JPH0381203B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnetic recording media such as video tapes, audio tapes, and computer tapes. Magnetic recording media that are currently widely used use thermoplastic resins such as vinyl chloride acetate resins, vinyl chloride-vinylidene chloride resins, cellulose resins, acetal resins, urethane resins, and acrylonitrile butadiene resins as binders, either singly or in combination. However, this method has the disadvantage that the abrasion resistance of the magnetic layer is poor and the running path of the magnetic tape is contaminated. Also known are a method using a thermosetting resin such as a melamine resin or a urea resin, or a method in which a crosslinkable binder such as an isocyanate compound or an epoxy compound is added to the thermoplastic resin through a chemical reaction. However, when the above-mentioned crosslinking binder is used, the storage stability of the resin solution in which the magnetic material is dispersed is poor. That is, it has the disadvantage of a short pot life, the disadvantage that the uniformity of the physical properties of the magnetic coating liquid and, by extension, the homogeneity of the magnetic tape cannot be maintained, and a heat treatment process is required to harden the coating film after coating and drying. However, the major drawback was that it took a long time to commercialize the product. In order to prevent these drawbacks, a method for producing magnetic materials using acrylic acid ester oligomers and monomers as binders and curing them by electron beam irradiation was proposed in Japanese Patent Publication No. 12423/1983 and Japanese Patent Application Laid-open No. 1983-12423.
13639, JP-A-47-15104, and JP-A-50-77433, or JP-A-56-1999 discloses a technique using a binder made of a blend of thermoplastic resin and electron beam curable resin.
No. 25231, JP-A-57-86130, JP-A No. 57-86131,
It is disclosed in No. 57-127926, etc. However, with the manufacturing method disclosed in the above patent, a magnetic recording medium having high electromagnetic conversion characteristics and running durability could not be obtained. In recent years, there has been a need to make the support thinner for long-term recording on magnetic tapes, and improvements in the mechanical properties of the magnetic layer have been required, as well as improvements in the dispersibility of the magnetic material in order to achieve higher recording densities. are required more than ever before, but the above techniques have not been able to impart properties that satisfy these demands to the magnetic layer. The present inventors have improved the drawbacks of conventional techniques such as methods using thermoplastic resins or thermosetting resins, methods adding crosslinkable binders by chemical reaction, and methods using curable binders by electron beam crosslinking. As a result of extensive research to achieve this goal, the present invention has been achieved. The purpose of the present invention is, firstly, to provide a magnetic recording medium with excellent electromagnetic conversion characteristics, and secondly, to provide a magnetic recording medium with excellent electromagnetic conversion characteristics.
The third object is to provide a magnetic recording medium with a smooth magnetic layer surface.The third object is to provide a magnetic recording medium in which the magnetic coating liquid has good storage stability and is homogeneous.
The second object is to provide a magnetic recording medium with excellent wear resistance, and the fifth object is to provide a magnetic recording medium that does not require a heat treatment step for curing the coating film. The above objects of the present invention are (1) at least one of a salt vinyl acetate resin and a nitrocellulose resin containing -CO ₂ H groups in an amount of 5 x 10 ^-5 to 1.7 x 10 ^-3 equivalents per gram of polymer; (2) urethane resin; This is achieved by a magnetic recording medium that contains a resin and (3) a compound obtained by modifying the isocyanate group of an isocyanate compound having two or more isocyanate groups with acryloyl as a binder, and is irradiated with an electron beam. That is, the characteristics of the present invention are that a vinyl chloride-vinyl acetate copolymer, a nitrocellulose resin, a urethane resin, and a compound obtained by modifying the isocyanate group of a compound having two or more isocyanate groups with acryloyl are used as a binder, and that the Due to the synergistic effect of these resins, electromagnetic conversion characteristics were greatly improved, and a magnetic recording medium with extremely excellent runnability and durability was obtained. It is presumed that this is because the compound (2) and the compound (3) have similar chemical structures (urethane bonds) and thus have good compatibility. Specific examples of the compound (1) include vinyl chloride-biacetic acid-maleic acid copolymer, vinyl chloride-biacetic acid-propionic acid copolymer, nitrocellulose resin, etc. Particularly preferred are vinyl chloride-biacetic acid-maleic acid copolymer. copolymers and cellulose dinitrate. In the case of a vinyl chloride-vinyl acetate copolymer, the -CO ₂ H group is 5x per gram of polymer.
The compound preferably contains 10 ^-5 to 1.7 x 10 ^-3 equivalents, particularly preferably 3 x 10 ^-4 to 1 x 10 ^-3 equivalents. Outside this range, the electromagnetic conversion characteristics deteriorate significantly. As the compound (2), a polyether type or polyester type urethane resin may be used. The preferred range of molecular weight is 5,000 to 500,000, particularly preferably 10,000 to 200,000. Outside this range, the dispersibility of the magnetic material deteriorates. The compound (3) may be any compound obtained by modifying the isocyanate group of a polyisocyanate compound having two or more isocyanate groups with acryloyl. Specifically, tolylene diisocyanate,
Polyisocyanates such as naphthylene-1,5-diisocyanate, o-toluylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, trimethylolpropane tolylene diisocyanate triadduct; It is a polyacrylate compound obtained by reaction with a hydroxyl group-containing acrylic ester such as 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate. These compounds can be used in combination. Furthermore, a compound having one carbon-carbon unsaturated bond in the molecule and capable of polymerization by electron beams may be mixed with the binder of the present invention. The preferable range of the composition ratio of the compound (1) and the compound (2) is 20 to 90 parts by weight/80 to 10 parts by weight. Particularly preferably 40 to 85 parts/60 to 15 parts. If the ratio of the compound (1) is below this level or the ratio of the urethane resin is below this level, durability cannot be obtained. Also,
The amount of the compound (3) is preferably 15 to 200 parts by weight, particularly preferably 20 to 100 parts by weight. If the ratio is higher than this, the amount of electron beam required for polymerization will become large, which is undesirable, and if it is lower, crosslinking will be insufficient and sufficient durability will not be obtained. As the ferromagnetic powder used in the present invention, ferromagnetic iron oxide fine powder, Co-doped ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, ferromagnetic alloy powder barium ferrite, etc. can be used. The acicular ratio of ferromagnetic iron oxide and chromium dioxide is 2/1 to 20/1.
degree, preferably 5/1 or more, average length is 0.2 to 2.0μ
A range of about m is effective. The ferromagnetic alloy powder has a metal content of 75 wt% or more, and 80 wt% or more of the metal content is ferromagnetic metal (i.e., Fe, Co, Ni, Fe-Co,
Fe−Ni, Co−Ni, Fe−Co−Ni) with a major axis of approx.
Particles of 1.0 μm or less. Organic solvents used for dispersing ferromagnetic powder and applying magnetic coating liquid include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid glycol monoethyl ether, etc. ester series;
Ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether,
Ethers such as dioxane; aromatic hydrocarbons such as benzene, toluene, and xylene; and chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene are selected. It can be used as Furthermore, additives such as lubricants, abrasives, dispersants, antistatic agents, and rust preventives may be added to the magnetic coating liquid of the present invention. In particular, lubricants include saturated and unsaturated higher fatty acids, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, food oils, and fuso-based compounds, which may be added when preparing the coating solution. Further, after drying, smoothing treatment, or electron beam curing, it may be dissolved in an organic solvent, or it may be applied or sprayed directly onto the surface of the magnetic layer. As the support to which the magnetic coating liquid is applied, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyethylene;
In addition to plastics such as polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, polycarbonate, polyimide, and polyamideimide, aluminum,
Non-magnetic metals such as copper, tin, zinc, or non-magnetic alloys containing these; plastics on which metals such as aluminum are vapor-deposited; papers such as paper and paper coated with or laminated with polyolefins can also be used. The form of the non-magnetic support may be any film, tape, sheet, disk, card, drum, etc., and various materials are selected as necessary depending on the form. The support of the present invention is back-coated on the side opposite to the side on which the magnetic layer is provided (back side) for the purpose of preventing static electricity, preventing transfer, preventing wow and flutter, improving the strength of the magnetic recording medium, and making the back side matte. You can leave it there. As the electron beam accelerator, scanning method, double scanning method, curtain beam method, broad beam curtain method, etc. can be adopted. As for electron beam characteristics, acceleration voltage is 100~
The voltage is 1000 kV, preferably 150 to 300 kV, and the absorbed dose is 1 to 20 megarads, preferably 3 to 15 megarads. When the accelerating voltage is less than 100 kV, the amount of energy transmitted is insufficient, and when it exceeds 1000 kV, the energy efficiency used for polymerization decreases, making it uneconomical. If the absorbed dose is less than 1 megarad, the curing reaction will be insufficient and the strength of the magnetic layer will not be obtained.
If it exceeds a mega ton, the efficiency of the energy used for curing decreases, the object to be irradiated generates heat, and especially the plastic support is deformed, which is not preferable. The present invention will be explained in more detail below using Examples and Comparative Examples. In the following Examples and Comparative Examples, all "parts" indicate "parts by weight." Example 1 γ-Fe ₂ O ₃ 400 parts PVC-acetic acid-maleic acid copolymer (3.4×10 ^-4 equivalent per 1 g of CO ₂ H group content polymer) 40 parts Urethane resin (adipic acid-butanediol-
Tolylene diisocyanate condensate) 20 parts CH ₂ = CHCO ₂ CH ₂ CH ₂ OCONH
(CH ₂ ) ₆ NHCO ₂ CH ₂ CH ₂ OCOCH=CH ₂ 40 parts lecithin 4 parts stearic acid 4 parts butyl stearate 4 parts α-Al ₂ O ₃ 4 parts carbon black 10 parts methyl ethyl ketone 1000 parts The magnetic coating liquid obtained by kneading for hours was applied onto a 15μ polyethylene terephthalate support using a doctor blade to a dry film thickness of 5μ, oriented using a cobalt magnet, and then the solvent was dried ( (100°C for 1 minute). Thereafter, smoothing treatment was carried out using a five-stage calender consisting of a group of cotton rolls and mirror-finished rolls (roll temperature: 60°C, pressure: 100 kg/cm ² ). Then, at an accelerating voltage of 200 kV and a beam current of 10 mA,
Irradiation was performed to give an absorbed dose of 10 Mrad. Let this sample be No. 1. Comparative Example 1 Sample No. 2 was obtained in the same manner as in Example 1 except that the binder used in Example 1 was changed as follows. Salt vinyl acetate resin (same as Example 1) 40 parts Urethane resin (same as Example 1) 20 parts Tetraethylene glycol diacrylate 40 parts Comparative example 2 Example by changing the binder of Example 1 as follows. Sample No. 3 was obtained by processing in the same manner as in 1. Nitrocellulose (Daicel RS1/2H) 40 parts Urethane resin same as Example 1 30 parts Trimethylolpropane triacrylate 30 parts Comparative Example 3 The vinyl chloride-acetic acid-maleic acid copolymer of Example 1 was mixed with vinyl chloride-vinyl acetate-maleic acid copolymer. Sample No. 4 was obtained in the same manner as in Example 1 except that a vinyl alcohol copolymer (vinyl alcohol content: 4%) was used. Example 2 Sample No. 5 was obtained in the same manner as in Example 1 except that the binder in Example 1 was changed as follows. PVC-acetic acid-maleic acid copolymer (CO ₂ H content: 1×10 ^-5 equivalent per gram of polymer) 40 g Urethane resin 30 g For the above samples, video sensitivity, video S/N, still durability, dirt on the video head after 100 runs, and video sensitivity after 100 runs were measured. The measurement method was to record a 50% setup gray signal using a Matsushita Electric Co., Ltd. NV8200 video tape recorder, and measure the video sensitivity and video S/N using a Shibasoku 925C S/N meter. Video sensitivity and video S/N are expressed as relative values when sample No. 1 is OdB. In addition, the video sensitivity after 100 runs indicates the decrease in output when the initial output of each sample is used as the standard (OdB). To check the dirt on the video head after running 100 times, insert each sample into a VHS cassette half and use the NV8200.
After running 100 times, the video head was observed, and those with no stains were marked with a circle, those with stains with an x mark, and the results are shown in Table 1.

[Table] From the results in Table 1, it can be seen how the tape of the present invention has excellent electromagnetic conversion characteristics and durability.

Claims (1)

[Claims] 1 Consisting of a support and a magnetic layer provided thereon, the magnetic layer is a vinyl acetate-based material containing 5×10 ^-5 to 1.7×10 ^-3 equivalents of (1)-CO ₂ H per gram of polymer as a binder. A magnetism comprising at least one of a resin and a nitrocellulose resin, (2) a urethane resin, and (3) a compound in which the isocyanate group of a polyisocyanate compound having two or more isocyanate groups is modified with acryloyl, and is irradiated with an electron beam. recoding media.