JPS6085423A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease tightening on winding of a vertical magnetization type magnetic recording medium by limiting the surface roughness of a radiation- cured back layer contg. resin having the acrylic double bond, maleic double bond or allyl double bond provided on the rear surface of the base on the side opposite from a magnetic layer. CONSTITUTION:A radiation-cured back layer contg. resin having acrylic double bond, maleic double bond or allyl double bond is provided on the rear of a plastic base having a vertical magnetization type magnetic layer. The surface roughness thereof is regulated to 0.04-0.6mum. The decreased tightening on winding, decreased tack, improved runnability and decreased dropout are caused even if the surface characteristic of the magnetic surface is improved by said layer. Curing of the coated back layer can be completed by irradiating radiation before the medium is taken up by using the radiation curable or sensitive resin. The smoothing of the back surface by a process such as of a calender or the like is possible before or after curing or simultaneously with curing. The desired surface characteristic is thus obtd. with both of the back surface and the magnetic surface.

Description

[Detailed description of the invention] The present invention relates to a perpendicular magnetization type magnetic recording medium.

Conventional technology There are two types of perpendicularly magnetized magnetic recording media: one is Co-Cr)F@-N formed by vapor deposition, sputtering, etc.
A metal thin film type in which a metal thin film such as i-CaSF*-Cts is attached to the surface of a plastic film base, and an axis of easy magnetization perpendicular to the base surface is formed by controlling the conditions at that time (for example, durable [58-91 The other type is a coating film type in which acicular magnetic powder such as the above alloy is dispersed in a binder resin and applied to a plastic film base and oriented in a magnetic field (for example, JP-A No. 111557-
No. 111852 #M). In any case, it indicates one direction for future magnetic recording media in that it is possible to record signals with a much shorter wavelength than conventional magnetic recording media whose easy axis of magnetization is parallel to the base surface.

However, in a perpendicularly magnetized magnetic recording medium, it is necessary to make the surface of the magnetic layer very smooth and to minimize the spacing between the magnetic head and the surface of the magnetic layer.

However, when the surface becomes smooth, friction increases, causing problems such as stopping during actual running and fluctuations in output due to irregular winding of the tape. In addition, the base thickness and the magnetic layer thickness of such tapes are decreasing, and bases with a thickness of about 10/J or less (&Lyethylene Tele 7 Talley FS1 Liethylene Naphthalate, 4 Liimide 1 Polyamide, etc.) are currently being considered. has been done. This kind of tape has a soft waist, and when it is wound, the winding becomes too tight, and the properties of the back side of the base are reflected on the magnetic surface, reducing the surface properties and causing stickiness, or the tape is rewound and the magnetic surface becomes sticky. When the base is separated from the base, so-called peeling electrification occurs, and dirt, dust, etc. are attracted, and dropout occurs due to an increase in spacer loss. These problems greatly limit the advantages of perpendicular magnetization type magnetic recording media.

Purpose The present invention aims to provide a perpendicularly magnetized magnetic recording medium that is less prone to such drawbacks, especially less tight winding.0 Structure and Effects of the Invention The present invention provides a perpendicularly magnetized magnetic recording medium having a perpendicularly magnetized magnetic layer on the back surface of the plastic base. Acrylic double bond! A radiation-cured batter layer containing a resin having a rhein double bond or an allylic double bond is provided, and its surface roughness is a04 to [L6μ
Improve the surface properties of the magnetic surface by specifying less than
Even if the surface roughness is reduced, it is possible to provide an excellent perpendicular magnetization type magnetic recording medium that has reduced winding tightness, reduced adhesion, improved runnability, and reduced dropouts.

The surface roughness of the batter layer, together with the material of the back layer, not only improves the running properties and abrasion resistance of the tape, but also reduces the adhesion and scinning phenomenon with the four magnetic layers, and further improves the surface roughness of the magnetic layer. It has been found that when the surface roughness of the backing layer is α6μ or less, 8/N can be maintained well in correlation with the high surface roughness of l1G8μ or less. It has been found that when the surface roughness is less than 0.04 μm, problems occur in the cinching phenomenon, adhesion, and runnability.

When a thermosetting resin is used for the batter layer, curing is not yet completed when the resin is rolled up after application. A considerable amount of energy is required to completely cure the resin, but since it affects the base, curing must be done gradually. At this time, the surface properties and resin components of the back surface are transferred to the magnetic surface, or, if the magnetic surface is uncoated, to the base surface. This has an adverse effect on the batter surface, magnetic surface or base surface. In the case of vertical coating, if the influence of the back surface is exerted on the magnetic surface due to curling, it causes problems such as fluctuations in output and reduction in output. Also, unlike horizontal coating, the magnetic powder is oriented vertically, so even if there is no backing layer or if it is rolled up, minute irregularities are likely to occur on the surface, causing output fluctuations. Bank coats are affected by both of these factors and are more prone to surface irregularities than conventional horizontal recording.

By using a radiation-curable or sensitive resin as in the present invention, the applied back layer can be completely cured by irradiation with radiation before being wound up. In addition, the back surface can be smoothed by calender treatment before, during or after curing. For this reason, the desired surface properties can also be obtained on the magnetic surface. Therefore, there is no tight winding and no output fluctuation. Radiation curing is very effective for vertical application.

The radiation-curable or sensitive resin used in the present invention is one that contains one or more unsaturated double bonds in its molecular chain, which can be crosslinked by generating radicals when exposed to radiation, and this also includes thermoplastic resins. It is also possible to make the radiation sensitive to radiation.

Specific examples of radiation-sensitive modification include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, which exhibit radically polymerizable unsaturated double bonds, and allylic double bonds such as diallylphthalate. ,
This method involves introducing into the molecule a group that can be crosslinked or polymerized and dried by radiation irradiation, such as an unsaturated 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-vinyl acetate-vinyl alcohol-#1
i combination, L'air chloride-vinyl alcohol-k copolymer, '11i vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-
Maleic acid copolymers, vinyl chloride-vinyl acetate-terminated OH [chain alkyl group copolymers, e.g. UCCi V
ROHlVYNC.

VYEGX@Also, UCC VEIiR, etc. can be mentioned.

(II) Saturated polyester resin Phthalic acid, isophthalic acid, Terephthalic acid, maleic acid,
Saturated polybasic acids such as maleic acid derivatives, succinic acid, adipic acid, sepacic acid, and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1.2-propylene dalicol, t3-butanediol,
Diethylene glyfur, 1,4\butanediol, t6
Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as hemosandiol, pentaerythritol, sorbyl F-ol, glycerin, neopentyl glycol, and t4-cyclohexane dimethanol, or these polyester resins. Resin modified with 5OsNa etc. (Vipon 558). (III) Unsaturated polyester resin A polyester compound containing a radiation-curable unsaturated double bond in the molecular chain, such as a thermoplastic resin described in item (If) A saturated polyester resin consisting of an ester bond of a polybasic acid and a polyhydric alcohol, and includes unsaturated polyester resins, prepolymers, and oligomers containing radiation-curable unsaturated double bonds in which part of the polybasic acid is maleic acid. be able to.

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 manufactured by a conventional method by adding maleic acid, fumaric acid, etc. to one or more polybasic acid components and one or more polyhydric alcohol components, that is, in the presence of a catalyst.
After dehydration or dealcoholization in a nitrogen atmosphere at ~200°C, the temperature was raised to 240~2.80°C, and 15~I MH
A polyester resin can be obtained by the condensation reaction of g under reduced pressure. The content of maleic acid, fumaric acid, etc. is 1 to 40 mol % in the acid component, preferably 10 to 30 mol %, in view of crosslinking during production, radiation curability, etc.

(IV) 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 modified by radiation sensitization using the method described later.

(V) Epoxy resin, epoxy resin produced by the reaction of phenolic resin bisphenol, epichlorohydrin, and methyl epichlorohydrin - Shell Chemical @ (Epicote 152.154/828.1oa1.1004.100
7) Manufactured by Dow Chemical (DEN4!1, DER732,
DFiR511, DER331), Dainippon Ink (Evicron 400, Evicron-aOO), and phenoxy resin (UCC), which is a high polymerization degree resin of the above epoxy.
PKHA, PKHC, PKHH) Copolymer of brominated bisphenol and epichlorohydrin, manufactured by Dainippon Ingo Chemical Industry Co., Ltd. (Eikukun 145.152.15L1120)
)etc.

Using the epoxy groups contained in these resins, radiation m
Sensitively modified (W) ili fiber derivativesFiber filament derivatives of various molecular weights are also effective as thermoplastic components. Among them, particularly effective ones include nitrified cotton, hepylose, a7acyl F1 ethyl hepse, butyl cell dayz, and acetyl heptarose, which activate the hydroxyl groups in the resin. ◆Other,
Resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyether ester resins, polyvinyl bipridone resins and derivatives (pvp olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, and hydroxyl groups. Acrylic resins containing at least one kind of acrylic ester and methacrylic ester as a polymerization component are also effective.

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 elastomers or prepolymers are similarly modified to be radiation sensitive. Elasto V- or prepoly Y- which can be combined with the radiation-sensitive resin described above is listed below.

(1) Polyurethane elastomer, prepolymer and telomer Polyurethane elastomer is particularly effective in terms of good abrasion resistance and good adhesion to PET film.

Examples of such urethane compounds include inocyanate such as 2.4-) luene diisocyanate, l-)
L3'-dimethyl-4,4'-diphenylmethane diisocyanate),
4.4'-diphenylmethane diisocyanate, 43'
-dimethylbiphenylene diisocyanate, 4.4'-
Hyphenylene diisocyanate, methylene diisocyanate, isophenyl diisocyanate, dicyclohexylmethane diisocyanate, desmodur L1
Various polyvalent isocyanates such as Desmodur N and linear saturated polyesters (ethylene glyfur, diethylene glycol, dali heptaline, trimethylolpurpane, t4
-butanediol, t6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol,
1.4-Condensation of polyhydric alcohols such as cyclohexylmethane with saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, monosaccharic acid, adipic acid, and sebacic acid. polymerization), linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetra 1 ethylene glycol), cabrelactam, and various polyesters such as doxyl-containing acrylic esters and hydroxyl-containing methacrylic esters. Polyurethane elastomer, pre-poly! −, telomer is 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 elassis ψ)Y- Acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as PolyBD liquid range manufactured by Sinclair Petrochemical Co., Ltd. or Hiker 1432J manufactured by Nippon Zeon Co., etc. The elastomer is particularly suitable as an elastomer component in which the double bond in butadiene generates radicals by radiation and is crosslinked and polymerized.

(DI) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group, such as PolyBD Retight Resin R-15 manufactured by Sinclair Petrochemical Co., is particularly suitable from the viewpoint of compatibility with thermoplastic plastics. R-15
Since the prepolymer has a hydroxyl group at the end of the molecule, it is possible to increase the radiation sensitivity by adding an acrylic unsaturated double bond to the end of the molecule, making it even more advantageous as a binder.

In addition, polybutadiene cyclized product Nippon Synthetic Rubber Co., Ltd. CBR-
M901 also exhibits excellent performance when combined with thermoplastics. 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 thermoplastic elastomers! - and its prepoly! - Suitable systems include styrene-butadiene rubber, chloride rubber, acrylic rubber, isoprene rubber and its cyclized product (Japan Synthetic Rubber @ ClR701), epoxy-modified rubber, internally plasticized saturated linear polyester (Toyobo Bay P> +
Elastomers such as 1oo) and the like can also be effectively used by subjecting them to the radiation sensitivity modification treatment described below.

Next, an example of synthesis of a radiation-sensitive binder will be explained. Production method of adduct of O-tolylene diisocyanate &) Synthesis of acrylic modified product of vinyl chloride-vinyl acetate copolymer resin (radiation-sensitive modified resin) Vinylite VAGH 750 parts Toluene 1250 parts Cyclohexanone 51 copies of 500 copies
Pour into a 4-necked 7-task tube and heat to dissolve. After raising the temperature to 80°C, add 614 parts of tolylene diisocyanate 2- and diethyl methacrylate adduct, and then add octylic acid
"[1012 parts, hydroquinone [LO12f[lI1
5. Let the mixture react with N at 80°C in an air stream until the NCO reaction rate reaches 90%. After the reaction is completed, the mixture is cooled and diluted with 1250 parts of methyl ethyl ketone.

Preparation of 2-hydroxyethyl methacrylate (2 parts gMA) adduct of tolylene diisocyanate (TDI) 348 parts of tolylene diisocyanate (TDI) were heated to 80°C in a fourth flask of 11 in a stream of N gas. , 260 parts of 2-5 xylene methacrylate, 07 parts of tin octylate α, and 0.05 parts of hydroquinone were added until the temperature inside the reaction vessel was 80~80 parts.
After completion of the dropwise addition, the mixture was stirred at 80°C for 6 hours to complete the reaction while cooling the mixture to 85°C. After the reaction was completed, it was taken out and cooled to obtain a white paste-like TDI 2HEM.

b) Synthesis of acrylic modified butyral resin (radiation-sensitive modified resin) 100 parts of butyral resin building blocks, handmade BM-8, were added to 1912 parts of toluene and 714 parts of citalohexanone in a 544-mouth 7-Tesco, dissolved by heating, and the temperature was raised to 80°C. Added 74 parts of ditolylene diisocyanate-hydroxyethyl methacrylate adduct, and further added tin octylate [1015 parts,
Add 15 parts of hydronon α0, cool at 80° C. after completing the NO ratio in a NiI air stream, and dilute with methyl ethyl ketone.

@) Synthesis of acrylic modified saturated polyester resin (radiation sensitive modified resin) 100 parts of Toyobo Vipun RV-200 and 1 part of toluene
16 parts, heated and dissolved in 116 parts of methyl ethyl ketone and 80
After raising the temperature to ℃, 455 parts of TDI's 2HEMA adduct was added.
0.07 parts of tin octylate α and 0.07 parts of Hydol® non-a are added, and the mixture is allowed to react at 80° C. in a N 2 stream until the NCO reaction rate reaches 90% or more.

d) Synthesis of acrylic modified epoxy resin (radiation-sensitive modified resin) 1 [400 parts of 107 made by Shell Chemical Co., Ltd.] After heating and dissolving in 50 parts of luene and 50 parts of MEK, 7120006 parts of NN-dimethylbenzyl and 3 parts of hydronon α00 were added. The temperature was then raised to 80°C, 49 parts of acrylic acid was added dropwise, and the mixture was allowed to react at 80°C until the oxidation level was 5 or less.

-) Synthesis of acrylic modified urethane elastomer (radiation-sensitive elastomer) Terminal isocyanate diphenylmethane diisocyanate (MDI) thread urethane prepolymer (Nitsupotsun 4040 manufactured by Nippon Polyurethane) 250 parts, 2HEMA
62.5 parts, hydrquinone α0 part, tin octylate [LOO 9 parts were placed in a reaction vessel, heated to 80°C and dissolved, then TD
I 4B. 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 NCO conversion rate reached 95% or more.

1) Synthesis of polyether-based urethane-modified elastomer acrylic modified product (radiation-sensitive ethics) W-) Polyether PTG-50 manufactured by Nippon Polyurethane Co., Ltd.
0250 parts of 2HEMA i, 2.5 parts of 2HEMA i, 007 parts of hydrononone α, and 009 parts of tin octylate were placed in a reaction can and heated to 80°C to dissolve, and then 15 parts of TD I J was added until the temperature inside the reaction can reached 80 to 90°C. The solution was added dropwise while being cooled, and after the completion of the addition, the reaction was allowed to proceed at 80'C until the NGO reaction rate reached 95% or more.

g) Synthesis of l-liptadiene elastomer acrylic modified product (radiation-sensitive elastomer) Low molecular weight terminal hydroxyl group polybutadiene polybutadiene polyBD Liquid Resin B-15250 parts manufactured by Sinclair Petrochemical Co., Ltd., 2HEMA 52.5 parts, Hydol Non-CLO lower part , 1009 parts of tin octylate was placed in a reaction vessel and heated to 80°C.
After heating and dissolving 445 parts of TDI, the temperature inside the reaction vessel was 80°C.
It is added dropwise while cooling to ~90°C, and after the dropwise addition is completed, it is allowed to react at 80°C until the NCO reaction reaches 95% or more.

Furthermore, it is known that some polymers disintegrate when exposed to radiation, while others cause crosslinking between molecules. Materials that cause crosslinking between molecules include polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyacrylamide, polyvinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein. If so, the crosslinking reaction will occur even without special modification as described above, so it can be used as it is as a backcoat resin for radial 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 also be used for puncture coating.

In addition, the active energy rays used for crosslinking the bank coat of the present invention include electron beams using a radiation accelerator as a radiation source;
r-line with Co” as the source, p with B, 11@ as the source
- line, x! ! X-l1 with i1 generator as a radiation source! etc. are used.

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

The radiation characteristics used when curing the back layer are as follows:
From the viewpoint of penetrating power, it is convenient to use a radiation accelerator with an accelerating voltage of 100 to 750 KV, preferably 150 to 300 KV, and irradiate at an absorbed dose of a5 to 20 megarads.

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 the secondary X@ inside the accelerator, etc. This is extremely advantageous.

Of course, the Vandedara 7 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 N, gas H, gas, etc.; This is extremely disadvantageous because radicals generated in the polymer due to the influence of Ofi and the like generated by irradiation prevent the advantageous conduction of crosslinking reactions.

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 Hl s H. or COI with a maximum oxygen concentration of 1-.

Other monomers having a sufficiently high boiling point to remain after the low boiling point solvent is removed by preliminary drying can be used. Specifically, for example, esters of acrylic acid or methacrylic acid in alkali having 4 or more oxygen atoms (hemosil, 2ethylhemoyl, lauryl, decyl, stearyl ester), high boiling point hydrocyatarylate or hydrocymarate, that is, acrylic. 2-hydro dipropyl acid, 4-acrylate and droxybutyl, 2-hydroxyethyl methacrylate, 6-methacrylate and droxyl,!
Mono(2-hydroxyethyl)leate, di(2-hydroxyethyl)maleate, atarylamide, methacrylamide, etc. are suitable, and high boiling point monomers having two or more vinyl groups to promote crosslinking, such as divinylstyrene, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetoteethylene glycol dimethacrylate), N,N' methylene bisacrylamide, ti-butylene dimethacrylate, diallyl phthalate, trimethylolpropane tri(meth)acrylate, It is even more effective to use pentaerythritol tri(meth)acrylate in combination.

In addition, in the present invention, conductive materials such as 1) graphite, carbon black, and 2) Si as an inorganic filler can be used together with the above-mentioned binder in the back layer.
02, T 10 times, Mu 1. Os, Cr1O1, Si
C, CaCO3, zinc oxide, goethite, αFe201
, talc, kaolin, C1804, boron nitride, Tef-P
powder*, graphite fluoride, and molybdenum disulfide. The amount of such filler used is 20 to 200 parts for 100 parts by weight of the binder for 1), and 10 to 200 parts for 2).
500 parts is appropriate; if the amount of filler is too large,
The drawback is that the coating film becomes brittle and dropouts occur more frequently.

Magnetic Layer 1 Magnetic ink raw materials having the following composition were kneaded using five rolls to prepare an electron beam curable ink.

Particle size 0.1/J bait thickness [102/J bait square barium ferrite 80 parts by weight Polyurethane arylate 10 l I-lyester acrylate 7 #F tritylolpropane triacrylate 5 # Apply the above ink to a polyester film After coating the coating film with a polypropylene film, it was placed in an orientator and vertically oriented. 150 at the same time in the director
5Mra using @V (15mA) curtain electron gun.
After the binder was polymerized and cured by irradiation with a dose of d, the propylene film was peeled off.

Magnetic Layer 2 A polyester film is sufficiently washed, degreased and dried, and a low coercive force material layer made of Mo-F.-Nl is formed thereon by sputtering. The formation conditions were 7 vacuum degree t5×lOtorr, argon pressure 2.2Xl0
High frequency power 450W at -2torr, substrate temperature 250W
Sputtering was carried out at a temperature of about 20 minutes to obtain a low coercive force material layer with a film thickness of about 1 mm and a coercive force (He) of about 5001 and a saturation magnetization (Ms) of about 600. Furthermore, a magnetic recording layer made of C0-Cr is formed thereon by sputtering. The formation conditions were a vacuum degree of t 5 X i O-'torr.

2 High frequency power 200W at argon pressure 2X10 torr
Then, sputtering was performed for about 1 hour until the film thickness was about full.
So, the Or content is about 18% by weight, the coercive force in the direction perpendicular to the film surface (H) is about 6500, and the saturation magnetization (quadruple M■) is 4110.
A 0G magnetic recording layer was obtained.

Example 1 Carbon platter 25 parts/4 50 parts by weight mixed solvent (M
IBK/) Luene = 171) 3o ay The above mixture was mixed in a ball mill for 5 hours, and coated on the back side of the polyester film on which the magnetic layer 1 was formed to a dry thickness of 5P, and then heated using an electric curtain type electron beam acceleration. Using the device acceleration voltage 150 K@V% electrode current 15 mA,
The back layer was irradiated with an electron beam in Ns gas at an absorbed dose of 5 Mrads, and after curing, it was calendered, wound up, and cut into a video width.

Example 2 Sin, (αIμs) 50 parts by weight mixed solvent (MIBK/) luene-1/1) soo p
A sample was prepared by applying the above mixture to the back surface of a polyester film on which the magnetic layer 2 was formed in the same manner as in Example 1.

Comparative Example 1 Car pump hook (2SSμ) 50 parts by weight PVC-vinyl alcohol copolymer 50 1 Polyurethane prepoly Y
-201 Mixed solvent (MIBK/ ) #! Shin-11) 500
#The above mixture was mixed in a ball mill for 5 hours to form magnetic layer 1.
It was coated on the back side of the preester film on which a dry thickness of 5 pans was formed, and after calendering, it was rolled up, cured at 60° C. for 24 hours, and cut into a 1P video width.

Comparative example 2 810! (al #ti) 50 layered lid vinyl alcohol copolymer soy polyurethane prepolymer 20 # mixed solvent (MIBK/) luene-1/1) soo # magnetic layer 2 is formed using the above mixture A sample was prepared by coating the back side of a polyester film in the same manner as in Comparative Example 1.

Comparative Example 3 Polyester film base with magnetic layer 1 (no back layer).

Comparative Example 4 Polyester film base with magnetic layer 2 (no batter layer).

The results of various tests performed on the tapes of each Example and Comparative Example 4 of Jamiyu are shown in the following table.

1aA-- In the case of vertical coating, fine protrusions are likely to occur because the magnetic powder is vertically oriented due to tight winding. If even a minute protrusion hits a head, guide ball, etc. while running, the load per unit area will be greater than that of a horizontally oriented one, so the surface of the minute protrusion is likely to be damaged. Therefore, it is necessary to eliminate tight winding on the magnetic surface. For this purpose, the radiation curing type is advantageous. Without a back surface, the vehicle would stop running due to high friction.

Note that the above measurements were performed as follows.

1 Coefficient of Friction Wrap the magnetic tape around a polished aluminum cylinder with a diameter of 4 m at an angle of 180° with the back side inside, and run at 2 km/sec to maintain tension on the sending and winding sides. It was determined by measurement and calculation.

2 Scinching phenomenon Using a commercially available VHg type VTR, after fast forwarding the entire length of the tape, it is returned flat, and stopped when 50 pieces of tape remain.
Then perform fast rewind to the end. After that, the winding state of the tape was visually observed.

A case where there was no gap between the tape layers and the winding condition was good was evaluated as good, and a case where a gap occurred between the tape layers was evaluated as poor.

3 Wear of back layer Using a commercially available VNS type VTR, the inside of the cassette case was observed for dirt after running it 100 times at a temperature of 40° C. and a relative humidity of 80%. The case where there was dirt was judged as poor, and the case where there was no dirt was judged as good.

4. Adhesiveness of magnetic layer and back layer The adhesive condition was visually evaluated when the film was wound onto a VHS reel and left in an environment at 60° C. for 5 days.

A case where there was no adhesion was considered good, and a case where adhesion occurred was judged as poor.

5 Surface roughness Determined by the 20-point average method from a chart obtained using Talystep (manufactured by TAYLOR-HOBSON). Kaftoo 7
(Ll 7■, needle pressure 2 cape, needle α1X2.5/l was used.

Claims (1)

[Claims] (1) In a magnetic recording medium in which a magnetic layer having perpendicular magnetic anisotropy suitable for perpendicular magnetization is formed on a plastic film base, an acrylic double bond, a male A magnetic recording medium, comprising a radiation-cured batter layer containing a resin having an in-type double bond or an allylic double bond, and having a surface roughness of 0.04 to L6 ps.