JPH02214019A - Magnetic recording medium having less drop out and excellent electromagnetic conversion characteristics - Google Patents

Abstract

PURPOSE:To enhance mechanical toughness as well as wear resistance and weatherability and to improve the dispersibility of magnetic powders so as to enhance electromagnetic conversion characteristics by using the respectively prescribed magnetic powders for the upper layer and lower layer on a nonmagnetic base. CONSTITUTION:The 1st magnetic layer (lower layer) and the 2nd magnetic layer (upper layer) are provided on the nonmagnetic base. The magnetite type magnetic powder [FeOx(x=>=1.3 to <1.5)] is used for the 1st magnetic layer and the Co-gamma-Fe2O3 magnetic powder having 40 to 70m<2>/g BET value and 800 to 1,000Oe HC is used for the 2nd magnetic layer. Polyurethane having the wear resistance is used as the binder. The film thickness of the 2nd magnetic layer is preferably specified to 0.1 to 1.4mum.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, magnetic floppy disks, etc., especially magnetic recording media suitable for video tapes for 5-VH3 video. It's about the medium.

[Background of the Invention] As is well known, 5-VHS is a new video standard that has emerged in recent years and is an evolution of the VHS format.

In other words, in the VH3 system, the horizontal resolution is 240
However, the 5-VHS format achieved over 400 copies. By expanding the luminance signal band in the high frequency direction in this way, the amount of information in the 5-VHS system is significantly increased compared to the VH3 system.

For this reason, it is thought that the 5-VH3 system will become the mainstream in the future.

By the way, in magnetic recording media (video tapes) for 5-VHS, conventionally either magnetic powder for 5-V) Is was used in a single layer or magnetite was used in a single layer. .

However, in the former case, the surface resistivity of the tape was high, resulting in many dropouts, and in the latter case, the dispersibility of the magnetic powder was poor, and therefore the electromagnetic conversion characteristics were at a low level.

[Object of the Invention] In view of the above-mentioned circumstances, the present inventors have conducted various studies aimed at improving the above-mentioned drawbacks found in conventional magnetic recording media (video tapes) for 5-VB2. It has been found that the present invention as presented achieves that objective.

[Structure of the Invention] That is, the present invention provides a magnetic recording medium comprising a first magnetic layer (lower layer) and a second magnetic layer (upper layer) on a non-magnetic support, in which the first magnetic layer contains magnetite-type magnetic powder. [Fe
0x (x = 1.3 or more, less than 1.5)], and the second magnetic layer has a BET value of 40 to 70 m''/gsHC of 800 to 1 OOO, Oe (Oersted) CO-γ.
The present invention relates to a magnetic recording medium characterized by using -Fe, 0° magnetic powder.

As for the magnetic material used in the present invention, magnetite represented by Fe0x (x=1.3 or more, less than 1.5) is used for the first magnetic layer as described above, and the BET value is 40 to 40 for the second magnetic layer. 70m”/g, IC 800~1000.Oe
(Oersted) Co-γ-Fe, 03 magnetic powder is used. C with a BET value of less than 40+a”/g in the second magnetic layer
If o-γ-Fe2O3 magnetic powder is used, it is undesirable because the electromagnetic conversion characteristics, especially video S/N, will deteriorate, and if Co-γ-Fe2O3 with an HC of less than 800 is used, the frequency band will deteriorate. This is not desirable because the output is at a low level throughout.

The binder used in the present invention includes abrasion-resistant polyurethane. It has strong adhesion to other materials, is mechanically strong to withstand repeated applied forces or bending, and has good abrasion and weather resistance.

Furthermore, if a cellulose resin and a vinyl chloride copolymer are used in combination with polyurethane, the dispersibility of the magnetic powder in the magnetic layer will be improved and its mechanical strength will be increased. However, if only the cellulose resin and the vinyl chloride copolymer are used, the layer becomes too hard, but this can be prevented by the presence of the above-mentioned polyurethane.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. The above polyurethane and vinyl chloride copolymers may be partially hydrolyzed.

Preferable examples of the vinyl chloride copolymer include a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol.

Phenoxy resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

These advantages are complementary to those of the polyurethane described above, and the stability of the physical properties of the magnetic recording medium over time can be significantly improved.

Furthermore, in addition to the binders described above, mixtures of thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used.

In order to improve the durability of the magnetic layer of the magnetic tape of the present invention, the magnetic paint can contain various curing agents, such as incyanate. Examples of aromatic isocyanates include tolylene diisocyanate (TDI) and adducts of these incyanates with active hydrogen compounds, and have an average molecular weight of 100 to 100.
A range of 3.000 is preferred.

Examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic incyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

A dispersant is used in the magnetic paint used to form the magnetic layer, and additives such as a lubricant, an abrasive, a matting agent, an antistatic agent, etc. may be included as necessary. Dispersants used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. It is also possible to use salts of polymeric dispersants having negative organic groups (for example -〇〇〇I()).

These dispersants may be used alone or in combination of two or more. In addition, as lubricants, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acids having 12 to 16 carbon atoms, and the number of carbon atoms of the fatty acids are used. Total number of carbon atoms is 2
Fatty acid esters (so-called waxes) consisting of 1 to 23 monohydric alcohols can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

Commonly used abrasive materials include various aluminas such as fused alumina and σ alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery (main components: corundum and magnetite). used. These abrasives have an average particle size of 0.05 to 5μ
The size of 0.1 mm is used, particularly preferably 0.1~
It is 2 μm.

These abrasives are used in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder.
It is added in a range of parts by weight.

As the matting agent, organic powder or inorganic powder may be used individually or in combination.

As the organic powder used in the present invention, acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin are preferred. Powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, titanium 11ide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, and calcium carbide. , σ-Fe,
0. , talc, kaolin, calcium sulfate, boron nitride,
Examples include zinc fluoride and molybdenum dioxide.

Antistatic agents include carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponin, alkylene oxides, and glycerin. Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphoniums or sulfoniums; Carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acids Anionic surfactants containing acidic groups such as ester groups and phosphate ester groups; amino acids;
Examples include amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

Solvents to be added to the above paint or diluting solvents during application of this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, lovanol, and butanol, and methyl acetate. , esters such as ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, Halogenated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-7-talate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polyamide and polycarbonate, and metals such as Cu, Aff, and Zn. , glass, boron nitride.

Ceramics such as Si carbide can also be used.

The thickness of these supports is approximately 3 to 100 μm thick in the case of a film or sheet, preferably 5 to 50 μm in thickness, and approximately 3011 m = 10 mm in the case of a disk or card shape, and approximately 3011 m = 10 mm in the case of a drum shape. is used in a cylindrical shape, and its shape is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, Spray coats, extrusion coats, etc. can be used, but are not limited to these.

When constructing a magnetic layer on a support using these coating methods, there are two methods: one method involves stacking the coating and drying steps layer by layer (so-called wet-on-dry coating method), and the other method involves stacking the coating and drying steps layer by layer (so-called wet-on-dry coating method). There is a method in which layers are coated simultaneously or sequentially (a so-called wet-on-wet semi-method), but either method can be used in manufacturing the magnetic recording medium of the present invention.

In the present invention, if the thickness of the second magnetic layer is made too thick, the performance of the first magnetic layer will be blocked and long wavelength signals will be difficult to be recorded in the lower layer, which is undesirable.
The thickness of the magnetic layer is usually preferably 0.1 to 1.4 microns.

Furthermore, other magnetic layers or nonmagnetic layers may be provided above and below or between the first magnetic layer and the second magnetic layer, without impairing the effects of the present invention.

The magnetic layer coated on the support by the method described above is optionally treated to orient the ferromagnetic metal oxide powder in the layer, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is approximately 500 to 50
00 Gauss, and the drying temperature is approximately 50 to 120°C.
degree, drying time is approximately 0. -5 to IO minutes. Further, if necessary, the magnetic recording medium of the present invention is manufactured by subjecting it to surface smoothing treatment or cutting it into a desired shape.

Next, the present invention will be explained with reference to examples, but it goes without saying that the present invention is not limited to these examples.

[Example] Examples and Comparative Examples 1 and 2 Magnetic paints for the lower layer (first magnetic layer) and upper layer (second magnetic layer) having the compositions listed in Tables 1 and 2 were kneaded to obtain each component. After well dispersing the paint, use a solvent (a mixture of methyl ethyl ketone and toluene) to reduce the viscosity of the paint to 1 to 1.
Adjusted to 20 poise.

After that, polyisocyanate [Nippon Polyurethane Industry Co., Ltd.
A magnetic paint for coating was prepared by adding 5 parts by weight of Coronate (trade name, manufactured by Co., Ltd.).

Next, a magnetic paint for the lower layer and a magnetic paint for the upper layer were coated in multiple layers according to a conventional method so that the thickness of the upper layer was within the range of 0.1 to 1.5 .mu.I, and dried to produce a magnetic recording medium.

Separately, for comparison, the lower layer (Comparative Example 2) and upper layer (
A magnetic recording medium consisting of only each single layer of Comparative Example 1) was manufactured.

The electromagnetic conversion characteristics and other characteristics of the magnetic recording medium thus obtained were measured.

Table 1: First magnetic layer (lower layer) Table 2: Second magnetic layer (upper layer) Table 3 As is clear from the results in Table 3, in the magnetic recording medium of the example, Comparative Examples 1 and 2 (this application The dropout is lower than that of the upper or lower magnetic layer (a layer consisting of a single upper or lower magnetic layer), and the RF output and Luminous S/N are also higher than those.

Therefore, it goes without saying that other electromagnetic conversion characteristics are also improved in parallel.

<Method for measuring characteristics in Examples and Comparative Examples> ・100% in a certain section (10 to 30 m) on a dropout magnetic recording medium
A white signal is input and played, and at that time, 15 dropouts are measured at a -12 dB level using a Shibaku Co., Ltd. counter (Model V IOIBZ) for 1 minute, and the average value of the total length of the measured part is taken as the measured value. do.

・Why by 5-VOS method on the RF output magnetic recording medium) 10
Input 0% signal at reference level, reproduced RF output signal at N
Input to F Design Block AC ammeter M-170L and read the output level.

・Lumi S/N White 100 by 5-VHS method on magnetic recording medium
% signal at reference level input playback video signal 925D
/1 Input into [noise meter manufactured by Shibatsu Co., Ltd.],
Read the Lumi S/N from the obtained noise absolute value.

[Effects of the Invention] The 5-VHS magnetic recording medium of the present invention has few dropouts and has excellent electromagnetic conversion characteristics, especially RF output and Luminous S/N.
Excellent.

Claims (2)

[Claims] (1) A first magnetic layer (lower layer) and a second magnetic layer on a non-magnetic support.
In a magnetic recording medium provided with a magnetic layer (upper layer), the first magnetic layer contains magnetite-type magnetic powder [FeO_x (x=1
．． 3 or more and less than 1.5)], and the second magnetic layer has a BET value of 40 to 70/g and a HC of 800 to 1000.
．． A magnetic recording medium characterized by using Oe (Oersted) Co-γ-Fe_2O_3 magnetic powder. (2) The magnetic recording medium according to claim (1), wherein the second magnetic layer has a thickness of 0.1 to 1.4 μm.