JPH08263833A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To improve electromagnetic transducing characteristics in a short wavelength region and to attain high recording density by regulating the weight ratio between magnetic powder and nonmagnetic powder contained in the lower one of magnetic layers to the range of 5:95 to 50:50. CONSTITUTION: This magnetic recording medium has two or more magnetic layers each consisting essentially of magnetic powder and a binder formed on the nonmagnetic substrate. The weight ratio between magnetic powder and nonmagnetic powder contained in the lower one of the magnetic layers is within the range of 5:95 to 50:50 and the amt. of the nonmagnetic powder blended is made larger than that of the magnetic powder. The generation of a demagnetizing field in the upper one of the magnetic layers by the lower one is suppressed and electromagnetic transducing characteristics in a short wavelength region are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called multi-layer coating type magnetic recording medium in which a lower layer composed of a magnetic powder and a binder and an upper layer are successively laminated on a non-magnetic support.

[0002]

2. Description of the Related Art In magnetic recording media such as video tapes, studies have been actively conducted on improvement of electromagnetic conversion characteristics for the purpose of high recording density and high image quality. In order to improve the electromagnetic conversion characteristics, a thin film medium such as a vapor deposition tape has been proposed in recent years and has already been put to practical use in some formats such as Hi-8 video. However, the thin film medium such as the vapor deposition tape is disadvantageous in terms of cost, and the conventional coating type magnetic recording medium is still the mainstream.

In this coating type magnetic recording medium, in order to improve the electromagnetic conversion characteristics, the magnetic characteristics are improved,
The reduction of spacing loss due to the mirror surface of the medium is being studied.

For example, from the viewpoint of raw materials, studies have been conducted on magnetic powders which are finer and have excellent magnetic characteristics, and binders and dispersants which can disperse the magnetic powders more uniformly. In terms of process, study of kneading method and mixing method to disperse the magnetic powder more uniformly, study of orientation method to obtain higher magnetic characteristics, and more magnetic characteristics to make the medium surface more mirror-like. Studies on calendering methods for finishing are being conducted.

Further, a so-called multilayer coating type magnetic recording medium having an upper layer and a lower layer on a non-magnetic support has been proposed.

As the multi-layer coating type magnetic recording medium,
For example, as described in JP-A-63-187418, a lower layer mainly composed of a non-magnetic pigment and a binder and an upper layer mainly composed of a magnetic powder and a binder are provided on a non-magnetic support. The upper layer is formed to have a thickness of 2 μm or less, and the magnetic powder contained in the upper layer is a ferromagnetic powder having a major axis length of 0.3 μm or less.
It is known that the thickness is 3.5 μm. In addition, JP-A-1
As disclosed in Japanese Patent Publication No. 19524, etc., the upper layer has a film thickness of 2 μm or less, a ferromagnetic alloy powder having a major axis length of 0.25 μm or less is used for the upper layer, and a major axis length of 0.25 to 0.25 is used for the lower layer.
A method using a ferromagnetic powder of 0.35 μm has also been proposed. By these methods, it is possible to improve the electromagnetic conversion characteristics while ensuring the light shielding property.

However, in such a multi-layer coating type magnetic recording medium, there is a problem that the electromagnetic conversion characteristics in the short wavelength region deteriorate due to the demagnetizing field of the lower layer.

On the other hand, for example, Japanese Patent Laid-Open No. 4-2178.
As disclosed in Japanese Patent Publication No. 2 etc., the lower layer is a non-magnetic layer,
A method for preventing the deterioration of the electromagnetic conversion characteristics due to the above-mentioned demagnetizing field has been proposed.

However, when the spherical non-magnetic powder is used in the lower layer as described above, the strength of the coating film in the longitudinal direction is insufficient, and a sufficient contact with the head cannot be obtained.

Further, when needle-like powder such as α-iron oxide is used for the lower layer, the contact with the head is not as good as when magnetic powder is used.

[0011]

Therefore, the present invention has been proposed in view of such circumstances, and in a multi-layer coating type magnetic recording medium, deterioration of the electromagnetic conversion characteristics due to the demagnetizing field of the lower layer is suppressed. An object of the present invention is to provide a magnetic recording medium capable of obtaining a satisfactory hit with respect to a head while preventing it.

[0012]

Means for Solving the Problems As a result of earnest studies that the above-mentioned objects cannot be achieved, the inventors of the present invention have added the non-magnetic powder contained in the lower layer in an amount not less than the compounding amount of the magnetic powder to obtain the obtained lower layer. The magnetic field orientation treatment in the undried state suppresses the deterioration of electromagnetic conversion characteristics due to the demagnetizing field and finds that a good contact with the head is obtained, and the present invention has been completed. .

That is, the magnetic recording medium of the present invention is a magnetic recording medium in which two or more magnetic layers mainly composed of magnetic powder and a binder are formed on a non-magnetic support, and the lower layer of the magnetic layer is formed. The weight ratio of the magnetic powder and the non-magnetic powder contained in is in the range of magnetic powder: non-magnetic powder = 5: 95 to 50:50.

As the magnetic recording medium to which the present invention is applied, there is a so-called multi-layer coating type magnetic recording medium in which a plurality of coating layers are basically provided on a non-magnetic support.

In the present invention, in the magnetic powder and the non-magnetic powder contained in the lower layer provided on the non-magnetic support, the blending amount of the non-magnetic powder is equal to or more than the blending amount of the magnetic powder. This suppresses the demagnetizing field from the lower layer to the upper layer, and improves the electromagnetic conversion characteristics in the short wavelength region.

The weight ratio of the magnetic powder and the non-magnetic powder contained in the lower layer is as follows: magnetic powder: non-magnetic powder = 5: 95-5
It is preferably within the range of 0:50.

The magnetic powder used in this lower layer is
The average major axis length is preferably 0.35 to 0.5 μm.
When the average major axis length of the magnetic powder is shorter than 0.35 μm,
The strength of the coating film in the longitudinal direction cannot be sufficiently improved and the contact with the head tends to decrease. On the contrary, when it is longer than 0.5 μm, the surface property of the interface between the upper and lower layers is deteriorated and the electromagnetic conversion characteristics are deteriorated. Tends to decrease.

In the upper layer formed on this lower layer, the weight ratio of the magnetic powder to the non-magnetic powder is 8 for the magnetic powder.
It is preferably 0% by weight or more.

The magnetic powder used in this upper layer is
It is preferable to use a fine powder having an average major axis length of 0.3 μm or less. This reduces noise and improves the surface properties of the tape. If the average major axis length of the magnetic powder is longer than 0.3 μm, the electromagnetic conversion characteristics tend to deteriorate.

The thickness of such an upper layer is preferably 1.5 μm or less. When the thickness of the upper layer exceeds 1.5 μm, the electromagnetic conversion characteristics in the short wavelength region deteriorate due to the influence of the demagnetizing field.

In the present invention, the magnetic powder forming the upper layer is most preferably a ferromagnetic metal powder made of a metal such as iron, cobalt or nickel, or an alloy containing them, but is not limited thereto. Plate-shaped hexagonal ferrite such as barium ferrite, γ iron oxide, cobalt-containing γ iron oxide, magnetite, cobalt-containing magnetite, CrO _{2 and the} like can also be used.

The magnetic powder used in the lower layer is iron,
Ferromagnetic metal powder consisting of metals such as cobalt and nickel and alloys containing these, γ iron oxide, cobalt-containing γ iron oxide, magnetite, cobalt containing-magnetite, Cr
O _{2 and the} like are preferable, and Co-containing γ-Fe ₂ O ₃ is preferably used.

The lower layer containing the needle-like magnetic powder is preferably subjected to a magnetic field orientation treatment in an undried state. Thereby, the strength of the coating film in the longitudinal direction is improved, and the contact with the head can be improved.

After forming the lower layer, it is desirable that the upper layer is formed while the lower layer is undried (so-called wet-on-wet method).

Examples of the non-magnetic powder include alumina, chromium oxide, titanium oxide, α-iron oxide, silicon carbide, calcium carbonate, barium sulfate, corundum, (artificial) diamond, carbon black and molybdenum sulfide. , Graphite and the like.

Particularly, as the non-magnetic powder used in the lower layer, titanium oxide, α-iron oxide, carbon black,
Alumina, calcium carbonate, barium sulfate and the like are suitable.

These non-magnetic powders may be added to the magnetic coating material in a powder state, and may be added to the magnetic coating material in the form of a slurry dispersed separately from the above magnetic powder at the initial stage, the middle stage, or the final stage of the mixing / dispersion of the magnetic coating material. May be.

In the present invention, as the binder, any of those usually used in this kind of magnetic recording medium can be used, and it is not particularly limited as long as it is a conventionally known material.

Specific examples include polyester, polycarbonate, or polyether polyurethane resin, polyester resin, vinyl chloride copolymer, cellulose derivative, phenoxy resin, acrylic ester copolymer, vinylidene chloride resin. Examples thereof include copolymers and styrene-butadiene copolymers.

In these binders, in order to obtain good dispersibility, a suitable polar group may be introduced into some or all of the binders used. In this case, as the polar group, for example, —SO ₃ M (M is H, Li, Na, K, −
Represents NR ₄ . R represents an alkyl group or H.
The same applies below. _{), - O-SO 3 M} , -COOM, -P = O
(OM) ₂ , -OP-O (OM) ₂ , -NR ₄ X (X is
Represents a halogen atom. ), —NR ₂ , —SH and the like.

The amount of these polar groups introduced is preferably 0.03 to 0.3 mmol per 1 g of the binder. If the introduced amount is less than 0.03 mmol, the effect on the dispersibility is small, and if it is more than 0.3 mmol, the hygroscopicity becomes high, and not only the weather resistance is deteriorated, but also the dispersibility may be deteriorated.

Only one kind of these polar groups may be contained, or two or more kinds thereof may be contained.

Polyisocyanate may be added as a curing agent to the binder to form a crosslinked structure. Examples of the polyisocyanate include isocyanates such as tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), hexanemethylene diisocyanate (HDI), xylene diisocyanate, and isophorone diisocyanate, and these isocyanates and trimethylolpropane. Adducts with polyhydric alcohols or condensation products of isocyanates can be used.

The magnetic recording medium of the present invention has a conventional anti-static agent effect, a light shielding effect, a friction reducing effect, a dispersing effect, a crosslinking promoting effect, a plasticizing effect, etc. Various known additives may be used.

For example, as the lubricant added as the above-mentioned additive, higher fatty acids such as myristic acid, palmitic acid and oleic acid and salts thereof with metals and amines,
Representative examples include ester compounds of fatty acids and monohydric alcohols.

As the ester compound of the above fatty acid, a monobasic fatty acid having 10 to 24 carbon atoms (each may contain an unsaturated bond or may be branched) and 1 carbon atom.
Up to 18 monohydric alcohols (each of which may contain an unsaturated bond or may be branched) and ester compounds composed of an alkylene oxide monoalkyl ether may be used.

Specific examples of these ester compounds include methyl stearate, ethyl stearate, propyl stearate, butyl stearate, sec-butyl stearate, tert-butyl stearate, isobutyl stearate, stearic acid. Pentyl,
Examples include heptyl stearate, octyl stearate, butoxyethyl stearate, butyl palmitate, pentyl palmitate, heptyl palmitate, octyl parimitinate, isooctyl palmitate, octyl myristate, oleyl oleate and the like.

Further, ester compounds of fatty acids and dihydric to hexahydric alcohols, silicone oils containing those modified with fatty acids, alkyl phosphates, etc. can also be used. These may contain other substituents such as an ether bond by addition of ethylene oxide or the like, or may partially contain fluorine.

Further, perfluoropolyether and its modified products can also be used.

Such a lubricant may be added at the initial stage, the middle stage, or the final stage of the mixing / dispersion of the magnetic coating material, and may be top-coated after the magnetic layer is formed.

These coating materials are coated on a non-magnetic support and dried to form the above-mentioned coating layer. When the coating material is made into a coating material, the solvent used is, for example, a ketone such as methyl ethyl ketone or cyclohexanone. , Alcohols such as methanol and isopropyl alcohol,
Examples thereof include esters such as ethyl acetate and butyl acetate, aromatic hydrocarbons such as toluene and benzene, chlorinated hydrocarbons such as carbon tetrachloride and chloroform, and ethers such as dioxane and diethylene glycol monoethyl ether.

Known methods can be used for the dispersion and kneading for preparing the above paint. For example, roll mill, ball mill, sand mill, tron mill, high speed stone mill, basket mill, disper,
A homomixer, a kneader, a continuous kneader, an extruder, a homogenizer, an ultrasonic disperser, etc. are used.

Further, as a method for coating the thus prepared coating material on the above-mentioned non-magnetic support, simultaneous multilayer coating by extrusion coating is suitable.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyamides such as aramid; polyamides or imides; polyolefins such as polypropylene; celluloses such as cellulose triacetate; polycarbonates; other plastics and aluminum. Examples of such metals include glass and other ceramics.

The basic structure of the magnetic recording medium according to the present invention has been described above. However, the structure of the magnetic recording medium is not limited to this. For example, the magnetic layer of the non-magnetic support is formed. A back coat layer mainly composed of non-magnetic powder or magnetic powder and a binder is formed on the surface (back surface) opposite to the magnetic recording medium for the purpose of improving the running property of the magnetic recording medium, preventing electrification, and preventing transfer. May be done. In this case, the back coat layer preferably has a thickness of 0.1 to 2.0 μm, more preferably 0.3 to 1.0 μm.

The non-magnetic powder contained in the back coat layer is generally composed mainly of carbon black, but other than this, calcium carbonate, alumina, titanium oxide, α-iron oxide and the like can also be used. .

On the other hand, as the magnetic powder, any of those exemplified above for the coating layer can be used.

These may be used alone or in combination.

An undercoat layer may be provided between the lower layer of the coating layer and the non-magnetic support for the purpose of enhancing the adhesion of the lower layer to the non-magnetic support.

[0050]

When forming a plurality of coating layers on the non-magnetic support, by blending the non-magnetic powder contained in the lower layer of the coating layer such that the blending amount is equal to or more than the blending amount of the magnetic powder,
The magnetic properties of the lower layer are suppressed low, and the demagnetizing field of the lower layer on the upper layer is suppressed. Therefore, the electromagnetic conversion characteristics in the short wavelength region can be improved.

By subjecting the lower layer to a magnetic field orientation treatment in an undried state, the strength of the coating film in the longitudinal direction is improved,
Good contact with the head.

[0052]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Example 1 First, magnetic powder a-1 shown in Table 1 below was used as the magnetic powder, and a magnetic coating material for the upper layer was prepared with the following composition.

<Composition of magnetic coating material for upper layer> Magnetic powder a-1 100 parts by weight Vinyl chloride copolymer 12 parts by weight (average degree of polymerization = 305, potassium sulfate salt 0.08 mmol / g as a polar group, Substituent: Epoxy group 0.8 mmol / g, Hydroxyl group 0.3 mmol / g) Polyester polyurethane resin 6 parts by weight (Number average molecular weight M = 21000, containing sodium sulfonate 0.12 mmol / g as polar group, polyester main component: isophthalate Acid-ethylene glycol, urethanated isocyanate: diphenylmethane diisocyanate) Abrasive: Alumina powder (alpha conversion = 85%, average particle size = 0.5 μm) 8 parts by weight Lubricant: Stearic acid 1.5 parts by weight Heptyl stearate 2 parts by weight Solvent: methyl ethyl ketone 120 parts by weight Cyclohexanone 60 parts by weight Toluene 60 parts by weight Tables 1 and 2 below as magnetic powders
Using the magnetic powder b-1 and the non-magnetic powders c-1 and c-3 shown in (4), magnetic coating materials for the lower layer were prepared with the following compositions.

<Composition of Magnetic Coating Material for Lower Layer> Magnetic powder b-1 10 parts by weight Nonmagnetic powder c-1 85 parts by weight Nonmagnetic powder c-3 5 parts by weight Vinyl chloride copolymer 12 parts by weight (average degree of polymerization) = 305, containing 0.08 mmol / g of potassium sulfate as a polar group, other main substituents: epoxy group 0.8 mmol / g, hydroxyl group 0.3 mmol / g) Polyester polyurethane resin 6 parts by weight (number average molecular weight M = 21000, sulfone) Acid sodium salt 0.12 mmol / g as a polar group, Polyester main component: isophthalic acid-ethylene glycol, urethane isocyanate: diphenylmethane diisocyanate) Lubricant: stearic acid 2.0 parts by weight Heptyl stearate 3.0 parts by weight Solvent : Methyl ethyl ketone 140 parts by weight Cyclohexanone 70 parts by weight Toluene 70 parts by weight After that was dispersed by the respective sand mill, a curing agent (manufactured by Nippon Polyurethane Co., Ltd., product name:
Coronate L) was added in an amount of 3 parts by weight, and these magnetic paints were coated with PET (polyethylene terephthalate) having a thickness of 7.5 μm.
The thickness after drying on the film is 0.5 μm in the upper layer, and the lower layer is 2.
It was applied in a wet-on-wet state by a die coater so as to have a thickness of 0 μm.

Thereafter, a magnetic field orientation treatment of 6 kOe is performed,
It was dried and wound up.

Then, calendering is performed at a temperature of 60.
Curing treatment was performed at 20 ° C. for 20 hours to form upper and lower magnetic layers.

Then, a back coat paint having the following composition was applied to the back surface of the magnetic layer forming surface of this magnetic film to form a back coat layer having a thickness of 0.5 μm.

<Composition of Backcoat Paint> Pigment: carbon black a 95 parts by weight (average particle size = 0.02 μm, DBP oil absorption = 105 cc / 100 g) carbon black b 3 parts by weight (average particle size = 0.35 μm, DBP oil absorption = 40 cc / 100 g) Titanium oxide (average particle size = 0.4 μm) 2 parts by weight Binder: Polyester polyurethane resin 50 parts by weight (number average molecular weight M = 24000, sodium sulfonate 0.08 mmol / g as polar group) Included as polyester main component: isophthalic acid, adipic acid-neopentylglycol, ethylene glycol, urethanated isocyanate; diphenylmethane diisocyanate) nitrocellulose 30 parts by weight (Asahi Kasei Co., Ltd., trade name: Sernova BTH1 / 2) Curing agent: polyisocyanate 10 Parts by weight (Nippon Poly Urethane (Trade name: Coronate L) manufactured by the company) Further, the wide tape thus obtained was slit into a width of 8 mm to prepare a sample tape.

Example 2 A sample was prepared in the same manner as in Example 1 except that the amounts of the magnetic powder and the nonmagnetic powder in the composition of the lower layer magnetic coating material in Example 1 were changed to 30 parts by weight and 70 parts by weight, respectively. A tape was made. It should be noted that 70 parts by weight of the above non-magnetic powder contains 5 parts by weight of the non-magnetic powder c-3 used in Example 1. Hereinafter, in each of the examples and comparative examples, 5 parts by weight of the non-magnetic powder c-3 is similarly included in all the lower layers.

Example 3 A sample was prepared in the same manner as in Example 1 except that the amounts of the magnetic powder and the nonmagnetic powder in the composition of the lower layer magnetic coating material in Example 1 were changed to 50 parts by weight and 50 parts by weight, respectively. A tape was made.

Example 4 The non-magnetic powders c-1 and c-3 used as the non-magnetic powder in the composition of the magnetic coating material for the lower layer in the above-mentioned Example 1 are shown in Table 2 below.
A sample tape was prepared in the same manner as in Example 1 except that the non-magnetic powder c-2 shown in was used.

Example 5 In the composition of the magnetic coating material for the lower layer in the above Example 1, the magnetic powder b-1 used as the magnetic powder was changed to the magnetic powder b-2 shown in Table 1 below, and otherwise the same as in Example 1. Then, a sample tape was prepared.

Example 6 In the composition of the magnetic coating material for the lower layer in the above-mentioned Example 1, the magnetic powder b-1 used as the magnetic powder was changed to the magnetic powder b-3 shown in Table 1 below, and otherwise the same as in Example 1. Then, a sample tape was prepared.

Example 7 In the composition of the magnetic coating material for the lower layer in the above-mentioned Example 1, the magnetic powder b-1 used as the magnetic powder was changed to the magnetic powder b-4 shown in Table 1 below, and otherwise the same as in Example 1. Then, a sample tape was prepared.

Example 8 In the composition of the magnetic coating material for the upper layer in the above-mentioned Example 1, the magnetic powder a-1 used as the magnetic powder was changed to the magnetic powder a-2 shown in Table 1 below, and otherwise the same as in Example 1. Then, a sample tape was prepared.

Example 9 In the composition of the magnetic coating material for the upper layer in the above-mentioned Example 1, the magnetic powder a-1 used as the magnetic powder was changed to the magnetic powder a-3 shown in Table 1 below, and otherwise the same as in Example 1. Then, a sample tape was prepared.

Example 10 The thicknesses of the upper and lower layers in the above Example 1 were 0.9 μm, respectively.
m was changed to 1.7 μm, and a sample tape was produced in the same manner as in Example 1 except for the above.

Example 11 The thicknesses of the upper and lower layers in the above Example 1 were 1.3 μm, respectively.
A sample tape was prepared in the same manner as in Example 1 except that m and 1.4 μm were used.

Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 except that the magnetic powder was not used in the composition of the lower layer magnetic coating material of Example 1 except that the nonmagnetic powder was changed to 100 parts by weight.

Comparative Example 2 In the composition of the magnetic coating material for the lower layer in the above Example 1, 95 parts by weight of non-magnetic powder c-2 shown in Table 2 below was used as the non-magnetic powder without using the magnetic powder, and the non-magnetic powder c- A sample tape was produced in the same manner as in Example 1 except that 1 was changed to 5 parts by weight.

Comparative Example 3 A sample tape was prepared in the same manner as in Example 1 except that the magnetic powder was changed to 60 parts by weight and the nonmagnetic powder was changed to 40 parts by weight in the composition of the lower layer magnetic coating material in Example 1 above. .

Comparative Example 4 In the above-mentioned Example 1, after forming only the lower layer, it was dried without magnetic field orientation treatment, then the upper layer was formed on the lower layer, subjected to magnetic field orientation treatment, and then dried and wound. Take the
Others were the same as in Example 1 to produce a sample tape.

Comparative Example 5 In the composition of the magnetic coating material for the upper layer in the above-mentioned Example 1, the magnetic powder a-1 used as the magnetic powder was changed to the magnetic powder a-4 shown in Table 1 below, and otherwise the same as in Example 1. Then, a sample tape was prepared.

Comparative Example 6 The thicknesses of the upper and lower layers in Example 1 above were set to 2.4 μm, respectively.
A sample tape was prepared in the same manner as in Example 1 except that m and 0.7 μm were changed.

[0076]

[Table 1]

In Table 1, the magnetic powders a-1, a-
2 contains aluminum and yttrium from the compound used as the sintering inhibitor, and the magnetic powders a-3 and a-4 contain aluminum.

[0078]

[Table 2]

Therefore, the sample tapes produced as described above were incorporated into a Hi-8 video cassette, and the contact characteristics with respect to the head and the electromagnetic conversion characteristics were examined by the following methods. The results are shown in Tables 3 and 4 below.

<Hit characteristics> At room temperature, 3 video decks are used, and 3 MH sample tapes of the same specifications are used for 7 MH
Each z signal was recorded for 5 minutes, and the reproduction output was observed with an oscilloscope. At the time of measurement, the maximum output value in one track of the reproduced waveform on each VTR was set to 100, and the inlet side was 1/1
The average value of three units of the minimum output value in 0 track was obtained.

<Y-C / N> Using a Hi-8 video deck for PAL, a 7 MHz signal was recorded for 10 minutes, and the output at 7 MHz detected before the limiter and -1 MH from it were recorded.
The difference from z noise was determined. The measured value was expressed as a relative value with the result of Comparative Example 3 being 0 dB.

[0082]

[Table 3]

[0083]

[Table 4]

As shown in Table 3, in Examples 1 to 11, as compared with Comparative Examples 1 to 4, the contact characteristics and Y-C /
The balance of N was good.

Further, in order to examine the ratio of the magnetic powder to the non-magnetic powder in the composition of the magnetic coating material for the lower layer,
Examples 1 to 3 and Comparative Examples 1 and 3, and Example 4 and Comparative Example 2
Were compared with each other.

As a result, the ratio of the magnetic powder to the non-magnetic powder in the composition of the magnetic coating material for the lower layer was a weight ratio of the magnetic powder:
With the sample tapes of Examples 1 to 4 in which the non-magnetic powder was in the range of 5:95 to 50:50, good hit characteristics were obtained. On the other hand, in Comparative Examples 1 and 3 in which the ratio of the magnetic powder to the non-magnetic powder is less than the range of the present invention, the hitting property is poor, and in Comparative Example 2 in which the ratio exceeds the above range, the hitting property is good. , Y-C / N was bad.

From the above, the ratio of the magnetic powder to the non-magnetic powder in the composition of the magnetic coating material for the lower layer is within the range of the present invention, that is, the weight ratio is magnetic powder: non-magnetic powder = 5: 95-.
It was found that by setting the ratio within the range of 50:50, it is possible to satisfy both the hitting characteristic and the electromagnetic conversion characteristic at a high level.

Further, the presence or absence of the magnetic field orientation treatment for the lower layer was compared between Example 1 and Comparative Example 4 in which sample tapes were manufactured under the same conditions, and Example 1 was performed for the magnetic field orientation treatment of the lower layer. Then, the hit property was good. On the other hand, in Comparative Example 4 in which the magnetic field orientation was not performed, the hit property was poor.

Therefore, the ratio of the magnetic powder to the non-magnetic powder in the composition of the magnetic coating material for the lower layer is in the range of 5:95 to 50:50 in the weight ratio of magnetic powder: non-magnetic powder as described above. It was found that by performing the magnetic field orientation treatment with the lower layer undried, it is possible to secure good hitting characteristics and electromagnetic conversion characteristics.

Further, in order to study the magnetic powder used for the lower layer, Examples 1, 5, 6 and 7 were compared. When the major axis length of the magnetic powder is short, the hitting characteristics deteriorate and When it was very long, the contact characteristics were improved, but the electromagnetic conversion characteristics tended to be slightly deteriorated.

Further, in order to study the magnetic powder used in the upper layer, the magnetic powders of Examples 1, 8, 9 and Comparative Example 5 were compared. It was found that the better the powder, the better the Y-C / N obtained. On the contrary, when the major axis length exceeds 0.3 μm, as is clear from the results of Example 9 and Comparative Example 5, the deterioration of YC / N tends to be large.

Further, regarding the thickness of the upper layer,
Comparison between 0 and 11 and Comparative Example 6 revealed that the thinner the upper layer, the better the Y-C / N obtained.
Further, from the comparison between Example 11 and Comparative Example 6, it was found that when the thickness of the upper layer exceeds 1.5 μm, the deterioration of YC / N tends to be large.

[0093]

As is clear from the above description, in the present invention, in the multilayer coating type magnetic recording medium in which the upper layer and the lower layer are formed on the non-magnetic support, the magnetic powder contained in the lower layer is Since the blending ratio of the non-magnetic powder is such that the blending amount of the non-magnetic powder is equal to or more than the blending amount of the magnetic powder, the magnetic properties of the lower layer can be suppressed low, and the demagnetizing field of the lower layer to the upper layer can be suppressed. Therefore, according to the present invention, it is possible to provide a magnetic recording medium having improved electromagnetic conversion characteristics in a low wavelength region and excellent in high recording density.

Further, in the present invention, the needle-like ferromagnetic powder is added to the lower layer, and after the lower layer is formed, it is longitudinally oriented in an undried state, so that the strength of the coating film in the longitudinal direction is maintained. The contact characteristics with respect to the head are improved. Therefore, according to the present invention, both the contact with the head and the electromagnetic conversion characteristics can be satisfied at a high level.

Claims (7)

[Claims] 1. A magnetic recording medium comprising two or more magnetic layers mainly composed of a magnetic powder and a binder formed on a non-magnetic support, wherein the magnetic powder and the non-magnetic material contained in a layer below the magnetic layer are non-magnetic. A magnetic recording medium characterized in that the weight ratio with the powder is in the range of 5:95 to 50:50. 2. The magnetic recording medium according to claim 1, wherein the lower layer is subjected to a magnetic field orientation treatment in an undried state. 3. The magnetic recording medium according to claim 1, wherein after forming the lower layer, the upper layer is formed on the lower layer while the lower layer is undried. 4. The magnetic recording medium according to claim 1, wherein the magnetic powder contained in the lower layer has an average major axis length of 0.35 to 0.5 μm. 5. Co as the magnetic powder contained in the lower layer
The magnetic recording medium according to claim 1, wherein the contained γ-Fe ₂ O ₃ is used. 6. A ferromagnetic metal powder having an average major axis length of 0.3 μm or less is used as the magnetic powder contained in the upper layer formed on the lower layer, and the upper layer has a thickness of 1.5 μm.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is m or less. 7. A ferromagnetic metal powder having an average major axis length of 0.3 μm or less is used as the magnetic powder contained in the upper layer formed on the lower layer, and the upper layer has a thickness of 1.5 μm.
The magnetic recording medium according to claim 4, wherein the magnetic recording medium is m or less.