JPH06309650A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in running stability and recording and reproducing characteristics by forming a magnetic layer so that a lubricant is contained in the layer by a prescribed amt. basing on the amt. of magnetic powder and imparting a prescribed amt. of protrusions each having a prescribed height to the magnetic layer. CONSTITUTION:A magnetic layer 2 with the highest protrusion 3, etc., is formed on a base film 1. Protrusions 5, 5' protrude from a horizontal face 4 positioned under the apex of the protrusion 3 in the perpendicular direction at 20nm interval and parallel to the base film 1. The magnetic layer 2 with many such fine protrusions 5, 5' is formed so that a lubricant is contained in the layer 2 by 8-30 pts.wt. per 100 pts.wt. magnetic powder. The number of the protrusions 5, 5' higher than the horizontal face 4 is regulated to 400-2,500 per 1mm<2>. The objective magnetic disk excellent in running stability and recording and reproducing characteristics is obtd..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium excellent in running stability.

[0002]

2. Description of the Related Art In recent years, in order to increase the capacity and density of magnetic recording media, studies have been conducted on the material of ferromagnetic metal powder and the like, and from the structural aspect of the magnetic layer. Attempts have been made to improve the performance of magnetic recording media.
An example thereof is to make the surface state of the magnetic layer as smooth as possible to reduce the spacing between the magnetic recording medium and the magnetic head.

Among so-called coating type magnetic recording media among the magnetic recording media, a magnetic layer is manufactured by coating a base material with a magnetic paint comprising a magnetic powder, a binder, a lubricant, a dispersant, an abrasive and the like. However, the surface condition of the magnetic layer is greatly influenced by the components that make up the magnetic paint. There is a center line surface roughness (Ra) as an index showing the surface condition of the magnetic layer, and it can be said that the smaller this value is, the less the surface irregularities are and the smoother the surface condition of the magnetic layer is.

[0004]

However, as the value of Ra on the surface of the magnetic layer decreases, the contact area between the magnetic head and the surface of the magnetic recording medium increases, the apparent coefficient of friction increases, and the running stability decreases. There was a problem of doing. Therefore, an object of the present invention is to solve the problem that the running stability is lowered due to the increase of the friction coefficient when the Ra value of the magnetic layer surface is made small, and to provide a highly reliable magnetic recording medium.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, completed the present invention.

That is, according to the present invention, in a magnetic recording medium in which a magnetic layer having a large number of fine protrusions on the surface is formed on a base film, the magnetic layer contains a lubricant in an amount of 8 to 100 parts by weight of magnetic powder. The number of protrusions is 30 to 30 parts by weight, and the number of protrusions located 20 nm vertically below the highest protrusion of the magnetic layer and higher than the horizontal plane parallel to the base film is 400 to 25.
The present invention provides a magnetic recording medium characterized by being 00 / mm ² .

The magnetic recording medium of the present invention is characterized in that a lubricant is blended with a magnetic powder in a specific amount and the magnetic layer has a specific surface condition. The state of the magnetic layer of the magnetic recording medium of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of a magnetic recording medium of the present invention, schematically showing the form of a magnetic layer. In the figure, 1 is a substrate, 2 is a magnetic layer, 3 is the highest protrusion, 4 is a horizontal plane that is located at a vertical direction of 20 nm from the apex of the protrusion 3 and is parallel to the base film, and 5 is a protrusion protruding from the horizontal plane 4. . Microscopically, a large number of protrusions are formed on the surface of the magnetic layer of the magnetic recording medium of the present invention, and the total number N of the protrusions 5 protruding from the horizontal surface 4 is 400 to 2500 / mm ² , preferably It is characterized in that it is 700 to 1500 pieces / mm ² . N is measured by a three-dimensional optical non-contact surface roughness meter or the like. The "highest" here is relative and means the highest protrusion in the desired range of the magnetic layer.

In the magnetic recording medium of the present invention, a magnetic paint containing 8 to 30 parts by weight, preferably 10 to 15 parts by weight of a lubricant, is applied to 100 parts by weight of magnetic powder on a base film and dried. However, it can be obtained by adjusting the polishing conditions. The polishing conditions for obtaining the magnetic recording medium of the present invention are, for example, using # 8000 to # 10000 polishing tape, a load of 100 to 2000 gf / cm ² , and a rotation speed of 3000 rp.
A method of polishing with m 2 for 2 to 10 seconds can be mentioned. Further, by optimizing the calendering conditions, the amount of the abrasive and the particle size thereof, the magnetic recording medium having the surface condition defined in the present invention can be obtained.

Examples of the substrate used in the magnetic recording medium of the present invention include synthetic resins (for example, polyesters such as polyethylene terephthalate, polyamides, polyolefins, cellulosics), non-magnetic metals, glass, ceramics and paper. , Its form is film, tape,
Used in sheets, cards, discs, etc. The thickness of these substrates is about 1 to 300 μm.

The magnetic powder used in the magnetic recording medium of the present invention includes γ-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder and Co-containing γ-Fe ₂
Various conventionally known magnetic powders such as O ₃ powder, Co-containing Fe ₃ O ₄ powder, CrO ₂ powder, Fe powder, Co powder, Fe-Ni powder, and barium ferrite powder can be widely used. The thickness of the magnetic layer is not particularly limited, but is about 0.3 to 5 μm. Further, the surface shape of the magnetic layer is formed with a large number of fine protrusions, but the height of the protrusions is not limited as long as it satisfies the above-mentioned regulations of the present invention and does not impair the performance as a magnetic recording medium.

The lubricant used in the magnetic recording medium of the present invention is a material exhibiting a lubricating action when the magnetic head and the magnetic recording medium are in contact with each other. Specifically, silicone oil such as various polysiloxanes, graphite, Inorganic powders such as molybdenum disulfide, plastic fine powders such as polyethylene and polytetrafluoroethylene, higher fatty acids, higher alcohols, higher fatty acid esters such as 2-decyltetradecyl oleate and tridecyl stearate, fluorocarbons and the like. . These lubricants are magnetic powder 100
It is blended in an amount of 8 to 30 parts by weight, preferably 10 to 15 parts by weight, based on parts by weight.

Examples of the binder used in the magnetic recording medium of the present invention include urethane resins, particularly polyurethane resins containing polar groups such as SO ₃ Na groups, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers. Polymers, vinyl chloride-copolymers such as vinyl chloride-acrylonitrile copolymers, especially vinyl chloride copolymers containing polar groups such as SO ₃ Na groups, butadiene-acrylonitrile copolymers, polyamide resins, Polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose propionate, nitrocellulose, etc.), styrene-
Butadiene copolymer, polyester resin, various synthetic rubber, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, polyester polyol And polyisocyanate mixture, urea formaldehyde resin,
Examples include a mixture of low molecular weight glycol / high molecular weight diol / isocyanate, and a mixture thereof.

As the organic solvent used for preparing the magnetic paint, the binder resin used, such as cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, benzene, toluene, xylene, dimethyl sulfoxide, tetrahydrofuran, dioxane, etc., is dissolved. The solvent suitable for is not particularly limited and may be used alone or as a mixture of two or more kinds.

Incidentally, various additives which are usually used, such as a curing agent, a dispersant and an abrasive, may be appropriately added to the magnetic paint. As the dispersant that can be used in the present invention, lecithin, nonionic surfactants, anionic surfactants, cationic surfactants and the like are used. As the polishing agent, fine powder having an average particle size of 0.05 to 0.5 μm such as α-alumina, fused alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, and diamond is used, and it is 0.5 per 100 parts by weight of the binder. ~ 100 parts by weight added.

[0016]

According to the magnetic recording medium of the present invention, the apparent friction coefficient between the magnetic head and the magnetic recording medium can be suppressed small. Therefore, the running stability of the magnetic recording medium,
A magnetic recording medium having improved durability and high operation reliability is provided.

[0017]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 100 parts by weight of barium ferrite ferromagnetic powder (plate ratio 3) 7 parts by weight of VAGH (vinyl chloride-vinyl acetate-vinyl alcohol copolymer manufactured by UCC) 7230 parts by weight of N2301 (Japan Polyurethane resin manufactured by Polyurethane Industry Co., Ltd.) Alumina 10 parts by weight Carbon black 4 parts by weight 2-decyl tetradecyl oleate 7 parts by weight Tridecyl stearate 7 parts by weight After sufficiently mixing the above components, this To 4 parts by weight of Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.) was added (to 100 parts by weight of magnetic powder) to prepare a magnetic paint, and this magnetic paint was made into a polyethylene terephthalate film (thickness: 75 μm). Apply on top, dry and calender. After that, punched out into a disk with a diameter of 86 mm and polishing tape # 8000 (Nippon Micro Coating
(Manufactured by Co., Ltd.) with a load of 700 gf / cm ²
Polishing was performed at 00 rpm for 3 seconds to obtain a magnetic disk.

Example 2 The polishing step in Example 1 was carried out using a # 10000 polishing tape (manufactured by Nippon Micro Coating Co., Ltd.) at 1000 gf.
A magnetic disk was obtained in the same manner as in Example 1 except that the polishing was performed by applying a load of / cm ² for 2 seconds at 3000 rpm.

Example 3 The polishing step in Example 1 was repeated with 400 gf of # 10000 polishing tape (manufactured by Nippon Micro Coating Co., Ltd.).
A magnetic disk was obtained in the same manner as in Example 1 except that the polishing was performed by applying a load of / cm ² for 2 seconds at 3000 rpm.

Example 4 The polishing step in Example 1 was carried out using a # 8000 polishing tape (manufactured by Nippon Micro Coating Co., Ltd.) at 1400 gf / cm.
^A magnetic disk was obtained in the same manner as in Example 1 except that a load of ² was applied and polishing was performed at 3000 rpm for 3 seconds.

Example 5 In the composition of the magnetic paint of Example 1, the amount of 2-decyltetradecyl oleate was 4 parts by weight and the amount of tridecyl stearate was 4 parts by weight, and the polishing step in Example 1 was carried out. # 8000 polishing tape (Japan Micro Coating
(Manufactured by Co., Ltd.) with a load of 700 gf / cm ²
A magnetic disk was obtained in the same manner as in Example 1 except that polishing was performed at 0 rpm for 3 seconds.

Example 6 In the composition of the magnetic paint of Example 1, the amount of 2-decyltetradecyl oleate was 15 parts by weight and the amount of tridecyl stearate was 15 parts by weight. # 8000 polishing tape (Japan Micro Coating
(Manufactured by Co., Ltd.) with a load of 700 gf / cm ²
A magnetic disk was obtained in the same manner as in Example 1 except that polishing was performed at 0 rpm for 3 seconds.

Comparative Example 1 The polishing step in Example 1 was carried out using a # 10000 polishing tape (manufactured by Nippon Micro Coating Co., Ltd.) at 50 gf /
A magnetic disk was obtained in the same manner as in Example 1 except that a load of cm ² was applied and polishing was performed at 3000 rpm for 1 second.

Comparative Example 2 The polishing step in Example 1 was carried out using a # 6000 polishing tape (manufactured by Nippon Micro Coating Co., Ltd.) at 4000 gf / cm.
^A magnetic disk was obtained in the same manner as in Example 1 except that a load of ² was applied and polishing was performed at 3000 rpm for 4 seconds.

Comparative Example 3 In the magnetic coating composition of Example 1, the amount of 2-decyltetradecyl oleate was 4 parts by weight and the amount of tridecyl stearate was 3 parts by weight. # 8000 polishing tape (Japan Micro Coating
(Manufactured by Co., Ltd.) with a load of 700 gf / cm ²
A magnetic disk was obtained in the same manner as in Example 1 except that polishing was performed at 0 rpm for 3 seconds.

Comparative Example 4 In the magnetic coating composition of Example 1, the amount of 2-decyltetradecyl oleate was 16 parts by weight and the amount of tridecyl stearate was 15 parts by weight. # 8000 polishing tape (Japan Micro Coating
(Manufactured by Co., Ltd.) with a load of 700 gf / cm ²
A magnetic disk was obtained in the same manner as in Example 1 except that polishing was performed at 0 rpm for 3 seconds.

<Characteristic Evaluation> With respect to the magnetic disks obtained in each of the above Examples and Comparative Examples, the surface shape was measured with a three-dimensional optical non-contact surface roughness meter (manufactured by ZYGO) within a range of 0.16 mm × 0.18 mm. . Center line average roughness (Ra), the number N (number / mm ² ) of protrusions higher than the horizontal plane when cut at a depth of 20 nm from the highest apex on the surface of the magnetic layer, and the magnetic head and magnetic The friction coefficient of the disk after running for 1 hour, and the cyclic condition of temperature and humidity were changed.
Output (%) with respect to the initial output after the continuous running test of 0,000,000 paths
Is shown in Table 1. Here, a graph showing changes in temperature and humidity is shown in FIG. The method of measuring the friction coefficient is as follows.

Friction coefficient measuring method The torque of a known value is forcibly applied to the drive motor, and the relationship between the motor load current I and the torque T is investigated. Thereby, the rotational torque of the flexible disk can be obtained by measuring the motor load current. When the above torque during head loading is T _on (g · cm) and the torque during head unloading is T _off (g · cm), it is caused by friction between the head and the disk surface (dynamic friction coefficient is μk). The torque T _{H / M} (g · cm) is given by T _{H / M} = T _on −T _off . The coefficient of dynamic friction μk is SIDE0 and SIDE1
The average value of is calculated by the following equation (1). μk = TH _{/ M} / (2 · r _m · M) (1) Here, r _m is the average value (cm) of the track radii of SIDE0 and SIDE1, and M is the head load (g). The measurement environment was 23 ° C. and 50% RH.

[0030]

[Table 1]

Note) * In the table, the compounding amount of the lubricant is parts by weight based on 100 parts by weight of the magnetic powder.

When the number of protrusions is less than 400 / mm ² as in Comparative Example 1, the head load is supported by the protrusions on the surface of the magnetic disk, so that local pressure is applied to the protrusions and the magnetic medium is easily damaged. Become. That is, the output after the continuous running test becomes low as in Comparative Example 1. On the contrary, when the number of protrusions is more than 2500 pieces / mm ² as in Comparative Example 2, the actual contact area between the head and the magnetic disk increases and the friction coefficient increases, so that the running becomes unstable. Even if the number of protrusions is in the range of 400 to 2500 / mm ² , if the compounding amount of the lubricant is less than 8 parts by weight with respect to 100 parts by weight of the magnetic powder,
The output after the continuous running test is low as in Comparative Example 3. Also, as in Comparative Example 4, when the amount of the lubricant compounded exceeds 30 parts by weight with respect to 100 parts by weight of the magnetic powder, the friction coefficient increases and the output after the continuous running test becomes low.

On the other hand, as in Examples 1 to 6, the number of protrusions is in the range of 400 to 2500 / mm ² , and the amount of the lubricant is 8 to 30 parts by weight with respect to 100 parts by weight of the magnetic powder. It can be seen that the friction coefficient is low and the output after the continuous running test is high in the range of the part. In particular, the number of protrusions is in the range of 700 to 1500 / mm ² , and the amount of lubricant is 100 parts by weight of magnetic powder.
Examples 1 and 2 in the range of 10 to 15 parts by weight show favorable results.

From the above results, it can be seen that the magnetic disk of the present invention is excellent in running stability and recording / reproducing characteristics.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a magnetic recording medium of the present invention.

FIG. 2 is a diagram showing cycles of changes in temperature and humidity for conducting a continuous running test in Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Magnetic layer 3 ... Protrusion 4 ... Horizontal surface 5 ... Protrusion

Claims (1)

[Claims] 1. A magnetic recording medium comprising a base film and a magnetic layer having a large number of fine projections on the surface thereof, wherein the magnetic layer contains a lubricant in an amount of 8 to 30 parts by weight per 100 parts by weight of the magnetic powder. Magnetic recording characterized in that the number of protrusions contained and located 20 nm vertically below the highest protrusion of the magnetic layer and higher than the horizontal plane parallel to the base film is 400 to 2500 / mm ^2. Medium.