is necessary to use an extruding method. Using a ruder or a co-kneader, the power Y (Watt / g / min) per unit weight of the magnetic paint for driving them and the average major axis length X (μm) of the magnetic powder contained in the magnetic paint are defined as -7.3 log X ≦ Y ≦ −21.9 log X [where Y = a / b, a is the power of extruder or co-kneader (unit: Watt), and b is the supply amount of magnetic paint (unit: g / min). ] Is set in the range.

As described above, the method for kneading magnetic powder according to the present invention uses an extruder or a co-kneader and optimizes the power Y per unit weight of the magnetic paint in accordance with the average major axis length X of the magnetic powder. Thereby, the magnetic powder can be uniformly dispersed.

When the power Y per unit of the magnetic paint is smaller than the above range, the dispersion is not sufficiently performed. When the power Y is larger than the above range, the quality of the magnetic powder is deteriorated, and in the obtained magnetic recording medium, Deterioration of magnetic properties such as a decrease in squareness ratio (Rs), an increase in sudden frequency fluctuation (SFD), and a decrease in output is observed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The method for kneading magnetic powder according to the present invention uses an extruder or a co-kneader when kneading a magnetic coating material containing a magnetic powder having an average major axis length of 1.0 μm or less. The power Y (Watt / g / min) per unit weight of the magnetic paint and the average major axis length X (μm) of the magnetic powder contained in the magnetic paint are calculated as follows: −7.3 log X ≦ Y ≦ −21.9 log X [where Y = A / b, a is the power of extruder or co-kneader (unit: Watt), and b is the supply amount of magnetic paint (unit: g / min). ] Range.

In order to obtain particularly good dispersion of the magnetic powder, the power Y (Watt / g / min) per unit weight of the magnetic paint for driving the extruder or the kneader and the average length of the magnetic powder contained in the magnetic paint are required. It is preferable to set the axial length X (μm) in the range of −12.8 logX ≦ Y ≦ −16.4 logX.

The power a (Watt) is calculated based on the magnetic paint b
(G / min) is the value obtained by subtracting the power required to drive the extruder or co-kneader when the magnetic paint is not supplied under the same conditions from the power required to drive the extruder or co-kneader when supplying (g / min). When the average major axis length X of the magnetic powder is 1.0 μm,
The power a is set to 0.

An extruder used as a kneader utilizes the principle of dispersing a magnetic paint by a shear force generated by rotation of a screw, and extrudes the magnetic paint in the same direction by engaging two screws in a deep groove. A typical example is a twin-screw extruder that performs kneading. Others have a single screw.

[0015] The co-kneader is in principle the same as the extruder, but the screw length is short, and thus the degree of mixing is usually lower than in the extruder.

As described above, the method of kneading magnetic powder according to the present invention uses an extruder or a co-kneader and optimizes the power Y per unit weight of the magnetic paint according to the average major axis length X of the magnetic powder. Thereby, the magnetic powder is in a state of being uniformly dispersed. In this kneading method, since the dispersion state of the magnetic powder is determined by the average major axis length X of the magnetic powder and the power Y per unit weight of the magnetic paint, it is possible to set the kneading conditions in advance for unknown magnetic powder. It is possible to set kneading conditions independent of the type and size of the kneader. further,
This kneading method is industrially useful because it is possible to predict whether or not conventional equipment can cope with the kneading of magnetic powder to be introduced.

In the magnetic recording medium having a magnetic layer formed by applying the above-described magnetic paint on a base film and drying, the magnetic powder is uniformly dispersed in the magnetic layer.
Excellent magnetic properties.

Here, the composition of the magnetic powder and the magnetic paint used is not particularly limited, but a binder serving as a binder, and a dispersant used as needed,
Conventionally known abrasives, antistatic agents, rust preventives, and solvents used for preparing these magnetic paints can be used.

As the magnetic powder, ferromagnetic iron oxide-based magnetic powder,
Examples include ferromagnetic chromium dioxide, ferromagnetic alloy magnetic powder, and iron nitride.

As the ferromagnetic iron oxide magnetic powder, maghemite (γ-Fe ₂ O ₃ ), magnetite (Fe ₃ O ₄ ), and solid solutions thereof can be used. Further, cobalt may be added to these ferromagnetic iron oxide magnetic powders for the purpose of improving coercive force.

As the ferromagnetic chromium dioxide, CrO ₂ ,
Alternatively, for the purpose of improving coercive force, Ru, Sn,
A material to which at least one of Te, Sb, Fe, Ti, V, and Mn is added can be used.

The ferromagnetic alloy magnetic powder includes Fe, Co,
Ni, Fe-Co, Fe-Ni, Fe-Co-Ni, F
e-Co-B, Fe-Co-Cr-B, Mn-Bi, M
n-Al, Fe-Co-V, etc. can be used, and Al, Si, Ti, Cr, M
Metal components such as n, Cu, and Zn may be added.

As the binder, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride Acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl chloride, vinylidene chloride-acrylonitrile copolymer Polymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, Rukido resins, urea - formaldehyde resin, or mixtures thereof. Magnetic powder is dispersed in these binders to form a magnetic layer.

Organic solvents for preparing the magnetic paint include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, and esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and glycol monoethyl ether ether. Solvent, glycol dimethyl ether, glycol monoethyl ether,
Glycol ether solvents such as dioxane, benzene,
Uses aromatic hydrocarbon solvents such as toluene and xylene, aliphatic hydrocarbon solvents such as hexane, and organic chlorine compound solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. it can.

[0025]

EXAMPLE An example in which a magnetic tape was manufactured by applying the present invention will be described below based on specific experimental results.

Example 1 Using a magnetic powder having an average major axis length of 0.35 μm, a magnetic paint for forming a magnetic layer was prepared in accordance with the composition shown in Composition 1.

<Composition 1> Magnetic powder 1000 kg Urethane resin 130 kg Vinyl chloride resin 60 kg Alumina powder 60 kg Carbon powder 20 kg Dispersant 30 kg Solvent (methyl ethyl ketone: toluene: cyclohexanone = 5: 3: 2) Magnetic paint solids 71.8% The magnetic paint was kneaded with an extruder (paddle pattern A) according to the kneading conditions shown in Table 1. Then, the obtained magnetic paint was applied on a polyethylene terephthalate film and dried, subjected to a magnetic field orientation treatment, subjected to a calender treatment, and cut into 1/2 inch width to prepare a sample tape.

It should be noted that the power a
Are different because the rotation speeds of the screws are different.

[0029]

[Table 1]

Example 2 Paddle pattern B using the same extruder as in Example 1
The kneading of the magnetic coating material was carried out according to the kneading conditions shown in Table 2 in the same manner as in Example 1 except for using, to prepare a sample tape.

Example 3 Except that a larger extruder was used than in Example 1,
In the same manner as in Example 1, kneading was performed according to the kneading conditions shown in Table 2 to prepare a sample tape.

[0032]

[Table 2]

Example 4 Using a magnetic powder having an average major axis length of 0.08 μm, a magnetic paint was prepared according to the composition shown in Composition 1. Except that this magnetic paint was used, Table 3 was used in the same manner as in Example 1.
The kneading was performed according to the kneading conditions shown in Table 1 to produce a sample tape.

[0034]

[Table 3]

Example 5 Using a magnetic powder having an average major axis length of 0.25 μm, a magnetic paint was prepared according to the composition shown in Composition 2. Except that this magnetic paint was used, Table 4 was used in the same manner as in Example 1.
The kneading was performed according to the kneading conditions shown in Table 1 to produce a sample tape.

<Composition 2> Magnetic powder 1000 kg Vinyl chloride resin 140 kg Urethane resin 60 kg Alumina powder 100 kg Additive 60 kg Solvent (methyl ethyl ketone: toluene: cyclohexanone = 5: 3: 2) Magnetic paint solids 74.2%

[0037]

[Table 4]

Comparative Example 1 Kneading was performed in the same manner as in Example 3 except that the power and the supply amount of the magnetic paint were changed, according to the kneading conditions shown in Table 5.
A sample tape was prepared.

Comparative Example 2 A sample tape was prepared by kneading according to the kneading conditions shown in Table 5 in the same manner as in Example 5 except that the power and the supply amount of the magnetic paint were changed.

[0040]

[Table 5]

With respect to the sample tapes of Examples 1 to 5 and Comparative Examples 1 and 2 produced as described above, the squareness ratio (Rs) and the sudden frequency fluctuation (SFD) were measured. The sample tape was evaluated. In the evaluation of the sample tape, the mark 極 め て is extremely good, the mark 良好 is good, the mark-is normal, and the mark X is bad. These results are shown in Tables 1 to 5 and FIG. 1 together with kneading conditions.

The squareness ratio (Rs) was measured by a sample vibration magnetometer. The sudden frequency fluctuation (SFD) was measured by drawing a hysteresis loop of the corresponding sample tape using a magnetic property measuring device (VSM) and taking a derivative of the loop inclination at that time.

As can be seen from FIG. 1, there is a correlation between the average major axis length X of the magnetic powder and the power Y per unit weight of the magnetic paint, and the range in which the magnetic powder takes a good dispersion state (−
7.3 logX ≦ Y ≦ −21.9 logX).

Further, it can be seen that, in order to obtain a particularly good dispersion of the magnetic powder, kneading is preferably performed within the range of -12.8 logX ≦ Y ≦ −16.4 logX.

As can be seen from Examples 2 and 3, the dispersion state of the magnetic powder is determined by the average long axis length X of the magnetic powder,
Since it is determined by the power Y per unit weight of the magnetic paint,
It does not change with the paddle pattern or the size of the device. Therefore, according to this kneading method, kneading conditions can be set in advance even for an unknown magnetic powder, and kneading conditions can be set regardless of the type and size of the kneader. Further, according to the kneading method, it is possible to predict whether or not the conventional equipment can cope with the kneading of the magnetic powder to be introduced.

[0046]

As is apparent from the above description, according to the magnetic powder kneading method of the present invention, the power per unit weight of the magnetic paint is optimized according to the average major axis length of the magnetic powder. Thereby, the magnetic powder can be in a good dispersion state in the magnetic paint. That is, a magnetic recording medium having good magnetic properties can be obtained.

Further, the method for kneading magnetic powder according to the present invention comprises:
The dispersion state of the magnetic powder is determined by the average major axis length of the magnetic powder and the power per unit weight of the magnetic paint, and does not change depending on the size and type of the device. Therefore, according to this kneading method, kneading conditions can be set in advance even for unknown magnetic powder, and kneading conditions can be set regardless of the type and size of the kneader. Further, according to this kneading method, it is possible to predict whether or not the conventional equipment can cope with the kneading of the fine particle magnetic powder to be introduced.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between an average major axis length of magnetic powder and power per unit weight of magnetic paint.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H01F 1/11 H01F 1/11 H (72) Inventor Takahashi etc. 6-7 Kita Shinagawa, Shinagawa-ku, Tokyo No. 35 Inside Sony Corporation

Claims (2)

[Claims] When kneading a magnetic coating material containing a magnetic powder having an average major axis length of 1.0 μm or less, an extruder or a kneader is used, and a power Y (W) per unit weight of the magnetic coating material for driving these is used.
att / g / min) and the average major axis length X (μm) of the magnetic powder contained in the magnetic paint are −7.3 log X ≦ Y ≦ −21.9 log X [where Y = a / b and a is The power (unit: Watt) of the ruder or co-kneader, and b is the supply amount (unit: g / min) of the magnetic paint. ] A method for kneading a magnetic paint, wherein the method is set in the following range: 2. A power Y (Watt / g / watt / g / unit) of magnetic paint for driving an extruder or a kneader.
Min.) And the average major axis length X (μ) of the magnetic powder contained in the magnetic paint.
m) is set in the range of -12.8 logX ≦ Y ≦ −16.4 logX.