JPS62154223A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve an electromagnetic conversion characteristic and durability by forming a coated film contg. a hydroxyl group-contg. resin curable by radiations and iscoyanate compd. as a binder component for magnetic powder on a substrate and irradiating the radiations thereto to cure the coated film thereby providing the magnetic layer. CONSTITUTION:A resin which has 5-1,000 hydroxyl group value and has >=1 double bonds and 1,000-40,000mol.wt. is perferably used as the hydroxyl group- contg. resin curable by radiations. The generation of flaws and ruggedness on the surface of the magnetic layer during the processing in a coating stage and calender treatment stage is obviated when the above-mentioned resin is used in combination with the isocyanate compd. The effect thereof is not enough if the hydroxyl group value is 15 or below and the solubility in an org. solvent is not satisfactory when said value is increased to 1,000 or above. Since the resin has >=1 double bonds, the tough magnetic layer is formed by the irradiation of the radiations after the calender treatment. The dispersibility and packability of the magnetic powder are good and the magnetic layer having the good dispersibliity and packability of the magnetic powder is formed if the mol.wt. is within the above-mentioned range.

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 electromagnetic conversion characteristics and durability.

[Conventional technology]

In recent years, in magnetic recording media such as magnetic tape, recording,
In order to lengthen playback time as much as possible, efforts are being made to make magnetic tapes thinner, and such thinner magnetic tapes are required to be strong and durable, as well as having excellent electromagnetic conversion characteristics. Ru.

For this reason, in recent years, radiation-sensitive resins have been used as binder components. For example, radiation-sensitive resins containing hydroxyl groups are used and hardened by irradiation with radiation to form a magnetic layer. ing. (Unexamined Japanese Patent Publication 1986-
No. 50721) [Problem to be solved by the invention] However, radiation-sensitive resins such as this hydroxyl group-containing radiation-sensitive resin are uncured until they are crosslinked and cured by irradiation with radiation. The strength of the magnetic layer is not yet sufficient during the magnetic paint coating and calendering steps until it is finished, and as a result, scratches and unevenness may occur on the surface of the magnetic layer during these coating and calendering steps. Because of this, it is not possible to obtain sufficiently satisfactory electromagnetic conversion characteristics, and the durability is still insufficient.

[Means for Solving the Problems] This invention was made as a result of various studies in view of the current situation, and it is based on the combination of a hydroxyl group-containing radiation-sensitive resin and an isocyanate compound as a binder component of magnetic powder. By adding an isocyanate compound to the magnetic paint, at the same time, the isocyanate compound is crosslinked with a hydroxyl group-containing radiation-sensitive resin, and the strength of the magnetic layer is made sufficient until it is coated on the substrate and irradiated with radiation. , the occurrence of scratches and unevenness on the surface of the magnetic layer during the coating process and calendering process is well prevented, and the electromagnetic conversion characteristics and durability are sufficiently improved.

The hydroxyl group-containing radiation-sensitive resin used in this invention preferably has a hydroxyl value of 15 to 1,000, has one or more double bonds, and has a molecular weight of 1,000 to 40,000, since it contains hydroxyl groups. When used in combination with an isocyanate compound, when the isocyanate compound is added to the magnetic paint, the contained hydroxyl groups crosslink with the isocyanate group of the isocyanate compound, and the magnetic paint is applied onto the substrate and irradiated with radiation. The strength of the magnetic layer is sufficiently strengthened.

Therefore, no scratches or irregularities will occur on the surface of the magnetic layer during the coating process and calendering process. Such effects are not sufficient when the hydroxyl value is less than 15.
If it is more than 000, is there tJl? The solubility for the drug No. 8 becomes insufficient. In addition, since it has one or more double bonds, it is cross-linked and hardened well by irradiation with radiation after calendering, forming a strong magnetic layer, and the molecular weight is within the range of 1,000 to 40,000. The magnetic powder has good dispersibility and filling properties, and a magnetic layer with excellent dispersibility and filling properties of the magnetic powder is formed. Therefore, when this type of hydroxyl group-containing radiation-sensitive resin is used in combination with an isocyanate compound, a sufficiently strong magnetic layer can be formed without causing scratches or unevenness on the surface of the magnetic layer during the manufacturing process of magnetic recording media. A magnetic recording medium with excellent electromagnetic characteristics and durability can be obtained.

Examples of such hydroxyl group-containing radiation-sensitive resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, butyral, nitrocellulose, and phenoxy resin. Preferably used are those in which some hydroxyl groups remain and radiation-sensitive groups are introduced, or radiation-sensitive urethane resins containing hydroxyl groups. Introduction of radiation-sensitive groups into these thermoplastic resins is described, for example, in JP-A-60-43222. Furthermore, a synthesis example of a radiation-sensitive urethane resin containing a hydroxyl group is shown in, for example, JP-A-59-223712.

In addition, the isocyanate compound used in combination is preferably one having at least one isocyanate group in one molecule, and when this type of isocyanate compound is used in combination with the above-mentioned hydroxyl group-containing radiation-sensitive resin, magnetic paint At the same time, the isocyanate group of the isocyanate compound and the hydroxyl group of the hydroxyl group-containing radiation-sensitive resin react and crosslink, and the magnetic paint is applied onto the substrate and irradiated with radiation. The strength of the magnetic layer is sufficiently strengthened. Therefore, no scratches or irregularities occur on the surface of the magnetic layer during the coating process and the calendering process, and the electromagnetic characteristics and durability are sufficiently improved.

Examples of such isocyanate compounds include ■
-Methylhenzole-2.4.6-triisocyanate, triphenylmethane-4,4°4-triisocyanate, trimethylolpropane tolylene diisocyanate, etc. are preferably used, and specific examples of commercially available products include, for example, Japan Examples include Coronate L, manufactured by Polyurethane Industries, Ltd., Desmodur Shi-75, manufactured by Bayer, and Takene 1-D 102, manufactured by Takeda Pharmaceutical Company.

The blending ratio of such an isocyanate compound and the above-mentioned hydroxyl group-containing radiation-sensitive resin is 9 by weight, in terms of hydroxyl group-containing radiation-sensitive resin to isocyanate compound.
Within the range of 5:5 to 60:40, preferably 90:10 to
The ratio is preferably within the range of 70:30; if the amount of isocyanate compound is too small, the strength of the magnetic layer cannot be sufficiently strengthened before irradiation with radiation, and if it is too large, unreacted isocyanate compound If there is too much, the strength of the magnetic layer will be insufficient.

In addition, in addition to the pond of isocyanate compounds, vinyl chloride resin, polyvinyl acecool resin, cellulose resin,
Thermoplastic resins commonly used in magnetic recording media, such as polyurethane resins and polyester resins, may be used in combination.

As the radiation used in polymerizing and curing the hydroxyl group-containing radiation-sensitive resin used in the present invention, β-rays such as electron beams, and T-rays such as ultraviolet rays and X-rays are preferably used. When using ultraviolet light, a sensitizer is used at the same time to make the effect of the 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 hydroxyl group-containing radiation-sensitive resin will be insufficient and the desired effect will not be obtained. .

The magnetic layer of the present invention is formed by dispersing and mixing the above-mentioned hydroxyl group-containing radiation-sensitive resin and an isocyanate compound together with magnetic powder, an organic solvent, and other necessary components to prepare a magnetic coating material, which is then applied to a polyester film or the like. After coating on a substrate, it is crosslinked and cured by irradiation with radiation.

As the magnetic powder used here, for example, r-Fe
203 powder, l';' 6304 powder, Co-containing r-F
In addition to e203 powder, Co-containing Fe3O4 powder, and CrO2 powder, various conventionally known magnetic powders such as gold powder 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, lubricants, abrasives, antistatic agents, and the like may be optionally added.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Hexamethylene diisocyanate 378 parts ffi, 2
-Butanone 300mj! was heated to 75°C in a fourth flask at 4β in a stream of N2. After heating, polyester diol (reaction product of adipic acid and 1,4-butanediol, Hitachi Kasei Polymer Co., Ltd., RiUDIOIO) 10
00 Senior Minister, N-isopropanoljetanolamine 163 i Lube, tin octylate 0.05 parts by weight, 2
- 500rni of butanone is added at a temperature of 75-80℃ in the reaction system.
The mixture was added dropwise while controlling the temperature so that the temperature was maintained at .degree. C., and after the addition was completed, the mixture was stirred at 80.degree. C. for 2 hours. Next, part of 2-hydroxyethyl acrylate-1-57iHi was added, and the mixture was further stirred for 3 hours to complete the reaction. The molecular weight of the obtained hydroxyl group-containing radiation-sensitive urethane resin was about 15,000.

The hydroxyl value was 35. Using the hydroxyl group-containing radiation-sensitive urethane resin thus obtained, α-Fe magnetic powder 100 parts by weight hydroxyl group-containing radiation-sensitive urethane resin 22.5 Tan resin carbon blank 2 Al2O3 powder 5 ・Myristic acid
4 Cyclohexanone 10
After mixing and dispersing the composition of 0 toluene and 100 in a ball mill for 48 hours, 2.5 parts by weight of Coronate L (a trifunctional low molecular weight isocyanate compound manufactured by Rohon Polyurethane Industries Co., Ltd.) was further added, and 1
A magnetic paint was prepared by mixing for 2 hours. This magnetic paint was applied to a polyester base film with a thickness of 11 μm to a coating thickness of about 3 μm, dried, and then calendered. It was cured by irradiation with radiation at a dose of . After that, they were cut to the specified width and made into video tapes.

Example 2 In the composition of the magnetic paint in Example 1, the amount of hydroxyl group-containing radiation-sensitive urethane resin used was changed from 22.5 parts by weight to 18.25 parts by weight, and the amount of Coronate L used was changed to 2.5 parts by weight. Except for changing from part to 6.25 parts by weight.
A videotape was made in the same manner as in Example 1.

Comparative Example 1 In the composition of the magnetic paint in Example 1, the amount of hydroxyl foundation and radiation-sensitive urethane resin used was changed from 22.5 parts by weight to 25 parts by weight, and Coronate L was omitted. I made a videotape in the same way.

1/2 of the videotape obtained in each example and comparative example
The video characteristics were investigated by loading the camera into an inch VHS type video deck and measuring the RF specific output chroma output, video S/N, and color S/N. Approximately 250 m of the video tapes obtained in each of the Examples and Comparative Examples were placed in a cassette and run 100 times on a 1/2 inch V 11 S type video deck, after which the decrease in RF output was measured to examine durability. The measured values are expressed as relative values based on the measured values of the videotape obtained in Comparative Example 1.

The table below shows the results.

□□- [Effects of the Invention] As is clear from the above table, the video tapes obtained in l1f6 Examples 1 and 2 had better video characteristics than the video tape obtained in Comparative Example 1. There was almost no decrease in RF output, which indicates that the magnetic recording medium obtained by the present invention has excellent electromagnetic conversion characteristics and durability.

Claims (1)

[Claims] 1. A magnetic layer formed by forming a coating film containing a hydroxyl group-containing radiation-sensitive resin and an isocyanate compound as binder components of magnetic powder on a substrate, and curing the film by irradiating it with radiation. A magnetic recording medium 2 characterized in that it is provided with a magnetic recording medium 2, a magnetic recording medium 3 according to claim 1, wherein the hydroxyl group-containing radiation-sensitive resin contained as a binder component has a hydroxyl value of 15 to 1000, and a binder. The magnetic recording medium according to claim 1, wherein the hydroxyl group-containing radiation-sensitive resin contained as a component has a molecular weight of 1,000 to 40,000.