JPH02249124A - Magnetic recording medium and its production - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Industrial Application Field) The present invention relates to a high-density recording medium suitable for short wavelength recording and a method for manufacturing the same.

(Prior Art) A coated magnetic recording medium is constructed by coating a strong acicular powder such as γ-Pe203Cr02 together with a binder onto a substrate surface such as a polyester film. Recently, in order to significantly improve magnetic recording density, perpendicular magnetic recording has been proposed as a method that exceeds the conventional longitudinal magnetic recording. Therefore, as a magnetic recording medium suitable for this perpendicular magnetic recording method, research and development has been conducted on a magnetic recording medium using hexagonal ferromagnetic powder, and it has been shown that it can be applied to high-density media. .

(Problems to be Solved by the Invention) Incidentally, when performing high-density recording, it is necessary to minimize the spacing between the head and the magnetic recording medium. For this purpose, it has been considered important to improve the surface precision of the head and medium.

However, for short wavelength recording with a recording wavelength of 0.8 μm or less, it is not enough to improve the surface precision of the magnetic recording medium; it is necessary to control the contact distance between the head and the magnetic powder on the surface of the magnetic recording medium. This situation can be easily understood by paying attention to modulation noise. In other words, high noise means that the head senses a discrete magnetic field from the magnetic recording medium, which increases the spacing between the head and the magnetic powder on the surface of the magnetic recording medium, resulting in short When wavelength recording is performed, the reproduction output decreases. Conversely, in a magnetic recording medium with low modulation noise, the head continuously contacts magnetic powder on the surface of the magnetic recording medium and senses the magnetic field. Therefore, the spacing between the head and the magnetic powder on the surface of the magnetic recording medium is small, and as a result, when short wavelength recording is performed, no reduction in reproduction output is observed.

Therefore, when creating (manufacturing) a magnetic recording medium, attention must be paid not only to the dispersion of the magnetic powder but also to the particle size, particle size distribution, etc. of the magnetic powder. For example, when using magnetic powder with a small particle size and a sharp particle size distribution, it becomes more difficult to orient the powder.

Furthermore, in the case of non-oriented magnetic recording media, even if the surface accuracy is high,
If a direct current alignment magnetic field is applied to achieve vertical alignment, the surface precision of the magnetic recording medium may be reduced, and a reduction in short wavelength output may be observed. In other words, when a direct current vertical alignment magnetic field used for alignment is applied to a coated magnetic paint layer, surface magnetic poles are generated on the paint surface, and a repulsive force of the same polarity naturally acts between these magnetic poles. , the surface tends to expand, resulting in a so-called negative surface tension state, and the hydrostatically smooth coating surface becomes disturbed during the orientation process.

The decrease in electrical properties due to this decrease in surface properties increases the loss due to head-magnetic recording medium spacing as the recording wavelength becomes shorter, so even if the orientation rate is improved, it is not suitable for high-density recording media.

In order to avoid these problems, the present inventors investigated various orientation methods. For example, attempts have been made to lower the strength of the direct current alignment magnetic field or to apply an alternating magnetic field, but this has not resulted in a sufficient alignment rate. In other words, when the magnetic field strength is reduced, the rotational torque obtained by applying a DC magnetic field decreases.
Eventually, the orientation rate decreases. In addition, the torque obtained by an alternating magnetic field is smaller than the torque obtained by a direct current magnetic field, and it has been impossible to achieve both a high orientation rate and good medium surface precision using conventional techniques.

The present invention was made to solve these conventional problems, and the magnetic recording medium according to the present invention has both a high orientation rate and good medium surface precision, and as a result, has good electrical properties. has been realized.

[Structure of the Invention] (Means for Solving the Problems) The magnetic recording medium of the present invention uses hexagonal crystal particles with an average particle size of 300 to 800 particles and a platelet ratio of 2.5 to 5 as magnetic powder in the magnetic layer. After applying and depositing a magnetic paint on a predetermined substrate surface using fine ferrite powder and, if necessary, a binder resin containing a sulfone group, the strength is at least 6 KOe.
As described above, the magnetic recording medium and its manufacturing method are characterized in that the magnetic recording medium is maintained in a magnetic field application region of preferably 8 KOe or more for, for example, 0.5 to 1.5 seconds to achieve vertical alignment.

The hexagonal ferrite fine powder used in the present invention includes ferrites such as Ba ferrite, Sr ferrite, Ca ferrite, Pb ferrite, solid solutions thereof, or ion substituted products represented by the following general formula, having a coercive force of 200 to 20,000e. An example is ultrafine powder.

AOn (FeM) 2031-
m rn (In the formula, A is any one element of Bas Srs Ca, Pb, H is Zn, Co, Ti5Ni, ln
At least one element selected from the group of s Cus, Ge5Nb, 5nsZrs Hf and A1, river is 0
~2, n represents a value of 5.4 to 6.0.

However, if M is an element with a valence of 2 or 4 or more, H is a combination of 2 or more elements with an average valence of 3) These ultrafine hexagonal powders are It has a hexagonal plate shape, and the average particle size is 300 to 8 when the length of the diagonal of the plate surface is the particle size.
The range of 00 people is used in the present invention. Here, 80
This is because if magnetic powder with a particle size of 0 Å or more is used, the surface properties of the medium will deteriorate and the modulation noise of the medium will increase, making it unsuitable for high-density recording.

In addition, when the average grain size becomes 300 Å or less, the magnetic properties of the medium, such as a decrease in the saturation magnetization amount and a decrease in the orientation rate, appear.
It becomes unsuitable for high-density recording.

The ratio of the diagonal length and thickness of the hexagonal plate surface in hexagonal ferrite powder is called the plate ratio, and according to the experiments of the present inventors, when the plate ratio becomes 5 or more, the magnetic powder becomes The saturation magnetization of the medium and the saturation magnetization of the medium decrease, making it unsuitable for high-density recording. Furthermore, if the platelet ratio is less than 2.5, the degree of vertical alignment will decrease, making it unsuitable for high-density recording.

The magnetic powder described above is mixed with a solvent and a binder resin to prepare a paint in order to coat it on a support such as a polyester film.

Binder resins include polyurethane resins containing sulfone groups, polyester resins, polycarbonate resins, polyacrylic resins, polyamide resins, epoxy resins, phenol resins, polyether resins, phenoxy resins, melamine resins, vinyl butyral resins, furan resins,
Examples include vinyl chloride resin, vinyl acetate resin, vinyl alcohol resin, and mixtures or copolymers thereof. Here, resins containing sulfone groups were selected because, according to the experiments of the present invention and the authors, using these resins allows for good dispersion of magnetic powder and improves the degree of vertical alignment. Furthermore, the dispersion stability of the magnetic powder is improved, and the coated surface is less likely to become rough even when a vertical or DC magnetic field is applied. In addition, resins containing carboxyl groups, OH groups, and phosphoric acid groups were tried, but they were not as good as resins containing sulfone groups.

As the solvent, one that dissolves the above resin, such as toluene, xylene, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, nitropropane, tetrahydrofuran, and isopropyl alcohol, is used.

Moreover, a dispersant, a lubricant, and an abrasive can be added to the paint component containing the hexagonal ferromagnetic powder, if desired. As the lubricant, a fatty acid or fatty acid alkyl ester type, a silicone type, a fluorinated hydrocarbon type, or a mixture or compound thereof can be used. As abrasives, TiO2, Cr203, Al103
, SiC, ZrO2, and other inorganic fractions having a Morse hardness of 5 or more are suitable. As the dispersant, anionic surfactants, cationic surfactants, and nonionic surfactants can be used, and silane coupling agents and titanium coupling agents can also be used.

The magnetic recording medium of the present invention is manufactured as follows. First, the ferromagnetic powder and binder resin are dispersed or dissolved in a solvent, and thoroughly mixed and dispersed using a sand grinder or the like. In the mixing and dispersion process, if desired,
Dispersants, lubricants, abrasives, etc. can be added.

The magnetic coating material obtained above is coated onto a substrate surface, for example, a polyethylene terephthalate film surface, by a known method using a reverse roll coater, a gravure roll coater, a doctor blade coater, or the like. Next, a vertical DC magnetic field is applied to the coated magnetic paint layer.
At this time, a vertical DC magnetic field is applied before the solvent is completely removed from the coating film. For vertical alignment, the magnetic field strength is at least 6 KOe or more, preferably 6 KOe or more. In other words, the magnetic powder sufficiently dispersed using the sulfone group-containing resin (resin) rotates in the coating film in smaller units of motion while experiencing the resistance of the binder resin, so it is necessary to apply torque to overcome this resistance. Because there is. Furthermore, the residence time in the magnetic base is preferably 0.5 to 1.5 seconds. This is because, although the magnetic moment instantaneously turns toward the magnetic field, it takes some time for the magnetic powder to complete its rotational movement due to the viscous resistance of the binder resin. If the magnetic field exceeds 1.5see and remains in a magnetic field for a long time, the coated surface tends to become rough. Further, the drying temperature in the magnetic field zone is preferably 50 to 90°C. In other words, this is because the temperature is such that the drying of the coating film is completed within the residence time in the magnetic field of 0.5 to 1.5 seconds. If the temperature is lower than this range, the coating film will dry after passing through the orientation zone, and the degree of orientation will decrease.

In addition, the effective magnetic field residence time is shorter at higher temperatures than the temperature range.
The orientation rate also decreases.

The surface of the coating film thus obtained is smoothed by calendering. The smoothness of the final coating film is extremely important, but what controls this is the particle size of the magnetic powder,
These are particle size distribution, magnetic powder dispersibility, magnetic field orientation conditions, and calender conditions.

(Function) According to the present invention, various conditions such as the particle size, particle size distribution, magnetic powder dispersibility, and magnetic field orientation of the magnetic powder in the magnetic recording medium layer as described above are selectively set. By selecting and setting the above-mentioned conditions for this magnetic recording medium layer, it can be used as a magnetic recording medium that has both a high orientation rate and medium surface properties suitable for short wavelength recording, and is capable of high-density recording. Recording media can be easily manufactured.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A magnetic paint was prepared by mixing the following magnetic paint components and thoroughly dispersing them using a sand grinder.

Co, Ti-substituted Ba ferrite 1-100 parts by weight (average particle size 500 particles, plate ratio 2.5) Sulfonated salt vinyl acetate 5 // Sulfonated polyurethane 5 Stearic acid
1〃Alumina
4.Furthermore, a curing agent was added to the magnetic paint obtained above and coated on the polyethylene terephthalate film surface using a reverse roll coater (the coating film thickness was 3 to 4 mm).
μm)L. On the other hand, the vertical orientation magnetic field strength was set to 8 KOe, the orientation zone drying temperature was set to 80°C, and the moving speed was adjusted so that the residence time in the magnetic field was 1 to 2 seconds. The film was transported and vertically aligned. Next, it was calendered and then cured at 60°C (31) to 1/2
It was cut into inch pieces and used as tape samples.

Example 2 Instead of the magnetic powder used in Example 1, magnetic powder with an average particle size of 800 and a platelet ratio of 5 was used, the vertical orientation magnetic field strength was set to 6 KOe, and the orientation zone drying temperature was set to 50°C. ,
The vertical alignment process was performed by adjusting the moving speed so that the residence time in the magnetic field was 0.5 seconds. Next, the tape was calendered, cured at 60° for 3 days, and cut into 1 inch pieces to obtain tape samples.

Example 3 Instead of the magnetic powder used in Example 1, magnetic powder with an average particle size of 300 and a platelet ratio of 2.5 was used, the vertical orientation magnetic field strength was set to 12 KOe, and the orientation zone drying temperature was set to 95°C. The vertical alignment process was performed by adjusting the moving speed so that the residence time in the magnetic field was 1.5 seconds. Next, this was calendered, cured for 3 days at 60°C, and cut into 1/2 inch pieces to obtain tape samples.

Comparative Examples 1 to 3 In place of the magnetic powder used in Example 1, magnetic powder with an average particle size of 830 and a plate ratio of 2.5 was used, and in addition, corresponding to the cases of Examples 1 to 3, respectively. Samples were made under the same coating and orientation conditions.

Comparative Example 4 A sample was made under the same coating and orientation conditions as in Example 1, using magnetic powder with an average particle size of 270 and a plate ratio of 2.5 instead of the magnetic powder used in Example 1. .

Comparative Example 5 A sample was made under the same coating and orientation conditions as in Example 1, using magnetic powder with an average particle size of 350 and a plate ratio of 2.3 instead of the magnetic powder used in Example 1. Ta.

Comparative Example 6 In place of the magnetic powder used in Example 1, magnetic powder with an average particle size of 3350 and a plate ratio of 5.2 was used, and Example 1
A sample was made under the same coating and orientation conditions as in the case of .

Comparative Example 7 A sample was prepared under the same conditions as in Example 1 except that the orientation magnetic field strength was set to 5 KOe.

Comparative Example 8.9 In the case of Example 1, the temperature of the alignment magnetic field application area was set to 47°.
Samples were prepared under the same conditions except that the temperature was set at 97°C or 97°C.

Comparative Example 10.11 The same Comparative Example 12 as in Example 1 except that the moving speed was set to 0.3 seconds or 1.7 seconds for the residence time in the magnetic field.
~14 A magnetic paint having the following composition was prepared in the same manner as in Example 1, and samples were prepared under the same coating and orientation conditions as in Examples 1.2 or 3.

Co, Ti-substituted Ba ferrite 100 parts by weight (particle size 500A, plate ratio 2.5) Salt vinyl acetate 5 // Polyurethane 5 Stearic acid
1〃Alumina
4 // Above Examples 1 to 3 and Comparative Examples 1 to 14
For each magnetic recording medium, orientation rate 2 surface property 10-2μ
The results of measuring m and output dB are shown in the following table.

Note that the output is a measurement value using an alloy head at a recording wavelength of 0.4 μm. (Hereinafter in the margin) [Effects of the Invention] As is clear from the above examples, the magnetic recording medium of the present invention has high perpendicular alignment and high surface properties, and performs excellent functions for high-density recording. Moreover, since the manufacturing method thereof does not require complicated operations, it can be said that it brings many practical advantages for use in the above-mentioned high-density recording or magnetic recording in the short wavelength region.

Applicant: Toshiba Corporation

Claims (6)

[Claims] (1) It includes a supporting base and a fine powder of ferromagnetic hexagonal ferrite deposited on the surface of the supporting base, and the axis of easy magnetization of the fine ferrite powder is oriented perpendicular to the surface on which the deposit is formed. 1. A magnetic recording medium comprising a perpendicular magnetic recording medium layer, wherein the perpendicular magnetic recording medium layer is oriented by applying a direct current alignment magnetic field of 6 KOe or more perpendicularly to the medium layer. (2) In claim 1, the ferromagnetic hexagonal ferrite fine powder has an average particle size of 300 to 800A and a plate ratio of 2.
A magnetic recording medium characterized in that the number is 5 to 5. (3) A step of coating a magnetic paint in which a fine powder of ferromagnetic hexagonal ferrite is dispersed in a binder resin on the substrate surface, and the easy axis of magnetization of the fine powder of ferrite in the coated layer is 1. A method for manufacturing a magnetic recording medium, comprising the step of applying a DC magnetic field of 6 KOe or more as an alignment magnetic field perpendicularly to a coated surface so as to be oriented perpendicularly to the coated surface. (4) In claim 3, a DC magnetic field of 0.
1. A method for manufacturing a magnetic recording medium, which comprises applying a voltage for 5 to 1.5 seconds to vertically align the medium. (5) A method for manufacturing a magnetic recording medium according to claim 3, characterized in that the coated layer is dried at 50 to 95° C. in a DC magnetic field application region to remove the solvent in the coating film. (6) The method of manufacturing a magnetic recording medium according to claim 3, wherein the binder resin contains a sulfone group-containing resin.