JPS61154013A - Manufacture of needle iron fine particle for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain the magnetic metal fine particles which is extraminute magnetic metal fine particles and in which secondary aggregates are extremely diminished and is capable of easy compounding of the highly dispersible mag netic coating compositions by milling the surface denaturated iron oxyhydroxide or iron oxide till 90% or over of secondary aggregates of which pass the screen of 100 mesh particle degree followed by gas-phase catalytic reduction to make them ferromagnetic iron fine particles. CONSTITUTION:A specific surface area 20-150m<2>/gr. of alpha-iron oxyhydroxide or alpha-iron oxyhydroxide in which at least one element selected out of Al. Ti, Cr, Mn, Co, Ni, Zn and etc. coprecipitates is coated with at least one element selected out of B, Al, Si, P, Ti, Zn, Cr, Mn, Co, Ni, Cu, Zr, Sn, Pb, Ca, Ba and etc. Then the dried surface denaturated alpha-iron oxyhydroxide is milled to compound the powder 90% of secondary aggregate of which pass the screen of 100 mesh, more preferably, 200 mesh particle degree. If necessary, calcination at 300-800 deg.C is done to make the powder the surface denaturated alpha-iron oxide, after which that is subjected to the gas-phase catalytic reduction at 300-500 deg.C by use of a reducing gas consisting of hydrogen gas.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to ferromagnetic metal powder particles as a magnetic material for high-density magnetic recording media mainly used for audio and video, and a method for producing the same.

<Prior art> Magnetic powders useful as magnetic tapes and magnetic recording media are
- Oxide was mainly used, but in recent years there has been a demand for high-density recording media for vT-kun and high-end audio, and gas-phase catalytic reduction of iron oxyhydroxide or iron oxide-based powder using reducing gas Magnetic powders having a high coercive force and mainly composed of metallic iron or cobalt obtained by reaction, or an alloy of nickel and iron have come to be used.

The coercive force of metal magnetic fine particles has strong shape anisotropy, so it depends on particle size, acicularity, etc., but for tape recording, an appropriate coercive force is required in consideration of the capabilities of the playback head and erase head. It is.

Magnetic recording media, whether used for audio or video, have a tendency to achieve higher output and lower noise in a wide recording frequency band. It is desired to further improve the compatibility, dispersibility, orientation and filling properties of coating films, and research is being carried out to improve binder resins and various additives, as well as paint dispersion and media processing technology (e.g. Okabe Akashi, "Advances in magnetic tape," Journal of the Japan Society of Applied Magnetics, 7(3), 185 (1983),).

-As the particles become finer, their surface energy increases, which leads to stronger secondary agglomeration. That is, in the case of magnetic powder, the finer primary particles of the material inevitably make it difficult to disperse the paint.

Fine metal particles as a magnetic material tend to aggregate due to their large saturation magnetization (δS), and when they are produced by gas-phase reduction of surface-modified iron oxyhydroxide, sintering between particles may occur, so dispersion operation is difficult. It also becomes difficult.

Therefore, reducing the secondary agglomerates of magnetic metal fine particles,
In order to improve the affinity with the binder resin, the technique of breaking up particles into individual particles before dispersion has become important.

Chemical treatments such as surface treatment of magnetic powder with a coupling agent, adsorption of surface active agents, polymerization resin treatment of organic monomers, and microencapsulation treatment, so-called surface modification, are performed using homomixers.
This is done in a system that is used in combination with mechanical dispersion treatment using a disper or the like (for example, Mawata Koishi and Mitsuo Tsunoda, "Surface Chemistry of Powder", Nikkan Kogyo Shimbun).

Magnetic metal fine particles produced by reduction of surface-modified iron oxyhydroxide are inherently porous, so γ-
The mechanical strength is extremely weak compared to iron oxide magnetic powder such as Fe2es. Therefore, various surface modification operations, especially atomization treatment for converting aggregates into primary particles, are usually performed with extreme caution.

Problems to be Solved by the Present Invention> Acicular magnetic metal powder as a magnetic material for high-density magnetic recording media mainly intended for audio and video is γ-Fe11Ost.
C A has greater cohesiveness and sinterability than 20g of cobalt-containing γ-Fe, and its acicular shape cannot be maintained because particles tend to collapse due to the atomization treatment used in conjunction with surface modification. There are cases.

It is difficult to select an atomization model and use conditions to reduce the number of secondary agglomerates, and the magnetic properties of magnetic powder, especially a decrease in coercive force and a decrease in squareness ratio (Br/8m) when processed with media, are difficult. etc,
At present, the original purpose of atomization processing is not necessarily achieved.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the object of the present invention is to provide a method for producing magnetic metal fine particles that can easily produce a highly dispersible magnetic paint with extremely few secondary agglomerates in ultrafine magnetic metal fine particles. That is.

Means for Solving the Problems> In order to solve the above problems, the inventors of the present invention have conducted extensive research and have discovered that fine needle-like Iron oxyhydroxide fine particles are synthesized, then subjected to adhesion modification treatment using a shape-retaining component, washed and dried as necessary, and then crushed until they pass through a sieve with a particle size of 100 mesh '1. The shape of the powder subjected to a gas phase catalytic reduction reaction with a reducing gas is such that it does not damage or destroy that of the iron oxyhydroxide fine particles used as the crude raw material. , and found that secondary agglomerates and interparticle sintering are extremely small, making it easy to prepare a highly dispersible magnetic paint, and have arrived at the present invention.

To describe the present invention in more detail below, specific surface area 20
~150♂/gr- α-iron oxyhydroxide or AI
α in which at least one element selected from elements such as -, Ti, Cr, Mn, Co, Ni, and Zn is co-precipitated.
- Iron oxyhydroxide to avoid sintering, maintain shape, control coercive force,
To improve corrosion resistance, etc., B, At, Si, P,
Ti, Zn, Cr, Mn, Co, Ni, Cu,
At least one element selected from elements such as Zr, Sn, Pb, Ca, Ba, etc. is adhered to the surface, and the dried surface-modified α-iron oxyhydroxide is ground and sieved to a particle size of 100.
A powder that passes through a mesh, preferably a sieve particle size of 200 mesh is prepared, and if necessary, calcined at 300 to 800°C to form a surface-modified α-iron oxide. These are metal magnetic fine particles mainly made of iron produced by subjecting them to a gas phase catalytic reduction reaction at ~500°C.

After surface modification and cleaning as necessary, 100-180
For pulverizing the iron oxyhydroxide powder dried at .degree. C., a commercially available impact pulverizer, such as Fuji Powder's cracked nick sample mill or Nara Seisakusho's free pulverizer, can be used.

That is, in the latter case, the rotation speed is 1000 to 3000 rpm,
, 0.1 to 3.0.5 zl to the bottom or side outlet of the grinding mill at a feed rate of 5 C1 to 500 Ky/hr.
If you attach a screen with a hole diameter of 200 mm and crush it once or twice, you can expect a dry powder of less than 200 mesh. It is not necessarily necessary to make the hole diameter of the attached screen mesh extremely small (the hole diameter mentioned above is sufficient to achieve the effect. Rather, extreme fine pulverization is due to the crushing force of the device. This is not preferable because it may cause the acicular shape of iron oxyhydroxide, which is the primary particle of the powder, to deteriorate.

The pulverized powder is calcined at 300 to 800°C as necessary to form surface-modified α-Fezes, and then charged into a reduction furnace.
300 to 50 by reducing gas mainly composed of hydrogen gas
The particle size of the metal magnetic fine particles obtained by vapor phase catalytic reduction at 0° C. is similar to or even finer than the particle size of the pulverized powder.

Since the metal magnetic fine particles are composed of extremely fine particles, they will spontaneously ignite in the atmosphere and return to iron oxide, so an oxide film is formed using a normal method.
Stabilize.

The slurry obtained by soaking the metal fine particles in various organic solvents can be easily pumped using a gear pump, Viking pump, etc., and the acicular shape of the magnetic metal powder is not destroyed during the feeding.

Since the secondary agglomerates in the paint ha of the metal magnetic fine particles are small, adsorption of various additives added as auxiliary agents for affinity and dispersibility with the binder resin progresses quickly and evenly, making it easy to absorb. It can be used as a magnetic coating material, and as a result, the orientation and filling properties of tape media are significantly improved.

Further, the effects of the present invention are remarkable when the powder is fluidized for the purpose of uniform calcination and reduction. That is, when powder is forcibly fluidized and mixed in a rotary or stirring heating furnace and calcined or gas phase catalytic reduction reaction is performed, the powder is rough (pulverized powder) compared to the fine pulverization specified in the present invention. The body becomes a so-called granulated powder with a hard, sand-like shape, and the fluidity of the organic solvent slurry of the manufactured magnetic metal fine particles is extremely poor (atomization treatment as a pretreatment for paint preparation is an essential condition). Therefore, the process becomes complicated, which is undesirable.However, as in the present invention, <100
Powder that has been pulverized to a size smaller than a mesh is not granulated, and the organic solvent slurry of the produced magnetic metal particles has good fluidity, and paint dispersibility is extremely easy.

Tsuki Kusaku〉 The characteristics of the ferromagnetic metal fine particles of the present invention are that compared to the primary particle size, there are fewer agglomerates than conventional ones, and the organic solvent slurry has good fluidity, which improves paint dispersibility. That's what it is.

In particular, when dry powder of surface-modified iron oxyhydroxide, which is a raw material, is forcibly fluidized and mixed in a rotary or stirring heating furnace and calcined or subjected to a gas phase catalytic reduction reaction, granulation occurs. Without this, the fluidity and paint dispersibility of the produced organic solvent slurry of magnetic metal fine particles are also improved, which is extremely preferable.

In addition, with the recent trend toward miniaturization of magnetic fine particles, the present invention is suitable for applications such as 8 m / m video applications, which require the use of acicular metal fine particles with a major axis diameter of 0.5 μ or less. A method for producing ferromagnetic metal fine particles can be an extremely useful means.

As a result, when media processing is performed, finer particles can be used as the raw material powder, making it possible to create a system with almost no change in magnetic properties.

As a direct result of this, the magnetic properties, which are strongly controlled by the particle size of the magnetic powder, that is, the electromagnetic conversion characteristics (sensitivity/output) and noise in the high frequency range, will be greatly improved. .

<Example> Hereinafter, the method and effects of the present invention will be described in detail with reference to Examples and Comparative Examples.

Example 1 This example is an example showing an overview of the method of the present invention and its effects regarding ferromagnetic metal iron fine particles containing metal iron as a main component for use in 8m x 7m video.

[Manufacture of raw material powder]

By the method described in JP-A No. 57-106527 and No. 57-96504, the weight ratio of P and Si components is P/Fe=0.
．． 3/100 and Si/Fe = 1.5/100
We synthesized acicular iron oxyhydroxide microparticles containing iron oxyhydroxide.

The shape of the fine particles has a specific surface area (SA) of 95. Or//gr, and the ratio of the major axis diameter (:L) to the minor axis diameter (:D), that is, the axial ratio (:L/D), calculated from a transmission electron microscope image at 60,000 to 90,000 times, is 15. there were.

Next, adhesion modification treatment with zinc borate was added by the method described in JP-A-58-48612 (B/Fe=0.6/10
0 weight ratio) and dried at 120°C overnight.

[Crushing of dry powder and measurement of particle size distribution]

The dry powder was pulverized once using a nick sample mill manufactured by Fuji Pakudal ■ using a screen mesh: L1m, 1'l.

The particle size distribution of the pulverized powder was measured as follows. That is, powder 10 gr, particle size 100 mesh and 200 m
Using an esh sieve (75w5l), a classification operation was performed by shaking and multiplying by 5-0. Next, the weight of the classified powder is measured, and each particle size distribution is expressed as a weight percentage (hereinafter, particle size distribution measurements will be performed using this method).
The results are shown in the table.

[Manufacture of reduced iron powder]

The powder was charged into a fixed-bed reduction furnace, and a gas phase catalytic reduction reaction using hydrogen gas (temperature = 375°C, gas hourly space velocity =
20 Nni'-H2/kgr-Fe, Hr
) to obtain reduced iron powder.

Next, after thoroughly immersing the fine particles in toluene, the fine particle slurry was transferred onto an enamel pear vat to a thickness of about 1 tMt, and subjected to toluene scattering treatment in the atmosphere.

When the smell of the solvent disappeared, the magnetic powder was collected and made into air-dried metal iron powder.

The particle size distribution of the air-dried metallic iron powder and the results of magnetic evaluation using a vibrating magnetic property measuring device (Model VSM-III manufactured by Toei Kogyo Co., Ltd.) are shown in the table.

[Evaluation of air-dried metal iron powder into paint, coating and tape properties]

10 grams of the air-dried metal iron powder was collected and put into a 550-pot pot along with the following materials, and mixed and dispersed for 5 hours using a paint shaker manufactured by Rhett Deville, USA. 211x gr α-alumina beads were used as the dispersion media.

-UCC Co., Ltd. Salt and Vinegar Polymer VAGH: 0.8
gr・Mitsui Toatsu Chemical Co., Ltd. table polyurethane NL-2448
: 1.2gr ・Phosphate ester AP-13 manufactured by Otona Kagaku Co., Ltd.: 0.5
r ・α-Alumina AKP-50 manufactured by Sumima Kagaku Co., Ltd.: 0.5
r・Solvent) Luey: 15gr, MEK: 15gr.

Next, the dispersion media was separated to obtain a magnetic paint, which was coated onto a 13 μm thick polyester film (Nilmirror 13W-QO6S) manufactured by Toray Industries using an applicator in a precision coater equipped with magnetic tape. After that, the coating surface was smoothed by calender roll treatment, and
The polyurethane curing reaction was completed by heat treatment at ℃ for 2 days. The sheet was cut to 8.00 m, and 8 m
A magnetic tape with the size specified for a 7m video cassette was manufactured.

The results of measuring the magnetic properties of the magnetic tape using the above-mentioned measuring device are shown in the table.

Example-2 Except for reducing the powder while fluidizing it using a stirring type (1 rpm) reduction furnace, the following steps were taken: production of raw material powder, pulverization of dry powder, measurement of particle size distribution, production of reduced iron powder, and air-drying of metallic iron. The powder was made into a paint, applied, and the tape properties were evaluated in the same manner as in Example 1 to obtain metallic iron fine particles. The results are shown in the table.

Comparative Example-1 The production of raw material powder, particle size distribution measurement, production of reduced iron powder, and air-dried metal iron powder were carried out except that dry powder was crushed using a milk wasp and the powder passed through a 16 mesh sieve was used. The coating, coating, and evaluation of tape properties were carried out in the same manner as in Example-1, and metallic iron fine particles were obtained. The results are shown in the table below.

Example-3 Except for using α-iron oxyhydroxide fine particles with a specific surface area of 90.1♂/gr, the following steps were taken: production of raw material powder, pulverization of dry powder, measurement of particle size distribution, production of reduced iron powder, and air-drying of metallic iron. The powder was made into a paint, applied, and the tape properties were evaluated in the same manner as in Example 1 to obtain metallic iron fine particles. The results are shown in the table.

Example 4 α-iron oxyhydroxide fine particles with a specific surface area of 90.1 m”/gr The production of raw material powder, particle size distribution measurement, production of reduced iron powder, making air-dried metal iron powder into paint, coating, and evaluation of tape properties were the same as in Example-2, except that it was crushed three times using 2m32F). The same method was used to obtain metallic iron fine particles.

The results are shown in the table.

Comparative Example-2 In the pulverization process, the manufacturing of raw material powder, measurement of particle size distribution, manufacturing of reduced iron powder, and air-drying of metal, except that the material was pulverized once using a free crusher manufactured by Nara Seisakusho (model % formula %). The coating of the iron powder, the coating, and the evaluation of the tape properties were carried out in the same manner as in Example 4, and metallic iron fine particles were obtained.

The results are shown in the table.

Comparative Example-5 Specific surface area 74.2r+? Except for the use of α-iron oxyhydroxide fine particles of /gr, the production of raw material powder, particle size distribution measurement, production of reduced iron powder, making paint from air-dried metallic iron powder, coating, and evaluation of tape properties were compared. Metallic iron fine particles were obtained in the same manner as in Example-2. The results are shown in the table.

Effects> The effects and effects of the present invention can be summarized as follows from the results of Examples and Comparative Examples.

That is, in acicular ferromagnetic metal iron powder fine particles as a magnetic recording material suitable for high-density magnetic recording, after finely pulverizing acicular iron oxyhydroxide fine particles that have been adhered and modified using an impact crusher or the like, By producing ferromagnetic reduced iron fine particles through a gas-phase catalytic reduction reaction using a reducing gas, (1) As for the metallic iron fine particles themselves, the shape of the raw material iron oxyhydroxide can be improved (while still exhibiting the inherited acicularity). , (2) The particle size of the secondary agglomerates has become extremely fine, and the fluidity of the organic solvent slurry of the metal iron particles has been greatly improved. , especially residual magnetization (Br) and squareness ratio (Br/8m)
It has been found that entertainment improves.

As described above, the present invention provides a method for manufacturing fine ferromagnetic metal iron particles that significantly improves quality without changing most of the conventional manufacturing processes and equipment.

Claims (2)

[Claims] (1) In a method for producing ferromagnetic iron fine particles suitable for magnetic materials for magnetic recording media by a gas phase catalytic reduction reaction of surface-modified iron oxyhydroxide or iron oxide with a reducing gas, two of the obtained ferromagnetic iron fine particles are obtained. 90% or more of secondary aggregates1
A method for producing acicular ferromagnetic iron fine particles, characterized in that the particles pass through a 00 mesh sieve particle size. (2) A patent that grinds surface-modified iron oxyhydroxide or iron oxide until more than 90% of the secondary aggregates pass through a 100-mesh sieve, and then transforms the surface into ferromagnetic iron fine particles through a gas-phase catalytic reduction reaction using a reducing gas. The method according to claim 1.