JPH01219103A - Magnetic metal powder for magnetic recording - Google Patents

Abstract

PURPOSE:To produce the title magnetic metal powder having prescribed coercive force by adding an Ni source compd. and an Al2O3 source compd. to acicular iron oxide particles having a specified axial ratio, carrying out surface treatment and reducing the resulting iron oxide powder under heating in the presence of an alkali metal salt and an S compd. CONSTITUTION:An Al2O3 source compd. such as aluminum sulfate is added to iron oxide powder consisting of acicular iron oxide particles having >=8 axial ratio in the presence of an Ni source compd. by about 3-6% (expressed in terms of Al) of the amt. of Fe and surface treatment is carried out. The resulting iron oxide powder is reduced under heating at about 320-400 deg.C in a flow of gaseous hydrogen in the presence of an alkali metal salt such as Na hydroxide or an alkaline earth metal salt and an S compd. such as an ammonium salt of S by which SO3 is provided by >=0.5% of the amt. of Fe. The amt. of the metal salt used is >=0.005% (expressed in terms of Na) of the amt. of Fe in case of Na hydroxide. Magnetic metal powder for magnetic recording having about 800-1,100 Oe coercive force (Hc) is obtd. while maintaining the acicular shape.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal magnetic powder for magnetic recording media containing Fe as a main component, which is obtained by heating and reducing iron oxide powder with hydrogen gas, etc. While maintaining the acicularity of each particle constituting the iron powder, the crystallinity of the Fe crystals present in the particles with the acicular shape is controlled, and the Fe constituting the oblique shape of each particle is controlled. The present invention relates to a metal magnetic powder prepared to exhibit a coercive force in the range of 800 to 1,1000 e by appropriately breaking bonds between crystals and reducing shape magnetic anisotropy.

In recent years, the aim has been to make video recording and reproducing equipment longer recording times, smaller and lighter, and in order to meet these demands, there is a strong demand for higher performance and higher recording density for magnetic tapes, which are magnetic recording media. Magnetic materials that have been or are currently used as magnetic recording media include Fe3.
04). 7'-Fe, 0. .

Cry, etc., and the coercive force (Hc
) is 250 to 5000e, and the saturation magnetization (・σS) is
It is about 70-85 emu/g. Co-containing Co-7''-Fe20s and CoFe5O4 are also used as magnetic materials for video tapes, but these have a large coercive force (Hc) of 500 to 1,0000e. However, the saturation magnetization (・υS) is 70
-80 emu is as low as 7g.

Recently, magnetic particles with characteristics suitable for high output and high density recording, that is, high saturation magnetization ■s, and high coercive force (Hc
) has been developed and is being put into practical use.

These metal magnetic particles, which are called acicular metal powders and whose main component is Fe, have a higher saturation magnetization (・σS) than conventional magnetic iron oxide particles and CO-containing magnetic iron oxide particles.
is extremely high at 120-130 emu/fi, and the coercive force (Hc) is also high at 1,400-1,6000e.

For this reason, under the current mainstream coating-type magnetic recording method, studies are being conducted to reduce noise and improve image quality, especially in magnetic materials for video, and from the standpoint of high output and high density recording, Higher saturation magnetization (・Os) than Co-containing magnetic iron oxide
The use of metal magnetic powders with high coercive force (Hc) has been investigated, 3//4 rryrLl'L Video, DAT
Some of them have been put into practical use.

However, in magnetic recording media that use metal magnetic powder with such a high coercive force (Hc), it is naturally necessary to perform magnetic recording by counteracting the coercive force held by the magnetic material. Mn is used as the head and playback head in general video tape recorders.
-Zn-Ni based ferrite heads cannot be used, and heads made of special materials such as amorphous alloys or sendust alloys must be used.

Recently, 5=V is used as a high-quality, high-power magnetic recording and reproducing method
It is well known that the H8 system has been proposed and uses a ferrite head and Co-7''-Fe 203 as the magnetic recording material.
e Saturation magnetization (G S) for 20s is high k 80emu/g
However, it shows good characteristics under the restriction of using a ferrite head. However, the demands of the times require even higher image quality and higher density recording. However, as long as a ferrite head is used, there is a limit to the coercive force (Hc) of the magnetic powder of the recording material used, and in order to achieve the objective under this constraint, it is necessary to increase the saturation magnetization of the magnetic material itself.
It is necessary to increase the power and output.

The present invention modifies metal magnetic powder containing Fe as a main component,
While maintaining its acicularity and saturation magnetization (transport), the coercive force (Ha) was adjusted to 80% to match the ferrite head specifications.
It is an object of the present invention to provide a metal magnetic powder adjusted to 0 to 1.1000 eK and a method for producing the same. As mentioned above, metal magnetic powder has extremely excellent magnetic potential, but the reason why it has not been used in video magnetic recording and reproducing equipment with ferrite heads is that conventional metal magnetic powder manufacturing technology cannot achieve the desired magnetic potential. The problem is that it has been difficult to adjust the coercive force (Hc) while maintaining the characteristics. That is, it is said that ferromagnetic metal powder used as a coated magnetic recording medium must have no bonding between particles due to sintering or the like, and must have an appropriate axial ratio. The stiffness is due to the coercive force of metal magnetic particles whose main component is Fe, mainly due to the shape magnetic anisotropy of the particles, Hc = 2KU/MS + N-MS...
・This value is expressed by the -0 formula, but since the value of N (shape magnetic anisotropy constant) increases as the axial ratio increases, the coercive force Hc becomes a large value when the axial ratio is large. This is to take.

However, in general, when acicular iron oxide is reduced by heating, approximately 4
A volume contraction of about 7% occurs, and at this time, the particles fuse together or the particles themselves sinter, resulting in deterioration of the axial ratio and collapse of the bulk particles. In order to prevent sintering of these particles, the raw material iron oxide is made of P, Si, Al, Zn,
Various methods have been disclosed for improving the characteristics of reduced magnetic powder by surface treating it with salts of various metals such as Zr and Ti or hydroxides of these metals (for example, Japanese Patent Publication No. 1572-1989).
04, 1986-162706, and many others).

According to these methods, during thermal reduction, the acicularity of the raw material is maintained and the value of N in equation 0 is kept at a large value, so that metal magnetic powder with a coercive force Hc of 1,400 to 1,6000e can be obtained. can get. Therefore, these disclosed methods have a coercive force Hc of 800 to 1,100 that meets the ferrite head specifications.
Metal magnetic powder of 0e cannot be obtained.

As a method of reducing the coercive force Hc of metal magnetic powder, it is possible to reduce the shape magnetic anisotropy by sintering the particles, but as a practical matter, the acicularity of the particles is lost, so tape The square shape, orientation ratio, Hc bowl, etc. are extremely poor when it is made, and it cannot be put to practical use. Also published patent in 1982
A metal magnetic powder with a coercive force Hc of 1,400 to 1,6000e and a saturation magnetization (R5) of 120 to 125 emu/g, which maintains its acicularity by the method disclosed in Japanese Patent Application No. 157204, etc., is obtained, and its surface is gradually polished. It is also conceivable to precipitate a nonmagnetic layer on the surface of the metal magnetic powder by oxidizing it to adjust the coercive force (Hc) to SOO to 1.1000e.

However, this method reduces the coercive force (Hc) to 800-1
, 1000e, but since a non-magnetic layer is deposited on the surface of the magnetic powder, the saturation magnetization ρS is significantly lowered and the properties of the metal magnetic powder as a recording material are significantly impaired. This is not the preferred method.

On the other hand, metal magnetic powder whose main component is Fe obtained by using short-axis iron oxide with a small axial ratio as a raw material for manufacturing metal magnetic powder has a small shape magnetic anisotropy of 1.0
It has a coercive force of less than 000e and a saturation magnetization/σS of 12
It shows a high level of 0-125 emu/g. However, since the metal magnetic powder obtained by this method has a small axial ratio, it is useful as a recording medium for floppy disks, rigid disks, etc. that are used without orientation, but it is useful for recording media such as floppy disks and rigid disks that are used without orientation. The recording material used for this purpose has an essential drawback in that it cannot produce as much output as acicular magnetic metal powder due to its lack of square shape, especially when it is made into a tape.

The present inventors have obtained a metal magnetic powder that is acicular particles that are compatible with magnetic recording and reproducing equipment using ferrite heads, has a high FS value, and has a coercive force (Hc) of 800 to 1,1000e. As a result of our investigation, we found that: 1) Si and Al, which are commonly used as heat-resistant treatment agents, behave completely differently during reduction; 2) When treating raw iron oxide with At in the presence of Ni as a reduction promoter, the third component As a result, the ferromagnetic metal magnetic powder obtained by thermal reduction can be saturated magnetized (・'s) by appropriately containing an alkali metal such as Na or an alkaline earth metal such as Ca, and 803.
To obtain a metal powder in which the needle-like shape of the raw material acicular iron oxide is inherited while being maintained at a high level of 120 emu/y or more, and the bonds of Fe crystals generated in the needle-like shape particles are broken. We have discovered that this can be done, and have arrived at the present invention.

The coercive force (Hc), which maintains the acicular shape obtained by the present invention and reduces the shape magnetic anisotropy of the particle by breaking the bonds of Fe crystals in the shape particle, is 800 to 1.
Metal magnetic powder whose main component is Fe adjusted to 1000e can be dispersed while retaining its shape when it is made into a paint, and applied to a base film and subjected to magnetic field orientation, so it exhibits good square shape and Its saturation magnetization ■s) is high, and therefore, if the magnetic powder of the present invention is used, ferrite
In magnetic recording and reproducing equipment that uses heads, it is possible to significantly improve recording density, high output, and high image quality.

The technical background of the present invention will be explained below.

Figures 1 and 3 show that acicular iron oxide particles with a specific surface area of 70 mj/g are wet-treated with a ratio of Si or Al to Fe of 50%.
S r 02·nHto or Al in an amount corresponding to % by weight
, O,・n H20 added to the surface and baked at 700°C for 30 minutes in the air. Heated the sample at 400℃ using hydrogen gas for 22 hours.
An X-ray diffraction pattern of metal powder obtained by subjecting it to light over time.

This is shown in the pattern.

1 and 2 are samples processed using 5in2, and FIGS. 3 and 4 are samples processed using Al, 0. This relates to samples treated using .

From FIGS. 1, 2, 3, and 4, the behavior of 5in2, Al, and 03 added to the raw iron oxide can be clearly identified. That is, in the case of heating in air, the main components α-Fe203 and 5 in Figures 1 and 3 are
Since iOz and α-Fe203 and Al 20°0 diffraction lines are observed, the raw iron oxide is dehydrated by heating and transformed into α-Fe203, and the silicon compound or aluminum compound used for surface treatment is also dehydrated and oxidized. It can be seen that each oxide exists as 5i02 or Altos.

On the other hand, when a sample heat-treated in air is reduced in a hydrogen stream at 400°C, only the α-Fe diffraction line appears when SiO2 is added, as shown in Figures 2 and 4, respectively. was observed, and S which was attached to the sample before reduction
The diffraction line at t 02 has disappeared, whereas the diffraction line at A l t
The sample treated with Os clearly contains Al, 0
．． It was found that there is a remarkable difference between the two in that the diffraction lines of

In the above experiment, Si or Al was 50% by weight relative to Fe.
Si and A were used in such large amounts during the reduction.
This is because the purpose was to clearly understand the difference in behavior from 1. It is self-evident that once the differences in behavior become known, the range of addition amount most suitable for the actual application can be determined by subsequent tests, depending on the type of treatment agent used.

The present inventors paid attention to this fact and used N as a reduction accelerator.
As a result of research on producing metal magnetic powder using Al2O as the main treatment agent in the coexistence of i, it was found that the amount of surface treatment reagent added was 1-10% by weight of Al relative to the weight of Fe in the raw material iron oxide.
Preferably, it is added in an amount of 3-6% for surface treatment, washed and dried, and fired in a non-reducing atmosphere to increase crystallinity, and then heated to 3208C to 400℃ in a hydrogen stream, preferably around 350℃. If it is heated and reduced, the coercive force (Hc) will be 1,
300 to 1.5000e was obtained.
It turns out that

In this case, if the firing temperature in a non-reducing atmosphere is too high, sintering of α-Fe203 will occur at this point.
A range of 509C to 800C is preferred. In some cases, it may be possible to adjust the temperature in the next reduction step without performing heat treatment.

Further, even when the reduction temperature is as high as 450° C. or higher, sintering of Fe crystals occurs during thermal reduction, the axial ratio decreases, and the coercive force Hc decreases. In such a case, the coercive force (Hc) is 800-1
．． 1000e, but as a magnetic recording medium, the squareness deteriorates significantly due to a decrease in the axial ratio, and the magnetic properties become extremely poor, which is not preferable.

In this way, Hc800 to 1,1000, which is the objective of the present invention,
In order to produce metal magnetic powder that has e and maintains a high σS value without impairing its acicularity, it is necessary to reduce the shape magnetic anisotropy while maintaining its acicularity. In order to solve the seemingly contradictory problem, Al t Os, which exhibits unique behavior as a heat-resistant treatment agent, was used, and Ni was used as a reduction accelerator.
Adding a predetermined amount of an alkali metal salt such as Na and/or S compound as a third component to the raw iron oxide in the presence of
The present invention was completed based on the discovery that by treatment, Hc can be adjusted to a desired range while retaining the needle-like shape.

That is, from detailed practical results, it is appropriate that the temperature for reduction with H2 gas is around 350°C, and for treatment with Al2O, when the amount of Al2O is less than 1% relative to Fe as Al, the metal powder obtained It is recognized that the retention of the needle-like structure is insufficient and Fe crystals exist alone. For this reason, it has been found that the appropriate amount of Al, O, used for surface treatment is 3% or more, which can maintain the needle-like shape of the product iron powder. Also, when 10% or more of Al, 03 is added,
It was observed that the saturation magnetization (s) of the obtained metal powder decreased.

In addition, when the amount of Al2O added is 6%, the influence of other components on the coercive force (Hc) increases by about 800e with an increase of 1% in the amount of Ni added in the range of 0.5 to 3% Ni. NaO,
In the range from 0.02 to 0.4%, there is a decrease of about 2500 e per 1% increase in Na O, and about 200 e per % increase in SOs between 0.02 and 0.7%. was discovered. Therefore, from the above, Al 20.
By appropriately selecting the ratio of Na and S content in the coexistence of Ni, it has an acicular shape, high Fs, and a coercive force Hc suitable for ferrite head specifications. Metal magnetic powder adjusted to a value of 800 to 1.1000e can be obtained.

Figure 5 shows Al2O, 6%, in the coexistence of 1% Ni,
Acicular iron oxide raw materials treated with 0.05% Na and 0.6% So, or containing those additives, were heat-treated at 700°C in air, and then heated using a fixed bed reduction device. reduction temperature 350℃, hydrogen gas flow t15NI/k
This is a 120,000x Seiko micrograph showing the particle structure of a metal magnetic powder containing Fe as a main component of Hc9800e obtained by reduction under conditions of g·Fe-hr.

From FIG. 5, it can be seen that each particle of the completely demagnetized magnetic powder containing Fe as a main component retains a needle-like shape, and that the bonds between Fe crystals in each particle having the shape are partially severed.

Although it is not clear why the bonds of Fe crystals in metal magnetic particles mainly composed of Fe that retain needle-like shapes are broken and the shape magnetic anisotropy decreases, in the case of 5if2 treatment, Na
, even when the S content is a few percent, the bond breakage in the Fe crystal is extremely small and the Hc value is 1.4000e or more.
We speculate that this is due to the interaction of 8.

At20. which can be used to practice the present invention. Examples of the source include aluminum compounds such as aluminum sulfate, sodium aluminate, and polyaluminum chloride;
Alkali metal sources used as components include Na, hydroxides, chlorides, sulfates, etc., and calcium salts are mainly used as alkaline earth metal sources. Ammonium salts and soda salts of S can be used as the S compound, but when performing surface treatment with Al 20°, it is also possible to adopt a method in which a predetermined number of compounds containing Na and S, such as Na2SO4, which are produced as reaction by-products, remain. Of course.

This will be explained below using examples.

Example 1 Yellow acicular iron oxide (specific surface area 55 mj/
9.5o30.72%) and then NiC1
, is 1% as N i /Fe, NaAlQ2 is A
After adding and mixing 6% of 1/Te, an aqueous NaOH solution was gradually added to adjust the pH to 7.5.

The resulting slurry is washed and filtered to form a cake, which is KN
a Cl wo Na /Fe and! , Te0.08%, (NH
4) 2so4 as SQ, /FetO, 0.76%
After adding it and kneading it with a kneader, it becomes 4Mvm in diameter.
It was molded into a +t rod shape and then dried.

The obtained dried product was heated at 750° C. in an electric furnace to obtain α-Fe203 having a crystallite diameter of 246 A calculated from the X-ray half width using the Scherrer equation.

The α-Fe203 thus obtained was placed in a fixed bed reduction device at a temperature of 350°C and a hydrogen gas flow rate of 15ONl/F.
Reduction was carried out under conditions of e-Kg-hr to obtain metal magnetic powder containing Fe as a main component. This metal magnetic powder was taken out in toluene, air was blown in to stabilize the surface of the metal magnetic powder by oxidation, and then air-dried.The reduced iron powder obtained had a specific surface area of 47.3g/g, and Seiko's micrograph showed that it was needles. It retains its shape,
Moreover, the bonds of Fe crystals in each needle-shaped skeleton particle were broken.

The coercive force (Hc) measured in an external magnetic field (10 kilogauss) by VSM is 1.0180e, the saturation magnetization (s) is 120 emu/g, and the coercivity/σS is 9.466, which is the magnetism of the ferrite head specification. As a recording material, it had a high saturation magnetization (excellent).

Example 2゜Example 1. Yellow iron oxide treated with or containing N1, Al, Na, and SO3 was heated in air at 775°C and 800°C, respectively, and the crystallite diameter determined from the X-ray half-width was 273° and 273°. Example 1 except that the number of people was 289. Metal magnetic powder was obtained by reduction in the same manner as above.

The obtained magnetic powder was observed using an electron microscope.
Hold the needle-like shape, and the shape! It was observed that the Fe crystal bonds in the particles were broken. The magnetic properties of the sample heat-treated at 775°C are Hc 8880e, '7
s 124 emu/g, the sample heat-treated at SOO℃ is Hc
8800e, 132 emu/g,
Both q r /q s were in the 0.42 range.

Comparative example 1゜Example 1. The yellow iron oxide treated with or containing Ni, Al, Na5303 used in
Example 1 except that the treatment was carried out at 0°C and the reduction temperature was 450°C. Metal magnetic powder was obtained by reduction in the same manner as above.

When observed using an electron microscope, the obtained magnetic powder had a acicular shape, and the Hc was as low as 6800e, and the r/ps was 0.39.
It was inferior.

Comparative Example 2゜3% Ni added, Na/Fe O, 03%, SOs/
Example 1 except that Fe0002% was used. Metal magnetic powder properties were obtained in the same manner as above. Although the obtained magnetic powder maintained an acicular shape, it had an Hc of 1,4800e and could not be used as a magnetic material for ferrite head specifications.

Comparative example 3゜Comparative example 2. The reduced metal magnetic powder obtained in step 1 was cooled to room temperature while flowing nitrogen gas, and then air was mixed into the nitrogen gas little by little to oxidize the surface of the metal magnetic powder.

By introducing air, the temperature of the system rose to 40°C, and finally a magnetic powder of Hc 9800e was obtained, but its qs was as low as 98 emu/:i, and its 0s, the most characteristic of metal magnetic powder, was inferior. It was something like that.

Comparative example 4゜Example 1. In this process, instead of treating Fe with AlK, Fe
Example 1 except that 5.3% by weight of 81 was used for the treatment. Metal magnetic powder was obtained in the same manner as above. Hc of this thing
was 1.5320e, Os was 123 emu/g, and the desired Hc of 800-1.1000e was not obtained.

[Brief explanation of the drawing]

Figure 1 shows yellow iron oxide with 50% Si by weight relative to Fe.
The raw material treated with an amount of S i Ot corresponding to 7
This is the X-ray diffraction pattern of α-Fe203 made by firing at 350°C for 30 minutes.
This is an X-ray diffraction pattern of a sample reduced with a hydrogen gas flow rate of 15ON1/Fe-Kg-h. 700℃
This is the X-ray diffraction pattern of α-Fe20s prepared by firing for 30 minutes at It is. FIG. 5 shows He 800-1.
An electron micrograph at a magnification of 120,000 times shows the particle structure of magnetic metal powder with a needle-like structure of 1,000 e. II Ward
Ward - Heima 恢Eeko Ward 1 inch Tsukakan 5 Mei Lβ25-1

Claims (6)

[Claims] (1) Consisting of metal crystal particles mainly composed of Fe that maintains the acicular morphology of acicular iron oxide with an axial ratio of 800 or more.
A metal magnetic powder for magnetic recording having a coercive force (Hc) in the range of ~1,100 Oe. (2) The metal magnetic powder for magnetic recording according to claim 1, which has a saturation magnetization (■s) of 120 emu/g or more. (3) Acicular iron oxide with an axial ratio of 8 or more, which is made of metal crystal particles containing Ni and Al and mainly composed of Fe, which retains the acicular morphology; The bonds between the Fe crystals contained in the particles and constituting the skeleton of the particles are moderately broken, and the
A metal magnetic powder for magnetic recording having a coercive force (Hc) of e and a saturation magnetization (■s) of 120 emu/g or more. (4) Inheriting the acicular form of acicular iron oxide with an axial ratio of 8 or more,
It is a metal magnetic powder containing Ni and Al, and further contains 0.05% by weight or more of Na and/or 0.5% by weight with respect to Fe.
Due to the addition of SO_3 above, fine Fe inside the skeleton particles is
2. The metal magnetic powder for magnetic recording according to claim 1, wherein shape magnetic anisotropy is attenuated by controlling the crystallinity of the crystal and breaking bonds between fine Fe crystal grains. (5) In acicular iron oxide powder that is surface-treated by adding a Ni source compound and an Al_2O_3 source compound to iron oxide powder consisting of acicular iron oxide particles with an axial ratio of 8 or more, or in acicular iron oxide powder with an axial ratio of 8 or more. Ni source compound and Al are added to iron oxide powder consisting of particles.
A suitable amount of a salt of at least one metal selected from alkali metals and alkaline earth metals and an S compound are present in a mixture obtained by simply adding and mixing a _2O_3 source compound, and the mixture is heated and reduced to form acicular particles. A method for producing metal magnetic powder for magnetic recording whose coercive force (Hc) is adjusted to a desired range while retaining its shape. (6) The metal salt is Na in an amount of 0.05% by weight or more based on the weight of Fe in the raw material iron oxide, and the S compound is SO_3 in a content of 0.5% by weight or more based on the weight of Fe in the raw material iron oxide.
The method according to claim 5, which is an S compound capable of providing.