JPH02273316A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To lessen the deterioration in electromagnetic conversion characteristics under high-temp. and high-humidity conditions by specifying the magnetic material of the uppermost layer and the magnetic material of a layer adjacent to the uppermost layer respectively and specifying the content of a carbon black. CONSTITUTION:The magnetic material in the uppermost layer is essentially required to be Co-contg. gamma -iron oxide. However, an arbitrary ferromagnetic material can be incorporated therein as far as the effect is not impaired. The magnetic layer adjacent to the uppermost layer is essentially required to be formed by using ferromagnetic metallic powder as the magnetic material. How ever, an arbitrary magnetic material may be used together with the essential component as far as the effect is not impaired. Further, the carbon black is essentially required to be incorporated into the magnetic layer adjacent to the uppermost layer at <=2wt.% content by the weight of the magnetic material. The surface roughness of the layer is deteriorated and the surface characteristics of the uppermost layer are adversely affected if the content is as large as to exceed 2wt.%.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, and magnetic floppy disks, particularly magnetic recording media that have excellent electromagnetic conversion characteristics and are suitably used as video tapes. Regarding the medium.

[Background of the Invention] Magnetic recording media usually contain ferromagnetic powder, abrasives, carbon black, etc. in various synthetic or natural polymeric materials (so-called resin materials) called binders.
A suitable solvent is added to a uniformly dispersed mixture of lubricants, dispersants, hardeners, and other components as needed, and the thus obtained magnetic paint is applied onto a support to form a magnetic layer. After forming the magnetic layer, the magnetic layer is oriented in a magnetic field and then dried.

In recent years, there has been an increasing demand for higher densities in magnetic recording media, and in particular, with the demand for higher recording frequencies in video tapes, extremely high-density recording is required and support is increasing. Various types of devices have been proposed in which a magnetic layer is provided on the magnetic body with a two-layer structure consisting of an upper layer and a lower layer, or a structure with three or more layers (hereinafter, these may be collectively referred to as a multilayer structure).

The use of ferromagnetic metal powder as a magnetic material in the uppermost layer of a magnetic recording medium having such a multilayer structure is disclosed in, for example, Japanese Patent Laid-Open Nos. 55-13526 and 1982-14.
This method has been proposed in Publication No. 4038 and the like.

However, if such a magnetic recording medium is left in a harsh environment such as high temperature and high humidity for a long time, there is a drawback that the electromagnetic conversion characteristics deteriorate significantly.

[Objective of the Invention 1] In view of the above, the inventors of the present invention have carried out various studies to develop a magnetic recording medium that does not exhibit the above-mentioned defects and has improved electromagnetic conversion characteristics, and has developed the following. The inventors discovered that the purpose could be achieved by a magnetic recording medium and arrived at the present invention.

[Configuration 1 of the Invention In other words, the present invention provides a magnetic recording medium comprising a plurality of magnetic layers on a non-magnetic support, in which (a) the magnetic material in the uppermost layer is Co-containing iron oxide; The magnetic material in the layer adjacent to the top layer is a ferromagnetic metal powder, and (b) the content of carbon black in the magnetic layer adjacent to the top layer is 2 weight or less relative to the magnetic material. The subject is magnetic recording media.

The present invention will be explained below. Conventionally, as a ferromagnetic material used in this type of magnetic recording medium, for example, γ
- Contains Fe, O,, Co - Fe2o3 or coated with Co - Co such as Fe20s - γ - Fe, O,, Fe5
0. , Co-containing Fe, O, or Co-coated Fe, Ot, oxide magnetic materials such as Co-γ-pe30, crO2, etc., such as Fe, Ni, Fe-Ni alloy, F
e-Co alloy, Fe-N1-P alloy, Fe-N1-C.

alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy,
Fe, Ni, such as Fe-Co-Ni-Cr alloy, Fe-Co-N1-P alloy, Co-P alloy, Co-Cr alloy, etc.
Various ferromagnetic materials such as metal magnetic powder whose main component is Co (
Powder) has been proposed, and these metal magnetic materials contain Si, Cu, Zn, AQ, P, Mn as additives.
It is said that elements such as , Cr, or compounds thereof may be included.

In the magnetic recording medium of the present invention, it is essential that the magnetic material in the uppermost layer is Co-containing iron oxide.

However, as long as the effects of the present invention are not impaired, any of the above-mentioned known ferromagnetic substances can be included in the uppermost magnetic layer in addition to the above-mentioned essential components.

Further, in the present invention, it is an essential requirement that ferromagnetic metal powder be used as the magnetic material in the magnetic layer adjacent to the uppermost layer.

However, as long as the effects of the present invention are not impaired, any known magnetic material may be used in the magnetic layer adjacent to the uppermost layer together with the above essential components.

Regarding the coercive force of the magnetic material in the magnetic layer adjacent to the top layer, improvement of low frequency characteristics, especially chroma output, chroma S/N
From the viewpoint of improving the viscosity, it is usually preferable to set it in the range of 600 to 900 oersted (Oe).

By setting such a coercive force, it is possible to optimize the head for a head with a small recording current, that is, a head other than a normal metal recording head.

Conventionally, various binders have been proposed for use in this type of magnetic recording medium, but in the present invention,
Any known binder can be included in the top layer and the magnetic layer adjacent to the top layer.

Suitable such binders include, for example, abrasion-resistant polyurethanes.

This polyurethane has strong adhesion to other substances,
It is mechanically strong and can withstand repeated applied force or bending, and has good abrasion resistance and weather resistance. Furthermore, 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 will be improved and its mechanical strength will be increased. However, if the fiber yarn resin and vinyl chloride copolymer are used alone, the layer will be too hard;
This can be prevented by the presence of the polyurethane mentioned above.

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 tape of the present invention, the magnetic paint can contain various curing agents, for example, isocyanate. Examples of aromatic incyanates include tolylene diisocyanate (TDI) and adducts of these incyanates with active hydrogen compounds, and have an average molecular weight of 100 to 100.
A range of 3,000 is preferred.

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic incynates, non-alicyclic incynates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic paint used to form the magnetic layer may contain additives such as a dispersant, a lubricant, an abrasive, a matting agent, and an antistatic agent, if necessary.

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. , and also negative organic groups (e.g. -〇〇〇〇)
It is also possible to use salts of polymeric dispersants having .

These dispersants may be used alone or in combination of two or more.

Examples of lubricants include silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acids having 12 to 16 carbon atoms, and the total number of carbon atoms of the fatty acids. Fatty acid esters (so-called waxes) made of monohydric alcohols having 21 to 23 carbon atoms can also 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.

As abrasives, commonly used materials such as fused alumina, various aluminas such as alpha alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery (main components dicorundum and magnetite) are used. be done. These abrasives have an average particle size of 0.05 to 5μ
m is used, particularly preferably 0.1 to
It is 2 μm. These abrasives are usually added in an amount of 1 to 20 parts by weight per 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 resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin are preferred. 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, α-Fe20
3. Talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

Conventionally, in order to impart conductivity and light-shielding properties to magnetic recording media, materials such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, etc. have been used in the magnetic layer and other layers. Conductive powder, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide, glycerin, and glycidol, higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphonium or sulfonium. cationic surfactants such as
Contains anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols. ing.

In the present invention, it is particularly essential that such carbon black be contained in the magnetic layer adjacent to the uppermost layer in an amount of 2% by weight or less based on the magnetic material.

If the amount of carbon black contained in the layer adjacent to the top layer exceeds 2% by weight, the surface roughness of the core layer will deteriorate, adversely affecting the surface properties of the top layer, and the chroma S/H
This is undesirable because it causes a decrease in the magnetic material filling rate and a decrease in chroma output.

Examples of diluent solvents for applying magnetic paint include carbons such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohols such as methanol, ethanol, propatool, and butanol, methyl acetate,
Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate-1-, ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran, benzene,
Aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-26-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate, but metals such as Cu1AQs Zn,
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 μm 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, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, Spray coats, extrusion coats, 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.

Note that a nonmagnetic layer may be provided above and below or between the magnetic layers without impairing the effects of the present invention.

The present invention does not particularly specify the thickness of the magnetic layer, but since it is not preferable to make the thickness too thick from the viewpoint of effectiveness, the thickness of the top layer is usually 0.1.
It is preferable to set the range to 1.5 μm.

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, 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 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 these examples.

[Example 1] After thoroughly kneading the magnetic paints for the top layer and the layer adjacent to the top layer having the compositions listed in Tables 1 and 2, polyisocyanate [Nippon Polyurethane Co., Ltd.] was added as a curing agent.
A magnetic coating material for coating was prepared by adding 5 parts by weight of Coronate L manufactured by Co., Ltd. (trade name).

Next, the magnetic paint for the top layer and the magnetic paint for the layer adjacent to the top layer were coated in multiple layers on the support according to a conventional method, and then subjected to magnetic field orientation treatment and drying treatment to produce a magnetic recording medium. .

The magnetic recording medium thus obtained was measured for electromagnetic conversion characteristics and tested for environmental resistance.

The type of ferromagnetic alloy and the film thickness of the magnetic layer used in each example and comparative example are shown in Table 3. B> Table 3 <Manufacturing conditions of magnetic recording media> The content of capon black in the B layer, the BET value and He value of the magnetic material* used are shown in Table 3.
Manufacturing conditions for magnetic recording media shown in Table 7 Characteristics of magnetic recording media shown in Table 5 Manufacturing conditions for magnetic recording media in Table 6 Manufacturing conditions for magnetic recording media shown in Table 6 *+2.5 = Environmental resistance test Measured value of a sample before being subjected to

+2.4=Measured value after environmental resistance test. Same below.

The environmental resistance test will be explained later.

As is clear from the results in Table 7, the magnetic recording medium of the present invention (each example) not only has a higher level of electromagnetic conversion characteristics than the magnetic recording medium not according to the present invention, but also has high temperature and high humidity. Excellent resistance under certain conditions (environmental resistance).

◎Measurement method in Examples and Comparative Examples Lumi S/N> Input a 100% white signal to the magnetic recording medium at the reference level, input the reproduced video signal to Noise Meter 925D manufactured by Shibaku Co., Ltd., and measure the noise obtained. Read the Lumi S/N from the absolute value.

<Chroma S/N> The difference in S/N was determined in comparison with a reference tape using the noise meter manufactured by Shibaku.

Chroma Output> The output during reproduction of a 500 kHz RF signal was determined.

Old 1-Fi audio output> The output characteristics of a 1.3 MHz unmodulated RF multiplied signal were measured.

<Environmental resistance test> A test in which a sample is left at a temperature of 60° C. and a relative humidity of 80% for 7 days.

[Effects of the Invention] The magnetic recording medium of the present invention not only has a higher level of electromagnetic conversion characteristics than conventional magnetic recording media, but also has excellent environmental resistance.

Claims (3)

[Claims] (1) In a magnetic recording medium consisting of a plurality of magnetic layers provided on a non-magnetic support, (a) the magnetic material in the uppermost layer is Co-containing γ;
- iron oxide, and the magnetic material in the layer adjacent to the top layer is a ferromagnetic metal powder; (b) the content of carbon black in the magnetic layer adjacent to the top layer is 2% relative to the magnetic material; % or less by weight. (2) The coercive force of the ferromagnetic metal powder is 600 to 900. Oe
A magnetic recording medium according to claim (1). (3) The magnetic recording medium according to claim (1) or (2), wherein the thickness of the uppermost layer is in the range of 0.1 to 1.5 μm.