JPS61174118A - Magnetic powder for vertical magnetic recording and its production - Google Patents

Abstract

PURPOSE:To produce the titled magnetic poser high in the saturation magnetizing quantity and low in the coercive force by regulating an aq. soln. of ferric salt, Ba salt, Co salt and Sn salt to the specified pH with alkali to deposit a coprecipitated material of hydroxide, washing, separating, heating and calcining it. CONSTITUTION:The following aq. soln. is regulated to >=7pH with alkali wherein ferric salt, at least one kind selected from Ba salt, Sr salt and Pb salt, at least one kind selected from Co salt and Ni salt, and Sn salt are dissolved and the coprecipitated material of a hydroxide is deposited. Then after washing this coprecipitated material with water and separating it, about 50-120pts.wt. flux such as NaCl per 100pts.wt. coprecipitated material is added and the mixture is heated and calcined at about 850-1,300 deg.C. Thereby the following hexagonal platy particulate magnetic powder of the vertical magnetic recording is obtained wherein <=25% Fe atom in a magnetoplumbite type structure shown in AO.nFe2 O3 [A is one kind of atom selected from Ba, Sr, Pb, and (n) is integer.] is substituted with Co or Ni and Sn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetoplumbite-type magnetic powder used as a magnetic recording element for magnetic tapes and other magnetic recording media, and a method for producing the same.

[Conventional technology]

In general, a magnetic recording medium is one in which a magnetic layer containing magnetic powder as a magnetic recording element and a binder to bind the powder is provided on a base such as a polyester film. The above-mentioned magnetic powder has conventionally been T-Fe203, Fe3O4, Co
Magnetic powders consisting of acicular particles such as gold-containing r-Fe20s and metallic Fe are commonly used, and these can be oriented along the base surface during magnetic layer formation to record magnetization components in the direction parallel to the magnetic layer surface. It is used for playback.

However, in recent years, with the increase in the density of magnetic recording, magnetoplumbite-type magnetic powders such as Ba and Sr%Pb ferrites, which can utilize the magnetization component perpendicular to the magnetic layer surface for recording and reproduction, are being used.

The above magnetoplumbite type magnetic powder is AO-nF e
203 (where A is at least one type of atom selected from Ba%Sr%Pb, n is an integer, generally 4 to '7), and consists of hexagonal plate-shaped particles with a structure shown in the vertical direction to the particle plate surface. By orienting the grain plate surface direction along the base surface when forming a magnetic layer with an easy axis of magnetization, the magnetization component perpendicular to the magnetic layer surface can be used for recording and reproduction, making it suitable for high-density magnetic recording. ing.

One way to obtain such a magnetoplumbite-type magnetic powder is to precipitate a hydroxide coprecipitate in an alkaline region by reacting an aqueous solution containing the constituent metals with an alkali, and then autoclave the precipitate in an alkaline region. A method is known in which a hydrothermal reaction is carried out at about 280 to 550°C in
-149328). However, this method has the drawback that it is not possible to increase the saturation magnetization (σS) of the magnetic powder, making it difficult to cope with higher density recording. This is presumed to be due to the fact that during the hydrothermal reaction, the pressure is high but the heating temperature is low, and particle growth is suppressed so that the saturation magnetization (σS) does not increase.

In addition, as a means of obtaining magnetic powder for magnets with a high saturation magnetization (σS), there is also known a method of heating and firing the hydroxide coprecipitate in the above method together with a flux at a high temperature of 800°C or higher (Japanese Patent Application Laid-Open No. 55-145303). However, in this method, the saturation magnetization (σS) of the magnetic powder is reduced to 5 Oemu
On the other hand, the coercive force (He) of the magnetic powder can be as high as /y or more.
becomes larger than 2,000 oersteds (Oe),
The coercive force (He 2 ) of a magnetic recording medium using this material also becomes too large, and a normal magnetic head is saturated during recording, which poses a practical problem.

On the other hand, as a means of lowering the coercive force (He) of such magnetoplumbite-type magnetic powder, a method of substituting a part of Fe atoms in the above structural formula with Co or Ni,
A similar method of substituting Co or Ni with Ti is known (document unknown).

[Problem that the invention seeks to solve]

However, when replacing with Co or Ni as described above, the axis of easy magnetization of the magnetic powder changes in the direction of the particle plate surface, so the original characteristics of the magnetoplumbite type magnetic powder for perpendicular magnetic recording are lost. There is a problem. In addition, in the magnetic powder substituted with Co or Ni and Ti as described above, the axis of easy magnetization becomes two components, one in the direction of the particle plate surface and the other in the perpendicular direction, and irregularly shaped particles are likely to be mixed together with the hexagonal plate-like particles. There is a problem that the original characteristics mentioned above are lost.

Therefore, in this invention, the axis of easy magnetization is substantially only in the direction perpendicular to the particle plate surface, and the amount of saturation magnetization (σS
) and a magnetic powder for perpendicular magnetic recording having a magnetoplumbite structure, which has a low coercive force (He) suitable for recording a magnetic recording medium using the same with an ordinary magnetic head, and a method for producing the same. The purpose is to

[Means for solving problems]

As a result of extensive studies for the above purpose, the inventor has determined that some of the Fe atoms in the above structural formula can be replaced with Co or Ni.
In the magnetoplumbite-type magnetic powder substituted with Sn and Sn, the axis of easy magnetization is essentially only in the direction perpendicular to the particle plate surface, and moreover, it has a high saturation magnetization (σS) and a magnetic recording medium cannot be used with a normal magnetic head. The present inventors have discovered that it is possible to provide a low coercive force (Hc) suitable for recording, and have accomplished this invention.

In other words, this invention uses AO・nFe203 (however, A
is at least one kind of atom selected from Ba, Sr, and Pb, and n is a well-formed hexagonal plate-like particle in which 25 atomic percent or less of the Fe atoms in the magnetoplumbite structure are replaced with Co or Ni and Sn magnetic powder for perpendicular magnetic recording, as well as a) ferric salt, b) barium salt,
An alkali is applied to an aqueous solution containing at least one salt selected from strontium salts and lead salts, C) at least one salt selected from cobalt salts and nickel salts, and d) tin salt, and the pH is adjusted to 7 or more. A method for producing magnetic powder for perpendicular magnetic recording, which comprises precipitating a hydroxide coprecipitate, washing the hydroxide coprecipitate with water and separating it into two parts, and then heating and baking it together with a flux at a high temperature. .

[Structure and operation of the invention]

The magnetic powder for perpendicular magnetic recording according to the present invention can be used as described above.
OnFe203 (A is Ba, Sr, P
At least 25 at % or less of the Fe atoms in the magnetoplumbite groove structure are Co or Ni, where at least one atom selected from b, n is an integer, generally 4 to 7)
and Sn. Such magnetic powder contains Sn as the above-mentioned replacement component.
Due to the existence of Furthermore, it is possible to have a low coercive force (Hc) of 2,000 Oe or less, and a high saturation magnetization (σS) of 50 emu/y or more depending on the degree of substitution and component ratio of the above-mentioned substitution components. be.

Here, when Ti is used together with Co or Ni as a replacement component as in the conventional case, the axis of easy magnetization is divided into two components, one in the direction of the grain plate surface and the other in the perpendicular direction, but by using Sn, it becomes only in the perpendicular direction. Although the reason is not clear, it is presumed as follows. That is, Ti and S
Both n acts to increase the perpendicular component of the axis of easy magnetization, but since the melting point of TiO2, which is an oxide, is ~1840°C, the melting point of SnO is as low as ~1630°C, so it is difficult to use when synthesizing magnetic powder. This is thought to be due to the fact that Sn diffuses more uniformly into the particles during heating and baking, making it easier to create a regular crystal structure. Moreover, this point is also assumed to be a factor in the mixture of irregularly shaped particles when Ti is used.

Note that if the amount of substitution of Co or Ni and Sn for the Fe atom is too large, it will cause a significant decrease in the saturation magnetization (σS). Should be. Furthermore, if the amount of substitution is too small, the coercive force cannot be lowered sufficiently, so it is preferably 12 atom % or more.

On the other hand, the usage ratio of Co or Ni and Sn is (C.

Or, it is better to set the atomic ratio of Ni)/Sn to be in the range of 4=1 to 1:2.
If the amount is too small, the effect of lowering the coercive force (Hc) will not be sufficiently exhibited, and conversely, if the amount of Co or Ni is greater than the above ratio, the component of the easy axis of magnetization in the direction of the grain plate surface will be large (which is not preferable).

Incidentally, Co and Ni may be used in combination in addition to being used alone, and it goes without saying that when they are used in combination, the above-mentioned substitution amount and atomic ratio are based on the total amount of both.

Furthermore, the average particle diameter (longest in the direction of the plate surface) of the above magnetic powder is
0.5 to 0.0 in terms of magnetic properties for magnetic recording media
Approximately 2/” is desirable.

Although there are various methods for obtaining such magnetic powder for perpendicular magnetic recording, a specific method for obtaining the preferable fine particles as described above is as follows.

That is, first, a) a ferric salt; b) at least one salt selected from barium salts, strontium salts, and lead salts; and d) at least one salt selected from cobalt salts and nickel salts. An alkali is applied to an aqueous solution containing a tin salt, and a hydroxide coprecipitate is precipitated at a pH of 7 or higher, particularly preferably at a pH of 10 or higher. At this time, the above a
As each group of -d, water-soluble salts such as chloride, sulfate, and nitrate are preferably used, and as the alkali, NaOH
Alternatively, KOH aqueous solution, NH3 water, etc. are used. It goes without saying that the molar ratio of each of the groups a to d should be set so that the atomic ratio of the finally obtained magnetic powder becomes a required value.

Next, the hydroxide coprecipitate is separated from the suspension by washing with water for two minutes, and then heated and calcined together with a flux at a high temperature of usually 800°C or higher, particularly preferably 850 to 1,300°C. In this case, it is also possible to mix the hydroxide coprecipitate with a powdered flux and provide it for firing, but since the hydroxide coprecipitate is in the form of fine particles, it is difficult to mix it uniformly. Accompany. For this reason, preferably, the hydroxide coprecipitate separated from the suspension is dispersed and mixed in an aqueous solution of a flux, filtered, and dried, so that the flux is applied to the particle surface of the hydroxide coprecipitate. It is recommended that the deposited state be subjected to firing.

The above fluxing agents include sodium, potassium, lithium,
Calcium chloride, bromide, iodide and fluoride,
At least one selected from sodium, potassium, lithium sulfates, etc. can be suitably used. Further, such a fluxing agent is used in an amount of 5 parts by weight per 100 parts by weight of the hydroxide coprecipitate.
It is preferable to use it in a range of about 0 to 120 parts by weight.

By such heating and calcination, the fine particulate hydroxide coprecipitate in the melted flux changes to the above-mentioned magnetoplumbite type structure, and grain growth occurs to a certain extent.
A high saturation magnetization amount (σS
) and an average particle diameter of 0.5 to 0.02. The magnetic powder for perpendicular magnetic recording of the present invention, which is l'l, is obtained. Note that if this heating and firing temperature is too low, the above-mentioned grain growth will not be sufficient and the saturation magnetization (σS) will decrease. It is better to set it as a degree. Further, the heating and baking time is usually about 2 to 5 hours.

A means for producing a magnetic recording medium such as a magnetic tape using the magnetic powder for perpendicular magnetic recording of the present invention may be carried out in accordance with a conventional method using this kind of magnetic powder. for example,
A magnetic paint containing the above magnetic powder, a binder, and various additives as necessary is prepared, and this magnetic paint is applied onto a base such as a polyester film so that the plate surface direction of the magnetic powder particles is in the direction along the base surface. That is, the magnetic layer may be oriented in a magnetic field in a direction in which the axis of easy magnetization is perpendicular to the base surface, dried to form a magnetic layer, and required surface treatment such as calendering may be performed.

Examples of the binder include vinyl chloride-vinyl acetate copolymers, cellulose resins, polyvinyl butyral, polyurethane, and incyanate compounds. The additives include dispersants, lubricants, abrasives, antistatic agents, fillers, colorants, etc., and these may be selected and used as appropriate depending on the properties of the intended magnetic recording medium.

[Effects of the Invention] The magnetic powder for perpendicular magnetic recording according to the present invention has a magnetoplumbite structure in which part of the Fe component is Co or N.
Because it is composed of hexagonal plate-shaped particles substituted with i and Sn, the axis of easy magnetization is substantially only perpendicular to the particle plate surface, even though Co or Ni is used as a substituted component. It has the original characteristics for perpendicular magnetic recording, and has a high saturation magnetization (σS) effective for high-density magnetic recording and a low coercive force (Hc) suitable for recording with a normal magnetic head. .

Further, according to the method for producing magnetic powder according to the present invention,
It is possible to easily and reliably obtain the above-described magnetic powder in the form of fine particles, which is particularly suitable as a recording element for a magnetic recording medium.

〔Example〕

Next, the present invention will be specifically explained based on Examples and Comparative Examples.

Example 1 Ferric chloride 400y (1.48 mol), barium chloride 4
3.5y (0,178 mol), cobalt chloride 35°:l
(0,148 mol) and stannic chloride 51.4y (0,
148 mol) was dissolved in water to make an aqueous solution of 51, and this was made into an aqueous solution 5I! containing 480y of sodium hydroxide! In addition, hydroxide was co-precipitated. The pH of this hydroxide coprecipitate suspension was 12 or higher.

Subsequently, this suspension was washed with water to bring the pH to 8.0 or less, and filtered to obtain a hydroxide coprecipitate cake, which was added to 21!
The particles were added to a saturated aqueous solution of potassium chloride, thoroughly stirred, filtered under suction, and dried at 100°C to obtain a hydroxide coprecipitate in which potassium chloride was adhered to the particle surface. The amount of potassium chloride deposited was 65 parts by weight per 100 parts by weight of the hydroxide coprecipitate.Next, the dried product was baked at 900°C for 2 hours, thoroughly washed with water, and dried. Barium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained.

Example 2 Ferric chloride was 381' (1,42 mol), cobalt chloride was 42.2 y (0,178 mol), and stannic chloride was 61.
Barium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in exactly the same manner as in Example 1 except that the amount was changed to 69 (0,178 mol).

Example 3 Ferric chloride 362p (1.34 mol), cobalt chloride 49.39 (0,207 mol), stannic chloride 81
．． Barium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in exactly the same manner as in Example 1 except that 9y (0,236 mol) was used.

Example 4 Barium ferrite consisting of hexagonal plate-shaped particles was prepared in the same manner as in Example 1 except that cobalt chloride was 31.7y (0,133 mol) and tin chloride was 45.8y (0,132 mol). A magnetic powder was obtained.

Example 5 Nickel chloride 35.29 (0°1
Barium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in exactly the same manner as in Example 1 except that 48 mol) was used.

Example 6 Lead nitrate instead of barium chloride 58.9 ? (0,17
Lead ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in exactly the same manner as in Example 1, except that 8 mol) was used.

Example 7 Strontium chloride 47°5p (
Strontium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in exactly the same manner as in Example 1, except that 0.178 mol) was used.

Comparative Example 1 Barium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in exactly the same manner as in Example 1 except that cobalt chloride and stannic chloride were not used.

Comparative Example 2 A barium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in the same manner as in Example 1 except that cobalt chloride was 35.2y (0,148 mol) and stannic chloride was not used. .

Comparative Example 3 Barium ferrite magnetic powder consisting of hexagonal plate-shaped particles was obtained in the same manner as in Example 1 except that the stannic chloride was 51.1' (0,148 mol) and cobalt chloride was not used. .

Comparative Example 4 Titanium tetrachloride 28.1 F/(0
Barium ferrite magnetic powder was obtained in exactly the same manner as in Example 1, except that an acidic aqueous solution containing 148 mol) was used. However, this magnetic powder contained a high proportion of irregularly shaped particles in addition to the hexagonal plate-like particles.

Comparative Example 5 Same as Example 1 except that cobalt chloride was 75.4y (0,317 mol) and tin chloride was 110.1y (0,317 mol). Ferrite magnetic powder was obtained.

Regarding the magnetic powders obtained in the above Examples and Comparative Examples, various magnetic properties, average particle diameter (longest length in the direction of the particle plate surface), and direction of the easy magnetization axis component with respect to the particle plate surface were investigated. The results are shown in the table below.

The direction of the easy axis component of magnetization was measured using the following method.

<Direction of easy magnetization axis component> A water paste of magnetic powder was applied onto a 9μ thick polyester film, dried in an IOK Gauss (G) magnetic field,
The resulting magnetic sheet was punched out into a circular shape with a diameter of 3aI, and this was used as a sample to measure the relationship between rotation angle and torque within the plane of the magnetic sheet in an IOK Oersted (Oe) magnetic field using a high-sensitivity magnetic torque meter (manufactured by Toei Kogyo Co., Ltd.). Find out. the result,
As shown in the theoretical curve diagrams in Fig. 3 (4) and (B), when the easy axis component of magnetization consists only of the direction perpendicular to the particle plate surface, there is a positive peak at the rotation angle of 0 to 90°; 90-180
When the rotation angle is 0 to 90°, the curve shows a negative peak [Figure 3 (A)], and when the rotation angle is 0 to 90°, the curve shows a negative peak, and when the rotation angle is 90 to 180°, it shows a positive peak [Figure 3 (A)]. 3 (B)], and when it consists of two components in the vertical and horizontal directions, the curve shape shows complicated changes depending on the ratio of the two components, but in all cases, the curve shape shows complicated changes depending on the ratio of the two components. Since the curves show positive and negative peaks in each range, this is used for discrimination.

Incidentally, FIG. 1 is a characteristic curve showing the rotation angle-torque relationship of the magnetic powder of Example 1, and shows a characteristic that the easy magnetization axis component is substantially only in the direction perpendicular to the particle plate surface. There is. Further, FIG. 2 is a characteristic curve showing the rotation angle-torque relationship of the magnetic powder of Comparative Example 4, which shows the characteristic that the easy magnetization axis components are in two directions, vertical and horizontal.

(*) Soil indicates the vertical direction, and ri indicates the horizontal direction.

As is clear from the results in the above table, all of the magnetic powders according to the present invention (Examples 1 to 7) are hexagonal plate-shaped particles in which the axis of easy magnetization is substantially only a component perpendicular to the particle plate surface. Moreover, it has a high saturation magnetization (σS) of about 50 emu/y or more and 2,000 oersteds (
It can be seen that it has a low coercive force (Hc) of less than Oe).

On the other hand, the coercive force (Hc) of ordinary magnetoplumbite-type magnetic powder (Comparative Example 1) is extremely high, and the coercive force (Hc) of one containing only Co as a substituted component (Comparative Example 2) is low. The axis of easy magnetization changes to a horizontal component, and C
O and Ti used together as replacement components (Comparative Example 4)
In this case, the coercive force (Hc) is similarly lowered, but the axis of easy magnetization becomes two components in the vertical and horizontal directions, both of which are found to be disadvantageous. Furthermore, one in which only Sn is a substituted component (
In Comparative Example 3), the coercive force (Hc) was not sufficiently lowered and C
It is also clear that even if o and Sn are used in combination, the saturation magnetization (σS) is extremely low in the case where the amount of substitution is too large (Comparative Example 5).

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the magnetic torque curve of the magnetic powder of Example 1 according to the present invention, FIG. 2 is a characteristic diagram showing the magnetic torque curve of the magnetic powder of Comparative Example 4, and FIG. @) is a reference diagram showing theoretical magnetic torque curves when the axis of easy magnetization of the magnetic powder is only in the vertical direction and only in the horizontal direction with respect to the particle plate surface. Patent applicant: Hitachi Maxell, Ltd. Day 1+ Figure 2+

Claims (4)

[Claims] (1) AO・nFe_2O_3 (A is Ba, S
At least one type of atom selected from r, Pb, n is an integer) in a magnetoplumbite type structure, in which 25 atomic % or less of the Fe atoms are substituted with Co or Ni and Sn. Magnetic powder for magnetic recording. (2) The magnetic powder for perpendicular magnetic recording according to claim (1), wherein the coercive force is 2,000 Oe or less and the easy axis direction of the magnetization consists essentially of only a component perpendicular to the particle plate surface. (3) The magnetic powder for perpendicular magnetic recording according to claim (1) or (2), which has a saturation magnetization of 50 emu/g or more. (4) a) ferric salt; b) at least one salt selected from barium salts, strontium salts, and lead salts; c) at least one salt selected from cobalt salts and nickel salts; d) An alkali is applied to an aqueous solution containing tin salt to precipitate a hydroxide coprecipitate at a pH of 7 or above, and this hydroxide coprecipitate is washed with water and separated, and then heated and calcined at a high temperature with a flux. A method for producing magnetic powder for perpendicular magnetic recording, characterized by: