JPH0430504A - Manufacture of magnetic particle powder for magnetic recording use - Google Patents

Abstract

PURPOSE:To obtain magnetic particle powder of high saturation magnetization value, excellent dispersibility, and low transmissivity by agitating and mixing a mixture suspension of a specific Co-deposited type acicular gamma-Fe2O3 particle powder and acicular CrO2 particle powder with a solution of a compound containing one or more two kinds or more of specific metals and by filtering and drying the mixture after adjustment at pH 6.0-9.0. CONSTITUTION:A powder of Co-deposited type acicular gamma-Fe2O3 particle with a BET specific surface area of 30 m<2>/g or more and a powder of acicular CrO2 particle powder with a BET specific surface area of 20 m<2>/g or more at a proportion of 5-100 wt% are dispersed in water into a mixture suspension of 3.0-10.0 wt%. This is loaded with an aqueous solution of a compound containing one or two or more kinds of metals selected from among Al, Si, Sn, Ba, Ca, Sr, Mg, Zn, Zr, Ni, and Mn to agitate and mix and then adjusted at ph 6.0-9.0 by addition with an acid or alkali solution. Next, the mixture suspension is filtered out and dried, every particle surface of the gamma-Fe2O3 particles and CrO2 particles is coated with a hydride or an oxide containing one or two or more kinds of the above-mentioned metals, thereby providing s magnetic particle powder consisting of Co-deposited acicular gamma-Fe2O3 particles and acicular CrO2 particles.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a Co-coated material having a high saturation magnetization value, excellent dispersibility, and low light transmittance, which is suitable as a magnetic particle powder for high-density recording. This is a method for producing magnetic particle powder consisting of a mixture of acicular 7-Fe2O3 particles and acicular CrO2 particles.

[Prior Art] In recent years, as magnetic recording/reproducing equipment and the like have become smaller and lighter, demands for higher performance and higher density recording of magnetic recording media such as magnetic tapes and magnetic disks have been increasing.

For example, on pages 185 to 187 of "Magnetic Recording Media Comprehensive Collection" (1985) published by Sogo Denshi Research, "...
...Recent technological innovations in magnetic tape have been remarkable...
- Efforts are being made to increase recording density. That is, whether it is audio equipment, video equipment, or floppy disk drives, emphasis has been placed on miniaturization, weight reduction, and ease of operation based on high-density, short-wavelength recording technology. ...In the fall of 1981, high-grade (HG) type video tapes using fine magnetic powder were introduced.
...As a future development for higher image quality, ultrafine magnetic iron oxide powder is used on the tape side...a dramatic improvement in image quality is expected. As stated in "...", even in recent years, there is no end to the demand for finer particles of magnetic particles.

-4. Since video equipment usually employs a mechanism that detects the end of a running tape using light, malfunctions may occur if the light transmittance of the video tape used becomes high. However, as the Co-coated γ-F+g03 particles, which are presently abundant and used in video tapes, become finer, the light transmittance increases.

Attempts have been made to improve light transmittance by adding a large amount of non-magnetic filler such as carbon black, but use of non-magnetic material such as carbon black hinders high-density recording.

In order to improve the light transmittance without using a non-magnetic material such as a carbon blank, ferromagnetic acicular CrO□ particle powder is
As a prior art in which o-containing 7-Fe2O1 particles are mixed with powder and used in video tapes, for example, Japanese Patent Application Laid-Open No. 61-9
Technical means disclosed in Japanese Patent Application Laid-Open No. 1988-132230 and the like can be cited.

[Problems to be Solved by the Invention] The above-mentioned Japanese Patent Application Laid-Open No. 61-919 discloses a technical means using a mixture of iron oxide magnetic powder and chromium oxide magnetic powder. It is stated that there is a problem with using only chromium oxide magnetic powder, so a considerable amount of carbon black is still required.

Also, in the aforementioned Japanese Patent Application Laid-Open No. 62-132230, CO-
Although a technical means using a mixture consisting of γFezes particles and Cr(h particles) is disclosed, in the same publication,
``...The poor dispersibility of Cr02 particles can be reduced by CO-γ-F.
Cor-Fe2O. It is said that the particles compensate for the poor dispersibility of CrO□ particles. However, as stated on page 189 of the above-mentioned document, [...Generally, when magnetic powder becomes fine, it becomes difficult to disperse in the binder, it is difficult to make the coating film highly filled, and there are problems with smoothing the surface of the coating film and durability. The tape manufacturing technology is considered to be the most important issue. ...As can be seen from the description J, Co-
Even if the 1-Fe2Oy particles are made into fine particles, their dispersibility will decrease. Therefore, even if the light transmittance is improved, the dispersibility is still insufficient.

In view of the above-mentioned prior art, the present invention provides a Co-coated acicular needle having a high saturation magnetization value, excellent dispersibility, and low light transmittance.
The technical problem is to establish a technical means capable of obtaining magnetic particle powder consisting of a mixture of Fe203 particles and acicular CrO□ particles.

[Means for Solving the Problems] The present inventor has arrived at the present invention as a result of various studies regarding the above-mentioned technical problems.

That is, the present invention provides CO-adhered acicular -Fe2O3 particles having a BET specific surface area of 30rd/g or more and the γ-Fe2
BET in a proportion of 5-100% by weight relative to O3 particle powder
Acicular CrO□ particles having a specific surface area of 20 nf/g or more are dispersed in water to form a mixed suspension of 3.0 to 10.0% by weight, and A1.5iSSn, Ba, and C are added to the mixed suspension.
a5Sr, -g, Zn, Zr.

A compound containing one or more metals selected from N1 and Mn is added in the form of an aqueous solution, stirred and mixed, and then an acid or alkali aqueous solution is added to adjust the pH to 6.0 to 90. Coating the surface of each of the 7-Peg'3 particles and the CrO2 particles with a hydroxide or oxide containing one or more of the metals by distributing the mixed suspension from door to door and drying it. This is a method for producing magnetic particles for magnetic recording comprising a mixture of Co-coated acicular 7-Fe2O3 particles and acicular CrO2 particles.

[Function] Co-coated acicular 7-Fe2O3 particle powder is described in "Powder and Powder Metallurgy," (1980) Vol. 27, No. 1, Page 1, published by the Powder and Powder Metallurgy Association. When γ-Fe2O3 particles are subjected to a heating reaction in a highly alkaline solution containing Co" and Fe", the coercive force increases significantly, and magnetic powder of type 2) is obtained. As described in "A product in which an oxide containing cobalt is formed on the surface of iron oxide)", the particles are alkaline because they are produced in a highly alkaline solution, and the particles are alkaline in an acidic solution. Co on the surface is eluted and the magnetic properties are also deteriorated.

In addition, acicular CrO□ particle powder is
Publication No. 7, column 4, pages 9 to 12: ``Chromium dioxide (CrOx) is stable in an acidic region, but becomes active in an alkaline region, so when it reacts in an alkaline solution, chromium dioxide (CrOx) ) exhibits acidity, as indicated by the statement, "First, some of the particles begin to dissolve from the surface...".

On the other hand, regarding the case of dispersing magnetic particles in a binder, see lines 6-7 on page 122 of "Powder Surface Modification Technology Collection" published by Chubu Soft Giken (1981).
・γ-Pe203, Co doped or coated γ-Fe2
03. Understand the tendency of metal particles to be easily dispersed in what kind of solvent and binder system.

As stated in ``...'', when using a mixture of two or more types of magnetic particles, the properties of the particle surface of each particle must be considered.

The present inventor has found from a number of experimental results that when using a mixture of Co-coated acicular 7-Fe2O3 particles whose particle surface is alkaline and acicular CrO□ particle powder whose particle surface is acidic, By dispersing each particle powder in the same water to make a mixed suspension and coating the surface of each particle with the same metal compound, it has a high saturation magnetization value, excellent dispersibility, and low light transmittance. It has been found that a particulate powder can be obtained.

The present inventor discovered that by coating the same metal compound at the same time, the surface of each particle of each magnetic particle powder is the same and uniformly charged with the same amount, so that the dispersion into the binder becomes uniform and the dispersibility improves. I believe that we were able to increase this.

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

In the present invention, Co-coated 7-Fe, O, particle powder having a BET specific surface area of 30 n(/g or more) can be used, but it is more preferably 35 to 10 rd/g.
When it is less than 0rtT/g, since the hiding power is large, the light transmittance is low even without mixing acicular Cry and particulate powder, so malfunctions due to light transmission do not occur. If it exceeds 70rd/g, dispersion becomes extremely difficult and it is difficult to obtain sufficient dispersibility.

The Co-coated acicular 7-Fe, O, particle powder used in the present invention is obtained by thoroughly dispersing ordinary acicular γ-Peg'3 particle powder in water to form an aqueous suspension, and adding a cobalt salt compound to the aqueous suspension. and a ferrous salt compound are added in the form of aqueous solutions, and stirred well. By adding an alkaline aqueous solution to this to cause a neutralization reaction, heating the liquid temperature to 50 to 100'C, and stirring well, Co is added to the particle surface of the γ-Fezes particles.
After the reaction is completed, the magnetic layer containing the
Obtained by drying and grinding.

In the present invention, acicular CrO2 particle powder having a BET specific surface area of 20 m/g or more can be used, but it is more preferably 30 to 50 rrf/g. 20m2/g
If the particle diameter is less than 1, it is not preferable because noise will occur due to the large particle diameter when used as a magnetic recording medium. 50rrf
/g, dispersion becomes extremely difficult and it is difficult to obtain sufficient dispersibility.

As the acicular CrO□ particles used in the present invention, CrO□ obtained by hydrothermal treatment in which chromium trioxide is placed in an autoclave and heated can be used. Additives such as sb, F, Ru, etc. to control coercive force if necessary.
Elements such as Mn and Fe may also be used.

In the present invention, the acicular Cry2 particle powder is Co-coated acicular 7-Fe2O, and the particle powder is 5 to 100 jir.
1%, more preferably 10 to 50% by weight.

If it is less than 5% by weight, the effect of reducing light transmittance is insufficient. If it exceeds 100%, the dispersibility deteriorates and it is difficult to obtain sufficient dispersibility.

The concentration of the aqueous mixed suspension in the present invention is 3.0 to 10
．． It is 0% by weight. If the amount is less than 3.0%, the coating metal compound will not be sufficiently deposited, and there will be little economic benefit. If it exceeds 10.0% by weight, it becomes difficult to coat the metal compound uniformly, which is not preferable.

In the present invention, ^1, Si, Sn, Ba, C
a, a compound containing one or more metals selected from Sr, Mg, Zn, Zr, Ni, and Mn.
The particle surfaces of the deposited acicular 1-Fe2O° particles and the acicular CrO□ particles are coated.

The metal compounds used in the present invention include A1,
Ammonium salts, sodium salts, potassium salts, etc. of Sl, Sn, Ba, Ca, Sr, and group G can be used. Among them, when ammonium salts are used, no alkali salt remains on the particle surface after drying. Therefore, it is preferable.

These compounds in the alkaline region are precipitated and coated on the surface of each particle by adding an acidic aqueous solution and performing PL (fil) adjustment.

Also, A1. , Zn, Zr, Ni, Mn and Sn
Compounds such as acetate, chloride, sulfate, and nitrate can be used, and among them, acetate is preferred because no acid salt remains on the particle surface after drying.

These compounds in the acidic region are precipitated and coated on the surface of each particle by adjusting the pH by adding an alkaline aqueous solution.

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

In addition, when using two or more types of metal compounds to be coated, the order of addition may be either first or simultaneously.

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 7-Fe2O3 particles and the acicular CrO□ particles.

If it is less than 0.05% by weight, the treatment effect will be difficult to show and high dispersibility will not be obtained. If it exceeds 6% by weight, the content of the nonmagnetic material increases, resulting in a decrease in the saturation magnetization value, and there is no economic advantage.

In the present invention, the pH when coating the particle surface with the above-mentioned metal compound is 6.0 to 9.0. If the pH is less than 6.0, it is undesirable because it is too biased toward the acidic side, inhibiting the precipitation of metal compounds, and in particular, Co on the surface of the Co-coated acicular-FezOz particles is eluted.

If the pH exceeds 9.0, it is undesirable because it is too alkaline, inhibiting the precipitation of metal compounds, and particularly causing Cr to be eluted from the surface of the acicular CrO□ particles.

In the present invention, as the aqueous solution for adjusting the pH, an acidic aqueous solution such as acetic acid, hydrochloric acid, or sulfuric acid is used for a compound in an alkaline region. In addition, for compounds in the acidic region, NHaOtl, NaOH1KOH, Na
An alkaline aqueous solution such as zCO= can be used. In addition, acetic acid, N)1. It is preferable to use each aqueous solution of OH because it does not remain as a salt on the surface of the particles after drying.

[Example] Next, the present invention will be explained in detail with reference to Examples and Comparative Examples.

In addition, the major axis diameter of the particles in the following examples and comparative examples,
The axial ratio (major axis diameter/minor axis diameter) was expressed as an average value of values measured from electron micrographs.

Also, Al, Si, Sn, 7. n, Zr, N
The contents of i, Mn and Co are shown as values measured by fluorescent X-ray analysis.

The magnetic properties are as follows: “Vibrating sample magnetometer VSM-35-15 (
The measurement was carried out by applying an external magnetic field up to 10 KOe using a "Toei Kogyo ■". The light transmittance of the magnetic sheet was expressed as a linear absorption coefficient measured using a photoelectric spectrophotometer UV-2100 (manufactured by Shimadzu Corporation). The linear absorption coefficient is defined by the following formula, and the larger the value, the more difficult it is for light to pass through.

Linear absorption coefficient <um −') = 42n (1/l)/F
TL: Light transmittance at λ-900 nm (-) FT: Thickness of magnetic layer of film used for measurement (μm) Example I Co-coated acicular 7-Fe201 particle powder (major axis diameter 0.2
0μ lock, axial ratio (major axis diameter/minor axis diameter) 6.0, BET specific surface area 40, Onf/g, Co 4. ht%, coercive force 84
00e, pH 8°5) and acicular CrO2 particle powder (major axis diameter 0.25 μm, axial ratio (major axis diameter/minor axis diameter) 80,
BET specific surface area 34.1d1g, coercive cuff 400e,
pH 3,0) 20g (Cr (the amount of h is γ-Fe
It corresponds to 25-t% with respect to 2O3. ) was suspended in 11 water.

Add a sodium silicate aqueous solution (No. 3 water glass) to the above suspension.
3.46g (manufactured by Tokuyama Soda ■) (Si
O□ corresponds to 1.0wt% in summer. ), and after dispersion mixing, add an acetic acid aqueous solution and adjust the pH to 7.0 to precipitate a silicon compound on the surface of each of the 7-Fe103 particles and CrO□ particles, and then heat in a furnace by a conventional method. Separately, it was dried to obtain a mixed particle powder.

The amount of silicon compound present on the surface of the obtained mixed particle powder was 1.0 wt% in terms of SiO□, and the coercive force was 825.
0e, and the saturation magnetization value was 75.8 emu/g.

Examples 2 to 11, Comparative Examples 1 to 6 Type and mixing ratio of particles to be treated, type and amount of coating compound added, and p)! Various coated mixed magnetic particle powders were obtained in the same manner as in Example 1, except that the type of regulator and p)I were varied.

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

<Manufacture of magnetic sheet> Using the treated mixed magnetic particle powders obtained in Examples 1 to 11 and Comparative Examples 1 to 6, the following components were placed in a sand grind mill containing Ims glass beads as a dispersion medium in the following proportions. After that, the magnetic paint prepared by mixing and dispersing for 6 hours was applied to a 14μ thick PET film to a thickness of 50μ using an applicator, then oriented using a 2000 Gauss magnet, and dried. A sheet sample piece was obtained by doing this.

Mixed magnetic particle powder to be treated 100.0 parts by weight Vinyl chloride vinyl acetate copolymer compound (manufactured by UCARMAG-527UCC> 1
6.0 Polyurethane resin (TI-1075 manufactured by Sanyo Chemical) 8.0 8
Dispersant (GAFACRE-610 manufactured by Toho Chemical) 4.0 Cyclohexanone 99.6 〃Methyl ethyl ketone 99.6 〃Toluene
Table 1 shows the coercive force, squareness ratio, degree of orientation, and light transmittance (linear absorption coefficient) measured for each of the sheet sample pieces obtained.

[Effects of the Invention] As shown in the above examples, the mixed magnetic particles according to the present invention have a high saturation magnetization value, excellent dispersibility, and optical i3
Since it is a magnetic particle powder with a low magnetic flux rate, it is suitable as a particle powder for high-density recording, which is currently most required. According to this patent, excellent effects can be obtained as magnetic particles used in video tapes.

Furthermore, since the particle surfaces of the powder particles are coated with the same metal compound, the bond with the resin used in the magnetic recording medium is strong, and a video tape with good durability can be obtained.

Claims (1)

[Claims] 1. Co-coated acicular γ-Fe_2O_3 particle powder with a BET specific surface area of 30 m^2/g or more and the γ-Fe_2O_
A mixed suspension of 3.0 to 10.0 weight % of 3.0 to 10.0 weight % of acicular CrO_2 particle powder with a BET specific surface area of 20 m^2/g or more is dispersed in water at a ratio of 5 to 100 weight % to the 3 particle powder. liquid, and the mixed suspension contains Al, Si, Sn, Ba, Ca.
, Sr, Mg, Zn, Zr, Ni, and Mn, a compound containing one or more metals selected from the group consisting of , Sr, Mg, Zn, Zr, Ni, and Mn is added in the form of an aqueous solution, stirred and mixed, and then an acid or alkali aqueous solution is added to adjust the pH to 6.0. The γ-Fe_
Co-adhered acicular γ-Fe_2 characterized in that each particle surface of the 2O_3 particles and the CrO_2 particles is coated with a hydroxide or oxide containing one or more of the above metals.
A method for producing magnetic particles for magnetic recording comprising a mixture of O_3 particles and acicular CrO_2 particles.