JPS59162640A - 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 a radiation curing resin as binder components and a small amount of an org. solvent. CONSTITUTION:A magnetic layer contg. dipentaerythritol hexaacrylate, the mono to pentaester of dipentaerythritol with acrylic acid, a radiation curing 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. As a result, the dispersibility and fillability of the magnetic powder can be improved. It is preferable that the radiation curing resin has <10,000mol.wt. and 2-4 functional groups.

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. 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 formation of the boronous layer, and the reaction is not complete, making it impossible to sufficiently improve durability.

Therefore, as a method to improve this, in recent years, radiation-sensitive modified resins such as acrylic double bond-introduced vinyl chloride-vinyl acetate copolymer and radiation-responsive elastomers such as acrylic double bond-introduced urethane elastomers have been mixed. A curable resin is used, this radiation curable resin is mixed and dispersed with magnetic powder, etc. to prepare a magnetic paint, and after this magnetic paint is applied onto a substrate, radiation is irradiated to cause the radiation curable resin to undergo radiation polymerization. A method of forming a magnetic layer has been proposed, but although this method improves the elastic modulus and abrasion resistance of the magnetic layer, and also improves the dispersibility and filling properties of magnetic powder, it is still insufficient and still remains unresolved. Fully satisfactory results have not been obtained.

The inventors conducted various studies in view of the current situation, and found that dipentaerythritol hexaacrylate,
When dipentaerythritol and an ester of 5 or less acrylic acid are mixed, it becomes liquid, and when such a liquid acrylic oligomer is used in combination with a radiation-curable resin as a binder component, the acrylic oligomer is liquid and can be used in combination. Since the binder component is also a radiation-curable resin, magnetic paints can be prepared with a small amount of organic solvent, and the dispersibility and filling properties of magnetic powders are sufficiently improved, making it possible to prepare magnetic paints containing these and magnetic powders. When applied onto a substrate and then irradiated with radiation, the acrylic oligomer and radiation-curable resin are polymerized and cured by the radiation, resulting in improved dispersibility and filling properties of the magnetic powder and further improved electromagnetic conversion characteristics. The inventors have discovered that a magnetic layer with improved mechanical strength can be obtained, and the abrasion resistance of the magnetic layer is improved, resulting in further improved durability and improved modulus of elasticity. He came up with an invention.

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 number of double bond groups per molecule. Because of the large amount of powder, it is possible to prepare magnetic coatings with a small amount of solvent, and the crosslinking density when polymerized and cured by radiation irradiation is high. Therefore, the dispersibility and filling properties of the magnetic powder can be improved, and the electromagnetic conversion characteristics can be improved. At the same time, the abrasion resistance and elastic modulus of the magnetic layer are also improved, and the durability and mechanical strength are further improved. The pentaerythritol type acrylate that is mixed and used in this way 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 When an ester of 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 liquefied by mixing and sufficiently improves the filling properties and crosslinking density of the magnetic powder. Therefore, the weight ratio of dipentaerythritol hexaacrylate to ester of dipentaerythritol and 5 or less acrylic acid is 10:1 to 1.
, 1:10, and more preferably, the average number of acrylic groups is 5 or more in order to obtain a sufficient crosslinking density and sufficiently improve mechanical strength and durability.

Further, the radiation-curable resin used in combination is not particularly limited, but those having a molecular weight of less than 10,000 and a number of functional groups of 2 to 4 are 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. It is possible to increase the content of curable resin, further reduce the amount of organic solvent used, and further improve the dispersibility and filling properties of the magnetic powder, as well as improve the mechanical strength and wear resistance of the magnetic layer. It can be improved further. Specific examples of such radiation-curable resins include urethane acrylic oligomers, epoxy acrylic oligomers, oligoester acrylic oligomers, and spiroacecool acrylic oligomers. U-782, U-783, U-788, U-893, Toagosei M-1100, M-1200, Showa Kobunshi Co., Ltd. 5P-4010, Celanese Co., Ltd. 3200.3500
．． 3600.3700, Toagosei M-6250, M
-7100, M-8030, Surabisoku U-3000, E-4000 manufactured by Showa Kobunshi Co., Ltd., and the like.

the dipentaerythritol hexaacrylate;
The mixing ratio of the liquid acrylic oligomer, which is a mixture of dipentaerythritol and an ester of 5 or less acrylic acid, and the radiation-curable resin is 1:99 to 99:1:1 to the radiation-curable resin, by weight. vs 1
The ratio should be within the range of 10 to 90 to 90.
It is preferable to mix the liquid acrylic oligomer within a range of 10 to 10. If the liquid acrylic oligomer is too small, the filling properties and dispersibility of the magnetic powder and the mechanical strength and abrasion resistance of the magnetic layer will not be sufficiently improved; If the amount is too high, the magnetic layer will become too hard and brittle, leading to decreased durability. Gamma 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 sunlight more efficient. It is preferable to irradiate such radiation using 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 liquid acrylic oligomer and radiation curing resin will be The desired effect cannot be obtained due to insufficient cross-linking.

To form the magnetic layer of the present invention, a liquid acrylic oligomer prepared by mixing the dipentaerythritol hexaacrylate, an ester of dipentaerythritol and 5 or less acrylic acid, and a radiation-curable resin are combined into an organic This is done by dissolving it in a solvent and dispersing and mixing magnetic powder in this solution to prepare a magnetic coating, which is applied onto a substrate such as a polyester film, and then irradiated with radiation to polymerize and harden.

As the magnetic powder used here, for example, rFe2
In addition to O3 powder, Fe3O4 powder, co-containing r-Fe203 powder, Go-containing Fe3O4 powder, CrO2 powder, F
Various conventionally known magnetic powders such as metal powders such as e powder, Co powder, and Fe-N+ 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, 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 dipentaerythritol hexa 20 acrylate dipentaerythritol penta 20 acrylate M-6250 (manufactured by Toagosei Co., Ltd., 160112 functional oligoester acrylate) myristic acid 15 n-butyl stearate 10〃Methyl isobutyl ketone
500〃Toluene 500〃
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 irradiating it with radiation at a dose of 7 Mrad using EPS-750 manufactured by Nishin High Voltage Co., Ltd., and was cut into a predetermined width to produce a magnetic tape.

Example 2 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 M-1200 (urethane acrylate manufactured by Toagosei Co., Ltd.) was used in place of M-0.

Example 3 In the composition of the magnetic paint in Example 1, M-625
A tape was made in the same manner as in Example 1, except that the same amount of 3200 (epoxy 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, M-625
omitting 0, dipentaerythritol to hexaacrylate-1
- 100 parts by weight of acrylic double bond-introduced vinyl chloride-vinyl acetate copolymer was used instead of 20 parts by weight, and 100 parts by weight of acrylic double bond-introduced urethane elastomer was used in place of 20 parts by weight of dipentaerythritol pentaacrylate. A magnetic tape was produced in the same manner as in Example 1 except for the following.

The magnetic tape prepared in each Example and Comparative Example was loaded into a video deck, a 4.5 MHz carrier signal was recorded, the playback output was extracted, and the ratio C between the peak value C and the integral value N of the total noise was determined. /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 a higher elastic modulus than the magnetic tape obtained in Comparative Example 1, and have longer steel properties and higher C/N. This shows 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. A magnetic recording medium having a magnetic layer containing dipentaerythritol hexaacrylate, an ester of dipentaerythritol and 5 or less acrylic acid, a radiation-curable resin, and a magnetic powder.