JPH01251602A - Method of treating magnetic iron oxide powder - Google Patents

Abstract

PURPOSE:To enable entangled particles to be disentangled sufficiently and to improve magnetic properties, by introducing magnetic iron oxide powder and a dispersing agent in a pan of an edge runner mill, that is a milling and blending apparatus principally composed of a pair of runner rollers and the pan, so that the agglomerated particles of the powder are disagglomerated sufficiently while they are directly blended with the dispersing agent. CONSTITUTION:Magnetic iron oxide powder is introduced in a pan 2 together with a dispersing agent 4. A roller assembly consisting of a pair of runner rollers 1 and a shaft 3 connecting these runner rollers 1 is rotated over the mixture, so that agglomerated magnetic iron oxide powder is disagglomerated and blended well with the dispersing agent. The magnetic iron oxide powder in the pan 2 is pressurized by the weight of the runner rollers 1 or by a pressurizing means through the shaft 3. The powder is subjected to preliminary treatments including milling while pressure of 10kg/cm or less is exerted on the rollers until bulk density of the powder becomes 1.05times or more as high as that of untreated magnetic iron oxide powder. The preliminary treated powder is then treated under a pressure of 10kg/cm or over.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for treating magnetic iron oxide powder to eliminate mutual agglomeration of the powder, and in particular to a method for treating magnetic iron oxide powder suitable for use in manufacturing magnetic recording media. This invention relates to a method for treating iron powder.
- (Prior art) Magnetic iron oxide powder used in magnetic recording media is r-F
e20a, Feso, powder, magnetic iron oxide powder of intermediate oxides of these, or these iron oxide powders containing CO or an oxide containing Co as a component in the particles or modified on the surface. Since these powders undergo high-temperature heat treatments such as dehydration, post-dehydration heat treatment, reduction, and oxidation during the manufacturing process, sintering between particles is likely to occur.

In particular, in recent years, particles have been made smaller in order to increase the density of recording, which has the effect of reducing noise, but as particles become extremely miniaturized, particles become tightly entangled with each other and form clumps. The problem arises that it is difficult to unravel.

The clumps created by this entanglement of particles deteriorate the dispersibility during the subsequent production of paint by dispersing into a binder, and the tape manufactured using the clumps has deteriorated orientation and filling properties. .

Conventionally, in order to disentangle the particles of magnetic iron oxide powder, a method of pulverizing the particles using a pulverizer having a normal kneading ability is known.

Edge Runner is said to be effective as a crusher for this purpose; for example, Shinto Kogyo's ``Mix Muller''
The "sand mill" of Matsumoto Foundry Iron Works is used. JP-A No. 61-243938 discloses a method of preparing magnetic iron oxide powder for magnetic recording media by coating magnetic iron oxide powder with a surfactant dissolved in water, filtering and drying the powder, and pulverizing it with a mixed muller. A manufacturing method is shown, but since the coating is done with a surfactant dissolved in water, the process is long and inefficient. In addition, in order for the magnetic recording medium manufactured using the magnetic iron oxide powder treated by this method to have the gloss of the magnetic layer and good electromagnetic conversion characteristics, the magnetic iron oxide powder must be 100% coated with the surfactant. However, in order to cover 100% of the magnetic iron oxide powder with the surfactant, a large amount of surfactant is required, and it is difficult to control the amount.

(Problems to be Solved by the Invention) The present invention attempts to sufficiently disentangle particles of magnetic iron oxide powder, thereby obtaining a magnetic recording medium with good magnetic properties. .

(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention made extensive studies and found that a dispersant works effectively in edge runner treatment. It has been found that the effect can be sufficiently achieved even when sprinkled with water, and in particular, it has been found that better results can be obtained than those using a dispersant dissolved or dispersed in water.

That is, in the present invention, magnetic iron oxide powder and a dispersant are placed in the tray of Edge Runner, which is a crushing and mixing device whose main parts are a pair of runner rolls and a tray, and the magnetic iron oxide powder is mixed by the runner rolls. This method of treating magnetic iron oxide powder is characterized by directly mixing it with the dispersant while loosening the agglomerated particles.

In addition, the present inventors further studied the conditions for achieving the above object, and found that the destruction of agglomerated particles in magnetic iron oxide powder by the edge runner described in the above publication is due to the force applied to the particles. It is caused when the force that maintains the shape of iron-based particles is overcome.For example, in the case of clay work, the clay is pulled out from between the fingers and the stress between the particles is relaxed, resulting in particle breakage. It is assumed that this will help avoid this.

As a result of various studies based on this idea, we found that when treating magnetic iron oxide powder with an edge runner, it is necessary to use a dispersant, and to use it directly without using water or organic solvents, first to destroy the particles. If the treatment is started under low pressure conditions and the dispersant is appropriately distributed around the magnetic iron oxide particles, even if the treatment is continued with strong force, the particles will not be substantially destroyed. We have discovered that it is possible to loosen pseudo aggregation while maintaining the shape of particles without causing it, and have arrived at the second invention of the present application.

That is, in the second invention of the present application, magnetic iron oxide powder is directly sprinkled with a dispersant, and in the edge runner, as a first step, from the start of treatment, the bulk density of the magnetic iron oxide powder is reduced to that of the untreated magnetic iron oxide powder. After performing preliminary treatment including crushing by applying a pressure of 10 kg/cm or less to the roll until the bulk density becomes 1.05 times or more,
The second step is a method for treating magnetic iron oxide powder, which involves treating at a pressure of 10 kg/am or higher.

When coating magnetic iron oxide powder with a dispersant using a solution in which the dispersant is dissolved in a solvent as in the prior art, the powder can be coated with the dispersant evenly, but after coating, the solvent must be removed by evaporation. In the present invention, even without such measures, the powder is sufficiently coated with the dispersant during the edge runner treatment.

The edge runner is a pulverizing and mixing device whose main parts are a pair of runner rolls 1 and a saucer 2, as shown in FIG.

In Fig. 2, magnetic iron oxide powder and dispersant 4 are placed in a saucer 2, and agglomeration is carried out by rotating a roll consisting of a pair of runner rolls 1 and a shaft 3 connecting the runner rolls 1 from above. At the same time as the magnetic iron oxide powder is loosened, it is mixed with a dispersant. Pressure can be applied to the magnetic iron oxide powder placed in the saucer by the weight of the runner roll or by pressure means (not shown) applied through the shaft 3. Further, the object of the present invention can also be achieved with a structure in which the runner roll and shaft are fixed and the tray is rotatable.

In addition, when putting magnetic iron oxide powder and a dispersant into a saucer, it is preferable to first put a part of the magnetic iron oxide powder into the saucer, then put the dispersant, and finally put the remaining magnetic iron oxide powder. By doing so, the dispersant does not directly adhere to the tray, and the magnetic iron oxide powder can be effectively deagglomerated and mixed with the dispersant.

In addition, in the second invention of the present application, as a first step, a preliminary treatment including crushing is performed with a weak pressure, and as a second step, a treatment is performed with a strong pressure. Although it is possible to change the roll from light to heavy, it is more efficient to use a device that can adjust the pressure from the outside on the shaft that holds the roll. The pressure is preferably 0.5-10 kg/cm in the first stage and 10-80 kg/am in the second stage.

Dispersants used in the present invention include fatty acids having 7 to 22 carbon atoms (e.g., caprylic acid, capric acid, lauric acid, myristic acid, palmyric acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, lyrinnic acid, stearolic acid), metal soaps consisting of the above fatty acids and alkali acid metals (e.g. lithium, sodium, potassium, barium), amine salts of the above fatty acids, esters of the above fatty acids and hydrogen of their compounds. Compounds in which part or all of are substituted with fluorine atoms, amides of the above fatty acids, primary, secondary, tertiary, and quaternary aliphatic amines or salts thereof, higher alcohols, polyalkylene oxide alkyls Phosphate esters, alkyl phosphate esters, or salts thereof, alkyl borate esters, or salts thereof, sarcosinates, alkyl ether esters, trialkyl polyolefins, oxyquaternary ammonium salts and lecithin, alkyl betaines, polyalkylene oxide monoalkyl ethers, Polyalkylene oxide dialkyl ether, polyalkylene oxide, carboxylic acid ester of monoalkyl ether, polyalkylene oxide monoacyl ester, polyalkylene oxide diester, sulfosuccinic acid ester, organic compound having a mercapto group, phosphonic acid, and sulfonic acid compound, Surfactants derived from amino acids, polyvalent carboxylic acid esters, alkyl sulfates or their salts, alkyl borates or their salts, alkyl orthotitanates, alkyl silicates, alkyl jetanolamines, alkenyl sulfates or a salt thereof, an alkenyl borate or a salt thereof, an alkenyl orthotitanate, an alkenyl silicate, an alkenyl jetanolamine, and other known dispersants.

When using a dispersant, it is 0.1 to 20 parts by weight, preferably 0.4 parts by weight, per 100 parts by weight of the ferromagnetic powder used.
It is used in a range of 10 parts by weight.

Preferred specific examples of commercially available dispersants are as follows.

The magnetic iron oxide powder obtained by the treatment according to the present invention has an increased bulk density, and due to this increase in bulk density, it can be used as a pretreatment for preparing magnetic paints.
By adding a binder to this magnetic iron oxide powder, the amount of binder required during kneading with an oven kneader or the like is extremely small, and strong kneading can be achieved. Therefore, the dispersion time for making the magnetic paint can be shortened, and the dispersion time can be shortened to achieve the same level of gloss when applying the magnetic paint.

Furthermore, a magnetic recording medium manufactured by coating using magnetic iron oxide powder treated in this way has a saturation magnetic flux density Bm
and residual magnetic flux density Br both increase.

〔Example〕

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Example Magnetic iron oxide coated with Co (average particle size 063 μm, axial ratio 1:10, coercive force 6100)
eSTD (bulk density) 0.92 g/crl, BE
Specific surface area by T method: 31 m'/g) Edge Runner (Matsumoto Cast Iron Works New Manufacturer, MPUV type, 5 horsepower) Treatment method 1st stage (pre-kneading) Presence/absence of additive (dispersant) Presence/absence of pressure 20.40.60 kg/ The conditions and results for each treatment are listed separately in the table below.

Magnetic iron oxide coated with Co on the surface 100 parts Vinyl chloride/vinyl acetate/vinyl alcohol copolymer (mole ratio 92:3:5, degree of polymerization 420) 15 parts Polyester polyurethane (molecules max. 130,000) 6 Part: Dimethylpolysiloxane (degree of polymerization: about 60): 0.5 parts: Methyl ethyl ketone: 220 parts: Cyclohexanone: 165 parts The above composition was cross-dispersed in a ball mill for 24 hours, and filtered through a filter having an average pore size of 3 μm to obtain a magnetic layer coating solution. was prepared. The obtained coating liquid (magnetic paint) was applied onto a polyethylene terephthalate film with a thickness of 20μ using a reverse roll so that the dry thickness was 5.5μ.
Magnetic field orientation treatment was performed using an electromagnet of 0 Gauss, followed by drying to obtain a magnetic sheet. The obtained magnetic sheet was sampled and measured using a vibrating sample magnetometer VSM-3 model (manufactured by Toshiba Industries, Ltd.).
Saturation magnetic flux density Bm and residual magnetic flux density Br were measured in the orientation direction at m 5 KOe. The measurement results are shown in the table below.

Table 1 Also, based on FIG. 1, the changes in the bulk density TD of the magnetic iron oxide powder due to the pressure of the edge runner when treated with an edge runner without a dispersant and with open dispersion are shown in Table 1.
As shown in the figure. As can be seen from FIG. 1, the TD value when treated with a dispersant is much higher than the TD value when treated without a dispersant.

Measurement of glossiness was measured using a digital glossmeter manufactured by Suga Test Instruments Co., Ltd. and specular reflectance at 45°.

〔Effect of the invention〕

According to the present invention, magnetic iron oxide powder with high bulk density can be obtained. Furthermore, magnetic recording media made using magnetic iron oxide powder treated according to the present invention have both high saturation magnetic flux density and high residual magnetic flux density.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing how the bulk density TD of magnetic iron oxide powder changes due to the pressure of the edge runner when the magnetic iron oxide powder is treated with an edge runner without a dispersant or with open dispersion. 2 is a schematic diagram of the main parts of the edge runner used in the present invention. A: No dispersant, B: Open dispersion, 1: Runner roll, 2: Receiver, 3: Shaft, 4: Magnetic iron oxide powder and dispersant. Figure 1

Claims (2)

[Claims] (1) Magnetic iron oxide powder and dispersant are placed in the trays of an edge runner, which is a grinding and mixing device whose main parts include two runner rolls and a tray, and the magnetic iron oxide powder is crushed by the runner rolls. A method for treating magnetic iron oxide powder, which comprises directly mixing the agglomerated particles with the dispersant while loosening them. (2) Magnetic iron oxide powder is directly sprinkled with a dispersant, and as a first step, the bulk density of the magnetic iron oxide powder is 1.0% of the bulk density of the untreated magnetic iron oxide powder from the start of the treatment in the edge runner. After performing preliminary processing including crushing by applying a pressure of 10 kg/cm or less to the roll until the size is 0.5 times or more, as a second step, 10K
A method for processing magnetic iron oxide powder, which comprises processing at a pressure of g/cm or more.