JP2775462B2 - Magnetic recording media with excellent electromagnetic conversion characteristics and running durability - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic disk, and a magnetic floppy disk, and more particularly to a magnetic recording medium suitably used as a video tape.

BACKGROUND OF THE INVENTION As is well known, a magnetic recording medium is usually prepared by mixing and dispersing a magnetic substance, a lubricant, carbon black, an abrasive, a dispersant, and other components in a binder (binder resin). A magnetic paint obtained by adding a curing agent for improving the durability of the magnetic layer, coating the support on a support, and drying.

The electromagnetic conversion characteristics and other characteristics of the magnetic recording medium manufactured as described above can be variously changed by appropriately changing the type of each component constituting the magnetic layer and the amount of use thereof.

By the way, in recent years, as the quality of magnetic recording media such as magnetic tapes has been improved, it has been required to increase the density of a magnetic material, and a two-layer structure composed of an upper layer and a lower layer or a structure of three or more layers (hereinafter, There are various proposals in which a magnetic layer having a multilayer structure is provided.

However, in conventional magnetic recording media having a multilayer structure, for example, the dispersibility of the magnetic material is poor, and the electromagnetic conversion characteristics are insufficient or the balance between the high-frequency characteristics and the low-frequency characteristics is not good. At present, no one having satisfactory characteristics that balance the above has yet emerged.

[Object of the Invention] From the above, the present inventors have conducted various studies with the aim of developing a magnetic recording medium with improved performance, especially electromagnetic conversion characteristics, running durability, and the like. The invention described has been reached.

[Constitution 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) provided on a non-magnetic support. Cobalt-containing iron oxide having a coercive force (Hc) of 750 to 1200 Oe (Oersted) and a Si content of 0.1 to 2% by weight in the magnetic material is used. The present invention relates to a magnetic recording medium characterized by using a modified vinyl chloride-vinyl acetate copolymer having a group and a modified polyurethane having a negative functional group in combination, and using chromium oxide as an abrasive.

As described above, the present invention provides a magnetic recording medium having a multilayer structure, in which a second magnetic layer (upper layer) includes a magnetic material as a magnetic material.
Cobalt-containing iron oxide having a coercive force (Hc) of 750 to 1200 Oe (Oersted) and a Si content of 0.1 to 2% by weight in the magnetic material is used. It is characterized by using a modified vinyl chloride-vinyl acetate copolymer having a group and a modified polyurethane having a negative functional group in combination, and using chromium oxide as an abrasive. It is not proposed to use such components in combination in the upper layer, but this is the first finding by the present inventors.

Hereinafter, the present invention will be described. The coercive force (Hc) used for the second magnetic layer (upper layer) of the magnetic recording medium of the present invention is as follows.
750 to 1200. Oe (Oersted), and as the cobalt-containing iron oxide containing Si (Co-γ-FeOx),
It is preferable to use x = 1.4 to 1.5, and the content of Si in the magnetic material is 0.1 to 2% by weight in the magnetic material, and preferably 0.1 to 1% by weight.

When the content of Si is less than 0.1% by weight, the dispersion of the magnetic substance in the magnetic coating material is poor, and the electromagnetic conversion characteristics of the magnetic recording medium are deteriorated. When the content exceeds 2% by weight, the preservation of the magnetic substance is prevented. It is not preferable because magnetic properties such as magnetic force are deteriorated.

In this way, the inclusion of Si in the magnetic material modifies the surface of the magnetic material, facilitating adsorption of the functional group-containing resin as a binder, and thereby dispersing the magnetic material in the magnetic paint. Can be improved.

The second layer (upper layer) has a coercive force (Hc) of 750 to 1200 Oe.
By using a magnetic material having a high coercive force such as (Oersted), the output of the magnetic recording medium in the high frequency band can be improved, and at the same time, the output of the low frequency band can be increased by the presence of the first layer (lower layer). be able to.

When the coercive force is smaller than 750.Oe (Oersted), the RF output and Lumi S / N of the magnetic recording medium decrease, while when the coercive force is larger than 1200.Oe (Oersted). In any case, the chroma S / N decreases, so it is not preferable in any case, and usually the coercive force is 800 to 1000.Oe
(Oersted) magnetic material is preferably used.

On the other hand, for the first magnetic layer (lower layer), in addition to the magnetic material used for the above-described second magnetic layer, any conventionally used magnetic material can be used.

For example, γ-Fe ₂ O ₃ , CO-containing γ-Fe ₂ O ₃ or Co-coated γ-
Co-γ-Fe ₂ such as _{Fe 2 O 3 O 3, Fe} 3 O 4, Co -containing Fe ₃ O ₄ or _{Co Co-γ-Fe 3 O} 4 as deposited Fe ₃ O _4, CrO _2, etc. Oxide magnetic material, 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-Ni
Various ferromagnetic materials (powder) such as metal magnetic powders containing Fe, Ni, and Co as main components, such as -P alloys, Co-P alloys, and Co-Cr alloys. As an additive to these metal magnetic materials,
Elements such as Si, Cu, Zn, Al, P, Mn, and Cr or compounds thereof may be included. Further, hexagonal ferrites such as barium ferrite, iron nitride and the like are also used.

For the second layer (upper layer) of the magnetic layer of the magnetic recording medium of the present invention, a modified vinyl chloride-vinyl acetate copolymer having a negative functional group and a modified polyurethane having a negative functional group are used in combination as a binder (binder resin). .

By using such a resin in combination, the dispersibility of the magnetic material can be improved, and the electromagnetic conversion characteristics of the magnetic recording medium can be improved.

The modified vinyl chloride-vinyl acetate copolymer having a negative functional group used in the present invention is a resin obtained by introducing a negative functional group into a so-called vinyl chloride-vinyl acetate copolymer, and is a vinyl chloride-vinyl acetate copolymer. In combination, for example, Cl-CH ₂ C
H ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₃ M,, Cl-CH ₂ COOM, (However, M, M ₁ and M ₂ each represent an alkali metal such as lithium, sodium and potassium.) Condensation of a compound containing chlorine and a negative functional group in the molecule by a dehydrochlorination reaction It is easily obtained by doing

Representative examples of the negative group in the copolymer include, for example, a sulfonic group, a carboxyl group, and the like, but are not limited thereto.

The modified polyurethane having a negative functional group used in the present invention is a resin obtained by introducing a negative functional group into a so-called polyurethane, and the polyurethane is, for example, Cl-CH ₂ C
H ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₃ M,, Cl-CH ₂ COOM, (However, M, M ₁ and M ₂ each represent an alkali metal such as lithium, sodium and potassium.) Condensation of a compound containing chlorine and a negative functional group in the molecule by a dehydrochlorination reaction It is easily obtained by doing

Representative examples of the negative group in the polymer include, for example, a sulfonic group, a carboxyl group, and the like, but are not limited thereto.

On the other hand, for the first magnetic layer (lower layer), in addition to the resin mixture used for the first magnetic layer, any known binder may be used, and a preferable example is a polyurethane resin having wear resistance. .

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

Also, when a cellulose resin and a vinyl chloride copolymer are used in combination with the polyurethane, 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.

Cellulose ether,
Cellulose inorganic acid esters and cellulose organic acid esters can be used. The above polyeletan and vinyl chloride copolymer may be partially hydrolyzed. As the vinyl chloride copolymer, preferably, a copolymer containing vinyl chloride-vinyl acetate or vinyl chloride-vinyl acetate-
Copolymers containing vinyl alcohol are exemplified.

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-described polyurethane, and can significantly improve the stability over time 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, and an electron beam irradiation curable resin may be used.

In order to improve the durability of the magnetic layer of the magnetic tape of the present invention, various hardeners can be contained in the magnetic paint, for example, isocyanate can be contained. Examples of the aromatic isocyanate include tolylene diisocyanate (TDI) and the adduct thereof with these isocyanate active hydrogen compounds, and have an average molecular weight of 100 to 3,0.
A range of 00 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 in the range of 100 to 3,000 are preferred. Of the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic paint used to form the magnetic layer usually has
Additives such as dispersants, lubricants, abrasives, matting agents, and antistatic agents are 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). You can also. These dispersants may be used alone or in combination of two or more.

Examples of the lubricant include silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, a monobasic fatty acid having 12 to 16 carbon atoms and the number of carbon atoms of the fatty acid. 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.

In the present invention, chromium oxide is used for the second magnetic layer (upper layer) as an abrasive.

By using chromium oxide as the abrasive for the second magnetic layer in this manner, when the magnetic recording medium is run under high temperature and high humidity conditions, it is possible to prevent the RF output from decreasing due to clogging of the magnetic head. . Therefore, the incorporation of chromium oxide in the second magnetic layer can be useful for improving the polishing power of the magnetic head.

The particle size of chromium oxide used for the second magnetic layer is usually 0.1
1.01.0 μm, preferably 0.1-0.5 μm.
When the particle size is smaller than 0.1 μm, the polishing effect is poor. When the particle size is larger than 1.0 μm, the electromagnetic conversion characteristics tend to deteriorate.

On the other hand, as the abrasive used for the first magnetic layer (lower layer), not only chromium oxide is used, but also commonly used materials, for example, various aluminas such as fused alumina and α-alumina, silicon carbide, 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, and particularly preferably 0.1 to 2 μm.
These abrasives are usually 1 to 2 parts by weight based on 100 parts by weight of the binder.
It is added in the range of 0 parts by weight.

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

As the organic powder that can be used, acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, Polyfluorinated ethylene resin powder and the like can also be used. As inorganic powder, silicon oxide, titanium oxide, aluminum oxide, potassium 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,
And molybdenum dioxide.

Examples of antistatic agents include conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; alkylene oxides; glycerin And glycidol-based nonionic surfactants; higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfoniums; carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid Anionic surfactants containing an acidic group such as an ester group or a phosphoric ester group; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric esters of amino alcohol;

Examples of the solvent to be blended in the paint or a diluting solvent at the time of applying the paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Alcohols such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane and tetrahydrofuran; , Toluene and 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 derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and 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, and 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 Are applied simultaneously or successively (so-called wet-on-wet method), but any method can be adopted in producing the magnetic recording medium of the present invention.

Note that a non-magnetic layer may be provided above, below, or between the first magnetic layer and the second magnetic layer without impairing the effects of the present invention.

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

In this case, the orientation magnetic field is about 500-5000 AC or DC.
The drying temperature is about 50 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. However, needless to say, the present invention is not limited to these examples.

[Examples] Examples and Comparative Examples After the respective components shown in Table 1 were well kneaded, a proper amount of a mixture of methyl ethyl ketone / cyclohexanone = 7/3 was added as a solvent to produce a magnetic paint.

Next, according to a conventional method, this magnetic paint was applied on a polyethylene terephthalate support in a multi-layered manner, and then oriented in a magnetic field, and then dried to produce a magnetic recording tape.

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

Table 1 shows the composition of the magnetic paint used, and Table 2 shows the measurement results of the characteristics of the magnetic recording tape.

As is clear from Table 2, according to the present invention (Example 1), the surface roughness of the magnetic recording medium before calendering was Ra compared to the case not following the present invention (Comparative Examples 1 to 3).
Value is small.

Therefore, it can be seen that the magnetic recording medium of the present invention has a good magnetic material dispersibility.

In addition, the magnetic recording medium of the present invention has higher video characteristics in the high frequency band (4.2 MHz) and lower frequency band since both the Lumi S / N value and the chroma S / N value are higher than those not according to the present invention. It can be seen that the characteristics of (0.5 MHz) are excellent in a well-balanced manner.

Furthermore, in the present invention, the RF after traveling 50 passes under the condition of 40 ° C. and 80% RH was compared with each comparative example.
Although the output drop is small, the RF output drop is an index of head cleaning, and the smaller the RF output drop, the better the cleaning condition of the magnetic head.

[Effects of the Invention] The magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics and running durability as is clear from the above description.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 5/706 G11B 5/706 5/708 5/708

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a first magnetic layer (lower layer) and a second magnetic layer (upper layer) provided on a nonmagnetic support, wherein the second magnetic layer has a coercive force (Hc) as a magnetic material. Is 75
0 to 1200 Oe (oersted), and Si in the magnetic material
Using a cobalt-containing iron oxide having a content of 0.1 to 2% by weight, using a modified vinyl chloride-vinyl acetate copolymer having a negative functional group and a modified polyurethane having a negative functional group in combination as a binder, And as an abrasive,
A magnetic recording medium characterized by using chromium oxide.