JPH0130221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium that has excellent wear resistance and surface smoothness, and has good electrical properties. Currently, cassette tape, open reel tape,
Many magnetic recording media such as video tapes, magnetic cards, and magnetic disks are made of polyester film, polyvinyl chloride film, polyacetate film,
A base film such as paper is coated with a coating material such as a paint containing a magnetizable metal oxide or metal material such as iron oxide, or a coating agent such as printing ink (hereinafter, the paint will be explained as an example), orientation, It is obtained through a drying and optionally curing process, and the resin paint binder is vinyl chloride copolymer,
Polyurethane, polyacrylic acid ester, and sometimes epoxy resin are used, and plasticizers, rubbers, dispersants, antistatic agents, pigments, etc. are generally added depending on the purpose. Although various binders can be used, hardening binders such as thermosetting resins are considered more preferable because of their physical properties such as abrasion resistance, heat resistance, and solvent resistance. For magnetic recording media such as magnetic recording tapes, one of the very important characteristics is the adhesion between the base material, such as a polyester film, and the magnetic coating film applied thereon. If this adhesive force is weak, the magnetic coating may peel off when some force is applied to the magnetic recording tape, for example, when strong instantaneous stress is applied to the tape. As a result, it becomes impossible to record the peeled portion, and furthermore, recorded information may be lost. In order to increase the adhesive force with polyester films, various treatments have been devised, such as chemical treatment of polyester films, surface roughening, and generally corona discharge. However, the current situation is that it is difficult to adhere to polyester films and the like used in magnetic recording tapes because they are crystalline polymers and have low polarity. Furthermore, the applied magnetic paint has a high pigment concentration and cannot wet the surface of the polyester film or the like well, which further reduces the adhesive strength. On the other hand, as a highly effective method for increasing adhesive strength, a so-called undercoating process in which a resin solution is applied onto a polyester film and a magnetic coating film is further applied thereon has been considered. However, in this case, when the magnetic layer is applied, the undercoat layer that has already been formed on the film is swollen by the organic solvent used in the magnetic paint, which causes uneven coating and the surface of the coating film. As a result, the smoothness of the magnetic layer is lost, resulting in a decrease in sensitivity. In addition, in order to eliminate this problem, if a thermosetting resin is used as the undercoat resin, the undercoat resin or unreacted materials of the curing agent will be thermoset during the heat treatment during curing, and the resin will be rolled up (overlaid). However, it was difficult to put this into practical use because the undercoat layer would stick to the base film. Moreover, in the case of thermosetting, there are problems with the pot life of the lacquer and because thermosetting takes time, it is not possible to continuously form the upper magnetic layer. In order to eliminate such drawbacks, the present inventors used a radiation-curable resin as the undercoat resin when forming each undercoat layer, and after applying the undercoat layer, performed an appropriate drying treatment as necessary. After that, radiation was applied to produce three-dimensional crosslinking, and then a magnetic layer was applied thereon, thereby achieving very favorable results. According to this method, the undercoat layer is already crosslinked when the magnetic layer is provided, so it is not swollen by organic solvents, and furthermore, the magnetic paint can be applied immediately, so there is no need to worry about the process. Continuation and simplification will be attempted. Further, even if the film is wound up after irradiation with radiation, the undercoat layer has already been cured, so there is an advantage that it can be stored without causing stickiness. If a radiation-curable resin is used as the undercoat resin in this way, all the disadvantages of conventional undercoat treatments can be eliminated. The radiation-curable resin used in the present invention refers to a resin containing one or more unsaturated double bonds in its molecular chain, which generates radicals when irradiated with radiation and is cured by crosslinking or overlapping. As a result of intensive research aimed at solving the above-mentioned problems in priming of magnetic recording media, the present inventors have achieved very good solvent resistance and adhesive properties in a short time by priming with a radiation-curable resin. The present invention has been completed based on the discovery that a magnetic recording medium with excellent surface smoothness and electrical properties can be obtained by forming a primer having the following properties. That is, the present invention provides a magnetic recording medium in which a magnetic layer is formed after a nonmagnetic undercoat layer is applied to a support, in which the undercoat layer (A) has two unsaturated double bonds that are curable by radiation. with a molecular weight of 5000 or more, preferably
8,000 or more; (B) A compound with a molecular weight of 400 or more and having one or more unsaturated double bonds that is curable by radiation and less than 5,000, preferably 600 to 3,000; (C) A compound that is curable by radiation. A compound with a molecular weight of less than 400 that has one or more unsaturated double bonds, and is formed by radiation irradiation using a radiation-curable paint containing at least two or more selected from the above (A), (B), and (C). It is a magnetic recording medium made of Furthermore, the radiation-curable paint contains at least two or more selected from (A), (B), and (C), and (A) is 0 to 90
The magnetic recording medium has a blending ratio of (B) of 0 to 80% by weight and (C) of 0 to 50% by weight. Further, the radiation-curable coating material contains (A) and (B) in a blending ratio of 20 to 95% by weight of (A) and 5 to 80% by weight of (B). A magnetic recording medium that uses electron beams for radiation irradiation. Furthermore, the radiation-curable paint further contains an effective polymerization sensitizer of 0.1 to 10% by weight based on the resin solid content,
This is a magnetic recording medium in which an undercoat layer is formed by irradiation with ultraviolet rays. Describing the method of the present invention in detail below, first, the compound constituting the radiation-curable paint used in carrying out the present invention is attached to the terminal or side chain of the molecule (meta).
A compound having one or more unsaturated double bonds that is curable by radiation such as an acryloyl group,
Usually, two or more types having different molecular weights and numbers of functional groups are used in combination. A suitable example is shown below. One molecule of a compound having one or more hydroxyl groups in the molecule is reacted with one isocyanate group of one or more molecules of a polyisocyanate compound, and then the compound has a group that reacts with the isocyanate group and an unsaturated double bond that has radiation curability. 2 moles of toluene diisocyanate are reacted with 1 mole of a difunctional polyether (ADEKA Polyether P-1000 manufactured by Asahi Denka Co., Ltd.), which is a reaction product with one or more monomer molecules, such as propylene glycol with propylene oxide added thereto, and then Examples include resins, prepolymers, oligomers, and telomers having two acrylic double bonds at the molecular ends obtained by reacting 2 moles of 2-hydroxyethyl methacrylate. Compounds containing one or more hydroxyl groups used here include Adeka Polyether P-700,
ADEKA Polyether P-1000, ADEKA Polyether G-1500 (manufactured by Asahi Denka Co., Ltd.), Polymeg
Polyfunctional polyethers such as 1000 and Polymeg 650 (manufactured by Quaker Oats); cellulose derivatives such as nitrocellulose, acetylcellulose, and ethylcellulose; partially saponified vinyl chloride-vinyl acetate copolymer; polyvinyl alcohol; polyvinyl formal; polyvinyl butyral; polycaprolactone PCP-0200, polycaprolactone
PCP-0240, polycaprolactone PCP-0300
Polyfunctional polyesters such as (manufactured by Chitsuso); phthalic acid, isophthalic acid, terephthalic acid,
Saturated polybasic acids such as adipic acid, succinic acid, and sebacic acid and ethylene glycol, diethylene glycol, 1,4-butanediol, 1,3
-Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as butanediol, 1,2-propylene glycol, dipropylene glycol, 1,6-hexane glycol, neopentyl glycol, glycerin, and trimethylolpropane pentaerythritol. ; Examples include acrylic polymers containing at least one kind of acrylic ester and methacrylic ester containing hydroxyl groups as a polymerization component. In addition, the polyisocyanate compounds used here include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,
Examples include 1,4-xylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, Desmodyur L, and Desmodyur IL (manufactured by Bayer AG, West Germany). Examples of monomers having a group that reacts with an isocyanate group and a radiation-curable unsaturated double bond include 2-hydroxyethyl ester, 2-hydroxypropyl ester, and 2-hydroxyoctyl ester of acrylic acid or methacrylic acid that have a hydroxyl group. Esters: Acrylamide, methacrylamide, N-methylol acrylamide, etc.; Allyl alcohol, maleic acid polyhydric alcohol ester compounds, mono- or diglycerides of long-chain fatty acids with unsaturated double bonds, etc. Active hydrogen that reacts with isocyanate groups Also included are these monomers containing unsaturated double bonds that have a long bond and are radiation curable. Compound 1 containing one or more epoxy groups in the molecule
A thermoplastic resin containing an epoxy group obtained by radical polymerizing a molecule and a group that reacts with an epoxy group and one or more molecules of a monomer having an electron beam curable unsaturated double bond, such as glycidyl methacrylate. By reacting with acrylic acid, a ring-opening reaction between a carboxyl group and an epoxy group,
Resins, prepolymers, or oligomers with pendant acrylic double bonds in the molecule, or radiation-curable unsaturated double bonds in the molecular skeleton through a ring-opening reaction between carboxyl groups and epoxy groups by reacting with maleic acid. Examples include resins, prepolymers, and oligomers. Examples of compounds containing one or more epoxy groups in the molecule include homopolymers of acrylic esters or methacrylic esters containing epoxy groups, such as glycidyl acrylate and glycidyl methacrylate, or copolymers with other polymerizable monomers; Epicote 828, Epicote 1001,
There are various other types of epoxy resins such as Epicote 1007 and Epicote 1009 (manufactured by Ciel Chemical Co., Ltd.). Examples of monomers having groups that react with epoxy groups and radiation-curable unsaturated double bonds include acrylic monomers containing carboxyl groups such as acrylic acid and methacrylic acid, methylaminoethyl acrylate, and methylaminomethacrylate. In addition to acrylic monomers having primary or secondary amino groups, polybasic acid monomers having radiation-curable unsaturated double bonds such as maleic acid, fumaric acid, crotonic acid, and undecylenic acid can also be used. 1 molecule of a compound containing one or more carboxyl groups in the molecule, a group that reacts with the carboxyl group, and a monomer 1 having a radiation-curable unsaturated double bond
Glycidyl methacrylate is reacted with a thermoplastic resin containing a carboxyl group obtained by solution polymerizing methacrylic acid with a reaction product with more than one molecule, and in the same way as in the above section, a ring-opening reaction between the carboxyl group and the epoxy group forms a reaction product in the molecule. Examples include resins, prepolymers, and oligomers into which acrylic double bonds have been introduced. Examples of 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,
These include homopolymers of radically polymerizable monomers such as methacrylic acid, maleic anhydride, and fumaric acid and having carboxyl groups, or copolymers with other polymerizable monomers. Examples of monomers having a group that reacts with a carboxyl group and a radiation-curable unsaturated double bond include glycidyl acrylate and glycidyl methacrylate. A polyester compound containing a radiation-curable unsaturated double bond in its molecular chain, for example, a saturated polyester resin consisting of an ester bond of a polybasic acid and a polyhydric alcohol as described in section 1, in which part of the polybasic acid is replaced with maleic acid. Examples include unsaturated polyester resins, prepolymers, and oligomers containing radiation-curable unsaturated double bonds. Examples of the polybasic acid and polyhydric alcohol components of the saturated polyester resin include the compounds listed in the section above, 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 dehydrating it under a nitrogen atmosphere at 180 to 200°C in the presence of a catalyst, or After dealcoholization reaction, 240~
A polyester resin can be obtained by raising the temperature 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. is 1 to 40% in the acid component due to crosslinking during manufacturing, radiation curing, etc.
It is preferably 10 to 30 mol%. Low molecular weight compounds having radiation-curable unsaturated double bonds can also be used depending on the purpose; such low molecular weight compounds include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, and diethylene glycol. diacrylate, diethylene glycol dimethacrylate,
1,6-hexane glycol diacrylate,
Examples include 1,6-hexane glycol dimethacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate (note that the compounds in item 1 are mainly the compounds in (C)). The radiation-curable paint in the present invention can be obtained by using the compounds described in Items 1 to 3, but when a compound containing an acrylic double bond and having a molecular weight of 400 or more is used alone, the molecular weight As the size increases, the electron beam curability tends to decrease due to the functional group density, thus requiring a high dose, and as the curability decreases, the heat resistance also tends to deteriorate. In addition, the adhesiveness may decrease as the curability increases. On the other hand, in the case of an electron beam curable resin having a molecular weight of less than 400, the electron beam curability is good and the solvent resistance, heat resistance, etc. are good, but there is a problem in adhesiveness. In this way, when a compound containing an acrylic double bond with a molecular weight of 400 or more or less than 400 is used alone,
It is difficult to obtain an undercoat paint that satisfies the wide variety of properties required of magnetic recording media in a well-balanced manner. In contrast, in the present invention, two or more types of compounds having different molecular weights are blended to obtain good adhesion and curability. In the present invention, if necessary, a non-reactive solvent is used. Although there is no particular restriction on the solvent, it is appropriately selected in consideration of the solubility and compatibility of the binder. For example, ketones such as acetone, methyl ole ketone, methyl isobutyl ketone, and cyclohexanone, esters such as ethyl formate, ethyl acetate, and butyl acetate, alcohols such as methanol, ethanol, isopropanol, butanol, and aromas such as toluene, xylene, and ethylbenzene. group hydrocarbons, isopropyl ether, ethyl ether,
Ethers such as dioxane, furans such as tetrahydrofuran and furfural, etc. are used as a single solvent or a mixed solvent thereof. The magnetic layer according to the present invention may of course be one using a thermoplastic resin or a thermosetting resin as a vehicle.
It may be formed by radiation irradiation using a radiation-curable resin such as that used for the primer layer, or it is also possible to irradiate the primer and the magnetic layer with radiation at the same time. The substrate on which the primer layer and magnetic paint according to the present invention are applied is polyethylene terephthalate film, which is currently widely used as a substrate for magnetic recording media, and polyimide film and polyamide film for applications that require further heat resistance. etc. are utilized. Particularly in the case of polyester films, thin films are often subjected to uniaxial or biaxial stretching. It is also used to coat paper. The radiation used for crosslinking and curing the radiation-curable paint according to the present invention includes electron beams using an electron beam accelerator as a radiation source, γ-rays using Co ⁶⁰ as a radiation source, and β-rays using Sr ⁹⁰ as a radiation source. X-rays, X-rays from an X-ray generator, and ultraviolet rays are used. In particular, as a radiation source, it is advantageous to use electron beams or ultraviolet rays from an electron beam accelerator from the viewpoints of controlling the absorbed dose, introducing into the manufacturing process line, blocking ionizing radiation, etc. Regarding the characteristics of the electron beam used when curing the coating film, in terms of penetrating power, an electron beam accelerator with an accelerating voltage of 100 to 750 KV, preferably 150 to 300 KV is used, and irradiation is performed so that the absorbed dose is 0.5 to 20 megarads. It is convenient to do so. The radiation-curable coating material of the present invention can also be cured by ultraviolet rays by adding a photopolymerization sensitizer. The photopolymerization sensitizer may be a conventionally known one, such as benzoin methyl ether, benzoin ethyl ether, α-methylbenzoin, α-
Benzoin series such as chlordeoxybenzoin, ketones such as benzophenone, acetophenone, bisdialkylaminobenzophenone, quinones such as anthraquinone and phenanthraquinone, sulfides such as benzyl disulfide and tetramethylthiuram monosulfide. etc. The photopolymerization sensitizer is 0.1 to 0.1% of the resin solid content.
A range of 10% is desirable. Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. In addition, "part" and "%" in the examples indicate parts by weight and weight %. Prior to Examples, resin synthesis examples will be shown. Resin synthesis example (a) Vinyl chloride/vinyl acetate/vinyl alcohol
After heating and dissolving 100 parts of a copolymer with a composition of 93/2/5 weight % and a molecular weight of 18,000 in 238 parts of toluene and 95 parts of cyclohexanone, the temperature was raised to 80°C, 7.5 parts of the following TDI adduct was added, and tin octylate was added. Add 0.002 part of hydroquinone and 0.002 part of hydroquinone, and react at 82°C in a N ₂ gas stream 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). Furthermore, the molecular weight of this resin is
It is 19200. Synthesis of TDI adduct 348 parts of tolylene diisocyanate (TDI) was mixed with _N2
After heating to 80℃ in a four-necked flask under air flow,
-Hydroxyethyl methacrylate (2HEMA)
260 parts, tin octylate 0.07 parts, hydroquinone
0.05 part was added dropwise while controlling the cooling so that the temperature inside the reaction vessel was 80 to 85℃, and after the dropping was completed, the temperature was increased to 80℃.
Stir for 3 hours to complete the reaction. After the reaction is complete, take it out, cool it, and remove the white paste of TDI.
Obtained 2HEMA adducts. Resin synthesis example (b) 100 parts of saturated polyester resin (L-411 manufactured by Dynamite Nobel) was heated and dissolved in 116 parts of toluene and 116 parts of methyl ethyl ketone, and after raising the temperature to 80°C, synthesized according to resin synthesis example (a). Add 2.84 parts of isophorone diisocyanate adduct to tin octylate.
Further add 0.006 parts and 0.006 parts of hydroquinone,
React at 80°C in a stream of _N2 gas until the NCO reaction rate reaches 90% or more. The obtained resin composition is referred to as (b). The molecular weight of this resin is 20,600. Resin synthesis example (c) 291.2 parts of dimethyl terephthalate, 291.2 parts of dimethyl isophthalate, 64.8 parts of dimethyl maleate,
251.2 parts of ethylene glycol, 364.8 parts of 1,4-butanediol, 81.2 parts of 1,3-butanediol, and 4.0 parts of tetra-n-butyl titanate were charged into a reaction vessel, and after a demethanol reaction at 180°C in a stream of _N2 gas, A linear unsaturated polyester resin having a molecular weight of 8000 was obtained by a condensation reaction under reduced pressure at a temperature of 240 to 260°C and a pressure of 0.5 to 1 mmHg. Resin synthesis example (d) NIAX polyol PCP-0200 (polycaprolactone manufactured by Chitsuso) 250 parts, 2-hydroxyethyl methacrylate 122.2 parts, hydroquinone 0.024
Place 0.033 parts of tin octylate in a reaction can, and add 80
After heating and dissolving at ℃, 163.6 parts of TDI was added dropwise while cooling the reaction vessel to a temperature of 80 to 90℃, and after the dropwise addition was completed, the reaction was allowed to occur at 80℃ until the NCO conversion rate reached 95% or more. The obtained resin composition is referred to as (d). The molecular weight of this resin is 1140. Resin synthesis example (e) 148 parts of phthalic anhydride, 65 parts of 1,3-butanediol
1 part, 30 parts of ethylene glycol, and 2.5 parts of para-toluenesulfonic acid were charged into a reaction vessel, and after esterification reaction at 150°C for 1 hour and 5 hours at 180°C under a _N2 gas stream, the mixture was cooled to 100°C, and 0.3 parts of hydroquinone,
28 parts of acrylic acid was added and an esterification reaction was carried out for 15 hours to obtain an oligoester acrylate with a molecular weight of 2000. Resin synthesis example (f) 250 parts of Adeka Polyether P-1000 (polyether manufactured by Asahi Denka Co., Ltd.), 65 parts of 2-hydroxyethyl methacrylate, 0.013 parts of hydroquinone, and 0.017 parts of tin octylate were placed in a reaction vessel and heated to 80°C. After dissolving, 87.0 parts of TDI was added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C, and after the dropping was completed, the temperature was increased to 80°C.
Let the reaction occur until the NCO reaction rate reaches 95% or more.
The obtained resin composition is referred to as (f). The molecular weight of this resin is 1610. Example 1 40 parts of the resin composition (a) 4 parts of the resin composition (d) Solvent (toluene/methyl ethyl ketone = 1/1)
56 parts The mixture of the above compositions was thoroughly mixed and dissolved to prepare a radiation-curable undercoating paint. After drying this paint in the form of a polyester film, it was applied using an electro-curtain type electron beam accelerator manufactured by ESI at an acceleration voltage of 160 KV and an electrode current of 160 KV.
The coating was cured by irradiation with an electron beam in an N ₂ atmosphere at a radiation dose of 10 mA and a radiation dose of 3 Mrad to form a primer layer. Next, the following magnetic paint was applied thereon, subjected to orientation treatment, surface smoothing treatment after drying, and cut into 1/2 inch width to obtain a videotape (sample #1). Manufacturing method of magnetic paint Nitrocellulose (manufactured by Asahi Kasei Corporation H1/2″) 8 parts Vinyrite VAGH (manufactured by Union Carbide Corporation)
10 parts urethane elastomer (Gutudoritsu, Ester 5703) 9 parts methyl isobutyl ketone 150 parts cyclohexanone Add 100 parts of magnetic powder (cobalt-coated iron oxide) to the solution obtained from 50 parts of α-Al ₂ O ₃ (0.5μ granules). ) 2 parts lubricant (higher fatty acid modified silicone oil) 1 part dispersant (soybean oil refined lecithin) 3 parts were blended and dispersed in a ball mill for 24 hours to prepare a magnetic paint. Example 2 The resin composition (c) 7 parts NK ester-A-4G (acrylic monomer manufactured by Shin Nakamura Chemical, molecular weight 198) 3 parts Solvent (toluene/methyl ethyl ketone = 1/1)
90 parts The mixture of the above compositions was thoroughly mixed and dissolved to prepare a radiation-curable undercoating paint. This paint is applied to a polyester film to a dry film thickness of 0.2μ, and after drying, the radiation dose is
A primer layer was cross-linked and cured by electron beam irradiation under _N2 atmosphere under conditions of 5M Rad. Next, a magnetic layer was provided in the same manner as in Example 1 to produce a videotape (sample #2). Example 3 6 parts of the above resin composition (b) 3 parts of the above resin composition (e) 1 part of 1,6 hexane glycol diacrylate 1 part of solvent (toluene/methyl ethyl ketone = 1/1)
90 parts A radiation-curable undercoating paint was prepared by thoroughly mixing and dissolving the mixture of the above compositions. This paint is applied to a polyester film to a dry film thickness of 0.1μ, and after drying, the radiation dose is
Electron beam irradiation was performed under N ₂ atmosphere under conditions of 2M Rad to provide a crosslinked and cured primer layer. Next, a magnetic layer was provided in the same manner as in Example 1 to produce a videotape (sample #3). Example 4 47 parts of the above resin composition (a) 3 parts of the above resin composition (f) 0.3 parts of benzophenone 0.1 part of triethanolamine Solvent (toluene/methyl ethyl ketone = 1/1)
50 parts The above composition was mixed and dissolved to prepare an ultraviolet curable undercoat paint. This paint was applied to a polyester film to a dry film thickness of 0.5μ, and after drying, a high-pressure mercury lamp (output
The coating film was cured by irradiating ultraviolet rays at a line speed of 10 m/min under 80 W/effective pipe length 1 cm). Next, the magnetic paint of Example 1 was applied on top of this,
After drying, the surface was smoothed and cut into 1/2 inch width to obtain a videotape (sample #4). Example 5 The above resin composition (d) 10 parts NK ester A ₄ G (manufactured by Shin Nakamura Chemical) 10 parts benzoin ethyl ether 0.3 parts Solvent (toluene/methyl ethyl ketone = 1/1)
80 parts The above composition was mixed and dissolved to prepare an ultraviolet curable paint. A videotape (sample #5) was prepared in the same manner as in Example 4, except that this paint was applied to a polyester film to a dry film thickness of 0.2 μm. Comparative Example 1 Vinyl chloride/vinyl acetate copolymer (Vinylite VAGH manufactured by Union Carbide)
10 parts Solvent (toluene/methyl ethyl ketone = 1/1)
90 parts Example 1 except that a paint obtained by mixing and dissolving the above composition was applied to a polyester film to a dry thickness of 0.5μ, and dried to form an undercoat layer.
A videotape (sample A) was prepared by providing a magnetic layer in the same manner as described above. Comparative Example 2 The magnetic paint of Example 1 was applied to a polyester film without a primer layer, and after drying, the surface was smoothed and cut into 1/2 inch width to obtain a videotape (Sample B). . Comparative Example 3 The resin composition (a) 50 parts solvent (toluene/methyl ethyl ketone = 1/1)
50 parts The above composition was mixed and dissolved to prepare a radiation-curable coating material, and a videotape (sample C) was produced in the same manner as in Example 1. Comparative example 4 NK ester-A-4G (manufactured by Shin Nakamura Chemical) 10 parts solvent (toluene/methyl ethyl ketone = 1/1)
89.5 parts Benzoin ethyl ether 0.5 parts The above composition was mixed and dissolved to prepare an ultraviolet curable paint, and a videotape (Sample D) was produced in the same manner as in Example 4. Example 6 Similarly to Example 3, a primer layer was provided on a polyester film. Next, the following radiation-curable magnetic paint was applied on top of the coating, dried, and then subjected to surface smoothing treatment.
A magnetic layer was provided by irradiating and curing with an electron beam in an N ₂ atmosphere under the conditions of 160 KV, electrode current of 10 mA, and irradiation dose of 5 Mrad. Then, it was cut into 1/2 inch width to obtain a videotape (sample #6). Method for producing radiation-curable magnetic paint Magnetic powder (cobalt-coated iron oxide) 120 parts The above resin composition (a) 15 parts (in terms of solid content) The above resin composition (d) 15 parts (in terms of solid content) Lubrication Agent 0.2 parts α-Al ₂ O ₃ (0.5μ granules) 2 parts Solvent (methyl ethyl ketone/toluene = 1/1)
200 parts The mixture of the above composition was dispersed in a ball mill for 24 hours to prepare a radiation-curable magnetic coating. Comparative Example 5 The radiation-curable magnetic paint of Example 6 was applied to a polyester film without providing a primer layer, and treated and cured in the same manner as in Example 6. then 1/
A videotape (sample #E) was obtained by cutting into a 2-inch width. Example 7 Similarly to Example 1, a primer layer was provided on a polyester film. Next, the following thermosetting magnetic paint was applied thereon, subjected to orientation treatment, drying, and smoothing treatment, and then thermally cured at 60° C. for 48 hours to form a magnetic layer. (Sample #7) Production of thermosetting magnetic paint Magnetic powder (cobalt-coated iron oxide) 100 parts Vinylite VAGH 15 parts Urethane elastomer (Ester 5703) 10 parts Methyl ethyl ketone 100 parts Methyl isobutyl ketone 100 parts Toluene 100 parts After the mixture was kneaded in a ball mill for 48 hours, 4 parts of Coronate L manufactured by Nippon Polyurethane Co., Ltd. was mixed as a crosslinking agent to prepare a magnetic paint. Comparative Example 6 In Comparative Example 1, only the formation of the magnetic layer was carried out in the same manner as in Example 7, and the rest was carried out in the same manner as in Comparative Example 1 to obtain Sample #F. Videotape samples #1 to #7 and #A to #F
Regarding the peel strength (adhesion) of the coating film and
Video sensitivity in VHS video deck (PF ₄ MHZ)
The results of the measurements are shown in Table 1. Regarding adhesion, all samples with appropriate undercoat treatment had higher values than those without treatment (#B), but those using a compound with a molecular weight of less than 400 (#D) had lower values. Therefore, the effect of using a high molecular weight component in combination was confirmed. or,
It was found that the samples subjected to the radiation curing treatment according to the present invention had higher values than the conventional ones (#A), and there were no problems with respect to adhesion. In addition, at 4MHZ video sensitivity, the undercoat layer is not cross-linked and hardened (#A).
The characteristics were lower than that of the untreated material (#B), and this is thought to be because the undercoat layer swelled when the magnetic layer was applied, damaging the surface smoothness of the magnetic layer. A similar tendency was observed with #C composed of a molecular weight of 8,000 or more and a low crosslinking density. On the other hand, since the sample subjected to the radiation hardening treatment of the present invention was easily subjected to surface smoothing treatment, the characteristics were actually improved compared to the untreated sample. 【table】

Claims (1)

[Scope of Claims] 1. A magnetic recording medium in which a magnetic layer is formed after a nonmagnetic undercoat layer is applied to a support, in which the undercoat layer (A) contains unsaturated double bonds that are curable by radiation. having a molecular weight of 5,000 or more, preferably having two or more
8,000 or more, (B) a compound with a molecular weight of 400 or more and less than 5,000, preferably 600 to 3,000, which has one or more unsaturated double bonds that are curable by radiation; (C) a compound that is curable by radiation. A compound with a molecular weight of less than 400 that has one or more unsaturated double bonds, and is formed by radiation irradiation using a radiation-curable paint containing at least two or more selected from the above (A), (B), and (C). A magnetic recording medium characterized by: 2 (A) has two or more unsaturated double bonds that are curable by radiation and has a molecular weight of 5000 or more, preferably
More than 8000 cellulose resins, vinyl chloride resins,
one or more selected from butyral resins, acrylic resins, and unsaturated polyester resins, and (B) has one or more unsaturated double bonds that are curable by radiation and has a molecular weight of 400 or more,
and less than 5,000, preferably from 600 to 3,000, of one or more selected from polyester resins, polyether resins, polyurethane resins, and epoxy resins. . 3. The radiation-curable paint contains at least two or more selected from (A), (B), and (C), and (A) is 0 to 95% by weight, (B) is 0 to 80% by weight, ( 3. The magnetic recording medium according to claim 1, wherein C) has a blending ratio of 0 to 50% by weight. 4. The radiation-curable paint contains (A) and (B), and (A)
The magnetic recording medium according to claim 1 or 2, wherein the blending ratio is 20 to 95% by weight of (B) and 5 to 80% by weight of (B). 5. The magnetic recording medium according to any one of claims 1 to 4, which is obtained by applying radiation after applying an undercoat layer and subsequently forming a magnetic layer. 6. The magnetic recording medium according to claim 5, wherein the magnetic layer is formed from a radiation-curable magnetic coating. 7. The magnetic recording medium according to any one of claims 1 to 6, wherein the radiation is an electron beam. 8 Radiation-curable paint further increases the resin solid content.
5. A magnetic recording medium according to claim 1, which contains 0.1 to 10% by weight of a photopolymerizable sensitizer and has an undercoat layer formed by irradiation with ultraviolet rays.