JPH1027335A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve magnetic characteristics and electromagnetic conversion characteristics and to enhance traveling durability while maintaining high polishing power by using alumina as an essential component and adding an alkaline metal, etc., and silicon atoms thereto. SOLUTION: This magnetic recording medium has a magnetic layer 2 contg. magnetic powder and polishing agent. The polishing agent comprises essentially the alumina having high purity and high crystallinity. The alkaline metal atoms at >=10 to <=250ppm of the polishing agent and the silicon atoms at <=0.1wt.% of the polishing agent are incorporated into the medium.

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 having a magnetic layer containing a magnetic powder and an abrasive.
The present invention relates to a coating type magnetic recording medium such as a magnetic tape, a magnetic disk, and the like having a magnetic layer containing magnetic powder, an abrasive and a binder as main components formed on a nonmagnetic support.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been used in, for example, audio equipment, video equipment, computers, and the like, and the demand for them has been remarkably growing.

[0003] Such a magnetic recording medium generally has a structure in which a magnetic layer made of a magnetic powder and an abrasive is provided on a non-magnetic support such as a polyester film. The magnetic layer is usually formed by applying or transferring a magnetic paint in which a magnetic powder or the like is dispersed in a composition containing a binder onto a non-magnetic support.

For example, on a non-magnetic support made of polyester or polyethylene terephthalate (PET) or the like, a magnetic oxide made of a magnetic oxide such as maghemite, magnetite or chromium oxide, or a magnetic alloy mainly containing Fe, Co, Ni or the like is used. A so-called coating type magnetic recording medium is widely used, in which a magnetic paint is prepared by dispersing a magnetic fine powder and a non-magnetic abrasive powder in a binder made of an organic polymer material, thereby forming a magnetic layer. Have been.

In magnetic recording media using such ferromagnetic fine powders, as recording wavelengths have become shorter and higher in density as seen in VTRs (video tape recorders) and the like, magnetic recording media such as video tapes and audio tapes have been developed. In order to improve the characteristics, high density packing of magnetic particles (magnetic powder) is attempted.

[0006] Therefore, in a coating type magnetic recording medium, it is required to dramatically improve the dispersibility of a magnetic paint in filling magnetic particles at a high density.

[0007] Further, with the increase in recording density, the surface of the magnetic layer has been smoothed, so that the abrasion resistance between the magnetic layer and the magnetic head has been reduced, and the surface of the magnetic head has been oxidized and discolored. There are problems such as that the surface is roughened and that deposits are deposited.

To prevent this, it is indispensable to add an abrasive to the magnetic layer for improving the wear resistance of the magnetic layer and for cleaning the surface of the magnetic head. Durability and running performance can be improved.

Known abrasives include α-alumina (α-Al ₂ O ₃ ), β-alumina (β-Al ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), Titanium oxide (TiO ₂ ), α-iron oxide (α-Fe ₂ O ₃ ) and the like are common.

However, when an abrasive is added, the surface properties and magnetostatic properties of the magnetic layer tend to deteriorate, which may be undesirable in terms of electromagnetic conversion properties.

As a countermeasure, an abrasive which can be easily dispersed in the magnetic layer, has little deterioration in the magnetic characteristics and electromagnetic conversion characteristics of the magnetic recording medium, and can impart sufficient running durability to a magnetic tape or the like can be used. It is desirable to use.

[0012]

DISCLOSURE OF THE INVENTION The present invention has been made in view of such conventional circumstances, and has as its object to improve the polishing force while maintaining a high polishing force by devising an abrasive.
It is an object of the present invention to provide a magnetic recording medium having good magnetic characteristics and electromagnetic conversion characteristics and excellent running durability.

[0013]

Means for Solving the Problems As a result of intensive studies, the present inventor has found that alumina containing high purity and high crystallinity as a main component and containing alkali metal or alkaline earth metal atoms in a specific amount, In addition, the inventors have found that the above-mentioned object of the present invention can be achieved by adding an abrasive containing silicon atoms in a specific amount or less, and have reached the present invention.

That is, the present invention provides a magnetic recording medium having a magnetic layer containing a magnetic powder and an abrasive, wherein the abrasive mainly comprises alumina having high purity and high crystallinity, and 10 ppm with respect to the abrasive. As described above, 250 ppm or less of alkali metal atoms and 0.1% by weight or less (this may be 0) of silicon atoms with respect to the abrasive are contained in the abrasive. (Hereinafter, may be referred to as the magnetic recording medium of the present invention).
It is related to.

According to the study of the present inventors, generally, the surface of pure fine particles of metal or ceramics has a very high activity, and the interparticle cohesion and catalytic activity are strong. Therefore, when some impurities such as alkali metal atoms and alkaline earth metal atoms are present on the surface of the metal or ceramic particles of the abrasive, the abrasive tends to be more excellent in dispersibility. However, when these impurities are too much, the crystallinity of the abrasive decreases,
The polishing power is easily reduced, and it reacts with fatty acids and the like added as a lubricant to form an insoluble salt in an organic solvent, and this salt precipitates on the surface of a tape or the like, and the surface properties and signal of the magnetic layer are reduced. The adverse effects such as the adverse effect on the electromagnetic conversion characteristics such as the lack of the particles are likely to occur.

According to the magnetic recording medium of the present invention, since the abrasive mainly comprises alumina of high purity and high crystallinity, it exhibits high polishing power, and at the same time, as a trace impurity on the surface, an alkali metal or It was found that dispersibility was improved by using alumina (particularly Al ₂ O ₃ ) containing 10 ppm or more of alkaline earth metal atoms and having as little as 0.1% by weight or less of silicon atoms. By specifying such an impurity amount, particularly in order to increase the surface basicity, a binder (a binder) having an anionic polar functional group (for example, a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphate group or a salt thereof). When ()) is used, the affinity of the abrasive for the binder is increased, so that the effect of dispersing the abrasive is remarkable.

In order to minimize damage due to impurities (decrease in polishing power), the content of alkali metal or alkaline earth metal atoms is 250 ppm or less, the content of silicon atoms is 0.1 wt% or less, Further, sufficient abrasiveness can be obtained by using alumina having an aluminum atom content of 99.5% by weight or more and excellent in crystallinity.

Alumina satisfying the above conditions, especially α-A
When l ₂ O ₃ is used, the magnetic characteristics and surface properties are improved, and the electromagnetic conversion characteristics are improved without lowering the durability.

Here, the expression "alumina, which is the main component of the abrasive," is "high purity and high crystallinity", which means that the half width of the X-ray diffraction spectrum described later is 0.300 or less.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the magnetic recording medium of the present invention,
Alkali metal atoms contained in the abrasive are lithium, sodium, potassium, rubidium and the like, and alkaline earth metal atoms are magnesium, calcium and the like.

If the content of the alkali metal or alkaline earth metal atom in the polishing agent is less than 10 ppm, the dispersibility of the polishing agent is deteriorated. If the content exceeds 250 ppm, fatty acids and the like added as a lubricant are used. To form a salt that is insoluble in the organic solvent, and this salt has a detrimental effect such as adversely affecting the electromagnetic conversion characteristics such as the surface properties of the magnetic layer and the lack of a signal when deposited on the surface of a tape or the like. 10pp
The content should be not less than m and not more than 250 ppm. The content of the alkali metal or alkaline earth metal atom is 2
0 to 180 ppm is more preferred.

It is desirable that the amount of silicon atoms is extremely small from the viewpoint of not impairing the crystallinity of the abrasive, but the silicon atoms also play a role in maintaining the shape of α-alumina, which is the main component of the abrasive. Yes, the particle size of the α-alumina particles can be controlled by including a small amount of this silicon atom in the abrasive at 0.1% by weight or less.

In the magnetic recording medium of the present invention, it is desirable to use an abrasive mainly composed of alumina, particularly an abrasive substantially composed of α-alumina.

In this case, it is desirable that the content of aluminum atoms is not less than 99.5% by weight based on the total amount of metal components of the abrasive.

This α-alumina (α-Al ₂ O ₃ )
Β-alumina (β-Al
₂ O ₃₎ excellent crystallinity compared to, chromium oxide (Cr ₂ O
Compared to ₃ ), Mohs' hardness is high and polishing power is very excellent.

The higher the content of aluminum atoms with respect to the total amount of metal components of α-alumina, the better. However, the content of this aluminum atom must not exceed the limit capable of retaining the above-mentioned content of alkali metal or alkaline earth metal atom and silicon atom.

The particle size of α-alumina is 0.1 to 0.1.
5 μm, the content in the magnetic layer is desirably 3 to 15 parts by weight.

As the abrasive, alumina such as the above-mentioned α-alumina is used as a main component.
A small amount of chromium oxide, titanium oxide, α-iron oxide, silicon carbide, corundum, (artificial) diamond or the like may be used in combination.

In the magnetic recording medium of the present invention, since the surface of the abrasive exhibits basicity, it is desirable that the binder contained in the magnetic layer has an anionic polar functional group.

That is, the abrasive can be uniformly dispersed in the magnetic layer through the binder by a predetermined amount of the binder having an anionic polar functional group.

The anionic polar functional group includes, for example, a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphate group, and the like, and salts thereof. In addition, one kind of the polar group may be used, but two or more kinds may be included.

The magnetic recording medium of the present invention is specifically a coating type magnetic recording medium in which a magnetic layer in which a magnetic powder and an abrasive are dispersed in a binder is provided on a non-magnetic support. .

In this magnetic recording medium, a ferromagnetic powder, a binder, a curing agent, an antistatic agent, a rust inhibitor, a non-magnetic support, or a solvent used for preparing a magnetic paint mixed in the magnetic layer. Any of conventionally known materials can be applied, and there is no limitation.

The above-mentioned additives may be added at any time during the initial, middle, or end of the mixing and dispersion of the magnetic paint, and may be added in the form of a powder or a slurry dispersed separately from the magnetic powder. May be added. The lubricant and the rust inhibitor may be top-coated after the magnetic layer is formed.

As the ferromagnetic powder, in addition to α-Fe, γ-Fe
FeO _x (x = 1.33 to 1.5), Co-modified γ-Fe
_{O X (x = 1.33~1.5),} Fe or Ni or the main component (75% or more) Co and ferromagnetic alloy, barium ferrite, strontium ferrite, etc., a known ferromagnetic materials can be used. In addition to these atoms, these ferromagnetic powders include Al, Si, S, Sc, Ti, V,
Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, S
b, Te, Ba, Ni, Ta, W, Re, Au, Hg,
Pb, Bi, La, Ce, P, Mn, Zn, Co, S
It may contain atoms such as r and B.

As the binder used for the magnetic layer, any known materials can be used. That is, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer Coalescence, acrylate-vinylidene chloride copolymer, acrylate-
Acrylonitrile copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer , Acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea A formaldehyde resin, a polyvinyl acetal resin, a mixture thereof, or the like can be used.

Of these, polyurethane resins, polyester resins, acrylonitrile-butadiene copolymers and the like, which impart flexibility, and cellulose derivatives, phenol resins, epoxy resins, and the like, which impart rigidity, are desirable.

The above-mentioned binder may be one which is improved in durability by being cross-linked with an isocyanate compound (curing agent), or one into which an appropriate polar group is introduced.

Examples of the curing agent include aromatic polyisocyanates and aliphatic polyisocyanates, and adducts of these with active hydrogen compounds are preferred.

As the aromatic polyisocyanate, toluene diisocyanate (TDI), 1,3-xylene diisocyanate, 1,4-xylene diisocyanate,
4,4'-diphenylmethane diisocyanate (MD
I), p-phenyl diisocyanate, m-phenyl diisocyanate, 1,5-naphthyl diisocyanate and the like.

As the aliphatic polyisocyanate, hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate (IP
DI) and the like.

The active hydrogen compounds forming adducts with these include ethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, diethylene glycol, trimethylolpropane,
Glycerin and the like, and the average molecular weight of the adduct is 100 to
Those in the range of 5,000 are preferred.

The content of these isocyanate-based curing agents is desirably 0 to 30 parts by weight based on 100 parts by weight of the binder.

As the lubricant, silicone oil, fatty acid-modified silicone, fluorine-containing silicone or other fluorine-based lubricant, polyolefin, polyglycol, alkyl phosphate and metal salt, polyphenyl ether, fluorinated alkyl ether, Alcohols having 12 to 24 carbon atoms (each may contain or be branched), higher fatty acids having 12 to 24 carbon atoms and fatty acid esters (each may contain or be unsaturated) ), Amine-based lubricants such as alkylcarboxylic acid amine salts and fluorinated alkylcarboxylic acid amine salts, and the like.

Specific examples of the above higher fatty acids and fatty acid esters include lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid, oleic acid, eicoic acid, elaidic acid, hebenic acid,
Linoleic acid, linoleic acid, octyl stearate, isooctyl stearate, octyl myristate, isooctyl myristate, butoxyethyl stearate,
Examples include butyl stearate and heptyl stearate.
The lubricant may be a mixture of a plurality of lubricants.

As the antistatic agent, known carbon black can be used. For example, acetylene black, furnace black, black for color and the like can be arbitrarily used. Also, to improve handling during the manufacturing process,
Granules may be used. It is preferable to use carbon black having a particle diameter in the range of 10 to 1000 nm.

As the material of the non-magnetic support, those generally used for magnetic recording media can be used. For example, polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; Cellulose triacetate, cellulose diacetate, cellulose derivatives such as cellulose acetate butyrate, polyvinyl chloride,
Vinyl resins such as polyvinylidene chloride, polycarbonate, polyimide, polyamide imide, other plastics, metals such as aluminum and copper, aluminum alloys,
Light alloys such as titanium alloys, ceramics, single crystal silicon, and the like.

The shape of the nonmagnetic support is not limited at all, and may be in any form such as a tape, a sheet, a drum and the like. Further, the nonmagnetic support may be subjected to a surface treatment for forming fine irregularities in order to control the surface property.

Solvents for preparing the magnetic paint include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, and methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethyl acetate monoethyl ether and the like. Ester solvents, glycol ether solvents such as glycol monoethyl ether and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, Chlorine-containing solvents such as chlorobenzene are exemplified. In addition, other conventionally known organic solvents can be used. Further, these solvents may be used in combination.

As a method for preparing the magnetic paint, any known method can be used. For example, roll mill, ball mill, sand mill, tron mill, high-speed stone mill,
Basket mills, dispersers, homomixers, kneaders, continuous kneaders, extruders, homogenizers, ultrasonic dispersers and the like can be used.

In applying the magnetic paint, an undercoat layer such as an adhesive layer may be formed before the magnetic paint is directly applied on the non-magnetic support, or a corona discharge treatment, an electron beam irradiation treatment or the like may be applied on the non-magnetic support. May be performed.

As a method of coating on a non-magnetic support,
Examples include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, gravure coat, transfer roll coat, cast coat, and other methods. it can.

The magnetic layer may be a single layer,
It may be a multilayer having more than two layers. Then, on the same side as the magnetic layer on the non-magnetic support, α-iron oxide, carbon black,
An undercoat layer mainly composed of a non-magnetic or very small powder such as titanium oxide, calcium carbonate, and alumina and a binder may be provided.

The above is the basic structure of the magnetic recording medium of the present invention. However, the structure of the magnetic recording medium is not limited to this. For example, the structure of the non-magnetic support is opposite to the side on which the magnetic layer is formed. A back coat layer mainly composed of a non-magnetic or magnetic powder and a binder may be formed.

As the non-magnetic powder used for the back coat layer, those mainly containing carbon black are generally used. In addition, calcium carbonate, alumina, titanium oxide, α-iron oxide and the like can be used. Further, as the magnetic powder, any of those described above as those used for the magnetic layer can be used. They may be used alone or in combination. As the binder and other additives, any of those described above for use in the magnetic layer can be used, and they may be used alone or in combination.

The magnetic recording medium of the present invention has a magnetic layer 2 formed on a non-magnetic support 1 as shown in FIG. Further, a back coat layer 3 may be provided on the surface of the support opposite to the magnetic layer as shown by a virtual line,
This need not necessarily be provided. An overcoat layer may be provided on the magnetic layer.

[0057]

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

The following various properties were measured and evaluated. These results are shown in Table 1 below.

1. Evaluation of abrasive powder alone (1) Impurity analysis Put 1 part by weight of abrasive and 99 parts by weight of pure water in a container, keep at 90 ° C in a water bath, and measure the liquid from which the deposits on the surface were extracted by ion chromatography. Container (Dionex 2000i / S
In P), soluble cations and a very small amount of anions were detected. The detected cations were sodium ions and calcium ions, and the anions were chloride ions and sulfate ions.

(2) X-ray Fluorescent Element Analysis The abrasive was solidified into a plate by a press machine, and the contents (% by weight) of silicon atoms and aluminum atoms contained in the abrasive were measured according to a standard method (measurement). Equipment: X-ray fluorescence spectrometer 3370E manufactured by Rigaku Denki Kogyo.

(3) X-ray Diffraction Approximately 5 parts by weight of the abrasive was fixed to the groove of the glass plate, and [1]
16] The half width of the plane diffraction peak was measured. The smaller the half width, the better the crystallinity (measurement equipment: Rigaku Denki Kogyo's X-ray diffractometer “RAD-IIC”, X-ray source: Cu
-Kα, Kβ radiation, filter: Ni).

(4) Measurement of pH value 5 parts by weight of an abrasive and 50 parts by weight of pure water were put in a container, boiled and returned to room temperature, and then an automatic pH meter (a glass electrode pH meter S HM manufactured by Toa Denpa Kogyo KK) was used. The pH value was measured at -50S).

2. Evaluation of coating film of abrasive alone Coating composition: α-alumina (abrasive) 100 parts by weight Polyester polyurethane resin (binder) 20 parts by weight (containing -SO ₃ Na group 0.08 mmol / g) (manufactured by Toyobo Co., Ltd.) (UR-8300) methyl ethyl ketone (solvent) 60 parts by weight toluene (solvent) 40 parts by weight cyclohexanone (solvent) 20 parts by weight

The whole amount of the composition is charged into a mixing vessel,
The mixture was mixed and dispersed using a sand mill for about 24 hours. After stirring, the paint was applied on a polyethylene terephthalate base film using a doctor blade, and the following measurement was performed.

(1) Abrasive force A steel ball (steel ball) was run on a coating film of an abrasive alone under a certain condition by using a wear tester (Surface property measuring device 14DR manufactured by Shinto Kagaku Co., Ltd.). The wear condition was photographed with a light microscope for the worn surface, and the wear diameter of the steel ball was measured.

However, the wear radius r (cm) and the steel ball radius R
(Cm), X ₀ = (R ² −r ² ) ^1/2, and abrasion deposit V = ２ / 3πR ² −πr ² X ₀ + ／ πX ₀ (the unit in Table 1 below is 10 ⁻⁶ cm ³ ).

(2) Dispersibility Gloss meter (VGS-sensor manufactured by Nippon Denshoku Industries Co., Ltd.)
Was used to measure the glossiness. However, the incidence / emission angle was 60 degrees. The values in Table 1 below are the reflectivity, and the larger the value, the better the dispersibility.

3. Evaluation of properties of tape provided with magnetic layer containing abrasive Coating composition: α-Fe (magnetic powder) 100 parts by weight Polyester polyurethane resin (binder) 10 parts by weight (containing 0.08 mmol / g of -SO ₃ Na group) ( Toyobo Co. UR-8300) vinyl chloride - vinyl acetate copolymer resin (binder) 10 parts by weight (-SO ₃ K groups 0.06 mmol / g containing) (Nippon Zeon MR-110) stearate ( Lubricant) 1 part by weight Butyl stearate (lubricant) 1 part by weight Methyl ethyl ketone (solvent) 80 parts by weight Toluene (solvent) 80 parts by weight Cyclohexanone (solvent) 40 parts by weight

10 parts by weight of an abrasive was added to this composition, and the mixture was charged into a sand mill and mixed and dispersed for about 5 hours.
Thereafter, a paint is applied on a polyethylene terephthalate base film using a gravure coat, and after a calendar treatment, a back coat layer is provided using a paint having the following composition.
After the curing treatment, the sample was cut into a width of 8 mm to prepare a sample tape. However, the thickness of the magnetic layer was 3 μm, the thickness of the base film (nonmagnetic support) was 7 μm, and the thickness of the back coat layer was 1 μm.

Backcoat layer coating composition: carbon black (non-magnetic powder) 100 parts by weight polyester polyurethane resin (binder) 50 parts by weight (containing -SO ₃ Na group 0.08 mmol / g) (UR- made by Toyobo Co., Ltd.) 8300) Oleic acid (lubricant) 3 parts by weight Methyl ethyl ketone (solvent) 70 parts by weight Toluene (solvent) 30 parts by weight

The thus prepared sample tapes were prepared by adding α-alumina of various compositions to the magnetic layer as an abrasive, as shown in Table 1 below. Each tape was evaluated as follows.

(1) Surface Properties The surface properties of the magnetic layer of the magnetic tape were measured using a non-contact three-dimensional roughness meter (Non-contact three-dimensional fine shape measuring device ET manufactured by Kosaka Laboratory Co., Ltd.).
-30HK), the average roughness (SRa) of the center line was measured.

(2) Squareness Ratio The magnetostatic properties (squareness ratio Rs: Br / Bm) of the magnetic tape were measured with a vibration sample type magnetic property measuring device (VSM manufactured by Toei Kogyo Co., Ltd.).

(3) Electromagnetic conversion characteristics A magnetic tape was assembled in a cassette, and a 5M video deck (EV-S2200 manufactured by Sony Corporation) was inserted into the cassette.
Measure the reproduction output when recording and reproducing the signal of Hz,
It was obtained as a relative value (dB) to a reference tape (reproduction output: 0 dB).

(4) Still Durability Modified 8 mm video deck (EV-S220 manufactured by Sony Corporation)
At 0), the recorded tape was reproduced in the still image mode, and the point where the signal output decreased by 3 dB or more was determined to be the life, and the endurance was obtained at 120 minutes to obtain the still durability (minute).

Here, in Table 1 below, Examples 1-4 used the organometallic method, and Examples 5-20 used the abrasive prepared by the improved Bayer method as the above-mentioned abrasive. However, the organometallic method is a method in which bauxite is electrolyzed, hydrolyzed by adding isopropyl alcohol, and then calcined to obtain α-Al ₂ O _{3. The} improved Bayer method dissolves bauxite with NaOH. Then, after cooling, washing with water (removing Na), and firing, α-Al ₂ O ₃ is obtained.

Examples 20 and 21 are samples using lithium and potassium instead of sodium as the alkali metal of the polishing agent, respectively. For Example 22,
This is a sample in which the abrasive is mixed and dispersed (separately dispersed) in advance, and further mixed and dispersed together with the magnetic layer components separately dispersed.
Example 23 is a sample with no resin -SO ₃ Na group as the binding agent. Example 24 is a sample obtained in Example 6 when calcium (alkaline earth metal) was added to the abrasive instead of sodium.

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] * Calcium ion

<Results> From Table 1, it was found that the content of the alkali metal atom contained in the abrasive was 10 ppm or more and 250 pp.
m or less is excellent in the dispersibility and crystallinity of the abrasive and the polishing power is sufficient, so that a magnetic tape excellent in squareness ratio, surface roughness, electromagnetic conversion characteristics and still durability can be obtained. Do you get it. This alkali metal atom is 20 to 1
More preferably, the content is 80 ppm.

Also, the sample containing 0.1% by weight or less of silicon atoms contained in the abrasive is excellent in the dispersibility and crystallinity of the abrasive and has sufficient polishing power. It was found that a magnetic tape excellent in surface roughness, electromagnetic conversion characteristics and still durability was obtained.

From Examples 20 and 21, it was found that a lithium atom and a potassium atom can be used as the alkali metal atom in addition to the sodium atom. Further, it was found that an alkaline earth metal atom (calcium atom) can be used in addition to the alkali metal atom.

Further, by using α-alumina having high crystallinity (the half width of the X-ray diffraction spectrum is 0.300 or less), it is possible to obtain a magnetic tape excellent in polishing power, dispersibility and surface properties. did it.

Also, as in Example 22, the sample in which the abrasive was mixed and dispersed in advance and further mixed and dispersed together with the components of the magnetic layer was also more excellent in squareness ratio, surface roughness, electromagnetic conversion characteristics, and still durability. Do you get it.

Further, from the comparison between Example 23 and Example 6, since the abrasive exhibits basicity (pH> 7), the use of a binder having a polar functional group improves the dispersibility and the like. I understood that.

Regarding the method for producing the abrasive, better results were obtained when the abrasive was manufactured by the improved Bayer method than when the abrasive was manufactured by the organic metal method.

[0091]

According to the present invention, as described above, in an abrasive mainly composed of alumina having high purity and high crystallinity, 10 ppm or more and 250 pp
m or less alkali metal or alkaline earth metal atoms and 0.1% by weight or less silicon atoms with respect to the abrasive,
By containing the abrasive, the surface properties, excellent polishing power, and, without causing adverse effects such as dropout, it is possible to obtain a magnetic layer excellent in dispersibility, further,
It is possible to provide a magnetic recording medium excellent in squareness ratio, surface roughness, electromagnetic conversion characteristics, and still durability.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of a magnetic recording medium according to the present invention.

[Description of Signs] 1 ... Nonmagnetic support, 2 ... Magnetic layer, 3 ... Backcoat layer

Claims (5)

[Claims] 1. A magnetic recording medium having a magnetic layer containing a magnetic powder and an abrasive, wherein the abrasive mainly comprises alumina having high purity and high crystallinity, and the abrasive has a ratio of 1 to the abrasive.
A magnetic recording medium characterized in that the abrasive contains 0 ppm or more and 250 ppm or less of alkali metal or alkaline earth metal atoms and 0.1% by weight or less of silicon atoms with respect to the abrasive. . 2. The main component of the polishing agent is substantially α-alumina, and the content of aluminum atoms is 99.5% by weight or more based on the total amount of metal components of the polishing agent. 2. The magnetic recording medium according to 1. 3. The magnetic recording medium according to claim 1, further comprising a coating type magnetic layer in which the magnetic powder and the abrasive are dispersed in a binder. 4. The magnetic recording medium according to claim 1, wherein the surface of the abrasive exhibits basicity. 5. The magnetic recording medium according to claim 1, wherein the binder has an anionic polar functional group.