JPS59162630A - 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, polyvinyl acetal resin and magnetic powder so as to improve the dispersibility and fillability of the magnetic powder. CONSTITUTION:The acrylic oligomer is prepd. by mixing dipentaerythritol hexaacrylate with the ester of dipentaerythritol with pentaacrylic acid or lower. Polyvinyl butyral resin or the like is suitable for use as the polyvinyl acetal resin used in combination with the liq. acrylic oligomer and the radiation curing resin, and for example, ''S-lec BLS'', ''S-lec BMS'', ''S-lec BL-1'' or ''Mowital B'' is used. The polyvinyl acetal resin is used by 1-80wt% of the total amount of the binder components. The magnetic powder is gamma-Fe2O3 powder, Fe3O4 powder or metallic powder such as Fe-Ni powder.

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 binder resins with high elastic modulus such as high molecular weight polyurethane resins or two-component reactive binder resins such as polyol and isocyanate compounds. 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, it has disadvantages such as heat treatment after formation of the magnetic layer, incomplete reaction, and insufficient 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 7 oligomers, and after coating the magnetic coating material on a substrate, radiation is irradiated to polymerize the 7 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.

The inventors have conducted various studies in view of the current situation, and have found that when dipentaerythritol hexaacrylate and an ester of dipentaerythritol and 5 or less acrylic acid are mixed, they become liquid. acrylic oligomer, polyvinyl acecool resin,
A magnetic paint containing magnetic powder is applied onto the 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 excellent electromagnetic conversion characteristics,
We also found that the abrasion resistance of the magnetic layer was improved, increasing its durability, and the elastic modulus was also improved, increasing its mechanical strength. Furthermore, when a radiation-curable resin is used in combination, the dispersibility and filling properties of the magnetic powder are further improved, and the abrasion resistance and elastic modulus of the magnetic layer are also further improved, resulting in even better electrical conversion characteristics, durability, and It was discovered that a magnetic recording medium with excellent mechanical strength can be obtained, and the present invention was completed.

The acrylic oligomer used in this invention, which is a mixture of dipentaerythritol hexaacrylate and an ester of dipentaerythritol and 5 or less acrylic acid, is liquid and has a large number of double bond groups per molecule, so it can be used in small amounts. It is possible to prepare a magnetic paint using a solvent, and when it is polymerized and cured by radiation irradiation, the crosslinking density is high, and therefore the dispersibility and filling properties of the magnetic powder can be improved, and the electromagnetic conversion characteristics can be improved. t
The abrasion resistance and elastic modulus of the magnetic layer are also improved to further improve 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
When this is mixed with solid or liquid dipentaerythritol and an ester of 5 or less acrylic acid, it becomes a liquid acrylic oligomer, and as mentioned above, magnetic paint can be prepared with a small amount of solvent, and it is also irradiated with radiation to increase the crosslinking density. is obtained. Such a mixing ratio of dipentaerythritol hexaacrylate-1- and an 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. In order to obtain a weight ratio of dipentaerythritol hexaacrylate to an ester of dipentaerythritol and acrylic acid of 5 or less, 10
It is preferable to mix within the range of 1:1 to 1:10, and furthermore, in order to have a sufficient crosslinking density and sufficiently improve mechanical strength and durability, it is preferable to mix so that the average number of acrylic groups is 5 or more. is more preferable. In addition, the amount of the liquid acrylic oligomer blended in this way is preferably within the range of 1 to 80% by weight based on the total amount of the binder components. If the mechanical strength and abrasion resistance are not sufficiently improved and the amount is too high, the magnetic layer becomes too hard (and becomes brittle), causing problems in durability.

In addition, 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 then irradiated with 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 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 further improved, and the mechanical strength and sealing resistance of the magnetic layer can be improved. Abrasion resistance can be further improved. Specific examples of such radiation-curable resins include:
For example, urethane acrylic oligomer, epoxy acrylic oligomer, oligoester acrylic oligomer,
Examples include spiroacecool acrylic oligomer,
As a specific example of a commercially available product, for example, M-
625 (1, M-7100, M-8130, M-110
0, M-1200, Thiokol u-782, U-7
83, U-788, U-893, 5P4 manufactured by Showa Kobunshi Co., Ltd.
010, U-3000, E-400 (1, Celanise company 32 (1 (1, 35 (1 (+, 3b00.37oO
etc. can be mentioned. The amount used is 1 to 4 based on the total amount of binder components.
It is preferable to use it within the range of 0 weight percent; 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 increased and the mechanical strength will not be sufficiently improved.

The polyvinyl acecool resin used in combination with the liquid acrylic oligomer and radiation-curable resin has good affinity with magnetic powder and has excellent dispersibility of the magnetic powder, so this type of polyvinyl acecool resin is used in combination. This further improves the dispersibility of the magnetic powder and improves the electromagnetic characteristics. As such a polyvinyl acecool resin, for example, polyvinyl butyral resin is preferably used, and specific examples include Eslenoku BLS and Eslec B manufactured by Tanezu Chemical Industry Co., Ltd.
MS, Eslenok BL-1, Mobicool B manufactured by Hequist Japan Co., Ltd., and the like. The amount used is preferably within the range of 1 to 80% by weight based on the total amount of the binder components; if it is too small, the dispersibility of the magnetic powder will not be sufficiently improved.
If the amount is too large, a sufficient modulus of elasticity cannot be obtained and 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
It is preferable to irradiate using 0 KV radiation so that the absorbed dose is 3 to 15 Mrad. If the absorbed dose is too small, the crosslinking of the liquid acrylic oligomer and radiation-curable resin will be insufficient and the desired effect will not be achieved. I can't get it.

To form the magnetic layer of the present invention, the above-mentioned dipentaerythritol hexaacrylate, a liquid acrylic oligomer prepared by mixing an ester of dipentaerythritol and 5 or less acrylic acid, a radiation-curable resin, and a polyvinyl Acecool resin is dissolved in an organic solvent, magnetic powder is dispersed and mixed in this solution to prepare a magnetic paint, and after coating this on a substrate such as a polyester film, it is polymerized and cured by irradiation with radiation. carried out by

As the magnetic powder used here, for example, γ-F6
203 powder, Fe1O* powder, Co-containing r-Fe203
powder, CO-containing Fe3O4 powder, CrO2 powder, F
Various conventionally known magnetic powders such as metal powders such as e-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, dimethyl formamide, etc. are used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, 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 BLS (manufactured by Suihiro Kagaku-1-4011 Gyosha, polyvinyl butyral tree JIFI> Dipentaerythritol hexa 60 acrylate Dipentaerythritol penta 60 Acrylate M-6250C bundle subsynthesis 40 Bifunctional oligoester acrylate) Myristic acid 15 - n-butyl stearate 10 Methyl isobutyl ketone 450 Toluene 45
0 This composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic paint, and this magnetic paint was applied onto 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 irradiation with radiation at a dose of 7 Mrad using NEPS-750 manufactured by Nishin High Voltage Co., Ltd., and cut into a predetermined size "1" to produce a magnetic tape.

Example 2 Implementation flit! In the composition of the magnetic paint in 1,
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of M-1100 (urethane acrylate manufactured by Toagosei Co., Ltd.) was used in place of M-6250.

Example 3 In the composition of the magnetic paint in Example, M-625
A magnetic tape was prepared in the same manner as in Example 1, except that 5 equivalent amounts of 3200 (epoxy acrylate manufactured by Celanese) were 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-300(] (pyroacecool acrylate manufactured by Showa Kobunshi Co., Ltd.) was used instead of 0.

Comparative Example 1 Example 1 except that 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. I made magnetic tape in the same way.

The magnetic tape obtained in each example and comparative example was loaded into a video deck, a carrier signal of 4.5 Mt (z) 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. The C/N was measured.The obtained magnetic tape was loaded into a video deck to measure the steel compatibility, and the elastic modulus of the iH 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 is the result.

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 C/
Therefore, the borium recording medium obtained by this invention has excellent mechanical strength and durability, good dispersibility and filling properties of magnetic powder, and excellent electromagnetic conversion characteristics. I know that there is.

Claims (1)

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