JPS59162636A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a high modulus of elasticity, superior mechanical strength and durability by preparing a magnetic coating material with a liq. acrylic oligomer and cellulosic resin as binder components and a small amount of an org. solvent. CONSTITUTION:A magnetic layer contg. dipentaerythritol hexaacrylate, the ester of dipentaerythritol with pentaacrylic acid or lower, cellulose resin and magnetic powder is formed. An acrylic oligomer prepd. by mixing the hexaacrylate with the ester is liq. and has many double-bond groups per one molecule, so a magnetic coating material can be prepd. with a small amount of a solvent, and high cross-linking density is attained by polymn. and curing under radiation. The cellulose resin has a great affinity for the magnetic powder and disperses well the powder. Accordingly, the dispersibility of the magnetic powder is further improved by adding the cellulosic resin, and the electromagnetic transducing characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and its purpose is to have a high elastic modulus, excellent mechanical strength and durability, good dispersibility and filling properties of magnetic powder, and electromagnetic conversion characteristics. The objective is to provide an excellent magnetic recording medium.

In recent years, in magnetic recording media such as magnetic tape, recording,
In order to lengthen playback time as much as possible, thinner magnetic tapes are sought after, and magnetic tapes that tend to be thinner must have particularly high elastic modulus, excellent mechanical strength, and durability to ensure running stability. A material with excellent properties in terms of performance and electromagnetic conversion properties is required.

For this reason, attempts have been made to improve the elastic modulus of the magnetic layer by using a high modulus binder resin such as a high molecular weight polyurethane resin or a two-component reactive binder resin such as a polyol and an isocyanate compound. However, when using a high modulus binder resin, a large amount of organic solvent is used, making it difficult to obtain good electromagnetic characteristics, and when using a two-component reactive binder resin, a large amount of solvent is used. On the other hand, there are drawbacks such as the need for heat treatment after the magnetic layer is formed, and the reaction is not complete, making it impossible to sufficiently improve durability.

Therefore, in recent years, as a method to improve this, the use of radiation-curable resins has been carried out. A method has been proposed in which a magnetic coating material is prepared by mixing and dispersing the oligomers together with other components, the magnetic coating material is applied onto a substrate, and then radiation is irradiated to polymerize the oligomers to form a magnetic layer. However, in this method, the modulus of elasticity of the magnetic layer is improved by using dipentaerythritol hexaacrylate with an acrylic group number of 6, and the No. 11 abrasion resistance is also improved, but the dipentaerythritol hexaacrylate used is Since a large amount of organic solvent must be used to dissolve the magnetic powder, the dispersibility and filling properties of the magnetic powder are not sufficient, and good electromagnetic conversion characteristics cannot be obtained.

As a result of various studies in view of the current situation, the inventors found that when dipentaerythritol hexaacrylate-1 and an ester of dipentaerythritol and 5 or less acrylic acid are mixed, they become liquid. When acrylic oligomer and cellulose resin are used in combination as binder components, since the acrylic oligomer is liquid, magnetic paint can be prepared with a small amount of organic solvent, and the cellulose resin used in combination improves the dispersibility of magnetic powder. Since the dispersibility and filling properties of the magnetic powder are sufficiently improved, a magnetic paint containing these and the magnetic powder is applied onto a substrate, and then,
When this is irradiated with radiation, the acrylic oligomer is polymerized and hardened by the radiation, forming a magnetic layer with good dispersibility and filling properties of the magnetic powder and further improved electromagnetic conversion characteristics, and the wear resistance of the magnetic layer is improved. The present inventors have discovered that a magnetic recording medium can be obtained which has improved durability, improved elastic modulus, and improved mechanical strength, and has thus come up with the present invention.

The acrylic oligomer used in this invention, which is a mixture of dipentaerythritol hexaacrylate-1 and an ester of dipentaerythritol and 5 or less acrylic acid, is liquid and has a large number of double bond groups per molecule. Magnetic coatings can be prepared with a small amount of solvent, and have a high crosslinking density when polymerized and cured by radiation irradiation. Therefore, the dispersibility and filling properties of magnetic powder can be improved, and electromagnetic conversion characteristics can be improved. The abrasion resistance and elastic modulus of the magnetic layer are also improved, and the durability and mechanical strength are further improved. Pentaerythritol type acrylate used in a mixture as described above is solid when the number of double bond groups is 4 or more, and dipentaerythritol hexaacrylate is solid, but in addition to this, solid or liquid dipentaerythritol type acrylate is solid. When esters of erythritol and 5 or less acrylic acid are mixed, a liquid acrylic oligomer is obtained, and a magnetic paint can be prepared with a small amount of solvent as described above, and a high crosslinking density can be obtained by irradiation with radiation. The mixing ratio of such dipentaerythritol hexaacrylate and the ester of dipentaerythritol and 5 or less acrylic acid is such that it becomes easily liquefied by mixing and sufficiently improves the filling properties and crosslinking density of the magnetic powder. Therefore, the weight ratio of dipentaerythritol to hexaacrylate-1 to the ester of dipentaerythritol and 5 or less acrylic acid is 10:1.
It is preferable to mix within the range of ~1:10, and it is more preferable to mix so that the average number of acrylic groups is 5 or more in order to obtain sufficient crosslinking density and sufficiently improve mechanical strength and durability. preferable.

In addition, the cellulose resin used in combination in this invention has good affinity with the magnetic powder and has excellent dispersibility of the magnetic powder. Therefore, when this type of cellulose resin is used in combination, the dispersibility of the magnetic powder is further improved. This further improves the electromagnetic conversion characteristics.

Preferred examples of such cellulose resins include nitrocellulose, acetylcellulose, acetylbutylcellulose, methylcellulose, ethylcellulose, hensylcellulose, carboxymethylcellulose, and hydroxycellulose. Specific examples include: For example, Asahi Kasei nitrocellulose Ll/
2, L1/4, L, 1, H1/4, H1/2, Hl
, H5, Daicel Nitrocellulose R31/16,
Examples include R3I/2, R3I, R32, and the like.

the dipentaerythritol hexaacrylate;
The mixing ratio of liquid acrylic oligomer, which is a mixture of dipentaerythritol and an ester of 5 or less acrylic acid, and cellulose resin is 8 to 2 to 2 to 2 to 1 liquid acrylic oligomer to cellulose resin, by weight. Preferably, the ratio is within the range of 4 to 4 to 6 to 6. If the liquid acrylic oligomer is too small, the filling properties of the magnetic powder and the mechanical properties of the magnetic layer may be affected. On the other hand, if the amount is too high, the magnetic layer will become too hard and brittle, and the dispersibility of the magnetic powder will not be good.

The radiation used to polymerize and harden the liquid acrylic oligomer is preferably β rays such as electron beams, and γ rays such as ultraviolet rays or X rays.
When using ultraviolet light, a sensitizer is used at the same time to make the effect of the irradiation more efficient. Such radiation irradiation uses radiation with an accelerating voltage of 150 to 750 KV,
It is preferable to irradiate at an absorbed dose of 3 to 15 Mrad; if the absorbed dose is too small, crosslinking of the liquid acrylic oligomer will be insufficient and the desired effect will not be obtained.

To form the magnetic layer of the present invention, a liquid acrylic oligomer prepared by mixing dipentaerythritol hexaacrylate described in Nij., an ester of dipentaerythritol and 5 or less acrylic acid, and fibers are used. A magnetic paint is prepared by dissolving the basic resin in an organic solvent and dispersing magnetic powder in this solution. After coating this on a substrate such as a polyester film, it is irradiated with radiation to polymerize and harden. It will be done.

As the magnetic powder used here, for example, r-Fe
203 powder, Fe5Q4 powder, Co-containing T-Fe203
In addition to powder, Go-containing 'Fe3O4 powder, and CrQ2 powder, various conventionally known magnetic powders such as metal powders such as Fe powder, Co powder, and Fe-Ni powder are widely used.

Further, as the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethylbormamide, etc. are used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, rJF abrasives, antistatic agents, etc. may be optionally added.

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 800 parts by weight Nitrocellulose 11 (manufactured by Asahi Kasei 9011, Etrocellulose) Dipentaerythritol hexa 55.I acrylate dipentaerythritol penta 55 Acrylate myristic acid 1511 n-butyl stearate 10/ l Methyl isobutyl ketone 500 Toluene 500
11 This composition was mixed and dispersed in a hole mill for 72 hours to prepare a magnetic paint, and this magnetic paint was coated on a polyester base film with a thickness of 10 μm to a coating thickness of 3 μm. Next, after calendering, the material was cured by irradiating it with radiation at an IMrad dose using EPS-750 manufactured by Nisshin High Holdage Co., Ltd., and cut into predetermined shapes to produce a magnetic tape.

Comparative Example 1 The composition of the magnetic paint in Example 1 was the same as in Example 1 except that dipentaerythritol pentaacrylate was omitted and the amount of dipentaerythritol hexaacrylate used was changed from 55 parts by weight to 110 parts by weight. I made magnetic tape.

The magnetic tapes obtained in the examples and comparative examples were loaded into a video deck, a carrier signal of 4.5 Mllz was recorded, the playback output was extracted, and the ratio of the peak value C to the integral value N of the total noise was calculated as C/, N was measured. Further, the obtained magnetic tape was loaded into a video deck and its steel properties were measured, and the elastic modulus of the obtained magnetic tape at 1% elongation was measured using a tensile tester. Steel properties are an indicator of wear resistance, and the longer this time, the better the wear resistance.

The table below shows the results.

- As is clear from Table 1, the magnetic tape obtained in Example 1 has almost the same elastic modulus and steel properties as the magnetic tape obtained in Comparative Example 1, and has a higher C/N. It can be seen from the above that the magnetic recording medium obtained by the present invention has excellent mechanical strength and durability, good dispersibility and filling properties of the magnetic powder, and excellent electromagnetic conversion characteristics.

Claims (1)

[Claims] 1. Dipentaerythritol hexaacrylate, dipentaerythritol and 5 or less acrylic. A magnetic recording medium having a magnetic layer containing an ester with fluoric acid, a cellulose resin, and a magnetic powder.