JPH0760515B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium having a non-magnetic support coated with a magnetic layer, and more particularly to a magnetic recording medium having improved running durability.

[Conventional technology]

Conventionally, γ-Fe has been used as a tape-shaped or disk-shaped magnetic recording medium for audio, video, computer, etc.
₂ O ₃ , Co-containing iron oxide, chromium dioxide, a magnetic recording medium in which a magnetic layer in which a ferromagnetic powder such as a ferromagnetic alloy powder is dispersed in a binder is coated on a non-magnetic support is used. . Recently, magnetic particles have been made into fine particles with the increase in density and S / N ratio of such magnetic recording media. Therefore, the running durability of the magnetic recording medium using such a magnetic material deteriorates. Further, this inclination is remarkable when a ferromagnetic alloy powder having a low hardness is used.

[Problems to be solved by the invention]

As a measure to prevent such deterioration of running durability, it has been conventionally proposed to add a granular abrasive such as Al ₂ O ₃ , SiC, Cr ₂ O ₃ to the magnetic layer. Addition of a large amount of abrasive material causes a problem of deterioration of electromagnetic conversion characteristics due to deterioration of surface orientation accompanied by deterioration of magnetic field orientation of magnetic recording medium, filling degree of magnetic powder, and deterioration of dispersibility.

Also, if the amount of abrasive added is reduced to improve surface properties, electromagnetic conversion characteristics improve, but the friction coefficient of the magnetic layer increases,
Problems such as sticking during running and poor running performance of the magnetic recording medium occur.

Accordingly, it is an object of the present invention to provide a magnetic recording medium in which the running durability and electromagnetic conversion characteristics of a magnetic layer are improved at the same time, and the running property is improved.

[Means for solving problems]

The present applicant has previously found that the major axis diameter is 0.1 μm or more and 1.0 μm or less and the minor axis diameter is 0.02 μm or more as means for achieving the above object.
It has been proposed to use an acicular inorganic substance having an acicular ratio of 5 to 20 and a Mohs hardness of 5 or more as a polishing agent (Japanese Patent Application No. 60-62938).

In the present invention, as a result of repeated studies for achieving the above-mentioned object and obtaining a magnetic recording medium with improved running property, among the abrasives proposed above, needle-like Cr ₂ O ₃ having the above-mentioned characteristics is particularly magnetic. The present invention has been accomplished by discovering that the running durability and electromagnetic conversion characteristics of the magnetic layer can be remarkably improved by forming the magnetic layer by dispersing the powder with a specific binder together with the powder.

That is, the present invention is a magnetic recording medium having a magnetic layer containing a magnetic powder dispersed in a binder on a non-magnetic support, wherein the magnetic layer has a major axis diameter of 1.0 μm or less and a minor axis diameter of 0.1 μm or less, Needle-shaped Cr ₂ O ₃ having a needle-shaped ratio of 5 to 20 is added to the magnetic powder in an amount of 1 to 2
Glass transition temperature (T
g) contains polyurethane of 0 to 95 ° C., which is a magnetic recording medium.

Hereinafter, the present invention will be described in detail.

The present invention can be applied to magnetic recording media using conventionally used iron oxide-based, Co-containing iron oxide-based ferromagnetic powders and chromium dioxide (CrO ₂ ) -based ferromagnetic powders, but so-called ferromagnetic alloy powders. , "Especially effective when using a ferromagnetic alloy powder having a specific surface area of 25 m ² / g or more". That is, the hardness of the ferromagnetic alloy powder is lower than that of other ferromagnetic powders,
A magnetic recording medium using this has a low abradability and a tendency of being inferior in running durability, but these problems can be effectively solved by applying the present invention.

The non-magnetic support used in the present invention is not particularly limited, and those commonly used can be used. Examples of materials forming the non-magnetic support include various synthetic resin films such as polyethylene terephthalate (PET), polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, and polyimide,
And metal foils such as aluminum foil and stainless steel foil. The thickness of the non-magnetic support is not particularly limited, but is generally 3 to 50 μm, preferably 5 to 30 μm.

The non-magnetic support may have a backing layer (backing layer) provided on the side where the magnetic layer described later is not provided.

The magnetic recording medium of the present invention has a magnetic layer in which a ferromagnetic powder is dispersed in a binder on the above-mentioned non-magnetic support.

As the ferromagnetic powder used in the magnetic layer of the present invention, a ferromagnetic alloy fine powder containing iron as a main component, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-modified ferromagnetic iron oxide CrO ₂ , and modified barium. There are ferrite and modified strontium ferrite, etc., but the present invention is a ferromagnetic alloy powder containing iron, cobalt or nickel, and when the specific surface area of the ferromagnetic alloy powder is 25 m ² / g or more is used as the ferromagnetic powder. Especially effective for.

As an example of this ferromagnetic alloy powder, the metal content in the ferromagnetic alloy powder is 75% by weight or more, and the metal content is 80% by weight.
The above is at least one kind of ferromagnetic metal or alloy, and an alloy which may contain other components within the range of 20% by weight or less of the metal content can be mentioned. Further, the ferromagnetic metal component may include a small amount of water, hydroxide or oxide. The method for producing these ferromagnetic metal powders is already known, and the ferromagnetic alloy powder, which is a typical example of the ferromagnetic powder used in the present invention, can also be produced according to these known methods.

When the ferromagnetic alloy powder is used, its shape is not particularly limited, but needle-shaped, granular, dice-shaped, rice granular, and plate-shaped particles are usually used. The specific surface area (S BET) of this ferromagnetic alloy powder is preferably 42 m ² / g or more, and more preferably 45 m ² / g or more.

The polyurethane used in the present invention has a glass transition temperature (Tg) of 0 to 95 ° C, preferably 0 to 75 ° C,
It is a polymer of isocyanates or a compound having a functional group capable of reacting with this and binding to form a polymer, which is appropriately selected and used. The preferred average molecular weight of these polyurethanes is 5,000 to 100,000.

Preferred polyurethanes include organic dibasic acids such as phthalic acid and adipic acid and glycols such as ethylene glycol, propylene glycol and butylene glycol,
Obtained by reaction with trimethylolpropane, hexanetriol, pentaerythritol, polyhydric alcohols such as cyclohexane-1,4-diol, phenols such as bisphenol A, and the like, preferably having an average molecular weight of 600 to 3000. Obtained by reacting propylene oxide, ethylene oxide or the like with a reactive polyester alone or mixed; preferably, an average molecular weight
600-3000 reactive polyethers, alone or mixed, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, polyester polyurethane obtained by reacting with isocyanates such as hexamethylene diisocyanate, or polyether polyurethane These may be used alone or as a mixture, or as a combination thereof.

In the present invention, the blending ratio of polyurethane is 10 to 90%, preferably 15 to 85% of the total weight of the binder.

Furthermore, by containing a low molecular weight polyisocyanate compound having a plurality of isocyanate groups as a binder, a molecular weight of 150 to 2000, it is possible to form a three-dimensional network structure in the magnetic layer to further improve the physical strength. You can
The amount of the low molecular weight polyisocyanate compound added is preferably 5 wt% to 100 wt% of the total amount of the binder. The low molecular weight polyisocyanate compound is an isocyanate monomer having a plurality of isocyanate groups, and a multimer thereof, or an adduct of the monomer or multimer with a compound such as the polyhydric alcohol. Includes.
Examples of the isocyanate monomer include ethane diisocyanate, 2,2,4-trimethylpentane diisocyanate, ω, ω′-diisocyanate-1,3-dimethylpenzole, ω, ω′-diisocyanate-1,2-dimethylcyclohexanediisocyanate. , Naphthalene-1,4
-Diisocyanate, triphenylmethane-4,4 ', 4 "
-Triisocyanates and the like.

As the binder other than the above, which is used together with the formation of the magnetic layer of the present invention, a commonly used thermoplastic resin, thermosetting resin, reactive resin or the like can be used. These resins can be used alone or as a mixture.

Generally, the average molecular weight of a thermoplastic resin is 10,000 to 20.
However, those having a degree of polymerization of about 200 to 2000 are used. Examples of such thermoplastic resins include vinyl chloride / vinyl acetate copolymer resins, vinyl chloride / vinylidene chloride copolymers, acrylic resins, cellulose derivatives, various synthetic rubber thermoplastic resins, polyvinyl fluoride, Examples thereof include polyamide resin, polyvinyl butyrate, styrene / butadiene copolymer and polystyrene resin,
These can be used alone or as a mixture.

As the thermosetting resin or the reactive resin, a resin having an average molecular weight of 200,000 or less in the state of a coating liquid is generally used, and a resin whose molecular weight becomes almost infinite due to a condensation reaction or an addition reaction after coating is used. . However, when these resins are thermosetting resins, it is preferable that the resins do not soften or dissolve due to heating during the process of curing. Examples of such resins include phenol /
Formalin novolac resin, phenol / formalin resol resin, phenol / furfural resin, xylene / formaldehyde resin, urea resin, melamine resin, drying oil modified alkyd resin, phenol resin modified alkyd resin, maleic acid resin modified alkyd resin, unsaturated polyester Examples thereof include a resin, a combination of an epoxy resin and a curing agent, and these may be used alone or in combination.

The amount of the binder used is generally in the range of 10 to 100 parts by weight, preferably 15 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

Cr ₂ O ₃ used in the present invention is acicular trichromium dioxide having a major axis diameter of 0.1 μm or more and 1.0 μm or less, a uniaxial diameter of 0.02 μm or more and 0.1 μm or less, and an acicular ratio (axial ratio) of 5 to 20. is there. The major axis diameter is 0.
1 to 0.95 μm, minor axis diameter 0.02 to 0.09 μm, needle ratio 8
Particularly preferred is Cr ₂ O _{3 of} -15.

When the major axis diameter of Cr ₂ O ₃ used as an abrasive is greater than 1.0 μm and the minor axis length is greater than 0.1 μm, and the acicular ratio of Cr ₂ O ₃ is less than 5 or greater than 20, Cr
The dispersibility of ₂ O ₃ is lowered, and the electromagnetic conversion characteristics are not sufficiently improved. Further, the magnetic field orientation treatment of the ferromagnetic powder may be adversely affected, and the electromagnetic conversion characteristics of the obtained magnetic recording medium may not be improved.

The upper limit values of the major axis length and the minor axis length defined in the present invention mean the upper limit values of the respective average values of the major axis length and the minor axis length of Cr ₂ O ₃ contained in the magnetic layer. Numerical values in respective preferable ranges have the same meaning.

The above Cr ₂ O ₃ used in the present invention has a Mohs hardness of about 9.

The acicular Cr ₂ O ₃ used in the invention can be produced, for example, by the following known method. That is, Cr
A mixture of O ₃ and Cr ₂ O ₃ is dispersed in water to form a water-dispersed slurry, which is heated in an autoclave at a temperature of 350 to 370 ° C and a pressure of 30.
Needle-like CrO ₂ obtained by hydrothermal reaction in the range of 0 to 500 atm
Is heated at 700 to 900 ° C., preferably 800 to 850 ° C. in air to obtain needle-like Cr ₂ O ₃ . Further, Cr ₂ (CrO ₄ ) ₃ obtained by partially reducing CrO ₃ may be used as a starting material.

In the present invention, the needle-like Cr ₂ O ₃ is contained in the magnetic layer in an amount of 1 to 20% by weight, preferably 2 to 15% by weight of the ferromagnetic powder.
To be contained in the magnetic layer.

Since the magnetic recording medium of the present invention contains the above needle-shaped Cr ₂ O ₃ in the magnetic layer, it is not necessary to add any other abrasive, but it is usually used in a range that does not hinder the achievement of the object of the present invention. It is also possible to add other abrasives.

Similarly, other granular additives (eg, carbon black having an average particle size of 0.015 to 0.2 μm as an antistatic agent) usually used within a range that does not hinder the achievement of the object of the present invention may be added. It is possible.

In the production of the magnetic layer of the magnetic recording medium of the present invention, first, a binder containing the above-mentioned needle-like Cr ₂ O ₃ and ferromagnetic powder such as a ferromagnetic alloy powder and the above-mentioned polyurethane, and other particles if necessary. It is formed by forming a magnetic coating material in which a filler is kneaded with a solvent, applying the coating material on a support, subjecting it to magnetic field orientation, etc., and then drying it.

As the solvent used for kneading, a solvent usually used for preparing a magnetic paint can be used.

As a kneading method, a method which is usually performed as a method for kneading a magnetic paint can be used. Further, the order of addition of each component can be appropriately set.

Various techniques are known as a technique for preparing a magnetic coating material, and in the production of the magnetic recording medium of the present invention, those known techniques can be arbitrarily used.

When preparing the magnetic paint, known additives such as a dispersant, an antistatic agent and a lubricant may be used together.

Examples of the dispersant include a fatty acid having 12 to 18 carbon atoms, a metal soap composed of the above fatty acid and an alkali metal or an alkaline earth metal, an ester of the above fatty acid, and a part or all of hydrogen of the compound as a fluorine atom. Compounds substituted with, amides of the above fatty acids, aliphatic amines, higher alcohols,
Examples of known dispersants include polyalkylene oxide alkyl phosphates, alkyl phosphates, alkyl borates, sarcosinates, alkyl ether esters, trialkylpolyolefinoxy quaternary ammonium salts and lecithin. When a dispersant is used, it is usually used in the range of 0.5 to 2.0 parts by weight based on 100 parts by weight of the binder used.

Examples of the antistatic agent include natural surfactants; nonionic surfactants; cationic surfactants; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, and phosphate ester group. Agents: amphoteric activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of aminoalcohols, and the like. When using conductive fine powder such as carbon black as an antistatic agent, for example, with respect to 100 parts by weight of the binder.
When it is used in the range of 0.2 to 20 parts by weight and a surfactant is used, it is used in the range of 0.1 to 10 parts by weight.

Examples of the lubricant include fatty acids composed of the above-mentioned fatty acids, higher alcohols, butyl stearate, sorbitan oleate, and the like, which have 12 to 20 carbon monobasic fatty acids and 3 to 20 carbon, monohydric or polyhydric alcohols. In addition to esters, mineral oils, animal and vegetable oils, olefin low polymers, α-olefin low polymers, known lubricants such as graphite fine powder and lubricants for plastics can be mentioned. The addition amount of the lubricant can be arbitrarily determined according to a known technique.

The additives such as the dispersant, the antistatic agent, and the lubricant described above are not those strictly limited to those having only the above-described action and effect. For example, the dispersant is a lubricant. Alternatively, it may act as an antistatic agent. Therefore, it is needless to say that the action and effects of the compounds exemplified by the above classification are not limited to the items described in the above classification, and when a substance having a plurality of action effects is used, it is added. The amount is preferably determined in consideration of the effect of the substance.

The magnetic coating material thus prepared is applied onto the above-mentioned non-magnetic support by a known method. Coating is usually performed directly on the non-magnetic support. However, it can also be applied on a non-magnetic support through an adhesive layer or the like.

The thickness of the magnetic layer thus coated is not particularly limited, but the thickness after drying is generally in the range of about 0.5 to 10 μm,
Usually, it is applied in a range of 1.5 to 7.0 μm.

The magnetic layer coated on the non-magnetic support is usually dried after the treatment for orienting the ferromagnetic powder in the magnetic layer, that is, the magnetic field orientation treatment. If necessary, surface smoothing treatment is performed. The magnetic recording medium that has been subjected to surface smoothing treatment is then cut into a desired shape.

Next, examples and comparative examples of the present invention will be shown. The indication "part" in the examples and comparative examples means "part by weight".

Example 1 A slurry obtained by dispersing an equimolar mixture of CrO ₃ and Cr ₂ O ₃ in water was placed in an autoclave at a temperature of 350 ° C. and a pressure of 300.
Hydrothermal reaction (reaction time: 5 hours) was performed under atmospheric pressure conditions to obtain needle-shaped CrO ₂ . This was heated in air at a temperature of 800 ° C. for 2 hours to obtain acicular Cr ₂ O ₃ .

The obtained needle-shaped Cr ₂ O ₃ was classified and used.

Next, a magnetic coating material having the composition shown below was prepared and applied onto a polyethylene terephthalate non-magnetic support having a thickness of 10 μm so that the thickness of the magnetic layer after drying was 3.0 μm.

Magnetic coating composition 100 parts of ferromagnetic alloy powder (Fe-Ni alloy, about 5% by weight of Ni) (specific surface area [S-BET]: 45 m ² / g) 12 parts of vinyl chloride / vinyl acetate / maleic anhydride copolymer ( Nippon Zeon Co., Ltd .: 400 × 110A) Polyurethane 8 parts (Molecular weight: 50,000, Tg: 45 ° C.) Isocyanate 8 parts (Nippon Polyurethane Co., Ltd .: Coronate L) Methyl ethyl ketone 150 parts The non-magnetic support coated with the magnetic paint was subjected to a magnetic field orientation treatment in a state where the magnetic paint was not dried, further dried and then subjected to a calendar treatment, and slit into an 8 mm width to produce an 8 mm video tape.

As a magnetic characteristic of this video tape, a B-H curve (B: magnetic flux density, H: external magnetic field) is measured and obtained, and from this value, a squareness ratio (Br / Bm, [Br: maximum residual magnetic flux density, Bm: The maximum magnetic flux density]) was obtained.

The resulting videotape is recorded on a video recorder (Ti UJIX-
8) was used to record and reproduce a 5 MHz signal. The reproduction output of the above video tape when the reproduction output at 5 MHz recorded on the reference tape (the tape for 8 mm video obtained in Comparative Example 1 below) was set to 0 dB, and the decrease in the reproduction output after 100 passes were measured. The C / N is shown by the ratio of the reproduced output at 5MHz and the noise at 4MHz.

The above video recorder was repeatedly run, and the number of runs until the magnetic head was clogged was examined.

The surface gloss was determined by measuring the total reflectance at an incident angle of 45 ° and a reflection angle of 45 ° with a standard gloss meter. The CrO ₂ standard tape was 150. The measuring device is a digital standard color difference photometer AUD manufactured by Suga Test Instruments Co., Ltd.
-CH-GV3 was used.

Comparative Example 1 A video tape was manufactured in the same manner as in Example 1 except that Cr ₂ O ₃ was replaced by a spherical shape (size 0.3 μm).

Comparative Example 2 A video tape was manufactured in the same manner as in Comparative Example 1 except that the polyurethane was changed to Tg: -27 ° C.

Example 2 Except that the addition amount of Cr ₂ O ₃ was changed to 15 parts in Example 1,
A video tape was manufactured in the same manner.

Example 3 Except that the addition amount of Cr ₂ O ₃ was changed to 2.5 parts in Example 1,
A video tape was manufactured in the same manner.

Comparative Example 3 Except that the addition amount of Cr ₂ O ₃ was changed to 0.5 part in Example 1,
A video tape was manufactured in the same manner.

Comparative Example 4 Except that the addition amount of Cr ₂ O ₃ was changed to 25 parts in Example 1,
A video tape was manufactured in the same manner.

Comparative Example 5 In Example 1, Cr ₂ O ₃ was used with a major axis diameter of 0.08 μm and a minor axis diameter of 0.02.
A video tape was manufactured in the same manner except that the tape having a thickness of 4 μm and an axial ratio of 4 was used.

Example 4 In Example 1, Cr ₂ O ₃ was added to have a major axis diameter of 0.9 μm and a minor axis diameter of 0.07 μm.
A video tape was manufactured in the same manner, except that the m tape having an axial ratio of 12.9 was used.

Comparative Example 6 In Example 1, Cr ₂ O ₃ was added to have a major axis diameter of 1.2 μm and a minor axis diameter of 0.06 μm.
A video tape was manufactured in the same manner except that a tape having an m and an axial ratio of 20 was used.

Comparative Example 7 A video tape was manufactured in the same manner as in Example 1, except that the polyurethane was changed to Tg: -27 ° C.

Example 5 A video tape was produced in the same manner as in Example 1 except that the polyurethane having Tg of 0 ° C. was replaced.

Example 6 A video tape was manufactured in the same manner as in Example 1 except that the polyurethane was changed to Tg: 70 ° C.

Comparative Example 8 A video rape was produced in the same manner as in Example 1 except that the polyurethane was changed to Tg: 98 ° C.

Comparative Example 9 In Example 1, needle-like α-Al ₂ O was used instead of needle-like Cr ₂ O _3.
3 (major axis diameter: 0.3 μm, needle ratio: 1/15)
A video tape was manufactured in the same manner.

The results are shown in the table. In the table, the “real” of the sample is the “example”,
“Ratio” represents “comparative example”.

(Effect of the invention) As is clear from the above results, in the present invention, by using specific acicular Cr ₂ O ₃ and polyurethane having a glass transition temperature (Tg) of 0 to 95 ° C. A magnetic recording medium having excellent conversion characteristics and improved running durability can be obtained.

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Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing magnetic powder dispersed in a binder on a non-magnetic support, wherein the magnetic layer has a major axis diameter of 0.1 μm or more and 1.0 μm or less and a uniaxial diameter of 0.
1 to 20% by weight of acicular Cr ₂ O ₃ with an acicular ratio of 5 to 20 and having a glass transition temperature (Tg) of 0 to 95 ° C. as a binder. A magnetic recording medium containing polyurethane.