JPH04236403A - Magnetic powder for magnetic recording medium and magnetic recording medium using same - Google Patents

Abstract

PURPOSE:To obtain compound type ferrite magnetic powder of hexagonal system ferrite and spinel ferrite which is excellent in temperature stability of coercive force and short wavelength characteristics. CONSTITUTION:In compound type ferrite magnetic powder, rectangularity ratio and SFD in the non-orientation state are selected and controlled in respective suitable ranges. Thereby function as magnetic powder wherein temperature dependency of coercive force is reduced without deteriorating short wavelength characteristics can be realized. By using this magnetic powder, magnetic recording medium excellent in short wavelength characteristics and temperature stability can be obtained.

Description

[Detailed description of the invention]

0001

[Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder for a composite ferrite magnetic powder of hexagonal ferrite and spinel ferrite, which is suitable for high-density recording media, and a magnetic recording medium using the same.

0003

[Prior Art] Magnetic recording media are used for audio, video,
It is used as a recording medium for recording a large amount of information in a wide range of fields such as computers and floppy disks. In recent years, with the remarkable increase in the amount of information to be recorded, there has been a demand for higher recording densities in magnetic recording media. Furthermore, as the recording capacity of magnetic recording media increases, the importance and value of magnetic recording media also increase, and requirements for durability and data storage reliability are becoming more stringent.

In order to meet these demands, perpendicular magnetic recording, which uses magnetization in the direction perpendicular to the medium surface, has been introduced, instead of the conventional magnetic recording method that uses magnetization in the longitudinal direction in the plane, for high-density magnetic recording. Therefore, it is currently attracting attention and development as a next-generation high-density recording method. Examples of magnetic recording media using this perpendicular magnetic recording method include:
A magnetic coating mainly composed of a Co-Cr metal thin film with an axis of easy magnetization perpendicular to the surface of the medium, or a hexagonal ferrite magnetic powder made of plate-shaped crystals with an axis of easy magnetization perpendicular to the plate surface, is coated with polyester. Recording media coated on a non-magnetic support such as a film and vertically oriented are mainly being studied.

By the way, among the magnetic materials to which the perpendicular magnetic recording method can be applied, the above-mentioned hexagonal ferrite magnetic powder exhibits a temperature characteristic in which the value of coercive force (Hc) increases as the temperature rises around room temperature. Therefore, a magnetic recording medium using this is relatively stable against temperature changes, but from a practical standpoint, even higher temperature stability is desired. The coercive force (H
Methods to improve the temperature stability of c) include replacing part of the Fe in the magnetic powder with other elements such as Sn, and using a hexagonal system with a positive temperature coefficient of coercive force (Hc). A method of compounding ferrite with negative spinel ferrite has been proposed.

[0006]

[Problems to be Solved by the Invention] By the way, in the case of a means for compounding hexagonal ferrite and spinel ferrite, according to experiments and studies by the present inventors, the temperature coefficient of the coercive force (Hc) of the magnetic powder can be approximately reduced. Although it is possible to control it to zero, it has been found that the problem is that the electromagnetic conversion characteristics in the short wavelength region tend to deteriorate. Therefore, the inventors of the present invention conducted extensive studies on the deterioration of the electromagnetic conversion characteristics in the short wavelength region observed in such composite ferrite magnetic powders, and as a result, they obtained the following knowledge. In other words, compared to single-phase powder of this type of composite ferrite, the squareness ratio or SFD (switching fi
It was found that the ld distribution) varies considerably. However, the reason for this is probably due to the difference in the composite state between hexagonal ferrite and spinel ferrite, and also when the squareness ratio or SFD of the magnetic powder due to the composite is selected and set within a predetermined range. It was confirmed that the material exhibited good short wavelength characteristics.

Based on the above findings, the present invention is based on hexagonal ferrite and spinel ferrite, which have good electromagnetic conversion characteristics in the short wavelength region and have a small temperature coefficient of coercive force (Hc) (excellent temperature stability). The purpose of the present invention is to provide a magnetic powder that is a composite of the magnetic powder, and a magnetic recording medium using the same.

[0008]

[Structure of the invention]

[0009]

[Means for Solving the Problems] The magnetic powder for magnetic recording media according to the present invention is a composite ferrite of hexagonal ferrite and spinel ferrite with an average particle size of 0.02 to 0.2 μm and a coercive force of 200 to 2000 Oe. SFD (Switching Field Di) is a magnetic powder in which the squareness ratio of the magnetic powder is 0.4 or more and in a non-oriented state.
The magnetic recording medium according to the present invention is characterized in that the value of stribution) is 0.4 to 1.3, and the magnetic recording medium according to the present invention mainly comprises a binder and the magnetic powder for magnetic recording media on a non-magnetic support. It is characterized by being provided with a magnetic layer.

In the present invention, the squareness ratio of the magnetic powder is defined as the residual magnetization relative to the saturation magnetization, but here, 0.1 g of the magnetic powder is 6 mm in diameter and 1 mm in thickness.
The residual magnetization obtained when a sample molded into a disk pellet shape is set in a vibrating sample magnetization measuring device (V.S.M.) and a magnetic field of maximum 10 kOe is applied parallel to the surface direction of the disk. (σr) and magnetization at 10 KOe (σ1
0) is adopted as the ratio (σr /σ10). In addition, the SFD of magnetic powder refers to the second
Differential curve in quadrant magnetization curve (dσ/dH)
It is defined as the value obtained by dividing the half-value width by the value of the coercive force (Hc) of the magnetic powder, and represents the slope of the magnetization curve near the coercive force (Hc). That is, this value is a parameter representing the variation in coercive force (Hc). To determine this SFD, generally magnetic powder is oriented in a coating film and determined from the gradient of the magnetization curve in the orientation direction. However, in reality, different types of magnetic powder have different orientation rates, and this orientation rate affects the slope of the magnetization curve, so it is difficult to compare SFD values between magnetic powders with different properties. Very difficult.

[0011] Therefore, in the present invention, in order to compare the SFD values between magnetic powders having different properties, a method was introduced in which the SFD values of the magnetic powders in a non-oriented state are compared. Since this is the value in a stable state of the magnetic powder with no orientation, it is possible to compare the SFD value as an inherent characteristic of the magnetic powder that is not affected by the orientation rate. The magnitude of the SFD value in the non-oriented state and the magnitude of the SFD value in the oriented state do not necessarily correspond, but may even be reversed. It has been discovered that the SFD value in this non-oriented state, together with the squareness ratio, are important indicators for characterizing the above-mentioned composite hexagonal ferrite magnetic powder.

In the present invention, the squareness ratio of the composite ferrite magnetic powder is limited to 0.4 or more. A magnetic recording medium using magnetic powder having a squareness ratio within this range was able to obtain sufficient reproduction output in the short wavelength region. Square ratio 0
．． In the case of a composite type ferrite magnetic powder with a particle size of less than 4, even if the saturation magnetization was large, the reproduction output of a magnetic recording medium produced using the powder was insufficient in the short wavelength region. Furthermore, in the present invention, SFD in a non-oriented state
The value of is limited to a range of 0.4 to 1.3. A magnetic recording medium using magnetic powder with an SFD value within this range has excellent orientation and high output in the short wavelength region.
Moreover, medium noise was small and a good S/N ratio was exhibited. In the case of magnetic powder with an SFD value of more than 1.3, the orientation is poor, and as a result, the reproduction output in the short wavelength region of the medium produced using it is reduced. In addition, magnetic powder with an SFD value of less than 0.4 has excellent orientation, but
The noise in the short wavelength region of the medium produced using this material became significantly large, and the S/N ratio tended to decrease. Although the reason for the fact that the short wavelength characteristics of the medium deteriorate even when the SFD is too small is currently not clear, this is a new finding obtained by the present inventors.

[0013]

[Operation] In the composite type ferritic powder according to the present invention configured as described above, the square ratio and the SFD in the non-oriented state are
By limiting the range of , the temperature stability of the coercive force Hc is improved while maintaining a state in which the electromagnetic conversion characteristics in the short wavelength region are not easily deteriorated. Therefore, when applied as a high-density magnetic recording medium, for example, the required high-density magnetic recording can always be performed stably in a wide wavelength range.

[0014]

[Examples] Examples of the present invention will be described below. Before explaining specific examples, a general explanation regarding the present invention will be given.

Composite ferrites that can be used in the present invention include, for example, the following general formula: A O·n(Fe12-x-y Mx M'y O
18-z) ......(I) (wherein, A is Ba, S
Any one element selected from the group r, Pb, Ca, M is any one element selected from the group Co, Ni, Cu, Zn, and M' is Ti, Sn, Nb, Sb.
, Zr. n is a number from 0.8 to 2.0, x is a number from 0.5 to
3.0 number, y is a number from 0 to 2.0, and z
represents a number of 0.05 or more. However, when the average valence of M' is m, z is z={x+(3-m)
y}/2).

[0016] Examples of methods for producing magnetic powder include the glass crystallization method disclosed in JP-A-56-67904, and the hydrothermal synthesis method disclosed in JP-A-61-168532. A firing method is suitable.

The average particle size of the magnetic powder according to the present invention is 0.0
Within the range of 2 to 0.2 μm, preferably 0.04 to
It is limited to those within the range of 0.1. Average particle size is 0.0
If the thickness is less than 2 μm, magnetization will hardly remain due to thermal fluctuations.
If it exceeds 0.2 μm, recording resolution in the short wavelength region will decrease, which is not preferable. On the other hand, regarding coercive force,
Within the range of 200 to 2000 Oe, preferably 40
Magnetic powders within the range of 0 to 1500 Oe can be used. This is because if the coercive force is less than 200 Oe, magnetization will hardly remain, and if it exceeds 2000 Oe, it will be difficult to write with a magnetic head.

Specific examples and comparative examples of the present invention will be explained below. In the above general formula (I), M
M'
Magnetic powder was manufactured using composite ferrite obtained by selecting Ti as a raw material and varying x, y, z, and n. The manufacturing method uses a glass crystallization method and a hydrothermal synthesis-calcination method, and by changing the process conditions of those manufacturing methods, the average particle size is about 0.05 μm,
Magnetic powders of Examples 1 to 6 and Comparative Examples 1 to 5 having coercive force (Hc) of 800 to 900 Oe, various squareness ratios, and SFD were obtained. The properties of these magnetic powders are listed in Table 1 below.
(Margin below)
Table 1 Magnetic powder | Average particle size Saturation magnetization Coercive force dHc/dT Squareness ratio
SFD sample No. (μm)
(emu/g) (Oe) (
Oe/℃)
1 ｜ 52
60 810 -0.2
0.41 0.86
Fruit 2 ｜ 49 62
850 +0.5 0.
50 0.85 3
｜ 54 61 880
0 0.41
1.25 Example 4 | 53
62 830
-0.3 0.50 1.28
5 | 54
61 850 +0.6
0.42 0.41
6 ｜ 54 59
860 +0.4
0.50 0.42
1 ｜ 53 65
820 -0.6 0.35
0.88 ratio 2 |
54 70 860
+0.5 0.50 1
．． 56 comparison 3 | 50
63 850 -0
．． 3 0.33 1.36
Example 4 | 54 6
1 840 +0.6
0.48 0.30
5 ｜ 52 68
830 -0.5 0.
36 0.36 Next, using each of the magnetic powders of Examples 1 to 6 and Comparative Examples 1 to 5, magnetic paints having the following compositions were prepared. Namely, 100 parts by weight of magnetic powder, 1 part of vinyl chloride vinyl acetate copolymer
0 parts by weight, 10 parts by weight of polyurethane, 4 parts by weight of lecithin, 93 parts by weight of methyl isobutyl ketone, 93 parts by weight of toluene
Parts by weight and 3 parts by weight of a polyisocyanate compound (trade name: Coronate L", manufactured by Nippon Polyurethane Co., Ltd.) were mixed by conventional means to prepare 11 types of magnetic paints.

Next, each of the above magnetic paints was filtered through a 1 μm filter and then applied onto a PET film. After that, 4000 mm was applied in the vertical direction of the PET film surface.
The magnetic powder was dried while being oriented by a magnetic field of Oe, and the surface was smoothed by calendering to obtain a magnetic recording medium. This was cut into 1/2 inch width to prepare magnetic recording medium samples (Examples 1 to 6 and Comparative Examples 1 to 5). here,
The sample number of the magnetic powder corresponds to the sample number of the magnetic recording medium.

After performing magnetic recording on these magnetic recording medium samples, the reproduction output was measured to examine the characteristics of the tape. The results are shown in Table 2 below. The magnetic head used at this time was a ring-type ferrite head, with a gap width of 0.3 μm, a track width of 35 μm, a relative speed between the head and the tape of 3.75 m/sec, and a recording frequency of 5 MHz. (Margin below)
Table 2 Media |
Playback output S/N
Sample No. (emu/cc) (vertical direction)
(dB) (dB)
1 ｜
155 0.75 +0.5
+0.5
Fruit 2 | 160
0.83 +1.5
+0.5
3 ｜ 158 0.
72 +0.1 +0.1
Example 4
| 160 0.75
+0.5 +0.2
5 |
158 0.78 +0
．． 6 +0.1
6 | 156
0.85 +1.2
+1.1
1 ｜ 163
0.55 -1.0 -
1.0 Ratio 2 | 170 0.58
-1.0 -1.1
Comparison 3 |
157 0.51
-2.0 -2.0
Example 4 | 1
56 0.86 -0.1
-1.0
5 | 169
0.68 -1.0
-1.5 As is clear from Tables 1 and 2, a composite of hexagonal ferrite and spinel ferrite with a squareness ratio of 0.4 or more and an SFD in the range of 0.4 to 1.3. The resulting ferrite magnetic powder has a small temperature dependence of coercive force, and a magnetic recording medium using this powder has excellent short wavelength output. Then, magnetic powder or SFD with a squareness ratio of less than 0.4
It is understood that a magnetic recording medium using magnetic powder with a ratio of less than 0.4 or more than 1.3 has a small short wavelength output or a small S/N at a short wavelength, even if the original saturation magnetization of the magnetic powder is high.

[0021]

[Effects of the Invention] As explained above, according to the present invention, the squareness ratio and SFD in a non-oriented state can be controlled within appropriate ranges in a composite ferrite magnetic powder of hexagonal ferrite and spinel ferrite. By doing so,
It becomes possible to function as a composite ferrite magnetic powder with reduced temperature dependence of coercive force without impairing short wavelength characteristics. Therefore, by using this composite ferrite magnetic powder for magnetic recording, it is possible to provide a magnetic recording medium with excellent short wavelength characteristics and temperature stability.

Claims (2)

[Claims] [Claim 1] Average particle size of 0.02 to 0.2 μm,
A composite ferrite magnetic powder of hexagonal ferrite and spinel ferrite having a coercive force of 200 to 2000 Oe, in which the squareness ratio of the magnetic powder is 0.4 or more and in a non-oriented SFD (Switching Field)
Distribution) value is 0.4 to 1.
3. A magnetic powder for magnetic recording media, characterized in that: Claim 2: On a non-magnetic support, an average particle size of 0.02
A composite ferrite magnetic powder of hexagonal ferrite and spinel ferrite with a coercivity of 200 to 2000 Oe and a coercive force of 200 to 2000 Oe, the magnetic powder having a squareness ratio of 0.2 μm and a coercive force of 200 to 2000 Oe.
4 or more and SFD in a non-oriented state (Switchin
1. A magnetic recording medium comprising a magnetic layer mainly composed of magnetic powder and a binder having a value of 0.4 to 1.3.