JPS59191135A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To decrease drop-out on the surface of a thin ferromagnetic film by forming a back layer of a binder which contains a radiant ray sensitive and curable resin and is dispersed therein with fillers and adjusting the surface roughness thereof to a specific range. CONSTITUTION:A radiant ray sensitive resin (a resin which can be cured when irradiated with radiant ray) is used as a binder and carbon black or graphite or an inorg. pigment is used as a filler. A back layer is formed by using a coating prepd. by mixing such materials and thereafter radiant ray is irradiated to said layer from an active energy ray source to cure the layer or after the back layer is subjected to a surface treatment as it is, the layer is subjected to the curing treatment to generate three-dimensional crosslinking in the back layer, thereby forming a strong and tough coating film. The material to be transferred from the back layer to the magnetic surface in the stage for producing a magnetic tape is thus obviated and the surface roughness of the back layer is selected to 0.05-0.6mu, by which the generation of drop-out is extremely easily suppressed not only in the initial period of use but also during repetitive use.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium and a method for manufacturing the same. More specifically, a thin film type magnetic recording medium is prepared by forming a ferromagnetic thin film on a support by electroplating, chemical plating, vacuum evaporation, spackling, ion blating, etc., and is then back coated with a radiation sensitive curable resin and cured. In this case, the surface of the hex layer is optionally treated to have a surface roughness of 0.05 to 0.6μ to lower the coefficient of friction, reduce dropouts on the ferromagnetic thin film surface, and improve the winding state. The present invention relates to an improved magnetic recording medium and a method for manufacturing the same.

Currently, video tape, computer tape, and high-performance audio tape are used as magnetic recording media.

Multi-coded tapes, magnetic disks, frossopy disks, magnetic cards, etc. are used, but the amount of information recorded on media is increasing year by year, and media are increasingly required to have high recording densities. It's coming. A short wavelength recording method is used for high-density recording, but this method is prone to dropout problems. Dropout is an error in which pulses that should exist are overlooked when reading information written on a magnetic tape, and this is mainly caused by an instantaneous increase in spacing loss between the magnetic tape and the magnetic head. It has become.

In the current recording method using a magnetic head, (dB
) (d: tape-helide distance, λ: recording wavelength). As can be seen from this equation, in short-wavelength recording with high recording density, the spacing loss is significantly larger than that in long-wavelength recording, so even if a very small foreign object is on the tape surface, the spacing loss will be large. This results in dropout.

Dropouts occur when foreign matter from the magnetic tape manufacturing or usage process is present on the tape surface, and these foreign matter act to widen the spacing between the head and the tape. Possible causes include thin film abrasion on the surface of the magnetic tape metal thin film due to deterioration of the metal thin film due to repeated stress, or thin film scraping off during running, or
Dust and the like electrostatically adhere to the base surface and further transfer to the metal thin film surface. In order to prevent these problems, for example, for the latter cause, a paint made by mixing carbon blank or graphite with an organic binder may be applied to the support surface (bank surface) opposite to the magnetic surface of the magnetic tape. Methods have been devised such as applying an inhibitor to reduce the electrification phenomenon of the heath, or applying a paint containing silicon oxide or the like mixed with an organic binder to make the heath tougher and reduce the chance of scratching of the heath. It's here. Through these processes,
The tendency for dropouts to increase due to repeated running can be significantly suppressed. However, the level
At present, it cannot be said to be perfect, and there is a need to further reduce it.

In order to further reduce dropouts, we investigated the causes of dropouts in detail and found the following.

Since the bank layer is required to be strong so that dropout does not increase even when the number of runs is increased, a thermosetting resin is usually used as a binder. In that case, after the hack layer has been applied, the tape will be wound up and subjected to a heat curing treatment.

However, at the time the coating is finished, the curing reaction has not yet started in the bank layer and the coating film is weak.Moreover, the hack surface and the magnetic surface are in close contact with each other, so the coating is filled into the hack layer coating. carbon black, graphite,
Alternatively, the surface of the hexagonal coating containing other inorganic fillers may be
It is easy to transfer to the magnetic layer surface on the opposite side with which it is in contact (,
It was discovered that this metastasized material was causing dropouts and head clogging. On the other hand, it has been found that even when the hack layer is applied before the magnetic layer, the hack layer is likely to transfer to the base surface, and the transferred dropouts also cause head clogging.

Further, it is thought that this phenomenon may occur in the case of thermoplastic resins as well. By providing a hack layer,
This is said to suppress the increase in dropouts due to repeated running, but this is the reason why dropouts are not so low when the number of runs is small.

In order to eliminate the above-mentioned problems in the bank layer forming process, the present invention uses a radiation-sensitive resin (resin that can be cured by radiation irradiation) as a binder and uses carbon blank, graphite, or inorganic pigment alone, carbon black, graphite, etc. Alternatively, or by using pigments etc. in addition, a hack layer is formed with a paint made by kneading these and then irradiated with radiation from an active energy ray source,
By applying a hardening treatment or directly applying a surface treatment followed by a hardening treatment to create three-dimensional crosslinking in the hack layer to create a strong coating film, the tape can be rolled up to produce the above-mentioned properties. This reduces dropouts due to various causes. According to this method, even if either the hack layer or the magnetic layer is formed first, the tape is wound up after the crosslinking reaction of the coating film is completed, so that the bank layer becomes the magnetic layer by winding. Even if the magnetic layer is brought into close contact with the magnetic layer, no transition occurs from the hack layer to the magnetic layer.

Consideration regarding the surface roughness of the hack layer is also required. If the surface roughness of the hack layer is too rough, output fluctuations during tape playback will increase, and in order to suppress output fluctuations below an allowable level, the surface roughness is preferably 0.6 μm or less. On the other hand,
It is preferable that the surface roughness is 0.05 μm or more in order to ensure that the air that is drawn in together with the tape when the tape is wound is released within a circle of 1N, and to maintain the safe running of the tape.

In this way, in the present invention, by eliminating transition substances from the hack layer to the magnetic surface in the magnetic tape manufacturing process and by appropriately selecting the surface roughness of the bank layer,
The occurrence of dropouts is extremely effectively suppressed not only during the initial use of the magnetic tape, but also during repeated use.

The radiation-sensitive resin used in the present invention is one that contains two or more unsaturated double bonds in its molecular chain, which can generate radicals and create a crosslinked structure when exposed to radiation, and this also includes thermoplastic resins. It is also possible through radiation sensitivity degeneration.

A specific example of radiation-sensitive modification is acrylic acid, which exhibits an unsaturated double bond that is radially polymerizable.

Groups that can be crosslinked or polymerized and dried by radiation irradiation, such as acrylic double bonds such as methacrylic acid or their ester compounds, allylic double bonds such as diallyl phthalate, and unsaturated bonds such as maleic acid and maleic acid derivatives. It is introduced into the molecule.

Any unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used.

Thermoplastic resins that can be modified into radiation-sensitive resins are shown below.

(1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-malein Acid copolymer.

Vinyl chloride - vinyl acetate - terminal ○H (i'l chain AJ
lz kill group copolymer, such as UCC VROII,
VYNC.

Examples include VYEGX and UCC's VERR.

By the method described later, an acrylic double bond, a maleic acid double bond, and an allylic double bond are introduced into the above copolymer to undergo radiation sensitivity modification.

(IT) Saturated polyester resin saturated polybasic acids such as phthalic acid, isophthalic acid, 5-terephthalic acid, succinic acid, adipic acid, sebacic acid and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane.

1.2 propylene glycol, 1.3 butanediol,
Dipropylene glycol, 1.4 butanediol, 1.
Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as 6-hexanediol, pentaerythritol, sorbitol, glycerin, neopentyl glycol, 1.4-cyclohexane dimetatool, or these polyester resins modified with SO3Na etc. Resin (Byron 53s). Radiation sensitivity degeneration is performed using the methods described below.

(I) Unsaturated polyester resin A polyester compound containing a radiation-curable unsaturated double bond in its molecular chain, such as an ester bond of a polybasic acid and a polyhydric alcohol as described in the thermoplastic resin of item (U). Examples include unsaturated polyester resins, prepolymers, and oligomers containing radiation-curable unsaturated double bonds in which part of the polybasic acid is maleic acid in saturated polyester resins.

Examples of the polybasic acid and polyhydric alcohol components of the saturated polyester resin include the compounds listed in item (1), and examples of the radiation-curable unsaturated double bond include maleic acid,
Examples include fumaric acid.

The method for producing radiation-curable unsaturated polyester resin is a rich method in which maleic acid, fumaric acid, etc. are added to one or more polybasic acid components and one or more polyhydric alcohol components, that is, a catalyst presence 180%.
After dehydration or dealcoholization under a nitrogen atmosphere at ~200°C, the temperature is raised to 240-280°C, and 0.5-1 ml (
A polyester resin can be obtained by the condensation reaction of g under reduced pressure. The content of maleic acid, fumaric acid, etc. in the acid component is 1 to 40 mol%, preferably 10 to 30 mol%, in view of crosslinking during production, radiation curability, etc.

(■) Polyvinyl alcohol resin polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components. The hydroxyl groups contained in these resins are subjected to radiation-sensitivity modification by a method described later.

(V) Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A, epichlorohydrin, and methyl epichlorohydrin - manufactured by Ciel Chemical (Epicote 1)
52.154,828°1001.1004.1007
), Dow Chemical! ! J (DEN 431゜DER
732, DER511, DER331), Dainippon Ink (Ebikuron-400, Ebikuron-800),
Furthermore, phenoxy resin (PKHA, PKI (C, PKl'lH) manufactured by UCC, which is a high polymerization degree resin of the above epoxy)
Copolymer of brominated bisphenol A and epichlorohydrin, manufactured by Dainippon Ink and Chemicals (Evicron 145, 1
52.153.1120) etc.

Radiation sensitivity modification is performed using the epoxy groups contained in these resins.

(VI) Cellulose Derivatives Cellulose derivatives of various molecular weights are also effective as thermoplastic components. Among them, particularly effective ones include nitrified cotton, cellulose acetobutyrate 5-ethyl cellulose, butyl cellulose, acetyl cellulose, etc., and radiation sensitivity modification is carried out by utilizing the hydroxyl groups in the resin by the method described later.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyether ester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, and phenol resins.

Also effective are spiroacecool resins, acrylic resins containing at least one polymerization component of acrylic esters and methacrylic esters containing hydroxyl groups.

Furthermore, by blending a thermoplastic elastomer or a prepolymer with the radiation-sensitive modified thermoplastic resin, a -Pt tough coating film can be obtained. Furthermore, as described below, it is more effective if these elastomers or prepolymers are similarly modified to be radiation sensitive.

Listed below are elastomers or prepolymers that can be combined with the radiation-sensitive resin.

(I) The use of polyurethane elastomers and prepolymers and telomer polyurethane elastomers provides abrasion resistance, PE
It is particularly effective in terms of its good adhesion to T-film.

Examples of such urethane compounds include 2.4-) luene diisocyanate 2.6-
) Luene diisocyanate.

1.3-xylene diisocyanate, 1.4-xylene diisocyanate, 1.5-knack diisocyanate, m-phenylene diisocyanate h p-phenylene diisocyanate 3,3゛-dimethyl-4,4゛
-diphenylmethane diisocyanate, 4.4'
-Diphenylmethane diisocyanate, 3.3°-
Dimethylbiphenylene diisocyanate, 4.4”-
Biphenylene diisocyanate, hexamethylene diisocyanate.

Isophorone diisocyanate 1-. Dicyclohexylmethane diisocyanate, various polyvalent isocyanates such as Desmodur and Desmodur N, linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,4-butanediol).

1.6-hexanediol, pentaerythritol.

With polyhydric alcohols such as sorbitol, neopentyl glycol, 1.4-cyclohexane dimetatool, and saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, succinic acid, adipic acid, and sebacic acid. condensation polymers of various polyesters such as linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetraethylene glycol), caprolactam, hydroxyl-containing acrylic esters, hydroxyl-containing methacrylic esters, etc. Polyurethane elastomers, prepolymers, and telomers consisting of are effective.

These elastomers may be combined as they are with various radiation-sensitive thermoplastics, but monomers having an acrylic double bond or allylic double bond that reacts with the terminal isocyanate group or hydroxyl group of the urethane elastomer may also be used. It is very effective to make it radiosensitive by reacting with the body.

(II) Acrylonitrile-butadiene copolymer elastomer An elastomer such as an acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as polyBD liquid resin manufactured by Sinclair Petrochemical Co., Ltd. or Hiker 1432 J manufactured by Nippon Zeon Co., Ltd. In particular, it is suitable as an elastomer component in which the double bonds in butadiene generate radicals by radiation and undergo crosslinking and polymerization.

(I) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group, such as PolyBD Liquid Resin R-15 manufactured by Sinclair Vetro Chemical Co., is particularly suitable in terms of compatibility with thermoplastic resins. R
Since the -15 prepolymer has a hydroxyl group at the molecular end, it is possible to increase the radiation sensitivity by adding an acrylic unsaturated double bond to the molecular end, making it more advantageous as a binder.

In addition, polybutadiene cyclized product Nippon Synthetic Rubber Co., Ltd. CBR-
M 901 also exhibits excellent performance in combination with thermoplastic resins. In particular, cyclized polybutadiene has excellent properties as a binder, as it is highly efficient in crosslinking polymerization by radiation due to the radicals of unsaturated bonds inherent in polybutadiene.

Suitable geothermal plastic elastomer and prepolymer systems include styrene-butadiene rubber, chloride rubber, acrylic rubber, isoprene rubber, and its cyclized product (Japan Synthetic Rubber jJJcIR701), epoxy-modified rubber, and internal plasticization saturation line. Elastomers such as polyester (Toyobo Vylon #300) can also be effectively used by subjecting them to the radiation-sensitive modification treatment described below.

Next, an example of synthesis of a radiation-sensitive binder will be explained.

*Manufacturing method of tolylene diisocyanate adduct a) Synthesis of acrylic modified vinyl chloride vinyl acetate copolymer resin (radiation sensitive modified resin) Vinyrite VAGH750
1,250 parts of toluene, and 500 parts of cyclohexanone were placed in four 5β flasks, heated and dissolved, and after raising the temperature to 80°C, 61.4 parts of 2-hydroxyethyl methacrylate adduct of tolylene diisocyanate was added, and further 0.012 parts of tin octylate. , 0.012 part of hydroquinone was added and allowed to react at 80° C. in a N2 stream until the NGO reaction rate reached 90%. After the reaction is completed, cool and methyl ethyl ketone 1
Add 250 parts and dilute.

*) Production method of 2-hydroxyethyl methacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) After heating 348 parts of tolylene diisocyanate to 80°C in a 1β fourth flask in a N2 stream, 2-hexaethylene was added. 260 parts of methacrylate.

After dropping 0.07 part of tin octylate and 0.05 part of hydroquinone while controlling cooling so that the temperature inside the reaction vessel is 80 to 85°C, the mixture is stirred at 80°C for 3 hours to complete the reaction. After the reaction was completed, the reactor was taken out and cooled to obtain TDI 2HEMA in the form of a white paste.

b) Synthesis of acrylic modified butyral resin (radiation-sensitive modified resin) 100 parts of butyral resin BM-3 manufactured by Building Blocks Chemical Co., Ltd. were mixed with 191.2 parts of toluene and 71.4 parts of cyclohexanone to 5'β4
After heating and melting the mixture in a double flask and raising the temperature to 80°C, 7.4 parts of 2-hydroxyethyl methacrylate adduct of tolylene diisocyanate was added, and 0 parts of tin octylate was added.
．． 015 parts and 0.015 parts of hydroquinone were added, and 80
The reaction was allowed to occur at ℃ in a N2 stream until the NGO reaction rate reached 90% or more. After the reaction is completed, it is cooled and diluted with methyl ethyl ketone.

C) Synthesis of acrylic modified saturated polyester resin (radiation-sensitive modified resin) 100 parts of Toyobo Vylon RV-200 was mixed with 11 parts of toluene.
Add 6 parts of methyl ethyl ketone to 116 parts of methyl ethyl ketone, dissolve and heat to 80°C.
1 part, 0.007 part of tin octylate, and 0.007 part of hydroquinone, and the mixture was reacted at 80°C in a N2 stream until the NGO reaction rate reached 90% or more.

d) Synthesis of epoxy resin acrylic modified product (radiation-sensitive modified resin) Iupicoat 10074009B manufactured by Shell Chemical Co., Ltd.) Chef 50 parts 1 After heating and dissolving in 1 MEK 50 parts, NN-dimethylhensylamine 0.006 part, hydroquinone 0.003
80°C, and 69 parts of acrylic acid was added dropwise to 80°C.
The reaction was allowed to take place at ℃ until the acid value reached 5 or less.

e) Synthesis of acrylic modified urethane elastomer (radiation-sensitive elastomer) Urethane prepolymer based on diphenylmethane diisocyanate (MDI) terminal isocyanate (Nilaporan 4040 manufactured by Nippon Polyurethane Co., Ltd.) 250 parts, 28
32.5 parts of MA, 0.07 parts of hydroquinone, and 0.009 parts of tin octylate were placed in a reaction can, heated and dissolved at 80°C, and then 43.5 parts of TDr was added until the temperature inside the reaction can was 80-9.
Drop it while cooling it to 0°C, and after dropping it,
The reaction was allowed to occur at °C until the NGO reaction rate reached 95% or more.

f) Synthesis of acrylic modified polyether-based urethane-terminated elastomer (radiation-sensitive elastomer) Polyether PTG-5002 manufactured by Nippon Polyurethane Co., Ltd.
50 parts, 2 32.5 parts of HEFIA, 0.007 parts of hydroquinone, and 0.009 parts of tin octylate were placed in a reaction can and heated to 80°C and dissolved, and then 43.5 parts of TDI was added until the temperature inside the reaction can was 80 to 90°C. After the dropwise addition was completed, the reaction was allowed to proceed at 80° C. until the NGO reaction rate reached 9 degrees or higher.

g) Synthesis of polybutadiene elastomer acrylic dimer (radiation-sensitive elastomer) Low molecular weight terminal hydroxyl group polybutadiene polybutadiene polyBD Liquid Resin R-15250 parts manufactured by Sinclair Petrochemical Co., Ltd., ZHE old 32.5 parts, hydroquinone 0.007 parts,
Put 0.009 parts of tin octylate into a reaction can, heat and melt at 80°C, then add 43.5 parts of TDI until the temperature inside the reaction can reaches 80°C.
Drop it while cooling it to ~90℃, and after the completion of dropping,
The reaction was allowed to proceed until the NGO reaction rate reached 95% or more at 0''c.

In addition to the above-mentioned modified polymers, there are known polymers that disintegrate upon radiation exposure and polymers that cause intermolecular crosslinking. Polyethylene, polypropylene, and polystyrene cause crosslinking between molecules.

Polyacrylic acid ester, polyacrylamide.

E+J Vinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein. If such a crosslinked polymer is used, the crosslinking reaction will occur even without the above-mentioned modification, so it can be used as it is as a backcoat resin for radiation crosslinking.

Furthermore, according to this method, even a solvent-free resin that does not use a solvent can be cured in a short time, so such a resin can be used for hack coating.

In addition, the active energy rays used for crosslinking the back coat of the present invention include electron beams using a radiation accelerator as a radiation source;
T-rays using Go'' as a radiation source, β-rays using Sr'' as a radiation source, X
X-rays or ultraviolet rays using a ray generator as a ray source are used.

In particular, as an irradiation source, it is advantageous to use radiation using a radiation accelerator from the viewpoints of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation.

The radiation characteristics used when curing the pack layer are as follows:
From the viewpoint of penetrating power, it is convenient to irradiate using a radiation accelerator with an accelerating voltage of 1010 to 750 KV, preferably 150 to 300 KV, so that the absorbed dose is 0.5 to 20 Megaland.

When curing the hack layer of the present invention, a low-dose type radiation accelerator (electrocurtain system) manufactured by Etage Science, Inc. in the United States is introduced into the tape coating processing line, and the secondary χ rays inside the accelerator are shielded. Of course, a van de Graaff type accelerator, which has been widely used as a radiation accelerating material, may also be used.

In addition, when crosslinking with radiation, the hack layer may be irradiated with radiation in an inert gas stream such as N2 gas or He scum, and irradiation with radiation in the air will cause the crosslinking of the baingu component. This is extremely disadvantageous because radicals generated in the polymer due to the influence of radiation, etc., caused by radiation irradiation inhibit the advantageous crosslinking reaction.

Therefore, the atmosphere of the area to be irradiated with active energy rays is
In particular, N2 with a maximum oxygen concentration of 5%. It is important to maintain an atmosphere of an inert gas such as He or CO□.

Further, in the present invention, fillers used in the hack layer together with the binder include (1) a conductive substance such as graphite carbon blank, and (2) CaC0*.

These are inorganic fillers such as goethite, curcum, kaolin, CaSO4, Teflon powder, graphite fluoride, and molybdenum disulfide. Combinations of (1) and (2) may also be used. The amount of filler used is expressed by weight.For (1), binder 100
For (2), 10 to 300 parts is appropriate.If the amount of filler is too large, the hack layer becomes thick and dropouts increase.

The back layer formulation thus produced is applied in a conventional manner to a predetermined thickness on the back side of the base on which the magnetic layer has been formed or on which the magnetic layer is to be formed. After application, a surface treatment may optionally be carried out such that the required surface roughness is in the range of 0.6μ by 0.1.

Furthermore, the surface roughness varies depending on the dispersion time, filler particle size and amount, etc.

Radiation is then applied to cure the coated bank layer.

As mentioned above, the applied puncture layer may be cured at any stage before or after the magnetic layer is formed, as long as it is before the tape is wound up.

Further, magnetic recording media that should be provided with such a hack layer include high-performance audio tape, video tape, computer tape, endless tape, multiplexed code tape, magnetic disk, floppy disk, and magnetic card, among others. It is quite effective for use in video tapes and computer tapes where dropout is one of the most important characteristics.

The ferromagnetic thin film magnetic recording medium is electroplated.

It can be obtained by chemical plating, vacuum evaporation, sputtering, ion blating, etc., but in the case of vacuum evaporation, a cobalt/nickel (atomic ratio 8/2) alloy ingot is prepared, and a long piece is formed by vacuum evaporation. A ferromagnetic thin film is formed on a polyethylene terephthalate base. Vapor deposition is performed by electron beam heating, and a so-called oblique vapor deposition method with a central incident angle of 70° is employed. A cylindrical can is used to cool the base film, and the cooling temperature is maintained at 5°C. The vacuum chamber is evacuated to 3 Xl0-''Pa, and oxygen gas is introduced into it until the pressure reaches 6.3 Xl0-''Pa to perform vapor deposition.

By adjusting the power given to the electron gun and the drive speed of the base film, the film thickness is made to be approximately 800 mm.

The ferromagnetic N film obtained in this way has a coercive force of about 100
00e and Br of about 8000 G, which is suitable as a magnetic recording medium for video.

Examples of the present invention will be described below.

Example 1 Carbon black Asahi H3500 manufactured by Asahi Carphone Co., Ltd. (particle size 81 mμ) 5
0 parts Acrylic modified chloride, vinegar, vinyl alcohol-copolymer (prototype) 30 parts Acrylic modified polyurethane elastomer (prototype) 20
300 parts of mixed solvent (MIBK/)luene-1/1) The above mixture was dispersed in a ball mill for 5 hours, and applied to the back side of the polyester film on which the ferromagnetic thin film surface was formed to a dry thickness of 0.5μ. Using an electro-curtain type electron beam accelerator, the bank layer was irradiated with an electron beam in Nz gas at an acceleration voltage of 150 KV, an electrode current of 10 mA, and an absorbed dose of 10 Mrad. After curing, the bank layer was wound up and cut into 1/2 video width. Then, dropout was measured using a VIIS deck.

In the above-mentioned dispersion using a hole mill, if the dispersion time is short, the surface roughness becomes large. Figure 1 shows the measurement results of the relationship between surface roughness and output reduction.

When the surface roughness exceeds 0.6μ, the output decreases significantly. Surface roughness of 0.05μ to 0.6μ is 200μ
Even after running several times, there was little increase in dropouts and the winding condition was good.

Further, FIG. 2 shows the relationship between the surface roughness of the bank layer and the amount of protrusion, and the amount of protrusion decreases rapidly when the surface roughness exceeds 0.05μ.

Let the sample of this example be No. 1.

Example 2 CaCO (particle size 0.08μ) 50 parts Acrylic modified chloride, vinyl acetate, vinyl alcohol copolymer (prototype) 30 parts Acrylic modified polyurethane elastomer (prototype) 20
300 parts of mixed solvent 1 il of the above mixture was prepared in the same manner as in Example 1 to obtain sample floor 2.

Example 3 Kaolin (particle size 2 μ) 25 parts Carbon blank Asahi H5500 manufactured by Asahi Carbon Co., Ltd. (particle size 81 μ) 25
Part acrylic modified group bee vinegar bee vinyl alcohol.

Copolymer 30 parts Acrylic modified polyurethane elastomer 20 parts Mixed solvent 300 parts The above mixture was prepared in the same manner as in Example 1 to obtain Sample No. 3.

The above sample No. 1. The output fluctuations, dropouts, and winding conditions of No. 2 and No. 3 were recorded 8 times on a VHS deck.

In all of these cases, image fluctuation was not a problem. Furthermore, even after these samples were run 200 times, there was little increase in dropouts, the winding condition was good, and the image condition was also very good with no fluctuation.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between bank layer surface roughness and output reduction, and FIG. 2 is a graph showing the relationship between bank layer surface roughness and protrusion amount. Patent applicant Tokyo Denki Kagaku Kogyo Co., Ltd. Representative Hiroshi Otoshi, 4'-, -, 1 Jiokemura Figure 1, 6F Surface roughness/lt,) Figure 2 1, (1 Surface roughness f )

Claims (1)

[Claims] 1. In a magnetic recording medium in which a ferromagnetic thin film is formed on one side of a support and a bank layer is provided on the other side, the bank layer is formed in a binder containing a radiation-sensitive curable resin. It is formed by dispersing filler and hardening it, and the surface roughness is 0.05 to 0.
．． 2. The magnetic recording medium according to claim 1, wherein the filler is only a powder of a conductive substance such as carbon black or graphite, or an inorganic pigment. . 3. The magnetic recording medium according to claim 1, wherein the filler contains powder of a conductive material such as carbon blank or graphite, and powder of a highly tough material such as pigment. 4. In a method for manufacturing a magnetic recording medium in which a ferromagnetic thin film is formed on one side of a support and a hack layer is provided on the other side, a filler is dispersed in a binder containing a radiation-sensitive curable resin in the bank layer. The surface roughness of the pack layer is 0.05 to 0.6.
1. A method for manufacturing a magnetic recording medium, which comprises performing a surface treatment so that the sensitive resin becomes μ, and curing the sensitive resin by irradiating it with active energy rays.