JP2893267B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, particularly to a magnetic recording medium suitably used as a video tape.

[Background of the Invention]

A magnetic recording medium is generally made of a ferromagnetic powder, a polymer material (resin material) called a binder.
Abrasives, antistatic agents such as carbon black, lubricants, curing agents and other additives evenly dispersed,
It is manufactured by applying a magnetic paint obtained by appropriately adding a solvent as needed to a support, and drying.

Conventionally, carbon black was added to a magnetic layer containing a barium ferrite (Ba-Fe) magnetic material consisting of ferromagnetic metal powder or tabular particles to improve the wear resistance of the magnetic layer and reduce the surface resistivity. A magnetic recording medium is known.

However, when carbon black is contained in the magnetic layer, there is a disadvantage that the electromagnetic conversion characteristics of the magnetic recording medium deteriorate due to the deterioration of the surface roughness of the magnetic layer and the decrease of the filling rate of the magnetic material.

In particular, carbon black excellent in wear resistance and having an average particle diameter of 50 μm or more increases the surface roughness of the magnetic layer and causes a decrease in the chroma S / N of the magnetic recording medium.

In addition, carbon black with an average particle diameter of 50 mμ or less and an oil absorption of 100 ml or more used for the purpose of lowering the surface resistivity of the magnetic layer is difficult to disperse in the magnetic layer, and reduces the orientation and filling rate of the magnetic material. As a result, the chroma output of the magnetic recording medium decreases.

As another prior art, it is known to provide a magnetic layer containing ferromagnetic metal powder or barium ferrite magnetic particles with a thickness of 4.0 μm or more on a dried film of an undercoat layer containing carbon black.

However, if the thickness of the magnetic layer (upper layer) is set to 4.0 μm or more, the effect of the carbon black undercoat layer is lost, and the surface resistivity of the magnetic layer does not decrease. And the dropout of the magnetic recording medium increases.

In addition, this method employs a so-called wet-on-dry multi-layer coating method in which a magnetic paint is multi-layer coated on a dried sub-layer, so that not only the process is complicated, but also the surface of the sub-layer is coated. The roughness adversely affects the magnetic layer and lowers the chroma S / N of the magnetic recording medium.

[Object of the invention]

In view of the above, the present inventors have made intensive studies to improve the above-mentioned conventional technology and provide a magnetic recording medium in which the above-mentioned drawbacks have been corrected. They have found that they are suitable and have reached the present invention.

[Configuration of the invention]

That is, the present invention, on a non-magnetic support, provided a non-magnetic layer containing 40 to 140 parts by weight of carbon black with respect to 100 parts by weight of the binder, further containing a Fe-Al ferromagnetic metal powder thereon A magnetic layer is provided, and the thickness of the magnetic layer is 0.3 to 2.5.
μm, and the non-magnetic layer and the magnetic layer
The present invention relates to a magnetic recording medium characterized by being simultaneously formed on the non-magnetic support by an on-wet multilayer coating (wet multilayer coating) method.

 Hereinafter, the present invention will be described.

Conventional ferromagnetic materials used in this type of magnetic recording medium include, for example, Co-γ-Fe ₂ such as γ-Fe ₂ O ₃ , C-containing γ-Fe ₂ O ₃ or Co-coated γ-Fe ₂ O _3. O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄
Or _{Co-γ-Fe 3 O 4} , CrO 2 oxide magnetic material such as Co-coated Fe ₃ O _4, and other, for example Fe, Ni, Fe-Ni alloy, Fe
-Co alloy, Fe-Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-
Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co
-Fe, Ni, Co such as Ni-P alloy, Co-P alloy, Co-Cr alloy
Various ferromagnetic materials (powder) such as metal magnetic powder mainly composed of
It has been proposed that elements such as Si, Cu, Zn, Al, P, Mn, and Cr or compounds thereof may be added as an additive to these metal magnetic materials.

In the magnetic recording medium of the present invention, Fe-
It is an essential requirement to use an Al-based ferromagnetic metal powder.

However, in addition to the above-mentioned essential components, any of the above-mentioned known magnetic materials may be contained in the magnetic layer without impairing the effects of the present invention.

As the binder (binder) used in the present invention,
Abrasion resistant polyurethane resin is exemplified.

It has strong adhesion to other substances, is mechanically tough against repeated applied forces or bending, and has good wear resistance and weather resistance.

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

Cellulose ether,
Cellulose inorganic acid esters and cellulose organic acid esters can be used. The above-mentioned polyurethane and vinyl chloride copolymer may be partially hydrolyzed.

As the vinyl chloride copolymer, preferably, a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol is used.

Vinyl chloride resin, vinyl chloride-vinyl acetate copolymer,
As the polyurethane resin or the like, it is particularly preferable to use a modified product containing a functional group, particularly a negative functional group.

Phenoxy resins can also be used. Phenoxy resin has high mechanical strength, excellent dimensional stability,
It has advantages such as good heat resistance, water resistance, chemical resistance and good adhesiveness.

These advantages are complementary to the above-mentioned polyurethane resin in length and length, and can significantly improve the temporal stability of the physical properties of the magnetic recording medium.

Further, in addition to the binder described above, a mixture with a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam irradiation-curable resin may be used.

Various hardeners can be contained in the magnetic paint to improve the durability of the magnetic layer of the magnetic recording medium of the present invention,
For example, an isocyanate can be contained. Examples of the aromatic isocyanate include tolylene diisocyanate (TDI) and the adduct thereof with these isocyanate active hydrogen compounds.
A range of 3,000 is preferred.

Examples of the aliphatic isocyanate include hexamethylene diisocyanate (HMDI) and the like, and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight of preferably
It is in the range of 100-3,000. Of the aliphatic isocyanates, 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 if necessary, a lubricant, an abrasive,
Additives such as a matting agent and an antistatic agent may be contained.

Examples of the dispersant used in the present invention include phosphate esters,
Amine compounds, alkyl sulfates, fatty acid amides,
There are higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinate, known surfactants and the like, and salts thereof, and use of a salt of a polymer dispersant having a negative organic group (for example, -COOH). Can also. These dispersants may be used alone or in combination of two or more.

As the lubricant, 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 and Fatty acid esters (so-called waxes) composed of monohydric alcohols having a total of 21 to 23 carbon atoms can also be used. These lubricants are added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As abrasives, commonly used materials include fused alumina, various aluminas such as α-alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond,
Garnet, emery (main components: corundum and magnetite) and the like are used. These abrasives have an average particle size of 0.05 to 5 μm
The size is used, particularly preferably 0.1 to 2 μm
m. These abrasives are added in the range of 1 to 20 parts by weight based on 100 parts by weight of the binder.

As the matting agent, an organic powder or an inorganic powder is used individually or as a mixture.

As the organic powder used in the present invention, acrylic styrene-based resin, benzoguanamine-based resin powder, melamine-based resin powder, and phthalocyanine-based pigment are preferable, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, and polyimide-based resin are preferable. Powders, polyfluorinated ethylene resin powders and the like can also be used. As inorganic powders, silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α-Fe ₂ O
₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide.

Conventionally, as an antistatic agent, including carbon black, graphite, tin oxide-antimony oxide compounds,
Conductive powders such as titanium oxide-tin oxide-antimony oxide-based compounds, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide-based, glycerin-based, and glycidol-based higher alkylamines, quaternary ammonium salts, Pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfoniums,
Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, phosphate group, etc. Although it is known to contain, in the present invention, in particular,
Usually, an undercoat layer comprising the above-mentioned binder and carbon black is provided on a support, and carbon black is contained in the undercoat layer.

The amount of the carbon black used is 40 to 140 parts by weight based on 100 parts by weight of the binder.

The thickness of the undercoat layer is usually preferably about 1.0 μm.

As long as the effects of the present invention are not impaired, in addition to the above-described antistatic agent together with carbon black in the undercoat layer,
Any known additives that help improve the abrasion resistance of the magnetic layer and reduce the surface resistivity can be included.

Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone are used as a solvent to be mixed with the magnetic paint or a diluting solvent at the time of applying the paint.
Alcohols such as methanol, ethanol, propanol, butanol, etc., esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate, ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran, benzene And aromatic hydrocarbons such as toluene, xylene, and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene.

Examples of the support include polyethylene terephthalate, polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose derivatives such as cellulose diacetate, polyamides, and plastics such as polycarbonate. Metals such as Cu, Al, and Zn, glass, boron nitride, and ceramics such as Si carbide can also be used.

The thickness of these supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of a film or a sheet, about 30 μm to 10 mm in the case of a disk or a card, and is cylindrical in the case of a drum. The type 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 doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, and spray coating. A coat, an extrusion coat and the like can be used, but not limited to these.

When a magnetic layer is formed on a support by these coating methods, a system in which coating and drying steps are stacked one by one (so-called wet-on-dry coating system) or a method in which the next layer is placed on a layer in a wet state that has not been dried Is applied simultaneously or successively (so-called wet-on-wet coating method = wet multilayer coating method). In manufacturing the magnetic recording medium of the present invention, wet-on-wet method is particularly preferred from the viewpoint of effect. Simultaneous multilayer coating by a multilayer coating method is performed.

If the thickness of the magnetic layer is too large, the significance of providing a layer containing carbon black as an undercoat layer is lost,
In the present invention, the thickness of the magnetic layer is in the range of 0.3 to 2.5 μm, particularly preferably 0.3 to 1.5 μm.

When the thickness of the magnetic layer exceeds 4.0 μm, the surface resistivity of the magnetic layer increases and the dropout of the magnetic recording medium increases. On the other hand, when the thickness of the magnetic layer is smaller than 0.3 μm, the influence of the undercoat layer appears strongly on the magnetic layer, the surface of the magnetic layer becomes rough, and the Lumi S / N and chroma S / N of the magnetic recording medium are reduced. descend.

According to such a method, the magnetic layer applied on the support is subjected to a treatment for orienting the ferromagnetic metal oxide powder in the layer if necessary, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is about 20 to 5000 gauss in AC or DC, the drying temperature is about 30 to 120 ° C., and the drying time is about 0.1 to 10 minutes. Further, the magnetic recording medium of the present invention is manufactured by performing a surface smoothing treatment or cutting it into a desired shape as necessary.

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

Example <Preparation of undercoat layer (underlayer) paint> Carbon black (average particle diameter 20mμ, oil absorption 115ml / 100)
g) 20 parts by weight and 15 parts by weight of a potassium sulfonate-containing polyurethane resin (trade name: UR8700, manufactured by Toyobo Co., Ltd.) are kneaded with a small amount of solvent in a kneader, and further diluted with a solvent to obtain a viscosity of 10 to 50 centipoise. After that, each component was dispersed in a sand mill, and 5 parts by weight of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to prepare a coating for an undercoat layer.

<Preparation of paint for magnetic layer (upper layer)> A magnetic paint having the composition shown in Tables 1 and 2 was kneaded with a small amount of a solvent in a kneader, and further mixed with a solvent mixture of cyclohexanone, methyl ethyl ketone and toluene to obtain a viscosity of 50%.
After diluting to a poise, each component was dispersed with a sand mill. Further, the mixture was diluted with the above mixed solvent so that the viscosity became 10 poise, and 5 parts by weight of polyisocyanate was added to prepare a coating material for a magnetic layer.

<Coating> The upper layer and the lower layer were simultaneously coated on the support by a wet-on-wet coating method using an extrusion-type coating coater.

At this time, the thickness of the lower layer was about 1 μm, and the thickness of the upper layer was 0.1 μm.
The discharge amount of the coating liquid was adjusted by a pump so as to be 3 to 4 μm.

After the upper layer and the lower layer were simultaneously coated on the support in this manner, the magnetic recording medium was manufactured by applying treatments such as magnetic field orientation and drying according to a conventional method.

Table 3 shows the manufacturing conditions of the magnetic recording medium, and Table 4 shows the characteristics of the obtained magnetic recording medium.

As is clear from Table 4, the magnetic recording medium of the present invention (Examples 1 and 2) has a higher filling factor of the magnetic material in the magnetic layer than the magnetic recording medium of Comparative Example 1 due to the presence of the lower layer containing carbon black. , The electromagnetic change characteristics, especially the chroma output, are improved.

Further, the magnetic recording medium of the present invention has an appropriate upper layer thickness (2.5 μm), and therefore has much less dropout than the magnetic recording medium of Comparative Example 3 (upper layer thickness of 4.5 μm).

Furthermore, the magnetic recording medium of the present invention has better chroma S / N ratio because it has better surface properties than the magnetic recording medium of Comparative Example 4 by the wet-on-dry multilayer coating method.

Further, the magnetic recording medium of the present invention has better electromagnetic conversion characteristics than the magnetic recording medium using a general Co-γ-iron oxide as a magnetic material (Comparative Example 5).

◎ Measuring method in Examples and Comparative Examples <RF output> Comparative Example 1
Was determined in comparison with the tape of Comparative Example 1 based on the tape of Example 1.

<Lumi S / N> A 100% white signal is input to a magnetic recording medium at a reference level, a reproduced video signal is input to a 925D (Shibasoku, noise meter), and the Lumi S / N is read from the obtained absolute noise value.

<Chroma output> The output during reproduction of an RF signal at 500 kHz was determined.

<Chroma S / N> The difference between the S / N of the sample in the chroma signal was determined in comparison with Comparative Example 1 using a noise meter manufactured by Shibasoku.

<Surface resistivity> Each slit tape is sandwiched between 1/2 inch wide electrodes,
A load was applied to both ends, and the electric resistance when a voltage of 500 V was applied was measured.

<Dropout> A 100% white signal is input to and reproduced from a magnetic recording medium in a fixed section (10m to 30m). At that time, 10μs at -14dB level
The dropout of Shivasoku Counter (Model
VHO1BZ), and the average value of the entire length of the measurement part is used as the measurement value.

〔The invention's effect〕

The magnetic recording medium of the present invention has improved electromagnetic conversion characteristics. That is, the chroma output is improved by improving the filling ratio of the magnetic layer, and the chroma
S / N is improving.

Further, since the absorption of dust is prevented by the reduction of the surface resistivity of the magnetic layer (4 × 10 ⁸ ohm level), the dropout is small.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-146210 (JP, A) JP-A-63-157313 (JP, A) JP-A-63-146209 (JP, A) JP-A-62-146210 287420 (JP, A) JP-A-63-144415 (JP, A)

Claims (1)

(57) [Claims] 1. A nonmagnetic layer containing 40 to 140 parts by weight of carbon black with respect to 100 parts by weight of a binder is provided on a nonmagnetic support, and further contains an Fe-Al ferromagnetic metal powder thereon. A magnetic layer is provided, the thickness of the magnetic layer is 0.3 to 2.5 μm, and the nonmagnetic layer and the magnetic layer are formed on the nonmagnetic support by a wet-on-wet multilayer coating (wet multilayer coating) method. A magnetic recording medium characterized by being formed at the same time.