JPH0222444B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a magnetic recording medium,
The purpose is to provide a magnetic recording medium that has excellent durability and improved dispersibility of magnetic powder. In general, magnetic recording media are made by coating a magnetic coating consisting of magnetic powder, a binder component, a solvent, and various additives on a substrate such as a polyester film to form a magnetic layer. It largely depends on the wear resistance of the magnetic layer. Therefore, in order to improve the durability of a magnetic recording medium, it is necessary to select a binder component that has excellent wear resistance. Polyurethane resins have already been proposed as the above binder component, and they provide good abrasion resistance to the magnetic layer, and their flexibility is an advantage for magnetic tape applications, but conventional polyurethane resins With resin, the dispersibility of magnetic powder is poor and sufficient electromagnetic conversion characteristics cannot be obtained. Furthermore, when crosslinking is carried out using low molecular weight polyisocyanates, heat resistance and chemical resistance are poor due to insufficient crosslinking properties. In order to eliminate the above-mentioned conventional drawbacks, the inventors conducted extensive research and found that the binder component of magnetic paint mainly contains molecules having hydroxyl groups at positions other than both ends of the main chain. When a modified polyurethane resin is used, good durability and excellent dispersibility of magnetic powder are achieved, and when this modified polyurethane resin and vinyl chloride-vinyl acetate copolymer are used together, output and The inventors discovered that electromagnetic conversion characteristics such as the S/N ratio could be further improved, leading to this invention. The above-mentioned modified polyurethane resins include those containing polyurethane molecules in which hydroxyl groups at positions other than both ends of the main chain are directly bonded to the main chain, those containing polyurethane molecules in which hydroxyl groups are bonded to side chains, and those containing both. Including those that primarily contain the above hydroxyl groups in the resin as an average value per molecule.
Those with a value of 0.5 or more, especially those with a value of 1.0 to 3.0 are good. Further, both ends of the main chain of the molecule may be either an isocyanate group, both a hydroxyl group, or one an isocyanate group and the other hydroxyl group. The average molecular weight of modified polyurethane resin is 10,000~
A molecular weight of about 100,000 is good; lower molecular weights are unsuitable because they tend to appear on the surface of the magnetic layer. Such modified polyurethane resins are produced by synthesizing a polyester from a dibasic acid such as adipic acid and a diol such as 1,6-hexanediol or 1,4-butanediol, and adding glycerin, trimethylol poupane, etc. to this polyester. No. 3
It is produced by mixing functional or tetrafunctional alcohols and reacting this mixture with a diisocyanate compound such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, etc., but it can also be synthesized by various other methods. I can't stand anything. A specific example of a commercially available product is TU-201 manufactured by Sanyo Chemical Co., Ltd. (molecular weight approx.
30000), Pandex T-5250 manufactured by Dainippon Ink Co., Ltd.
(molecular weight approximately 20,000). The above-mentioned modified polyurethane resin used in the present invention mainly contains polyurethane molecules having hydroxyl groups at positions other than both ends of the main chain. Therefore, it is presumed that the dispersibility of the magnetic powder is improved due to the influence of this hydroxyl group. moreover,
When crosslinking is performed using a low molecular weight polyisocyanate or the like, the crosslinking occurs at the hydroxyl group position, increasing the crosslinking density and improving heat resistance, chemical resistance, and abrasion resistance. On the other hand, in the conventional polyurethane resin, even if there is a hydroxyl group, it is at both ends of the main chain,
It does not exist in any position other than at both ends. in this way,
It is not clear why the effect of oxidation differs depending on the position of the hydroxyl group, but as the molecular weight increases, the end of the main chain is more likely to be wrapped or entangled in other parts of the molecule or in the entanglements of other molecules. It is presumed that this is because the hydroxyl group at the end of the main chain becomes less likely to perform its function and cannot sufficiently contribute to improving the dispersibility and crosslinking properties of the magnetic powder. Vinyl chloride used in combination with modified polyurethane resin
Vinyl acetate-based copolymers include binary copolymers consisting of vinyl chloride and vinyl acetate, and ternary or more copolymers in which other monomers such as vinyl alcohol, maleic acid, and acrylic ester are added to both. do. The degree of polymerization is preferably 200 to 600; lower degrees of polymerization result in insufficient coating film strength and thermal stability, while higher degrees of polymerization result in poor solubility and dispersibility of the magnetic powder. A specific example of a commercially available vinyl chloride-vinyl acetate copolymer is UCC Co., Ltd.
VYHH (vinyl chloride-vinyl acetate copolymer, weight ratio 86:14), VAGH (vinyl chloride-vinyl acetate)
vinyl alcohol copolymer, weight ratio 91:3:6),
VMCH (vinyl chloride-vinyl acetate-maleic acid copolymer, weight ratio 86:13:1), Denka #LOH manufactured by Denki Kagaku (vinyl chloride-vinyl acetate-vinyl alcohol copolymer, weight ratio 80:10:10) ), Denka B
-1 (vinyl chloride-vinyl acetate-acrylic acid ester-vinyl alcohol copolymer, weight ratio 80:
5:5:10), Esrex A-5 manufactured by Sekisui Chemical Co., Ltd.
(vinyl chloride-vinyl acetate-vinyl alcohol copolymer, weight ratio 86:2:12). The vinyl chloride-vinyl acetate copolymer is well compatible with the above-mentioned modified polyurethane resin, further improving the dispersibility of the magnetic powder and improving the surface condition of the magnetic layer, improving electromagnetic conversion such as output and signal-to-noise ratio. Works to further improve properties. The blending ratio of the modified polyurethane resin and the vinyl chloride-vinyl acetate copolymer is preferably in the range of 9:1 to 1:9 by weight, and outside this range the above-mentioned effects are sufficiently exhibited. Not done. In addition, in this invention, the above-mentioned modified polyurethane resin and vinyl chloride are used as binder components.
In addition to the vinyl acetate copolymer, a low molecular weight polyisocyanate can be used in combination, and in this case there is an advantage that not only durability is improved, but also heat resistance and chemical resistance are improved. This effect is due to the fact that the above-mentioned modified polyurethane resin mainly contains molecules that have hydroxyl groups at positions other than both ends of the main chain. It is presumed that this is due to the fact that crosslinking with the low molecular weight polyisocyanate is sufficiently performed compared to the case of the present invention. As such polyisocyanate, 2.4
-Tolylene diisocyanate, m-phenylene diisocyanate, 4,4-bisphenylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 1,6-hexamethylene diisocyanate, 4- Any commercially available diisocyanates and polyisocyanates such as chloro-1,3-phenylene diisocyanate and 1,5-naphthalene diisocyanate can be used. Specific examples of commercially available products include Coronate L, Coronate HL, Conate 2036, Conate 2014, Coronate 3015, Conate 3030 manufactured by Nippon Polyurethane Co., Ltd., Desmodyur L, Desmodyur 15, Desmodyur E14, Sumidyur L, and Sumidyur manufactured by Sumitomo Bayer Urethane Co., Ltd.
IL, Sumidyur T80, Sumidyur 44V-20,
Sumidyur PF, Takenate manufactured by Takeda Pharmaceutical Company Limited
D102, Takenate D103, Takenate D103H, Takenate D204, Takenate D110N, Takenate
D120N, Takenate M402, Takenate M408,
Examples include Krisbon NX, Krisbon CL-2, and Burnock DN-950 manufactured by Dainippon Ink and Chemicals. The blending amount of the low molecular weight polyisocyanate is preferably in the range of 3 to 50% by weight based on the total amount of the above-mentioned modified polyurethane resin and vinyl chloride-vinyl acetate copolymer, and should not be too small. There is virtually no effect, and if too much, the flexibility of the coating film will be impaired. The magnetic recording medium of the present invention can be manufactured according to a conventional method, for example, on a substrate such as a polyester film, magnetic powder, the above-mentioned binder component of the present invention,
The magnetic layer may be formed by applying a magnetic paint containing a solvent, various additives, etc. by known means. Magnetic powders that can be used include r-Fe ₂ O ₃ and Co.
There are oxide powders such as r-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , and CrO ₂ , and metal powders such as Fe, Co, Ni, and alloys thereof. Examples of solvents include ketone solvents such as cyclohexanone, methyl isobutyl ketone, and methyl ethyl ketone, ester solvents such as ethyl acetate,
Hydrocarbon solvents such as toluene, alcohol solvents such as isopropyl alcohol, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydrofuran and dioxane, and mixed solvents thereof are used. can. Furthermore, various commonly used additive components such as dispersants, lubricants, abrasives, and antistatic agents may be added to the magnetic paint, and these can be selected as appropriate depending on the application and required performance. and use it. The present invention will be explained in detail below with reference to Examples.
In the Examples, all parts are by weight. Example 1 80 parts of Co-containing r-Fe ₂ O ₃ powder, 16 parts of TU-201 (modified polyurethane resin, mentioned above), 4 parts of VAGH (vinyl chloride-vinyl acetate copolymer, mentioned above), 50 parts of cyclohexanone A magnetic paint was prepared by mixing and dispersing paint components consisting of 50 parts of methyl ethyl ketone and 50 parts of methyl ethyl ketone in a ball mill for 70 hours. This was applied onto a polyester film with a thickness of 11 μm to a dry film thickness of 6 μm, and after drying. A magnetic tape was obtained by cutting it into 3.8 mm width. Example 2 A magnetic tape was produced in the same manner as in Example 1, except that 2 parts of Coronate L (low molecular weight polyisocyanate, described above) was added to the coating components in Example 1. Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1, except that the same amount of Paraprene 22S (conventional polyurethane resin, manufactured by Honpolyurethane Co., Ltd.) was used in place of TU-201 in Example 1. Comparative Example 2 A magnetic tape was manufactured in the same manner as in Example 2, except that Paraprene 22S (described above) was used instead of TU-201 in Example 2. Regarding the magnetic tapes obtained in the above examples and comparative examples, the magnetic tape industry association standard MTS -
The table below shows the results of measuring output, output fluctuation, adhesion, and SN ratio in accordance with 102. The output fluctuation is the value after 600 runs, and the tackiness is determined under the conditions of 45℃ and 80%RH. As is well known, output fluctuation is an indicator of durability, output and SN ratio are indicators of the dispersibility of the magnetic powder, and tackiness is an indicator of heat resistance because it appears as softening of the magnetic layer at high temperatures.

[Table] As shown in the test results of the above Examples and Comparative Examples, the magnetic recording medium of the present invention uses a specific modified polyurethane resin and a vinyl chloride-vinyl acetate copolymer as binder components of the magnetic powder. Because it contains the above-mentioned binder, it has the same excellent durability as those using conventional polyurethane resin, and has good dispersibility of magnetic powder and excellent electromagnetic characteristics such as output and signal-to-noise ratio. If a low molecular weight polyisocyanate is further used as a component, durability and heat resistance are synergistically improved.

Claims (1)

[Claims] 1. A magnetic recording medium in which magnetic powder is coated on a substrate together with a binder component, which contains polyurethane molecules having hydroxyl groups at positions other than both ends of the main chain as the binder component. A magnetic recording medium containing a modified polyurethane resin and a vinyl chloride-vinyl acetate copolymer. 2. The magnetic recording medium according to claim 1, further comprising a low molecular weight isocyanate as a binder component.