JPH02227820A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having excellent electromagnetic conversion characteristics by using cobalt-contg. iron oxide contg. 0.1 to 2.0pts.wt. silicon (Si) for the uppermost layer and applying a combination of a lubricant and polishing agent to the uppermost layer of the magnetic recording medium consisting of double layers structure. CONSTITUTION:The magnetic material of the uppermost layer of the magnetic recording medium having plural magnetic layers on a nonmagnetic base is the cobalt-contg. iron oxide (Co-gamma-FeOx) contg. 0.1 to 2.0pts.wt. silicon (Si) per 100pts.wt. and the uppermost layer contains at least one kind selected from oleic acid and stearic acid as the lubricant and contains chromium oxide as the polishing agent. The electromagnetic conversion characteristics are improved in this way; in addition, the polishing power of the magnetic recording medium on a magnetic head is improved and the clogging of the head is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, magnetic floppy disks, etc., and particularly to magnetic recording media suitably used as video tapes.

Background of the Invention 1 As is well known, magnetic recording media usually contain a magnetic material, carbon black, a dispersant, a lubricant, a matting agent, and other additives in a binder resin (binding agent). Knead to uniformly disperse each of these components in the resin,
It is manufactured by adding a curing agent to the obtained magnetic coating to improve the durability of the magnetic layer, coating it on a support, then aligning it in a magnetic field, and then drying it.

In this way, the characteristics (electromagnetic conversion characteristics, mechanical characteristics, etc.) of the magnetic recording medium can be changed by variously changing the type of the valley bottom 9 used, the amount added, etc., but this method has not been proposed in the past. Many magnetic recording media have insufficient characteristics, especially electromagnetic conversion characteristics, and in particular many do not have a good balance between high side wave characteristics (RF specific output and low frequency characteristics (chroma output)).

Purpose of the Invention 1 In view of the above circumstances, the inventors of the present invention have sought to prevent clogging of the head by improving the abrasive force for the magnetic head of a magnetic recording medium in addition to improving the electromagnetic conversion characteristics. As a result of various research aimed at improving the friction coefficient of magnetic recording media and improving the running properties of the media, we found that the following objectives could be achieved by the present invention, and completed the present invention. I let it happen.

[Configuration 1 of the Invention] In other words, the present invention provides that in a magnetic recording medium having a plurality of magnetic layers on a non-magnetic support, the uppermost layer magnetic material contains 0.1 silicon (Sl) per 100 parts by weight of the magnetic material. ~2.0
Parts by weight of cobalt-containing iron oxide (C.

γ-FeOx), and the top layer contains at least one selected from oleic acid and stearic acid as a lubricant, and chromium oxide as an abrasive. The gist is "media".

As described above, the magnetic recording medium of the present invention includes, in the uppermost layer, (1) using iron oxide containing 0.1 to 2.0 parts by weight of silicon (Si); (2) using olefin as a lubricant; The three essential requirements are the use of at least one selected from acid and stearic acid, and (1) the use of chromium oxide as an abrasive, but such a layer structure in a magnetic recording medium is conventional. is known for magnetic recording media consisting of a single layer, but there has been no report yet on the application of such a combination to the top layer of a magnetic recording medium consisting of a multilayer structure, and this was discovered for the first time by the present inventors. It is a fact that

Hereinafter, the present invention will be explained. As mentioned above, in the magnetic recording medium of the present invention, silicon (Si) is contained at 0.00% per 100 parts by weight as the magnetic material in the uppermost layer.
Cobalt-containing acid containing 1 to 2.0 parts by weight (wt%)
Ferrite is used.

If cobalt-containing iron oxide with a silicon content of less than 0.1 part by weight is used in the top layer, the iron oxide powder has poor wettability when dispersed in a binder resin, resulting in magnetic recording. This impedes the improvement of the electromagnetic conversion characteristics of the medium.

On the other hand, if cobalt-containing iron oxide with a silicon content of 2 parts by weight or more is used in the uppermost layer, it is not preferable because the magnetic properties of the iron oxide magnetic powder, especially the coercive force (Hc), are decreased. .

For this reason, silicon-containing cobalt-containing iron oxide (Co-γ-
The content of silicon in FeOx is preferably 0.3 to 1.0 parts by weight based on 100 parts by weight of the cobalt-containing iron oxide.

The present invention does not particularly specify the magnetic material used in layers other than the uppermost layer of the magnetic recording medium of the present invention, and any known magnetic material may be used.

For example, the above cobalt-containing iron oxide (Co-γ-FeOx
), γ-Fe! Os % Co-containing - Fe, O,
or Co-1-Fex such as CO-coated γFe, O,
Os, FezO4: Co-containing Fe, O.

or Co-γ-Fe30 such as CO-coated Fe5Oa
4; Oxide magnetic materials such as Cry, others, such as Fe
, Ni, Fe-Ni alloy, Fe-Cqp gold, Fe-N1
-P alloy, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-C.

-F of Ni-P alloy, Go-P alloy, Co-Cr alloy, etc.
Examples include various ferromagnetic materials (powders) such as metal magnetic powders containing e, Ni, and Co as main components.

SL is an additive to these metal magnetic materials.

Elements such as Cu, Z n *^(1, P, Mn, Cr, etc.) or compounds thereof may be included. Hexagonal ferrite such as barium ferrite, iron nitride, etc. are also used.

Preferred binder resins used in the present invention include abrasion-resistant polyurethane.

It has strong adhesion to other materials, is mechanically strong to withstand repeated applied forces or bending, and has good abrasion and weather resistance.

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

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like.

The above polyurethane and vinyl chloride copolymers may be partially hydrolyzed. Preferable examples of the vinyl chloride copolymer include a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol.

Phenoxy resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

These advantages are complementary to those of the polyurethane described above, and the stability of the physical properties of the magnetic recording medium over time can be significantly improved.

Furthermore, in addition to the binders described above, mixtures of thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used.

In order to improve the durability of the magnetic layer of the magnetic recording material of the present invention, the magnetic paint can contain various hardening agents, such as incyanate. Examples of aromatic incyanates include tolylene diisocyanate (TDI) and adducts of these incyanates with active hydrogen compounds, and the average molecular weight is 10.
A value in the range of 0 to 3.000 is preferred.

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these incyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3.000 are preferred. Among the aliphatic incyanates, 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.

Dispersants used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. , negative organic groups (e.g. -COO
It is also possible to use salts of polymeric dispersants having H). These dispersants may be used alone or in combination of two or more types.

Various lubricants have been proposed to be included in the magnetic layer, but in the present invention, at least one compound selected from oleic acid and stearic acid is used as the lubricant for the uppermost layer. is selected.

On the other hand, the present invention does not particularly specify the lubricant for the calendar month other than the top layer, and in addition to the above-mentioned lubricants, any known lubricant may be used, such as silicone oil, graphite,
Carbon black graft polymer, molybdenum disulfide,
Fatty acid ester consisting of tungsten disulfide, lauric acid, myristic acid, a monobasic fatty acid having 12 to 16 carbon atoms, and a monohydric alcohol having 21 to 23 carbon atoms in total with the number of carbon atoms in the fatty acid ( So-called wax) etc. can be used.

These lubricants are usually added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder resin.

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

Conventionally, commonly used abrasives include fused alumina,
Various types of alumina such as a alumina, silicon carbide, Mized ROM,
Corundum, artificial corundum, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. are known, but in the present invention, chromium oxide is adopted as the abrasive for the upper layer.

On the other hand, the present invention does not particularly specify the abrasive used for layers other than the last layer, and conventionally known abrasives can be used.

These abrasives have an average particle diameter of 0.05 to 5/Al+, particularly preferably 0.1 to 2 μm. These abrasives are added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.

As the matting agent, organic powder or inorganic powder may be used individually or in combination.

As the organic powder used in the present invention, acrylic styrene-based flank, benzoguanamine-based resin powder, melamine-based resin powder, and 7-lycyanine-based pigment are preferable, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, and polyimide-based resin powder are preferred. Resin powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate,
barium sulfate, zinc oxide, tin oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide, a-Fetu
s, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

Antistatic agents include carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponin, alkylene oxides, and glycerin. Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acids Anionic surfactants containing acidic groups such as ester groups and phosphate ester groups; amino acids;
Examples include amphoteric activators such as aminosulfonic acids, VL acids or phosphoric acid esters of amino alcohols.

The solvent to be added to the above paint or the diluting solvent during application of this paint includes ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Alcohols such as methanol, ethanol, propatool, butanol; esters such as 8-methyl vinegar, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate, etc. Ethers: aromatic hydrocarbons such as benzene, toluene, xylene, etc.; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, dichlorobenzene, etc. can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastins such as polyamide and polycarbonate, and Metal; glass, boron nitride, ceramics such as Si carbide, etc. can also be used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm,
In the case of a disk or card, the diameter is about 30 μ3 to 10 mm, and in the case of a drum, the diameter is cylindrical, and the shape 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 knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, bath roll coating, trans 770-rufut, gravure coating, kiss coating, Cast coat, sub-coat, extrusive tan coat, etc. can be used, but are not limited to these.

When constructing a magnetic layer on a support using these coating methods, there are two methods: one method involves stacking the coating and drying steps layer by layer (so-called wet-on-dry coating method), and the other method involves stacking the coating and drying steps layer by layer (so-called wet-on-dry coating method). There is a method in which layers are coated simultaneously or sequentially (so-called wet-on-wet method), but any method can be used in manufacturing the magnetic recording medium of the present invention.

In the magnetic recording medium of the present invention, a nonmagnetic layer may be provided above and below or between the magnetic layers without impairing the effects of the present invention.

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

In this case, the orientation magnetic field is approximately 500 to 50
00 Gauss, and the drying temperature is about 50~120
'C, drying time is about 0.1-10 minutes.

Further, the magnetic recording medium of the present invention is manufactured by subjecting it to surface smoothing treatment or cutting it into a desired shape, if necessary.

Next, the present invention will be explained with reference to examples, but it goes without saying that the present invention is not limited to the following examples.

[Example 1 Co-γ-FeOx (x-1,4
-1,5, Hc=900, Oe, average major axis ratio 0.25μ
m) 100 parts by weight, vinyl chloride vinyl acetate-maleic anhydride copolymer (copolymerization ratio -87:8:5, degree of polymerization 600
) 12 parts by weight, polyester polyurethane resin [manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name: Crispon 720
9] 6 parts by weight of butyl stearate, 2 parts by weight of conductive carbon black (average particle size 10 μts), lubricants such as stearic acid, oleic acid, palmitic acid and chromium oxide, such as alumina. After adding an appropriate amount of abrasive (the amount listed in Table 1, parts by weight) and kneading each component thoroughly, an appropriate amount of a mixture of methyl ethyl ketone/cyclohexanone = 773 was added as a solvent, and polyisocyanate [Japan Polyurethane (Japan Polyurethane)] was added as a hardening agent. A magnetic paint was prepared by adding 7 parts by weight of Coronate L-75) manufactured by Co., Ltd.
tko.

Next, this magnetic coating material was coated on a polyethylene terephthalate support according to a conventional method, followed by magnetic field orientation, drying, and calendering to produce a magnetic recording medium.

Table 1 shows 1 nji% of iron oxide (Co-7-Fe0x).Table 2 shows the results of measuring the characteristics of the magnetic recording medium thus obtained.

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

In Comparative Example 2, since alumina is used as the abrasive, the abrasiveness is low, and therefore the RF output is greatly reduced.

In comparative fR3, since the silicon content in iron oxide is high, He is reduced and the electromagnetic conversion characteristics are reduced.

In Comparative Example 4, since palmitic acid is used as a lubricant, running properties are poor.

Further, in Comparative Example 5, since the magnetic layer was a single layer, the chroma S/N was low, and the high-frequency and low-frequency characteristics were particularly unbalanced.

On the other hand, according to the present invention, as seen in Example 1, by using a magnetic material with a Si content of 0.7% by weight in the upper layer, the dispersibility of the magnetic material is good, and electromagnetic The conversion characteristics were improved. In addition, by using 2% by weight of stearic acid in the upper and lower layers, 40℃, RH80%
The driving test was good.

In addition, in Example 2, the dispersibility of the magnetic material was good as in Example 1, and due to the use of stearic acid and oleic acid as the upper layer lubricants, the running test at 40°C and R880% was also good. .

Furthermore, in Example 3 as well, 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 no lubricant was added to the lower layer, and the chroma S/N value was rather improved.

-Method for measuring characteristics in Examples and Comparative Examples <Surface roughness> Surface roughness was measured using a surface roughness analyzer (manufactured by Koita Research Institute, rsE-3FK).

Kurumi S/N> Input a 100% white signal to the magnetic recording medium at the reference level. The playback video signal is 925D/l (manufactured by Jino).

noise meter) and read the Lumi S/N from the obtained absolute noise value.

Chroma S/N> Using a noise meter manufactured by Mbasoku Co., Ltd., the difference in S/H of the sample in the chroma signal was determined in comparison with Example 1.

Running test> The sample was run repeatedly 50 times under the conditions of 40°C and R880%. At this time, if the test is repeated 50 times without stopping, the test is determined to have completed the test and passed.

<RF output decrease> When the sample is repeatedly run 50 times under the conditions of 40°C and R880%, the RF specific output signal at the first run (record the signal in advance) and the RF specific output at the 50th run Let the difference be the RF output reduction.

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

Furthermore, since the magnetic recording medium of the present invention has good polishing power, little decrease in RF output after repeated running, and moderately good coefficient of friction, it can be expected to improve running performance.

Claims (1)

[Claims] (1) In a magnetic recording medium having a plurality of magnetic layers on a nonmagnetic support, the uppermost layer magnetic material contains 0.1 to 2.0 parts by weight of silicon (Si) per 100 parts by weight of the magnetic material. It is cobalt-containing iron oxide (Co-γ-FeOx), and the top layer contains at least one selected from oleic acid and stearic acid as a lubricant, and chromium oxide as an abrasive. A magnetic recording medium characterized by: