JPH02227822A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the multiple-layer magnetic recording medium which is excellent particularly in electromagnetic conversion characteristics and has less drop-outs and excellent traveling durability by lacking a polishing agent component in layers exclusive of the uppermost layer and lacking at least one component selected from a group consisting of a carbon black, lubricant, dispersant, and hardener therein. CONSTITUTION:Plural magnetic layers are provided on a nonmagnetic base. The respective components including ferromagnetic powder, a binder, the carbon black, the lubricant, and the polishing agent are incorporated as essential components into the uppermost layer in this case. The binder to be used is exemplified by polyurethane having wear resistance. The layers exclusive of the uppermost layer lack the polishing agent component and lack at least one component selected from the group consisting of the carbon black, lubricant, dispersant and hardener. The multiple-layer magnetic recording medium which is excellent particularly in the electromagnetic conversion characteristics and has the less drop-outs and the excellent traveling durability is obtd. in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, magnetic floppy disks, etc., and particularly relates to magnetic recording media such as magnetic tapes, magnetic disks, and magnetic floppy disks. The present invention relates to a magnetic recording medium suitable for use as a video tape with good running durability.

[Background of the Invention 1 In recent years, there has been an increasing demand for higher densities in magnetic recording media, and in particular, for example, with the demand for higher recording frequencies in video tapes, it has become possible to perform extremely high-density recording. In response to this demand, various proposals have been made for providing a magnetic layer on a support with a two-layer structure consisting of an upper layer and a lower layer, or a structure of three or more layers (hereinafter, these may be collectively referred to as a multi-layer structure). There is.

As is well known, magnetic recording media usually contain ferromagnetic powder, abrasives, carbon black, etc. in various synthetic or natural polymer materials (so-called resin materials) called binders. A suitable solvent is added as necessary to a uniformly dispersed mixture of lubricants, dispersants, hardeners, and other components, and the resulting magnetic paint is applied onto a support to form a magnetic layer. Afterwards, the magnetic layer is manufactured by aligning the magnetic layer in a magnetic field and then drying it.

Incidentally, there are various factors that affect the electromagnetic conversion characteristics and mechanical characteristics of a magnetic recording medium, and representative factors include the type and amount of each component used.

These factors interact with each other and affect the characteristics of magnetic recording media, but in conventional magnetic recording media, in each layer, for example, even in layers other than the upper layer, the components used in the upper layer The current situation is that similar ingredients are used over and over again.

However, according to the research of the present inventors, when similar components are used in duplicate in each layer,
Although it has the advantage of being able to essentially improve electromagnetic conversion characteristics as in the case of ferromagnetic components, depending on the component, the amount used may be too large and the disadvantages may outweigh the advantages.

For example, if the amount of carbon black component added is too large, it will mainly cause surface deterioration of the magnetic recording medium and decrease in the amount of magnetic material filled, resulting in a decrease in electromagnetic conversion characteristics, and if the amount of abrasive added is too large. and the surface roughness of the tape deteriorates, resulting in a similar decline in electromagnetic conversion characteristics.

Furthermore, if the amount of lubricant added is too large, the binding strength of the binder to other components will be reduced (adhesion to the support will be reduced), and dropout of the magnetic recording medium will increase.

Regarding dispersants, as long as the magnetic material is well dispersed,
It is advantageous not to add this substance in terms of improving the filling rate of the magnetic material and the running durability of the magnetic tape, but if it is added, it acts as a thinning agent for the magnetic paint.
The production efficiency of magnetic paint can be improved.

However, if the content of this substance is too large, it acts as a plasticizer for the binder resin, reducing the rigidity of the tape and reducing its running durability.

Furthermore, if the amount of curing agent added is too large, the adhesion of the magnetic layer to the support decreases, resulting in increased dropout of the magnetic recording medium.

[Object of the Invention] In view of the above, the present inventors have improved the conventional drawbacks and created a magnetic recording medium that has various characteristics superior to the conventional ones, in particular, has excellent electromagnetic conversion characteristics and has no dropout. We conducted extensive research with the aim of developing a multilayer magnetic recording medium that is small in amount and has excellent running durability; as a result, the top layer contains the following components: ferromagnetic material, binder, carbon black, lubricant, and abrasive. The layer other than the top layer contains the abrasive component as an essential component, and its purpose is achieved by lacking the abrasive component and at least one component selected from the group consisting of carbon black, a lubricant, a dispersant, and a hardening agent. The present invention was realized based on the knowledge that this can be achieved.

[Structure of the Invention] That is, the present invention provides a magnetic recording medium comprising a plurality of magnetic layers on a non-magnetic support, in which the first layer contains a ferromagnetic material,
Containing each component of a binder, carbon black, a lubricant, and an abrasive as an essential component, layers other than the top layer lack an abrasive component, and are selected from the group consisting of carbon black, a lubricant, a dispersant, and a hardening agent. The subject matter is a magnetic recording medium characterized by lacking at least one selected component.

As mentioned above, the magnetic recording medium of the present invention usually includes a ferromagnetic material, a binder, an abrasive, carbon black,
Contains lubricant and curing agent components as essential components,
The layers other than the top layer lack an abrasive component and lack at least one component selected from the group consisting of carbon black, a lubricant, a dispersant, and a hardening agent, but can be used in the present invention. Examples of the ferromagnetic material include Co-γ-FetO3, Fe3 such as γ4e201, Go-containing-Fe,03 or Co-coated-Fe203.
O4; Co-containing Fe50. or C0 deposited Fe, O,
Go-γ-Fe30a such as; oxide magnetic materials such as CrO2; others such as Fe, Ni, Fe-Ni alloy, Fe-C.

alloy, Fe-N1-P alloy, Fe-Ni-Co alloy,
Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe
-Co-Ni-Cr alloy, Fe-Go-Ni-P alloy,
Fe, Ni, Go-P alloy, Co-Cr alloy, etc.
Examples include various ferromagnetic materials (powders) such as metal magnetic powders containing Go as a main component. Additives to these metal magnetic materials may include elements such as Si, Cu, Zn, AQ, P, Mn, and Cr, or compounds thereof. Hexagonal ferrite such as barium ferrite, iron nitride, etc. are also used.

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.

Phenoquine 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 the present invention, the binder, like the ferromagnetic material, is used not only in the top layer but also in layers other than the top layer.

In order to improve the durability of the magnetic layer of a magnetic recording medium, magnetic paints usually contain various hardening agents.

For example, incyanate can be included. Examples of aromatic incyanates include tolylene diisocyanate (TDI) and adducts of these incyanates with active hydrogen compounds, and the average molecular weight is 10.
A range of 0 to 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 incyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic incynates, non-alicyclic incynates and adducts of these compounds with active hydrogen compounds are preferred.

In the present invention, a hardening agent may not be used in any layer other than the top layer. Generally, a dispersant is used in magnetic paints, and additives such as lubricants and abrasives are contained as necessary.

Examples of dispersants include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof; Salts of polymeric dispersants having groups (eg -COOH) can also be used. These dispersants may be used alone or in combination of two or more.

Dispersants are usually not used as an essential component in the upper layer in the present invention because they are useful for improving the filling rate of the ferromagnetic material and improving the durability of the tape, but when used, they can be used as thinning agents. It can also be used as needed, since it can act as a magnetic recording medium and improve the productivity of magnetic recording media.

In addition, as lubricants, silicone oil, graphite, carbon black graft polymer molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid,
Fatty acid esters (so-called waxes) consisting of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 21 to 23 carbon atoms in total can also be used. These lubricants are usually added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder.

In the present invention, lubricants may not be used in layers other than the top layer.

As abrasives, commonly used materials include fused alumina, various aluminas such as σ alumina, silicon carbide, chromium oxide, corundum, artificial corantum, artificial diamond, garnet, emery (main ingredients: corundum and magnetite), etc. be done. These abrasives have an average particle size of 0.05 to 5μ
A weight of 0.1 to 0.1 is particularly preferred.
2μ shoulder. These abrasives are usually added in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder.

In the present invention, the abrasive is usually used only on the top layer;
Do not use on layers other than the top layer.

Carbon black is usually used for the purpose of imparting conductivity and light-shielding properties, but it is also used for the purpose of preventing static electricity, such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide. conductive powder such as system compounds: natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, vg quaternary ammonium salts, pyridine, and other heterocycles; Cationic surfactants such as phosphonium or sulfoniums; carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester groups,
Anionic surfactants containing acidic groups such as phosphate groups;
Examples include amphoteric activators such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols.

Note that in the present invention, carbon black may not be used in layers other than the top layer.

Solvents blended into magnetic paints 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, furopanol, and butanol; methyl vinegar, 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, and ethylene Halogenated hydrocarbons such as chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

Examples of the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. But, Cu, 14. Metallic glass such as Zn, boron nitride, ceramic such as S1 carbide, etc. 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 thick.
In the case of a disk or card shape, the diameter is about 30 μm to 10 arms, and in the case of a drum shape, a cylindrical shape is used, and the 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 (so-called wet-on-wet method), but any method can be used in manufacturing the magnetic recording medium of the present invention.

Note that other or nonmagnetic layers may be provided above and below the magnetic layer or between the magnetic layers without impairing the effects of the present invention.

By such a method, the magnetic layer coated on the support 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, 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 subjecting it to surface smoothing treatment or cutting it into a desired shape, if necessary.

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] Magnetic paints having the compositions listed in Table 1 (upper layer) and Table 2 (lower layer) were kneaded to disperse each component well in the paint.
Thereafter, a mixture of methyl ethyl ketone and toluene was added as a solvent to adjust the viscosity to 1 to 20 poise.

Next, 5 parts by weight of Coronate (a product of Nippon Polyurethane Co., Ltd., trade name) was added as a hardening agent (this hardening agent is added as an essential component to the magnetic paint for the upper layer, but is not used in the magnetic paint for the lower layer). ).

The above magnetic paint was coated in multiple layers on a polyethylene terephthalate support according to a conventional method so that the dry film thickness was 3.0 μm.

Next, magnetic field orientation treatment, drying treatment, and calender treatment are performed.
; Afterwards, it was wound up to produce a magnetic recording tape.

Table 2 (Lower Layer) Table 3 shows the composition of the lower layer of the magnetic tape produced in this way and the results of measuring the characteristics of the tape.

In addition, the description of "present" or "absent" for each component in the "lower layer composition column" of Table 3 means that "presence" indicates that the component is added to the lower layer, and "absence" indicates that the component is added to the lower layer. Hail brush if not added.

The amount of each component added in the case of "Yes" is as shown below.

・Carbon black・・・・・・・・・・・・5 parts by weight・
Lubricant Myristic acid: 1 part by weight Stearic acid: 1 part by weight Dispersant: 2 parts by weight Curing agent: ・...5 parts by weight (among the above ingredients,
As for the types of dispersants and hardeners, as is clear from Table 3, according to the present invention, the lower layer lacks an abrasive component and is selected from the group consisting of carbon black, lubricants, dispersants, and hardeners. When at least one component is omitted, the electromagnetic conversion characteristics and other properties are better than when it is omitted (comparative example).

◎Measurement method in Examples and Comparative Examples Chroma output> Determine the output during reproduction of the 500K, RF multiplied signal.
.

<Lumi S/N> Input a white 100% signal to the magnetic tape at the reference level, input the reproduced video signal to 9250/L (noise meter, manufactured by Shibaku), and from the absolute noise value obtained, Lumi S/N is determined. Read N.

Chroma S/N> Using a noise meter manufactured by Shibaku Co., Ltd., and using the tape of Example 1 as a reference, the difference in S/N of the sample in the chroma signal was determined in comparison with the tape of Example 1.

Dropout> A 100% white signal is input to a certain section (10 to 30m) of the magnetic tape and played back, and at that time, the dropout of 10 μS at a -12 dB level is measured in 1 minute units using a Shibaku counter (VHOIBZ). The average value of the total length of the measured portion was taken as the measured value.

Running Durability> The decrease in RF output was measured after running the magnetic tape 50 times under the conditions of 40° C. and 80% RH.

Tape edge damage The magnetic tape after running 200 times was visually evaluated.

[Effects of the Invention] The magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics, less dropouts, and excellent running durability.

Claims (1)

[Claims] (1) In a magnetic recording medium consisting of a plurality of magnetic layers on a non-magnetic support, the top layer contains a ferromagnetic material, a binder, carbon black, a lubricant, and an abrasive as essential components. , layers other than the top layer lack abrasive components,
A magnetic recording medium characterized in that it lacks at least one component selected from the group consisting of carbon black, a lubricant, a dispersant, and a hardening agent.