JPH0413765B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a magnetic recording medium, which comprises coating a non-magnetic support with a magnetic paint and forming a magnetic layer thereon. More specifically, the present invention features a thermosetting and radiation curable binder and a curing method thereof, which provide a magnetic recording medium with excellent coating film properties such as durability, oil resistance, and heat resistance of the magnetic layer. It is something that you have. In recent years, there has been an increasing demand for improvements in the strength of magnetic tape coatings, and thermosetting resins that are crosslinked and cured using polyfunctional isocyanates have been used. However, since these binders have a high proportion of isocyanate compounds, the pot life is short, the storage stability of the paint is reduced, and it is necessary to perform surface treatment and other steps after coating in a short period of time. In addition, long-time heating is required for crosslinking and curing, and during this time, blocking occurs, the surface roughness of the back surface of the substrate changes, etc., and it is difficult to obtain a smooth surface of the magnetic layer. In recent years, magnetic paints using radiation-curable resins have been proposed as a way to improve these drawbacks, and with pot life and online curing,
Rolling up after curing has become possible, which has improved the surface roughness transition, but many radiation-curable resins use low molecular weight components, and it is not possible to achieve a sufficient high molecular weight by curing with short-term radiation irradiation. Also, since the crosslinking density is high, the coating film height is good, but the flexibility is poor and it is difficult to obtain a magnetic recording medium with excellent wear resistance. The present invention was achieved as a result of intensive research in order to improve these drawbacks, and by utilizing the rapid curing properties of radiation-curable resin and the effect of increasing the molecular weight through isocyanate crosslinking, it has achieved excellent physical properties of the coating film. discovered that magnetic recording media could be obtained,
This completes the present invention. That is, the present invention provides a magnetic recording medium in which a magnetic coating mainly consisting of ferromagnetic fine powder, a binder, and a solvent is coated on a non-magnetic support, dried, and then cross-linked and cured to form a magnetic recording layer on the non-magnetic support. In the production method, the binder includes (1) (a) monomers, oligomers, and polymers containing at least one acrylic unsaturated double bond in the molecule and containing no active hydrogen group capable of reacting as an isocyanate group; , and (b) one or more monomers, oligomers, and polymers containing at least one acrylic unsaturated double bond in the molecule and an active hydrogen group capable of reacting with an isocyanate group.
99.5% by weight, (2) 80% by weight of one or more compounds, oligomers, and polymers containing at least one active hydrogen that can react with isocyanate groups in the molecule.
and (3) 0.5 to 25% by weight of an isocyanate compound having two or more isocyanate groups in the molecule or an isocyanate compound having one or more isocyanate groups and one or more acrylic unsaturated double bonds in the molecule. or (1) one or more monomers, oligomers, and polymers containing at least one acrylic unsaturated double bond in the molecule and an active hydrogen group capable of reacting with an isocyanate group. 99.5
% by weight, and (2) 0.5 to 25% by weight of an isocyanate compound having two or more isocyanate groups in the molecule or an isocyanate compound having one or more isocyanate groups and one or more acrylic unsaturated double bonds in the molecule. %, is applied onto a non-magnetic support, and after drying, is cross-linked and cured by simultaneously performing electron beam irradiation and heat treatment, or by irradiating radiation and then heat treatment. A method for manufacturing a magnetic recording medium characterized by: That is, by applying a magnetic paint using the binder of the present invention to a base material, drying it, and then irradiating it with radiation, a linear or network structure is formed by a radical reaction of acrylic unsaturated double bonds. On the other hand, a crosslinked structure is also formed by reaction between active hydrogen groups and isocyanate groups by heating at a predetermined temperature and for a predetermined time as necessary. Therefore, it is thought that a combination of both crosslinking and curing reactions results in a high-order crosslinked structure with a high molecular weight, resulting in a magnetic recording layer with excellent coating film hardness and abrasion resistance. Further, the proportion of the isocyanate compound in the present invention may be relatively small compared to conventional thermosetting resins, and a sufficient pot life can be obtained.
In the curing method of the present invention, when the heat treatment necessary for crosslinking and curing with isocyanate is performed simultaneously with or after radiation irradiation, a three-dimensional network structure is formed by radiation curing, and for example,
Even if heat treatment is performed after winding into a roll,
The coating film does not soften and the surface roughness does not transfer to the surface of the magnetic layer. On the other hand, when heat treatment is first performed and then radiation irradiation is performed, the heat treatment is usually carried out by winding it into a roll, which softens the uncrosslinked coating film and causes a change in surface roughness. Curing properties during radiation irradiation were low, and high-dose irradiation was required. In order to eliminate such drawbacks, in the curing method of the present invention, it is important to apply the magnetic paint, dry it, and then perform the heat treatment necessary for crosslinking and curing with isocyanate simultaneously with or after irradiation with radiation. . As the radiation-curable component in the present invention, that is, component (1), a compound having one or more acrylic unsaturated double bonds in the molecule is used. Also,
Component (1) may have an active hydrogen group such as a hydroxyl group, a carboxyl group, an amino group, an amide group, etc. that can react with an isocyanate group. In the present invention, the compound containing an acrylic unsaturated double bond, that is, the component (1), is a compound having various reactive groups, such as a compound such as component (2), by a conventionally known method. A compound in which an acrylic unsaturated double bond group is bonded to the chain is used. Compounds with an acrylic unsaturated double bond group attached to the terminal or side chain of the compound include:
These include: () 1 mole or more of a reaction product of a polyisocyanate compound and a (meth)acrylic ester monomer having a group that is reactive with an isocyanate group, and 1 mole of a compound having one or more hydroxyl groups in the molecule. Examples include reaction products and reaction products obtained by changing the reaction order of these three components. In addition, by reacting with an isocyanate compound smaller than the equivalent of the hydroxyl group of the oligomer or polymer, prepolymers and oligomers having hydroxyl groups and acrylic unsaturated double bonds,
Alternatively, polymers can be obtained. () A reaction product of one molecule of a compound containing one or more epoxy groups in the molecule and one or more molecules of a monomer having an electron beam-curable unsaturated double bond and a group that reacts with the epoxy group. It is known that a hydroxyl group is produced as a by-product through the reaction of an epoxy group with acrylic acid, methacrylic acid, etc., and is used as a compound having an acrylic unsaturated double bond and a hydroxyl group. () Solution polymerization of a reaction product of one molecule of a compound containing one or more carboxyl groups in the molecule and one or more molecules of a monomer having a group that reacts with carboxyl groups and a radiation-curable unsaturated double bond, such as methacrylic acid. A resin or prepolymer obtained by reacting glycidyl methacrylate with a thermoplastic resin containing a carboxyl group obtained by the above process, and introducing an acrylic double bond into the molecule by the ring-opening reaction of the carboxyl group and the epoxy group as in the above. and polymers. Furthermore, by reacting with a monomer having fewer epoxy groups than the equivalent of carboxyl groups in the oligomer or polymer, a prepolymer, oligomer or polymer having a carboxyl group and an acrylic unsaturated double bond can be obtained. () As the monomer containing an acrylic unsaturated double bond, conventionally known monomers may be used, such as methyl (meth)acrylate, ethyl (meth)acrylate, etc.
Acrylates, butyl (meth)acrylate, etc., and (meth)acrylic acid esters of polyhydric alcohols include, for example, diethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and the like. Further, a compound having a group reactive with an isocyanate group and an acrylic unsaturated double bond can be obtained by esterifying a part of a polyhydric alcohol with (meth)acrylic acid. For example, trimethylolpropane di(meth)acrylate, pentaerythritol triacrylate, etc. can be mentioned. Component (2) in the present invention is a compound, oligomer or polymer containing an active hydrogen group that can react with an isocyanate group, such as a hydroxyl group, a carboxyl group, an amino group, etc., such as ADEKA Polyether P-700, Adeka polyether P-
Polyfunctional polyethers such as 1000, Adeka Polyether G-1500 (manufactured by Asahi Denka Co., Ltd.), Polymeg 1000, and Polymeg 650 (hereinafter manufactured by Quaker Oats), fibers such as nitrocellulose, acetylcellulose, and ethylcellulose. elementary derivative, vinylite
Partially saponified vinyl chloride-vinyl acetate copolymer with hydroxyl groups such as VAGH (manufactured by Union Carbide, USA), polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polycaprolactone PCP-0200, polycaprolactone PCP- 0240, polycaprolactone PCP−0300
(manufactured by Tetsuso), saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, adipic acid, succinic acid, and sebacic acid, and ethylene glycol, diethylene glycol, and 1,4-butane. Diol, 1,3
- terminals obtained by ester bonding with polyhydric alcohols such as butanediol, 1,2-propylene glycol, dipropylene glycol, 1,6-hexane glycol, neopentyl glycol, glycerin, trimethylolpropane, pentaerythritol, or Saturated polyester resin having a hydroxyl group in the side chain, acrylic polymer containing at least one kind of acrylic ester and methacrylic ester containing a hydroxyl group as a polymerization component, Epicote 828, Epicote 1001, Epicote 1007,
Other various types of epoxy resins include Epicote 1009 (manufactured by Ciel Kagaku Co., Ltd.). Compounds containing one or more carboxyl groups in the molecule include polyesters containing carboxyl groups in the molecular chain or at the end of the molecule, acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, etc., which have radical polymerizability and have carboxyl groups. Examples include homopolymers of monomers having groups and copolymers with other polymerizable monomers. Further, as the polyisocyanate compound which is the component (3) in the present invention, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,4-xylene diisocyanate, m-
Examples include phenylene diisocyanate, p-phenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, Desmodyur L, Desmodyur IL (manufactured by Bayer AG, West Germany), and the like. Examples include polyurethane prepolymers or polymers having isocyanate groups at the ends obtained by the reaction of polyols and polyisocyanates. The component (3) may also be a compound containing an acrylic unsaturated double bond and an isocyanate group. For example, the above polyisocyanate compound is combined with an acrylic monomer containing less hydroxyl groups than the equivalent of the isocyanate group. The compounds obtained by the reaction are used. The binder of the present invention contains 20 to 99.5% by weight of the radiation curable component (1) and the thermosetting component (1).
(2) is 0 to 80% by weight, and component (3) which is a curing agent is
It is used in a range of 0.5 to 25% by weight. Component (1) is 20
If the amount is less than 1% by weight, a sufficient network structure cannot be obtained by radiation irradiation, and the coating film may be softened during heat treatment. In addition, the same drawback occurs even when the content of component (2) is 80% by weight or more, and surface roughness and dislocation occur due to softening, making it impossible to obtain a smooth magnetic layer. If component (3) is less than 0.5% by weight, the effect of improving physical properties by heat treatment will be small, and if it is more than 25% by weight, the pot life of the paint will be significantly shortened, making it difficult to handle. The magnetic paint according to the present invention is appropriately used in a range of magnetic particles/binder (weight ratio) of 86/14 to 65/35 based on the magnetic properties and mechanical properties of the coating film formed on the base material. Ru. A non-reactive solvent is used in the magnetic paint of the present invention. There are no particular restrictions on the solvent, but it is appropriately selected in consideration of the solubility and compatibility of the binder. For example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, esters such as ethyl formate, ethyl acetate, and butyl acetate, aromatic hydrocarbons such as toluene, xylene, and ethylbenzene, isopropyl ether, ethyl ether, dioxane, etc. ethers, tetrahydrofuran, furfurals such as furfural, etc. can be used as a single solvent or a mixture of these solvents. The substrate to which the magnetic paint using the binder of the present invention is coated may be any material that is currently widely used as a substrate for magnetic recording media, such as polyethylene terephthalate film, and other materials that require heat resistance. For this purpose, polyimide film, polyamide film, etc. are used. Particularly in the case of polyester films, thin films are often subjected to uniaxial or biaxial stretching treatment. It is also used to coat paper. The magnetic fine powder used 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, Co-doped γ
-Fe ₂ O ₃ , Co-based compound-coated Fe ₃ O ₄ (including intermediate oxidation state with γ-Fe ₂ O ₃ ; Co-based compounds referred to here include cobalt oxide, cobalt hydroxide, cobalt ferrite, This shows a case where the magnetic anisotropy of cobalt, such as a cobalt ion adsorbent, is used to improve coercive force)
It is. A wet reduction method using a reducing agent such as BH ₄ whose main component is a ferromagnetic metal such as Co, Fe-Co, Fe-Co-Ni, Co-Ni, etc., or after treating the iron oxide surface with a Si compound, H ₂ These are metal fine particles and single crystal barium ferrite fine powder obtained by various manufacturing methods such as a dry reduction method using a gas or the like or a method obtained by vacuum evaporation in a low-pressure argon gas stream. The above-mentioned magnetic fine particles are in the form of needles or particles, and are selected depending on the intended use as a magnetic recording medium. High bias HiFi audio cassette tapes, video cassette tapes, master tapes for videotape contact transfer printing, etc., which have undergone remarkable technological progress in recent years and whose marketability is expanding, contain the binder of the present invention and the above-mentioned magnetic fine powder. By combining cobalt-modified acicular iron oxide (cobalt-doped type or cobalt-based compound coated type), which is especially advantageous for high-density recording applications, or acicular alloy fine particles with high coercive force, extremely good electromagnetic conversion characteristics can be achieved. A high-performance tape with reliable physical properties could be obtained. Regarding the magnetic paint of the present invention, various commonly used antistatic agents, lubricants, dispersants,
A sensitizer, a leveling agent, an abrasion resistance imparting agent, a coating strength reinforcing additive, etc. can be used. Moreover, resins that do not participate in the reaction can also be used as necessary. When manufacturing a magnetic recording medium according to the present invention, such as a magnetic tape for video, for example, first (1) and (2)
A magnetic paint is prepared by dispersing the binder component, magnetic powder, and other additives in a solvent, and then applied to the magnetic paint.
Add the isocyanate compound of (3) and apply to the substrate. The solvent is then evaporated by heating,
Processing such as surface treatment is performed, and then radiation is irradiated. Then, it can be wound into a roll and heated at a predetermined temperature for a predetermined time to be cured with an isocyanate compound. In the present invention, the radiation used for curing includes an electron beam using an electron beam accelerator as a radiation source, Co ⁶⁰
γ-rays using Sr90 as a source, β-rays using Sr ⁹⁰ as a source,
X-rays using an X-ray generator as a radiation source are used. In particular, as an irradiation source, from the standpoint of controlling absorbed dose, introducing into structural process lines, and shielding from ionizing radiation,
Preference is given to methods using electron beams from electron beam accelerators. As an irradiation source, electron beam accelerators are recommended for the following reasons: control of absorbed dose, self-shielding of ionizing radiation when introduced into the manufacturing process line, ease of connection with sequence control of process line equipment, etc. is advantageous.
As electron beam accelerators, various types of accelerators have been put into practical use, such as Kotscroft type, Pandegraph type, resonant transformer type, iron core insulated transformer type, and Liner accelerator type, mainly due to differences in the method of obtaining high voltage. . However, magnetic recording media can only be used for general purpose applications.
Most have a thin magnetic film thickness of less than a micron, and are therefore commonly 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. Such a low accelerating voltage accelerator is particularly advantageous not only in terms of lower costs for the system itself, but also in terms of ionizing radiation shielding equipment. The standards shown in the table below have been reported regarding whether the shielding equipment should be made of lead or concrete, and the thickness of the shielding (Radiation Utilization Research Group Report, p. 8).
August 1979, Japan Atomic Energy Council)

[Table] As shown in the table above, at electron beam accelerating voltages of 300KV or less, leakage of X-rays can be prevented by using a lead plate with a maximum thickness of 3 cm as a shielding material to cover the entire acceleration tube that surrounds the electron beam irradiated area. It can be blocked sufficiently.
Therefore, there is no need to separately provide an expensive electron beam irradiation chamber, and the irradiation system itself can be incorporated as an I system in the magnetic recording media manufacturing line.
Therefore, it becomes possible to conduct the drying and curing process of the magnetic recording medium using an electron beam online. Specific examples of such systems include the low-dose type electron beam accelerator (electrocurtain system) manufactured by Energy Sciences, Inc. in the United States, and the self-shielding scanning type low-dose type electron beam manufactured by Hollimar Physics of West Germany. Accelerators are a suitable example. In addition, during radiation crosslinking, it is important to irradiate the recording medium with radiation in an inert gas flow such as N ₂ gas, He gas, CO ₂ gas, etc. Since the coating film with high oxidation rate is extremely porous, irradiation with radiation in the air is effective because the radicals generated in the polymer due to the influence of O ₃ etc. generated by radiation irradiation during crosslinking of the binder component are effective. inhibits the cross-linking reaction. The effect is that 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 to be irradiated with active energy rays should be N ₂ , Ne, Ne, etc. with a maximum oxygen concentration of 1%.
It is important to maintain an atmosphere of inert gas such as CO ₂ . In addition, the heat treatment for the crosslinking reaction of the isocyanate compound in the present invention may be performed under conventionally known conditions.
For example, it is well known that heat curing is performed at 60°C for about 24 hours. The present invention will be explained in more detail below using Examples and Comparative Examples. In each example, "parts" indicate parts by weight. First, an example of synthesis of the resin used in the present invention will be illustrated. Synthesis of TDI adduct 348 parts of tolylene diisocyanate (TDI)
80°C in a _N2 stream in a four-necked flask.
After heating, 260 parts of 2-hydroxyethyl methacrylate (2HEMA), 0.07 part of tin octylate and 0.05 part of hydroquinone were added until the temperature inside the reaction vessel was 80-85.
The mixture was added dropwise while controlling the cooling so that the temperature was maintained at 80°C, and after the addition was completed, the reaction was completed by stirring at 80°C for 3 hours.
After the reaction was completed, the contents were taken out, and after cooling, a white paste-like TDI 2HEMA adduct was obtained. Resin synthesis example (a) Vinyl chloride/vinyl acetate/vinyl alcohol
100 parts of a copolymer with a molecular weight of 18,000 with a composition of 93/2/5% by weight was mixed with 238 parts of toluene and cyclohexanone.
After heating and dissolving in 95 parts, the temperature was raised to 80℃, 15 parts of the following TDI adduct was added, and 0.002 parts of tin octylate was added.
part and add 0.002 parts of hydroquinone, and 82 parts
The reaction is allowed to occur at ℃ in a stream of _N2 gas until the reaction rate of isocyanate (NCO) reaches 90% or more. After the reaction is completed, the mixture is cooled and diluted with 238 parts of methyl ethyl ketone. The obtained resin composition is referred to as (a). In this resin, approximately 55% of the hydroxyl groups in the vinyl hydrochloride resin remain unreacted. Resin synthesis example (b) 250 parts of NIAX polyol PCP-0200 (polycaprolactone manufactured by Chitsuso Corporation), 122.2 parts of 2-hydroxyethyl methacrylate, 0.024 parts of hydroquinone and 0.033 parts of tin octylate were placed in a reaction vessel.
After heating and dissolving at 80°C, 163.6 parts of TDI was added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C. After the dropwise addition was completed, the reaction was continued at 80°C until the NCO reaction rate reached 95% or higher. urge The obtained resin composition is referred to as (b). This resin does not contain hydroxyl groups. Resin synthesis example (c) 148 parts of phthalic anhydride, 65 parts of 1,3-butanediol
A reactor was charged with 30 parts of ethylene glycol and 2.5 parts of paratokonsulfonic acid, and after esterification reaction at 150°C for 1 hour under a nitrogen gas stream and then at 180°C for 5 hours, the mixture was cooled to 100°C and 0.3 parts of hydroquinone was added. 1 part and 28 parts of acrylic acid were added, and the esterification reaction was carried out for 15 hours. The obtained resin composition is referred to as (c). This resin does not contain hydroxyl groups. Resin synthesis example (d) 174 parts of TDI, 87 parts of methyl ethyl ketone and 87 parts of toluene were placed in a reaction vessel, heated to 80°C, and then Adeka Polyether G-400 (polyether manufactured by Asahi Denka Co., Ltd.) was added.
133 parts of triol was added dropwise and reacted for 3 hours while keeping the temperature at 80-90°C, followed by 65 parts of 2-hydroxyethyl methacrylate and 0.005 parts of hydroquinone.
1 part and 0.005 part of tin octylate were added dropwise, and after the dropwise addition was completed, the reaction was carried out at 80° C. until the NCO reaction rate reached 95% or more to obtain a compound having an isocyanate group and an acrylic unsaturated double bond. The obtained resin composition is referred to as (d). Resin synthesis example (e) Put 10 parts of 2-hydroxyethyl methacrylate, 40 parts of butyl acrylate, 37.5 parts of toluene and 37.5 parts of methyl isobutyl ketone into a reaction vessel,
After heating to ℃, 30 parts of 2-hydroxyethyl methacrylate, 120 parts of butyl acrylate, and 8 parts of benzoyl peroxide as a polymerization initiator were mixed with 112.5 parts of toluene and methyl isobutyl ketone.
After dropwise addition, 28 parts of TDI adduct was added to 330 parts of the reaction product, and NCO reaction was carried out at 80°C in the presence of 0.012 parts of tin octylate and 0.012 parts of hydroquinone. Rate 90%
Let them react to the above. The obtained resin composition (e)
shall be. This resin contains acrylic unsaturated double bonds and hydroxyl groups. Resin synthesis example (f) After heating and dissolving 200 parts of Epicote 828 (epoxy resin manufactured by Ziel) in 25 parts of toluene and 25 parts of methyl ethyl ketone, dissolve N,N-dimethylbenzylamine.
Add 2.7 parts and 1.4 parts of hydroquinone and heat to 80°C.
Then, 69 parts of acrylic acid was added dropwise to react at 80°C until the acid value reached 5 or less. This resin is referred to as (f). Example 1 Cobalt-coated acicular γ-Fe ₂ O ₃ 120 parts Carbon black (Mitsubishi MA-600) 5 parts α-Al ₂ O ₃ (0.5μ granules) 2 parts Dispersant (soybean oil refined lecithin) 3 parts Solvent (Methyl ethyl ketone/toluene = 50/
50) 100 parts of the above composition were premixed in a ball mill, and then: 18 parts of the resin of Synthesis Example (a) (in terms of solid content) 12 parts of the resin of Synthesis Example (b) (in terms of solid content) Lubricant (high grade) fatty acid modified silicone oil)
3 parts solvent (methyl ethyl ketone/toluene = 50/
50) 200 parts of the composition was added and thoroughly dispersed in a ball mill. Next, three times the solid content of a trifunctional isocyanate compound (Desmodyur L, manufactured by Peyer) was added and mixed in a mixer to prepare a magnetic paint. This paint was immediately applied onto a 12 μ polyester film, subjected to magnetic field orientation treatment and dry surface smoothing treatment, and then an electron beam of 160 KV (acceleration voltage) was applied to the magnetic layer for 5 Mrad in a nitrogen atmosphere.
Irradiated. Then, it was kept in a heat treatment furnace kept at 80°C for 48 hours. The obtained sample was cut into 1/2 inch width to obtain a videotape (sample No. 1). Comparative Example 1 In Example 1, a paint was prepared without using the trifunctional isocyanate (Desmodyur L), and the resulting sample was cured under the same conditions as Example 1 and cut into 1/2 inch width. A tape (sample A) was obtained. Comparative Example 2 The magnetic paint of Example 1 was applied onto a polyester film, subjected to dry magnetic field orientation treatment and surface smoothing treatment, and then irradiated with an electron beam of 5 Mrad under the same conditions as Example 1. 1/2 of the obtained sample
A videotape (Sample B) was obtained by cutting into inch width pieces. Figure 1 shows the signal recorded on a videotape using an EIAJ unified standard open reel VTR (NV-3120 manufactured by Matsushita Electric Industrial Co., Ltd.).
This shows the amount of attenuation (still playback) with respect to the playback output when still image reproduction is performed with a tension of gram. As is clear from the figure, despite severe wear conditions where the relative speed between the magnetic coating and the head was as high as 11 m/sec, sample No. 1 showed significantly less signal attenuation. On the other hand, in Samples A and B, relatively good coating films were formed by electron beam curing alone, but attenuation was observed. Figure 2 shows the temperature from -10℃ and relative humidity from 0% to 60℃.
℃, 5 cycles of videotape in the 80% range, 5
After keeping it for a day, return it to room temperature, leave it still for 24 hours,
Same VTR used for scale playback test
A tension analyzer model IVA-500 manufactured by Nippon Automatic Control Co., Ltd. was set between the head drum and the pinch roller, and changes in tension on the winding side during running were investigated with respect to running time. This test not only evaluates the level of the friction coefficient of the magnetic coating itself, but also makes it possible to evaluate the deterioration of tape running performance and stability against environmental conditions such as temperature and humidity. As is clear from the figure, Sample No. 1, which was subjected to electron beam irradiation and then heat treatment, had a small change in the coefficient of friction of the tape and good running stability against changes in temperature and humidity. Example 2 Fe alloy acicular magnetic powder 120 parts Dispersant (oleic acid) 2 parts Solvent (methyl ethyl ketone/toluene = 50/
50) 100 parts of the above composition were premixed in a ball mill, and then: Resin of Synthesis Example (c) (in terms of solid content) 15 parts Polyurethane resin (Nysten 5703 manufactured by BF Gudritsch) (in terms of solid content) 15 parts Solvent (methyl ethyl ketone) /Toluene=50/
50) 200 parts of lubricant (higher fatty acid) 3 parts of the composition was added and thoroughly dispersed in a ball mill. Next, the resin of Synthesis Example (d) was calculated in terms of solid content.
After adding 10 parts and thoroughly mixing with a mixer, it was immediately coated on a 12 μ polyester film, and after magnetic field orientation, solvent drying, and surface smoothing treatment, it was irradiated with an electron beam of 5 Mrad at an acceleration voltage of 160 KV under a nitrogen atmosphere. . The mixture was then kept in a heat treatment furnace kept at 80°C for 48 hours. The obtained sample was cut to a width of 3.8 mm to obtain an alloy audio cassette tape (sample No. 2). Example 3 Curing was carried out under the same conditions as in Example 2, except that 3 parts of Coronate L was added instead of the isocyanate component in Synthesis Example (d), and the obtained sample was cut into 3.8 mm wide samples. An alloy audio cassette tape (Sample 3) was obtained. Comparative Example 3 Using the coating material of Example 2, it was coated on a polyester film and then processed and wound into a roll. After that, it was placed in a heat treatment furnace kept at 80℃.
Hold for 48 hours. Thereafter, radiation irradiation was performed under the same conditions as in Example 2 to prepare sample c. The heat-treated sample adhered to the base film and lost its surface smoothness. Table 1 shows the properties of the alloy audio cassette tape. Samples 2 and 3 have long pot lives;
Because it has excellent surface moldability after application, and because it is radiation-cured before heat treatment, it does not undergo thermal softening and can provide extremely smooth surface properties and high residual magnetic density. Therefore, at the low frequency 333Hz
Highly sensitive tapes ranging from MoL to high-frequency 16KHz MoL were obtained; on the other hand, sample C, which was heat-cured first, lost its surface smoothness due to softening during heat treatment, resulting in a decrease in sensitivity. did. In addition, Sample 2 exhibited better performance than Sample 3 in terms of the running time until the tape makes a squeaking sound, which are the reliability physical properties of the tape, and the durability of reciprocating running on a car stereo. This is because the isocyanate component has radiation curing and thermosetting properties.
This is thought to be because it acts as a crosslinking agent between (1) and (2).

[Table] Example 4 γ-Fe ₂ O ₃ 120 parts Carbon black (Mitsubishi MA600) 5 parts α-Al ₂ O ₃ powder (0.5μ granules) 2 parts Dispersant (solvitamin monooleate) 3 parts Solvent (methyl ethyl ketone) /Toluene=50/
50) 100 parts of the above composition were premixed in a ball mill, and then: 15 parts of the resin of Synthesis Example (e) (in terms of solid content) 15 parts of the resin of Synthesis Example (f) (in terms of solid content) Lubricant (manufactured by Dupont) 3 parts solvent (methyl ethyl ketone/toluene = 50/
50) 200 parts of the composition was added and thoroughly dispersed in a ball mill. Next, a trifunctional isocyanate compound (Desmodyur L manufactured by Bayer) was added to
Add twice as much and mix thoroughly with a mixer to create a magnetic paint. This paint was immediately coated on a 118μ polyester film to a thickness of about 10μ and dried, followed by surface smoothing treatment and curing treatment under the same conditions as in Example 1. The obtained sample was punched out into a disk shape (diameter 65 mm) to obtain a magnetic disk (sample No. 4). Comparative Example 4 Curing was performed under the same conditions as in Example 3, except that the isocyanate compound (Desmodyur L) was not used, and the obtained sample was shaped into a disk (diameter 65 mm).
The disk was punched out to obtain a magnetic disk (sample D). Comparative Example 5 Using the coating material of Example 4, it was coated on a polyester film under the same conditions, post-processed, and wound up into a roll. Thereafter, it was kept in a heat treatment furnace kept at 40° C. for 72 hours, and then irradiated with an electron beam under the same conditions as in Example 3. The obtained sample was punched out into a disk shape (diameter 65 mm) and placed into a magnetic disk (sample E).
I got it. Each magnetic disk was loaded into a recording/reproducing device and run at a speed of approximately 2 m/sec while sliding against a magnetic head (batt E 40 g/cm ² ), and the running time until the cumulative number of dropouts reached 1000 was measured. . Table 2 shows the results obtained and the surface condition of the magnetic layer.

[Table] Sample 4 of the present invention has good running stability and surface condition, but Sample D, which was subjected to only electron beam irradiation, has poor durability. In addition, for sample E, which had the same composition and was heat-cured first, the running time was shorter;
Similarly, the durability was decreased, and it is presumed that the curability of the radiation-curable resin was decreased.

[Brief explanation of drawings]

1-2 are graphs illustrating the performance of magnetic recording media in accordance with the present invention.

Claims (1)

[Claims] 1. Coating a magnetic paint mainly consisting of ferromagnetic fine powder, a binder and a solvent onto a non-magnetic support,
In a method for producing a magnetic recording medium in which a magnetic recording layer is formed on a nonmagnetic support by crosslinking and curing after drying,
The binder is (1) (a) a monomer, oligomer, or polymer that contains at least one acrylic unsaturated double bond in the molecule and does not contain an active hydrogen group that can react as an isocyanate group, and (b) 20 to 20 to more than one selected from monomers, oligomers, and polymers containing at least one acrylic unsaturated double bond in the molecule and an active hydrogen group capable of reacting with an isocyanate group.
99.5% by weight, (2) 80% by weight of one or more compounds, oligomers, and polymers containing at least one active hydrogen that can react with isocyanate groups in the molecule.
and (3) 0.5 to 25% by weight of an isocyanate compound having two or more isocyanate groups in the molecule or an isocyanate compound having one or more isocyanate groups and one or more acrylic unsaturated double bonds in the molecule. , is applied on a non-magnetic support, and after drying is cross-linked and cured by simultaneously performing electron beam irradiation and heat treatment, or by irradiating radiation and then heat treatment. Features: Manufacturing method for magnetic recording media. 2. Applying a magnetic paint mainly consisting of ferromagnetic fine powder, a binder and a solvent onto a non-magnetic support,
In a method for producing a magnetic recording medium in which a magnetic recording layer is formed on a nonmagnetic support by crosslinking and curing after drying,
The binder comprises: (1) one or more monomers, oligomers, and polymers containing at least one acrylic unsaturated double bond in the molecule and an active hydrogen group that can react as an isocyanate group;
~99.5% by weight, and (2) 0.5% of an isocyanate compound having two or more isocyanate groups in the molecule or an isocyanate compound having one or more isocyanate groups and one or more acrylic unsaturated double bonds in the molecule. ~25% by weight, is applied onto a non-magnetic support, and after drying, crosslinking is achieved by simultaneously performing electron beam irradiation and heat treatment, or by irradiating radiation and then heat treatment. A method for manufacturing a magnetic recording medium, characterized by hardening it.