JP2000231714A - Magnetic recording medium and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To achieve excellent electromagnetic conversion characteristics and achieve excellent productivity by coating a lower underlayer and an upper magnetic layer with high accuracy. SOLUTION: A lower underlayer formed by applying a nonmagnetic support, a lower underlayer paint, and an upper magnetic layer formed by applying an upper magnetic layer paint are provided. The lower underlayer paint and the upper magnetic layer are provided. 20 (Pa) ≦ G ′ (1) ≦ 60 (Pa) 20 (Pa) ≦ G ′ (10) ≦ 90 (Pa) 1.0 <G ′ (10) / G ′ (1) ≦ 2 0.0 0.5 <G * (0) / G * (120) ≦ 4.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a lower underlayer on which magnetic recording is not possible and an upper magnetic layer on which magnetic recording is possible, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks, and the like. In this magnetic recording medium, the recording density is increasing year by year, and analog and digital recording methods are being studied. In response to this demand for high-density recording, a magnetic recording medium formed by forming a thin metal magnetic thin film has been proposed as a magnetic recording medium. However, the magnetic recording medium having the metal magnetic thin film is not sufficient in practical reliability such as productivity and corrosiveness.

[0003] As a magnetic recording medium, a so-called coating type in which a magnetic layer formed by applying a magnetic coating material obtained by dispersing a magnetic powder in a binder onto a non-magnetic support and drying the coating is applied. is there. This coating type magnetic recording medium is
It is superior to a magnetic recording medium having the above-mentioned metal magnetic thin film in terms of practical reliability such as productivity and corrosiveness. However, the coating type magnetic recording medium is inferior in electromagnetic conversion characteristics because the filling degree of the magnetic material in the magnetic layer is lower than that of the metal magnetic thin film.

In order to improve the electromagnetic conversion characteristics of the coating type magnetic recording medium, improvement of the magnetic characteristics of the magnetic material to be used and smoothing of the surface have been studied and proposed. However, the conventional magnetic recording medium cannot be said to have sufficiently achieved high-density recording.

On the other hand, in a magnetic recording medium employing a digital recording system, it is known to reduce the thickness of a magnetic layer in order to improve performance. However, when a thin magnetic layer is formed by applying a magnetic paint on a non-magnetic support, coating defects such as pinholes and streaks are likely to occur due to the thinning of the magnetic layer, and a sufficient yield cannot be obtained. , There are production problems. Further, in this case, even if the formed magnetic layer is subjected to the calendering treatment, the molding effect by the calendering treatment is small, so that the surface properties are poor and the electromagnetic conversion characteristics are not good.

In order to solve such a problem, a coating-type magnetic recording medium has a lower underlayer having a predetermined thickness and a thickness of about 2 mm.
It is conceivable that a calender treatment is performed after a thin upper magnetic layer having a thickness of not more than μm and a multilayer magnetic layer are coated and formed at the same time. In such a magnetic recording medium having the lower underlayer and the upper magnetic layer, as described above, it is possible to solve the deterioration of the electromagnetic conversion characteristics caused by the coating defect and the poor surface property of the upper magnetic layer.

In such a magnetic recording medium, the upper magnetic layer contains a ferromagnetic material and is used as a recording layer for performing magnetic recording, and the lower underlayer contains a soft magnetic material so that a magnetic field from a magnetic head is generated. Acts to pull in. As a result, the magnetic field applied from the magnetic head is applied to the upper magnetic layer in a narrow range. Therefore, in this magnetic recording medium, high-density recording can be performed on the upper magnetic layer. In this magnetic recording medium, no data is recorded on the lower underlayer.

[0008]

When manufacturing this multilayer coating type magnetic recording medium, how to uniformly coat the lower underlayer and the upper magnetic layer on the nonmagnetic support is important. Has become a very important technical issue. To cope with such a problem, for example, Japanese Patent Application Laid-Open No. 63-88080 proposes a so-called wet-on-wet multilayer coating method in which a lower nonmagnetic layer and an upper magnetic layer are coated in a wet state. I have.

However, in the above-described magnetic recording medium, the lower underlayer and the upper magnetic layer cannot be coated with high accuracy, and the electromagnetic conversion characteristics cannot be sufficiently improved. Further, when manufacturing the above-described magnetic recording medium, there is a problem that application unevenness of the coating material for the lower underlayer and the coating material for the upper magnetic layer occurs, resulting in poor productivity.

Accordingly, the present invention provides a magnetic recording medium having excellent electromagnetic conversion characteristics and a method of manufacturing a magnetic recording medium having excellent productivity by coating a lower underlayer and an upper magnetic layer with high precision. The purpose is to do.

[0011]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in order to achieve the above object, the static viscosity of the paint for the lower underlayer and the paint for the upper magnetic layer was simultaneously determined in the film formation process. Oscillation of the coating due to pulling and shrinking (shaking movement) is fundamentally involved in the state of the coating,
It has been found that it is important to regulate the paint for the lower underlayer and the paint for the upper magnetic layer based on the dynamic viscoelastic properties.

That is, the magnetic recording medium according to the present invention comprises:
A non-magnetic support, a lower underlayer formed by applying a lower underlayer coating mainly composed of a soft magnetic powder and a binder on the nonmagnetic support, and a ferromagnetic powder on the lower underlayer; A magnetic recording medium having an upper magnetic layer formed by applying an upper magnetic layer coating mainly composed of an agent and the lower underlayer coating and the upper magnetic layer coating, using a strain control type viscoelasticity meter. The storage elastic modulus G '(1) at a strain of 1% and an angular frequency of 1 rad / sec, and the storage elastic modulus G' (10) at a strain of 1% and an angular frequency of 10 rad / sec, respectively, were measured using the lower layer. 20 (Pa) ≦ G ′ (1) ≦ 60 (Pa) 20 (Pa) ≦ G ′ (10) ≦ 90 (Pa) 1.0 <G ′ (10) for both the coating for the formation layer and the coating for the upper magnetic layer. /G′(1)≦2.0, the paint for the lower underlayer and the upper paint Immediately after the initial shear for 60 seconds at a strain of 1000% and an angular frequency of 2πrad / sec applied to the coating material for the magnetic layer, the time was set to 0 second, and the strain at 1% and the angular frequency of 2πrad / sec at the time of 0 second. And the complex elastic modulus G * (120) at an angular frequency of 2πrad / sec at a point of time when 120 seconds have elapsed from time 0 seconds, the complex elastic modulus G * (0) at The paint for the upper magnetic layer is characterized in that 0.5 <G * (0) / G * (120) ≦ 4.0.

In the magnetic recording medium according to the present invention having the above-described structure, when the coating material for the lower underlayer defined as described above is used, the coating film is stretched and shrunk during the coating film forming process. Therefore, disturbance of the interface between the lower underlayer and the upper magnetic layer and surface roughness of the upper magnetic layer are prevented. In other words, in the present invention, not only the wet-on-dry coating method, but also the wet-on-dry coating method is performed by adjusting the paint for the lower underlayer and the paint for the upper magnetic layer to have similar viscoelasticity. The interface is not disturbed when coated by the wet coating method, and good coating characteristics and a good surface without pinholes or cissing can be obtained.

Further, the method for producing a magnetic recording medium according to the present invention is characterized in that a coating for a lower underlayer mainly composed of a soft magnetic powder and a binder and a ferromagnetic powder and a binder are mainly formed on a non-magnetic support. In the method for producing a magnetic recording medium in which a lower magnetic layer and an upper magnetic layer are formed by sequentially applying upper magnetic layer paints, the lower underlayer paint and the upper magnetic layer paint are strain-controlled viscoelastic. The storage elastic modulus G ′ (1) at a strain of 1% and an angular frequency of 1 rad / sec, and the storage elastic modulus G ′ (10) at a strain of 1% and an angular frequency of 10 rad / sec, respectively, were measured using a measuring device. 20 (Pa) ≦ G ′ (1) ≦ 60 (Pa) 20 (Pa) ≦ G ′ (10) ≦ 90 (Pa) 1.0 <G ′ for both the lower base layer coating and the upper magnetic layer coating. (10) / G ′ (1) ≦ 2.0. Immediately after the initial shear for 60 seconds at a strain of 1000% and an angular frequency of 2πrad / sec was applied to the material and the coating material for the upper magnetic layer, the time was set to 0 seconds. The complex elastic modulus G * (0) at 2πrad / sec, the strain 1% at the point when 120 seconds have elapsed from time 0 sec, and the complex elastic modulus G * (120) at an angular frequency of 2πrad / sec are as follows. The coating material for the upper layer and the coating material for the upper magnetic layer are characterized in that 0.5 <G * (0) / G * (120) ≦ 4.0.

In the method of manufacturing a magnetic recording medium according to the present invention having the above-described structure, when the coating material for the lower underlayer defined as described above is used, the coating film is subjected to the pulling and shrinkage in the process of forming the coating film. Oscillation of the film is suppressed, and disturbance of the interface between the lower underlayer and the upper magnetic layer and surface roughness of the upper magnetic layer are prevented. In other words, in the present invention, by adjusting the paint for the lower underlayer and the paint for the upper magnetic layer to have similar viscoelasticity to each other, the wet
Not only the on-dry coating method but also the wet-on-wet coating method can provide good coating characteristics and a good surface with no disturbance of the interface and no pinholes or cissing.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of a magnetic recording medium and a method for manufacturing the same according to the present invention will be described below.

The magnetic recording medium shown in this embodiment is similar to that shown in FIG.
As shown in FIG. 1, at least a non-magnetic support 1 and a lower underlayer 2 formed on one main surface of the non-magnetic support 1
And an upper magnetic layer 3 formed on the lower underlayer 2. This magnetic recording medium has a back coat layer (not shown) formed on the other main surface of the non-magnetic support 1.
Or a top coat layer (not shown) formed on the upper magnetic layer 3.

In this magnetic recording medium, the lower underlayer 2
Is a layer formed by applying a coating for a lower underlayer comprising at least a soft magnetic powder and a binder on one main surface of the nonmagnetic support 1. The upper magnetic layer 3 is a layer formed by applying an upper magnetic layer paint including at least a ferromagnetic powder and a binder onto the lower underlayer 2. At this time, the paint for the lower underlayer and the paint for the upper magnetic layer may be applied by any of a so-called wet-on-dry coating method and a wet-on-wet coating method. Wet on
According to the wet coating method, it is not necessary to dry the paint for the lower underlayer, so that the lower underlayer 2 and the upper magnetic layer 3 can be formed with high productivity.

First, the paint for the lower base layer forming the lower base layer 2 will be described. The paint for the lower underlayer is prepared mainly by dispersing a soft magnetic powder and a binder in a solvent.

The soft magnetic powder is not particularly limited, and those used for so-called weak electric devices such as a magnetic head and an electronic circuit can be used. Further, in this soft magnetic powder, the average particle diameter is desirably 0.3 μm or less. When the average particle size of the soft magnetic powder exceeds 0.3 μm,
There is a possibility that the surface smoothness of the upper magnetic layer 8 is deteriorated.

As such a soft magnetic powder, a soft magnetic material having a high magnetic susceptibility and a low coercive force, such as a metal, a metal oxide, an alloy, and an amorphous alloy can be used. Specifically, iron-silicon alloy, iron-aluminum alloy, iron-nickel alloy, iron-cobalt alloy, iron-cobalt-nickel alloy, nickel-cobalt alloy, sendust, manganese-
Examples include zinc-based ferrite, nickel-zinc-based ferrite, magnesium-zinc-based ferrite, and magnesium-manganese-based ferrite.

Further, in the paint for the lower underlayer, an inorganic powder or an organic powder can be used in addition to the soft magnetic powder. Examples of the inorganic powder include carbon black, graphite carbon, alumina, iron oxide, titanium oxide, barium sulfate, and calcium carbonate. Also, as the organic powder, polystyrene powder, nylon powder,
Polymer beads such as benzoguanamine resin beads, polyacrylic acid-based polymer beads, and polyvinyl chloride resin beads can be used. Their average particle size is preferably 0.3 μm or less. Further, the weight ratio of the soft magnetic powder to the other powder (total of the inorganic powder and the organic powder) is preferably soft magnetic powder: other powder = 100: 0 to 10:90. If the content of the other powder exceeds 90% by weight, the high frequency characteristics of the magnetic recording medium may be undesirably reduced.

In the coating for the lower underlayer, any of a thermoplastic resin, a thermosetting resin, a reactive resin and the like may be used as the binder, but the number average molecular weight is from 5,000 to 1
It is preferably 00000. Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, and vinyl chloride.
Vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer Polymer, acrylate-acrylonitrile copolymer, acrylate-
Vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose Diacetate, cellulose propionate,
Nitrocellulose), styrene-butadiene copolymer,
Examples thereof include polyurethane resins, polyester resins, amino resins, and synthetic rubbers. Examples of the thermosetting resin and the reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, and urea formaldehyde resin. . During such _binders, -SO 3 _M, -OSO
_{3 M, -COOM, -P = O} (OM) 2, -NR 1 R 2, -
^{_{NR 1 R 2 R 3 + X}} -,> NR 1 R 2 + X -, -OH, -SH,
A polar functional group such as -CN or an epoxy group (M is a hydrogen atom or an alkali metal such as lithium, potassium, and sodium, R is a hydrogen atom or a hydrocarbon, and X is a halogen atom or an organic substance). At least one may be contained. The addition amount of these polar functional groups is 10 ^-1 to
Is preferably 10 ^-8 mol / g, further ^10-2
More preferably, it is 10 to 10 ^-6 mol / g.

Furthermore, a polyisocyanate for crosslinking and curing may be added to these binders.
As the polyisocyanate, for example, at least one of toluene diisocyanate, alkylene diisocyanate, and an insoluble substance thereof can be used. The blending amount of the polyisocyanate in the binder is 100
The amount is preferably from 5 to 80 parts by weight, more preferably from 10 to 50 parts by weight, based on parts by weight.

Further, the paint for the lower underlayer may contain a lubricant. Examples of the lubricant include graphite, molybdenum disulfide, tungsten disulfide, silicon oil, fatty acid having 10 to 22 carbon atoms, fatty acid ester composed of alcohol having 2 to 26 carbon atoms, terpene compounds, and oligomers thereof. can do.

When preparing the coating for the lower underlayer, the above-mentioned soft magnetic powder, binder and the like are dispersed in a solvent. As the solvent used, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, ketones such as tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, alcohols such as methyl cyclohexanol, Esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate and glycol acetate; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether and dioxane; and fragrances such as benzene, toluene, xylene, cresol and chlorobenzene. Group hydrocarbons, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
Chlorinated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformamide, hexane and the like can be exemplified. A plurality of these solvents can be used in a predetermined ratio.

Next, the paint for the upper magnetic layer for forming the upper magnetic layer 3 will be described. The paint for the upper magnetic layer is prepared mainly by dispersing a ferromagnetic powder and a binder in a solvent.

Examples of the ferromagnetic powder include metals such as Fe, Co, and Ni, Fe—Co, Fe—Ni, Fe—Al, and Fe—
Ni-Al, Fe-Al-P, Fe-Ni-Si-A
1, Fe-Ni-Si-Al-Mn, Fe-Mn-Z
n, Fe-Ni-Zn, Co-Ni, Co-P, Fe-
Co-Ni, Fe-Co-Ni-Cr, Fe-Co-N
i-P, Fe-Co-B, Fe-Co-Cr-B, Mn
Alloys such as Bi, Mn-Al, Fe-Co-V, iron nitride, iron carbide, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and a belt-ride compound of γ-Fe ₃ O ₄ and Fe ₃ O ₄ , Co-containing γ-Fe ₂
O ₃ , Co-containing Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃
A belt write compound of Fe ₃ O _4, 1 or more metal elements CrO _2, for example Te, Sb, Fe, B
, Hexagonal plate-like ferrite, M
-Type, W-type, Y-type, and Z-type barium ferrite, strontium ferrite, calcium ferrite, lead ferrite, and ferrites such as Co-Ti, Co-Ti-
ZnCo-Ti-Nb, Co-Ti-Zn-Nb, Cu
It is preferable that at least one of -Zr, Ni-Ti and the like is added.

Such a ferromagnetic powder preferably has an average major axis length of 0.3 μm or less, more preferably 0.05 to 500 μm.
More preferably, it is within the range of 0.3 μm. If the average major axis length is less than 0.05 μm, dispersion in the paint for the upper magnetic layer may be difficult, and the average major axis length is 0.3 μm.
If it exceeds, the noise characteristics may deteriorate, which is not preferable. The crystal size of these ferromagnetic powders by X-ray diffraction is preferably 300 or less. When the crystal size of the ferromagnetic powder is within the range of 300 or less, the ferromagnetic powder involves fine particles, so that high-density recording of the magnetic recording medium becomes possible and a magnetic recording medium having excellent noise characteristics can be obtained. it can. Further, the ferromagnetic powder has an axial ratio of 2
It is preferably from 15 to 15. If the axial ratio is less than 2,
There is a possibility that the orientation of the ferromagnetic powder is reduced and the output is reduced. If the axial ratio is 15 or more, the output of the short-wavelength signal may be reduced, which is not preferable. When plate ferrite is used as the ferromagnetic powder, the plate diameter is 0.01 to 0.5 μm.
It is preferable to use those having a thickness of about 0.001 to 0.2 μm. The major axis length, the axial ratio, the plate diameter and the plate thickness are actually measured for 100 or more samples randomly selected from a transmission electron micrograph, and the average value of these measured values is adopted.

In the paint for the upper magnetic layer, the binder and the polyisocyanate used in the paint for the lower underlayer described above can be used. In the paint for the upper magnetic layer, the binder is based on 100 parts by weight of the ferromagnetic powder.
The content is preferably 1 to 200 parts by weight, and more preferably 10 to 50 parts by weight. If the content of the binder is larger than the above range, the proportion of the ferromagnetic powder in the upper magnetic layer 3 will be relatively reduced, which may cause a decrease in output, and the If the content is less than the above range, the mechanical strength of the upper magnetic layer 3 is reduced, and the upper magnetic layer 3 is likely to be brittle, and the running durability may be deteriorated.

Further, a lubricant may be added to the paint for the upper magnetic layer, similarly to the paint for the lower underlayer described above.
Furthermore, abrasive particles may be added to the paint for the upper magnetic layer. Examples of the abrasive particles include aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, titanium carbide, and titanium oxide (rutile, anthesis). be able to.

Next, the viscoelastic properties of the lower base layer paint and the upper magnetic layer paint will be described.

In this magnetic recording medium, the lower underlayer 2
The upper magnetic layer 3 is formed using a lower base layer paint and an upper magnetic layer paint having the following viscoelastic properties. That is, when the paint for the lower underlayer and the paint for the upper magnetic layer are measured using a strain control type viscoelasticity meter, respectively, the storage elastic modulus G ′ (1) and the strain at a strain of 1%, an angular frequency of 1 rad / sec. 1%, angular frequency 10 rad
The storage elastic modulus G ′ (10) at / sec is 20 (Pa) ≦ G ′ (1) ≦ 60 (Pa) 20 (Pa) ≦ G ′ (for both the lower underlayer coating and the upper magnetic layer coating. 10) ≦ 90 (Pa) 1.0 <G ′ (10) / G ′ (1) ≦ 2.0 Also, with respect to the paint for the lower underlayer and the paint for the upper magnetic layer, the strain is 1000% and the angular frequency is 2πrad.
Immediately after the initial shearing of 60 sec / sec, the time was set to 0 sec, the strain at this time 0 sec was 1%, and the angular frequency was 2πra.
Complex modulus G * (0) at d / sec and time 0 sec to 12
Distortion 1%, angular frequency 2πra at time 0 seconds
The complex elastic modulus G * (120) at d / sec is 0.5 <G * (0) / G * (120) ≦ 4.0 for both the lower base layer paint and the upper magnetic layer paint. ing.

Here, the storage elastic modulus and the complex elastic modulus will be described in detail. In the field of rheology, deformation when a force is applied to a substance is roughly classified into elastic deformation and flow,
The flows are further classified into viscous flows and plastic flows. here,
As used to form magnetic and non-magnetic coatings,
A dispersion in which a solid powder is dispersed in a solvent exhibits physical properties (viscoelasticity) such as a combination of elasticity and viscosity in rheology, and is called a viscoelastic body.

Such a viscoelastic body generally exhibits a unique behavior (dynamic properties) when a stress or strain that changes periodically with time is applied.

For example, when the strain γ is applied to the perfect elastic body while changing it sinusoidally, as shown in FIG. 2, the strain γ and the stress σ are observed as sine waves having the same frequency without a phase difference. In a completely viscous body, as shown in FIG. 3, the strain γ is observed with a phase difference δ of 90 ° behind the stress σ.

On the other hand, in a viscoelastic body, as shown in FIG.
The strain γ is observed after the stress σ with a phase difference δ of 0 ° <δ <90 °. That is, the stress σ in the viscoelastic body
Is a complex number composed of a real part (elastic component) having the same phase as the distortion γ and an imaginary part (viscous component) having a phase advanced by 90 °, and the phase advances by δ from the distortion γ as a whole.

The elastic modulus of such a viscoelastic body is generally represented by a complex number. That is, the complex elastic modulus G * is defined as the ratio of stress σ to strain γ, the real part G ′ is called the storage elastic modulus (elastic element), and the imaginary part G ″ is called the loss elastic modulus (viscous element). When the phase difference between σ and distortion γ is δ, G *,
G ′ and G ″ are represented as follows.

Complex elastic modulus G * = σ / γ = G ′ + iG ″ (i ² = −1) Storage elastic modulus G ′ = G * cos (δ) Loss elastic modulus G ″ = G * sin (δ) In order to control the oscillation of the lower coating film during the coating film formation process using the viscoelastic body having such characteristics, the storage elastic modulus G ′ and the complex elastic modulus G
It is important to regulate *.

That is, in a dispersion liquid that is a viscoelastic material, generally, when the relationship between the angular velocity ω of the applied strain γ and the storage elastic modulus G ′ of the dispersion is viewed in the flow region, the storage elastic modulus G ′ is generally The lower the angular velocity ω, the lower the change. However, as the angular velocity ω is reduced, and within a certain range, a flat region where the storage elastic modulus G ′ hardly changes appears. This flat region strongly reflects the properties of the three-dimensional stitch structure formed by the interaction between the solid powders, and is considered to be important in controlling the oscillation of the coating film. Further, when observing the change with time of the complex elastic modulus G * of the dispersion at a constant small strain γ and a constant angular velocity ω, the complex elastic modulus G * after the initial shear of the excessive strain γ is applied with time. It changes in various ways. For example, in a certain magnetic paint, the complex elastic modulus G * decreases with time with respect to applied strain γ.

The measuring device, measuring mode and geometry used for measuring the viscoelastic properties are as follows.

Apparatus: Strain control type viscometer (trade name: RFS-II, manufactured by Rheometrics Co., Ltd.) Measurement mode: Frequency shift (fixed at 1% strain): When measuring storage elastic modulus G ′ Step strain (frequency: 2πrad / Second fixed): Complex elastic modulus G * measurement Geometry: Titanium 50 mm diameter parallel plate In this magnetic recording medium, G ′ (1) and G ′ (10) of the lower base layer paint and the upper magnetic layer paint ),
G '(10) / G' (1) and G * (0) / G * (12
By regulating 0) to a predetermined value, the viscoelastic properties of the paint for the lower underlayer and the paint for the upper magnetic layer are controlled. Therefore, when a coating film is formed by using the coating material for the lower underlayer and the coating material for the upper magnetic layer, oscillation in the film forming process, that is, swinging motion can be suppressed.

Further, G ′ (10) /
The value of G '(1) is _Kl , and the value of G' (1)
0) / G 'value of (1) is taken as K _u, with K _l / K _u is a _{0.5 ≦ K l / K u ≦} 2.0, paint underlayer underlayer G * ( 0) / G *
The value of (120) is defined as M _l , and the G *
(0) / G * values of (120) when the M _u, M _l /
It is preferred that M _u is the _{0.125 ≦ M l / M u ≦} 8.0.

By defining K ₁ / K _u and M ₁ / M _u in this manner, the viscoelastic properties of the lower base layer paint and the viscoelastic properties of the upper magnetic layer paint are further approximated. . For this reason, in this case, a coating film in which oscillation is further suppressed can be formed by the coating material for the lower underlayer and the coating material for the upper magnetic layer.

Next, the non-magnetic support 1 to which the paint for the lower underlayer and the paint for the upper magnetic layer are applied will be described.

The non-magnetic support 1 is not particularly limited, and any material may be used as long as it is used for a magnetic recording medium. Examples of the nonmagnetic support 1 include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins, polyimides and polycarbonates. It is made of a typical polymer material, or a metal, glass, or ceramic. Further, the nonmagnetic support 1 may be subjected to a surface treatment such as a corona discharge treatment, or may be formed with an organic material layer such as an easily adhesive layer on the surface.

Next, a method of applying the above-described paint for the lower underlayer and the paint for the upper magnetic layer on the non-magnetic support 1 will be described.

When applying the coating material for the lower underlayer and the coating material for the upper magnetic layer on the non-magnetic support 1, the coating material for the upper magnetic layer is applied when the coating material for the lower underlayer is wet. A wet-on-wet method is used.

Specifically, when the lower underlayer 2 and the upper magnetic layer 3 are formed on the nonmagnetic support 1 by a wet-on-wet method, for example, a coating film forming apparatus as shown in FIG. 10 is used.

The coating film forming apparatus 10 is provided with a winding roll 12 and a supply roll 13 which are formed by winding the non-magnetic support 1 formed in a long shape and wrapping around the non-magnetic support 1.
A coating device 14 for applying a lower base layer coating material and an upper magnetic layer coating material on the non-magnetic support 1 pulled out from the supply roll 13, an orientation magnet 15 for determining the magnetization direction of the upper magnetic layer 3, A drier 16 for drying the paint and a calender device 17 for performing a calendering process are provided.

That is, in the coating film forming apparatus 10, the non-magnetic support 1 is transported from the supply roll 13 to the take-up roll 12, and the coating device 14 is oriented along the transport direction. Magnet 15, dryer 16,
The calendar devices 17 are arranged in this order.

In the coating film forming apparatus 10, first, the coating material for the lower underlayer and the coating material for the upper magnetic layer are applied in multiple layers on the nonmagnetic support 1 by the coating device 14. As shown in FIG. 6, the coating device 14 includes a first extrusion coater 18 for applying a non-magnetic coating and a second extrusion coater 18 for applying a magnetic coating.
And an extrusion coater 19. Further, in the coating apparatus 14, the second extrusion coater 19 is arranged on the sending side of the non-magnetic support 1, and the first extrusion coater 18 is arranged on the introduction side of the non-magnetic support 1.

The first extrusion coater 18 and the second
The extruder coater 19 has slit portions 20 and 21 formed at the tip thereof for extruding the paint, and paint pools 22 and 23 for supplying the paint on the back side of the slit portions 20 and 21, respectively. I have. In such a first extrusion coater 18 and a second extrusion coater 19, the paint for the lower underlayer or the paint for the upper magnetic layer supplied to the paint reservoirs 22 and 23 is supplied to the slit portion 2.
It is extruded to the coater tip through 0 and 21, respectively.

Then, the non-magnetic support 1 to which the paint is applied
Is transported along the distal end surfaces of the first extrusion coater 18 and the second extrusion coater 19 in the direction of arrow D in FIG.

Non-magnetic support 1 conveyed in this way
On the upper side, first, when passing through the first extrusion coater 18, the lower base layer coating material extruded from the slit portion 20 is applied to form the lower base layer coating film 24. Then, when passing through the second extrusion coater 19, the upper magnetic layer coating material extruded from the slit portion 21 is applied on the lower underlayer coating film 24 in a wet state, and the upper magnetic layer coating film 25 is formed. You.

The first extrusion coater 18
The supply of the paint to the second extrusion coater 19 may be performed via an inline mixer.

The non-magnetic support 1 on which the lower underlayer coating film 24 and the upper magnetic layer coating film 25 are formed is transported to the magnet 15 for orientation, the dryer 16 and the calender 17 in this order.

In the magnet 15 for orientation, the magnetic coating film 25 to be a magnetic layer is subjected to a magnetic field orientation treatment. As the magnet 15 for orientation, a magnet for longitudinal orientation or a magnet for vertical orientation, or a magnet for random orientation when a magnetic disk or the like is manufactured. These orientation magnets 15 are appropriately selected according to the type of magnetic powder contained in the magnetic layer 3. Generally, the magnetic field of the magnet 15 for orientation is desirably about 20 to 10,000 gauss, but is not limited to random orientation.

In the drier 16, the upper magnetic layer coating film 24 and the lower underlayer coating film 25 are dried by hot air from nozzles arranged above and below the drying device 16. The drying conditions at this time are preferably a temperature of about 30 to 120 ° C. and a drying time of about 0.1 to 10 minutes.

The non-magnetic support 1 having passed through the dryer 16 is further guided to a calender 17 and subjected to a surface smoothing process. In the surface smoothing process by the calendar device 17, the temperature, the linear pressure, the transport speed, and the like are important. That is, the temperature is 50 as the surface smoothing condition.
１４０140 ° C., the linear pressure is preferably 50-1000 kg / cm ² , and the transfer speed is preferably 20-1000 m / min. If these conditions are not satisfied, the upper magnetic layer 3
May be impaired.

In the coating film forming apparatus 10, the coating material for the lower underlayer and the coating material for the upper magnetic layer are applied by separate coaters, but the invention is not limited to such an application device 14. Absent. That is, as shown in FIG. 7, a coating apparatus 27 including an extrusion coater 26 in which the first extrusion coater 18 and the second extrusion coater 19 are integrated may be used.

Further, in the above-described coating film forming apparatus 10, the coating apparatuses 14 and 27 in which the coating for the lower underlayer and the coating for the upper magnetic layer are sequentially applied are used. A coating device for simultaneously applying the underlayer coating and the upper magnetic layer coating may be used. That is, as shown in FIG. 8, a coating device 29 including an extrusion coater 28 in which two slits are formed close to each other is used, and the coating for the lower layer and the coating for the upper magnetic layer are simultaneously applied by the extrusion coater 28. You may do it.

Further, the above-mentioned coating apparatuses 14, 27, 29
In, extrusion coater was used, but berth roll, gravure roll, air doctor coater, blade coater, air knife coater, squeeze coater,
An impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater, or the like may be used. At this time, the method of applying the paint for the lower underlayer and the method of applying the paint for the upper magnetic layer may be the same or different. Therefore, for example, it is also possible to apply a reverse roll and an extrusion coater or a combination of a gravure roll and an extrusion coater to apply the lower base layer coating material and the upper magnetic layer coating material.

In the magnetic recording medium and the method of manufacturing the same as described above, the G ′ of the paint for the lower underlayer and the paint for the upper magnetic layer
(1), G '(10), G' (10) / G '(1) and G * (0) / G * (120) are regulated to predetermined values. Therefore, the paint for the lower underlayer and the paint for the upper magnetic layer can be controlled to have desired viscoelastic properties. In particular, as described above, the coating material for the lower underlayer has the desired viscoelasticity since it has the soft magnetic powder. Thereby, in the above-described magnetic recording medium, the viscoelasticity of the paint for the upper magnetic layer having the ferromagnetic powder and the viscoelasticity of the paint for the lower underlayer can be approximated. Therefore, when a coating film is formed using the coating material for the lower underlayer and the coating material for the upper magnetic layer, oscillation in the film forming process, that is, swinging motion can be suppressed.

Therefore, in this magnetic recording medium,
The lower underlayer 2 and the upper magnetic layer 3 are coated with high precision, and their interfaces are not disturbed.
There will be no pinholes or cissing. In other words, by using the above-described paint for the lower underlayer and the paint for the upper magnetic layer, it is possible to form a high-precision coating film without pinholes or cissing, and has the lower underlayer 2 and the upper magnetic layer 3. The magnetic recording medium can be manufactured with high yield. The manufactured magnetic recording medium has excellent surface properties, and thus has excellent electromagnetic conversion characteristics.

In the above-described paint for the lower underlayer and the paint for the upper magnetic layer, the type and molecular weight of the binder used in the paint, the content of the solid powder component such as magnetic powder or nonmagnetic powder, the type of solvent, and the dispersion By controlling the degree, the storage elastic modulus and the complex elastic modulus G * can be adjusted.

In the above-described magnetic recording medium, the thickness of the upper magnetic layer 3 is preferably 2 μm or less, and more preferably 0.7 μm or less. By setting the thickness of the upper magnetic layer 3 to 2 μm or less, it becomes suitable for short-wavelength recording, and high-density recording can be achieved. Further, the thickness of the upper magnetic layer 3 is set to 0.7 μm
By defining the following, the self-demagnetization loss can be reduced, and the electromagnetic conversion characteristics can be improved.

Further, in the above-described magnetic recording medium,
The soft magnetic powder contained in the lower underlying layer 2 causes the lower underlying layer 2 to act to draw the recording magnetic field from the magnetic head. As a result, in the magnetic recording medium, the spread of the head magnetic field in the high frequency region can be suppressed, and recording and reproduction can be performed in a state closer to perpendicular magnetization. Therefore, in this magnetic recording medium, the high-frequency characteristics and the envelope characteristics are improved. At this time, if the coercive force of the soft magnetic powder is specified to be 5 to 200 Oe, the magnetic recording medium can further improve the high-frequency characteristics and the envelope characteristics described above. When the coercive force Hc of the soft magnetic powder is less than 5 Oe, it is difficult to adjust the shearing properties of the coating material for the lower underlayer, and there is a possibility that the effect of improving the electromagnetic conversion properties may not be obtained much. Further, the coercive force Hc of the soft magnetic powder is 2
If it exceeds 00 Oe, a slight recording magnetic field may remain in the lower underlayer, and the electromagnetic conversion characteristics may be degraded. In order to adjust the viscoelasticity of the paint for the lower underlayer and prevent deterioration of the electromagnetic conversion characteristics, a magnetic powder such as a ferromagnetic magnetic powder, cobalt-modified iron oxide, which cannot be magnetically recorded, is used for the lower underlayer. May be used.

Further, in this magnetic recording medium, the average major axis length of the ferromagnetic powder measured by a transmission electron microscope was 0.30.
By setting the thickness to μm or less, recording and reproduction corresponding to short-wavelength recording can be performed. That is, when the average major axis length of the ferromagnetic powder measured by a transmission electron microscope is 0.30 μm or more, there is a possibility that recording cannot be performed on a magnetic recording medium using a head magnetic field in a high-frequency region. The ferromagnetic powder preferably has a coercive force in the range of 2000 to 2500 Oe. Ferromagnetic powder holding power Hc is 20000
If it is less than e, the output at a short wavelength is not sufficient, and if the holding power of the ferromagnetic powder exceeds 2500 Oe, it may be difficult to perform recording with the current head.

Further, in the magnetic recording medium, the thickness of the lower underlayer 2 is preferably 0.5 to 3.5 μm. When the thickness of the lower base layer 2 is less than 0.5 μm, it may be difficult to apply the coating for the lower base layer with high accuracy, and when the thickness of the lower base layer 2 exceeds 3.5 μm, Since the ratio to the total thickness of the magnetic recording medium is increased, it may be difficult to reduce the thickness of the magnetic recording medium.

Further, in the magnetic recording medium, the thickness of the upper magnetic layer 3 is preferably 2.0 μm or less. If the thickness of the upper magnetic layer exceeds 2.0 μm, it becomes difficult to perform good recording with a head magnetic field in a high-frequency region, and there is a possibility that short-wavelength recording characteristics cannot be obtained.

[0072]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments to which a magnetic recording medium according to the present invention and a method of manufacturing the same are applied will be described. Further, a comparative example was prepared for comparison with this example, and characteristics of the example and the comparative example were evaluated.

Example 1 First, the components of the paint for the upper magnetic layer and the paint for the lower underlayer were weighed according to the following composition, and kneaded and dispersed using a continuous twin-screw kneader and a sand mill. A paint for the magnetic layer and a paint for the lower underlayer were prepared.

<Coating Material for Upper Magnetic Layer> 100 parts by weight of ferromagnetic iron fine powder (coercive force Hc: 2000 Oe, specific surface area by BET method: 55 m ² / g, major axis diameter: 0.25 μm, needle ratio: 10, Saturation magnetization σs: 120 emu / g) Binder: 14 parts by weight of vinyl chloride resin containing potassium sulfonate group (trade name: MR-110, manufactured by Zeon Corporation) 6 parts by weight of polyurethane resin containing sodium sulfonate group (manufactured by Toyobo Co., Ltd.) Brand name UR-8700) α-alumina 5 parts by weight Myristic acid 1 part by weight butyl stearate 1 part by weight Solvent 350 parts by weight (Methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1 mixed solvent)

<Coating for Lower Underlayer> Soft magnetic magnetic powder 80 parts by weight (Coercive force Hc: 150 Oe, sendust powder having an average particle diameter of 0.03 μm) Carbon black 20 parts by weight Binder: vinyl sulfonate containing potassium sulfonate group Resin 14 parts by weight (trade name: MR-110, manufactured by Zeon Corporation) 6 parts by weight of sodium sulfonate group-containing polyurethane resin (trade name: UR-8700, manufactured by Toyobo Co., Ltd.) 1 part by weight of butyl stearate 220 parts by weight of solvent (methyl ethyl ketone: toluene) : Cyclohexanone (weight ratio) = 1: 1: 1 mixed solvent)

The coating material for the upper magnetic layer and the coating material for the lower underlayer thus prepared were mixed with a polyisocyanate compound (Coronate L, trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.).
After the addition of parts by weight, the viscoelasticity was measured using a strain control type viscoelasticity meter. The apparatus, measurement mode, and geometry (here, the shape of the portion holding the non-magnetic paint as a test sample) used for this measurement are as follows.

Apparatus: Strain control type viscoelasticity measuring device (trade name: RFS-II, manufactured by Rheometrics Co., Ltd.) Measurement mode: storage elastic modulus measurement → frequency subtraction complex elastic modulus measurement magnetism → step strain (frequency 2πrad / sec) Fixed) Geometry: Titanium, 50mm diameter parallel plate

Next, using a coating film forming system as shown in FIG. 5, a non-magnetic support composed of polyethylene terephthalate having a thickness of 7.5 μm was formed on a non-magnetic support having a thickness of 7.5 μm by a wet-on-wet coating method. And a coating for the upper magnetic layer is applied in multiple layers, and while the coating film is in an undried state (wet state), a magnetic field orientation treatment is performed, followed by drying and a surface smoothing treatment by a calender to perform a lower soft magnetic layer, An upper magnetic layer was formed. In addition, the film thickness configuration (dry film thickness)
The lower underlayer was 1.5 μm, and the upper magnetic layer was 0.15 μm.

Next, a coating material for a backcoat layer having the following composition is applied to the surface of the non-magnetic support opposite to the surface on which the lower soft magnetic layer and the upper magnetic layer are formed, dried, and calendered by calendering. A back coating layer having a thickness of 0.8 μm was formed by performing a surface treatment to obtain a wide magnetic tape raw material.

<Coating for Back Coat Layer> Carbon black (average particle diameter 26 nm) 40 parts by weight Barium sulfate (average particle diameter 300 nm) 10 parts by weight Nitrocellulose 25 parts by weight Polyurethane resin 25 parts by weight (manufactured by Nippon Polyurethane Industry Co., Ltd.) N-2301) Polyisocyanate compound 10 parts by weight (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) Solvent 900 parts by weight (Methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1 mixed solvent)

The magnetic tape raw material thus obtained was cut into a tape width of 8 mm to produce a magnetic tape.
Electromagnetic conversion characteristics (10 MHz output) and envelope characteristics (output fluctuation) were measured, and the yield was confirmed.

Example 2 The ferromagnetic powder of the upper magnetic layer was Hc = 2500 Oe, the ferromagnetic iron fine powder of the major axis diameter = 0.20 μm, the soft magnetic powder of the lower underlayer was the sendust powder of Hc = 10 Oe, the lower layer Example 1 except that the coating thickness of the underlayer was changed to 3.5 μm
A magnetic tape was produced in the same manner as described above.

Example 3 A magnetic tape was produced in the same manner as in Example 1 except that the coating thickness of the upper magnetic layer was changed to 1 μm.

Example 4 Example 1 was repeated except that the coating thickness of the upper magnetic layer was changed to 2 μm, the soft magnetic powder of the lower underlayer was changed to Sendust powder of Hc = 200 Oe, and the coating thickness of the lower underlayer was changed to 0.5 μm. A magnetic tape was produced in the same manner as described above.

Example 5 The soft magnetic powder of the lower underlayer was made of Ni—Z with Hc = 50 Oe.
A magnetic tape was produced in the same manner as in Example 1 except that n-ferrite was used.

Example 6 The soft magnetic powder of the lower underlayer was made of Ni—Hc = 100 Oe.
A magnetic tape was produced in the same manner as in Example 1, except that the coating thickness of the Zn ferrite and the lower underlayer was changed to 3.5 μm.

Example 7 The soft magnetic powder of the lower underlayer was changed to a ferromagnetic magnetic powder cobalt-modified iron oxide (Hc = 950 Oe, specific surface area = 58 m ² / g, crystal size = 250, needle ratio =
8, a major axis diameter = 0.20 μm), except that the magnetic tape was manufactured in the same manner as in Example 1.

Example 8 A magnetic tape was produced in the same manner as in Example 1 except that the wet-on-wet coating method was changed to the wet-on-dry coating method.

Example 9 The soft magnetic powder of the lower underlayer was made of Fe-
A magnetic tape was produced in the same manner as in Example 1, except that the powder was changed to Co-Ni alloy powder.

Example 10 The soft magnetic powder of the lower underlayer was made of granular F of Hc = 150 Oe.
A magnetic tape was produced in the same manner as in Example 1, except that the powder was changed to e powder.

Example 11 The soft magnetic powder of the lower underlayer was made of Mg—
A magnetic tape was produced in the same manner as in Example 1 except that the powder was changed to a Mn-based ferrite powder.

Comparative Example 1 The ferromagnetic iron fine powder of the upper magnetic layer was prepared by adding Hc = 1600 Oe,
A magnetic tape was produced in the same manner as in Example 1 except that the major axis diameter was changed to 0.35 μm.

Comparative Example 2 The ferromagnetic iron fine powder of the upper magnetic layer was prepared by adding Hc = 2600 Oe,
Example 1 except that the major axis diameter was changed to 0.3 μm.
A magnetic tape was produced in the same manner as described above.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1, except that the soft magnetic powder of the lower underlayer was changed to Sendust with Hc = 250 Oe.

COMPARATIVE EXAMPLE 4 A soft magnetic powder was not blended in the lower underlayer, and the lower underlayer was made non-magnetic.
_A magnetic tape was produced in the same manner as in Example 1, except that the ratio of ₂ O ₃ inorganic powder: carbon black was changed to 10: 0.

COMPARATIVE EXAMPLE 5 The lower underlayer was made non-magnetic without blending soft magnetic powder,
_A magnetic tape was produced in the same manner as in Example 1 except that the ratio of ₂ O ₃ inorganic powder: carbon black was changed to 4: 6.

Comparative Example 6 A magnetic tape was produced in the same manner as in Example 1, except that the lower magnetic layer was not formed and only the upper magnetic layer was formed on a nonmagnetic support.

Characteristic Evaluation Test Examples 1 to 11 and Comparative Examples 1 to 11 produced as described above
6 for each magnetic tape (10 MHz
Output), envelope characteristics (output fluctuation),
The yield was confirmed.

<Electromagnetic conversion characteristics>
The measurement was carried out using a fixed head type telemeter. This fixed head type electronic measuring instrument is composed of a rotating drum and a magnetic head mounted thereon, and has a configuration in which a magnetic tape is wound around the drum. In actual measurement, first, a 10-MHz rectangular wave signal was recorded at the optimum recording current of each magnetic tape, and 10 MHz was recorded by a spectrum analyzer.
The output level of z was detected. The relative speed between the magnetic tape and the magnetic head was 3.33 m / S, and an 8 mm Hi8 tape manufactured by SONY was used as a reference (0 db).

<Envelope Characteristics> As for the envelope characteristics, at the output level of 10 MHz in the above-mentioned electromagnetic conversion characteristics, the value of the output fluctuation between one track defined by the following equation was measured.

Output fluctuation (%) = B / A × 100 A: Maximum value [V] of output between one track B: Minimum value [V] of output between one track That is, the output fluctuation obtained by the above equation (V) %) Indicates a better envelope characteristic with less output fluctuation.

<Yield> The yield indicates the percentage of non-defective products after the end of cutting. Usually, 97% or more is required.

Tables 1 and 2 show the results of the viscoelastic properties of the paint for the lower underlayer and the paint for the upper magnetic layer together with the results of these measurements.

[0104]

[Table 1]

[0105]

[Table 2]

As is clear from Tables 1 and 2, Examples 1 to 11 show good results in output, envelope characteristics and yield at 10 MHz. In comparison, Comparative Examples 1 to 6 were not good in at least one of the 10 MHz output, the envelope characteristic, and the yield.

From the above, as in Examples 1 to 11, the viscoelasticity of the paint for the lower underlayer and the paint for the upper magnetic layer was respectively 20 (Pa) ≦ G ′ (1) ≦ 60 (Pa). 20 (Pa) ≦ G ′ (10) ≦ 90 (Pa) 1.0 <G ′ (10) / G ′ (1) ≦ 2.0 0.5 <G * (0) / G * (120) ≦ By defining the ratio to be 4.0, a magnetic recording medium having excellent electromagnetic conversion characteristics can be manufactured with high productivity.

[0108]

As described in detail above, the magnetic recording medium according to the present invention is formed by using the coating material for the lower underlayer and the coating material for the upper magnetic layer defined so as to have predetermined viscoelastic properties. A lower underlayer and an upper magnetic layer. Therefore, the magnetic recording medium has excellent surface properties and excellent electromagnetic conversion characteristics.

Further, in the method for manufacturing a magnetic recording medium according to the present invention, the lower underlayer and the upper magnetic layer may be coated with a lower underlayer coating and an upper magnetic layer coating defined to have predetermined viscoelastic properties. It is formed using. Therefore, according to this method, the lower underlayer and the upper magnetic layer can be formed with high precision without causing inconveniences such as uneven coating and streaks. Therefore, according to this method, a magnetic recording medium having a lower underlayer and an upper magnetic layer can be manufactured with excellent productivity.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a magnetic recording medium according to the present invention.

FIG. 2 is a characteristic diagram showing an oscillation waveform of a completely elastic body.

FIG. 3 is a characteristic diagram showing an oscillation waveform of a completely viscous body.

FIG. 4 is a characteristic diagram showing a viscoelastic oscillation waveform.

FIG. 5 is a schematic view showing a coating film forming apparatus for forming a lower non-magnetic layer and a magnetic layer by a wet-on-wet coating method.

FIG. 6 is a schematic view showing an example of a coating apparatus of the coating film forming apparatus.

FIG. 7 is a schematic view showing another example of the coating apparatus.

FIG. 8 is a schematic diagram showing another example of the coating apparatus.

[Explanation of symbols]

 1 Non-magnetic support, 2 Underlayer, 3 Upper magnetic layer

Continued on the front page F term (reference) 4J038 CR001 DN001 HA066 HA216 KA07 KA20 MA07 MA10 NA22 PA12 PB11 5D006 BA01 BA08 BA19 CA03 CA05 EA01 FA09 5D112 AA03 AA05 BB01 BB06 BB17 BD08 BD09 CC02

Claims (11)

[Claims] 1. A non-magnetic support, a lower base layer formed by applying a coating for a lower base layer mainly composed of a soft magnetic powder and a binder onto the non-magnetic support, and In a magnetic recording medium having an upper magnetic layer formed by applying an upper magnetic layer paint mainly composed of a ferromagnetic powder and a binder, the lower underlayer paint and the upper magnetic layer paint are strain-controlled. The storage elastic modulus G ′ at a strain of 1% and an angular frequency of 1 rad / sec was measured using a viscoelasticity meter.
(1) and the storage elastic modulus G ′ (10) at a strain of 1% and an angular frequency of 10 rad / sec are 20 (Pa) ≦ G ′ (1) ≦ for both the lower base layer coating material and the upper magnetic layer coating material. 60 (Pa) 20 (Pa) ≦ G ′ (10) ≦ 90 (Pa) 1.0 <G ′ (10) / G ′ (1) ≦ 2.0, and the paint for the lower underlayer and the upper layer Immediately after the initial shearing of the magnetic layer paint for 60 seconds at a strain of 1000% and an angular frequency of 2πrad / sec, the time was set to 0 second.
Complex elastic modulus G * (0) at 1% strain in second and angular frequency 2πrad / sec and complex elastic modulus G * at 1% strain and angular frequency 2πrad / sec at time 120 seconds after time 0 seconds. (120) The magnetic recording medium according to (1), wherein both the paint for the lower underlayer and the paint for the upper magnetic layer satisfy 0.5 <G * (0) / G * (120) ≦ 4.0. 2. G '(10) /
The value of G ′ (1) is K _l , and G ′ of the paint for the upper magnetic layer is G ′.
_Assuming that the value of (10) / G ′ (1) is Ku, 0.5 ≦ K ₁ / K _u ≦ 2.0, and G * (0) / G * of the paint for the underlayer. The value of (120) is represented by M _l , and G * (0) / G * of the coating material for the upper magnetic layer.
The value of (120) when the M _u, magnetic recording medium according to claim 1, wherein it is _{0.125 ≦ M l / M u ≦} 8.0. 3. The magnetic recording medium according to claim 1, wherein the thickness of the upper magnetic layer is 2 μm or less. 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder of the upper magnetic layer has an average major axis length of 0.3 μm or less. 5. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder of the upper magnetic layer has a coercive force of 2000 to 2500 (Oe). 6. The soft magnetic powder of the lower underlayer has a coercive force of 5 to 200 (Oe).
The magnetic recording medium according to the above. 7. The thickness of the lower underlayer is 0.5 to 3.5.
2. The magnetic recording medium according to claim 1, wherein the diameter of the magnetic recording medium is μm. 8. The magnetic recording medium according to claim 1, wherein the lower underlayer and the upper magnetic layer are applied by a wet-on-wet coating method or a wet-on-dry coating method. . 9. A coating for a lower underlayer mainly composed of a soft magnetic powder and a binder and a coating for an upper magnetic layer mainly composed of a ferromagnetic powder and a binder are sequentially applied on a nonmagnetic support. In the method for producing a magnetic recording medium for forming a lower underlayer and an upper magnetic layer, the paint for the lower underlayer and the paint for the upper magnetic layer are each measured using a strain control type viscoelasticity meter, and the strain is 1% , Storage elastic modulus G 'at an angular frequency of 1 rad / sec.
(1) and the storage elastic modulus G ′ (10) at a strain of 1% and an angular frequency of 10 rad / sec are 20 (Pa) ≦ G ′ (1) ≦ for both the lower base layer coating material and the upper magnetic layer coating material. 60 (Pa) 20 (Pa) ≦ G ′ (10) ≦ 90 (Pa) 1.0 <G ′ (10) / G ′ (1) ≦ 2.0, and the paint for the lower underlayer and the upper layer Immediately after the initial shearing of the magnetic layer paint for 60 seconds at a strain of 1000% and an angular frequency of 2πrad / sec, the time was set to 0 second.
Complex elastic modulus G * (0) at 1% strain in second and angular frequency 2πrad / sec and complex elastic modulus G * at 1% strain and angular frequency 2πrad / sec at time 120 seconds after time 0 seconds. (120) wherein both the paint for the lower underlayer and the paint for the upper magnetic layer satisfy 0.5 <G * (0) / G * (120) ≦ 4.0. Method. 10. G '(10) of the paint for the lower underlayer
/ G '(1) value K _l of, G for coatings the upper magnetic layer'
(10) / G 'of the value of (1) is taken as K _u, is _{0.5 ≦ K l / K u ≦} 2.0, G * (0) of the paint above the lower base layer / G The value of * (120) is M _l , and G * (0) / G * of the coating material for the upper magnetic layer.
10. The method according to claim 9, wherein when the value of (120) is M _u , 0.125 ≦ M ₁ / M _u ≦ 8.0. 11. The magnetic recording according to claim 9, wherein the coating for the lower underlayer and the coating for the upper magnetic layer are applied by a wet-on-wet coating method or a wet-on-dry coating method. The method of manufacturing the medium.