JPS58199726A - Manufacture of cobalt modified ferromagnetic iron oxide - Google Patents

Abstract

PURPOSE:To manufacture ferromagnetic iron oxide for magnetic recording with high transfer characteristics and high saturation magnetizability by heat treating gamma-Fe2O3 at a specified temp. and by modifying it with Co. CONSTITUTION:In the manufacture of Co modified ferromagnetic iron oxide by modifying ferromagnetic gamma-Fe2O3 particles with Co combined optionally with one or more among Fe<2+>, Fe<3+>, Ni<2+>, Zn<2+>, Cu<2+>, Al<3+>, Mn<2+> and Mg<2+>, the fer romagnetic gamma-Fe2O3 is heat treated at a temp. by 200 deg.C below the critical temp. to a temp. by 30 deg.C above the critical temp. prior to the Co modification. The critical temp. of ferromagnetic gamma-Fe2O3 is defined as a heat treatment temp. at which partial transition from the gamma-FE2O3 to alpha-Fe2O3 is caused and the saturation magnetizability is reduced to 99% of the original value before heat treatment. Thus, ferromagnetic iron oxide for magnetic recording with superior magnetic characteristics, especially high transfer characteristics and high saturation magnetizability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ferromagnetic iron oxide, and more particularly to a method for producing ferromagnetic iron oxide for magnetic recording, which has excellent magnetic properties, particularly high transfer properties and high saturation magnetization (σS). Iron oxide production method.

In recent years, more′? A magnetic recording medium with a density of R, is required. The characteristics of a magnetic material that satisfies this requirement are that it has a high Pj magnetic force (Hc), a high saturation magnetization (σS), and that the magnetic material itself has low noise.

In order to achieve the above conditions, conventional methods have been proposed. For example, in order to obtain a high consolation power (Hc),
Widely used methods include a method of increasing the acicular specific sound of α-Fo00H, which is a raw material for magnetic iron oxide, a method of firing without destroying the acicular nature, and a method of incorporating magnetic iron oxide ICCo.

-The most effective way to reduce the noise of the magnetic material itself is to make the magnetic material particles into fine particles. However, as the particles become smaller, the magnetization unit becomes smaller and the magnetization becomes thermally unstable.At the same time, the transfer characteristics (8/P) when used as a magnetic tape become worse. Become. Figure 1 is a graph showing the relationship between crystallite size and transfer characteristics.
Cobalt-modified iron oxide (Of:l) obtained by conventional technology
In i), the transfer characteristics (S/P) worsened as the crystallite size decreased, and it was impossible to exceed the limit shown by the broken line.

Furthermore, by making the magnetic material fine particles, the saturation distribution (σ
There is also the disadvantage that S) is low).

Conventionally, a method for producing divine cobalt-modified highly abrasive iron oxide has been known.

枦-+': 15 method of solid dissolving copal in iron oxide, US fiJ patent 3. //No. 7,933, Special Public Shogu-6
No. 331, JP Sho≠8-10/j Tata No., Glaze Sho Geter San 26v, Sho μ/-277/ri (corresponding patent: U.S. Patent No. 3.!73.De10), Sho Da Zaichi/j7!
RI No., Special Public Sholl-10 Tata No. 4A, U.S. Patent No. 3.4
7/, μ3j issue, and Tokuko Sho μ2-61/3. When magnetic recording bodies are created using cobalt-containing iron oxide obtained by these methods, these magnetic recording bodies are unstable to pressure and heating;
It had the disadvantage that the recorded magnetic haiku name was weakened, and the transfer was greatly reduced by 1 degree. )□ The second method is to use cobalt! (There is a method of depositing a cobalt compound, cobalt ferrite layer tube, or growing it on many surfaces of magnetic iron oxide powder that is not solid solution. !0-374
No. 47, JP18T.

-376z1, Tokuko Shobi Tari 2hiro 7! , Tokukai Showa Cter 10r! Tata, No. 70-774≦7, PlrO-
No. 37461, No. 10-12074, Same! λ-! ≠2
No. 7, same λ-! Mairi No. 1, same jj-/Kotali reference,
West German patent 1t (OL8) λ.

01,312, etc.

The magnetic iron oxide powder obtained by these methods is more stable against pressure and heating than that obtained by dissolving it in cobalt, and has a high resistance to transfer. Although many improvements were made in the properties, it was still not possible to achieve anything better than the broken grapes shown in Figure 1 mentioned above.

Conventionally, γ-F e 20 S used for cobalt modification is
Usually 17) r-Fe203 (!: Similarly, (1) a-F
e00Hf300~700' (dehydrated with a-Fe2
0 m, and (2) further 300 m in a reducing gas atmosphere.
- Reduce with oo 0c to F e 304, (3)
This is then generally oxidized at a low temperature of about 5200 to 300'C to obtain ferromagnetic r -Fe 203 f.

Here, in the oxidation step of *i, the temperature is 200 to 300°C.
This relatively low WAt is used because if the complete oxidation is carried out at higher temperatures, part of r-Fe203 will irreversibly transfer to non-extractable stable α-Fe203 and the magnetism will decrease. This is because it is generally believed that

The present inventors have conducted extensive research to break down the relationship between the above-mentioned transfer characteristics and the particle size of the magnetic material, and as a result, the γ-F
In this method of cobalt modification using e2θs1r raw material, first, rFezO3f is heat-treated in advance,
It has been found that by modifying such a bond with cobalt, its transferred properties are significantly the same as those described above.

That is, in the present invention, in step (3), γ-
This method is characterized in that Fe 203 is heat treated at a higher WA degree than the conventional oxidation temperature and then subjected to cobalt modification.

This heat treatment ranges from -0°C to +10'( :, (preferably -100"C to +O@C
). When the heat treatment temperature is very low, there is almost no effect, and when the heat treatment temperature is high,
The improvement effect of transfer is saturated, but σS is significantly reduced.

Figure 2 shows the relationship between the heat treatment temperature, the saturation magnetization (σS) of the obtained fcr-Fe20B, and the transferred physical properties of the ferromagnetic iron oxide obtained by modifying this as a raw material with cobalt. Saturation canning (σ3) increases as the temperature increases,
Critical temperature -100" (:, or critical temperature -S OoC
However, when treated at a higher temperature, it begins to drop, and at the critical rIA degree it falls below σsl before the heat treatment. The transfer characteristics improve as the processing temperature increases, and the critical rj7A
It becomes more noticeable than #-tooC. When the critical temperature is reached, it becomes a value, and even if the temperature #Lt is avoided, the vIt
It does not change.

The critical temperature has a large relationship with the α transition temperature of r-Fe20a. Further, since r-Fe20B is a metastable substance, the transition temperature f to α-Fe203 varies depending on the raw materials, manufacturing method, purity, etc.

Furthermore, even if the same r-Fetus is used, the a degree at which it transitions will vary depending on the temperature increase rate and holding time. Therefore, in carrying out the present invention, the critical mf must be determined according to the temperature increase rate, holding time, and other heating conditions during heat treatment.6 Also, the critical temperature fl r −F e 2
There is a strong relationship with the transition temperature from 03 to a-Fe203, and since the transition from r-Fe203 to α-Fe203 is an exothermic reaction, the above critical rI! A# can be easily measured by differential thermal analysis (DTA) or differential blue calorimetry (D8
C) A rough estimate can be made using Q. As shown in the third prisoner, [DTA
In addition, there are two types of 1-1D8c with two exothermic peaks and one type with one exothermic peak. The transition humidity in the DTA(I)8C) measurement is determined as dRr in the figure. α-F e 203 from F e 203 when heated using a normal kiln
Critical temperature for transition to lO at FXqTA or DEC
°C/min TJjll L7 to 1111f
``''lrl shift 0-7ta 0C is so low.

The effect of improving transfer and σS by the heat treatment of the present invention is also effective for r -F e 203 such as. That is, starting material (cl -F e OOHor r-Fe00H
), firing method, r −F e 203 f) specific area, p
Regardless of the H, a transition temperature or the number of DTA peaks, the improvement by epithermal JilK is reduced. Also, r −
In addition to heat-treating 20 g of Fe804
Similar effects can be obtained even if the oxidation temperature from to r-Fe203 is carried out within the above temperature range. However, the transition temperature at this time is r obtained by 2jO'C'c oxidation in advance.
- Determined from Fe 203.

It is currently not clear why the above-mentioned magnetic properties occur due to the heat treatment in the present invention, but by heat treatment, the r -F
Since the DTA curve of e 203 becomes sharp,
It is thought that the imperfections in the crystal structure have become smaller and the magnetic coupling has become stronger.

Next, the present invention will be explained by examples. The specific surface area of the powder was determined by N2 adsorption, and the pH was determined by the J I 8-A method. Temperature increase rate 10 @C/m using transition m degree fiDTA
in 'I'll decide.

The conditions under which a powder sample was made into a tape for transfer measurement in the present invention are as follows. In addition, in the following explanation, "part"
indicates "parts by weight".

Magnetic powder 10H Hanawa Vinyl Acetate Co-Hyayabusa compound (rVAGHJ manufactured by UCC) 10 parts Polyurethane (Nitsubolanko 30/J manufactured by Nippon Polyurethane Co., Ltd.) 10＠Polyincyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 3 parts Noya Lecithin 1 part MEK
/10sMIBK
tJo part After dispersing the above raw materials in a ball mill (')I polyisocyanate is added at the end of dispersion)
, filtered, applied, applied a magnetic field, and dried. Next, after performing fc calender treatment, it was slit to a width of 3.1 mm.

The base was made of PET with a smooth surface and a thickness of 11 μm.

Transfer characteristics (・S/P) were measured as follows.

3. Incorporate the tμmμm-p into the compact cassette. After bulk erasing, a signal of 1 m is recorded at the standard input power level (according to the standard MT8-io of the Tape Industry Association). After parking this in 10"C4A for 1 hour,
After reproducing and passing the output signal through a filter with a center frequency t K Hz s bandwidth //J octave≦dB, the signal level and the output level of the transfer were measured.

The crystallite size was calculated from the crystallite size calculated from the half width of (220) djJ of the X-ray diffraction peak and the key of the (reference μO) plane, and was determined by dividing the large crystal size by half.

Regarding the magnetic properties, please refer to the vibrating sample type 1 bundle type U made by Norei Kojo Co., Ltd.
Using an 8M gate, the external S magnetic field was constant at jKO=.

Example L Goethite generated on the alkaline side is exposed to 60(1)Q in air.
C and reduced in hydrogen at 320°C.

He oxidized r-Fe2θ3 in 2IO'C in air.
I got it.

This r-F e 203 was heated at 100C/mi by DTA.
The transition temperature was examined at a heating rate of n and was found to be 67!0C. This powder jOf was put into a quartz glass retort container with one end open and the internal volume 1, and was heated to 10oDc%sso'.
c, tpoo°C, held at 6200C for 10 minutes each and measured its σS, it rose at zzoocmt and z
At oo0C, it is about /emu/f lower than the value before wire heat treatment,
At 4.2θ0C, it decreased to 504, which was before the linear heat treatment. This revealed the rate at which the critical temperature is Tata j0C. This r-F e 203 aoo'c, zoo'c%
zzo'c.

600°C, 4/toCK/r min~4'811
Heat treated.

3009 each of the obtained fcr −F e 203
was dispersed in 2 tons of water, and (iilfa! cobalt (C
oS04・7H20) 3/, 6 f dissolved in water/lK2)
- added. Nitrogen scum 0.57'/min
The mixture was vigorously stirred while being blown in with. After lO min Na(JHμ
After m9f was dissolved in 1/1 water and added, the temperature was raised while continuing to blow in 9 atoms and stirring, and the reaction was carried out for V hours while maintaining the concentration of 0CK. Obtained magnetic material tK material /-/, /-2, /-j
, l- reference, /- evening, /-6. -10,000, similarly modified with cobalt using r-Fe 203 without heat treatment. This is the total comparison sample 1. Table of characteristics of these magnetic materials/
Shown below.

Note that the raw materials γ-F e 203 n, Hc392Ck,
σs4ri, A, p)if, ! , crystallite size 30
0A1 specific surface area J o , a m /fT;

o (>c>Ofalse) It can be seen that the higher the false treatment temperature is, the better the transfer characteristics are, and the improvement is already saturated at the critical at.On the other hand, σ.

It can be seen that the temperature increases with heat treatment and then decreases again after peaking at zzo'c.

Example 2 The same goethite as that used in Example 1 was used under the same conditions as T r -F e 20 g.

The obtained r -F e 20 B B, Hc 4IO&
Ck, σ86ri, 76mu/f, specific surface area 30
,tm/f.

The crystallite size was ztoA.

This r-Fe 203 was modified with cobalt according to the example. The obtained magnetic powder is used as a sample.

EXAMPLE The same goethite used in the example was dehydrated and reduced under the same conditions. After that, it was oxidized with zzo'c (, r-Fe2
0g and 90 obtained 1t-r-Fe203 is Hc uλJ0, σS'
73.2 emu/fs pH 1, I, crystallite size 3<7A.

Using this r-Fe 203, cobalt feeding was carried out under the same conditions as in the example. The obtained nine magnetic powder is designated as Sample 3.

The characteristics of Samples 3 and 3 are shown in Table 3 together with Comparative Sample 1.

Table λ Hc ((h) 8Q as<emu/f)
Transfer dB) Sample J +6p o, rs 6
t, r zt, i sample 3 6! Ta 0.11
2 61.2 j6.7 Dan Oanba / 670
0.10 61. T! J,/heat treatment, r-
Effects on transfer and σS are observed even if the firing is continued during firing of Fe203, or even if the oxidation temperature itself is increased.

Example Hcl/40e%σs extracted from this lepidocrocite
7a, aemulfs specific surface area 3.1 m/f.

Crystal rhinoceros, <aoo^, pHj, j4', tvr-F
The gelatinization transition temperature and critical temperature of e 20 B were determined in the same manner as in Examples and were found to be 1 cta'c% 41100C.

This r - Fe 203 and reference io 'c, 1t
The sample was heat treated at o0c for 1 hour and then modified with cobalt according to the example. Comparison sample 2 and sample μ of the obtained good magnetic powder
m/, 4'-J. These characteristics are shown in i13.

Example & Nine Hc3/I (k, dB
7 J, P emu/l, specific surface area, 7 m
/f, pH 3,69, crystal size (I J OAOr-
The gelatinization transition temperature and critical i11 degrees of Fe 203 were determined in the same manner as in the example and were found to be 4tIt0C%aoo'c.

This r-F e 20 B and 370 'C, p00'
The material heat-treated with C was modified with cobalt according to the example. Comparative sample J1 of the obtained magnetic powder! -/, t-2
shall be. The characteristics are shown in *3.

To the examples, the pH value baked by the conventional method,! ,σS73,ri,
HcjJ/(h, specific surface area, 2m 7y.

The gelatinization transition temperature and critical a degree of r -F e 203 with crystal size μlOA were determined in Example 1. The temperature was determined in the same manner as above, and it was found to be 6hiro2°C%17!0C.

This r −F e 2θ3 and this at 170°C5z3
After heat treatment at 0°C for 1 hour, the sample was modified with cobalt according to Example 1. The obtained magnetic powder was compared with sample μ,
Samples 4-/, 6-2. Table 3 shows the characteristics of these magnetic powders.
Shown below.

Table 3 HC ((k) a@(emv'y) 4(dB)
Sample μ-/Aμ2 73.0 12.2μm2
431 73.1! 1, 10 73. / 1t, Z sample tar/jrit ≦! ,0! ? , 7j-ko
401 7 pieces, 4 I&, / comparative sample J 40λ 72. Q Haden? Sample, g-76317, 7 40.76-2
≦qko 73.3 j7.0 comparative sample Hiroshi 61,0 7J, 7! J, r sample 7-
/6334ri,ko j9.17-24,072,
Ko ! II, 3 comparative sample j 630
7/# j7. jFrom the characteristics of the samples and comparative samples shown in Table 3, regardless of the specific surface area, crystallite size, pH1 transition temperature, and critical temperature of r-F e 203, the crystal form of hydrated iron and its production. Even if the conditions are acidic or alkaline, r
It can be seen that by heat-treating -F 62 Q 3, the transfer of copal if properties is significantly improved.

Example 7 Hc327 obtained from goethite produced on the acidic side
(k, a S 7 j , Oemu/fq ratio!! Area 2
The gelatinization transition temperature and critical temperature of r-F e 203 of 3.3ml 1t% pH 3, r, large crystallite size OA were determined in the same manner as in the example, and heated at 44A3°C and 114oC.

This r-Fe20g and this z6o”c, zlθ0C
The rFe2O3 obtained by heat treatment for 1 hour in Example 1. It was modified with cobalt using the method shown in . A comparison sample of the obtained magnetic powder! , Sample 7-/, 7-J. Table 3 shows the properties of these magnetic powders.

Example a r-Fe203 used in Example t and its temperature at 600°C
The r -F e 20 B annealed for 7 hours was modified with cobalt in the following manner.

Cobalt chain acid (Co5O4m7H20) J/ in water λt.

At is dissolved and r-Fe 103 JOOf is dispersed therein. While stirring strongly, add NaOH/74f to water.
Add the dissolved material to the solution, and then raise the temperature to zOc. Here, ferric oxalate (Fe2(leak)4)3.7820)
/ j, tf dissolved in water/l is 14 d 7
It was added over 1 hour at a rate of min. After the addition, heating and stirring were continued for another 3 hours, and after reacting for a total of 3 hours, the mixture was washed with water, dehydrated, and dried.

The obtained magnetic powder is referred to as a comparative sample 4% sample 1.

The characteristics are shown in Table 1.

Practical meeting.

f-Fe20B used in the example and this too”0
．． The r -Fe 2031fC annealed for 1 hour was modified with cobalt in the following manner.

Disperse 1 oot of water x Ycr-Fe20B into this, blow nitrogen gas at 0 Jl/min and stir vigorously.
, 6fs** Ferrous (Fe3O47H20) If I
A solution of f mixed with water o and zlK was added. After 10 minutes, a solution of NaOH/girt in water was added and the temperature was raised. After being kept at TanaoC for one hour, it was washed with cold water and dried. The nine magnetic powders obtained were designated as comparative sample 7 and sample sample. The characteristics were shown to Omotehiro.

Example 1a Magnetic material was obtained under the same conditions as Example 1.
Heat treatment was performed for zo0Cλ time. The obtained magnetic bodies are respectively referred to as a comparative sample and a 1% sample io. Characteristic t-Il! See below.

Example 11゜Actual Th? IJQ is a sample of a fresh air atmosphere in which a magnetic material was obtained under the same conditions, and is referred to as sample //. The characteristics are shown in the table.

Table reference transfer (dB) Sample 1 22.3 Comparative sample t! Hiro, O sample ta j! ,! \ Comparative sample 7 j/, J Sample 10 j! , 7 Comparative sample 1 j/, J sample // j7.3 Comparative sample P ri, as shown in Table V, was subjected to r-Fe2031 heat treatment, postmortem, cobalt denaturation, and untreated. It is clear that the transfer is better than when the cobalt is directly modified.

[Brief explanation of drawings]

Fifth? , 60 is a graph showing the relationship between crystallite size and transfer properties of FJA2O3.
203, and Δ is this γ-F e 203
Figure 2 shows the characteristics of r-F e 203 which has been extensively treated according to the present invention. FIG. 2 is a graph showing the relationship between the processing temperature when heat-treating r-Fe 203, the saturation magnetization (σS), and the transfer characteristic (SP) when it is modified with cobalt. Figure 3 shows differential thermal analysis (DTA) of r-F e 203.
FIG. 2 is a schematic diagram showing the relationship between temperature and heat generation cost when analyzed in . FIG. V is a schematic diagram of the DTA curves of rFe203f: before and after the heat treatment according to the present invention. All before heat treatment and B are DTA curves after heat treatment. Patent Applicant Fuji Photo Film Co., Ltd. Procedural Amendments Commissioner of the Patent Office 4 1. Indication of Case 1981 Patent Application No. rotoi
No. 2, Name of issue (q) Manufacturing method of cobalt-modified ferromagnetic iron oxide 3, Relationship with the case of the person making the amendment % Applicant Address Kanagawa Onnanjingara i'1rTl' Swamp 210-4, Subject of amendment Details Column 5 of “Detailed Description of the Invention” and “Brief Description of Drawings” of the Book, Contents of Amendment (1) “Description” in line 1 on page 3 of the specification of the present application is amended to “described”. (2) ``Oxidation degree area'' on page 1, line 3 of the same book is corrected to ``specific surface area.'' (3) ``Oxidation temperature'' on page 1, line 7 of the same book is corrected to ``oxidation.'' (4) Box of the same book. Correct page r, line 0, rTJ to “de”. (5) Change “crystal size” to “crystal size” in page 10 of the same book, line //, line 1 from the bottom of page 1!, and line l1 of page 16. (6) The same book, page 23, line 1 (temperature) is corrected to “temperature”. (7) The same book, page 23, line 10, “calorific value” is corrected to “calorific value”.

Claims (1)

[Claims] Ferromagnetic γ-F e 203 particles Kecobalt and optionally Fe++, Fe+1+, Ni++, Zn++, C
n++. In the method for producing cobalt-modified ferromagnetic toughened iron which is f-characterized with Al++, Mn juice, Mg++ or a mixture, γ-Fe2 (part of J3 becomes α-Fe203) ferromagnetic γ-F at a temperature between -200 and +30 °C with respect to the critical m degree defined by the heat treatment a degree where the saturation magnetization decreases evenly.
A method for producing cobalt-modified ferromagnetic iron oxide, which is characterized by heat-treating the cobalt-modified ferromagnetic iron oxide.