JPH036573B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a magnetic recording medium,
More specifically, the present invention relates to a magnetic recording medium using a binder that particularly improves adhesiveness to a non-magnetic support and can improve abrasion resistance and solvent resistance when used as a magnetic layer. Known trifunctional urethane acrylic resins have a larger molecular weight than commercially available acrylic oligomers and have urethane bonds in their molecules, so they are expected to have improved abrasion resistance and adhesive properties when used as binders for magnetic recording media. is expected.
However, although this single binder system of trifunctional urethane acrylic resin can be recognized to have improved abrasion resistance and adhesive properties compared to commercially available acrylic oligomers such as trimethylolpropane acrylate, when used as a magnetic tape, It cannot be said that these characteristics are sufficient compared to magnetic tape. Therefore, the present inventors have made it possible to practically apply such properties of trifunctional urethane acrylic resin, which may yield favorable results in terms of abrasion resistance and adhesion when used as a binder for magnetic recording media. As a result of intensive research, we found that if thermoplastic resins such as urethane resin and vinyl chloride resin are mixed in a specific ratio, abrasion resistance and adhesion will be improved, and compared to conventional thermosetting resins. The present invention was completed based on the discovery that since a higher crosslinking density can be obtained, solvent resistance is also significantly improved. Therefore, the present invention provides magnetic recording with improved abrasion resistance, adhesiveness, and solvent resistance by using a composition obtained by mixing a trifunctional urethane acrylic resin and a thermoplastic resin as a binder. It provides a medium. The trifunctional urethane acrylic resin used in this invention has the general formula: (In the formula, R means a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms, R ₁ , R ₂ and R ₃ each mean a lower alkylene group having 1 to 3 carbon atoms, m is 0 or 1,
n ₁ , n ₂ and n ₃ each mean an integer from 1 to 8, and uA means a diisocyanate residue, provided that when R is a hydrogen atom, m is 0 and R is a lower In the case of an alkyl group, m
is 1). In the general formula,
A lower alkyl group is a linear or branched monovalent saturated hydrocarbon residue, including a methyl group, an ethyl group, a propyl group, and an isopropyl group,
In addition, a lower alkylene group is a linear or branched divalent saturated hydrocarbon residue, and is a methylene group,
It includes ethylene group, propylene group, methylethylene group, etc. Furthermore, the diisocyanate residue means a residue of a diisocyanate compound in which a hydroxyalkyl ester of acrylic acid or methacrylic acid is added to one of its isocyanate groups, and a particularly preferred example of such a diisocyanate compound is 2-hydroxyethyl. Examples include aromatic diisocyanates such as tolylene diisocyanate and diphenylmethane-4,4'-diisocyanate in which acrylate or 2-hydroxyethyl methacrylate is added to one of the isocyanate groups. The trifunctional urethane acrylic resin used has a molecular weight between functional groups of about 300 to 800. is preferable. The above-mentioned trifunctional urethane acrylic resin can be produced by a conventional method. For example, a polyether triol is produced by reacting a triol such as glycerin or melimethylolpropane with an alkylene oxide such as ethylene oxide or propylene oxide. This triol can then be reacted with an addition type diisocyanate as described above. Next, other components of the composition used in the present invention include thermoplastic resins such as urethane resins, vinyl chloride resins such as vinyl chloride-vinyl acetate-vinyl alcohol copolymers, and celluloses such as nitrocellulose. Examples include derivatives. Further, such a thermoplastic resin is preferably appropriately selected and blended so that the glass transition temperature Tg thereof is about 25° C. to 80° C. in a system mixed with the above-mentioned trifunctional urethane acrylic resin in a specific ratio. Further, the mixing ratio of the trifunctional urethane acrylic resin and the thermoplastic resin as described above is preferably about 95/5 to 20/80. Any conventionally used magnetic powder can be used in the present invention, and examples of such magnetic powder include γ-Fe ₂ O ₃ ,
Fe ₃ O ₄ , iron oxide with an oxidation state intermediate between γ-Fe ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , Co
Iron oxide in an oxidation state intermediate between γ-Fe ₃ O ₄ and Fe ₃ O ₄ , iron oxide containing one or more metal elements (particularly transition metal elements), iron oxide containing Co oxide Oxide-based magnetic powders such as those with a coating layer mainly composed of hydroxides or hydroxides, CrO ₂ , CrO ₂ surface reduction treatment to form a Cr ₃ O ₂ layer, or Fe, Co, Ni, etc. metal or Fe-Co
Alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Co-Ni
-P alloy, Co-Ni-Fe-B alloy, Fe-Ni-Zn
Examples include ferromagnetic fine powders such as alloys, Fe-Mn-Zn alloys, and Fe-Co-Ni-P alloys. The magnetic paint made of electron beam curable resin and magnetic powder used in this invention also contains aluminum oxide, chromium oxide, silicon oxide as an abrasive, carbon black as an antistatic agent, and molybdenum disulfide as a lubricant. , graphite,
Silicone oil, olive oil, etc. can be added. Solvents that can be used to prepare such magnetic paints include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol; esters such as methyl acetate, ethyl acetate, butyl acetate, and ethyl butyrate; Glycol ethers such as ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, and dioxane;
Examples include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and heptane; and mixtures thereof. Furthermore,
Materials for the non-magnetic support that can be used include, for example, polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polycarbonates,
Examples include polyvinyl chloride, polyimide, metals such as aluminum and copper, and non-magnetic materials such as paper. It is preferable to apply the magnetic paint having the above-mentioned structure onto a non-magnetic support by a conventional method, dry it, and then irradiate it with an electron beam, but it is also possible to perform a calender treatment before or after irradiation. In addition to electron beams, neutron beams and γ
Ionizing radiation such as a beam can be used, and from an industrial perspective, an electron beam is preferable. Also, the irradiation amount is approximately 1 to 10 Mrad.
Good. When using an electron beam accelerator for irradiation, the irradiation energy is preferably about 100 KeV or more. Hereinafter, an example of manufacturing a trifunctional urethane acrylic resin used in Examples of this invention will be described. Production example 1 43g (0.37mol) was added to a solution of 65g (0.37mol) toluene diisocyanate dissolved in ethyl acetate.
0.5 of 2-hydroxyethyl acrylate per minute
It was added dropwise at a rate of cc. The reaction temperature in this case is approximately 60
℃, and the solids content was 75%. Further, the polymerization inhibitor was used at a ratio of about 0.03% to 2-hydroxyethyl acrylate. Separately, a solution of polyether triol with a molecular weight of 510 and an OH value of 513 dissolved in ethyl acetate (solid content 60
%) was prepared. To this solution, toluene diisocyanate to which 2-hydroxyethyl acrylate obtained as described above was added was added,
The reaction was carried out at a temperature of 60°C to obtain the desired trifunctional urethane acrylic resin. Glass transition temperature Tg of this resin
The temperature was approximately 100℃. Production Example 2 A trifunctional urethane acrylic resin was obtained in the same manner as Production Example 1 except that a polyether triol having a molecular weight of 960 and an OH value of 219 was used. The glass transition temperature Tg of this resin was about 65°C. Production Example 3 A trifunctional urethane acrylic resin was obtained in the same manner as Production Example 1 except that a polyether triol having a molecular weight of 1850 and an OH value of 105 was used. The glass transition temperature Tg of this resin was -25°C. A magnetic tape was prepared in the following manner using the trifunctional urethane acrylic resin obtained as described above. Example 1 A magnetic paint having the following composition was prepared. Composition Weight part γ-Fe ₂ O ₃ 50 Resin obtained in Production Example 1 8.75 Polyurethane resin 3.75 (Product name “N-5033” Nippon Polyurethane Industries Co., Ltd.)
Lecithin 1.5 Methyl ethyl ketone: 64 Toluene (1:1) mixed solvent A magnetic paint with the above composition was kneaded in a ball mill for 24 hours, coated on a 15 μm thick polyethylene terephthalate film to a coating thickness of approximately 7 μm, and dried. After that, it was irradiated with an electron beam of 10 Mrad.
However, no calendaring treatment was performed. Example 2 The weight of the polyurethane resin was 1.25 parts by weight, and the resin of Production Example 2 was used instead of the resin of Production Example 1.
A magnetic tape was produced in the same manner as in Example 1 except that 11.25% by weight was used. Example 3 8.7 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (trade name "VAGH", manufactured by Union Carbide) was used instead of the polyurethane resin, and instead of the resin obtained in Production Example 1. A magnetic tape was prepared in the same manner as in Example 1, except that 3.75 parts by weight of the resin obtained in Production Example 3 was used. Comparative Examples 1 to 3 Examples except that the resin obtained in Production Example 1 (Comparative Example 1) and Production Example 2 (Comparative Example 2) and trimethylolpropane triacrylate (Comparative Example 3) were each used alone as a binder. A magnetic tape was produced in the same manner as in Example 1. The characteristics of the magnetic tapes obtained in the Examples and Comparative Examples described above were measured as follows. 1. Powder removal test A load of 50 g was applied to one end of a tape cut to a length of 30 cm and a width of 1/2 inch (approximately 1.2 cm), and the tape was sanded 10 times at a speed of 2.5 cm/sec using No. 1000 sandpaper.
The amount of wear was measured from the change in weight before and after shedding. The results are shown in Table 1.

[Table] From the results, it is clear that in the present invention, the amount of falling powder is clearly reduced and the wear resistance is improved. 2 Adhesive Strength Test Using a tensile testing machine, 180° peeling was performed at a peeling speed of 100 mm/min. The results are shown in Table 2.

【table】

[Table] From these results, it is clear that the adhesive strength of the binder used in this invention is significantly improved. 3 Solvent Resistance Test The coating film was rubbed using gauze impregnated with methyl ethyl ketone, and the number of times until the coating film was completely lost was indicated. Conventional examples include polyurethane resin (product name "N-5033"), vinyl chloride resin (product name "VAGH"), and trifunctional isocyanate (product name "Coronate L", produced by Nippon Urethane Kogyo Co., Ltd.).
A binder made by Co., Ltd. was used. The results are shown in Table 3.

[Table] From the above results, when using the binder used in this invention, compared to the conventional example,
It is clear that the solvent resistance is improved due to the high crosslinking density. Note that FIGS. 1 and 2 show changes in the glass transition temperature Tg when the ratio of the binder composition used in Examples 1 to 3 was changed.

[Brief explanation of drawings]

FIGS. 1 and 2 are graphs showing the relationship between the composition and the glass transition temperature Tg.

Claims (1)

[Claims] 1. A trifunctional urethane acrylic resin having a molecular weight between functional groups of about 300 to 800 and a thermoplastic resin are mixed at a mixing ratio of 95/5 to 20/80, and the glass transition temperature of the composition is Tg is approx.
A magnetic recording medium characterized in that a composition prepared at a temperature of 25°C to 80°C is used as a binder in a magnetic layer, and the magnetic layer is cured by irradiating the magnetic layer with an electron beam.