JPS59162629A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic transducing characteristics by forming a magnetic layer contg. a liq. acrylic oligomer, a radiation curing resin, vinyl chloride resin and magnetic powder so as to improve the dispersibility and fillability of the magnetic powder as well as the durability of the layer. CONSTITUTION:The acrylic oligomer is prepd. by mixing dipentaerythritol hexaacrylate with the ester of dipentaerythritol with pentaacrylic acid or lower, and the oligomer is used by 1-80wt% of the total amount of the binder components. A urethane-acrylic oligomer, a spiroacetal-acrylic oligomer or the like having <5,000mol.wt. and 2-4 functional groups is suitable for use as the radiation curing resin, and it is used by 1-40wt% of the total amount of the binder components. The vinyl chloride resin is used by 1-80wt% of the total amount of the binder components.

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, and good dispersibility and filling properties of magnetic powder, so that electromagnetic conversion is possible. The objective is to provide a magnetic recording medium with excellent characteristics.

In recent years, in magnetic recording media such as magnetic tape, recording,
In order to extend the playback time as much as possible, magnetic tapes are made thinner, and magnetic tapes that tend to be thinner have particularly high elastic modulus, excellent mechanical strength, and durability for 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. 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 required. 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, as a method to improve this, in recent years, radiation-curable resins have been used. For example, acrylic oligomers such as dipentaerythritol hexaacrylate are combined with vinyl chloride resin, magnetic powder, and other necessary ingredients. A method has been proposed in which a magnetic coating material is prepared by mixing and dispersing the oligomers, the magnetic coating material is coated on a substrate, and then radiation is irradiated to polymerize the oligomers to form a magnetic layer. However, although this method improves the elastic modulus of the magnetic layer and improves the abrasion resistance by using dipentaerythritol hexaacrylate with an acrylic group number of 6, the dipentaerythritol hexaacrylate used is solid. However, 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 still insufficient, making it impossible to obtain good electromagnetic conversion characteristics.

As a result of various studies in view of the current situation, the inventors have already found that when dipentaerythritol hexaacrylate, dipentaerythritol and 5L/), and the following ester of acrylic acid are mixed, it becomes liquid. A magnetic paint containing such liquid acrylic oligomer, vinyl chloride resin, and magnetic powder is applied onto a substrate and then irradiated with radiation. The acrylic oligomer is polymerized and hardened by the radiation, and the magnetic powder is dispersed. A magnetic layer with good electromagnetic properties (( However, as a result of further machining, we found that the use of a radiation-curable resin as a binder component improves the dispersibility and filling properties of the magnetic powder, and also improves the abrasion resistance and elasticity of the magnetic layer. It has been found that a magnetic recording medium with even better electromagnetic conversion characteristics, durability, and mechanical strength can be obtained by further improving the conversion rate, and has thus come up with the present invention.

Dipentaerythritol used in this invention -
・Acrylic oligomer, which is a mixture of hexaacrylate, dipentaerythritol, and an ester of 5 or less acrylic acid, is liquid and has a large number of double bond groups per molecule, so it is possible to prepare magnetic paint with a small amount of solvent. In addition, it has a high crosslinking density when polymerized and hardened by radiation irradiation, which improves the dispersibility and filling properties of the magnetic powder, improving the electromagnetic conversion characteristics, as well as improving the abrasion resistance and elastic modulus of the magnetic layer. This further improves durability and mechanical strength. 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 an ester of erythritol and 5 or less acrylic acid is mixed, a liquid acrylic oligomer is obtained, and as mentioned above, a magnetic paint can be prepared with a small amount of solvent, 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 liquid upon mixing and sufficiently improves the filling properties and crosslinking density of the magnetic powder. In order to achieve this, it is preferable to mix dipentaerythryl 1-1-1 hexaacrylate to dipentaerythryl-1-- and an ester of 5 or more acrylic acid in a weight ratio of 10"IA1 to 10" to 10. Furthermore, it is more preferable to blend the liquid acrylic oligomer so that the average number of acrylic groups is 5 or more in order to sufficiently improve the mechanical strength and durability by increasing the crosslinking density. The amount used is preferably within the range of 1 to 80% by weight based on the total amount of binder components; if it is too small, the filling properties of the magnetic powder and the mechanical strength and wear resistance of the magnetic layer will not be sufficiently improved. ,
If the amount is too high, the magnetic layer becomes too hard and brittle, causing problems in durability.

The radiation-curable resin used in combination is not particularly limited, but has a molecular weight of less than 5,000 and a functional group number of 2 to 2.
4 is preferably used. This type of radiation-curable resin is liquid and has excellent dispersibility and filling properties for magnetic powder, and when it is coated on a substrate together with magnetic powder and exposed to slow radiation, it crosslinks and forms a moderately polymerized and hardened magnetic layer. The mechanical strength and wear resistance of the magnetic layer are improved. In addition, it has good compatibility with the liquid acrylic oligomer, and the acrylic oligomer does not become hard even when irradiated with radiation. The content of the radiation-curable resin can be increased, the amount of organic solvent used can be further reduced, the dispersibility and filling properties of the magnetic powder can be greatly improved, and the mechanical strength and strength of the magnetic layer can be improved. Wear resistance can be further improved. Specific examples of such radiation-curable resins include urethane acrylic oligomers, epoxy acrylic oligomers, oligoester acrylic oligomers, spiroacecool acrylic oligomers, etc. Specific examples of commercially available products include, for example, Toagosei Co., Ltd. Company-made M
-6250, M-7100, M-8030, M-110
0, M-1200, Thiokol U-782, U-7
83, U-788, U-893, 5P manufactured by Showa Shoshokusha Co., Ltd.
Examples include -4010, U-3000, F, -4000, and 3200.3500.3600.3700 manufactured by Celanese. The amount used is preferably within the range of 1 to 40% by weight based on the total amount of binder components; if it is too small, the filling properties of the magnetic powder will not be sufficiently improved, and if it is too large, the elastic modulus will not be sufficiently high. Mechanical strength is not sufficiently improved.

The vinyl chloride resin used in combination with the liquid acrylic oligomer and radiation-curable resin has good affinity with the magnetic powder and has excellent dispersibility of the magnetic powder. This further improves the dispersibility of the magnetic powder and improves its electromagnetic properties.The hinyl chloride resin cross-links with the liquid acrylic oligomer when irradiated with radiation, which improves the wear resistance of the magnetic layer. Such vinyl chloride resins include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-hinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, Vinyl chloride-vinyl propionate copolymers are preferably used, and specific examples include V Y Hl-(, VAGH-VM
CH, Suikagaku Kogyo Dakko Varnish I/Tsuku A, Eslenoku C
N, Ryuron QS-430 and Ryuron QA-431 manufactured by Toyo Soda. The amount used is preferably within the range of 1 to 80% by weight based on the total amount of the binder component. If it is too small, the dispersibility of the magnetic powder will not be sufficiently improved, and if it is too large, the elastic modulus will not be sufficiently high. Therefore, the mechanical strength cannot be sufficiently improved.

The radiation used to polymerize and cure the liquid acrylic oligomer and radiation-curable resin described above is preferably beta rays such as electron beams, and gamma rays such as ultraviolet rays or X-rays. When doing so, a sensitizer is used at the same time to make the effect of irradiation more efficient. Irradiation with such radiation requires an accelerating voltage of 150 to 75
Using 0KV radiation, the absorbed dose is 3-1.5 Mra
It is preferable to irradiate in such a manner that the absorbed dose is too small, and the crosslinking between the liquid acrylic oligomer and the radiation-curable resin 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 the dipentaerythritol hexaacrylate 1, an ester of dipentaerythritol and 5 or less acrylic acid, and a radiation-curable IL・Prepare a magnetic paint by dissolving 1 resin and vinyl chloride resin in an organic solvent, dispersing and mixing magnetic powder in this solution, and applying this to a substrate such as a polyester film 2, then irradiating it with radiation. This is done by polymerization and curing.

As the magnetic powder used here, for example, r-Fe
203 powder, Fe3O4 powder, CO-containing -Fe203
powder, Co-containing Fe30C1 powder, CrO2 powder,
Various conventionally known magnetic 111 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, dimethylformamide, etc. are used alone or in combination of two or more.

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

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 800 parts by weight Esresoku Δ (manufactured by Miki Kagaku Kogyo Co., Ltd. 40~, vinyl chloride-vinyl acetate-vinyl alcohol co-in> dipentaerythritol hexa 60 acrylate dipentaerythritol penta 60 acrylate).

M-6250 (manufactured by Toagosei Co., Ltd., 40 Bifunctional oligoester acrylate) Myristic acid 15 N-butyl stearate 10 Methyl isobutyl ketone
450〃1~Luen 45(
1. A magnetic paint was prepared by mixing and dispersing this composition in a hole mill for 72 hours, and this magnetic paint was applied onto a polyester heath film having a thickness of 10 μm to a coating thickness of 3 μm. After calendering, the tape was cured by irradiating it with radiation at a dose of 7 Mrad using F, PS-75'O manufactured by Nishin High Voltage Co., Ltd., and cut into a predetermined width to produce a magnetic tape.

Example 2 Considering the composition of the magnetic paint in Example 1, M-62
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of U-893'' (urethane acrylate manufactured by Thiokol) was used in place of 50.

Example 31 In the composition of the magnetic paint in Example 1, M-625
A magnetic tape was prepared in the same manner as in Example 1 except that the same amount of 3200 (7 doxy acrylate manufactured by Celanese) was used instead of 0.

Example 4 In the composition of the magnetic paint in Example 1, M-625
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of U-3000 (spiroacecool acrylate manufactured by Showa Kobunshi Co., Ltd.) was used instead of U-3000.

Comparative Example 1 In the composition of the magnetic paint in Example 1, dipentaerythritol pentaacrylate and M-6250 were omitted, and the amount of dipentaerythritol hexaacrylate used was changed from 60 parts by weight to 160 parts by weight. A magnetic tape was made in the same manner as in Example 1.

The magnetic tape obtained in each example and comparative example was loaded into a video deck, a carrier signal of 4.5 Mllz was recorded, jl + raw output was output, and the ratio of the peak value C to the integral value N of the total noise was calculated. 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 the above table, the magnetic tapes obtained in Examples 1 to 4 have almost the same elastic modulus as the magnetic tape obtained in Comparative Example 1, and have longer steel properties and a lower C/N. This indicates that the magnetic recording medium obtained by the present invention has excellent mechanical strength and durability, good dispersibility and filling properties of the boron powder, and excellent electromagnetic conversion characteristics.

Claims (1)

[Claims] 1. Magnetic recording having a magnetic layer containing dipentaerythritol hexaacrylate, an ester of dipentaerythritol and 5 or less acrylic acid, a radiation-curable resin, a vinyl chloride resin, and a magnetic powder. medium