JPS6251026A - Magnetic powder for high-density magnetic recording and magnetic recording medium using said powder - Google Patents

Abstract

PURPOSE:To improve a temp. characteristic by incorporating a prescribed ratio of an Sn element into hexagonal ferrite. CONSTITUTION:This magnetic powder consists of a hexagonal ferrite crystal having 0.01-0.2mum average grain size and 200-2,000 Oe coercive force and the hexagonal ferrite contains 0.1-1.0 piece of Sn element for each one chemical formula together with the substitution element for controlling the coercive force. The reason for limiting the content of the Sn element in the hexagonal barium ferrite to a 0.1-1.0 piece range lies in that the temp. coefft. of Hc is not substantially improved if the content of the Sn element is below 0.1 and conversely the temp. coefft. of Hc is improved but the saturation magnetiza tion of the magnetic powder is considerably deteriorated and the functions as a magnetic recording material are debased when the content of the Sn ele ment exceeds 1.0.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a magnetic powder for high-density magnetic recording and a magnetic recording medium using the same.

[Technical background of the invention and its problems] A coated magnetic recording medium is a magnetic recording medium mainly composed of a non-magnetic support such as polyethylene terephthalate, magnetic fine particles provided on the support, and a resin binder. It is composed of layers.

As magnetic particles, γFe203, cro
Acicular magnetic particles such as 2 and co-7're203 are widely used. Recently, in order to significantly improve magnetic recording density, there has been a strong demand for magnetic recording media that can perform perpendicular magnetization recording, and ultrafine hexagonal ferrite magnetic particles have been used as magnetic recording media suitable for this purpose. It has been discovered that high-density recording is possible.

Incidentally, even in a magnetic recording medium using the above-mentioned hexagonal ferrite as magnetic fine particles, the magnetic properties thereof need to be stable against temperature changes. In other words, if the magnetic properties change significantly with temperature, the recording and reproducing characteristics of the magnetic recording medium will vary significantly with changes in the ambient temperature during use, causing a practical problem. A magnetic recording medium using hexagonal ferrite exhibits a characteristic temperature characteristic in which the value of coercive force (Ho) increases as the temperature rises even at around room temperature, making it a relatively stable medium against temperature changes. .

However, from a practical standpoint, even higher temperature stability has been desired for this hexagonal ferrite.

[Purpose of the Invention] In order to address the above-mentioned circumstances, the present inventors have conducted intensive research to improve the temperature characteristics of coercive force of magnetic recording media using hexagonal ferrite fine particles. It has been found that temperature characteristics are improved by incorporating a predetermined amount of 3n into crystalline ferrite.

The present invention was made based on this knowledge, and an object of the present invention is to provide a magnetic powder for high-density magnetic recording with improved temperature characteristics and a magnetic recording medium using the same.

[Summary of the invention] That is, the present invention provides an average particle size o, oi ~ 0.2 μm
Magnetic powder for high-density magnetic recording, consisting of hexagonal ferrite crystals having a coercive force of 200 to 2000 Oe, and containing 0.1 to 1.0 Sn atoms per chemical formula of the hexagonal ferrite; This invention relates to a magnetic recording medium attached to the surface of a support.

The hexagonal ferrite crystal used in the present invention includes:
For example, type M (Ha(lnetoplumbite ti
pe), W-type hexagonal barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, or solid solutions or ion-substituted products thereof. As the hexagonal barium ferrite used in the present invention, those having a coercive force of 200 to 2000 Qe among these macrogonal barium ferrite crystals are used.

The average grain size of the above-mentioned -axis anisotropic hexagonal barium ferrite crystal was limited to the range of 0.02 to 0.2 μm because 0
．． If it is less than 0.02 μm, the magnetization and coercive force will decrease, and the reproduction output of the magnetic recording medium will decrease. On the other hand, if it exceeds 0.2 μm, the coercive force will decrease and noise during reproduction will be significant during high-density recording. To become.

Generally, in hexagonal barium ferrite, HC
The temperature coefficient (ΔHc/Hc)/ΔT shows a positive value (
ΔHc indicates a change in HC corresponding to a change in measured temperature ΔT. ). When Sn is added to this orthogonal barium ferrite, the temperature coefficient of HC decreases as the amount added increases, passes through zero, and then takes a negative value.

Therefore, by controlling the 3n content within a certain range, a magnetic powder with a smaller temperature change in HC than conventional hexagonal barium ferrite can be obtained. In the present invention, the Sn content of the hexagonal barium ferrite is limited to a range of 0.1 to 1.0 per chemical formula, because if the 3n content is less than 0.1, the temperature coefficient of Hc is insufficient. On the other hand, if the 3n content exceeds 1.0, the temperature coefficient of 1-1c will be improved, but the saturation magnetization of the magnetic powder will drop significantly, and its function as a magnetic recording material will deteriorate. This is to put it away.

The hexagonal barium ferrite of the present invention is usually used as a magnetic recording medium by being coated on the surface of a supporting substrate together with a binder resin. Examples of the binder resin that constitutes the magnetic layer together with the magnetic fine particles include vinyl chloride-vinyl acetate copolymer, vinylidene chloride copolymer, acrylic ester copolymer, polyvinyl butyral resin, polyurethane resin, and polyester resin. Resins, cellulose derivatives, epoxy resins, or mixtures of two or more of these are used. Further, in addition to the magnetic fine particles and the binder resin, additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, and the like can be appropriately contained in the magnetic layer as necessary.

[Embodiments of the invention] Next, examples of the present invention will be described.

Example 1 M-type holegonal 3a ferrite BaF C12-2X T substituted with Ti and Co! Ferrite B aF 01 in which part of Ti in X COX 019 is replaced with Sn
2-2(X+Y) T' X S nY C0X+Y
In 019, Co substitution amount (number of atoms per chemical formula) X+V7! Four types of ferrite fine particles having a constant i-0.85 and a Sn substitution amount in the range of 0.1 to 0.7 were produced by the following method.

First, Bad1Fe20, which was formulated to constitute the above-mentioned 3a fluorite composition, was added to B2O3/BaO glass.
3, add TiO2,5n02, COO component, 130
After melting at a temperature of 0° C. or higher, the glass was rapidly cooled by rolling to produce a glass containing the above components. Next, heat this glass to 800℃.
By heating for 4 hours at
Ba ferrite substituted with Sn and CO was precipitated. Finally, this glass was washed with acetic acid to obtain Ba ferrite magnetic powder. The average particle size of the obtained magnetic powder is approximately 800
It was a person.

Next, a magnetic paint having the following composition was prepared using these 3a flute light particles (parts indicate parts by weight).

Ti-3n-Co substituted Ba ferrite particles 100 parts Vinyl chloride-vinyl acetate copolymer 10 parts Polyurethane 10 parts Aluminum oxide
two part lubricant
1.5 Partial dispersant (lecithin)
2 parts methyl ethyl ketone 70
Part toluene 70 parts Cyclohexanone 40 parts Hardening agent
5 parts The five types of paint thus obtained were applied onto a polyethylene terephthalate film with a thickness of 15 μm, and calendering and slitting were performed to form a magnetic layer with a thickness of 3.5 μm to form a magnetic tape. Example 2 in which Go-3n@ exchanged Ba ferrite B a F C12,,2XCOX S nx 01
In g, four types of Ba with substitutions ranging from 10.5 to 1.2
Ferrite fine particles were produced in the same manner as in Example 1.

The average particle size was approximately 800-900 particles.

These samples were made into paint using the same process as in Example 1,
Created magnetic tape.

Comparative Example Co-T i-substituted 3a ferrite BaFe12-2XT fXCoXo19,
Five kinds of magnetic powder samples having a range of 0.71 to 0.84 were prepared in the same manner as in the above example.

The average particle size of these samples was approximately 800 particles.

These samples were made into paint by the same process as in the above example, and magnetic tapes were produced.

For each magnetic tape obtained in Example 1, Example 2, and Comparative Example, HC at room temperature and temperature change (Δ)lc/HC)/ΔT in Hc at 20 to 100°C were measured. The results are shown in Tables 1, 2 and 3.

Note that Tables 1, 2, and 3 are for Example 1, respectively.
．． These are the measurement results for magnetic tapes 2 and 3.

(Hereinafter in the margin) (Hereinafter in the margin) The temperature coefficient of HC of the 3n-added fluorite fine particles in Table 1 (Example 1) and Table 2 (Example 2) was replaced with Ti-co in Table 3 (Comparative example). When comparing samples with a value of -1c (almost the same as that of 3a ferrite), it is clear that the absolute value of the temperature coefficient of HC is smaller in the 5n-doped Ba ferrite than in the comparative example, and the temperature of Hc is smaller than that of the comparative example Nori. It can be seen that the coefficients are significantly improved.

Further, from Tables 1 and 2, it can be seen that the temperature dependence of HC is improved by a 3n substitution amount of 0.1 or more. Fourth
The table shows the dependence of the saturation magnetization of the BaF 012-2X COX S, nx 01g fine particles of Example 2 on the amount of substitution (X).

(Margin below) From the results in Table 4, it can be seen that when the amount of 5n substitution exceeds 1.0, the saturation magnetization itself of the magnetic powder decreases significantly, and the function as a high-density magnetic recording material deteriorates.

[Effect of the invention] As is clear from the above examples, according to the present invention,
It is possible to effectively improve the temperature characteristics of coercive force of magnetic powder and recording media using the magnetic powder.

Claims (5)

[Claims] (1) Average particle size 0.02~0.2μm, coercive force 200~
2000 Oe of hexagonal ferrite, the number of atoms per chemical formula of the hexagonal ferrite is 0.1
A magnetic powder for high-density magnetic recording characterized by containing Sn atoms in a range of 1.0 to 1.0. (2) Claim 1, wherein the hexagonal ferrite is magnetoplumbite ferrite.
Magnetic powder for high-density magnetic recording as described in . (3) Average particle size 0.02~0.2μm, coercive force 200~
At 2000 Oe, the number of atoms per chemical formula is 0.1
1. A magnetic recording medium, characterized in that hexagonal ferrite containing Sn atoms in the range of 1.0 to 1.0 is attached to the surface of a support. (4) Claim 3, characterized in that the hexagonal ferrite is magnetoplumbite ferrite.
The magnetic recording medium described in Section 1. (5) Hexagonal ferrite together with binder resin,
5. The magnetic recording medium according to claim 3, wherein the magnetic recording medium is coated on a supporting surface.