JPH04170714A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium excellent in electric characteristics and durability by constituting the medium of magnetic powder subjected to surface treatment by silazan of a hydrophobic radical containing a radiation functional group, and of radiation-setting resin, and by setting a magnetic layer by the application of radiation. CONSTITUTION:The surfaces of particles of magnetic powder are treated with silazan having a hydrophobic radical containing a radiation functional radical and, this treated magnetic powder being used together with radiation-setting resin, a magnetic layer is formed of them by applying radiation thereto. By this process, the dispersibility of the magnetic particles is improved, bonding between the powder and bonding agent resin is strengthened and both electric characteristics and mechanical characteristics are improved. The hydrophobic radical of the silazan is not limited herein particularly, and ordinary hydrophobic radicals of alkyl, fluoride or the like, for instance, may be used, while the hydrophobic radical may also contain a radiation functional group having double bond of radiation polymerization. In order to prepare this medium, these materials are dissolved in a solvent and then filtered and dried in the state of slurry.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium with excellent electrical characteristics and durability.

[Conventional technology]

Generally, magnetic recording media are made by applying and drying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film. It is required to have excellent physical properties, good mechanical properties, and excellent durability.

For this reason, conventional efforts have been made to improve the dispersibility of magnetic powder by making the particle surface of magnetic powder hydrophobic and increasing the leakage of the magnetic powder to organic solvents.
In addition, in order to improve mechanical properties, reactive functional groups such as amino groups and epoxy groups are introduced onto the particle surface of magnetic powder using a silane camping agent, and a crosslinking agent containing isocyanate groups is used to improve magnetic properties. A strong chemical bond between the powder and the binder resin has been used.

(JP-A No. 62-202327, JP-A No. 49-5960
(No. 8) [Problem to be solved by the invention] However, when the particle surface of magnetic powder is treated to make it hydrophobic, the interaction between the magnetic powder and the binder resin becomes weaker, resulting in the deterioration of mechanical properties. In addition, reactive functional groups such as amino groups and epoxy groups begin a crosslinking reaction the moment they are mixed with a crosslinking agent containing an isocyanate group, which increases the viscosity of the magnetic paint and shortens its pot life. Problems such as this occur.

[Means for Solving the Problems] This invention was made as a result of various studies in view of the current situation, and includes treating the particle surface of magnetic powder with silazane having a hydrophobic group containing a radiation functional group, This treated magnetic powder is used in combination with a radiation-curable resin and irradiated with radiation to form a magnetic layer, thereby improving the dispersibility of the magnetic powder and strengthening the bond between the magnetic powder and the binder resin. It has sufficient properties, sufficiently improved electrical properties, and good mechanical properties to sufficiently improve durability.

The silazane used in this invention, which has a hydrophobic group containing a radiation functional group, has a 5i-N bond that reacts extremely well with the hydroxyl group on the particle surface of the magnetic powder, and when it comes into contact with the magnetic powder, silane force and compression It has a much stronger adsorption force than agents such as titanate coupling agents and titanate coupling agents, and easily chemically adsorbs to the surface of magnetic powder particles at room temperature. In addition, because it has a hydrophobic group, magnetic powder surface-treated with this silazane has greatly improved leakage to organic solvents, and as a result,
The dispersibility of the magnetic powder in the magnetic paint is improved, and the electrical properties are further improved.

In addition, since this silazane contains a radiation functional group in its hydrophobic group, when used together with a radiation curable resin, the radiation functional group in the hydrophobic group reacts with the radiation curable resin due to radiation irradiation, and this reaction occurs. As a result, the magnetic powder and the radiation-curable resin are chemically strongly bonded via the silazane, and the mechanical properties are greatly improved. Then, the cross-linking reaction between the radiation-curable resin and the radiation-curable resin is caused by the radiation functional group of silazane fixed on the particle surface of the magnetic powder by chemical adsorption.
This does not occur until the magnetic paint is applied and irradiated with radiation after drying, so the viscosity of the paint may increase during the magnetic paint stage.
Or, the pot life will not be shortened.

The hydrophobic group of such silazane is not particularly limited, and includes, for example, a conventional hydrophobic group such as an alkyl group or a fluoride group, and a radiation-functional group having a radiation-polymerizable double bond in the hydrophobic group. Hydrophobic groups containing these radiation functional groups can be introduced and used without particular restrictions.

To treat magnetic powders with silazane having hydrophobic groups containing such radiofunctional groups, this kind of silazane can be mixed with ethyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, benzene, toluene, tetrahydrofuran, dioxane. The magnetic powder can be mixed and dispersed in this solution using a homomixer, sand mill, ball mill, etc., and the magnetic powder treated with silazane in this way can be mixed and dispersed into a slurry. A magnetic paint is prepared by adding it as it is or after filtering and drying it at any stage during the preparation of a magnetic paint. In addition, this type of silazane may be added directly during the preparation of the magnetic coating material, for example, the required amount of silazane may be directly added to the magnetic coating material during the kneading step or sand mill dispersion step. Furthermore, in any of these methods, it goes without saying that not only magnetic powder but also solid additive particles such as alumina and carbon blank may be treated together.

In this way, the treatment concentration of this kind of silazane on the particle surface of the magnetic powder to be surface-treated depends on the specific surface area of the magnetic powder, but is generally 0.1 to 1
Preferably, the amount is within the range of 0% by weight, and particularly preferably 0.5-3% by weight.

In addition, the radiation-curable resin used in this invention is a monomer, oligomer or polymer having a radiation-polymerizable double bond, has excellent dispersibility and filling properties for magnetic powder, and has a hydrophobic property containing a radiation-functional group. It also has good compatibility with silazane having groups. Therefore, a magnetic paint is prepared by using this radiation-curable resin in combination with a magnetic powder whose surface is treated with silazane having a hydrophobic group containing a radiation-functional group, and after coating it on a substrate, it is irradiated with radiation and polymerized. When cured, a strong magnetic layer with excellent electrical properties is formed, resulting in a magnetic recording medium with excellent electrical properties and durability.

As such radiation-curable resins, radiation-curable resins commonly used in magnetic recording media are widely used.
For example, acrylic thread additives such as methyl methacrylate, methyl acrylate, butyl acrylate, acrylic acid, methacrylic acid, or mixtures thereof, mixtures of styrene, vinyl acetate, and acrylonitrile, 2-hydroxyethyl methacrylate and dimethylaminoethyl Mixture of methacrylate and glycidyl methacrylate, trimethylolpropane trimethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol pentaacrylate, urethane acrylic oligomer, epoxy acrylic oligomer, polyester acrylic oligomer, polybutadiene acrylic oligomer, polyamide acrylic oligomer, poly Ether acrylic oligomers, oligoester acrylic oligomers, spiroacecool acrylic oligomers, and the like are preferably used.

When using a radiation-curable resin in this way, a thermoplastic resin may also be used in combination. Examples of the thermoplastic resin used in combination include vinyl chloride-vinyl acetate copolymer, polyvinyl acetal resin, and cellulose resin. , polyester resin, incyanate compound, etc., which are generally used in magnetic recording media, can be used.

The magnetic layer of the present invention is formed by using a magnetic powder surface-treated with silazane having a hydrophobic group containing a radiation-curable resin, a radiation-curing resin, a binder resin used in combination as necessary, an organic solvent, and a radiation-curing resin. This is carried out by dispersing and mixing with other necessary components to prepare a magnetic paint, applying this onto a substrate such as a polyester film, and then irradiating it with radiation to polymerize and harden it.

Here, when irradiating radiation to polymerize and harden, the radiation used is β rays such as electron beams, ultraviolet rays,
T-rays such as UV rays are preferably used, and when ultraviolet rays are used, a sensitizer is used at the same time to make the effect of irradiation more efficient. It is preferable for such radiation irradiation to use radiation with an accelerating voltage of 150 to 750 KV so that the absorbed dose is 3 to 15 Mrad. If the absorbed dose is too small, the crosslinking of the radiation-curable resin may be insufficient. The desired effect cannot be obtained.

Further, as the magnetic powder, for example, γ-Fe203 powder, FezOa powder, Co-containing 7-Fe2O3 powder, C
In addition to o-containing Fe, O, powder, Cry□ powder, Fe powder,
Various conventionally known magnetic powders are widely used, such as metal powders such as Co powder and Fe-Ni powder, and hexagonal ferrites such as barium ferrite and strontium ferrite.

Examples of organic solvents include cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, toluene, isopropyl alcohol, dimethyl formamide, tetrahydrofuran, dioxane, etc. The solvent used to dissolve the binder resin used is not particularly limited.
Used alone or in combination of two or more.

Incidentally, various commonly used additives such as dispersants, lubricants, abrasives, antistatic agents, etc. may be optionally added to the magnetic paint. Further, the magnetic layer formed on the substrate in the present invention may be a single magnetic layer or a multilayer magnetic layer.

[Example] Next, embodiments of the invention will be described.

Example 1 Using silazane represented by the structural formula (%), 100 parts by weight of Co-containing 7-Fe2O3 powder (BET
Specific surface area, 50 bo/g) Radiation functional group-containing vinyl chloride copolymer 12.52 bodies (-CO
OH, OH group-containing type) Silazane 2 Alumina (
Average particle size 0.2 μm) IQ // Cyclohexanone 20〃Toluene
The composition No. 20 was kneaded in a kneader for 2 hours to obtain a kneaded product.

Next, this kneaded product was mixed with a polyurethane resin (Dainippon Inn, 7.5 parts by weight, manufactured by Seikagaku Kogyo Co., Ltd., T-5201), a trifunctional low molecular weight isocyanate compound (manufactured by Nippon Polyurethane Industries, Ltd.; Coronate L), cyclo Hexanon 60〃Toluene
60〃 was added thereto and mixed and dispersed for 10 hours using a sand grind mill to prepare a magnetic paint. This magnetic paint was applied onto a polyester hair film with a thickness of 14 μm so that the coating thickness after drying was approximately 3 μm, and then mirror-finished and cured by irradiation with radiation at a dose of 6 Mrad. . After that, it was cut to a specified width to make magnetic tape.

Comparative Example 1 A magnetic tape was prepared in the same manner as in Example 1, except that the radiation irradiation was omitted.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1 except that silazane was omitted from the composition of the magnetic coating material in Example 1.

Regarding the magnetic tapes obtained in each example and comparative example,
The output of the carrier at 8 MHz and the elastic modulus at 0.3% elongation were measured to examine durability. Durability was determined by observing the degree of damage after running the obtained magnetic tape on a deck 100 times. No damage was observed at all (◎), and slight damage was observed (△). , cases where damage was observed were evaluated as (×).

Table 1 below shows the results.

Table 1 C Effects of the Invention] As is clear from Table 1 above, the magnetic tape obtained in this invention (Example 1) has a higher elastic modulus than the magnetic tape obtained in Comparative Example 1. In addition, compared to the magnetic tape obtained in Comparative Example 2, the output of the 8 MHz carrier is higher, the elastic modulus is higher, and the durability is better. It can be seen that the recording medium has good dispersibility of magnetic powder, excellent electrical properties, good mechanical properties, and excellent durability.

Claims (1)

[Claims] 1. Contains magnetic powder surface-treated with silazane having a hydrophobic group containing a radiation functional group and a radiation curable resin,
Magnetic recording medium with a magnetic layer hardened by radiation irradiation