JPS63161526A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the smoothness of the surface of an undercoat layer even when a nonsolvent type paint is in use by heating the paint in advance to decrease the viscosity and then coating the paint onto a nonmagnetic support in coating the undercoat layer having no solvent onto the nonmagnetic substance. CONSTITUTION:The nonsolvent paint constituting the undercoat layer is heated and the undercoat layer with the heated paint coated on the nonmagnetic support is formed and the layer is cured by the radiation of a radiant ray. While a paint using a conventional solvent is subjected to solvent evaporation due to heating and the viscosity of the coating film gets higher, the nonsolvent paint dose not act in such a way and since the paint is not dried till the coating film drying due to the radiation of the radiant ray, the viscosity reduction due to heating is attained. Thus, even when the undercoat paint which is the nonsolvent paint is used, the smoothness of the surface of the undercoat layer is improved.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention provides a radiation-curable undercoat layer between a non-magnetic support and a magnetic layer or between a non-magnetic support and a backcoat layer. The present invention relates to a method of manufacturing a magnetic recording medium having the present invention.

(Prior Art) Magnetic recording media such as magnetic tapes and magnetic disks have a structure in which a magnetic layer made of fine magnetic powder and a binder (binding resin) is provided on a non-magnetic support such as a polyester film. In recent years, in order to improve various properties, an undercoat layer has been provided between a nonmagnetic support and a magnetic layer, or between a nonmagnetic material and a backcoat layer.

The undercoat layer, which uses radiation-curable resin as the binder and uses radiation curing such as electron beam or ultraviolet rays as the curing method, has various industrial advantages such as high-speed curing and excellent productivity. has.

One of the features of undercoat paints using radiation-curable resins is that they can be made into so-called solvent-free compositions by using low-viscosity radiation-curable tops and oligomers as reactive diluents. It may not require dilution with a solvent like normal paints.

This solvent-free coating can be said to be a technology that is particularly suited to modern times, as it brings many advantages such as saving resources, space, and energy by omitting the solvent drying process, and preventing environmental pollution caused by the use of solvents. .

(Problems to be Solved by the Invention) However, the viscosity of solvent-free radiation-curable undercoat paints cannot be reduced arbitrarily from the viewpoint of desired physical properties of the coating film, and conventional solvent-based The viscosity is not reduced sufficiently compared to paints.

For this reason, the leveling of the coating surface is insufficient when coating on a non-magnetic support, and when smoothing treatment is performed using a smoother to compensate for this, the viscosity of the coating material is too high, which adversely affects the smoothness of the undercoat layer. There were problems such as reduction in film thickness and unevenness in film thickness.

As a result of intensive studies aimed at solving these various problems, the present inventors have discovered that a method for manufacturing magnetic recording media in which paint is applied in a specific state can eliminate the above-mentioned drawbacks. , which led to the completion of the present invention.

An object of the present invention is to provide a method for manufacturing a magnetic recording medium having a radiation-curable undercoat layer, in which the surface of the undercoat layer has good smoothness even when a solvent-free undercoat paint is used. The purpose of this invention is to provide a method for manufacturing the same.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized in that, in a method for manufacturing a magnetic recording medium having a radiation-curable undercoat layer, a solvent-free undercoat layer is formed on a non-magnetic material. When applying the paint, the viscosity is lowered by heating the paint in advance, and then it is applied onto the non-magnetic support under a heated, low-viscosity condition, which eliminates the undercoat paint. It is possible to avoid the high viscosity of paint and the difficulties associated with forming a paint film, which are the fate of using solvents.

If leveling is still insufficient, the heated paint is applied onto the non-magnetic support, and then the layer is smoothed with a smoother while it is in a low viscosity state to improve the surface quality. This makes it possible to further improve the

This is because in paints that use normal solvents, the solvent evaporates when heated, making the paint film even more viscous, but with solvent-free paints, this does not occur, and the paint film remains undried until it is dried by radiation. Therefore, it becomes possible to reduce the viscosity by heating for the first time, and it becomes possible to manufacture high-quality magnetic recording media with high productivity by taking advantage of the advantages of being solvent-free.

(Example) The present invention provides a method for manufacturing a magnetic recording medium having a radiation-curable undercoat layer between a nonmagnetic support and a magnetic layer or between a nonmagnetic support and a backcoat layer. , a step of heating the paint constituting the undercoat layer, a step of forming an undercoat layer coated with the heated paint on a non-magnetic support, and a step of curing the layer by irradiation with radiation. The feature is that, following the step of applying a heated paint onto a non-magnetic support to form an undercoat layer, the layer is smoothed with a smoother, and then the layer is irradiated with radiation. Furthermore, the paint constituting the undercoat layer contains no solvent at all, or contains 20 parts or less of solvent per 100 parts (by weight, the same hereinafter) of the total binder. It is characterized in that the undercoat layer is applied by a gravure coating method, and the paint constituting the undercoat layer has a photopolymerization initiation rate based on a total of 100 parts of the binder. It is characterized in that it contains 1 part or more and 20 parts or less of an agent, and that the type of radiation is ultraviolet rays.

The method for manufacturing the magnetic recording medium of the present invention can be carried out by a general method for manufacturing a magnetic recording medium, except that the undercoat layer is applied under the above conditions. More specifically, the paint constituting the undercoat layer is heated, the heated paint is applied onto the surface of the non-magnetic support, and if necessary, the layer is smoothed with a smoother, and then This is a method in which a magnetic paint is applied and cured on top of an undercoat layer obtained by curing the layer by irradiating the layer with radiation. It is also possible to form a back coat (back coat) layer by using a back coat paint.

Furthermore, by repeating this process on the front and back sides of the same non-magnetic support, it is also possible to obtain a magnetic recording medium having an undercoat layer/magnetic layer on both sides.

The radiation-curable undercoat layer of the present invention has a radiation-curable resin as a main component, a reactive diluent consisting of a radiation-curable monomer and an oligomer, and optionally a thermoplastic resin and a thermosetting resin. The paint is prepared by curing the binder alone or by appropriately blending various fillers, additives, etc. with the binder by UV rays.

As the radiation curable resin of the present invention, various known radiation curable resins can be used.

Examples include resins with unsaturated double bonds such as vinyl groups, allyl groups, acryloyl groups, methacryloyl groups, epoxy groups, etc.; It is common to use resins such as molds, radical addition types such as polyene-polythiol types, and cationic polymerization types such as epoxy resins. Among them, acrylate resins with (meth)acryloyl groups are curable and harden the cured product. Since it has an excellent balance of physical properties, it is optimal for use in the present invention.

This acrylate resin has one or more (meth)acryloyl groups in its molecule, and has a molecular weight of 20
Oligomers in the range of 0 to 50,000 are preferred.

Examples include urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyol (meth)acrylate, polybutadiene (meth)acrylate, melamine (meth)acrylate, polyacetal (meth)acrylate, silicone (meth)acrylate. There are acrylates, polyamide (meth)acrylates, heterocycle-containing (meth)acrylates, etc., but in addition to these, it is also possible to use resins in which various paint resins are modified and (meth)acryloyl groups are introduced into the molecule. These can be used alone or in combination.

As the reactive diluent of the present invention, known radiation-curable monomers and oligomers can be used. Radiation-curable monomers and oligomers refer to the radiation-curable resins mentioned above that have a relatively low molecular weight and low viscosity, and although there is no clear distinction, they mainly contain (meth)acryloyl groups in the molecule. Acrylate resins having one or more monomers and oligomers having a molecular weight in the range of 200 to 700 are suitable.

Examples are butyacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate.

Monofunctional monomers such as 2-hydroxy-3-phenoxypropyl acrylate and glycidyl acrylate; 1,
3-Butanediol diacrylate.

1.4-butanediol diacrylate, 1゜6-hexane diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate,
Trifunctional monomers and oligomers such as hydroxypivalic acid ester neopentyl glycol diacrylate, polyfunctional monomers such as trimethylolpropane triacrylate, pentaerythritol triacrylate, cyclamethylolmethanetetraacrylate, dipentaerys, litol hexaacrylate, oligomers There is,
These can be used alone or in combination.

When ultraviolet rays are used as curing radiation for the undercoat layer of the present invention, it is necessary to contain various known photopolymerization initiators.

Examples include acetophenone, acetophenone diethyl ketal, diacetyl, benzyl, benzyl dimethyl ketal, 1-hydroxycyclohexylphenyl ketone,
Phenylketones such as 2-hydroxy-2-methylphenylpropanone; benzophenone, bis4.4゛-dialkylaminobenzophenone, 3.3=-dimethyl-4
- Benzophenones such as methoxybenzophenone; benzoins such as benzoin and benzoin alkyl ether; xanthones such as chlorothioxanthone, dimethyloxanthone and diethyloxanthone; others include anthraquinones and sulfides.

There are phenyloximes and the like, and these are used singly or in combination.

If the amount added to the binder is small, the curing speed will be slow and curing will be insufficient, while if it is too large, various problems such as bleeding from the cured film will occur. Particularly suitable is a range of less than 100 parts.

When the undercoat layer of the present invention is cured in the air or an atmosphere containing oxygen, it is preferable to contain various known curing accelerators in order to prevent curing inhibition caused by oxygen.

An example is N,N-dimethylethanolamine.

Aliphatic amines such as N-methyljetanolamine, triethanolamine, tripropaturamine; bis-4
, 4'-dialkylaminobenzophenone, N,N-dimethylaminobenzoic acid alkyl, and other aromatic amines; and polyamine compounds which are polymerized products of these, and these may be used singly or in combination.

As with the photopolymerization initiator, the amount added to the binder is preferably in the range of 1 part or more and 20 parts or less based on 100 parts of the total binder.

The undercoat layer of the present invention may contain various known fillers as necessary for the purpose of imparting various properties, such as improving antistatic properties and light-shielding properties, and improving the physical properties of the coating film as an extender pigment.

Examples are carbon black and graphite.

Fluorinated graphite, calcium carbonate, magnesium carbonate.

Aluminum silicate, magnesium silicate, barium sulfate, silica, zinc oxide, aluminum oxide.

Indium oxide, chromium oxide, tin oxide, titanium oxide,
Inorganic substances such as vanadium oxide, boronic nitride, talc, kaolin, clay, molybdenum disulfide, and inorganic pigments; organic substances such as polyethylene terephthalate, fluororesin, phenol resin, urea resin, benzoguanamine resin, various resin powders, and organic pigments. , these can be used singly or in combination.

In principle, the paint constituting the undercoat layer of the present invention has a so-called solvent-free composition that does not use a solvent.
For fine adjustment of viscosity during coating, etc., it is possible to contain a small amount of various known solvents as necessary.

Examples include aliphatic hydrocarbons such as n-hexane and cyclohexane; aromatic hydrocarbons such as toluene, xylene and solvent naphtha; methylene chloride.

1.1.1-1 Lichloroethane, chlorobenzene.

Chlorinated hydrocarbons such as 0-dichlorobenze; 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,
Ketones such as methyl isobutyl ketone and cyclohexanone; esters such as ethyl formate, ethyl acetate, and butyl acetate; and glycol ethers, N-methylpyrrolidone, dimethylformamide, diacetone alcohol, isophorone, etc. Use a mixture of several.

If the amount added to the binder is too large, the viscosity of the coating will increase due to drying of the solvent, just like in normal paints.
This works to counteract the decrease in viscosity caused by heating, so
It is particularly preferred that the solvent is not added at all or in an amount of 20 parts or less based on 100 parts of the total binder.

The paint constituting the undercoat layer of the present invention can also contain various known additives, if necessary.

Examples include lubricants 1 dispersants, leveling agents, antifoaming agents, antistatic agents, surfactants, coating film modifiers, adhesion improvers, wetting improvers, antisettling agents, and viscosity modifiers.

There are stabilizers, rust preventives, etc.

As the non-magnetic support of the present invention, various known non-magnetic supports for magnetic recording media can be used.

Examples include plastic film, paper, non-magnetic metal foil, coatings and laminates thereof.

There are laminar processed products, among which various plastic films are suitable from the viewpoint of physical properties required as a support.

Examples include regenerated cellulose and ethyl cellulose.

Cellulose derivatives such as cellulose acetate butyrate, cellulose diacetate, cellulose triacetate; polyethylene, polypropylene.

Polyolefins such as polybutylene; polyvinyl chloride; polyvinylidene chloride, polyvinyl alcohol.

Polyesters such as polyethylene terephthalate and polyethylene 2゜6-naphthalate; polycarbonate; polystyrene; polyarylate; polyetheretherketone; polyamide; polyimide; polyamideimide; polyetherimide; polyparabanic acid; There are fluorine-based films such as vinylidene chloride, and both stretched and unstretched films may be used, and they may be surface-treated.

The method for producing the paint constituting the undercoat layer of the present invention is to mix various fillers and additives (photopolymerization initiator, curing accelerator, etc.) with a mixture of binder components as necessary. .

Various known dispersion methods can be used to disperse the filler in the paint constituting the undercoat layer of the present invention.

Examples include attritors, high speed impeller dispersers, high speed impact mills, high speed stone mills, colloid mills, kneading extruders, sand grinders, dough mills, kneaders, Banbury mills, and pebble mills.

Homogenizer, 1 or 2 ball mills, roll mill.

There are three-roll mills, etc.

Various known coating methods can be used to coat the undercoat layer of the present invention.

Examples include curtain coat, gravure offset coat, gravure coat, spin code, spray coat, dip coat, (air) doctor coat, transfer roll coat, (air) knife coat, blade coat, reverse roll coat, etc., but for comparison. Since it is necessary to apply a highly viscous paint, the use of gravure coating is particularly suitable.

The thickness of the undercoat layer is 0.1 μm after drying and curing.
It is preferable that the thickness is in the range of 5.0 μm or more.

Various known heating methods can be used to heat the paint constituting the undercoat layer of the present invention.

Examples include a method of heating within a paint tank, a method of providing a heating device between the tank and the coating device, and a method of heating directly within the coating device, such as a paint reservoir in gravure coating.

The heating temperature is not limited as long as the coating temperature of the undercoat layer rises from the temperature at the time of application, but if it is low, the viscosity reduction will not be sufficient, and if it is high, the radiation added as a reactive diluent will be heated. Volatilization of curable monomers and oligomers,
Since deterioration occurs and the risk of ignition increases, the temperature is preferably in the range of 40°C or higher and 120°C or lower. In addition, long-term heating causes deterioration of the paint due to thermal polymerization, so
The heating time should be kept as short as possible, and care should be taken when storing the paint once it has been heated.

As the method of smoothing the undercoat layer of the present invention using a smoother, various known smoothing methods using a smoother can be used.

Examples include metal smoothers, glass smoothers, film smoothers, etc.

In some cases, it may be preferable to supplementally reheat the coating film on the nonmagnetic support before the smoother treatment, and various known heating methods can be used for reheating.

Examples include heat roll method, hot air heating method, infrared heating method, high frequency heating method, etc.

Various known radiation curing methods can be used for curing the undercoat layer of the present invention.

Examples include radiation (gamma ray) curing method, electron beam curing method, ultraviolet curing method, etc. Among them, ultraviolet curing method is particularly suitable in terms of operation, equipment cost, and safety.

Various known electron beam generators can be used as curing equipment when applying the electron beam curing method.

Examples are curtain beam type, laminar type, broad type, and near beam type.

Although there are pulse type, scanning type, etc., a curtain beam type irradiation device is preferable because it has a relatively low equipment cost and can easily shield secondary X-rays inside the accelerator. In addition, the conditions during curing include an accelerating voltage of 150 to 200 KeV;
It is preferable that the total irradiation amount be in the range of 3 or more and 15 Mrad or less.

Furthermore, when curing with an electron beam is performed in the air or an atmosphere containing oxygen, the electron beam irradiation is performed in an inert gas (N2, He, etc.) to prevent the generation of ozone.

C02) Must be carried out in an atmosphere.

Various known ultraviolet light generating devices can be used as curing equipment when applying the ultraviolet curing method.

Examples are low pressure mercury lamps and chemical lamps.

There are high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal highland lamps, arc lamps, xenon lamps, etc., but in general, high-pressure mercury lamps or Metal highland lamps are preferred.

Furthermore, from the standpoint of further reducing the temperature rise associated with ultraviolet irradiation, it is possible to cut wavelengths other than those involved in curing with a cold mirror, heat absorption filter, etc., and to cool the irradiated object by an appropriate method.

In either method, the irradiation method may be any method as long as it can irradiate the undercoat layer forming surface of the nonmagnetic support with radiation, and the irradiation output and number of irradiation devices are determined.

The distance, angle, etc. from the irradiation source are not similarly limited.

As the composition of the magnetic paint of the present invention, various known compositions can be used.

Examples of magnetic powder for magnetic paint include γ-F C2o3, F C3o, 'Go-containing γ-Fe2
03, Co-containing Fe304. CrO2゜Co, F
e-Co, Co-Ni, Fe-Co-Ni,
There are powders such as barium ferrite, and examples of binders in magnetic paints include vinyl chloride copolymer resins, polyurethane resins, polyester resins, cellulose resins, etc.
Examples include polyvinyl acetal resins and epoxy resins, and may also contain various known fillers, solvents, additives, and the like.

The present invention will be explained below using specific examples.

Sample 5 In-body Example: Sample 2.3 Comparative Example; Samples 1, 4 Undercoat paint A prepared according to Table 1 (Samples 1 to 3)
3) The same B (sample 4) was heated to the temperature shown in Table 2, and then applied to a 14 μm thick polyester film with a width of 30 α using the gravure coating method, and for samples 1 to 3, the coating film was smoothed using a metal smoother. After the treatment, and for sample 4, after removing the solvent by drying, the coating was cured using an 80W/a1 high-pressure mercury lamp under the conditions shown in Table 2, and the thickness was 0.3 to 064 μm.
Each undercoat layer was obtained. Magnetic paint C prepared according to Table 1 was applied to this upper layer by a reverse roll coating method, and after drying, the surface was smoothed using a super calender device, and cured at 40°C for 24 hours to a thickness of 5.
．． Each magnetic tape was obtained by making the magnetic layer 0 μm thick and slitting it into 1/2 inch width.

Comparative Example: Sample 5 A magnetic tape was obtained by conducting a trial production under the same conditions as in Example 1, except that an undercoat layer was not provided on the polyester film.

performance test Regarding these, various evaluations shown in Table 2 were conducted.

The evaluation method is as follows.

Undercoat layer; average surface roughness (Ra): (Uses Crystal Tube manufactured by Taylor Hobson) Video S/N: Relative value to comparative example (sample 4) Dropout: Number of dropouts per minute (According to the dropout counter = 15 μsec, -16 dB, Shibatsu VHOIBZ type used) [Effects of the invention] As can be seen from Table 2, the undercoat layer of the example has a 100% improvement even when a solvent-free undercoat paint is used.
The surface smoothness of the undercoat layer is improved, and problems such as an increase in the initial dropout value due to poor leveling of the layer do not occur. Furthermore, it can be seen that the magnetic tape having this undercoat layer suppresses the increase in dropouts after 5,000 bus runs, as in the case where a conventional solvent-based undercoat paint is used.

Therefore, according to the present invention, it is possible to easily obtain a high-quality magnetic recording medium having excellent electromagnetic conversion characteristics and durability with high productivity in a magnetic recording medium having a radiation-curable undercoat layer.

Claims (5)

[Claims] (1) In a method for manufacturing a magnetic recording medium having a radiation-curable undercoat layer between a nonmagnetic support and a magnetic layer or between a nonmagnetic support and a backcoat layer, the formation of the undercoat layer Magnetic recording comprising the steps of heating the constituent paint, forming an undercoat layer by coating the heated paint on a non-magnetic support, and curing the layer by irradiation with radiation. Method of manufacturing media. (2) In a method for manufacturing a magnetic recording medium having a radiation-curable undercoat layer between a nonmagnetic support and a magnetic layer or between a nonmagnetic support and a backcoat layer, the formation of the undercoat layer After performing a step of heating the constituent paint, a step of applying the heated paint onto a non-magnetic support to form an undercoat layer, and a step of smoothing the layer using a smoother, the layer is exposed to radiation. 1. A method for manufacturing a magnetic recording medium, comprising the step of producing an effect by irradiating with. (3) The paint constituting the undercoat layer does not contain any solvent, or the total amount of binder is 100 parts (parts by weight,
The method for producing a magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium is prepared by blending 20 parts or less of a solvent with 20 parts or less of a solvent (the same applies hereinafter). (4) The method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the method for applying the undercoat layer is a gravure coating method. (5) The paint constituting the undercoat layer is composed of a photopolymerization initiator mixed in a range of 1 part to 20 parts with respect to 100 parts of binder in total, and the type of radiation is ultraviolet rays. A method for manufacturing a magnetic recording medium according to claim 1 or 2.