JPH07105533A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having satisfactory electromagnetic transducing characteristics even for Hi-8 high vision, not causing head clogging even at high temp. or low temp., ensuring stable running even at low temp. and high humidity and excellent in running durability. CONSTITUTION:In this magnetic recording medium with plural magnetic layers on the nonmagnetic substrate, the thickness of the upper magnetic layer on dry basis is <0.5mum and the total thickness of all the magnetic layers on dry basis is <=2.5mum. The upper magnetic layer contains alpha-Al2O3 or Cr2O3 powder having <=0.30mum average particle diameter and the lower magnetic layer contains Cr2O3, red iron oxide or alpha-Al2O3, powder whose average particle diameter is equal to or larger than that of the powder in the upper magnetic layer.

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 containing an abrasive in an upper layer and a lower layer of a plurality of magnetic layers.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for performance adaptation to magnetic recording media such as magnetic tapes for high-eight (Hi-8) or high-definition purposes.

In order to support Hi-8 and high-definition, it is essential to make the magnetic layer ultra-smooth, but it is necessary to make not only the magnetic powder but also the polishing agent into fine particles. Japanese Patent Application Laid-Open No. 63-74118 discloses a technique in which ₅ to 15 wt% of α-Al ₂ O ₃ having a particle size of 1/2 or less of the average particle size of ferromagnetic powder and less than 0.1 μm is added as an abrasive. It is disclosed. However, since the magnetic layer has a single layer structure, when the ferromagnetic metal powder is used, the lubricant is likely to be strongly adsorbed to the magnetic powder, which causes a problem in running durability.

Further, Japanese Patent Application Laid-Open No. 2-110823 discloses a technique for improving C / N by using two or more magnetic layers and using cobalt-containing iron oxide having a BET value of 35 m ² / g or more as a lower layer. . However, since the amount of α-alumina used is relatively small and fine particle carbon black is used, there is a problem in running durability under high temperature and high humidity and low temperature.

Further, in Japanese Patent Laid-Open No. 2-208822, a magnetic layer is formed into multiple layers, and an abrasive having an average particle size of 0.3 μm or less is polished on the uppermost layer and an average particle size of 0.3 μm or more is polished on the magnetic layers other than the uppermost layer. There is disclosed a technique of improving sliding noise and head turbidity while maintaining electromagnetic conversion characteristics by using an agent. This technique is well suited for S-VHS image quality systems,
As the tape for i-8 and hi-vision, the abrasive used in the lower layer is too large to obtain desired electric characteristics. That is, the surface property of the uppermost layer is strongly influenced by the surface of the layer adjacent thereto, and the surface property of the adjacent layer strongly depends on the average particle size of the abrasive contained therein. Hi-
In 8 and HDTV tape, in order to improve the surface property of the uppermost layer, it is necessary to greatly improve the surface property of the layer adjacent to the uppermost layer.

Further, JP-A-1-106331 and 1-1.
In the technique disclosed in No. 06332, since the lower layer does not contain the abrasive, the powder falling from the tape edge portion becomes a problem and the head clog may occur. Japanese Patent Laid-Open No. 3-4
In 0217, this point is improved,
Since an abrasive having an average particle size of 0.3 μm is used for both the upper and lower layers, it may not be possible to obtain electromagnetic conversion characteristics suitable for Hi-8 and HDTV.

Further, in each of the above magnetic recording media, the film thickness of the uppermost layer is 0.5 μm or more, which is relatively large, and the film thickness of the entire magnetic layer is relatively large, resulting in a large film thickness loss. There is an inconvenience that a satisfactory electromagnetic conversion characteristic cannot be obtained.

[0008]

It is an object of the present invention to have sufficient electromagnetic conversion characteristics even for Hi-8 and high-definition TVs, to prevent head clogs at high and low temperatures, and to provide stable running durability even at low temperatures and high humidity. It is an object to provide an excellent magnetic recording medium.

[0009]

The above object of the present invention is to provide a magnetic recording medium having a plurality of magnetic layers on a non-magnetic support, wherein the magnetic layer located on the upper side of the magnetic layers has a dry film thickness of 0.5 μm.
and the dry film thickness of the entire magnetic layer is 2.5 μm.
And the average particle size of the upper magnetic layer is 0.30.
It contains α-Al ₂ O ₃ or Cr ₂ O ₃ powder of μm or less, and the magnetic layers other than the upper layer side are equivalent to the α-Al ₂ O ₃ or Cr ₂ O ₃ powder contained in the upper magnetic layer. Or, Cr ₂ O _{3 having} a large average particle size, red iron oxide or α-Al ₂ O
_This is achieved by a magnetic recording medium containing ₃ powders.

According to the structure of the present invention, various running durability can be improved without deteriorating the electromagnetic conversion characteristics even if the thickness of the uppermost layer is reduced and the total thickness of the magnetic layer is reduced. Further, as an aspect of the present invention, the abrasive used in the upper magnetic layer of the present invention is preferably α-Al ₂ O ₃ having a particle size of 0.30 μm or less, more preferably 0.05 μm or more and 0.25 μm or less.

Further, the upper magnetic layer (hereinafter referred to as the uppermost layer) has a ferromagnetic metal alloy powder and an average particle size of 35 to 35.
80 mμ, preferably 40-70 mμ of carbon black is included in the magnetic powder in an amount equal to or less than 1% by weight of the magnetic powder (hereinafter abbreviated as 1% wt), preferably 0.2 to 0.8% wt. It is preferable that the abrasive is used as a magnetic layer containing 4% by weight or more of magnetic powder, and Co-containing iron oxide is used for the magnetic layers other than the uppermost layer.

The BET value of the carbon black is 80 m
It is more preferable that the oil absorption is ² / g or less and the oil absorption is 100 ml / 100 g or more. Further, the iron oxide of the ferromagnetic powder used for the magnetic layers other than the uppermost layer is preferably a core-shell type (Co-deposited) iron oxide having a shell of Co whose surface is treated with Si and / or Al.

Conventionally, various abrasives used for magnetic recording media include organic powders and inorganic powders. As a result of studying various abrasives, in the embodiment of the present invention, a magnetic layer other than the uppermost layer is used. Mohs hardness (MS) 6
A specific one of the above inorganic powders is used. That is, as an abrasive having a Mohs hardness of 6 or more, α-Al ₂ O ₃ (M
S9), TiO ₂ (MS6.5), SiO ₂ (MS
7), SnO ₂ (MS6.5), Cr ₂ O ₃ (MS
9), SiC (MS9) and TiC (MS9) can be mentioned, but in the present invention, they are chromium oxide, red iron oxide or α-Al ₂ O ₃ . Then, α-Al ₂ O ₃ or chromium oxide having a Mohs hardness of 9 or more is used for the uppermost layer.

Further, in order to obtain the effect of the present invention, the average particle size of the abrasive is 0.30 μm or less when used in the uppermost layer, and the above-mentioned uppermost layer when used in at least one layer other than the uppermost layer. The particle size must be the same or larger, and the uppermost layer is preferably monodisperse α-Al ₂ O ₃ (corundum) obtained by an organic alumina method or the like. This organic alumina method is based on the following reaction.

2 AlR ₃ + 4 H ₂ O → Al ₂ O ₃ .H ₂ O +6 RH (alkyl alumina) (boehmite) Al ₂ O ₃ .H ₂ O → Al ₂ O ₃ + H ₂ O heat The above reaction α-Al ₂ O ₃ by the thin particles are particles having a particle size of the particle size distribution is uniform well narrow.

Α-Al produced by the organic alumina method
_{The 2} O ₃ particles can be obtained as fine particles of α-Al ₂ O ₃ which cannot be obtained by other production methods, depending on the firing conditions, and the α-crystallization rate in the crystal can be controlled. High crystallinity in alpha ratio _α-Al 2 _{O 3} is low alpha ratio _α-Al 2 _{O 3}
Has higher polishing ability and wear resistance than Since a head cleaning effect is required as a polishing agent for high-quality video tapes, α-Al ₂ O ₃ having an α conversion rate of 50% or more has both a polishing effect and a head cleaning effect, so that polishing for high-quality video tapes is possible. Suitable as an agent.

The α-Al ₂ O ₃ particles used in the present invention are preferably 4% by weight or more of the magnetic powder, and more preferably 5%.
Used in the range of ~ 15% wt. If it is less than 4% by weight, it is difficult to obtain the effects of head wear, head adhesion and head damage, and if it is more than 15% by weight, output fluctuation and reduction may occur.

In the ferromagnetic powder forming a plurality of magnetic layers according to the present invention, Fe--Al based ferromagnetic alloy powder is used in the uppermost magnetic layer, and Fe--Al alloy powder,
Fe-Al-Ni alloy powder, Fe-Al-Ca alloy powder, Fe-Al-Ca-Ni alloy powder, Fe-Ni-C
Examples thereof include ferromagnetic alloy powders such as o-Al-Si alloy powder, Fe-Ni-Si-Al alloy powder, and Fe-Ni-Si-Al-Mn alloy powder.

Of these, the atomic weight ratio (Fe: Al) is preferably (100: 0.5) to (100: 2).
It is the alloy powder of 0).

The ferromagnetic alloy powder preferably has a crystallite size of less than 200Å, preferably less than 180Å, and an average major axis length of less than 0.25 μm, more preferably 0.20.
Less than μm is used. Specific surface area of the ferromagnetic powder (B
By ET method), usually, ^{25 m} 2 / g or more, preferably 30~80m ² / g. The coercive force of the ferromagnetic powder is usually 500 to 2,000 oersteds, preferably 600 to 1.700 oersteds.

Then, as the ferromagnetic powder for forming the magnetic layer other than the uppermost layer, Co-deposited or Co-containing C is used.
o-γ-Fe ₂ O ₃ powder, Co-Fe ₃ O ₄ powder, Co
Examples include iron oxide magnetic powder such as -FeOx (4/3 <x <3/2) powder.

In addition, these magnetic layers have a crystallite size of 4
Fe ²⁺ with an average major axis length of less than 0.25 μm, less than 50Å
Co-iron oxide in which the atomic ratio Fe ²⁺ / Fe ³⁺ between Fe ³⁺ is 0.08 or more is preferable. The axial ratio of the magnetic powder in the present invention is the ratio of the average major axis length measured for 500 particles in an electron micrograph and the average minor axis length.

The binder used in the present invention generally has an average molecular weight of about 10,000 to 200,0.
Resins within the range of 00 can be used.

Specifically, for example, urethane polymer, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide. Resin, polyvinyl butyral, cellulose derivative (eg cellulose acetate butyrate,
Cellulose diacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubber binders, phenol resins, epoxy resins, urea resins, melamine resins, silicone resins, acrylic reaction resins, Examples thereof include a mixture of a high molecular weight polyester resin and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a urea formaldehyde resin, a mixture of a low molecular weight glycol and a high molecular weight diol compound, and a mixture thereof.

In the present invention, these resins are used in combination,
Alternatively, a resin having a negative functional group may be preferably used alone. The resin having the negative functional ^{_{groups, -SO 3 M 1, -OSO 2}} M 1, -OSO 3 M 1 and - ^{[(M 2 O-) PO (-OM} 3) ] (wherein, M ¹ is a hydrogen atom, an alkali metal,
M ² and M ³ are each a hydrogen atom, an alkali metal or an alkyl group. Further, M ² and M ³ may be different from each other or may be the same. ) And the like.

The resin having a negative functional group is, for example,
It can be obtained by modifying a resin such as a vinyl chloride resin, a polyester resin or a polyurethane resin to introduce the negative functional group. The amount of the negative functional group in the resin having the negative functional group is 0.005 to 1.0 mmo.
It is preferably 1 / g.

In the resin in which the amount of the negative functional groups is regulated, the dispersibility of the ferromagnetic powder is good, the output of the magnetic recording medium is large, and the running stability is improved. On the contrary, if the amount is out of the above range, these effects may not be sufficiently obtained.

When the resin having the negative functional group is used, the compounding amount thereof is usually 2 to 50% by weight, preferably 5 to 40% w with respect to 100 (weight) of the ferromagnetic powder.
t. If the blending ratio is less than 2% by weight, the desired effect to be obtained when the resin having the negative functional group is blended may not be sufficiently exhibited. 50% wt
If the amount is increased, sliding noise and white turbidity of the head may be deteriorated.

In the present invention, the durability of the magnetic layer can be improved by using a polyisocyanate type curing agent together with the resin having a negative functional group. Examples of the polyisocyanate-based curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name; manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (product) Name: Bayer)
Any of those that have been conventionally used as a curing agent, such as trifunctional isocyanates such as, or urethane prepolymers containing isocyanate groups at both ends, and those that are polyisocyanates that can be used as a curing agent. Can also be used. The amount of the curing agent used is usually 5 to 80 parts by weight based on the total amount of the binder.

In the present invention, in addition to the various binders, as a dispersant which is an optional component, for example, lecithin, phosphate ester, fatty acid, amine compound, alkyl sulfate,
Fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid esters, known surfactants and the like, and salts thereof, negative organic groups (for example, --CO
OH, _-PO 3 H) or the like can be used salts of the polymeric dispersant.

These may be used alone or in combination of two or more. Further, in the present invention,
A fatty acid ester can be used as a plasticizer which is an optional component. Examples of the fatty acid ester include oleyl oleate, oleyl stearate, isocetyl stearate, dioleyl maleate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, amyl stearate, amyl palmitate. Tate, stearyl stearate, lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate,
Butoxyethyl palmitate, butoxyethyl stearate, 2-ethylhexyl stearate, 2-ethylhexyl myristate, ethyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, isooctyl palmitate,
Examples include isooctyl myristate, butyl laurate, cetyl-2-ethylhexarate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate and the like. Of these, butyl stearate, butyl palmitate, butoxyethyl palmitate, butoxyethyl stearate, isooctyl palmitate, and isooctyl myristate are particularly preferred.

The above various fatty acid esters may be used alone or in combination of two or more.
By reducing the amount of the dispersant such as lecithin or the like and the plasticizer such as the fatty acid ester or the like, the running durability of the magnetic recording medium can be improved especially under high temperature and high humidity.

The magnetic layer in the magnetic recording medium of the present invention is
It may contain a lubricant. As the lubricant, for example, fatty acid, silicone lubricant, fatty acid modified silicone lubricant, fluorine lubricant, liquid paraffin, squalane,
Examples thereof include carbon black, graphite, carbon black graft polymer, molybdenum disulfide, and tungsten disulfide. These may be used alone or in combination of two or more.

In the present invention, among the above-mentioned lubricants, fatty acids can be preferably used. Examples of the fatty acid include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid,
Isostearic acid, linolenic acid, linoleic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, Octanedicarboxylic acid and the like can be mentioned. Among these, particularly preferred are myristic acid, oleic acid,
It is stearic acid.

The blending ratio of the lubricant is usually 20% by weight or less, preferably 10% by weight or less, based on 100 (weight) of the ferromagnetic powder. This blending ratio is 20% w
When it exceeds t, blooming and bleed-out may occur easily.

In the present invention, the magnetic layers other than the uppermost layer may contain carbon black having an average particle size of 10 to 100 mμ.

When the magnetic layer contains carbon black having an average particle size of 10 to 100 mμ, preferably 20 to 40 mμ, running durability is further improved without deteriorating the improved electromagnetic conversion characteristics of the magnetic recording medium of the present invention. Can be improved. However, when the average particle diameter of carbon black is less than 10 mμ, running durability may be poor. On the other hand, when the average particle size of carbon black exceeds 100 mμ, the electromagnetic conversion characteristics may be deteriorated when the addition amount is increased.

Further, the blending ratio of the carbon black for sufficiently exhibiting the effect expected in the present invention is preferably 0 to 1% by weight with respect to 100 (weight) of the ferromagnetic powder.

The magnetic layer may further contain an abrasive and an antistatic agent, which are not included in the present invention, in addition to the above various components.
The antistatic agent or the dispersant described above does not have only a single action, but for example, one compound may act as a lubricant and an antistatic agent. Therefore, the above-mentioned classification in the present invention shows main actions, and the action of the classified compounds is not limited by the action shown in the classification.

In the present invention, the characteristics are adjusted by stacking a plurality of magnetic layers having different characteristics so that the magnetic layers have a multilayer structure. The dry film thickness of the uppermost magnetic layer is 0.05 to less than 0.5 μm, more preferably 0.05 to 0.3 μm or less, and the dry film thickness of all magnetic layers is 0.5 to 2.5 μm. Or less, more preferably 0.5 to 2.3 μm or less.

Examples of the material for forming the non-magnetic support used in the present invention include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate. And plastics such as polycarbonate, aromatic polyamide, and polyimide. Further, metals such as Cu, Al and Zn, glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can be used. The thickness of the support is usually 3 to 150 μm, preferably 4 to 100 μm.

In the present invention, a back coat layer may be provided on the back surface of the non-magnetic support for the purpose of improving the running property of the magnetic recording medium, preventing charging and preventing transfer. However, in the present invention, good electromagnetic conversion characteristics, runnability and durability can be obtained without providing a back coat layer. Further, an intermediate layer (eg, an adhesive layer) may be provided on the surface of the non-magnetic support on which the magnetic layer is formed for the purpose of improving the adhesiveness between the magnetic layer and the non-magnetic support. Further, a protective layer may be provided on the uppermost layer. The magnetic layer formed on the non-magnetic support directly or through an appropriate intermediate layer is formed by dispersing ferromagnetic powder in a binder.

In the magnetic recording medium of the present invention, a magnetic paint is prepared by kneading and dispersing the abrasive, the ferromagnetic powder, the binder such as vinyl chloride resin having a negative functional group, and other magnetic layer forming components in a solvent. After that, the magnetic coating material can be applied onto the non-magnetic support and dried.

Examples of the solvent used for kneading and dispersing the magnetic layer forming components include acetone and methyl ethyl ketone (M
EK), methyl isobutyl ketone (MIBK) and cyclohexanone and other ketone systems; methanol, ethanol, propanol and butanol and other alcohol systems;
Ester systems such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate; ether systems such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane; aromatic carbonization such as benzene, toluene and xylene. Hydrogen; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene can be used.

In kneading the composition of the components for forming the magnetic layer,
The above-mentioned ferromagnetic powder and other magnetic paint ingredients are charged into a kneader simultaneously or individually. For example, first, the ferromagnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and further kneading is performed to obtain a magnetic paint.

For kneading and dispersing, various kneaders can be used. Examples of the kneader include a two-roll mill, a three-roll mill, a pressure kneader, a continuous kneader, an open kneader, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high speed impeller disperser, a high speed stone mill, a high speed impact mill, and a disper. A kneader, a high speed mixer, a homogenizer, an ultrasonic disperser, etc. may be mentioned.

As a coating method that can be used for coating the magnetic paint, for example, gravure roll coating,
Examples include Mayer bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, skies coating, kiss coating, extrusion coating and fantin coating.

A wet-on-dry or wet-on-wet system is optionally used for the multi-layer coating. In this way, after applying the magnetic layer forming component, magnetic field orientation treatment is performed in the undried state, if necessary, and surface smoothing treatment is further performed using, for example, a super calender roll. Then, by cutting into a desired shape, a magnetic recording medium can be obtained.

The magnetic recording medium of the present invention can be used as, for example, a magnetic tape such as a video tape or an audio tape by cutting into a long shape, or a floppy disk or the like by cutting into a disk shape. . Further, like a normal magnetic recording medium, it can be used in a card shape, a cylindrical shape, or the like.

[0050]

EXAMPLES Next, examples and comparative examples of the present invention will be shown.
The present invention will be described more specifically. In the examples and comparative examples described below, "part" means "part by weight".

Magnetic coating for the uppermost layer Ferromagnetic metal powder 100 parts Hc: 17400c δs: 125 emu / g Crystallite size: 150Å Si content 1.4% by weight, Al content 2.1% by weight, Co content 3. 8 wt% (relative to metal powder) Vinyl chloride resin containing sulfonic acid metal salt 10 parts (MR-110 manufactured by Zeon Corporation) 5 parts Polyurethane resin containing sulfonic acid metal salt 5 parts (UR-8700 manufactured by Toyobo Co., Ltd.)

Abrasives See Table 1 for types of abrasives Carbon black Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts

Magnetic coating material for lower layer Co-γ-Fe ₂ O ₃ 100 parts (surface treatment with Si, Al compound, Si content 0.1% by weight, Al content 0.8% by weight) (based on magnetic powder) ) Metal sulfonic acid salt-containing vinyl chloride tree species 12 parts (Zeon Corporation MR-110) Sulfonic acid metal salt-containing polyurethane resin 8 parts (Toyobo Co., Ltd. UR-8200)

Abrasives See Table 1 for types of abrasives Stearic acid 1 part Myristic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts

The above-mentioned magnetic coating materials for the uppermost layer and the lower layer were prepared by kneading and dispersing the respective prescription compositions in a kneader and a sand mill. Next, 5 parts of polyisocyanate (Coronate L; manufactured by Nippon Polyurethane Co., Ltd.) was added to each of the obtained paints,
After applying to the non-magnetic support polyethylene terephthalate with a thickness of 10 μm by the wet-on-wet method,
A magnetic field orientation treatment was performed while the coating film was not dried, and subsequently, after drying, a surface smoothing treatment was performed using a calendar to form a magnetic layer.
The calender conditions were a temperature of 80 ° C. and a pressure of 300 Kg / cm ² , the upper layer film thickness was 0.4 μm, and the lower layer film thickness was 2.0 μm. The web obtained as described above is cut into 8
mm video tape was made. Table 1 shows the configurations and performance evaluation results of these video tape samples.

[Head Clog] Under a high temperature (40 ° C.) and a low temperature (0 ° C.) environment, the tape was run for the full length using S-550 (manufactured by Sony Corporation), and the decrease in RF output was 2
The number of occurrences was counted, with the head clogging when it occurred continuously for at least dB and for 1 second or more.

[RF output] Shiba Soku noise meter 9
It was measured using 8 mm video movie V900 (manufactured by Sony Corporation) using 25C.

[Running Durability] Running Durability at -40 ° C. and 80% RH Under the environment of -40 ° C. and 80% RH, the full length running of the tape was 50 using S-550 (manufactured by Sony Corporation). Pass, 50
The jitter value after passing was measured. VTR jitter meter "MK-61" manufactured by Meguro Electronics Co., Ltd.
24 ”(measurement unit: μs).

[0059]

[Table 1]

As can be seen by simply looking at Table 1, there is a clear difference between the examples of the present invention and the comparative examples, and the effect of the present invention is clear.

[0061]

EFFECTS OF THE INVENTION According to the present invention, it has sufficient electromagnetic conversion characteristics even for Hi-8 and high-definition television, does not cause head clog even at high temperature and low temperature, and runs stably even at low temperature and high humidity. It has become possible to provide a magnetic recording medium having excellent properties.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hisato Kato, 1st Sakura-cho, Hino-shi, Tokyo Konica stock company (72) Inventor Takahiro Mori 1st Sakura-cho, Hino-shi, Tokyo Konica stock company (72) Invention Takahiro Hayashi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Corporation

Claims (1)

[Claims] 1. A magnetic recording medium having a plurality of magnetic layers on a non-magnetic support, wherein the magnetic layer located on the upper side of the magnetic layers has a dry film thickness of less than 0.5 μm and an all magnetic layer. Α-Al ₂ O having a dry film thickness of 2.5 μm or less and the upper magnetic layer having an average particle size of 0.30 μm or less.
₃ or Cr ₂ O ₃ powder, and the magnetic layer other than the upper layer side has the same or larger average particle diameter than the α-Al ₂ O ₃ or Cr ₂ O ₃ powder contained in the upper magnetic layer.
A magnetic recording medium containing ₂ O ₃ , red iron oxide, or α-Al ₂ O ₃ powder.