JP2906075B2 - Manufacturing method of magnetic particle powder for magnetic recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is suitable as a magnetic particle powder for high density recording,
This is a method for producing magnetic particle powder comprising a mixture of Co-coated acicular γ-Fe ₂ O ₃ particles and acicular CrO ₂ particles having a high saturation magnetization value, excellent dispersibility, and low light transmittance. .

[Conventional technology]

In recent years, as the size and weight of magnetic recording / reproducing devices and the like have been reduced, the demand for higher performance and higher density recording of magnetic recording media such as magnetic tapes and magnetic disks has been increasing.

For example, “Electronic Research Research,“ Magnetic Recording Media Comprehensive Data Book ”(Showa 60), pp. 185-187,“… Recent technological innovations in magnetic tapes are remarkable, and… In other words, audio equipment, video equipment, and floppy disk drives can be made smaller, lighter,
Emphasis has been placed on ease of operation. … High-grade (HG) type using fine-particle magnetic powder in the fall of 1982 for video tape …… Ultra-fine magnetic iron oxide powder was used on the tape side in the future to develop higher image quality… …
Dramatic improvements in image quality are expected. ...... ", there is no end to the demand for finer magnetic particles even in recent years.

On the other hand, video equipment usually employs a mechanism for detecting the end of a running tape with light, so that a malfunction occurs when the light transmittance of a video tape used increases.
However, there is a problem in that the light transmittance increases as the Co-coated γ-Fe ₂ O ₃ particles, which are currently most frequently used for video tapes, become finer.

Attempts have been made to improve the light transmittance by adding a large amount of non-magnetic filler such as carbon black. However, when a non-magnetic material such as carbon black is used, high-density recording is hindered.

Prior to the use in a video tape by mixing the acicular CrO ₂ particles of Co-containing γ-Fe ₂ O ₃ particles as the ferromagnetic to improve the light transmittance without using the non-magnetic material such as carbon black Examples of the technique include technical means disclosed in JP-A-61-919 and JP-A-62-132230.

[Problems to be solved by the invention]

Japanese Patent Application Laid-Open No. 61-919 discloses a technical means using a mixture of an iron oxide-based magnetic powder and a chromium oxide-based magnetic powder. Therefore, it is described that a considerable amount of carbon black is still required.

Further, in the above-mentioned Japanese Patent Application Laid-Open No. 62-132230, Co-γ-Fe ₂ O
_{Although a} technical means using a mixture of ₃ particles and CrO ₂ particles is disclosed, the same publication discloses that `` ‥‥ The poor dispersibility of CrO ₂ particles is used in combination with Co-γ-Fe ₂ O ₃ particles. As described in ‥‥, C-γ-Fe ₂ O ₃ particles
It is said to compensate for the poor dispersibility of the rO ₂ particles. However, when the magnetic powder is finer in general, it is difficult to disperse in the binder, it is difficult to highly fill the coating film, and there is a problem in smoothing and durability of the coating film surface. It is the most important issue in the tape manufacturing technology.
Dispersibility decreases when even -fe ₂ O ₃ particles are micronized. Therefore, even if the light transmittance is improved,
Dispersibility is still inadequate.

In view of the above prior art, the present invention has a high saturation magnetization value,
Co-coated needle-like γ- with excellent dispersibility and low light transmittance
A technical object is to establish a technical means capable of obtaining a magnetic particle powder composed of a mixture of Fe ₂ O ₃ particles and acicular CrO ₂ particles.

[Means for Solving the Problems] The present inventor has arrived at the present invention as a result of various studies on the aforementioned technical problems.

That is, the present invention provides a Co-coated acicular γ-Fe ₂ O ₃ particle powder having a BET specific surface area of 30 to 70 m ² / g and 5 to 100% by weight based on the γ-Fe ₂ O ₃ particle powder. BET specific surface area of 20-50 m ² / g needle shape
The CrO ₂ particle powder is dispersed in water to form a mixed suspension of 3.0 to 10.0% by weight, and the mixed suspension is mixed with Al, Si, Sn, Ba, Ca, S
r, Mg, Zn, Zr, a compound containing at least one metal selected from Ni and Mn is added in the form of an aqueous solution and stirred and mixed. 9.0
Then, the mixed suspension is separated and stirred to form a surface of each of the γ-Fe ₂ O ₃ particles and the CrO ₂ particles with water containing one or more of the metals. Co-coated needle-like γ- comprising coating with oxide or oxide
This is a method for producing magnetic particle powder for magnetic recording comprising a mixture of Fe ₂ O ₃ particles and acicular CrO ₂ particles.

[Action]

Co-coated needle-like γ-Fe ₂ O ₃ particles are described in “Powder and Powder Metallurgy” (1980), Vol. 27, No. 1
No. 1, page 1, the coercive force is significantly increased when the ‥‥ γ-Fe ₂ O ₃ particles are heated and reacted in a highly alkaline solution containing Co ²⁺ and Fe ²⁺ , and the magnetic powder of type 2) is produced. Obtained (2)
Is an oxide containing cobalt and an oxide containing cobalt formed on the surface of iron oxide), and as described above, is produced in a highly alkaline solution. Inside, Co on the surface of the particles elutes, and the magnetic properties also deteriorate.

Moreover, acicular CrO ₂ particles is of the 9-12 row column 4 JP-B-50-17197 "‥‥ chromium dioxide (CrO ₂₎ is stable in an acidic region, to activate the alkaline range Therefore, if reacted in an alkaline solution, chromium dioxide (Cr
O ₂ ) begins to partially dissolve from the particle surface.
As shown in the description of "‥", it indicates acidic.

On the other hand, in the case of dispersing the magnetic particle powder in a binder, see “Powder Surface Modification Technology Data Book” (published by Chubu Soft Giken) (Showa 57), p. 122, lines 6 to 7, “Δγ-Fe ₂
The tendency of O ₃ , Co-doped or coated γ-Fe ₂ O ₃ , metal particles, and the like in which solvent or binder system is easily dispersed is grasped. When two or more kinds of magnetic particle powders are used as a mixture as described in “‥‥”, the properties of the particle surface of each particle powder must be considered.

The inventor of the present invention has found that a mixture of a Co-coated acicular γ-Fe ₂ O ₃ particle powder whose particle surface shows alkalinity and an acicular CrO ₂ particle powder whose particle surface shows acidity from numerous experimental results is used. In, each particle powder is dispersed in the same water to form a mixed suspension,
By simultaneously coating the surface of each particle with the same metal compound, the saturation magnetization value is high and the dispersibility is excellent,
In addition, it has been found that a magnetic particle powder having a low light transmittance can be obtained.

The inventor of the present invention has found that, by simultaneously coating the same metal compound, each particle surface of each magnetic particle powder has the same and uniform charge, so that the dispersion in the binder becomes uniform and the dispersibility We think that we were able to raise.

Next, conditions for implementing the present invention will be described.

In the present invention, Co-coated γ-Fe ₂ O ₃ particles having a BET specific surface area of 30 to 70 m ² / g can be used, and more preferably 35 to 70 m ² / g. In the case of less than 30m ² / g is,
Since the hiding power is large, the light transmittance is low even without mixing the acicular CrO ₂ particle powder, so that malfunction due to light transmission does not occur.
If it exceeds 70 m ² / g, dispersion becomes extremely difficult and sufficient dispersibility is hardly obtained.

The Co-coated acicular γ-Fe ₂ O ₃ particles used in the present invention are:
Disperse ordinary needle-like γ-Fe ₂ O ₃ particles in water well,
An aqueous suspension was prepared, and a cobalt salt compound and a ferrous salt compound were added thereto in the form of aqueous solutions, followed by thorough stirring. An alkaline aqueous solution is added to this to cause a neutralization reaction,
By heating the liquid temperature to 50-100 ° C and stirring well,
A magnetic layer containing Co is formed on the surface of the γ-Fe ₂ O ₃ particles, and after the reaction is completed, it is obtained by washing with water, separating, drying and pulverizing.

In the present invention, the BET specific surface area is 20 to 50 m ² / g acicular CrO
₂ particle powder can be used, more preferably 30
~50m is a ² / g. If it is less than 20 m ² / g, noise is generated due to a large particle diameter when used as a magnetic recording medium, which is not preferable. If it exceeds 50 m ² / g, dispersion becomes extremely difficult and sufficient dispersibility is hardly obtained.

As the acicular CrO ₂ particle powder used in the present invention, CrO ₂ or the like obtained by hydrothermal treatment in which chromium trioxide is placed in an autoclave and heated can be used. If necessary, an element such as Sb, F, Ru, Mn, or Fe may be used as an additive to control the coercive force.

In the present invention, the acicular CrO ₂ particle powder is 5 to 100% by weight, more preferably 10 to 50% by weight, based on the Co-coated acicular γ-Fe ₂ O ₃ particle powder. If the amount is less than 5% by weight, the effect of reducing the light transmittance is insufficient. If it exceeds 100% by weight, the dispersibility will be poor and sufficient dispersibility will not be obtained.

The concentration of the aqueous mixed suspension in the present invention is 3.0 to 10.0.
% By weight. If the amount is less than 3.0% by weight, the metal compound to be coated is insufficiently deposited, and the economical advantage is small. If it exceeds 10.0% by weight, it is difficult to uniformly coat the metal compound to be coated, which is not preferable.

In the present invention, Al, Si, Sn, Ba, Ca, Sr, Mg, Z
A compound containing at least one metal selected from the group consisting of n, Zr, Ni, and Mn is obtained by using Co-coated acicular γ-Fe ₂ O ₃ particles and acicular CrO ₂
The surface of each particle is coated.

As the metal compound used in the present invention, Al,
Ammonium salts of Si, Sn, Ba, Ca, Sr and Mg, sodium salts, potassium salts and the like can be used, and among them, ammonium salts are preferred because alkali salts do not remain on the particle surface after drying. . For compounds in these alkaline regions, add acidic aqueous solution to adjust the pH.
By performing the adjustment, the particles are deposited and coated on the surface of each particle.

Also, Al, Zn, Zr, Ni, Mn and Sn acetate, chloride,
Compounds such as sulfates and nitrates can be used, and among them, acetates are preferable since no acid salts remain on the surface of the dried particles. The compounds in these acidic regions are added to an alkaline aqueous solution to adjust the pH, thereby precipitating and coating each particle surface.

In the present invention, the reason that each metal compound to be coated is added in the form of an aqueous solution is to uniformly coat the surface of each particle powder.

When two or more metal compounds are used, the order of addition may be either first or simultaneous.

The amount of each metal compound to be coated in the present invention is Co
The amount is 0.05 to 6% by weight, more preferably 0.1 to 3% by weight, based on the total amount of the adhered acicular γ-Fe ₂ O ₃ particles and the acicular CrO ₂ particles. If the amount is less than 0.05% by weight, the effect of the treatment is hardly exhibited, and high dispersibility cannot be obtained. When the content exceeds 6% by weight, the saturation magnetization value is decreased due to an increase in the content of the nonmagnetic material, and there is no economic merit.

In the present invention, the pH when the particle surface is coated with the above-mentioned metal compound is 6.0 to 9.0. If the pH is less than 6.0, it is too lean to the acidic side to inhibit the precipitation of metal compounds,
In particular, it is not preferable because Co on the particle surface of the Co-coated needle-like γ-Fe ₂ O ₃ particles elutes. If the pH is more than 9.0, it is not preferable because the metal compound is deviated too much to the alkaline side to inhibit the precipitation of the metal compound, and particularly, Cr elutes from the particle surface of the acicular CrO ₂ particles.

As the aqueous solution for adjusting the pH in the present invention, an acidic aqueous solution such as acetic acid, hydrochloric acid, or sulfuric acid is used for a compound in the alkaline region. For compounds in the acidic region, an alkaline aqueous solution such as NH ₄ OH, NaOH, KOH, or Na ₂ CO ₃ can be used. Incidentally, it is preferable to use aqueous solutions of acetic acid and NH ₄ OH because salts do not remain on the particle surfaces after drying.

〔Example〕

Next, the present invention will be described in detail with reference to Examples and Comparative Examples.

In addition, the major axis diameter and the axial ratio (major axis diameter / minor axis diameter) of the particles in the following Examples and Comparative Examples are all shown as average values of the numerical values measured from electron micrographs. Also, Al, Si,
The contents of Sn, Zn, Zr, Ni, Mn and Co were shown by values measured by X-ray fluorescence analysis. The magnetic properties were measured using an "oscillating sample magnetometer VSM-3S-15" (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of up to 10 KOe. The light transmittance of the magnetic sheet was represented by a linear absorption coefficient measured using a “photoelectric spectrophotometer UV-2100 (manufactured by Shimadzu Corporation)”. The linear absorption coefficient is defined by the following equation, and the larger the value, the more difficult it is to transmit light.

Linear absorption coefficient (μm ⁻¹ ) = ln (1 / t) / FT t: light transmittance at λ = 900 nm (−) FT: magnetic layer thickness of the film used for measurement (μm) Example 1 Co-coated type Acicular γ-Fe ₂ O ₃ particle powder (major axis 0.20 μm,
Axial ratio (major axis / minor axis) 6.0, BET specific surface area 40.0m ² / g, Co
80 g of 4.2 wt%, coercive force 840 Oe, pH 8.5) and acicular CrO ₂ particle powder (major axis diameter 0.25 μm, axial ratio (major axis / minor axis diameter) 8.0, BET specific surface area 34.1 m ² / g, 20 g (the amount of CrO ₂ is equivalent to 25 wt% based on γ-Fe ₂ O ₃ ) was suspended in 1 water.

3.46 g of an aqueous solution of sodium silicate (No. 3 water glass manufactured by Tokuyama Soda Co., Ltd.) was added to the above suspension (SiO ₂ was added to the particles to be treated).
It corresponds to 1.0 wt% in conversion. ) Was added and dispersed and mixed, and an aqueous acetic acid solution was added to adjust the pH to 7.0, thereby precipitating a silicon compound on the surface of each of the γ-Fe ₂ O ₃ particles and the CrO ₂ particles. Separately and dried according to the method to obtain mixed particle powder.

The amount of the silicon compound present on the surface of the obtained mixed particle powder was 1.0 wt% in terms of SiO ₂ , the coercive force was 825 Oe, and the saturation magnetization was 75.8 emu / g.

Examples 2 to 11, Comparative Examples 1 to 6 In the same manner as in Example 1 except that the type and mixing ratio of the particles to be treated, the type and amount of the coating compound, and the type and pH of the pH adjuster were variously changed. Various coating mixed magnetic particle powders were obtained.

 Table 1 shows the main manufacturing conditions and various characteristics at this time.

<Manufacture of Magnetic Sheet> Using the mixed magnetic particles to be treated obtained in Examples 1 to 11 and Comparative Examples 1 to 6, the following components were used as dispersion media.
After being placed in a sand grind mill containing 1 mm glass beads at the following ratio, the magnetic paint prepared by mixing and dispersing for 6 hours was applied on a 14 μm thick PET film to a thickness of 50 μm using an applicator, Then, 2000Ga
A sheet sample piece was obtained by orienting with a uss magnet and drying.

Powdered magnetic particles to be treated 100.0 parts by weight Vinyl chloride-vinyl acetate copolymer (UCARMAG-527 UCC) 16.0 ポ リ ウ レ タ ン Polyurethane resin (TI-1075 manufactured by Sanyo Chemical) 8.0 分散 Dispersant (GAFAC RE-610 manufactured by Toho Chemical) 4.0 〃 Cyclohexanone 99.6 メ チ ル methyl ethyl ketone 99.6 ト ル エ ン toluene 99.6 諸 Table 1 shows various properties of the coercive force, squareness ratio, degree of orientation, and light transmittance (linear absorption coefficient) measured for each of the obtained sheet sample pieces.

[Effects of the Invention] The mixed magnetic particle powder according to the present invention is a magnetic particle powder having a high saturation magnetization value, excellent dispersibility, and low light transmittance, as described in the above-described Examples. It is suitable as the most required particle powder for high density recording. In particular, excellent effects can be obtained as magnetic particle powder used as a video tape.

Further, since the particle surface of the particle powder is coated with the same metal compound, the bond with the resin used for the magnetic recording medium is strengthened, and a video tape with good durability can be obtained.

Continuation of the front page (72) Inventor Mamoru Kagaki 4-1-2, Funariminami, Naka-ku, Hiroshima City, Hiroshima Pref.

Claims (1)

(57) [Claims] 1. A. 5 to BET specific surface area relative to the Co-coated acicular γ-Fe ₂ O ₃ particles and the γ-Fe ₂ O ₃ particles as 30 to 70 m ² / g
Needle-like CrO _{2 with} a BET specific surface area of 100% by weight and a BET specific surface area of 20 to 50 m ² / g
The particle powder is dispersed in water to form a mixed suspension of 3.0 to 10.0% by weight, and Al, Si, Sn, Ba, Ca, Sr, M
g, Zn, Zr, after adding and stirring and mixing a compound containing one or more metals selected from metals selected from Ni and Mn in the form of an aqueous solution, adding an acid or alkali aqueous solution to pH 6.0 to 9.0. Then, the mixed suspension was filtered off and dried, whereby the surface of each of the γ-Fe ₂ O ₃ particles and the CrO ₂ particles was treated with water containing one or more of the metals. Co-coated acicular γ- characterized by being coated with oxide or oxide
A method for producing magnetic particle powder for magnetic recording, comprising a mixture of Fe ₂ O ₃ particles and acicular CrO ₂ particles.