JPS61214211A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics such as video S/N ratio, color S/N ratio and erasing characteristic by using cobalt-contg. iron oxide magnetic powder having prescribed characteristics to constitute the magnetic layer on a substrate. CONSTITUTION:The cobalt-contg. magnetic powder of which the intensity ratio of Co2p/Fe2p and the intensity ratio of O<-2>1s/Fe2p measured by an X-ray spectroscopic method decrease both at a specified ratio from the particle surface toward the particle inside and the gradient of the characteristic straight line obtd. by expressing the relation between both changes by taking the intensity ratio of Co2p/Fe2p at the axis of abscissa and the intensity ratio of O<-2>1s/Fe2p at the axis or ordinate is in a 0.5-1.0 range is used as the magnetic powder to constitute the magnetic layer on the substrate. The oxide is obtd. by adding an aq. caustic soda soln. to an aq. dispersion contg. Fe2O3 and cobalt sulfate (2-4wt% Co by the total weight of the powder), depositing Co hydroxide, washing and drying the deposit and subjecting the powder to a vacuum heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape using cobalt-containing iron oxide magnetic powder as a recording element.

[Prior Art] With the demand for higher performance of magnetic recording media, many studies have been conducted on magnetic powders as recording elements.
There are a wide variety of magnetic powders currently in use. Among them, cobalt-containing iron oxide magnetic powders, such as T-Fe203, in which Co is introduced into iron oxide, have been praised for their large coercive force and excellent electromagnetic conversion characteristics (documents unknown).

[Problem that the invention seeks to solve]

However, the above cobalt-containing iron oxide magnetic powder has c.
There are various types, such as types in which o is uniformly dissolved inside the particles and types in which a cobalt oxide layer is formed on the particle surface.
The magnetic properties also vary considerably depending on the type. Therefore, in order to obtain the desired electromagnetic conversion characteristics, it is necessary to appropriately select and use a material with suitable magnetic characteristics, but this selection is not so easy, and there are Generally speaking, these magnetic powders were not satisfactory in terms of video S/N ratio, color S/N ratio, and erasing characteristics.

Therefore, the present invention aims to improve the electromagnetic conversion characteristics such as the video S/N ratio, color S/N ratio, and erasing characteristics of a magnetic recording medium using CO-containing iron oxide magnetic powder, and to improve the stable magnetic properties of these characteristics. The purpose is to provide recording media.

[Means for Solving the Problems] In the course of intensive studies to achieve the above object, the inventor first focused on the crystal structure of this type of magnetic powder, and investigated the relationship between this structure and electromagnetic conversion characteristics. After conducting a detailed study, it was found that the concentration distribution of Fe ions, Co ions, and oxygen ions from the particle surface to the inside of the particle is a major factor that influences the electromagnetic conversion characteristics.

Based on this knowledge, we repeated a wide range of experimental studies and found that in this type of magnetic powder, both Co ions and oxygen ions decrease and change from the particle surface side to the particle interior, and that both Co ions and oxygen ions decrease and change. When changes satisfy certain relationships, video S/N ratio, color S/N
The present inventors have discovered that it is possible to manufacture a magnetic recording medium that has excellent electromagnetic conversion characteristics such as ratio and d-erasure characteristics and is stable in these characteristics, and has completed the present invention.

That is, the present invention provides a magnetic recording medium in which a magnetic layer containing a cobalt-containing iron oxide magnetic powder and a binder is provided on a substrate, in which the magnetic powder contains Co2p/2 as measured by X-ray photoelectron spectroscopy. The intensity ratio of Fe 2p and [O-
2] The intensity ratio of 1s/Fezp (however, CO21) is C
o ion's 2p electron orbital strength, Fe2p is the Fe ion's 2p electron orbital strength, [0] IS is the oxygen ion's IS.
The intensity of the electron orbit) decreases at a constant rate from the particle surface toward the inside of the particle, and the relationship between these two changes is expressed as the C02p/Fe2p intensity ratio on the horizontal axis.
Magnetism characterized by using cobalt-containing iron oxide magnetic powder whose straight line slope is in the range of 0°5 to 1°0 when expressed by taking the intensity ratio of [0]18/Fe21) on the vertical axis. This relates to recording media.

[Structure and operation of the invention]

The cobalt-containing iron oxide magnetic powder used in this invention has Co2p/Fezp measured by X-ray electron spectroscopy.
The intensity ratio of [0]xs/Fe2p both decrease at a constant rate from the particle surface toward the inside of the particle. In other words, it has a particle structure in which the amount of carbon meon and the amount of oxygen ions decrease at a constant rate from the particle surface toward the inside of the particle.

Therefore, the above-mentioned magnetic powder is made of the conventional general-purpose T-Fe.
20. , which is essentially different from the type in which Co is uniformly dissolved inside the powder. On the other hand, the conventional general-purpose T-F
It is thought that the type of e203 powder in which a cobalt oxide layer is formed on the particle surface has a particle structure similar to that of the present invention, since it is thought that a part of Co enters into the inside of the particle during the manufacturing process. It is presumed that some of them existed.

However, the above-mentioned cobalt-containing iron oxide magnetic powder according to the present invention has Co2p/
It is also a major feature that the change in Fe2p and the change in [0. There are no reports of such cases.

That is, in this invention, the relationship between the above two changes is plotted as C02p/C02p on the horizontal axis, as shown in FIG. 1 and FIG.
When the intensity ratio of Fe2p is expressed by taking the intensity ratio of [0]/Fe21) on the vertical axis, the slope of the straight line is 0°5 to 1.
It is important to use a cobalt-containing iron oxide magnetic powder in the range of 0.0, particularly preferably in the range of 0.6 to 0.8, and this only improves the video S/N ratio and the color S/N ratio. It has now become possible to obtain a magnetic recording medium that has excellent electromagnetic conversion characteristics such as ratio and erasure characteristics and has stable these characteristics.

Furthermore, the reason why the conventional cobalt-containing iron oxide magnetic powder was inferior in the above-mentioned properties is that even if this powder had a particle structure similar to that of the present invention, the slope of the above-mentioned straight line was within the above-mentioned range. In other words, it can be said that it was less than 0.5 or more than 1.0.

In the present invention, there are no limitations on the method for obtaining such specific cobalt-containing iron oxide magnetic powder. One method is to disperse iron oxide magnetic powder in an aqueous solution containing a cobalt salt or a ferrous salt dissolved therein, and then add an alkali to this to coat the surface of the powder with cobalt hydroxide.

Or a method of precipitating this and ferrous hydroxide and then heat-treating the powder, the properties of the iron oxide magnetic powder as the powder to be treated and the conditions of the heat treatment are selected, for example, the powder to be treated is The purity of the heat treatment is 60~1s0.
It is easy to obtain the cobalt-containing iron oxide magnetic powder according to the present invention under gentle conditions of about 60 to 180 minutes at ℃.

The iron oxide magnetic powder as the powder to be treated is particularly preferably made of T-Fe203 from the viewpoint of erasing properties.
Further, from the viewpoint of electromagnetic conversion characteristics, it is preferable that the powder be an acicular powder with an average major axis diameter of 0.1 to 0.5 μ and an average axial ratio (average major axis diameter/average minor axis diameter) of 7 or more. The cobalt content in this powder can be appropriately selected depending on the desired coercive force, but is generally preferably 2 to 6 parts by weight per 100 parts by weight of the powder to be treated.

In the magnetic recording medium of the present invention, a magnetic paint containing the above-mentioned cobalt-containing iron oxide magnetic powder and a binder is prepared, this is applied onto a substrate such as a polyester film, and then the required treatment such as calendering is carried out. It can be obtained by applying

As the above-mentioned binder, any of the conventionally known binders may be used, such as resins such as vinyl chloride-vinyl acetate copolymers, polyurethane resins, polyvinyl butyral resins, cellulose resins, and polyester resins, and crosslinking agents such as polyisocyanate compounds. is also available.

In addition, dispersants, lubricants,
It goes without saying that various conventionally used additives such as abrasives and antistatic agents may be included.

[Effects of the Invention] As described above, in this invention, by using the specific cobalt-containing iron oxide magnetic powder as a recording element, video S/N ratio, force 5-5/N ratio, erasing characteristics, etc. It is possible to provide a magnetic recording medium with improved electromagnetic conversion characteristics and stable characteristics.

[Examples] Below, examples of the present invention will be described in more detail. In addition, in the following, parts shall mean parts by weight. Further, cobalt-containing iron oxide magnetic powders A-D and A' to D used in the following Examples and Comparative Examples were obtained by the following method.

<Cobalt-containing iron oxide magnetic powder A-D) T-Fe203 powder as the powder to be treated and cobalt sulfate in a ratio such that the amount of cobalt contained in this powder after treatment is 2 to 3 parts per 100 parts of the above powder. An aqueous dispersion containing the above was prepared and maintained at 45±0.5°C, and the amount of [OH]- was 2 mol/1! After adding caustic soda corresponding to the above and stirring and mixing well to precipitate cobalt hydroxide, the mixture was washed with water and dried, and then subjected to vacuum heat treatment at 1s0±0.5°C for 3 hours.

In this method, T-Fe20 as the powder to be treated is
3 powder, the specific surface area by nitrogen adsorption method is 35 to 50.
rrf/? range, average axial ratio is in the range of 8 to 11, saturation magnetization is in the range of 70 to 71 emu/y, coercive force is in the range of 290
Cobalt-containing iron oxide magnetic powders A to D having the magnetic properties shown in Table 1 below were prepared by using four types of acicular T-Fe203 powders in the range of ~310 oersted and different impurity contents such as sulfur content. I got it.

<Cobalt-containing iron oxide magnetic powder A' to D'> T-Fe203 powder as the powder to be treated, and the amount of cobalt contained in this powder after treatment is 3 to 4 parts per 100 parts of the above powder.
An aqueous dispersion containing cobalt sulfate in a proportion of 1.5% and ferrous sulfate in an amount of 7.8% by weight as Fe2+ ions was prepared, and this was maintained at 45 ± 0.5°C, and [OH] −
Add caustic soda corresponding to Te 2-T-/I// 1, stir well and mix to co-precipitate cobalt hydroxide and ferrous hydroxide, wash with water and dry, then add 1s0±0
．． Vacuum heat treatment was performed at 5°C.

In this method, T-Fe203 as the powder to be treated
Cobalt-containing iron oxide magnetic powders A' to D' having the magnetic properties shown in Table 1 below were prepared by using the same four kinds of acicular T-Fe203 powders as in the powders A to D as powders.
I got it.

<Measurement of the particle structure of the above powders A-D and X2> A portion of each powder obtained by the above method was taken, and 5 tons/a
The pellets were molded into pellets with a diameter of 10 m and a thickness of 0.5 to 1 mm. This is carried out using an X-ray photoelectron spectrometer (VG).
After mounting on an ESCA-5 manufactured by Co., Ltd., it was irradiated with MgKOL X-rays equivalent to 300 W, and the intensity of each electron orbit of Fe2p, Co2p, and [O]1s was measured. Next, 5
Argon ions were irradiated at a rate of 1 pA/d at an accelerating voltage of KV, and the sample surface was sputtered (etched) for 30, 60, and 90 minutes, and the intensity of each electron trajectory was measured at each time in the same manner as above. It was measured. That is, each of the above-mentioned intensities from the particle surface side to the inside of the particle was measured using this method.

Figures 1 and 2 show the intensity ratio of Co2p/Fezp and [o-2]ls/ after each time from the above measurement values.
The intensity ratio of F e 21) was determined and plotted with the former on the horizontal axis and the latter on the vertical axis. Symbol A- in the figure
D and A'-D' are the types of magnetic powder A-D and A
' to D'. The slope of the straight line showing the relationship between the two intensity ratios thus determined was as shown in Table 1 below.

Table 1 Example 1 Cobalt-containing iron oxide magnetic powder A 250 parts Carbon black 12 parts Granular α-iron oxide 10 parts Nitrified cotton 22 parts Polyurethane resin 19 parts Trifunctional low molecular weight incyanate compound 7 parts Cyclohexanone 340 parts Truen
340 parts n-butyl stearate
3 parts liquid paraffin 2 parts myristic acid 2 parts A magnetic paint was prepared according to the above formulation by thoroughly dispersing and mixing in a ball mill. Apply this paint to a dry thickness of 5 pn on a 14 pn thick polyester film.
After coating and drying, the magnetic tape of the present invention was subjected to surface treatment and slit to a predetermined width.

Examples 2 to 4 Cobalt-containing iron oxide magnetic powder B (Example 2), A' (Example 3), and B' (Example 4) were used in the same amount in place of cobalt-containing iron oxide magnetic powder. A three-cover magnetic tape of the present invention was obtained in the same manner as in Example 1 except for the following.

Comparative Examples 1 to 4 Instead of cobalt-containing iron oxide magnetic powder A, cobalt-containing iron oxide magnetic powder C (Comparative Example 1), D (Comparative Example 2), C
Four types of magnetic tapes for comparison were produced in the same manner as in Example 1, except that the same amounts of ' (Comparative Example 3) and D' (Comparative Example 4) were used.

The video S/N ratio, color S/N ratio, and erasing characteristics of each of the magnetic tapes of Examples 1 to 4 and Comparative Examples 1 to 4 were measured using the methods below. The results are shown in Table 2 below. It was as shown.

<Video S/N ratio> A VTR 50% white signal was recorded and reproduced, the noise component of the video signal portion was measured, the video S/N ratio was determined, and the value is expressed as a relative value with respect to the reference tape.

Color S/N Ratio Using a VTR, record and play back the one-color chroma signal from a color video noise measuring device, measure the AM noise, and calculate the color S/N ratio.
The N ratio was calculated and expressed as a relative value to the reference tape.

Erasing characteristics> An IKHz audio signal was recorded in saturation, and the difference was expressed as the difference in the reproduction level of the IKHz signal before and after erasing the same location.

Table 2 As is clear from the above results, the magnetic tape of the present invention is excellent in all of the video S/N ratio, color S/N ratio, and erasing characteristics.

[Brief explanation of drawings]

Figure 1 shows CO21)/Fe2p for cobalt-containing iron oxide magnetic powders according to Examples 1 and 2 and Comparative Examples 1 and 2.
The intensity ratio of

[0] Characteristic diagram showing the relationship with the strength ratio of IS/Fe2p, Figure 2 shows the same relationship as in Figure 1 above for the cobalt-containing iron oxide magnetic powders of Examples 3 and 4 and Comparative Examples 3 and 4. FIG.

Claims (1)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing cobalt-containing iron oxide magnetic powder and a binder is provided on a substrate, Co as the magnetic powder is measured by X-ray photoelectron spectroscopy.
_2/Fe_2p intensity ratio and [O^-^2]_1s/F
e_2p intensity ratio (where Co_2p is the intensity of the _2p electron orbit of Co ions, and Fe_2p is the intensity of _2p electron orbits of Fe ions.
The intensity of the p-electron orbital ([O^-^2]_1s is the intensity of the _1s electron orbit of oxygen ions) decreases at a constant rate from the particle surface toward the inside of the particle, and both of these changes occur. Co_2p/Fe_
The intensity ratio of 2p is plotted on the vertical axis as [O^-^2]_1s/Fe_
The slope of the straight line when expressed by taking the intensity ratio of 2p is 0.
A magnetic recording medium characterized by using cobalt-containing iron oxide magnetic powder having a cobalt content in the range of 5 to 1.0.