JPH0219529B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for manufacturing magnetic recording media such as video tapes, computer tapes, audio tapes, or floppy disks. <Prior art> Conventionally, this type of magnetic recording medium generally uses a thermosetting binder, and reacts with a crosslinking agent represented by a polyvalent isocyanate group-containing compound and a hydroxyl group, an amino group, etc. in the binder. Through a chemical reaction with the functional group, a three-dimensional network structure is formed between the binders, and by adding a lubricant to this, it is possible to improve the durability, runnability, and environmental reliability of the magnetic recording medium. It has been done. As the lubricant, silicone oil, fatty acid, fatty acid ester, molybdenum disulfide, graphite, etc. are conventionally known. Among them, RCO groups (alkyl groups,
However, it contains a fatty acid ester with R=CnH _2o+1 ) and a fatty acid with a melting point of 44 to 70°C, and due to the synergistic effect of both, it has extremely excellent wear resistance under a wide range of operating temperatures from 0 to 40°C. A magnetic recording medium with guaranteed lubricity has been proposed (Japanese Patent Publication No. 51-39081) and has been widely used in thermosetting binders. <Problems to be Solved by the Invention> However, the conventional technology typified by Japanese Patent Publication No. 51-39081 required the use of a thermosetting binder, and therefore had the following drawbacks. (b) After applying the magnetic paint containing the fatty acid ester and the fatty acid as additives onto the support and drying it, a calender treatment is performed and the thermosetting reaction has not started when the tape is wound.
The magnetic coating film is not strong and blooming occurs in the additives in the coating film. For this reason, there is a restriction that the range of the fatty acid esters and fatty acids that can be used as additives is narrowed. (b) Conventional thermosetting magnetic recording media are coated with magnetic paint and then heated for 2 to 30 minutes at a temperature of, for example, 70°C.
It was necessary to heat cure the material in an oven for as long as 20 hours. In order to avoid blocking, curling, etc. that occur during this heat curing process, restrictions had to be placed on the types of additives. Therefore, an object of the present invention is to provide a method for manufacturing a magnetic recording medium that eliminates the above-mentioned conventional drawbacks and expands the range of use when fatty acid esters and fatty acids having alkyl groups are used as additives. It is to provide. <Means for Solving the Problems> In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a magnetic recording medium having a magnetic recording layer in which a binder contains a fatty acid ester and a fatty acid having an alkyl group, in which the binder contains a fatty acid ester and a fatty acid. It is made of a radiation-sensitive resin and is characterized by being cured by irradiation with radiation after calendering and before winding. <Function> As mentioned above, instead of conventional thermosetting resin,
Using a radiation-sensitive resin as a binder, after applying a magnetic coating containing the radiation-sensitive resin to a support, drying it, and calendering, the radiation-sensitive resin contained in the magnetic coating is removed by radiation irradiation before winding. When cured, the coating becomes stronger when rolled up. Therefore, when the magnetic recording medium is wound up, there is no blocking of additives in the coating film, and the usable range of additives is expanded compared to the case of conventional thermosetting binders. For example, in the conventional example shown in Japanese Patent Publication No. 51-39081, only fatty acid esters having an RCO group having 10 to 16 carbon atoms and fatty acids with a melting point of 44 to 70°C could be used, but in the present invention, carbon atoms It becomes possible to use fatty acid esters having an RCO group of 9 or more and fatty acids having a melting point of 32 to 81°C. Furthermore, since the method for producing a magnetic recording medium according to the present invention involves curing by irradiation with radiation, the conventionally necessary heat curing step is no longer necessary, and restrictions on the types of additives are relaxed. Furthermore, in order to commercialize a videotape with stable still images for a long time and no bleed under a wide range of temperature conditions from 0 to 60°C, it is necessary to
It has been found that fatty acid esters preferably having an RCO group having 10 to 18 carbon atoms and fatty acids having a melting point of 32 to 81°C can be used. In addition, these lubricants are
Satisfactory results cannot be obtained with either one alone.
It was found that a synergistic effect can only be obtained by combining the two types. The radiation-sensitive resin used in the present invention is a resin containing one or more unsaturated double bonds in its molecular chain, which generates radicals when exposed to radiation and is cured by crosslinking or polymerization. It is known that some polymeric substances disintegrate when irradiated with radiation, while others cause crosslinking between molecules. Examples of the latter include polyethylene, polypropylene, polystyrene, polyacrylic ester, polyacrylamide, polyvinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, polyacrolein, etc., and such crosslinked polymers can be used as they are in the magnetic layer. used. Furthermore, the radiation sensitive resin used in the present invention is
It can also be prepared by radiation-sensitive modification of a thermoplastic resin, which is preferable in terms of curing speed and the like. 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. , maleic acid, maleic acid derivatives, etc., which are crosslinked or polymerized and dried by radiation irradiation, such as unsaturated bonds, are introduced into the molecule. In addition, any unsaturated double bond that can be crosslinked and polymerized by radiation irradiation can be used. A specific example is shown below. (A) 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 copolymers, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymers, etc. Product names include, for example, UCC's VROH, VYNC, and VYEGX.
Or VERR etc. can be mentioned. The above-mentioned copolymer is subjected to radiation sensitivity modification by introducing an acrylic double bond, a maleic acid double bond, or an allylic double bond by a method described later. (B) Saturated polyester resins Saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, maleic acid derivatives, 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, 1.6 hexanediol, pentaerythritol, sorbitol,
Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as glycerin, neopentyl glycol, 1.4 cyclohexanedimethanol, or these polyester resins
Resin modified with SO ₃ Na etc. (Vylon 53S). These are also subjected to radiation sensitization by the method described later. (C) Unsaturated polyester resin A polyester compound containing radiation-curable unsaturated double bonds in its 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 (B) above, and a radiation-curable unsaturated double bond with maleic acid as part of the polybasic acid. Examples include unsaturated polyester resins, prepolymers, oligomers, and the like. Examples of the polybasic acid and polyhydric alcohol components of the saturated polyester resin include the compounds listed in section (A) above, and examples of radiation-curable unsaturated double bonds include maleic acid and fumaric acid. can. The radiation-curable unsaturated polyester resin is produced by adding maleic acid, fumaric acid, etc. to one or more polybasic acid components and one or more polyhydric alcohol components, and heating at 180 to 200°C in the presence of a catalyst. Under temperature conditions,
After dehydration or dealcoholization under nitrogen atmosphere,
A polyester resin can be obtained by raising the temperature to 240 to 280°C and carrying out a condensation reaction under reduced pressure of 0.5 to 1 mmHg. 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 and radiation curability during production. (D) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components. The hydroxyl groups contained therein can also be radiation-sensitized by the method described later. (E) Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A with epichlorohydrin or methylepichlorohydrin. For example, Epicote 152 manufactured by Ciel Chemical Co., Ltd.
154, 828, 1001, 1004, 1007, DEN431, DER732, DER511, DER331 manufactured by Dow Chemical Company or Epicron 400, Epicron manufactured by Dainippon Ink Company
800 etc. Furthermore, phenoxy resin (PKHA,
PKHC, PKHH), a copolymer of brominated bisphenol A and epichlorohydrin, Epiclon 145, 152, 153, 1120 manufactured by Dainippon Ink, etc. These resins are also subjected to radiation sensitivity modification using the epoxy groups contained therein. (F) Cellulose Derivatives Cellulose derivatives of various molecular weights are also effective as thermoplastic components. Among them, particularly effective ones include nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, and acetyl cellulose. These materials are also subjected to radiation sensitivity modification using the hydroxyl groups in the resin by a method described later. Other resins that can be used for radiation sensitivity modification include polyether ester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, and acrylic resins containing hydroxyl groups. Acrylic resins containing at least one kind of ester and methacrylic ester as a polymerization component are also effective. Other usable binder components include monomers such as acrylic acid, methacrylic acid, acrylamide, and methacrylamide. Binders with double bonds include various polyesters,
Polyols, polyurethanes, etc. can be modified with compounds having acrylic double bonds. Products with various molecular weights can be obtained by blending polyhydric alcohol and polyhydric carboxylic acid as necessary. The examples listed above are only some of the radiation-sensitive resins. Furthermore, by blending a thermoplastic elastomer or a prepolymer with the radiation-sensitive modified thermoplastic resin, an even tougher coating film can be formed. In addition, it is even more effective if these elastomers or prepolymers are likewise modified to be radiation sensitive. Next, examples of elastomers or prepolymers that can be combined with the radiation-sensitive modified thermoplastic resin will be given. (A) Polyurethane elastomers, prepolymers and telomers. Polyurethane elastomers are particularly effective in terms of abrasion resistance and adhesion to polyethylene terephthalate films. Examples of such urethane compounds include, as isocyanates, 2.4-toluene diisocyanate, 2.6-toluene diisocyanate, 1.3-xylene diisocyanate, and 1.4-toluene diisocyanate.
Xylene diisocyanate, 1.5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3.3'-dimethyl-4.4'-diphenylmetadiisocyanate, 3.3'-dimethylbiphenylene diisocyanate, 4.4'-biphenylene diisocyanate, Various polyvalent isocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, Desmodyur L, Desmodyur N, and linear saturated polyethers (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1.4
- polyhydric alcohols such as butanediol, 1,6-hexanediol, bentaerythritol, sorbitol, neobentyl glycol, 1,4-cyclohexanedimethanol and phthalic acid, isophthalic acid, terephthalic acid, maleic acid, succinic acid, adipic acid (by condensation polymerization with saturated polybasic acids such as sebacic acid, Polyurethane elastomers and telomers made of polycondensates of various polyesters such as acrylic esters are effective. These elastomers may be combined as they are with various radiation-sensitive thermoplastics, but in addition, 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 be used. It is also very effective to make it radiosensitive by reacting with the body. (B) Acrylonitrile-butadiene copolymer elastomer Acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group, commercially available as PolyBD Liquid Range, manufactured by Sinclair Vetro Chemical Co., Ltd., or Hiker 1432J, manufactured by Nippon Zeon Co., Ltd.
These elastomers are particularly suitable as elastomer components in which the double bonds in butadiene generate radicals by radiation and are crosslinked and polymerized. (C) Polybutadiene elastomer A prepolymer having a low molecular weight hydroxyl group such as PolyBD Liquid Range R-15 manufactured by Sinclair Vetrochemical Co., Ltd. is particularly suitable in terms of compatibility with thermoplastic plastics. In the R-15 prepolymer, the molecular terminal is a hydroxyl group, so
By adding an acrylic unsaturated double bond to the end of the molecule, it is possible to increase the radiation sensitivity, making it more advantageous as a binder. Furthermore, CBR-M901 manufactured by Japan Synthetic Rubber Co., Ltd., which is a cyclized product of polybutadiene, also exhibits excellent performance when combined with thermoplastic plastics. especially,
Cyclized polybutadiene has high efficiency in crosslinking polymerization by radiation using radicals of unsaturated bonds inherent in polybutadiene, and has excellent properties as a binder. Other suitable thermoplastic elastomer and prepolymer systems include styrene-butadiene rubber, chloride rubber, acrylic rubber, isobrene rubber, and cyclized products thereof (manufactured by Nippon Gosei Rubber Co., Ltd.).
CIR701), epoxy-modified rubber, and elastomers such as internally plasticized saturated linear polyester (Toyobo Vylon #300) can also be effectively used by subjecting them to radiation-sensitive modification treatment. In the present invention, when a solvent is used, ketones such as acetone, methyl, isobutyl, ketone, and cyclohexanone, methanol, ethanol,
Alcohols that cannot be used with isocyanate-based thermosetting binders such as isopropanol and butanol, substances with ether bonds such as tetrahydrofuran and dioxane, solvents such as dimethylformamide, vinylpyrrolidone, and nitropropane, and aromas such as toluene and xylene. A group hydrocarbon diluent or solvent is used. The supporting substrate used for coating is polyethylene terephthalate film, which is currently widely used as a substrate for magnetic recording media, and
For applications requiring heat resistance, polyimide films, polyamide-imide films, etc. are used, and in particular, polyester films are often used after being uniaxially stretched or biaxially stretched when used on a thin basis. The magnetic fine powder utilized in the present invention is γ
-Fe ₂ O ₃ , Co-doped γ- Fe ₂ O ₃ , Co-doped γ-
Fe ₂ O ₃ −Fe ₃ O ₄ solid solution, CrO ₂ or Co-based compound-coated type γ-Fe ₂ O ₃ , Co-based compound-coated type Fe ₃ O ₄ (γ
-Includes intermediate oxidation states of Fe ₂ O ₃ . Furthermore, the Co-based compounds referred to herein refer to those that utilize the magnetic anisotropy of cobalt to improve coercive force, such as cobalt oxide, cobalt hydroxide, cobalt ferrite, and cobalt ion adsorbates. ), and Co, Fe−Co, Fe−Co
The main component is a ferromagnetic metal element such as -Ni or Co-Ni. The manufacturing methods include a wet reduction method using a reducing agent such as _NaBH4 , a dry reduction method in which the iron oxide surface is treated with a Si compound and then reduced with _H2 gas, or a vacuum method in which vacuum evaporation is performed in a low-pressure argon gas stream. Examples include vapor deposition methods. Furthermore, single-crystal barium ferrite fine powder can also be used. The above-mentioned magnetic fine particles may be acicular or granular, and are selected depending on the intended use of the magnetic recording medium. In the method for producing a radiation-curable magnetic recording medium according to the present invention, it is also effective to add various antistatic agents, abrasives, etc. that are used in ordinary magnetic recording media to the binder depending on the purpose. be. The active energy rays used to cure the magnetic coating film containing the radiation-sensitive resin include:
An electron beam using an electron beam accelerator as a source is particularly effective for the following reasons. However, in addition to these, γ-rays using ^Co60 as a source, β-rays using ^Sr90 as a source, and
X-rays using radiation as a radiation source can also be used. In other words, when using an electron beam accelerator as a radiation source, it is necessary to control the absorbed dose, self-shield ionizing radiation for introduction into the manufacturing process line, ease of connection with process line equipment and sequence control, etc. It is advantageous in this respect. Conventionally, various types of electron accelerators have been put into practical use, such as a Kotscroft type, a Van de Graaff type, a resonant transformer type, an iron-core insulated transformer type, and a linear accelerator type, mainly due to the difference in the method of obtaining high voltage. However, when magnetic recording media are used for general purposes, most of them are thin magnetic films of 10 microns or less, and are usually used in the above accelerators.
High accelerating voltage over 1000KV is unnecessary,
An electron beam accelerator with a low accelerating voltage of 300KV or less is sufficient. In a low accelerating voltage accelerator, the cost of the system itself is reduced, but it is also advantageous in terms of the cost of shielding equipment for ionizing radiation. Table 1 shows the advantages of this shielding equipment cost.

[Table] As shown in Table 1, in electron accelerators of 300KV or less, leakage of X-rays is sufficiently prevented by covering the entire acceleration tube, including the electron beam irradiated area, with a lead plate of maximum 3 cm as a shielding material. can be shut off. Therefore, there is no need to separately provide an expensive electron beam irradiation chamber, and the system itself can be incorporated into a magnetic recording medium manufacturing line.
Curing can now be processed online. Examples of such specific systems include the low-voltage electron beam accelerator (Electro Curtain System) manufactured by Energy Sciences, Inc. (ESI) in the United States, the RPC electron accelerator (Broad Beam System), A self-closing scanning type low voltage type electron beam accelerator manufactured by West German Polymer Physics is suitable. When a 150 to 300 KV low voltage accelerator is used to cure the aforementioned binder coating containing a radiation-sensitive resin, if the absorbed dose exceeds 5 Mrad during high-temperature, high-humidity running durability, the head for audio and memory applications will fail. In video applications, the magnetic film may fall off, and the amount of similar adhesion to rotating cylinders increases, which is undesirable. On the other hand, 0.5~
At an absorbed dose of 5 Mrad, the electron beam polymerization and crosslinking density are appropriate, so the magnetic coating has a good balance of appropriate flexibility and rigidity, and the wear resistance between the magnetic layer and the head is also good. An excellent magnetic recording medium with no head adhesion or cylinder adhesion can be obtained. In addition, for radiation crosslinking, use _N2 gas or
It is important to irradiate the recording medium with radiation in an inert gas stream such as He gas. A coating film with a very high packing density of magnetic pigments, such as the magnetic coating film of a magnetic recording medium, is highly porous, so irradiating it with radiation in the air can cause crosslinking of the binder components. , O ₃ produced by radiation irradiation
Under the influence of these factors, radicals generated in the polymer are inhibited from effectively working for the crosslinking reaction. This effect affects the binder crosslinking not only on the surface of the magnetic layer but also on the inside of the coating film due to its porous nature.
Therefore, the atmosphere in the area to be irradiated with active energy rays should have an oxygen concentration of at most 1%, preferably
It is particularly important to maintain an atmosphere of inert gas such as N ₂ , He, Co ₂ or the like below 3000 ppm. A ball mill or the like is used as a dispersing machine. .
In addition to ball mills, various devices such as sand grind mills, roll mills, high-speed impeller dispersers, homogenizers, and ultrasonic dispersers can be used. Next, the content of the present invention will be explained in more detail with reference to Examples and Comparative Examples. <Example 1> Magnetic powder Co-adhered acicular γ-Fe ₂ O ₃ 100 parts by weight (major axis 0.4μ, single axis 0.05μ, Hc600Oe) Antistatic agent Carbon black 5 parts by weight (Mitsubishi Carbon Black, MA-600) ) α-Al ₂ O ₃ (0.5μ granules) 2 parts by weight Dispersant 3 parts by weight Soybean oil refined lecithin Solvent 100 parts by weight Methyl ethyl ketone/toluene (50/50) The above components were mixed in a ball mill for 3 hours,
The acicular magnetic iron oxide γ-Fe ₂ O ₃ is better wetted by the dispersant. Next, vinyl chloride-vinyl alcohol copolymer
15 parts by weight (degree of polymerization approximately 300) Acrylic double bond introduced polyether 15 parts by weight Urethane elastomer (solid content equivalent) Solvent Methyl ethyl ketone/toluene 200 parts by weight (50/50) Fatty acid ester Type X 2 parts by weight Fatty acid Type Y 1 weight Mix and dissolve the mixture well. This was put into the ball mill that had previously been treated with magnetic powder, and again
Mix and disperse for 42 hours. The magnetic paint obtained in this way was applied onto a 15μm polyester film, and a permanent magnet (1600μm) was applied.
After drying the solvent using an infrared lamp or hot air and subjecting it to surface smoothing treatment, an accelerating voltage of 150 KV and electrode current was applied using an ESI electrocurtain type electron beam accelerator.
Under the conditions of 10mA and total irradiance of 0.5Mrad to 8Mrad,
Electron beam irradiation was performed in an N ₂ gas atmosphere at a residual O ₂ concentration of around 500 ppm to perform polymerization, drying, and curing reactions of the magnetic coating. The magnetic recording medium thus obtained was cut into 1/2 inch width pieces to obtain video tapes. In this case, the fatty acid ester species was X species, the fatty acid species was Y species, and experiments were conducted with various X and Y species selected. With a wide range of combinations containing fatty acids of 0.degree. C., videotapes were obtained that were free of bleed over the temperature range of 0.degree. to 60.degree. C. and had stable still images for long periods of time. This will be explained in detail next. First, a still image reproduction experiment was carried out in an environment of -10°C by adding fatty acid ester and fatty acid alone, and a runnability test was conducted based on the leaching phenomenon after being taken out at 60°C and 60% high temperature and high humidity. When fatty acid ester was added alone, 60℃, 60℃
%, in a running test under high temperature and high humidity, the running stopped immediately, and when fatty acid was added alone, -10
Still image playback time was short, less than 15 minutes in an environment of ℃. Next, regarding fatty acid ester X type and fatty acid Y type, fatty acid ester type X is (a) caprylic acid ester C ₇ H ₁₅ COOC ₄ H ₉ (b) capric acid ester C ₉ H ₁₉ COOC ₄ H ₉ (c) myristic acid Ester C ₁₃ H ₂₇ COOC ₄ H ₉ (d) Stearic acid ester C ₁₈ H ₃₇ COOC ₄ H ₉ Fatty acid type Y (1) Caprylic acid Melting point 17℃ (2) Capric acid Melting point 32℃ (3) Myristic acid Melting point 54 (4) Stearic acid, melting point: 69°C (5) Behenic acid, melting point: 81°C (6) Cerotic acid, melting point: 88°C, and runability tests were conducted on each combination of Types X and Y. The results are shown in FIG. Figure 1 shows the EIAJ standard open reel VTR after storing the videotape for 40 hours at 60°C and 60% high temperature and humidity.
(NV-3120, manufactured by Matsushita Electric), and a tension analyzer model IVA-500 manufactured by Japan Automatic Control Co., Ltd. was set between the head drum and the pinch roller, and the running performance against running time was investigated. 1st
In the figure, fatty acid ester type X is taken on the horizontal axis,
The vertical axis shows the friction caused by the VTR with the fatty acid type Y as a parameter. As is clear from Figure 1, fatty acid ester
When a cabrylic acid ester (a) having an alkyl group having 8 carbon atoms is used as a seed, the running friction becomes so large that the running friction does not run at all from the beginning. Among fatty acids type Y, caprylic acid (1) has melting points of 17°C and 88°C.
Similar results were also obtained with cerotinic acid (6). When we examined these non-running samples, we found that the paint film was sticky. On the other hand, when capric acid ester (b) to stearic acid ester (d) having an alkyl group having 10 to 19 carbon atoms are used, fatty acid Y with a melting point of 32 to 81℃ is used.
Depending on the combination of species, the running friction will be a small value of about 100 to 170, resulting in very good running performance. Next, in order to compare the radiation-curable magnetic recording medium obtained according to the present invention with a thermosetting type,
A sample of a thermosetting magnetic recording medium was manufactured according to the following comparative example. <Comparative example> Magnetic powder Co-adhered acicular γ-Fe ₂ O ₃ 120 parts (long axis 0.4 μ, single axis 0.05 μ, Hc600 Oe) Antistatic agent Carbon black 5 parts (Mitsubishi Carbon Black, MA-600) α -Al ₂ O ₃ (0.5μ granules) 2 parts Dispersant Soybean oil refined lecithin 3 parts Solvent Methyl ethyl ketone/toluene 100 parts (50/50) The above components were mixed in a ball mill for 3 hours,
The acicular magnetic iron oxide γ-Fe ₂ O ₃ is better wetted by the dispersant. Next, 15 parts of vinyl chloride-vinyl acetate copolymer (VAGH manufactured by Union Carbide Co.) 15 parts of thermoplastic urethane resin (Nituporan 3032 manufactured by Nippon Polyurethane Co.) Solvent 200 parts of methyl ethyl ketone/toluene (50/50) Fatty acid ester Mix and dissolve a mixture of 2 parts of type X and 1 part of fatty acid type Y. In this case, fatty acid ester X type and fatty acid Y type are variously selected according to Example 1. These were placed in the ball mill that had previously been treated with magnetic powder, and mixed and dispersed again for 42 hours. After dispersion, an isocyanate compound (manufactured by Bayern AG,
5 parts (in terms of solid content) of Desmodyur L) were added to the above ball milled paint and mixed for 20 minutes. The magnetic paint obtained in this way was applied onto a 15μm polyester film, and a permanent magnet (1600μm) was applied.
After drying the solvent with an infrared lamp or hot air, a surface smoothing treatment was performed, and after this, the film was kept in an open state at 80°C for 48 hours to promote the crosslinking reaction with an isocyanate compound. Cut the resulting tape into 1/2 inch wide pieces.
Got the videotape. FIG. 2 shows the running performance test results of the above comparative example.
The test method, graph axes, parameters, etc. are the same as in the case of FIG. As is clear from Fig. 2, in the case of thermosetting type,
The combination of fatty acid esters b to d, which showed good running properties in the case of radiation curing type, with capric acid 2 and behenic acid 5, results in extremely high running friction.
It hasn't run at all since the beginning. As fatty acid type Y, the combination with myristic acid 3 and behenic acid 4 is only barely practical. That is, in the case of a thermosetting type, the range of application of additives is narrower than in the radiation curing type according to the present invention. <Example 2> Fe alloy acicular magnetic powder 120 parts by weight (long axis 0.3 μm, short axis 0.04 μm, Hc 1100 Oe) Dispersant oleic acid 2 parts by weight Solvent methyl ethyl ketone/toluene 100 parts by weight (50/50) Above composition Mix the ingredients in a high-power mixer for 3 hours,
Wet the magnetic alloy fine powder well with the dispersant.
Next, 18 parts by weight of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., BL3) (solid content conversion) Acetyl group 5 mol% Butyral group 40 mol% Formal group 20 mol% Hydroxyl group 35 mol% Degree of polymerization approximately 300 Acrylic double bond Introduced urethane Elastomer 12 parts by weight (solid content equivalent) Solvent Methyl ethyl ketone/toluene 200 parts by weight (50/50) Butyl myristate 3 parts by weight Capric acid 1 part by weight of the mixture was well dissolved. This was mixed with the previously treated magnetic powder using a high-speed mixer for 1 hour and 10 minutes, and mixed and dispersed using a sand grind mill for 4 hours. The magnetic paint thus obtained was applied onto a 15 μm polyester film, subjected to necessary treatments such as magnetic field orientation, solvent drying, and surface smoothing treatment, and then coated using an electrocurtain type electron beam accelerator. , acceleration voltage 150KeV, electrode current 10mA,
The coating film was cured by irradiation with an electron beam in an N ₂ gas atmosphere at an absorbed dose of 5 Mrad. The resulting tape was cut into 1/2 inch width to create a videotape. When this was evaluated in the same manner as in Example 1, similar results were obtained. <Example 3> Fe alloy acicular magnetic powder 120 parts by weight (major axis 0.3 μm, short axis 0.04 μm, Hc1100 Oe) Carbon black 5 parts by weight (Mitsubishi Carbon Black MA-600) α-Al ₂ O ₃ (0.5 μm Granular) 2 parts by weight Dispersant Oleic acid 2 parts by weight Solvent Methyl ethyl ketone/toluene 100 parts by weight (50/50) The above powder composition was mixed for 3 hours to thoroughly disperse the magnetic alloy fine powder in the dispersant. Next, 15 parts by weight of saturated polyester resin (manufactured by Dynamite Nobel, L-411) 15 parts by weight of acrylic double bond-introduced polycabrolactam urethane prepolymer Solvent 200 parts by weight of methyl ethyl ketone/toluene (50/50) Amyl palmitate A mixture of 1.5 parts by weight and 0.5 parts by weight of myristic acid was mixed with the magnetically treated product for 1 hour and 10 minutes using a high-speed mixer, and then mixed using a sand mill for 4 hours.
We performed time dispersion. Thereafter, in accordance with the same method as in Examples 1 and 2, treatments such as formation of a magnetic coating film on the supporting substrate, radiation curing treatment, and tape formation were performed to prepare similar video tapes. When the videotape thus obtained was subjected to the same evaluation test as in Examples 1 and 2, similar results were obtained. <Effects of the Invention> As described above, according to the present invention, the following effects can be obtained. (a) The binder is made of a radiation-sensitive resin, which is hardened by irradiation with radiation after calendering and before winding, so it is possible to produce a magnetic recording medium that does not block additives in the coating and do not tighten during winding. can do. (b) Since blocking and tightening are eliminated, it is possible to provide a method for manufacturing a magnetic recording medium in which the usable range of additives is expanded compared to the case of conventional thermosetting binders. (c) Since the binder is a radiation-sensitive resin, there is no need for a thermosetting process that was necessary for conventional thermosetting binders, and it is possible to provide a method for manufacturing magnetic recording media in which restrictions on additive types are further relaxed. . (d) Since the binder is a radiation-sensitive resin and has a magnetic recording layer containing a fatty acid ester and a fatty acid having an alkyl group, it can be used at rest under a wide range of temperature conditions, for example from 0 to 60°C. It is possible to produce a magnetic recording medium that has stable images for a long time, does not bleed out, has extremely excellent wear resistance and lubricity, and is suitable for video tapes. The present invention can be widely applied not only to magnetic tapes for recording purposes but also to magnetic recording media having a structure in which a magnetic recording layer made of a binder and a powder magnetic material is formed on a non-magnetic substrate.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the results of a runnability test of a magnetic recording medium obtained by the manufacturing method according to the present invention, and FIG.
The figure shows the running performance test results of a thermosetting magnetic recording medium obtained by a conventional manufacturing method.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a magnetic recording medium having a magnetic recording layer in which a binder contains a fatty acid ester and a fatty acid having an alkyl group, wherein the binder is made of a radiation-sensitive resin and is rolled up after calendering. A method for manufacturing a magnetic recording medium, which comprises first curing the medium by irradiating it with radiation. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the fatty acid ester has an alkyl group having 9 or more carbon atoms. 3. The method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the fatty acid has a melting point of 32 to 81°C. 4. According to claim 1, 2 or 3, the magnetic recording layer contains at least one kind of magnetic particles selected from cobalt-modified magnetic iron oxide and alloy magnetic particles. A method for manufacturing a magnetic recording medium. 5. The method for manufacturing a magnetic recording medium according to claim 1, 2, 3, or 4, wherein the binder is irradiated with radiation in an inert gas stream. .