JPH0417113A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve output, S/N and durability and to enable high-density recording by using a mixture of two types of magnetic powder each having specified most frequent aspect ratio. CONSTITUTION:The first magnetic powder is a hexagonal magnetic powder with the most frequent aspect ratio between >=2.0 and <=10.0, and the second magnetic powder is a hexagonal magnetic powder having the most frequent aspect ratio between >=2.0 and <=10.0, different from that of the first magnetic powder. By using two or more kinds of powders each having the specified most frequent aspect ratios as above described, reaggregation of the powder can be suppressed and dispersion of the powder can be improved compared to the use of one kind of magnetic powder. Thereby, the obtd. medium has high output and durability, magnetic stability, high reliability and large recording capacity.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic recording medium, and in particular to a magnetic coating material in which hexagonal magnetic powder capable of high-density recording is dispersed in a binder. The present invention relates to a magnetic recording medium coated with

(Prior Art) In recent years, with the spread of home videos, personal word processors, personal computers, etc., many magnetic recording media such as magnetic tapes and floppy disks have come on the market. There is currently a high demand for increased capacity for magnetic recording media such as magnetic tapes and floppy disks.

Therefore, in place of the conventional longitudinal recording method, a perpendicular magnetic recording method that has less demagnetizing effect between adjacent bits has been proposed and is being put into practical use. As a result, magnetic recording media suitable for perpendicular magnetic recording methods have been proposed, which are different from magnetic recording media suitable for conventional longitudinal recording methods.

The most suitable magnetic recording media for perpendicular magnetic recording with high recording density include those in which the magnetic layer is made of a ferromagnetic metal film formed perpendicularly by a method such as sputtering, or one in which the magnetic layer is formed in the form of a plate and is formed in a direction perpendicular to the plate surface. There are those manufactured by dispersing magnetic powder having an axis of easy magnetization in a binder and coating it on a support.

In particular, since the latter type of magnetic recording medium can be manufactured by coating, it is attracting attention because it has excellent mass productivity and can be provided at low cost.

(Problem to be Solved by the Invention) By the way, the biggest problem with magnetic recording media that can be manufactured by coating as described above is how to improve the dispersibility of the fine particle size magnetic powder in the binder. It depends on whether you can do it.

If it becomes possible to highly disperse the magnetic powder in the binder, it will not only be possible to improve the packing density of the magnetic powder and obtain high output and S/N, but also to obtain high coating film strength and durability. can also be improved.

Regarding high dispersion of magnetic powder in a binder, a lot of research and development has been carried out on dispersants and dispersion resins.
There is a magnetic recording medium described in the publication No.

This magnetic recording medium has a particle size of 0.01 μm or more and 0.1 μm or more.
A product that uses a mixture of magnetic powder of µm or less and magnetic powder of 0.1 µm or more and 0.5 µm or less, and by doing so, it is possible to improve the dispersion of the magnetic powder in the binder. is.

However, in magnetic recording media using the two types of magnetic powders described above, it has been difficult to achieve a sufficiently high recording density to meet the demands for large capacity because the magnetic powders themselves are large.

The present invention was created in view of the above-mentioned problems, and by improving output and S/N through high dispersion of magnetic powder and ensuring even higher durability, it can fully meet the demands for large capacity. The purpose is to provide a magnetic recording medium.

[Structure of the Invention (Means for Solving the Problems) The present invention provides a magnetic layer including at least a first magnetic powder and a second magnetic powder on at least one main surface of a non-magnetic support, The first magnetic powder is a hexagonal magnetic powder with a mode plate ratio of 2.0 or more and 10.0 or less, and the second magnetic powder has a mode plate ratio of the first magnetic powder. different from the ratio and 2.0 or more 10.
It is characterized by being a hexagonal magnetic powder of 0 or less.

(Function) As a result of various studies on how to highly disperse magnetic powder with a fine particle size, the present inventor found that two particles with different mode plate ratios were used.
By mixing and using more than one type of magnetic powder, even if the paint composition or manufacturing method is the same as before, the output
It has been found that the S/N ratio and durability are significantly improved, and high-density recording is fully possible.

In order to obtain the effects of the present invention, at least a first magnetic powder having a mode plate ratio of 2.0 or more and 10.0 or less, and a mode plate ratio of the first magnetic powder having a mode plate ratio of at least 2.0 or more and 10.0 or less are required. and 2.0 or more 1
It is essential to use it in combination with a second magnetic powder of 0.0 or less.

By using two or more types of magnetic powder with such a mode plate ratio, it is possible to suppress reagglomeration of the magnetic powders and increase the dispersion of the magnetic powder in the binder compared to when the same type of magnetic powder is used. I can do it.

Among these, it is preferable that the average plate ratio (calculated value) of the mixed magnetic powder, which is a mixture of the first magnetic powder and the second magnetic powder, is in the range of 3.0 to 6.0. The plate ratio is 3.5
By setting it in the range of ~4.5, it becomes possible to easily obtain high dispersion of the magnetic powder in the binder and ensure good surface properties. As a result, it is possible to obtain a magnetic recording medium that has excellent output, S/N, and durability and is suitable for high-density recording.

Furthermore, by using a mixture of the first magnetic powder and the second magnetic powder, each having a mode plate ratio of 1.0 or more, it is possible to suppress re-aggregation of the magnetic powders and achieve good dispersion. This makes it possible to perform close packing. Thereby, a magnetic recording medium that can obtain high output suitable for high-density recording can be obtained.

Furthermore, high-density recording can be achieved not only by mixing two types of magnetic powders with different mode plate ratios, but also by mixing three or four types of magnetic powders with different mode plate ratios. It can be used as a suitable magnetic recording medium. Although the present invention naturally includes such materials, in consideration of production or manufacturing costs, it is most preferable to mix two types of magnetic powders having different mode plate ratios.

As the magnetic powder of the magnetic recording medium of the present invention, various hexagonal ferrite magnetic powders such as barium ferrite and strontium ferrite can be used. It can be easily produced by methods such as synthesis and coprecipitation.

In addition, binders for dispersing such magnetic powder include vinyl chloride resin; phenoxy resin; cellulose resin such as nitrocellulose; polyurethane, polycarbonate polyurethane, phenol resin, polyvinyl butyral resin, epoxy resin, or the resins mentioned above. polar group (
For example, various types can be used, such as those into which -COOH group, 5O3H group, -PO3H group, etc.) are introduced.

Supports coated with magnetic paint include polyester resins such as polyethylene terephthalate and polyethylene 2°6-naphthalate; polyvinyl resins such as polyvinyl chloride; polycarbonate, polyamide, polyimide, or metal substrates such as aluminum and copper. is available.

Further, instead of applying the magnetic powder directly onto the support, an undercoat layer may be provided on the support to improve adhesion to the magnetic layer.

(Example) The magnetic recording medium of the present invention will be described in detail below with reference to specific examples and comparative examples.

(Specific Example 1) (Magnetic powder) Partially Co-Ti substituted Ba-ferrite mixed powder (See Table 1) 100.0 parts by weight (Dispersant) Lecithin 1.0 parts by weight (Resin) Polyurethane 12.0 parts by weight Nitro Cellulose 8.0 parts by weight (solvent) Methyl ethyl ketone 76.5 parts by weight Anone 17.0 parts by weight Toluene
76.5 parts by weight (abrasive) α-alumina (particle size 0.2 μm) 6.3 parts by weight (
Conductive agent) Conductive carbon 3.5 parts by weight (lubricant) Stearic acid 1.5 parts Butyl stearate 5.5 parts by weight The above-mentioned various materials were dispersed with magnetic powder using a dispersion machine to obtain a magnetic paint. After that, 6 parts by weight of isocyanate was added and stirred, and then coated on a polyethylene terephthalate film with a film thickness of 75 microns using a gravure coater so that the dry film thickness was 2.5 microns.

After drying in a drying oven, the magnetic layer was subjected to a calendering process using a calendering device, and further, the magnetic layer was sufficiently cured in a curing tank.

Thereafter, a 3.5-inch disc was punched out, a metal hub was installed in the center, and the disc was rotatably housed in a node case to obtain a 3.5-inch magnetic disk cartridge.

In Table 1, d represents the most frequent particle diameter of the magnetic powder, d/l represents the most frequent plate ratio of the magnetic powder, and D/T represents the average plate ratio of the magnetic powder.

(Specific Examples 2 to 11) In the following, magnetic recording media were prepared using the same paint composition as in Specific Example 1, except that the mixed powder shown in Table 1 was used as the magnetic powder, and then a 3.5-inch magnetic disk was prepared. Got the cartridge.

(Specific Example 12) After creating a magnetic recording medium with the same paint composition as in Specific Example 1 except that three types of partially Co-Ti substituted barium ferrite magnetic powders shown in Table 1 were used as magnetic powders, 3.5% An inch-sized magnetic disk cartridge was obtained.

(Specific Example 13) After creating a magnetic recording medium with the same paint composition as in Specific Example 1 except that three types of partially Co-Ti substituted barium ferrite magnetic powders shown in Table 1 were used as magnetic powders, 3.5 An inch-sized magnetic disk cartridge was obtained.

(Comparative Example 1) A magnetic recording medium was prepared with the same paint composition as in Example 1, except that the partially Co-Ti substituted barium ferrite magnetic powder shown in Table 1 was used alone as the magnetic powder, and then a 3.5-inch size magnetic recording medium was prepared. obtained a magnetic disk cartridge.

(Comparative Examples 2 to 5) Hereinafter, some Co-T shown in Table 1 was used as magnetic powder in the same manner.
A magnetic recording medium was prepared using the same coating composition as in Example 1 except that i-substituted barium ferrite magnetic powder was used alone, and a 3.5-inch magnetic disk cartridge was obtained.

(Comparative Example 6) After creating a magnetic recording medium with the same paint composition as in Example 1 except that the mixed powder shown in Table 1 was used as the magnetic powder, 3.
A 5-inch magnetic disk cartridge was obtained.

(Comparative Example 7) A magnetic recording medium was prepared with the same paint composition as in Example 1, except that the mixed powder shown in Table 1 was used as the magnetic powder, and then 3.
A magnetic disk force cartridge of 5 inch size was obtained.

Table 2 shows the results of measuring the playback output, S/N 1 cycle durability, and magnetic stability of the magnetic disk cartridges of the specific examples and comparative examples described above.

The playback output and S/N in Table 2 are calculated using a magnetic head with an effective rad gap of 0.29 μm and a rotation speed of 300 tpm from the center of the magnetic disk.
This was obtained by reproducing a recorded signal of 35 KBPl at a position of 2 mm (track 79).

In addition, the cycle durability is -5℃lO% in a 24-hour cycle.
Under environmental changes of RH ~ 60°C and 160% RH, each magnetic disk cartridge is installed in a double-sided head drive device with a rotation speed of 30 Qrpm, and the playback output from the magnetic disk cartridge is 70% or less of the intended playback output. It shows the value obtained by rounding down the number of passes to the nearest 100,000. The magnetic stability indicates the ratio of the initial coercive force of the magnetic recording medium to the coercive force of the magnetic recording medium after being left in the above-mentioned cycle environment for 108 hours.

Table 2 From the above-mentioned specific examples and comparative examples, it is found that by mixing at least two types of magnetic powders with different mode plate ratios within the range of the present invention and making a magnetic recording medium, the dispersibility of each magnetic powder can be improved. It is possible to obtain high playback output, S/N, and durability.

Further, even under harsh environments, fluctuations in coercive force can be made very small, making the reliability of the magnetic recording medium even higher.

For example, even if there is a magnetic powder whose coercive force is highly dependent on temperature or humidity, several types of magnetic powders with different temperature or humidity dependencies may be used to cancel each other's temperature or humidity dependence. By using a mixture of these, it is possible to form a magnetic layer that is stable as a whole.

The present invention also makes good use of this fact, and the above-mentioned unique effects can be obtained.

Furthermore, at least two or more magnetic powders having a mode plate ratio of 1 or more are mixed, and the average plate ratio of the mixed magnetic powder is set to 3.5.
By setting it in the range of ~4.5, the above-mentioned effects become even more remarkable, and in particular, the magnetic stability, which has been completely unthinkable in the past, becomes even more remarkable.

This example describes only a small part of the example, and it has been confirmed that the same effect can be obtained even if other resins, lubricants, etc. are used.

[Effects of the Invention] As described above, according to the present invention, high dispersibility of magnetic powder can be obtained, high reproduction output and high durability can be obtained, and
It provides unprecedented magnetic stability and is ideal as a highly reliable, large-capacity magnetic recording medium.

Claims (1)

[Claims] On at least one main surface of the non-magnetic support, at least the first
magnetic powder and a second magnetic powder, the first magnetic powder is a hexagonal magnetic powder with a mode plate ratio of 2.0 or more and 10.0 or less, and the second A magnetic recording medium characterized in that the magnetic powder is a hexagonal magnetic powder having a mode plate ratio different from the mode plate ratio of the first magnetic powder and from 2.0 to 10.0.