JPH0777021B2 - Magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium such as a video tape, an audio tape, and a computer tape.

Currently, magnetic recording media that are generally widely used include vinyl chloride-based resins, vinyl chloride-vinylidene chloride-based resins, and
There is a method of using a thermoplastic resin such as a cellulose resin, an acetal resin, a urethane resin, or an acrylonitrile butadiene resin alone or in combination, but in this method, the wear resistance of the magnetic layer is poor and the running path of the magnetic tape is soiled. It had a drawback.

Further, a method using a thermosetting resin such as a melamine resin or a urea resin, or a method of adding a crosslinkable binder such as an isocyanate compound or an epoxy compound by a chemical reaction to the thermoplastic resin is known. However, when the above crosslinkable binder is used, the storage stability of the resin solution in which the magnetic material is dispersed is poor. That is, the pot life has a shortcoming that the uniformity of the magnetic coating liquid physical properties has the disadvantage that the homogeneity of the magnetic tape cannot be maintained, and a heat treatment step is required to cure the coating film after coating and drying, It had a big defect that it took a long time to commercialize it.

In order to prevent these drawbacks, a method for producing a magnetic material in which an acrylic acid ester-based oligomer and a monomer are used as a binder and cured by electron beam irradiation is disclosed in JP-B-47-
No. 12423, JP-A-47-13639, JP-A-47-15104, JP-A-50-77433, or a technique using a binder made of a blend of a thermoplastic resin and an electron beam curable resin is disclosed in JP-A-
56-25231, JP-A-57-86130, 57-86131, 5
No. 7-127926. However, the manufacturing method disclosed in the above patent cannot provide a magnetic recording medium having high electromagnetic conversion characteristics and running durability.

In recent years, it has been required to make the support thinner to record a magnetic tape for a long time, and to improve the mechanical properties of the magnetic layer, or to improve the dispersibility of the magnetic material to increase the recording density. More than ever before,
It has been unsuccessful to impart the properties satisfying these requirements to the magnetic layer in the above technique.

The present inventors have improved the shortcomings of the conventional techniques such as the method of using a thermoplastic resin or a thermosetting resin, the method of adding a crosslinkable binder by a chemical reaction, and the method of using a curable binder by electron beam crosslinking. Therefore, as a result of earnest studies, the present invention has been achieved.

An object of the present invention is, firstly, to provide a magnetic recording medium having excellent electromagnetic conversion characteristics, and secondly to provide a magnetic recording medium having a magnetic layer having excellent durability. 3 is to provide a homogeneous magnetic recording medium with good storage stability of the magnetic coating liquid, 4th is to provide a magnetic recording medium which does not pollute the traveling route, and 5th, An object of the present invention is to provide a magnetic recording medium that does not require a heat treatment process for curing a coating film.

The above-mentioned object of the present invention is (1) at least one of a vinyl chloride-based resin and a nitrocellulose resin containing 5 × 10 ^{−5 to} 1.7 × 10 ⁻³ equivalent of (1) -CO ₂ H group per 1 g of polymer (2). This can be achieved by a magnetic recording medium comprising an urethane resin and (3) at least one monomer of an aromatic or alicyclic compound having two or more vinyl bonds in the molecule as a binder and electron beam irradiation.

That is, a feature of the present invention is to use a vinyl chloride-vinyl acetate copolymer or a nitrocellulose resin, a urethane resin and a monomer of an aromatic or alicyclic compound having two or more vinyl bonds in the molecule as a binder, It is to irradiate this with electron beam, and due to the synergistic effect of these resins,
Electromagnetic conversion characteristics were greatly improved, and a magnetic recording medium having extremely excellent running property and durability was obtained. That is, although the vinyl chloride-based resin and the nitrocellulose resin are relatively hard and highly dispersible binders, and the urethane resin is a relatively soft and highly tough binder, a vinyl bond is further added to the molecule. A hard cyclic structure by using a monomer of an aromatic or alicyclic compound containing at least one,
Due to the effect of increasing the crosslinking density due to the use of the monomer, the elastic modulus of the EB-irradiated cured product is increased due to the synergistic effect of these three components, and the durability is greatly improved.

Specific examples of the compound (1) include vinyl chloride, vinyl acetate, maleic acid copolymer, vinyl chloride-vinyl acetate-propionic acid copolymer, and nitrocellulose resin, and particularly preferably vinyl chloride-vinyl acetate. Maleic acid copolymer and cellulose dinitrate. In the case of a vinyl chloride-vinyl acetate-based copolymer, it is preferable that the --CO ₂ H group is contained in an amount of 5 × 10 ^{−5 to} 1.7 × 10 ⁻³ equivalent, and particularly preferably 3 × 10 ⁻⁴ to 1 × g. It is a compound containing 1 × 10 ⁻³ equivalent. If it deviates from this range, the electromagnetic conversion characteristics will be greatly deteriorated.

As the compound (2), a polyether type, a polyester type, or a urethane resin may be used. The preferable range of the molecular weight is 5,000 to 500,000, particularly preferably 1
It is 0,000 to 200,000. If it deviates from this range, the dispersibility of the magnetic material will deteriorate.

The compound monomer (3) may be any compound having two or more vinyl bonds in the molecule and having an aromatic ring or an alicyclic ring.

Specific examples of these compounds include divinylbenzene,
Vinyl and allyl compounds such as diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate; cyclohexanediol,
Hydroxybenzyl alcohol, decalin diol, 1,
5-dihydroxy-1,2,3,4-tetrahydronaphthalene,
2,2'-diphenyl 1,3-propanediol, 2,2'-bis (4-hydroxyethoxyphenyl) propane, 2,
Polyacrylic acid ester and methacrylic acid ester such as 2'-bis (4-hydroxypolyethoxyphenyl) propane, 2,2'-bis (4-hydroxypolyethoxycyclohexyl) propane, tris (2-hydroxyethyl) isocyanurate And so on.
Of these compounds, compounds having two or more acryloyl groups in the molecule are preferable. You may mix and use these compounds.

Further, the binder of the present invention may be mixed with a compound having one carbon-carbon unsaturated bond in the molecule and capable of being polymerized by an electron beam.

The preferred range of the composition ratio of the compound (1) to the compound (2) is 20 to 90 parts by weight / 80 to 10 parts by weight. It is particularly preferably 40 to 85 parts / 60 to 15 parts. If the compound (1) is less than this ratio or the urethane resin is less than this ratio, durability cannot be obtained. In addition, the compound of (3) is 15-20
0 parts by weight is preferable, but 20 to 100 parts by weight is particularly preferable. If the amount is larger than this ratio, the electron dose required for polymerization becomes large, which is not preferable, and if it is smaller than the above range, the crosslinking is insufficient and sufficient durability cannot 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 about 2/1 to 20/1, preferably 5/1 or more, and the average length is 0.2 to
A range of about 2.0 μm is effective. The ferromagnetic alloy powder has a metal content of 75 wt% or more, and a metal content of 80 wt% or more is a ferromagnetic metal (that is, Fe, Co, Ni, Fe-Co, Fe-Ni, Co-Ni, Fe).
-Co-Ni) with a major axis of about 1.0 μm or less. As an organic solvent used for dispersing the ferromagnetic powder and applying the magnetic coating solution, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; methyl acetate,
Esters such as ethyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether acetate; ethers such as ether tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether, dioxane; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride , Ethylene chloride, carbon tetrachloride, chloroform, chlorinated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene can be selected and used.

Further, additives such as a lubricant, an abrasive, a dispersant, an antistatic agent and an anticorrosive agent may be added to the magnetic coating liquid of the present invention.
In particular, the lubricant includes saturated and unsaturated higher fatty acids, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, food oils, fusso-based compounds, and the like, which may be added during preparation of the coating solution, Further, it may be dissolved in an organic solvent after being dried or after being smoothed or after being cured with an electron beam, or may be directly applied or sprayed on 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; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; polycarbonates, polyimides, polyamideimides, and other plastics. Other non-magnetic metals such as aluminum, copper, tin, zinc or non-magnetic alloys containing these, plastics deposited with metals such as aluminum; paper, paper such as paper coated or laminated with polyolefins, etc. Kinds can also be used.

The form of the non-magnetic support is film, tape, sheet,
It may be a disc, a card, a drum, etc., and various materials are selected as necessary according to the form.

Further, the support of the present invention has a surface (back surface) opposite to the side provided with the magnetic layer for the purpose of preventing electrification, transfer, prevention of wow-flutter, improvement of the strength of the magnetic recording material and matting of the back surface. It may be back-coated.

As the electron beam accelerator, a scanning method, a double scanning method, a curtain beam method, or a broad beam curtain method can be adopted.

As electron beam characteristics, the acceleration voltage is 100 to 1000 kV, preferably 150 to 300 kV, and the absorbed dose is 1 to 20 megarads, preferably 3 to 15 megarads. Accelerating voltage is 100k
When it is less than V, the energy transmission amount is insufficient, and when it exceeds 1000 kV, the energy efficiency used for polymerization is reduced, which is not economical. If the absorbed dose is less than 1 megarad, the curing reaction is insufficient to obtain the strength of the magnetic layer, and if it exceeds 20 megarads, the energy efficiency used for curing is reduced, and the irradiated body heats up, especially the plastic support. It is not preferable because it deforms the body.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following examples and comparative examples, all "parts" indicate "parts by weight".

Example 1 400 parts of γ-Fe ₂ O ₃ PVC-vinyl acetate-maleic acid copolymer (Co ₂ H group content polymer
Per 1 g 3.4 × 10 ^-4 eq) 45 parts Urethane resin (adipic acid - butanediol - tolylene diisocyanate condensate) 20 parts 2,2'-bis (4-acryloyl Loki Schiff enyl) propane 35 parts lecithin 4 parts of stearic Acid 4 parts Butyl stearate 4 parts Carbon black 10 parts α-Al ₂ O ₃ 4 parts Methyl ethyl ketone 1000 parts The magnetic coating liquid obtained by kneading the above components with a ball mill for 50 hours is applied onto a polyethylene terephthalate support of 15μ, and a doctor. After coating with a blade to a dry film thickness of 5 μm and orienting with a cobalt magnet, the solvent was dried (100 ° C. for 1 minute). After that, smoothing treatment (roll temperature: 60 ° C.) was performed with a 5-stage calender consisting of a group of Kotton rolls and mirror-finished rolls.

Then, irradiation was performed at an acceleration voltage of 200 kV and a beam current of 10 mA so that the absorbed dose was 10 Mrad. This sample is No. 1.

Comparative Example 1 Sample No. 2 was obtained by treating in the same manner as in Example 1 except that the binder in Example 1 was changed as follows (however, the calender roll temperature was 30 ° C.).

The same urethane resin as in Example 1 65 parts 2,2'-bis (4-acryloyloxyethoxyphenyl) propane 35 parts Comparative Example 2 The same as in Example 1 except that the binder in Example 1 was changed as follows. Sample No. 3 was obtained by treatment (however, the roll temperature of the calender was 60 ° C).

The same vinyl chloride-vinyl acetate-maleic acid copolymer as in Example 1 65 parts 2,2'-bis (4-acryloyloxyethoxyphenyl) propane 35 parts Comparative Example 3 The binder of Example 1 was prepared as follows. Instead, the same treatment as in Example 1 was performed to obtain sample No. 4.

Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 45 parts The same urethane resin as in Example 1 20 parts Trimethylolpropane triacrylate 35 parts Example 2 The same as Example 1 except that the binder of Example 1 was changed as follows. It processed and obtained sample No. 5.

PVC-vinyl acetate-maleic acid copolymer (Co ₂ H group content polymer
1 × 10 ⁻⁵ equivalent per 1 g) 40 parts Urethane resin 30 parts Tris (β-acryloyloxyethyl) isocyanurate 30 parts Example 3 The binder of Example 1 was changed as follows, and the same as Example 1. Sample No. 6 was obtained.

Nitrocellulose resin (RSP1 / 2H manufactured by Daicel) 40 parts Urethane resin 20 parts Cyclohexane diacrylate 40 parts Comparative Example 4 The binder of Example 1 was changed as follows and treated in the same manner as in Example 1 to obtain Sample No. Got 7.

45 parts of the same vinyl chloride-vinyl acetate-maleic acid copolymer as in Example 1 20 parts of the same urethane resin as in Example 1 35 parts of trimethylolpropane triacrylate Video sensitivity, still durability and
The dirt on the video head after 100 runs was measured.

The measuring method was to record a 50% set-up gray signal using an NV8200 video tape recorder manufactured by Matsushita Electric Co., Ltd., and measure the video sensitivity with a 925C type S / N meter manufactured by Shibasoku.
Video sensitivity is shown as a relative value when sample No. 1 is set to 0 dB.

Still durability refers to the time until a still image reproduced by recording a constant video signal on each sample using HR3600 manufactured by Victor Co., Ltd. loses sharpness. As for the dirt on the video head after 100 times of running, each sample was installed in the VHS cassette half and repeatedly run 100 times with the NV8200, and then the video head was observed and found to be completely free of dirt. It is terrible thing XX and the result is combined first
Shown in the table.

As is clear from the results in Table 1, (1)-
If even one of the three constituents of (3) is missing, the effect of the present invention cannot be obtained, and sample Nos. 1 and 5 of the present invention satisfying all the three constituents of (1) to (3). It can be seen that only Nos. 6 and 6 simultaneously improve the electromagnetic conversion characteristics and durability.

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Claims (1)

[Claims] 1. A support and a magnetic layer provided thereon, wherein the magnetic layer comprises a polymer containing a (1) -CO ₂ H group as a binder.
At least one of vinyl chloride-vinyl acetate resin and nitrocellulose resin containing 5 × 10 ^{−5 to} 1.7 × 10 ⁻³ equivalent per 1 g, (2) urethane resin, and (3) aromatic containing two or more vinyl bonds in the molecule. And a magnetic recording medium containing at least one monomer of an alicyclic compound and being irradiated with an electron beam.