JPS59172166A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a particularly large reproduced output in recording short wavelength of <= several mu by using an electron ray curable resin and an org. solvent as a binder for a magnetic layer, and applying simultaneously a vertical magnetic field and electron ray on the magnetic layer during the time since a magnetic coating liquid is applied thereon until the liquid is dried and cured. CONSTITUTION:A magnetic coating (magnetic coating liquid) 1' which is not dried yet is applied on a non-magnetic base 2, and the base travels in the direction of an arrow facing the left. The pulverous ferromagnetic powder in the magnetic coating liquid is vertically oriented by a magnet 3 and on the other hand, an electron beam 5 is applied on the magnetic coating liquid from an electron beam irradiating device 5, by which a binder (electron beam curable resin) is cured and dried. The magnetic layer or the liquid forming the magnetic layer consists essentially of pulverous ferromagnetic powder, electron curable resin and org. solvent. The pulverous ferromagnetic powder is enumerated by gamma-Fe2O3, Co-contg. gamma-Fe2O3, Co-Ni-P alloy, etc. The electron beam curable resin is enumerated by a silicon modified unsatd. polyester resin, urethane-formed fatty acid modified unsatd. polyester resin, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method of manufacturing a magnetic recording medium particularly suitable for high-density recording.

Prior Art In recent years, with the development of electronic devices such as audio, video, and computers, short wavelength recording of several micrometers or less has become necessary for magnetic recording media such as magnetic tapes and magnetic flexible disks that record and reproduce the output of these devices. There is a strong demand for high-density recording that can provide high reproduction output.

In general, a magnetic recording medium is formed by providing a magnetic layer mainly composed of ferromagnetic fine powder and a binder made of a polymeric material on a nonmagnetic support made of a polymeric material such as polyester. In this case, so-called orientation is performed in which a magnetic field is applied in the in-plane direction of the magnetic layer to align the grain direction of the ferromagnetic fine powder when it is in an undried state containing a solvent. It is well known that this orientation improves the reproduction output of the magnetic head. However, this orientation tends to become less effective as the recording wavelength becomes shorter, such as several microns or less. In addition, it is possible to improve the reproduction output by making the magnetic layer thinner to reduce self-demagnetization, or by increasing the coercive force of the magnetic layer, but if the coercive force is too high, e.g. However, the reality is that no magnetic head has yet been developed that can effectively record and read information on such a magnetic layer with high coercive force.

In order to solve these drawbacks of the longitudinal recording method, a perpendicular magnetic recording method has been proposed in which recording is performed in a direction perpendicular to the surface of the magnetic recording medium. In this perpendicular magnetic recording method, as the recording wavelength becomes shorter, the demagnetizing field acting within the magnetic layer becomes smaller, making it possible to greatly increase the residual magnetization of short wavelength signals compared to the conventional longitudinal recording method. There are advantages that can be achieved.

C as a magnetic recording medium suitable for the above perpendicular magnetic recording method.
(+ - There are products in which a ferromagnetic metal thin film such as Cr is provided on a non-magnetic support, but these generally have poor productivity and are expensive, and have many problems in practical use, such as lacking wear resistance.) have.

As mentioned above, it is effective to orient the axis of easy magnetization of the ferromagnetic fine powder perpendicularly to obtain a magnetic recording medium capable of high-density recording. The ferromagnetic fine powder placed in the
The original direction, which has a random easy axis of magnetization, is easily lost, and when a magnetic field is applied in the perpendicular direction, the ferromagnetic fine powder becomes magnetized and aggregates, making it impossible to obtain a high squareness ratio in the perpendicular direction. However, there is a method to reduce the content of ferromagnetic fine powder per unit volume, but this will lower the residual magnetic flux density even if the squareness ratio is high, and therefore, high reproduction output for high-density recording can be achieved. I can't. In addition, the viscosity of the magnetic coating liquid can be increased (
Although it is effective to eliminate the above drawback, in this case, the ferromagnetic fine powder becomes difficult to move (therefore, a large magnetic field is required, which eventually causes agglomeration and is not a fundamental solution). Must not be.

As a means to solve the above-mentioned problems and drawbacks, a method of using electron beam curable resin as a binder (Japanese Patent Application Laid-open No. 57-1998-
111832, JP-A-57-164436, etc.). This is because the axis of easy magnetization of the fine ferromagnetic powder is oriented vertically, and then the binder is hardened by irradiation with electron beams, so that the axis of easy magnetization that was vertically oriented returns to its original state, and the fine ferromagnetic powder agglomerates. This is a very effective way to prevent this from happening.

However, according to the inventor's experiments, in the method using the electron beam curable resin, the viscosity of the magnetic coating liquid required for dispersion is insufficient if only a dispersant is added to the electron beam curable resin. It was found that sufficient dispersibility of the ferromagnetic fine powder could not be obtained. Particularly in recent years, ferromagnetic fine powder used for high-density recording has been made into ultrafine particles in order to obtain a high "/N", and deterioration of dispersibility has become a major technical issue.

Purpose The present invention was made in order to solve the above-mentioned drawbacks of coated perpendicular magnetic recording media, and to provide a magnetic recording medium that can obtain a particularly large reproduction output in short wavelength recording of several microns or less. A manufacturing method is provided.

5- Configuration As a result of intensive research to achieve this purpose, the inventor of the present invention found that
If an electron beam curable resin and an organic solvent are used as binders for the magnetic layer, a magnetic coating liquid in which fine ferromagnetic powder is sufficiently dispersed can be obtained, and after this magnetic coating liquid is applied, it is dried and hardened. We have found that the above-mentioned objective can be fully achieved by simultaneously applying a perpendicular magnetic field and an electron beam to the magnetic layer during the period of time. The present invention was completed based on this knowledge.

That is, in the method for producing a magnetic recording medium of the present invention, after coating a magnetic coating mainly composed of ferromagnetic fine powder, electron beam curable resin, and organic solvent on a nonmagnetic support, the coating film is still dry. It is characterized by applying a perpendicular magnetic field to the coating film while it is not cured, and simultaneously applying an electron beam while the coating film is in the magnetic field to harden the coating film and form a magnetic layer.

Representative examples of the support used in the present invention include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, and cellulose derivatives such as cellulose triacetate.

Although the thickness of the support is not particularly strictly defined, it is suitably about 5 to 200 microns.

The magnetic layer or the magnetic layer forming liquid mainly contains a ferromagnetic fine powder and an electron beam curable resin, and the magnetic layer forming liquid contains an organic solvent.

A typical example of ferromagnetic fine powder is r-Fel.
OHa Ca-containing r -re, o, s F@@0
4 ・cro.

, Co gold-containing F・,01, iron nitride acicular fine powder, C0-
Characteristic powders such as N1-P alloy, conomalt fine particles, parium ferrite, and strontium ferrite can be mentioned, and those having an average particle size of about 0.1 to 0.5 are suitable. The shape of these ferromagnetic fine powders may be spherical, acicular, hexagonal plate, or the like.

Typical examples of electron beam curable resins include silicone-modified unsaturated polyester resins; urethanized or vinylized fatty acid-modified unsaturated polyester resins; polyesters, acrylic resins, or epoxy resins with maleoyl groups introduced into side chains or terminals; acryloyl groups. Acrylic resins having two or more in the molecule; reaction products of terminal incyanate urethane prepolymers and acrylates or methacrylates having hydroxyl groups, such as urethane acrylates, ester urethane acrylates, ether urethane acrylates; epoxy acrylates; silicone acrylates etc. or a mixture of these and an electron beam curable monomer. The terminal isocyanate urethane prepolymer is obtained by reacting a polyol (polyester or polyether type) with a diisocyanate.

Examples of monofunctional electron beam curable monomers include vinylpyrrolidone, 2-ethylhexyl acrylate, lauryl acrylate, hydroxyethyl acrylate, ethoxymethoxy acrylate, and tetrahydrofurfuryl acrylate.

Examples of the bifunctional electron beam curable monomer include diethylene glycol diacrylate, tetraethylene glycol diacrylate, neopentyl glycol diacrylate, and the like.

Trimethylolpropane triacrylate, tetramethylolmethanetetraacrylate, and the like are exemplified as trifunctional or higher polyfunctional electron beam curable monomers.

The electron beam curable resins may be used alone or in combination of two or more.

In addition to the above-mentioned binder and fine ferromagnetic powder, the magnetic layer or magnetic layer forming liquid contains additives.

Dispersants, lubricants, abrasives, antistatic agents, etc. may be added.

9- Dispersants include caprylic acid, capric acid, lauric acid,
Fatty acids with 12 to 18 carbon atoms (RICOOaR
l is an alkyl or alkenyl group having 11 to 17 carbon atoms); an alkali metal of the above-mentioned fatty acid (Lis Nas K
etc.) or alkaline earth metals (Mg, ca, Ba)
A fluorine-containing compound of the above-mentioned fatty acid ester; an amide of the above-mentioned fatty acid; a polyalkylene oxide alkyl phosphate ester; lecithin, etc. are used. These dispersants are binders (electron beam curable resins)
It is added in an amount of 0.5 to 20 parts by weight per 100 parts by weight.

As lubricants, conductive fine powders such as cardan black, graphite, and carbon black graft polymers; inorganic fine powders such as molybdenum disulfide and tungsten disulfide; polyethylene, polypropylene, and polyethylene chloride.
10- Plastic fine powders such as vinyl copolymers and ethylene tetrafluorocarbons; α-olefin polymers; unsaturated aliphatic hydrocarbons that are liquid at room temperature (compounds in which an n-olefin double bond is bonded to the terminal carbon, carbon Number approximately 20); carbon number 1
Fatty acid esters consisting of 2 to 20 monobasic fatty acids and monohydric alcohols having 3 to 12 carbon atoms can be used. These lubricants contain 0.00 parts by weight per 100 parts by weight of binder.
It is added in an amount of 2 to 20 parts by weight.

As an abrasive, molten alkaline is used as a commonly used material.
silicon carbide chromium oxide, corundum, artificial corundum,
Diamonds, synthetic diamonds, 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 used in an amount of 0.5 to 100 parts by weight of the binder.
It is added in an amount of 20 parts.

As antistatic agents, car in black, graphite,
Conductive fine powder such as carin black graft polymer; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts, f Cationic surfactants such as lysine and other heterocycles, phosphoniums or sulfoniums; carboxylic acids,
Anionic surfactants containing acidic groups such as sulfonic acid, boric acid, sulfuric ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols are used. These antistatic agents have a cO of 11 to 30 parts per 100 parts by weight of binder.
It is added in a range of parts by weight.

When the method of the present invention was actually carried out, the above-mentioned ferromagnetic fine powder,
A magnetic layer forming liquid (magnetic paint) is prepared by containing a binder (electron beam curable resin) and an organic solvent as essential components, and adding the various additives mentioned above as necessary, and applying this to a non-magnetic support. apply a perpendicular magnetic field to the coating film before it dries to orient it, and
While the coating film is in a magnetic field, it may be irradiated with an electron beam to harden the coating film to form a magnetic layer having a thickness of 1 to 20 μm.

The organic solvents used in the method of the present invention include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; methyl acetate,
Ester systems such as ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether; ether, glycol dimethyl! -f Glycol ethers such as glycol, glycol monoethyl ether, and dioxane; tars (aromatic hydrocarbons) such as benzene, toluene, and xylene
; Examples include chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene 13-chlorohydrin, and dichlorobenzene.

One embodiment of the method of the present invention is shown in the accompanying drawings. 1' is coated on a non-magnetic support 2 with a magnetic paint (magnetic coating liquid) which has not yet been dried, and the entire coating is moving in the direction of the arrow pointing leftward in this device.

3 is a magnet which vertically aligns the ferromagnetic fine powder in the magnetic coating liquid, while the electron beam 5 from the electron beam irradiation device 4 is applied to the magnetic coating liquid, and the binder (electron beam curable resin) is oriented vertically. hardened and dried.

Create a magnetic recording medium with vertical orientation. In the drawings, reference numeral 1 represents a magnetic layer in a dried state and having vertical orientation.

According to the vertically oriented magnetic recording medium manufactured in this way, it has been recognized that the reproduction output can be improved with a commonly used ring-type head without using a special head called a perpendicular head. High density recording is possible.

14- Example 1 A mixture consisting of acrylic resin 20 1 unsaturated polyester 1flRFJrl 201 lauric acid 21 carin black 15 g was dispersed with a three-way filter, and then filtered through a filter with an average pore size of about 3μ to obtain a magnetic layer forming liquid. (magnetic paint) was prepared.

This magnetic paint was applied onto a polyethylene terephthalate film (non-magnetic support) having a thickness of about 75 μm using a doctor blade so that the thickness when dried and cured was about 1.8 μm.

Next, this is held together with a permanent magnet. Pass through the middle of a 2000 Gauss DC magnetic field.

Subsequently, using a curtain type electron beam accelerator with an accelerating voltage of 300 KV and a beam current of 15 mA, the magnetic paint was irradiated with an absorbed dose of 10 Mrad at a dose rate of 5 Mrad/sec.

After the oriented disk and the paint had been dried and hardened, it was further subjected to Soo A-calendering, punched out to a predetermined size, and the surface was polished to create a 5.25-inch magnetic flexible disk (Product 1 of the present invention). .

For comparison, a 5.25-inch magnetic flexible disk (comparative product 1) was prepared in exactly the same manner as above except that the magnetic field orientation operation was omitted.

Furthermore, for comparison, a 5.25-inch magnetic flexible disk (comparative product 2) was prepared in exactly the same manner as above except that the toluene-methyl ethyl ketone-cyclohexanone mixed solvent was not used.

A 5.25-inch flexible disk drive (head gap length 1.3μ) was used for these samples.
Recording and reproduction were performed at 3.7μ and 1.8μ, and the average reproduction output was measured.

The measurement results are shown in Table-1.

Example 2 A mixture consisting of lauric acid 4I and silicone oil 6I was dispersed in I-lumil for 11S hours. Then,
28 parts by weight was added to this dispersion and dispersed in a Seel kil for 15 hours. Furthermore, 17-Carne Black 71 was added to this dispersion and 1
g-) A magnetic layer forming solution was obtained by dispersing in a V mill for about 15 hours.

This viscous dispersion (magnetic layer forming liquid) was applied onto a polyethylene terephthalate film (approximately 7 sμ thick) using a 2-3 mil doctor blade, and the solvent was removed by drying at 100-120°C. Using an ESI (curtain type) electron beam accelerator with an accelerating voltage of 300 KV and a beam current of 1010-15, electron beam irradiation was performed at an absorbed dose of IMrad, and after polymerization and hardening to some extent, a group of cotton rolls and mirror-finished rolls was formed. The smoothing process was performed using a three-stage calendar consisting of: Next, using the electron beam accelerator described above, electron beam irradiation was performed at an absorbed dose of 10 Mrad to polymerize and harden the disk, which was then punched out to a predetermined size and surface polished to form a 5.25-inch magnetic flexible disk (
Invention product 2) was created.

For comparison, a magnetic layer forming solution was prepared in exactly the same manner except that the mixed solvent of toluene-methyl ethyl ketone-Schiff tetrahexanone was not used. However, this liquid was solidified like a pudding and did not become a viscous dispersion, making it impossible to form a magnetic layer.

The average reproduction output of the above sample was measured in the same manner as in Example 1. The results were as shown in Table-1.

Table 1 Note) The squareness ratio in the vertical direction is measured by VSM and is the residual magnetization ratio.
/Ms.

Here, Mr is the residual magnetic flux density, and M8 is the saturation is the sum magnetic flux density.

[Brief explanation of drawings]

The drawings are diagrams for explaining one embodiment of the method of the present invention.

Claims (1)

[Claims] 1. After applying a magnetic paint mainly composed of ferromagnetic fine powder, electron beam curable resin, and organic solvent onto a non-magnetic support, apply a magnetic field perpendicular to the paint film before it dries and hardens. 1. A method for producing a magnetic recording medium, comprising: applying an electron beam to the coating film to orient it, and curing the coating film while the coating film is in a magnetic field to form a magnetic layer.