JPS63239619A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase the adhesive power of a magnetic layer and nonmagnetic base and to improve running durability by subjecting the base to an electron ray projection treatment, coating the magnetic layer on one face thereof, coating a back layer on the other face, and projecting radiations thereto. CONSTITUTION:The magnetic layer is provided to one face of the nonmagnetic base and the back layer to the other face. This nonmagnetic base is subjected to the electron ray projection treatment, by which a hydrophilic property is imparted simultaneously to the front and rear faces of the base. The magnetic layer and back layer are coated and provided directly on the base after the treatment. The coating is dried while a magnetic field is oriented at need after coating of the magnetic layer and thereafter, the coating is subjected to a smoothing treatment by a super calender and is further subjected to the radiation projection treatment. The adhesion of the high-property magnetic layer and the back layer and the nonmagnetic base having the smooth surface is thereby improved and the magnetic recording medium having the excellent electromagnetic conversion characteristic and running durability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing magnetic recording media such as video tapes, audio tapes, computer tapes, etc.

[Prior art]

Magnetic recording media that are currently widely used include vinyl chloride acetate resin, vinyl chloride vinylidene chloride resin, and binder.
There is a method of using thermoplastic resins such as cellulose resin, acetal resin, urethane resin, and acrylonitrile butadiene resin alone or in combination, but with this method, the abrasion resistance of the magnetic layer is poor and the running path of the magnetic tape is contaminated. It had the disadvantage that it could be damaged.

Also known are methods of using thermosetting resins such as melanin resins and urea resins, and methods of adding crosslinking properties such as isocyanate compounds and epoxy compounds to the thermoplastic resins through chemical reactions. However, when a crosslinking binder is used, the storage stability of the resin solution in which the magnetic material is dispersed is poor, that is, the pot life is short. It had the disadvantages of not being able to maintain the homogeneity of the tape, and (1) requiring a heat treatment process to harden the coating film after coating and drying, and the major disadvantages being that it took a long time to commercialize the product.

In order to prevent these drawbacks, methods for manufacturing magnetic materials using acrylic acid ester oligomers and monomers as binders and curing them by electron beam irradiation after drying are disclosed in Japanese Patent Publication No. 47-12423 and Japanese Patent Application Laid-open No. 47-13639. , JP-A-47-15104, JP-A-50-77433,
It is disclosed in various publications such as Japanese Patent Laid-Open No. 56-25231.

However, with the manufacturing method disclosed in the above patent publication, a magnetic recording medium having high electromagnetic conversion characteristics and durability could not be obtained.

[Problems to be Solved by the Invention] In recent years, there has been a demand for higher image quality in magnetic recording media, and this requires closer contact between the surface of the magnetic layer and the video head and audio head. For this reason, it is necessary to have a smooth surface of the magnetic recording medium and to remove foreign matter.

Most of the foreign matter on the surface of the magnetic layer is magnetic stone powder that has been peeled off from the support during the process or during running, and to prevent this from occurring, it is necessary to strengthen the adhesive force between the magnetic layer and the support. Furthermore, the smoother the surface of the magnetic layer, the greater the friction in the running system inside the video tape recorder.

As running tension increases, magnetic recording media are required to have increasingly severe running durability.

For this reason, conventional manufacturing methods for magnetic recording media have not been able to provide magnetic recording media that have these surface smoothness, adhesive strength between the support and the magnetic M, and running durability.

The present inventors have proposed a method using a thermoplastic resin, a thermosetting resin, and a method of adding a crosslinking binder through a chemical reaction.
Furthermore, the present invention was achieved as a result of intensive research to improve the drawbacks of conventional techniques such as methods using curable binders by electron beam crosslinking.

The first object of the present invention is to provide a method for manufacturing a magnetic recording medium with excellent running durability.

The second object is to provide a method for manufacturing a magnetic recording medium with strong adhesive force between the magnetic layer and the support, and the third object is to provide a method for manufacturing a magnetic recording medium with excellent electromagnetic conversion characteristics.
A fourth object is to provide a method for manufacturing a magnetic recording medium that does not require a heat treatment step for curing the coating film.

c. Means for Solving Problems] The above objects of the present invention are achieved by the present invention described below.

That is, in the present invention, a nonmagnetic support is subjected to electron beam irradiation treatment, a radiation-curable magnetic layer is coated on one side of the support, a back layer is coated on the other side, and the back layer is coated before or after the back layer is coated. This method of manufacturing a magnetic recording medium is characterized in that the magnetic layer M is irradiated with radiation after the layer is provided.

The present invention will be explained in detail below.

Materials for the non-magnetic support used in the present invention include polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; polycarbonate, polyimide, polyamideimide, etc. Plastic film is used. In the present invention, polyethylene terephthalate is particularly preferably used.

The thickness of the support is 3 to 100 μm or less, preferably 5 to 3 μm.
It is 0μ field.

Surface roughness Ra) is 0.05 μm or less, preferably 0
．． 0.02 μm or less, more preferably 0.015 μm to 0.02 μm or less.
0.004 μm, and the present invention is particularly effective when using a support having a smoothness of 0.02 μm or less.

In the present invention, the above-mentioned nonmagnetic support is subjected to electron beam irradiation treatment.

As the electron beam accelerator, a scanning method, a double scanning method, a curtain beam method, a broad beam curtain method, etc. can be adopted.

As for electron beam characteristics, acceleration voltage is 1oo~100OKV
.

Preferably it is 150 to 300 KV and the absorbed dose is 0.5 to 20 t4rad. Acceleration voltage is 100KV
In the following cases, the amount of energy transmitted is insufficient, ], 00
If it exceeds 0 KV, the effect of the energy used for hydrophilic treatment decreases, making it uneconomical. As absorbed dose, 0.5Mra
If it is less than d, the hydrophilic treatment is insufficient and adhesion strength with the magnetic layer and back layer cannot be obtained, and if it is more than 20 megarads, the energy efficiency used for the hydrophilic treatment decreases or the non-magnetic support generates heat. However, it is undesirable because the support may be deformed or the tensile stress may be reduced.6 It is industrially advantageous to carry out the treatment with as low an amount as possible.

The temperature of the irradiation atmosphere may range from 10 to 100°C. At temperatures below 10°C, the efficiency of the hydrophilic treatment is poor.
If the temperature is higher than 0°C, the nonmagnetic support tends to deform, which is not preferable. In addition, the oxygen concentration in the irradiation atmosphere is 5000 ppm or less,
Preferably 100 to 2000 ppm, more preferably 1
It is in the range of 50 to 11000 pp. If it is more than 5,000 ppm, ozone is generated so strongly that it adversely affects the process, the equipment, and the nonmagnetic support, which is not preferable.

To lower the oxygen concentration, an inert gas such as N2 may be used. If the oxygen concentration is too low, the efficiency of the treatment for making the support hydrophilic will be poor and at the same time it will be difficult to set the process conditions. The processing speed may normally be 10 to 100 m/n+in.

It was found that the thickness of the nonmagnetic support and the accelerating voltage are related to the hydrophilic treatment. The present invention is characterized in that both sides of the non-magnetic support are made hydrophilic at the same time (determined by the contact angle on the support surface). The level of sexuality changes. To maintain adhesion, use the approximate formula V>D+145 [where V is acceleration voltage (KV)].

It was found that D should maintain the relationship shown by μ11)), which is the thickness of the support. In the electron beam irradiation treatment of the present invention, it is not preferable to roughen the surface of the nonmagnetic support, and it is usually preferable to maintain the surface properties before irradiation. however,
Depending on the purpose, surface roughening may be effective.

The time required for coating the magnetic layer and the back layer after the electron beam irradiation treatment of the present invention is not particularly limited, which is advantageous in terms of the process.

In the present invention, a radiation-curable magnetic layer is provided on one side of the support that has been subjected to electron beam irradiation treatment as described above, and a back layer is provided on the other side. The order in which the two layers are applied may be either first, and if the back layer is applied after the magnetic layer is provided, it may be applied after or before the magnetic layer is irradiated with radiation. In particular, as will be described later, when a radiation-curable binder is also used for the back layer, both layers may be irradiated with radiation at the same time after being coated.

As the binder used in the radiation-curable magnetic layer of the present invention, any known compound that can be polymerized by radiation irradiation may be used. For example, polyvinyl chloride (meth)acrylate having a polar group, cellulose (meth)acrylate, urethane (meth)acrylate having a polar group, vinyl monomer, etc. may be used alone or in combination.

The polyvinyl chloride (meth)acrylate containing a polar group used in the present invention (hereinafter acrylate and methacrylate are collectively referred to as (meth)acrylate,
Acryloyl group and methacryloyl group are collectively called (
meth)acryloyl group), C02 as a polar group
H,011,So,H,SO,Na,OPO,II,O
These are (meth)acrylates of copolymers such as vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl propionate copolymers, and vinylidene chloride-vinyl acetate copolymers containing PO and Na groups.

Preferred polar groups are Co and H1011 groups, more preferably Co and H groups. The polar group is C
021 (when it is a group, the Co, H content is 1 to 1 in terms of acid value)
It is preferable to contain about 30, more preferably 3 to 20.
It is.

If it is outside this range, the dispersibility of the ferromagnetic fine powder will be poor and the electromagnetic conversion characteristics will also be significantly reduced.

The average content of (meth)acryloyl groups is 1.5 to 20 per molecule, preferably 2 to 10.

Outside this range, curing properties may be poor or durability may be poor.

These compounds are based on polyvinyl chloride polymers such as vinyl chloride-vinyl acetate, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and vinyl chloride-vinyl acetate copolymer. Vinyl acetate-maleic acid-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-maleic quasi-vinyl copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinylidene chloride-vinyl acetate-maleic acid copolymer , vinyl chloride copolymers such as vinylidene chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-acrylic acid copolymer, vinyl chloride-vinyl acetate-acrylic acid-vinyl alcohol copolymer, and These copolymers may be used after being saponified.

As a method for introducing (meth)acrylate groups, a part of the hydroxyl group or carboxyl group of these copolymers or a part of the hydroxyl group generated by saponification is introduced into a polyfunctional isocyanate (for example, 2, 4
-Tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1
, 4-xylylene diisocyanate.

1.5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate,
3,3-dimethylphenylene diisocyanate, 4.4
-diphenylmethane diisocyanate, 3,3-dimethyl-4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate 3-adduct of trimethylolpropane, etc.), The remaining NGO group (
Active hydrogen compounds having a meth)acryloyl group (e.g. acrylic acid, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methacrylic acid, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate, acrylamide, N-methylolacrylamide, etc.).

Furthermore, examples of methods for introducing polar groups include the following methods. A part of the hydroxyl group or carboxyl group of the above-mentioned pace copolymer,
Alternatively, a part of the hydroxyl group generated by saponification is reacted with one NGO group of a polyfunctional isocyanate, and the remaining NGO group is converted into Co2H group, 5o3Na group, OP
It can be obtained by reacting a hydroxyl compound containing O, Na groups, etc. It is also possible to introduce the polar group simultaneously with the (meth)acryloyl group. Alternatively, a compound having both a polar group and a (meth)acryloyl group may be used. The method of introducing these groups is not limited to the above-mentioned method.

As the cellulose-based (meth)acrylate used in the present invention, resins containing a (meth)acryloyl group such as cellulose nitrate, cellulose acetate butyrate, cellulose acetate propionate, and cellulose diacetate are preferred. The preferred range is:
The degree of polymerization of cellulose is 50 to 400, more preferably 8
It is 0-200. If it is out of this range, the viscosity of the magnetic coating liquid increases and the dispersibility deteriorates, which is undesirable.As the base cellulose, cellulose acetate propionate and cellulose acetate butyrate are preferable from the viewpoint of safety.

These (meth)acrylate compounds of celluloses are produced by reacting cellulose with polyisocyanates and then reacting with active hydrogen compounds (such as β-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, etc.). It can be obtained by (meth)acryloylating the 011 group by reacting it with hydroxy(meth)acrylates).

The urethane (meth)acrylate containing a polar group used in the present invention may have a main chain skeleton of polyester, polyether, or polyester ether, and a specific example of the dibasic acid that can be mixed with these is citrus acid. , malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanoic acid, maleic acid, fumaric acid, itaconic acid,
Trimethyladipic acid, hexahydrophthalic acid, tetrahydrophthalic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, etc. can be used. Examples of dihydric alcohols include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 2,2-dimethylpropane-1,3 -diol, 2,2-diethylpropane-1,3-diol, cyclohexane-1,3
-diol, cyclohexane-1,4-diol, cyclohexane-1,4-dimetatool, cyclohexane-
1,3-dimethatol, 2,2-bis(4-hydroxyethoxy-cyclohexyl)propane, 2,2-bis(
4-hydroxyethoxy-phenyl)propane, 2,2
-bis(4-hydroxyethoxyethoxy-phenyl)
Propane etc. can be used. In addition, γ-butyrolac 1-
It is also possible to use a lactone-based polyester skeleton made of lactone, δ-valerolactone, ε-caprolactone, or the like. Isocyanates that form urethane bonds include 2.4-tolylene diisocyanate, 2. [i-Tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 1゜5
-Naphthalene diisocyanate, m-phenylene diisocyanate, P-phenylene diisocyanate, 3.3
-dimethylphenylene diisocyanate, 4,4-diphenylmethane diisocyanate, 3,3-dimethyl-4
, 4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,
Polyhydric isocyanates such as dicyclohexylmethane diisocyanate and tolylene diisocyanate triadduct of trimethylolpropane can be used. Furthermore, the 6CO, 11 groups and the acryloyl group, in which a portion of the dibasic acid and dihydric alcohol may be replaced with trivalent or higher acid and alcohol, may be present at the ends of the polyurethane or in the side chains.

Methods for introducing these groups include 1) trivalent or higher acid;
One or more types of alcohol and isocyanate are incorporated into the urethane skeleton, and Co2Hi, 011 groups or N are added to the side chain.
2) urethane that retains GO groups is reacted with carboxylic acid compounds and acryloyl compounds that can react with these saws, or 2) urethane that has isocyanate groups at the terminals is treated with Co, one ++ group, one acryloyl group, and one OH group each. It can be obtained by reacting active hydrogen compounds having the above.

The preferred acid value of the urethane (meth)acrylate used in the present invention is 1 to 30, more preferably 3 to 2.
0, more preferably 5-15. The molecular weight is i,ooo~100,000, preferably 2.000~50,000, particularly preferably 3,000~
30,000. If the acid value is out of this range, the dispersibility of the ferromagnetic fine powder will be poor, leading to a decrease in electromagnetic conversion characteristics and deterioration in durability. Moreover, the average content of (meth)acryloyl groups is 1.5 to IO per molecule, preferably 2 to 8 IO.

When the molecular weight is less than 1000, the magnetic layer of the obtained magnetic recording medium becomes too strong, causing problems such as cracking when bent, and curling of the magnetic recording medium due to curing shrinkage after electron beam irradiation. Cheap. On the other hand, the molecular weight is 10
If it exceeds 0,000, the solubility of urethane (meth)acrylate in solvents tends to be poor, which not only makes handling inconvenient, but also deteriorates the dispersibility of the magnetic material and requires a large amount of energy for curing. Undesirable.

Furthermore, vinyl monomers can be added to the present invention. Vinyl monomers include compounds that can be polymerized by radiation irradiation and have one or more carbon-carbon unsaturated bonds in the molecule, such as acrylic esters, acrylamides, methacrylamides, and methacrylic esters. kind.

Allyl compounds, vinyl ethers, vinyl esters,
Vinyl heterocyclic compounds, N-vinyl compounds, styrenes,
Examples include acrylic acid, methacrylic acid, crotonic acids, itaconic acids, and olefinic acids. Among these, preferred are the following compounds containing two or more acryloyl groups or methacryloyl groups. in particular.

To polyethylene glycol acrylates such as diethylene glycol diacrylate, triethylene glycol diacrylate, and tetraethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol Hexaacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate.

Tetraethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, 1-lis (β-acryloyloxyethyl) isocyanurate, bis (β-acryloyloxyethyl) isocyanurate, or polyisocyanate (2,4 - tolylene diisocyanate, 2.
6-tolylene diisocyanate, 1.3-xylylene diisocyanate, 1.4-xylylene diisocyanate, 1.5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3-dimethylphenylene diisocyanate, 4,
4-diphenylmethane diisocyanate, 3,3-dimethyl-4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diinecyanate, trimethylolpropane tolylene diisocyanate.
adduct) and a hydroxyacrylate compound (β-hydroxyethyl acrylate, β-hydroxypropyl acrylate, etc.).

Alternatively, there are other polyrylates having two or more functionalities. These monomers may be used alone or in combination of two or more.

The ferromagnetic fine powder used in the present invention includes ferromagnetic iron oxide fine powder, Co-doped ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, and ferromagnetic alloy powder.

Barium ferrite etc. can be used. ferromagnetic iron oxide,
It is effective that the acicular ratio of chromium dioxide is 271 to 20/la degree, preferably 5/1 or more and the average length is about 0.2 to 2.0 μm. The metal content of the ferromagnetic alloy powder is 75wt.
% or more, and 80wt% or more of the metal content is ferromagnetic metal (
That is, Fa, Co, Ni, Fe-Ni, Co-
These are particles of Ni, Fe-Co-N1) with a major axis of about 1.0 μm or less. Particularly effective in the present invention is that the ferromagnetic fine powder is difficult to disperse and the ET specific surface area is 30, preferably 4.
It is a ferromagnetic iron oxide powder with fine particles of 0 rd/g or more or a ferromagnetic alloy powder with fine particles of 42 rtf/g or more, preferably 50 rrr/g or more.

Organic solvents used for dispersion and application of magnetic coating liquid include acetone, methyl ethyl ketone, methyl isobutyl ketone,
Ketones such as cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid glycol monoethyl ether; ethyl ether, glycol dimethyl ether, glycol monoethyl ether,
Ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; methylene chloride and ethylene chloride.

Carbon tetrachloride 1. Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, and dichlorobenzene can be selected and used.

Further, additives such as a lubricant, an abrasive, a dispersant, an antistatic agent, and a rust preventive may be added to the magnetic coating liquid of the present invention. In particular, lubricants include saturated and unsaturated higher fatty acids with 12 or more carbon atoms, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils, fluorine compounds, etc., and these are used when preparing magnetic coating liquids. It may be added, or it may be dissolved in an organic solvent after drying or irradiation with radiation, or it may be directly applied to the surface of the magnetic layer.

May be sprayed.

In addition, the forms of non-magnetic supports are films and tapes.

It may be a sheet, a disk, a card, a drum, etc., and various materials are selected as necessary depending on the form.

In addition, the support of the present invention has a so-called so-called Back coat is done.

The back layer is, for example, a thin film layer of 0.6 μm or less in thickness made of carbon black and a binder in which inorganic filler particles having a Mohs hardness of 5 or more are dispersed, and can be obtained by a known method. As the binder, the aforementioned binder polymerizable by radiation irradiation or thermosetting binder is used.

Examples of binders used in the back layer include vinyl chloride copolymers (e.g., vinyl chloride/vinyl I9 acid copolymers,
Copolymers of vinyl chloride and vinyl acetate with monomers such as vinyl alcohol, maleic anhydride, or acrylic acid, vinyl chloride/vinylidene chloride copolymers, vinyl chloride/acrylonitrile copolymers, polar sulfonic acid groups, etc. ethylene/vinyl acetate copolymers, cellulose derivatives such as nitrocellulose resins, acrylic resins, polyvinyl acetal resins,
Examples include polyvinyl butyral resins, epoxy resins, phenoxy resins, and polyurethane resins (eg, ordinary polyurethane resins, polyester polyurethane resins, polyurethane resins having polar groups such as sulfonic acid groups, and polycarbonate polyurethane resins). Although the resin components can be used alone, two or more resins are usually used in combination, such as a vinyl chloride resin and a polyurethane resin, or a cellulose derivative and a polyurethane resin.

In conventional magnetic recording media of the mocha structure, in which a magnetic layer is simply provided on one side of a non-magnetic support and a back layer is provided on the other side, the magnetic layer and the back layer have high physical properties, as described above. Young's modulus and Tg are becoming higher, and on the other hand, due to the smoothing of the surface of the non-magnetic support, the adhesion between the support and the magnetic layer and back layer decreases, leading to problems with running durability (dropout, magnetic head eyesight). clogging, etc.). Therefore, measures have been taken such as providing an undercoat layer on the nonmagnetic support to maintain adhesion. Providing an undercoat layer for each of the magnetic layer and the back layer not only complicates the process but also increases costs.

Furthermore, although improvements have been made to the undercoat layer, it has become insufficient in adhesion to the high physical properties magnetic layer and back layer. The present invention uses a simple method to improve the adhesion between a highly physical magnetic layer and back layer and a non-magnetic support with a smooth surface, thereby obtaining a magnetic recording medium with excellent electromagnetic conversion characteristics and running durability.

That is, by subjecting a non-magnetic support to electron beam irradiation treatment, the front and back surfaces of the support are rendered hydrophilic at the same time. After the above treatment, a magnetic layer and a back layer may be directly coated on the support.

At that time, a thick magnetic layer (1 to 7 .mu.m) is coated on the other side to avoid irradiation, and a backing Ji (0.6 .mu.m or less) is coated to an appropriate thickness. However, the configuration may be reversed.

After applying the magnetic layer, it is dried while being oriented in a magnetic field if necessary. After that, a smoothing process is performed using a super calendar, and then a radiation irradiation process is performed.

Next, it is slit to a predetermined width.

In the present invention, it is preferable to apply the magnetic paint as described above, perform calendar treatment, and then irradiate radiation.
It is also possible to carry out calender treatment after irradiation. Alternatively, it is also possible to irradiate one more time.

The radiation irradiated to the magnetic layer of the present invention includes electron beam, γ
Although rays, β rays, ultraviolet rays, etc. can be used, electron beams are preferable. As the electron beam accelerator, a scanning method, double scanning method, curtain beam method, broad beam curtain method, etc. can be adopted.

As for the electron beam, the accelerating voltage is 100 to 100 OKV, preferably 150 to 300 KV, and the absorbed dose is 1
~20 Mrad, preferably 3 to 15 Mrad. If the accelerating voltage is less than 100KV, the amount of energy transmitted is insufficient, and if it exceeds 100OKV, the energy efficiency used for polymerization decreases, making it uneconomical.If the absorbed dose is less than I Mrad, the curing reaction is insufficient and magnetic If layer strength is not obtained and the layer strength exceeds 20 Mrad, the energy efficiency used for curing may decrease, and the irradiated object may generate heat.
This is particularly undesirable since the plastic support is deformed.

〔Example〕

Next, Examples and Comparative Examples of the present invention will be shown. In addition, the expression "r part" in Examples and Comparative Examples indicates "1 part by weight".

Example 1 The composition described below was subjected to cross-dispersion using a ball mill for 48 hours, and then filtered using a filter having an average pore size of 1 μm to prepare a 6J& color paint.

Cobalt coated V-FetOa (specific surface area: 50rrr
/g) 100 parts trimethylolpropane triacrylate 8 parts abrasive Cr20i (average particle size: 0.5 μm)
Bipartite oleic acid
1 part Butyl stearate 1
300 parts of methyl ethyl ketone or the composition described below was dispersed for 3 hours using a sand mill and filtered using a filter having an average pore size of 1 μm to prepare a paint for the back layer.

Masu Kusatsurin Onikatsarakai Carbon Black (Average particle size = 0.05μm)
35 parts nitrocellulose 2
0 parts methyl ethyl ketone 600
Nissin High Voltage (
Acceleration voltage: 200 KV, irradiation dose: 2.5 Mrad, irradiation atmosphere: 30°C, 600pp using Curetron ■ manufactured by Co., Ltd.
Electron beam irradiation treatment was carried out at a speed of 300 m/min at 3° m Oz, and then the above magnetic paint was applied on the irradiated side to a dry thickness of 0.4 μm, and on the other side to a dry thickness of 4.0 μm. The above-mentioned back layer paint was applied and dried. In the above step, magnetic field orientation treatment was performed using a 2000 Gauss magnet while the magnetic paint was not dried. After further drying, the film was subjected to supercalender treatment and electron beam irradiation treatment, and then slit to a width of 172 inches to produce a VH5 videotape.

The electron beam irradiation treatment was performed at an accelerating voltage of 200 KV, an irradiation dose of 2.5 Mrad, and an irradiation atmosphere of 70°C and 50 ppmO□.
It was carried out at a speed of 300+a/min at a concentration.

A commercially available VH5 was added to the videotape obtained as described above.
A 5 MHz signal was recorded and played back using a commercial video recorder. The relative playback output of the videotape was measured when the 5MHz playback output recorded on the reference tape (videotape manufactured in Comparative Example 1) was set as OdB.

The above videotape and video recorder were used to run at a normal running speed, and the number of runs until clogging occurred (in Table 1, this is indicated as "Number of times clogging did not occur") was determined. .

In addition, using the above videotape and video recorder and using a dropout counter VD-30 made by Victor Co., Ltd., a drop of 10 dB or more in 15 x 10'''6 seconds per minute after running 100 passes on the VHS deck was measured. I checked the number of outs.

The results are shown in Table 1.

In Comparative Example 1 shown below, the reproduction output, the number of runs until clogging occurred, and the number of dropouts of the videotape were measured by the above-mentioned method. The surface contact angle (H,
0) was measured at 23°C and 70%RH, and the irradiated surface 5
8°, and the other side was 59°. Contact angle is from Kyowa Science Co., Ltd.
A contact angle measuring device manufactured by Kogyo Co., Ltd. was used.

[Comparative Example 1] A VH5 videotape was produced in the same manner as in Example 1 except that the support was not subjected to electron beam irradiation treatment.

Table 1 shows the playback output of the obtained videotape, the number of runs until clogging occurred, and the still life. In addition, the surface contact angle of polyethylene terephthalate is 01
20) had an angle of 71° on both the front and back surfaces.6 Example 2 The following composition was cross-dispersed for 4 hours using a sand mill, and then filtered using a filter with an average pore size of 1 μm to prepare a 1-meter paint. did. The same liquid as in Example 1 was used for the back layer paint.

l1 Fe alloy powder (15000e, BET surface area, 50
rrr/g) 1.00 parts Binder composition Stearic acid 4 parts Butyl stearate 4 parts A1□0
, 4 parts carbon black 10 parts methyl ethyl ketone 800 parts A polyethylene terephthalate support with a thickness of 10 μm and a surface roughness (Ra) of 0.008 μm was heated with an acceleration voltage of 200 KV and an irradiation dose of 5 Mrad using a Curetron Co., Ltd. manufactured by Nissin High Voltage Co., Ltd. , irradiation atmosphere was 30℃, 150ppm O
Electron beam irradiation treatment was performed at a speed of 80 m/min at a concentration of 100 m/min (purged with N2 gas). The contact angle [H20] of the irradiated surface of polyethylene terephthalate is 55° and the other side is 56°.
Met.

The non-irradiated polyethylene terephthalate was 72@ on both sides.

Using the polyethylene terephthalate support made hydrophilic by the above electron beam irradiation treatment, a magnetic paint was coated on the irradiated surface side at a speed of 80 a+/min to a dry film thickness of 3.0 μm.

The non-magnetic support coated with the magnetic paint was subjected to magnetic field orientation treatment using a 3000 Gauss magnet while the magnetic paint was not dried. Furthermore, a back layer was applied on the other side in the same manner as in Example 1,
Dry. After further drying, it was subjected to super calender treatment and electron beam irradiation treatment, and slit into 8 mm width to produce 8 mm video tape. The electron beam irradiation treatment was carried out at an acceleration voltage of 200 KV, an irradiation dose of 5 Mrad, an irradiation atmosphere of 70° C., and a concentration of 10 ppmO at a speed of 80 m/min.

The 8 mm video tape obtained as described above was recorded at 5 MHz using an 8 mm video recorder (FUJIX-8).
The signal was recorded and played back. The relative playback output of the videotape was measured when the playback output of 5MIIz recorded on the reference tape (videotape manufactured in Comparative Example 2) was set as OdB.

Using the above videotape and video recorder, using Victor's dropout counter DV-30,
15xlO- per minute after running 100 passes of Detsuki
We investigated the number of dropouts that decreased by 10dB or more per second.

In addition, the video tape and video recorder were run at a normal running speed to determine the number of times until clogging occurred.

The results are shown in Table 1.

The playback output, still life, and number of runs until clogging occurred of the videotape in Comparative Example 2 shown below were measured by the methods described above.

Comparative Example 2 In Example 2, a conventionally used undercoat was provided instead of electron beam irradiation treatment of polyethylene terephthalate.

The dissolved composition of the undercoat layer is shown below.

Door JLi, two ships ■Methyl ethyl ketone 250 copies■
Toluene 250 parts The above dissolved composition was first applied to one side of polyethylene terephthalate 1- to a dry thickness of 0.4 μm, dried to form an undercoat layer, and a magnetic layer was formed on the undercoat layer. was coated and dried in the same manner as in Example 2 so that the thickness after drying was 2.2 μm. Next, an undercoat layer was applied to the other side in the same manner and dried, and a back layer was applied and dried in the same manner as in Example 2. Thereafter, an 8 mm videotape was manufactured in the same manner as in Example 2. The contact angle (+-
120) was 74'' on both sides.

These samples were evaluated as follows, and the obtained results are shown in Table 1.

Table 1: Number of times clogging did not occur "100 times or more" means that no clogging occurred even after 100 runs.

The adhesion strength of the magnetic layer and back layer of the tapes obtained in Example 1.2 and Comparative Example 1.2 was measured.

(Table 2) "No peeling" in Table 2 means that peeling occurred between the adhesive tape and the magnetic surface or back surface, but no peeling occurred from the support. The adhesion strength was measured at 8 mm in both cases.
Attach the tape with a slit in the width to the adhesive tape for 180 minutes.
The adhesion strength was defined as the force required for 6 strokes. The vA constant conditions are 23°C and 50% R1.

〔Effect of the invention〕

As is clear from the above results, according to the present invention, the adhesion strength between the magnetic layer and back layer and the support is dramatically improved, and the reproduction output is improved, and head clogging, dropout, etc. are reduced. A magnetic recording medium is obtained.

Procedural amendment May 20, 1986

Claims (4)

[Claims] (1) A non-magnetic support is subjected to electron beam irradiation treatment, a radiation-curable magnetic layer is coated on one side, a back layer is coated on the other side, and the back layer is coated before or after the back layer is coated. A method for manufacturing a magnetic recording medium, which comprises irradiating the magnetic layer with radiation after the magnetic layer is provided. (2) Electron beam irradiation treatment is carried out at an acceleration voltage of 150 KV or more, an irradiation dose of 0.5 Mrad or more, and an irradiation atmosphere temperature of 10°C to 1.
The method for manufacturing a magnetic recording medium according to claim (1), which is carried out at 00° C. in an irradiation atmosphere with an oxygen concentration of 5,000 ppm or less. (3) Oxygen concentration in the irradiation atmosphere is 100 ppm to 2,000 ppm
The method for manufacturing a magnetic recording medium according to claim (2), wherein the content is in the range of 0 ppm. (4) The method for manufacturing a magnetic recording medium according to claim (2), wherein the irradiation dose is in the range of 1 to 20 Mrad.