JPS6275928A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the preservable property and durability of a magnetic layer by forming a coated film contg. >=2 kinds of radiation sensitive resins having mol.wt. of a prescribed value or above and prescribed value or below and thermoplastic resin as a binder component for magnetic powder on a substrate and irradiating a radiation thereon to cure the coated film, thereby providing the magnetic layer. CONSTITUTION:The coated film contg. the radiation sensitive resin having >=8,000mol.wt. and radiation sensitive resin having <=2,000mol.wt. and the thermoplastic resin as the binder component for the magnetic powder is formed on the substrate and the radiation is irradiated thereon to cure the coated film, by which the magnetic layer is formed. The radiation sensitive resin having >=8,000mol.wt. to be used is an urethane acrylate having an acryloyl group, has the good dispersibility and packability with the magnetic powder and has good compatibility with the radiation sensitive resin having <=2,000mol.wt. and thermoplastic resin and contributes to the formation of the strong and tough magnetic layer having a high modulus of elasticity and adequate elongation. The magnetic recording medium having a good electromagnetic conversion characteristic and excellent durability and shelf life is thus obtd.

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 storage stability and durability.

[Conventional technology]

In recent years, in magnetic recording media such as magnetic tape, recording,
In order to make the playback time as long as possible, thinner tapes are being made, and magnetic tapes that tend to be thinner in this way are strong, have excellent storage stability, and are durable.
A material with excellent electromagnetic conversion characteristics is required.

For this reason, in recent years, St radiation-sensitive resins have been used as binder components, for example, with a molecular weight of 20
A magnetic layer is formed by using a radiation-sensitive resin of 00 or less together with a thermoplastic resin and curing the radiation-sensitive resin by irradiation with radiation. (Unexamined Japanese Patent Publication No. 5
7 8613 (No. 1) [Problems to be solved by the invention] However, the conventionally used h (ray-sensitive resin)
Since it is a low molecular weight with a molecular weight of 2000 or less, the magnetic layer after cross-linking and curing is very flexible, and when stored in a high-grade product under high humidity, glabellar adhesion occurs between the magnetic layers, resulting in normal running conditions. To overcome this problem, attempts have been made to improve the flexibility of the magnetic layer by increasing the number of radiation-sensitive double bonds introduced into the molecule. While this makes the magnetic layer harder and improves storage stability, it also increases the brittleness of the magnetic layer, causing clogging of the magnetic head.
Sufficient durability has not yet been achieved, with powder falling from the cut edges and increased dropouts when the tape is cut in a predetermined manner.

[Means for solving problems]

This invention was made as a result of various studies in view of the current situation, and consists of a St radiation-sensitive resin with a molecular weight of aooo or more, a radiation-sensitive resin with a molecular weight of 2000 or less, and a thermoplastic resin as binder components. By using them together and curing them with radiation to form a magnetic layer, the magnetic layer can be made tough and the storage stability and durability of the magnetic layer can be sufficiently improved.

The radiation-sensitive resin with a molecular weight of 8,000 or more used in this invention is a urethane acrylate having an acryloyl group, and has excellent dispersibility and filling properties for magnetic powder.
It also has good compatibility with radiation-sensitive resins and thermoplastic resins having a molecular weight of 2000 or less. Therefore, the molecular weight of this species is 8
A magnetic coating is prepared by using a radiation-sensitive resin with a molecular weight of 000 or more in combination with a radiation-sensitive resin and a thermoplastic resin with a molecular weight of 2,000 or less, and after coating it on a substrate, it is polymerized and cured by irradiation with radiation. As a result, a strong magnetic I- having a high elastic modulus and appropriate elongation is formed, and a magnetic recording medium with good electromagnetic conversion characteristics and excellent durability and storage stability is obtained. As such radiation-sensitive resins having a molecular weight of 8,000 or more, those having 1 to 6 double bonds per molecule are preferably used. For example, acryloyl elastomer synthesized from polyester polyol and diisocyanate Polyurethane acrylates having groups introduced at the ends of the molecules or into the molecular chains are preferably used. A specific example of a printing product is Unidic 20-8 manufactured by Dainippon Ink and Chemicals.
13, Unidic 20-887-1 Unidic 20
-887-3, Unidic 19-8830-2, etc.

In addition, radiation-sensitive resins with a molecular weight of 2,000 or less are liquid and can be used to prepare magnetic paints with a small amount of solvent, so the dispersibility and filling properties of magnetic powder are good, and electromagnetic conversion characteristics can be improved. Furthermore, the magnetic layer is well polymerized and cured by irradiation with radiation, and a magnetic layer having excellent dispersibility and filling properties of the magnetic powder is formed. Also, the molecular weight is 800
hI has good compatibility with radiation-sensitive resins of 0 or more and has a molecular weight of aooo or more! When used in combination with a radiation-sensitive resin, the radiation-sensitive resin with a molecular weight of 2,000 or less and the radiation-sensitive resin with a molecular weight of 8,000 or more are crosslinked by radiation irradiation, resulting in a radiation-sensitive resin with a molecular weight of 8,000 or more. When polymerized and cured without using a mold resin, the flexibility is improved and a strong magnetic layer with appropriate elongation is formed.

Therefore, even when stored under high temperature and high humidity conditions, glabellar adhesion does not occur, and a magnetic layer with further improved storage stability and durability is formed. If such a molecular weight is 200
0X;), as the radiation-sensitive resin below, those having 1 to 20 double bonds per molecule are preferably used, such as methyl methacrylate, methyl acrylate,
Acrylic monomers such as butyl acrylate, acrylic acid, methacrylic acid or mixtures thereof; mixtures of styrene, vinyl acetate and acrylonitrile; mixtures of 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and glycidyl methacrylate; Mixture, trimethylolpropane trimethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol pentaacrylate, urethane acrylic oligomer, epoxy acrylic oligomer, polyester acrylic oligomer, polybutadiene acrylic oligomer, polyamide acrylic oligomer, polyether acrylic oligomer, oligoester Radiation-sensitive resins such as acrylic oligomers and subiroahicuru acrylic oligomers are preferably used. A specific example of a commercially available product is, for example, TMPT manufactured by Shin-Nakamura Chemical Industry Co., Ltd.

DPHA, DPPA manufactured by Nippon Kayaku Co., Ltd., M-6 manufactured by Toagosei Co., Ltd.
250, M-7100, M-8030, M-1100,
M-1200, Thiokol U-782, U-783
, U-788, U-893, 5P-4 manufactured by Showa Kobunshi Co., Ltd.
010, U-3000, E-4000, 3200.3500.3600.3700 manufactured by Celanese, UV U-512 manufactured by Kochu Kasei, and the like.

The mixing ratio of the radiation-sensitive resin with a molecular weight of 2000 or less and the radiation-sensitive resin with a molecular weight of 8000 or more is the weight ratio of the radiation-sensitive resin with a molecular weight of 2000 or less to the radiation-sensitive resin with a molecular weight of 8000 or more. Make it into resin 2
It is preferable to mix within the range of 0:80 to 80:20, preferably within the range of 30:70 to 70:30,
If the amount of the radiation-sensitive resin having a molecular weight of 2,000 or less is too large, the magnetic layer will become excessively flexible, and if it is too small, the magnetic layer will become brittle.

In addition, the thermoplastic resin used in combination with the radiation-sensitive resin having a molecular weight of 8,000 or more and the radiation-sensitive resin having a molecular weight of 2,000 or less includes (vinyl chloride)!
1 resin, polyvinyl acecool resin, cellulose resin, polyester resin, etc., which are generally used in magnetic recording media, are preferably used. All of these thermoplastic resins have good affinity with magnetic powder and have excellent dispersibility of magnetic powder, so when these types of thermoplastic resins are used together, the dispersibility of magnetic powder is further improved. and the electromagnetic conversion characteristics are increased by 11+1. vinyl chloride
Examples of vinyl-based resins include vinyl chloride-ffi-vinyl acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maltwin acid copolymer, and vinyl chloride-vinyl propionate copolymer. Copolymers and the like are preferably used, and specific examples include, for example, US+1. V Y HII manufactured by C.C.

VAG Is, VMCN, Sekisui Chemical Company ijl
I-SLETSUKU A, SRESOK CN, LURERON QS-430, LURERON QA-431 manufactured by Toyo Soda Co., Ltd., and the like. Further, as the polyvinyl acecool resin, for example, polyvinyl butyral resin is suitably used, and specific examples include S-Resoku BLS, S-Resoku BMS, S-Resoku B L-1, and Hoechst manufactured by Block Chemical Industry Co., Ltd. Examples include Mobital B manufactured by Javan.

Examples of cellulose resins include nitrocellulose, acetylcellulose, acetylbutylcellulose, methylcellulose, ethylcellulose, benzylcellulose,
Carboxymethylcellulose, hydroxycellulose, etc. are preferably used, and specific examples include nitrocellulose L1/2 and Ll/4 manufactured by Asahi Kasei Corporation.
, T-1,) 11/4, II 1/2, Hl,
1] 5, Nitrocellulose R3I/16 manufactured by Daicel Corporation,
Examples include R3I/2, R81, and R32. Further, as the polyester resin, commonly used saturated or unsaturated polyester resins having a molecular weight of about 10,000 to 30,000, or polyester resins containing sulfonic groups or sulfonic acid bases are preferably used, Specific examples include Byron #200, Byron #300, Byron #400, and polyester GX-W1 manufactured by Toyobo Co., Ltd.

The blending ratio of such a thermoplastic resin and the radiation-sensitive resin, which is the sum of the radiation-sensitive resin with a molecular weight of 8,000 or more and the radiation-sensitive resin with a molecular weight of 2,000 or less, is based on the weight ratio of the thermoplastic resin to the radiation-sensitive resin. The ratio of radiation-sensitive n1 fat is preferably within the range of 30:70 to 80:20,
If the amount of thermoplastic resin is too small, the dispersibility of the magnetic powder will not be good, and if the amount of radiation-sensitive resin is too small, a sufficiently strong magnetic layer will not be obtained.

The radiation used in polymerizing and curing the radiation-sensitive resin used in the present invention is β radiation such as an electron beam.
rays, and gamma rays such as ultraviolet rays and X-rays are preferably used. When ultraviolet rays are used, a sensitizer is used at the same time to make the effect of irradiation more efficient. It is preferable to irradiate such radiation using radiation with an accelerating voltage of 150 to 75 (!KV) so that the absorbed dose is 3 to 15 Mrad. If the absorbed dose is too small, crosslinking of the radiation-sensitive 414 resin will occur. The desired effect cannot be obtained due to insufficient binding.

The magnetic layer of the present invention is formed using the radiation-sensitive resin having a molecular weight of 8,000 or more and the above-mentioned radiation-sensitive resin having a molecular weight of 2.
:000 or less radiation sensitive tree and thermoplastic resin,
A magnetic paint is prepared by dispersing and mixing magnetic powder, an organic solvent, and other necessary components, and this is applied onto a substrate such as polyester film, followed by polymerization and curing by irradiation with radiation.

Examples of magnetic powder used for the head include r-F'
e203 powder, Fe3O4 powder, CO-containing T-Fe20
In addition to the Co-containing Fe50+I'fl powder, CrO2 powder, various conventionally known magnetic 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 singly or in a mixture of two kinds.

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

〔Example〕

Next, embodiments of the invention will be described.

Example 1 α-F6 magnetic powder 100 Car M part Esresoku A (manufactured by Block Chemical Industry Co., Ltd. 15.36, vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Unidic+9-8830- 3.84 〃2 (large Nippon Ink Kagaku Kogyo Co., Ltd., polyurethane acrylate, molecular weight approximately 10,000. Number of double bonds per molecule: 2) r) PIIA (Nippon Kakane Co., Ltd., Gibe 1.28) -l and dipentaerythritol pentaacrylate]-1, molecular weight approximately 600. Number of double bonds per molecule: 6)
powder 5
〃Myristic acid 4 〃Cyclohexanone 100〃L・Luene
100 This composition was mixed and dispersed in a ball mill for 96 hours to prepare a magnetic paint, and this magnetic paint was applied onto a polyester hex film having a thickness of 1171 In to a coating thickness of about 3 pm. After calendering, the film is cured by irradiating it with radiation at a dose of 8 Mrad using a curtain-type electron beam irradiation device manufactured by F, SI, and then cut into a predetermined width to make a videotape.

Examples 2 to 5 In the composition of the magnetic paint in Example 1, Eslesoku A, Unidy 7li 19-8830-2 and D P
A videotape was made in the same manner as in Example 1, except that the blending ratio of the radiation-sensitive resin, including the total amount of HA, was changed as shown in Table 1 below.

Table 1 Examples 6 to 10 The composition of the magnetic paint in Example 4 was the same as that of Example 4, except that the blending ratio of Unidic 19-8830-2 and DPI (A) was changed as shown in Table 2 below. A videotape was made in the same manner as in step 4.

Table 2 Example 11 In the composition of the magnetic paint in Example 4, Unidic 2 (1-
A videotape was made in the same manner as in Example 4, except that the same amount of 887-4 (manufactured by Dainippon Ink and Chemicals, polyurethane 7 acrylate, molecular weight 50,000, number of double bonds per molecule was 6) was used. .

Ml; A videotape was made in the same manner as in Example 6, except that the same amount of number 3) was used.

Comparative Example 1 A videotape was produced in the same manner as in Example 4, except that only D P 11 A was used as the radiation-sensitive resin in the composition of the magnetic paint in Example 4.

Comparative Example 2 In the composition of the magnetic paint in Comparative Example 1, DP HA
A videotape was made in the same manner as in Comparative Example I, except that the same amount of Cl-201 (manufactured by Mitsubishi Kasei Corporation, polyurethane acrylate, molecular weight approximately 1100. number of double bonds per molecule was 3) was used instead of Cl-201. .

Videotape 1' obtained in each example and comparative example
/ We investigated storage stability, clogging, and dropout. The storage stability was determined by winding the obtained videotape in a glass tube with a diameter of 3 cm at a tension of Ikg, overlapping it by about 1 m, and then keeping it at a temperature of 60°C.
℃ and 40% humidity for 90 hours, and then gently unrolled without tension to observe the presence or absence of interlayer adhesion.If no glabellar adhesion was observed (
(○), cases where it was slightly observed (△), and cases where it was observed a lot (x). To check for clogging, approximately 250 m of the obtained videotape was installed in a VH3 type cartridge and run on a 1/2 inch VHS video deck, and the number of runs until head clogging occurred was measured. Note that the upper limit of the number of runs was 100. Furthermore, dropouts were investigated by counting the number of dropouts per minute using a dropout counter.

Table 3 below shows the results.

Table 3 [Effects of the Invention] As is clear from the above table, the videotapes obtained in Examples 1 to 12 had a longer running time before clogging occurred than the videotapes obtained in Comparative Examples 1 and 2. The magnetic recording medium obtained by the present invention is strong and has excellent storage stability and durability.

Claims (1)

[Claims] 1. A coating film containing a radiation-sensitive resin with a molecular weight of 8,000 or more, a radiation-sensitive resin with a molecular weight of 2,000 or less, and a thermoplastic resin as binder components of magnetic powder is formed on the substrate, and this is exposed to radiation. A magnetic recording medium characterized by having a magnetic layer hardened by irradiation with