JPS5857708A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium which is excellent in the dispersion of magnetic powder and the orientation and further has the good surface smoothness and erasing characteristic, by applying the ferromagnetic powder or iron oxide, wherein the diameter of the major axis, the axis ratio and the specific surface area by a BET method are specified, on a base body together with a coupling resin resulting in a magnetic recording medium wherein the coercive force is 15.9KA/m or more. CONSTITUTION:The ferromagnetic powder of iron oxide wherein the diameter of the major axis is 300nm or less, the axis ratio is 5 or less and further the specific surface area by a BET method is 40m<2>/g or less is applied on the base body together with the coupling resin resulting in the recording medium wherein the coercive force is 15.9KA/m or more. In other words, the solution of ferric chloride is added to the aqueous solution of sodium hydroxide resulting in the generation of hydrothermal reaction, and the yellow sediment which is obtained is washed in water, filtered and dried resulting in the powder of alpha-oxy iron hydroxide. Next, it is placed into an electric furnace and reduced by using H2 gas resulting in the powder of Fe3O4 and further oxidized in the air resulting in the powder of gamma-Fe2O3. Thereafter, it is dispersed into the composites of vinyl-vinyl acetate.vinyl alcohol copolymer, synchro-hexane, toluene, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and its object is to provide a magnetic layer that has excellent dispersibility and orientation of magnetic powder, low noise, and excellent surface smoothness and erasing characteristics. The object of the present invention is to provide a magnetic recording medium having the following characteristics.

Magnetic recording media usually uses magnetic powder as a binder and resin! : Both are made by coating on a substrate such as polyester film, and the magnetic powder used at this time has excellent magnetic properties, good dispersibility and orientation, low noise, and improves the surface smoothness of the magnetic layer. What is desired is something that can be used and has excellent erasing characteristics.

Traditionally, F
e, 04 powder and γ-Fe20. Magnetic iron oxide powder such as powder is widely used.

However, the magnetic iron oxide powder that has been widely used
Generally, a ferrous salt aqueous solution and an alkaline aqueous solution are mixed together.
The raw material is a-iron oxyhydroxide powder obtained by air fermentation at a temperature of 0 to 60'C, and it is reduced or obtained by the most northerly process after reduction. Although it is easy to obtain magnetic iron oxide powder with a large σ-
Not only can the magnetic properties, dispersibility, orientation, and surface smoothness of the magnetic iron oxide powder obtained in the above process not be improved, but also the noise cannot be reduced. Furthermore, after thermal reduction or thermal reduction, the specific surface area of the magnetic iron oxide powder measured by the BET method increases, and when preparing a magnetic paint, the viscosity of the magnetic paint increases due to the magnetic chemical iron powder with a large specific surface area. However, there are some drawbacks such as difficulty in preparing it properly.

The inventors discovered that the particle structure of α-iron oxyhydroxide powder greatly affects the particle structure and magnetic properties of ferromagnetic iron oxide powder obtained by reducing or oxidizing it after reduction. As a result of various studies, we added an aqueous solution containing trivalent iron ions to an equivalent amount or more of an alkaline aqueous solution at a temperature of 30°C or less, caused a reaction, and produced ferric hydroxide, which was heated to 100°C. After aging for at least 10 minutes, usually at room temperature for at least 30 minutes, a hydrothermal reaction is performed in an autoclave to obtain fine α-iron oxyhydroxide powder with a small axial ratio. When oxidized after Fi reduction, the axial ratio is small, so crystal formation is difficult to occur, and the major axis diameter is 300.
A ferromagnetic iron oxide powder with an axial ratio of 5 or less and a specific surface area of 40rrI79 or less by the BET method is obtained, and a magnetic recording medium obtained using this powder has a coercive force of 15.9.
In addition, the magnetic properties are improved at A/m or higher, and the dispersibility of the ferromagnetic iron oxide powder (tropism is good, noise is reduced, surface smoothness is improved, and the erasing property is also improved. The ferromagnetic iron oxide powder used in this invention has a major axis diameter of 300 nm.
If the axial ratio is larger than m, the noise will not decrease, and if the axial ratio is larger than 5, it will be difficult to prepare the magnetic paint, and the surface smoothness will be sufficiently improved and the longevity will be long. The following is sufficient. Practically, those having a major axis diameter of 50 to 300 nm and an axial ratio of 1.5 to 5 are preferably used. Also, for the same reason, the short axis diameter is 30
~100 nm is preferably used.

Further, the specific surface area of this ferromagnetic iron oxide powder by the BICT method is preferably 40 ttf/9 or less, because if it exceeds 40 ttf/9, the viscosity will increase during the preparation of the magnetic paint, making it difficult to make a good magnetic paint. Those having a specific surface area of 20 to 40 -/- are preferably used. Furthermore, this ferromagnetic iron oxide powder has a coercive force of 1 when applied to a substrate together with a binder resin to form a magnetic recording medium.
If it is smaller than 5.9 KA/m, sufficient magnetic properties cannot be obtained, so a coercive force of 15.9 KA/m or more is preferable, and a coercive force of 159 to 27.9 KA/m is preferable. used.

Such ferromagnetic iron oxide powder is produced by adding an aqueous solution containing trivalent iron ions to an equivalent amount or more of an alkaline aqueous solution at a temperature of 30°C or less, causing the reaction to produce ferric hydroxide, and then producing ferric hydroxide at room temperature. After aging, this water and fermented ferric iron are hydrothermally reacted in an autoclave to produce α-iron oxyhydroxide powder,
It is produced by reducing or oxidizing after reduction, and the production reaction of ferric hydroxide is carried out at low humidity below 30 degrees Celsius, and after being aged at room temperature, a hydrothermal reaction is carried out in an autoclave, so it is fine and has an axial ratio. A homogeneous α-iron oxyhydroxide powder with a small one-bite distribution is obtained, and this fine α-iron oxyhydroxide powder is reduced or oxidized after reduction to produce ferromagnetic Fe3O4 powder or Vi-folded γ-Fe20. Since it is in the form of a powder, it is possible to obtain the fine powder with a small axial ratio and a small specific surface area by the BET method, which improves dispersibility, orientation, surface smoothness, erasing characteristics, magnetic properties, etc., and reduces noise. sufficiently reduced.

The magnetic recording medium of the present invention may be produced by a conventional method, for example, by depositing the above-mentioned ferromagnetic iron oxide powder, binder resin, organic solvent, and other necessary components on a substrate such as a polyester film. The magnetic paint can also be applied using a proprietary coating method such as a P-L coater, and then dried.

As the binder 1 resin used here, conventionally widely used binder resins such as #i1 vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, polyurethane resin, and nitricellulose are widely used.

Organic solvents include toluene, methyl isobutyl ketone,
The organic solvent is appropriately selected from conventionally widely used organic solvents such as methyl ethyl ketone, cyclohexanone, tetrahydro7rane, and ethyl acetate, and these are used alone or in a mixture of two or more.

However, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

Next, embodiments of the invention will be described.

Example 1 Ferric chloride (FeCl, , 6H20H0 mol in water 3
IJ
A sodium hydroxide aqueous solution was prepared by dissolving 60 moles of sodium hydroxide in 601 moles of water, and a ferric chloride aqueous solution was added to the sodium hydroxide aqueous solution at a temperature of θ°C to obtain a brown precipitate. Next, after aging this at room temperature for 18 hours, a portion of the supernatant liquid was removed,
The remainder was placed in an eau de crepe and subjected to a hydrothermal reaction at 180°C for 1 hour.

After the reaction was completed, the yellow precipitate produced was washed with water, filtered, and dried to obtain d-iron oxyhydroxide powder.

Next, the obtained α-oxyhydride iron powder 800 was spread on a quartz board, placed in a tubular electric furnace, hydrogen gas was passed through at a rate of 517 minutes, and reduced at 300°C. teFe,
04 powder was obtained and further oxidized in air at a temperature of 250°C to obtain r-Fe20. A powder was obtained. Friend gained
For Fe, O, powder, the major axis diameter is 120 nm and the minor axis diameter is 30 nm.
The specific surface area according to the BET method is 32 with an am s axial ratio of 4.0.
．． It was 1 tri/9.

Also, coercive force (Hc) Ifi 19.9 KA/m
-C1 square shape (dr/σS) was 0.4. Thus, the obtained γ-Fe20. Using powder, r-Fe205 powder 80 parts by weight VA
GH (US [manufactured by fU, C, C, chloride 11 vinyl-acetate-vinyl alcohol copolymer] Bandex T-5250 (manufactured by Oguchi 7I Hon Ink Co., Ltd., urethane elastomer) Coronate Shikoku Nippon Polyurethane 21 Kogyo Co., Ltd. A magnetic paint was prepared by mixing and dispersing a composition consisting of 60 l of cyclohexanone and 60 l of toluene for 72 hours in a ball mill. This magnetic paint was applied onto a polyester paste film having a Q of 12 μm to a dry thickness of 4 μm, dried, surface treated, and then cut to a predetermined width r to produce a magnetic tape.

Example 2 Example IK The same procedure as in Example 1 was carried out except that the temperature when adding the ferric chloride aqueous solution to the sodium hydroxide aqueous solution was 10°C, and the major axis diameter was 200 nm and the minor axis diameter was 50 nm.
s-axis ratio 4.0, specific surface area 25.0 d/ by BET method
11, coercive force (Hc) 23.9 KA/m, square shape (
An r-Fe205 powder with a gr/as) of 0.45 was obtained, and a magnetic tape was made in the same manner as in Example 1 using this r-Fe205 powder.

Example 3 In Example I, a ferric chloride aqueous solution was added to a sodium hydroxide aqueous solution (except that the temperature at the time of addition was 20° C.) in the same manner as in Example 1, with a major axis diameter of 240 nm and a minor axis diameter fJ O
nm s-axis ratio 40, specific surface area 25 d/ by BET method
r-Fe20. with f coercive force (He) 25.5 KA/m, -square (er/am) 0.45. A magnetic tape was prepared in the same manner as in Example 1 using the obtained powder.

Example 4 In Example 1, a ferric chloride aqueous solution in which 15 moles of ferric chloride was dissolved in 30 IK of water, and a sodium hydroxide aqueous solution in which 60 moles of sodium hydroxide were dissolved in 601 K of water were used. Iron aqueous solution to sodium hydroxide aqueous solution Etl
The major axis diameter was 10100n, the minor axis diameter was 30 nm s, except that the temperature when applying rK was -2"C.
Axial ratio 3.3, specific surface area 33.4rt/f by BET method
Coercive force (He) at 1 g, 3 KA/tn.

Square ('r/'s) 0.4 r-Fe, 0. A magnetic tape was produced in the same manner as in Example 1 using this r -Fe2O3 powder.

Comparative Example 1 10 moles of ferrous sulfate (FeSO4,7H20) in 4 parts of water
An aqueous solution of ferrous sulfate dissolved in 01 and a sodium hydroxide aqueous solution prepared by dissolving 70 moles of sodium hydroxide in 401 water were prepared, and sulfur V! was dissolved at a temperature of 25°C. A sodium hydroxide aqueous solution was added to the ferrous aqueous solution to obtain a pale green precipitate. Next, this suspension was heated to 40°C in a constant temperature water bath while air was blown into the suspension at a rate of 10/min to carry out an oxidation reaction for 6 hours to obtain a yellow precipitate, which was washed with water, filtered, and dried. teσ−
Iron oxyhydroxide powder was obtained.

Next, this α-iron oxyhydroxide powder was reduced in the same manner as in Example 1, and further oxidized to yield γ-Fe 2 c.

Get some powder. The obtained r-Fe20. The powder has a long axis diameter of 2
00nmq minor axis diameter '30nm s axis ratio 6.7, BET
Coercive force (Hc) 14. Specific surface area 50 rl/9 by method.
3 KA/m s square shape (0170 g) was 0.3.

Next, this r-Fe20. A magnetic tape was made in the same manner as in Example 1 using the powder.

Comparative Example 2 Comparison @ IK At a temperature of 25°C, an aqueous sodium hydroxide solution was added to an aqueous solution of 11-iron to form a pale green precipitate, and the suspension was then heated to 50°C in a thermostatic water bath. A major axis diameter of 280
mm N minor axis diameter 40nms axial ratio 7, specific surface area 40rrl/f by BET method, coercive force (Hc) 1g, 3KA/
m, square shape (#r/as) 0.35 T-Fe 20
B powder was obtained, and a magnetic tape was made in the same manner as in Comparative Example 1 using the r -Fe20B powder.

Regarding the magnetic tapes obtained in each example and each comparative example, coercive force (He), residual magnetic flux density (Br), square shape (Br
/Bs), DC5/N and AC5/N were determined.

The table below shows the results.

As is clear from the table above, the magnetic tapes obtained according to the present invention (Examples 1 to 4) are superior to conventional magnetic tapes (Comparative Examples 1 to 2) in terms of coercive force, residual magnetic flux density, and angle. The type is high and DcS/N and AC5/N are low. Therefore, the magnetic recording medium obtained by this invention has excellent dispersibility and orientation of magnetic powder, excellent surface smoothness, and sufficiently reduced noise. I know that there is.

Patent applicant Makoto Ishizaka, Director of the Agency of Industrial Science and Technology - Patent applicant Representative of Hitachi Maxell Co., Ltd. Atsushi Mizuben Designated representative Director of the Osaka Institute of Industrial Science and Technology Naito Naito

Claims (1)

[Claims] 1. The major axis diameter is 300 nm or less, the axial ratio is 5 or less, and B
A magnetic recording medium with a coercive force of 15.9 KA/m or more, which is obtained by applying ferromagnetic iron oxide powder with a specific surface area of 40w1/9 or less by the ICT method to a substrate together with a binder resin.