JPS6116018A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the triboelectrification of a magnetic layer without spoiling the electromagnetic conversion characteristic thereof by forming a primer coating layer contg. an emulsion and pulverous conductive powder on a non-magnetic substrate and forming a magnetic coated film thereon. CONSTITUTION:The primer coating layer contg. the emulsion of a styrene/butadiene copolymer having >=60% gel molar fraction and others as well as the pulverous conductive powder such as carbon black and pulverous metallic powder of Ag, Ti, Cu, Sn, etc. is formed on the non-magnetic substrate consisting of plastic, etc. and a magnetic paint consisting essentially of magnetic powder and binder is coated thereon to form the magnetic coated film. The electrification of the magnetic layer is thus prevented without spoiling the electromagnetic conversion characteristic.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to magnetic recording media.

[Background technology and its problems]

A magnetic recording medium usually consists of a non-magnetic support and a magnetic layer formed thereon, and this magnetic layer generally contains magnetic powder, a binder component, an organic solvent, and other additives added as necessary. Magnetic paint consisting of agent is placed on a non-magnetic support@
Formed by cloth and drying.

Polyester films, particularly polyethylene terephthalate films, are widely used as nonmagnetic supports for magnetic recording media. Polyethylene terephthalate has excellent mechanical strength, heat resistance, moisture resistance, chemical resistance, etc.
On the other hand, it has the disadvantage of high electrical resistance.

In addition, γ-FezO8 and cobalt-containing iron oxide are used as magnetic powders, but in addition to having high electrical resistance, the binder is a poor conductor, so the magnetic layer of a magnetic recording medium has a high surface electrical resistance. As a result, they are easily charged and generate noise during discharge, and dust adheres to them, causing dropouts during recording or playback.

In order to improve these drawbacks, conventional methods have been to coat a non-magnetic support with a paint in which magnetic powder and conductive powder are dispersed in a binder, or to disperse magnetic powder on a non-magnetic support in a binder. In some cases, a so-called Tsubatsu coach ink was applied, in which a paint containing conductive powder dispersed in a binder was applied to the side opposite to the side to which the paint was applied.

However, in the former case, the surface smoothness of the magnetic layer deteriorates, and non-magnetic conductive powder is mixed into the magnetic layer, which impairs the electromagnetic conversion characteristics of the magnetic recording medium. In the latter case, the electrical conductivity of the magnetic layer is not improved at all, and the paint must be applied to both sides of the non-magnetic support. The paint must be applied again to the other surface, which is disadvantageous in terms of manufacturing.

It has also been practiced to form a metal thin film layer or a layer coated with a conductive paint in which conductive powder is dispersed in a binder between the nonmagnetic support and the magnetic layer.

In the former case, large-scale manufacturing equipment is required to form the metal thin film layer by means such as vapor deposition or plating, and there are also problems with the adhesion between the metal thin film layer and the magnetic layer, and between the metal thin film layer and the nonmagnetic support. there were.

In the latter case, the conductive paint coated on the non-magnetic support contains a binder, and since the binder is compatible with the solvent in the magnetic paint, uneven coating of the undercoat layer may occur. This tends to cause the surface properties to become very poor, and furthermore, when a magnetic layer is formed on the surface, thickness unevenness tends to occur in the magnetic layer, and this thickness unevenness deteriorates the electromagnetic conversion characteristics of the ba magnetic recording medium, such as the S/N ratio. .

[Purpose of the invention]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic recording medium that can prevent the magnetic layer from being charged without impairing the electromagnetic conversion characteristics.

[Means for solving problems]

That is, the magnetic recording medium according to the present invention is characterized in that an undercoat layer containing an emulsion and a conductive fine powder is formed on a non-magnetic support, and a magnetic coating film is formed on the undercoat layer. It is something.

The emulsion used in the present invention may be one that is insoluble in the organic solvent of the magnetic layer, specifically an emulsion having a gel fraction of 60 or more by weight. Kel here refers to a state in which monomers are three-dimensionally polymerized. The more the degree of this three-dimensional polymerization progresses, the more difficult it becomes to dissolve in a solvent. Therefore, the degree of three-dimensional polymerization of gel is determined from its solubility, and since the solubility differs depending on the solvent used, the definition of the degree of three-dimensional polymerization of gel differs depending on the solvent. In other words, Kel is a three-dimensionally copolymerized state, and the degree of three-dimensional polymerization is such that it does not dissolve even if purified tetrahydrofuran is immersed for a period of time.

Therefore, the gel fraction in the present invention refers to a value determined by the following calculation formula.

where Wl: polymer Mr#'W2:2 in the collected sample
The vacuum-dried sample at 0°C is kept in purified tetrahydrofurano at 20'C for 48 hours and filtered for 1 hour.

Dry the P liquid obtained by combing Weight of solid obtained. That is, Wl is eluted in tetrahydrofuran is the weight of the components.

Emulsions include styreneophthalene copolymer and styrene isobrene copolymer. Styrene-roloprene copolymer, styrene-acrylonitrile copolymer,
Styrene-acrylic acid ester copolymer, phthadiene-acrylonyl/l/ copolymer, butane-methyl methacrylate copolymer, vinyl acetate-acrylic acid ester copolymer, polystyrene-acrylic acid ester copolymer, polystyrene-acrylic acid ester copolymer Seven/
copolymer, polyvinyl acetate, polyacrylic ester,
Examples include emulsions of polyester and polyurethane.

In addition, as conductive fine powder, carbo black, Δg, T
Fine metal powder such as i, Cu, Sn, etc. can be inserted.

In addition, the mixing ratio of the emulsion and the conductive fine powder is such that when both are taken as 100, the conductive fine powder has a volume ratio of 5 to 70.
More preferably, it is 5 to 50% by volume.

The thickness of the undercoat layer made of emulsion and conductive fine powder is preferably 0.1 to 3 microns.

The non-magnetic supports used in the present invention 1+-1"'L, , , -, include polyesters such as polyethylene terephthalate and -, polyolefins such as polyethylene and polypropylene, cellulose triacetate, cellulose guaacetate, and cellulose acetate. cellulose derivatives such as chloride, polyvinyl chloride, polychloride 7
Plastics such as vinyl resins such as polycarbonate, polyimide, polyamideimide, and the like can be mentioned. The nonmagnetic support may be in the form of a film, tape, sheet, tissue, card, or the like.

The magnetic coating film is formed by applying a magnetic paint containing magnetic powder and a binder as main components, as well as an organic solvent and additives.

The ferromagnetic powders used in the present invention include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powders, and the like.

As the ferromagnetic iron oxide particles, when expressed by the general formula FeOx, the value of
, 50), McJR-Tite (Fe30+, X=
1.3'3), and the solid solution of KotL et al. (FeOx,
1.33(X(1,50).

γ-Fe20s and Fe50+ are usually obtained by the following manufacturing method. Ferrous hydroxide is produced by adding an alkali to a ferrous salt solution, and oxidized by blowing air at a predetermined temperature PH to obtain acicular hydrated iron oxide. It is heated and dehydrated at a temperature of 0.degree. C., and then reduced by heating at 300 to 450.degree. C. in a reducing atmosphere to obtain acicular macnetite particles. Furthermore, if necessary, add 200% of the macnetite.
Acicular macnetite (γ-Fe2) is reoxidized at ~350℃.
0+).

Cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. There are two types of cobalt-containing magnetic iron oxide: doped type and deposited type.

The methods for producing CO-doped iron oxide particles include (1) a method in which ferric hydroxide containing cobalt hydroxide is hydrothermally treated in an alkaline atmosphere, and the resulting powder is reduced and oxidized; (2) ketite is During synthesis, a cobalt salt solution is added in advance, and goethite containing cobalt is synthesized while adjusting the pH, and this is reduced and oxidized (31 Co-free cokeite is used as a core, and a A method in which a reaction similar to the reaction in (2) is carried out to grow Co-depleted keikite, followed by reduction, oxidation, and oxidation. (4) In an alkaline aqueous solution containing Co salt on the surface of acicular keiteite or makhemite. There are methods such as treating with water to adsorb CO compounds, followed by reduction/oxidation or heat treatment at a relatively high temperature.

In addition, CO-coated iron oxide magnetic particles are produced by mixing cylindrical magnetic iron oxide and cobalt salt in an alkaline aqueous solution and heating the mixture, and adsorbing a cobalt compound such as cobalt hydroxide onto the iron oxide particles. It can be obtained by washing and drying the product and then heat-treating it in a non-reducing atmosphere such as N2 scum in the air. C.

Adhesive type particles j: 1: Compared to Co h-type particles, when formed into a tape, it has excellent transfer characteristics and #magnetic characteristics.

As the ferromagnetic chromium dioxide, CrO2 or (well, for the purpose of improving Hc, Ru, Sn, Te
.

A material to which at least one of Sb, Fe, Ti, V, -□, etc. is added can be used. CrOz is basically obtained by thermally decomposing chromium trioxide (Cro++) at 400-525°G at 500 atmospheres without the presence of water. Further, as a synthesis method under atmospheric pressure, there is also a method in which CrOa is decomposed at 250 to 375° C. in the presence of nitrogen oxide (NO) in addition to oxygen.

Ferromagnetic alloy powders include Fe, Co, Ni,
F”e-Co.

P' e -Ni or Fe-Co-Ni can be used, and Al! ,
S i, T + .

Some contain metal components such as Cr, Mn, Cu, and Zn.

Methods for producing ferromagnetic alloy powder include: (1) thermal decomposition of organic acid salts (mainly oxalate) of ferromagnetic metals and alloys, and reduction with reducing gas; (2) acicular iron oxyhydroxide or C.

(3) Method of evaporating ferromagnetic metals and alloys in inert gas (4) Method of decomposing metal carbonyl compounds (5) Mercury A method of separating and removing mercury after depositing ferromagnetic metal powder by electrolysis (6) A method of separating and removing mercury after depositing ferromagnetic metal powder by electrolysis. There are methods such as wet reduction.

Also, as a binder, vinyl chloride-hinyl acetate is used.

system copolymer, vinyl chloride-hinylidene chloride copolymer, hinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-hinylidene chloride copolymer, meccrylic acid ester-hynylidene chloride copolymer, meccryl Acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl chloride, hynylidene chloride-acrylonitrile copolymer, butanene-acrylonitrile copolymer,
Polyhinyl butyral, polyhinyl acetal, cellulose derivatives, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea formaldehyde resin, etc. can be mentioned.

Examples of solvents include ketones (e.g. acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone), alcohols (e.g. methanol, ethanol, propatool, phthanol), esters (e.g. methyl acetate, ethyl acetate, ethyl acetate, ethyl lactate, glycol ethers (e.g. ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane), aromatic hydrocarbons (e.g. ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane),
xylene), aliphatic hydrocarbons (e.g. hexane, heptano), and the like.

Additives include dispersants, lubricants, and abrasives.

There are rust preventives, etc.

Dispersants (pigment wetting agents) include caprylic acid, capric acid, lauric acid, myristic acid, balmitic acid, stearic acid, oleic acid, elaidine phosphoric acid, linoleic acid, darulenoic acid, stearolic acid, etc. having 12 to 18 carbon atoms. fatty acids (Rt C00I-1, Rt is an alkyl or alkenyl group having 11 to 17 carbon atoms);
The alkali metals (Li, Na, etc.) of the aforementioned fatty acids.

etc.) or alkaline earth metals (Ume, Ca, Ba),
Metal soaps consisting of; fluorine-containing compounds of the above fatty acid esters; amides of the above fatty acids; polyalkylenoxide alkyl phosphates; lecithin; trialkyl polyolefin oquine quaternary ammonium salts (alkyl has 1 to 1 carbon atoms 5, ole/fino, ethylene, propylene, etc. are used. In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters can also be used. These dispersants are added in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the binder.

As a lubricant, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkyl polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms, alkoxy silicone oil such as phenylporin loxane, fluoroalkylpo IJ-7b xane (alkyl has 1 to 5 carbon atoms); electrically conductive fine powder such as graphite; molybdenum disulfide, Inorganic fine powder such as tanksten sulfide; plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene; α-olefin polymer; unsaturated aliphatic hydrocarbon (n -A compound in which an olefinic double bond is attached to the terminal carbon, approximately 2 carbon atoms
0); Monobasic fatty acids with 12 to 20 carbon atoms and 3 carbon atoms
Fatty acid esters consisting of ~12 monohydric alcohols, fluorocarbons, etc. can be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder.

Commonly used abrasives include fused alumina, silicon carbide, chromium oxide (Cr20a), corundum, artificial corundum, diamond, artificial diamond,
Garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have a Mohs hardness of 5 or more and an average particle size of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm. These abrasives are added in an amount of 0.5 to 20 parts by weight per 100 M parts of the binder.

Rust inhibitors include phosphoric acid, sulfamide, quanidine,
Pyridine, amines, urea, zinc chromate, calcium chromate, strontium chloride.

Among the examples that can be used are dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, jetanolamine phosphate, cyclohexylammonium carbonate, hexamethylene diamine carbonate, 70-ropyrenonoamine stearate, The use of volatile rust inhibitors (inorganic or organic acid salts of amines, amides, or imides) such as Quanino 7-carbonate, Tri-1-Cutur-Amino-Nitride, and Morpholinostear-1. Improves rust effect. These rust inhibitors are made of ferromagnetic fine powder 100
It is used in a range of 0.01 to 20 parts by weight.

Hereinafter, the present invention will be explained by examples.

Example 1 On a polyethylene terephthalate film with a thickness of 12 μm, an undercoating liquid in which colloidal carphone was mixed and dispersed in an acrylic acid ester emulsion with a gel fraction of 80% by weight was applied so that the thickness after drying was 0.5 μm. An undercoat layer was formed. The content of colloidal carbon in the above undercoating liquid is 3
It has a volume ratio of 0.

Co adhesion 7- FezOa 100 parts by weight Vinyl chloride-hinyl acetate copolymer 1o (VA
GH: Made by U, C, C, Inc.) Polyurethane resin 15 (N-3
022: Nippon Polyurethane Co., Ltd.) Cr2Qa2. tt silicone oil 1 〃lentin], 11 methyl ethyl keto 7 100.

Methyl isobutylke! / 50 parts by weight Toluene 50 After dispersing the above composition in a whole mill for 24 hours, 2.5 parts by weight of a curing agent (TisModur L-75: manufactured by Bayer AG) was added and shear dispersion was performed for 2 hours to form a magnetic paint. It was created. This magnetic paint was applied onto the undercoat layer to a dry thickness of 4.5 μm, subjected to magnetic field orientation treatment, and dried to form a magnetic layer. Thereafter, it was calendered and cut into a predetermined width to create a magnetic tape.

Example 2 On a polyethylene terephthalate film with a thickness of 12 μm, an undercoating liquid in which titanium metal powder was mixed and dispersed in a styrene-butadieno copolymer emulsion with a Kel fraction of 90% by weight was applied to a polyethylene terephthalate film with a JL-shape of 0 after drying. An undercoat layer was formed by coating the film to a thickness of .5 μm. The content of titanium metal powder in the undercoating liquid is 30 parts by volume.

A magnetic tape similar to that in Example 1 was applied on the undercoat layer, and a magnetic tape was prepared in the same manner as in Example 1.

Comparative Example 1 The same magnetic paint as in the previous example was applied on a 12 μm thick polyethylene terephthalate film to a dry thickness of 4.5 μm.
A magnetic tape was prepared in the same manner as in Example 1.

Comparative Example 2 One portion of carbon black was added to the same magnetic paint as in Example 1 above.
0 parts by weight was added, and this was applied onto a polyethylene terephthalate film having a thickness of 12 μm so that the dry thickness was 4.5 μm, and a magnetic tape was prepared in the same manner as in Example 1.

The half-life of the charge amount, Y-8/N (luminance signal/noise ratio), and C-8/N (chroma signal/noise ratio) of the magnetic tapes prepared in Examples and Comparative Examples were measured.

The measurement results are shown in the table below.

As is clear from the table, the magnetic recording medium according to the present invention can reduce the magnetic layer band without impairing the electromagnetic conversion characteristics.

It can be seen that static electricity is prevented and problems caused by static electricity are improved.

〔Effect of the invention〕

As is clear from the description of the above embodiments, since the present invention provides an undercoat layer made of emulsion and conductive fine powder, antistatic properties of the magnetic layer and improvement of electromagnetic conversion characteristics can be achieved at the same time. , a magnetic recording medium with less noise can be obtained.

Claims (1)

[Claims] A magnetic recording medium characterized in that an undercoat layer containing an emulsion and conductive fine powder is formed on a nonmagnetic support, and a magnetic coating film is formed on the undercoat layer.