JPS6157037A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve an electromagnetic conversion characteristic and to decrease demagnetization by incorporating acid anhydrides into a magnetic layer. CONSTITUTION:The acid anhydrides are incorporated into the magnetic layer of a magnetic recording medium constituted by providing the magnetic layer consisting of ferromagnetic powder and binder on a non-magnetic substrate. The acid anhydrides to be used are the compd. expressed by the general formula (RCO)2O in which the two molecules of a carboxylic acid are condensed by losing one molecule of water or the present compd. expressed by the general formula in which the water is lost from the two carboxylic groups of the dicarboxylic acid having two carboxylic acids in the same molecule. The former is exemplified by acetic anhydride, propionic anhydride and valeric anhydride. The latter is exemplified by succinic anhydride, maleic anhydride, glutaric anhydride, glutaconic anhydride, phthalic anhydride, itaconic anhydride, diglycolic anhydride and citraconic anhydride.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media, and more particularly to improved magnetic recording media.

[Prior art] Ferromagnetic materials conventionally used for magnetic recording media such as video tapes, audio tapes, memory tapes, magnetic sheets, magnetic cards, etc. include ferromagnetic iron oxide, cobalt ferrite, ferromagnetic chromium dioxide, and ferromagnetic materials. There are fine metal powders and ferromagnetic metal thin films. Recently, emphasis has been placed on methods for recording short-wavelength signals with high density.

Along with this, ferromagnetic materials are required to have magnetic recording properties suitable for high-density recording (e.g., higher coercive force, higher residual magnetic flux density), and ferromagnetic metal materials are considered the most promising ferromagnetic materials that can meet these requirements. has been done.

However, as the coercive force of the magnetic powder increases and/or the residual magnetic flux density increases, the interaction between the particles decreases and dispersion becomes difficult. Furthermore, when alloy metal powder is used as the ferromagnetic powder, since this type of powder inherently has the property of being easily oxidized, the magnetic tube properties are more likely to deteriorate over time than oxide-based magnetic powder.

[Object of the invention].

The seventh purpose of the present invention is to provide a magnetic recording medium with excellent electromagnetic conversion characteristics, and the second purpose is to provide a magnetic recording medium using ferromagnetic powder with little demagnetization.

[Structure of the invention]

As a result of repeated research to achieve the above object, the present inventors have found that when an acid anhydride is contained in a magnetic layer containing ferromagnetic powder, or when a ferromagnetic powder is surface-treated with an acid anhydride. The present invention was based on the discovery that significant effects can be achieved by using the following.

That is, the present invention relates to a magnetic recording medium comprising a magnetic layer made of ferromagnetic powder and a binder provided on a non-magnetic support, wherein the magnetic layer contains an acid anhydride. Regarding.

The acid anhydride used in the present invention is a compound represented by the general formula (RCO) 20 in which carboxylic acid comolecules are condensed by losing 7 water molecules, or a dicarboxylic acid having two carboxylic acids in the same molecule. It is a cyclic compound with a single molecule.

Examples of the former include acetic anhydride, propionic anhydride, valeric anhydride, isovaleric anhydride, benzoic anhydride, isoracic anhydride, cinnamic anhydride, and toluic anhydride.

); Examples of the latter include succinic anhydride, maleic anhydride, glutaric anhydride, glutaconic anhydride, phthalic anhydride, itaconic anhydride, diglycolic anhydride, citraconic anhydride,
Examples include diphenic anhydride, naphthalic anhydride, nitrophthalic anhydride, pyromellitic anhydride, phthalic anhydride, pulpic anhydride, mellitic anhydride, and lanolic anhydride.

The latter acid anhydride formed by losing water/molecule from two carboxyl groups in the same molecule is more preferred in the present invention.

The acid anhydrides of the present invention can be used alone or in combination of two or more.

In the present invention, in order to obtain a greater effect and to prevent side reactions with active groups in the binder, it is preferable to use ferromagnetic powder whose surface has been previously treated with an acid anhydride. The surface treatment is carried out, for example, by immersing the ferromagnetic powder in an organic solvent in which an acid anhydride is dissolved to form a slurry, and then removing the solvent by filtration or distilling it off under reduced pressure. Effect 1 will be even greater if the slurry is heated during this surface treatment.

In either case, it is desirable to remove as much water as possible from the solvent. The amount of acid anhydride added is 7
The g-portion is required to be at least /θ-7 mol, and preferably at most /θ-3 mol. If it is not mixed well, its effect will not be fully demonstrated. On the other hand, if the amount is too large, excess acid anhydride precipitates, causing clogging of the head and deterioration of the strength of the magnetic layer.

Ferromagnetic powders include r-Fe20s, Fe5O4, and C
Iron oxide-based ferromagnetic material such as OXZ H in which other metals are dissolved in solid solution, CrO2 or Li, Na,
Sn, PbXFeXCo, Ni.

Chromium dioxide-based ferromagnetic materials such as solid solutions of metal atoms such as Zn, halogen atoms, etc., fine Ba-ferrite powder, metals and alloy metal magnetic materials made of Co, Li'e, Ni, etc. be. The pot magnetic material has its saturation magnetization (σB
) is particularly preferred in the present invention because it has the advantage of providing a magnetic recording medium with a large coercive force (He), high S/N, and high recording density.

Although the method for producing the ferromagnetic metal fine powder used in the present invention is not particularly limited, it can be produced, for example, by the following method.

one! - (1) A method of hydrolyzing an organic acid salt of a ferromagnetic metal and reducing it with a reducing gas.

(2) A method of reducing acicular oxyhydroxides, those containing other metals, or acicular iron oxides obtained from these oxyhydroxides.

(3) A method in which ferromagnetic metal is evaporated in a low-pressure inert gas.

(4) A method of thermally decomposing a metal carbonyl compound.

(5) A method of electrodepositing ferromagnetic metal powder using a mercury cathode and then separating it from mercury.

(6) A method in which a ferromagnetic powder is obtained by reducing a metal salt capable of producing a ferromagnetic substance using a reducing substance (borohydride compound, hypophosphite, hydrazine, etc.) in an aqueous solution.

Furthermore, an oxide film can be provided on the particle surface of the ferromagnetic metal powder in order to improve its chemical stability.

In the present invention, the ferromagnetic metal powders produced by the above methods (2), (3), and (6) are easy to use, and in particular, the powder obtained by method r2) has low cost and quality.
− Most desirable in that sense.

In addition, in order to obtain a magnetic recording medium with a higher S/N ratio by the method of the present invention, the specific surface fJi of the ferromagnetic metal powder must be 3θ
m2/? r 2, desired-I L<ti<t om2
/9r or more, the saturation magnetization (σs) is /io emu
/gr or more, preferably /-20 emu/gr or more.

The magnetic layer of the magnetic recording medium of the present invention consists of a magnetic coating liquid whose main components are ferromagnetic powder, a binder, and a coating solvent, and which also contains additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent. It can be obtained by kneading and uniformly dispersing the mixture, coating it on a support, and then subjecting it to orientation, drying, and calendering.

The binder used in the present invention includes conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof.

Examples of thermoplastic resins include vinyl chloride-vinylacetate+1 copolymer, vinyl chloride-vinylidene chloride copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-acrylonitrile copolymer, and (meth)acrylic acid ester-acrylonitrile. Copolymer, (meth)acrylic acid ester-vinylidene chloride copolymer, (meth)acrylic acid ester-styrene copolymer, urethane distomer, urethane resin, polyvinyl fluoride, butadiene acrylonitrile copolymer, polyamide resin , polyvinyl acecool resin, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose diacetate, cellulose acetate glopionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, etc. There are thermoplastic resins.

Thermosetting resins or reactive resins are those whose molecular weight becomes infinite through condensation or addition reactions when heated or exposed to light, such as phenol resins, epoxy resins, polyurethane curable resins, urea resins, and melamine. There are resins, unsaturated polyester resins, acrylic acid ester resins, etc. Furthermore, in order to improve durability, it is also possible to include a polyincyanate compound as a crosslinking agent. These binders may be used alone or in combination of two or more. The amount of binder used is per 100 parts by weight of powder! -,2! Parts by weight.

Coating solvents include ketones such as methyl ethyl ketone and cyclohexanone, alcohols, esters such as ethyl acetate and butyl acetate, cellosolves, ethers, aromatic solvents such as toluene, and chlorinated solvents such as carbon tetrachloride and chloroform. Organic solvents such as hydrocarbon solvents are used.

Examples of lubricants include silicone oils such as various polysiloxanes, inorganic powders such as graphite and molybdenum disulfide, fine plastic powders such as polyethylene and polytetrafluoroethyl, higher fatty acids, higher alcohols, higher fatty acid esters, and fluorocarbons. binder 10
It is added at a ratio of 0.7 to 20 parts by weight relative to 0 parts by weight.

As abrasives, alumina, silicon carbide, chromium oxide (
Cr203), corundum, diamond, etc. average particle diameter O0θ! ~θ, tμ fine powder is used as binder-1
0 parts by weight of θ,j-2-tar are added to 0 parts by weight of θ.

As the antistatic agent, conductive powder such as graphite, carbon flank, carbon flake craft polymer, etc., nonionic surfactant, anionic surfactant, cationic surfactant, etc. are used.

As the non-magnetic support, synthetic resins (for example, polyester, polyamide, polyolefin, cellulose derivatives), non-magnetic metals, glass, ceramics, paper, etc. can be used, and the forms include films, tapes, sheets, cards, and disks. , drums, etc.

The ferromagnetic powder, the aforementioned acid anhydride, dispersant, lubricant, abrasive, antistatic agent, solvent, etc. are kneaded to form a magnetic paint.

For cross-talk, the magnetic powder and the above-mentioned components are all fed into the mixer at the same time or one after the other. Various types of crosstalk machines are used to disperse crosstalk, and for details, see T.C. Patton's ``PointFlow and
Pigment Dispersion” IO- (79 years, John Willey & 5ons
Company).

As a method for coating the magnetic recording layer on a support,
Various methods are possible, specifically the one published by Shokusho Shoten
It is described in detail in ``Coating Engineering'' (published in the Showa era).

By such a method, the magnetic layer coated on the support is optionally treated to orient the magnetic powder in the layer, and then the formed magnetic layer is dried.

However, a smoothing treatment (eg, smoothing treatment before drying, calendering treatment after drying, etc.) may be performed to enhance the magnetic properties.

Additionally, polishing with a whetstone or sliding treatment with a blade to remove deposits, protrusions, and other things that cause dropouts and scratches on the surface of the magnetic recording medium can also improve the characteristics. In particular, since recording media using fine ferromagnetic metal powder are used at high recording densities, finer surface defects than before in terms of draw-outs become a problem. Such surface shaping treatment of the magnetic layer is effective.

In order to improve the running properties and durability of magnetic recording media, it is effective to provide various back coat layers on the surface of the support opposite to the magnetic layer. The present invention is no exception, and particularly when ferromagnetic metal powder is used as the magnetic material, the thickness of the magnetic recording medium tends to become thinner, and the provision of a back coat layer is even more effective. The thickness of the back coat layer is O0/
~Ko.

It is θμ and mainly consists of binder and fine powder. Fine powders include carbon black, graphite, calcium carbonate, alumina, titanium oxide, StC, SiO2
Mainly used are inorganic powders such as chromium oxide, boron nitride, MgO, and CaO.

Among these, carbon black is preferable because it prevents the tape from being charged during running. carbon black and chromium oxide,
It is also possible to use a mixture of calcium carbonate, SiO2, titanium oxide, etc.

The additives, supports and manufacturing methods exemplified above are described in Japanese Patent Publication No. 0, Sho Jt-2, No.

〔Example〕

The present invention will be specifically explained with reference to the following Examples and Comparative Examples. Note that "parts" refer to "parts by weight".

Example-/, Comparative Example-/ Saturation magnetization as/, 2 temu/gr, drag force He/!
FOoe, specific surface area! F'e -Ni of θm2/gr
Alloy powder (Ni approx.!%) of maleic anhydride, 2wt
% methyl ethyl ketone solution, stirred, left for about 7 θ hours, filtered and dried, and the amount of maleic anhydride bound to the particle surface was about θ, 4 twt% of the magnetic powder. A treated powder was obtained.

For comparison, a powder treated in the same manner with toluene, which does not praise the acid anhydride, was also prepared. After cross-dispersing the above composition in a ball mill for about /θ hours, 2.0% of oleic acid is added. parts, 4 parts of stearic acid, 6 parts of butyl stearate, and 2 parts of stearic acid.
j part triisocyanate compound (manufactured by Bayer AC “
Desmodule L-7! 7) wt % ethyl acetate solution of ``2'') was added and stirred at high speed for further 7 hours to obtain a uniform magnetic coating solution.

The coating solution was applied onto a polyethylene terephthalate film, oriented in a magnetic field, dried, and then calendered, followed by slitting to a predetermined width to obtain a magnetic tape.

The magnetic properties of powder and magnetic tape are all measured using a vibrating sample magnetometer (Vibration Sample Magnetometer).
The magnetic properties of the ferromagnetic metal powder and the magnetic tape are the values of the measured external magnetic field (Hm)/θkoe.

゛ The video characteristics are based on the recording/playback head combined with Sendust/
This is the value obtained by measuring the MHz playback output using a VH8 type VTR (manufactured by Matsushita Electric Industrial Co., Ltd., trade name: rNV-Zaza θθ) modified to 4t-gold. The standard tape is VH8 tape T/koθE (manufactured by Fuji Photo Film C).

The CN ratio is determined by recording the IM Hz carrier signal and calculating the reproduced amplitude modulation signal by 3. This is the CN ratio when the level at θMHz is taken as the noise level.

To demagnetize, place the tape in an atmosphere of θ'C-90°RH.
After leaving it for a week, the rate of decrease in maximum magnetic flux density was examined.

The properties of the obtained magnetic tape are shown in Table 7.

The surface gloss of the magnetic layer is that of comparative example -/, with /θO as
Relative values are shown.

By treating with maleic anhydride, the squareness ratio: t
d: , h < fi magnetism 1″ table 0 property ′ek
jl i h e f + characteristics are improved. Furthermore, stability is improved and demagnetization is reduced.

Example 2 In Comparative Example 2, 2g of maleic anhydride was added to the composition and cross-dispersed for /θ hours using a ball mill, but the other samples were prepared in the same manner.

As in Example-/, each characteristic was improved.

Example 3 A sample was prepared in the same manner as in Example 7 except that phthalic anhydride was used instead of maleic anhydride.

Similar to Example-/, improvements were seen in each characteristic.

Example 3 A sample was prepared in the same manner as in Example 3, except that the slurry was maintained at about /100C for 3 hours when the ferromagnetic powder was treated with phthalic anhydride.

As a result, characteristics that were further improved compared to Example 3 were obtained.

Example-j1 Comparative Example-2 In Example-/ and Comparative Example-/, iron oxide whose surface was subjected to CO modification treatment was used instead of the ferromagnetic metal powder.
Berridox ■) and other samples were prepared in the same manner.

In Example - Example B-/, itaconic anhydride was used as the acid anhydride.

771 [Effects of the Invention] According to the present invention, ferromagnetic powder can be easily dispersed, the dispersion time can be shortened, and the load on the dispersion machine can be reduced. Even under the same dispersion conditions as in the prior art, a coating liquid with good dispersibility can be obtained.

In addition, agglomeration of particles occurs over time after dispersion, so that the so-called pot life of the liquid can be improved.

The above advantages are thought to be due to the fact that the acid anhydride adsorbed on the surface of the ferromagnetic powder particles prevents the magnetic particles from aggregating with each other.

This effect is particularly important for ferromagnetic metal powders due to their saturation magnetization (
It is effective when σS) is large and the specific surface area is large.

As σS increases, the specific surface area increases, and the particle size decreases, it is expected that the sensitivity will increase and s,/N will also increase. However, in the past, technology 1 did not always work that way. In other words, as σB and specific surface area increase, particles become more difficult to disperse, and even once dispersed, they tend to aggregate and become smooth. It is difficult to obtain a magnetic layer.Therefore, the output is not as high as expected, the noise is high, and a high S/N ratio cannot be obtained.

σS is /20 emu or more, specific surface area is 30 m 272
In this case, the difference between the prior art and the present invention becomes significant, and a magnetic recording medium with good electromagnetic conversion characteristics can be obtained.

According to the present invention, since the particles can be easily dispersed, the load in the dispersion process can be reduced, such as by shortening the dispersion time and reducing the number of dispersion machines.

Further, according to the present invention, the viscosity of the liquid can be reduced, so that the amount of solvent used can be reduced, and the load on the drying process can also be reduced. As described above, according to the present invention, the load in the process can be reduced and the manufacturing cost can be reduced.

According to the present invention, the orientation of particles in a magnetic field is improved, a recording medium with a large squareness ratio can be obtained, and from this point of view, it is also possible to improve electromagnetic conversion characteristics. 1. According to the present invention, stability, which is a problem with ferromagnetic metal powders, can be improved. Due to the presence of acid anhydride on the particle surface, oxidation does not progress easily in the air even in powder form. Furthermore, even in the medium after being kneaded with the binder, deterioration of magnetic properties (demagnetization) due to oxygen, moisture, etc. in the air is less likely to occur.

Patent applicant: Fuji Photo Film Co., Ltd.-,2/-

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of ferromagnetic powder and a binder provided on a non-magnetic support, wherein the magnetic layer contains an acid anhydride.