JPH0610859B2 - Magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to improving the composition of magnetic powder used in the magnetic recording medium.

Prior Art Conventionally, acicular iron oxide has been mainly used as a powder magnetic material for magnetic recording media.

However, in recent years, the spread of household VTRs, high-performance audio cassette tapes, video tapes, computer tapes,
As represented by the practical application of multi-coated tapes, magnetic disks, floppy disks, magnetic cards, etc., as the recording density of signals used in magnetic recording media increases,
Needle iron oxide alone cannot cope with high density magnetic recording, and various magnetic materials having high coercive force and high magnetic flux density have been developed.

As one of such magnetic powder materials, metal magnetic particles using magnetic metal have been studied and put to practical use in high-performance audio cassettes, video tapes, various magnetic disks, and the like.

However, some problems remain with this magnetic metal.

That is, there is a problem that the magnetic metal has low wear resistance, is prone to deterioration due to use, and is very easily oxidized, and even when it is used as a magnetic recording medium, the magnetic flux density is reduced due to the oxidation, resulting in a reduction in output.

When a magnetic recording medium using magnetic metal is run on a sendust or amorphous magnetic head,
A so-called "burn-in" phenomenon is often observed in which a matte discoloration layer having a color different from that of the head material is formed on the head surface. This is considered to be a chemical-physical alteration phenomenon of the sendust surface or amorphous metal surface due to sliding friction between the magnetic recording medium and the magnetic head.

In order to prevent the image sticking phenomenon, it is considered effective to give the magnetic recording medium a certain polishing effect and successively polish the magnetic head while the magnetic recording medium is running.

As a method of imparting a polishing effect to the magnetic recording medium, a polishing agent for the magnetic recording medium, for example, Cr ₂ O ₃ or Al ₂ O _{3 is used.}
A method is known in which uniform particles are added to a magnetic recording medium.

However, as a result of examination by the present inventors, in order to prevent the image sticking, the above-mentioned abrasive was mixed with the magnetic powder in an amount of 3 times.
Since more than 10 wt% of the abrasive must be added to the magnetic recording medium, the saturation magnetic flux density of the magnetic recording medium decreases, and as a result, It was confirmed that the electromagnetic conversion characteristics of the magnetic recording medium were deteriorated.

Furthermore, when forming a magnetic recording medium using metal magnetic particles, it is inevitable that an oxide film is formed on the surface of the particles during the process of handling the metal magnetic particles. In addition, an oxide film may be intentionally formed.

Thus, the magnetic recording medium or the metal magnetic particles having an oxide film on the particle surface has the effect of preventing the deterioration of the characteristics due to the decrease of the magnetic flux density due to the external environment such as temperature and humidity and the rust of the magnetic layer. Electric resistance increases due to the surface oxide film and the surface of the magnetic recording medium is charged,
There is a problem that foreign matter adheres to the surface of the magnetic recording medium to cause dropout, or discharge noise occurs due to peeling charging, resulting in deterioration of tape performance.

II Object of the invention The present invention eliminates the above-mentioned drawbacks of magnetic recording media using magnetic metal particles, has high wear resistance and does not deteriorate due to use, has good oxidation resistance characteristics, and does not show a burn-in phenomenon, An object is to provide a magnetic recording medium having a high antistatic effect.

Such an object is achieved by the present invention described below.

That is, an object of the present invention is a magnetic recording medium obtained by coating a substrate with a magnetic coating material in which magnetic powder is dispersed in a binder, wherein the magnetic powder is a powder obtained by mixing metal magnetic particles and metal carbide magnetic particles, The magnetic recording medium is characterized in that the iron carbide magnetic particles have a composition represented by FenC (n is 2 or more).

III Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.

The magnetic metal particles of the present invention include: 1) α-FeOOH (Goethite), β-FeOOH (Ak
aganite), γ-FeOOH (Lepidocrocite), and the like; α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ -Fe ₃ O ₄ (solid solution) Iron oxide such as; or one or more metals such as Co, Mn, Ni, Ti, Bi, Bo, Ag, etc., which are doped, and whose surface is adsorbed and adhered with an aluminum compound or a silicon compound, A method for producing iron or a magnetic powder containing iron as a main component by heating and reducing in a reducing gas flow, 2) a method for producing by liquid phase reduction from an aqueous solution of a metal salt with NaBH ₄ , 3) or a low pressure It can be obtained by a method of evaporating a metal in an inert gas atmosphere.

The composition of the metal magnetic particles includes simple elements of Fe, Co and Ni, alloys of these elements, or Cr, Mn, Co, Ni, Zn, Cu and Z in addition to these simple elements and alloys.
A metal added with r, Al, Ti, Bi, Ag, Pt or the like can be used.

Further, even if a small amount of a non-metal element such as B, C, Si, P or N is added to these metals, the effect of the present invention is not lost.

Alternatively, the magnetic particles may be partially-nitrided metal particles such as Fe ₄ N.

Further, the metal magnetic particles may have an oxide film on the particle surface.

The magnetic recording medium using the metal magnetic particles having such an oxide film is advantageous for the deterioration of the magnetic flux density due to the external environment such as temperature and humidity and the deterioration of the characteristics due to the rust of the magnetic layer. Rises, and problems due to charging during use tend to occur. By mixing this with iron carbide particles, it is effective to prevent electrification due to a decrease in electric resistance.

The metallic magnetic particles have a needle shape or a granular shape, and are selected according to the use as a magnetic recording medium. When used for a magnetic tape having a video tape size, a needle-shaped one is preferable. Long axis 0.3 μm to 0.1 μm Short axis 0.04
It is preferably about 0.01 μm.

The metal carbide particles may be carbides of metal magnetic particles, but iron carbide particles are particularly preferable.

As the iron carbide particles, fine iron carbide powder obtained by mixing an iron cyanide compound with a sulfate, a sulfite, or a sulfide, placing the mixture in an iron reactor, introducing CO, and heating and reducing it and then cooling is used.

Further, a slurry-like mixture of the above-mentioned iron oxide hydroxide or acicular iron oxide and the suspension of the aqueous colloidal carbon black particles may be adjusted by heating at 600 ° C. for about 10 hours by hydrogen reduction.

Other than these, hexacyano iron salts such as turnblu blue and berlin white, ferro or ferricyan compounds such as yellow blood potassium, yellow blood soda, red blood potassium, and red blood soda are used as iron cyanide compounds, and potassium sulfate is used as an additive. Sulfates such as sodium sulfate, ammonium sulfate, iron sulfate, sodium hydrogen sulfate, potassium hydrogen sulfate, potassium sulfite, sodium sulfite, ammonium sulfite, sulfites such as potassium hydrogen sulfite, sodium thiosulfate, potassium thiosulfate, sodium sulfide, Sulfides such as potassium sulfide, iron sulfide, rodan sorter, potassium rhodanide, sodium isothiocyanate, and potassium isothiocyanate can be used.

The gas used for these heating and reducing atmospheres is not limited to CO, but C
A carbon-containing reducing gas such as H ₄ , water gas or propane may be used.

Further, after forming pure iron particles, the above various heat reduction treatments may be performed.

The reduction may be performed at a heating temperature of 300 to 700 ° C. and a heating time of 30 minutes to 10 hours.

As the iron carbide particles produced, in FenC, n
≧ 2, especially 2-3.

In this case, n is an integer and does not need to have a stoichiometric composition, but Fe ₂ C, Fe ₅ C ₂ , and Fe ₃ C are mainly produced.

Even if there is a certain concentration gradient in the particles, C
Exists in the entire area and forms so-called iron carbide bulk particles.

The iron carbide particles have a needle shape or a granular shape and are selected depending on the use as a magnetic recording medium. Needles in the form of needles are preferred when used for video tape size magnetic tapes, with the major axis of 0.3 μm to 0.1 μm,
A short axis of 0.04 to 0.01 μm is preferable.

If the mixing ratio of the metal magnetic particles and the iron carbide magnetic particles is set to 97: 3 by weight, particularly 90:10 or more,
The effect of improving the oxidation resistance can be obtained.

Further, when the mixing ratio of the metal magnetic particles and the iron carbide magnetic particles is 97: 3 or more by weight, the effect of sufficiently preventing seizure can be obtained.

On the other hand, other magnetic properties are not significantly affected by the mixing of iron carbide magnetic particles.

However, if it exceeds 20:80, the polishing effect of the magnetic recording medium is excessively increased, the surface of the magnetic head is roughened, the wear amount of the magnetic head is increased, and the life of the head is shortened, or a medium using metal magnetic particles is used. The excellent residual magnetic flux density and coercive force, which are the characteristics of the above, are reduced, and the electromagnetic conversion characteristics are reduced.

Therefore, the mixing ratio of the metal magnetic particles and iron carbide is 20:80.
Is the limit.

A thermoplastic binder, a thermosetting binder, or an electron beam curable binder can be used as the binder used when the magnetic powder is used as the magnetic paint.

The mixing ratio of the magnetic powder and the binder is 6 by weight.
It is set to about / 1 to 3/1.

In any binder, it is effective to use various antistatic agents, lubricants, dispersants, coating film strength reinforcing additives and the like depending on the application, if necessary.

The thickness of the magnetic layer is about 0.5 to 5.0 μm.

IV Specific Actions and Effects of the Invention Since iron carbide magnetic particles have higher hardness than metal magnetic particles, the magnetic recording medium of the present invention comprising metal magnetic particles containing iron carbide magnetic particles has excellent wear resistance and Almost no deterioration.

Further, since it is chemically stable, it has oxidation resistance and can prevent deterioration of magnetic flux density due to external environment such as temperature and humidity and deterioration of characteristics due to rusting of the magnetic layer.

On the other hand, by utilizing the property of high hardness, the magnetic head can be successively polished while the magnetic recording medium is running,
It is possible to prevent seizure, prevent surface roughness, and prevent deterioration in output and the like over time.

Further, since the carbide magnetic particles have conductivity, it is possible to prevent electrification on the magnetic recording medium, for example, the tape surface,
Prevents foreign matter from adhering to the surface of the tape to cause discharge noise and dropout, thus improving the tape performance.

V Specific Examples of the Invention Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example A magnetic coating material was prepared in the following weight ratio.

Magnetic powder (Table 1) 100 parts by weight Vinyl chloride-vinyl acetate copolymer 15 parts by weight Polyurethane resin 10 parts by weight Surfactant 1 part by weight Methyl ethyl ketone 150 parts by weight Methyl isobutyl ketone 150 parts by weight Lubricant 3 parts by weight However, the above magnetic properties The powder is a mixture in which the mixing ratio (weight ratio) of the acicular Fe powder and the FenC powder is changed, as shown in Table 1 below.

Here, the acicular Fe powder is obtained by reducing acicular α-FeOOH with hydrogen, has an average particle length of 0.2 μm, an axial ratio of 8, a coercive force Hc = 1450 Oe, and a saturation magnetization σs = 155 emu /
g of powder.

The needle-shaped FenC powder is obtained by kneading 90 parts by weight of needle-shaped α-FeOOH and a carbon black water-based suspension (10 parts by weight of carbon solid content) having an average particle diameter of 30 mμ into a slurry, dewatering and drying, and then pulverizing the mixture to prepare an electric powder. In the furnace, C
6 in an atmosphere of a mixed gas of O and H ₂ (mixing ratio 1: 1)
It was obtained by heating at 00 ° C. for 5 hours.

It was confirmed by X-ray diffraction that the obtained product was a mixed crystal of Fe ₃ C and Fe.

The acicular iron carbide mixed crystal particles retain the original shape of the acicular iron powder, and have a coercive force Hc = 12500e and a saturation magnetization σs = 10.
It was 2 emu / g. The above composition was kneaded in a ball mill for 24 hours, coated on a polyester base, dried, and mirror-finished to prepare a magnetic tape having a video tape size.

With respect to the obtained magnetic tape, magnetic properties, oxidation resistance, head burn-in, head surface roughness, head wear, and conductivity (electric resistance) were measured.

Further, the number of dropouts per minute at the beginning of use and the number of dropouts per minute after 200 passes were measured, and the increase ratio thereof was calculated.

The results are shown in Table 3.

Here, the magnetic characteristics (coercive force Hc, saturation magnetic flux density Bm) were measured with a vibration trial magnetometer.

As for oxidation resistance, the magnetic tape is used at a humidity of 98% and a temperature of 60 ° C.
After holding for a day, magnetic measurement was carried out, and the reduction rate ΔBr of the residual magnetic flux density Br from the initial state was shown.

Head burn and head surface roughness were observed with a microscope after running a magnetic tape (relative speed 5.8 m / sec) in a laboratory for 20 hours on a VHS deck using an amorphous magnetic head. The evaluation is as follows.

Head burn-in 〇 No discoloration part △ Partially discolored × Whole surface discoloration Head surface roughening 〇 No surface roughening △ Some surface roughening × Surface roughening × Surface roughness 4MHz output decrease due to head burning Table 3
Shown in.

Head wear is VH using amorphous magnetic tape.
The amount of head wear after running the magnetic tape (relative speed 5.8 m / sec) in the laboratory for 200 hours on the S deck.

Furthermore, Example 11 was prepared using an electron beam curable binder using the mixture of iron carbide and Fe particles.

The composition is as follows.

First, Fe needle magnetic powder 8 wt% FeC needle magnetic particles 2 wt% solvent 90 wt% (methyl ethyl ketone / toluene 50/50) These compositions were mixed in a ball mill for 3 hours.

Next, saturated polyester resin with acrylic double bond introduced (solid content) 6 wt% Acrylic double bond-introduced vinyl chloride copolymer (solid content) 3 wt% Acrylic double bond introduced polyether urethane elastomer (solid content) 3 wt% solvent 87 wt% (methyl ethyl ketone / toluene 50/50) lubricant 1 wt% (higher fatty acid modified silicone oil) A binder mixture was thoroughly mixed and dissolved.

This is put into the ball mill containing the magnetic powder, and it is put in the
The mixture was dispersed for 2 hours.

The magnetic coating material thus obtained was applied onto a 15 μm polyester film, and a permanent magnet (1600 gauss) was applied.
Oriented above and solvent dried by infrared lamp.

After that, a surface smoothing treatment is performed, and an accelerating voltage of 1 is obtained by using an ESL electric curtain type radiation accelerator.
Under a condition of 50 KeV, electrode current 20 mA, and total irradiation amount 10 M rad, radiation was irradiated under N ₂ atmosphere to cure the coating film.

Comparative Example A magnetic tape prepared in the same manner as in Example except that the magnetic powder in the magnetic paint in Example was changed as shown in Table 2 was subjected to the same measurement as in Example. In Comparative Example 3, in order to enhance the magnetic head polishing effect, A which has been conventionally added is used.
and Comparative Example was added to l ₂ O _3.

From the results shown in Table 3, the effect of the present invention is clear.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a substrate coated with a magnetic coating material in which magnetic powder is dispersed in a binder, wherein the magnetic powder is a mixture of metal magnetic particles and iron carbide magnetic particles. A magnetic recording medium, wherein the iron magnetic particles have a composition represented by FenC (n is 2 or more). 2. The magnetic recording medium according to claim 1, wherein the mixing ratio of the metal magnetic particles and the iron carbide magnetic particles is 97: 3 to 20:80 by weight.