JPH01294221A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording tape having an excellent orientation characteristic by reducing SiO2-contg. iron oxide in an atmosphere of hydrogen, etc., to convert the same to acicular magnetic metal iron, mixing the same with a binder and coating the mixture on a substrate. CONSTITUTION:The alkaline aq. slurry of the acicular hydrous iron oxide or acicular iron oxide is prepd. by using said iron oxide as a starting material and water soluble silicate is mixed with this slurry and is subjected to a heat treatment at and under a suitable temp. and pressure in a hermetic vessel such as autoclave; thereafter, the mixture is rinsed, separated and dried to form the SiO2-contg. iron oxide. The excellent acicular metal iron is obtd. by reducing such iron oxide. The metal iron is coated on the substrate to form the magnetic tape. The high-orientation tape which cannot be attained by the conventional treatment for preventing the deformation and fusion of particles is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording tape having particularly excellent orientation in a magnetic recording medium using metallic iron-based magnetic particles.

Generally speaking, the important characteristics of magnetic powder for recording include the coercive force of the magnetic particles, the dispersibility of the particles when made into paint, and the orientation of the particles in the tape, but these are the final factors. It is well known that this is a factor that greatly influences the characteristics of recording tapes.What is directly related to these characteristics of zero particles is the shape of the particles.For example, as in ordinary recording materials, shape anisotropy If the coercive force is obtained by the properties of the particles, the coercive force will increase if the acicularity of the particles improves, and the less branching or curvature of the particles, the better the dispersibility. Since steric hindrance factors during processing are also eliminated, orientation is improved and the recording properties of the tape are improved. Therefore, when producing magnetic powder for recording, it is important to use magnetic particles with good acicularity and less branching.

In the case of metal magnetic particles, hydrated ferric oxide (mainly αFe0), which tends to grow as needle-shaped particles, is used for this purpose.
The method that is mainly adopted is to first prepare OH (goethite) and reduce it with hydrogen or the like in a gas phase to obtain acicular magnetic metal particles. In this method, the particles obtained take on the shape of the starting goethite and become skeleton particles, so it is first necessary to control the shape of the starting goethite particles. Since the movement of atoms occurs, it has the disadvantage that it tends to cause deformation of the particles and fusion of particles, and as will be explained later, this causes a limit to the orientation when oriented on a tape. The present invention has succeeded in eliminating this drawback and inventing a tape that is different from conventional tapes in terms of orientation. Details will be explained below.

The orientation of magnetic tape is the orientation of the acicular particles in the longitudinal direction of the tape, but in the case of acicular magnetic metal particles mainly made of iron, the magnetic anisotropy is ideally determined by the orientation of the acicular particles in the longitudinal direction of the tape. Since it is in the acicular direction, as the orientation of the particles in the tape increases, the residual magnetic flux density in the longitudinal direction of the tape approaches the saturation magnetic flux density, and the residual magnetic flux density in the tape width direction approaches 0. Ratio of residual magnetic flux density (Br) to saturation magnetic flux density (Bm),
That is, if the squareness ratio (B r / B m ) is measured in the longitudinal direction and the width direction of the tape, the squareness ratio (Br78m)zz in the longitudinal direction approaches 1 as the orientation increases, while the squareness ratio in the width direction approaches 1. The ratio of the squareness ratio (Br78m) in the longitudinal direction to the squareness ratio (Br78m) z/, that is, (Br
78m), 7/(Br78m) (hereinafter referred to as the degree of orientation) theoretically becomes infinitely large. From the value of the longitudinal squareness ratio (Br78m) 11 (hereinafter simply referred to as squareness ratio), the orientation in the longitudinal direction is determined, and from the degree of orientation, for example, an increase in the magnetization component in the tape width direction due to branching of acicular particles, etc. As shown in FIG. 1, it has been experimentally confirmed that the degree of orientation and the squareness ratio have a roughly constant relationship. Figure 1 shows the characteristics of known examples when metal magnetic particles are made into a tape under certain tape-making conditions, and commercially available tapes ((trade names) 3M Metafine, Sony Metallic, Fuji Super Range, Maxell MX, Ba5f Meta
The characteristics of IX) are plotted.

As can be seen from the figure, the relationship between the degree of orientation and the squareness ratio is almost linear, and the magnetic tape using these metal magnetic particles (
The degree of orientation of metal tape) is [degree of orientation] = 4.90X
[The relationship is approximated by a squareness ratio of 2.07 (correlation coefficient R=0.949).

In general, the orientation of magnetic tape is determined by the shape of the particles.
Since they vary depending on post-processing conditions, such as the method of dispersion, coating conditions, orienting magnetic field, etc., the squareness ratio and degree of orientation of the tape vary in various ways even when the same particles are used. Therefore, even if the value of the squareness ratio or the degree of orientation is specified alone, the uniqueness of the tape cannot be defined. However, when these two values are combined, it can be seen that in the conventional metal tape, the degree of orientation corresponding to a certain squareness ratio generally deviates as shown in FIG. From now on, these tapes, or the magnetic powder used in them,
It is presumed that there are common elements. Possible common factors include deviation from the acicularity of particles, branching, curvature, or fusion of particles, which can cause particles that should be magnetically uniaxial to become multiaxial. It is thought that as long as the particles are not destroyed, they remain unchanged under any dispersion or coating conditions, giving the relationship shown in Figure 1. It is thought that this multiaxial component causes the magnetization component in the width direction to always increase at a constant ratio with respect to the orientation in the longitudinal direction of the particle. are considered to be almost the same in terms of squareness ratio and degree of orientation, and exhibit a constant relationship as shown in FIG. Therefore, the above-mentioned multiaxiality in the particles can be considered as a kind of inherent property of the powder, and this also means that the tape forming conditions as post-processing conditions can be adjusted to increase the squareness ratio of the tape. This can also be said to mean that there is a limit to the degree of orientation that can be achieved no matter how you change . For the known magnetic tape shown in FIG. 1 or for the currently commercially available magnetic tape, the straight line 2 in the figure is the limit line of the degree of orientation in the above sense.

In the present invention, an alkaline aqueous slurry is made from acicular hydrated iron oxide or acicular iron oxide as a starting material, a water-soluble silicate is mixed with this slurry, and the mixture is heated in a sealed container such as an autoclave at an appropriate temperature. Hydrothermal treatment is then carried out under pressure, followed by washing with water, separation and drying to obtain 5iOz-containing iron oxide, which is then reduced according to a conventional method to obtain excellent acicular metallic iron. The feature of the method of the present invention is that 5iO
To produce Z-containing iron oxide, hydrated iron oxide or a dehydrated iron oxide starting material is impregnated with silicon under elevated pressure and temperature in a sealed container, thereby replacing the conventional simple silicon impregnation. It is possible to obtain a magnetic recording material that has much better acicularity than metallic iron obtained by reducing the SiO□-containing oxide. In this case, the pH of the starting iron oxide or hydrous iron oxide slurry is 8.
14, the silicate is 0.1 to 10% in molar ratio of SiOx to iron, and the temperature of the hydrothermal treatment is 1.
It is desirable to set it as 00-250 degreeC.

Examples will be discussed in detail later, but it has been found that the characteristics of the magnetic recording medium manufactured from acicular metal iron of the present invention essentially exceed the level of the conventional magnetic recording medium examined earlier. Ta.

Figure 2 shows the characteristics of the magnetic strip according to the present invention plotted in the same manner as in Figure 1 and compared with Figure 1.As can be seen from the figure, even with the same squareness ratio, the degree of orientation has been significantly improved, which will be discussed later. As shown in the measurement results and Table 3, it can be seen that the degree of orientation is higher by at least 0.2 (i.e. [degree of orientation]
≧4.90 This shows that the magnetic tape according to the present invention is essentially different from the conventional example in terms of the magnetic uniaxiality of the particles because there is no bending or fusion of the particles.

The straight line ◎ in the figure indicates the lowest line of the degree of orientation of the magnetic tape according to the present invention, and the degree of orientation of the present invention is all above this line, that is, [degree of orientation] ≧ 4.90X [squareness ratio] -1 ,8
It is represented by 7.

On the other hand, based on the known example shown in FIG. 1, it is clear that all magnetic tapes and commercially available tapes are below this line.

Next, the differences between the present invention and the prior art will be specifically explained.

First, the starting material αFe0OH is produced by oxidizing the precipitated hydroxide of a ferrous salt in an alkaline, neutral or acidic aqueous solution, or by producing the hydroxide of a ferric salt. A method of pressurized hydrothermal treatment of precipitates in an alkaline solution in an autoclave is known, and the former in particular is widely used as an industrial production method.By dehydrating and reducing these particles while heating them in a gas phase, metals can be Magnetic iron particles are obtained, but this process is a process in which iron microcrystals are generated and grown in the goethite particles, and if the iron powder grows rapidly, the starting goethite particles may be deformed or the particles may fuse together. This will have a negative effect on the orientation.Therefore, as a technique to prevent particle deformation and fusion, Si,
Many methods have been proposed for adding or adsorbing B, Ti, and other secondary or tertiary elements to starting particles.

Representative examples of these include JP 52-19541, JP 53-30114, JP 48-82395, JP 52-72354, JP 52-121799, JP 52-134858, JP 53 -10100 was selected, particles were created according to each example, and the results were made into a tape.
This was considered as part of a comparative example of the present invention. Furthermore, tapes currently available on the market were also used as controls for comparative examples. It can be considered that all of the prior art is represented by these. The differences between the present invention and the prior art are, firstly, that goethite is used as a starting material, which has significantly improved acicularity compared to the prior art, and secondly, this goethite has a double structure and the outer layer uniformly contains Si. This forms a goethite layer, which significantly contributes to preventing particle deformation. Thirdly, in order to create such goethite, goethite is subjected to pressurized hydrothermal treatment, which makes it difficult to prevent conventional particle deformation and adhesion prevention treatment. They succeeded in creating a highly oriented tape that was previously unattainable.

Example: 12.2 in solution II2 containing 3 mol of F e C1s
An aqueous solution containing 1 mol of NaOH at 4.5°C was added dropwise at a rate of 50 cc per minute, and the resulting ferric hydroxide precipitate was directly poured into 2
The mixture was left to mature at room temperature for 4 hours. After 24 hours, the mixture was placed in an autoclave together with the slurry mother liquor, and subjected to a hydrothermal reaction under pressure and heating at 200° C. for 2 hours. The generated slurry is referred to as slurry ■.

(Example 2) 5.4 g of a 20% sodium silicate solution in terms of S i 02 was added to the slurry I obtained in Example 1, stirred well, and then put into an autoclave with the mother liquor for 20 minutes.
Hydrothermal treatment was carried out at 0'C for 1 hour, followed by washing, filtration, drying and pulverization. This was reduced in an electric furnace at 450°C in a hydrogen stream for 5 hours to obtain magnetic powder. For 5 parts of the obtained magnetic powder,
A magnetic paint was prepared using 1 part of urethane resin and coated on a polyester film to a thickness of 2 to 5 μ while orienting the particles in a magnetic field, and calendered to obtain a magnetic tape. The obtained sample tape is designated as E-2.

(Example 3) In Example 2, 13.5 g of 20% sodium silicate aqueous solution was added. The sample tape obtained by carrying out all other procedures in the same manner as in Example 2 was designated as E-3.

(Example 4) 340 g of KC103 was added to the slurry I obtained in Example 1.
Aqueous solution containing 29 moles of dissolved NaOH 8.612
After adding, stir well and add 2.7 mol of FeS.
After adding 2.74 g of an aqueous solution containing O4 and stirring vigorously, 9 g of the above-mentioned 20% sodium silicate solution was added, and the mixture was subjected to pressurized hydrothermal treatment together with the mother liquor in an autoclave at 200° C. for 3 hours. Then, it was made into a tape in the same manner as in Example 2. This sample tape is designated as E-4.

(Example 5) FeSO41k added in Example 4 was set to 1 mol, and 20
% sodium silicate solution was changed to 3 g. The obtained sample tape is designated as E-5.

(Example 6) An aqueous solution containing 3 mol of FeSO4 at 10°C was mixed with IN NaO
Place in a reaction vessel containing 10°C of H aqueous solution and heat at 5°C/m
The mixture was heated to 50° C. while bubbling air in an amount of i. The resulting slurry containing goethite is referred to as Slurry II.

15 g of a 20% aqueous sodium silicate solution was added to Slurry II and stirred thoroughly, then put into an autoclave together with the mother liquor as it was, and subjected to pressure hydrothermal treatment at 160° C. for 3 hours.

Thereafter, it was made into a tape in the same manner as in Example 1. The obtained sample tape is designated as E-6.

(Comparative Example 1) 5.4 g of a 20% sodium silicate aqueous solution was added to the slurry I obtained in Example 1, stirred well, washed, filtered, dried, ground, and reduced in a condensate gas stream at 400°C for 5 hours. to obtain magnetic powder. This was made into a tape in the same manner as in the example. This is C
-1.

(Comparative Example 2) The same procedure as in Comparative Example 1 was carried out except that 13.5 g of 20% sodium silicate solution was added. This is designated as C-2.

(Comparative Example 3) 6 g of a 20% sodium silicate aqueous solution was added to Slurry II shown in Example 6, stirred thoroughly, and then washed, filtered, and dried. This was made into a tape in the same manner as Comparative Example 1. This is designated as C-3.

(Comparative Example 4) In Comparative Example 3, 15 g of 20% sodium silicate aqueous solution was added and stirred well. A tape made in the same manner as in Comparative Example 1 in other respects is referred to as C-4.

(Comparative Examples 5 to 11) Magnetic powder was obtained according to the known patent examples, and was made into a tape by the method of Example 1. Table 1 shows the relationship between sample numbers and working patent examples.

(Table 1) (Comparative Examples 12 to 17) Commercially available metal cassette tapes from various companies were measured as comparative examples. Table 2 shows the relationship with the sample number.

(Table 2) Measurement of each sample i) Method of measuring magnetic properties The sample tapes of E-1 to E-6 and C-1 to C-11 were as follows:
Cut into 6 mm width and 5 cm length (orientation direction is 5 cm),
A sample for magnetic measurement was folded three times in the length direction to a size of approximately 6 mm square. Also C-12 to 17
was cut into a length of 9 cm and folded four times to prepare a sample.

A vibrating sample magnetometer (VSM-3 model) manufactured by Toei Kogyo was used as a measuring device, and the measurement was performed at room temperature with an applied magnetic field of 50,000 e.

ii) Measurement results The measurement results are shown in Table 3. As already mentioned, the squareness ratio is the ratio of the residual magnetic flux density Br in the longitudinal direction of the tape to the maximum magnetic flux density Bm (B r / B m ), and the orientation degree is (B r / B m1tt / (B r / B m
)1 (orientation degree (obs) in Table 3).

The relationship between the two in the comparative example is plotted in FIG. The relationship between the two can be approximated by the least squares method [degree of orientation] = 4.9
0X [Square ratio 1-2.07...■ (Correlation coefficient R=0.949). (Line A in Figure 1.2) Table-3
The degree of orientation calculated using the formula 0 above the squareness ratio is shown as the degree of orientation (Cal), and the difference from the degree of orientation (obs) is shown as the degree of Δ orientation. It is clear that the degree of Δ orientation is 0.2 or more in all Examples. FIG. 2 also shows the relationship between the degree of orientation and the squareness ratio in Examples. Therefore, it can be seen that the degree of orientation of the magnetic tape of the example shown in FIG. 2 has the relationship shown by the following formula (% formula %) (FIG. 2, straight line C).

1ii) The Mössbauer resonance absorption spectrum of the sample tape was measured using the measuring instrument due to the Mössbauer effect. All the spectra had six absorption lines represented by E-3 in FIG. 3, and completely matched the spectra of standard metallic iron thin films, confirming that they were composed of metallic iron.

iv) Measurement of electromagnetic properties of magnetic tape In order to investigate the relationship between orientation effects and tape properties, the video properties of the tape were measured using a rotating drum of VH8 type with a diameter of 62 mm.

The measurement samples and results are shown in Table 4. The head used was made by Sendust and had a gap of 0.3 μm and a track width of 20 μm.

As input signals, f,=5.4MHz (Y signal) and ft+=629KHz (C signal) are superimposed, and VH
Recorded in S standard. The playback output of the Y signal and C signal is
Table 4 shows out and C-out.

These reproduction outputs are shown in FIGS. 4 and 5 as dependence on the coercive force of the medium. As can be seen from the figure, the characteristics in the example are improved for the same coercive force. In the case of Yout, the improvement in characteristics is thought to be due to increased uniformity due to the particles being aligned in a bundle in the medium. On the other hand, Cout has a small coercive force because the input level is low (the smaller the Br, the better the characteristics generally are).

Therefore, as shown in FIG. 5, the output per Br increases as the coercive force is lower, but it can be seen that the example is also improved in this case.

It is thought that the improvement in the degree of orientation efficiently enhances the effect as Br.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between squareness ratio and degree of orientation in a conventional magnetic tape, FIG. 2 is a graph simultaneously showing the relationship shown in FIG. 1 and a similar relationship in the magnetic tape according to the present invention, and FIG. is a graph of the magnetic powder of the present invention, FIG. 4 is a graph showing the relationship between magnetic tape coercive force and output Y output, and FIG. 5 is a graph showing the relationship between magnetic tape coercive force and C output. 55-; (Sr78m)++ A Br/8m) orientation diagram (Br/Bm stone/(Br/8m)L, i!l self direction ke)←
reason

Claims (1)

[Claims] 1. Prepare an alkaline aqueous slurry using acicular hydrated iron oxide or acicular iron oxide as a starting material, mix water-soluble silicate with this slurry, and seal the autoclave etc. Hydrothermal treatment is carried out under elevated temperature and pressure in a vessel, and the treated slurry is then dehydrated and dried to form Si.
A method for producing a magnetic recording medium, which consists of making O_2-containing iron oxide, converting it into needle-shaped magnetic metal iron by reducing it in an atmosphere such as hydrogen, mixing this with a binder and coating it on a substrate. . 2. In the manufacturing method described in item 2 above, the pH of the aqueous slurry is 8 to 14, and the amount of silicate added is 0.1 with respect to iron.
~10 mol%, the temperature of the hydrothermal reaction is 100~250°C,
A method for manufacturing a magnetic recording medium, wherein the hydrothermal reaction time is 5 minutes or more.