JPH0610865B2 - 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, it has been used as a magnetic recording medium as typified by the popularization of household VTRs and the practical use of high-performance audio cassette tapes, video tapes, computer tapes, multi-coated tapes, magnetic disks, floppy disks, magnetic cards and the like. As the recording density of recorded signals increases, acicular iron oxide alone cannot cope with higher 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, the metal magnetic particles have low wear resistance, are prone to deterioration due to use, and are very easily oxidized, and even when used as a magnetic recording medium, a decrease in magnetic flux density occurs due to oxidation, resulting in a decrease in output. There's a problem.

Further, when a magnetic recording medium using metal magnetic particles is run on a sendust-based or amorphous-based magnetic head, a so-called discoloration layer having a color different from that of the head material is formed on the head surface. The phenomenon of "burn-in" is often seen. This is considered to be a chemical-physical alteration phenomenon of the sendust surface or the 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 image sticking, the above-mentioned abrasive must be added to the magnetic powder in an amount of 3 wt% or more, and the abrasive is non-magnetic. It was found that when 10 wt% or more of an abrasive was added to the magnetic recording medium, the saturation magnetic flux density of the magnetic recording medium decreased, resulting in deterioration of the electromagnetic conversion characteristics of the magnetic recording medium.

Further, when a magnetic recording medium is formed by using metal magnetic powder particles, it is unavoidable that an oxide film is formed on the surface of the particles in the process of handling the metal magnetic particles. In addition, an oxide film may be intentionally formed.

As described above, the use of the metal magnetic particles having the oxide film on the particle surface and the magnetic recording medium have an effect of preventing 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. , The electrical resistance increases due to the surface oxide film, the surface of the magnetic recording medium is charged, and foreign matter adheres to the surface of the magnetic recording medium, resulting in dropout, or discharge noise due to peeling charging, resulting in deterioration of tape performance. There's a problem.

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, and has a burn-in phenomenon. First, it is intended 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 to provide 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 has metal magnetic particles and magnetic metal particles having a metal carbide coating film on the surface. And a powder of FenC.
The magnetic recording medium is characterized by having a composition represented by (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 oxides such as; and 1 of metals such as Co, Mn, Ni, Ti, Bi, B and Ag
One or two or more of which are doped with an aluminum compound or a silicon compound adsorbed and deposited on the surface thereof,
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.

As the composition of the metal magnetic particles, simple elements of Fe, Co and Ni and alloys thereof, or simple elements and alloys thereof such as Cr, Mn, Co and
Ni, further Zn, Cu, Zr, Al, Ti, Bi,
A metal added with 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 in preventing a decrease in magnetic flux density due to an external environment such as temperature and humidity and prevention of characteristic deterioration due to rust in the magnetic layer. The electric resistance of is increased, and troubles 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 video tape size magnetic tape,
Needle-like shape is preferred, long axis 0.3 μm to 0.1 μm short axis
It is preferably 0.04 to 0.01 μm.

The magnetic metal particles having a metal carbide coating on the surface thereof may be various, but are generally particles having an iron carbide coating on the surface, particularly iron particles (hereinafter surface iron carbide coating particles).

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

Alternatively, the slurry-like mixture of the hydrous iron oxide or acicular iron oxide and the aqueous colloidal carbon black particle suspension may be reduced by hydrogen at 600 ° C. for about 10 hours to be adjusted.

Alternatively, the hydrogen reduction may be replaced with CO reduction.

In addition to this, hexacyano iron salts such as turnbull 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. , Sodium sulfate, ammonium sulfate, iron sulfate, sodium hydrogen sulfate, potassium bisulfate, and other sulfates, potassium sulfite, sodium sulfite, ammonium sulfite, potassium sulfite, and other sulfites, sodium thiosulfate, potassium thiosulfate, sodium sulfide, Sulfides such as potassium sulfide, iron sulfide, sodium rhodanide, 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.

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 coating 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.

The thickness of the coating is preferably about 50 to 100Å, and the core is preferably mainly composed of iron.

Note that such particles have a needle-like shape or a granular shape and are selected depending on the use as a magnetic recording medium. When used for magnetic tape of video tape size, needle-shaped one is preferable, with long axis 0.3 μm to 0.1
μm and minor axis 0.04 to 0.01 μm are preferable.

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

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

On the other hand, other magnetic properties are not significantly affected by the mixing of the surface iron carbide coated 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 the surface iron carbide coated particles is limited to 2: 8.

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 Surface iron carbide coated particles have a higher hardness than metal magnetic particles, so the magnetic recording medium of the present invention comprising metal magnetic particles containing surface iron carbide coated particles has excellent wear resistance, Almost no deterioration due to use.

Further, since it is chemically stable, it has oxidation resistance and can prevent a decrease in magnetic flux density due to an 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 surface iron carbide coated particles have conductivity, it is possible to prevent electrification on the magnetic recording medium, for example, the tape surface, and foreign matter adheres to the tape surface to cause dropout or discharge noise. To prevent tape damage and improve tape performance.

In this case, in the present invention, not the bulk particles but the metal magnetic particles forming the surface carbonized layer are used, and the hardness is inferior to the lump type, so that the seizure prevention effect due to the polishing effect is slightly inferior to the lump type. .

However, since it is a semi-metal particle as a whole, B
It has excellent magnetic properties such as m and Br, and has a high chemical stability due to the surface being a carbide, which reduces the magnetic flux density due to the external environment such as temperature and humidity during use and the deterioration of properties due to rusting of the magnetic layer. It has a protective effect, has a lower electric resistance than the magnetic molecules forming surface oxides, has an antistatic effect, and is less likely to cause electrostatic sticking, so it has excellent runnability and drops due to the adhesion of foreign matter. Since there is no output, noise does not occur in the circuit system.

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 acicular Fe powder having an iron carbide coating 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,
The powder has a coercive force Hc = 1450 Oe and a saturation magnetization δs = 155 emu / g.

The needle-shaped FenC powder having the surface iron carbide coating is needle-shaped α-
Needle-like Fe powder obtained by hydrogen reduction of FeOOH (average particle length 0.3 μm, axial ratio 9, coercive force Hc = 1550 Oe, saturation magnetization σs = 160 emu / g 1 kg) was mixed in an aqueous solution containing dark blue 200 gr. , Degreasing navy blue on the surface of needle-like Fe powder,
It was obtained after dehydration drying, pulverization, and heating in an electric furnace at 600 ° C. for 1 hour in a mixed gas atmosphere of CO and H ₂ (mixing ratio 1: 1). The obtained product was analyzed by microscopic X-ray diffraction to obtain F
It was confirmed to be a mixed crystal of e ₃ C and Fe.

Further, when the distribution of Fe ions and C ions in the depth direction of this powder having a surface iron carbide coating was examined, Fe ions increased and C ions decreased as the etching from the surface proceeded.

From these, it can be judged that the powder obtained here is a powder in which the surface layer of the acicular Fe particles is Fe ₃ C.

The powder in which the surface layer of the needle-like Fe particles is Fe ₃ C has no change in shape from the original needle-like Fe powder, and has a coercive force Hc.
= 1330 Oe, and saturation magnetization s = 135 emu / g.

The carbonized surface layer had a thickness of about 0.01 μm.

The above composition was kneaded in a ball mill for 24 hours, coated on a polyester base, dried and mirror-finished,
A magnetic tape having a video tape size was produced. With respect to the obtained magnetic tape, magnetic characteristics, oxidation resistance, head burn-in, head surface roughness, head wear, and conductivity (electrical 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 by a vibration test magnetometer.

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

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.

In addition, the decrease in output at 4 MHz due to head burn-in is shown in Table 3.
Shown in.

Head seizure 〇 No discoloration part △ Partially discolored × Whole surface discoloration Head surface roughness 〇 No surface roughness △ Some surface roughness × Surface roughness × Severe head wear VH using amorphous magnetic head
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.

Further, Example 11 was prepared using an electron beam curable binder.

The composition is as follows.

First, acicular iron having a surface iron carbide coating 2 wt% acicular iron powder 8 wt% solvent 90 wt% (methyl ethyl ketone / toluene 50/50) These compositions were mixed in a ball mill for 3 hours, and then acryl double bond Introduced saturated polyester resin (solid content) 6 wt% Acrylic double bond-introduced vinyl chloride / acetate copolymer (solid content) 3 wt% Acrylic double bond-introduced polyether uretanelastomer (solid content) 3 wt% Solvent 87 wt% ( Methyl ethyl ketone / toluene 50/50) A binder mixture consisting of a lubricant 1 wt% (higher fatty acid-modified silicone oil) was thoroughly mixed and dissolved.

This was put into the ball mill that had been subjected to the magnetic powder treatment described above, and was mixed and dispersed again for 42 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.

Then, after the surface smoothing treatment, an accelerating voltage of 150 is applied by using an electric curtain type radiation accelerator manufactured by ESL.
The coating film was cured by irradiating with radiation under N ₂ atmosphere under the conditions of KeV, electrode current of 20 mA, and total irradiation amount of 10 Mrad.

The resulting tape is referred to as Example 11.

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 comprises metal magnetic particles and magnetic metal particles having a metal carbide coating on the surface. A magnetic recording medium, which is a mixed powder, wherein the metal carbide coating film has a composition represented by FenC (n is 2 or more). 2. The mixing ratio of the metal magnetic particles and the metal magnetic particles whose surface is carbonized is 97: 3 to 2 in weight ratio.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 0:80.