JPH01251421A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the dispersibility at the time of prepn. of a coating compd. and to improve an output characteristic and noise characteristic by specifying the contact angle of magnetic powder with a prescribed solvent. CONSTITUTION:The magnetic recording layer is formed by the magnetic coating compd. essentially consisting of the magnetic powder (A) and the resin binder. The magnetic powder having 25-50dyne/cm surface tension and 0 deg. (degree) contact angle with the solvent is used for the component A. The powder of uniaxially anisostropic hexagonal ferrite which is subjected to a treatment for imparting a lipophilic property by a silane coupling agent, etc., is usable as the above-mentioned component A. The fit to the vehicle is improved too much and the coefft. of friction of the medium increases if the above-mentioned contact angle exceeds 0 deg. (degree) and, therefore, such angle is undesirable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium in which the dispersibility of magnetic powder in a magnetic paint is improved.

(Prior Art) Generally, magnetic recording media are produced by preparing a magnetic paint by dispersing a predetermined magnetic powder in a resin binder such as vinyl chloride-vinyl acetate copolymer together with a dispersant such as stearic acid. It is manufactured by applying this magnetic paint to the surface of a supporting substrate made of resin such as polyester to form a magnetic recording layer.

For magnetic recording and reproduction on such magnetic recording media,
Conventionally, a method has been frequently used in which magnetic powder having acicular crystals such as 7-Fe2O3 or CrO2 is oriented in the in-plane longitudinal direction of a recording medium and residual magnetization in the in-plane longitudinal direction is utilized.

However, as magnetic recording devices have progressed in recent years, the magnetic recording media used therein are also required to have higher recording densities. In response to these demands, it is difficult to achieve high-density recording with the above-mentioned method that utilizes magnetization in the in-plane longitudinal direction due to reasons such as the demagnetizing field increasing with higher recording density. there were.

For this reason, in contrast to the conventional method that uses magnetization in the in-plane longitudinal direction, a perpendicular magnetization recording method that uses residual magnetization in the direction perpendicular to the surface of the magnetic recording medium has been proposed. , considerable high-density recording is now being achieved.

Magnetic powders that are advantageous for such perpendicular magnetization recording methods include hexagonal ferrite powders that have a hexagonal plate-like crystal structure and an axis of easy magnetization perpendicular to the plate surface, and substituted type ferrite powders. Hexagonal ferrite powder is known.

(Problem M to be solved by the invention) However, due to its shape, the hexagonal ferromagnetic powder as described above has a large magnetic cohesive force between particles, and it is difficult to uniformly disperse it when producing a magnetic paint. It was extremely difficult. In particular, this tendency becomes more pronounced as the particle size becomes finer. As a result, the perpendicular alignment of the resulting magnetic recording medium deteriorates, leading to problems such as reproduction output characteristics being significantly lower than expected values and noise characteristics becoming low.

Therefore, it is strongly desired to improve the dispersibility of hexagonal ferromagnetic powder in magnetic paints.

The present invention was made in order to address the problems of the prior art, and is aimed at improving dispersion when producing magnetic paint using magnetic powder with strong magnetic cohesive force, such as hexagonal ferromagnetic powder. The purpose of the present invention is to provide a magnetic recording medium with improved performance, output characteristics, and noise characteristics.

[Structure of the Invention (Means for Solving the Problems) In other words, the present invention provides a magnetic recording layer formed by coating a magnetic paint containing at least magnetic powder and a resin binder on a supporting substrate to form a magnetic recording layer. In the recording medium, the magnetic powder is characterized in that it exhibits a contact angle of 0 degrees with respect to any solvent having a surface tension of 25 dyn/cm to 50 dyn/cm.

The magnetic powder used in the present invention has a contact angle of 25 dyn/
It indicates 0 degrees for a solvent having a surface tension of cm to 50 dyn/cth.

In addition, the contact angle of magnetic powder with respect to a solvent as used in the present invention refers to the contact angle measured by forming magnetic powder into pellets with a pressure of 50 kg/cTI, dropping a solvent with a known surface tension onto the pellets, and measuring the contact angle. The surface tension of the solvent is shown by dropping the solvent in descending order of surface tension, and when the contact angle reaches 0 degrees.

Magnetic powder exhibiting such characteristics can be easily obtained, for example, by subjecting its surface to lipophilic treatment under appropriate conditions.

This lipophilic treatment includes, for example, a silane coupling agent, a titanate coupling agent, an aluminum coupling agent, a zirconate coupling agent, a neoalkoxy coupling agent, a chromium coupling agent, an organic phosphate coupling agent, and an organic coupling agent. Examples include a method of surface treatment using a ring agent, a silyl peroxide coupling agent, an amine coupling agent, a carboxylic acid coupling agent, or various surfactants.

The reason why the contact angle of the magnetic powder to the solvent is limited to the above value is as follows.

In other words, in the case of a magnetic powder that shows a contact angle of 0 degrees only with a solvent with a surface tension of less than 25 dyn/cm, that is, in the case of a magnetic powder whose contact angle with a solvent with a surface tension of 25 dyn/cm or more is greater than 0 degrees, the magnetic powder and the magnetic The paint is too compatible with the vehicle made of the resin binder and dispersion medium during paint production, resulting in an overdispersed state. Therefore, the friction coefficient of the recording medium may increase, and for example, the friction coefficient may become 0.3 or more. When the friction coefficient of the surface of the recording medium exceeds 0.3, the frictional force between the head and the recording medium becomes too large, causing a stick-slip phenomenon or, in the worst case, a cue sound. When this phenomenon occurs, jitter becomes large and, for example, in a magnetic recording tape for a VTR, screen shake occurs.

In addition, in the case of magnetic powder that shows a contact angle of 0 degrees with respect to a solvent with a surface tension of 50 dyn/cm or more, the compatibility between the magnetic powder and the vehicle is poor, and the dispersion in the magnetic paint is insufficient, resulting in poor output characteristics. descend.

The magnetic powder to be used has a crystal structure having a plate-like structure, a plate-like ratio in the range of 1 to 15, and a particle size of 0.
In the range of 0.005 μl to 0.3 μm, the coercive force (Ilc) was adjusted to the range of 2000 e to 20000 e.
For example, it has the general formula AO-n(Fe203) (wherein A represents at least one element selected from Ba, Sr, and PbSCa, and n represents a number of 5 to 6. However, part of Pe is Tis 00 % Zn,, !nSM
n500% Gas Nb5Zr, V, AI, S
It may be substituted with one or more metals such as n. ) Uniaxially anisotropic hexagonal ferrite powder is suitable.

The magnetic recording medium of the present invention is manufactured, for example, as follows.

That is, first, a magnetic powder that meets the above conditions is dispersed in a resin binder together with a dispersant such as lecithin to create a magnetic paint, and after applying this to the surface of a supporting substrate, it is subjected to an orientation treatment and a drying treatment. It can be easily prepared by performing the following steps.

As the resin binder for producing the above-mentioned magnetic paint, it is possible to use various conventionally used and well-known resin binders, such as polyurethane resins, polyester resins, phenol resins, epoxy resins, Examples include vinyl chloride resin. In addition, the magnetic paint contains anionic and cationic surfactants, lubricants such as lauric acid, valmitic acid, and stearic acid, fillers such as alumina powder and chromium oxide powder, and charged materials such as carbon black. It is possible to use appropriate amounts of various additives such as inhibitors.

Furthermore, as the support substrate used in the present invention, various known materials used as bases for various magnetic tapes, floppy disks, etc. can be used. For example, as a tape base, a polyester film, etc. can be used.
Also, polyester sheets, aluminum substrates, etc. are used as the floppy disk base.

(Function) In the magnetic recording medium of the present invention, for example, by subjecting the magnetic powder to lipophilic treatment, the contact angle with respect to various solvents can be reduced to 0 with respect to solvents having a surface tension of 25 dyn/cm to 50 dyn/cm. I am using something that has a certain degree of accuracy. This magnetic powder exhibits good and appropriate dispersibility in a vehicle when producing a magnetic coating material. Therefore, magnetic recording media made using such magnetic paints are
The magnetic powder in the magnetic recording layer is uniformly dispersed, resulting in excellent reproduction output characteristics and noise characteristics. Further, the friction coefficient of the surface of the recording medium can be set to an appropriate value of, for example, 0.3 or less, and the electromagnetic conversion characteristics can also be improved.

(Example) Next, examples of the present invention will be described.

Example 1 First, Co-Tl substituted Ba ferrite powder (average particle size 0.08 um, He 7000e) 100
Part by weight was dispersed in methyl ethyl ketone, 3 parts by weight of phosphatidylcholine was added as a lipophilic treatment agent to this dispersion, and the mixture was thoroughly stirred to coat the surface of the magnetic powder with the lipophilic treatment agent. The dispersion medium was removed by drying at ℃ for 24 hours. The magnetic powder obtained in this way was
Pelletize at a pressure of 0 kg/cvf, drop solvents with different surface tensions onto the pellets in order from the one with the highest surface tension, and measure the contact angle referred to in the present invention from the surface tension of the solvent whose contact angle is 0 degrees. As a result, the surface tension was 50d
0 degree was shown for the solvent of yn/Cm.

Next, using the magnetic powder subjected to the lipophilic treatment, a composition having the following composition was sufficiently kneaded with a sand grinder to prepare a magnetic paint.

Magnetic powder 80 parts by weight Vinyl chloride-vinyl acetate copolymer resin 10 Polyurethane resin 10 Lecithin
3 // Stearic acid
0.1” lobethyl stearate
0,1 l'methyl ethyl ketone
8011 cyclohexane 8011
Toluene 8011 then
After filtering this magnetic paint, 3 mm part of an isocyanate compound as a hardening agent was added and kneaded, and then applied onto a PET film, dried and hardened, and further calendered to produce a magnetic recording medium.

Examples 2 to 4, Comparative Examples 1 to 2 Using the magnetic powder used in Example 1 above, lipophilization treatment was performed in the same manner as in Example 1 under the conditions shown in the following table, and the surface tension shown in the following table was obtained. Magnetic powders having a contact angle of 0 degrees with respect to the solvent were obtained.

In addition, each comparative example in the table is one in which no lipophilic treatment was performed and one in which the contact angle was outside the range of the present invention.

Using each of these magnetic powders, magnetic recording tapes were produced under the same conditions as in Example 1.

(Left below) The magnetic recording media obtained in each of the above examples and comparative examples were
A magnetic recording tape that can be cut into 2-inch widths and capable of determining 1iDI was obtained, and the carrier signal to noise ratio (C/N ratio) was set to all+ under the conditions of a carrier frequency of 4 M II z and a tape speed of 3.5 m/s. Established. The results are shown in FIG. Note that the Al11 constant value is expressed as a relative level with Comparative Example 1 as a reference. Further, each of the above 1/2 inch wide tapes was wound around a stainless steel drum having a diameter of 80+n+u, and the coefficient of friction was determined from the initial tension (To) at a weight of 50 g and the tension during sliding (T1). The results are also shown in FIG. Note that the friction coefficient μ was determined by the following formula.

μk −−1n (T 1/T o)π As is clear from Figure 1, the contact angle with various solvents is 0 degrees with any of the solvents having a surface tension of 25 dyn/cm to 50 dyn/cm. By using the magnetic powder shown in Fig. 1, the dispersibility in the magnetic paint is good and appropriate, and the coefficient of friction of the magnetic recording medium is reduced, and the C/N ratio is excellent.

[Effects of the Invention] As is clear from the above examples, the magnetic recording medium of the present invention has good dispersibility of the magnetic powder during the preparation of the magnetic paint in the manufacturing process within an appropriate range. Therefore, a state in which the magnetic powder is uniformly dispersed in the magnetic recording layer can be obtained, and a magnetic recording medium with excellent output characteristics and sliding contact characteristics with a magnetic head can be provided.

[Brief explanation of the drawing]

Figure 1 shows the contact angle of magnetic powder in an example of the present invention.
The surface tension of the solvent and the relative C/ of the magnetic recording medium when indicating the degree of
It is a graph showing the relationship between the N value and the coefficient of friction. Applicant Toshiba Corporation Representative Patent Attorney Sasa Suyama −

Claims (1)

[Claims] (1) A magnetic recording medium in which a magnetic coating containing at least a magnetic powder and a resin binder is coated on a supporting substrate to form a magnetic recording layer, wherein the magnetic powder has a density of 25 dyn/cm to 50 dyn/cm.
The contact angle is 0 for any solvent with a surface tension of
A magnetic recording medium characterized in that it shows a degree.