KR930007057B1 - Magnetic recording media - Google Patents

Abstract

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Description

Magnetic recording media

Field of invention

FIELD OF THE INVENTION The present invention relates to a magnetic recording medium that exhibits sufficient noise reduction and large output in high density recording as required, such as small video tapes with extremely good image quality.

In particular, the present invention has a magnetic layer and a back coating layer (backcoating layer), the total thickness of the base material, the magnetic layer and the back coating layer is 14㎛, used in a wound form and noise even after long-term storage The purpose is to maintain the reliability of magnetic recording media, such as this non-increasing magnetic tape.

Related Technology

In general, a magnetic recording medium is a substrate made of a polyester film, and a magnetic paint obtained by dispersing a magnetic powder, a binder, an inorganic powder, a lubricant, and the like in an organic solvent is applied to the surface of the substrate, and then dried. It is a magnetic layer formed on the substrate surface.

In particular, in the case of a video tape, a back coating layer containing a binder, an inorganic powder, a lubricant, and the like is formed on the back of the substrate to improve the smooth operating characteristics.

It has been proposed to prevent abrasion that occurs during contact with magnetic heads or guide rollers by adding inorganic powders with a Moh's hardness of 5 or more to the magnetic and backside coating layers. The technique of adding inorganic powder having a hardness of 5 or more to the backside coating layer is disclosed in Japanese Patent Application Laid-Open Nos. 112/1987, 38525/1987, 38526/1987, 38527/1987 and 38528/1987. Japanese Patent Publication Nos. 18572/1972, 15003/1973, 39402/1974, 28642/1977, and the technique of adding inorganic powder having a Mohs hardness of 5 or more to the magnetic layer, 49961/1977 and 15771/1980. In order to achieve high density recording, the recording wavelength must be shortened. Therefore, magnetic powder with much smaller particle size than the recording wavelength is used. Numerous proposals have been made to improve the magnetic properties in order to obtain a large output. For example, Japanese Patent Publication No. 37661/1986 uses a ferromagnetic metal powder with large saturation magnetization to produce a large output. Is getting.

Furthermore, in order to reduce noise, Japanese Patent Publication Nos. 17404/1977 and 12688/1985 describe processing techniques for super calendering the surface of a magnetic layer to make it smooth. However, the magnetic recording medium containing ferromagnetic metal powder as a magnetic recording element and the surface treatment method, although the original noise is small, the noise gradually increases after storage.

This problem is remarkable when the particle size of magnetic powder is smaller and softer magnetic powder is used than iron oxide base magnetic powder. The fact that it is confirmed is that noise occurs for a signal of frequency corresponding to recording wavelength of about 0.8㎛. to be.

This problem occurs in almost all typical magnetic recording media, while in the case of typical magnetic recording media without a back coating layer, the noise is inherently small.

Therefore, the inventors have thoroughly studied that this problem occurs in the backside coating layer. As a result, when the magnetic recording medium is wound, the inventors shift the surface roughness of the backside coating layer to the magnetic layer surface. It was confirmed that noise was generated due to surface roughness, and that the increase in noise was remarkable in the wound type magnetic recording medium having a total thickness of 14 μm or less for the substrate, the magnetic layer, and the back coating layer.

This is because a magnetic recording medium with a larger number of windings is wound than a thick magnetic recording medium having a total thickness of about 20 μm in a unit winding diameter, and a winding force acts greatly near the hub.

Japanese Patent Laid-Open Publication No. 32,122 / 1985 describes a similar phenomenon, the latter of which is higher than the former inorganic powder when a combination of inorganic powder having a hardness of 5 or more and a particle size of about 0.2 μm and a soft inorganic powder is used. It is proposed to prevent defects of the tape guide by using a large amount of inorganic powder.

Japanese Patent Laid-Open Publication No. 255,584 / 1988 recognizes that the transfer of the surface roughness of the rear coating layer to the surface of the magnetic layer reduces the S / N and C / N of the magnetic recording medium. The amount is related to this problem.

However, the above patent documents relate to a VHS-type magnetic recording medium and a cobalt-containing iron oxide magnet powder having a total thickness of the substrate, the magnetic layer and the back coating layer of about 20 μm.

Since the shortest recording wavelength of the white level in the VHS system is only 1.3 [mu] m, the above patent documents contain ferromagnetic metal powder as a magnetic recording element and have a central recording wavelength of 0.8 [mu] m. There is no suggestion regarding noise reduction.

Detailed description of the invention

The inventors first confirmed that the defects easily appear in the magnetic layer and the back coating layer not only because of the hardness of the particles contained in each layer but also because of the particle size and when the particle size is less than a special size. Reinforcing effect is reduced. It is further confirmed from this fact that the particle size of the inorganic powder of the rear coating layer is changed to prevent the damage of the magnetic layer surface caused by the inorganic powder having a Mohs hardness of 5 or more contained in the rear coating layer when the magnetic recording medium is wound up. It should be made much smaller than the principal axis of the magnetic powder of the query.

Second, carbon black must be included in the backside coating layer to improve operating characteristics.

As disclosed in Japanese Patent Application Laid-Open No. 8,328 / 1987, fine carbon black having a particle size of 10-30 µm and coarse nonmagnetic powder having a particle size of 200-500 µm are coated on the reverse side. It is proposed to extend the operational durability of the magnetic recording media by preventing the drop out phenomenon from being added to the coating layer.

However, this patent document does not describe the relationship between the principal axis size of the ferromagnetic metal powder in the magnetic layer and the primary particle size or particle size of the carbon black agglomerate, or use ferromagnetic metal particles having small particle size. There has never been a study of the relationship between noise for signals with frequencies corresponding to recording wavelengths below 0.8 μm and the primary particle size or particle size of carbon black agglomerates.

Therefore, in completing the present invention, a study on the relationship between the principal axis size of the ferromagnetic metal powder in the magnetic layer and the primary particle size or particle size of the carbon black agglomerate is apparent. If the size is larger than the ferromagnetic metal powder, it can satisfy the low noise condition at high power.

This is remarkable in magnetic recording media that require a high recording density, in particular magnetic recording media having a thickness of about 3.0 mu m, which satisfies satisfactory conditions as the thickness of the magnetic layer is thinner.

It was confirmed in the present invention that each surface of the nonmagnetic substrate has a magnetic layer and a coating layer on the back to exhibit a high output, even after long-term storage can suppress noise increase during high density recording at a central recording wavelength of about 0.8 μm. In order to provide a magnetic recording medium, it is preferable that the magnetic field has a squareness ratio of at least 0.85, the coersive force of at least 1500Oe under an applied magnetic field of 10 KOe, and the surface roughness of the magnetic layer is a mean of the centerline. The surface roughness of the back coating layer should be about 0.01 µm when expressed as a roughness, and the particle size of the inorganic powder having a Mohs hardness of 5 or more should be larger than the main shaft size of the metallic magnetic powder. It should be small.

It was unexpected to damage the surface of the magnetic layer because the carbon black contained in the backside coating layer was soft.

However, it was confirmed that carbon black having a small particle size damaged the surface of the magnetic layer because magnetic metal particles having a main axis size of 0.2 μm or less added to achieve high density recording at a central recording wavelength of about 0.8 μm. This is because the reinforcing effect is not sufficient in the magnetic layer that is mainly contained, and strong winding force is applied to the thin magnetic recording medium to achieve high density recording under severe conditions with high rotational speed. In this case, if the back coating layer contains carbon black with a primary particle size or particle size larger than the principal axis size of the ferromagnetic metal powder, particles with much smaller particle size enter into the gap formed between the carbon black particles with larger particle size. As a result, small particles cannot protrude from the backside coating layer surface.

Preferably, the particle size of the inorganic powder having a MOS hardness of 5 or more contained in the backside coating layer should be smaller than the main shaft size of the magnetic powder of metal. When a magnetic recording tape having such a configuration is wound around a hub made of a polyoxymethylene resin or the like, it is preferable to install a tape wound in a cassette casing made of an ABS resin containing a pigment having a Mohs hardness of 2-4. .

Examples of the nonmagnetic substrate material used in the present invention include polyester (e.g. polyethylene terephthalate, polyethylene 2,6-naphthalate, etc.), polyolefin (e.g. polyethylene, polypropylene, etc.), cellulose derivatives (e.g. cellulose acetate, Cellulose diacetate, etc.), vinyl resins (eg, polyvinyl chloride, polyvinylidene chloride, etc.), polycarbonates, polyimides and polyamides, and polyamides.

Among these, biaxially stretched polyesters such as polyethylene terephthalate or polyethylene 2.6-naphthalate having a Young's modulus in the longitudinal direction of at least 700 kg / mm2, a Young's modulus in the width direction of at least 400 kg / mm2 and a surface roughness of about 0.01 μm desirable. One surface of the substrate is coated with a magnetic paint made by dispersing a magnetic powder and an inorganic powder having a Mohs hardness of 5 or more in a binder resin dissolved in an organic solvent, followed by drying by magnetic orientation treatment. To form.

Examples of the magnetic powder contained in the magnetic layer include ferromagnetic powders of metals (iron, cobalt, nickel, etc.), alloys such as iron, cobalt, nickel, and zinc, and metals or alloy particles coated with oxides of iron, aluminum, or silicon. have. The principal axis size of the ferromagnetic metal powder is about 0.8 μm in view of the center recording wavelength, but about 0.2 μm in view of resolution. Of these, ferromagnetic metal powders containing at least 0.1 wt% of manganese based on the weight of iron and iron are preferred.

Particularly preferred are ferromagnetic metal powders containing at least 0.1 wt% manganese and 1 to 50 times the amount of alkaline earth metals (eg calcium or magnesium) based on the weight of iron and iron because of their relatively high hardness. It is large and has good magnetic properties, so it has an electromagnetic conversion characteristic and the inorganic powder with MOS hardness of 5 or more on the back coating layer surface contains magnetic powder which shows insufficient reinforcing effect. It is hard enough.

Preference is given here to the presence of manganese on the surface of the ferromagnetic powder particles in the form of oxides or hydroxides since a uniform and dense coating is formed from manganese oxide or manganese hydroxide.

In addition, in the preparation of an alloy powder composition containing nickel and cobalt, it is desirable to make the nickel weight at least 2wt% and the weight ratio of cobalt and nickel at least 110wt% because of the magnetic recording medium at 60 ° C. and 90% RH. After 1 week of saturation, the saturation magnetization reduction is less than 30%. It is preferable that the ratio of the half width of the anisotropic magnetic distribution to the coersive force is at least 3.2 to maintain the erase characteristic. Examples of inorganic powders having a MOS hardness of 5 or more include metal oxides, metal carbides, and metal nitrides.

Out of these -Fe ₂ O ₃ (6), Al ₂ O ₃ (9), Cr ₂ O ₃ (9), SiO ₂ (6), TiO ₂ (6), ZrO ₂ (6), SiC (9), TiC ( 9), h-BN (9), Si ₃ N _4, and the like are preferable. The number in parentheses is the Morse longitude.

These inorganic powders are available in suitable particle sizes and are chosen according to the literatures listed above.

As the carbon black contained in the back coating layer according to the present invention, channel black, furnace black, acetylene black, thermal black, and the like may be used. Black is preferred. Furthermore, as in Japanese Patent Laid-Open No. 22,424 / 1986, graphitized carbon black in which carbon black particles are coated with a graphite layer may be used.

Examples of commercially available carbon blacks include Black pearl 700 (particle size 18mμ), Mogal L (particle size 20mμ), ELFTEX pellets-115 (particle size 27mμ), Legal 300 (particle size 27mμ), Vulcan XC-72 (particle size) 30mμ), Sterling NS and R (particle size 75mμ, all above are from Cabot, USA): Laben 8000 (particle size 13mμ), Laben 5250 (particle size 20mμ), Laben 890 (particle size 30mμ), Laben 450 (Particle size 62mμ), Laben 410 (particle size 70mμ), Laben MT-P bead (particle size 280mμ (0.28μm)) and Laben Sebacalb MT-CI (particle size 300μm (0.30μm), all above Columbian Carbon, Inc.: HS-500 (particle size 75mμ) and # 60H (particle size 35mμ) (all are from Asahi Carbon, Japan): Seast 5H (particle size 20mμ: manufactured by Tokai Carbon, Japan ): Ketchen Black EC (particle size 30mμ: manufactured by Akzo of the Netherlands): and # 4040 (particle size 20mμ), # 4330BS (particle size 23mμ), # 4350 BS (particle size 45mμ) and # 40 10 (particle size 80mμ), all of which are manufactured by Mitsubishi Chemical of Japan. Since carbon black having various particle sizes can be easily obtained, it is appropriately selected according to the main shaft size of the magnetic powder of the metal based on the above technical contents of the present invention. In the case where the particle size is relatively small, it is preferable to use the ability of the carbon black to form an agglomerate structure to form a carbon black agglomerate composed of several primary particles.

In this case, the agglomerate has one carbon black particle logger function. Inorganic powder and carbon black are added to the magnetic paint and the backside coating to satisfy the relationship between the particle sizes shown above. Examples of the binder resin contained in the magnetic layer and the back coating layer include vinyl chloride resins such as vinyl chloride / vinyl acetate copolymers, vinyl chloride / vinyl acetate vinyl alcohol copolymers, vinyl chloride / acrylate copolymers, vinyl chloride / vinylidene Chloride copolymer, vinyl chloride / acrylonitrile copolymer and vinyl chloride / vinylacetate / maleic acid copolymer), thermoplastic polyurethane resin, thermosetting polyurethane resin, polyester resin, phenoxy resin, polyvinyl butyral resin, cellulose Derivatives, epoxy resins, and mixtures thereof. Hydrophilic groups (such as carboxylic acid groups, sulfonic acid groups, sulfonate groups, phosphate groups, phosphate groups, amine groups, or ammonium salt groups, etc.) are introduced into these resins to improve the dispersibility of powder particles in the resin, or An acrylic double bond is introduced into the resin to irradiate and cure the resin. Examples of solvents used to prepare the paint for forming each layer include alcohol (e.g. ethanol, propanol, butanol, etc.), esters (e.g. methyl acetate, ethyl acetate, butyl acetate, etc.), ketones (e.g. methyl ethyl ketone, methyl iso Butyl ketone, cyclohexanone, etc.), ethers (e.g., tetrahydrofuran, dioxane, etc.), aromatic hydrocarbons (e.g., benzene, toluene, xylene, etc.), aliphatic hydrocarbons (e.g., heptane, hexane, cyclohexane, etc.), Chlorinated hydrocarbons such as methylene chloride, ethylene chloride, chloroform and the like, of which mixed solvents of cyclohexanone and toluene are preferred.

In each layer described above, lubricants (eg saturated or unsaturated higher fatty acids, higher fatty acid amides, fatty acid esters, higher alcohols, silicone oils, mineral oils, edible oils, fluorinated oils, etc.) may be added as additives.

Each of the above components is dispersed in a ball mill or sand mill in a predetermined amount to prepare a magnetic paint or a coating for backside coating, and then coated on a nonmagnetic substrate. While dispersing the paint, excessive force should be applied to the carbon black or inorganic powder particles so as not to change the particle size of the carbon black blended according to the mixing design. To coat the paint, first the magnetic paint is coated, subjected to magnetic field orientation, dried and then surface treated to make the surface smooth, followed by the first winding and then the back coating paint. This process step is disclosed in Japanese Patent Publication No. 23,647 / 1983. The magnetic layer or the back coating layer may be a single layer or a composite layer. Of course, you can coat the magnetic layer and the back coating layer at the same time. After coating, the magnetic recording medium is cut to a certain width with a slitting machine, and in general, each tape is wound on a hub and installed in the cassette casing with the rear coating layer inside. Since a strong winding force is applied to the hub acting as a core, the sink must be adjusted to 5 μm or less on the peripheral surface of the hub to prevent the tape from curling. The backside coating layer is made of ABS resin in cassette casing or at least tapeguide means because noise is reduced when it comes into contact with the tape guide means in the cassette casing. To the resin, which is the raw material for the cassette casing or the tape guide means, a pigment having a MOS hardness of 2-4 is added to prevent the backside coating layer from being damaged. Addition of an antistatic agent such as carbon black and quaternary ammonium salts (e.g. polyoxyethylene alkylamine) to the cassette casing to reduce electrostatic noise, or a fluidizing agent for molten resins such as ethylenebisstearoamide Add. After melting the resin composition, it is injected into a metal mold to produce a cassette casing.

According to the above method, it is possible to manufacture a magnetic recording medium which has high power in short wavelength recording at the center melt wavelength of 0.8㎛ and suppresses noise increase even after storage.

Preferred Embodiments of the Invention

end. Magnetic layer formation

Aluminum coated iron particles containing 0.2wt% manganese and 1.0wt% calcium based on the weight of iron, 1600Oe coercivity, 120emu / g saturation magnetization degree, 0.18㎛ main shaft size, and axial ratio 100 parts by weight of ferromagnetic metal iron powder having a weight of 10, 10 parts by weight of a vinyl chloride resin having a degree of polymerization of 340 and a hydroxyl group, 7 parts by weight of a thermoplastic polyurethane resin, 10 parts of a vinyl chloride resin having a degree of polymerization of 340 and having a hydroxyl group Parts, 7 parts by weight of a thermoplastic polyurethane resin, 8 parts by weight of alumina having a particle size of 0.2 μm, 2 parts by weight of myristic acid, red oxide (red oxide) -Fe ₂ O ₃ ) 2 parts by weight, # 4010 carbon black (manufactured by Mitsubishi Chemical, Japan) having a particle size of 80 μm, 1 part by weight and particle size of 20 μm Seast 5H carbon black (manufactured by Tokai Carbon, Japan) 2 By weight, 70 parts by weight of cyclohexanone and 70 parts by weight of toluene were added, and the resulting composition was mixed and dispersed in a ball mill for 96 hours.

To this mixed composition, 5 parts by weight of trifunctional polyisocyanate compound was added and mixed to prepare a magnetic paint. Magnetic paint was coated on a biaxially stretched polyethylene terephthalate film having a thickness of 10 μm to a thickness of 2.5 μm, dried, and calendered to prepare a magnetic recording medium.

B, back coating layer formation

60 parts by weight of Seast 5H carbon black (manufactured by Tokai Carbon, Japan) with a particle size of 20 mμ, 7.5 parts by weight of Laben MT-P beads carbon black (manufactured by Columbian Carbon, USA) with a particle size of 280 mμ (0.28 μm), particle size 30 parts by weight of calcium carbonate having a diameter of 0.05 μm, 2.5 parts by weight of red oxide having a particle size of 0.1 μm, 45 parts by weight of thermoplastic polyurethane resin, 40 parts by weight of nitrocellulose, and 15 parts by weight of trifunctional isocyanate crosslinking agent 330 weight of cyclohexanone And the composition added to 330 parts by weight of toluene were mixed and dispersed for 96 hours in a ball mill to prepare a coating for the backside coating. This backside coating paint was coated to a layer thickness of 1.0 μm on the back side of the magnetic recording medium coated with the magnetic layer, dried, and cured at 60 ° C. for 20 hours. The total thickness of the magnetic recording medium thus produced was 13.5 μm. This was cut to a certain width to make a tape, and the polyoxymethylene resin was injection-molded and wound with the back coating layer on the inner side around the hub made by suppressing the sink around the peripheral surface to about 0.1 μm. .

All. Cassette casing manufacturers

100 parts by weight of ABS resin (NA-1060, manufactured by Denki-kabaku logyo, Japan), 23 parts by weight of carbon black pigment treated with Ferrocyanine Blue, 35 parts by weight of calcium carbonate (particle size 0.5 μm) 2 parts by weight of polyoxyethylene alkylamine and 3 parts by weight of ethylene bistearoamide were mixed in a mixer for 1 minute at 110 ° C., and then extruded at 220 ° C. in a twin screw extruder to form pellets. made.

The pellet was melted at 240 ° C with 1500 parts by weight of the same ABS resin as described above and injected into a mold kept at 30 ° C to form a cassette casing. In this cassette casing, a magnetic recording medium was assembled by setting a tape wound around a hub.

Example 2

When forming the back coating layer, instead of 7.5 parts by weight of Laben MT-P beads (made by Columbian Carbon, USA) having a particle size of 280 mμ (0.28 μm), the same amount of Laben Sebacalb MT-CI having a particle size of 300 mμ was used. Magnetic recording media were prepared in the same manner.

Example 3

Instead of 7.5 parts by weight of Laben MT-P beads (made by Columbian Carbon, USA) having a particle size of 280 mμ (0.28 μm), the same amount of # 4010 (manufactured by Mitsubishi Chemical, Japan) with the same particle size was used. The mixture was mixed in a ball mill for 22 hours to prepare a magnetic recording medium in the same manner as in Example 1. Magnetic paints were observed after mixing for 22 hours in the ball mill. As a result, carbon black particles formed agglomerates of 13 particles on average, and the size of the particles was 210 mμ.

Example 4

When forming the back coating layer, instead of 7.5 parts by weight of Laben MT-P beads (made by Columbian Carbon, USA) having a particle size of 280 mμ (0.28 μm), use the same amount of # 4010 (manufactured by Mitsubishi Chemical, Japan) with a particle size of 80 mμ. A magnetic recording medium was prepared in the same manner as in Example 1.

Magnetic paints were observed after 96 hours of mixing in the ball mill.

Example 5

A magnetic recording medium was prepared in the same manner as in Example 1 using red oxide having a particle size of 0.8 μm instead of 2.5 parts by weight of red oxide having a particle size of 0.1 μm.

Comparative Example 1

Instead of the ferromagnetic metal used in forming the magnetic layer in Example 1, the same amount of ferromagnetic metal powder having a coercivity of 1600Oe saturation magnetization degree of 120 emu / g, a main axis size of 0.35 μm, and an axial ratio of 10 was used, and a back coating layer was formed. A magnetic recording medium was manufactured in the same manner as in Example 1, using the same amount of red oxide having a particle size of 0.8 μm instead of 2.5 parts by weight of red oxide.

Comparative Example 2

Laben MT- having a particle size of 280 mμ (0.28 μm) using the same amount of red oxide having a particle size of 0.8 μm instead of 2.5 parts by weight of red oxide having a particle size of 0.1 μm used in forming the backside coating layer in Example 1 Magnetic recording medium was prepared in the same manner as in Example 1, using the same amount of # 4010 (manufactured by Mitsubishi Chemical, Japan) having a particle size of 80 mμ instead of 7.5 parts by weight of P beads (Column Carbon, USA).

The surface roughness of each of the magnetic layer and the back coating layer of each of the magnetic recording media prepared in Examples 1 to 4 and Comparative Examples 1 and 2 was measured using a tracer type surface roughness tester and a 0.08 mm tracer. Measured at cut-off R, this is expressed as the mean line roughness.

The coercive force and the square ratio of the magnetic layer in the applied magnetic field of 10 KOe were measured. After recording the signals at 7 MHz and storing them for 60 days, or by reproducing these signals immediately after winding on the hub, the noise level at 6 MHz was measured and the noise level of Example 1 immediately after winding on the hub was 0 dB. It is expressed as the noise ratio for the value. The results are shown in the following table.

TABLE 1

As can be clearly seen in the above table, the magnetic recording medium of each example shows no noise increase even after storing for 60 days, while the magnetic recording medium of the comparative example shows an increase of noise after storing. The magnetic recording medium of the present invention is suitable for short wavelength recording because it shows little increase in noise even after long-term storage.

Claims (12)

The magnetic layer formed on one side of the substrate contains a metallic magnetic powder having a major axis size of about 0.2 μm and an inorganic powder having a MOS hardness of at least 5. The back coating layer formed on the other side of the substrate has a main shaft of metallic magnetic powder. A magnetic recording medium having a magnetic layer on one side of a substrate and a backside coating layer on the other side of the substrate, wherein the substrate has a particle size smaller than the size and contains an inorganic powder having a hardness of at least 5. It has a magnetic layer on one side of the substrate, and a backing coating layer on the other side of the substrate, and is used to record information at a central recording wavelength of about 0.8 μm. A magnetic recording medium containing an inorganic powder, wherein the rear coating layer contains an inorganic powder having a particle hardness of at least 5 having a particle size smaller than the major axis size of the metallic magnetic powder. One side of the substrate has a magnetic layer containing a metallic magnetic powder and an inorganic powder having a MOS hardness of at least 5. The other side of the substrate has a MOS hardness of at least 5 having a particle size smaller than the major axis size of the metallic magnetic powder. It has a back coating layer containing phosphorus inorganic powder, and it is used to record information at the center recording wavelength of about 0.8㎛, and the back coating layer is moved inward to wind the magnetic tape around the hub, and the Mohs hardness is 2-4. A magnetic recording medium made of magnetic tape which is put into a cassette casing made of an ABS resin containing a pigment. It has a magnetic layer on one side of the substrate and a back coating layer on the other side of the substrate, and is used to record information at a central recording wavelength of about 0.8 μm. The magnetic layer has a surface roughness of 0.004 μm with a centerline average roughness. In the case of 10KOe, the squared ratio is at least 0.85 and contains the inorganic powder and the metal magnetic powder with a mohs hardness of at least 5, and the back coating layer has a surface roughness of 0.01 µm with a centerline average roughness and smaller than the principal axis size of the metallic magnetic powder. A magnetic recording medium containing an inorganic powder having a particle size of at least 5 Mohs hardness. It has a magnetic layer on one side of the substrate and a back coating layer on the other side of the substrate, and is used to record information at a central recording wavelength of about 0.8 μm. The magnetic layer has a surface roughness of 0.004 μm with a centerline average roughness and coercive force. Containing at least 1500Oe of inorganic powder and metal magnetic powder with a hardness of at least 5, and the rear coating layer has a surface roughness of 0.01 µm with a median average roughness and a particle size of less than the principal size of the metallic magnetic powder. A magnetic recording medium containing inorganic powder having a hardness of at least 5. The magnetic layer formed on one side of the substrate contains metallic magnetic powder and inorganic powder having a MOS hardness of at least 5. The rear coating layer formed on the other side of the substrate has a particle size smaller than the major axis size of the metallic magnetic powder. A magnetic recording medium comprising a magnetic tape containing an inorganic powder having a Mohs hardness of at least 5 and a total thickness of the substrate, the magnetic layer and the back coating layer of about 14 μm. The magnetic layer formed on one side of the substrate contains iron, a metallic magnetic powder containing at least 0.1 wt% of manganese by weight of iron, and an inorganic powder having a MOS hardness of at least 5, and a rear surface formed on the other side of the interposition. The coating layer is a magnetic recording medium having a magnetic layer on one side of the substrate to have a particle size smaller than the major axis size of the metallic magnetic powder and containing at least 5 inorganic powders and a rear coating layer on the other side of the substrate. The magnetic layer formed on one side of the substrate contains metallic magnetic powder made of iron, manganese and alkaline earth metals and inorganic powder having a MOS hardness of at least 5. The backside coating layer formed on the other side of the substrate has a main axis of metallic magnetic powder. A magnetic recording medium having a magnetic layer on one side of a substrate and a backside coating layer on the other side of the substrate, the inorganic powder having a particle size smaller than the size and having an inorganic powder of at least 5 Mohs hardness. The magnetic layer formed on one side of the substrate contains metallic magnetic powder made of iron, manganese and alkaline earth metal and inorganic powder having a MOS hardness of at least 5. The rear coating layer formed on the other side of the substrate is made of metallic magnetic powder. It contains an inorganic powder with a particle size smaller than the major axis size and has a Mohs hardness of at least 5, and has a surface roughness as a centerline average surface smaller than the major axis size of the metallic magnetic powder, and has a magnetic layer on one side and a back coating layer on the other side. Magnetic recording media consisting of. The magnetic layer formed on one side of the substrate contains metallic magnetic powder, and the back protective layer formed on the other side of the substrate is made of inorganic powder having a particle hardness of at least 5 having a particle size smaller than the major axis size of the metallic magnetic powder. It also has a surface roughness as a central mean surface smaller than the main axis size of the metallic magnetic powder, and the magnetic layer on one side and the back side on the other side, having a total thickness of about 14 μm of the substrate, the magnetic layer and the back coating layer. Magnetic recording medium consisting of a coating layer. The magnetic layer formed on one side of the substrate contains metallic magnetic powder and inorganic powder having a MOS hardness of at least 5. The rear coating layer formed on the other side of the substrate has a particle size smaller than the major axis size of the metallic magnetic powder. A magnetic recording medium containing carbon black of primary particles or agglomerates and used to record information at a central recording wavelength of about 0.8 μm. One side of the substrate has a magnetic layer containing a metallic magnetic powder and an inorganic powder having a MOS hardness of at least 5. The other side of the substrate has agglomerates or primary particles having a particle size smaller than the major axis of the metallic magnetic powder. ABS has a back coating layer containing carbon black and is used to record information at a central recording wavelength of about 0.8 μm, and the back coating layer is wound inward and wound around the hub to contain a pigment having a Mohs hardness of 2-4. Magnetic recording media made of magnetic tape mounted on a resin cassette casing.