JPH03201214A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve the orientation property and output of a medium by applying a magnetic coating material containing Co-contg. iron oxide powder having specified BET specific surface area, orienting the coating layer with specifying the ratio of longitudinal squareness ratio to the transverse squareness ratio. CONSTITUTION:The Co-contg. iron oxide powder has 45 - 55 m<2>/g BET specfic surface area and is covered with a Co ferrite layer as the surface layer. This Co-contg. iron oxide power is mixed and dispersed with a binder resin, org. solvent and other necessary components to prepare the magnetic coating material, and then applied to a substrate by an arbitrary method. Then the coating film if oriented by use of a continuous orienting machine equiped with two or more pairs of magnets. Good orientation can be obtained since magnetic repulsion among particles can be enough suppressed, so that high orientation with >=3.5 ratio of the longitudinal squareness ratio to the transverse squareness ratio can be realized. By this method, good orientation and higher output can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium using fine particles of cobalt-containing iron oxide magnetic powder as magnetic powder and a method for manufacturing the same, and more specifically, to a magnetic recording medium suitable for high-density recording. The present invention relates to a magnetic recording medium having fine particles of cobalt-containing iron oxide magnetic powder with good orientation and excellent electrical properties, and a method for manufacturing the same.

[Conventional technology]

In recent years, the recording density of magnetic recording media has increased, and the magnetic powder used has become increasingly finer. Especially in video tapes, etc., which use fine particles of cobalt-containing iron oxide magnetic powder, the BET ratio has increased. Surface area is 40n
A cobalt-containing iron oxide magnetic powder finely divided into particles of f/g or more is used. (Unexamined Japanese Patent Publication No. 63-102036)
[Problems to be Solved by the Invention] However, although this type of cobalt-containing iron oxide magnetic powder improves the recording density as the particles become finer, it has the property that orientation becomes difficult due to mutual magnetic repulsion. If a material having a BET specific surface area of 40 nf/g or more is used, there is a problem that the orientation deteriorates, the output decreases, and good electromagnetic conversion characteristics cannot be obtained.

[Means to solve the problem]

This invention was made as a result of intensive studies in view of the current situation, and it was found that a BET specific surface area of 45 to 55 nm was formed on the substrate.
A magnetic paint containing a cobalt-containing iron oxide magnetic powder having a cobalt ferrite layer on the surface layer is applied at f/g, and then the above-mentioned cobalt-containing iron oxide magnetic powder is applied using a continuous alignment treatment device equipped with two or more pairs of magnets. By orienting
Sit ) / (Br/Bs) is set to 3.5 or more, and fine particles of cobalt-containing iron oxide magnetic powder are well oriented to improve output, reduce noise, and improve the electrical performance of magnetic recording media. It has sufficiently improved characteristics.

The cobalt-containing iron oxide magnetic powder used in this invention is B
A cobalt-containing iron oxide magnetic powder having an ET specific surface area of 45 to 55 rrf/g and a cobalt ferrite layer on the surface layer is preferably used. If the provided orientation treatment device is used, it is not possible to suppress the magnetic repulsion between the particles, and deterioration of the orientation is inevitable.
When the particles are oriented using a continuous alignment processing apparatus equipped with a pair or more of magnets, the magnetic repulsion between the particles is sufficiently suppressed and the particles are oriented well. Therefore, the longitudinal squareness ratio B r
/ B s tt and the ratio of the widthwise squareness ratio Br/BSA (Br/B s n )/(Br/B s
A high orientation of 3.5 or more can be easily obtained. In addition, this type of fine-particle cobalt-containing iron oxide powder has a high saturation magnetization, and since the fine-particle cobalt-containing iron oxide powder with a high saturation magnetization is highly oriented, the output is dramatically improved and noise is reduced. As a result, the electrical characteristics are sufficiently improved.

On the other hand, when the BET specific surface area is smaller than 45 rrr/g or larger than 55 rrrf/g, the effect of magnetic field orientation cannot be obtained sufficiently, so a continuous alignment treatment device equipped with two or more pairs of magnets is required. Even if the orientation is made using
Ratio of r/Bs (B r / B s ■) / (
B r /B sh ) cannot be made to be 3.5 or more, and high orientation cannot be achieved.

In addition, even if a cobalt-containing iron oxide magnetic powder with a BET specific surface area of 45 to 55 rrf/g and a cobalt ferrite layer on the surface layer is used and oriented using a continuous alignment treatment device, the squareness ratio in the longitudinal direction Br/ Bs, and the squareness ratio B in the width direction
Ratio of r/Bs at (Br/Bs at)
/ (B r / B S A ) smaller than 3.5, a sufficiently high orientation cannot be obtained and the output cannot be sufficiently improved. By adjusting the orientation processing device, the squareness ratio B in the longitudinal direction can be adjusted.
It is preferable to orient so that the ratio between r/Bs■ and the squareness ratio in the width direction (Br/Bs, t)/(Br/BS) is 3.5 or more. ,
As a continuous alignment processing device used for such alignment processing, for example, one equipped with two or more solenoids or one equipped with two or more pairs of permanent magnets is used, and the alignment processing conditions are as follows: A magnetic field strength of about three times the coercive force of the magnetic powder is preferably used, but it may be larger or smaller than this; if it is larger, fewer magnets are needed, and if it is smaller, the number of magnets can be increased. be.

In this way, the BET specific surface area is 45 to 55rrf/
The cobalt-containing iron oxide magnetic powder having a cobalt ferrite layer on the surface layer is subjected to orientation treatment using a continuous orientation treatment apparatus in g.
Longitudinal squareness ratio B r /B s .

and the squareness ratio Br/Bs in the width direction (Br/Bsn)
/ (Br/Bs) is 3.5 or more magnetic recording media obtained by forming a magnetic layer has a coercive force in the longitudinal direction for compatibility with recording and reproducing devices used such as 5-VHS video systems. is preferably 900 Oe or more.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, if the BET specific surface area is 45 to
Cobalt-containing iron oxide magnetic powder having a cobalt ferrite layer on the surface layer at 55rrf/g is mixed and dispersed with a binder resin, an organic solvent, and other necessary components to prepare a magnetic paint, and this magnetic paint is applied to a polyester film or the like. The cobalt-containing iron oxide magnetic powder is applied onto the substrate by any means such as spraying or roll coating, and then the cobalt-containing iron oxide magnetic powder is applied using a continuous alignment treatment device equipped with two or more pairs of magnets.
The ratio of the squareness ratio B r / B s n in the longitudinal direction to the squareness ratio B r / B S in the width direction (B r / B
s,/)/(Br/Bs,) is 3.5 or more, and then dried.

Examples of binder resins used here include vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, polyurethane resins, polyester resins, isocyanate compounds, etc., which have traditionally been used for magnetic recording media. Binder resins commonly used are widely used.

Further, as the organic solvent, organic solvents commonly used for magnetic recording media such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, ethyl acetate, tetrahydrofuran, dioxane, toluene, and xylene are used alone or in a mixture of two or more kinds. .

Note that various commonly used additives such as dispersants, lubricants, fillers, antistatic agents, etc. may be optionally added to the magnetic coating material.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Co-containing y-Fe having 100 parts by weight of cobalt ferrite layer in the surface layer.

03 powder (BET specific surface area 50 po/g, coercive force 800 Elsterado) VAGH (manufactured by U, C, C, vinyl chloride 11.25-vinyl acetate-vinyl alcohol copolymer) N-2309 (Nippon Boliureta 10 .0 Polyurethane resin (manufactured by Nippon Kogyo Co., Ltd.) Coronae) L (Nippon Polyurethane Co., Ltd. 3.75) α-AIltOs powder 6.0 (Average particle size 0.2 μm) Carbon black 0.5” myristic acid 1.0〃cyclohexanone
150 Toluene 15
0 This composition was mixed and dispersed to prepare a magnetic paint, this magnetic paint was applied onto a 14 μm thick polyester base film, and while this was in an undried state, 8 solenoids were arranged. The material was aligned using a continuous alignment device with a magnetic field strength of 3000 G in the longitudinal direction, dried, and then calendered to form a magnetic layer with a dry thickness of 4 μm. After that, they were cut to the specified width and made into video tapes.

Example 2 In the composition of the magnetic paint in Example 1, Co-containing 7-Fe having a cobalt ferrite layer on the surface layer with a BET specific surface area of 50rd/g and a coercive force of 800 oersteds was used.
z0=Instead of powder, BET specific surface area is 45rrf/g
A videotape was made in the same manner as in Example 1, except that the same amount of Co-containing 7-Fez0 powder having a cobalt ferrite layer on the surface layer and having a coercive force of 800 oersted was used.

Example 3 In the composition of the magnetic paint in Example 1, Co-containing 7-F having a cobalt ferrite layer on the surface layer has a BET specific surface area of 50 rrf/g and a coercive force of 800 oersteds.
e, O, in place of powder, BET specific surface area is 55rrf/
A videotape was made in the same manner as in Example 1, except that the same amount of Co-containing 7-FezOs powder having a cobalt ferrite layer on the surface layer and having a coercive force of 800 oersted was used.

Comparative Example 1 In the composition of the magnetic paint in Example 1, Co-containing 1-Fe having a cobalt ferrite layer on the surface layer has a BET specific surface area of 50rd/g and a coercive force of 800 Oe.
, O, in place of powder, BET specific surface area is 40rrf/g
A videotape was made in the same manner as in Example 1, except that the same amount of Co-containing 7-Fe 03 powder having a cobalt ferrite layer on the surface layer and having a coercive force of 800 oersted was used.

Comparative Example 2 In the orientation treatment of the magnetic paint in Example 1, a conventional orientation treatment device equipped with ⊥ solenoids was used instead of the continuous orientation treatment device, and the magnetic field strength in the longitudinal direction was 3000 G.
A videotape was produced in the same manner as in Example 1, except that the orientation treatment was carried out.

Comparative Example 3 In the orientation treatment of the magnetic paint in Example 2, a conventional orientation treatment device equipped with ⊥ solenoids was used instead of the continuous orientation treatment device, and the magnetic field strength in the longitudinal direction was 3000 G.
A videotape was produced in the same manner as in Example 2, except that the orientation treatment was carried out.

Comparative Example 4 In the orientation treatment of the magnetic paint in Example 3, a conventional orientation treatment device equipped with ⊥ solenoids was used instead of the continuous orientation treatment device, and the magnetic field strength in the longitudinal direction was 3000 G.
A videotape was produced in the same manner as in Example 3, except that the orientation treatment was carried out.

Comparative Example 5 In the orientation treatment of the magnetic paint in Comparative Example 1, a conventional orientation treatment device equipped with ⊥ solenoids was used instead of the continuous orientation treatment device, and the magnetic field strength in the longitudinal direction was 3000 G.
A videotape was produced in the same manner as in Comparative Example 1, except that the orientation treatment was carried out.

The RF output and chroma output were measured for the videotapes obtained in each Example and Comparative Example. The RF and chroma outputs connect the resulting videotape to a 5-VHS
It was measured using a video deck according to the standard evaluation method for 5-VHS video tapes.

Table 1 below shows the results.

Table 1 Also, in Example 1 and Comparative Example 2, Co-containing -Fe, O, powders having a cobalt ferrite layer on the surface layer were used with various BET specific surface areas ranging from 40 to 55rd/g. Example 1 and Comparative Example 2
A large number of videotapes were made in the same manner. and,
The longitudinal squareness ratio B r of these many videotapes
/ B s ■ and the squareness ratio in the width direction B r / B s , and the ratio of these squareness ratios (B r / B s ,
t)/(Br/Bsd) was calculated. FIG. 1 shows this result in a graph. From this graph, it can be seen that the larger the BET specific surface area of a videotape obtained by orientation processing using a conventional orientation processing apparatus, the lower the longitudinal squareness ratio Br/B. s H and width direction squareness ratio Br/Bs
The ratio (Br/Bs)/(Br/Bs) decreases and the orientation deteriorates significantly, but the orientation of the videotape obtained by orientation processing using a continuous orientation processing device is significantly improved. In particular, Co-containing 1-F having a BET specific surface area of 45 to 55 rrr/g and a cobalt ferrite layer on the surface layer.
e, 0. When using powder, the longitudinal squareness ratio B r
/ B s ■ and the squareness ratio in the width direction Br / B s
Yoto ratio (B r/B s 77) / (B r/
It can be seen that a videotape with a BS of 3.5 or higher can be obtained.

〔Effect of the invention〕

As is clear from the above Table 1 and FIG. The squareness ratio B r / B s ■ and the squareness ratio B in the width direction
Ratio of r/B S (B r/B S n)
/(Br/Bs) is high when it is 3.5 or more, and the RF output and chroma output are also high. Therefore, the magnetic recording medium obtained by this invention has a BET specific surface area of 45 to 5.
It can be seen that the cobalt-containing iron oxide magnetic powder having a cobalt ferrite layer on the surface layer at 5rrf/g has good orientation, high output, and excellent electrical properties.

[Brief explanation of drawings]

FIG. 1 shows the ratio of the squareness ratio in the longitudinal direction (Br/Bs) and the squareness ratio in the width direction (Br/Bs) of the video tapes obtained in each Example and Comparative Example. ■
) / (Br/B s) and BE of cobalt-containing iron oxide magnetic powder having a cobalt ferrite layer on the surface layer.
It is a relationship diagram with T specific surface area.

Claims (1)

[Claims] 1. Cobalt-containing iron oxide magnetic powder having a BET specific surface area of 45 to 55 m^2/g and a cobalt ferrite layer on the surface layer is contained in the magnetic layer, and the longitudinal squareness ratio Br/ B
The ratio between s_■ and the squareness ratio Br/Bs_⊥ in the width direction (Br/
A magnetic recording medium 2 characterized in that Bs_■)/(Br/Bs_⊥) is 3.5 or more, a magnetic recording medium 3 according to claim 1 having a coercive force in the longitudinal direction of 900 Oe or more, on a substrate. , BET specific surface area is 45 to 55 m^2/g
Then, a magnetic paint containing cobalt-containing iron oxide magnetic powder having a cobalt ferrite layer on the surface layer is applied, and then the cobalt-containing iron oxide magnetic powder is orientated using a continuous alignment processing device equipped with two or more pairs of magnets. After drying, the squareness ratio in the longitudinal direction Br/Bs_■ and the squareness ratio in the width direction Br/Bs
A method for producing a magnetic recording medium characterized by forming a magnetic layer having a ratio of (Br/Bs_■)/(Br/Bs_⊥) to _⊥ of 3.5 or more.