JPS59172208A - Magnetic powder and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve smoothness of the surface of a magnetic layer, and to contrive to enhance dispersibility of magnetic powder by a method wherein wet treatment of the magnetic powder is performed using an organic solvent containing nitrocellulose of 40 thousand or less of weight-average molecular weight, and is dried to form a film consisting of 40 thousand or less of weight-average molecular weight on the surface of the powdered grain. CONSTITUTION:Surface treatment of magnetic powder according to nitrocellulose of 40 thousand or less of weight-average molecular weight is performed according to a method to dissolve such a kind of nitrocellulose in an organic solvent such as methyl isobutyl ketone, methyl ethyl ketone, benzene, toluene, etc., and after the magnetic powder is dispersed using the proper means of a kneader, etc. in the solution thereof, to perform drying, etc. The amount to be used is made to be in the range of 0.1-30wt% to the magnetic powder, and desirably to use in the range of 0.5-4wt% is favorable. As the magnetic powder, magnetic powder of various kinds widely known in the past such as gamma-Fe2O3 powder, Fe3O4 powder, gamma-Fe2O3 powder containing Co, Fe2O3 powder containing Co, Fe-Ni powder, etc. are broadly contained, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic powder suitable for use in magnets or magnetic recording media, and a method for producing the same, and an object thereof is to provide a magnetic powder with excellent dispersibility.

Magnetic powder is usually kneaded with a binder component, an organic solvent, etc. and then molded into a magnet, or a magnetic paint is prepared by kneading it with a binder component, an organic solvent, and other necessary components, and then It is used as a recording element in magnetic recording media, etc., which is made by coating and drying on a substrate such as a polyester film, and it has good dispersibility and can impart excellent electrical properties to magnets and magnetic recording media. required. However, it is difficult to disperse fine-grained magnetic powder, which is particularly suitable for high-density recording, in a binder component, and the dispersibility of magnetic powder is not sufficiently good. Powders tend to aggregate and are difficult to disperse well.

Therefore, in order to improve the dispersibility of magnetic powder, methods such as coating nitrocellulose on the surface of magnetic powder particles or surface-treating magnetic powder with a low-viscosity dispersant are used to improve the dispersibility of magnetic powder. Nitrocellulose, which has traditionally been used to improve the dispersibility of magnetic powder, has a relatively large weight average molecular weight of 45,000 or more. However, the dispersibility of magnetic powder has not yet been sufficiently improved, and even methods such as treating magnetic powder with a low-viscosity dispersant have not yet sufficiently improved the dispersibility of magnetic powder.
Moreover, when this type of dispersant is used, there are problems such as a decrease in abrasion resistance.

The inventors conducted various studies in view of the current situation, and found that magnetic powder was subjected to a 7EA wet treatment with an organic solvent containing nitrocellulose having a weight average molecular weight of 40,000 or less, and then dried to form a surface of the powder particles. When a coating made of nitrocellulose with a weight average molecular weight of 40,000 or less is formed on the magnetic powder, the dispersibility of the magnetic powder is sufficiently improved, and when this is used for magnetic recording media, the surface smoothness of the magnetic layer becomes even better. It was discovered that excellent magnetic properties or electromagnetic conversion properties can be obtained, and that the magnetic properties of a magnet using the same can be sufficiently improved, leading to the present invention.

The nitrocellulose used in this invention is low molecular weight nitrocellulose with a weight average molecular weight of 40,000 or less. This type of low-molecular-weight nitrocellulose can become highly viscous or gel, but this type of low-molecular-weight nitrocellulose has good affinity with magnetic powder and adheres well to the surface of magnetic powder particles. to form a film and improve the dispersibility of the magnetic powder. Therefore,
If a magnetic layer is formed using magnetic powder coated with this type of nitrocellulose, the surface smoothness of the magnetic layer will be good, and the magnetic properties or electromagnetic conversion properties will be sufficiently improved. As such nitrocellulose, those with a weight average molecular weight of 40,000 or less are preferable, but those with a weight average molecular weight of 3
10,000 or less is more preferably used, and specific examples include, for example, nitrocellulose Seltsva E manufactured by Asahi Kasei Corporation.
Examples include X-2.

The surface treatment of magnetic powder with nitrocellulose having a weight average molecular weight of 40,000 or less is carried out by dissolving this type of nitrocellulose in an organic solvent such as methyl isobutyl ketone, methyl ethyl ketone, benzene, or toluene, and then adding the magnetic powder to this solution. This is carried out by a method such as dispersing using an appropriate means such as a kneader and then drying. The amount used is within the range of 0.1 to 30% by weight based on the magnetic powder,
It is preferable to use it within the range of 0.5 to 4% by weight; if it is too small, the desired effect cannot be obtained, and if it is too large, the mechanical strength of the resulting magnet and magnetic recording medium will deteriorate.

Examples of magnetic powder include γ-Fe203 powder, F
e3O4 powder, Co-containing r-Fe203 powder, Co-containing Fe3O4 powder, CrO2 powder, Fe powder, Co powder,
Various conventionally known magnetic powders such as Fe-Ni powder are widely included.

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 100 parts by weight Nitrocellulose Cerno 2 EX-2 (nitrocellulose manufactured by Asahi Kasei Corporation) Methyl isobutyl ketone A composition of 50% was mixed and dispersed in a kneader to perform surface treatment on the magnetic powder. went. The amount of nitrocellulose Seltsuba EX-2 deposited on the α-Fe magnetic powder obtained by surface treatment in this way was 15
■/g.

Using the α-Fe magnetic powder thus obtained, α-Fe magnetic powder 100 parts by weight Nitrocellulose Seltsuba 20〃EX-2 (nitrocellulose manufactured by Asahi Kasei Corporation) Methyl isobutyl ketone 146〃Toluene
A magnetic coating material was prepared by mixing and dispersing a mixture having a composition of 73 in a ball mill for about 72 hours.

This magnetic paint was applied onto a 10 μm thick polyester film to a dry thickness of about 3.5 μm, dried, surface treated, and then cut to a predetermined width to produce a magnetic tape.

Comparative Example 1 In Example 1, nitrocellulose Seltsuba EX-
α-Fe magnetic powder was surface-treated in the same manner as in Example 1 except that the same amount of nitrocellulose H1/4 was used instead of 2, and this magnetic powder was used as the α-Fe magnetic powder used in Example 1.
A magnetic tape was produced in the same manner as in Example 1, except that the same amount was used in place of the magnetic powder.

Comparative Example 2 In Example 1, nitrocellulose Seltsuba EX-
α-Fe magnetic powder was surface-treated in the same manner as in Example 1 except that the same amount of low-viscosity dispersant was used in place of Example 2, and this magnetic powder was added to the α-Fe magnetic powder used in Example 1. Instead, a magnetic tape was made in the same manner as in Example 1 except that the same amount was used.

When the weight average molecular weight of the nitrocellulose used in Example 1 and Comparative Example 1 was measured under the following conditions, the nitrocellulose Seltsuba EX-2 used in Example 1 was 2.
3900, nitrocellulose H1,/4 is 53000
Met.

<Measurement conditions for weight average molecular weight> Equipment Nigel permeation chromatograph, GPC-244
(WATER3) Data processing: TRC GPC data processing system Column: TSK-GEL-GMHe (2) Solvent: Tetrahydrofuran Flow rate: 2 mA/min Temperature: 25°C Sample concentration: 0.2% (wt/vol) Solubility: Complete melt filtration: 0.5 μm FHLP FILTER (MI
LL T PORE) Injection amount: 0.5mj2 Detector: Differential refractive index detector, R-401 (WATE
R) Molecular weight calibration: POLYSTYRENE standard In addition, the viscosity of the magnetic paint prepared in Example 1 and each comparative example was measured, and the surface smoothness and sensitivity of the magnetic layer were further measured for the magnetic tapes obtained in Example 1 and each comparative example. was measured. Note that surface smoothness and sensitivity were measured by the following methods.

0 <Surface smoothness> Using a stylus type roughness meter, the surface roughness of the magnetic layer was measured at a stylus speed of 0.06 cm/sec and a cutoff of 0.08 mm.

L, ^) was measured, and the quality of the surface smoothness was determined based on the relative value calculated according to the following formula with reference to that of Example 1.

<Sensitivity> The 5 MHz output (dB) of each sample was determined using the example 1 as a reference (OdB).

The table below shows the results.

As is clear from the table above, the magnetic paint obtained in Example 1 did not thicken or gel, and the magnetic tape obtained in Example 1 was superior to the magnetic tapes obtained in Comparative Examples 1 and 2. ,
The surface smoothness is good and the sensitivity is high. Therefore, according to this invention, the dispersibility of the magnetic powder is sufficiently improved, and as a result, the surface smoothness of the magnetic layer is also good, and the electromagnetic conversion characteristics are improved. I know that there is.

Claims (1)

[Claims] 1. Magnetic powder comprising a coating made of nitrocellulose having a weight average molecular weight of 40,000 or less on the surface of the powder particles 2. Magnetic powder containing nitrocellulose having a weight average molecular weight of 40,000 or less After wet treatment with an organic solvent,
A method for producing magnetic powder, which comprises drying to form a coating made of nitrocellulose having a weight average molecular weight of 40,000 or less on the surface of the powder particles.