JPS6231025A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase the supply amt. of the lubricating agent to be contained in a magnetic layer to the surface of the magnetic layer and to obtain the good runnability by drying a coating layer then irradiating specific electron rays to the surface of the coating layer. CONSTITUTION:A magnetic coating compd. contg. a binder, lubricating agent, pulverous ferromagnetic powder and org. solvent is coated on a nonmagnetic base to form the coating layer and after the coating layer is dried, the electron rays of which the ion acceleration voltage is in a 100-1,000V range is irradiated to the surface of the coating layer. The binder on the surface of the magnetic layer is thereby removed and fine recesses are formed. The lubricating agent existing in the deep part of the magnetic layer is smoothly supplied from the recesses to the surface of the magnetic layer, by which the runnability of a magnetic recording medium is improved. The effective removal of the binder on the surface of the coating layer is not possible when the electron rays of which the ion acceleration voltage is below 100V are used. On the other hand, the binder on the surface of the coating layer is excessively removed when the electron rays are irradiated and such is undesirable when the electron rays of which the ion acceleration voltage exceeds 100V are used.

Description

[Detailed description of the invention] [Field of invention] The present invention relates to a novel method for manufacturing magnetic recording media.

[Background of the Invention] Recently, magnetic recording media have been widely used as audio tapes, video tapes, computer magnetic tapes, and the like.

A magnetic recording medium basically consists of a non-magnetic support and a magnetic layer laminated on the non-magnetic support, and generally such a magnetic recording medium is coated with a lubricant.

A magnetic paint is prepared by kneading an organic solvent, ferromagnetic fine powder, and a binder, and this magnetic paint is applied onto a non-magnetic support. Before the magnetic paint dries, a magnetic field orientation treatment is performed to form a magnetic layer. manufactured by an operation that includes the step of forming.

Recently, magnetic recording media such as audio tapes, video tapes, and computer magnetic tapes have been designed to have smooth magnetic layer surfaces to reduce spacing loss between the magnetic layer surface and magnetic head in order to improve playback output. Improvements have been made to.

However, although smoothing the surface of the magnetic layer improves the adhesion with the magnetic head, it conversely increases the coefficient of friction between the surface of the magnetic layer and the member that comes into contact with it, reducing the running performance of the magnetic recording medium. There is.

Generally, a method of incorporating a lubricant into a magnetic layer is used to improve the running properties of a magnetic recording medium. There are two types of lubricants: solid lubricants such as graphite, and lubricants such as fatty acids that form a film on the surface of the magnetic layer to provide a lubricating effect. Generally, they are often used together.

However, the only lubricant that contributes to the runnability of a magnetic recording medium is the lubricant that exists on the surface of the magnetic layer, and lubricants that form a film on the surface of the magnetic layer and have a lubricating effect, such as fatty acids, do not coat the surface. The existing lubricant is gradually removed by contact with a magnetic head or the like during running, so the surface must be replenished one after another. Generally, the above-mentioned replenishment of lubricant is supplied to the surface of the magnetic layer by seeping out of the binder.

However, by making the surface of the magnetic layer smooth, the surface area of the magnetic layer decreases, and the amount of lubricant supplied to the surface tends to decrease, resulting in a decrease in the running properties of the magnetic recording medium.

[Object of the Invention] An object of the present invention is to provide a method for easily manufacturing a magnetic recording medium having good running properties.

More specifically, the present invention provides a method for easily producing a magnetic recording medium exhibiting good running properties by increasing the amount of lubricant contained in the magnetic layer supplied to the surface of the magnetic layer. With the goal.

[Summary of the Invention] The present invention involves coating a magnetic paint containing a binder, lubricant 1 ferromagnetic fine powder, and an organic solvent on a non-magnetic support to form a coating layer, drying the coating layer, A method for manufacturing a magnetic recording medium, characterized in that the surface of the coating layer is irradiated with an electron beam having an ion acceleration voltage within a range of 100 to 1000V.

[Detailed Description of the Invention] Generally, magnetic recording media are produced by preparing a magnetic paint by kneading a binder, lubricant, ferromagnetic fine powder, etc. with an organic solvent, and coating this magnetic paint on a non-magnetic support. Form a coating layer,
The method for manufacturing the magnetic recording medium of the present invention, which is manufactured by performing a magnetic field orientation treatment on this coating layer in an undried state and then drying and curing it to form a magnetic layer, also basically follows the above method. It is. However, the manufacturing method of the present invention
The main feature is that a magnetic paint is applied onto a non-magnetic support, and once the applied layer has dried, a specific electron beam is irradiated from the surface of the applied layer.

When carrying out the manufacturing method of the present invention, first a magnetic paint is prepared.

The magnetic paint consists of a binder, a lubricant, a ferromagnetic fine powder, an organic solvent, and optionally added additives.

As the binder, thermoplastic resins, thermosetting resins, and reaction-curing resins that are commonly used for forming magnetic layers of magnetic recording media are used.

Examples of binders include vinyl chloride-vinyl acetate copolymer resins, cellulose derivatives, vinylidene chloride resins, polyester resins, (meth)acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins, and butadiene-acrylonitrile resins. Among thermoplastic resins such as polymer resins, polyamide resins, polyvinyl fluoride resins, and nylon/silicon resins, the softening temperature is 150°C.
Polyurethane resins, urea resins, melamine resins, phenoxy resins, epoxy resins, urethane epoxy resins, polyester polyols and polyisocyanates. Among thermosetting resins and reaction curable resins, such as mixtures of urea/formaldehyde resins, polyamide resins, mixtures of low molecular weight glycols/high molecular weight diols and triphenylmethane triincyanate, the average molecular weight before curing is Examples include those having a molecular weight of 200,000 or less and whose molecular weight becomes almost infinitely large due to the curing reaction. These resins can be used alone or in combination.

In particular, it is preferable to use a combination of vinyl chloride/vinyl acetate copolymer and polyurethane resin.

When a combination of a polyurethane resin and a vinyl chloride/vinyl acetate copolymer is used as a binder, it is preferable to use a polyisocyanate compound as a curing agent in combination, since this improves the running durability of the magnetic layer.

Generally, the amount of the binder used is within the range of 10 to 50% by weight based on the ferromagnetic fine powder described below.

When using a vinyl chloride/vinyl acetate copolymer, a polyurethane resin, and a polyisocyanate compound as a binder, the vinyl chloride/vinyl acetate copolymer and the polyurethane resin have a ratio of 0.61 to 1:1. The polyurethane resin and the polyisocyanate compound are preferably used in a blending ratio (weight) of 1:1 to 1:3.

In the above case, when preparing the magnetic paint, it is preferable to add the polyisocyanate compound after adding and sufficiently kneading the other components forming the magnetic paint. By adding the polyisocyanate compound last, it is possible to prevent agglomeration of the magnetic paint, and the polyisocyanate compound effectively acts as a curing agent to produce a magnetic recording medium having a strong magnetic layer. I can do it.

As the ferromagnetic fine powder, a commonly used ferromagnetic fine powder is used.

Examples of the ferromagnetic fine powder include ferromagnetic iron oxide fine powder, cobalt-coated ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, ferromagnetic metal powder and barium ferrite.

For example, when using fine powder of cobalt-coated ferromagnetic iron oxide 1 ferromagnetic iron oxide or ferromagnetic metal oxide such as chromium dioxide, the acicular ratio is generally 2/1 to 20/2.
1, preferably 5/1 to 20/1, and preferably has an average length of 0.2 to 2.0 m.0 When using ferromagnetic metal powder, ferromagnetic metal powder Of the metal content, 75% by weight or more (preferably 80% by weight or more) is ferromagnetic gold FA (e.g., Fe, Go, Ni, Fe-C01F).
e-Ni, Co-Ni, Fe-Co-Ni), preferably particles with a major axis of 1.0 pm or less.The shape of the ferromagnetic fine powder is limited to acicular. It is not possible to use a conventionally used shape such as a rice grain shape or a plate shape.

As a ferromagnetic fine powder, the specific surface area is generally 42rn'/g.
The above ferromagnetic fine powder is used. Furthermore, the specific surface area is 5
When 01TI'7g or more of ferromagnetic fine powder is used, the electromagnetic conversion characteristics are significantly improved.

It is particularly preferable to use a ferromagnetic metal powder having the above specific surface area.

Generally, lubricants such as silicone oil, aliphatic alcohol, fatty acid amide, fatty acid, fatty acid ester, and alkyl phosphorus ester are used alone or in combination.

An example of silicone oil is a viscosity of 0.65 to 100.
Silicone oils within the range of 1,000,000 can be mentioned.

Examples of fatty acids include fatty acids having 8 to 22 carbon atoms.

Examples of fatty acid esters include esters of monobasic fatty acids having 8 to 22 carbon atoms and monovalent to hexahydric alcohols.

Examples of aliphatic alcohols include aliphatic alcohols having 8 to 22 carbon atoms.

Examples of fatty acid amides include fatty acid amides having 8 to 22 carbon atoms.

Examples of alkyl phosphate esters include mono-, di- and tri-esters of phosphoric acid and fatty acids having 8 to 22 carbon atoms, and esters having a structure similar to lecithin and cephalin.

These lubricants can be used alone, but it is also possible to use two lubricants with different properties, for example, a combination of a lubricant that operates at relatively low temperatures and a lubricant that operates at relatively high temperatures. It is preferable to use a combination of two or more types.

The amount of lubricant to be blended is generally set within the range of 10 to 20 parts by weight per 100 parts by weight of the binder.

Furthermore, as a lubricant, a solid lubricant such as graphite, molybdenum disulfide, boron nitride, or graphite fluoride can also be used in combination.

Examples of organic solvents used for crosstalk dispersion include ketone solvents, ester solvents, glycol ether solvents,
Examples include aromatic hydrocarbon solvents and halogenated hydrocarbon solvents, and these can be used alone or in combination.

The magnetic paint may also contain commonly used additives such as abrasives, dispersants, antistatic agents and rust inhibitors.

The above-mentioned binder, ferromagnetic fine powder, lubricant and solvent, as well as optionally added abrasives, dispersants, antistatic agents and rust inhibitors are kneaded to form a magnetic paint.

The crosstalk dispersion method for the magnetic paint can be carried out according to a conventional method using a commonly used crosstalk dispersion device.

Examples of dispersion equipment include sand mills, ball mills, roll mills, thoron mills, sand grisogoos, and seguhari (
Szegvari) attritors, high-speed impeller dispersers, high-speed stone mills, high-speed mixers, homogenizers and ultrasonic dispersers.

The magnetic paint prepared as described above is applied onto a non-magnetic support to form a coating layer. As the coating method, a commonly used method can be used. Examples of coating methods include knife coating, reverse roll coating and gravure coating.

Usually, the coating thickness of the magnetic paint is the thickness of the magnetic layer, which is 2.0
It is set within the range of ~10 pm.

Examples of materials forming the non-magnetic support include polyester resins, polyolefin resins, cellulose derivatives,
Examples include polycarbonate resins, polyimide resins, and polyamideimide resins. In addition, depending on the purpose, non-magnetic metals such as aluminum, copper, tin and zinc, or non-magnetic metals containing these, plastics with vapor-deposited metals such as aluminum, paper and paper coated or laminated with polyolefins, etc. Paper can also be used. Although there is no particular restriction on the form of the nonmagnetic support, a sheet-like support is usually used. However, the nonmagnetic support may be in the form of a film, tape, disk, card, or drum.

When using a sheet-like non-magnetic support, the non-magnetic support generally has a thickness within the range of 2 to 50 JLm.

The nonmagnetic support may be provided with a backconite layer on the surface on which the magnetic layer is not provided.

Usually, the coating layer thus coated on the non-magnetic support is subjected to a magnetic field orientation treatment before the magnetic paint is dried. The magnetic field orientation treatment is generally carried out by passing the non-magnetic support coated with the coating layer between a pair of magnets of 1000 to 3000 Gauss, for example.

The magnetic recording medium subjected to the magnetic field orientation treatment is subjected to a drying process to remove the organic solvent in the coating layer. In the drying step, for example, the magnetic recording medium subjected to the magnetic field orientation treatment is heated to a temperature near the melting point of the organic solvent used in preparing the magnetic paint by 0.1%.
This is done by heating for ~5 minutes.

In the manufacturing method of the present invention, it is possible to immediately irradiate the coated layer dried in this way with an electron beam, but by performing surface smoothing treatment before electron beam irradiation, the ferromagnetic fine powder is This increases the filling rate and improves electromagnetic conversion characteristics.

The surface smoothing treatment can be carried out according to a conventional method. Examples of the surface smoothing treatment device include a stone-step calender roll in which mirror rolls and cotton rolls are arranged alternately, or a normal Suher calender roll. can be mentioned.

The coating layer thus dried or subjected to surface smoothing treatment is irradiated with a specific electron beam. The electron beam is applied to the surface of the coating layer (the surface not facing the non-magnetic support).

The irradiated electron beam collides with the coated layer and removes a part of the binder coating the ferromagnetic fine powder near the surface of the coated layer, and also removes the ferromagnetic fine powder and the ferromagnetic fine powder adjacent to the ferromagnetic fine powder. It acts to remove part of the binder in the gap between the ferromagnetic fine powder and form a four-part in this part.

Then, by irradiating with a specific electron beam, the removal of the binder can be controlled to usually IJLm (preferably within the range of 0.5JLm) from the surface of the '/44i layer, and from the formed recesses near the surface. Lubricant is sequentially replenished onto the surface,
1lf (contributes to improvement of slipperiness) of magnetic recording media.

In order to carry out the above-described processing, an ion accelerating voltage within the range of 100 to 100 OV is used. In particular, it is preferable to use an ion accelerating voltage in the range of 300 to 900V.

Even if an electron beam with an ion acceleration voltage of less than 100V is used, it is not possible to effectively remove the binder on the surface of the coating layer.On the other hand, if an ion acceleration voltage of more than 100OV is used, the electron beam irradiation will cause especially magnetic This is not preferable because the binder on the surface of the layer is excessively removed.

In addition, the ion current density of the electron beam is 0.1 to 1,0 m
A/crrI' (preferably 0.1~.0.8m A
/ crrr' ). If an electron beam with an ion current density of less than 0.1 mV is used, the binding agent on the surface may be insufficiently removed; on the other hand, if an electron beam with an ion current density exceeding 1-OmV is used, The electron beam can penetrate deep into the magnetic layer and remove even binder that is unrelated to the lubricant supply.

Since the electron beam used in the present invention has low energy, it can effectively remove only the binder near the surface of the coating layer. When a high-energy electron beam is irradiated, the binder in the entire magnetic layer may be affected, but it cannot be applied only to the binder near the surface of the magnetic layer.

In electron beam irradiation, the internal gas is usually replaced with argon gas, etc., and the pressure is reduced (e.g., 2 x 10-'Torr or less).
It is carried out in a device maintained at

The device for performing electron beam irradiation is not particularly limited as long as it can irradiate the electron beam as described above. An example of an electron beam irradiation device is an ion milling device.

The magnetic recording medium irradiated with the electron beam is then cut into a desired shape, such as a tape, sheet, or disc.

[Effects of the Invention] According to the manufacturing method of the invention, a magnetic recording medium having good running properties can be easily manufactured.

That is, in the magnetic recording medium obtained by the manufacturing method of the present invention, the binder on the surface of the magnetic layer is removed to form fine four parts, and the lubricant deep in the magnetic layer is released from the recesses into the magnetic layer. It is smoothly supplied to the surface, improving the running properties of the magnetic recording medium.

Patent applicant: Representative of Miyashi Photo Film Co., Ltd.
Patent Attorney Yasushi Yanagawa Otani "-Zokune City Seigaku 2 August 29, 1985

Claims (1)

[Claims] 1. A magnetic paint containing a binder, a lubricant, a ferromagnetic fine powder, and an organic solvent is coated on a non-magnetic support to form a coated layer, and after drying the coated layer, A method for manufacturing a magnetic recording medium, which comprises irradiating the surface of a coating layer with an electron beam having an ion acceleration voltage within a range of 100 to 1000V. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the dried coating layer is subjected to surface smoothing treatment and then irradiated with an electron beam. 3. The ion current density of the irradiated electron beam is 0.1 to 1.0.
3. The method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium is within a range of mA/cm^2. 4. Claim 1, characterized in that the lubricant is at least one type of lubricant selected from the group consisting of silicone oil, fatty acids, fatty acid amides, fatty alcohols, fatty acid esters, and alkyl phosphate esters. A method for manufacturing a magnetic recording medium according to item 1 or 2. 5. The magnetic recording according to claim 1 or 2, wherein the binder is a cured product of a polyisocyanate compound and a resin component containing a vinyl chloride/vinyl acetate copolymer and a polyurethane resin. Method of manufacturing media. 6. Claim 1 or 2, characterized in that the specific surface area of the ferromagnetic fine powder is 42 m^2/g or more.
A method for manufacturing a magnetic recording medium as described in .