JP2784655B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic disk, and a magnetic floppy disk, and more particularly to a magnetic recording medium suitably used as a video tape.

BACKGROUND OF THE INVENTION As is well known, a magnetic recording medium generally contains a magnetic material, carbon black, a dispersant, a lubricant, a matting agent, and other additives in a binder resin (binder). After kneading, these components are uniformly dispersed in the resin, a hardener for improving the durability of the magnetic layer is added to the obtained magnetic paint, and then applied on a support, and then magnetic field orientation It is manufactured by letting it dry.

By the way, the characteristics (electromagnetic conversion characteristics, mechanical characteristics, and the like) of the magnetic recording medium can be changed by variously changing the type and the addition amount of each of the components used. The recording medium has its characteristics,
In particular, many of them have insufficient electromagnetic conversion characteristics, and in particular, many have poor balance between high-frequency characteristics (RF output) and low-frequency characteristics (chroma output).

[Object of the Invention] In view of the above-mentioned circumstances, the present inventors have proposed, in addition to improving the electromagnetic conversion characteristics, improving the polishing force of a magnetic recording medium on a magnetic head to prevent clogging of the head. As a result of various studies for the purpose of improving the friction coefficient of the magnetic recording medium and improving the running property of the medium, etc., it was found that the object can be achieved by the present invention described below, and the present invention was completed. I let it.

[Constitution of the Invention] That is, the present invention relates to "a magnetic recording medium having a plurality of magnetic layers on a non-magnetic support, wherein the uppermost magnetic substance contains 0.1 to 2.0 parts by weight of silicon (Si) based on 100 parts by weight of Parts by weight containing cobalt-containing iron oxide (Co-γ-FeOx), and the uppermost layer contains at least one selected from oleic acid and stearic acid as a lubricant and oxidizes as an abrasive. A magnetic recording medium characterized by containing chromium ".

As described above, the magnetic recording medium of the present invention has
Using cobalt-containing iron oxide containing 0.1 to 2.0 parts by weight of silicon (Si), using at least one selected from oleic acid and stearic acid as a lubricant, and using chromium oxide as an abrasive Although such a layer configuration in a magnetic recording medium is conventionally known for a magnetic recording medium having a single layer, such a combination is known. The application to the top layer of the medium has not been reported yet, and is a fact first discovered by the present inventors.

Hereinafter, the present invention will be described. In the magnetic recording medium of the present invention, as described above, the magnetic material in the uppermost layer contains silicon (Si) in an amount of 0.1 to 2.
A cobalt-containing iron oxide containing 0 parts by weight (% by weight) is used.

In the uppermost layer, when cobalt-containing iron oxide having a silicon content of less than 0.1 part by weight is used, when the iron oxide powder is dispersed in a binder resin, the powder has poor wettability, and the magnetic recording medium has This hinders the improvement of the electromagnetic conversion characteristics.

On the other hand, when a cobalt-containing iron oxide having a silicon content of 2 parts by weight or more is used in the uppermost layer, the magnetic properties of the iron oxide magnetic powder, particularly the coercive force (Hc), are lowered. .

Therefore, the silicon-containing cobalt-containing iron oxide (Co-γ-) used in the uppermost layer in the present invention.
The content of silicon in FeOx) depends on the cobalt-containing iron oxide 10
Usually, it is preferably 0.3 to 1.0 part by weight based on 0 part by weight.

The magnetic material used for the layers other than the uppermost layer of the magnetic recording medium of the present invention is not particularly limited in the present invention, and any known magnetic material is used.

For example, in addition to the above-mentioned cobalt-containing iron oxide (Co-γ-FeOx), γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ or Co-coated γ-Fe ₂ O
Co-γ-Fe ₂ O _3, such as _3, Fe ₃ O _4; Co-containing Fe ₃ O ₄ or Co
Co-γ-Fe ₃ O ₄ as deposited Fe ₃ O _4; oxide magnetic material such as CrO _2, other, for example Fe, Ni-Fe-Ni alloy, Fe-Co alloy, F
e-Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe-N
i-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co
Various ferromagnetic materials (powder) such as a metal magnetic powder containing Fe, Ni, and Co as main components such as a -P alloy and a Co-Cr alloy.

Additives for these metallic magnetic materials include Si, Cu, Z
Elements such as n, Al, P, Mn, and Cr or compounds thereof may be contained. Further, hexagonal ferrites such as barium ferrite, iron nitride and the like are also used.

Preferred examples of the binder resin used in the present invention include abrasion-resistant polyurethane.

It has strong adhesion to other materials, is mechanically tough against applied force or bending applied repeatedly, and has good abrasion resistance and weather resistance.

Also, when a cellulose resin and a vinyl chloride copolymer are used in combination with the polyurethane, the dispersibility of the magnetic powder in the magnetic layer is improved, and the mechanical strength is increased. However, the layer becomes too hard with only the cellulose resin and the vinyl chloride copolymer, but this can be prevented by the presence of the above-mentioned polyurethane.

Cellulose ether,
Cellulose inorganic acid esters and cellulose organic acid esters can be used.

The above-mentioned polyurethane and vinyl chloride copolymer may be partially hydrolyzed. As the vinyl chloride copolymer, preferably, a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol is used.

Phenoxy resins can also be used. Phenoxy resin has high mechanical strength, excellent dimensional stability,
It has advantages such as good heat resistance, water resistance, chemical resistance and good adhesiveness.

These advantages are complementary to the above-described polyurethane in length and length, and can significantly improve the temporal stability of the physical properties of the magnetic recording complex.

Further, in addition to the binder described above, a mixture with a thermoplastic resin, a thermosetting resin, a reactive resin, and an electron beam irradiation curable resin may be used.

Various hardeners can be contained in the magnetic paint to improve the durability of the magnetic layer of the magnetic recording material of the present invention,
For example, an isocyanate can be contained. Examples of the aromatic isocyanate include tolylene diisocyanate (TDI) and the adduct thereof with these isocyanate active hydrogen compounds.
A range of 3,000 is preferred.

Examples of the aliphatic isocyanate include hexamethylene diisocyanate (HMDI) and the like, and adducts of these isocyanates and active hydrogen compounds. In the names of these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, the preferred molecular weight is
It is in the range of 100-3,000. Of the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

A dispersant is used in the magnetic paint used to form the magnetic layer.

Examples of the dispersant used in the present invention include phosphate esters,
Amine compounds, alkyl sulfates, fatty acid amides,
There are higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinates, known surfactants and the like, and salts thereof, and negative organic groups (for example, -COO).
It is also possible to use salts of polymer dispersants having H). These dispersants may be used alone or in combination of two or more.

Conventionally, various types of lubricants to be contained in the magnetic layer have been proposed. In the present invention, at least one compound selected from among oleic acid and stearic acid is particularly preferred as the lubricant for the uppermost layer. Is selected.

On the other hand, as the lubricant for layers other than the uppermost layer, the present invention is not particularly limited. In addition to the above-mentioned lubricants, any known lubricants such as silicone oil, graphite, carbon black graft polymer, Molybdenum sulfide, tungsten disulfide, lauric acid, myristic acid,
Fatty acid esters (so-called waxes) composed of monobasic fatty acids having 12 to 16 carbon atoms and monohydric alcohols having 21 to 23 carbon atoms in total with the number of carbon atoms of the fatty acid can be used.

These lubricants are usually added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder resin.

In the present invention, chromium oxide is used as an abrasive in the uppermost layer.

Conventionally, generally used abrasives include fused alumina, various aluminas such as α-alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond,
Although garnet and emery (main components: corundum and magnetite) are known, in the present invention, chromium oxide is adopted as a polishing agent for the upper layer.

On the other hand, the present invention does not particularly limit the abrasive used for layers other than the uppermost layer, and conventionally known abrasives are used.

These abrasives have an average particle size of 0.05 to 5 μm, and particularly preferably 0.1 to 2 μm.
These abrasives are added in the range of 1 to 20 parts by weight based on 100 parts by weight of the binder.

As the matting agent, an organic powder or an inorganic powder is used individually or as a mixture.

As the organic powder used in the present invention, acrylic styrene-based resin, benzoguanamine-based resin powder, melamine-based resin powder, and phthalocyanine-based pigment are preferable, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, and polyimide-based resin are preferable. Powders, polyfluorinated ethylene resin powders and the like can also be used. As inorganic powders, silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α-Fe ₂ O
₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide.

Examples of antistatic agents include conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; alkylene oxides; glycerin And glycidol-based nonionic surfactants; higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfoniums; carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid Anionic surfactants containing an acidic group such as an ester group or a phosphoric ester group; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric esters of amino alcohol;

Examples of the solvent to be blended in the paint or a diluting solvent at the time of applying the paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Alcohols such as methanol, ethanol, propanol, and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; , Toluene and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene.

Examples of the support include polyethylene terephthalate, polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Cu, Al, and Zn; glass, boron nitride, and ceramics such as Si carbide can also be used.

The thickness of these supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of a film or a sheet, about 30 μm to 10 mm in the case of a disk or a card, and is cylindrical in the case of a drum. The type is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Coating methods for forming the magnetic layer on the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, and spray coating. Coats, extrusion coats, etc. can be used, but are not limited thereto.

When a magnetic layer is formed on a support by these coating methods, a system in which coating and drying steps are stacked one by one (so-called wet-on-dry coating system) or a method in which the next layer is placed on a wet layer that has not been dried Are applied simultaneously or successively (so-called wet-on-wet method), but any method can be adopted in producing the magnetic recording medium of the present invention.

In the magnetic recording medium of the present invention, a non-magnetic layer may be provided above, below, or between the magnetic layers so as not to impair the curing of the present invention.

According to such a method, the magnetic layer applied on the support is subjected to a treatment for orienting the ferromagnetic metal oxide powder in the layer if necessary, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is about 500-5000 AC or DC.
The drying temperature is about 50 to 120 ° C., and the drying time is about 0.1 to 10 minutes.

Further, the magnetic recording medium of the present invention is manufactured by performing a surface smoothing treatment or cutting it into a desired shape as required.

Next, the present invention will be described with reference to examples, but needless to say, the present invention is not limited to the following examples.

Example Co-γ-FeOx containing silicon (Si) (x = 1.4 to 1.5, Hc
= 900. Oe, average long axis ratio 0.25 µm) 100 parts by weight, vinyl chloride-vinyl acetate-maleic anhydride copolymer (copolymerization ratio = 8
7: 8: 5, polymerization degree 600) 12 parts by weight, 6 parts by weight of a polyester polyurethane resin [Chrisbon 7209, trade name, manufactured by Dainippon Ink and Chemicals, Inc.], 2 parts by weight of butyl stearate, conductive carbon black (average To 1 part by weight of a particle having a particle size of 10 mμm, an appropriate amount of a lubricant such as stearic acid, oleic acid and palmitic acid and an abrasive such as chromium oxide and alumina (the amount described in Table 1 by weight) are added. After kneading the components well, an appropriate amount of a mixture of methyl ethyl ketone / cyclohexanone = 7/3 as a solvent and 7 parts by weight of a polyisocyanate (Coronate L-75, manufactured by Nippon Polyurethane Co., Ltd.) as a curing agent are added to obtain a magnetic paint. Prepared.

Next, after applying this magnetic paint on a polyethylene terephthalate support according to a conventional method, a magnetic field orientation,
The magnetic recording medium was manufactured by processing in the order of drying and calendering.

Table 2 shows the results obtained by measuring the characteristics of the magnetic recording medium thus obtained.

As is clear from the results in Table 2, in Comparative Example 1, since the silicon content in the iron oxide was as small as 0.03%, the dispersibility of the iron oxide was poor and the electromagnetic conversion characteristics were low.

In Comparative Example 2, since alumina was used as the polishing agent, the polishing property was low, and the RF output was greatly reduced.

In Comparative Example 3, since the silicon content in the iron oxide is large, Hc decreases, and the electromagnetic conversion characteristics decrease.

In the comparative example, since palmitic acid was used as the lubricant, the running property was poor.

In Comparative Example 5, since the magnetic layer was a single layer, the chroma S / N was low, and particularly, the high range and low range characteristics were not balanced.

On the other hand, according to the present invention, as shown in Example 1, by using a magnetic material having an Si content of 0.7% by weight in the upper layer, the dispersibility of the magnetic material is good and the electromagnetic conversion characteristics are improved. It became good. By using 2% by weight of stearic acid in the upper and lower layers, the running test at 40 ° C. and 80% RH was good.

Also, in Example 2, the dispersibility of the magnetic material was good as in Example 1, and the running test at 40 ° C. and RH 80% was also good by using stearic acid and oleic acid as the upper layer lubricant. .

Furthermore, also in Example 3, the dispersibility of the magnetic material was good, and as a result, the electromagnetic conversion characteristics were good. The running test was also good due to the use of oleic acid in the upper layer. In this case, there was no problem even if the lubricant was not added to the lower layer, and the chroma S / N value was rather improved.

-Method of measuring characteristics in Examples and Comparative Examples <Surface Roughness> Surface roughness was measured by a surface roughness analyzer (SE-3FK, manufactured by Kosaka Laboratory).

<Lumi S / N> A 100% white signal is input to the magnetic recording medium at the reference level. Input the playback video signal to 925D / 1 (Shibasoku. Noise meter) and obtain the Lumi S / N from the noise absolute value obtained.
Read.

<Chroma S / N> The difference between the S / N of the sample and the chroma signal was determined in comparison with Example 1 using a noise meter manufactured by Shibasoku Co., Ltd.

<Running test> The sample is run repeatedly 50 times under the conditions of 40 ° C and 80% RH. At this time, if the 50 runnings are repeated without stopping, the running is judged to be complete.

<Reduced RF output> When the sample was run 50 times repeatedly under the conditions of 40 ° C and 80% RH, the RF output during the first run (recording the signal in advance) and the 50th RF output The difference is defined as RF output reduction.

[Effects of the Invention] According to the present invention, a magnetic recording medium having excellent electromagnetic conversion characteristics, particularly a magnetic recording medium having a good balance between Lumi S / N and chroma S / N can be obtained.

Further, the magnetic recording medium of the present invention has a good polishing force, a small decrease in RF output after repeated running, and a moderately good friction coefficient, so that improvement in running performance can be expected.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 5/706 G11B 5/708 G11B 5/71 G11B 5/716

Claims (1)

(57) [Claims] In a magnetic recording medium having a plurality of magnetic layers on a non-magnetic support, the uppermost magnetic substance contains 0.1 to 2.0 parts by weight of silicon (Si) per 100 parts by weight of cobalt. Iron oxide (Co-γ-FeOx), and the top layer contains at least one selected from oleic acid and stearic acid as a lubricant, and contains chromium oxide as an abrasive. Characteristic magnetic recording medium.