JPS62112221A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled magnetic recording medium having excellent electromagnetic transducing characteristic and traveling durability by using ferromagnetic alloy powder and using 10-20wt% acicular Cr2O3 powder, based on the magnetic powder, as an abrasive. CONSTITUTION:The magnetic layer contg. magnetic powder dispersed in a binder is formed on a nonmagnetic carrier to obtain the magnetic medium. The magnetic powder is composed of ferromagnetic alloy powder and the magnetic layer contains 10-20wt%, based on the ferromagnetic alloy powder, of acicular Cr2O3 having <=1.0mum major axis, <=0.1mum minor axis, and 5-20 acicular ratio. When Cr2O3 is used as the abrasive among others, the adhesive can be added without deteriorating the electromagnetic transducing characteristic, and the grinding property and traveling durability of the magnetic layer are remarkably improved. Ferromagnetic alloy powder having >=25m<2>/g surface area and contg. iron, cobalt, and/or nickel is used as the ferromagnetic alloy powder used in the magnetic layer and the powder in the region appropriate for an audio film can be effectively used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic recording medium in which a magnetic layer is coated on a non-magnetic support, and particularly to a magnetic recording medium with improved running durability.

[Conventional technology]

Conventionally, r
F]203, a magnetic recording medium is used in which a magnetic layer in which ferromagnetic powder such as Co-containing iron oxide, chromium dioxide, or ferromagnetic alloy powder is dispersed in a binder is coated on a non-magnetic support. . Recently, the density of such magnetic recording media has increased, and high S
/Nization has been carried out to make magnetic materials finer particles, but as the particles become finer, the abrasiveness of the magnetic materials decreases, and as a result, the running of magnetic recording media using such magnetic materials becomes difficult. Durability deteriorates. Moreover, this slope is remarkable when a ferromagnetic alloy powder with low hardness is used.

As a measure to prevent such deterioration of running durability, it has been proposed to add granular abrasives such as Al2O3 and SIC5Cr20* to the magnetic layer. This poses a problem of deterioration of electromagnetic conversion characteristics due to deterioration of surface properties accompanied by deterioration of magnetic field orientation of the magnetic recording medium, deterioration of filling degree of magnetic powder, and deterioration of dispersibility.

In addition, reducing the amount of abrasive added to improve the surface properties improves the electromagnetic characteristics, but the R9 friction coefficient of the magnetic layer increases and the running properties of the magnetic recording medium deteriorate, such as sticking during running. Problems such as this arise.

One of the inventors of the present invention collaborated with other inventors to solve the above-mentioned problems by having a major axis diameter of 1.0 μm or less and a minor axis diameter of 0.0 μm or less.
(Japanese Patent Application No. 60-62938) proposes the use of an acicular inorganic substance having a diameter of 1 μm or less, an acicular ratio of 5 to 20, and a Mohs hardness of 5 or more as an abrasive material.

[Problem that the invention seeks to solve]

In the above proposed invention, by using a specific acicular inorganic substance as an abrasive, the amount added can be considerably increased compared to conventional granular abrasives, improving electromagnetic conversion characteristics and running durability. However, 10 of the magnetic powder
If it exceeds % by weight, the degree of filling and dispersibility deteriorates and is considered undesirable.

However, when using a ferromagnetic alloy powder suitable for high density and high S/N, this alloy powder has lower hardness than other ferromagnetic powders, so it can be used to increase running durability without deteriorating electromagnetic conversion characteristics. It has become desirable to improve gender.

Therefore, an object of the present invention is to provide a magnetic recording medium that uses ferromagnetic alloy powder as the magnetic powder and has excellent electromagnetic conversion characteristics and running durability.

[Means for solving problems]

As a result of further research into the invention proposed earlier (Japanese Patent Application No. 60-62938) to achieve the above object, the present inventors used ferromagnetic powder as the magnetic powder and acicular-shaped abrasive material. It has been discovered that when Cr2O3 is used, it can be used in an amount of 10 to 20% by weight of the magnetic powder without impairing the surface properties of the magnetic layer and therefore the electromagnetic conversion characteristics, and that running properties and running durability can be improved. The present invention has been achieved.

In addition, in the previously proposed invention, it was said that the ferromagnetic alloy powder should preferably have a specific surface area of 45 m'/g or more to be suitable for video tapes, but especially when acicular Cr2O is used as an abrasive, was found to be suitable for audio tapes of 25 m'/g or more, which is the range suitable for audio tapes.

That is, the present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder dispersed in a binder on a non-magnetic support, wherein the magnetic powder is made of a ferromagnetic alloy powder, and the magnetic layer has a long sleeve diameter. 1.0μm or less, minor axis diameter 0. The present invention is a magnetic recording medium characterized by containing 10 to 20% by weight of ferromagnetic alloy powder of acicular Cr2O3 with an acicular ratio of 5 to 20 at 1 Atm or less.

The present invention will be explained in detail below.

Ferromagnetic alloy powder has excellent electromagnetic properties such as coercive force and saturation magnetization, and is preferably used in magnetic recording media for high-density recording.However, it has lower hardness than other ferromagnetic powders, and magnetic properties using it are The abrasiveness of the layer was low, and the running durability tended to be poor. The present invention has found that, among the proposed abrasive materials, when using Cr2O3 having an acicular structure as described above, scales can be added in an amount of 10 to 20% by weight of the magnetic powder without impairing the magnetic conversion properties. Therefore, it was possible to significantly improve the polishability and running durability of the magnetic layer using the ferromagnetic alloy powder.

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

The nonmagnetic support may be provided with a backing layer on the side on which the magnetic layer described below is not provided.

As described above, the magnetic recording medium of the present invention is one in which a magnetic layer in which ferromagnetic alloy powder and acicular Cr2O3 are dispersed in a binder is provided on a nonmagnetic support.

The ferromagnetic alloy powder used for the magnetic layer in the present invention has a surface area of 2
It is a ferromagnetic alloy powder containing 5 m'/g or more of iron, cobalt, and/or nickel.

In the present invention, as described above, by using acicular Cr2O3 having a specific acicular structure as an abrasive, a ferromagnetic alloy powder with a specific surface area of about 42 m''/g or more, which is in the suitable range for video film, can be obtained. In addition, it is also possible to effectively use materials suitable for audio films of up to about 25 m'/g.

An example of the ferromagnetic alloy powder used in the present invention is that the metal content in the ferromagnetic alloy powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one type of ferromagnetic metal or alloy. , alloys that may contain other components within a range of 20% by weight or less of the metal content. Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide. Methods for producing these ferromagnetic metal powders are already known, and 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 using ferromagnetic alloy powder, there are no particular restrictions on its shape, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used.

The abrasive material used in the present invention has a long sleeve diameter of 1.0 μm or less, a short axis diameter of 0.1 μm or less, and an acicular ratio of 5 to 20, especially a long sleeve diameter of 0.
．． 1 to 0.95 μm, short axis diameter 0.02 to 0.09 μm,
Acicular Cr2O3 having an acicular ratio of 8 to 15 is contained in the magnetic layer of the ferromagnetic alloy powder in an amount of 10 to 20% by weight.

When the long axis diameter of Cr2O3 used as an abrasive is larger than 1.0 μm and the short axis length is larger than 0.1 μm, and when the acicular ratio of Cr2O3 is smaller than 5 or larger than 20, the dispersibility of Cr2O3 Further, the electromagnetic conversion characteristics are not sufficiently improved. Furthermore, it may have an adverse effect on the magnetic field orientation treatment of the ferromagnetic powder, and the electromagnetic conversion characteristics of the resulting magnetic recording medium may not be improved.

The upper limit values of the major axis length and minor axis length defined in the present invention mean the upper limit values of the average values of the major axis length and minor axis length of Cr2O3 contained in the magnetic layer. The numerical values in each preferable range also have the same meaning.

The above-mentioned Cr2O3 used in the present invention has a Mohs hardness of about 9.

The acicular Cr2Off used in the present invention can be produced, for example, by the following known method. That is, a mixture of CrO2 and Cr2O3 is dispersed in water to form a water-dispersed slurry, and this is heated in an autoclave at a temperature of 3.
The acicular CrO
Acicular Cr2O3 is obtained by heating in air at a temperature of 800-850°C. Also C r 0
Cr2(CrO2)3 obtained by partial reduction of 3 may be used as a starting material.

The magnetic recording medium of the present invention has the above-mentioned acicular Cr2O3 in the magnetic layer.
Although it is not necessary to add other abrasives because the abrasives contain , it is also possible to add other abrasives that are commonly used as long as they do not interfere with achieving the object of the present invention.

As the binder used to form the magnetic layer of the present invention, commonly used thermoplastic resins, thermosetting resins, reactive resins, and the like can be used.

These resins can be used alone or in combination.

Thermoplastic resins generally have an average molecular weight of 10,000 to 2.
00,000 and a polymerization degree of about 200 to 2,000. 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, urethane elastomers,
Examples include polyvinyl fluoride, polyamide resin, polyvinyl butyrate, styrene/butadiene copolymer, and polystyrene resin, and these can be used alone or in combination.

Thermosetting resins or reactive resins are generally resins with an average molecular weight of 200,000 or less in the coating liquid state. Resins are used.However, when these resins are heat-cured resins, it is preferable that the resins do not soften or melt due to heating in the process of curing. Examples of such resins include: Phenol/formalin/novolak resin, phenol/formalin/resol resin, phenol/furfural resin, xylene/formaldehyde resin, urea resin, melamine resin, drying oil-modified alkyd resin, phenolic resin-modified alkyd resin, maleic acid resin-modified alkyd resin, Examples include saturated polyester resins, combinations of epoxy resins and curing agents, terminal isocyanate polyether moisture-curable resins, polyisocyanate prepolymers, and combinations of polyisocyanate prepolymers and resins containing active hydrogen. Alternatively, they can be used in combination.

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

First, the magnetic layer of the magnetic recording medium of the present invention is made of the above-mentioned acicular C.
r2O3 and ferromagnetic alloy powder are kneaded with a binder and, if necessary, other granular fillers with a solvent to form a magnetic paint, which is coated on a non-magnetic support such as PET and oriented in a magnetic field if necessary. etc., and then drying.

As the solvent used during kneading, a solvent commonly used for preparing magnetic paints can be used.

As for the kneading method, a method commonly used for kneading magnetic paints can be used. Further, the order of addition of each component can be set as appropriate.

Various techniques are known as techniques for preparing magnetic paints, and any of these known techniques can be used in manufacturing the magnetic recording medium of the present invention.

When preparing a magnetic paint, known additives such as dispersants, antistatic agents, lubricants, etc. can also be used.

Examples of dispersants include fatty acids having 12 to 18 carbon atoms;
Metal soaps made of the above fatty acids and alkali metals or alkaline earth metals, esters of the above fatty acids and compounds in which part or all of the hydrogen of the compounds is replaced with fluorine atoms, amides of the above fatty acids, aliphatic amines, Known dispersants such as higher alcohols, polyalkylene oxide alkyl phosphate esters, alkyl phosphate esters, alkyl borate estenopesarcosinates, alkyl ether esters, trialkyl polyolefin oxy quaternary ammonium salts, and lecithin are used. can be mentioned.

When a dispersant is used, it is usually used in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the binder used.

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

Examples of lubricants include the above-mentioned fatty acids, higher alcohols, fatty acids consisting of monobasic fatty acids with 12 to 20 carbon atoms, such as butyl stearate, and sorbitan oleate, and monohydric or polyhydric alcohols with 3 to 20 carbon atoms. esters,
In addition to mineral oils, animal and vegetable oils, olefin low polymers and α-olefin low polymers, known lubricants such as fine graphite powder and lubricants for plastics can be mentioned.

The amount of lubricant added can be arbitrarily determined according to known techniques.

Note that the above-mentioned additives such as dispersants, antistatic agents, and lubricants are not strictly limited to having only the above-mentioned effects; for example, if the dispersant is a lubricant, Alternatively, it may act as an antistatic agent. Therefore, it goes without saying that the effects of compounds etc. exemplified by the upper classifications are not limited to those listed in the above classifications, and when using substances that have multiple effects, it is necessary to The amount is preferably determined in consideration of the effects of the substance.

The magnetic paint thus prepared is coated on the above-mentioned non-magnetic support according to a known method. Coating is usually carried out directly on the non-magnetic support. However, it can also be applied onto a non-magnetic support via an adhesive layer or the like.

There is no particular limit to the thickness of the magnetic layer coated in this way, but the thickness after drying is generally in the range of about 0.5 to 10 μm, usually in the range of 1.5 to 7.0 μm. is applied to.

A magnetic layer coated on a non-magnetic support is usually subjected to a treatment for orienting the ferromagnetic powder in the magnetic layer, that is, a magnetic field orientation treatment, and then dried. Also, 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.

〔Example〕

Next, Examples and Comparative Examples of the present invention will be shown. Note that "parts" in Examples and Comparative Examples indicate "parts by weight."

[Example 1] A slurry obtained by dispersing a mixture of equal amounts of CrO:+ and Cr2O5 in water was subjected to a hydrothermal reaction (reaction Time: 5 hours) to obtain acicular CrO2. This was heated in air at a temperature of 800°C for 2 hours to form acicular Cr2.
Obtained O3.

The obtained acicular Cr2O3 was classified and used.

Next, a magnetic paint having the composition shown below was prepared and coated on a polyethylene terephthalate nonmagnetic support having a thickness of 10 μm so that the thickness of the magnetic layer after drying was 3.0 μm.

Magnetic paint composition: 100 parts of ferromagnetic alloy powder (Fe
-Ni alloy, Ni approximately 5% by weight) (Specific surface area [5-BET]: 40m'/g, 6s
: 132 parts mn/g> Vinyl chloride/vinyl acetate/maleic anhydride copolymer
12 parts (Nippon Zeon Co., Ltd.: 400XLIOA) polyurethane resin
8 parts (manufactured by Nippon Polyurethane Co., Ltd.: N-2
301>Polyisocyanate 1
2 parts (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) Carbon black 1 part (average particle size: 0.1 μm) Methyl ethyl ketone 300 parts Acicular C
r2O3 (major axis diameter 0.3 μm, 5 part minor axis diameter 0.
03 μm Acicular ratio 10) The non-magnetic support coated with the magnetic paint was subjected to a magnetic field orientation treatment while the magnetic paint was not dry, and after drying, calender treatment was performed, and portions were slit into 2-inch widths. ,
A VH3 type videotape was manufactured.

The magnetic properties of this video tape are determined by measuring the B-8 curve (B magnetic flux density, H: external magnetic field), and from this value the squareness ratio (Br/8m, [Br: maximum residual magnetic flux density, Bm
: maximum magnetic flux density]) was determined. The saturation magnetic ratio σe1 was measured with an external magnetic field of 5KOe. The obtained video tape was recorded on a video recorder (Video Tape Recorder V-5 manufactured by Toshiba Corporation).
00D) to record and reproduce a 5 MHz signal. Relative playback output and S/N of the above videotape when the 5 MHz playback output and S/N recorded on the reference tape (videotape obtained in Comparative Example 1) are O, and the playback output after 1QQpass The decline was measured.

The video recorder described above was run repeatedly to determine the number of runs until the magnetic head became clogged.

The surface gloss was determined by measuring the total reflectance at an incident angle of 45 degrees and a reflection angle of 45 degrees using a standard gloss meter. The value of CrO2 standard tape is 1
It was set at 50%. The measuring device used was a digital standard color difference photometer AUD-CH-GV3 manufactured by Suga Test Instruments Co., Ltd.

Comparative Example 1 In Example 1, Cr, 03 was granulated (size (], 3
A videotape was produced in the same manner except that the tape was replaced with one (μm).

Comparative Example 2 In Example 1, Cr 203 was replaced with granular T-A12o3 (
A videotape was produced in the same manner except that the size was changed to 0.20 μm).

Example 2 A videotape was produced in the same manner as in Example I except that Cr2O3 was replaced with one having a major axis diameter of 9 μm and a short axis diameter of 0.07 μm.

Comparative Example 3 A videotape was produced in the same manner as in Example 1 except that Cr2O3 was replaced with one having a major axis diameter of 0.08 μm and a minor axis diameter of 0.02 μm.

Example 3 A video cheese was produced in the same manner as in Example 1 except that the amount of Cr2O3 added was changed to 15 parts.

Comparative Example 4 A videotape was produced in the same manner as in Example 1 except that the amount of Crz03 added was 25 parts.

Example 4 In Example 1, 5 BET on ferromagnetic powder; 29m
A videotape was produced in the same manner except that 135 emn/g was used instead.

Comparative Example 5 In Example 4, Cr2O3 was granulated (size 0.3μ
A videotape was produced in the same manner except that step m) was used instead.

The results are shown in the table.

〔Effect of the invention〕

According to the present invention, ferromagnetic alloy powder is used to form an acicular Cr2
By using O3 powder as an abrasive in an amount of 10 to 20 percent of the magnetic powder, a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability can be obtained. Furthermore, a ferromagnetic alloy magnetic recording medium suitable not only for video tapes but also for audio tapes can be obtained.

Claims (2)

[Claims] (1) In a magnetic recording medium having a magnetic layer containing magnetic powder dispersed in a binder on a non-magnetic support, the magnetic powder is made of a ferromagnetic alloy powder, and the magnetic layer has a major axis diameter of 1
．． 0μm or less, short axis diameter 0.1μm or less, needle ratio 5-20
A magnetic recording medium comprising acicular Cr_2O_3 in an amount of 10 to 20% by weight of the ferromagnetic alloy powder. (2) The magnetic recording medium according to claim 1, wherein the ferromagnetic alloy powder has a specific surface area of 25 m^2/g or more.