JPH0315257B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium that has excellent wear resistance and lubricity by adding a certain amount of fatty acid to a binder that is crosslinked and polymerized by radiation. . Traditionally, videotape, computer tape,
Magnetic recording media such as audio tapes and floppy disks generally use a thermosetting binder to fix magnetic powder processed materials to the tape, and a crosslinking agent typified by a polyvalent isocyanate group-containing compound.
A three-dimensional network structure is formed between the binders through a chemical reaction with reactive functional groups such as hydroxyl groups and amino groups in the binder, and by adding a lubricant to this, the durability and runnability of magnetic recording media are improved. , aiming to improve environmental reliability. For this magnetic recording medium, known lubricants include silicone oil, fatty acids, fatty acid esters, molybdenum disulfide, and graphite.
In Japanese Patent Publication No. 51-39081, the applicant proposed that a fatty acid ester having an RCO group having 10 to 16 carbon atoms (where R=CnH _2o+1 ) and a fatty acid with a melting point of 44 to 70°C be contained to have a synergistic effect. According to
It has been disclosed that extremely excellent wear resistance and lubricity can be obtained under a wide range of operating temperature conditions of 0 to 40°C, and it is currently widely used in conventional thermosetting binders. However, in contrast to thermosetting binders, so-called radiation-curable binders, which are crosslinked and polymerized by radiation, have been developed. Thermosetting binders have not yet begun to thermoset when the tape is rolled up after being calendered through the coating and drying process, so the coating film is not strong and the additives in the coating film may bloom. ,
In addition, there are restrictions on the types of additives because blocking and tightness occur due to thermal curing. On the other hand, when a radiation-curable binder is used, the resin is hardened by radiation irradiation after calendering and before the tape is wound up, so the coating film becomes strong and when the tape is wound up, , there is no blocking of additives in the coating film, and a wider range of additives can be used than in the case of thermosetting binders. The inventors have focused on the durability and runnability of magnetic recording media, as well as their environmental reliability, such as the fact that still images remain stable for long periods of time and do not bleed, even under humid conditions and a wide range of temperatures from 0 to 60 degrees Celsius. For radiation curable binders as above to obtain an improvement in
As a result of intensive research focusing on the fact that a wide range of additives can be used, the inventors discovered that the mixture of fatty acids described below can be suitable for the purpose, and based on this knowledge, the present invention was made. That is, the present invention provides a binder that is crosslinked and polymerized by radiation, and that has 10 or more carbon atoms.
Fatty acid ester with RCO group and melting point 32-81℃
The present invention provides a magnetic recording medium containing at least one of the above fatty acids and a fatty acid having one or more polymerizable unsaturated double bonds and having a melting point of 16 to 81°C. 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 exposed to radiation and others that cause cross-linking between molecules. Examples of the latter include polyethylene, polypropylene, polystinone, polyacrylic acid ester, polyacrylamide, and polyvinyl chloride. , polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, polyacrolein, etc., and such crosslinked polymers are used as they are in the magnetic layer. Furthermore, the radiation-sensitive resin used in the present invention can also be prepared by radiation-sensitizing a thermoplastic resin, which is preferable from the viewpoint of curing speed and the like. Specific examples of radiation-sensitive modification include acrylic double bonds such as those in acrylic acid, methacrylic acid, or their ester compounds, which exhibit radically polymerizable unsaturated double bonds, and allylic double bonds such as diallyl phthalate. , 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. Other unsaturated double bonds that can be crosslinked and polymerized by radiation irradiation can be used. Specific examples include: () 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-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, and trade names include, for example, VROH, VYNC, VYEGX made by UCC, and VERR made by UCC. The above-mentioned copolymer is subjected to radiation sensitivity modification by introducing an acrylic double bond, a maleic acid double bond, and an allylic double bond by a method described later. () Saturated polyester resin Phthalic acid, isophthalic residue, terephthalic acid, maleic acid, maleic acid derivatives, saturated polybasic acids such as 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, glycerin, neopentyl glycol,
Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as 1,4 cyclohexanedimethanol, or resins obtained by modifying these polyester resins with SO ₃ Na, etc. (Vylon 53S). These are also subjected to radiation sensitivity modification using the method described later. () 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 (), containing a radiation-curable unsaturated double bond in which part of the polybasic acid is maleic acid. Mention may be made of unsaturated polyester resins, prepolymers, and oligomers. Examples of the polybasic acid and polyhydric alcohol components of the saturated polyester resin include the compounds listed in item (), and examples of the radiation-curable unsaturated double bond include maleic acid and fumaric acid. 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
That is, after dehydration or dealcoholization in the presence of a catalyst at 180 to 200° C. in a nitrogen atmosphere, the temperature is raised to 240 to 280° C., and a polyester resin can be obtained by condensation reaction under reduced pressure of 0.5 to 1 mmHg. The content of maleic acid, fumaric acid, etc. is preferably 1 to 40 mol% in the acid component due to crosslinking during manufacturing, radiation curability, etc.
It is 10 to 30 mol%. () Polyvinyl alcohol resin Polyvinyl alcohol, buteral resin, acetal resin, formal resin, and copolymers of these components. These resins are also subjected to radiation sensitization modification of the hydroxyl groups contained therein by the method described later. () Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A, epichlorohydrin, and methyl epichlorohydrin - manufactured by Ciel Chemical (Epicote 152, 154, 828,
1001, 1004, 1007) Made by Dow Chemical (DEN431,
DER732, DER511, DER331) made by Dainippon Ink (Epiclon 400, Epiclon-800), and phenoxy resins made by UCC (PKHA, PKHC, PKHH), which are high polymerization resins of the above epoxy, and brominated bisphenol A and epichlorohydrin. Copolymer, manufactured by Dainippon Ink and Chemicals (Epicron 145,
152, 153, 1120) etc. These resins are also subjected to radiation sensitivity modification using the epoxy groups contained therein. () 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 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-sensitive modification include polyfunctional polyester resins, polyether ester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiroacetal resins, and hydroxyl resins. at least one acrylic ester and methacrylic ester containing
Acrylic resins containing more than one species as a polymerization component are also effective. Other binder components that can be used include:
Examples of monomers include 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. By blending a polyhydric alcohol and a polyhydric carboxylic acid as necessary, products with various molecular weights can be produced. The above information is only a partial list of the radiation sensitive resins. Further, by blending a thermoplastic elastomer or a prepolymer with the radiation-sensitive modified thermoplastic resin, an even tougher coating film can be obtained. In addition, it is even more effective if these elastomers or prepolymers are similarly modified to be radiation sensitive. Examples of elastomers or prepolymers that can be combined with the radiation-sensitive modified thermoplastic resin are listed below. () Polyurethane elastomers, prepolymers and telomers Polyurethane elastomers have abrasion resistance,
It is particularly effective in adhesion to PET film. Examples of such urethane compounds include 2,4 toluene diisocyanate, 2,6 toluene diisocyanate, and 1,3 toluene diisocyanate.
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' biphnylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, Desmodyur L, Desmodyur Various polyvalent isocyanates such as N and linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin,
Trimethylolpropane, 1,4 butanediol, 1,6 hexanediol, pentaerythritol, sorbitol, neopentyl glycol,
Linear (by condensation polymerization of a polyhydric alcohol such as 1,4 cyclohexanedimethanol with a saturated polybasic acid such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, succinic acid, adipic acid, and sebacic acid) Polyurethane elastomers made of condensation products of various polyesters such as saturated polyethers (polyethylene glycol, polypropylene glycol, polytetraethylene glycol), caprolactam, hydroxyl-containing acrylic esters, hydroxyl-containing methacrylic esters, etc.
Prepolymers and telomers are effective. These elastomers may be combined as they are with various radiation-sensitive thermoplastics, but monomers having an acrylic double bond or allylic double bond that reacts with the terminal isocyanate group or hydroxyl group of the urethane elastomer may also be used. It is very effective to make it radiosensitive by reacting with the body. () Acrylonitrile-butadiene copolymer elastomer Elastomers such as an acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group, commercially available as PolyBD Liquid Resin manufactured by Sinclair Petrochemical Co., Ltd., or Hiker 1432J manufactured by Nippon Zeon Co., Ltd., are particularly suitable for butadiene. It is suitable as an elastomer component whose double bond is crosslinked and polymerized by generating radicals by radiation. () Polybutadiene elastomer A prepolymer having a low molecular weight terminal hydroxyl group, such as PolyBD Liquid Resin R-15 manufactured by Sinclair Petrochemical Co., is particularly suitable from the viewpoint of compatibility with thermoplastic plastics. Since the R-15 prepolymer has a hydroxyl group at the end of the molecule, it is possible to increase radiation sensitivity by adding an acrylic unsaturated double bond to the end of the molecule.
It is further advantageous as a binder. In addition, polybutadiene cyclized products manufactured by Japan Synthetic Rubber
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 using radicals of unsaturated bonds inherent in polybutadiene. Other suitable thermoplastic elastomer and prepolymer systems include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, isoprene rubber, and its cyclized products (manufactured by Japan Synthetic Rubber Co., Ltd.).
CIR701), epoxy-modified rubber, internally plasticized saturated linear polyester (Toyobo Vylon #300), and other elastomers can also be effectively used by applying the radiation-sensitive modification treatment described below. When the present invention uses a solvent, acetone,
Methyl ethyl ketone, methyl isobutyl ketone,
Ketones such as cyclohexanone, alcohols that cannot be used with isocyanate-based thermosetting binders such as methanol, ethanol, isopropanol, butanol, and those with ether bonds such as tetrahydrofuran and dioxane, dimethylformamide, vinylpyrrolidone, nitropropane, etc. A solvent, an aromatic hydrocarbon diluent or solvent such as toluene or xylene is used. The substrate used for coating is polyethylene terephthalate film, which is currently widely used as a substrate for magnetic recording media, and for applications that require further heat resistance, polyimide film, polyamide-imide film, etc. are used, especially polyester In the case of thin film, uniaxial or biaxial stretching is often applied to the film. The magnetic fine powder utilized in the present invention is γ-
Fe ₂ O ₃ , Fe ₃ O ₄ , Co-doped γ-Fe ₂ O ₃ , Co-doped γ-Fe ₂ O ₃ -Fe ₃ O ₄ solid solution, CrO ₂ , Co-based compound-coated γ-Fe ₂ O ₃ , Co-based compound coated Fe ₃ O ₄ (γ-
Also includes intermediate oxidation states with Fe ₂ O ₃ . Also, Co here
The system compounds include cobalt oxide, cobalt hydroxide,
Co, Fe-Co, Fe-Co-Ni, Co-
The main component is a ferromagnetic metal element such as Ni. The manufacturing method is a wet reduction method using a reducing agent such as _NaBH4 , a dry reduction method using _H2 gas after treating the iron oxide surface with a Si compound, or a vacuum evaporation method in a low-pressure argon gas stream. Examples include methods for obtaining such information. Furthermore, single crystal barium ferrite fine powder can also be used. The above-mentioned magnetic particles are in the form of needles or particles, and are selected depending on the intended use as a magnetic recording medium. Regarding the binder for radiation-curable magnetic recording media according to the present invention, various antistatic agents, dispersants, abrasives, etc. that are commonly used in the application may be added in addition to the additives of the present invention depending on the application. It is valid. As the active energy ray used for crosslinking the magnetic coating film of the present invention, an electron beam using an electron beam accelerator as a ray source is particularly advantageous for the reasons described below. However, in addition to these, γ-rays using Co ⁶⁰ as a source, β-rays using Sr ⁹⁰ as a source, and X-rays using an X-ray generator as a source are also used. As an irradiation source, it is recommended to use an electron beam accelerator from the viewpoints of controlling the absorbed dose, self-shielding ionizing radiation for introduction into the manufacturing process line, and ease of connection with sequence control with various process line equipment. It's advantageous. Conventional electron beam accelerators are Kotscroft type, Van de Graaff type, commutative transformer type, iron core isolation transformer type,
Various types of accelerators, such as linear accelerator types, have been put into practical use, mainly due to differences in the methods of obtaining high voltage. However, when magnetic recording media are used for general purposes, most of them have a thin magnetic film thickness 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 further advantageous in terms of equipment costs for shielding ionizing radiation. Next, Table 1 shows the advantages of shielding equipment costs.
Shown below.

[Table] As shown in Table 1, in electron beam accelerators of 300 KV or less, lead plates (maximum 3 cm) are used as shielding materials.
By using this to cover the entire accelerating tube surrounding the electron beam irradiated area, leakage of X-rays can be sufficiently blocked. This eliminates the need for a separate, expensive electron beam irradiation room, and the system itself can be integrated into a magnetic recording media manufacturing line.For example, magnetic tapes and magnetic sheets can be dried and cured using electron beams online. It becomes possible to do so. Specific examples of such systems include the low-voltage electron beam accelerator (Electro Curtain System) manufactured by Energy Sciences (ESI) in the United States, the RPC electron beam accelerator (Broad Beam System), and the West German Polymer Physics. A self-shielding scanning type low-voltage electron beam accelerator manufactured by Co., Ltd. is suitable. When the aforementioned binder coating is cured using a 150-300KV low voltage accelerator,
In terms of high-temperature, high-humidity running durability, the absorbed dose
If it exceeds 5 Mrad, it is undesirable because the magnetic film may fall off from the head in audio and memory applications, and similar adhesion to the rotating cylinder increases in video applications. On the other hand, at an absorbed dose of 0.5 to 5 Mrad, the electron beam polymerization and crosslinking density are appropriate, so the magnetic coating has an appropriate balance of flexibility and rigidity, and the abrasion resistance between the magnetic layer heads is improved. It becomes an excellent magnetic recording medium with no adhesion or cylinder adhesion. In addition, during radiation crosslinking, it is important to irradiate the recording medium with radiation in an inert gas stream such as N ₂ gas or He gas, and coatings with a high degree of magnetic pigment filling such as magnetic coatings are extremely Due to its porous nature, irradiation with radiation in the air may occur due to radiation irradiation during crosslinking of the binder component.
Radicals generated in the polymer due to the influence of O ₃ etc. are inhibited from effectively working on the crosslinking reaction. Since the surface of the magnetic layer is naturally porous, the inside of the coating film is also affected by the binder's crosslinking inhibition. Therefore, the atmosphere in the area where active energy rays are irradiated should preferably have a maximum oxygen concentration of 1%.
It is important to maintain an atmosphere of inert gases such as N ₂ , He, and CO ₂ at 3000 ppm or less. As a dispersing machine, a ball mill or the like is used for sufficient kneading and dispersion. In addition to ball mills, various devices such as sound grind mills, roll mills, high-speed impeller dispersers, homogenizers, and ultrasonic dispersers can be used. The polymerizable unsaturated double bond used in the present invention is 1
If the fatty acid has -CH=
CH ₂ , −CH ₂ −CH=CH ₂ , −CONH−CH=CH ₂
etc. is desirable. Next, the present invention will be explained based on examples. Example 1 Cobalt-coated acicular γ-Fe ₂ O ₃ (long axis 0.4μ, short axis
0.05μ, HC 600Oe) 120 parts by weight Carbon Black (for antistatic use, Mitsubishi Carbon Black MA-600) 5 parts by weight α-Al ₂ O ₃ powder (0.5μ powder) 2 parts by weight Dispersant (refined lecithin in soybean oil) 3 parts by weight Partial solvent (methyl ethyl ketone/toluene, 50/50)
100 parts by weight The above ingredients were mixed in a ball mill for 3 hours,
The acicular magnetic iron oxide is better wetted by the dispersant. Next, 15 parts by weight of vinyl chloride vinyl alcohol copolymer (degree of polymerization: approx. 300) 15 parts by weight of acrylic double bond-introduced polyether urethane elastomer (calculated as solid content) Solvent (methyl ethyl ketone/toluene, 50/50)
A mixture of 200 parts by weight of vinyl fatty acid (x), 2 parts by weight of fatty acid (y) and 1 part by weight is thoroughly mixed and dissolved. This was placed in the ball mill that had been treated with the magnetic powder above and mixed and dispersed again for 42 hours. The magnetic paint obtained in this way was applied onto a 15μ polyester film, oriented on a permanent magnet (1600 Gauss), dried the solvent with an infrared lamp or hot air, and then subjected to surface smoothing treatment. Acceleration voltage 150KV, electrode current 10mA, total irradiation dose using curtain type electron beam accelerator
Polymerization drying and curing reactions of the magnetic coating were carried out by electron beam irradiation under conditions of 0.5 Mrad to 8 Mrad under N ₂ atmosphere and residual O ₂ concentration of around 500 ppm. The obtained tape was cut into 1/2 inch width to obtain a videotape. An experiment was carried out with the fatty acid vinyl type x and the fatty acid type y, and a wide range of combinations containing fatty acids with a melting point of 16 to 81 °C with polymerizable unsaturated double bonds and fatty acids with a melting point of 32 to 81 °C were found to be 0. This will be explained because a stable still image was obtained with no oozing in the temperature range of ~60°C. We were conducting a still image reproduction experiment in an environment of 10℃. After being taken out at 60°C and 80% high temperature and high humidity, a runnability test was conducted based on the oozing phenomenon. First, we conducted tests on the effects of fatty acid esters and fatty acids alone, and found that fatty acid esters alone were
%, the running stopped immediately, and with fatty acids alone, the still image playback time at 10°C was less than 15 minutes. So, regarding various x and y,

[Table] Figure 1 shows the results of an experiment where x is a fatty acid vinyl composed of the above fatty acids and y is the corresponding fatty acid. As can be seen from Figure 1, among various combinations of fatty acid vinyls with a melting point of -3.4°C, the stored samples did not run at all from the initial stage, and fatty acids with a melting point of 17°C showed similar results. When these samples were examined, it was found that the non-running samples had a sticky coating. Figure 1 shows the tape after being stored at 60°C, 80% for 40 hours, and then run on an EIAJ standard open reel VTR (NV-3120 manufactured by Matsushita Electric) at room temperature. A tension analyzer model IVA-500 made by Kansai was set up and the running time was investigated. Example 2 A similar experiment was carried out in Example 1 using 2 parts by weight of fatty acid vinyl (x) and fatty acid ester (y) and 1 part by weight, and a fatty acid ester having an RCO group having 10 or more carbon atoms and a melting point of 16 to 81°C were obtained. It was found that a combination containing a fatty acid having one or more polymerizable unsaturated double bonds is good. These results are shown in FIG. When compared with the thermosetting type below, it can be seen that it is superior to the thermosetting type. Comparative example Cobalt-coated acicular γ-Fe ₂ O ₃ 120 parts (major axis 0.4μ short axis 0.05μHc600 Oe) Carbon black 5 parts (Mitsubishi Carbon Black MA-600 for antistatic use) α-Al ₂ O ₃ powder (0.5 μ granules) 2 parts powder (soybean oil refined lecithin) 3 parts solvent (methyl ethyl ketone/toluene, 50/50)
100 parts The above composition was mixed in a ball mill for 3 hours,
The acicular magnetic iron oxide 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 Nitsuporan 3022 manufactured by Nippon Polyurethane Co. Solvent (methyl ethyl ketone/toluene, 50/50)
Mix and dissolve a mixture of 200 parts fatty acid ester (x), 2 parts fatty acid, and 1 part. This was put into the ball mill that had undergone the magnetic powder treatment earlier, and then
Disperse for 42 hours. After dispersion, an isocyanate compound that can react with and crosslink with the functional groups, mainly hydroxyl groups, of the binder in the magnetic paint (Desmodyur L manufactured by Bayer AG)
Add 5 parts (solid content equivalent) to the above ball mill preparation paint.
Mixing was performed for 20 minutes. The magnetic paint was applied onto a 15μ polyester film, oriented on a permanent magnet (1600 gauss), the solvent was dried using an infrared lamp or hot air, the surface was smoothed, and the film was rolled in an oven maintained at 80℃. was maintained for 48 hours to promote the crosslinking reaction by isocyanate. The obtained tape was cut into 1/2 inch width to obtain a videotape. Example 3 Compared to Example 1, in which (x) was a fatty acid ester, as shown in Figure 3, the polymerizable unsaturated double bond was polymerized by radiation, making it applicable to a wider range. The selection range of additives has become wider. Since the lubricant used in the present invention is chemically bonded to the binder by radiation, a lubricant film is efficiently formed. It reacts with the binder etc. inside, giving the coating a complex crosslinked structure. Therefore, there is little change in friction even with repeated running, and its change over time is also small. Example 4 Fe alloy acicular magnetic powder (long axis 0.3μ, short axis 0.04μ, Hc
1100 Oe) 120 parts by weight Dispersant (oleic acid) 2 parts by weight Solvent (methyl ethyl ketone/toluene, 50 parts by weight)
50) 100 parts by weight The above composition was mixed for 3 hours with a powerful mixer,
Wet the magnetic alloy fine powder well with the dispersant. Next, polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd.)
BL3) (acetyl group 5 mol%, butyral group 40 mol%,
20 mol% formal groups, 35 mol% hydroxyl groups, degree of polymerization approx. 300) (solid content equivalent) 18 parts by weight Acrylic double bond-introduced urethane elastomer (solid content equivalent) 12 parts by weight Solvent (methyl ethyl ketone/toluene, 50/50)
A mixture of 200 parts by weight of allyl oleate, 3 parts by weight of capric acid, and 2 parts by weight is thoroughly mixed and dissolved. This was sufficiently mixed with the previously treated magnetic powder using a high-speed mixer for 1 hour, and mixed and dispersed using a sand grind mill for 4 hours. The magnetic paint thus obtained was applied onto a 15μ polyester film, subjected to magnetic field orientation, solvent drying, and surface smoothing treatment.
The coating film was cured by irradiation with an electron beam in an N ₂ gas atmosphere under the conditions of an electrode current of 10 mA and an absorbed dose of 5 Mrad. The obtained tape was cut into 1/2 inch width to obtain a videotape. When this was evaluated in the same manner as in Example 1, no problems were found. Example 5 Fe alloy acicular magnetic powder 120 parts by weight (long axis 0.3μ, short axis 0.4μ, Hc1100 Oe) Carbon black (Mitsubishi Carbon Black MA-
600) 5 parts by weight α-Al ₂ O ₃ (0.5μ granules) 2 parts by weight Dispersant (oleic acid) 2 parts by weight Solvent (methyl ethyl ketone/toluene, 50/50)
100 parts by weight The above composition is mixed for 3 hours to thoroughly wet the magnetic alloy fine powder with the dispersant. Next, 15 parts by weight of saturated polyester resin (L-411 manufactured by Dynamite Nobel) 15 parts by weight of polycaprolactam urethane prepolymer with acrylic double bond introduced Solvent (methyl ethyl ketone/toluene, 50/50)
A mixture of 200 parts by weight of vinyl palmitate, 1.5 parts by weight, and 0.5 parts by weight of myristic acid was mixed with the previously treated magnetic powder for 1 hour and 10 minutes using a high-speed mixer, and then dispersed for 4 hours using a sand mill. A videotape was obtained from this in the same manner as in Example 1.
When this tape was evaluated, no problems were found. As mentioned above, in the interface that crosslinks and polymerizes upon radiation, (a) a fatty acid ester having an RCO group having 10 or more carbon atoms and a fatty acid having a melting point of 16 to 81°C and having one or more polymerizable unsaturated double bonds; (b) Contains a fatty acid with a melting point of 16-81°C and one or more polymerizable unsaturated double bonds, and (a) contains a fatty acid with a melting point of 32-81°C, there is little change in friction due to repeated running. However, the friction shows a higher value than the initial value. There is no problem because the frictional change is small, but by incorporating fatty acids with a melting point of 32 to 81°C, the friction is lower than the initial value and the frictional change is small. Although (a) has no practical problems, it is more preferable to add a fatty acid. As described above, in the magnetic recording medium of the present invention, (a) a fatty acid ester having an RCO group having 10 or more carbon atoms and a fatty acid having a melting point of 16 to 81°C are combined with a polymerizable unsaturated double bond in a radiation-curable binder; Contains one or more fatty acids with a melting point of 16 to 81°C (b) Contains fatty acids with one or more polymerizable unsaturated double bonds and a fatty acid with a melting point of 32 to 81°C (c) (a) and Contains (b) A magnetic recording medium characterized by containing one of (a), (b), and (c). To show the change in friction,

[Table] Although the present invention has been variously explained above using preferred embodiments, the present invention is not limited to these embodiments, and many modifications can be made without departing from the spirit of the invention. Of course.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of a running test using various fatty acid vinyls, and FIGS. 2 and 3 are graphs showing the relationship between the mixture of various fatty acids and various fatty acid esters and the results of the running test.

Claims (1)

[Claims] 1. A binder that is crosslinked and polymerized by radiation, at least one of a fatty acid ester having an RCO group having 10 or more carbon atoms and a fatty acid with a melting point of 32 to 81°C, and a polymerizable unsaturated A magnetic recording medium containing a fatty acid having one or more double bonds and a melting point of 16 to 81°C. 2. The magnetic recording medium according to claim 1, wherein the radiation irradiation is performed in an inert gas stream.