JPS63173224A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To smooth the magnetic surface of the title medium and to improve productivity by forming the undercoat layer with the layer of a resin cured by the irradiation of radiation, and forming the magnetic layer obtained by heating, drying, and curing a magnetic paint coated layer. CONSTITUTION:The undercoat layer and the magnetic layer contg. fine ferromagnetic particles are successively formed on a nonmagnetic supporting body. The undercoat layer is composed of the layer of a resin cured by the irradiation of radiation, and the magnetic layer is formed by heating, drying, and curing a magnetic paint coated layer. UV rays can be used as the radiation, and fine hexagonal ferrite particles having 0.01-0.3mum mean particle size are used as the fine ferromagnetic particles. Various public-known nonmagnetic supporting body used for magnetic recording mediums can be used as the nonmagnetic carrier, and plastic film, paper, the nonmagnetic foil of aluminum, etc., or their coating material, laminate, laminar work, etc., can be exemplified. As a result, coating streaks are eliminated, adhesion is improved, and a thinnly coated magnetic layer having a smooth surface can be obtained.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a magnetic recording medium and a method for manufacturing the same.

(Prior art) Generally, magnetic recording media such as magnetic tapes and magnetic disks are
It is constructed by providing a magnetic layer containing ferromagnetic powder and binding resin as main components on a non-magnetic support such as polyester.

In recent years, with the progress of a highly information-oriented society, it has become desirable to increase the density of magnetic recording media.

Conventionally, general methods for increasing the density of magnetic recording media include reducing the particle size of ferromagnetic particles in the magnetic layer, filling the magnetic layer with high ferromagnetic particles, and Methods for smoothing the surface are known. Furthermore, among ferromagnetic fine particles, those suitable for high-output, low-noise magnetic recording media include metal or alloy magnetic powder produced by wet reduction method or dry reduction method, and hexagonal crystal structure produced by glass crystallization method. Magnetic powder, hexagonal ferrite fine particles produced by a hydrothermal method, etc. are known.

In such high-density magnetic recording media, in order to improve the adhesion of the magnetic layer to the non-magnetic support, an undercoat layer is provided between the non-magnetic support and the magnetic layer. Conductive powder such as carbon black is contained in such an undercoat layer to impart antistatic properties to the magnetic layer, thereby minimizing the amount of conductive powder added to the magnetic layer and improving electromagnetic conversion characteristics. It is also known to measure

The undercoat layer that provides functions such as antistatic functions to the magnetic layer is preferable for magnetic recording media, but the surface properties and solvent resistance of this undercoat layer are important factors for magnetic recording media. related to characteristics. In other words, if the surface roughness of the undercoat layer is large, the surface properties of the magnetic layer will be insufficient, and if the solvent resistance is insufficient, the magnetic layer will have streaks, pinholes, etc. Defects are more likely to occur.

On the other hand, from the viewpoint of productivity, it is advantageous in terms of the process to form the undercoat layer and the magnetic layer continuously on the same line.

However, if a conventional magnetic recording medium with a lower 11M using a conventional thermosetting/thermoplastic bonding resin is manufactured using this method, it will take a long time to dry and harden the resin, and the equipment will become huge. However, it has the disadvantage that defects such as scratches and pinholes are more likely to occur in the magnetic layer.

(Problems to be Solved by the Invention) As mentioned above, with the conventional undercoat layer using thermosetting/thermoplastic resin, it takes a long time to dry and harden the resin and requires huge equipment. There is a problem with doing so. In addition, if drying and curing take a long time, the solvent resistance of the undercoat layer is also limited, making it easy for smearing to occur on the surface of the magnetic layer, and especially when the magnetic layer is made thin, it may not be smooth. There was a problem that it became difficult to obtain a magnetic layer surface.

The present invention has been made to solve these conventional difficulties, and by utilizing radiation curing methods such as electron beam curing and ultraviolet curing that can be cured in a short time to form an undercoat layer, It is an object of the present invention to provide a high-density magnetic recording medium with a smooth magnetic surface and high productivity, and a manufacturing method capable of manufacturing the high-density recording medium with high productivity without increasing the size of equipment.

[Structure of the Invention] (Means for Solving the Problems) The magnetic recording medium of the present invention is a magnetic recording medium comprising an undercoat layer and a magnetic layer containing ferromagnetic fine particles provided in this order on a non-magnetic support. In the recording medium, the lower Km is made of a cured resin layer hardened by radiation irradiation, and the magnetic layer is made of a hardened magnetic layer hardened by heating and drying a magnetic paint coating layer, and The method for manufacturing a magnetic recording medium of the present invention includes forming an undercoat layer on a non-magnetic support and forming a magnetic layer thereon. a step of applying a resin to form an undercoat layer; a step of irradiating the undercoat layer with radiation to cure it; and a step of forming a magnetic layer on the cured undercoat layer;
The method is characterized in that it has at least a step of heating, drying, and curing the magnetic layer, and that each of these steps is performed continuously on the same line.

As the non-magnetic support used in the present invention, non-magnetic supports used in various known magnetic recording media can be used. Examples of such non-magnetic supports include plastic films, paper, non-magnetic metal foils such as aluminum, coated products, laminates, and laminated products of these materials. In particular, various plastic films are suitable because they satisfy the physical properties required as a nonmagnetic support.

Plastic films suitable for the nonmagnetic support include cellulose derivatives such as regenerated cellulose, ethyl cellulose, cellulose acetate butyrate, cellulose diacetate, and cellulose triacetate; polyolefins such as polyethylene, polypropylene, and polybutylene; polyvinyl chloride; and polyvinylidene chloride. polyvinylalconyl; polynisdel such as polyethylene terephthalate and polyethylene-2°6-naphthalate; polycarbonate; polystyrene; polyacrylate; polyamide; polyimide; polyamideimide; polyvinyl fluoride;
Examples include various films made of fluororesins such as polyvinylidene fluoride. These films can be either stretched or unstretched, and may or may not be surface-treated.

Radiation that can be used in the present invention includes radiation (γ rays),
Examples include electron beams and ultraviolet rays, but ultraviolet rays are particularly suitable because they are relatively inexpensive, do not cause the problem of ozone generation, and are not limited to an inert atmosphere.

The radiation-curable resin used to form the undercoat layer is a compound having one or more carbon-carbon unsaturated bonds, such as an acryloyl group, a methacryloyl group, an acrylamide group,
Mention may be made of compounds containing allyl groups, vinyl ether groups, vinyl thioale groups, etc., and unsaturated polyesters.

Examples of compounds having one carbon-carbon unsaturated bond in the molecule include unsaturated fatty acid acids such as acrylic acid and 2-butenoic acid, maleic acid, fumaric acid, 2-fan-1,4-dicarboxylic acid, and muconic acid. unsaturated polybasic acids such as acrylamide, crotonamide, 2-pentenamide, unsaturated fatty acid amides such as maleamide, acrylic acid alkyl esters such as methyl acrylate and its congeners, styrene and its congeners α- Methylstyrene, β-
Chlorstyrene, etc., acrylonitrile, vinyl acetate,
Examples include vinyl propionate.

Examples of compounds having two or more carbon-carbon unsaturated bonds in the molecule include unsaturated esters of polyols, such as ethylene diacrylate, diethylene glycol diacrylate, glycerol triacrylate, ethylene diacrylate, pentaerythritol tetraacrylate, and epoxy groups. Examples include glycidyl acrylate and the like. Note that it is also possible to use a mixture of a compound having one unsaturated bond and a compound having two or more unsaturated bonds in the molecule.

Furthermore, these compounds may be polymer chains, or such polymer chains and monomers may be mixed together.

Examples of UV-curable resins include those similar to the above-mentioned radiation-curable resins, but among them, acrylate-based resins containing (meth)acryloyl groups have high curability,
The cured product has excellent physical properties. This acrylate resin is a resin that has one or more (meth)acryloyl groups in the molecule, and among them, the molecular size is 200 or more, 5ooo
Oligomers in the range of 0 or less are suitable. Examples of such resins having one or more (meth)acryloyl groups in the molecule include polyurethane (meth)acrylate, epoxy (meth)acrylate resin, and polyester (meth)acrylate.
Acrylate, polyol (meth)acrylate, polybutadiene (meth)acrylate, melamine (meth)acrylate resin, polyacetal (meth)acrylate, silicone (meth)acrylate resin, polyamide (
Examples include meth)acrylate and heterocycle-containing (meth)acrylate resins, but in addition to these, resins in which a (meth)acryloyl group is introduced into the molecule by modifying the binding resin may also be used, or a mixture of these may be used. It's okay.

Note that when an ultraviolet curable resin is used as the radiation curable resin, a photoinitiator and, if necessary, a photoinitiation accelerator are used. The photoinitiation promoter acts to prevent curing inhibition caused by oxygen when ultraviolet irradiation is performed in the atmosphere or other oxygen-containing atmosphere.

Examples of the above photoinitiators include phenyl ketones such as acetophenone, acetophenone diezyl ketal, diacetyl, benzyl, benzyl dimethyl ketal, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-2-methylphenylpropanone: Benzophenone, bis-4,4'-dialkylaminobenzophenone, 3.3
benzophenones such as '-dimethyl-4-methoxybencyfurone;bezoins; xanthones such as chlorothioxanthone, dimethylthioxanthone, and dimethylthioxanthone; anthraquinones, sulfides, phenyloximes, etc.; You may use a mixture of two or more.

As photoinitiation accelerators, aliphatic amines such as N-methylgetanolamine and N-dimethylgetanolamine:
Bis-4,4'-dialkylaminobenzophenone, N
, aromatic amines such as alkyl N-dimethylaminobenzoate; and polyamine compounds which are polymerized products thereof, and a plurality of these may be used in combination.

The amount of the photoinitiator and photoinitiation accelerator added is preferably 1 part or more and 20 parts or less per 100 parts of the ultraviolet curable resin. In addition to the radiation-curable resin, the undercoat layer may contain a thermosetting/thermoplastic resin and various additives, if necessary.

Examples of thermosetting/thermoplastic resins include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, acrylic ester-acrylonitrile copolymer, polyamide resin, polyvinyl butyral resin, cell+1-s Derivatives, polyester resins, polyurethane resins, urea resins, melamine resins, silicone resins, acrylic resins,
Examples include phenol resins and epoxy resins alone or a mixture thereof.

Various additives that can be used in the present invention include antistatic agents,
Abrasives, AIWJ agents, dispersants, leveling agents, antifoaming agents,
Examples include surfactants, coating film modifiers, adhesion improvers, wetting improvers, antisettling agents, viscosity modifiers, stabilizers, and the like.

As an electron beam accelerator for electron beam irradiation among radiation irradiation, a Pandegraaf scanning method, a double scanning method, a curtain beam method, a broad beam curtain beam method, a pulse method, etc. can be adopted. Among these, curtain beam type electron beam accelerators are relatively inexpensive and can provide high output. The acceleration voltage of these electron beam accelerators is 100 to 1000 ke.
V is preferred. The equipment required for electron beam irradiation is as follows:
Other examples include an X-ray shielding device and an irradiation atmosphere adjusting device.

Ultraviolet generating lamps used for ultraviolet irradiation include low-pressure mercury lamps, chemical lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, arc lamps, and xenon lamps, but lamps are preferred due to equipment cost and ease of maintenance. A high-pressure mercury lamp or metal halide lamp with an output of 30 to 200 units per IC is recommended. Further, in order to appropriately suppress the temperature rise of the irradiated object due to light irradiation, unnecessary wavelength ranges other than the wavelengths involved in curing (200 to 450 nm) may be cut using a filter or the like.

In order to prevent the irradiated object from generating heat due to radiation irradiation and, in particular, from deforming the plastic support, the irradiated object may be cooled by a suitable method.

As the ferromagnetic fine particles forming the magnetic layer, γ-Fe20
3. Acicular fine powders such as CrO2, Co-7Fe203, metallic iron, and metal alloys: Examples include hexagonal ferrite fine particles such as barium ferrite and strontium ferrite, and MnBi optical ferromagnetic fine powders, but the particle size distribution is Preferably, the particles are sharp and have a small average particle diameter. In particular, hexagonal ferrite fine particles are stable oxides and can achieve high density magnetic recording by utilizing magnetic anisotropy in the perpendicular direction. Such hexagonal ferrite fine particles include various cobalt-substituted products of barium ferrite, various cobalt-substituted products of strontium ferrite, and various W
Examples include barium ferrite, various types of W and strontium ferrite, and the average grain size is 0.01~
0.3 μm is preferred.

As the binding resin in the magnetic layer, known thermoplastic resins and thermosetting resins can be used alone or in combination. Furthermore, if necessary, antistatic agents, abrasives, lubricants, etc. may be added to the magnetic layer.
Dispersants, leveling agents, antifoaming agents, surfactants, coating film modifiers, adhesion improvers, wetting improvers, antisettling agents, viscosity modifiers, stabilizers, and the like may be added.

Solvents used in primer paints and magnetic paints include aliphatic hydrocarbons such as n-hexane and cyclohexane; aromatic hydrocarbons such as 1-luene, V-sylene, and solvent naphtha; methylene chloride, 1,1, 1-1-lichloroethane,
Chlorinated hydrocarbons such as chlorbezene; Alcohols such as methanol, ethanol, isopropanol, butanol, and benzyl alcohol; Ethers such as dimethyl ether, methyl isobutyl ether, tetrahydrofuran, and dioxane; Acetone, methyl ethyl ketone, and methyl isobutyl ketone. Ketones such as cyclohexanone and cyclohexanone:
Nisdels such as ethyl formate, ethyl acetate, butyl acetate;
Examples include glycol ethers, N-methylpyrrolidone, dimethylformamide, diacetone alcohol, and isophorone, which may be used alone or in combination.

In order to produce an undercoat paint and a magnetic paint, various fillers and additives may be added to the mixture of the above-mentioned resin components as necessary. When using a solvent together, you can dissolve each resin component in an appropriate solvent to make a resin solution, and then perform the same blending. Alternatively, you can mix each component without a solvent and dilute it with a solvent. The viscosity may also be adjusted.

Various additives can also be blended after being made into a solution using an appropriate solvent.

For primer paints and magnetic paints (dispersion methods for fillers include attritor, high-speed impeller dispersion, high-speed impact mill, high-speed stone mill, colloid mill, kneading extruder,
Examples include a sand grinder, dough mill, kneader, Banbury mill, pebble mill, homogenizer, ball mill, two-roll mill, three-roll mill, and the like.

Application methods for the undercoat and magnetic layer include curtain coating, gravure offlet coating, gravure coating, spin cord, spray coating, dip coating, and (air) coating.
Doctor coat, transfer coat, (air)
Examples include knife coating, blade coating, and reverse roll coating.

The thickness of the undercoat layer is applied so that the dry thickness is in the range of 0.1 to 5.0 μm. This dry thickness is determined by the curing characteristics of the undercoat layer, the characteristics of the coating film, etc. After applying the undercoat layer,
After drying with heat or cold air and irradiating with radiation, or while irradiating with radiation, a magnetic layer is applied. The radiation direction may be from the undercoat layer side or from the nonmagnetic support side opposite to the undercoat layer.

The thickness of the magnetic layer is suitably in the range of 0.3 to 5.0 μm in terms of dry thickness.

It is preferable that the above-mentioned coating steps, irradiation, and drying steps are performed continuously on the same line.

(Example) The present invention will be explained below using specific examples.

Example 1 FIG. 1 is a diagram schematically showing the apparatus used in the method of this example.

In the figure, a non-magnetic support 2 that is continuously fed out from a supply reel 1 is coated on one side with an undercoat 5 supplied from an undercoat tank 4 in an undercoat tank 3, and then in an irradiation chamber 6 with an ultraviolet source 7. The undercoat layer is irradiated with ultraviolet light and cured.

Next, the magnetic paint 10 sent to the magnetic paint tank 8 and supplied from the magnetic paint tank 9 is applied onto the undercoat paint layer, and the magnetic fine particles in the magnetic paint layer are oriented in the easy magnetization axis direction by the orientation magnet 11. The material is dried and hardened through a dry air 12, cooled by a cooling roll 13, and then wound onto a take-up reel 14.

In this example, undercoat A and magnetic paint F prepared according to Table 1 were used. First, undercoat A was applied onto a 75 μm thick polyethylene terephthalate sheet using the above-mentioned apparatus, and the coating film was dried. thickness 0.4μm),
Irradiate ultraviolet light using an 80w/cm high-pressure mercury lamp (
2J/cn) L/L, then magnetic paint F was applied thereon to form a magnetic layer with a dry thickness of 2.4 μm.

Thereafter, the surface was smoothed using a super calender, and after hardening at 40° C. for 24 hours, a magnetic disk was punched out into a 3.5-inch disk shape.

Examples 2 to 6 Various magnetic disks were produced in the same manner as in Example 1, except that the thickness of the magnetic layer was varied from 0.5 to 3.1 μm.

Comparative Example 1 Undercoat paint B prepared according to Table 1 was coated on a 15 μm thick polyethylene terephthalate sheet using conventional equipment (dry thickness 0.4 μil) and cured at 60° C. for 96 hours to prepare an undercoat layer. did.

Magnetic paint F was applied on this undercoat layer to a dry thickness of 2.5 μm.
m magnetic layers were formed. A 3.5-inch magnetic disk was produced by subjecting the material to an immersion supercalender treatment and simultaneously curing it at 40° C. for 24 hours.

Comparative Examples 2 to 6 Various magnetic disks were produced in the same manner as Comparative Example 1 except that the thickness of the magnetic layer was changed from 0.5 to 3.1 μm.

Comparative Examples 7 to 9 Magnetic disks having various undercoat layers were produced in the same manner as in Comparative Example 1, except that undercoat paints C%D and E with varying amounts of curing agent were used.

The magnetic disks prepared in the above Examples and Comparative Examples were recorded and reproduced using a ring-type ferrite head with a gap of 0.35 .mu.m and a width of 125 .mu.m at a recording density of 35 FRPI, and an envelope test was performed using a synchroscope. The results are shown in Table 2.

(The following is a blank space) Table 1 Table 2 As is clear from Table 2, the magnetic disk produced according to the present invention exhibits a good envelope.

(Effects of the Invention) As is clear from the above examples, the magnetic recording medium of the present invention has excellent curing properties of the undercoat layer, so there are no coating streaks and good adhesion. It has a thin magnetic layer with a smooth surface and is suitable as a high-density magnetic recording medium.

Further, according to the manufacturing method of the present invention, the resin of the undercoat layer can be dried and cured in a short time, and therefore productivity can be improved without requiring a huge amount of equipment.

[Brief explanation of the drawing]

The drawings schematically show apparatuses used in embodiments of the invention.

Claims (5)

[Claims] (1) In a magnetic recording medium in which an undercoat layer and a magnetic layer containing ferromagnetic fine particles are sequentially provided on a nonmagnetic support,
A magnetic recording medium characterized in that the undercoat layer is made of a cured resin layer cured by radiation irradiation, and the magnetic layer is made of a cured magnetic layer cured by heating and drying a magnetic paint coating layer. (2) The magnetic recording medium according to claim 1, wherein the radiation is ultraviolet rays. (3) The magnetic recording medium according to claim 1 or 2, wherein the ferromagnetic fine particles are hexagonal ferrite fine particles having an average particle size of 0.01 to 0.3 μm. (4) In a method for manufacturing a magnetic recording medium, in which an undercoat layer is formed on a non-magnetic support and a magnetic layer is formed thereon, a radiation-curable resin is coated on the non-magnetic support, and the undercoat layer is formed on the undercoat layer. A step of forming a layer, a step of curing this undercoat layer by irradiating it with radiation, a step of forming a magnetic layer on the hardened undercoat layer, and a step of heating and drying and curing this magnetic layer. 1. A method for manufacturing a magnetic recording medium, comprising at least the steps of: performing each of these steps continuously on the same line. (5) The method for manufacturing a magnetic recording medium according to claim 4, wherein the radiation is ultraviolet rays.