JPS6050619A - Magnetic disc and its production - Google Patents

Abstract

PURPOSE:To obtain a magnetic disc with which curling and drop-out in particular are eliminated by providing a back layer consisting of conductive powder and powder or a high toughness imparting material dispersed with a binder contg. a radiation sensitive curing resin. CONSTITUTION:A magnetic layer is formed on one surface of a magnetic disc base body and thereafter a soln. prepd. by dispersing uniformly a radiation sensitive modified resin, for example, a vinyl chloride/vinyl acetate copolymer resin, together with powder of a conductive material such as carbon black as an antistatic filler and further powder of a high toughness imparting material such as SiO2, TiO2, SiC, ''Teflon'', MoS2, etc. in an org. solvent is coated on the opposite side and after drying, the coating layer is cured by irradiation in an inert gas such as N2, CO2, etc. by using an electron ray accelerator to form a back layer. The floppy disc which is free from transfer from the back layer to the magnetic layer and dislodging of powder from the magnetic layer, is hardly stuck with dust, etc. and has excellent runnability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic disk and a method for manufacturing the same, and particularly to a magnetic disk that eliminates the problems of disk curl and dropout.

Magnetic disks are now widely used in the fields of computers and magnetic cameras. Along with this, the amount of information to be recorded on magnetic disks is increasing year by year, and magnetic disks with high density recording capability are increasingly required.

As recording density increases, the dropout problem becomes more prominent. In other words, in the current recording method using a magnetic head, the spacing loss between the disk and the head is 54
．． 6T [aB) (a: distance between disk and head,
λ: recording wavelength).

As can be seen from this equation, in short wavelength recording with high recording density, the rate of output reduction due to spacing is significantly greater than that in long wavelength recording. Therefore, even if a small foreign object is present on the disk, it will be detected as a dropout.

Possible causes of dropouts include magnetic particles falling off from the coating surface of the magnetic disk resulting from deterioration of the coating due to repeated stress, or particles and dust generated when the base is scraped off during running. An example of this is when electrostatically adheres to the base surface and then transfers to the coating surface.

In order to prevent these problems, several efforts have been made to strengthen the coating film for the former cause, and for the latter cause, the support surface opposite to the magnetic surface of the magnetic disk (back Apply a paint made by kneading carbon black or graphite with an organic binder to the
Methods have been devised to reduce the charging phenomenon of the base by applying an antistatic agent, or to make the base tougher and less likely to scratch it by applying a paint containing silicon oxide, etc., mixed with an organic binder phase. There is. Through these processes, the tendency for dropouts to increase due to repeated driving can be significantly suppressed.

However, the current level is still not perfect and needs to be further reduced.

In order to further reduce dropouts, we have conducted a detailed investigation into the causes of their occurrence and have discovered a method. When forming the back surface, if the back surface is formed before the magnetic surface, the unevenness of the back surface will be transferred to the magnetic surface during surface smoothing by calendering after forming the magnetic surface, and the smoothing of the magnetic coating will be difficult. Not enough is done. Therefore, back coating treatment is usually performed on the back surface of the support after a magnetic coating film is formed on the support. Since the backing 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 backing layer is applied, the tape is 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 pack layer and the coating is weak.Moreover, the back surface and magnetic surface are in close contact with each other. The back coating surface containing carbon black, graphite, or other inorganic fillers is likely to transfer to the opposite magnetic layer surface with which it is in contact, causing dropouts and head eyes. It turned out that this was the cause of the blockage. Further, it is thought that this phenomenon may occur in the case of thermoplastic resins as well.

In order to eliminate the above-mentioned problems in the back layer forming process, the present invention uses a radiation-sensitive resin (resin that can be cured by radiation irradiation) as a binder, which is kneaded with carbon black, graphite, or other inorganic fillers. After forming a backing layer with paint, it is irradiated with radiation from an active energy ray source and hardened, or the surface is treated as is and then hardened to create three-dimensional crosslinking in the backing layer, making it tough. By winding up the tape after forming a coating film, dropouts due to the causes mentioned above are reduced. According to this method, the tape is wound up after the cross-linking reaction of the coating film has finished, so even if the back layer is brought into close contact with the magnetic layer by winding, there is no transition from the back layer to the magnetic layer. , magnetic disks have a curl problem. In single-sided magnetic disks, this curling is thought to occur because the coating film and the support are not mechanically balanced. That is, since the Young's modulus of the coating film is greater than the Young's modulus of the support, warpage occurs on the coating film side. Curling has a negative effect on head touch and running performance, so it is preferable to reduce the curl by /J% as much as possible. Therefore, a back surface coating containing carbon black, graphite, or other inorganic filled paulownia is provided on the support opposite to the magnetic layer, and by creating a mechanical balance between the magnetic surface and the pace/back surface, head touch is improved. It may be possible to improve the warping of the disc, which is a problem with runnability, but in the case of heat curing, since the heat treatment is performed in a rolled state, curling may occur in the winding direction, or it may cause shrinkage of the base and cause curling. It will help. However, in the case of electron beam curing, since the curing can be done online, there is no problem with thermal curing, and curling can be advantageously improved.

In this way, in a magnetic disk having a magnetic layer on one side of the support, a back layer containing a filler in the binder is provided on the back side, and a radiation-sensitive curable resin is used as the binder. Disc warpage and dropout problems are solved all at once.

Thus, the present invention provides a support comprising a magnetic layer on one side and a back layer on the other side, the back layer comprising a filler dispersed in a binder containing a radiation-sensitive curable resin. To provide a magnetic disk characterized by the fact that it is a magnetic disk. Furthermore, in the present invention, after forming a magnetic layer on one side of the support,
By applying a paint in which a filler is dispersed in a binder containing a radiation-sensitive curable resin to the other side of the support as a back layer, and then irradiating active energy rays to cure the radiation-sensitive curable resin. A method of manufacturing a memorandum magnetic disk is also provided.

The radiation-sensitive resin used in the present invention is one that contains two or more unsaturated 2M bonds in its molecular chain, which generate radicals by radioactive niI radiation and form a crosslinked structure. This is also possible by modifying the plastic resin to make it radiation sensitive.

Specific examples of radiation-sensitive modification include acrylic double bonds such as acrylic acid, meccrylic acid, or their ester compounds, which exhibit radically polymerizable unsaturated double bonds, acrylic triple bonds such as diallylphthalate, This method involves introducing into a molecule a group that can be crosslinked or polymerized and dried by radiation irradiation, such as a maleic acid double bond such as maleic acid or a maleic acid derivative.

Other unsaturated double bonds that can be crosslinked and polymerized by radiation irradiation can be used.

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

-(I) Vinyl chloride copolymer Vinyl chloride-acetic acid and vinyl alcohol copolymer, chloride and vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-acetic acid Vinyl-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal O■ side chain alkyl group copolymer. For example, the product name is UOO company VRO.
H, YYNOlVYEGX etc. also Uac tjvgu,
rt, etc. `` Acrylic double bonds are introduced into the above-mentioned copolymer using the method described later to cause radiation-sensitivity modification.

Goods] Saturated polyester resin phthalic acid, isophthalic acid, terephthalic acid, maleic acid,
Saturated polybasic acids such as maleic acid derivatives, cono-phosphoric acid, adipic acid, sebacic acid and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane', 1,2 propylene glycol, 1,3 butadiol, diethylene glycol, 1,4 butanediol, 1,
Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as 6-hexanediol, penquerystrit, nrubitol, glycerin, neopentyl glycol, and 1.4-cyclohairsanedimethanol, or these polyester resins modified with 5oeNa, etc. Resin (Byron 53S). These were subjected to radiation sensitivity modification using the method described later.

Saliva Unsaturated polyester resin A polyester compound containing a radiation-curable unsaturated double bond in the molecular chain, for example, a saturated polyester resin consisting of an ester bond of a polybasic acid and a polyhydric alcohol described as a thermoplastic resin in Item 0. Examples include unsaturated polyester resins, prepolymers, and oligomers containing radiation-curable unsaturated double bonds in which part of the polybasic acid is maleic acid.

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

The radiation-curable unsaturated polyester resin is produced by a conventional method, in which maleic acid, fumaric acid, etc. are added to one or more polybasic acid components and one or more polyhydric alcohol components, i.e., in the presence of a catalyst.
After dehydration or dealcoholization reaction in a nitrogen atmosphere at 0 to 200"C, the temperature is raised to 240 to 280°C, and the temperature is increased to 0.5 to 0.
．． A polyester resin can be obtained by condensation reaction under reduced pressure of 1 mvmg. The content of maleic acid, fumaric acid, etc. in the acid component is preferably 1 to 40 mol %, and <G-110 to 30 mol %, considering crosslinking during production, radiation curability, etc.

W Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components. The hydroxyl groups contained in these resins have been subjected to radiation-sensitive denaturation using the method described later.

(9) Epoxy resin, phenoxy resin produced by the reaction of bisphenol, epichlorohydrin, and methyl epichlorohydrin
07) Manufactured by Dow Chemical (DEN4.31, DER732
, J) ER51], DNR331), Dainippon Ink (
Evicron 400, Evicron-800), phenoxy resin (PKm, PKHOlPKE) manufactured by UOO, which is a high polymerization degree resin of the above epoxy, and a copolymer of brominated bisphenol and epichlorohydrin, manufactured by Dainippon Ink & Chemicals (・Ebikuron 145.152.153
．． 1120) etc.

These resins have undergone radiation-sensitivity modification using the epoxy groups contained in them.

■ Cellulose derivatives Cellulose derivatives of various molecular weights are also effective as thermoplastic components. Among these, particularly effective ones are nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, acetyl cellulose, etc., which have undergone radiation sensitivity modification by the method described later by activating the hydroxyl groups in the resin. .

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyether ester resins, polyvinyl bistolydone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, and spiroacecool. Also effective are resins, acrylic resins containing at least one kind of acrylic ester and methacrylic ester containing hydroxyl groups as polymerization components.

Furthermore, by blending a thermoplastic elastomer or prepolymer with the radiation-sensitive modified thermoplastic resin,
An even tougher coating film can be obtained. Furthermore, as described below, it is more effective if these nidistomers or prepolymers are similarly modified to be radiation sensitive. Listed below are nidistomers or prepolymers that can be combined with the above radiation-sensitive resin.

(I) Polyurethane elastomers, prepolymers, and telomer polyurethane distoners are particularly effective in terms of good abrasion resistance and good adhesion to PET films.

Examples of such urethane compounds include, as the isocyanate, 2,4-)luene diisocyanate, 2,6
-Toluene diisocyanate, 1.3=xylene diisocyanate, 1.4-xylene diisocyanate, 1.
5-naphthalene diisocyanate, m-phenylene diisocyanate, 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, Dicyclohexylmethane diincyanate, Desmodur L1, Desmodur N, and other multifunctional polyvalent incyanates, and flocculent saturated polyesters (ethylene glycol,
Polyhydric alcohols such as diethylene glycol, glycerin, trimethylolpropane, 1,4-butadiol, 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexane dimetatool, and heptallic acid. , linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol) )
Polyurethane elastomers, prepolymers, and telomers made of condensation products of various polyesters such as caprolactam, hydroxyl-containing acrylic esters, and hydroxyl-containing methacrylic esters are effective.

These nidistomers may be combined as they are with various radiation-sensitive thermoplastics, but urethane nidistomers may also have an acrylic double bond or acrylic double bond that reacts with the incyanate group or hydroxyl group at the end of the urethane nidistomer. It is very effective to modify it to make it radiosensitive by reacting it with a single J1° form.

GD Acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as PolyBD Retired Resin manufactured by Sinclairvetro Chemical Co., Ltd., or Nippon Zeon Co., Ltd. Hiker 1432, T, etc. ,
In particular, the double bond in butadiene generates radicals by radiation, making it suitable as a didistomer component for crosslinking and polymerization.

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

In addition, polybutadiene cyclized product Nippon Synthetic Rubber Co., Ltd. 013R
-M 901 also exhibits excellent performance in combination with thermoplasticity. 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.

Other suitable thermoplastic elastomer and prepolymer systems include ethylene-butadiene rubber, chlorinated rubber, acrylic rubber, imprene rubber and its cyclized product (0IR701 manufactured by Nippon Synthetic Rubber), epoxy-modified rubber, and internally plasticized rubber. Elastomers such as saturated linear polyester (Toyobo Byronna 300) can also be effectively used by subjecting them to the radiation-sensitive modification treatment described below.

Synthesis examples of radiation-sensitive binders will be shown later.

Furthermore, some polymers are known to disintegrate when exposed to radiation, while others cause intermolecular crosslinking.

Examples of substances that cause crosslinking between molecules include polyethylene, polypropylene, polystyrene, polyethyl acrylate,
polyacrylamide, polyvinyl chloride, polyester,
These include polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein.

If such a crosslinked polymer is used, the crosslinking reaction will occur even without special modification such as double-curing, so it can be used as it is as a backcoat resin for radiation crosslinking.

Furthermore, according to this method, a solvent is used.

Even if it is a non-useful type resin, it can be cured in a short time, so such a resin can also be used as a glue coat.

The active energy rays used for crosslinking the back coat of the present invention include electron beams using a radiation accelerator as a source, CO
γ-ray with 60 as the source, β with B r 90 as the source
- rays, X-rays using an X-ray generator as a radiation source, etc. are used.

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

The radiation characteristics used when curing the back layer are as follows:
From the viewpoint of penetrating power, it is convenient to irradiate using a radiation accelerator with an accelerating voltage of 100 to 750 kV, preferably 150 to 300 kV, so that the absorbed dose is 0.5 to 20 megaland.

When curing the back layer of the present invention, a low-dose type radiation accelerator (Electro Curtain System) manufactured by Energy Sciences, Inc. in the United States is introduced into the tape coating processing line, shielding secondary X-rays inside the accelerator, etc. This is extremely advantageous.

Of course, a van de Graaf type accelerator, which has been widely used as a radiation accelerator, may also be used.

In addition, during radiation crosslinking, it is important to irradiate the back layer with radiation in an inert gas stream such as N2 gas or HI3 gas. This is extremely disadvantageous because the radicals generated in the polymer due to the influence of 08 etc. generated by this will inhibit the advantageous crosslinking reaction.

Therefore, the atmosphere of the area to be irradiated with active energy rays is
In particular, it is important to maintain an atmosphere of an inert gas such as N2, lJe, or COQ with a maximum oxygen concentration of 1%.

Further, in the present invention, the filler used in the back layer together with the above-mentioned binder includes l) graphite, which is conductive;
Carbon black and 2) Ha8i0Q as an inorganic filler
, TiO2, Al2O8,0rQOB, 5iO1aa
ao8, zinc oxide, goethite, α-Fe20g, talc, kaolin, CaSO4, boron nitride, Teflon powder,
Graphite fluoride and molybdenum disulfide are used alone or in combination. The appropriate amount of filler to be used is 20 to 100 parts per 100 parts by weight of the binder for l), and 10 to 300 parts for 2). The drawback is that the material becomes brittle and dropouts occur more frequently.

Of course, in forming the back layer, conventionally used dispersants, lubricants, etc. can be used.

As the support, polyethylene terephthalate film, polyimide, polyamide, etc. can be used.

As for the magnetic layer, any conventionally used coated magnetic layer can be used, including γ-F e 20B, F es
04, CO-coated or doped γ-Fe9IQ3, and metal or alloy magnetic powders such as Fe, N1, CO, or alloys thereof may be used as appropriate.

When the magnetic layer is an electron beam-curable magnetic coating, forming the same coating as the magnetic layer as the back coat layer is extremely effective in preventing curl. All processes can be done online, and since there is no rolling condition, longitudinal curling is improved.

The thickness of the back layer is selected in the range of 1 to 10 microns, preferably 2 to 4 microns.

Providing such a back coat layer has the effects of improving dropout, preventing electrification, improving running performance, and reducing warping of the disk toward the magnetic layer side.

Further, magnetic disks that should be provided with such a back layer include computer disks and magnetic camera disks, and since dropout is an important characteristic for the former and warpage of the disk is an important characteristic for the latter, the back coat of the present invention can be used. It is effective to use it for these purposes.

Examples will be shown below, but first a synthesis example of a radiation-sensitive binder will be described.

1L vinyl acetate copolymerized N (h”i
.

750 parts of vinylite VAGH, 1250 parts of toluene, and 500 parts of cyclohexanone were placed in a 574-necked flask, heated and dissolved, and the temperature was raised to 80°C to form ditolylene diisocyanate-hydroxyethyl methacrylate adduct (radiation-sensitive modified resin). For the manufacturing method, see the notes below), add 61.4 parts, and further add 0.01 parts of tin octylate.
Add 2 parts and 1012 parts of hydroquinone and react at 80°C in a N gas stream until the NOO reaction rate reaches 90%. After the reaction is complete, cool and dilute with 1250 parts of methyl ethyl ketone.

Method for producing 2-hydroxyethyl methacrylate (2EEMA) adduct of tolylene diisocyanate (TDl) After heating 348 parts of tolylene diisocyanate to 80°C in a fourth flask in a N2 stream, 2-hexane 260 parts of ethylene methacrylate, 0.
07 parts, hydroquinone 0. ．． After the dropwise addition of 0.5 g of the reactor was completed while controlling the cooling so that the temperature inside the reaction vessel was 80 to 85°C, the reaction was completed by stirring at 8Q''C for 3 hours.

After the reaction was completed, the reactor was taken out and cooled to obtain TDI 2Hli:MA in the form of a white paste.

514 parts of butyral resin EM-8 manufactured by Building Blocks Chemical Co., Ltd. was added to 191.2 parts of toluene and 71.4 parts of cyclohexanone.
Add 7.4 parts of ditolylene diisocyanate-hydroxyethyl methacrylate adduct, and add 7.4 parts of ditolylene diisocyanate-hydroxyethyl methacrylate adduct.
．． 015 parts and 0.015 parts of hydroquinone were added, and 80
The reaction was allowed to occur at °C in a N gas stream until the NGO reaction rate reached 90% or more. After the reaction is completed, the mixture is cooled and diluted with methyl ethyl ketone.

Add 100 parts of Toyobo M Byron V-200 to 11 parts of toluene.
6 parts, dissolved in 116 parts of methyl ethyl ketone and heated to 80°C.
After raising the temperature, add 3.55 parts of TD engineered two-layer kite adduct, 0.007 parts of tin octylate, and 0.007 parts of hydroquinone.
90% NCo reaction rate at SO''C in N, air flow.
Let it react until it reaches the above level.

d) Synthesis of acrylic modified epoxy resin (400 parts of Epicoat 1007 manufactured by Radiation Shell Chemical Co., Ltd. was heated and dissolved in 50 parts of toluene and 50 parts of (2), and then 0.006 parts of N,N-dimethylbenzylamine and 0.003 parts of hydroquinone were added. The temperature was then raised to 80°C, 69 parts of acrylic acid was added dropwise, and the mixture was allowed to react at 80°C until the acid value reached 5 or less.

250 parts of diphenylmethane diisocyanate (MDI)-based urethane prepolymer with terminal incyanate (Nipporan 4040 manufactured by Nippon Polyurethane), 2-loss Sui A32
-5 parts, hydroquinone 0.07 parts, tin octylate 0
．． Pour 009 parts into a reaction can, heat to 80°C and dissolve, then TDI
43.5 parts were added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C, and after the dropwise addition was completed, the reaction was allowed to proceed at 80°C until the NOO reaction rate reached 95% or more.

- Synthesis of acrylic modified product (radiation-sensitive elastomer → Polyether PTG manufactured by Nippon Polyurethane Co., Ltd. -500250
Part, 2] IEMA 32.5 part, Hyde day quinone 0,0
07 parts and 9.009 parts of tin octylate into a reaction vessel.
After heating and dissolving at 0°C, 43.5 parts of 'rDI was added dropwise while cooling so that the temperature inside the reaction vessel was 80 to 90°C.
After completion of the dropwise addition, the reaction was allowed to proceed at 80° C. until the NCo reaction rate reached 95% or more.

Low molecular weight terminal hydroxyl group polybutadiene polybutadiene FD liquid resin R-15250 parts manufactured by Sinclair Vetrochemical Co., 2HEMA 32.5 parts, hydroquinone 0.007
Place 0.009 parts of tin octylate in a reaction vessel, and add 80 parts of tin octylate.
After heating and dissolving at 0.degree. C., 43.5 parts of TDI is added dropwise while cooling the reaction vessel to a temperature of 80 to 90.degree. C. After completion of the dropwise addition, the reaction is allowed to proceed at 80.degree. C. until the NOO reaction rate reaches 95% or more.

Example 1 Carbon black manufactured by Asahi Carbon Co., Ltd. Asahi n5soo (particle size 81 mμ)
50 parts Acrylic modified chloride, vinyl chloride, vinyl acetate, vinyl alcohol copolymer (prototype) 30 parts Acrylic modified polyurethane elastomer (prototype) 2
0 parts mixed solvent (MfBK/toluene = 171) 300 parts The above mixture was dispersed in a ball mill for 5 hours, applied to the back side of the polyester film where the magnetic surface was formed to a dry thickness of 3μ, and electrocurtain type electron beam Using an accelerator, the acceleration voltage was 150 KeV and the electrode current was 10
mA, absorption fc 10 Mrad.

The back layer was irradiated with an electron beam in N3 gas to cure it, then wound up and punched into a 5" floppy disk. This sample is referred to as AI.

The magnetic layer was made of cobalt-coated acicular γ-FegOa (major axis 0.4μ, short axis 0.05μ), 120 parts chloride, vinyl acetate, vinyl alcohol co-M combination (v, 01 parts, VA manufactured by 1 company).
GH) 30 parts polyurethane distomer (N5033 manufactured by Nippon Polyurethane Co., Ltd.) 20 parts carbon black (for antistatic use, Mitsubishi Carbon Black MA -
600) 5 parts α-AI, O, powder (0.5μ) 2 parts Solvent (methyl ethyl ketone/toluene = 50150) A mixture consisting of 200 parts was dispersed in a ball mill for 5 hours, and 10 parts of incyanate (Japan Polyurethane, Coronate L) In addition,
It was formed by coating to a dry thickness of 3 μm.

Example 2 SiO2 (particle size 2 μ) 50 parts Acrylic modified polyurekne elastomer (prototype) 2
0 parts Mixed solvent 300 parts The above mixture was prepared in the same manner as in Example 1 to obtain Sample Boiled 2.

Example 3 Carbon black “Asahi JJS500 Asahi Carbon Co., Ltd.”
50 parts acrylic modified polyester resin (prototype) 6
0 parts Mixed solvent 300 parts The above mixture was prepared in the same manner as in Example 1 to obtain sample A3.

Example 4 Carbon black “Asahi H8500 Asahi Carbon Co., Ltd.” 5
0 parts Acrylic modified polyurethane elastomer (prototype)
30 parts Mixed solvent 300 parts The above mixture was prepared in the same manner as in Example 1 to obtain sample A4.

Example 5 α-A1. , O, Powder (0.5μ granules) 2 parts Disperse (refined soybean lecithin) 3 parts Solvent (methyl ethyl ketone/toluene 50150) 1
00 parts The above composition was mixed in a bowl for 3 hours to wet the acicular magnetic iron oxide with the dispersant.

Acrylic double bond-introduced salt-vinyl acetate copolymer 10 parts (solid content equivalent) Solvent (methyl ethyl ketone/toluene 50150) 2
00 parts Lubricant (higher fatty acid modified silicone oil) 3 parts The above mixture of binders is thoroughly mixed and dissolved. This was put into the ball mill that had been subjected to the magnetic powder treatment and mixed and dispersed again for 42 hours.

The magnetic paint thus obtained was applied to one side of a polyester film to a dry thickness of 3μ and cured with electron beams, and then the same paint was applied to the other side of the film to a dry thickness of 3μ and electron beams were applied. The sample A5 was cured and punched into a 5" floppy disk.

Comparative Example E-carbon black "Asahi ES 500" 50 parts mixed solvent 300 parts The above mixture was made into a paint in the same manner as in Example 1, and then 1 part of isocyanate (Nippon Polyurethane, Coronet) L)
0 parts were added, and the coating was applied to a dry thickness of 3 μm. after that,
After being heat-cured for 24 hours at 60°C, 5'φ
It was punched out. This will be referred to as sample A6.

Comparative Example 2 The magnetic medium used in Examples and Comparative Example 1 without bank coating was designated as Sample A7. This is a 5'φ floppy disc with a magnetic coating coated on a polyester film.

Dropout and warpage were evaluated for the samples A1 to A7.

Dropout Test A single signal of 125 KHz was recorded and the number of times when the reproduced signal was less than 40% of the average reproduction level for 8 μsec or more was counted for all tracks. table
1 As can be seen from Table 1, samples A1 to A5#:t subjected to radiation curing treatment had much less dropout than the normal thermosetting type A5.

Warp test: Place the punched disk at 8'φ on a horizontal surface T/r- and observe it. The M distance d of the outer peripheral edge of the disk floating above the horizontal plane was measured using an lk mirror. The measurement results are shown in Table 2.

Table 2 From these results, the back-coated samples have less curl than the non-back-coated samples, and even the back-coated samples A1 to A5 that have been subjected to radiation curing treatment have less curl. It can be seen that there is less curl than normal thermosetting type A6.

Claims (1)

[Claims] l) A support having a magnetic layer on one side and a back layer on the other side, the back layer comprising a filler dispersed in a binder containing a radiation-sensitive curable resin. A magnetic disk characterized by being a magnetic disk. 2) The magnetic disk according to claim 1, wherein the filler is a powder of a conductive substance such as carbon black or graphite. 3) The filler is 8109, Tie,, Al@O,,0rH
O@, SiO, OeOg, 0aOOB, zinc oxide, goethite, α-IPego8, talc, kaolin, Of
! L804% boron nitride, Teflon powder, graphite fluoride,
The magnetic disk according to claim 1 or 2, which is a powder of a highly tough material such as molybdenum disulfide or zirconia. After forming a magnetic layer on one side of the support, a paint containing a filler dispersed in a binder containing a radiation-sensitive curable resin is applied as a back layer to the other side of the support. A method of manufacturing the above-mentioned magnetic disk by curing the radiation-sensitive curable resin by irradiating with. 5) The method for manufacturing a magnetic disk according to claim 4, wherein the filler is a powder of a conductive substance such as graphite or carbon black. 6) The filler is B1. OQ, 'I'10s, Al g
OB, 0rQOB, sio, 0θ09.0aO06,
The magnetic disk according to claim 4 or 5, which is a highly tough material such as zinc oxide, goethite, α-FeIlOa1 talc, kaolin, CaSO4, boron nitride, Teflon powder, graphite fluoride, molybdenum disulfide, zircon, etc. How to make ri. 7) The irradiation of active energy rays is carried out in an inert gas using a 100-750 kV electron beam accelerator as an active energy ray source so that the absorbed dose is 0.5-20 Mrad. 4. The method for manufacturing a magnetic disk according to item 5 or 6.