JPS60212821A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium which has excellent wear resistance, oxidation resistance and antistatic effect and does not gall to a magnetic head. CONSTITUTION:The magnetic metallic (including alloy) particles or magnetic metallic particles (a) having an oxide film on the surface and the magnetic metallic particles (b) formed with an iron carbide film on the surface to about 50- 100Angstrom thickness by a method for reducing the Fe powder formed by hydrogen reduction of alpha-FeOOH and iron cyan compd., to reduce the same, under introduc tion of CO after mixing the same with sulfate (sulfite) are mixed at 97:3-20:80 ratio between the particles (a) and the particles (b) by weight to prepare the magnetic powder. The magnetic layer is formed by dispersing such magnetic powder into the binder and is provided on the substrate. The iron carbide film is expressed by FenC in which (n) is preferably >=2 and may not be a stoichiometrical compd. Since the iron carbide film has the high hardness, there is no need for adding the polishing agent to the magnetic layer and since said film has electrical conductivity, the good antistatic effect is obtd. The recording medium having the excellent electromagnetic conversion characteristic, wear resistance, oxidation resistance, etc. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Background of the Invention Technical Field The present invention relates to magnetic recording media, and more particularly to improving the composition of magnetic powder used in magnetic recording media.

PRIOR ART Traditionally, acicular iron oxide has been used as a powder magnetic material for magnetic recording media.

However, in recent years, as exemplified by the spread of home VTRs and the practical use of high-performance audio cassette tapes, hiteo tapes, computer tapes, multi-coated tapes, magnetic disks, floppy disks, magnetic carts, etc., the use of magnetic recording media has increased. As the intensity of recording signals increases,
Acicular iron oxide alone cannot meet the demands of high-density magnetic recording, and various magnetic materials having roughly 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 into practical use in high-performance audio cassettes, video tapes, various magnetic disks, and the like.

However, some problems remain with this magnetic metal.

In other words, metal magnetic particles have low abrasion resistance, deteriorate rapidly with use, and are extremely susceptible to oxidation. Even when used as a magnetic recording medium, oxidation causes a decrease in magnetic flux density, resulting in a decrease in output. There's a problem.

Furthermore, when a magnetic recording medium using metal magnetic particles is run on a Sendust-based or amorphous-based magnetic head, a so-called dull discolored layer is formed on the head surface with a color different from that of the head material. The phenomenon of ``burn-in'' is often observed. This is thought to be a chemical and 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 this burn-in phenomenon, it is considered effective to provide the magnetic recording medium with a certain degree of polishing effect and to sequentially polish the magnetic head while the magnetic recording medium is running.

As a method of imparting a polishing effect to a magnetic recording medium, an abrasive for magnetic recording media, such as Cr203 or A120, is used.
A method of adding tertiary fine particles into a magnetic recording medium is known.

However, according to the results of the studies conducted by the present inventors, in order to prevent burn-in, the above-mentioned abrasive must be added in an amount of 3 wt% or more to the magnetic powder, and since the abrasive is non-magnetic, It has been found that when an abrasive of 10 wt % or more is added to a magnetic recording medium, the saturation magnetic flux density of the magnetic recording medium decreases, resulting in deterioration of the electromagnetic conversion characteristics of the magnetic recording medium.

Furthermore, when forming a magnetic recording medium using metal magnetic particles, it is inevitable that an oxide film is formed on the particle surface during the process of handling the metal magnetic particles. There are also cases where an oxide film is intentionally formed.

In this way, magnetic recording media using metal magnetic particles with an oxide film on the particle surface have the effect of preventing a decrease in magnetic flux density due to the external environment such as temperature and humidity, and preventing characteristic deterioration due to rusting of the magnetic layer. The electrical resistance increases due to the surface oxide film, and the surface of the magnetic recording medium becomes electrically charged, causing foreign matter to adhere to the surface of the magnetic recording medium, resulting in dropouts, or discharge noise due to peeling and charging, resulting in deterioration of tape performance. There's a problem.

II. OBJECTIVES OF THE INVENTION The present invention eliminates the drawbacks of the magnetic recording media using magnetic metal particles as described above, and has high abrasion resistance, no deterioration due to use, good oxidation resistance, and no burn-in phenomenon. First, it is an object of the present invention to provide an Ia magnetic recording medium with a high antistatic effect.

Such objects are achieved by the present invention as described below.

That is, one object of the present invention is to provide a magnetic recording medium comprising a substrate coated with a magnetic paint in which magnetic powder is fractionated in a paint.

The magnetic recording medium is characterized in that the magnetic powder is a mixed powder of metal magnetic particles and magnetic metal particles having a metal carbide coating on the surface.

■Specific structure of the invention Hereinafter, a specific configuration of the present invention will be explained in detail.

The metal magnetic particles of the present invention include: 1) a-Fe OOH (Goethite);
β-FeOOH (Akaganite), y-F
e OOH (Lepidocr.

iron sulfur hydroxide such as cite); a-Fe203, γ-Fe203.

Fe304, y-Fe203-Fe304 (solid solution)
iron oxides such as; metals such as Co, Mn, Ni, Ti, Bi, B, Ag, etc.
A magnetic powder containing iron or iron as a main component is produced by heating and reducing the material, which is topped with one or two or more aluminum compounds and adsorbed and adhered to the surface of the aluminum compound or silicon compound, in a reducing gas stream. 2) A method in which a metal salt aqueous solution is subjected to liquid phase reduction with NaBH4; 3) A method in which a metal is evaporated in a low-pressure inert gas atmosphere.

The composition of the metal magnetic particles is Fe, Co.

Ni simple substance and alloys thereof, Or Cr in these simple substances and alloys.

M n , G o , N i , and even Zn ,
Cu.

Metals to which Zr, AI, Ti, Ei, Ag, Pt, etc. are added can be used.

Furthermore, the effects of the present invention are not lost even when small amounts of nonmetallic elements such as B, C, Si, P, and N are added to these metals.

Alternatively, partially chambered metal magnetic particles such as Fe4N may be used.

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

A magnetic recording medium using metal magnetic particles having such an oxide film is advantageous in preventing a decrease in magnetic flux density due to external environments such as temperature and humidity, and in preventing characteristic deterioration due to rusting of the magnetic layer. The electrical resistance of the product increases, which can easily cause problems due to charging during use. By mixing iron carbide particles with this material, it becomes effective to prevent electrification by reducing electrical resistance.

The metal magnetic particles used are acicular or granular, and are selected depending on the intended use as a magnetic recording medium. When using magnetic tape with video tape dimensions,
Preferably needle-shaped, long sleeves 0.3 um ~ 0
．． 1 gm short axis 0.04~0, Olm is preferable.

There may be various kinds of magnetic metal particles having a metal carbide coating on the surface, but they are generally particles having an iron carbide coating on the surface, particularly iron particles (hereinafter referred to as 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, reducing the mixture by heating while introducing CO, and cooling the mixture is used.

Alternatively, a slurry-like mixture of the hydrated iron oxide or acicular iron oxide and an aqueous colloidal carphone blank particle suspension may be heated and reduced by hydrogen reduction for about 600 mm for about 10 hours.

Alternatively, this hydrogen reduction may be replaced by CO reduction.

In addition, iron cyanide compounds such as hexacyano iron salts such as Turnpul blue and Berlin white, ferro or ferricyanide compounds such as anemia potash, anemia sorta, blush potash, blush sorta, etc. are used, and as additives, potassium sulfate and sodium sulfate are used. , ammonium sulfate, iron sulfate, 4 & oxyhydrogen sorter, sulfates such as potassium hydrogen sulfate, sulfites such as potassium sulfite, sodium Mate, ammonium sulfite, potassium hydrogen sulfite, or sodium thiosulfate, potassium thiosulfate, sulfide sorter, Sulfides such as potassium sulfide, iron sulfide, rotane soda, rogunkali, inthioanic acid sorter, and potassium inthiocyanate can be used.

The gas used in these heating reduction atmospheres is not limited to CO, but also C
Carbon-containing a-based gases such as H4, aqueous scum, and propane may also be used.

In addition, during reduction, the heating temperature is 300 to 700°C1
The heating time may be about 30 minutes to 10 hours.

As the iron carbide film produced, in FenC, n
≧2. Especially 2-3.

In this case, n is an integer and does not need to be a stoichiometric composition, Fe2'C, Fe5 C2.

Fe5C is mainly produced.

Preferably, the thickness of the coating is about 50 to 100, and the core is mainly made of iron.

Incidentally, such particles may be acicular or granular, and are selected depending on the intended use as a magnetic recording medium. When used as a magnetic tape with the size of a video tape, a needle-shaped one is preferable, with a long sleeve of 0.3 g.
~0. It is preferable that the short axis is 0.04 to 0.01 gm.

The effect of improving oxidation resistance can be obtained by setting the mixing ratio of metal magnetic particles and surface iron carbide coated particles to a weight ratio of 97:3, particularly 90.10 or more.

Further, if the mixing ratio of the metal magnetic particles and the surface iron carbide coated particles is set to a weight ratio of 97 to 3 or more, a sufficient anti-seizing effect can be obtained.

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

However, if the ratio exceeds 20:80, the polishing effect on the magnetic recording medium increases too much, causing surface roughness of the magnetic head, increasing wear of the metal henode, shortening the life of the head, or when using metal magnetic particles. This reduces the excellent residual magnetic flux density and coercive force that characterize the medium, and deteriorates the electromagnetic conversion characteristics.

Therefore, the mixing ratio of metal magnetic particles and surface iron carbide coated particles is limited to 228.

The binder used when making magnetic powder into a magnetic paint may be a thermoplastic binder, a thermosetting paint, or an electron beam curing paint.

The mixing ratio of magnetic powder and pinter is 6 by weight.
/l to about 3/1.

In any binder, it is effective to use various antistatic agents, lubricants, dispersants, coating film strength reinforcing additives, etc. as necessary depending on the purpose.

Note that the thickness of the magnetic layer is approximately 0.5 to 5.0 g.

IV. Specific Effects of the Invention Since surface iron carbide coated particles have higher hardness than metal magnetic particles, the magnetic recording medium of the present invention made of metal magnetic particles including surface iron carbide coated particles has excellent wear resistance. There is almost no deterioration due to use.

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

On the other hand, by taking advantage of its high hardness, the magnetic head can be polished sequentially while the magnetic recording medium is running.
Burn-in can be prevented, and roughness can also be prevented, and a decrease in output over time can be prevented.

In addition, since the surface iron carbide coating particles have conductivity, they can prevent charging on the surface of a magnetic recording medium, such as a tape, and prevent foreign matter from adhering to the tape surface, causing dropouts and discharge noise. This improves tape performance.

In this case, in the present invention, metal magnetic particles forming a surface carbonized layer are used instead of bulk particles, and since the hardness is inferior to that of lump-like particles, the anti-seize effect due to the polishing effect is slightly inferior to that of lump-like particles. .

However, since it is a semimetal particle as a whole, B
It has excellent magnetic properties such as m and By, and since the surface is made of carbide, it has high chemical stability, and does not deteriorate its characteristics due to a decrease in magnetic flux density due to the external environment such as temperature and humidity during use or rusting of the magnetic layer. Compared to magnetic molecules that form surface oxides, the electric resistance is lower and has an antistatic effect, making it less likely to cause electrostatic adhesion, so it has excellent running properties and is free from drops caused by foreign matter adhesion. Since there is no out, no noise is generated in the single circuit system.

(2) Specific Examples of the Invention The present invention will now be explained in more detail with reference to Examples and Comparative Examples.

Branch j Magnetic paints were prepared with the following weight ratios.

Magnetic powder (Table 1) 10 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 powder As shown in Table 1 below, these are mixtures in which the mixing ratio (ffil ratio) of acicular Fe powder and acicular Fe powder having an iron carbide coating is changed.

Table 1 The above acicular Fe powder is obtained by hydrogen reduction of acicular α-FeOOH, and has an average particle length of 0.2 gm, an axial ratio of 8, a coercive force Hc = +4500e, and a saturation magnetization δs.
= 155 emu/g powder.

The acicular FenC powder with a surface iron carbide coating has an acicular α-
Acicular Fe powder obtained by hydrogen reduction of FeOOH (average particle length 0.3 gm, axial ratio 9, coercive force HC = +5500
e, saturation magnetization crs = 160 emu/g 1
kg) in an aqueous solution containing 200g of Prussian blue, the surface of the acicular Fe powder was degreased with Prussian blue, and after dehydration and drying, it was crushed.
'Mixture of CO and H2 in an electric furnace (1:1 ratio)
It was obtained by heating in an atmosphere for 600"01 hours. The obtained product was confirmed to be a mixed crystal of Fe5C and Fe by micro-angle X-ray diffraction.

In addition, when the distribution of Fe ions and C ions in the depth direction of this powder, which has a surface iron carbide coating, was investigated by XPS, it was found that as the etching progressed from the surface, Fe ions increased and C ions decreased. .

From these facts, it can be determined that the powder obtained here is a powder in which the surface layer of acicular Fe particles is Fe5C.

This acicular Fe particle whose surface layer is Fe5C has no change in shape from the original acicular Fe powder, and has a coercive force Hc=
13300e・, saturation magnetization σs= 135 eIIu/
It was g.

Note that the thickness of the surface carbonized layer was approximately 0.01#Lm.

The above composition was subjected to IRm in a ball mill for 24 hours, applied to a polyester haze, dried, and finished to a mirror finish to produce a fa magnetic tape having the dimensions of a video tape. Regarding the magnetic tape obtained, magnetic properties, oxidation resistance, vent burn-in, head surface roughness, etc. 7):'! Abrasion and conductivity (electrical resistance) were measured.

In addition, the number of dropouts per minute at the beginning of use and the number of trompouts per minute after 200 passes were measured, and the rate of increase was calculated.

The results are shown in Table 3.

Here, the magnetic properties (coercive force Hc, saturation magnetic flux density Bm) were measured using a vibrating sample magnetometer.

The oxidation resistance was measured by magnetic measurement after holding the magnetic tape at a humidity of 98% and a temperature of 60''C for 7 days, and was expressed as the rate of decrease ΔBr in the residual magnetic flux density Br from the initial state.

Head burn-in and surface roughness were observed using an m-microscope after a magnetic tape was run in a laboratory for 20 hours (relative speed 5.8 m/5ee) on a VHS digital camera using an amorphous magnetic head. The evaluation is as follows.

Table 3 shows the 4MHz output drop due to head burn-in.
Shown below.

Head burn-in 0 No discoloration Δ Partial discoloration
This is the amount of head wear after running a magnetic tape on an S deck in a laboratory for 200 hours (relative speed 5.8w/5ee).

Furthermore, Example 11 was created using an electron beam curable binder.

The composition is as follows.

First, 2 wt% needle iron with surface iron carbide coating, 8 wt% needle iron powder, 90 wt% solvent (methyl ethyl ketone/toluene 50150), these compositions were mixed in a ball mill for 3 hours, and then acrylic double bond introduction saturation. Polyester resin (solid content equivalent) 6wt% Acrylic double bond-introduced salt-vinyl acetate copolymer (solid content equivalent) 3wt% Acrylic double bond-introduced polyether urethane elastomer (solid content equivalent) 3wt% Solvent 8
7wt% (methyl ethyl ketone/toluene 50150) lubricant
A paint mixture consisting of 1% (higher fatty acid denatured silicone oil) was thoroughly mixed and dissolved.

This was placed in the ball mill that had been subjected to the magnetic powder treatment, and mixed and dispersed again for 42 hours.

The magnetic paint thus obtained was applied onto a 15 gm polyester film, and a permanent magnet (1600 Gauss) was applied.
The solvent was dried using an infrared lamp.

Next, after surface smoothing treatment, an acceleration voltage of 150 was applied using an electric curtain type radiation accelerator manufactured by ESL.
KeV, electrode current 20 mA, total irradiation dose 10 M r a
The coating film was cured by irradiating radiation under the conditions of d in an N2 atmosphere.

The obtained tape is referred to as Example 11.

Comparison L Comparison The same measurements as in the example were carried out on magnetic tapes prepared in the same manner as in the example except that the magnetic powder in the magnetic paint in the example was changed as shown in Table 2. Regarding Comparative Example 3, in order to enhance the magnetic head polishing effect, A, which has been conventionally added, was
1203 was added as a comparative example.

Table 2 From the results shown in Table 3, the effects of the present invention are clear.

Applicant TDC Co., Ltd. Procedural amendment (voluntary) May 18, 1980 Patent Application No. 68529 2, Name of invention Magnetic recording medium 3, Person making the amendment Relationship to the case Appointment of patent applicant Address: 13-1 Nihonbashi-chome, Chuo-ku, Tokyo Name:
(306) TDC Co., Ltd. Representative Hiroshi Otoshi 4, Agent 101 Address 411+5 Chiyoda Iwamoto Building, 3-2-2 Iwaki-cho, Chiyoda-ku, Tokyo "3. Detailed Description of the Invention J" in the specification Column 6, Contents of amendment 1. The statement in column 13, Detailed explanation of the invention 1 of the specification is amended as follows.

1) In the 5th line of page 17, "minimal angle J" is corrected to "minimal area 1."

2) On page 17, line 17, replace r retention force J with “
Correct the coercive force to 1.

Claims (1)

[Scope of Claims] 1) A magnetic recording medium in which a magnetic paint in which magnetic powder is dispersed in a heat exchanger is coated on a substrate, wherein the magnetic powder includes metal magnetic particles and a magnetic material having a metal carbide coating on the surface. A magnetic recording medium characterized by being a powder mixed with metal particles. 2) The magnetic recording medium according to claim 1, wherein the metal carbide film has a composition represented by FenC (n is 2 or more). 3) The magnetic recording according to claim 1 or 2, wherein the mixing ratio or weight ratio of the metal magnetic particles to the metal magnetic particles whose surfaces are carbonized is 97:3 to 20:80. Medium.