JPH0935244A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability at high and low temps. and to ensure fitness for high density recording as well as to enhance dispersibility and the mechanical characteristics of a coating film by specifying a surface modifying material for magnetic powder and a binder. SOLUTION: A magnetic layer contg. ferromagnetic powder and a binder is formed on a flexible nonmagnetic substrate to obtain the objective magnetic recording medium. Ferromagnetic powder with a coating film of an inorg. Si compd. on the surface is used as the ferro-magnetic powder and a resin having tert. amino groups or quat. ammonium groups is used as the binder. A compd. represented by the formula SiO2 .nH2 O (0<n<2) is used as the inorg. Si compd. The resin for the binder is selected from among various resins, but since vinyl chloride resin and cellulosic resin have high ability to disperse ferromagnetic powder and polyurethane resin gives a magnetic coating film excellent in wear resistance, one or more of these resins are used as the binder.

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 specifically, it is suitable for high-density recording in which the dispersibility of magnetic powder is enhanced and the strength of a magnetic layer is improved to improve mechanical properties and durability. It exists in a magnetic recording medium.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been required to have higher performance, and magnetic tapes, floppy disks and the like having high electromagnetic conversion characteristics capable of high density recording have been desired. In particular, in a high-density magnetic recording medium, it is necessary to improve the S / N and increase the saturation magnetization in order to obtain sufficient recording / reproducing characteristics, and further finer particles of the magnetic powder and higher dispersion are required. .

On the other hand, there is a demand for an increase in recording density and an increase in the speed of data recording / reproduction. Therefore, even if the magnetic recording medium is required to have higher reliability, the magnetic layer is destroyed even if it is rubbed by a magnetic head during repeated use. There is a demand for a magnetic recording medium that does not cause noise. Conventionally, various binders have been proposed in order to satisfy these properties. Generally, vinyl chloride-vinyl acetate copolymers, cellulose derivatives, polyurethane resins and the like are mainly used as binder resins for magnetic recording media because of their excellent mechanical properties. On the other hand, in response to the recent increase in the specific surface area of magnetic powder, it becomes more difficult to disperse the magnetic powder, and it is necessary to improve the dispersibility. Therefore, a dispersant such as lecithin has been conventionally used. Since the dispersant has excellent dispersibility, it has one side that impairs the mechanical properties of the magnetic layer.Therefore, in order to enhance the affinity between the binder and the magnetic powder surface, acidic polar groups such as sulfonic acid groups and carboxyl groups have been introduced. Binders have become widely used. Resins having these acidic polar groups are disclosed in, for example, JP-A-54-157603, in which -SO ₃ Na is contained in polyester polyurethane.
It can be obtained by introducing a group.

[0004]

A binder having a polar group has been effective in improving dispersibility and coating film strength, but recently, a fine magnetic powder having a particle size of less than 0.1 μm was used. Is no longer available. In addition, in a magnetic coating material that uses an organic solvent that is essentially weak in polarity, if a resin having a hydrophilic polar group is contained, the viscosity of the magnetic coating material is increased, and the coating material characteristics deteriorate, making it difficult to handle. A problem has arisen.

On the other hand, as another method for improving the dispersibility of the magnetic powder in the magnetic coating material, a non-magnetic film is formed on the surface of the magnetic powder or non-magnetic particles are adhered to the magnetic powder so that Attempts have been made to weaken the magnetic interaction and prevent aggregation. However, with respect to the magnetic powder for high density in recent years, the dispersibility was not improved as much as expected, and there were problems in durability and magnetic characteristics when used as a magnetic recording medium, and it was not satisfactory. . In particular, it has been difficult to say that it is effective for a binder having an acidic polar group, which is considered to be effective for both the dispersibility of magnetic powder and the mechanical properties of the magnetic layer. Rather, the dispersibility was inferior and the durability was sometimes deteriorated. The reason for this is beyond speculation, but the strong interaction due to the acidic polar groups causes the surface coating layer, which cannot be said to adhere strongly to the magnetic powder, to peel off in the paint,
It is thought that it may be dissolved or deteriorated, and the dispersibility and durability may be deteriorated.

In particular, it is promising as a magnetic powder for a magnetic recording medium, which has been proposed as a system for high density magnetic recording and which supports a perpendicular magnetic recording system utilizing magnetization in a direction perpendicular to the surface of the magnetic recording medium. For a certain hexagonal ferrite such as BaFe ₁₂ O _19, it has not yet been reported that the dispersibility and durability are simultaneously satisfied. The hexagonal ferrite has a flat plate shape, and the easy axis of magnetization is perpendicular to the plate surface, so that there is an advantage that vertical orientation can be easily performed by magnetic field orientation processing or mechanical orientation processing. Further, each particle of the hexagonal ferrite magnetic powder is composed of a single crystal, and very fine and dense particles can be obtained. Therefore, even when used as an in-plane oriented medium, a magnetic recording medium having a sharp reversal magnetization distribution and low noise can be obtained. However, since the hexagonal ferrite particles have a tabular shape, the particles are likely to be piled up to form an agglomerate, and the dispersibility in the magnetic paint is likely to be lowered. Further, the fine particles make it more difficult to disperse. As described above, it is the current situation that the magnetic recording medium using the fine magnetic powder for high density recording in recent years cannot satisfy the requirements of dispersibility, durability, mechanical properties and the like at the same time. It is an object of the present invention to provide a magnetic recording medium using fine magnetic powder suitable for high density recording, which has improved mechanical properties, durability and runnability as well as improved dispersibility and coating properties.

[0007]

[Means for Solving the Problems] In order to obtain a magnetic recording medium having excellent dispersibility, durability, etc., the inventors of the present invention have conducted extensive studies and specified the surface modifying substance for magnetic powder and the type of binder. As a result, they have found that a magnetic recording medium excellent in dispersibility, mechanical properties and durability can be realized even if magnetic powder having a fine particle diameter is used, and completed the present invention. That is, the gist of the present invention is a magnetic recording medium comprising a magnetic layer containing a ferromagnetic powder and a binder on a flexible non-magnetic support, the ferromagnetic powder comprising an inorganic compound of silicon on the surface. And a binder having a tertiary amino group or a quaternary ammonium salt group.

According to the present invention, even when hexagonal ferrite magnetic powder, which is difficult to disperse, is used, sufficient dispersibility can be ensured, and high density recording excellent in mechanical characteristics and electromagnetic conversion characteristics is achieved. It has become possible to obtain a magnetic recording medium suitable for. Hereinafter, the present invention will be described in detail. The magnetic powder having an inorganic compound film of silicon on the surface used in the present invention can be produced by any known method.

For example, magnetic powder is dispersed in water to form a slurry, to which is added an aqueous solution of a water-soluble compound of silicon such as sodium silicate, the mixture is stirred, and then neutralized with an acid to form silicon on the surface of the magnetic powder. To precipitate the inorganic compound. When this is washed with water, filtered, and dried, magnetic powder having an inorganic compound film of silicon on the surface is obtained. Examples of the water-soluble silicon compound to be added include salts of orthosilicic acid and metasilicic acid such as sodium and potassium. Also, a sol-gel method using alkoxysilane or the like, a CVD method using alkylsilane, etc. can be used.

In the present invention, a preferable inorganic compound film of silicon formed on the surface of the magnetic powder is 100% after the inorganic compound of silicon is formed on the surface of the magnetic powder by precipitation from an aqueous solution by the above-mentioned method. It is obtained by heat treatment at ˜250 ° C. The precipitate generated by neutralizing the aqueous solution of the silicon compound is considered to be amorphous silicic acid or a hydrated oxide, but a good film can be obtained only by drying this at a temperature of less than 100 ° C. It is hard to be formed, and the saturation magnetization amount of the magnetic powder is smaller than that of the one heat-treated at 100 to 250 ° C.
On the contrary, if the heat treatment is performed at a high temperature exceeding 250 ° C., the dispersibility of the magnetic powder may be reduced. It is unclear why a good film is formed by heat treatment at 100 to 250 ° C.
Part of water is desorbed from the silicic acid or hydrated oxide coating the surface of the magnetic powder, and SiO ₂ · nH ₂ O (0
It is considered that this is due to the change to the composition formula <n <2). When dried below 100 ° C., the silicic acid or hydrated oxide is not firmly bound to the magnetic powder and has a large amount of hydroxyl groups that interact with the functional groups of the binder. It is considered that when the magnetic coating is prepared, the film of the silicon compound is peeled off, dissolved or altered due to the interaction with the functional group of the binder, and the intended purpose is not achieved. Further, when heat treatment is performed at a temperature higher than 250 ° C., a large amount of hydroxyl groups are lost due to dehydration, so that the interaction with the functional groups of the binder is weakened and the desired purpose is not achieved. On the other hand, the one heat-treated at 100 to 250 ° C is dehydrated moderately and the amount of hydroxyl groups is appropriate,
Although it has an affinity for the functional group of the binder, it is considered to exhibit good characteristics without being dissolved or altered by reacting with it. In any case, the one heat-treated at 100 to 250 ° C. has a lower viscosity of the magnetic paint and the improvement of the magnetic paint characteristics than the one heat-treated at a temperature less than 100 ° C. Further, compared with the one heat-treated at a temperature higher than 250 ° C., the dispersibility is improved because the interaction with the functional group of the binder is stronger. It should be noted that although the one heat-treated at 100 to 250 ° C. remains amorphous, it is considered that when treated at a temperature higher than 250 ° C., crystallization progresses at the same time as dehydration and becomes non-hydrophilic. It may contribute to the poor dispersibility of the magnetic powder having the film heat-treated at a temperature exceeding the above.

The amount of silicon inorganic compound in the magnetic powder surface coating is
Silicon / magnetic powder weight ratio of 0.1-2% by weight, especially 0.3
It is preferably in the range of from 1.5 to 1.5% by weight. If this ratio is small, the effect of improving dispersibility cannot be expected. On the contrary, if it is too large, the amount of non-magnetic component increases and it becomes unsuitable for high-density magnetic recording, and the silicon compound coating the surface is a polar group of the binder. In some cases, the deterioration of properties may occur due to elution with the tertiary amino group or the quaternary ammonium base.

The magnetic powder used in the present invention is, for example, F
e, Ni, Co, Fe-Co alloy, Fe-Ni alloy, F
e-Co-Ni alloy, Fe-Ni-Zn alloy, Fe-C
Powder of ferromagnetic metal such as iron such as o-Ni-Cr alloy, Co-Ni alloy, nickel, cobalt or the like, or magnetic alloy containing these as main components, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co
Various ferromagnetic powders such as iron oxide magnetic powders such as γ-Fe ₂ O ₃ containing and Fe ₃ O ₄ containing Co, and metal oxide magnetic powders such as Cr ₂ O ₃ can be mentioned. In particular, since hexagonal ferrite is originally difficult to disperse, the effect of the present invention is remarkable. Examples of suitable hexagonal ferrite magnetic powder include barium ferrite magnetic powder and strontium ferrite magnetic powder. Various elements may be internally added to these hexagonal ferrites depending on the purpose. A method for producing these hexagonal ferrites is described in JP-A-56-6
7904 and the glass crystallization method described in JP-A-56-49776 and the like, but other known methods such as a coprecipitation method and a coprecipitation / salt catalyst method may be used.

The magnetic powder usually has an average particle size of 0.1.
The one having a size of μm or less is used. Particularly, it is preferable to use one having a thickness of 0.08 μm or less. It is possible to use magnetic powder having an average particle size of more than 0.1 μm, but for the purpose of obtaining a magnetic recording medium for high density, which is the object of the present invention, a powder having a particle size of 0.1 μm or less is used. Is desirable. The average particle diameter is obtained by observing the magnetic powder with a transmission electron microscope to find the maximum diameter of each particle, and taking the arithmetic mean thereof as the average particle diameter. When calculating the average particle size, 0.
Particles of 01 μm or less are excluded.

In the magnetic recording medium of the present invention, the amount of ferromagnetic powder used is preferably such that the content in the magnetic layer is 50 to 90% by weight, particularly 55 to 85% by weight. The specific surface area of the ferromagnetic powder itself is preferably 30 to 65 m ² / g. In particular, a ferromagnetic powder having a small particle size and a high specific surface area is preferable. When a magnetic powder having a specific surface area of less than 30 m ² / g is used, it is often not necessary to have such a high filling factor in practice, and there is little advantage of using the formulation of the present invention. For magnetic powders of 65 m ² / g or more, the method according to the present invention can provide significantly better characteristics than the conventional methods, but the high specific surface area of the magnetic powder makes it difficult to disperse and the characteristics deteriorate. I cannot avoid coming. Suitable specific surface area of the magnetic powder is 35 to 65 m ² / g, especially 45 to 55 m ² / g
It is.

The binder used in the present invention has a tertiary amino group or a quaternary ammonium base in the molecule. As a result, the silicon inorganic compound film on the surface of the magnetic powder having hydrophilicity and the polar tertiary amino group or quaternary ammonium base exhibit an appropriate interaction derived from the polar bond, and the desired dispersion is obtained. It is possible to secure the mechanical properties and mechanical properties. Further, the polarities of the tertiary amino group and the quaternary ammonium salt group are not as strong as those of the acidic polar group, so that the characteristics of the paint are not deteriorated.

Tertiary amino group or quaternary ammonium
The binder having a base is, for example, JP-A-63-1211.
It can be obtained by the method shown in FIG. Tertiary amino group
Or, the content of the quaternary ammonium salt group is usually
30 × 10 per gram of mixture ^-6~ 200 × 10^-6In equivalent
Yes, preferably 70 x 10 per gram of binder^-6~ 1
50 × 10^-6It is equivalent. Low amount of these functional groups
If it is cut off, adsorption to the surface of the magnetic powder will decrease, and
The characteristic cannot be maintained. On the contrary, too much
And the solubility of the binder in the solvent deteriorates and the viscosity of the paint
Increase the difficulty of preparing the paint.

As the resin having a tertiary amino group or a quaternary ammonium base, any resin having a skeleton structure can be used, and examples thereof include polyurethane resin, polyester resin, cellulose acetate butyrate, cellulose diacetate and nitrocellulose. Cellulose derivative, vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinyl chloride resins such as vinylidene chloride copolymers and vinyl chloride-acrylic copolymers, various synthetic rubbers such as styrene-butadiene copolymers, epoxy resins, phenoxy resins and the like can be used. Of these, vinyl chloride resins and cellulose resins have high dispersibility of ferromagnetic powder, and polyurethane resins have excellent abrasion resistance of the magnetic coating film. Therefore, it is preferable to use these alone or in combination. The molecular weight of the binder resin is preferably in the range of 10,000 to 100,000. If the molecular weight is too high, the viscosity of the paint becomes high and it becomes difficult to prepare the paint. On the other hand, if the molecular weight is too low, the mechanical strength of the coating film decreases.

The binder may be used in combination with a known curing agent such as isocyanate for curing treatment. For example, by using a low molecular weight polyisocyanate compound having a plurality of isocyanate groups together as a curing agent, a three-dimensional network structure can be formed in the magnetic layer and its mechanical strength can be improved. Examples of the low molecular weight polyisocyanate compound include aromatic diisocyanates such as tolylene diisocyanate, 4,4 ′ diphenylmethane diisocyanate, xylylene diisocyanate and meta-xylylene diisocyanate, hexamethylene diisocyanate,
Examples thereof include aliphatic isocyanates such as resin isocyanate and trimethylhexamethylene diisocyanate, and adducts of these isocyanates with active hydrogen compounds, for example, trimethylolpropane adduct of tolylene diisocyanate. The average molecular weight of these isocyanate compounds is preferably in the range of 100-5000.

The amount of the binder including the curing agent in the magnetic layer is usually 2 to 35 parts by weight, preferably 5 to 15 parts by weight, based on 100 parts by weight of the ferromagnetic powder. The curing agent is preferably used in a proportion of 5 to 100% by weight with respect to the binder. If the amount of the curing agent is small, the desired improvement in mechanical strength cannot be achieved. On the other hand, if the amount is large, the original function of the resin as the binder may be impaired, and the coating film strength and durability may decrease.

Examples of the material for forming the non-magnetic support used in the present invention include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polyethylene and polypropylene, cellulose triacetate and cellulose diacetate. Examples thereof include cellulose derivatives such as polyimide, polyimide, polyamide, polyimideamide, and polycarbonate. Further, metal foil such as aluminum foil, paper, etc. can be used.

The form of the non-magnetic support is arbitrary, but is mainly tape, film, sheet, card, disk, drum or the like. The thickness is not particularly limited, but is usually 3 to 100 μm, preferably 5 to 75 μm. The non-magnetic support may have a single-layer structure or a multi-layer structure. In addition, in order to improve the adhesion between the non-magnetic support and the magnetic layer, a surface treatment such as corona discharge treatment, treatment with a surface modifying agent such as alkane, amine aqueous solution, trichloroacetic acid, phenols, etc. is performed. It may be

Further, various additives such as a lubricant, an abrasive, an antistatic agent, and a dispersant can be further compounded in the magnetic coating material for forming the magnetic layer. As the lubricant, various kinds of lubricants such as aliphatic type, fluorine type, silicone type and hydrocarbon type can be used. Examples of the aliphatic lubricant include fatty acids, fatty acid metal salts, fatty acid esters, fatty acid amides, and aliphatic alcohols. Among them, when a fatty acid is used, it is presumed that the carboxyl group interacts with the tertiary amino group of the binder or the quaternary ammonium base, but a magnetic layer excellent in durability and friction characteristics can be obtained.

Examples of the fatty acid include oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid,
Examples thereof include isostearic acid and behenic acid. Examples of the fatty acid metal salt include magnesium salts, aluminum salts, sodium salts and calcium salts of these fatty acids. Examples of the fatty acid ester include butyl ester, octyl ester, stearyl ester, oleyl ester, isostearyl ester, and glyceride of the above fatty acid, and examples of the fatty acid amide include amides of the above fatty acids, linoleic acid amide, and caproic acid amide. Can be mentioned. Examples of the aliphatic alcohol include lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol and the like.

Examples of the fluorine-based lubricant include perfluoroalkyl polyethers, perfluoroalkyl carboxylic acids, perfluoropolyethers, fluorocarbons, and lubricants of the type in which fluorine is partially introduced. Examples of the silicone lubricant include silicone oil and modified silicone oil. In addition, solid lubricants such as molybdenum disulfide and tungsten disulfide, and phosphate esters can also be used. Examples of hydrocarbon lubricants include paraffin and squalane. Furthermore, animal and vegetable oils, mineral oils and the like can also be used.

These lubricants can be used alone or in combination. The lubricant is
The content in the magnetic layer is usually 0.1 to 20% by weight, preferably 1 to 10% by weight. When the magnetic layer is formed in two layers, the upper layer and the lower layer are
The type and content of the lubricant may be changed.

Examples of the abrasive include alumina, fused alumina, corundum, silicon carbide, chromium oxide, silicon nitride and the like, and among these, those having a relatively high hardness are preferably used. The particle size (number average particle size) is preferably 2 μm or less. The content of the abrasive in the magnetic layer is preferably in the range of 1 to 20% by weight.

As the antistatic agent, carbon black,
Graphite, tin oxide, indium tin oxide, fine powder of conductive metal and conductive compound such as metal powder and oxide, natural surfactant such as saponin, nonionic surfactant such as alkylene oxide and glycerin , Cationic alkylamines, quaternary ammonium salts, pyridinium salts, other heterocyclic salts, and other cationic surfactants, and carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, sulfuric acid ester groups, phosphoric acid ester groups, and other acidic groups. Anionic surfactants, amphoteric surfactants such as amino acids, amino sulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. In addition, these surfactants also
They may be used alone or as a mixture of some.

The amount of the antistatic agent used is usually in the range of 1 to 15% by weight in the magnetic layer. As the dispersant, fatty acids such as capric acid, lauric acid, myristic acid, oleic acid, and linoleic acid, metal soaps composed of alkali metal or alkaline earth metal salts of these fatty acids, fatty acid amides, fatty acid esters, higher alcohols, fats Group amines, polyalkylene oxides, alkyl phosphates, sugars, lecithin and the like are used.

The additives such as lubricants, dispersants and antistatic agents given as examples here are not limited to those having only the above-mentioned action and effect, but actually, for example, lubrication It is possible that an additive may have multiple effects, such as the agent also acting as a dispersant. Therefore, it is needless to say that the action of the compounds exemplified above is not limited to the above, and when an additive having a plurality of effects is used, the amount to be used is determined in consideration of the effects.

Examples of the solvent used for preparing the magnetic paint containing the above components include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohols such as methanol, ethanol, propanol, butanol and isopropyl alcohol, acetic acid. Esters such as methyl, ethyl acetate, butyl acetate and glycol acetate, ethers such as monoethyl ether, diethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane and tetrahydrofuran, aromatic compounds such as benzene, toluene and xylene. Hydrocarbons, hexane, heptane,
Aliphatic hydrocarbons such as nitropropane and their derivatives are included.

In the present invention, the above-mentioned surface-treated ferromagnetic powder, binder and other auxiliary agent added as necessary are mixed and kneaded with a solvent to disperse the magnetic powder well to prepare a magnetic coating material. Mixing, kneading, and dispersion can be performed by various known methods, and the apparatus used therefor is not particularly limited. In addition, the order of addition of each component can be arbitrarily set.

For example, as an apparatus used for kneading and dispersing,
2-roll mill, 3-roll mill, ball mill, sand mill, sand grinder, co-ball mill, high speed impeller disperser, high speed impact mill, disper, high speed mixer, homogenizer, ultrasonic disperser, open kneader, continuous kneader, pressure kneader, etc. Can be mentioned. The magnetic coating material thus prepared is applied to the above-mentioned non-magnetic support after filtering with a suitable filter if necessary.
The coating can be performed directly on the support, but an adhesive layer,
It can also be applied via an intermediate layer such as a conductive layer.

The method of coating the magnetic layer on the flexible non-magnetic support is arbitrary, and examples thereof include a gravure method, a reverse method and an extrusion method. When used as a tape-shaped magnetic recording medium, the magnetic layer coated on the non-magnetic support is preferably subjected to a magnetic field orientation treatment in order to orient the ferromagnetic powder in the magnetic layer. When used as a disk-shaped magnetic recording medium, in order to remove the direction dependence of the magnetic characteristics, non-orientation treatment with a magnetic field may be performed and then drying. After this,
The surface of the magnetic recording medium is subjected to a surface smoothing treatment with a calendar if necessary, and further subjected to a heat curing treatment and a radiation curing treatment, and then cut into an appropriate shape to obtain a magnetic recording medium according to the present invention.

[0034]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples. All "parts" in the examples are "parts by weight". Example 1 Flat barium ferrite [coercive force (Hc); 590
Oe, specific surface area; 31 m ² / g, average particle size; 0.05 μ
m, axial ratio (D / t); 3/1] 100 g, 1900 g
Was uniformly dispersed in pure water. While stirring this, 4% by weight of sodium silicate (Na ₂ O: SiO ₂ = 1: 2)
(Molar ratio) 100 g of an aqueous solution was added and stirring was continued to obtain a uniform slurry. Then, 0.3 mol / 1 diluted sulfuric acid was gradually added dropwise to obtain a suspension having a pH of 7. This suspension was washed with water and filtered repeatedly to remove sodium ions and sulfate ions. After pre-drying at 90 ° C for 12 hours, 150
Hydrated oxide (SiO ₂ · nH ₂
A film of a silicon compound estimated to be O, 0 <n <2) was formed on the surface of the flat barium ferrite. . As a result of chemical analysis, the weight ratio of silicon / barium ferrite in the magnetic powder was 4.4 × 10 ⁻³ . Also was calculated weight increase of the magnetic powder by the process, the weight of the coating, silicon present is an oxide when a (SiO ₂₎ and orthosilicate (H ₄ Si
It was in the middle of the case of O ₄ ), and it was confirmed that the above-mentioned hydrated oxide (SiO ₂ · nH ₂ O, 0 <n <2) was assumed. The surface-coated barium ferrite was mixed with a binder and the like according to the following composition and dispersed by a ball mill.

Magnetic powder 100 parts Quaternary ammonium salt group-containing vinyl chloride copolymer 4 parts (number average molecular weight; 20000 quaternary ammonium salt group content: 80 μeq / g) Polyurethane resin 4 parts Nitrocellulose resin 4 parts Dispersion Agent (GAFAC RE610, phosphoric acid type dispersant) 2.5 parts Alumina fine particles (average particle size 0.5 μm) 5 parts Carbon black (average particle size 0.03 μm) 6 parts Stearate ester 5 parts Oleic acid 1.5 parts Methyl ethyl ketone 150 parts Cyclohexanone 150 parts

Thereafter, 2 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added thereto, and the dispersion treatment was further performed for 1 hour to prepare a magnetic coating material. After filtering this magnetic paint with a filter having an average pore size of 2 μm,
It was applied onto a polyester film having a thickness of 75 μm so that the thickness after drying would be 2 μm, and after mirror finishing, it was cured.
This was punched into a disk having a diameter of 3.5 inches to prepare a floppy disk, and various characteristics were evaluated.

Example 2 First, polyester polyol 1 having an average molecular weight of 1000
00 parts, 0.17 parts of N-methyldiethanolamine and 8.8 parts of butanediol were dissolved in 600 parts of a 1: 1 solvent of toluene: methyl ethyl ketone. While stirring this solution, 53 parts of diphenylmethane diisocyanate was gradually added to prepare polyester polyurethane. To this, 0.05 part of hydrochloric acid was added to hydrochloric acid the tertiary amino group derived from N-methyldiethanolamine. The molecular weight of this product was 29500 as measured by GPC method, and the amount of the tertiary amino group was 86 μeq / g. A floppy disk was prepared in the same manner as in Example 1 except that 4 parts of the quaternary ammonium salt group-containing vinyl chloride copolymer was replaced with 4 parts of the resin obtained above.

Example 3 A surface-coated barium ferrite was prepared in the same manner as in Example 1 except that the drying condition was changed from 150 ° C. × 4 hours to 400 ° C. × 4 hours when preparing the surface-coated barium ferrite, and Using this, a floppy disk was manufactured in the same manner as in Example 1. When dried at 400 ° C. for 4 hours, the silicon compound coating the surface of barium ferrite becomes silicon oxide (SiO ₂ ).

Comparative Example 1 4% by weight of sodium silicate (Na ₂ O: SiO ₂ =)
1: 2) 100 g of pure water was used instead of 100 g of the aqueous solution,
A barium ferrite surface treatment was performed in the same manner as in Example 1 except that the neutralization operation was omitted, and using this, a floppy disk was prepared in the same manner as in Example 1.

Comparative Example 2 4% by weight of sodium silicate (Na ₂ O: SiO ₂ =)
1: 2) Performed except that 100 g of a 6 wt% titanium sulfate aqueous solution was used instead of 100 g of the aqueous solution, and 0.6 mol / 1 sodium hydroxide was used instead of 0.3 mol / 1 dilute sulfuric acid. A barium ferrite surface treatment was performed in the same manner as in Example 1, and using this, a floppy disk was prepared in the same manner as in Example 1. As a result of chemical analysis, the deposited amount of titanium was 6.1 × 10 ⁻³ in terms of titanium / barium ferrite weight ratio.

Comparative Example 3 Except that the quaternary ammonium salt group-containing vinyl chloride copolymer in Example 1 was changed to an acidic polar group-containing vinyl chloride copolymer (EC110, manufactured by Sekisui Chemical Co., Ltd.). A floppy disk was manufactured in the same manner as in Example 1. Comparative Example 4 Example 4 except that the quaternary ammonium salt group-containing vinyl chloride-based copolymer was changed to a polar group-free vinyl chloride-vinyl acetate copolymer (number average molecular weight: 20000). A floppy disk was prepared in the same manner as in 1. Performance Test Various characteristics of the floppy disk obtained above were measured. The results are shown in Table 1.

[0042]

Table 1 Gloss% Static friction (g / cm) Durability (10,000 passes) Peelability Example 1 133 26.7 800 1 Example 2 139 22.0 800 1 Example 3 129 20.1 600 1 Comparison Example 1 135 32.4 400 0 Comparative Example 2 125 23.0 400 -1 Comparative Example 3 123 23.9 350 0 Comparative Example 4 118 20.7 300 -1

The measuring method of each characteristic is as follows. Gloss: Measure the magnetic surface of the magnetic sheet after mirror surface treatment with a digital gonio-gloss meter at an incident angle of 60 degrees and a reflection angle of 60 degrees so that the incident surface is parallel to the longitudinal direction of coating. did. Static friction: Using a device in which the rotary shaft of the floppy disk drive was connected to a torque meter, the maximum torque at the time of starting the rotation of the floppy disk was read, and the maximum torque at the time of starting the rotation when an empty shell was set was deducted as the static friction value.

Durability: Floppy disk at temperature, 25
It was rotated in a floppy disk drive placed in an environment of ° C and humidity of 50%, and the number of times of running until a clear scratch was visually observed was measured. Peelability: 100g with adhesive tape attached to the magnetic layer surface
After rubbing three times with a load of f to make them adhere, the adhesive tape is peeled off at a speed of 2 cm / s in a direction perpendicular to the surface of the magnetic layer,
The amount of magnetic powder adhering to the surface of the adhesive tape was visually determined. 1: No peeling is observed. 0: There is slight peeling and the adhesive tape becomes light brown. -1: Clear peeling is observed and the adhesive tape becomes brown.

[0045]

As is apparent from the table, all of the examples using the magnetic powder coated with the inorganic compound of silicon in combination with the binder having a tertiary amino group or a quaternary ammonium salt group as a functional group are good. Excellent dispersibility, drivability, durability,
The magnetic layer mechanical properties are shown. Particularly, the characteristics of Examples 1 and 2 in which the compound of silicon on the surface is a hydrated oxide having an intermediate composition of silicon dioxide and orthosilicic acid are high. On the other hand, Comparative Example 1 having no coating layer on the surface has a problem in running property and durability, and Comparative Example 2 having a coating of a Ti compound has excellent running property, but has problems in dispersibility and durability. The mechanical properties of the magnetic layer are extremely poor. Further, in Comparative Example 4 in which the magnetic powder coated with the inorganic compound of silicon is used in combination with the binder containing no functional group, the running property is excellent, but the dispersibility is low, and the durability is extremely deteriorated. Further, in Comparative Example 3 using a resin having an acidic polar group as a functional group as a binder, the dispersibility and mechanical properties are improved, but the durability remains poor.

As is clear from the above examples, according to the present invention, it is possible to provide a magnetic recording medium having good dispersibility, running property, durability and mechanical properties of the magnetic layer.

Claims (6)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing a ferromagnetic powder and a binder on a flexible non-magnetic support, the ferromagnetic powder being a film made of an inorganic compound of silicon on the surface. And a binder having a tertiary amino group or a quaternary ammonium base as a functional group. 2. An inorganic silicon compound is obtained by neutralizing an aqueous solution of a silicon compound to form a precipitate on a ferromagnetic powder, and then subjecting this to heat treatment at 100 to 250 ° C. The magnetic recording medium according to claim 1, wherein: 3. The inorganic compound of silicon is SiO ₂ .nH ₂
The magnetic recording medium according to claim 1, which is represented by a composition formula of O (0 <n <2). 4. The magnetic recording medium according to claim 1, wherein the inorganic compound of silicon is amorphous. 5. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is hexagonal ferrite. 6. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder has an average particle size of 0.1 μm or less.