JPS5829120A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To enhance the wear resistance and magnetic characteristics by using a radiation-polymerizable oligoester acrylate or oligoester methacrylate as a binder component. CONSTITUTION:Magnetic powder is dispersed in an oligomer represented by the general formula (where R1 is H or CH3, R2 is alkyl, and n is an integer of 1-20), having about 500-20,000mol.wt., and obtd. by bonding acrylic acid to the terminals of oligoester consisting of phthalic acid and alkylene glycol by esterification, and they are mixed to prepare a magnetic coating. The coating is applied to a substrate, and it is polymerized and hardened by irradiation at about 150-750kV acceleration voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium and a method for manufacturing the same, and an object thereof is to provide a magnetic recording medium having a magnetic layer with excellent wear resistance and electrical properties.

Magnetic recording media are usually made by applying a magnetic coating consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating.
A material with excellent electrical properties and durability is required. Therefore, it is desirable that the binder component used be one that has excellent dispersibility of the magnetic powder, can impart excellent electrical properties to the magnetic recording medium, and has excellent abrasion resistance. Vinyl-vinyl acetate copolymers are widely used.

However, the electrical properties are still not completely satisfactory, and in addition, when resins with large molecular acids are used as binder components, harmful substances that dissolve the binder resin when preparing magnetic paints are used. Since a large amount of organic solvent is used, there is a problem with pollution, and the three-dimensional crosslinking of the binder in the magnetic coating film is insufficient, so that the abrasion resistance is not fully satisfactory.

Therefore, as a method to improve this, in recent years, a magnetic paint has been prepared by mixing and dispersing a urethane acrylate oligomer, etc., in which acrylic acid is ester bonded at both ends of the urethane oligomer, together with magnetic powder and an organic solvent. A method has been proposed in which a paint is applied onto a substrate and then irradiated with radiation to polymerize the urethane acrylate oligomer to form a magnetic layer. The result is F, which is not so good in terms of gender and is still quite satisfactory! Not obtained.

The inventors conducted various studies in view of the current situation, and found that a magnetic material containing an oligomer in which acrylic acid is ester-bonded to the end of an oligoester consisting of phthalic acid and alkylene glycol, and magnetic powder is formed on a substrate. When the paint is applied and then irradiated with radiation, the oligomers are polymerized and hardened by the radiation, resulting in good magnetic powder filling properties, excellent electrical properties and wear resistance, and furthermore, no solvent is used at all. The inventors have discovered that it is possible to use a solvent such as ethanol which has a low boiling point and low toxicity even when used, and the problem of pollution can be solved, and this invention has been completed.

In the present invention, the oligoester consisting of phthalic acid and alkyl L/> glycol is ester-bonded with terminal niacrylic acid or methacrylic acid. ,
n is an integer from 1 to 20. ) with a molecular weight of 500 to 20,000
are preferably used. This type of oligoester acrylate and oligoester methacrylate has a lower viscosity than urethane acrylate oligomer, and when preparing a magnetic paint, it is possible to fill in more magnetic powder to reach the same viscosity and apply it on the substrate together with the magnetic powder. After being exposed to radiation, the terminal double bonds are opened and cross-linked, forming a magnetic layer that is moderately polymerized and hardened with high cross-linking density and excellent filling properties of the magnetic powder, resulting in improved electrical properties. This further improves the wear resistance as well. The amount used is preferably within the range of 20 to 60 kg based on the total amount of magnetic powder. If it is too small, the desired effect cannot be obtained, and if it is too large, the magnetic powder content will be low. If it is too high, it will not be possible to obtain the electrical characteristics necessary for a magnetic tape.

The magnetic powder used in this development is r-
Fe20. Powder, Fe 304 powder, Co containing r
In addition to Fe20B powder, Co-containing Fe504 powder, and CrO2 powder, various conventionally known magnetic powders such as metal powders such as Fe powder, CO grain powder, and Fe-Ni powder are widely included.

To form the magnetic layer of the present invention on a substrate, magnetic powder is dispersed and mixed in the oligomer to prepare a magnetic coating material, which is coated on a substrate such as a polyester film, and then irradiated with radiation. Alternatively, the oligomer described above can be dissolved in an organic solvent, magnetic powder can be dispersed and mixed in this solution to prepare a magnetic paint, and this can be coated on a substrate such as a polyester film, followed by preheating. This is done by removing the organic solvent contained in the magnetic paint and then irradiating it with radiation to polymerize and harden it. When an organic solvent is used, the viscosity of the magnetic paint becomes lower and more magnetic powder is dispersed Because mixing is possible,
The filling properties of the magnetic powder in the magnetic layer can be further improved, and the electrical characteristics of the resulting magnetic recording medium can be further improved.

When using an organic solvent, any of the solvents conventionally used in preparing magnetic paints, such as methyl isobutyl ketone, Schiff-tetrahexanone, toluene, and dimethylformamide, can be suitably used. Because of its good solubility in organic solvents, low-boiling point, low-toxicity solvents such as ethanol, n-hebutane, and n-hexane can also be suitably used. Therefore, using these low-boiling point, low-toxicity solvents will reduce pollution. The above problem is solved, and if the magnetic paint is applied and preheated, these low boiling point solvents can be easily removed, making it easier to recover the solvent.

For radiation irradiation, it is preferable to use radiation with an accelerating voltage of 150 to 750 KV and irradiate KN so that the absorbed dose is 3 to 15 Mrad. If the absorbed dose is too small, the cross-linking of the oligomers will be insufficient and the desired effect will not be achieved. is not obtained.

In addition, various additives commonly used in magnetic coating materials, such as dispersants, lubricants, abrasives, antistatic agents, etc., may be added as appropriate.

Next, embodiments of the invention will be described.

Example 1 Oligoester acrylate represented by the structural formula was used, and the composition was as follows: Co-containing r-Fe203 magnetic powder 60 parts by weight Oligoester acrylate 40 l ethyl alcohol/methyl ethyl ester 25 # methyl ketone mixed solvent [mixing ratio 1/1] A magnetic paint was prepared by mixing and dispersing the composition in a ball mill for 72 hours.
*: After preheating at 90'O for 1 minute to remove the ethyl alcohol/methyl ethyl ketone mixed solvent, a 0-order coated film with a coating thickness of 4# was applied to a polyester base film. Manufactured by EPS-750
The material was cured by irradiating it with radiation at a dose of 7 Mrad, and after calendering, it was cut into a predetermined width to produce a magnetic tape.

Example 2 The composition of the magnetic paint in Example IK was the same as Example 1 except that the ethyl alcohol/methyl ethyl ketone mixed solvent was omitted and the amount of oligoester acrylate used was changed from 40 parts by weight to 50 parts by weight. I made magnetic tape.

Comparative Example 1 In the composition of the magnetic paint in Example 1, Parnock DF-30-55 was used instead of oligoester acrylate.
(Polyether urethane manufactured by Dainippon Ink Chemical Co., Ltd.) 164
parts by weight, tolylene diisocyanate 7.8 parts by weight, 2
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of polyether polyurethane acrylate oligomer consisting of 6.1 parts by weight of J-do-xyethyl acrylate was used.

Comparative Example 2 Co-containing r-Fe20. Magnetic powder 78 parts by weight VAG
H (manufactured by U, C, C, USA, salt 12 vinyl chloride-acetane vinyl-vinyl alcohol copolymer) Nissan 5702 (USA, Gutsud 8 parts by weight, manufactured by Rich Chemical Company, urethane elastomer) Ko4nee) L (Japan) Boliureta 2 Manufactured by #N Co., Ltd.
trifunctional isocyanate compound) cyclohexanone 90 #silene
#90 This composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic paint. This magnetic paint was applied onto a polyester base film with a thickness of 15 μm so that the dry thickness would be 4 tones, dried, calendered, and then cut into a predetermined width to produce a magnetic tape.

The squareness (Br/Bm) of the magnetic tapes obtained in each example and each comparative example was measured, and in order to further examine the wear resistance, each magnetic tape was loaded into a tape recorder.
．． g C11l / 66 (travel speed r 600
The output fluctuation was measured after running the vehicle twice.

The table below shows the results.

As is clear from the table above, the magnetic tapes obtained by the present invention (Examples 1 and 42) are different from the conventional magnetic tapes (Comparative Example 1).
and 2), the square shape is larger and the output fluctuation is smaller, which indicates that the magnetic recording medium obtained by the present invention has further improved magnetic properties and improved wear resistance.

Claims (1)

[Claims] 1. On a substrate, a coating film containing an oligomer formed by ester bonding acrylic acid and methacrylic acid and magnetic powder is carved on the terminal end of an oligoester made from Ksy taric acid and alkylene glycol, A magnetic recording medium characterized by having a magnetic layer that is polymerized and hardened by irradiating it with radiation! On the substrate, a magnetic paint containing an oligomer made of phthalic acid and alkylene glycol with ester-bonded acrylic IL'rll or methacrylic alcohol at the end of 6 oligoester, and magnetic powder is applied. A method for producing a magnetic recording medium, characterized in that a magnetic layer is formed by irradiating the oligomer with radiation to polymerize and harden the oligomer. A magnetic paint containing an oligomer having an ester bond, a magnetic powder, and a solvent is applied, and then, before irradiation with radiation, preheating is performed to remove the solvent contained in the magnetic paint. Method for manufacturing a magnetic recording medium according to item 2