JPH02192017A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the S/N of the magnetic recording medium having >=2 layers of magnetic layers by adjusting the moisture of the ferromagnetic materials of upper and lower layers. CONSTITUTION:The ferromagnetic material subjected to humidity control to >=0.8wt.% and <=2.0wt% adsorbed moisture is used for the upper layer and the ferromagnetic material which has <0.8wt.% adsorbed moisture and is lower in adsorbed moisture by >=0.1wt.% than the ferromagnetic material of the upper layer is used for the lower layer. Namely, the dispersibility and orientability are inferior and the S/N is deteriorated if the adsorbed moisture of the ferromagnetic material of the upper layer is below 0.8wt.%. Kneading is insufficient and the squareness ratio is low if the adsorbed moisture exceeds 2.0wt.%. The pot life is degraded and the surface characteristic is deteriorated by the degradation of calenderability if the adsorbed moisture of the ferromagnetic material of the lower layer is >=0.8wt.%. The upper layer is, therefore, enhanced in the dispersibility and orientability by the specific humidity control and the lower layer is enhanced in the surface characteristic by the improved calenderability and pot life. The magnetic recording medium having the high S/N is obtd. in this way.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer, and more particularly to a magnetic recording medium having at least two or more magnetic layers. particularly regarding videotapes.

[Conventional technology]

Magnetic recording media are required to have sophisticated characteristics, and various improvements have been made. One of these characteristics is the S/N ratio. In order to improve the S/N ratio of a coated magnetic tape, it is required that the ferromagnetic material be uniformly dispersed in the binder and that the coated magnetic layer have a smooth surface. From this point of view, JP-A-60-187931 stipulates that the moisture adsorbed by the ferromagnetic material should be controlled to 0.8 wt % or more.

[Problem that the invention seeks to solve]

However, in these technologies, the moisture content of the ferromagnetic material is reduced to 0,
Since the content is 8 wt% or more, the dispersibility and orientation are improved, but the pot life of the coating solution is reduced due to the reaction between the moisture on the surface of the ferromagnetic material and the incyanate compound in the coating solution. The surface properties of the obtained magnetic tape deteriorate. Furthermore, for the same reason, the reaction of the isocyanate compound becomes faster and the coating film cures faster. For this reason, in actual production, calender formability deteriorated, magnetic tape surface properties deteriorated, and a sufficient S/N ratio could not always be obtained.

[Means to solve the problem]

The present invention has been made to solve the above-mentioned problems, and is directed to a magnetic recording medium comprising two or more magnetic layers each having a ferromagnetic material dispersed in a binder on a non-magnetic support. , 0°3 wt% or more of adsorbed moisture in the upper layer is 2.3 wt%
A ferromagnetic material whose humidity has been adjusted as follows is used, and the adsorbed moisture in the lower layer is 0.
The present invention relates to a magnetic recording medium characterized in that it uses a ferromagnetic material that adsorbs less than 3 wt% of moisture and adsorbs less water by 0.1 wt% or more than the ferromagnetic material in the upper layer. By adjusting the water content of the ferromagnetic material in the upper and lower layers, a magnetic tape with good dispersibility, calendar moldability, pot life, good surface properties, and good S/N ratio can be obtained.

Here, the moisture content adsorbed by the upper layer of ferromagnetic material is 383 wt% or more2
, 3wt% or less, particularly 0.8wt% or more1.
It is preferably 2 wt% or less. If it is less than 0.8 wt%, the dispersibility and orientation will be poor, and the S/N ratio will deteriorate, which is undesirable. If it is more than 2.3 wt%, kneading will be insufficient and the squareness ratio will decrease, which is undesirable. The adsorbed water content of the ferromagnetic material in the lower layer is preferably less than 0.8 wt%, particularly 0.8 wt%. 3wt%
At less than 0.8wt%, O,1w is lower than the upper layer ferromagnetic material.
It is preferable that the amount of adsorbed water is less than t%. 0. 3wt
% or more, the reactivity of the isocyanate compound increases, resulting in a decrease in pot life and calendar moldability, resulting in deterioration of surface properties, which is undesirable. In this way, in this patent, the upper layer improves dispersibility and orientation, and the lower layer improves calender formability and
S/N is improved by improving surface quality by improving pot life.
A magnetic recording medium with a high ratio can be obtained. Further, unless the difference in water content between the upper and lower ferromagnetic layers is 0.1 wt% or more, the above effect cannot be clearly achieved.

The ferromagnetic material used in the present invention is not particularly limited, and includes metal oxides such as ferromagnetic iron oxide, cobalt-added ferromagnetic iron oxide, etc., such as rFe2O3, Co-containing (coated,
r-Fe203, Fe3O4, Co-containing (deposited, metamorphosed, doped) Fe3O4, FeOx, C
o-containing (adhered, metamorphosed, doped) FeOx (X=1.
33-1, 50), cro2, Rn, Te, 5bS
An alloy or single metal system such as CrO2 containing at least one of Sr, Fe, TiSVSMnSCrzO+, for example, the metal content is 75% by weight or more, and 80% by weight or more of the metal content is at least one ferromagnetic metal or alloy. (e.g., Fe, Co, Nl5Fe-CoSFe-N
iSCo-Ni, Co-Ni-Fe5Co-Ni-P,
Co-N1Fe-B, Fe-Ni-Zn5Fe-Co-
Cr), and other components (eg, AI, Si, S, Sc, Ti, v) within a range of 20% by weight or less of the metal content.

Cr, Mn, CuSZn, Y, Mo1RhSPd.

Ag5STI, 5bSTe, Ba, Ta, WSRe, A
u, Hg, Pb, Bi, La, Ce, Pr.

Examples include other metal systems such as alloys that may contain Nd, B, P), such as iron nitride, or alloy systems containing hydroxides or oxides, and mixtures of these systems.

When these ferromagnetic materials are used, the water content of the coating liquid is 0.
,00-0.5Qwt%. These ferromagnetic materials are
Sr, PbSMn within 1wt%.

It is preferable that heavy metals such as N1, Cd, Cr, AI, Si, T+, Cu, and Zn are included. Alumina or the like may be deposited and melted on these ferromagnetic materials.

Further, as the ferromagnetic material used in the present invention, barium ferrite in the form of a plate can also be used. The particle size of barium ferrite is about 0.001 to 1 micron in diameter, and the thickness is 1/2 to 1/20 of the diameter. The specific gravity of barium ferrite is 4 to 6 g/CC, and the specific surface area is 1 m'/g.
~70 m'/g.

The surface of these ferromagnetic materials may be impregnated with a dispersant, a lubricant, an antistatic agent, etc., which will be described later, in a solvent prior to dispersion and adsorbed thereto for each purpose.

In particular, examples of methods for producing ferromagnetic alloy powder include the following methods.

(a) Method of reducing complex organic acid salts (mainly oxalates) with a reducing gas such as hydrogen: (b) Obtaining Fe or Fe-Co particles by reducing iron oxide with a reducing gas such as hydrogen Method: (c) Method of thermally decomposing a metal carbonyl compound (d) Method of reducing a ferromagnetic metal aqueous solution by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine (e) Mercury cathode (f) A method of evaporating the metal in a low-pressure inert gas to obtain a fine powder; When using a ferromagnetic alloy powder, There is no particular restriction on its shape, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used. The specific surface area (SRET) of this ferromagnetic alloy powder is 35 m'/g or more, preferably
40 m'/g or more, more preferably 45 m'/g or more.

It is preferable that the coercive force of the ferromagnetic material of the upper layer is larger than that of the lower layer, that the specific surface area measured by the BET method is larger than that of the lower layer, and that the average major axis diameter and crystallite size are smaller than that of the lower layer.

Furthermore, it is possible to impart the water content of the present invention to a ferromagnetic material without using any particularly new method.

This is possible, for example, in the process of making cobalt-doped ferromagnetic iron oxide. That is, this can be achieved by coating the iron oxide magnetic powder with a cobalt compound, then washing with water, filtering, and drying, and controlling the moisture content in the drying process. Alternatively, this can be achieved by providing a humidity conditioning process as a post process.

Further, the water content in the present invention refers to the content measured using the principle of water measurement by the Karl Fischer method.

The thickness of the upper layer is preferably 1.5 μm or less, more preferably 1.0 μm or less, and most preferably 0.5 μm or less.

Further, the coating method may be a simultaneous multilayer coating method as shown in Japanese Patent Application No. 124631/1988.

As the binder used in the magnetic layer of the present invention or the optional back layer, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 300,000, and a degree of polymerization of about 50 to 2.
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer. Polymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicon resin, nitrocellulose-polyamide resin , polyfukkavinyl, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, ethyl cellulose, methyl cellulose, propyl cellulose, methyl ethyl cellulose, carboxymethyl cellulose, acetyl cellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amine resins, various synthetic rubber-based thermoplastic resins, and their Mixtures etc. are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin,
Melamine resins, alkyd resins, silicone resins, acrylic reactive resins, epoxy-polyamide resins, nitrocellulose melamine resins, mixtures of high molecular weight polyester resins and incyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, poly These include mixtures of Nistel polyol and polyisocyanate, urea formaldehyde resins, mixtures of low molecular weight glycol/high molecular weight diol/triphenylmethane triisocyanate, polyamine resins, polyimine resins, and mixtures thereof.

These binders may be used alone or in combination;
Other additives may be added. The mixing ratio of the ferromagnetic material and the binder in the magnetic layer is in the range of 5 to 300 parts by weight per 100 parts by weight of the ferromagnetic material. The mixing ratio of the fine powder and the binder in the back layer is in the range of 30 to 300 parts by weight based on 100 parts by weight of the fine powder.

Additives include dispersants, lubricants, abrasives, antistatic agents, antioxidants, solvents, and the like.

These thermoplastic resins, thermosetting resins, and reactive resins are
In addition to the main functional groups, acidic groups such as carboxylic acid, sulfinic acid, sulfenoic acid, sulfonic acid, phosphoric acid, sulfuric acid, phosphonic acid, phosphine, boric acid, sulfuric ester group, phosphoric ester group, and alkyl ester groups thereof (These acidic groups may be in the form of Na salts, etc.), amino acids; aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, amphoteric groups such as alkyl betaine types, amino groups, imino groups, imido groups, Amide group, epoxy group,
In addition, it usually contains one to six types of hydroxyl group, alkoxyl group, thiol group, halogen group, silyl group, and siloxane group, and each functional group is contained in an amount of 1 x 10-6 per gram of resin.
It is preferable to include eq-1x 10-2eq.

Examples of polyisocyanates used in the present invention include tolylene diisonanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-15-diisocyanate, 0-toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane diisocyanate. Isocyanates such as isocyanate and inphorone diisocyanate, products of the isocyanates and polyalcohols, and 2-
A 15-mer polyisocyanate or the like can be used. The average molecular weight of these polyisocyanates is 10
A value of 0 to 20,000 is preferable. Commercially available product names of these polyisocyanates include Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL (manufactured by Nippon Polyurethane), Takenate D-102, Takenate D-LLON, Takenate D-200. , Takene)
D-202, Takenate 300S1 Takenate 500
(manufactured by Takeda Pharmaceutical ■), Sumidur T-80, Sumidur 44S1 Sumidur PF, Sumidur L1 Sumidur N1 Desmodule L1 Desmodule IL, Desmodule N1 Desmodule HL, Desmodule T65, Desmodule 15, Desmodule R1 Desmodinir RF, Tesmodinil SL, Desmodur Z4273 (manufactured by Sumitomo Bayer), etc. are available, and these can be used alone or in combination of two or more by taking advantage of the difference in curing reactivity.

In addition, for the purpose of promoting the curing reaction, hydroxyl groups (butanediol, hexanediol, molecular weight 1000-10000)
Polyurethane, water, etc.), compounds having amino groups (monomethylamine, dimethylamine, trimethylamine, etc.), and metal oxide catalysts can also be used together.

It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanates are preferably used in an amount of 5 to 4 Qwt% of the total amount of binder.

Dispersants used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, stearolic acid, etc. 10-2
6 fatty acids (RICOOH, R, is an alkyl group having 9 to 25 carbon atoms), alkali metals (L i
, Na5KsNH, Φ, etc.) or alkaline earth metals (M
(G, CaBa, etc.), Cu, Pb, etc., fatty acid amides of the above-mentioned fatty acids; lecithin, etc. are used. In addition, higher alcohols having 4 or more carbon atoms (butanol, octyl alcohol, myristyl alcohol, stearyl alcohol) and their sulfuric acid esters, phosphoric acid esters, amine compounds, etc. can also be used. Further, polyalkylene oxides and their sulfuric acid esters, phosphoric acid esters, amine compounds, etc., sulfosuccinic acid, sulfosuccinic acid esters, etc. can also be used. It is also possible to introduce substituents 81 and F into these compounds in order to change their compatibility with the binder and their properties. One or more types of these dispersants are usually used, and one type of dispersant is added in an amount of 0.005 to 20 parts by weight per 100 parts by weight of the binder. These dispersants may be used by depositing them on the surface of the ferromagnetic material or non-magnetic fine powder in advance, or by adding them during dispersion.

In addition, preferred compounds as dispersants include surfactants such as carboxylic acids and phosphoric esters, and fluorochemical surfactants such as Florard FC95, FCl29, FC430, and FCl29.
C431 can be used.

A lubricant used in the magnetic layer or back layer of the present invention,
Antioxidants include inorganic fine powders such as molybdenum disulfide, boric acid nitride, graphite fluoride, calcium carbonate, barium sulfate, silicon oxide, titanium oxide, zinc oxide, tin oxide, and tungsten disulfide, and fine acrylic styrene resin powders. , benzoguanamine resin fine powder, melamine resin fine powder, polyolefin resin fine powder, polyester resin fine powder, polyamide resin fine powder, polyimide resin fine powder, polyfluoroethylene resin fine powder, etc. , silicone oil, fatty acid-modified silicone oil, graphite, fluorinated alcohol, polyolefin (polyethylene wax, etc.), polyglycol (polyethylene oxide wax, etc.), tetrafluoroethylene oxide wax, polytetrafluoroglycol, perfluoro fatty acid, perfluoro fatty acid ester, Perfluoroalkyl sulfate ester, perfluoroalkyl phosphate, alkyl phosphate, polyphenyl ether, carbon number 10-20
A fatty acid consisting of a monobasic fatty acid and one or more of a -hydric alcohol having 3 to 12 carbon atoms, a dihydric alcohol, a trihydric alcohol, a tetrahydric alcohol, or a hexahydric alcohol. Organic compound lubricants such as fatty acid esters consisting of esters, monobasic fatty acids having 10 or more carbon atoms, and monovalent to hexavalent alcohols having a total of 11 to 28 carbon atoms. can be used. Also, fatty acids or fatty acid amides having 8 to 22 carbon atoms,
Aliphatic alcohols can also be used.

Specific examples of these organic compound lubricants include butyl caprylate, octyl caprylate, ethyl laurate,
Butyl laurate, octyl laurate, ethyl myristate, butyl myristate, ethyl myristate, ethyl palmitate, butyl palmitate, octyl palmitate, ethyl stearate, butyl stearate,
Octyl stearate, amyl stearate, anhydrosorbitan distearate, anhydrosorbitan distearate, anhydrosorbitan distearate,
There are anhydrosorubicune tetrastearate, anhydrosorubicune ethylene oxide monostearate, oleyl oleate, oleyl alcohol, lauryl alcohol, etc., and they can be used alone or in combination. In addition, so-called lubricating oil additives can be used alone or in combination as the lubricant used in the present invention, such as antioxidants (alkylphenols, etc.), rust inhibitors (naphthenic acid, alkenylsuccinic acid, dilauryl phosphate, etc.). ), oily agents (rapeseed oil, lauryl alcohol, etc.), extreme pressure agents (dibenzyl sulfide, tricresyl phosphate, tributyl phosphite, etc.), detergents and dispersants, viscosity index improvers, pour point depressants, foam stoppers There are drugs etc. These lubricants are binder 100
It is added in an amount of 0.05 to 20 parts by weight.

Further, as the antioxidant, heterocyclic compounds and heterocompounds such as benzotriazine, benzothiazole, benzodiazine, and EDTA can be used.

The antistatic agents used in the present invention include graphite, carbon black, carbon black graft polymer, tin oxide-antimony oxide, tin oxide, titanium oxide-tin oxide-
Conductive powders such as antimony oxide; natural surfactants such as saponin; nonionic surfactants such as alkylene oxides, glycerin, glycidol, polyhydric alcohols, polyhydric alcohol esters, and alkylphenol EO adducts; higher alkyl amines cationic surfactants such as cyclic amines, hydantoin derivatives, amidoamines, ester amides, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums;
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, amino sulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and alkyl betaine types. agents etc. are used. These surfactants may be added alone or in combination. In addition, these surfactants are applied to the surface of the magnetic recording medium at a concentration of 1 mg/my to 550 m.
g/m' may be overcoated.

The amount of these surfactants used in the magnetic recording medium is 0.01 to 10 parts by weight per 100 parts by weight of the ferromagnetic material. Although these are used as antistatic agents, they are sometimes used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

The abrasive for the magnetic layer or back layer used in the present invention is a commonly used material with an abrasive or polishing effect, such as α-alumina, γ-alumina, α-γ-alumina, fused alumina, silicon carbide, and chromium oxide. , cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery (main components: corundum and magnetite), garnet, silica, silicon nitride, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, quartz , Tripoli, diatomaceous earth, dolomite, etc., which mainly have a Mohs hardness of 6 or more, preferably 8 or more, are used in combinations of 1 to 4. These abrasives have an average particle size of 0°005 Sizes of ~5 microns are used, particularly preferably 0.01-2 microns. These abrasives are added in an amount of 0.01 to 20 parts by weight per 100 parts by weight of the binder.

Organic solvents used in the dispersion, kneading, and coating of the present invention include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran; methanol, ethanol, propatool, butanol, and isobutyl; Alcohols such as alconohisopropyl alcohol and methylcyclohexanol; esters such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate monoethyl ether; diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether,
Ethers such as dioxane; tars (aromatic hydrocarbons) such as benzene, toluene, xylene, cresol, chlorobenzene, and styrene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc. chlorinated hydrocarbons, N,N-dimethylformaldehyde, hexane, and the like can be used.

There are no particular restrictions on the kneading method, and the order of addition of each component can be set as appropriate. For the preparation of magnetic paints and back layer paints, conventional kneading machines are used, such as two-roll mills, three-roll mills, ball mills, pebble mills, thoron mills, sand grinders, Szegv.
ar i), attritor, high speed impeller, dispersing machine, high speed stone mill, high speed impact mill, disper, kneader high speed mixer, ribbon blender, co kneader intensive mixer, tumbler, blender disperser, homogenizer, axle screw extruder ,
A twin screw extruder, an ultrasonic dispersion machine, etc. can be used. For details on technology related to crosstalk distribution, please refer to T.
, written by C0FATTON (Chi, See, Paraton) “Pa
1nt Flow and Pigment Dispe
rsion” (Paint Flow and Pigment Disversion) 1964 John Wil
Published by Ey & 5ons (John Wiley & Sons), "Industrial Materials" by Shin Tanaka, Vol. 25, 37 (1)
977> etc. and in the cited literature of the book,
For continuous processing, these cross-dispersing machines are used in appropriate combinations to feed and coat the liquid. It is also described in specifications such as US Pat. No. 2,581,414 and US Pat. No. 2,855,156. In the present invention, the magnetic paint and the back layer paint can also be prepared by carrying out crosstalk dispersion according to the method described in the above-mentioned book or the cited literature of the book.

To form the magnetic layer, the above compositions are arbitrarily combined and dissolved in an organic solvent, and a coating solution is coated on the support and dried. When used as a tape, the thickness of the support is 2.5~
The thickness is about 100 microns, preferably about 3 to 70 microns. In the case of a disk or card, the thickness is 0.
03 to 10 m0, and in the case of a drum, it can also be used in a cylindrical shape. Materials include polyesters such as polyethylene terephthalate and polyethylene naphthalate,
Polyolefins such as polypropylene and polyethylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, plastics such as polycarbonate, polyamide, and polysulfone, as well as metals such as aluminum and copper, Ceramics such as glass can also be used. Prior to coating, these supports may be subjected to corona discharge treatment, plasma treatment, undercoating treatment, heat treatment, dust removal treatment, metal vapor deposition treatment, and alkali treatment.

Methods for coating the magnetic layer and back 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. Coatings, barcodes, spin codes, etc. can be used, and other methods are also possible, and detailed explanations of these can be found in "Coating Industry" published by Asakura Shoten, pages 253 to 277 (1977).
．． 3. 20. Publication). In particular, when the magnetic layer has a multilayer structure, a so-called wet-on-wet coating method in which a lower layer coating liquid and an upper layer coating liquid are applied in a wet state in a superimposed manner is preferred.

As a wet-on-wet method, Japanese Patent Application Laid-Open No. 611399
The coating method described in Japanese Patent No. 29 can be used.

Further, details of the method of dispersing the above-mentioned ferromagnetic powder and binder and the method of coating it on a support are described in various publications such as JP-A-5446011 and JP-A-54-21805.

By such a method, the magnetic layer coated on the support is immediately subjected to a treatment to orient the ferromagnetic powder in the layer in a desired direction while drying, if necessary, and then the formed magnetic layer is dried. The transport speed of the support at this time is usually 10
m/min to 1000 m/min, and the drying temperature is 20 m/min to 1000 m/min.
It is controlled at ℃~130℃. Further, the magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing processing and cutting it into a desired shape, if necessary. In these manufacturing methods, it is preferable that the steps of surface treatment of the filler, kneading/dispersion, coating, heat treatment, calendar radiation irradiation (EB) treatment, surface polishing treatment, and cutting are performed continuously. Moreover, the process can be divided into several parts as necessary.

In these processes, temperature and humidity are controlled, and the temperature is 10°C to 130°C, and the humidity is expressed as the amount of moisture in the air.
5 mg/m' to 20 mg/m'.

These include, for example, Japanese Patent Publication No. 40-23625, Japanese Patent Publication No. 3! It-28368 Publication, US-Japan Patent No. 347
No. 3960, etc.

Furthermore, the method disclosed in Japanese Patent Publication No. 41-13181 is considered to be a basic and important technique in this field.

The present invention will be explained in more detail below using Examples. It will be readily understood by those skilled in the art that the ingredients, proportions, order of operations, etc. shown herein may be modified without departing from the spirit of the invention.

Therefore, the invention should not be limited to the examples below. Note that the parts in Examples and Comparative Examples indicate overlapping and placing parts.

(Example) Coating liquid A (upper layer) 100 parts of cobalt-containing iron oxide (moisture content is shown in Table 1) (coercive force = 690 oersteds, average major axis diameter = 0.2 μ, crystallite size = 330 angstroms) vinyl chloride vinyl acetate Copolymer 15 parts (carboxyl group 0.5%
Contains, degree of polymerization 42o) polyester polyurethane
5 parts (contains 0.3% carboxyl group) Polyisocyanate (Coronet) 6.7 parts Oleic acid 2 parts Butyl stearate 1 part Conductive carbon (0.05μ) 3 parts α-Alumina (0
, 4 μ) 3 parts Methyl ethyl ketone/cyclohexane = 773 200 parts solvent Coating solution a (Lower layer) Cobalt-containing iron oxide (water content in Table 1) 100 parts (coercive force = 640 Oe, average major axis diameter: 0.24 μ, crystallite Size: 450 angstroms) Vinyl chloride vinyl acetate copolymer 15 parts (carboxyl group 0,5
% content, degree of polymerization 420) Polyester polyurethane
5 parts polyisocyanate (Coronet) L)
6.7 parts oleic acid
2 parts butyl stearate 1
3 parts Conductive carbon (0.05μ) 3 parts Methyl ethyl ketone/cyclohexanone = 773 Solvent
20
0 parts For each of the above two paints, each component was kneaded using a continuous kneader and then dispersed using a sand mill. To the obtained dispersion, 5 parts of polyisocyanate was added to the coating solution for the first layer, 6 parts to the coating solution for the second layer, and 40 parts of butyl acetate were added to each, and a filter having an average pore size of 1 μm was added. Coating liquids for forming the first magnetic layer and for forming the second magnetic layer were prepared.

The obtained coating liquid for the first magnetic layer has a thickness of 3.0 after drying.
Immediately thereafter, simultaneous multilayer coating was performed on a polyethylene terephthalate support with a thickness of 15 μm so that the thickness of the second magnetic layer was 1.0 μm, and both layers were still in a wet state. After drying, which was oriented using a cobalt magnet with a magnetic force of 3000G and a solenoid with a magnetic force of 1500G, it was processed at a temperature of 120℃ in a seven-stage calender consisting only of metal rolls.
The tape was slit to a width of 2 inches to produce a videotape. The tape thus obtained was sample No. 1.
~13 and its properties are shown in Table 1.

Sample No. 14.15 has a thickness of 4゜0μ after drying.
A single magnetic layer was provided as shown in Table 1 so that the magnetic field was m.

1 ro■■tocoω 0← ωgusuri■NzC'J C
L'5 If') In Cfl 14") "x
Force IO'Q CQ co
(Dye upper layer squareness ratio: A tape with a single upper layer was prepared, and using a vibrating sample type magnetometer (manufactured by Toei Kogyo), Hm 5KOe and Br78m were determined.

Using a video S/N Nijiback noise meter (925c) and using Comparative Example 7 as the reference tape, the difference in S/N ratio was determined.

The noise level was measured using a bypass filter of 10 KHz and a low pass filter of 4M11z.

The VTR used was Kenshi NV-8300.

Ra: The center line average roughness Ra specified in JIS 80601 was calculated using a surface roughness meter 5E3AK manufactured by Koita Research Institute. Note that cut off was performed at 0.25+n+n.

As shown in Table 1, the videotape of the present invention had a high squareness ratio, good video S/N, and small surface roughness (Ra).

Claims (1)

[Claims] (1) In a magnetic recording medium in which two or more magnetic layers are provided on a nonmagnetic support by dispersing a ferromagnetic material in a binder,
The upper layer uses a ferromagnetic material with moisture content adjusted to 0.8 wt% or more and 2.0 wt% or less, and the lower layer has an adsorbed water content of 0.8 wt%.
1. A magnetic recording medium characterized by using a ferromagnetic material that adsorbs less water by 0.1 wt% or more than the ferromagnetic material in the upper layer.