JPS5837613B2 - isotropic magnetic sheet - Google Patents

Description

[Detailed description of the invention] The present invention relates to a magnetic sheet.

More specifically, the present invention relates to a magnetic sheet characterized by preventing the orientation of the magnetic material in the magnetic coating film and making it isotropic.

In magnetic recording sheets, which have recently become popular as educational equipment, the recording and/or playback head rotates in an arc or spiral, and has electromagnetic conversion characteristics that are different from those of magnetic tape, that is, a fixed straight line. It is required to have output stability not only in the direction but also in the arcuate or spiral direction.

Acicular γ-iron monoxide is generally used as a magnetic recording material, but during coating, the long axis of γ-iron monoxide powder tends to be naturally oriented in the flow direction of the coated paper.

That is, there is a disadvantage that only a magnetic sheet with directionality can be obtained if the method is left as it is.

In order to obtain stable output corresponding to a head moving in an arc or spiral, an isotropic magnetic sheet is desirable.

For this reason, it has been proposed and practiced to prevent natural orientation by providing permanent magnets, air-core solenoids, and the like.

However, these methods have many drawbacks in terms of equipment.

For example, due to changes in the type of paint, changes in the flowability of the paint, changes in coating conditions, etc., it is necessary to change the installation location of the equipment in accordance with each condition, which is extremely troublesome in terms of work management and process.

The present invention was completed as a result of studies to eliminate the above-mentioned drawbacks.

The feature of the present invention is that in preventing the natural orientation, ■ No orientation prevention equipment such as magnets is required.

@ Cubic magnetic material is used in the range of 5 to 50% of the total magnetic material.

It is at 02 points.

It is well known that the cubic magnetic material itself has no directionality (its axial ratio is approximately 1), so no orientation phenomenon occurs during coating. The effect of the present invention is that it has been found that adding 5 to 50% of cubic magnetic material is effective in suppressing the natural orientation of needle-like magnetic materials that have natural alignment properties. There is.

As the magnetic material used in the present invention, any material used for magnetic recording can be used.

As the binder used in the present invention, thermoplastic resins, thermosetting resins, reactive resins, etc., whether natural or synthetic, can be used alone or as a mixture.

Other additives such as a dispersant, an antifoaming agent, a lubricant, and an antistatic agent can be added to the paint as necessary.

To disperse the paint, a dispersing machine such as a three-roll mixing roll, attritor, sand grinder, or ball mill can be used.

The dispersion medium may be either an organic solvent or water, but water is more preferable in terms of safety, workability, and cost.

Supports include paper, plastic, synthetic paper, metal foil,
Any non-magnetic material such as glass fiber mixed paper can be used.

The coating method is not limited to any method as long as a uniform coating can be obtained, such as a roll coater or a flake coater.

It is desirable that the drying conditions after coating be determined so that the binder used exhibits a sufficient binding effect.

After drying, it is preferable to smooth the coated surface using a gloss calender, a super calender, or the like.

Examples of the present invention will be shown and specifically explained below.

Example 1 Acicular γ iron monoxide (MRM 95 parts 400 manufactured by Toda Kogyo)
) (Axial ratio 1: approx. 5.7) Cubic gamma iron monoxide. parts (Toda Kogyo CM-3) Sodium pyrophosphate 0.5 parts Styrene maleic acid copolymer 15 parts (Daido Kogyo Styrite) Water 100 parts After dispersing the above composition in a ball mill for 24 hours, add 15 parts of acrylic emulsion latex. By adding
A magnetic paint was prepared.

Using a roll coater, the above magnetic paint was coated and dried on mirror-finished clay coated paper at a dry coating amount of 20 fl/m, and a super calender finish was applied to create a magnetic recording sheet. Obtained.

The residual magnetic flux density of this sheet was measured under the condition of an applied magnetic field of 10,000 e.

The measurement results are shown in the table.

Example 2 The composition in Example 1 was prepared as follows.

Acicular γ Iron monoxide 75 parts Cubic γ
Iron monoxide 25 parts Sodium pyrophosphate
0.5 parts Styrene maleic acid copolymer 15 parts Water 10
0 parts After obtaining a magnetic sheet by the same method as in Example 1, the residual magnetic flux density was measured and the results are shown in the table.

Example 3 Acicular γ iron monoxide cubic γ iron monoxide pyrophosphate soda styrene maleic acid copolymer water 50 parts 50 parts 0.5 parts 15 parts 100 parts A magnetic sheet was prepared in the same manner as in Example 1 using the above assembly. The results of measuring the residual magnetic flux density are shown in the table.

Comparative example 1 Acicular γ Iron monoxide Cubic γ Iron monoxide Styrene maleic acid copolymer Water 100 parts 0.5 parts 15 parts 100 parts Comparative example 2 Acicular γ Iron monoxide 25 parts Cubic γ
Iron monoxide 75 parts Sodium pyrophosphate
0.5 parts styrene maleic acid copolymer 15 parts water io
After obtaining magnetic sheets in the same manner as in Example 1 for each set of o parts, the residual magnetic flux density was determined and the results are shown in Table 1.

From these results, it is clear that natural orientation is prevented by adding cubic magnetic material to the acicular magnetic material with excellent recording properties as the main material.

Claims (1)

[Claims] 1. In a magnetic sheet on which a recording and/or reproducing head rotates and moves in an arc shape or a spiral shape, a cube-shaped magnetic material is blended with a needle-shaped magnetic material, and the blending ratio is 95:5 to 50:
An isotropic magnetic sheet 1. characterized in that a support is provided with a magnetic paint having a composition of No. 50.