JPH05135352A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent generation of jitter under high temperature and high humidity by making a surface of a magnetic layer into less than a specified waviness and incorporating ferromagnetic metallic powder having specified characteristics in the uppermost layer. CONSTITUTION:A waviness as of the magnetic layer is less than 0.22mum and the uppermost layer incorporates the ferromagnetic metallic powder less than 0.25mum, the average length of the major axis and less than 200Angstrom of the crystal size with measurement by X-rays. Also a waviness Bs of a magnetic layer forming surface of a nonmagnetic supporting body is less than 0.020mum and the numbers (n) of the projections more than 0.01mum which are existing on the forming surface are >=200 pieces per 1mm of the measuring length and the numbers N of the projections more than 0.3mum are <=500 pieces per 400mm of the measuring length. Besides the average height Hm of the projections is 0.1-0.25mum, a ratio Hmax/Hm of the max. height Hmax of the projections to the average height Hm of the projections is made to be <=10. Thus the magnetic layer surface of the uppermost layer is made to a slightly coarse surface in such a degree that the electric characteristics are not dropped by affect of fine projections on the nonmagnetic supporting body and then the friction coefficient does not increase.

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 improvement of running property.

[0002]

2. Description of the Related Art In recent years, the demand for magnetic tapes for high-eight (Hi-8) or high-definition has become more and more strict, and ultra-smooth magnetic layer surfaces using ultra-smooth supports, and fillers such as carbon are highly filled. There is a growing need for a magnetic layer that has been turned into a magnetic material.

However, super-smoothing of the magnetic layer surface and removal of fillers such as carbon from the magnetic layer increase the friction coefficient of the magnetic layer, impair the running property, and cause problems such as blocking of the magnetic tape.

In the Hi-8 system, high-frequency characteristics are extremely important. However, the above-mentioned measures reduce the initial RF output especially in low humidity where the polishing power of the magnetic tape decreases, and the jitter during running in high temperature and high humidity. Problems such as frequent occurrence occur.

In order to solve such problems, it has been proposed to improve the running property of the magnetic tape and improve the electromagnetic conversion characteristics by using a laminated support having fine projections on the surface of the non-magnetic support. (Japanese Patent Laid-Open No. 3-176807, 176808, 176809).

Further, there is known a technique for improving performance by using a ferromagnetic metal powder for the uppermost magnetic layer which is a laminated magnetic layer (Japanese Patent Laid-Open No. 19524/64, Japanese Laid-Open Patent Publication No. 2-110823).

However, the performance requirements for the magnetic tape require a more precise factor configuration.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is, in view of the above-mentioned circumstances, that the R is under a low humidity condition with a small spacing and a small friction coefficient.
The purpose of the present invention is to provide a magnetic tape which has negligible F output reduction and jitter generation under high temperature and high humidity and has excellent corrosion resistance.

[0009]

The object of the present invention is to provide a magnetic recording medium in which a plurality of magnetic layers are provided on a non-magnetic support, wherein the surface waviness As of the magnetic layer is 0.022 μm or less, and the average length of the uppermost layer is It contains a ferromagnetic metal powder with an axial length of less than 0.25 μm and a crystallite size of less than 200Å by X-ray measurement, and the surface waviness Bs of the magnetic layer forming surface of the non-magnetic support is 0.020.
The number n of protrusions of not more than μm and not less than 0.01 μm existing on the formation surface
Is 200 or more per 1 mm measuring length, and the number N of protrusions of 0.3 μm or more
Is less than 500 per 400 mm measuring length, and the average protrusion height Hm is
This is achieved by a magnetic recording medium characterized by having a ratio Hmax / Hm of 0.01 to 0.25 μm, and a ratio of the maximum protrusion height Hmax to the average protrusion height Hm of 10 or less. According to the configuration of the present invention, the surface of the uppermost magnetic layer is slightly roughened to the extent that the electrical characteristics are not deteriorated due to the influence of the fine protrusions on the non-magnetic support, and carbon black or the like is removed as much as possible. Even in the case of the ultra-smooth magnetic layer, the friction coefficient does not increase.

By the way, it is preferable to appropriately combine the following means in order to obtain electric characteristics, running durability, and corrosion resistance that are compatible with Hi-8 and high-definition.

(1) In the uppermost layer, the average major axis length is less than 0.25 μm,
Use a ferromagnetic metal powder having a crystallite size of less than 200Å, (2) the ferromagnetic powder contains Fe and Al, and the atomic weight ratio of Fe and Al is Fe: Al = 100: 0.5 to 100: 20. ) Average major axis length 0.25μ in at least one layer other than the top layer
Ferromagnetic powder of less than m and crystallite size of less than 450Å is included. (4) The top layer contains ferromagnetic powder with an axial ratio of less than 10. (5) At least one layer other than the top layer is Fe ²⁺ and Fe. Includes Co-containing iron oxide with an atomic ratio of ³⁺ (Fe ²⁺ / Fe ³⁺ ) of 0.08 or more. (6) On the back surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed A layer having uniform fine projections is laminated, and (7) the weight of the carbon black contained in the uppermost layer is less than 1 part by weight with respect to 100 parts by weight of the magnetic powder, and the more preferable range is (1) above. For the ferromagnetic metal powder with an average major axis length of less than 0.20 μm and a crystallite size of less than 180Å, (2) Fe: Al = 100: 1 to 100: 20, in (3), less than 0.22 μm and a crystallite size of less than 420Å , (4), the axial ratio was 6 to 9, (5) Fe ²⁺ / Fe ³⁺ was 0.15 to 0.45, and (7) carbon black. It is more preferable that the weight of the particles is less than 0.5 parts by weight, and the ratio of (maximum protrusion height) / (average protrusion height) is 5 or less in the protrusions on the surface of the non-magnetic support.

Next, the present invention will be described in detail.

The surface waviness Bs of the surface of the non-magnetic support on which the magnetic layer is formed (hereinafter referred to as the abdomen) is 0.020 μm or less, preferably
By setting the thickness to 0.018 μm or less, and more preferably 0.015 μm or less, the surface waviness As of the magnetic layer can be reduced and the electromagnetic conversion characteristics (particularly the chroma S / N) can be improved.

On the contrary, the surface waviness BsHm of the abdominal surface is 0.020.
When it exceeds μm, the surface waviness As of the magnetic layer exceeds 0.022 μm and becomes too large, which causes deterioration of electromagnetic conversion characteristics.

Further, in the non-magnetic support of the present invention, the number n of protrusions present on the abdominal surface having a height of 0.01 μm or more is 200 or more, preferably 200, per 1 mm of measurement length.
The number N of protrusions is not less than 2000 and not more than 2000, and the number N of protrusions having a height of 0.30 μm or more is 500 or less, preferably 100 or less per measurement length 400 mm, and the average protrusion height Hm is 0.01 to 0.25 μm.
m, and on the ventral surface of the non-magnetic support (maximum protrusion height Hma
x) / (average protrusion height Hm) ratio is 10 or less, preferably 5
It must be:

The number n'of protrusions having a height of 0.01 μm or more existing on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed (hereinafter, this surface is referred to as the back surface) is 1 mm. 200 or more, preferably 200 or more and 2000 or less per
Further, the number N'of protrusions having a height of 0.30 μm or more is 500 or less, preferably 100 or less per 400 mm of measurement length,
The ratio of (maximum protrusion height H'max) / (average protrusion height H'm) on the back surface is 10 or less, preferably 5 or less.

By controlling the surface waviness and roughness on the ventral surface and the back surface of the non-magnetic support as in the present invention, a sliding recording noise is reduced, and a magnetic recording medium excellent in transportability and runnability is provided. It is possible to provide a magnetic recording medium which is excellent in running property and is less likely to have a flaw on the back surface of the non-magnetic support when the magnetic recording medium is wound up. Further, the surface waviness As of the magnetic layer is controlled to improve electromagnetic conversion characteristics, and projections are protected and stored in the coating process and the calendar process of the magnetic paint to provide a magnetic recording medium in which dropout is unlikely to occur. it can.

Examples of the material for forming the non-magnetic support which gives such characteristics are polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose such as cellulose triacetate and cellulose diacetate. Derivatives; and plastics such as polycarbonate, aromatic polyamide and polyimide. Furthermore, metals such as Cu, Al, Zn, glass, so-called new ceramics (eg boron nitride, silicon carbide, etc.)
Various types of ceramics such as the above can also be used.

The thickness of the support is usually 3 to 150 μm,
It is 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.

An intermediate layer (eg, an adhesive layer) may be provided on the surface of the nonmagnetic support on which the magnetic layer is formed for the purpose of improving the adhesiveness between the magnetic layer and the nonmagnetic support.

The magnetic layer formed on the non-magnetic support directly or via an appropriate intermediate layer is formed by dispersing ferromagnetic powder in a binder.

In the present invention, the surface waviness As of the magnetic layer is 0.022 μm or less, preferably 0.020 μm or less, and more preferably 0.018 μm or less. To provide the surface waviness As of the magnetic layer, After applying the magnetic coating material for forming the magnetic layer on the non-magnetic support, a surface smoothing treatment using, for example, a super calender roll, a ferromagnetic powder having a small particle size, or the like may be selected. In addition, the surface waviness As of the magnetic layer can be improved by improving the dispersibility of the ferromagnetic powder, such as the general use of a resin having a functional group as a binder and the use of a device with high shearing force such as a pressure kneader.
It can be 0.022 μm or less.

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 are used.
Alloy powder, Fe-Al-Ca alloy powder, Fe-Al-Ca-Ni alloy powder, F
e-Ni-Co-Al-Si alloy powder, Fe-Ni-Si-Al alloy powder, Fe-Ni-
Examples include ferromagnetic alloy powders such as Si-Al-Mn alloy powders.

Among these, alloy powder having an atomic weight ratio (Fe: Al) of (100: 5) to (100: 20) is preferable.

The shape of the ferromagnetic alloy powder is the crystallite size.
Less than 200Å, preferably less than 180Å, average major axis length 0.25μm
Less than, preferably 0.20 μm is used.

The specific surface area of the ferromagnetic powder (by BET method) is usually, 25 m ² / g or more, preferably 30~80m ² / g.

The ferromagnetic powder has a coercive force of 500 to 2,000 oersteds, preferably 600 to 1.700 oersteds.

Next, as the ferromagnetic powder for forming the magnetic layers other than the uppermost layer, Co-deposited or Co-containing Co-γ-
Examples thereof include iron oxide magnetic powders such as Fe ₂ O ₃ powder, Co-Fe ₃ O ₄ powder, and Co-FeOx (4/3 <x <3/2) powder.

In addition, a crystallite size of 45 is included in these magnetic layers.
Less than 0 Å, Fe ²⁺ in less than an average major axis length 0.25 [mu] m, the atomic ratio between Fe ³⁺ Fe ²⁺ / Fe ³⁺ is preferably 0.08 or more Co- iron oxide.

As the binder used in the present invention, a resin having an average molecular weight of about 10,000 to 200,000 can be generally 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, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates , 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.

Examples of 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) ] (where formula In the above, M ¹ is a hydrogen atom or 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 the 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 preferably 0.005 to 1.0 mmol / g.

In the resin in which the amount of 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, when the amount is out of the above range, these effects may not be sufficiently obtained.

When the resin having a negative functional group is used, its amount is usually 2 to 50 parts by weight, preferably 5 to 40 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

If this blending ratio is less than 2 parts by weight, the desired effect to be obtained when the resin having a negative functional group is blended may not be sufficiently exhibited. If the amount is more than 50 parts by weight, sliding noise and head turbidity may be deteriorated.

In the present invention, the durability of the magnetic layer can be improved by using a polyisocyanate curing agent together with the resin having the negative functional group.

Examples of the polyisocyanate type curing agent include, for example, tolylene diisocyanate, diphenylmethane diisocyanate, hexane diisocyanate, and the like.
Functional isocyanate, Coronate L (trade name; manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (trade name;
A trifunctional isocyanate such as Bayer), or a urethane prepolymer having an isocyanate group at both ends, which has been conventionally used as a curing agent, or a polyisocyanate usable as a curing agent. Any one can be used.

The amount of the above 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, phosphoric acid ester, fatty acid, amine compound, alkyl sulfate,
Fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acid, sulfosuccinic acid esters, known surfactants and their salts, negative organic groups (eg -COO
H, -PO ₃ H) A polymer dispersant salt or the like can be used.

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, isooctyl myristate, Butyl laurate, cetyl-2-ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate and the like can be mentioned. 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.

When the amount of the dispersant such as lecithin or the plasticizer such as fatty acid ester added is reduced, 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.

Examples of the lubricant include fatty acids, silicone lubricants, fatty acid-modified silicone lubricants, fluorine lubricants, liquid paraffin, squalane, carbon black, graphite, carbon black graft polymers, molybdenum disulfide, and tungsten disulfide. And so on.

These may be used alone or in combination of two or more.

In the present invention, fatty acids can be preferably used among the above lubricants. 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.

Of these, myristic acid, oleic acid and stearic acid are particularly preferable.

The blending ratio of the lubricant is the ferromagnetic powder.
Generally, 20 parts by weight or less, preferably 1 part by weight per 100 parts by weight
It is 0 parts by weight or less. If this blending ratio exceeds 20 parts by weight, blooming and bleed-out may occur easily.

In the present invention, the magnetic layer has an average particle size of 10 to 10
It may contain 100 mμ of carbon black.

The magnetic layer has an average particle size of 10 to 100 mμ, preferably
By containing 20 to 40 mμ of carbon black,
The running durability can be further improved without inducing the improved electromagnetic conversion characteristics of the magnetic recording medium of the present invention. However, the average particle size of carbon black is 10 mμ
If it is less than this, running durability may be poor. On the other hand, if the average particle size of carbon black exceeds 100 mμ, the electromagnetic conversion characteristics may be deteriorated when the addition amount is increased.

The blending ratio of the carbon black for sufficiently exhibiting the effect expected in the present invention is 0 to 1 part by weight with respect to 100 parts by weight of the ferromagnetic powder.

The magnetic layer may further contain an abrasive and an antistatic agent 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 the main action, and the action of the classified compound 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.

In the magnetic recording medium of the present invention, the ferromagnetic powder, the binder such as vinyl chloride resin having a negative functional group, and the other components for forming the magnetic layer are kneaded and dispersed in a solvent to prepare a magnetic coating material. It can be produced by coating a magnetic coating on the non-magnetic support and drying.

Examples of the solvent used for kneading / dispersing the magnetic layer forming components include acetone and methyl ethyl ketone (ME
K), ketone systems such as methyl isobutyl ketone (MIBK) and cyclohexanone; alcohol systems such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate. System; ether system such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane; aromatic hydrocarbon such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene And the like can be used.

When 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 this 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 which 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 method or a wet-on-wet method is optionally used for multi-layer coating.

The thickness of the magnetic layer thus coated is a dry thickness, usually 0.1 to 10 μm, preferably 0.5 to 5
μm.

Thus, after applying the magnetic layer-forming component,
In the undried state, magnetic field orientation treatment is performed if necessary, and further surface smoothing treatment is performed using, for example, super calender rolls.

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.

[0071]

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".

First, the characteristics of the magnetic powder, carbon black and non-magnetic support used in Examples and Comparative Examples will be listed.

[0073]

[Table 1]

[0074]

[Table 2]

[0075]

[Table 3]

[0076]

[Table 4]

: Magnetic coating for top layer, formulation A: GA1: [Fe-Al based ferromagnetic metal powder (M) * 100 parts GA2: Potassium sulfonate modified vinyl chloride resin 10 parts Sodium sulfonate modified polyurethane resin 5 parts Alumina (Average particle size 0.2 μm) 6 parts Carbon black (CB) ** 0.4 parts Myristic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 100 parts Cyclohexanone 100 parts Toluene 100 parts: Magnetic coating for lower layer, formulation B: GB1: [Co coating Iron oxide (MO) * 100 parts GB2: [= GA2: magnetic coating for lower layer, formulation B ': GB'1: [= GB1 GB'2: nitrocellulose 5 parts sodium sulfonate-modified polyurethane resin 5 parts carbon black ( CB1) * 10 parts Methyl ethyl ketone 100 parts Toluene 100 parts * Change depending on the sample (see Tables 5-8) ** For samples Ri type and amount changes (see Table 5-8) wherein the upper-layer, the lower layer magnetic paint was finished each formulation composition kneaded by kneader and a sand mill, the dispersion to the paint.

Next, 5 parts of polyisocyanate (Coronate L; manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to each of the obtained coating materials, and the surface waviness and the surface roughness listed in Table 4 having a thickness of 10 μm was obtained by a wet-on-wet method. After being coated on the magnetic support polyethylene terephthalate, a magnetic field orientation treatment was performed while the coating film was not dried, and subsequently, after drying, a surface smoothing treatment was performed with a calendar to form a magnetic layer. The calender conditions are a temperature of 80 ° C and a pressure of 300 kg / cm ² , and the upper layer thickness is
The thickness was 0.5 μm and the thickness of the lower layer was 2.5 μm.

When a back coat layer (BC layer) is further provided, a back coat layer coating composition having the following formulation is provided on the back surface of the non-magnetic support so as to have a film thickness of 0.5 μm after drying.

: Coating for back coat layer: Carbon black (average particle size 26 mμ) 40 parts Barium sulfate (average particle size 300 mμ) 10 parts Nitrocellulose 25 parts Polyurethane (N-2301; Nippon Polyurethane Co.) 25 parts Polyisocyanate ( Coronate L; manufactured by Nippon Polyurethane Co., Ltd.) 25 parts cyclohexanone 400 parts methyl ethyl ketone 250 parts toluene 250 parts The web thus obtained was cut into 8 mm video tapes. The configurations and performance evaluation results of these video tape samples are shown in Tables 5-8.

[0081]

[Table 5]

[0082]

[Table 6]

[0083]

[Table 7]

[0084]

[Table 8]

In Example 24 having three magnetic layers, the thicknesses of the upper, middle and lower layers were 0.3, 0.3 μm and 2.0 μm, and the thickness of Comparative Example 21 of the single magnetic layer was 3.0 μm. Is.

The method of evaluating the above performance is shown below.

(A) RF output and chroma output; 8 mm video movie-V900 using a Shiba Soku noise meter 925C
(Manufactured by Sony Corporation).

(B) Lumi S / N: A white 100% signal was input on the sample tape at the reference level, and the reproduced video signal was input to 921D / 1 (a noise meter manufactured by Shibasoku Co., Ltd.) to obtain noise. Lumi S / N was read from the absolute value.

(C) Chroma S / N: Using a noise meter manufactured by Shibasoku Co., Ltd., the difference between the S / N of the sample tape in the chroma signal was determined in comparison with the reference tape.

(D) Jitter value after running; the tape was run for 100 hours in an environment of 40 ° C. and RH80%, and the jitter value after running was measured using a VTR jitter meter “MK-6124” manufactured by Megroelectronics. Was measured. (Unit of measurement: μ
s) (e) Corrosion resistance (clogging; weather resistance); After leaving the tape in an NO ₂ (5 ppm) environment for 30 days, the image quality is evaluated and the clogging of the magnetic head is checked (yes: × ,Nothing:
○).

(F) Output decrease (ΔRF) under low humidity (40 ° C., 20% RH); The tape was allowed to run for 2 full lengths in an environment of 40 ° C., RH 20%, and the RF output decrease was measured. E for measurement
V-S1 (manufactured by Sony Corporation) was used.

As can be seen by simply looking at Tables 5 to 8, the effects of the present invention are clearly different between the examples of the present invention and the comparative examples.

[0093]

According to the present invention, it is possible to provide a magnetic recording medium having a small spacing friction coefficient, preventing RF output reduction under low humidity and preventing jitter generation under high temperature and high humidity.

Claims (7)

[Claims] 1. In a magnetic recording medium having a plurality of magnetic layers provided on a non-magnetic support, the surface waviness As of the magnetic layer is
0.022 μm or less and the average major axis length of 0.25 μm on the top layer
Less than 200 .mu.m, the surface undulation Bs of the magnetic layer forming surface of the non-magnetic support is 0.020 .mu.m or less, and 0.01 .mu.m existing on the forming surface. The number n of protrusions above is 200 per 1 mm of measuring length
Number of protrusions N or more, 0.3 μm or more, N is 500 per 400 mm measuring length
The average protrusion height Hm is 0.01 to 0.25 μm, and the ratio of the maximum protrusion height Hmax to the average protrusion height Hm is Hmax / Hm.
The magnetic recording medium is characterized in that 2. The number of protrusions n ′ of 0.01 μm or more existing on the back surface of the non-magnetic support opposite to the magnetic layer forming surface is 200 or more and 0.3 μm or more per measurement length 1 mm. N'is less than 500 per 400 mm of measuring length, average protrusion height H'm is 0.01 to 0.25 μm, and maximum protrusion height H'ma
The magnetic recording medium according to claim 1, wherein a ratio H'max / H'm of x to the average protrusion height H'm is 10 or less. 3. The ferromagnetic metal powder contains iron (Fe) and aluminum (Al), and the atomic weight ratio of Fe and Al (Fe: Al).
3. The magnetic recording medium according to claim 1, wherein: (100: 0.5) to (100: 20). 4. The magnetic recording medium according to claim 1, wherein the uppermost magnetic layer contains a ferromagnetic metal powder having an axial ratio of less than 10. 5. The magnetic recording medium according to claim 1, wherein the weight of carbon black contained in the uppermost magnetic layer is less than 1 part by weight with respect to 100 parts by weight of magnetic powder. 6. A ferromagnetic powder having an average major axis length of less than 0.25 μm and a crystallite size of less than 450Å by X-ray measurement is contained in at least one layer other than the uppermost layer.
6. The magnetic recording medium according to any one of 1 to 5. 7. Fe ^{2+ in at} least one layer other than the top layer
The magnetic recording medium according to either of claims 1 to 6, characterized in that it comprises a Co-containing iron oxide atomic ratio Fe ²⁺ / Fe ³⁺ and Fe ³⁺ is 0.08 or more and.