JPH0679371B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium such as a video tape, an audio tape, a computer tape, and a floppy disk.

[Conventional technology]

Conventional binders for magnetic recording media include vinyl chloride-based binders such as vinyl chloride-vinyl acetate copolymers, vinyl chloride-propionic acid copolymers and vinyl chloride-vinyl acetate-vinyl alcohol copolymers. Among them, vinyl chloride contributes to the dispersibility of the magnetic powder, and active hydrogen of the hydroxyl group reacts with isocyanate compounds to form a crosslinked structure and increase the mechanical strength of the coating film. -Vinyl acetate-vinyl alcohol copolymers are widely used.

However, with the recent increase in the specific surface area of magnetic powder due to atomization and the increase in cohesive force due to the increase in magnetic force, satisfactory dispersibility and surface properties cannot be obtained with the above-mentioned binders. Increasing the powder packing density is also difficult. Therefore, durability,
The magnetic characteristics and electromagnetic conversion characteristics were also insufficient. Alternatively, for example, a method of using a surfactant as a dispersant has been considered, but in this case, the presence of this surfactant in the magnetic layer due to the low molecular weight of the surfactant. As a result, there is a problem in mechanical strength such as blooming due to powder falling and aging and durability, and the like.

Under such circumstances, there is a demand for a binder capable of further improving such properties. For example, an acid or its alkali metal is added to the side chain of a vinyl chloride-vinyl acetate copolymer or a vinyl chloride-vinyl acetate-vinyl alcohol copolymer. A technique has been proposed in which a polymer having a polar group introduced therein such as a salt, acidic sulfuric acid or an alkali metal salt thereof, a carboxylic acid or a metal salt thereof is applied as a binder.

However, the binders obtained by these techniques show some effect in improving the dispersibility as compared with the conventional binders in which a polar group is not introduced. Performance on powder was unsatisfactory.

[Problems to be Solved by the Present Invention]

 In recent years, higher image quality of magnetic recording media has been demanded.

For this purpose, it is necessary to make more intimate contact between the magnetic layer surface and the video head and audio head,
It is important to improve the smoothness of the surface of the magnetic recording medium and further dramatically improve the dispersibility of the ferromagnetic fine powder. On the other hand, the smoother the surface of the magnetic layer, the greater the friction in the running system inside the video tape recorder, the greater the charging of the tape, and the higher the running tension, the more demanding the running durability of the magnetic recording medium is. Is done. For this reason, a conventional magnetic recording medium manufacturing method has not been able to obtain a magnetic recording medium having the surface smoothness of the magnetic layer, the dispersibility of the ferromagnetic fine powder, and the running durability.

The present inventors have found that conventional techniques such as a method using a thermoplastic resin and a thermosetting resin, a method of adding a crosslinkable binder by the above chemical reaction, and a method of using a curable binder by radiation crosslinking, etc. The present invention has been achieved as a result of intensive studies to improve the drawbacks.

Therefore, the object of the present invention is a characteristic that cannot be achieved by the conventional magnetic recording medium, that is, 1) is excellent in electromagnetic conversion characteristics, and 2) is excellent.
Excellent dispersibility of the ferromagnetic fine powder, 3) reduced charge of the magnetic layer during running, 4) excellent runnability and reduced dropout, and 5) excellent running durability. It is to provide a magnetic recording medium.

[Means for solving problems]

The above problems can be solved by the following means. That is,
The present invention provides a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic fine powder dispersed in a binder on the support, wherein the magnetic layer has a vinyl compound having a nitrogen-containing heterocycle (provided that A magnetic recording medium containing a copolymer of 0.01 to 15 wt% (excluding 2-vinylpyridine), 75 to 98 wt% of vinyl chloride and 0.5 to 20 wt% of other copolymerizable vinyl compound. Regarding

As for the vinyl compound having a nitrogen-containing heterocyclic ring which is a component of the above-mentioned copolymer used in the present invention, N-vinyl is used as the nitrogen-containing heterocyclic compound. There is.

The copolymer of the present invention is formed from the vinyl compound and vinyl chloride containing these nitrogen-containing cyclic compounds and, if desired, the other copolymerizable vinyl compound (Y).

I.e. In the above formula, N represents an atomic group having a nitrogen-containing ring.

In the above general formula, each component of the compound is described for convenience so as to be regularly arrayed, but each component may be regularly arrayed at a constant ratio other than in the above general formula. It may be arranged randomly.

Two or more kinds of atomic groups each having a nitrogen-containing ring and Y may be contained.

The vinyl monomer for copolymerization represented by Y in the above formula is vinyl acetate, vinyl alcohol, maleic acid, maleic anhydride, acrylic acid, acrylic acid ester, acrylic acid or methacrylic acid ester having a glycidyl group, methacrylic acid, A vinyl group copolymerizable with vinyl chloride is added to at least one selected from methacrylic acid ester, acrylonitrile, vinylidene chloride, vinyl propionate and the like.

The vinyl chloride component ratio is preferably 75 to 98 wt%, solubility,
It is effective in strengthening the physical properties of the film.

The vinyl compound having a nitrogen-containing ring is preferably 0.01 to 15 wt%, more preferably 0.1 to 10 wt%, most preferably 0.5 to
It is 5 wt%.

The component represented by the general formula Y of the copolymerization component can be copolymerized for the purpose of improving solubility, film physical properties, adhesion to a support, and the like. When copolymerizing, 0.5 to 20 wt% is preferable.

The molecular weight is preferably 10,000 to 50,000, more preferably 15,000 to 30,000.

The vinyl chloride copolymer is contained in the magnetic layer in an amount of preferably 1 to 90% by weight, more preferably 5 to 80% by weight, based on the total amount of the binder.

The compound represented by the above general formula may be used as a mixture with another binder. As such a binder, those conventionally used as a binder for magnetic recording media can be used, including vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride. -Vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid ester- Vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer Polymer, polybi Butyral, cellulose derivatives, styrene - butadiene copolymer, polyester resins, phenolic resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea - Horumuadehido resin or a mixture thereof, and the like. Among them, polyurethane resin, polyester resin, acrylonitrile butadiene copolymer, etc., which are said to impart flexibility, are preferable. Further, as the cross-linking agent, for example, a trifunctional isocyanate compound, 1 mol of trimethylolpropane and tolylene diisocyanate 3
Durability and the like can be further improved by using a reaction product or the like with a mole.

As the ferromagnetic powder used in the present invention, ferromagnetic iron oxide fine powder, Co-doped ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, ferromagnetic alloy powder, barium ferrite, etc. can be used. The acicular ratio of ferromagnetic iron oxide and chromium dioxide is about 2/1 to 20/1, preferably 5/1 or more and the average length is 0.2 to
A range of about 2.0 μm is effective. The ferromagnetic alloy powder has a metal content of 75 wt% or more, and a metal content of 80 wt% or more is a ferromagnetic metal (that is, Fe, Co, Ni, Fe-Ni, Co-Ni, Fe-Co-N).
In i), the particles have a major axis of about 1.0 μm or less. Particularly effective in the present invention is a fine particle ferromagnetic alloy powder having a BET specific surface area of 30, preferably 45 m ² / g or more, in which it is difficult to disperse the ferromagnetic fine powder.

As the organic solvent used for dispersion and application of the magnetic coating liquid, acetone, methyl ethyl ketone, methyl isobutyl ketone,
Ketone-based compounds such as cyclohexanone; ester-based compounds such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether acetate; ethyl ether, glycol dimethyl ether, glycol monoethyl ether,
Ether-based compounds such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride,
Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, and dichlorobenzene can be selected and used.

Further, additives such as a lubricant, an abrasive, a dispersant, an antistatic agent and an anticorrosive agent may be added to the magnetic coating liquid of the present invention. In particular, lubricants include saturated and unsaturated higher fatty acids having 12 or more carbon atoms, fatty acid esters, higher fatty acid amides, higher alcohols, and silicone oils, mineral oils, vegetable oils, fluorine compounds, etc. It may be added, or may be dissolved in an organic solvent after drying, or may be directly applied or sprayed on the surface of the magnetic layer.

The magnetic coating liquid is applied to the substrate material such as polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; polycarbonate, polyimide;
In addition to plastics such as polyamide-imide, other non-magnetic metals such as aluminum, copper, tin, zinc or non-magnetic alloys containing them, or plastics deposited with a metal such as aluminum can be used.

The form of the non-magnetic support is film, tape, sheet,
It may be a disc, a card, a drum, or the like, and various materials are selected as necessary according to the form.

The support of the present invention has a so-called back coat on the surface opposite to the side provided with the magnetic layer (back surface) for the purpose of preventing electrification, transfer prevention, wow fratter prevention, improving the strength of the magnetic recording medium, and matting the back surface. May have been done.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

In the following examples and comparative examples, all "parts" indicate parts by weight.

Example A magnetic coating solution having the following composition was kneaded with a ball mill for 50 hours.

Strong magnetic Fe alloy powder (1500 Oe, BET surface area 50 m ² / g) 100 parts Vinyl chloride copolymer 10 parts Polyurethane resin (N-230 manufactured by Nippon Polyurethane Co., Ltd.)
4) 6 parts Butyl stearate 1 part Al ₂ O ₃ 2 parts Carbon black 2 parts Methyl ethyl ketone 100 parts Toluene 120 parts After kneading, add 5 parts of Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd., and further kneading with a ball mill for 10 minutes, then the thickness 10 μm
Was coated on the polyethylene terephthalate support of 1. using a doctor blade so that the dry film thickness was 4 μm. Then, after orientation using a cobalt magnet, the solvent was dried, calendered and heat cured at 60 ° C. for 72 hours.

A sample tape was made by slitting into a 1/2 inch band.

Examples of vinyl chloride-based copolymers as shown in Table 1
I got a sample of. The evaluation results are summarized in Table 2.

Evaluation method Video S / N: Video tape recorder NU83 made by Matsushita Electric Industrial
10 was used to record a 50% set-up gray signal, noise was measured with a 925C S / N meter manufactured by Jiba Soku, and the relative value when Example 1 was set to 0 dB was shown.

Dynamic friction coefficient: Using the above video tape recorder, when the tape tension on the feeding side of the rotating cylinder is T ₁ and the tape tension on the winding side is T ₂ , the dynamic friction coefficient (μ) is defined by the following equation. The running tension was evaluated by μ.

T ₂ / T ₁ = exp (μ * π) Measurement was at 23 ° C., 65% RH Charged potential measurement: The charged potential of the tape at the outlet of the rotating cylinder when the video tape recorder was run was measured.

Measurement of dropout number: Using the dropout counter VD-3D manufactured by Victor Company, the above video tape recorder 10
The number of drop-ups of 15 × 10 ⁻⁶ seconds or more per minute after running 0 pass was examined.

Storage stability: After storing the magnetic coating liquid for 24 hours at room temperature,
After stirring for 10 minutes, a magnetic tape was prepared by the method described in Example 1 and the video S / N was measured. The storage stability was evaluated by setting the video S / N of each sample when not stored to 0 dB.

[Effect of the Invention] The magnetic recording medium having the combination of the binder of the present invention is
It can be seen that good electromagnetic conversion characteristics are exhibited, and triboelectric charging is small during running in the magnetic recording apparatus, so that dust and dirt are less adhered, dropout is reduced, and excellent still durability is exhibited. Furthermore, in the production of the magnetic recording medium of the present invention,
It was confirmed to have excellent storage stability.

Claims (1)

[Claims] 1. A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic fine powder dispersed in a binder on the support, wherein the magnetic layer has a nitrogen-containing heterocycle. 0.01 to 15 wt% (excluding 2-vinylpyridine)
%, Vinyl chloride 75 to 98 wt% and other copolymerizable vinyl compound 0.5 to 20 wt% copolymer.