JP2000011359A - Magnetic recording media - Google Patents

Abstract

(57) [Solution] A so-called simultaneous multi-layer coating method in which an upper magnetic layer and a lower non-magnetic layer are simultaneously coated on a non-magnetic support by a die coater is an effective method. If vortex convection occurs in the drying stage, the surface of citron skin or the like is roughened. The present invention solves this problem and obtains a magnetic recording medium having high electromagnetic conversion characteristics suitable for high-density recording. SOLUTION: A non-magnetic layer 4 is provided on a non-magnetic support 1,
A specific silicone-based surfactant was contained in the magnetic layer 2 of the multilayer coating type magnetic recording medium having the magnetic layer 2 provided thereon. The amount of the silicone-based surfactant is 0.1 to 1.5 parts by weight based on 100 parts by weight of the coating material for forming the magnetic layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer coated magnetic recording medium having an extremely thin magnetic layer of 0.5 .mu.m or less, and more particularly to a magnetic recording medium suitable for high-density recording.

[0002]

2. Description of the Related Art Magnetic recording media include audio tapes,
Video tape, backup data cartridge,
Widely used as floppy disks and the like. In particular, recently, studies on high-density recording, such as shortening the recording wavelength or digital recording, have been actively conducted, and the development of magnetic recording media having excellent electromagnetic conversion characteristics has been demanded.

[0003] In a coating type magnetic recording medium, thinning of a magnetic layer has been studied in order to improve electromagnetic conversion characteristics. This is a method for improving the electromagnetic conversion characteristics by reducing the self-demagnetization loss during recording, and various coating methods have been proposed in recent years. When a thin magnetic layer of 1 μm or less is provided as a single layer on a non-magnetic support, the influence of the surface shape of the support tends to appear, and it is difficult to obtain a smooth surface. A method has been devised in which a nonmagnetic undercoat layer is provided between nonmagnetic supports to reduce the thickness of the magnetic layer and to realize a smooth surface. On the other hand, in the application of a magnetic recording medium having such two layers, for the purpose of improving electromagnetic conversion characteristics and reducing noise, it is required to form a uniform coating film without coating defects and stripes, As a method therefor, there has been proposed a so-called simultaneous multilayer coating method in which an upper magnetic layer and a lower nonmagnetic layer are simultaneously coated on a nonmagnetic support by a die coater. Further, the coating method is also effective as a method for improving the adhesiveness of the interface between the upper and lower layers, and is becoming the main coating method for recent multilayer coating type magnetic recording media.

[0004] Improvement of ferromagnetic powder is also an effective technique. Specifically, (1) use of a ferromagnetic alloy powder as the ferromagnetic powder, (2) miniaturization of the ferromagnetic powder, (3) increase in coercive force of the ferromagnetic powder, uniform distribution of coercive force, and the like. Can be As for (1) and (2), as a result of aggressive improvement of magnetic materials, the saturation magnetization is now 140 Am
Ferromagnetic powders exceeding ² / kg and ferromagnetic powders having a major axis length of 0.1 μm or less have been developed. For (3),
Ferromagnetic powder having a coercive force exceeding 160 kA / m has appeared, and remarkable developments have been seen, such as a very uniform particle size distribution reflecting the coercive force distribution. Further, smoothing of the medium surface has been studied in order to minimize spacing loss during recording and reproduction. In particular, in high-density recording, since the recording wavelength used is short, it is easily affected by surface roughness, and control of surface roughness is important. Methods for smoothing the surface include highly dispersing the powder in the paint and strengthening the calendering treatment. Both are effective methods, but advanced dispersion technology is required to cope with the ultra-fine powder which is the mainstream in recent years, and the demand for calendar technology is extremely high. This is the stage where is being done.

[0005] On the other hand, it is generally known that when vortex convection occurs in a drying step from a paint to a coating film, surface roughness such as citron skin occurs. This is a phenomenon that occurs with an increase in the surface tension of the surface layer during drying, and leads to deterioration of the surface properties of the coating film, which can be a serious defect for a magnetic recording medium. In particular, in the case of a multilayer magnetic recording medium, since the organic solvent, the binder, and the like used for the upper and lower layers are different, a case where the condition for generating the vortex convection is likely to occur. Therefore, development of a paint that does not cause such a phenomenon, that is, development of a composition of a magnetic recording medium has been demanded.

[0006]

The object of the present invention is to provide a.
An object of the present invention is to provide a magnetic recording medium having high electromagnetic conversion characteristics suitable for high-density recording in a multilayer coating type magnetic recording medium having an extremely thin magnetic layer of 5 μm or less.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above situation, the present inventors have obtained the following knowledge. That is, the present invention provides a lower non-magnetic layer obtained by dispersing a non-magnetic powder in a binder on a non-magnetic support, and the lower non-magnetic layer is provided with a ferromagnetic powder while the lower non-magnetic layer is in an undried state. In a multilayer coating type magnetic recording medium provided with an upper magnetic layer dispersed in a binder, the average thickness of the upper magnetic layer is 0.5 μm or less, and the upper magnetic layer has the following structural formula. The coating composition for forming the upper magnetic layer contains a silicone-based surfactant and the amount of the silicone-based surfactant contained in the upper magnetic layer is
The magnetic recording medium is provided in an amount of 0.1 to 1.5 parts by weight with respect to 00 parts by weight.

[0008]

Embedded image Here, m, n, m ', n', a, and b each independently represent an integer, and R represents an alkyl group or a phenyl group.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention
A lower non-magnetic layer (hereinafter simply referred to as "non-magnetic layer" or "lower layer") in which a non-magnetic powder is dispersed in a binder is provided on a non-magnetic support. An upper magnetic layer (hereinafter simply referred to as “magnetic layer” or “upper layer”) in which a ferromagnetic powder is dispersed in a binder is provided on the nonmagnetic layer. The non-magnetic layer is applied in a wet state. When the average thickness of the magnetic layer is, for example, 0.5 μm or less after calendering, the effect of the present invention is particularly remarkable. That is, since the thickness of the magnetic layer is 0.5 μm or less, recording demagnetization can be reduced, and output at short wavelengths and electromagnetic conversion characteristics such as overwriting are improved.

In the present invention, the magnetic layer contains a silicone surfactant having the above structural formula. In the above structural formula, m, n, m ', n', a, b
Each independently represents an integer and is not particularly limited, but is preferably an integer in the range of 1 to 10. R
Represents an alkyl group or an aryl group, and examples thereof include a methyl group, a phenyl group, and an ethyl group.

The amount of the silicone surfactant contained in the magnetic layer is preferably 0.1 to 1.5 parts by weight based on 100 parts by weight of the coating material for forming the magnetic layer. More preferably, it is 0.3 to 1.2 parts by weight.

[0012] By including a silicone-based surfactant in the magnetic layer, eddy convection can be suppressed, and the organic solvent can be evaporated without impairing the surface smoothness. It is considered that the suppression of the vortex convection is based on the following principle. When two liquids having different densities and surface tensions come into contact with each other, vortex convection due to energy takes precedence over interdiffusion when the relationships γ ₁ > γ ₂ and ρ ₁ <ρ ₂ hold. here,
The suffixes 1 and 2 represent the upper and lower liquids, respectively. usually,
The surface tension of the organic solvent is 20 to 30 dyn / cm, whereas the surface tension of the resin used as the binder is 30 to 30 dyn / cm.
It is estimated to be 50 dyn / cm. Therefore, due to the evaporation of the solvent, the surface tension of the upper layer (surface layer) paint becomes larger than that of the lower layer paint, and vortex convection is generated. Silicone surfactants are effective as surface tension lowering agents and can suppress the generation of eddy convection. In the case of a multilayer magnetic recording medium, the binder and the organic solvent used in the upper and lower layers are often different from each other, and in such a system, a silicone-based surfactant exhibits a particularly great effect. Further, since the silicone-based surfactant in the present invention has a polyoxyalkylene chain as described above, it has excellent compatibility with various organic solvents.

The ferromagnetic powder used in the magnetic layer of the present invention includes metals such as Fe, Co and Ni, Fe--Co, Fe
-Ni, Fe-Al, Fe-Ni-Al, Fe-Al-
P, Fe-Ni-Si-Al, Fe-Ni-Si-Al
-Mn, Fe-Mn-Zn, Fe-Ni-Zn, Co-
Ni, Co-P, Fe-Co-Ni, Fe-Co-Ni
-Cr, Fe-Co-Ni-P, Fe-Co-B, Fe
-Co-Cr-B, Mn-Bi, Mn-Al, Fe-C
alloys such as o-V, iron nitride, iron carbide and the like. Of course, the effect of the present invention is not impeded even if an appropriate amount of a light metal element such as Al, Si, P, or B is added for the purpose of preventing sintering or maintaining the shape during reduction.
Further, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and Fe ₃
Belt compound with O ₄ , Co-containing γ-Fe ₂ O ₃ ,
Co-containing Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ and Fe
Examples include a beltride compound with ₃ O _4, and an oxide of CrO ₂ containing one or more metal elements, such as Te, Sb, Fe, and B. Further, hexagonal plate-like ferrites can also be used, and M-type, W-type, Y-type, and Z-type barium ferrites, strontium ferrites, calcium ferrites, lead ferrites, and, for the purpose of controlling coercive force, Co-Ti, Co-Ti-Zn,
Co-Ti-Nb, Co-Ti-Zn-Nb, Cu-Z
Those to which r, Ni-Ti, etc. are added can also be used. These ferromagnetic powders can be used alone or in combination of two or more. Also,
The specific surface area of the ferromagnetic powder used in the present invention is from 30 to 80.
m ² / g, preferably 40 to 70 m ² / g. When the specific surface area is in the above range, high-density recording can be performed with the formation of fine particles of the ferromagnetic powder, and a magnetic recording medium having excellent noise characteristics can be obtained. Further, the ferromagnetic powder used in the present invention preferably has a major axis length of 0.05 to 0.30 μm and an axial ratio of 5 to 15. When the major axis length is less than 0.05 μm, dispersion in the magnetic paint becomes difficult, and when the major axis length exceeds 0.30 μm, noise characteristics may be deteriorated, which is not preferable. If the axial ratio is less than 5, the orientation of the ferromagnetic powder decreases and the output decreases. If the axial ratio exceeds 15, the short-wavelength signal output may decrease, which is not preferable. In the case of plate-shaped ferrite, the plate diameter is 0.01 to 0.5 μm,
It is preferably about 1 to 0.2 μm. Long axis length, axis ratio, plate diameter,
As the plate thickness, an average value of 100 or more samples randomly selected from a transmission electron microscope photograph is adopted.

In the present invention, the magnetic layer can contain abrasive particles. Examples of these include:
Aluminum oxide (α, β, γ), chromium oxide (Cr ₂
O ₃ ), silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, anatase), corundum and the like. These particles are used in an amount of 20 parts by weight or less, preferably 10 parts by weight or less, based on 100 parts by weight of the ferromagnetic powder. Mohs hardness is 4 or more, preferably 5 or more,
The specific gravity is in the range of 2 to 6, preferably 3 to 5, and the average particle size is 0.5 μm or less, preferably 0.3 μm or less. As the average particle size, an average value of 100 or more samples randomly selected from a transmission electron microscope photograph is adopted. The abrasive may be used in a method of mixing and dispersing with the ferromagnetic powder, and dispersed in a binder in advance to form an abrasive paint, and then added to a magnetic paint mainly composed of ferromagnetic powder and a binder. Is also good.

In the present invention, the nonmagnetic powder contained in the nonmagnetic layer may be, for example, α-Fe ₂
Non-magnetic iron oxide such as O ₃ , goethite, rutile titanium oxide, anatase titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide, cerium oxide,
Titanium carbide, BN, α-alumina, β-alumina, γ-alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate,
There are barium carbonate, strontium carbonate, barium titanate and the like, and these powders can be used alone or in combination of two or more. The non-magnetic powder can be doped with an appropriate amount of impurities depending on the purpose, and has improved dispersibility, imparted conductivity,
Al, Si, Ti, Sn, S
Surface treatment with compounds such as b and Zr is also possible.
The specific surface area of the non-magnetic powder is 30 to 80 m ² / g, preferably 40 to 70 m ² / g. If necessary, carbon black such as rubber furnace, pyrolytic carbon, color black, and acetylene black may be contained. Specific surface area is 100 to 400 m ² / g,
The DBP oil absorption is preferably from 20 to 200 ml / 100 g. When the specific surface area of the non-magnetic powder and carbon black is in the above range, accompanied by fine particles of the shape,
Since the nonmagnetic layer is smoothed and the magnetic layer can be smoothed as a result, it is possible to obtain a magnetic recording medium that has excellent modulation noise characteristics and is less affected by spacing loss. Non-magnetic powder has no magnetic cohesion and is easier to disperse than ferromagnetic powder.However, if the specific surface area is larger than the above range, the powder of the present invention can be used as a powder. Becomes difficult to disperse. If the specific surface area is too small, surface smoothness that can withstand high-density recording cannot be secured.

In the present invention, the binder contained in the magnetic layer and the non-magnetic layer and the binder dispersing the abrasive particles are known thermoplastic resins conventionally used as binders for magnetic recording media, and thermosetting resins. Resins, reactive resins and the like can be used, and the number average molecular weight is 5,000 to 100,000.
Are preferred. Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, and acrylic acid. Ester-vinyl chloride-
Vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer,
Methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate Butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber and the like. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curing resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a polyamine resin, and a urea formaldehyde resin. Also to all binding agents described above, -SO ₃ M for the purpose of improving the dispersibility of the pigment, -O
Polar functional groups such as SO ₃ M, —COOM, and P ＝ O (OM) ₂ may be introduced. Here, M in the formula is a hydrogen atom or an alkali metal such as lithium, potassium, and sodium. Further, as the polar functional group, -NR ₁
There are a side chain type having a terminal group of R ₂ and —NR ₁ R ₂ R ₃ ⁺ X−, and a main chain type of> NR ₁ R ₂ ⁺ X ⁻ . Here, in the formula, R ₁ , R ₂ and R ₃ are a hydrogen atom or a hydrocarbon group, and X ⁻ is a halogen element ion such as fluorine, chlorine, bromine or iodine or an inorganic or organic ion. Also, -O
There are also polar functional groups such as H, -SH, -CN, and epoxy groups. The amount of these polar functional groups is 10 ^-1 to 10 ^-8 mol /
g, preferably 10 ⁻² to 10 ⁻⁶ mol / g. These binders can be used alone or in combination of two or more. These binders in the coating are used in an amount of 1 to 200 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic or nonmagnetic powder. If the amount of the binder used is too large, the ratio of the ferromagnetic powder in the magnetic layer relative to the magnetic layer decreases, and the output decreases.
If the amount of the binder is too small, the mechanical strength of the coating film decreases, and the running durability of the magnetic medium decreases.

In the present invention, it is possible to use a polyisocyanate for crosslinking and curing the above binder. Examples of the polyisocyanate include toluene diisocyanate and its adduct, alkylene diisocyanate, and its adduct. The mixing amount of these polyisocyanates with the binder is 100
5 to 80 parts by weight, preferably 10 to 10 parts by weight
To 50 parts by weight. These polyisocyanates can be used for both upper and lower layers, or can be used by limiting to only one layer. When used in both the upper and lower layers, the compounding amount can be added to each layer in the same amount, or can be changed at an arbitrary ratio.

In the present invention, a lubricant and a surfactant can be contained in the magnetic layer and the non-magnetic layer as needed. As the lubricant, graphite,
Molybdenum disulfide, tungsten disulfide, fatty acids having 10 to 22 carbon atoms, and 2 to 26 carbon atoms
And terpene compounds, and oligomers thereof. These lubricants can be added only to the upper layer, or can be added to both upper and lower layers. Examples of the surfactant include nonionic, anionic, cationic and amphoteric surfactants. These surfactants can be selectively used for the upper and lower layers depending on the purpose and amount of the surfactant, or may be used for only one layer.

In the lower layer, as nonmagnetic reinforcing particles, aluminum oxide (α, β, γ), chromium oxide, silicon carbide,
It may contain diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, anatase) and the like. These particles are 20 parts by weight with respect to 100 parts by weight of the nonmagnetic powder.
Preferably, the amount is 10 parts by weight or less. The Mohs hardness is 4 or more, preferably 5 or more, the specific gravity is in the range of 2 to 6, preferably 3 to 5, and the average particle size is 1.0 μm or less, preferably 0.5 μm or less. The average particle size of the non-magnetic reinforcing particles is also measured from a transmission electron micrograph and determined by statistical processing.

Examples of the nonmagnetic support 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. And a support formed of metal, glass, ceramics, or the like.

In order to form a coating film on the non-magnetic support, the above-mentioned upper and lower layer forming materials are coated as a coating material and dried. The solvent used for forming the coating material is acetone,
Methyl ethyl ketone, methyl isobutyl ketone, ketone solvents such as cyclohexanone, alcohol solvents such as methanol, ethanol, propanol, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester solvents such as ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyquinethanol, tetrahydrofuran and dioxane, aromatic hydrocarbon solvents such as benzene, toluene, xylene, methylene chloride, ethylene chloride, carbon tetrachloride , Chloroform, chlorobenzene, and other halogenated hydrocarbon solvents. When the magnetic recording medium is in the form of a tape, the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) is used to improve the runnability of the magnetic recording medium, prevent charging and prevent transfer. , A back coat layer may be provided. In addition, an undercoat layer may be provided between the lower layer and the nonmagnetic support for the purpose of enhancing the adhesion between the coating film and the support. Needless to say, this is different from the lower non-magnetic layer in the present invention.

The preparation of the paint is carried out by kneading, mixing and dispersing steps. For dispersion and kneading, roll mill, ball mill, sand mill, agitator,
Kneaders, extruders, homogenizers, ultrasonic dispersers and the like are used.

Further, it is preferable to apply the coating material thus formed on the non-magnetic support at the same time in a multi-layered manner. For this purpose, a die coater is mainly used. As the lip configuration of the die coater, a two-lip method, a three-lip method, a four-lip method, or the like is used.

FIG. 1 shows an example (8 mm data tape) of the magnetic recording medium of the present invention. That is, a magnetic layer 2 (upper layer) containing ferromagnetic powder and a binder is provided on one surface of a nonmagnetic support 1 via a nonmagnetic layer 4 (lower layer) containing a nonmagnetic pigment and a binder. are doing. Further, on the other surface, a back coat layer 3 mainly composed of a non-magnetic powder and a binder may be provided as indicated by a chain line. When the nonmagnetic layer 4 and the magnetic layer 2 are formed on a nonmagnetic support, a method of coating and drying one layer at a time (so-called wet
An on-dry coating method) and a method of applying a magnetic layer on a non-magnetic layer in a wet state that has not been dried (so-called wet-on-wet coating method = wet multilayer coating method). FIG. 2 shows an example of a preferred manufacturing method according to the present invention. In this manufacturing method, for example, in manufacturing the magnetic recording medium shown in FIG. 1, first, the film-shaped non-magnetic support 1 unwound from the supply roll is fed by the extrusion-type extrusion coater 5 while being fed in the direction of arrow A. The paints 4 ′ and 2 ′ for the non-magnetic layer 4 and the magnetic layer 2 are simultaneously applied in multiple layers.
The extruder coater 5 is provided with liquid pools 6 and 7, and the paints 2 ′ and 4 ′ are simultaneously overlapped by a wet-on-wet method. In such a wet-on-wet simultaneous wet application method, the magnetic paint 2 'of the upper magnetic layer 2 is applied while the non-magnetic layer 4 is in a wet state 4', so that the surface of the lower layer (that is, the upper layer) is coated. The boundary surface is smoothed, the surface properties of the upper layer are improved, and the adhesion between the upper and lower layers is improved. As a result, in particular, the performance required for a magnetic recording medium requiring high output and low noise for high-density recording is satisfied, film peeling is eliminated, and film strength is improved. In addition, dropout can be reduced, and reliability is improved. In contrast,
For example, in the case of a wet-on-dry method as disclosed in Japanese Patent Application Laid-Open No. 6-236543,
It is necessary to select a material having sufficient solvent resistance to the coating material of the upper magnetic layer 2. In addition, the smoothness of the surface is impaired, and as a result, the electromagnetic conversion characteristics are affected. When the upper and lower layers formed by the wet-on-wet multi-layer coating method have a boundary area in which components of both layers are mixed with a certain thickness, except when a clear boundary substantially exists. However, the upper layer and the lower layer excluding such a boundary region may be a magnetic layer and a nonmagnetic layer, respectively. Either case is included in the scope of the present invention.

After the above-mentioned multi-layer coating, it is introduced into a drier and, if necessary, guided to a calender and wound up on a take-up roll. Further, after a back coat layer is applied to the opposite surface of the multilayer coating layer, the tape is slit into, for example, 8 mm width to prepare a magnetic tape, and the magnetic tape is accommodated in a cassette to manufacture a tape cassette.

[0026]

EXAMPLES The present invention will be described below with reference to examples, but it is needless to say that the present invention is not limited to these examples. Examples 1 to 8 and Comparative Examples 1 to 4 A magnetic layer and a non-magnetic layer were formed into a paint with the following compositions. According to a conventional method, a paint, a pigment, an abrasive, a binder, an additive, and a solvent were mixed, kneaded with an extruder, and then dispersed in a sand mill for 4 hours.

<Magnetic Layer Coating Composition> 100 parts by weight of Fe-based metal ferromagnetic powder (coercive force = 160 kA / m, saturation magnetization = 145 Am ²⁾
/ Kg, specific surface area = 51 m ² / g, major axis length = 0.1 μm
m, needle ratio = 5) Polyvinyl chloride resin (MR-110 manufactured by Zeon Corporation)
14 parts by weight Polyester polyurethane resin (manufactured by Toyobo) 3 parts by weight α-Al ₂ O ₃ (average particle size = 0.2 μm) 5 parts by weight Silicone surfactant (shown in FIG. 3) Stearic acid 1 weight shown in FIG. 3 Part heptyl stearate 1 part by weight methyl ethyl ketone (γ = 25 dyn / cm) described in FIG. 3 toluene (γ = 29 dyn / cm) described in FIG. 3 cyclohexanone (γ = 35 dyn / cm) described in FIG. 3

<Non-magnetic layer coating composition> 100 parts by weight of α-Fe ₂ O ₃ (specific surface area = 53 m ² / g, major axis length = 0.15 μm, needle ratio = 11) Polyvinyl chloride resin (manufactured by Zeon Corporation) MR-110)
13 parts by weight Polyester polyurethane resin (manufactured by Toyobo) 4 parts by weight Stearic acid 1 part by weight Heptyl stearate 1 part by weight Methyl ethyl ketone 70 parts by weight Toluene 70 parts by weight Cyclohexanone 70 parts by weight

To the magnetic layer and the non-magnetic layer, 3 parts by weight and 2 parts by weight of
Using a lip type die coater, PEN having a thickness of 5 μm
(Polyethylene 2-6-naphthalate) A magnetic layer was simultaneously coated on the film so as to have a thickness of 0.2 μm and a non-magnetic layer was 2 μm on a film, and after orientation treatment was performed using a solenoid coil,
Drying, calendering, and curing were performed. Further, a back coating having the following composition was applied to the opposite side of the application surface, and the
It was slit to m width and taped.

<Back coating composition> Carbon black Asahi # 50 100 parts by weight Polyester polyurethane Nipporan N-2304
100 parts by weight Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight

The measurement of the electromagnetic conversion characteristics was carried out using a fixed head type electronic measuring device. This measuring machine is composed of a rotating drum and a head that comes into contact with the rotating drum, and the tape is wound around the drum. In the actual measurement, first, a 10-MHz rectangular wave signal is recorded at the optimum recording current of each tape, and a 10-MHz output level is detected by a spectrum analyzer. The relative speed between the tape and the head was 3.33 m / s, and the reference (0 dB) was S
An ONY 8 mm Hi8 tape was used. Also, 5MH
Recording and reproduction were performed at a frequency of z, and the power spectrum was examined. From this power spectrum, C / N was determined by taking the ratio of the output level of the carrier signal to the output level at 4.8 MHz. The output in the vicinity of the carrier represents noise caused by the surface roughness of the medium, and reflects the surface smoothness. For each tape, A
The center line average roughness (Ra) was measured by FM (trade name: Nano Scope 3). Measurement area is 50 × 50
μm. FIG. 3 shows the results.

FIG. 3 shows that the embodiment of the present invention has a smooth surface and excellent electromagnetic conversion characteristics. Comparative Examples 1 and 2 are examples that do not contain a silicone-based surfactant, and all have a rougher surface and inferior electromagnetic conversion characteristics as compared with the examples. In particular, Comparative Example 2 has a large surface tension of the solvent and a large surface roughness.

[0033]

According to the present invention, it has high electromagnetic conversion characteristics suitable for high-density recording and has realized excellent reliability.
A multilayer coated magnetic recording medium having an extremely thin magnetic layer of 0.5 μm or less can be obtained.

[Brief description of the drawings]

FIG. 1 shows an example (a data 8 mm tape) of a magnetic recording medium of the present invention.

FIG. 2 shows an example of a preferred production method according to the present invention.

FIG. 3 is a diagram showing measurement results of electromagnetic conversion characteristics.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support, 2 ... Magnetic layer (upper layer), 3 ... Backcoat layer, 4 ... Nonmagnetic layer (lower layer), 5 ... Extrusion coater, 6, 7 ... Liquid pool part, 2 ', 4' ... paint.

Claims (1)

[Claims] 1. A non-magnetic support, comprising: a lower non-magnetic layer in which a non-magnetic powder is dispersed in a binder; and a ferromagnetic powder in which the lower non-magnetic layer is in an undried state. In a multilayer coated magnetic recording medium provided with an upper magnetic layer dispersed in a binder, the average thickness of the upper magnetic layer is 0.5 μm or less, and the upper magnetic layer has the following structural formula: A silicone surfactant is contained, and the amount of the silicone surfactant contained in the upper magnetic layer is 0.1 to 1.5 parts by weight based on 100 parts by weight of the coating material for forming the upper magnetic layer. A magnetic recording medium, which is a unit. Embedded image Here, m, n, m ', n', a, and b each independently represent an integer, and R represents an alkyl group or a phenyl group.